Simultaneously enhanced permeability, selectivity and anti-plasticization of polyimide membrane for natural gas purification by incorporating surface-engineered DD3R zeolite

Towards natural gas purification, polymeric membranes generally face challenges of trade-off between permeability and selectivity, as well as CO2-induced plasticization effect. Previous works demonstrated that incorporating high-performing nanofillers and crosslinking the polymers are effective methods to overcome these two issues, respectively. In this work, we aimed to simultaneously improve permeability, selectivity and plasticization resistance of polymeric membranes by incorporating surface-engineered nanoporous fillers for CO2/CH4 separation. DD3R zeolite nanoparticles with high purity were synthesized and then surface-functionalized by 3-aminopropyl trimethoxysilane (APTMS) to serve as the filler. Mixed-gas permeation measurements showed that DD3R zeolites offered CO2-selective channels in 6FDA-DAM polyimide based on molecular sieving effect of zeolitic aperture. 30 wt% DD3R-APTMS zeolite imparted the membrane with CO2 permeability of 1661 Barrer (increased by 71.7%) and CO2/CH4 selectivity of 28.0 (increased by 44.5%), which was beyond the upper-bound of polymeric membranes. Meanwhile, the hydrogen bond interaction between amino groups on APTMS and carboxyl groups on 6FDA-DAM rendered the resulting DD3R-APTMS MMMs highly enhanced plasticization resistance over 40 bar when equimolar CO2/CH4 mixture as the feed. This work demonstrates a facile approach to simultaneously enhance separation performance and mitigate the plasticization effect.