Membranes with high selectivity for complex hydrocarbon mixtures and high permeability can potentially reduce the energy footprint of the chemical industry. Ren et al. describe the development of a family of aryl amine polymers with pendent fluorocarbon side chains for organic solvent reverse osmosis. The authors synthesized fluorine containing poly(arylene amine) polymers to fabricate supported thin-film composite membranes with a thickness of 0.2 to 0.3 micrometers. The advantage of these membranes is the suppression of swelling, which typically occurs when polymer membranes are exposed to organic solvents. Membranes were tested for a range of hydrocarbon mixtures that mimic the feed in a Fischer-Tropsch process. —Marc S. Lavine Both existing and emerging liquid fuel-processing systems rely on the separation of complex mixtures of aliphatic compounds ( 1– 4). For instance, the Fischer-Tropsch (FT) synthesis, which converts a mixture of carbon monoxide and hydrogen into a wide range of aliphatic hydrocarbons, is receiving increasing attention because it can use nonfossil feedstocks for producing high-value hydrocarbons ( 5, 6). A typical FT process produces a broad distribution of typically linear alkanes, along with some linear olefin by-products. These raw FT mixtures need to be fractionated into various product streams (e.g., fuels, chemicals, and lubricants; Fig. 1AOpens in image viewer, pink dashed box). The light hydrocarbons can then be further processed into fuels through a refinery system in which the oligomerized branched isomers are separated from linear hydrocarbons ( Fig. 1AOpens in image viewer, green dashed box). Olefins can also be removed from these light fractions and serve as high-value products with end uses in plastics and pharmaceutical intermediates ( Fig. 1AOpens in image viewer, blue dashed box). In contrast to conventional thermal separations such as distillation, membrane-based separations have the potential to provide a more energy- and carbon-efficient approach for purifying and upgrading hydrocarbon mixtures ( 7– 12).