Steam reforming of methane and methanol in simulated macro & micro-scale membrane reactors: Selective separation of hydrogen for optimum conversion

Abstract

Various configurations of membrane reactor for steam reforming of methane and methanol are studied here using mathematical model. Micro-scale membrane reactor is conceptualized as a channel with one wall coated with catalyst material, and the other wall permeating hydrogen through a layer of palladium. The membrane layer helps in removal of hydrogen from the reaction site, thereby shifting the equilibrium conversion. In comparison with macro-scale model, the membrane micro-reactor required a shorter residence time to achieve the same level of conversion. This is primarily because of better removal of hydrogen, and is true even when the dispersed catalyst density remained same in both macro and micro models. Any perturbation in the rate constants of sub-reactions that could be arising from catalyst site rearrangements in the micro-fabricated layer does not significantly affect the conversion. Effects of the thickness of the membrane and operating temperature on the conversion are discussed. The pressure drop along the length of the channel arising from friction, reaction stoichiometry, and permeation of product component was estimated. The ratio of membrane area to the catalytic surface area in the channel as a function of distance from the inlet end should be such that the conversion is maximized. This is observed that with selective placement of membrane and catalyst, a methane conversion of more than 95% can be achieved by considering only 40% of the wall, covered with membrane.