Field evaluation of carbon molecular sieve membranes for the separation and purification of hydrogen from coal- and biomass-derived syngas

Abstract High-temperature gas separations (GS) with inorganic membranes have attracted attention recently. In particular, the use of such membranes in membrane reactors (MR) has the potential to enhance process intensification and to increase energy savings and/or product yield. Though the potential benefits of high-temperature GS and/or MR processes are substantial, commercialization still remains elusive. A major technical barrier is the lack of robust inorganic membranes and full-scale modules which are suitable for use at the high-temperature and high-pressure conditions required. Carbon molecular sieve membranes (CMSM) were recently tested in the laboratory by this team for the “one-box” process. This technology combines into a single MR unit contaminant removal and coal-derived and/or biomass-derived syngas conversion via the water gas shift reaction to produce high-purity hydrogen for power generation and/or chemical use. Towards technology commercialization, 86-tube CMSM modules have been constructed and characterized comprehensively. Furthermore, multiple field-tests, under non-reactive conditions, of these 86-tube CMSM modules were conducted at the US National Carbon Capture Center coal gasification facility under conditions suitable for the “one-box” process. This paper details the results of these tests which address key GS aspects of field implementation, including inorganic membrane/module scale-up, syngas contaminants removal, and membrane material and performance stability. During continuous use (more than 300 h) in raw coal-derived and/or biomass-derived syngas, the CMSM successfully rejected tar-like species present in the syngas without any evidence of fouling, as long as the operating temperature was maintained above 250 °C. Moreover, the membrane permeation properties remained unchanged throughout this extended test. Simulations, based upon membrane GS properties measured during these field tests, demonstrate that the “one-box” process, operating on a typical oxygen-blown gasifier off-gas, can deliver more than 90% hydrogen recovery at more than 90% purity (dry-basis), and thus shows good promise for commercial application. The successful preparation and deployment by this team of the 86-tube CMSM module overcomes some of the technical barriers which have, so far, hampered the commercial implementation of inorganic membranes for high-temperature and high-pressure gas separation applications.