Solvent permeability in commercial ultrafiltration polymeric membranes and evaluation of the structural and chemical stability towards hexane

The membrane technology application in the vegetable oil processing is associated to the hexane recovery from the miscella obtained during the extraction, degumming and subsequent refining stages, where the presence of the hexane results in higher permeate flux. However, the development of this technological alternative depends on membrane chemical stability. The objective of this work was to evaluate six flat-sheet polymeric membranes in relation water affinity, permeability and flux of water, ethanol and hexane, with the purpose of characterizing their hydrophobic and hydrophilic profiles and resistance to hexane. The equipment used was a stirred cell. The following commercial flat membranes were used: 30 kDa and 50 kDa PVDF (polyvinylidene fluoride); 10 kDa PES (polyethersulfone); 0.05 μm PC (polycarbonate); 0.05 μm and 0.025 μm CME (mixed cellulose esters). Membrane permeability with water, ethanol and hexane was evaluated in a laboratory unit at 4 bar, 200 rpm and 40 °C. Regarding flux rates with the tested solvents, the 50 kDa PVDF membrane revealed the highest permeability to water, two of the membranes were characterized as less hydrophilic (PC and PES) and the remaining ones were more hydrophobic. The membrane structural stability towards the hexane was verified by visual observation, filtering area variation (shortening or intumescence) and permeate flux assessments. The permeation with hexane was conducted for 12 h, at 1.5 bar, 200 rpm and 40 °C, with constant flux in all of the membranes during the experiment. Membranes untreated, submersed in hexane for 48 h and submitted to hexane permeation for 12 h were examined by scanning electron microscopy (SEM) in order to verify possible microscopic alterations. All the membranes were hexane-resistant, indicating that they are suitable for use with this solvent.