Zeolite/Polymer Composite Membranes for Carbon Dioxide Separations
Zeolite/polymer composite membranes for carbon dioxide separations
The energy and environmental markets are producing a great research and development race to improve membranes for the fuel cell market to replace petroleum-based energy sources, to improve hydrogen production for use as a fuel in vehicles, and to sequester carbon dioxide to reduce the greenhouse effect and global warming that results from burning fossil fuels. Carbon management and sequestration offers an opportunity for reducing greenhouse gas emissions that can complement current nationwide strategies of improving energy efficiency and increasing the use of non-fossil energy resources. Polymer-zeolite membrane separations represent a growing technological area with potentially high economic reward that can be used to meet these low energy requirements. The incorporation of zeolite in a polymeric membrane is able to significantly improve the separation performance of the membrane due to the combined effects of molecular sieving action, selective adsorption, and difference in diffusion rates. Zeolites possess high mechanical strength, good thermal and chemical stability, and thus, the resulting filled membranes can be used over a wide range of operating conditions.
Researchers at The Ohio State University, led by Dr. Winston Ho, developed a novel membrane and separation process based on a facilitated transport mechanism in which CO2 transport through the membrane is enhanced, by reaction within the membrane, and H2 is rejected. Additionally, a process for the separation of CO2 from nitrogen in a gas mixture containing CO2 (flue gas, etc.) based upon the transmembrane permeation was developed. The identified membranes – consisting of a polymer support substrate, a zeolite layer, and a polymer cover layer – have high CO2 permeability and CO2/H2 selectivity at 50-180ºC. The selectivity increase is due to the facilitated transport with a higher CO2-amine reaction rate and lower H2 solubility in the membrane as temperature increases. Zeolite membranes in particular combine pore size and shape selectivity with the inherent mechanical, thermal, and chemical stability necessary for long term separations.