Sorption-Enhanced Variable-Volume Batch–Membrane Steam Methane Reforming at Low Temperature: Experimental Demonstration and Kinetic Modeling

To meet the stringent requirements of distributed hydrogen production, combined reaction–separation approaches to the endothermic steam methane reforming process have been investigated widely as a potential means to reduce the required reaction temperature, ratio of steam to methane in the fuel (or steam to carbon ratio), and number of sequential unit operation steps. CHAMP-SORB (CO2/H2 active membrane piston reactor in combination with in situ CO2 adsorption) is a new reactor technology for distributed hydrogen production from methane that incorporates both a hydrogen-selective membrane and CO2 adsorption into a variable volume batch operation using a four-stroke cycle. Active control of the reactor volume, and hence pressure, in combination with continuous removal of both reaction products allows CHAMP-SORB to circumvent the equilibrium limitations of the steam methane reforming (SMR) reaction, which otherwise limit fuel conversion, especially at temperatures below 500 °C with a stoichiometric fuel mixture. In this work, we present the first demonstration of an operating CHAMP-SORB reactor, achieving SMR at temperatures as low as 400 °C and at a steam-to-carbon ratio of 2:1. A kinetic model of the CHAMP-SORB process is developed; verified for agreement with detailed experimental measurements; and used to investigate the interactions between the reaction, permeation, and adsorption processes. Time scale analysis is introduced to explore the relationship between reactor component design characteristics and the rate-limiting steps of the CHAMP-SORB process. Supported by the results of kinetic simulations, the scaling analysis provides a powerful tool for rapid exploration of the operating space, including operating temperatures and hydrogen collection and utilization pressures.