Iranian Journal of Chemical Engineering (IJChE)

Abstract The applicability of the space-time conservation element and solution element (CESE) method to the numerical simulation of gas-liquid flow in a bubble column is investigated. A transient two-dimensional Eulerian-Eulerian model is developed for an air-water system operating at a superficial gas velocity of 0.01 m s−1. Under the considered operating conditions, the flow is modeled using a laminar formulation, while mass and heat transfer are neglected. The governing conservation equations are solved using the CESE method on a uniform rectangular mesh. The numerical results are analyzed in terms of overall gas holdup, gas distribution, and gas and liquid velocity fields. The predicted overall gas holdup shows reasonable agreement with the experimental measurement, with a deviation of approximately 9%. A grid-independence analysis further demonstrates that refinement beyond the selected 150 × 114 mesh produces only minor changes in the predicted gas holdup. Within the assumptions and operating conditions considered in this study, the results demonstrate the applicability of the CESE formulation to the numerical simulation of the basic hydrodynamic behavior of gas-liquid bubble-column flows.

Abstract In this research, silica gel as a low-cost adsorbent for the uptake of carbon dioxide was investigated experimentally. The samples were characterized by XRD, BET and FT-IR. It shows that as pressure was increased from 2 to 8 bar, the CO2 adsorption capability improved over time. At a pressure of 6 bar and a dose of 1 g of silica gel, the impact of temperature (25, 45, 65, and 85 °C) on the CO2 adsorption capacity (mg/g) was determined. The process behavior was investigated using isotherm, kinetics and thermodynamic models. As the temperature rises at a constant pressure, the adsorption capacity decreases. The experimental data of the carbon dioxide adsorption using silica gel have a high correlation coefficient with both Langmuir (0.998) and Freundlich (0.999) models. The results of the carbon dioxide adsorption kinetics with the silica gel adsorbent show that the correlation coefficient (R2) of the second-order model and Ritchie's second model are equal to 0.995 and have the highest value. The total pore volume was 0.005119 (cm3 g-1) and the specific surface area was 2.1723 (m2g−1). The maximum CO2 adsorption capacity at 25 °C near 8 bar was 195.8 mg/g.

Abstract In this work, zeolite 13X with porosity structure has been used as an adsorbent for adsorption of CO2 flue gas. The effect of operating conditions including pressure and time on adsorption capacity were investigated. The experiments conditions are constant temperature, the range of pressure 1 - 9 bar and the registration of adsorption capacity with passing of time. Experimental data were adjusted with adsorption isotherm models including two and three parameters isotherm. Also the process was studied in terms of kinetic models and after the implementation of the experimental data with kinetic models, the speed of this process equations were obtained. The best kinetic model for this process was selected first order equation. The results showed that adsorption capacity of 13X is 71.5 mg/g at pressure of 8 bars. Also the result indicate that 13x has high capacity at low pressures. With regard to achieved results for adsorption isotherm modeling, the adsorption isotherm followed of the three-parameter and among three-parameter models, Toth isotherm can be interpreted the process. Also the results of the fixed bed indicate a very high adsorbent selectivity to carbon dioxide adsorption and there was little oxygen and nitrogen adsorption.

Abstract In the Bayer process, the reaction of silica in bauxite with caustic soda causes the loss of great amount of NaOH. In this research, the bound-soda losses in Bayer process solid residue (red mud) are predicted using intelligent techniques. This method, based on the application of regression and artificial neural networks (AAN), has been used to predict red mud bound-soda losses in Iran Alumina Company. Multilayer perceptron (MLP), radial basis function (RBF) networks and multiple linear regressions (MLR) were applied. The results of three methodologies were compared for their predictive capabilities in terms of the correlation coefficient (R), mean square error (MSE) and the absolute average deviation (AAD) based on the experimental data set. The optimum MLP network was obtained with structure of two hidden layer including 13 and 15 neurons in each layer respectively. The results showed that the RBF model with 0.117, 5.909 and 0.82 in MSE, AAD and R, respectively, is extremely accurate in prediction as compared with MLP and MLR.

Abstract Continuous bioreactors are critical unit operations in a wide variety of biotechnological processes. Due to the level of detail built in their mathematical formulation, cell population balance models represent the most accurate way of describing the microbial population heterogeneity in continuous bioreactor. In this work,the equation set of the model was solved numerically using rigorous'space–time conservation element and solution element' CE/SE method.MATLAB/Simulink pre-existing blocks are used for modeling and control of the different moments of cell mass distribution in a continuous bioreactor. For investigating the efficiency of automatic controller, 10% increase in maximum specific growth rate in Ks, was considered. The set point for zeroth, first and second moments of distribution were taken to be; M0,sp =0.6706 , M1,sp =0.1541 , M2,sp =0.0505, which correspond to a dilution rate of 0.953 h -1 and 0.6 h -1 . In the first case the controller response after 10 hours was (0.92 h -1 ± .05), (0.87 h -1 ± 0.4) and (0.92 h -1 ± 0.2). For the second case the controller response was close to set point(0.6 h -1 ± .001) after 20 hours.

Abstract In this work, recovery of uranium from industrial waste was investigated experimentally using solvent extraction technique. Di 2-ethyl hexyl phosphoric acid (D2EHPA), tri-n-octyl phosphine oxide (TOPO) and their synergetic mixture was used as extractant in the experiments. Nitric acid solution was selected the best medium for extraction of uranium from the industrial waste. The extraction process has been investigated as a function of extractant concentration, diluents type, nitride acid pH, contact time, initial uranium concentration and temperature. The experiments were performed in batch mode. Kerosene was selected as the best diluent for the extractants. In the experiments it was found that, high temperature is beneficial for TOPO or D2EHPA extraction but low temperature is profitable for their synergistic effect. The results indicate that the extraction rate for uranium was controlled by diffusion. The best stripping agent for TOPO 0.05M or D2EHPA 0.15M and their mixture were Na2CO 3 2M, by 96.2%, 54.3% and 57% uranium recovery respectively. McCabe curve showed that single theoretical stage is sufficient for uranium extraction more than 95 percent.

Abstract In this work, a dynamic model has been developed for prediction of biofilters performance. The model includes most of the phenomena occurring in a biofilter. For biodegradation of pollutants in the biofilm, the Michaelis-Menten kinetic has been considered. The model equations including gas phase and biofilm partial differential equations were solved simultaneously using finite difference and method of lines. The model parameters were evaluated by sensitivity analysis to determine their respective effects on the model performance. The model predictions were validated by experimental data for mixture of methyl propyl ketone, toluene, p-Xylene and n-Butyl acetate. The simulation results of empty bed  residence times 30, 60, 90 seconds were compared with experimental data. The comparison of results showed the model
predictions had a good agreement with experimental data. The sensitivity analysis of the model parameters showed that Henry's constant and specific area of biofilter had the strongest influence on biofilter performance.

Abstract In this research, reactive absorption of hydrogen sulfide using diglycolamine solution in an industrial tray column was investigated. A nonequilibrium stage model has been developed based on dynamic film model for modeling of hydrogen sulfide reactive absorption into diglycolamine solution. In the model, simultaneous heat and mass transfer and reactions rate were considered. The model equations including partial and ordinary differential equations were solved numerically using the method of lines technique. The simulation results are presented in steady and unsteady state conditions. An industrial absorption column was employed to obtain the experimental data in both low and high pressure. The model results were evaluated using the steady state experimental data. A comparison of the experimental and simulation results showed that the average of correlation coefficient error for high pressure absorption process is 8.5 percent whereas the average of correlation coefficient error for low pressure absorption process is 7 percent.