Molecular-level petroleum refining by graded membranes.

Light naphtha is a critical feedstock whose full value relies on molecular-level fractionation into value-specific streams. Achieving such precise separation remains difficult because its components exhibit extremely similar physicochemical properties. Here, we address this challenge by developing a graded membrane cascade based on metal-organic framework CuBTC whose pore size and surface chemistry are continuously tuned through mild tannic acid treatment. Membranes with distinct sieving characteristics were created to sequentially co-separate linear and mono-branched alkanes and then selectively permeate aromatics. The integrated cascade fractionated a 15-component C5-C7 mixture into three high-purity streams, ethylene feedstock, chemical intermediates, and gasoline fuel, with recoveries of 85%-90% and an estimated 91% reduction in energy consumption compared to conventional distillation. This strategy establishes an energy-efficient route toward molecular refining.