Simulation of Coupled Membrane/PSA Processes for Gas Separation

An integrated model that successfully predicts the process characteristics of a novel hybrid gas separation process combining membrane permeation and pressure swing adsorption (PSA) is presented. The membrane performs most of the bulk separation operating in counter-current flow mode to maximize the average driving force and therefore providing the most efficient arrangement. Permeate and residue streams are fed to the PSA at different steps of the cycle for higher purity and enhanced recovery.

Our simulation work shows that the efficiency of the pressurization and high-pressure adsorption steps increase, thereby improving the separation performance as compared to a standalone PSA. The process has been successfully applied to the bulk separation of a mixture of 50/50 H2/CH4 and preliminary results have been obtained for CO2/CH4 and H2/CO2/CH4 mixtures. The H2/CH4 mixture was selected because it is a challenging separation to show the benefits of the hybrid process since the selectivity between CH4/H2 on activated carbon is high, making the PSA alone a very efficient separation process for this mixture. Nevertheless, even in this unfavorable case the membrane enhances the separation performance. It is expected that using the operating pressure of the PSA bed as the driving force for membrane permeation minimizes recompression work and enhances productivity.