CO2-permselective membrane reactor for steam reforming of methane

Abstract

Steam reforming of methane (SRM) for hydrogen production with simultaneous CO2 removal in a CO2-permselective membrane reactor is studied experimentally and analyzed by a mathematical model. The membrane consists of a thick porous BYS (Bi1.5Y0.3Sm0.2O3-δ)-SDC (Sm0.2Ce0.8O2-δ) support layer and a thin, dense SDC-carbonate dual-phase layer (∼150 μm) for CO2 separation. Experimental results of CO2 permeation in the BYS-SDC membrane and SRM reactions in a fixed-bed reactor were conducted to obtain the CO2 permeation and SRM reaction rate parameters for the model. The model's reliability is confirmed by comparing the simulation results with atmospheric pressure experimental data for SRM in the BYS-SDC membrane reactor. Simulation results are presented to show the effects of permeation number (θ) and Damkohler number (Da) (which respectively represent membrane CO2 permeance and SRM reaction rate), feed pressure in the reaction side, and sweep side conditions on the performance of SRM in the membrane reactor. Overall, increasing θ results in an increase of H2 yield, retentate H2 concentration, CO2 recovery, and a decrease of retentate CO concentration, with such effects being enhanced at higher Da and feed pressure or vacuum in the sweep side. CO2 permeance affects CH4 conversion only at high feed pressures. At feed pressure of 5 atm and applying vacuum at the sweep side of the membrane reactor, the simulation results show that the membrane reactor can achieve over 99% CH4 conversion, H2 yield, and CO2 recovery and produce an essentially pure H2 stream with zero CO concentration at Da >10,000 and θ > 1.