CO₂-permselective membrane reactor for steam reforming of methane

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 (Bi_1.5Y_0.3Sm_0.2O_3-δ)-SDC (Sm_0.2Ce_0.8O_2-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.