Fluorinated MOF-808 with various modulators to fabricate high-performance hybrid membranes with enhanced hydrophobicity for organic-organic pervaporation

Abstract

Highly efficient PDMS based membranes with a new type of fluorinated MOF-808 were successfully prepared and used for the first time in pervaporation (PV). Two types of ligands i.e. trifluoroacetic acid (TFA) and pentafluoropropionic acid (PFPA) were used during the MOF synthesis. These ligands with slightly different size and chemical character influenced the material properties of the membranes, i.e. roughness, contact angle, surface free energy, and thermal features. Incorporation of MOFs enhanced the membrane hydrophobicity and the performance in organic-organic PV for the separation of industrially important mixtures like, ethyl acetate-EtAc and ethyl tert-butyl ether-ETBE. The filled membranes possessed much better transport and separation features than the pristine PDMS. Substantial improvement of modified membrane performance with 5 wt% MOF (normalized Pervaporation Separation Index – PSIN = 1540 µm kg m−2 h−1) was observed in relation to pristine PDMS (PSIN = 780 µm kg m−2 h−1) and commercial Pervap™4060 (PSIN = 150 µm kg m−2h−1), during the separation of ETBE/EtOH. An important added value was the study of the impact of water traces (in the range 0.1–0.3 wt%) in the feed on the membrane performance. The level of water in the permeate was dependent on the membrane material composition, i.e. the MOF loading, since the presence of hydrophobic MOF restricted the transport of water to the permeate side.