High performance ZIF-8/6FDA-DAM mixed matrix membrane for propylene/propane separations

We report significantly enhanced propylene/propane (C ₃H ₆/C ₃H ₈) selectivity in mixed matrix membranes fabricated using 6FDA-DAM polyimide and a zeolitic imidazolate framework (ZIF-8). Equilibrium isotherms and sorption kinetics of C ₃H ₆ and C ₃H ₈ at 35°C were studied on a 200nm commercially available ZIF-8 sample produced by BASF. Mixed matrix dense films were formed with 6FDA-DAM and 200nm BASF ZIF-8 particles. SEM imaging showed generally good adhesion between the ZIF-8 and 6FDA-DAM without the need for surface-treating ZIF-8. Pure gas permeation showed significantly enhanced mixed matrix ZIF-8/6FDA-DAM membrane C ₃H ₆/C ₃H ₈ separation performance over the pure 6FDA-DAM membrane performance. A C ₃H ₆ permeability of 56.2Barrer and C ₃H ₆/C ₃H ₈ ideal selectivity of 31.0 was found in ZIF-8/6FDA-DAM mixed matrix membrane with 48.0wt% ZIF-8 loading, which are 258% and 150% higher than the pure 6FDA-DAM membrane, respectively for permeability and selectivity. Permeation properties of C ₃H ₆ and C ₃H ₈ in ZIF-8 were back-calculated by the Maxwell model for composite permeability using pure gas permeation data, leading to a C ₃H ₆ permeability of 277Barrer and C ₃H ₆/C ₃H ₈ selectivity of 122. Mixed gas permeation also verified that selectivity enhancements were achievable in mixed gas environment by ZIF-8.