Patent ID: 6896717

Claim:
A gas separation process, comprising: (a) providing a membrane having a feed side and a permeate side and comprising; (i) a base membrane comprising a selective layer of a first polymer on the feed side, and (ii) a C 3+ hydrocarbon-resistant coating layer of a second polymer coating the base membrane on the feed side; wherein, when measured under the same conditions and in the absence of C 3+ hydrocarbons, the first polymer has a higher hydrogen/methane selectivity and a lower hydrogen permeability than the second polymer; and wherein the second polymer has a fractional free volume no greater than about 0.3 and a glass transition temperature of at least about 100° C., and is chosen from the group consisting of (I) polymers comprising repeating units having a fluorinated cyclic structure of an at least 5-member ring and (II) polymers having a ratio of fluorine to carbon atoms in the polymer greater than 1:1; (b) passing a gas mixture comprising a first gas that is not a C 3+ hydrocarbon, a second gas that is not a C 3+ hydrocarbon and a C 3+ hydrocarbon across the feed side; (c) providing a driving force for transmembrane permeation; (d) withdrawing from the permeate side a permeate stream enriched in the first gas compared to the gas mixture; (e) withdrawing from the feed side a residue stream depleted in the first gas compared to the gas mixture.