Polymers are unarguably the most broadly used membrane materials for molecular separations and beyond. Motivated by the commercial success of membrane‐based desalination and permanent gas separations, glassy polymer membranes are increasingly being studied for hydrocarbon separations. They represent a class of challenging yet economically impactful bulk separations extensively practiced in the refining and petrochemical industry. This review discusses recent developments in membrane‐based hydrocarbon separations using glassy polymer membranes relying on the sorption‐diffusion mechanism. Hydrocarbon separations by both diffusion‐selective and sorption‐selective glassy polymer membranes are considered. Opinions on the likelihoods of large‐scale implementation are provided for selected hydrocarbon pairs. Finally, a discussion of the challenges and outlook of glassy polymer membrane‐based hydrocarbon separations is presented.

Aromatic polyamides (aramids) are broadly used to manufacture desalination membranes; however, they are rarely considered for gas separation. Here, we report precise hydrogen sieving in ultramicroporous carbon molecular sieve (CMS) membranes derived from an uncrosslinked aramid synthesized by stirred interfacial polymerization of diamine and mixed diacid chloride monomers. While hydrogen bonds gave the aramid precursor unattractive separation performance, they were leveraged to provide aramid-derived CMS membranes with ultrahigh H2/CO2 selectivity exceeding all known CMS membranes. Adsorption in aramid-derived CMS membranes suggested their ultrahigh H2/CO2 selectivity was attributable to diffusion selectivity above 3000. The excellent solution processability of uncrosslinked aramids allowed the fabrication of scalable CMS hollow fiber membranes. The findings of this work open the door to a new class of highly selective CMS membranes for H2 separation and CO2 capture.