Band 15, Heft 2 -

The drag coefficient plays a vital role in the modeling of gas-solid flows. Its knowledge is essential for understanding the momentum exchange between the gas and solid phases of a fluidization system, and correctly predicting the related hydrodynamics. There exists a number of models for predicting the magnitude of the drag coefficient. However, their major limitation is that they predict widely differing drag coefficient values over same parameter ranges. The parameter ranges over which models possess a good drag prediction accuracy are also not specified explicitly. Accordingly, the present investigation employs Geldart’s group B particles fluidization data from various studies covering wide ranges of Re and ε s to propose a new unified drag coefficient model. A novel artificial intelligence based formalism namely genetic programming (GP) has been used to obtain this model. It is developed using the pressure drop approach, and its performance has been assessed rigorously for predicting the bed height, pressure drop, and solid volume fraction at different magnitudes of Reynolds number, by simulating a 3D bubbling fluidized bed. The new drag model has been found to possess better prediction accuracy and applicability over a much wider range of Re and ε s than a number of existing models. Owing to the superior performance of the new drag model, it has a potential to gainfully replace the existing drag models in predicting the hydrodynamic behavior of fluidized beds.

Natural iron oxide was used as catalyst for a heterogeneous photo-Fenton-like process and it was characterized by X-ray diffraction, X-ray fluorescence, Raman spectroscopy, scanning electron microscopy and N 2 adsorption volumetry measurement. Natural iron oxide consists mainly of hematite (76 %). Rhodamine B was mineralized by iron oxide/oxalic acid/UV system, involving creation of dissolved Fe-oxalate and adsorption of Fe-oxalate on the iron oxide surface. The effects of the initial concentration of oxalic acid and pH value, amount of natural iron oxide and concentration of dye, temperature and sunlight irradiation on the kinetics of photodegradation of rhodamine B were investigated. Excellent degradation rate was achieved with 5 mmol.L −1 of oxalic acid at a pH around 2–4. During the process, the formation of Fe 2+ , H 2 O 2 and the pH of the solution were strongly dependent on the initial concentration of oxalic acid. Use of t -butanol (2.0 %) confirms that hydroxyl radicals are the entities responsible for the rhodamine B photodegradation. The use of the natural iron oxide as a catalyst in wastewater treatment is very interesting; because it is an abundant mineral and easy to separate from the solution in the end of treatment.

Esterification reaction between glycerol and lauric acid in the presence of STA/MCM-41 and H 2 SO 4 catalysts indicated that the activity of synthesized catalyst had been comparable to H 2 SO 4 . On the other hand, only di glyceride formation instead of favored mono glyceride has been observed with H 2 SO 4 which had rendered the use of heterogeneous STA/MCM-41 catalyst preferable. Temperature had a decreasing effect on lauric acid conversion due to competitive adsorption of water on catalyst structure. The high mono glyceride selectivity obtained in favor of the desired product was due to shape selectivity of the catalyst. High glycerol amount in feed ratio resulted in deformation of long range order of the catalyst structure and hence a decrease in mono glyceride selectivity. Experiments conducted in identical conditions in the presence of recovered catalysts showed a decrease in lauric acid conversion which had been due to loss of STA from catalyst structure.

This study attempts to comprehend the thermal degradation behaviour of different blends of petroleum coke (denoted as PC) and wood pellets (denoted as WP) (1:0, 3:1, 1:1. 1:3 and 0:1) using thermogravimetric (denoted as TG) analysis under N 2 atmosphere with constant particle size range of 500–850 µm and at constant heating rate of 5 °C/min. TG experiments indicated that it is difficult to predict the pyrolysis characteristics of their blends accurately based on individual components and blending ratios. The non-additive behaviour of TG curves of the blends indicates presence of synergistic effects which could further promote the volatile yields during the co-pyrolysis process. The mixed model including homogeneous reaction model (denoted as HRM) and shrinking core model (denoted as SCM) models were used to predict the variation in kinetic parameters (activation energy and pre-exponential factor) with different blend ratios. The most obvious synergistic effects were observed when the blending ratio was 25 % on account of maximum mass loss rate from the differential thermogravimetry (denoted as DTG), maximum deviation based on root mean square (denoted as RMS) value as well as divergence in the differential thermogravimetric analysis (denoted as DTA) curve.

Photocatalytic treatment of a binary dye mixture (Acid Blue 113 (AB113) and Acid Red 114 (AR114)) has been done in a slurry pond reactor using TiO 2 as a photocatalyst with UV light irradiation (UV-C). Two different methods, namely multivariate calibration and first order derivative spectrophotometric were used to quantify each dye separately in binary dye solutions. The behavior of the photocatalytic degradation of a binary dye mixture was predicted using an artificial neural network (ANN) model. Five process parameters (initial concentration of AB113 dye, initial concentration of AR114 dye, TiO 2 dose, initial pH of the dye mixture and time were used as inputs and decolorization efficiency of AB113 and AR114 were used as output of the ANN. The parametric optimization has been done by the multi-response optimization with desirability function methodology. Optimization by Central Composite Design (CCD) effectively handles the relations among optimizing process variables and its prediction concurred well with the experimental run and artificial neural network (ANN) model. The reaction kinetic rates of decolorization of both dyes (AB113 and AR114) were found to be first order. Total organic carbon (TOC) removal and possible reaction pathway show the total mineralization of both dyes in binary dye mixture.

In this study, the biosorption of lead (Pb(II)), copper (Cu(II)), and cadmium (Cd(II)) ions from aqueous solution using waste of cabbage leaves powder (CLP) was investigated as a function of pH, shaking time, initial metal concentration, and biosorbent dose. The maximum removal efficiency at optimum condition in single biosorption system was 95.67, 92.42, and 88.92 % for Pb(II), Cu(II), and Cd(II) ions, respectively. These values reduced in ternary systems in the same sequence. Langmuir and extended Langmuir isotherm models were found to be the best fit of the isotherm data for single and ternary biosorption systems, respectively. The kinetic data of the three metals were better fit by the pseudo-second-order model with higher coefficient of determination and more closely predicted uptake. In addition, the results showed that the intraparticle diffusion was the dominating mechanism. Thermodynamic study showed that the biosorption of Pb(II), Cu(II), and Cd(II) onto CLP was a chemical reaction which was exothermic in nature. Finally, SEM image shows that CLP has a number of heterogeneous small pores while the Fourier transform infrared (FTIR) spectroscopic analysis showed that the carboxyl, amine, and hydroxyl groups are the major groups that are responsible for the biosorption process.

Microfluidic mixing is an essential part of the process of microfluidic chip technology in the analysis, and micromixer has also become the key components of microfluidic chip analysis system. For DNA hybridization, protein folding and enzyme reaction, some biochemical processes need to react quickly to achieve on analysis and research has the vital significance. A simple, rapid and low-cost passive micromixer is presented in this paper. In order to improve the mixing efficiency of the species, the concept of a splitting and recombination (SAR) was used to shorten the mixing time of the species. This study simulated the species mixing in a micromixer with traditional T-type micromixer and diamond-like micropillar in laminar flow state through COMSOL multiphysics 3.5a to computational fluid dynamics (CFD). Linking artificial neural network (ANN) and CFD was used to optimize the diamond-like micropillar. Finally, simulation results proved that the micromixer with SAR diamond-like concept achieves a high-efficiency mixing than T-type micromixer. Numerical results also show that the mixing efficiency of the SAR micromixer with diamond-like micropillar can be up to 99 %, and that efficiency can reach rapidly 90 % in a short channel distance.

Hydrodynamics of gas-liquid flow in a round-bottom stirred tank is modelled at two gas flow rates, constant bubble size and agitator speed of 300 rpm. A round-bottom tank equipped with four baffles and a Rushton turbine was chosen to represent a typical reactor used in hydrometallurgical processes operating under pressure. The applicability of different momentum interchange models and the Realizable k-ε, SST k-ω, and RSM turbulence models was studied using CFD software. The results were compared and validated against experimental data from Particle Image Velocimetry measurements by means of liquid and gas velocity distributions. In addition, energy balance between power input and dissipation energy was compared for the different turbulence models. The CFD model was found to be in good agreement with the measurements. Of the turbulence models studied, the Realizable k-ε model showed best agreement with the measured velocity profiles. Popular drag force models proposed in the literature were assessed, as was the influence of inclusion of non-drag forces. Gas flow was found to affect the liquid phase flow in the tank by generating an additional secondary circulation loop in the upper part of the reactor.

This paper describes the effect of hydrothermal dewatering of lignite on pyrolysis products characterization and dynamic behaviors. The effects of different hydrothermal temperature (200 °C, 250 °C, 300 °C) on pyrolysis products were tested. The pyrolysis of hydrothermal dewatering lignite (300 °C) resulted in the solid yields of up to 77.98 %, and gaseous product by 11.73 % yield. Analysis showed that all the hydrothermal dewatering promoted the solid products yields and the reducing of the gaseous and solid products yields. The chemicals in the pyrolysis gas from lignite with and without hydrothermal dewatering were mainly H 2 , O 2 , N 2 , CH 4 , CO, and CO 2 . The quality of pyrolysis gas of hydrothermal dewatering lignite was obviously higher than that of raw lignite. The effect of hydrothermal dewatering on the characteristics of pyrolysis carbocoal was explored by MIP, and TG analyses. The pore volume for the lignite treated in hydrothermal dewatering processing conditions is in the macropore size region. The gasification reactivity and ignition temperature of pyrolysis carbocoal of hydrothermal dewatering lignite were reduced, respectively. Kinetic parameters were obtained by Coats–Redfern method and used to model the TG curve. The average activation energy was increased with the increase of hydrothermal temperature. The obtained activation energy for first stage (400–500 °C) pyrolysis was comparably higher than that for the second stage (500–600 °C). The experiments results help to understand and predict the pyrolysis behaviors and propose pre-treatment technology for low rank coals.

0.1 % Pd/ZrO 2 was synthesized and characterized by various physicochemical techniques and was successfully used as catalyst for solvent free oxidation of toluene in the presence of molecular oxygen using batch reactor. The catalytic performance of Pd/ZrO 2 was explored in terms of effect of catalyst loading, reaction time, temperature and partial pressure of oxygen on oxidation of toluene in solvent free conditions. Pd/ZrO 2 was found as a stable catalyst under the reaction conditions. Used catalyst exhibited the same catalytic efficiency as fresh catalyst under similar reaction conditions. Reaction was taking place according to Langmuir-Hinshelwood type of mechanism.

Y-shape micro-reactor is designed, developed and implemented to investigate the effect of reactor miniaturization on chemical engineering kinetics, where, an esterification reaction of fatty acid (2- ethyl hexanoic acid) is considered as a case study. In order to investigate the differential change of micro-reaction conversion along the channel axis; a micro-reactor with multi-channel is designed in a manner that enables collecting the samples. The kinetics of esterification reaction of ethanol and fatty acid was explored under various operating conditions; Molar Ratio (MR) of ethanol to fatty acid at temperatures 25–65 °C. The conversion reached almost 99.3 % after 30 s at MR 4:1 and 25 °C. Steady and unsteady state axial dispersion mathematical models were developed; the latter approach resulted in fair agreement with the experimental results.

This study investigates mathematical modeling of carbon nanotubes (CNTs) formation on catalyst particulate in a fluidized bed chemical vapor deposition (FBCVD) reactor. The mass of CNTs formed corresponds to the catalyst activity directly. The catalyst deactivation occurs as active sites are occupied by CNTs and thus causes unsteady state behavior of the process. The effects of catalyst loading (as bed height) as well as reaction temperature on the reaction progressing were investigated. The model, validated with our experimental data, indicates a good accuracy to predict the yield of CNTs formation for a given operating conditions. The model presented also can predict the optimized time as well as the suitable amount of catalyst loading to produce CNTs for a given reactor conditions.

This paper presents the study on active chlorine mediated electrochemical oxidation of model solutions that simulate textile effluents containing an indigoid dye (indigo carmine) and sodium chloride (0.05 M) using a new Sb 2 O 5 -doped Ti/RuO 2 -ZrO 2 electrode. The study was carried out in a filter-press electrochemical reactor specially designed to minimize flow deviations and provide homogeneous mass transfer flux over the electrode surface. Firstly, the mass-transfer-limited chloride oxidation reaction was studied in the absence of dye in order to understand the active chlorine formation process. Changes in pH, chloride concentration and UV-visible absorption spectra during electrolysis reveal the formation of active chlorine (mainly hypochlorite) with current efficiencies for chloride oxidation of 0.558 and 0.503 at 10 and 20 mA cm −2 , respectively. Secondly, chloride oxidation was investigated in the presence of indigo carmine dye (0.5 mM) where in-situ generated active chlorine was responsible for -C=C- bond breaking and dye degradation. The solution discoloration followed a pseudo-first order kinetics where kinetic coefficient was inversely proportional to dye concentration. The oxidation with active chlorine had an average efficiency of 0.7 and a very competitive energy consumption between 49.2 and 128.5 kW h (kg COD removed) −1 depending on current density and flow rate.

As(III) removal from aqueous solution was conducted using low-cost adsorbents like unmodified raw coconut husk (RCH) and modified iron impregnated coconut husk (IICH). Prepared both adsorbents was characterisation by using elemental analyses, FTIR, TGA, SEM and EDX. The analysis behaviour indicates, both adsorbents are highly suitability for As(III) removal. The effects of operational parameters, such as pH, adsorbent dose and initial concentration on these adsorbents were investigated and compared with other agriculture based adsorbent. The result reveals that the As(III) removal capacity is effective in the pH range of 6.2–7.8 and the optimum pH and adsorbents dose was found as 7.0 and 40 g l −1 , for RCH and IICH, respectively. Kinetic and equilibrium studies over a wide range of operating conditions are tested to evaluate the effectiveness of RCH and IICH to remove As(III) from water. The values of both k f1 and k s2 values are found to be nearly same and same trend was observed at higher 50 mg l −1 and lower arsenic concentration 25 mg l −1 for RCH and IICH. But the kinetic data is fitted better in the pseudo-second-order kinetic model than the pseudo-first order model. The effective intraparticle diffusion coefficient of As(III) ions in RCH and IICH is observed to be 2.145×10 −9  cm 2 s −1 and 1.838×10 −10  cm 2 s −1 , which indicates that the overall As(III) adsorption on both adsorbents are intraparticle diffusion control. Equilibrium isotherms for the adsorption of As(III) on RCH and IICH were analyzed at different dose and different initial concentration. At different concentration system, Freundlich isotherm and Redlich-Peterson are best fitted followed by Langmuir and Temkin isotherm models and for varying doses, all equilibrium models give almost similar fitness.

Sb-CdS catalysts with good crystalline structure were prepared by chemical precipitation and hydrothermal method. The results showed that hydrothermal treatment is an effective method to prepare CdS based catalysts of hexagonal structure. Single Sb 2 S 3 catalyst has spherical and Sb doped CdS catalysts have hexagonal structure. Sb doped CdS which is prepared by Na 2 S with chemical precipitation, has cubic structure. The band gap energies of Sb doped CdS photocatalysts were estimated using UV-visible reflectance spectra to be about the range of 2.35–2.57 eV. In particular, the photoluminescence (PL) spectra show enhancing emission peaks that strongly decrease with a doping Sb where the catalyst was prepared with ethylenediamine (EDA) and thioacetamide (TAA), has shown the lowest luminescence intensity. Photocatalytic degradation of methylene blue was carried out using Sb doped and Sb 2 S 3 -CdS binary catalysts under a 400 W medium-pressure mercury lamp of visible light irradiation (λ>420 nm). Higher photocatalytic degradation was achieved by adding Sb to CdS catalyst with using hydrothermal method and EDA as coordinating agent compare with the other catalysts. In this case the photocatalytic degradation of the Sb-CdS-EDA-TAA photocatalyst after 4 h irradiation time was about 84 %.