Asymmetrical polyimide membranes with programmable polymer chain architectures for liquid hydrocarbon fractionation.

Conventional fractionation of liquid hydrocarbons relies on energy-intensive distillation. While organic solvent reverse osmosis provides an energy-efficient alternative, the challenge lies in engineering membranes with accurately tailored molecular differentiation for complex hydrocarbons. Here, we develop diverse fluorinated polyimide membranes featuring programmable polymer chain architectures for efficient hydrocarbon separation. By stoichiometry-controlled polycondensation, the chain packing and microporosity of synthesized polyimides are finely regulated, verified by molecular simulations. The corresponding asymmetrical membranes with defect-free thin layers of 100 to 250 nanometers are prepared via solution casting and thermal annealing steps. Such programmed membranes enable tunable permselectivity for hydrocarbons with less than 40 carbon atoms. The fractionation of kerosene-paraffin mixture in toluene is demonstrated through a two-stage process containing the optimized membranes. The cascade process remarkably enriches the C-C hydrocarbons from 50% up to 97%. The demonstrated polyimide membranes with on-demand molecular discrimination capability provide a potential candidate for the membrane-based hydrocarbon fractionation.