A simple model for a water gas shift membrane reactor

Abstract

A simplified process model was developed to simulate a catalytic membrane water gas shift (WGS) reactor. A number of computer simulations were conducted to determine the potential of increased carbon monoxide (CO) conversion in WGS reaction due to simultaneous separation of product hydrogen (H2) from the reactant mixture. Gas separation factors based on Knudsen diffusion were used in these simulations to assess the feasibility of inorganic and ceramic membranes in a high-temperature, high-pressure (HTHP) coal gasification environment. The simulations indicated that although the increase in CO conversion and hydrogen concentration in a single membrane reactor stage was significant, a multistage membrane separation system would be needed to increase the hydrogen product concentration above 90%. As expected, increasing the feed pressure to permeate pressure ratio was found to increase the CO conversion and the product hydrogen concentration. At low feed to permeate pressure ratios, the model predicted a much better membrane reactor performance with a countercurrent feed and permeate flow scheme when compared with a concurrent flow scheme. The membrane performance, of course, depends strongly on the gas separation factors. With gas separation factors lower than the ideal Knudsen diffusion separation factors (e.g. H2 to CO2 separation factor of 2 instead of the ideal Knudsen value of 4.7), the model simulation predicted a much smaller increase in CO conversion and product hydrogen concentration.