Study on the recycling of zeolitic imidazolate frameworks and polymer Pebax® 1657 from their mixed matrix membranes applied to CO2 capture

Mixed matrix membranes (MMMs) consisting of fillers (e.g. metal organic frameworks (MOFs)) in polymer matrix are considered as an interesting alternative for capturing post combustion CO2 towards a sustainable development. This research is focused on the recycling of MMMs made of polymer Pebax® 1657 and MOF ZIF-94. Upon MMM preparation, characterization and testing, MMMs were dissolved to recover polymer and MOFs separately. Recovered products were characterized by SEM, EDX, FTIR, TGA, XRD, DLS, mass spectrometry and N2 adsorption to compare their size, shape and other properties with those of fresh ones. Mean particle size of fresh and recycled ZIF-94 were 148 ± 44 nm and 164 ± 32 nm, respectively. Incorporation of recycled ZIF-94 in MMMs produced defect free membranes which was confirmed by SEM and gas separation measurements. These MMMs, with a 10 wt% ZIF-94 loading, were tested for the separation of the CO2/N2 mixture with a CO2 permeability of 157 ± 6.5 Barrer (with 67 % improvement compared to fresh pure polymer membrane with 94 ± 2 Barrer) and a CO2/N2 selectivity of 27.5 ± 1.4 (5 % lower than that of the fresh MMM, 29.3 ± 1.8, but 20 % higher than the corresponding to the pure polymer membrane, 23 ± 2). Demonstrating its wide feasibility, the proposed methodology was also applicable for recycling of ZIF-8 from Pebax® 1657 based MMMs.