Performance comparison of methanol steam reforming integrated to Pd-Ag membrane: Membrane reformer vs. membrane separator

Abstract

Abstract Integration of methanol steam reforming with hydrogen selective dense Pd-Ag membranes makes membrane reformers compact and efficient for ‘on-board’ hydrogen generation. However, hydrogen permeation through standalone dense Pd-Ag membranes is largely reported to be limited by gas mixtures such as CO, CO 2 and steam. These gas mixtures are also basic constituents of methanol reformate with approximately 60% hydrogen by mole. Therefore, it is mostly assumed that such gas inhibition behavior would significantly affect membrane reformer performance. Apparently, this assumption is not valid until a comparison is made under similar experimental conditions for the same membrane. Using 100 µm thick self-supported dense Pd-Ag membrane, the current work compares the performance of membrane reformer with membrane separator under similar operating conditions. By definition, membrane separator is principally a purifier which is used to separate hydrogen from various components such as CO 2 , H 2 O, CH 4 and CO. On the other hand, membrane reformer is a system which generates hydrogen from a reaction such as steam reforming and simultaneously separates it using membranes, integrated in the same physical device. In this study, membrane reformer performance was optimized with effect of steam/methanol ratio, temperature and pressure. Under optimal conditions, synthetic gases of similar composition as of produced reformate were used to evaluate membrane separator performance. No significant inhibition was observed due to CO, CO 2 and steam at optimal temperature 673 K and pressure 3 bar. Presence of excess steam however dilutes the hydrogen partial pressure in reformate which reduced hydrogen flux. Comparison of membrane reformer vs. membrane separator further showed equivalent flux as well as high hydrogen purity indicating a good feasibility of these systems to be tested further for pilot scale studies.