Enhanced R410A separation performance of mixed matrix membrane using different degrees of fluorinated UiO-66

Difluoromethane (R32) is a good additive to improve the coefficient of performance (COP) of hydrofluoroolefins (HFOs) which are the next generation of refrigerants. Therefore, it is important to efficiently recover Difluoromethane (R32) from R410A(a blend of 50 % R32 and 50 % pentafluoroethane (R125)) which will be eliminated due to high global warming potential (GWP). In this work, fluorinated UiO-66 was synthesized by replacing the terephthalic acid ligand in UiO-66 with an organic ligand containing fluorocarboxylic acids to enchance the separation performance of mixed matrix membranes (MMMs) as filler, and the effect of the fluorine content of the fluorinated UiO-66 was investigated. In this study, Fluorinated UiO-66/Pebax MMMs were successfully prepared, with the fluorine content tailored by using different ligands. The separation performance increased with the amount of fluorine in the MOFs, namely UiO-66-(CF₃)₂/Pebax > UiO-66-F₄/Pebax > UiO-66-F₂/Pebax > UiO-66-F/Pebax > UiO-66/Pebax MMMs. The 20 wt% UiO-66-(CF₃)₂/Pebax achieved an ultra-high P_R32 of 979.53 Barrer (397 % of pure Pebax membrane) while maintaining a high ɑ_R32/R125 (16.64, 251 % of pure Pebax membrane).The tested results showed that the fluorinated UiO-66/Pebax MMMs sigificantly improved permeability and selectivity for R410A due to the higher R32 solubility caused by C-F…H hydrogen bonding network formed between the fluorine groups and R32 as well as the better sieving ability caused by the decrease in the pore size of UiO-66. The fluorinated MOFs/Pebax MMMs prepared in this work simultaneously achieved better R32/R125 selectivity and R32 permeability,than the exsited membranes, enabling effective separation and recycle R32 from R410A.