Application of hydrocarbon–fluorocarbon interactions in membrane-based gas separations

To control membrane plasticization in natural gas streams containing higher hydrocarbon compounds, we propose to coat a hydrocarbon-based polymer gas separation membrane with a fluoropolymer layer to reduce the hydrocarbon penetrant partial pressure to which the hydrocarbon membrane is exposed. A theoretical analysis is presented which addresses the trade-offs between reducing membrane plasticization, reduction in gas flux through the composite membrane and reduction in product purity due to the fluoropolymer layer. The analysis reveals that an effective plasticization-resistant, hydrocarbon–fluorocarbon composite membrane would consist of a fluoropolymer that has a lower ratio of hydrocarbon gas to CO2 solubility and a higher size-selectivity than the hydrocarbon polymer. Model cases are presented to illustrate the possibilities and limitations of this approach.

A hydrocarbon–fluorocarbon composite membrane consisting of a fluoropolymer that has a lower ratio of hydrocarbon gas to CO2 solubility and a higher size-selectivity than the hydrocarbon polymer might be used to reduce plasticization of hydrocarbon-based gas separation membranes by higher hydrocarbon vapors. Commercial fluoropolymers are available that have lower b values (approx. 0.007 K!1) than typical hydrocarbon polymers (b approx. 0.016 K!1). However, these fluoropolymers usually have moderate sizeselectivities. Therefore, moderately size-sieving hydrocarbon polymers (e.g., ethyl cellulose, cellulose acetate, etc.) might benefit more from