Ultramicroporous Membranes for Hydrogen Separation

Fuel cell systems offer excellent efficiencies when compared to internal combustion engines, which result in reduced fuel consumption and greenhouse gas emissions. One of the areas requiring research for the success of fuel cell technology is the H2 fuel purification to reduce CO, which is a poison to fuel cells. Molecular sieve silica (MSS) membranes have a potential application in this area. In this work showed activated transport, a characteristic of ultramicroporous (dp<5Å) materials in which the permeation increased with temperature. H2 permeance resulted in 1.2 x 10 mol.m.s.Pa and a H2/CO permselectivity of 33 (200C, 2 bar P). Observations made during surface preparation showed that the permeance was not hindered by the intermediate layers, and that only the top (selective) layer played a significant role in reducing gas permeance. The pressure difference across the membrane showed that the permeance was pressure independent, except at pressures below 2 bar, which resulted in a higher permeance. High quality membranes purified a mixed gas containing 42% H2 by over two fold with the remainder being made up of N2, CO2 and CO. These are encouraging results for applying MSS membranes to environmentally promising fuel cell systems.