Silane Modification of Cellulose Acetate Dense Films as Materials for Acid Gas Removal

The modification of cellulose acetate (CA) films via grafting of vinyltrimethoxysilane (VTMS) to -OH groups, with subsequent condensation of hydrolyzed methoxy groups on the slime to form a polymer network is presented. The technique is referred to as GCV-modification. The modified material maintains similar H2S/CH4 and CO2/CH4 selectivities compared to the unmodified material; however the pure CO2 and H2S permeabilities are 139 and 165 barrers, respectively, which are more than an order of magnitude higher than the neat polymer. The membranes were tested at feed pressures of up to 700 psia in a ternary 20 vol. %H2S/20 vol. % CO2/60 vol. % CH4 mixture. Even under aggressive feed conditions, GCV-modified CA showed comparable selectivities and significantly higher permeabilities. Furthermore, GCV-modified membrane had a lower T-g, lower crystallinity, and higher flexibility than neat CA. The higher flexibility is due to the vinyl substituent provided by VTMS, thereby reducing brittleness, which could be helpful in an asymmetric membrane structure.