(27a) A Carbon Molecular Sieve Membrane-Based Reactive Separation Process for Pre-Combustion CO2 Capture

Reactive separation processes, such as membrane reactors (MRs) and adsorptive reactors (ARs), are attracting increased interest for industrial applications. We study here a hybrid system combining a MR and an AR in tandem (with the AR following the MR, and the MR’s reject stream serving as the AR’s feed). We apply this system to the water gas shift (WGS) reaction in the context of its application in the IGCC process for H₂ generation and simultaneous CO₂ capture from coal/biomass. The MR-AR hybrid system under study attains a high WGS reaction conversion exceeding equlibrium, produces a pure H₂ product for power generation, and delivers a high-pressure CO₂ stream ready for sequestration. In our research, specifically, we use carbon molecular sieve (CMS) membranes. Following the field-testing and performance-validation of these CMS membranes under coal/biomass gasification conditions, experiments have been carried-out in the laboratory to determine the membrane characteristics, and the MR performance under the IGCC-relevant conditions, i.e., for temperatures up to 300 ⁰C and pressures up to 25 bar, with different syngas compositions. In our research, the CMS membranes and the commercial sour-shift WGS catalyst (Co/Mo/Al₂O₃) we use in the MR have displayed very robust and stable performance during a long-term run (~750 hr of H₂S exposure). Further, we have experimentally evaluated the MR-AR hybrid system in multiple-cycle runs (10-16 cycles, with the AR in the reaction/adsorbent regeneration operation mode), and the system has demonstrated superior performance to that of a conventional PBR with high purities for the hydrogen product which can be directly usable in a hydrogen turbine for power generation. As part of this work, we have also carried-out parametric studies for optimization of the operation of the MR-AR hybrid system by investigating various operating conditions for both the MR and the AR, and a detailed model for the MR-AR system was also developed and validated using the experimental data. Using this model, a technical and economic analysis (TEA) was carried-out for process design/optimization and economic evaluation of the WGS-MR-AR system for a broad range of operating conditions and design parameters. The experimental and model findings manifest the ability of the WGS-MR-AR process to operate under the desired conditions and to improve the efficiency of the WGS reaction. They demonstrate, in addition, the potential of the system to carry out the in-situ separation of H₂ and CO₂ using the CMS membranes. We conclude from our study, that the CMS-membrane-based WGS-MR-AR system is a good candidate technology for incorporation into IGCC power plants for environmentally-benign power generation.