(681c) A Hybrid Membrane/Adsorptive Reactor Process for Pre-Combustion CO2 Capture. Experimental, Modelling and TEA Studies

The growing demand for energy worldwide combined with concerns about global warming due to CO₂ emissions from fossil fuel-burning power plants motivates advanced approaches that can produce electricity from fossil fuels without harmful CO₂ emissions. One popular approach is the Integrated Gasification Combined Cycle (IGCC) power generation process integrated with carbon capture and storage (CCS) technologies. In IGCC plants, the fossil fuel (e.g., biomass/coal) is first gasified to produce a syngas mixture which is then first cooled-down and treated in a cold-gas-clean-up unit (CGCU) to remove trace contaminants (e.g., COS, H₂S, HCI, Hg, etc.), and is then heated-up to the appropriate temperature to further convert the CO into H₂ and CO₂ via the water gas shift (WGS) reaction. In its place this group has proposed a hybrid membrane/adsorptive reactor (MR-AR) process with enhanced yield and selectivity due to the simultaneous removal from the reaction zone of both H₂ and CO₂, to help overcome the equilibrium limitations of the WGS reaction. This technology provides added flexibility for the IGCC application for which, in addition to efficient high-purity H₂ production, CO₂ recovery and purity are also key drivers.

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 Integrated Gas Combined Cycle (IGCC) process for H₂ generation and simultaneous CO₂ capture from coal and biomass. The MR-AR hybrid system under study attains a high WGS reaction conversion exceeding equilibrium, produces an ultra-high purity H₂ product for power generation, and delivers a high-pressure CO₂ stream ready for sequestration. A carbon molecular sieve membrane (CMSM – previously field-tested by this team) and a sour shift WGS catalyst (Co/Mo/Al₂O₃) is used in the MR and a hydrotalcite adsorbent is used in the AR. Lab experiments were carried-out to investigate the membrane characteristics, and the performance of the individual MR and AR components and combined MR-AR system under IGCC-relevant conditions. Multi-cycle experiments were carried-out to validate the MR-AR system’s performance with respect to CO conversion, H₂ and CO₂ purity and recovery, and to monitor whether membrane, adsorbent, and catalyst are stable during each run, and to compare results with those from a lab-scale packed-bed reactor (PBR) under same operating conditions. 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 generated 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 and demonstrate the potential of the system to be achieved in H₂ and CO₂ separationwith the CMS membranes.

During the experiments involving ~ 750 hr of syngas exposure, the CMSM, adsorbent and the catalyst all displayed robust and stable performance. The MR-AR multi-cycle runs demonstrated performance superior to a conventional PBR with attaining conversions >>95%, while the AR is functional, by producing a high-purity hydrogen product, which can be directly usable in a hydrogen turbine for power generation, and a pure high-pressure CO₂ stream ready for sequestration. By employing a steam sweep in the permeate side of the MR and appropriately adjusting the permeate-side pressure >2 bar, we were able to protect the catalyst in the AR from deactivating, avoid carbon loss and reduce the energy penalty of IGCC with CCS. The CMSM-based MR-AR system is, therefore, deemed a good candidate technology for environmentally benign power generation. We are currently constructing a pilot-scale system for field demonstration of the technology to commence in late 2020.