Structure–Property Relationships in 6FCDA-Based Fluorinated Copolyimide Membranes for Energy-Efficient Light Olefin/Paraffin Separation

Olefin/paraffin separations, particularly through cryogenic distillation, are highly energy- and cost-intensive processes in the petrochemical industry, consuming ~0.15 Quads annually. To reduce this burden, alternative technologies such as membrane- and adsorption-based separations have gained attention for their potential to improve efficiency and lower operational costs. Among these, membrane-based gas separation is especially promising due to its reduced energy use, operational simplicity, scalability, and lower environmental impact. This study focuses on membrane-based separation of propylene (C₃H₆) from propane (C₃H₈), a challenging yet industrially critical process due to the similar physicochemical properties of the two gases. Despite extensive research, achieving adequate C₃H₆/C₃H₈ selectivity and long-term stability remains difficult. The objective of this work was to design, synthesize, and process a new class of fluorinated copolyimide membranes capable of combining high thermal and chemical stability with desirable permeability, selectivity, and processability. Six 6FCDA-based fluorinated copolyimides were synthesized and characterized to investigate how fluorine content and segmental rigidity influence gas transport and sorption behavior. The effects of temperature and pressure on C₃H₆/C₃H₈ sorption and separation were evaluated to assess membrane performance under realistic operating conditions and to clarify the structure–property relationships governing transport. Overall, the results demonstrate that 6FCDA-based fluorinated copolyimides offer scalable, thermally robust membrane platforms with tunable performance, showing strong potential for next-generation, energy-efficient olefin/paraffin separations.