(97b) H2 Purification and CO2 Capture in a Post-Biomass-Gasifier Membrane Reactor

NETL envisions that the gasification of carbonaceous feedstocks may be the near- to mid-term sources of hydrogen for the transition to a renewable, hydrogen-based economy. However, the environmental impacts associated with the generation and emission of greenhouses gases from the gasification process remains a substantial concern. Therefore, NETL has devoted substantial resources towards the identification of efficient hydrogen separation and carbon capture/sequestration technologies. Hydrogen membranes integrated into a water-gas shift membrane reactor have been identified as a promising means of maximizing the production of pure hydrogen while simultaneously yielding a high-pressure, concentrated CO2 containing stream ready for sequestration.

In the gasification process the carbonaceous feedstock (biomass, coal, petroleum resid, etc.)is converted to ?synthesis gas? in the presence of steam and oxygen. The gasifier effluent, which is primarily composed of CO, CO2, H2, H2O and contaminants such as H2S and NH3, can exhibit temperatures and pressures as high as 1000 C and 7 MPa, respectively. The high-pressure, high-temperature gasifier effluent stream then proceeds through various processes, each process operating at a lower temperature than the previous. These process steps are used to remove particulates and sulfur compounds and further shift the CO-rich effluent stream to H2 and CO2 via the water-gas shift reaction. Finally the potential for hydrogen separation, carbon dioxide capture and power generation can be realized.

Process simulation studies have shown that the integration of membrane technologies into the gasification process can both increase efficiency and reduce the cost of hydrogen production while yielding a CO2 stream ready for sequestration. However, for this integration to be realized, viable membranes must be identified that exhibit the required permeability, selectivity, chemical resistance and mechanical stability.

Research groups, including NETL, are exploring the viability of dense metal hydrogen membrane technologies to enhance the production and separation of hydrogen as well as the capture of carbon dioxide from the coal gasification process. Areas of research to ensure the success of dense metal membrane technologies for implementation into the gasification scheme includes the fabrication of thin metallic films and support materials, an understanding of the interaction of membrane materials in the presence of both major and minor gas constituents, chemical and temperature induced morphological changes and the identification of new membrane materials through experimental and computational exploration.