Carbon molecular sieve membranes derived from crosslinkable polyimides for CO2/CH4 and C2H4/C2H6 separations

Carbon molecular sieve (CMS) membranes were fabricated using carboxylated polyimides with various 6FpDA:DABA molar ratios. The as-prepared 6FDA-6FpDA:DABA multiblock polyimide, thermally crosslinked ones, and CMS membranes were characterized for CO2/CH4 and C2H4/C2H6 separation performance. Thermally crosslinked polyimide membranes due to decarboxylation exhibited increased gas permeability over uncrosslinked ones. All CMS membranes had enhanced gas separation performance as compared to their unmodified precursor polymer. A representative CMS membranes pyrolyzed at 576 °C had CO2 and C2H4 permeability of 3573 and 244.6 Barrer with a CO2/CH4 and C2H4/C2H6 ideal selectivity of 51.5 and 4.80. A CMS membrane pyrolyzed at 800 °C had a C2H4 permeability of 10.4 Barrer and a C2H4/C2H6 ideal gas selectivity of 24.1. Increasing polyimide pyrolysis temperature improved CMS membrane gas selectivity but reduced its permeability. Zn2+ functionalized CMS membranes exhibited enhanced gas selectivity with a slight permeability reduction. The CMS membranes excellent gas separation performances surpassed Robeson's upper-bound. These materials hold great potential for industrial applications such as CO2 separation and olefin recovery.