Novel composite membranes for gas separation: Preparation and performance

High performance composite membranes based on molecular sieving silica (MSS ) were synthesized using sols containing silicon co-polymers (methyltrietho xysilane and tetraethylorthosilicate). Alpha alumina supports were treated with hydrochloric acid prior to sol deposition. Permselectivity of CO2 over CH4 as high as 16.68 was achieved whilst permeability of CO2 up to 36.7 GP U (10(-6) cm(3) (STP) cm(-2) . s(-1) . cm Hg-1) was measured. The best memb rane's permeability was finger printed during various stages of the synthes is process showing an increase in CO2/CH4 permselectivity by over 25 times from initial support condition (no membrane film) to the completion of pore structure tailoring. Transport measurement results indicate that the membr ane pretreated with HCl has highest permselectivity and permeation rate. In particular, there is a definite cut-off pore size between 3.3 and 3.4 angs troms which is just below the kinetic diameters of Ar and CH4. This demonst rates that the mechanism for the separation in the prepared composite membr ane is molecular sieving (activated diffusion), rather than Knudsen diffusi on.