(433f) A Comprehensive Model for Gas Permeation and Separation in Asymmetric Hollow Fiber Membranes Considering Non-Ideal Conditions

Abstract

Prediction and analysis of the gas permeation and separation performance in membranes require development of robust models that can account for the non-idealities and complexities involved in a real process. Pressure losses within the membrane module, real behavior of the gas molecules in the mixture, concentration polarization, temperature change due to permeation and its subsequent effect on the permeation performance, and temperature-, pressure- and concentration-dependence of the fluid viscosity are among the major deviations from ideal conditions. These parameters have been shown to play important roles in determining the accuracy of the models for performance evaluation. However, to our best understanding, despite numerous studies focused on this subject and various models presented in the literature, no specific study could be identified encompassing the role and influence of all these parameters in a single model.

This study aims to offer a comprehensive model that accounts for all of the above parameters in order to improve the accuracy of the performance prediction for hollow fiber gas separation membranes. Fundamental equations were based on the permeation, mass transfer and momentum equations for a feed containing a two-component ideal gas mixture. Then the effect of real gas behavior was included by considering fugacity coefficients and using the SRK equation of state. The effect of concentration polarization was considered by accounting for the relationship between the bulk and membrane surface concentrations. The temperature drop due to permeation was considered through calculation of the Joule-Thomson coefficient and its effect on the equations.  The effects of pressure drop on both the shell and lumen side of the hollow fibers was accounted for by using the governing equations of fluid mechanics. The effects of temperature, pressure and concentration dependency of the fluid viscosity were accounted for at both the low and high pressure ranges. All these parameters and their effects were appropriately accounted in a model that was solved using MATLAB codes. This model was then extended to account for the calculation of the membrane performance for multi-component gas mixtures. The influence of non-ideal effects on the module efficiency were investigated and verified using available experimental and/or plant data from various processes.