A reactive separation process for pre-combustion CO2 capture employing oxygen-blown coal gasifier off-gas

Abstract

We present here an experimental study of a reactive separation system, consisting of a membrane reactor (MR) and an adsorptive reactor (AR) operating in tandem, with the MR’s reject stream serving as the AR’s feed. We investigate the feasibility of applying this MR-AR system for high-purity H2 production and simultaneous CO2 capture via the water gas shift (WGS) reaction in the context of Integrated Gas Combined Cycle (IGCC) power generation employing oxygen-blown gasifier syngas from biomass and coal. We previously studied this MR-AR system for the IGCC process employing air-blown gasifier syngas, for which it demonstrated good performance, attaining high conversion exceeding equilibrium, producing ultra-pure H2 for power generation, and a CO2 stream ready for sequestration. In this study, we focus on oxygen-blown gasifier off-gas that contains no N2, with composition distinctly different from the air-blown gasifier syngas which has a large N2 content. We employ a carbon molecular sieve membrane (CMSM), a commercial sour-shift WGS catalyst, and a hydrotalcite (HTC) adsorbent. We carried out experiments to determine membrane performance and to identify promising operating conditions in an IGCC-relevant environment. The CMSM proved robust during a long-term (~344 hr) experimental run under high temperature and pressure maintaining a high He/N2 selectivity (~170). Multi-cycle runs were carried out during which the MR-AR system displayed superior performance to that of a packed-bed reactor (PBR), by producing a H2 product with higher purity than that from the PBR which can be directly usable in power generation. Therefore, the findings from this study demonstrate the ability of the MR-AR system to operate stably for a broad range of gasifier off-gas compositions, and indicate its potential for integration into IGCC plants for power generation with CO2 capture.