Catalytic Pd0.77Ag0.23 alloy membrane reactor for high temperature water-gas shift reaction: Methane suppression

A catalytic membrane reactor was constructed using inner coated Pd0.77Ag0.23 (mass fraction) alloy membrane on Al2O3 hollow fiber substrate, prepared by electroless plating method and packed with Ni-Phyllosilicate catalyst for high temperature water gas shift (WGS) reaction. The performance of the ultra-thin similar to 1 mu m membrane was evaluated in a temperature range of 300-500 degrees C and hydrogen partial pressure of 50-200 kPa. The membrane showed high hydrogen permeance of 5.11 x 10(-4) mol.m(-2) s(-1) Pa-0.65 at 100 kPa pressure and 500 degrees C. WGS reaction was carried out using the membrane reactor at temperature range of 400-500 degrees C, the effect of pressure, steam to carbon ratio and GHSV on CO conversion and methane formation were evaluated. Results showed increase in H-2 permeation with increase in temperature and pressure, which eventually helps surpass the thermodynamic equilibrium CO conversion at high temperatures. H-2 recovery and CO conversion decreased with increase in GHSV from 2896 h(-1) to 11008 h(-1). In this study, the shifting of equilibrium conversion and suppressed methane formation is also demonstrated at a temperature range of 400-600 degrees C. WGS reaction was performed in a catalytic membrane reactor at 600 degrees C for 100 h and it was found to be stable in terms of CO conversion and H-2 recovery for the entire range of investigation. Finally, the membrane was tested for its performance using a reformate gas mixture similar to the gasification plant without any diluents and the conversion was found to be enhanced by 28% in terms of CO conversion at 500 degrees C using a membrane reactor.