Asymmetric polybenzimidazole membranes with thin selective skin layer containing ZIF-8 for H2/CO2 separation at pre-combustion capture conditions

Abstract

This work addresses an optimization in the fabrication of flat PBI membranes containing ZIF-8 nanoparticles for gas separation purposes. The PBI membranes were prepared in an asymmetric configuration on P84® supports, representing a new way of preparing flat PBI membranes. An optimization of the conditions for the PBI phase inversion preparation method, including the dope composition (in the 15–26 wt% range), has been carried out to obtain PBI membranes with a 1 µm selective skin layer. The asymmetric membranes showed an unprecedented gas separation capacity in pre-combustion CO2 capture, much superior to that of dense membranes, under harsh operating conditions (250 °C and 6 bar feed), performing up to 20.3 GPU of H2 and a H2/CO2 selectivity of 35.6. Their much thinner selective layer made possible the increase in selectivity because of the saturation of the CO2 flow at high pressures. The reduction in the amount of ZIF-8 for obtaining a membrane with the same filler loading (3.7 vs. 9.3 g/m2) was also possible; the performance of this ZIF-8 containig membrane was 22.4 GPU of H2 and a H2/CO2 selectivity of 22.3. The activation energy of the membranes, as well as the flow resistances, were calculated, providing a resistance in series model to understand the flow inside the membrane.