Flux behavior in a hydrophobic dense membrane with undiluted and hexane-diluted vegetable oils

▶ Hexane dilution improved oil flux by one order of magnitude in dense membrane. ▶ Triglycerides were not rejected due to a positive flow coupling with hexane. ▶ Vegetable oils exhibited an inverse relationship between viscosity and total flux. ▶ Interestingly, oil flux followed an inverse relationship with the average MW of TGs. ▶ FA varying in carbon chain length could be used for characterizing dense membranes. The flux behavior of a hydrophobic dense membrane (NTGS-2200) with polydimethylsiloxane as active layer and polyimide as support layer was studied with various vegetable oils under undiluted and hexane-diluted conditions. Hexane dilution improved the permeate oil flux in all the vegetable oils by at least one order of magnitude and applied pressure increased the total flux as well as oil flux. The dense membrane did not reject triglycerides (TG) over a wide range of hexane dilution (5–80% oil concentration) and operating pressure (0.5–4 MPa) due to a positive flow coupling with hexane. All the oils exhibited an inverse relationship between viscosity and total flux under undiluted and various levels of hexane-diluted conditions. The results revealed that the oil flux followed an inverse relationship with average molecular weights of TG despite their narrow range (670–961 Da) of existence in various vegetable oils, interestingly even under hexane-diluted conditions. Although both viscosity and TG molecular weight showed good correlation with permeate flux, the latter displayed a much better correlation hitherto unexplored and unexploited. This remarkable observation could be supportive in characterizing hydrophobic dense membranes specifically for nonaqueous applications.