Sorption-Enhanced Variable-Volume Batch–Membrane Steam Methane Reforming at Low Temperature: Experimental Demonstration and Kinetic Modeling
journal contributionposted on 02.09.2015, 00:00 by David M. Anderson, Mohamed H. Nasr, Thomas M. Yun, Peter A. Kottke, Andrei G. Fedorov
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.