Multi-layered silica-carbon molecular sieve membranes for CO/sub 2/ separation

With growing concerns in CO₂ emissions, cost effective processes for CO₂ capture at massive scales are being developed. Membranes show great potential in this field due to their simple operation and durability. Carbon molecular sieve (CMS) membranes can separate gases in a unique mechanism which targets CO₂. In this work, CMS films was prepared from proprietary Novolak and Resole phenolic resins on existing high gas selectivity silica membranes developed from multiple silica layers using dip coating and vacuum impregnation. CMS layers were coated with various resin dilutions followed by pyrolysis in N₂. Precise control of the thickness and dilution was found to be critical to uniform, defect free films. Effective CMS membranes resulted in He/CO₂ permselectivity less than unity, as low as 0.5 indicating 'reverse selectivity'. In this mechanism, the more sorbing molecule (CO₂) diffuses faster than the smaller, but non-sorbing He. The same membranes also displayed the best selectivity of CO₂ to N₂ confirming the adsorption selective transport. This initial work showed Novolak resins lead to better CMS structures than Resole, with optimum dilutions and curing techniques. Combining dip coating with vacuum impregnation confirmed better selectivities can be achieved from CMS/silica films. Further development of the promising CMS on silica membrane technology is required to increase selectivity for cost effective CO₂ capture