Enhancement of the gas separation performance of mixed matrix membranes (MMMs) with functionalized triptycene hypercrosslinked polymers of intrinsic microporosity (HCP-PIMs)

In this work, we report a series of Matrimid®9725 based mixed matrix membranes (MMMs) containing 10 wt% and 20 wt% of highly microporous hypercrosslinked triptycene PIMs (HCP-PIMs) fillers. The latter were used either in their pristine hydrocarbon form, or functionalized with nitro, amino, or sulfonic groups. Single gas time-lag measurements show that the combination of the lowly permeable polymeric matrix and the highly porous fillers leads to an enhancement of gas selectivity (up to 29 % for CO2/CH4) and, depending on the filler, to an up to twofold increased permeability for CO2. The selectivity increase seems influenced by the nature of the functional groups, while the permeability by the filler's high surface areas. Specifically, an enhancement of the permeability is observed across all MMMs, with the best results achieved with the hydrocarbon and the nitro functionalized HPC fillers (PIM-Trip-H and PIM-Trip-NO2), which show an up to twofold increment of the permeability compared to the pure Matrimid, accompanied by a further improvement of the selectivity for gas pairs such as CO2/CH4 and O2/N2. Thermal studies show that permeability increases upon heating for all MMMs, while the selectivity decreases for gas pairs involving condensable gases such as CO2. For instance, from 25 °C to 45 °C the permeability of CH4 increases up to about 300 % and that of CO2 only between 25 % and 50 %. Finally, the entropic and energetic contributions to diffusion selectivity are analyzed, providing insight into the varying influences of diffusivity and selectivity for different gases.