Volume 4, Issue 1

This paper concentrates on the practical implications of bifurcation and chaos on novel approaches for the production of the clean fuels: hydrogen and ethanol, and the simulation of the acetylcholine neurocycle in the brain. One problem from the field of chemical reaction engineering and two from the field of biological reaction engineering, the three problems have one thing in common: the practical implications of bifurcation and chaos. The novel approach for hydrogen production is based on a novel circulating fluidized bed catalytic membrane reformer configuration achieving, simultaneously, both autothermicity and breaking the thermodynamic barriers using different techniques (membranes and/or CO2 sequestration). The static bifurcation characteristics of the autothermic process and their implications on design and operation for maximum hydrogen yield and productivity are addressed. Experimental set-up for this novel process is being developed at University of British Columbia (UBC).The novel approach for the ethanol production does not use a novel configuration, however it uses a classical configuration but with a novel mode of operation. A CSTR fermenter is used exploiting bifurcation and chaos theories to maximize ethanol yield and productivity. The sequence of research work consisted of: developing a reliable and relatively simple model to describe the fermentation process, verification of the model against experimental results, using the model in an extensive bifurcation and chaos analysis investigation to identify the regions of bifurcation and chaos and their characteristics. This is followed by using these results to guide an experimental investigation of bifurcation and chaos and their implications on improving ethanol yield and productivity.This paper also introduces our preliminary efforts to investigate the bifurcation and chaotic behavior of acetylcholine neurocycle in the brain using diffusion-reaction models in order to gain some insight into their possible connection to Alzheimer and Parkinson Diseases (AD/PD).

Nickel bioleaching from copper flotation concentrate assumes greater significance because of its value and not many studies are carried out in these lines. Hence, nickel leaching was attempted and several process parameters of bacterial oxidation for copper flotation concentrate were examined for optimization. The parameters considered for shake flask leaching experiments were temperature, pulp density, particle size, agitation, residence time and inoculum size. The effect of variable proportions of each parameter on nickel leachability was studied. Optimum values of pulp density (10%) and agitation (140 rpm) played an important role in controlling the mass transfer resistance during leaching process. Increase in temperature from 27oC to 30oC has accelerated the bacterial oxidation process while initial concentration of inoculum (1-10%) has not shown considerable variation in nickel leachability. A particle size of ±60#size was found to be essential for bacterial attack. Maintenance of optimum conditions of leaching has yielded considerable nickel recovery (55%) compared to low recovery under unoptimal conditions.

The gas-liquid mass transfer from bubbles is estimated by Direct Numerical Simulation for fully contaminated bubbles behaving as solid spheres, partially contaminated spherical bubbles and clean spherical bubbles. Partial contamination of bubble interface is accounted by the Stagnant Cap Model to show the effect of the surfactant on hydrodynamic and mass transfer at low Reynolds number. Hydrodynamics results are validated by comparison with other works of the literature. The numerical mass transfer is then analysed in term of local and averaged Sherwood numbers. The comparison of DNS results with classical relations gives the good scaling of Sherwood with Pe1/3 and Pe1/2 respectively for solid sphere and clean bubble in creeping flow. For partially contaminated bubble and after validation of simulated drag coefficient, the effect of the contamination on mass transfer is shown for several Peclet numbers. A correlation for Sherwood number in function of contamination angle is then proposed in creeping flow.

Nano-nickel particles were prepared using hydrogen arc plasma method and new nano-nickel hydrogenation catalysts were prepared through calcinating mixtures of the plasma-prepared nano-nickel particles and a ?-alumina support. The catalysts were characterized by using SEM, XRD, and TPR. The activities of the catalysts were evaluated through the hydrogenation of toluene in a fixed be microreactor. Catalysts prepared by conventional comulling and impregnation methods were also examined for comparative purposes. The characterization results showed that the nano-nickel catalysts had an egg-shell structure in terms of nickel-alumina distribution, with most of the nickel located at the outer surface of the catalyst particles. The hydrogenation experiments showed that the nano-nickel catalyst provided much higher activities than those co-precipitated and impregnated nickel catalysts with similar nickel contents. However, both types of catalysts followed first-order reaction kinetics and similar activation energies were observed.

Flow induced by a dual turbine stirred tank was characterized measuring local velocities with a LDV and drawing the main velocity fields and the maps of turbulence intensities. The hydrodynamic regime studied in all the experiments was the so-called merging flow regime. Two impeller configurations were studied. In the first one, two disk style turbine of the same dimensions (configuration A) were used, while in the second one, the dimensions of the upper turbine were 20 % proportionally smaller than those of the lower turbine (configuration B). The agitation and turbulence indices were used to evaluate, as a first order approximation, the power consumption distribution between convective and turbulent flows. The comparison of the two-phase agitation systems studied showed that configuration B seems to be more efficient than configuration A, since both induce a similar global convective flow, but the first one assures a significant reduction of power consumption. The distribution of power consumption between convective and turbulent flows was evaluated using the agitation index and a new global parameter: turbulence index.

Catalytic membrane reactors are multifunctional reactors, which provide improved performance over conventional reactors. These are used mainly for conducting hydrogenation/ dehydrogenation reactions, and synthesis of oxyorganic compounds by using inorganic membranes. In this paper, comprehensive model has been developed for a tubular membrane reactor, which is applicable to Pd or Pd alloys membrane, porous inorganic membranes. The model accounts for the reaction on either side, tube or shell, isothermal and adiabatic conditions, reactive and non reactive sweep gas, multicomponent diffusion through gas films on both sides of membrane, and pressure variations. Equations governing the diffusion of gaseous components through stagnant gas film, and membranes have been identified and described. The model has been validated with the experimental results available in literature. By using the developed model catalytic dehydrogenation of ethylbenzene to produce styrene in a tubular membrane reactor have been simulated. Four catalysts available for this reaction have been evaluated for their performance. It is our view that the model may be used to develop general purpose software for the analysis and design of tubular catalytic membrane reactors through numerical simulation.

Recombinant human interleukin-11(rhIL-11) is still the only therapy drug for thrombocytopenia. Although the biological properties and clinical behaviors of rhIL-11 have been studied extensively, bioprocess development work has rarely been reported. In this study, a three-compartment structured model was developed to simultaneously simulate batch cultivation of bacteria growth, substrate utilization and intracellular rhIL-11 production with recombinant E. coli. A genetic algorithm was formulated and successfully applied to the estimation of the model parameters, which simulated the experimental data obtained from flask cultivation experiments quite well. The results of this work indicate that combination of structured modeling and genetic algorithm could be a simple and effective way for simulating the fermentation of recombinant microorganisms with over-production of foreign proteins.

A dynamic model was developed describing emulsion copolymerization of styrene and MMA within a batch/semibatch stirred tank reactor. This model includes the initiation, propagation, transfer and termination steps of the monomers styrene and MMA. It also includes the mass and energy balance equations for the polymeric radicals. Energy balance equations incorporate the heat of reaction, internal and external heat transfer effects, as well as heat losses. The resulting sets of (differential/algebraic) equations were solved for both species concentrations and temperature profiles as functions of time. Experiments were conducted in a laboratory reactor, instrumented with platinum resistance thermal transducers and gravimetric conversion measurement devices. Thermal measurements in conjunction with the energy equations helped estimate monomer conversions as a function of time. The kinetic model predictions of conversion compared well with inferential calorimetric measurements, which were validated using gravimetric data. The experiments were run at variable operational conditions in terms of feed rate, temperature and monomers feed ratio. The calorimetric model was used as a soft sensor for the prediction of the rate of reaction, conversion and molar mass.

Local instantaneous pressure signals obtained through a magneto-fluidized bed have been analyzed using both classical and advanced signal analysis methods, which can deliver the necessary information about the presence of the bubbling and turbulent flow pattern. The conventional signal processing tool such as autocorrelation and cross correlation were used as preliminary tools to analyze the data. Evaluation of the dominant bubble frequency was completed using the autocorrelation function and power spectral density function. Mutual information function was used to identify the periodicity and the predictability of the local instantaneous pressure signals. Since it does not demand any particular functional relationships between the data points, it is a better method (compared to autocorrelation function) for measuring the predictability of nonlinear systems.

This study reports a comprehensive multiphase gas-solid dynamic mathematical model that successfully describes the batch growth of silicon particles in a CVD submerged spouted bed reactor. This multiphase reactor model takes into account the hydrodynamics and interphase mass exchange between the different fluidized bed regions (spout or grid zone, bubbles and emulsion phase) and uses applicable kinetic rate models to describe both heterogeneous and homogeneous reactions. The model also incorporates a population balance equation representing particle growth and agglomeration.The CVD submerged spouted bed reactor operation is simulated by means of a sequential modular procedure, which involves the solution of the reactor model and the population balance equation.It is shown that the proposed CVD multiphase reactor model successfully simulates experimental data obtained from batch operation in a pilot scale reactor at REC Silicon Inc. The modeling of experiments obtained for different operating conditions allows correlating the scavenging factor as a function of the silane concentration for short- and long-term operations.

An intercooled double-bed reactor for industrial Low Temperature WGS reaction, subject to catalyst deactivation by irreversible chlorine chemisorption is modelled and optimised.Decline of the catalyst activity due to poisoning by chlorine decreases the reactor CO outlet conversion. After some time of operation, the lowest targeted CO conversion is reached, and further operation is inefficient. The reactor Efficient Production (EP) is calculated as the total amount of CO converted until the CO outlet conversion falls below the permissible minimum value, namely 0.85, which occurs at the operation time called the Catalyst Lifetime (CLT).Deactivation kinetics was assumed to be first order to chlorine partial pressure, and both the chlorine adsorption and deactivation rate constants were considered independent of temperature. For computation, spatio-temporal discretization of the reactor was adopted, and maximum CLT of 26 kh has been assumed.As the operation temperature is determining the overall reactor performance, two inlet temperature strategies for both reactors have been employed to maximise the EP: (a) isothermal and (b) time-trajectory.For a base case, optimum inlet isothermal temperatures for the first and second reactors of 483 and 458 K were found, respectively, at which 972.0 kmol of CO were converted within the CLT of 25.584 kh, being the EP of 958.6 kmol of CO. The maximum EP of 971.0 kmol was achieved for 483 and 462.3 K, for the first and second reactor, respectively. Varying the inlet temperature for both reactors along the time, higher production and EP were achieved.In comparison to the EP obtained for the single-bed reactor, the intercooled double-bed reactor allows to achieve higher EP, for both strategies.Also a sensitivity study to other operational variables, such as steam to gas ratio and total inlet flow, was carried out, in order to investigate their influence on optimal inlet temperatures.

A multiphase reaction engineering model is being developed to investigate the dynamic and steady state behaviour of fluidized-bed catalytic reactors. It accounts for transients, axial and radial dispersion, temperature and pressure profiles, interphase mass and heat transfer, different hydrodynamic flow regimes, catalyst deactivation, reactions with changes in molar flows and various energy options. The model is general enough that it can treat catalytic systems, subject to mass and energy transfer resistances within the phases, as well as permeating membranes. It is able to handle multiple phases and regions (low-density phase, high-density phase, freeboard region and permselective membranes). The model reduces as special cases to a number of simpler fluidized bed reactor models previously reported in the literature, allowing evaluation of the influence of different simplifying assumptions. As a case study, the model is shown to simulate oxy-chlorination fluidized-bed reactors for the production of ethylene dichloride from ethylene, extending a recent paper by Abba et al. (Chem. Eng. Sci., (2002) 57, 4797-4807).

Combinations of Plug Flow Reactor (PFR) and continuous Perfectly Mixed Reactor (PMR, also known as Continuous Stirred Tank Reactor - CSTR) are widely known to give superior performance over a single reactor especially when multiple reactions take place in the reactor. The occurrence of a PMR in an optimal reactor network requires presence of inflection condition in the space of variables describing the reactor objective. The mathematical equation for inflection of multi-dimensional trajectories is derived and applied to five cases of well-known models of kinetic schemes. The previously known results are confirmed or improved upon by applying the technique. A general algorithm for PFR/PMR network synthesis for arbitrary kinetic models is presented.

In this paper, the influence of carbon and silica particle slurry concentration up to 20 g/l (4 vol%) on regime transition, gas hold-up, and volumetric mass transfer coefficient is studied in a 2-dimensional slurry bubble column. From high speed video image analysis, the average large bubble diameter, the frequency of occurrence of large bubbles, the gas-liquid interfacial area, and the large bubble hold-up are obtained. The liquid side mass transfer coefficient is calculated from the volumetric mass transfer coefficient and the gas-liquid interfacial area. The lyophilic silica particles are rendered lyophobic by a methylation process to study the influence of particle wettability. The influence of organic electrolyte (sodium gluconate) and the combination of electrolyte and particles is also studied. It is found that lyophilic silica, lyophobic silica, and lyophobic carbon particles at concentrations larger than 2 g/l (0.4 vol%) decrease the gas hold-up and shift the regime transition point (where the first large bubbles appear) to a lower gas velocity. The volumetric mass transfer coefficient increases with gas velocity, increases with electrolyte concentration, decreases with slurry concentration, and is higher for lyophobic particles. The liquid side mass transfer coefficient increases with gas velocity, bubble diameter, and is higher for lyophobic particles. A correlation for the mass transfer coefficient based on dimensionless numbers is proposed for the heterogeneous regime.

Phase Transfer Catalyst (PTC) is used in more than 600 commercial processes, with wide ranging applications in the pharmaceuticals, agrochemicals, polymer industries. Despite thousands of publications on the PTC, several intricacies of PTC in reactions are not understood or properly modeled. Liquid-liquid (L-L) PTC is inferior to solid-liquid (S-L) phase transfer catalyzed reactions, which in turn can be converted into Solid (reactant)-Liquid-(aqueous omega)- Liquid (organic) using trace quantities of water to realize 100% selectivity to the product. There is great enhancement in rates of reactions in comparison with corresponding S-L or L-L PTC. Thus, the O-alkylation of sodium salt of 2'-hydroxy acetophenone was achieved using 1-bromopentane using tetrabutylammonium bromide as the catalyst at 90 0C.2’-Pentyloxy acetophenone is used as a starting material for synthesis of fungicides. The current study deals with the efficacy of so-called omega phase with special emphasis on kinetic and modeling aspects.

The applicability of conical spouted bed reactors for the treatment of cork caps has been studied by means of a hydrodynamic study with homogeneous beds of cork of different size in different experimental conditions. The validity of the ranges of the geometric factors of the contactor and of the contactor-particle system for stable spouting established in previous papers and of the equation for the calculation of the minimum spouting velocity proposed for granular materials and glass spheres has been proven for beds consisting of cork. The suitable design of the conical spouted bed reactor for the combustion of cork wastes requires the previous knowledge of the ranges of the geometric factors of the contactor and of the contactor-particle system for stable spouting.

The biosorption of eight different metals from aqueous solutions of combined industrial effluent by live or dead cells of Phanerochaete chrysosporium was investigated. Growth rate studies of P. chrysosporium were carried out in a selected medium as well as in the effluent. The specific growth rate of the fungus was in the range of 0.089–0.102 h–1 in the medium. The biosorption of metal ions increased as the initial concentration of metal ions increased in the medium. Biosorption equilibrium was established in about 1 h and the concentration of adsorbed metal ions did not change further with time. The equilibrium was well described by Langmuir, Freundlich and Reidlich – Peterson isotherms. The dead fungal biomass was more effective than living fungus for biosorption of metals. The optimum pH for the fungal growth was at 4.5 but enhanced Biosorption was at pH 6 for maximum reduction of hexavalent chromium to trivalent.

Straight chain C10 to C13 di-olefins were selectively hydrogenated to increase the mono-olefins content in the feed to alkylation reactor in the process of production of Linear Alkyl Benzene (LAB). The reaction was carried out in a liquid phase up-flow fixed bed reactor at temperature of 448-503 °K and pressure of 1.08-1.96 MPa, which keeps hydrogen dissolved in the hydrocarbon feed. Under the above process conditions the reactor will be virtually two phase (solid-liquid) instead of three phase (solid-liquid-vapour). Kinetics of hydrogenation of straight chain C10 to C13 di-olefins on nickel – alumina (Ni/Al2O3) catalyst was studied in the temperature range of 458-488 °K. The reaction scheme considered includes two consecutive hydrogenation reactions. Various rate models based on the modified Power Law, Horiuti-Polanyi mechanism & proposed by Somers. A.; were derived for the two consecutive hydrogenation reactions and subjected to model discrimination. Parameter estimation was done utilizing the Levenberg-Marquardt Algorithm for global convergence using MATLAB software. Out of the various models tested, rate model based on power law with modification fitted the data well. The estimated rate constants of the best model are thermodynamically sound and statistically consistent.

Hydrogen sulfide sorption activities of manganese oxide and Mn-Fe-Cu mixed oxide sorbents were examined in a fixed bed reactor. Sulfur retention capacity of Mn-O sorbent was found to be quite high at 600 °C both in the absence and presence of hydrogen gas (0.17 and 0.14 g S/g sorbent, respectively). This sorbent has a high porosity and a relatively high surface area. Best regeneration temperature of this sorbent was found as 700 °C, with a gas stream containing 6% oxygen in nitrogen. Mn-Fe-Cu mixed oxide sorbent had a lower sulfur retention capacity (0.07 g S/g sorbent). However, both of these sorbents gave quite high initial sorption rate constants, resulting very sharp breakthrough curves. Deactivation model was shown to give good agreement with the experimental H2S breakthrough curves.

In this paper, the primary components of a PEM fuel cell for automotive applications, using methane as a fuel, are analyzed. Basic chemical engineering principles are utilized to assess the role of thermodynamics, heat transport, and reaction kinetics. The amount of methane required is calculated as function of hydrogen produced as well as the power produced. The heat duty for thermal control of the system is analyzed.

A two-stage, micro trickle-bed reactor (for studies of the effects of hydrogen sulfide on hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) of Athabasca bitumen-derived heavy gas oil over commercial NiMo/Al2O3 catalyst) has been simulated. One dimensional homogeneous mass transfer and a two dimensional heat transfer models were developed. The essence of the simulation was to enhance the understanding of the effects of hydrogen sulfide in the hydrotreating catalyst bed in a two-stage mode and also to predict the catalyst requirements for deep HDS and HDN processes. The kinetic model used in the simulation was based on the Langmuir-Hingshelwood method of rate determination. Adsorption constants were estimated by non-linear least squares method. The kinetic models were tested on independent set of data and found to predict the experimental data satisfactorily. The mass transfer simulation considered the effects of variables such as temperature and catalyst loading or liquid hourly space velocity (LHSV) on the trends of hydrogen sulfide generation and, sulfur and nitrogen conversions along the catalyst bed. The model was numerically solved using a fourth-order Runge-Kutta technique. The 1:3 wt/wt catalyst loading with inter-stage hydrogen sulfide removal was found to give the best HDN and HDS activities. Simulated results showed that doubling the present catalyst mass and operating at 653 °C with inter-stage hydrogen sulfide removal would give 6 and 179 ppm product sulfur and nitrogen, respectively. On the other hand, without hydrogen sulfide removal, only 49 and 302 ppm product sulfur and nitrogen could be attained, respectively. The heat transfer simulation compared temperature profiles in the two-stage process to a single stage process for the 1:3 wt/wt catalyst loading at 653 K. The temperature regime in Stage II was found to be more uniform unlike Stage I and the single stage. Crank Nicholson algorithm was used to solve the 2-D partial differential equations.

Using ‘flame-synthesized’ nanoparticles (nps) as one prototypical application, we illustrate our recent progress in two broad areas of current CRE-interest, viz., the development of: 1. Improved rate laws/transport coefficients for next-generation Eulerian, multi-(state) variable population-balance formulations, and 2. Quadrature-based multi-variate moment methods (hereafter QMOM) suitable for articulation with evolving Eulerian CFD simulation methods Admittedly, in previous work much insight was obtained by introducing deliberately (over-) simplified rate laws (for nucleation, Brownian coagulation, vapor growth/evaporation, sintering, thermophoresis,…) into the generally nonlinear integro-partial differential equation called the ‘population balance’ equation (PBE). However, despite the complexity of this equation, and the need to satisfy it along with many other local PDE-balance principles in multi-dimensional CRE environments, in our view current requirements for reactor design, as well as the frequent need to infer meaningful physico-chemical parameters based on laboratory measurements on populations rather than individual ‘particles’, make the introduction of more accurate rate/transport laws essential for next-generation particle synthesis reactor models. Our present examples are motivated both by measurements/calculations of the structure of laminar counterflow flames synthesizing Al2O3 nps and/or the predicted performance of well-mixed steady-flow devices in which sintering or sublimation occurs. Corresponding illustrative results, which focus on the rate laws for sphere dissolution or aggregate Brownian coagulation support our contentions that: i) systematic introduction of more accurate rate laws (including nucleation, sintering, growth, …)/transport coefficients will be essential to meet the quantitative demands of next-generation PBE-based CRE-simulation models for high-value particulate synthesis equipment, and, ii) QMOM is able to incorporate realistic rate laws and faithfully generate their effects on important ‘moments’ characterizing the product joint distribution functions.

Transient and steady state reactor data for the partial oxidation of butane to maleic anhydride were collected in a fluid bed over DuPont commercial vanadium pyrophosphate catalyst (VPO) principally under butane rich, oxygen deficient operating conditions. Under moderate reducing conditions, oxygen becomes the determining factor for maleic anhydride productivity and selectivity. As the oxygen becomes depleted, minor changes in butane conversion impacts the selectivity substantially. However, when VPO catalyst is pre-exposed to oxygen for a substantial period of time (as practiced in Circulating Fluidized Bed technology), selectivity may be improved and maleic anhydride yields four times the steady state operation values are achieved. As the butane-to-oxygen ratio rises above 1, carbon deposits onto the surface of the catalyst, resulting in lower activity and selectivity. Based on a detailed reaction engineering model, the re-oxidation rate of the adsorbed carbon is 1st order with respect to the carbon adsorption sites and ½ order in oxygen. The re-oxidation rate of the reduced catalyst appears to be 1st order in sites and oxygen.

A mathematical model is proposed for the partial oxidation on n-butane to maleic anhydride (MAN) in a gas-solid fluidized bed reactor. The reactor consists of two regions, i.e., a lower dense region and an upper dilute region. The dynamic two-phase structure was used for modeling the lower dense bed hydrodynamics. The upper region hydrodynamics was modeled by a cluster based approach. This allows the porosity distribution to be calculated for plug flow reactor model assumed for the gas phase in this region. The basic assumption in the cluster based approach is that the solid particles move only as clusters and the amount of single particles in the upper region is negligible. The mathematical model was obtained from coupling the kinetic sub-model, obtained from the literature, with this hydrodynamics sub-model. Comparing the results of the model with the experimental data available in the literature showed close agreement. Two other methods (i.e., particle based approach and short-cut) were also tested in this work. However, it was found that the cluster based approach modeling is quite suitable for the fluidized bed reactor used in this study. The short-cut method seems reasonably applicable for the prediction of the overall conversion but does not provide any local information (such as concentration profiles, yield, etc.) within the fluidized bed reactor.

A new wet FGD process in which sulfur dioxide was absorbed in the bubble reactor using granular limestone simultaneously adding acetic acid had been proposed. The main difference compared to conventional wet FGD process was the ability of the new process to utilize granular limestone directly as a desulphurization reagent simultaneously adding acetic acid. Thus, the pulverizing of limestone, which causes power consumption, can be saved. Only using granular limestone directly as absorbent without acetic acid, SO2 removal efficiency and limestone utilization were too low. Adding some concentration of acetic acid, the performance of the new wet FGD process was confirmed to be equal to or higher than that of a conventional process in various tests. Various parameters of the new FGD process which would affect the sulfur dioxide removal efficiency and limestone utilization were studied.

A detailed investigation of local hydrodynamics in a pilot plant bubble column has been performed using various techniques, exploring both axial and radial variations of the gas hold-up, bubble average diameter and frequency, surface area. A wide range of operating conditions has been explored up to large gas and liquid flow rates, with two sparger types. Two main complementary techniques were used: a quasi local measurement of gas hold-up via series of differential pressure sensors to get the axial variation and a double optic probe giving radial variations of gad hold-up, bubble average size and frequency and surface area.According to axial evolutions, three zones, where radial evolutions have been detailed, have been separated: at the bottom the gas injection zone, the large central region or column bulk and the disengagement zone at the column top. It was found that significant axial and radial variations of the two phase flow characteristics do exist even in the so called homogeneous regime. The normalized profiles of bubble frequency appear sparger and gas velocity independent contrary to bubble diameter, gas hold-up and interfacial area normalized profiles. In any case bubbles are larger in the sparger zone than elsewhere.The main result of this work is the very strong effect of liquid flow on bubble column hydrodynamics at low gas flow rate. First the flow regime map observed in batch mode is dramatically modified with a drastic reduction of the homogeneous regime region, up to a complete heterogeneous regime in the working conditions (uG> 0.02 m/s). On the contrary, liquid flow has limited effects at very high gas flow rates.A large data bank is provided to be used for example in detailed comparison with CFD calculations.

The present article describes an algorithm developed for computing the position and the equivalent diameter of bubbles featuring in two-dimensional fluidized beds simulated by means of Computational Fluid Dynamics (CFD) multiphase-flow codes. The program is presented for two-dimensional systems; nevertheless, following the same logic herein outlined, it can be easily extended to the more general case of three-dimensional beds. In this work, by “equivalent diameter” it is meant the diameter of the circle having the same area as the bubble. The procedure is intended as a useful tool in the validation of the results of numerical simulations aimed at investigating the fluid-dynamic behavior of fluidized beds operating in the bubbling regime. The algorithm, presented here without making reference to any specific programming language, can be run in any CFD commercial code, provided that the language and the syntax used are consistent with those required by the particular code adopted. The logic of the program is first illustrated in general terms, and afterwards by making reference to an illustrative example regarding a Geldart Group B powder fluidized by means of air. In this specific case, the equations of motion used to describe the dynamics of the system have been based on the work by Mazzei et al. (2006), the commercial CFD code used has been CFX 4.4 and the programming language applied to implement the algorithm has been Visual Fortran 6.6.

To further the understanding of fine particle spouting phenomenon that has not been fully experimentally investigated until now, this article discusses some fundamental aspects of the computational fluid dynamics (CFD) simulation of fine particle spouting. Using the two-fluid method (TFM) embedded in the commercial CFD simulation package Fluent (Version 6.1), the spouting hydrodynamics of fine particles in a cylindrical-conical spouted bed is simulated and compared with the experimental data of Chen [“Spouting of fine particles at elevated pressure”, (M. A. Thesis), Beijing, University of Petroleum, (1999)]. The results show that for the CFD simulation of fine particle spouting, the Gidaspow [“Multiphase flow and fluidization”, Academic Press, San Diego, (1994)] model gives the best predictions of the flow pattern and the minimum spouting velocity; the influence of frictional stress is much more significant than for the CFD simulation of coarse particle spouting; the influences of the coefficient of restitution of particles on the fine particle spouting cannot be neglected, identical with the case of coarse particle spouting. Then, some typical hydrodynamic properties of fine particle spouting are simulated using the related models with suitable parameters. The results reveal that the flow regime transition of fine particle spouting is very similar to that of coarse particle spouting, but fine particle spouting is less stable and is limited to a more restricted region; the McNab [“Prediction of spout diameter”, Brit. Chem. Eng. Proc. Tech., 17, 532-541, (1972)] spout diameter correlation derived from experiments of coarse particle spouting is also suitable for fine particle spouting; the denser zone surrounding the spout axis in the spouted bed of fine particles is more obvious than that in the spouted bed of coarse particles; the particles in the spouted bed of fine particles are much quickly accelerated to their maximum velocities than those in a spouted bed of coarse particles. These differences are mainly caused by the aggregating tendency of fine particles.

The effect of silica support on the V-Mg-O catalyst is studied for conducting the oxidative dehydrogenation (ODH) of propane on unsupported 30% V-Mg-O catalyst and the effect of silica support on the activity and selectivity of 30% V-Mg-O catalyst. Among the different loadings of support, the most selective catalyst is chosen for kinetic investigation using Genetic Algorithms. This also includes the effect of parameters like Propane to Oxygen ratio, Contact time and Temperature on the performance of catalysts. Later it is extended to other catalysts also. Modeling was done in the light of experimental data and the parameters in these models were estimated. The characterization of the catalysts was done to understand the behavior of the catalyst.

A well dispersed Co0 supported on deficient LaCo1-xO3-delta perovskite was formed after reduction of LaCoO3 by hydrogen. The formation of some metal cobalt was achieved at the first step of reduction corresponding to reduction of bulk Co3+ to Co2+. The LaCoO3 perovskites were synthesized by reactive grinding, a technique which allows the preparation of nanocrystalline mixed oxides. The H2 reduction of Co is easier in the perovskites prepared this way, due to high surface area and small perovskite crystal domains. The reduction thus happens at lower temperature which helps avoiding metal sintering. This work is a systematic study of the cobalt metal masses generated in strictly controlled reduction conditions. It shows that the perovskites made by reactive grinding are potentially significant for the preparation of supported transition metals with possible applications in several environmental catalysis processes.

Turboxal™, a mixing system used for the oxygenation and the mixing of wastewater biological treatment tanks previously studied, shows a low gas flooding rate. In order to increase the gas flooding rate, two of the three impellers used are replaced by only one new turbine. This new turbine comes from a previous work and has been designed partially by computational fluid dynamics (CFD). The gas flooding rate of the new system, called Turboxal-2™, is increased of about 120% on average compared to the Turboxal™ standard and the mass transfer capacities of the new system are quite similar to those of the previous device.

Catalytic cracking of waste plastics is an interesting option for selectively recovering raw materials or for obtaining fuels. In this paper, a new recycling strategy is proposed, which consists of upgrading the waxes obtained by flash pyrolysis of polyolefins in a FCC (Fluidized Catalytic Cracking) unit. The waxes have been obtained by flash pyrolysis of polypropylene at 500 ºC and they have been dissolved (20 wt% wax) in the vacuum gasoil (VGO) of a FCC unit. The runs have been carried out in a CREC-UWO Riser Simulator Reactor (atmospheric pressure; 500-550 ºC; C/O = 5.5; contact times, 3-12 s). A commercial catalyst and a hybrid one (containing HZSM-5 zeolite) have been used. The cracking of the mixture leads to higher yield of gasoline than in the cracking of VGO with a higher content of olefins. The results of the effect of the operating conditions (temperature and contact time) are qualitatively similar to those corresponding to standard feed. Consequently, no difficulties inherent to the presence of waxes in the feed are expected in the treatment of mixtures at industrial conditions. The presence of HZSM-5 zeolite in the catalyst causes a significant increase in the amount of LPG (especially C3-C4 olefins), at the expense of a decrease in the gasoline fraction, whose RON is 1-2 points higher than that corresponding to the commercial catalyst. The gasoline obtained also has a higher content of olefins (especially C5-C7) and benzene at the expense of a decrease in the amount of C6-C10 i-paraffins.

Fatty acid esters are currently produced in batch processes. The production of fatty acid esters in a catalytic distillation column is a promising alternative to the conventional sequential process. In the present study, a steady state equilibrium model was developed for the production of iso-propyl palmitate in a catalytic distillation column catalyzed by zinc acetate supported on functionalized silica gel. The model incorporated reaction kinetics and vapor-liquid non-idealities into the MESH (Material balance, Equilibrium relationship, Summation equation and Heat balance) equations. The model was solved with the numerical method coupled with the relaxation method. To ensure the applicability and reliability of the proposed model, it was validated by comparing the simulated results of a similar endothermic fatty acid esterification (decanoic acid with methanol) in a catalytic distillation column, with the published simulation results and the pilot plant data from the literature. The model was capable of predicting the performance of a catalytic distillation column for an endothermic fatty acid esterification.To ensure the most effective reactive distillation process for the esterification of palmitic acid with iso-propanol, several key design parameters such as reactant ratio, column pressure, number of equilibrium stages, catalyst weight and reflux ratio were investigated by sensitivity analysis. The results showed that the operation at maximum possible pressure is beneficial for this process due to the endothermicity of the reaction. It was found that the reactant ratio of 1.3-1.7 was sufficient to give high palmitic acid conversion without affecting the iso-propyl palmitate purity. It was observed that low reflux ratios resulted in higher conversion of palmitic acid. However, the number of rectifying and stripping stages was of minor importance for the performance of the overall process. The simulation results could serve as the basis of designing a pilot-scale catalytic distillation unit.

Nanoparticles of SiO2 have been produced in an inductively coupled thermal plasma reactor. The resulting nanoparticles were characterized based on their morphology and size distribution. Scanning electron microscopy, nitrogen absorption (BET method), laser diffractometry and X-ray diffraction techniques were used to characterize and to measure the equivalent diameter (D(1,0), D(3,2) and D(4,3)) of the resulting nanopowders. The computational fluid dynamics (CFD) software FluentTM 6.1 with the Fine Particle Model (FPMTM) was used to simulate the whole synthesis process. The nanoparticles of SiO2 produced at the exit (filter) and on the reactor wall had primary particles diameter between 10-300 nm while the aggregates were of much larger size, between 1 and 4 micrometers. The simulation predictions were used to gain more insight into the experimental results.

The last generation of catalysts for automotive emissions has substituted the traditional ceria by cerium-zirconium mixed oxides, due to their increased oxygen storage capacity, selectivity to the desired products (mostly N2) and durability; while increasing the proportion of palladium, due to its interesting behavior. Using simplified feed-streams with only three components: propylene, NO and O2, plus the N2 carrier, and with data of integral reactor in the range 200–300ºC, we have performed experiments in order to obtain kinetic data with a 0.5 %Pd/Ce0.68Zr0.32O2 catalyst. The results have shown that, in the studied range, inlet reaction rates of reactants consumption and products formation can be explained by a Mars-Van Krevelen mechanism in which O2 and NO oxidize the support, and products formation takes place via reduction of the support by the rest of the reactants. Net formation of NO is observed in the low-temperature range, while the opposite is truth in the high-temperature range. Although this behavior has no effect during normal operating conditions in the automobile, it could during cold start up. Also, it is interesting to note that, at low temperature, a significant amount of NH3 —decreasing with temperature— and some N2O —with a maximum at intermediate temperature (around 275ºC)— are formed even though the conditions were highly oxidizing, provided that C3H6 is present. NO, on the other hand, is the precursor for NO2.

Hydrodynamics of two external loop circulating bubble columns with open channel gas separators were investigated experimentally. The effects of three operating parameters and one design parameter on hydrodynamics were investigated experimentally in two external loop circulating bubble columns with open channel gas separators. The operating parameters were superficial gas velocity in the riser, UGR, gas-liquid dispersion property, and efficiency of gas separation, TVR. The design parameter was the scale-up factor of the riser to downcomer cross-sectional area AD/AR. The gas-liquid dispersion property was varied by using various concentrations of additives like antifoam, alcohols, and wettable suspended solids. All experiments were conducted using compressed air and tap water from the university main supply system. Time-dependent hydrodynamics variation related to air-water quality was minimized by using consistent air-water samples in order to satisfy experimental reproducibility. The results show that for any gas-liquid-additive system, there is an optimum volume of the liquid in the gas separator, TVRO, that gives the minimum gas recirculation in the downcomer. At any AD/AR and TVR, the effects of antifoam and suspended solids were found to reduce the gas holdup, while the alcohols were found to increase gas holdup. At TVRO, the efficiency of the gas separator was improved significantly by increasing the scale-up factor, AD/AR. Liquid circulation was increased in the antifoam system, but reduced in the presence of wettable suspended solids. The best design and operating conditions were found at scale-up factor AD/AR=0.5 and volume ratio TVR>20% for all the additives investigated.

Free radical polymerization kinetics of diallyl terephthalate (DAT) in solution was investigated with two different peroxide initiators: dicyclohexyl peroxydicarbonate (CHPC) and benzoyl peroxide (BPO) in temperature range from 50°C to 110°C, where ortho-xylene was used as a solvent. Conversion points were measured using Fourier Transform Infrared (FTIR) measurements. Previously developed kinetic model for bulk DAT polymerization, was extended to solution DAT polymerization. The ratio of solvent chain - transfer rate constants to propagation rate constants of the polymerization system were found between 1.25 10-4 to 1.68 10-4 for various reaction conditions. They were obtained using the calculated initial polymerization rates and the number average molecular weight measurements made by GPC. The effect of different solvent fractions and initiator concentrations on the diffusion limitations were investigated. Only two kinetic parameters, kpd0 and ktd0 were obtained by fitting the kinetic model onto measured conversions for various reaction conditions at 0.2, 0.5 and 0.8 solvent fractions. Thus obtained kpd0 and ktd0 kinetic parameters were extrapolated to zero solvent fractions and from obtained values of kinetic parameters the conversion points for bulk DAT polymerization were calculated and compared to measured conversion points.

Underground Coal Gasification (UCG) is the process of in-situ conversion of coal into combustible products (syngas) which can be used either as fuel or as a chemical feedstock. In this study, the gasification channel is viewed as a one-dimensional packed bed reactor. The packed bed reactor model is solved incorporating chemical reactions and mass transfer effects. A pseudo-transient model is simulated for temperature and composition profiles of the gas and solid phases. The movements of the pyrolysis and the reaction front are obtained. The model results are in qualitative agreement with literature. The effects of various operating parameters are studied in detail. Steam/O2 ratio, inlet O2 and total pressure determine the solid temperature profile and hence the outlet gas composition. The simulations are performed for two sets of kinetics parameters. The solid temperature profile and outlet gas compositions change significantly with a change in kinetics parameters. The main motivation behind this study is to provide a theoretical base for understanding the critical aspects of UCG and to provide a tool which coupled with experiments will help in determining the commercial feasibility of the UCG process.

A new combustion process called chemical-looping combustion, has been suggested as an energetically efficient method for separation and capture of the carbon dioxide, generated by the combustion of fossil's fuels. This process consists of a reversible combustion, based on successive fuel oxidation via the reduction of metallic oxide followed by its regeneration by air oxidation. The generated products are: the reduced oxygen carrier, which is regenerated in a second reactor by air and recycled, and a flue gas, mainly composed of CO2 and H2O, which could be separated by condensation.In chemical-looping combustion process, it is important that the metallic oxide, used as an oxygen carrier, has a high reactivity with the fuel and good regeneration ability. It should have also good mechanical characteristics, in order to avoid its attrition and agglomeration during the successive cyclic reactions.In this work, the reactivity study of various oxygen carriers was carried out, during ten successive oxidation and reduction cycles, using a thermal gravimetrical analysis apparatus. From the results obtained, two types of oxygen carriers were identified: very reactive oxygen carriers, with a decreasing of their reactivity during the successive cycles of reduction and oxidation, and oxygen carriers with low and constant reactivity during the successive cycles.In order to improve the capacity of regeneration of the reactive oxygen carrier, several mixtures were prepared by adding stable and non-reactive metallic oxide, which acts as binder or doping agent by the mechanical properties of the mixed oxygen carrier improvement.The results obtained showed that, for all mixtures prepared and tested, the addition of binders to the reactive metallic oxides improve their regeneration ability. The best results, concerning the reactivity and the regeneration performances, were obtained with Fe2O3 mixed with CaO, TiO2 or MgO, followed by NiO mixed with CaO or TiO2 and finally CuO mixed with TiO2 or MgO.

A membrane reactor consisting of a reactor and a separation membrane may be suitable to provide hydrogen from hydrocarbon in order to reduce carbon dioxide. In this study, a catalytic membrane reactor, a type of membrane reactor, was designed and tested to prove if both the reactions (dehydrogenation of ethane, and reduction of carbon dioxide to carbon monoxide) occur on each side of the membrane in the reactor as expected. As membrane materials, copper-plated LaNi5 and CaNi5 were chosen. In the first step, lower hydrocarbons including ethane was dehydrogenated at one side of the membrane; another side was swept by an inert gas. In the second step, simultaneous feed of ethane (one side) and carbon dioxide (another side) was tried if both the reactions (dehydrogenation of ethane and reduction of carbon dioxide) occur. Carbon dioxide was reduced to carbon monoxide; ethane was dehydrogenated to give ethene.

One of the most thoroughly studied systems in chemical engineering is the classic problem of a first-order exothermic reaction in a diabatic CSTR. In this paper, an extension of the classic problem, in which the reactor vessel temperature varies independently of its contents, is considered. A bifurcation analysis showed that a CSTR in an oscillatory state may be stabilized by the use of a reactor with the appropriate combination of thermal characteristics. Stabilization of an oscillatory state was demonstrated for a variety of scenarios that had been previously shown by Uppal, Ray and Poore to be representative cases of phase diagrams that exhibit limit-cycle behavior.