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

Abstract

The modification of cellulose acetate (CA) films via grafting of vinyltrimethoxysilane (VTMS) to −OH groups, with subsequent condensation of hydrolyzed methoxy groups on the silane to form a polymer network is presented. The technique is referred to as GCV-modif ication. The modified material maintains similar H 2 S/CH 4 and CO 2 /CH 4 selectivities compared to the unmodified material; however the pure CO 2 and H 2 S 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. %H 2 S/20 vol. % CO 2 /60 vol. % CH 4 mixture. Even under aggressive feed conditions, GCV-modified CA showed comparable selectivities and significantly higher permeabilities. Furthermore, GCVmodified 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.

A high-performance hydroxyl-functionalized polymer of intrinsic microporosity for an environmentally attractive membrane-based approach to decontamination of sour natural gas

“…Several modifications were made to the standard permeation system design to ensure safety when handling H 2 S and high concentration H 2 S gas mixtures. 4, 22 The permeation cell was additionally enclosed in a large ventilated cabinet as a secondary compartment to prevent H 2 S exposure if a leak was to occur in the system. In addition, two pneumaticallyactuated valves were used in place of standard hand-operated valves and controlled by a Labview ® program for additional safety.…”

“…A pressure decay sorption apparatus was used to measure the sorption isotherms of the PIM-6FDA-OH dense film at 35 °C. 42 These systems have been described in detail elsewhere, but a few minor alterations were made to ensure operator safety when experimenting with H 2 S. 4, 22 The density of the polymer was determined gravimetrically by their measured weight, area, and film thickness. 35 The density measurement was used to calculate the fractional free volume of the polymer and the sorption capacities.…”

“…4 Both low and high pressures were studied to compare the transport properties of these annealed films with values reported in previous literature. 35 All permeability calculations used the fugacity driving force definition of dense film permeability that has been reported for highly aggressive feed streams, such as those with elevated CO 2 or H 2 S levels.…”

“…22 Swelling-induced plasticization is a common phenomenon for polymer membranes in gas separations involving aggressive feed streams, such as CO 2 and H 2 S in sour gas. 4 Plasticization occurs when a penetrant significantly increases the mobility of polymer chain segments, thereby increasing the diffusion coefficients of all penetrants in the membrane. Penetrant molecules with higher critical temperatures like H 2 S and CO 2 are more capable of inducing swelling, because they have a considerably higher sorption capacity, particularly in glassy polymers 4,8,22,24 .…”

“…3 Recently, H 2 S removal has received more attention, because in certain areas in the US, Canada, Russia, and the Middle East, oil and gas reservoirs were reported to contain H 2 S as well as CO 2 at varying high levels. [4][5][6] Currently, amine absorption dominates acid gas (CO 2 and H 2 S) separation technology to reduce CO 2 and H 2 S to meet the pipeline requirement (<2% CO 2 , <4 ppm H 2 S). Such processes present environmental concerns as well as high capital and maintenance costs of the large absorption units.…”