Effective separation of propylene/propane is necessary due to propylene is a feedstock for a variety of chemicals. The process that meets the purity requirement is cryogenic distillation, which is an energy-intensive process and consumes enormous cost and space. Thus, membrane/distillation hybrid process with high selective membranes has been suggested. Considerable research has been done in glassy polyimides for the membrane material, which has superior thermal, physical and chemical stability, but poor processability due to hard backbone structure. Various attempts have been made to overcome the deficiencies, including the introduction of flexible segments into the polymer backbone. In this study, we demonstrate highly selective membranes by introducing bulky ethyl substituents into the polyimide. The ethyl groups, which are placed ortho to the imide nitrogen, hinder the chain packing and increase chain stiffness and the distance between polymer chains. As the diffusion length increased, the diffusion selectivity of propylene/propane was increased. These polyimides were synthesized from various aromatic dianhydrides and 4,4'-methylenebis(2,6-diethylaniline) (MDEA), and its gas transport properties were investigated. The highest C3H6/C3H8 selectivity was about 14.5 and C3H6 permeability about 7 Barrer of 6FDA-MDEA among the three synthesized polyimides. BTDA-MDEA and OPDA-MDEA showed C3H6 permeability about 1.8 and 2.2 respectively, and C3H6/C3H8 selectivity 11.9 and 9.1 at 35 oC. Synthesized polyimide membranes increase the feasibility of more economic propylene separation process than conventional polyimide materials.

Synthesis and characterization of polyimides containing bulky ethyl substituents for propylene/propane separation

2019 Spring National Meeting

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