Advanced CO2- and H2S-Selective Membranes

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This NSF award by the Chemical and Biological Separations program supports work by Professor Winston Ho and his students to synthesize advanced CO2- and H2S-selective membranes by incorporating new multi-walled carbon nanotubes (MWNTs) and silica with sterically hindered amines into the polymer membrane matrix and to study the effects of MWNTs and silica for improved resistance to membrane compression under high pressures and for enhanced transport of the acid gases. The state-of-the-art process for the removal of CO2 and H2S from gases, including synthesis gas and natural gas, uses aqueous amine solutions, where steam is used for regeneration and the steam stream containing the acid gas is then condensed to separate/release the acid gas. This process involves cumbersome operations, high energy consumption, and capital-intensive equipment. Furthermore, it is limited by the thermodynamic equilibrium on acid gas solubility during absorption, resulting in an increased solution circulation rate and consequently large equipment. Thus, it is important to develop an effective process with both capital and energy savings. This work is aiming at developing the energy-efficient membrane process, featuring a simple pressure-driven process with no moving parts. The proposed process combines the absorption and stripping of acid gas into one step. This one-step process simplifies the acid gas separation and overcomes the thermodynamic solubility limitation.The proposed membrane is the first of the kind capable of possessing high CO2 and H2S permeabilities and selectivities vs. hydrogen and nitrogen at relatively high temperatures (100 - 120C) and pressures (1 - 30 atm), which is needed for energy-efficient purification of syngas from coal and biomass as well as for CO2 capture. This research not only is of a great scientific interest but also may provide improved membranes of significant technological importance. We believe that it represents a significant contribution to expanding the scientific knowledge and understanding in the gas separation. Potential impacts of the proposed research are significant as this research is aiming at the novel CO2-selective membrane and process to overcome many deficiencies of the commercial gas treating technology. This proposed one-step process not only simplifies the separation process, but also eliminates the needs for the absorber, the regenerator, two pumps for the loaded and regenerated amine solutions, and the pumping operations between the absorber and regenerator. It also eliminates the energy-intensive regeneration of the amine solution due to the high heat capacity of water and the use of temperatures swing to drive gas desorption. Thus, this membrane process will have both significant capital and energy savings. The proposed membranes have many potential applications including the purification of syngas derived from coal and biomass to produce high purity H2 for fuel cells, CO2 capture from flue gas for its sequestration, and CO2 removal from biogas, natural gas, confined space air, and ambient air. We will present and publish this research each year. Furthermore, this research provides the education of 1 Ph.D. graduate student and 2 undergraduate students for conducting not only the work on advanced membranes but also that with technological significance.