Band 6, Heft 1

New regulations aim to achieve a drastic sulfur emission reduction in fuels and impose very low sulfur concentration caps (30 ppm in gasoline and 15 ppm in diesel) that will be in full force in 2009. FCC gasoline represents almost 40% of the total gasoline pool and it is the major sulfur contributor, with up to 85–95%. To deal with this situation, most refiners have adopted post-treating FCC gasoline processes given they are more viable and less costly for meeting sulfur environmental regulation limits. In this respect, one should notice that conventional hydro-treating of FCC gasoline removes sulfur decreasing gasoline quality with octane number losses. The use of hydrogen also adds important costs to the desulfurization. As a result, new promising catalytic desulfurization processes are being proposed using zeolites as adsorbents/catalysts. These new approaches may lead to novel technologies, for example, with the case of gasoline de-hydrosulfidation with no hydrogen addition and alternatively to adsorption processes with co-feeding of an H-donor being pioneered at CREC University of Western Ontario. In both approaches sulfur is efficiently removed leaving the gasoline octane number index intact. The zeolite structure, the framework composition and the properties of the charge compensating cations are all parameters with major impact on catalytic desulfurization. In particular, shape selectivity is expected to play an important role in determining product selectivity when condensation reactions are significant. In this respect, the H-ZSM5 zeolite appears to have the adequate balance of Brönsted acidity and Lewis basicity to efficiently convert thiophene to H2S, with minimal transformation of benzothiophene and oligomers into coke. From a chemical reactor engineering point of view, novel gasoline desulfurization can be implemented using both fixed and fluidized bed reactors. Fluidized circulating bed reactors display high sulfur removal ability allowing frequent catalyst removal from the catalytic bed and coke combustion in a twin fluidized regeneration unit. Fixed bed units with adsorption/desorption cycles, used in conjunction with and without H donor co-reactants, lead to selective adsorption and efficient removal of sulfur species.

The transformation of biomass into fuel and chemicals is becoming increasingly popular as a way to mitigate global warming and diversify energy sources. Biomass is a renewable, carbon-neutral resource, and fuels derived from biomass usually burn more cleanly than fossil fuels. It has been estimated that biomass could provide about 25% of global energy requirements. In addition, biomass can also be a source of valuable chemicals, pharmaceuticals and food additives. Several kinds of biomass can be converted to fuel and chemicals. Examples are wood and wood waste, agricultural crops, agricultural waste, litter from animal feedlots, waste from food processing operations and sludge from water treatment plants.Various processes can be used to convert biomass to energy. The biomass can be burned, transformed into a fuel gas through partial combustion, into a biogas through fermentation, into bioalcohol through biochemical processes, into biodiesel, into a bio-oil or into a syngas from which chemicals and fuels can be synthesized. Wood combustion, bioethanol production from either sugarcane or corn, and biodiesel production from oilseeds are currently the most economically significant processes but still need significant improvements. A detailed review of the many processes that can convert biomass into fuels and chemicals shows that no individual process is without drawbacks. As a result, it is recommended that a biorefinery is the best solution to combine and integrate various processes to maximize economic and environmental benefits, while minimizing waste and pollution.

In gas-solid fluidized beds, the distribution of the particles typically varies both in time and space. Since the gas-solids distribution and its variation have a strong influence on the performance of a fluidized bed for a given process, it is very important to accurately measure the gas-solids or voidage distribution. This paper reviews techniques for measuring the voidage distribution in gas-solid fluidized beds, with a focus on the developments during the last ten years. We will treat subsequently direct visualisation, tomography, optical probes, capacitance probes, and pressure measurements.Dense gas-solids flows are typically opaque to visible light. This makes optical techniques only of limited use in dense gas-solids flow. However, direct visualization can be useful for very dilute systems, pseudo 2-D beds, and the outer layer of dense, 3-D systems. Tomography is frequently used to obtain the voidage distribution in a horizontal cross-section of the bed. Electric capacitance tomography is fast, but its spatial resolution is limited and image reconstruction is still troublesome. Although some steps forward have been made, research is continuing at this point. For nuclear (X-ray and gamma-ray) tomography, the image reconstruction is much easier and the spatial resolution better, but its temporal resolution is typically much lower. Therefore, research efforts for nuclear tomography are mainly aimed at increasing the measurement frequency. Optical probes determine the voidage as a function of time in a small measurement volume, either by the degree of reflection or by the degree of transmission of a light bundle. Capacitance probes determine the voidage as a function of time in a small measurement volume by measuring the dielectric permittivity of the gas-solids suspension in the measurement volume. Both optical and capacitance probe techniques are reasonably well-developed; the current research effort spent at improving them seems limited, especially for capacitance probes. Time-averaged pressure measurements are commonly used to determine the average bed density and bed height. By sampling the local pressure at a sufficiently high frequency (typically in the order of 200 Hz), much more information can be obtained about the fluidized bed hydrodynamics. However, obtaining quantitative voidage data from pressure fluctuations measurement remains a difficult task; in-bed pressure fluctuation (and acoustic) measurements are mostly used to determine changes in the voidage dynamics and distribution.

In the last decade it has been a special interest to incorporate the hydrodynamics in packed bed reactor models. This seems to be important in the case of highly exothermic partial oxidation reactions normally performed in packed beds with low tube/particle diameter ratio (dt/dp< 5) because of the large void distributions in the radial and axial directions, which have a direct impact on the magnitude of radial, angular and axial profiles of the velocity field, and consequently on both, the temperature and concentration profiles in the catalytic reactor. A successful reactor model needs an adequate hydrodynamic description of the packed bed, and for this reason several models additionally incorporate empirical expressions to describe radial voidage profiles, and use viscous (Darcy) and inertial (Forchheimer) terms to account for gas-solid interactions, via Ergun's pressure drop equation. In several cases an effective viscosity parameter has also been used with the Brinkman's viscous term. The use of these various approaches introduce some uncertainty in the predicted results, as to which extent the use of a particular radial voidage expression, or the use of an effective viscosity parameter, yield reliable predictions of measured velocity profiles.In this work the predictions of radial velocity profiles in a packed bed with low tube to particle diameter ratio from six hydrodynamic models, derived from a general one, are compared. The calculations show that the use of an effective viscosity parameter to predict experimental data can be avoided, if the magnitude of the two parameters in Ergun's equation, related to viscous and inertial energy losses, are re-estimated from velocity measurements, for this particular packed bed. The predictions using both approaches adequately fit the experimental data, although the results are analyzed and discussed.

Natural cellulose fibres have been employed for packaging applications for a long time. Their use, however, has been hampered by their high hydrophilicity and their moisture sensitivity. It has, thus, been proposed to circumvent this problem through the hydrophobic modification of their surface thanks to the use of molecular grafting approaches.In this work, we describe the use of a novel solvent-free chemical pathway for molecular grafting that we have coined chromatogenic chemistry. It involves a reaction between a solid substrate and a reagent which is in a vapour-liquid equilibrium and diffuses within the solid substrate through a mechanism of adsorption/desorption akin to gas chromatography.Chromatogenic chemistry phenomenon has been studied and modelled through the extensive use of a new specific test, the Droplet Surface Migration Test. It involves the deposition upon a porous substrate of a small amount of reagent and in studying its subsequent migration and grafting. Whatman paper and various long chain acid chlorides were used for this modelling. The acid chloride carboxylic ends react with the external hydroxyl groups of cellulose fibres to give rise to the formation of long chain hydrophobic ester bonds. Upon immersion of the paper sheet in distilled water, a hydrophobic spot, extending well over the initial depot zone, could then be clearly visualized, allowing to follow conveniently the reagent migration and reaction. Grafting densities were performed by using the HPLC technique.The results obtained through the use of this test allowed a better understanding of chromatogenic chemistry phenomenon and an identification of the main parameters which affect the process: the nature of the reagent, the temperature, the reaction time, the nature of the substrate, etc. We have more particularly shown that the diffusion and grafting yields were maximal for a specific temperature which increases with the boiling point and therefore with the chain length of the reagents. We have proposed that this temperature should correspond to a compromise between the diffusion and reactivity properties of the reagent, its evaporation and its degradation by hydrolysis.

The batch cooling crystallization of an industrial active pharmaceutical ingredient that exhibits a needle-like habit was investigated. A model of the time variations of key physical properties of particles (crystal size distribution CSD and specific area) was designed using an approach based on the simple population balance equation. The experiments were monitored thanks to three in-situ process analytical sensors (Mid-IR spectroscopy, in-situ microscopy and laser backscattering). Primary and secondary surface nucleation mechanisms as well as growth of the main crystal dimension (length) were described resulting in a six parameter model. The model roughly represents the effects of different cooling strategies on the supersaturation profile, the CSD and the specific area of the final particles. First, a very weak primary nucleation occurs leading to an initial population of a few large crystals. A second population of crystals is generated afterwards through secondary nucleation mechanisms. The particles issued from the second burst of nucleation largely dominate (in mass and in number) the final overall population. Second, two important features of the crystallization process are outlined, which are commonly observed during the industrial crystallization of APIs (Active Pharm. Ing.) in impure mother liquors.

This work deals with the study of the gas-liquid mass transfer, coupled with chemical reactions. The case of carbonic gas absorption in a brine of sodium carbonate and bicarbonate is investigated. It is performed in collaboration with Solvay SA. The aim of this work is to get a better understanding of this phenomenon. It would permit an optimization of the refined sodium bicarbonate production process. The basis of developed mathematical models is presented. The CO2 absorption is coupled with several chemical reactions taking place in the liquid phase. A mathematical modelling of this coupling is first developed. The equations of the model are solved numerically, using COMSOL Multiphysics. To model the bubble-liquid mass transfer of CO2, this diffusion-reaction model is completed by a representation of the liquid phase flow around the bubble. In order to validate experimentally each scale of modelling, two experimental devices are proposed.

Nanostructured manganese oxides were synthesized towards the catalytic decomposition of hydrogen peroxide. The effect of the type of precipitant (Na2CO3 and NH4OH) over the particle size and crystallographic phase was determined. Also, the influence of particle size and crystal phase over the catalytic activity was established. Characterization of the obtained nanoparticles was performed through XRD analysis, BET surface area and TEM microscopy. Catalytic activity was followed through gasometry of the oxygen evolution [H2O2(l) ? H2O(l) + O2 (g)] at 25°C. Na2CO3 (Mn-1) and NH4OH (Mn-2) precipitants produced nanoparticles with average sizes of 5-10 nm and 20 nm, respectively. This result was attributed to higher pH stability of precipitant Na2CO3 during the synthesis process. XRD results revealed the presence of ß-MnO2, Mn5O8 and Mn3O4 crystal phase mixture for Mn-1 and Mn5O8 for Mn-2 catalyst. Catalytic activity resulted in intrinsic rate constants (kint = min-1m-2) of 5.2 and 2.3 for Mn-1 and Mn-2, respectively. The greater catalytic activity of Mn-2 catalyst was attributed to the presence of the Mn55O8 phase.

A biofilter of 0.05m diameter and 0.58m height has been studied for the removal of styrene from a simulated air-styrene mixture through the microbial route using Pseudomonas putida. Coconut coir and other waste materials have been used as the immobilization matrix for the microorganisms. Gas flow rate (0.005-0.01kgm-2s-1), micronutrient liquid flow rate (5-10 kgm-2s-1), inlet styrene concentration (0.05-1.20 gm-3) and packing size (de = 0.08 - 0.18cm) have been used as parameters. The kinetic parameters of growth rate equation of bacterial strain have been determined using batch type experimental data. A Monod type reaction model has been observed to be appropriate for the explanation of growth kinetics of the microorganisms. The values of the kinetic parameters used are Ks = 0.8gm-3, µmax = 45h-1. A three-phase deterministic mathematical model has been developed incorporating the synergistic effect of simultaneous reaction and interphase (gas to liquid to biofilm) mass transfer of styrene using experimentally determined kinetic parameters and mass transfer coefficients calculated using standard correlations. Simulated results based on the model have been compared with the experimental ones satisfactorily.

Hypersonic flight is expected to be achieved in the coming years by use of Supersonic Combustion RAMJET (SCRAMJET). One of the main issues is the thermal management of the overall vehicle and more specifically the cooling of the engine. In order to simulate the behaviour of an actively cooled SCRAMJET by use of supercritical endothermic fuel, a one-dimensional transient numerical model has been developed with heat and mass transfer, fluid mechanics and detailed pyrolysis chemistry. A dedicated experimental test bench is now available since 2006 at the LEES laboratory of Bourges to study supercritical fuel pyrolysis under steady-state and transient conditions. It aims to provide understanding of coupled phenomena, validation data for the numerical code and evaluation of onboard and real-time measurement methods for industrial use. A brief overview of the numerical code and a presentation of the experimental bench are proposed in this paper. Experimental results are discussed and a comparison is provided between numerical and experimental data. Discrepancies are shown to be lower than a few percent in terms of molar chemical compositions. This is due to uncertainties on experimental temperature measurement and to 2-D effects, which are not taken into account by the modelling. The numerical code appears to be of great importance in accessing unmeasured data and providing new understanding of coupled phenomena. Experimental and numerical tools are proved to be efficient to test future measurement methods under extreme conditions, especially at supercritical states.

Phenol biodegradation by mixed culture was studied in a membrane bioreactor (MBR) over a period of 285 days. Activated sludge was used as the MBR biomass, after controlled acclimation to high phenol concentrations. The MBR permeate flux was stabilized quickly (in a few hours) and always maintained above 90 L.h-1.m-2.bar-1. The acclimatized activated sludge allowed significant phenol degradation (95% average COD removal efficiency and greater than 99% phenol removal efficiency) without supplemental reagent addition. After sludge acclimatization, the Haldane kinetics model for a single substrate was used to obtain the maximum specific growth rate (µm = 0.438 h-1), the half saturation coefficient (Ks = 29.54 mg.L-1) and the substrate inhibition constant (Ki = 72.45 mg.L-1). Biodegradation experiments were conducted at different phenol concentrations (4.9 – 8.5 g.L-1 d-1). Although the phenol concentration was high, the Haldane model was still acceptable, and removal capacities were in agreement with literature. Excellent effluent quality was obtained regardless of the extremely short SRT (5 – 17 days). This work shows the potential of MBR for toxic chemical elimination, charged effluents treatment and process stability.

This work deals with microbial growth onto filter media and focuses on the ability of microbial communities to proliferate onto filter media. Two microorganism types are studied: microorganisms from activated sludge of wastewater treatment plant (SM) and a toluene specific consortium (TSC). The filter media considered for this study contain activated carbon fibres (ACF), combined volatile organic compounds (VOC), particles treatment purposes, activated carbon fibres felt (ACFF) and activated carbon and cellulose fibres felt (AC2F2). Using a static growth procedure during 10 days under 100 % relative humidity, artificially contaminated filters are submitted to microbial colonisation. The final concentration of microorganisms per gram of filter have been assessed using a method developed in the lab, based on filter protein content assay. The average surface charge of inocula and filter's fibres are measured to assess the influence of microorganisms adhesion on contamination. The influence of soot particles on TSC proliferation onto AC2F2 filter is then studied. Zeta measures enable the assessment of the implication of soot in microorganisms adhesion onto filter fibres. Consequences of microbial contamination on filter permeability and downstream particles released have then been assessed in a filtration device. Results demonstrate a better resistance of AC2F2 to microbial colonisation. However, SM have more difficulties to proliferate on ACFF than TSC, whereas SM colonise easier AC2F2 than TSC. Charge surface assay has defined an optimal electrostatic compatibility for TSC and AC2F2 and a minimum for SM and ACFF. When soot is added to TSC solution before introduction in AC2F2, high contamination shapes were observed whereas only a slight one occur without soot addition. Zeta potential measures show favourable charge conditions for adhesion of soot on AC2F2 fibres and TSC on soot particles. The soot may thus have played an interface role in microbial adhesion onto media. This means that electrostatic compatibility between particles is a good approach for assessing microbial adhesion onto filters but could not explain the whole mechanism of microbial proliferation. Other parameters like nutrition preferences are certainly involved. The contamination have induced filter characteristics modification. Permeability have decreased until 20 % with microbial concentration. Colonised filters have released up to 450 microbial particles/cm3. Such a release was only observed when AC2F2 was contaminated with fungi using spore as the reproduction vector (inoculum containing TSC and soot).

Effective removal of heavy metals from wastewater is one of the most important environmental challenges facing the world. Various techniques are used to remove the metals. Biosorption has gained credibility in the last decade because of its good performance and low cost. The objective of this study is to explore the use of olive pits for cadmium wastewater removal. The effects of mixing rate, pH, particle size, biomass and initial concentration and equilibrium metal ion concentration are evaluated. Results indicate nearly linear uptake by the biomass with increasing initial cadmium concentration. Adsorption increases rapidly in the pH range of 3-9, then levels off. Cadmium concentration uptake increase with increasing biomass concentration until reaching 5 g/L. Mixing rates up to 250 rpm increase uptake, however, higher mixing rates result in a vortex that incorporated air into the mixture, this resulted in a decrease in uptake. The adsorption isotherm appears to follow the Langmuir model.

Economically and technically interesting, the bioreactor phenomena are studied on both micro (pore and particle size) and macro (bioreactor) levels, to describe synergetic between bio-dynamics and physicochemical dynamics. Still, the three-phase bioreactors modelling remains complex. It requires taking into account numerous factors: the pollutant biodegradation rate in the biofilm, the reactant interfacial gas-liquid and liquid-solid mass transfer, the biofilm composition and growth, the granular structure and all the transfer phenomena occurring between phases in presence. The aim of this paper is to present a model based on biofilm composition and growth, the fluidized bed structure and its hydrodynamics. The simulation results are compared with our experimental data obtained for a biological treatment, carried out in three-phase fluidized bed reactor for hydrocarbons removal from refinery wastewaters. The equipment used is laboratory scale and the obtained results show that we could degrade hydrocarbons efficiently.

The aim of this work is to design an ethanol steam reformer to produce a hydrogen stream capable of feeding a 60 kW PEM fuel cell applying the plug flow model, considering the presence of the catalyst bed (heterogeneous model). The Dusty-Gas Model is employed for the catalyst, since it better predicts the fluxes of a multicomponent mixture. Moreover, this model has shown to be computationally more robust than the Fickian Model. A power law-type kinetics was used. Results showed that it is possible to carry out the ethanol steam reforming in a compact device (1.66 x 10 -5 to 5.27 x 10 -5 m3). It was also observed that this process is determined by heat transfer.

The experimental study that concerns the extraction of alkali picrates with the bis-crown-6-calix[4]arene in a hollow fibers membrane contactor, validates a dynamic model described in a previous paper [D. Trébouet, Sep. Pur. Tech., 50, 97-106, 2006]. The experimental data confirm the influence of parameters as the aqueous and organic phase flowrates and module capacity factor on the sensitivity of the system. It appears clearly that the closed extraction system operates in an unsteady state until equilibrium is reached and so only dynamic models can represent mass transfer within reasonable accuracy. The overall mass transfer coefficient is determined even in the case where the equilibrium is described by a non-linear distribution isotherm. The determination of an overall mass transfer coefficient shows that the diffusion of the metal complex in the microporous is the main limiting step of mass transfer.

Theoretical and experimental analysis was conducted in a bench scale, atmospheric fluidized bed gasifier, designed and constructed for exploitation of residues issued from olive oil production activity and other agricultural residues. Research was focused on the effect of bed material quantity and particle size diameter on the fluidization quality, characterized by regarding bed pressure drop and minimum fluidization velocity. Experiments were carried out, under cold conditions, with a bed with an external diameter of 60 mm (internal 54,4 mm), and a comparison of the first experimental data with theoretical results that addressed the validity of the theoretical model.

Magnetic titanium dioxide particles were prepared by depositing different amounts of TiO2 on magnetite powder using a sol-gel process. Adsorptivity of TiO2/Fe3O4 particles was increased by carbon coating which was carried out by mixing the particles with poly (vinyl alcohol) as a source of carbon. The carbon coating and calcination of particles were carried out simultaneously by heating the mixture at different temperatures. X-ray diffraction, energy dispersion fluorescence x-ray spectrometry, carbon-nitrogen analyzer and surface area analysis were used for the characterization of the prepared samples. The phase transition temperature of TiO2 from anatase to rutile was found to decrease by decreasing titanium tetraisopropoxide to magnetite (TTIP:Fe3O4) ratio while BET surface area increased by increasing this ratio. Carbon content had a significant effect on the formed phases and surface areas of the samples. The photocatalytic efficiencies of the prepared samples were investigated against degradation of methyl orange. The effect of TTIP:Fe3O4 ratio and carbon content on the degradation rate were studied. Methyl orange degradation rate increased with the increase in TTIP:Fe3O4 ratio but decreased by increasing carbon content.

As one of the fundamental issues of the new poly-generation system on the basis of gasification gas and coke oven gas, carbon dioxide reforming of methane experiments have been performed over coal chars derived from different parent coals in a lab-scale fixed-bed reactor (internal diameter 12 mm, length 700 mm). The char derived from TongChuan coal exhibited higher activity than other samples employed under the same conditions. After the reforming reaction, the char samples were covered with different amounts of carbon deposition which resulted in the surface areas decrease. As the flow rate of feed gas increased from 200 ml/min to 600 ml/min over the Xuzhou char sample at 1050 degrees Celsius, the conversion of methane decreased from 52.7% to 17.5% and the H2 /CO dropped from 0.75 to 0.55. While maintaining the flow rate of CO2 at 20ml/min at 1050 degrees Celsius, the mole ratio of reactants CH4/CO2 was varied from 1 to 1.75 which led to the H2/CO ratio increase from 0.75 to 1.2.

This paper is focused on the study of the viscous flow behaviour of blends of polyethylene and Vacuum Gas Oil (VGO) under dynamic shear. The application of different models for the prediction of the shear viscosity under different industrial operating conditions of shear rates, temperature and base components weight fractions has also been investigated. Viscosimetry measurements of the blends with different polymer fractions between 0 and 10 % wt., temperatures between 333 K and 433 K at shear rates up to 10000 1/s were performed. These blends were shown to have peculiar flow behaviour: exhibiting Newtonian fluid flow property at higher temperatures and lower polymer concentrations, while at lower temperatures and at higher polymer concentrations, showing non-Newtonian shear thinning or pseudo-plastic behaviour. These properties have been shown to be more pronounced at lower shear rates than at higher shear rates. As for the prediction of the blends shear viscosity under simultaneous varying shear rate, polymer weight fraction and temperature changes, a very good fit of the experimental viscosimetry data to the proposed unified Sisko-Arrhenius model has been obtained, especially considering the high number of experimental data fitted and model parameters simultaneously optimised.

A batch kraft cooking simulator has been developed with the purpose of simulating the cook of wood chip mixtures. Surveyed equations are modelling diffusion and simultaneous reactions inside a planar chip and external transfers in the outer liquor phase. Three reaction phases (initial, bulk and residual) are described by apparent first-order kinetics, affected by temperature (Arrhenius law). Cooking is controlled by reagent charges, heat-up time and plateau temperature and time. In past works, kraft modelling had been designed for batch cooks of mono-species chips. In this work, simulation was upgraded to allow the cook of chip mixtures: either mixed-size chips, according to a thickness distribution law, or mixtures of different wood species. In the latter case, initial composition, morphological characteristics and chemical kinetics are proper for each wood category. Simulation results are average parameters such as lignin content (also given as kappa number), pulp yield and residual alkali as well as chip profiles (lignin, polysaccharides and alkali), from which homogeneity indexes are calculated. The effects of thickness distribution law and oversized chips in the population are first studied. Oversized chips cook much less when they are in few numbers in a large population of small chips. This affects mean cooking results and extent of lignin distribution within chips. Studying chip mixtures from different woods focused first on the effect of morphological parameters such as wood porosity which effected delignification rates and apparent activation energies. Porosity acts on the inner-outer liquor and alkali partition, also affected by diffusion. Morphological characteristics were compared to chemical effects by varying chemical reaction activation energies. It was found that a difference of 20% on the activation energies of two woods cooking together acted dramatically on cooking results. As a consequence, lignin content and pulp yield within chips at the end of the cook were widely distributed. Finally, cooking results are more affected by chemical differences than by morphological differences, but both effects cumulate and contribute to spread lignin and polysaccharide content distributions in the final pulp.

The cyclic water gas shift reactor (CWGSR) is based on the repeated reduction of a fixed bed using a mixture of hydrogen and carbon monoxide and its subsequent oxidation with steam to produce pure hydrogen. The reactor is analyzed on a conceptual level using a spatially distributed, dynamic model. The model assumptions and the resulting model equations are presented, and important parameters are discussed. Simulation results show that the CWGSR reactor has a poor performance for co-flow configuration of the gases during reduction and oxidation phase, but the reverse-flow configuration seems to be a very attractive option. Parameter variation of the duration of the reduction phase indicates that especially short cycling times not only yield high energetic performance, but they also decrease thermal and morphological stress on the fixed bed material. In addition, the counter-flow CWGSR with short cycling times shows an inherent heat integration like in a Matros reactor, which opens attractive options for system integration of this reactor with other process steps. The behavior of the CWGSR is compared to a pressure swing adsorption reactor (PSA), which shows common features, but also significant differences between both types of cyclic fixed bed reactors.

The operation of continuously stirred tank bioreactors (CSTBs) at minimum cost is a major concern of operators. In this work, a CSTB design strategy is presented where impeller stirring speed and aeration rate are optimized to meet the oxygen demand of growing cells, simultaneously minimizing the capital and operating cost. The operating cost is limited to the cost of utilities. The optimization scheme assumes a given fermentor tank size, and that the properties of the culture medium and the oxygen respiratory requirements of the microorganisms being cultivated are known. It is possible to choose between two different turbine impellers during the design process. The equations, constraints, and the CSTB design strategy employed by the program are described. The effect of microbial species, ions in the culture medium, impeller style, as well as changing CSTB size and biomass input density on the optimum operating conditions, is examined. The mass transfer coefficient, gas holdup, mixing speed, and aeration rate are all reported at optimized cost conditions. A study of the effects of various parameters on the CSTB design are shown.

Exergetic Life Cycle Assessment (ELCA) is applied to a wastewater treatment plant (WWTP) by activated sludge in order to demonstrate the environmental and exergetic effect of biogas recovery within the whole system boundaries. Two methods of recovery are compared: a simple burner (Burner scenario) and a combined heat and power engine (CHP scenario). The results showed that biogas recovery reduces the depletion of natural resources and decreases ecological impacts. Eutrophication, toxicity and ecotoxicity impacts are not affected by biogas recovery in the Burner scenario and the change is not significant in the CHP scenario. Irreversibility is added to the system by biogas recovery. This is because of the nature of the burnt mixture, which is different from conventional fossil fuel and because of the addition of units such as CHP and heat exchangers. The CHP fed with the biogas cannot fulfill the total demand in thermal energy for heating and drying in comparison to the burner. Natural gas should be burnt additionally and a heat exchanger introduced. The irreversibility of the CHP scenario is larger than the Burner's one, but the former allows reducing electricity consumption by 22.7%. Moreover, exhaust gas has a positive effect from the exergy point of view. It contains an excess potential work which could be recovered in another function. Based on ozone layer depletion, photochemical oxidation, acidification and marine aquatic ecotoxicity impacts, biogas recovery with a CHP scenario is better than with a Burner scenario. But based on abiotic resources depletion, global warming potential, irreversibility and excess potential work the second strategy, with a Burner scenario, is the best one. In process optimization, the focus should not be only on potential impacts reduction. The decrease of the irreversibility produced by new functions introduced in the system should also be taken into account. The other subsystems within the system boundaries should be looked at especially those related to electricity production. The ELCA is a useful tool for system ecodesign and for finding the best way to promote renewable fuels versus fossil ones.

The direct electrochemistry of catalase (Cat) immobilized in agarose hydrogel film on glassy carbon (GC) electrode was investigated. A pair of well-defined and quasi-reversible redox peaks both in aqueous buffer and ethanol-aqueous mixture was obtained. The formal potential (E°') indicates the reactions origin from the direct electron transfer between the CatFe(III)/(II) couple and the electrode surface. The E°' is linearly dependent on solution pH (redox Bohr effect), indicating the electron transfer of the CatFe(III)/(II) redox couple accompanied with the transfer of a proton. The electron transfer can be facilitated in ethanol-aqueous mixture for the reason of partial dehydration of the distal heme pocket. The water pools in agarose hydrogel play an important role in preventing either the change of conformation or the inactivity of Cat from polar organic solvent. Cat retains its original conformation in the agarose film that was confirmed by UV-Vis spectra and electrochemical behaviors in comparison to the controlled experiments using free hemin. The catalytic reactions to peroxides (hydrogen peroxide, cumene hydroperoxide, t-butyl hydroperoxide, 2-butanone peroxide) using Cat-agarose modified electrode were also explored both in aqueous buffer and ethanol-aqueous mixture. The method could be application to the preparation of the hydrogel based third generation biosensors or bioreactors in organic media.

The intensified technologies offer new prospects for the development of hazardous chemical syntheses in safer conditions: the idea is to reduce the reaction volume by increasing the thermal performances and preferring the continuous mode to the batch one. In particular, the Open Plate Reactor (OPR) type ``reactor/exchanger" also including a modular block structure, matches these characteristics perfectly. The aim of this paper is to study the OPR behaviour during a normal operation, that is to say, after a stoppage of the circulation of the cooling fluid. So, an experiment was carried out, taking the oxidation of sodium thiosulfate with hydrogen peroxide as an example. The results obtained, in particular with regard to the evolution of the temperature profiles of the reaction medium as a function of time along the apparatus, are compared with those predicted by a dynamic simulator of the OPR. So, the average heat transfer coefficient regarding the ``utility" fluid is evaluated in conductive and natural convection modes, and then integrated in the simulator. The conclusion of this study is that, during a cooling failure, a heat transfer by natural convection would be added to the conduction, which contributes to the intrinsically safer character of the apparatus.

In the last few years, the interest on nanomaterials and their applications have increased in a considerable way. Hence, the knowledge of the possible hazards on human health becomes necessary. Besides the description of the toxicological effects of nanomaterials, the exposure level on the worksites is one of the key data of the problem. The present work aims at studying the resuspension of ultrafine particles in the air during the falling of nanostructured powders.A numerical approach has been developed aiming at simulating the free falling of a powder cluster. The results show that a resuspension of particles occurs following the powder cluster deformation during the free fall of the particles in the air. Isolated particles remain suspended in the air for a long time.Free falling experiences have been carried out in a 180*50*80 cm chamber with TiO2 and SiO2 nanostructured powders. An Electric Low Pressure Impactor (ELPI) has been used for measuring the particle number concentration as well as the size distribution of the generated aerosols (particle suspension in the air). The agglomerates constituting the original powder were resuspendend in the air. The presence of ultrafine aggregates of TiO2 and SiO2 nanoparticles in the air has been checked by ELPI measurements and SEM visualizations of the ELPI stages. The aerosol size distribution is bimodal with two populations, concerning a micrometric nanostructured agglomerates, and ultrafine aggregates coming from micrometric agglomerates break-up. The influence of the height of the fall upon the aerosol concentration is significant. However, the aerosol size distribution remains roughly constant for a given powder, independently of the height of the fall.

An experimental study of isolated mixing regions (IMRs) in a cylindrical vessel stirred by three different impellers (a six-blade Rusthon turbine, a four-blade Lightnin A315 impeller and an axial CPE RTF4 impeller) has shown the existence of IMRs in all three systems at low Reynolds numbers. Calculations of the Re ranges in which IMRs exist, torque measurements and flow visualizations enabled the analysis of the effects of impeller type and the flow structures when IMRs were present. Particular attention was given to the case of the Rushton turbine, where digital image analysis revealed that the mechanism of IMR disappearance can be described as a period-doubling locus in the physical space, in which IMRs completely disappear at a critical Re, resulting in global mixing.

Proton-exchange membrane fuel cells (PEMFC) are regarded as a possible alternative power source for stationary and mobile applications. Due to the catalyst costs, many researchers have been studying the membrane and the electrode assembly (MEA) manufacturing processes that can reduce the content of Pt in the electrocatalyst layer while maintaining the performance. The MEA is the heart of the PEMFC and the catalyst plays an important role in the fuel cell operation.There are different methods to prepare MEA. In this work, the catalyst ink was straightly applied on the gas diffusion layer (GDL) by an aerograph. Then, this electrode was assembled to the membrane by hot press.From the point of view of operation, the main variables are: temperature, pressure and time of press. Operational range was established from previous experiments to find roughly the optimal conditions. Finally, these MEAs were tested in a 5 cm2 PEMFC. The operational temperature was 30°C. Due to higher temperatures it was difficult to keep the humidity of the membrane constant. The operational pressure and flow were constant throughout the experiments. Different techniques to characterize the MEAs, linear sweep voltammetry and cyclic voltammetry were applied. With these techniques the permeation of hydrogen and the electrochemically active surface area of electrode catalyst were determined.With the results obtained in the experiments, the optimal values of the fabrication parameters were established.

A new process combining non-thermal plasma treatment and filtration has been studied for the treatment of diluted gaseous effluents containing VOCs. The removal of a VOC model molecule, beta-pinene, in air was studied. The results showed that the pollutant was chemically modified by soft oxidation reactions in the plasma treatment step and that the resulting products could be trapped on a filter with high efficiency. As a result, the process was less energy-consuming compared to complete oxidation. The pollutant could be injected before or after the discharge zone without affecting the performance of the process. Nopinone, identified by GC-MS analyses, is the main product of the plasma treatment step. It was hypothesized that this product results from the oxidation of beta-pinene by 'excited' ozone produced by the discharge and the destruction of beta-pinene. The product was therefore modelled by a second-order reaction between beta-pinene and ozone. In the second part of this work, a semi-industrial scale pilot capable of treating a gas flowrate of 50 m3/h was built. The pilot was designed with the assistance of process simulations made by coupling a flow model (obtained by a CFD code) and the previous kinetic model. The results show that the performances of the pilot measured experimentally were in agreement with the predicted ones.

We present a mathematical method for efficiently compounding information from different models of species diffusion from a chemically reactive boundary. The proposed method is intended to serve as a key component of a multiscale/multiphysics framework for heterogeneous chemically reacting processes. An essential feature of the method is the merging of wavelet representations of the different models and their corresponding time and length scales. Up-and-down-scaling of the information between the scales is accomplished by application of a compounding wavelet operator, which is assembled by establishing limited overlap in scales between the models. We show that the computational efficiency gain and potential error associated with the method depend on the extent of scale overlap and wavelet filtering used. We demonstrate the method for an example problem involving a two-dimensional chemically reactive boundary and first order reactions involving two species.

The synthesis of pyridine bases from acetaldehyde, formaldehyde and ammonia through aminocyclization continues to provide the best prospect for meeting growing demand. A proper selection of catalyst and standardization of process parameters are vital to achieve a market friendly product distribution and reactor operation. In this work, the major responsible factors for enhancing the activity and selectivity of HZS-5 catalysts have been identified and their individual and combined effects on aldehyde conversion, coke formation and selectivity to pyridine formation have been assessed. A priori assessment of catalyst time on stream behavior has been achieved by modeling the catalyst deactivation process.

In this experimental work, the ethanol steam reforming reaction for producing hydrogen was studied in both a traditional reactor (TR) and a Pd-Ag dense membrane reactor (MR). Both reactors have been packed with a commercial Ru-based catalyst. The experimental tests have been performed in the temperature range 400-500 °C and in the pressure range 2.0-3.6 bar.The results are reported in terms of ethanol conversion, hydrogen production, product selectivities and hydrogen recovery (for the MR only). It has been found that the MR is able to increase the ethanol conversion as well as increase the hydrogen production with respect to a traditional reactor. Moreover, part of the hydrogen produced in the MR is recovered as a CO-free hydrogen stream and is suitable for feeding a PEM fuel cell system.

Spouted beds have a widespread application in the processing industry for efficient contacting of large particles with a gas. However, there is no detailed understanding of the complex behaviour of these systems, especially for fine particles, which means significant scale-up problems in industry. This paper approaches fundamental aspects of the computational fluid dynamic simulation of fine particle spouting. Using the commercial CFD simulation package Fluent (version 6.3), the spouting hydrodynamics of fine particles in a conical spouted bed is simulated and compared with experimental data.Fluent code offers a variety of models to describe the physical phenomena occurring in these kinds of reactors. In some cases, the choice is straightforward, whereas in other cases more than one option is valid a priori, and so the best one has to be selected. The main choices are the Lun et al. (1984) approach for granular kinetics and the Gidaspow model for drag force.In order to validate this selection process, model predictions are compared with experimentally observed hydrodynamic patterns, whereby CFD model parameters can be tuned. It has been proven that after this tuning, the model explains the hydrodynamic behaviour of the bed and the influence of geometric parameters and bed nature (sand, glass beads) concerning spout stability and minimum spouting velocity. Nevertheless, peak pressure drop values predicted by the model are considerably smaller than the experimental values. The model also provides reasonable predictions for spout shape, local bed voidage and air and particle velocities.

In the nuclear industry, large volumes of liquid wastes with a low radioactivity have to be treated. The method which is commonly applied to remove contaminants consists of the use of an insoluble finely divided solid material formed in situ by precipitation in the waste stream. In this study, a new mathematical approach of the adsorption of radioactive strontium on growing barium sulphate precipitate is established and used for the decontamination process modeling in both continuous and semi-continuous stirred tank reactors. The comparison of the two types of reactors is carried out under the same operating conditions by studying the influence of the stirring speed and, respectively, the mean residence time (for continuous stirred tank reactor) and/or process time (for semi-batch stirred tank reactor) on the efficiency of the decontamination process. Simulations have shown that the mean residence time is the critical parameter in controlling decontamination in the continuous reactor, while the stirring speed plays a minor role. Comparison of results indicates that the best configuration to carry out the decontamination process is the semi-batch stirred tank reactor.

The aim of this paper was to characterize and to scale-up the CNBr chemical activation of Sepharose CL-4B in a stirred tank reactor to purify the recombinant Hepatitis B surface antigen for use in vaccines. The activation quality was assessed measuring the concentration of the cyanate esters and the percentage of nitrogen in the activated matrix. The Sepharose CL-4B incorporated less than 50% of the initial CNBr amount added to the matrix, but the monoclonal antibody CB.Hep-1, used as immunoligand to purify the rHBsAg, was efficiently immobilized in a weakly activated matrix (<8 ?mol/mL of matrix). The impellent type has a significant influence on activated matrix quality. The constant power per volume unit was a proper criterion to scale-up the Sepharose CL-4B March's modified chemical activation procedure with CNBr.

A new method for designing an immobilized column reactor is proposed. The method is iterative and minimizes an energy-cost function to determine the column reactor dimensions. The column reactor dimensions obtained by employing this method take into account the material balance, process constraints and productivity targets. The problem is formulated in such a way that it addresses and resolves multiple goals simultaneously to achieve the desired productivity. A case study of the application of this method for designing an immobilized cell column reactor for L–methionine production is presented.

This paper presents a thermodynamic model for the estimation of impurities in the raw synthesis gas and in the slag resulting from gasification of solid waste. Based on thermodynamic equilibrium calculations and mass balances, the model takes into account the possibility of each impurity becoming an oxide, a chloride, or remaining in its elemental form. The model includes a comprehensive set of thermodynamic data for a wide variety of chemical species used to estimate the equilibrium constants. By solving the equilibrium reaction equations, the model predicts which pollutants are formed and in what amounts as well as their distribution in the raw synthesis gas and in the slag. Predicting the distribution and fate of these pollutants is particularly important for the design of a gas cleaning system for the raw synthesis gas and for deciding on the disposal options of the slag. The model can be applied to different waste materials, including municipal solid waste, mixed plastics waste, auto-shredder residue (ASR) and biomass. A comparison between the model predictions and the operational data from a commercially-available gasification process (Thermoselect) shows a close agreement between the estimated and real data.

The concepts of equilibrium and optimum have always been placed at the heart of chemical engineering science. Their understanding is extremely important both from the academic and practical aspects. In this paper, a complete analysis of the concept of equilibrium and optimum in terms of how they are related conceptually, graphically and mathematically is provided. The analyzed problem can be considered as a ``Germinating Seed Problem (GSP)", which gives rise to a ``Growing Tree" of problems.

An extremely simple and elementary, but rigorous derivation of temperature distribution of a reaction-diffusion process is given using the variational iteration method. In this method, a trial function (an initial solution) is chosen with some unknown parameter, which is identified after a few iterations according to the given boundary conditions. Comparison with the exact solution shows that the method is very effective and convenient.

An agitated two-phase flow and the mixing progress in an oil-water stirred tank are studied numerically using FLUENT software. The stirred cylindrical tank is equipped with an axial-type turbine and a radial-type impeller. The full Eulerian multiphase approach coupled with the standard turbulence model is performed to deal with two-phase flow with a higher volume fraction of the second (dispersed) phase. The computation is completed by using unstructured meshes in a multiple reference frame (MRF). For the initial condition of the simulation, oil is set on the top part of the tank with 30% of the total fluid volume. The simulation is conducted to get distributions of two-phase flow speed, pressure and volume fraction and to successfully illustrate how the mixing of two-phase components progresses in the stirred tank. The computational results obtained in this study would be useful for explaining the two-phase flow patterns on the mixing process and extending the applications of multiphase stirred reactors.

A three–component particle–dynamics anemometer is used to measure, in the near–burner region, the influence of the primary air ratio on the gas/particle two–phase characteristics for a centrally fuel rich swirl coal combustion burner, on a gas/particle two phase test facility. Velocities, particle volume flux profiles and particle relative number concentrations were obtained. With a low primary air ratio, the axial velocities for gas and particles on the chamber axis are always small and easily reach the negative, and the central recirculation zone is easily formed and much closer to the outlet of the burner. In each cross–section, in the radius range from R<d=0 to 0.11, the particle volume flux with r1=23.85% is always larger than that with r1=16.56%, which means the degree penetration with a high primary air ratio is higher than that with a low primary air ratio. The influence of gas/particle flow characteristics with a different primary air ratio on combustion has been analyzed.

This work deals with the theoretical and experimental study of the transient behaviour of a membrane-attached biofilm reactor (MARB) when it is exposed to a series of pulse injections of concentrated solutions of sodium acetate, used as a synthetic wastewater. The MARB is connected to a reservoir tank with full recirculation containing the synthetic wastewater, and oxygen permeates through the wall membrane to the biofilm attached to it. For the two experiments reported in this work air is also sparged into the residual water in the tank providing an extra source of oxygen that diffuses simultaneously from the membrane and from the liquid into the biofilm. A pseudo-heterogeneous model using Monod kinetics with dual substrate limitation was employed to predict the observed evolution of substrate and dissolved oxygen concentrations in the MABR. The model accounts for the counter-diffusion of substrate and oxygen as well as for the reaction within the biofilm. It also predicts biomass growth and the production of extra cellular polymers, which in turn causes the biofilm to grow. Transport and kinetic parameters previously estimated, are used in the model to predict the growth rates in the biofilm and allow the analysis of the relative contribution of the rates of mass transport by diffusion, convection and growth reaction.

The present investigation attempts to study the hydrodynamic characteristics of the fluidized bed electrode. A core-annular flow model with a transfer of particles between core-annular layers has been proposed to describe the flow behavior of conducting particles in the fluidized bed electrode. The effect of individual parameters on the rate of the particle transfer across the layer and thickness of the core-annular has been critically examined and the model simulation has been verified with the data reported in the literature.

Gas flow in a gas–solid fluidized bed is characterized by the predominance of bubbles. When gas flow is more than the minimum fluidization velocity, the top of the fluidized bed may fluctuate vigorously leading to unstable operation. Bed fluctuation and fluidization quality are interrelated. The quality of fluidization can largely be improved by introducing baffles in bubbling and turbulent fluidized beds. In the present work three baffle geometries, i.e., circular, triangular and square are used to determine different hydrodynamic parameters such as minimum fluidization velocity, bed expansion, pressure drop across the bed, fluctuation ratio, expansion ratio, etc. in a bubbling fluidized bed. A new parameter blockage ratio is introduced to analyze the behaviour of baffled fluidized beds. It is found from the current experimental studies that the blockage ratio mainly influences the hydrodynamics of the bed rather than the shape of the baffle.

This paper presents a Fault Detection and Isolation (FDI) method for stochastic nonlinear dynamic systems. First, the developed fault detection method is based on statistical information generated by the extended Kalman filter (EKF) and is intended to reveal any drift from the normal behaviour of the process. A fault of a chemical origin in a perfectly stirred batch chemical reactor, occurring at an unknown instant, is simulated. The purpose is to detect the presence of this abrupt change, and pinpoint the moment it occurred. It is also shown that the convergence of the EKF is accomplished more or less rapidly according to the nature of the noise generated by the measurement sensors. The state estimate is observed and discussed, as well as the time delay in detection according to the decision threshold. Then, this study shows another method of tackling the problem of the physical origin diagnosis of faults by combining the technique based on the standardized innovations and the technique using the multiple extended Kalman filters for a strongly non-stationary nonlinear dynamic system. The usefulness of this combination is the implementation of all the fault dynamics models if the decision threshold on the standardized innovation exceeds a determined threshold. In the other case, one EKF is enough to estimate all the process state. An algorithm is described and applied to a perfectly stirred chemical reactor operating in a semi-batch mode. The chemical reaction used is an exothermic second order one.

A liquid-solid circulating fluidized bed (LSCFB) is operated at high liquid velocity, where particle entrainment is highly significant and between the conventional liquid fluidized bed and the dilute phase liquid transport regimes. In the present work, systematic experiments were carried out in a 0.094 m ID and 2.4 m height laboratory-scale liquid-solid circulating fluidized bed apparatus by using various solid particles and tap water as a fluidizing medium to study the hydrodynamics (axial solids holdup and solids circulation rate). The effects of operating parameters, i.e., primary liquid flow rate in the riser (jf), auxiliary liquid flow rate (ja), total liquid flow rate (jl), particle density (?s), particle diameter (dp) and solids feed pipe diameter (do) on the axial solids holdup distribution were analyzed from the experimental data. Finally, a correlation was developed from the experimental data to estimate average solid holdup in the riser, and it was compared with present experimental and available data in the literature. They agree well with a maximum root-mean-square deviation of 9.12 %.

Experimental and numerical studies for natural convection in two dimensional regions formed by a constant flux heat horizontal elliptic tube concentrically located in a larger, isothermally cooled horizontal cylinder were investigated. Both ends of the annulus are closed. Experiments were carried out for the Rayleigh number based on the equivalent annulus gap length ranges from 1.12x107 up to 4.92x107; the elliptic tube orientation angle varies from 0o to 90o and the hydraulic radius ratio, HRR, was 6.4. These experiments were carried out for the axis ratio of an elliptic tube (minor/major=b/c) of 1:3. The numerical simulation for the problem is carried out by using commercial CFD code. The effects of the orientation angle as well as other parameters such as elliptic cylinder axis ratio and hydraulic radius ratio on the flow and heat transfer characteristics are investigated numerically. The numerical simulations covered a range of elliptic tube axis ratios from 0.1 to 0.98 and for the hydraulic radius ratios from 1.5 to 6.4. The results showed that the average Nusselt number increases as the orientation angle of the elliptic cylinder increases from 0o (the major axis is horizontal) to 90o (the major axis is vertical) and with the Rayleigh number as well. Also, the average Nusselt number decreases with the increase of the hydraulic radius ratio. An increase up to 1.75 and further increases in the hydraulic radius ratio leads to an increase in the average Nusselt number. The axis ratio of the elliptic cylinder has an insignificant effect on the average Nusselt number. Both the average and local Nusselt number from the experimental results are compared with those obtained from the CFD code.Both the fluid flow and heat transfer characteristics for different operating and geometric conditions are illustrated velocity vectors and isotherm contours that were obtained from the CFD code. Also, two correlation equations that relate the average Nusslet number with the Rayleigh number, orientation angle, and hydraulic radius ratio and axis ratio are obtained.

Experimental investigations on the mixing behavior of a spherical particle in a spout-fluid bed with a cross section of 0.1 m×0.03 m and height of 0.5 m were carried out. The image processing technology and bed-frozen method were employed to measure the axial and radial concentration of the tracer at different times. Four various initial conditions (top, side, bottom and middle loading) were used to examine the influence of the tracer location on the mixing. In addition, the underlying mixing mechanisms were preliminarily discussed in terms of the evolution of the mixing index. It is shown that the initial tracer location affects the initial mixing rate but not the final mixing degree. The top and bottom loading cases characterised by dominant axial mixing perform significantly better than the side loading case characterised by dominant radial mixing. Due to the axial rapid convection and radial intense diffusion, the mixing speed for a middle loading case is much faster compared to other cases. The results also demonstrate that the convection caused by the circulation and diffusion among the circulation rolls are two main mixing mechanisms in a spout-fluid bed.

The present work deals with the catalytic behaviour of a series of ceria and manganese-based catalysts for the deep single combustion chlorinated compounds in air. Our attention is focused on both activity and product selectivity of Ce/Zr and Mn/Zr in the oxidation of 1,2-dichloroethane (1,000 ppm) and trichloroethylene (1,000 ppm). This study also makes an attempt to establish a correlation between physico-chemical properties and catalytic performance.Both series of mixed oxides exhibited a noticeable activity in the combustion of both compounds, Ce0.5Zr0.85O2, Ce0.5Zr0.5O2 and Mn0.4Zr0.6O2 being the samples with the most promising catalysts. A remarkable acidity and readily accessible active oxygen species played a key role in determining the catalytic behaviour. As for the product selectivity, CO2, CO, HCl and Cl2 were the main products. The yield of CO2 and Cl2 was favoured as cerium or manganese content was increased. However, selectivity to chlorine was noticeably limited by the addition of stream in favour of HCl.

Direct Methanol Fuel Cells (DMFCs) have recently attracted the interest of portable applications due to their superior specific energy density compared to the best rechargeable battery and for their potentialities of instantaneous refueling. The most recent literature in the field of DMFCs has directed increasing interest on the role of the flow fields on the performance of the FC itself. The most "primitive" designs (e.g. parallel channels) have generally been dismissed and substituted by serpentine or interdigitated flow patterns. The serpentine pattern forces the entire feed flow rate to pass through a serpentine spanning over the entire electrode surface. This system is particularly suited to drive gas bubbles out of the system and therefore it seems to be particularly suited for the methanol side. The interdigitated flow field pattern is particularly suitable only for the air feed to the DMFC. The effect of the channel and graphite rib geometries is of critical importance. The choice of the correct geometry is thus a question of compromise which can be drawn on the grounds of modeling calculations and experimental checks. A series of simulations in CFD (fluent 6.1) were thus performed on a multichannel serpentine matrix for the anode side (methanol feed) piled up in a stack hosting 40 MEAs (nominal power 250 W; 222 cm2 membrane surface per cell). Three different channel geometries were modeled. This paper shows that a series flow is not suitable for the too high pressure drop and average velocity into channels it implies. Optimal flow distribution (i.e. low pressure drop, acceptable average velocity and a good methanol distribution) seems to be guaranteed with three serpentines per cell for fuel cell stacks of a nominal power of 250 W.

Titanium dioxide photocatalysis is an emerging and very promising technology to reduce odorous industrial pollution. Using an adsorbent could offer an interesting way to enhance the pollutants photodecomposition rate. Our project deals with industrial emissions that contain a high concentration of esters such as ethyl hexanoate (EH) which has a very low olfactory detection threshold and it is very unpleasant both in industrial indoor air and in outer emission.Photocatalysis is performed here within a mixed flow reactor involving two fibrous media. The first one is a media coated with TiO2, SiO2 and zeolite and the second one is a mixture of TiO2, SiO2 and activated carbon (AC). A three-level full factorial design of experiments is performed with TiO2 – zeolite media. It permits us to determine the impact of two main parameters on adsorption and photocatalysis phenomena; moisture inflow (from 0 to 15 g.m-3) and pollutant concentration (from 50 to 150 mg/m3). Adsorption capacity ranges between 4 to 37 mg EH/g of media. It decreases while humidity increases due to competitive adsorption of water and pollutants on photocatalyst sites. Moreover the EH conversion rate increases when inlet concentration decreases. An optimal relative humidity can be deduced to reach an optimal conversion rate for a fixed inlet concentration. Conversion rate values of 24, 39 and 25 % are observed at respective humidity values of 0, 7.5 and 15 g.m-3 for a 100 mg/m-3 inlet concentration. The designs of the experiment are descriptive and predictive for adsorption capacity and degradation rates.With TiO2 – AC media, experiments are carried out at 15 g.m-3 of humidity and 100 mg/m3 of EH inlet concentration. As expected, a high-grade adsorbent media leads to a higher adsorption capacity compared with TiO2 – zeolite media (130 instead of 4 mg EH/g of media). Nevertheless, even if adsorption capacity is higher, conversion rate decreases (23 % instead of 46 %). Thus, in our experimental conditions, a very high content of adsorbent in the photocatalyst media does not improve the global degradation efficiency probably due to the lack of desorption of pollutants from AC.

An industrial steam reforming reactor producing hydrogen is simulated using the three-dimensional Computational Fluid Dynamics (CFD) technique. The fixed bed reactor is filled with a nickel oxide catalyst. Effects of operating conditions such as temperature and steam to methane ratio on the reformer performance are investigated. Simulation results show that a steam to carbon ratio of more than 4 increases in the ratio does not have a notable influence on methane yield. Moreover, it shows that methane conversion is strongly affected by reactor skin temperature and higher skin temperature leads to an increase in the methane conversion. The results were successfully validated with industrial data obtained from a hydrogen plant at a Tehran refinery.

A thermodynamic analysis for the process concept of hydrogen production based on the combination of the water gas shift (WGS) and CO2 capture reactions (Absorption Enhanced Water Gas Shift, SEWGS) is presented. The chemical equilibrium analysis of this reaction system was performed to select the proper CO2 absorbent among: calcined dolomite (CaO•MgO), Li4SiO4 and Na2ZrO3 to be used in the process. Results indicate that the use of Na2ZrO3 produced the highest hydrogen concentration among absorbents studied. Results also revealed that the maximum hydrogen concentration (97% mol) can be achieved with a feed molar ratio of CO/Na2ZrO3/H2/O = 1/1/2 at 500°C at atmospheric conditions. The use of a catalyst for such processes may not be needed, since the high temperature at which these reactions are proposed may promote homogeneous non-catalyzed reactions. However, if the combination of both reaction kinetics (WGS and carbonation) are not fast enough to reach equilibrium, a new non-conventional WGS catalyst may be needed.

Inclusions removal by flotation in mechanically agitated vessels is widely used in liquid aluminium treatments. Originating from different sources (oxide skins, refractory or recycling wastes), inclusions may have disastrous repercussions, such as physical properties alterations of the final products or difficulties during forging processes.With the aim of both a better understanding of the physical processes acting during flotation and the optimization of the refining process, a mathematical modelling of the behaviour of the inclusions population has been set up. Agglomeration, flotation and settling of inclusions are considered here. The model is divided in two steps: a 3D calculation of the biphasic liquid aluminium/bubbles fluid flow based on an Euler/Lagrange approach and a population balance. The population balance is performed with the assumption of a perfectly stirred reactor, and the calculation of agglomeration and flotation rates relies on mean values of fluid flow properties provided by the CFD simulation. Kruis & Kusters' model is employed for the calculation of the agglomeration rate and Kostoglou's model is used for the flotation rate. The fixed pivot method of Kumar & Ramkrishna is employed for the resolution of the population balance equation.A laboratory scaled flotation vessel is modeled and results of a simulation are presented.

This paper outlines the development of a microwave heated apparatus for the production of silicon carbide (SiC) based ceramic matrix composites via chemical vapor infiltration. An innovative pilot scale reactor was designed and built. A coupled thermal and electromagnetic model was developed in order to predict the temperature profile inside the reactor. The results obtained from the model demonstrated that the electric field inside the sample was constant. This fact is particularly important in order to prevent the thermal instabilities (run-aways) that are typical in the case of microwave heating. Therefore the heating was uniform with the aid of a mode stirrer that achieved a better distribution of the microwave power and then improved the process efficiency. The infiltration cycles were carried out on SiC fiber preforms and resulted in an excellent average weight increase with respect to the initial sample. By using microwave heating, the treatment times were considerably reduced with respect to the conventional process times reported in the literature. The microstructure of the SiC composites were observed by scanning the electron microscopy in order to evaluate the quality and the degree of densification which was achieved within the fiber tows. The SiC deposition inside of the sample was sufficiently homogeneous and compact, even if a certain degree of inter-tow porosity was still evident.

Peirce-Smith converters (PSC) are chemical reactors where copper matte reacts with air. A conventional PSC is a long horizontal cylinder where air is injected laterally into the cooper bath through submerged tuyeres. In these PSC, air is injected at high velocities to obtain an adequate mixing of the copper bath and to avoid tuyere blockage. An alternative PSC configuration uses top blowing of air accompanied by gentle nitrogen bottom stirring. In this work, the direct bottom injection of air at low inlet velocity was studied by means of transient multiphase 3D CFD numerical simulations considering three blowing conditions. The ?-? turbulence model and the volume of fluid model (VOF) were used in order to model the turbulent nature of the flow and to deal with the multiphase flow. Special attention was paid to the air bubbles formation and its effect on the copper bath mixing. The dynamic behavior of turbulent kinetic energy and the average velocity of the copper matte were analyzed. The numerical simulations suggest that the relationship between air inlet velocity and bath mixing is non linear. However, using the air bottom injection at low velocities, the obtained copper bath nominal velocity is similar to that reported in a conventional PSC.

In this study, the influence of hydrodynamic models on dynamics of the fluidized bed polyethylene production process has been investigated via modeling. The overall fluidized bed model consists of two integrated sub-models. The hydrodynamic sub-models, which are the simple and dynamic two-phase, well mixed and tanks in series models, were used in the study along with the reaction sub-model from the literature. The hydrodynamic sub-models differ from each other in terms of flow structure and the presence of solids in the disperse phase. The conventional PID controllers were used to control the reactor conditions for these different hydrodynamic conditions. The results of this study showed that a choice of a hydrodynamic model for the fluidized bed polyethylene reactor has a minor effect on the dynamic response and the grade transition of the polyethylene production process and a simple hydrodynamic sub-model can be used for the proper dynamic modeling and control of the process.

The aim of this study is to develop a two-steps process of thermal valorisation of wood waste containing urea-formaldehyde and melamine-formaldehyde resins such as wood board or laminated flooring. The first step of the process known as "refinement" is a low temperature pyrolysis between 250°C and 300°C which aims to remove nitrogen thermally. This step is studied by IRTF spectrometry. Ultimate analysis enables the assessment of the efficiency of the process in terms of nitrogen removal. It is shown that around 68 wt% of nitrogen can be removed during this first stage and that a 250°C treatment gives the best results in terms of energy recovery. The second step is a fast pyrolysis of the residue of the first step which aims to produce combustible gas. Three temperatures of pyrolysis are studied (800°C, 900°C and 1000°C) by GC-TCD analysis. It is shown that the temperature of the pyrolysis has an influence on the volume of gas produced and on its Low Heating Value. The best results are obtained with the 1000°C pyrolysis which produces a higher volume of gas and gives the best energetic efficiency. The residual char after fast pyrolysis step still contains energy and nitrogen. Its combustion would improve the energetic efficiency of the process but a conversion into an activated char has to be considered to improve the economic efficiency of such a type of waste disposal process.

Catalytic vapor phase alkylation of aniline with ethanol was effected in the presence of a zeolite catalyst in a fixed bed reactor at atmospheric pressure and moderate temperatures. Experimental runs were carried out at five different temperatures (350, 370, 390, 410 and 430 °C) with a constant aniline to ethanol ratio (1:5) and different catalyst loadings to find the limits of external and internal resistance zones. The resistance due to external mass transfer was overcome by operating at high velocities and the pore diffusion resistance was nullified by conducting experiments with different particle sizes of the catalyst. The effectiveness factor was determined experimentally and the optimum zone of operation where the diffusional resistances are absent was obtained for kinetic experiments to be conducted. The results indicated that below 0.6 cm/sec velocity external mass transfer was likely to influence the rate of reaction. The effect of pore diffusion was accounted for by the effectiveness factor which was nearly unity for an operative range of particle size < 2 mm. Pore diffusion will therefore play a role for a particle size > 2 mm.

The enhancement of the surface incident radiation on the walls of an externally-irradiated bubble tank photoreactor was studied and modeled by solving the radiation transport equation (RTE) in conjunction with the continuity, momentum and k-e turbulence equations. Computational fluid dynamic (CFD) simulation results were complemented with actinometric runs to determine the effect of the gas flow rate on the radiation loss by reflection at the surface of the gas-liquid mixture due to bursting of the bubbles. The model assumed that the gas-liquid mixture is a semitransparent medium where the light is scattered as a result of specular reflection and refraction when the light rays impinge on the air bubbles. The superficial reflectivity at the top of the gas-liquid mixture was linearly correlated with the superficial gas velocity. In particular, the simultaneous solution of the hydrodynamics and radiation transport equation using CFD allowed us to establish the relationship between the light scattering coefficient and the bubble size and the gas hold-up. The excellent agreement obtained between the experimental data and the CFD model validates the proposed model.

Polymeric cation exchange membranes (PEM) are used in fuel cell technology. These membranes act like a physical barrier between the anode and cathode but the diffusion through the membrane should allow the transport of protons from the anode to cathode at a rate that is enough to supply the energy requirements. They avoid the direct reaction of oxygen and hydrogen that would diminish fuel cell efficiency.The membrane has to be conditioned before use. This conditioning step changes the membrane counter-ion and modifies its water content which affects the diffusion coefficients. Diffusion experiments were carried out in a reactor with two semi-cells of 250 mL with the membrane placed between the semi-cells. Diffusion through the membrane was studied using two system configurations: without applying any potential and applying zero potential drop across the membrane using two Ag/AgCl electrodes.Diffusion of chloride through the membrane is related to membrane permselectivity. Diffusion of hydrogen chloride was followed by measuring the pH of the diluted dissolution and the potential drop across the membrane with two Ag/AgCl reference electrodes. Several experiments were carried out using initial concentrations between 10-3 M to 0.1 M. Results were modelled using Nernst–Planck equations. Results obtained show that the diffusion of a co-ion is a very slow process and that the conditioning step enhances proton transport. Diffusion coefficients obtained were in the range of 10-11 cm2/s for chloride and 10-7 for proton.

In the present work, we have simulated gas-liquid flows in a tall stirred reactor equipped with dual Rushton turbines. A two fluid model along with the standard k-? turbulence model and modified drag coefficient, (proposed by Khopkar & Ranade, 2006) accounting for the effect of bulk turbulence, was used to simulate the dispersed gas-liquid flow in a stirred reactor. The multiple reference frames (MRF) approach was used to simulate impeller rotation in a fully baffled reactor. The computational model was mapped on to a commercial solver FLUENT 6.2 (of Fluent Inc. USA). The model was used to simulate three distinct flow regimes in a gas-liquid stirred reactor: L33-VC (lower impeller-upper impeller), S33-VC and VC-VC. The model predictions were compared with the published experimental data of Bombac & Zun (2000). The predicted results show good agreement with the experimental data for all the three flow regimes. The computational model presented in this work would be useful for simulating different flow regimes in a gas-liquid stirred vessel.

Many interesting problems that include convective transport arise in chemical reactor engineering (for example, tubular reactors). To solve these boundary-value problems, finite-difference schemes with a type of discretization of the convection term have been traditionally used. Some controversy about the discretization form of the convection term has arisen because of the different possibilities, including backward, forward and central discretizations. To overcome this problem, the usage of Green's function formulations for the numerical solution of typical chemical engineering problems with both linear and nonlinear kinetics, diffusion and convection phenomena, is presented. A distinctive feature of the proposed scheme is that boundary conditions are exactly incorporated. The results show that the integral formulation is, in general, superior in accuracy to the different finite-differences schemes. That is, more accurate calculations of the performance factor are obtained in terms of less mesh points and computer time.

Organized systems such as micelles, reverse micelles, vesicles, polyelectrolyte capsules, liquid crystals, etc., formed through a self-assembling process represent nanoreactors that can be used for preparing nanostructured materials. Besides a fascinating academic subject, these nanoreactors provide a unique way to develop a special type of advanced material for a wide variety of applications in electronics, photonics, biomedical and other areas. The article examines the formation, functioning, properties and special attributes of these nanoreactors with a view towards their engineering analysis, design and possible integration in manufacturing technology.

The complete BSM1 model is recognized as representative of activated sludge plants. However, its large number of states may render it inadequate for development of state observers and for control. Thus, a reduced model has been developed for the two main sections of the plant, the anoxic and aerobic reactors. Concepts of model reduction of biological models based on the analysis developed by Bernard (Bernard2005a, Bernard2005b) have been used. The output data have been obtained by simulating the inlet by data representative of dry weather. After transformation and treatment of the data, it has been shown that a kinetic model reduced to two reactions is able to represent 80% of the total variance. The pseudo-stoichiometric coefficients have been estimated and the pseudo reaction scheme has been validated with respect to the actual concentrations at the outlet of a considered section. The dynamics are generally well represented by the reduced model.

In this paper, the design of a miniaturized methanol reformer is considered that can operate in two different modes to produce sufficient hydrogen for generating a net power of 24 W and 72 W. The reformer is modeled as a radial flow packed bed reactor and the Ergun equation is used to model the pressure drop. Simulation studies are conducted to study the effect of steam to methanol ratio, inlet pressure and reactor temperature on the production of hydrogen. It is shown that a volume of 20 ml is required to produce sufficient hydrogen for generating the necessary power if an inlet pressure of 202 kPa and a steam to methanol ratio of 1.5 is used. A temperature of 500 K is required for the lower power application while a temperature of 550 K is required for the higher power application.

Inhibitors of an angiotensin I-converting enzyme were produced from ?-zein in a batch reactor under subcritical and supercritical water conditions. Inhibitors produced under supercritical conditions in a flow reactor assembly were more sensitive. In a flow reactor system 5 mg of inhibitors were produced from 1 micromole of ?-zein. The hydrolysis products of ?-zein obtained in the flow reactor had a higher ACE inhibitory activity of 78% compared to 69% obtained using the batch reactor. An angiotensin I-converting enzyme [EC 3.4. 1 5. l] (ACE) is used to catalyze the production of vasoconstrictor angiotensin II and for the inactivation of the vasodilator bradykinin.

Based on the scale up parameter, X (theoretical power per unit volume = F4/3 R1/3, where F is the impeller Froude number and R is the impeller Reynolds number), it is presented that the said parameter is useful in scaling up the micromixing time in surface aeration systems. Scale up equations correlating X with micromixing time have been presented for the geometrically similar circular surface aeration systems.

Biosorption of Acid Blue 5 dye by the Eichhornia crassipes was investigated in batch and column studies. Batch experiments were conducted to study the effect of initial solution pH and dye concentration. Langmuir and Freundlich sorption models were used to represent the equilibrium data. Experimental breakthrough curves in a column were obtained with bed height (5, 10 and 15 cm), flow rate (20, 25 and 30mL/min) and initial dye concentration (50, 75 and 100 mg/L). An increase in bed height and initial dye concentration favors the dye biosorption, while the minimum flow rate produced maximum dye biosorption. It was observed that the uptake of Acid Blue 5 using a bed height of 15 cm, flow rate of 20 mL/min and initial dye concentration of 100 mg/L was found to be more when compared to all other bed height, flow rate and initial dye concentration studied in the present investigation. The Bed Depth Service Time (BDST) model was used for the evaluation of continuous sorption data.

Carbon/silica nanocomposite films with a hexagonal P6mm structure were fabricated directly by the oxidation and carbonization of surfactant/silica nanocomposite films, which were obtained by a dip-coating technique through a combination of sol-gel and evaporation-induced self-assembly. The as-synthesized nanocomposite films were characterized by scanning electron microscopy, X-ray diffraction, transmission electron microscopy and N2 adsorption-desorption. These analyses reveal that the carbon/silica nanocomposite films, with a narrow pore size distribution of mesopores, have an ordered symmetric structure. The pore sizes of this hybrid film can be controlled within a certain range by changing the carbonization temperature. In addition, the films are composed of a continuous silica matrix and a continuous carbon coating in about 1 nm adhered well to the silica matrix. The formation of carbon coatings from surfactant acts as a framework support to prevent the pore size of the silica matrix from shrinking.

An advanced oxidation study using Fenton's reagent, i.e., ferrous sulfate and hydrogen peroxide was carried out for studying oxidation of eosin dye. Effects of concentration of various reagents on the degradation of dye were explored during an advanced oxidation process. It was found that ferrous concentration plays a major role in dye decomposition. Rate of dye decomposition is faster with an increase in ferrous sulfate concentration compared to the increase in hydrogen peroxide concentration. A detailed kinetic model was proposed. Profiles for eosin, hydrogen peroxide and various intermediates were also generated. The rate constant of the reaction of eosin with a hydroxyl radical was found to be of the order of 109 l/mol.s.

Kinetic studies of the catalytic hydrogenation of vegetable oils and fatty acid methyl esters in liquid-phase are commonly performed in the framework of the Langmuir-Hinshelwood-Hougen-Watson (LHHW) formalism using the competitive and non-competitive adsorption models, which are certainly extreme. Based on the advanced concepts of multicentered adsorption and semi-competitive adsorption, mechanistic kinetic models including a distinction between occupied-sites and covered-sites by the large molecules of FAMEs were formulated without expressing an opinion a priori on whether the adsorption regime is competitive or non-competitive. The theoretical basis of the advanced kinetic modeling is described and successfully applied to three application examples of increasing complexity, including: (a) the hydrogenation of methyl oleate without cis-trans isomerization distinction, (b) the cis-trans isomerization and hydrogenation of the methyl oleate, and (c) the methyl linoleate hydrogenation including the cis-trans isomerization of the methyl oleate. The kinetic studies were carried out using a Ni/?-Al2O3, at 398, 413, 428 and 443 K, under isobaric conditions at hydrogen pressures of 370, 510, and 650 kPa, in the absence of mass-transport limitation. After model discrimination based on statistical analysis and taking into account the physical meaning of the estimated parameters, semi-competitive adsorption models were found to be more realistic than the classical LHHW competitive and non-competitive ones, mainly because they give additional information indicating that the adsorbed molecules of methyl linoleate and methyl oleate could cover up to 12 and 7 surface sites, respectively. These values are in adequate agreement with those expected from a rough computational simulation and seem to be the most interesting result, since they are factual and unattainable from the classical LHHW approaches.

The fixed-bed reactors of circular cylindrical geometry with heated or cooled walls are frequently used to carry out heterogeneous reactions of solid-gas type in engineering applications. The design of a fixed bed reactor requires an extensive knowledge of heat transfer characteristics within the packed bed. In this sense, this work presents a three-dimensional mathematical model to predict the heat transfer inside a fixed bed elliptical cylinder heat exchanger. The model considers uniform velocity and temperature profiles of the fluid phase at the entrance of the reactor, and constant thermo-physical properties. The surface of the equipment convective boundary condition is assumed to be constant. The energy equation, written in the elliptical cylindrical coordinates, was discretized using a finite-volume method considering a fully implicit formulation, and WUDS interpolation scheme. Numerical results of the dimensionless temperature profiles inside the packed bed reactor at a steady state are presented and temperature distribution is interpreted. To validate the model, numerical results obtained for the circular cylinder are compared with analytical results from literature and a good agreement was obtained.

An artificial neural network (ANN) was applied for the prediction of the heat transfer coefficient in bubble columns, in order to obtain a general model and to facilitate the scale up of these multiphase contactors, covering a wide range of operating conditions, physical properties, and column dimensions, obtained from literature. A large number of data was collected (more than 1000) via a comprehensive literature survey. Selected parameters affecting the heat transfer coefficient were organized in six groups to serve as the input parameters. These were: gas superficial velocity, gas density, liquid density, diameter of the column, liquid viscosity, and gas hold-up. Four Back-Propagation Networks (BPNNS) were built. Two were trained using a different number of input parameters. The first ANN was trained with six inputs, which were the aforementioned parameters. The second was trained with three inputs only. These were gas velocity, liquid viscosity and gas hold-up. Each ANN was examined for two structures i.e., one hidden layer and two hidden layers. Comparison between these networks was made to find the optimal ANN structure with minimum %AARE and the maximum correlation coefficient (%R). It was found that the ANN structure of [6-13-1] with a %AARE of 16.2 and a %R of 94 was the best.

Catalytic partial oxidation of methane in short residence time rhodium coated monolithic reactors offers an attractive route for syngas production. The plug flow and boundary layer flow approximations are considered as computationally efficient substitutes for the full Navier-Stokes model of the reactor while including detailed heterogeneous and homogeneous chemistry. The one dimensional plug flow model has trivial computational demands but only a limited range of application. The boundary layer model provides an excellent, computationally manageable substitute for the full Navier-Stokes model over a wide range of operating conditions. Using the 38-step elementary surface reaction mechanism of Deutschmann et al. (2001a) and the full GRI 3.0 mechanism for gas phase oxidation of methane, the boundary layer model can predict the experimental data of Hickman et al. (1993a) and Horn et al. (2007) with high accuracy. Sensitivity analyses with the boundary layer model delineate the complex surface phenomena responsible for the sharp transitions in reactor performance observed experimentally on increasing the feed methane to oxygen ratio. The detrimental influence of gas phase reactions on increasing the pressure to industrial levels (>20 bars) is also clearly demonstrated.

Gas hydrates are now gaining importance in oil and gas industries because they are considered a future source of energy and a means for the transport of natural gas. On the other hand gas hydrates create problems by plugging the pipelines during transportation. Obviously, predicting the conditions in which hydrates are formed would be valuable. In the present study, experiments were performed to observe the conditions, which favor the formation of an ethane gas hydrate. The results of the hydrate formation are elucidated with the help of a conceptual kinetic model. An empirical correlation is developed to predict the rate of formation of the hydrate in terms of the operating and geometric variables of the system. A simple kinetic model based on the dissolved ethane gas is also developed which shows that the hydrate formation follows the first order rate equation.

This work deals with the evaluation of the hydrodynamic characteristics and fermentation parameters of a bench-scale three-phase fluidized bed reactor (FBR) with cells of the yeast Candida guilliermondii immobilized calcium alginate beads for xylitol production. The effects of the following hydrodynamic variables on cell immobilization were evaluated: total particle density, terminal velocity, particles drag force, minimum fluidization velocity and bed porosity (?). According to the results obtained, the reactor was shown to operate similar to a fixed-bed bioreactor at ? < 0.5 and a fluidized bed bioreactor at ? > 0.5, respectively. The maximum flowrate needed to obtain maximum bed fluidization in the reactor was equal to the terminal velocity of the immobilized cell particles. As for the fermentation parameters, the effects of the aeration rate and fermentation time on the process productivity and yield were analyzed. The maximum xylitol concentration of 28.9 g xylitol/l was obtained at a high aeration rate of 600ml/min after 70h of fermentation, indicating that the use of a high aeration rate in this system is favored for better oxygen transfer into the immobilized cells. The specific xylitol productivity and the xylitol yield were of 0.41 g xylitol/l.h and 0.582 g xylitol/g xylose respectively. After 90h of fermentation xylitol productivity and yield decreased to 0.256 g xylitol/l.h and 0.47 g xylitol/g xylose respectively, indicating the beginning of xylitol consumption by the yeast.

In combustion applications of fluidised bed reactors, the solid particles are subject to heterogeneous gas-solid chemical reactions, abrasive attrition and other thermal and mechanical processes. The resulting changes in the overall solid phase significantly influence reactor performance. This paper illustrates a particle balance model which accommodates particle distributions dependent on both size and density as well as populations consisting of multiple solids. The proposed model is tested using literature data on coal conversion obtained in a pilot scale circulating fluidised bed combustor. Model simulations give a fair representation of experimental results for different coal ranks and in a range of operating conditions, including varying temperature of combustion, excess of oxygen and superficial gas velocity in the bed.

Multiple steady states in an isothermal CSTR for reaction rates of the form R=kC/(1+KC)2 exhibit concentration multiplicity for a certain parameter range of the Damkohler number, Da. The unstable steady state of the above reaction rate form is very difficult to be observed and maintained. In this work the graphical solution method as proposed by Chen and Crynes (1987) is modified to attain a cascade of CSTRs that are capable of achieving this inaccessible steady state. The modified numerical scheme is based on optimization search. This method was successful in achieving the inaccessible steady state by two CSTRs cascade. The comparison with the graphical method showed that the modified method is faster and more accurate in solving the CSTR problem. The CSTR cascade gives better stability and tolerance to a probable control system failure.

The present study aims at assessing the effect of microwave irradiation against thermal heat on the production of N-acetyl-p-anisidine by acetylation of p-anisidine. The acetylation of p-anisidine under microwave irradiation produces N-acetyl-p-anisidine in shorter reaction times, which offers a benefit to the laboratories as well as industries. It also eliminates the use of excess solvent. Effects of operating parameters such as reaction time, feed composition, and microwave energy and reaction temperature on selectivity to the desired product have been investigated. The results indicate as high as a 98% conversion of N-acetyl-p-anisidine can be achieved within 12-15 minutes using acetic acid. The use of acetic acid as an acetylating agent against conventionally used acetic anhydride eliminates the handling of explosive acetic anhydride and also the energy intensive distillation step for separation of acetic acid. Organic solvent like acetic anhydride are not only hazardous to the environment, they are also expensive and flammable.

A high-flux circulating fluidized bed coal gasifier cold model which consists of a vertical riser (0.06m-I.D.×5m-high), two downcomers (0.04m-I.D.×3.5m-high and 0.1m-I.D.×3m-high), an inertial separator, a cyclone and two solid feeding devices were established. Geldart group B particles with mean diameters of 140 ?m and densities of 2700 kg/m3 were used as bed materials. Flow behaviors were investigated with the solid mass flux ranges from 108 to 395 kg/m2 and the superficial gas velocity ranges from 7.6 to 10.2 m/s. The pressure drop, apparent solids holdups, average slip velocity and solids-to-air mass flow ratio under different operating conditions were obtained. The results showed that the riser total pressure drop increased sharply with bed height in the low elevation but slowly in the high elevation, since the solids holdup was higher in the low region than that in the high region. The solids holdup increased with the increasing of solids mass flux while it decreased with increasing superficial gas velocity. A dense suspension upflow flow (DSU) structure was found only existing in the low elevation while the rest upper region was still in the dilute phase, and the length of DSU flow structure increased with solids mass flux. The average slip velocity was found to be the strong function of apparent solids holdup; increasing apparent solids holdup leads to the increase of slip velocity. The riser total pressure drop and apparent solids holdup increase with the solids-to-air mass flow ratio.

Hydrogen adsorption was studied on treated multi-walled carbon nanotubes (MWCNTs). The amounts of hydrogen adsorbed on this adsorbent were measured at three temperatures (298, 273 and 263 K) and various pressures from 10 up to 70 bar in a volumetric adsorption apparatus. In the studied ranges of operational conditions, the maximum adsorbed hydrogen was determined as 0.28 wt%, at the lowest temperature of 263 K and the highest pressure of 70 bar, by the static measurements at the equilibrium condition. The experimental adsorption isotherms were obtained at different temperatures and they were correlated by Dubinin-Astokhov (DA), Sips, Freundlich and Dubinin-Rudushkevich (DR) equations. The isosteric heat of adsorption was determined from both experimental isosters and isotherm models as a function of the adsorbed amount. The isosteric heats of adsorption revealed that MWCNTs would be an energetically heterogeneous surface. Sips model showed a better fitting of the experimental and theoretical isosteric heats of adsorption values and indicated a weak temperature dependency of the isosteric heat.

In this paper the effects of particles configuration and particles distance on the heat transfer rate in a gas phase olefin polymerization reactor have been studied using the computational fluid dynamic (CFD) modeling approach. The goal was to determine the causes of particle overheating in this reactor. It has been shown that classic correlations such as Ranz-Marshall are sufficiently adequate when far away particles with no interactions are to be modeled. However, when particles are sufficiently close to having interactions, these correlations fail to satisfactorily predict the convective heat transfer coefficient. The results indicate an increase in particle distance leads to an increase in the Nusselt number on the particle surface. Therefore, for particles with a large distance and triangular or rotated square configurations, the local Nusselt number is closer to the Nusselt number for a single particle.

Considerable work published on chemical reaction-diffusion systems investigates mainly mathematically coupled nonlinear differential equations. This study presents the modeling of a simple elementary chemical reaction with thermodynamically and mathematically coupled heat and mass transport with external mass and heat transfer resistances. The thermodynamic coupling refers that a flow occurs without or against its primary thermodynamic driving force, which may be a gradient of temperature or chemical potential. The modeling is based on the linear nonequilibrium thermodynamics approach and phenomenological equations by assuming that the system is in the vicinity of global equilibrium. This approach does not need detailed coupling mechanisms. The modeling equations contain the cross coefficients controlling the coupling between heat and mass flows in terms of transport coefficients and surface conditions. These coefficients need to be determined for rigorous analysis of chemical reaction systems with thermodynamically coupled transport phenomena. Some representative numerical solutions of the modeling equations are presented to display the effect of coupling on concentration and temperatures in time and space for simple exothermic catalytic reactions.

The present study examines the effect of hydrogen distribution (HD) along a Co/SiO2 catalyst bed on Fischer-Tropsch (FT) synthesis. The synthesis is performed under two pressures of 1.0 and 9.0 atm and different H2/CO ratios. The results are compared to those of the usual co-feed, in which both CO and H2 are introduced to the bed inlet. By HD strategy, the methane selectivity is suppressed by as much as 25% and the C11+ selectivity is enhanced up to 26%. CO conversion and product selectivity exhibited a strong dependence on the operating pressure and H2/CO ratio, when hydrogen is distributed.

Exothermic packed bed catalytic reactors are usually characterised by a low diameter-aspect ratio to facilitate heat transfer. In operation, these reactors often exhibit localized regions with much higher temperatures referred to as hot spots. A new model based on a 2-D network-of voids (NoV) has been devised to explore wall heat transfer behaviour for such low aspect ratio packed tubes. Random placement of (packing) particles is used to provide a simple NoV framework for implicitly creating the tortuous fluid flows amongst the resulting randomized inter-connecting voids. This is a computationally tractable strategy for exploring the haphazard appearance of individual tube pin-hole burn-outs amongst the typically thousands, or tens of thousands, of tubes within high temperature industrial multi-tubular configurations. Although presently limited to 2-D, the model captures many natural features of the flow and heat transfer of randomly packed tubes, especially huge variations in wall and cross flows and consequently massive variations in local wall heat transfer coefficients along the length of individual tubes. The model is potentially superior to those based upon averaged properties, which do not properly distinguish the solid and fluid phases. The network-of-voids concept is readily extended to 3-D, in order to achieve geometric congruence of the model and assemblies of individual particles.

In this study numerical solutions are obtained using quasi steady state and unsteady state conditions to predict the reduction in concentrations of polluting hydrocarbons. Before their release to the atmosphere these gases undergo catalytic after-treatment in a converter, causing a decrease in their concentrations. Both homogenous as well as heterogeneous reactions are considered for hydrocarbons propylene and propane. Quasi steady and unsteady state models are developed to simulate heat and mass transfer between the exhaust gas and the catalyst surface, convective heat and mass transport, chemical reactions and the related heat release along with heat conduction in the substrate.

In this paper we tackle the on-line estimation of state variables in MIMO continuous stirred chemical reactor (CSTR) using a nonlinear observer. We prove the asymptotic stability of the resulting error system. Moreover, this observer has robust performance in the presence of model uncertainty and measurement noise. Finally, computer simulations are developed for showing the performance of the proposed nonlinear observer.

The natural organic matter (NOM) is a mixture of many organic compounds that can be dispersed in superficial water. The NOM is due to the compounds formed in the biologic degradation process of the vegetable organic matter and its interaction with the clay and the other hydrographic basin soil constituents, besides algae and other microorganism activity. Many researchers have obtained results that indicate that the coagulation/flocculation process is an effective process in the NOM reduction without committing the non-stabilization colloidal particles. So, with the intuit to guarantee a better final water quality in the water treatment plants, different studies were evaluated based on the coagulation diagram for obtaining the best concentration of the chitosan coagulant as function of the pH for the NOM removal for obtaining potable water. The data for the coagulation diagram construction will be obtained by a series of tests in a jar-test apparatus. Different concentrations of the coagulant solution (0.1% w/v of chitosan) will be studied. The pH will be varied (4.0 – 8.5) with sodium hydroxide solution (NaOH) and hydrochloric acid (HCl) 25 and 50%. The rapid mixture gradient, the coagulation time, the slow mixture gradient and the flocculation time will be maintained constant during this experiment. The process efficiency will be evaluated by the color, turbidity and compounds with absorption in UV-254nm removal. The best results of removal were found for the chitosan in the concentration of 1.0mg/L and pH between 4.0-5.0, approximately.

Fluidization, mixing and segregation of a biomass-sand mixture in a 3D gas-fluidized bed have been investigated by means of visual observation, pressure fluctuation analysis and the bed-frozen method. Three types of mixtures are considered, in which biomass is a thin long stalk, and sand belongs to the Geldart B category. Experiments are carried out in a segmented fluidized bed equipped with multiple pressure transducers. Three initial packing conditions and two experiment procedures are used. The fluidization velocity varies to cover a wide range. Results show that in the local fluidization region, the mixing and segregation patterns are sensitive to the initial packing condition. In the case of a fully segregated state with biomass at the bottom, the bed inversion can be significantly observed due to the great segregation tendency of biomass. Further analyses indicate that the mixing ratio exerts a subtle influence on the competition between mixing and segregation by disturbing the coalescence and break-up of the bubble. In addition, the pressure fluctuation signal proves to be helpful in understanding the dynamic features of the phenomenology.

A simulation tool for gasification based processes is presented for an equation-oriented, steady state modelling environment. The approach aims at an adequate description of phenomena linked to gasification. Background information is provided regarding the structure of the framework, thermodynamic data processing, and on the formulation of the model equations. The implemented substance streams are water/steam, ideal gases, inorganic solids, and organic mixtures. The models are based upon mass and energy balances and feature thermodynamic considerations. The addition of correlations for fluid dynamics or chemical kinetics is generally possible but not within the focus of this paper. The key-aspects of the typical unit-models, like pumps, turbines, heat exchangers, separators and chemical reactors are highlighted. The model of a dual-fluidized bed biomass gasifier is presented in detail. In a final case study, the suitability of the simulation tool is demonstrated for the description of the gasification-based biomass combined heat and power plant in Güssing/Austria.

This work presents the study of mixing a three phase non-Newtonian system in a QVF gas sparged vessel. The three phase system consists of air-non Newtonian liquid (polyacrylamide solution)–solid (alumina catalyst). The critical gas velocity for complete suspension of solid particles, mixing time, and bubble characteristics (bubble rise velocity, bubble diameter, bubble frequency, gas hold up, and number of bubbles) was studied with different polyacrylamid (PAA) concentrations (0.01, 0.03,0.05, 0.07) wt%, different particle diameters of alumina (63-500)µm, and different solid loading of alumina (0.5, 1.0, 1.5, 2.0)Kg. The critical gas velocity was found to increase with increasing apparent viscosity, solid loading, and particle diameter. Mixing time increases with increasing apparent viscosity, and decreases with increasing solid loading, and particle diameter. Bubble characteristics were measured axially and radially using a modified electroconductivity probe consisting of four tips, an interface, a visual basic program, and a personal computer. The results showed that increasing apparent viscosity and particle diameter caused an increase of bubble coalescence and hence, an increase in bubble diameter and bubble rise velocity and a decrease in gas hold up.

This paper describes the results of computational fluid dynamic modeling of hydrodynamics, heat and mass transfer simultaneously in Flexipac 1Y operated under a counter-current gas-liquid flow condition. The simulation was performed for a binary mixture of methanol-isopropanol distillation. The pressure drop, the height of equivalent to theoretical plate (HETP) and temperature distribution across the column were calculated and compared with experimental data. The mean absolute relative error (MARE) between CFD predictions and experimental data for the pressure drop, HETP and temperature profile are 20.7%, 12.9% and 2.8%, respectively.

An analysis is carried out to study the flow and heat transfer characteristics of a non-Newtonian power-law fluid over a stretching surface in the presence of radiation and slip condition at the surface. The local similarity solution is used to transform the system of partial differential equations, describing the problem, into a system of highly coupled non-linear ordinary differential equations. The transformed system of equations is solved numerically using the fourth order Runge-Kutta method coupled with the shooting technique. The effects of the radiation parameter and the slip parameter on both the flow and the heat transfer are investigated and discussed. Also, it is found that the local skin-friction coefficient decreases as the slip parameter increases. However, it is found that increasing the slip parameter or the radiation parameter has the effect of decreasing the local Nusselt number.

Pervaporation has emerged as an energy efficient and highly selective separation process in the last few years for the separation of volatile products and for the dehydration of organic chemicals. The productivity and conversion rate can be significantly increased when reaction is coupled with pervaporation, i.e., pervaporation reactor. Techno-economic studies revealed that pervaporation reactors have good market potential in process industries. An esterification reaction between an alcohol and an acid in the presence of a catalyst is the most common reaction system studied in pervaporation reactor. This is reversible reaction and industrial high conversion can be achieved by adding a large excess of acid. A water selective pervaporation membrane can be used in the esterification reactor; which can shift the equilibrium to the right, thus reducing the excess reactants. In the present paper, modeling and simulation of esterification of acetic acid with n-butanol coupled with pervaporation (pervaporation reactor) were carried out. The model was validated using available experimental data and a good agreement was found. Effects of various parameters, such as process temperature, initial mole ratio of acetic acid over n-butanol, and the ratio of the effective membrane area over the volume of reacting mixture and catalyst content, flux on the esteri?cation reaction in pervaporation reactor were discussed. The following optimum conditions were obtained: temperature = 800C, catalyst concentration = 0.0298 kmol/m3, initial molar reactant ratio (acetic acid/n-butanol) = 1.3, ratio of effective membrane area to the reaction volume = 23 m-1, flux = two times of base value. Presented model can be used for the performance study of pervaporation reactor for various esterification reactions.

Anaerobic digestion of solid wastes is an emerging solution for both waste management and energy production. The high complexity of the process is mostly attributed to the absence of descriptors for the design and the prediction of such a process. This paper presents an approach for the description of organic matter based on several biochemical parameters, established on 22 different organic wastes. The lignocellulosic content is the most important parameter for the prediction of anaerobic biodegradability and methane production; in addition, the knowledge of the carbohydrate, lipid and protein contents is also crucial and makes possible a prediction of the intrinsic kinetics of the reaction.

Laboratory-scale aerobic composting tests with mixture of poultry manure and wheat straw were conducted in closed thermally insulated column reactors with effective volumes of 1 L and 32 L. Two 14-day experiments with two different mixture ratios (manure to straw, 2.77:1 and 5.25:1 on dry weight, respectively) were performed in order to compare the performances of composting process in both reactors as well to obtain the parameter values in the kinetic model and to validate proposed kinetic and reactor model in this work. The maximum temperature of 64.6°C was reached after 2.1 days in the large reactor and 64.5°C after 1.3 days in the small reactor. The temperature in these reactors was maintained above 55°C for 2 days, which should be sufficient to maximize sanitation and to destroy pathogens. The greatest mass of carbon dioxide was generated during the first 3 days. The maximum consumption of oxygen was noticed in the exit gas mixtures from both reactors after the first day of the process (the small reactor 16.0 vol. %, the large reactor 11.7 vol. %). The maximum emission of ammonia was observed from the small reactor after first day and from large reactor after the third day. The organic matter content of the materials decreased in both reactors during the process, but this reduction was greater in the large reactor (47.60%) than in the small reactor (41.36%). The proposed kinetic and reactor model was described by a differential equation set with 12 dynamic state variables: mass of organic matter, mass of oxygen, mass of dissolved carbon dioxide, mass of dissolved ammonia, mass of water in the substrate, molar amount of O2 (gas phase), molar amount of CO2 (gas phase), molar amount of NH3 (gas phase), molar amount of H2O vapour (gas phase), molar amount of N2 (gas phase), temperature of gas phase, temperature of solid-liquid phase. In the proposed kinetic model, four kinetic parameters were calculated. The model was validated by the results of several experimentally measured dynamic state variables (temperature of substrate, conversion of organic matter conversion, concentration of carbon dioxide, concentration of oxygen). Comparisons of experimental and simulation results showed good agreement during the whole duration of the process in a reactor, except for ammonia (good agreement was achieved for the first four days and for the last three days of the process). Different simulation scenarios were performed with the model in order to study the effects of initial moisture content, airflow rates and air temperature on the substrate temperature and organic matter conversion. A sensitivity analysis showed that two of four kinetic parameters had a great influence on all three objective functions (maximum conversion of organic matter, maximum concentration of carbon dioxide and maximum substrate temperature).

Amorphous and low-ordered photosensitive materials are not usually considered to be promising photocatalytic agents because of extremely short free charge carrier (FCC) lifetimes in their active components deprived of well-defined electronic structures. Using active supports favoring an efficient FCC separation in situ, it is possible to protect free charge carriers from the immediate recombination, so even the disordered photosensitive composites can be provided with important photocatalytic capacities. The examples of some environmental applications of this type of active materials, such as volatile organic compound (VOC) photocatalytic removal and bacteria sterilization, are presented in this paper.

Chlorine and hydrogen chloride are classified as potentially hazardous and toxic chemicals. Large-scale industrial processes worldwide use chlorine as primary raw material from which hydrogen chloride is obtained as a major byproduct. Hydrogen chloride is sold as aqueous HCl or used as a raw material for the production of chlorinated products, but the quantity of HCl produced by chlorine processes is much more than what the market can absorb, resulting in a toxic waste disposal problem. Recovery of material chlorine from this hydrogen chloride is very important and is of utmost industrial interest as it would cut down on the production of chlorine at the same time solve the waste disposal problem. It is theoretically possible to convert hydrogen chloride to chlorine for the recycling and reuse of chlorine. In this paper we have developed a process for recovery of chlorine from anhydrous hydrogen chloride obtained as a byproduct during low temperature vapor phase hydrolysis of titanium chloride to get TiO2. It is a two-stage process where chlorination is carried out in a fixed bed reactor using copper oxide catalyst at a temperature in the range of 423-523 K followed by oxidation of copper chloride catalyst in a second fixed bed reactor operating at 573-653 K. This process operates under conditions in which the catalyst does not volatilize and in which the activity of the catalyst remains stable. Operation at relatively moderate temperature prevents corrosion and minimizes the extrinsic energy input required. The chlorine recovery process makes the new generation chloride process for synthesis of TiO2 economical.

How does turbulence rise? For a long time, a century, the Taylor-Couette system was a paradigm for the researchers who tried to get answers to this question. Fascinating structures and patterns observed in the flow have attracted the interest of many researchers, both experimentalists and theorists. During the last century, many works were done on the closed Taylor-Couette systems. At the end of the seventies, after thousands of contributions, experiments performed in the Taylor-Couette system confirmed a theoretical analysis which concluded that a finite number of instabilities, two or three, are sufficient to lead to chaos or weak turbulence. Our own experiments were conducted at that time on a Taylor-Couette system with a moderate aspect ratio. They were analyzed from visual observation and fine local measurement with an electrochemical method. Scalar time series and data pointed out the frequencies characteristic of the flow. Many geometrical effects are considered by researchers. When the gap is horizontal and not completely filled, the flow obtained is called Taylor-Dean flow. We obtained similar flow in an azimuthally open Taylor-Couette system where a combination of the inner cylinder rotation and external fluid pumping, the Dean flow, produces the so called Taylor-Dean flow. Measurements and analysis were carried out by visualization and Laser Doppler Velocimetry. In addition to the experimental approach, we used Computational Fluid Dynamics analysis to complete the flow study. Numerical and experimental investigations reveal a class of instabilities of the Taylor-Dean flow not previously observed in the Taylor-Couette flow due to the cylinder rotation neither in the Dean flow due to the external pumping fluid.

The reduction of NO over coal-derived chars and the catalytic effect of Fe on NO-char reaction during char combustion were investigated in a drop-tube furnace in a temperature range of 1323-1523K. The catalytic characteristics of Fe in the NO–char reaction were studied in detail. The results show that iron (Fe) is an effective catalyst for the NO reduction by char derived from de-ashed coal at a high temperature, i.e., the chars with catalysts have high activity in the NO-char reaction. Furthermore, the stoichiometric ratio (SR) in the reaction zone has a significant influence on the catalytic activity of Fe-catalysts, which will be more effective in SR=0.7-0.9. The catalytic activity of Fe depends slightly on its loading amount, while the specific activity of the catalyst obviously decreased with the increasing of the Fe-loading amount. The effect of the temperatures used in the experiments on the NO reduction is small, which suggests the NO-char reaction mainly depends on the diffusion of reactants to char, the reactants' surface adsorption, and the desorption of products under high temperature. However, the effect of the temperature on NO reduction by metal-free char is much more important than that of NO reduction by Fe-loaded char.

Titanium dioxide was immobilized onto spherical activated carbon particles via the sol-gel coating method. The photo-catalyst, annealed at 500 °C, was found to posses the highest activity according to the results of a bench-scale test. The photocatalytic performance of the immobilized photocatalyst was studied in a three-phase fluidized bed photoreactor, with the use of phenol as the model pollutant. Effects of both liquid and air flow rates on the phenol degradation rate were examined. The experimental results showed that the increase of liquid and air flow rates may enhance the phenol degradation rate. However, very high liquid and air flow rates could lead to the decrease in the performance of the three-phase fluidized bed photoreactor. The results on the effect of initial phenol concentration on the degradation rate indicated that the photocatalytic reaction in the three-phase fluidized bed followed the first order kinetics and could be reasonably fitted by the Langmiur-Hinshelwood kinetics model. Compared to the three-phase fluidized bed in which air is introduced into the bed from the distributor, the liquid-solids fluidized bed in which oxygen is provided by injecting air into the freeboard region of the reactor showed a better phenol destruction performance and is thus preferred for photodegradation of water contaminants.

The upflowing and downflowing particle velocities are investigated by using a two-optical fiber probe system in the dense gas-solid fluidized bed with an inner diameter of 0.185 m and a height of 3.000 m. Two kinds of glass ballotinis, belonging to Geldart type B classification, are selected as solid material. Experiments are conducted under different operating gas velocities, static bed heights, and particle diameters. The results indicate that the upflowing particle velocity is a strong function of operating gas velocity and particle diameter, while the downflowing particle velocity depends mainly on the operating gas velocity. When the ratio of the operating gas velocity to the minimum fluidization velocity of the particles keeps the same constant, the effect of the particle diameter on the upflowing and downflowing particle velocities can be ignored. Both direction and size of the solid particle velocity are related to the bubble behaviors in the fluidized bed, and the upflowing particle velocity is lower than the bubble rise velocity. Furthermore, the across-sectional, non-uniform flow structure in the bed increases slightly with increasing static bed height at the high operating gas velocity.

Biosorption of lignin compounds by the Eichhornia crassipes was investigated in batch studies. Batch experiments were conducted to study the effect of initial sorbent dosage, solution pH and lignin compounds concentration. Langmuir and Freundlich adsorption isotherm models were used to represent the equilibrium data. The Freundlich isotherm model was found to be fitted very well with the experimental data when compared to Langmuir isotherm model. The results showed that the equilibrium uptake capacity was found to be increased with decrease in biomass dosage. The lignin compound removal was influenced by the initial lignin compounds concentration. The sorption results were analysed for pseudo first order and pseudo second order kinetic model. It was observed that the kinetic data fitted very well with the pseudo second order rate equation when compared to the pseudo first order rate equation. Sorption results were analyzed for the intra particle diffusion model.

Hydroxyapatite (HAP), described by the formula Ca10(PO4)6(OH)2, is one of the inorganic components of the hard tissues of living bodies such as bones and teeth. HAP is a calcium phosphate-based bio-ceramic, which has been used for several years in medicine and dentistry because of its excellent biocompatibility with human tissues. The success of its application in these fields depends upon factors such as the composition, crystallinity, size and morphology of HAP particles. This paper describes the work performed regarding the synthesis of this compound by a wet method comprising the direct precipitation of orthophosphoric acid solution to a calcium hydroxide solution, the process being described by the following reaction: 10 Ca(OH)2 + 6 H3(PO4) <=> Ca10(PO4)6(OH)2 + 18 H2O. Synthesis was performed in a laboratory reactor, 700mL in capacity, which was instrumented and controlled using a computer interface, so that the influence on process variables, such as reaction temperature, pH, medium inertization by N2, velocity of stirring and the flow rate input of H3(PO4), could be assessed. The influence of these parameters was, therefore, evaluated in terms of the required composition and morphology of HAP formed particles. The particles were analysed by FTIR, XRD, SEM and EPMA for the determination of the Ca/P ratio. From the obtained results, it can be concluded that HAP particles, having suitable properties for use in medicine, could effectively be prepared by this technique, provided that a good control of the involved process variables is maintained.

This paper reports the results of a study on a three-dimensional computational fluid dynamics (CFD) simulation for a study of gas catalytic oxidation of ethyl acetate over Cr-HZSM-5 catalyst. A gaseous stream, containing N2, O2 and ethyl acetate (in which ethyl acetate concentration in mixture was 2000 ppmV) with GHSV= 32000 h-1 as the feed, was inserted into a glass reactor, charged with a required amount of Cr-HZSM-5 catalyst under atmospheric pressure. The catalytic reactions were allowed to occur at atmospheric pressure and at different temperatures. Fluent 6.2 was used for the simulation of the catalytic process. The simulation was present for the model geometry of 20 solid spheres in a tube with a tube-to-particle diameter ratio equal to 2. Results of the simulation showed a good agreement with the experimental results. It was experimentally, and by simulation, observed that the increasing of the temperature and the decreasing of the inlet mass flow rate led to the increase of ethyl acetate conversion. Velocity vector profiles of the fluid were obtained with an emphasis on the catalytic region. Temperature and pressure contours of the fluid inside the reactor were predicted by simulation. Furthermore, the surface deposition rate of oxygen (during the step of catalyst oxidation) and species concentration along the reactor were obtained. This study revealed that CFD is the best tool to study detailed homogeneous and heterogeneous reaction schemes, even for complex catalyst geometries.

Experiments are carried out for passive mixing in order to obtain local mean and turbulent velocities and concentrations. The mixing takes place in a square channel with two inlets separated by a block. A combined PIV/PLIF technique is used to obtain instantaneous velocity and concentration fields. Three different flow cases are studied. The 2D numerical predictions of the mixing channel show that none of the k - ? turbulence models tested is suitable for the flow cases studied here. The turbulent Schmidt number is reduced to obtain a better agreement between the measured and predicted mean and fluctuating concentrations. The multi-peak presumed PDF mixing model is tested and comparisons with experiments are encouraging.

The objective is the adaptation of an existing UV spectrophotometer for the on-line monitoring of nitrate, nitrite and soluble COD during cycles of SBRs. An on-line filtering system was also developed in order to provide particle-free fluids to the sensor. The modified UV-spectrophotometer sensor (called "STAC") was implemented into a pilot-scale bioreactor at INRA-Narbonne, treating a semi-synthetic dairy wastewater. After a calibration and validation steps, results obtained during five months have shown that the on-line spectrophotometer sensor was able to efficiently monitor on-line nitrate, nitrite in SBR content. Ranges of detection were between 0 to 40 mg/L for nitrate and 0 to 18 mg/L for nitrite, with an accuracy of about 10 %. The on-line estimation of soluble COD was less efficient. The major drawback was the time-consumption for the cleaning of the homemade on-line filter.

A model of slurry polymerization of ethylene in a multistage continuous stirred-tank reactor (CSTR) was developed in order to find the effect of stagewise variation of parameters on polymer polydispersity and rate of polymerization. Higbie's penetration theory has been used to calculate monomer absorption rate in the presence of micron-sized single site type catalyst in slurry phase. The residence time distribution of the growing polymer particles in an ideal CSTR was modelled by a relaxation-type unsteady state approach. The effect of gas-liquid mass transfer limitations on polymer properties is predicted for various reactor configurations. An analysis of various possible configurations of two-stage CSTR with stagewise variation of the partial pressures of ethylene and/or hydrogen has been made.

A batch kraft cooking non-isothermal digester was modelled based on chemical kinetics and mass transfer equations for softwood. Kraft pulping modelling had been designed for non-isothermal batch cooks of chip mixtures: either mixed-size chips, according to a thickness distribution law, or mixtures of different wood species. The case of existing linear or non-linear radial temperature gradients in a digester was examined. Several chip populations with different thickness distribution were used: normal (major abundance of 3-5 mm chips); uniform (equal abundance of chips in the range 3-12 mm); Gaussian-type (centred on 7 mm chips); Poisson-type (major abundance of 3 mm chips). The effect on cooking results due to temperature gradients in digester was predicted along with the existing non-uniformity arising from the effect of chip size distribution, density, and wood mixtures of different composition and chemical properties (rate constants, activation energies). Results are presented as a kappa number, yield and rejects distributions and mean values. The rather sharp kappa number distributions obtained for isothermal cooks were found to be severely spread in the linear temperature gradient case. The above effects were attenuated when a central core in the digester was kept isothermal. The stratification of chips resulted in significantly reduced width in kappa number distributions. Highest density chips cooked lower; however, since diffusion effects were more prominent in them, their apparent activation energy was also less. So they were slightly less affected by temperature gradients in the digester. Cooking different wood species together also affected the spread of the kappa number distribution. This cumulated more or less to temperature gradients effects, depending on chemical activation energy data and possible differences between species.

A one-dimensional, isothermal mathematical model for methane reforming with carbon dioxide in a conventional fixed bed reactor (FBR) and a porous Vycor glass membrane reactor (MR) has been developed. The reactors are packed with alumina-supported Rh catalyst. A simulation study shows that conversion of methane is higher in MR than that of FBR at all temperatures. In order to analyze the overall performance of MR, a detailed simulation study has been carried out to elucidate the effect of temperature, sweep gas flow rate, dilution ratio, feed ratio on percent conversion of methane, yield of hydrogen and carbon monoxide, and ratio of hydrogen to carbon monoxide in produced syngas. Besides, a comprehensive investigation on the effectiveness of the catalysts for methane reforming with carbon dioxide reaction has been made and presented.

The paper discusses the influence of adsorption/desorption phenomena on the purification performance of the reverse-flow catalytic incinerator for abatement of volatile organic compounds (VOC). It is shown that the reversible adsorption of VOC at the catalyst surface may occur at the catalyst bed inlet in the end of the cycle, followed by desorption into outlet gases after flow reversal leading to decrease of the process purification efficiency. The mathematical modelling results showed that inert material beds in combination with proposed process control strategy are needed to avoid negative influence of adsorption effects.

Predicting the amount of attrition that will occur in a pneumatic transport system is very important in preventing product degradation. Considerable work has been performed on the mechanisms of attrition in fluidized beds; hence, they are well understood. On the other hand, there are fewer correlations that can be used to predict the attrition rate in pneumatic transport and spouted beds. In this study, polymethyl methacrylates particles were attrited in a pneumatic transport pilot plant and the experimental attrition rate was determined. The same particles were also used in a spouted bed with a sonic attrition jet and the attrition rate was measured. Finally, a fluidized bed correlation was applied to the spouted bed and a model was used to determine whether the attrition mechanism in pneumatic transport can be related to the attrition mechanism in the spouted bed.

Catalytic hydrogenation of nitro aromatics is an important class of reactions in the pharmaceutical and fine chemical industries. These reactions are extremely fast and highly exothermic in nature; hence, mass and heat transfer limitations play an important role when these reactions are conducted in conventional batch reactors. The use of a micro-channel reactor for such reactions provides improved mass transfer rates which may ensure that the reaction operates close to intrinsic kinetics. In the present study, the hydrogenation of a model aromatic nitro ketone was conducted in a packed-bed microreactor. The effects of different processing conditions were studied using 5%Pd/Alumina catalyst, viz.: hydrogen pressure, substrate concentration, temperature, and residence time on the conversion of substrate, Space Time Yield (STY), and selectivity of product. Internal and external mass and heat transfer limitations in the microreactor were examined. The kinetic study was undertaken in a differential reactor mode, keeping the conversion of the reactant at less than 10%. The overall reaction was treated as comprising two separate reactions: first, the reduction of the nitro compound to hydroxylamine and then, the reduction of the hydroxylamine to amine. Two rate equations for the two consecutive reactions assuming the Langmuir-Hinshelwood mechanism provided the best fit to the experimental data. These two rate equations predicted the experimental rates satisfactorily and the differences were within 10% error. Experiments were also carried out in an integral reactor, and the reactor performance data were found to be in agreement with the predictions of the theoretical models.

An industrial ammonia synthesis reactor was studied in order to optimize its operational conditions by means of increasing overall ammonia production. A heterogeneous, one-dimensional model and a two-dimensional rigorous model were utilized to evaluate the process behavior. The simulation results of the two models were compared with data from an industrial ammonia plant. The one-dimensional model was found to be adequate for optimization purposes. Applying the Genetic Algorithm (GA) as a powerful method for complex problems, the model was employed to optimize the reactor performance in varying its quench flows. The optimal temperature profile along the fixed bed reactor was studied by changing independent variables including the quench temperature and the quench flow rates. Optimization results show that the optimum quench temperature is about 615°K and that the optimum quench flows can enhance ammonia production rate by 3.3%.

In the food industry, rheological properties, such as viscosity, shear rate, and shear stress, are the most important parameters required in the design of a technological process. Therefore, in this study, we determined the flow behavior and the time-dependent flow properties of Turkish Delight (TD) in the temperature range of 25-75°C using a capillar rheometer. The structure and thermal properties of TD were investigated by XRD and a simultaneous DTA/TG analysis. The shear rate values ranged from 5 to 300s-1. We found that: (i) TD behaved as non- Newtonian pseudoplastic foodstuff; (ii) while the measurement temperature increased, viscosity decreased; and (iii) TD was a rheopectic material. The effect of temperature on viscosity was described by means of the Arrhenius equation. The activation energies for the flow of pseudoplastic TD varied from 50.1-74.2 kJ/mol, depending on shear rate. Three models were used to predict the flow behavior of TD, namely, the Power law, Bingham and Casson models. The Power law model adequately described well the flow behavior of TD at different temperatures.

The bioethanol industry expects a huge expansion and new technologies are being implemented with the aim of optimizing the fermentation process. The behavior of cells of Saccharomyces cerevisiae immobilized in PVA-LentiKats, during the production of bioethanol in two reactor systems, was studied. The entrapped cell in LentiKats lenses showed a different profile using stirred tank reactor (STR) and packed column reactor (PCR). Low free cells accumulation in the medium was observed for the STR after 72 h of fermentation. On the other hand, no free cells accumulation was observed, probably due to the absence of mechanical agitation in PCR configuration. Better fermentation results were obtained working with STR (final cellular concentration = 13 g.L-1, Pf = 28 g.L-1, Qp = 1.17 g.L-1.h-1,and Yp/s = 0.3 g.g-1) in comparison to PCR (final cellular concentration = 11.4 g.L-1, Pf = 20 g.L-1, Qp = 0.83 g.L-1.h-1,and Yp/s = 0.25 g.g-1). Such results are probably due to the mechanical agitation of the medium provided by STR configuration, which permitted a better heat and mass transference.

The catalytic wet air oxidation (CWAO) of a simulated phenolic wastewater was investigated at temperatures up to 200ºC and 15 bar of air partial pressure. Laboratorial (Mn-Ce-O 70/30 IMP, Mn-Ce-O 70/30 CP, MnCu 70/30, MnCu 50/50) and a commercial catalyst (N140: CuO-MnOx 22/50) were used to evaluate the catalytic activity in terms of Total Organic Carbon (TOC). Among the manganese/cerium and manganese/copper catalysts tested with different molar ratios, Mn-Ce-O was the most active leading to the complete mineralization after 120 min of an aqueous solution containing six representative phenolic acids. The co-oxidation effect was identified when comparing the oxidation of global phenolic mixture and the individual parent compounds' depletion. The catalyst preparation method had no significant differences in terms of catalytic activity. During the CWAO experiments, acetic acid and phenol were detected and measured by HPLC as the main reaction intermediate compounds. Concerning catalytic stability, manganese and copper catalyst revealed good properties in terms of active metal leaching to the bulk liquid as well as in the deposition of only 3.152% (W/W) of carbonaceous material on the catalyst surface for the co-precipitated Mn-Ce-O 70/30 catalyst.

Reforming of diesel fuel is challenging but very attractive for hydrogen production. It can facilitate the market entrance of fuel cells due to the existing infrastructure for distribution of diesel fuel. Reforming in micro reactors enables good heat transfer and therefore small and compact fuel processing systems e.g. for electrical energy generation in auxiliary power units.Due to the complexity of diesel, reforming of different diesel components and conversion intermediates in a micro reactor is investigated systematically within this work. Methane and propane were applied as conversion intermediates and hexadecane as a diesel surrogate. All experiments were conducted over a rhodium catalyst on Al2O3 or CeO2.For evaporation of the higher boiling hydrocarbons a micro structured injection nozzle was fabricated to create a fine hydrocarbon spray which evaporates in water vapour. Furthermore a complex gas chromatographic method to analyse hydrocarbons up to C16 and the permanent gases in one analysis run was developed.Experimental results show that the turnover frequency of the fuel molecules in the feed decreases linearly for straight chain hydrocarbons with an increasing number of carbon atoms. Calculations show that the observed conversions and product gas compositions are close to the thermodynamic equilibrium. The catalyst system Rh/CeO2 offers better reforming performance and higher resistance to coking apparently due to less acidic sites compared to Al2O3 and the oxygen storage capacity of CeO2.The ongoing work will examine the reforming behaviour of more model diesel fuel components e.g. mixtures of hexadecane and methylnaphthalene or synthetic diesel fuel. Experiments will be conducted in an optimised micro reformer, which disposes the heating energy by burning e.g. fuel cell off-gases. This also offers the consideration of start up and load changing behaviour.

A general methodology for photoreactor analysis and design based on the fundamentals of chemical reaction engineering and radiative transfer in participating media is presented. Three applications in the field of advanced oxidation processes are considered to illustrate the proposed approach: (i) a photocatalytic reactor for air purification, (ii) a homogeneous photo-Fenton solar reactor, and (iii) a heterogeneous photocatalytic slurry reactor. In the first case, the procedure is exemplified with the modeling of a multiannular photocatalytic reactor for perchloroethylene removal from contaminated air streams. A rigorous physical and mathematical model of the multiannular concentric photoreactor was developed and experimentally verified. The second approach is illustrated with the degradation of a model pollutant by the Fenton and photo-Fenton reactions in a nonconcentrating, flat-plate solar reactor. Formic acid was chosen as the model substrate. The effect of the reaction temperature on the pollutant degradation rate is analyzed. In the case of the slurry photoreactor, the intrinsic kinetics of the photocatalytic decomposition of a toxic organic compound in aqueous solution, using suspended titanium dioxide catalytic particles and ultraviolet polychromatic radiation, is studied. The kinetic parameters are evaluated for different catalyst loadings, irradiation levels and pollutant initial concentrations. By means of these illustrative examples, the need of a systematic and rigorous approach to the analysis and design of photoreactors is emphasized.

In this paper, the 1-soliton solution of the nonlinear reaction-diffusion equation is obtained. The solitary wave ansatz is employed to obtain the solution.

Electrocoagulation (EC) has been used to treat a wide variety of wastewaters, including textile, dye, electroplating, chemical mechanical polishing wastewaters, etc. Excessive coagulant material may be avoided by electrocoagulation. The contaminants present in wastewaters are maintained in solution by electrical charges. The metal ions of opposite electric charge, provided by an electrocoagulation system, may become unstable and precipitate in a form that is usually very stable. In the present work, the decolorization of navy blue-3G from synthetic wastewaters by an electrocoagulation method has been studied. In the EC of navy blue-3G, the effect of the initial concentration of dye, type of electrode, voltage, pH, turbidity and time on the efficiency of EC process are tested. The experimental results revealed that the color of navy blue-3G in an aqueous phase is effectively removed up to 95% and 93% with aluminum and iron electrodes, respectively.

Rate of coke formation during steam pyrolysis of naphtha has been investigated in a laboratory CSTR reactor both for uncoated SS321 and metal coating constructed with thermal spray method with metal powders of aluminum, aluminum-magnesium and zinc. Rate of coke formation was studied in different temperatures and amount of coke as a function of run time has been studied too. The results of the study show that passivating the surface of SS321 with a coating of aluminum and aluminum-magnesium can significantly reduce the rate of coke deposition during naphtha pyrolysis. The results obtained from zinc coated show decoking carry out during thermal cracking. The scanning electron microscope (SEM) was carried out for morphology studied of coke deposited on the different metal surfaces.