Deacidification and solvent recovery of soybean oil by nanofiltration membranes

Four tailor-made flat composite membranes of poly(vinylideneflouride) (PVDF) as a support and polydimethylsiloxane (PDMS) or cellulose acetate (CA) as coating layer, and a commercially available composite membrane (Solsep 030306) were used to remove hexane and free fatty acid (FFA) from crude soybean oil–hexane mixture. The effects of transmembrane pressure (Δp=10–20 bar), temperature (T=30–50 °C) and feed oil concentration (Cf=10–35 w/w%) on membrane selectivity and permeation flux were determined. The PVDF-12% siloxane composite nanofiltration membrane achieved the best results, being stable in commercial hexane and having promising permselectivity properties to separate soybean oil/hexane miscella. Improved separation performance was obtained at Cf=25%, Δp=20 bar, and T=30 °C, achieving a permeate flux of 20.3 Lm−2 h−1, 80% oil retention, 58% FFA removal.

► Membrane efficiency for FFA and hexane recovery from miscellas has been evaluated.
► Solvent-resistant composite PVDF–PDMS and PVDF–CA membranes were synthesized.
► PVDF–12%PDMS membrane showed the best FFA–soybean oil–hexane separation.
► The best performance was 80% oil retention, 58% FFA removal, 20 l/m2h permeate flux.
► Suitable membrane design can lead efficient hexane recovery and FFA–oil separation.