Highly stable PDMS–PTFPMS/PVDF OSN membranes for hexane recovery during vegetable oil production

Abstract

There is a lack of stable and hydrophobic organic solvent nanofiltration (OSN) membranes meaning that their implementation in non-polar solvent nanofiltration remains a challenge, typically in solvent (e.g. hexane) recovery during vegetable oil production (e.g. soybean oil/hexane). Considering this, novel trifluoropropylmethylsiloxane dimethylsiloxane (PDMS–PTFPMS)/polyvinylidene fluoride (PVDF) membranes, with both high hexane permeability of PDMS and excellent hexane stability of PTFPMS, were successfully developed to recover hexane via OSN. Their microstructure and surface properties were characterized by SEM, FTIR, DSC, TGA, XPS and contact angle measurements. We explored the effects of the ratio of the PTFPMS segment in polymer chain and polymer viscosity on membrane performance. With regards to the F50-M membrane, we also conducted a comprehensive study on the OSN performance of the F50-M membrane under different operational conditions. The oil rejection was above 95% with stable hexane permeability of 3.06 kg⁻¹ μm m⁻² h⁻¹ bar⁻¹ over a 32-day period. Experimental results confirmed its ability to recover hexane under various operational conditions, showing high oil rejection and excellent long-term operational stability. We attributed its outstanding performance to its unique microstructure and surface properties due to the fluorine-containing PTFPMS segment. This study indicates that fluoropolymer membranes are promising candidates in OSN processes, offering a wider choice of membrane materials and application fields.