Composite catalytic-permselective membranes: Modeling analysis for H2 purification assisted by water–gas-shift reaction

Abstract

Composite catalytic-permselective (CCP) membrane designs, wherein a catalytic film is applied to the retentate surface of a permselective film, are capable of enhancing gas permeation rates and permselectivities by modifying the gas composition in contact with the permselective film surface via reaction–diffusion within the catalytic layer. Isothermal, two-dimensional models are employed to compare performance of a CCP membrane system against (i) an un-modified permselective film in a gas purification membrane (GPM) system, and (ii) an equivalent packed-bed membrane reactor (PBMR) system, for coupling water–gas-shift reaction with H2 purification from a typical heavy hydrocarbon reformate mixture (9%CO, 28%H2, 15%H2O, 3%CO2). Analysis is provided for the case of (i) an infinitely H2-permselective Pd film, for exploring the potential for alleviating surface inhibition via CO using the CCP design, and (ii) a moderately CO2-permselective polymeric film, for exploring the potential for enhancing CO/CO2 separation via CCP design as compared to PBMR designs. For the former case, the CCP design is capable of enhancing overall permeation rates in GPM and PBMR configurations via alleviation of surface inhibition. In the latter case, simulations predict up to a 40% enhancement in reaction product-reactant (CO2–CO) separation, at the cost of reduced product-product (CO2–H2) separation.