Zeolite/Polymer Composite Membranes for CO2 Capture From Flue Gas
Membrane technology provides a promising approach for CO2 capture from post-combustion flue gas due to its smaller footprint and potentially lower energy cost than the traditional amine scrubbing process. Thin inorganic membranes with high selectivity and flux have been conventionally supported by inorganic materials , which are expensive and difficult for scale-up in a continuous manner and fabrication into a high packing density in terms of high surface area/volume due to their brittle nature. In this work , a thin zeolite seed layer (< 1 µm) has been successfully deposited on a flexible polymer support for the first time , which enables the continuous roll-to-roll fabrication of the membrane and the configuration of spiral-wound membrane modules with a high packing density. Zeolite-Y with pore size of about 7 Å was specially selected for CO2/N2 separation from flue gas , due to the preferential adsorption of CO2 molecules with a larger quadrupole moment and higher polarizability. This is known as the "surface diffusion" mechanism along with the blocking of N2 molecules due to the adsorbed CO2 molecules. In addition , a polymer cover layer containing fixed polyamine and mobile amine carriers was applied on top of the zeolite seed layer by knife-casting to utilize the advantages of both inorganic and polymer membranes for CO2 capture from flue gas. The thickness of polymer cover layer varied from 0.5 µm to 10 µm. The separation performance of the synthesized zeolite/polymer composite membrane was characterized under humid flue gas composition at close to atmospheric feed pressure and 102oC. The resulting membrane showed a CO2 permeance greater than 1100 GPU and a CO2/N2 selectivity above 400. Based on the transport results , a process and cost modeling study will be discussed in view of achieving the DOE targets of < 35% increase on the cost of electricity and < $40/tonne CO2 captured for 2025. Considering the real application in a power plant , SO2 tolerance of the aforementioned membrane was evaluated under different SO2 concentrations in feed gas. When SO2 concentration in feed gas was below 1 ppm , the separation performance of the composite membrane was not affected at all. When 5-ppm SO2 was supplied , a reduction of CO2 permeance was observed. However , the CO2 permeance recovered back to about 80 ?C 85% of its original value within 24 hours after exposure to the feed gas without containing the SO2 , which could be crucial if the up-stream SO2 polishing step fails.
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