JOURNAL OF SEPARATION SCIENCE AND ENGINEERING
Year:2016 | Volume:8 | Issue:2|Papers Count:9

This paper presents control structure design and dynamic modeling of atmospheric distillation column using relative gain array (RGA) and relative normalized gain array (RNGA). Nonsquare control structure selection for atmospheric distillation has not been addressed in the literature. The column has been modeled and simulated for 40, 000 and 60, 000 bbl/day capacities in order to examine the control performance of the column. Output performances of control structure were examined by ±5% step change in feed rate. Based on the results, the output responses for both RGA and RNGA methods show good control performance for 60, 000 bbl/day capacity, while the output responses for 4, 000 bbl/day capacity suggest change in control structure for both methods.

Separation of alkanes isomers by zeolite has a special importance. In this study, Monte Carlo technique was employed to molecular simulate the adsorption of pure and binary mixtures of pentane isomers in MFI zeolite. The influences of the aluminium content on pentane isomers adsorption on MFI zeolites (Si/Al ratios 18, 31 and ∞) were investigated. Results of this study show different adsorption and selectivity properties with different Si/Al ratios that related to straight and zigzag channels structure of MFI zeolite. MFI selectivity for adsorption of linear alkanes was increased with increasing pressure. Due to adsorption competition, adsorption selectivity in mixture was more than pure. Increase the temperature result in decreasing adsorption amount and selectivity that related to the adsorption pressure.

In this study, membrane contactors are modeled for removal of CO2 and H2S from natural gas stream. In this modeling, the effects of different parameters such as the inlet flow rates, and different types of liquid, as well as wetting phenomenon are investigated. The results showed that NaOH and monoethanol amine (MEA) are the best candidates to remove H2S and CO2. Also, wetting - which was ignored in the previous studies - has a considerable effect on this process. As a result, in the case of 50% wetting, CO2 and H2S removal reduced down to 50%. Finally, it can be concluded that although NaOH showed the highest amount of gas removal, MEA could be a better absorbent from an economic point of view.

Adsorption behavior of most of the batch mode adsorption processes are defined by non-linear isotherms models such as Redlich-Peterson, Radke-Prausnitz, Sips, Koble–Corriganmodel, etc. To determine the isotherms’ parameters of this type of adsorption models, a trial and error based optimization methods are inevitable which are time consuming as usually are sensitive to the chosen first guess. Therefore, in the present paper an explicit method with no need to trial and error for the determination of the non-linear adsorption models’ parameters was presented. In this approach, first the differential form of the adsorption isotherm is achieved and then the exponential parameter is determined through the intercept of this equation. Having the exponential parameter in hand, the other constants of the isotherm are obtained from the slope and intercept of the linear plot of the concentration and the adsorption capacity. To validate the method, catecholamine modified polysulfone was synthesized for the adsorption of chromium (VI), and different adsorption models were fitted to the resultant data. In the exponential parameter determination, in comparison with the trial and error method, the relative error was less than one percent.

In the present study volume of fluid based (VOF) interface tracking method has been used for the simulation of hydrodynamics of Taylor bubble flow in one unit cell. In this case the stationary bubble is supposed in an axis symmetric domain and the liquid flows over it. Afterwards, the effects of different parameters such as capillary number, gas volume fraction, unit cell length and capillary diameter on interphase mass transfer in Taylor flow have been investigated. Finally based on CFD simulation results a correlation has been proposed for interphase mass transfer coefficient. The ability for prediction of mass transfer coefficient in wide range of capillary number is the great advantage of the proposed correlation. In this correlation the change of bubble shape with capillary number has been regarded.

Prediction of solubilities of industrial solid compounds in supercritical carbon dioxide (SC-CO2) have been a challenge since the last two decades. In this study, the Peng-Robinson-Stryjek-Vera equation of state (PRSV EoS) and the Soave-Redlich-Kwong equation of state (SRK EoS) were applied to estimate the solubilities of 10 common solid compounds in supercritical carbon dioxide. Simulation results showed that the PRSV EoS had good agreement with experimental data.Both EoS needed binary interaction parameter for prediction of phase behavior of solid-supercritical. In addition, with use of genetic algorithm, parameter for solid compounds and SC-CO2 were calculated. Due to the lack of comprehensive correlations for prediction of solubilities of CO2+solids, in this work a correlation to predict the solubility of solid in SCCO2 was proposed. The main advantage of this correlation is its simplicity and having only two inputs, namely temperature and pressure. Minimum value of the average absolute percent deviation (AAPD) was for PRSV EoS and carbon dioxidenaphthalene system (2.77%) and maximum value of this parameter was for SRK EoS and carbon dioxide- anthracene system (19.38%).

In this study the modelling and simulation of methanol steam reforming in a membrane reactor is investigated. The palladium based membrane with Cu/ZnO/Al2O3 catalyst are carried out as the model system for hydrogen production. For modelling a rigorous 2-dimensioanl mathematical model is considered and then the results of simulation are compared with the experimental data. The result shows a very good agreement between the simulation and experimental results with mean relative error of almost 8%. Furthermore, the influence of some effective parameters such as the pressure of retentate zone, steam to methanol ratio and sweep gas factor on the hydrogen selectivity were studied. The results perform that increasing of pressure from 1.5 to 2.5 bar can increase the selectivity about 3%. Also, increasing the ratio of water to methanol from 1 to 3 can increase the selectivity of hydrogen nearly 13%. Change in the sweep gas factor affects the hydrogen selectivity in the way that increasing of sweep gas factor up to 7 can increase the selectivity about 4.5%.Furthermore, the 2D concentration profile analysis for methanol concentration in the radial and axial directions has shown that the changes in the radial direction is negligible because of the small reactor diameter.

In this work, the effluent of Merox unit of Kermanshah Oil Refinery was used for un-hairing (tanning) regional sheep skin in leather production process. Four main factors influencing the hair removal process were studied in three levels including: the weight percentage of sodium sulfide (0.2-2%), calcium carbonate (4-6%), temperature (25-45°C) and time (30-90 min). Design of experiments (Design Expert software) was conducted with four mentioned variables and their effect on un-hairing efficiency (response factor) was investigated. The results showed the highest efficiency (99%) was achievable under optimum conditions of highest level of variables, while the 63% efficiency was obtained using tap water (instead of wastewater) under similar experimental conditions (level of variables). Moreover, the qualitative characteristic of un-haired hide was the same in two experiments. Adding calcium carbonate had no significant effect on un-hairing due to high alkalinity of wastewater.Using wastewater, considering 2% content of sodium hydroxide, increased efficiency and decrease the needs for calcium carbonate and sodium sulphide significantly. Using wastewater of Merox unit in skin-tanning leads to a decrease in unpleasant effluents of oil refineries and therefore the needs for chemicals and raw water in leather production industry, and as a consequence a reduce in environmental pollution generation.