Seyed Saeid Hosseini

Phenomenological modeling and analysis of gas transport in polyimide membranes for propylene/propane separation

Olefins and paraffins are the main building blocks for many products in the petrochemical industry. Various research studies have demonstrated the viability of polyimide membranes for high performance olefin/paraffin separation. Further advancements in this field require a thorough understanding of both sorptive and diffusive factors of permeation. This research study presents an extensive analysis on using frame of reference/bulk flow and Maxwell–Stefan models in order to elaborate on the transport and prediction of the performance in the case of propylene/propane separation using polyimide membranes. Sorption data of pure gases are utilized to calculate the sorption level of gases in a binary mixture. The contribution of kinetic and thermodynamic coupling effects (TCE) are assessed using the Maxwell–Stefan approach. Moreover, the dual-mode diffusion coefficients are evaluated and optimized for achieving higher accuracy predictions in the case of a binary gas mixture. The results reveal the significant role of thermodynamic compared to kinetic coupling effects in governing the transport properties. Overall, the Maxwell–Stephan model with the contribution of TCEs offers improved predictions compared to the frame of reference/bulk flow model. The findings highlight the inevitable role of taking into account the prominent interactions of feed components in model development for better prediction of performance and evaluation of the propylene/propane separation unit using polyimide membranes.

Simulation and sensitivity analysis of transport in asymmetric hollow fiber membrane permeators for air separation

Development of high performance membranes requires deep insights about the various design, fabrication and operational parameters involved in the process. In the present study, the influence of input parameters such as active fiber length, feed temperature, feed composition and feed pressure is investigated to analyze the efficiency of the mathematical models developed for the separation of O2/N2 mixtures in an asymmetric hollow fiber membrane permeator. In addition, the effect of various non-idealities on the membrane performance are studied, individually. Results reveal that in contrast to pressure, temperature changes have no influential effects on the concentrations of O2 and N2 at permeate and retentate streams. The influence of feed composition on the product purities is more significant compared to active fiber length. Moreover, analysis of non-ideal effects indicates that pressure changes and concentration polarization are the most significant non-idealities among the effects. Results of this investigation can effectively be used for having a comprehensive overview about the impact of influential parameters and non-ideal effects on the membrane performance for O2/N2 separation application.

Gas permeation and separation in asymmetric hollow fiber membrane permeators: Mathematical modeling, sensitivity analysis and optimization

Mathematical modeling is useful for analysis of process design and performance and is widely used for membrane separation and other important technologies in the energy sector. This study presents the results of our investigations on the mathematical modeling and optimization of hollow fiber membrane permeators specifically used for air separation as well as natural gas purification. The governing equations and mathematical models are developed based on the consideration of ideal and non-ideal conditions often involved in the separation of gas mixtures using membrane permeators. The influence and consequences of adoption of two distinct numerical methods for solving governing equations are investigated in details. The results obtained by using the models as well as the effect of numerical method type are examined and compared to the experimental data. The findings highlight the important role of the solution method on the validity and accuracy of the models. Moreover, the effect of variations in the operating conditions and physical geometries of the membrane are investigated through comprehensive sensitivity analysis. Accordingly, a set of optimal input parameters is determined using an appropriate statistical method. The findings provide useful information for the design and development of high performance membrane permeators and processes particularly in the case of binary gas mixtures for energy applications.

Mathematical Modeling of Natural Gas Separation Using Hollow Fiber Membrane Modules by Application of Finite Element Method through Statistical Analysis

Abstract Hollow fiber membrane permeators used in the separation industry are proven as preferred modules representing various benefits and advantages to gas separation processes. In the present study, a mathematical model is proposed to predict the separation performance of natural gas using hollow fiber membrane modules. The model is used to perform sensitivity analysis to distinguish which process parameters influence the most and are necessary to be assessed appropriately. In this model, SRK equation was used to justify the nonideal behavior of gas mixtures and Joule-Thomson equation was employed to take into account the changes in the temperature due to permeation. Also, the changes in temperature along shell side was calculated via thermodynamic principles. In the proposed mathematical model, the temperature dependence of membrane permeance is justified by the Arrhenius-type equation. Furthermore, a surface mole fraction parameter is introduced to consider the effect of accumulation of less permeable component adjacent to the membrane surface in the feed side. The model is validated using experimental data. Central Composite Designs are used to gain response surface model. For this, fiber inner diameter, active fiber length, module diameter and number of fibers in the module are taken as the input variables related to the physical geometries. Results show that the number as well as the length of the fibers have the most influence on the membrane performance. The maximum mole fraction of CO2 in the permeate stream is observed for low number of fibers and fibers having smaller active lengths. Also results indicate that at constant active fiber length, increasing the number of fibers decreases the permeate mole fraction of CO2. The findings demonstrate the importance of considering appropriate physical geometries for designing hollow fiber membrane permeators for practical gas separation applications.

Enhancing removal and recovery of magnesium from aqueous solutions by using modified zeolite and bentonite and process optimization

Natural and modified zeolite and bentonite are investigated and characterized for extraction of magnesium from aqueous solutions. Magnesium removals as high as 85.21% and 81.73% were achieved by calcined bentonite and microwave radiated zeolite, respectively. The effects of various operational parameters were studied and optimized using selected isotherms. Maximum Mg (II) adsorption capacities of 26.24 and 35.67mg·g−1 were obtained on pristine and calcined bentonites, respectively. Thermodynamic studies suggest that magnesium adsorption on natural bentonite is spontaneous and endothermic (9.13 kj·mol−1). Also, desorption study of natural bentonite demonstrates that HNO3 is more effective by offering 89.11% desorption than other desorptive counterparts.

Mathematical Modeling and Investigation on the Temperature and Pressure Dependency of Permeation and Membrane Separation Performance for Natural gas Treatment

Abstract Due to special features, modules comprising asymmetric hollow fiber membranes are widely used in various industrial gas separation processes. Accordingly, numerous mathematical models have been proposed for predicting and analyzing the performance. However, majority of the proposed models for this purpose assume that membrane permeance remains constant upon changes in temperature and pressure. In this study, a mathematical model is proposed by taking into account non-ideal effects including changes in pressure and temperature in both sides of hollow fibers, concentration polarization and Joule-Thomson effects. Finite element method is employed to solve the governing equations and model is validated using experimental data. The effect of temperature and pressure dependency of permeance and separation performance of hollow fiber membrane modules is investigated in the case of CO2/CH4. The effect of temperature and pressure dependence of membrane permeance is studied by using type Arrhenius type and partial immobilization equations to understand which form of the equations fits experimental data best. Findings reveal that the prediction of membrane performance for CO2/CH4 separation is highly related to pressure and temperature; the models considering temperature and pressure dependence of membrane permeance match experimental data with higher accuracy. Also, results suggest that partial immobilization model represents a better prediction to the experimental data than Arrhenius type equation.

Significance, evolution and recent advances in adsorption technology, materials and processes for desalination, water softening and salt removal

Desalination and softening of sea, brackish, and ground water are becoming increasingly important solutions to overcome water shortage challenges. Various technologies have been developed for salt removal from water resources including multi-stage flash, multi-effect distillation, ion exchange, reverse osmosis, nanofiltration, electrodialysis, as well as adsorption. Recently, removal of solutes by adsorption onto selective adsorbents has shown promising perspectives. Different types of adsorbents such as zeolites, carbon nanotubes (CNTs), activated carbons, graphenes, magnetic adsorbents, and low-cost adsorbents (natural materials, industrial by-products and wastes, bio-sorbents, and biopolymer) have been synthesized and examined for salt removal from aqueous solutions. It is obvious from literature that the existing adsorbents have good potentials for desalination and water softening. Besides, nano-adsorbents have desirable surface area and adsorption capacity, though are not found at economically viable prices and still have challenges in recovery and reuse. On the other hand, natural and modified adsorbents seem to be efficient alternatives for this application compared to other types of adsorbents due to their availability and low cost. Some novel adsorbents are also emerging. Generally, there are a few issues such as low selectivity and adsorption capacity, process efficiency, complexity in preparation or synthesis, and problems associated to recovery and reuse that require considerable improvements in research and process development. Moreover, large-scale applications of sorbents and their practical utility need to be evaluated for possible commercialization and scale up.