Water and hexane permeate flux through organic and ceramic membranes

The aim of this work was to study the behaviour of several organic and inorganic membranes in the presence of organic solvents (hexane) for their application in edible oil processing. Ceramic membranes (CM) with a zirconia filtration layer and molecular weight cut-offs (MWCO) of 1000 and 5000 g/mol and polyethersulfone (PES) membranes with MWCO of 4000 and 9000 g/mol were tested in pilot-plant scale equipment. The effect of pretreatment, consisting in soaking the membranes in mixtures of solvents of decreasing polarity, on the performance of both types of membranes was evaluated. The pretreatment was very effective for PES membranes, but ineffective for zirconia membranes. Ceramic membranes were also tested with hexane of two different grades (industrial and analytical). Permeate flux was observed to decrease with time and between successive runs with both types of hexane, thus indicating a possible “interaction” between the solvent and the membrane material and/or adsorption of the solvent onto the membrane surface. Moreover, hexane flux was higher through pretreated PES membranes than through ceramic membranes with higher MWCO. The results obtained may be explained by the different hydrophilicity of PES and ceramic membranes. The Hagen-Poiseuille equation was not able to predict the results on permeate flux, which indicates that other parameters apart from viscosity should be taken into account (surface tension, hydrophobicity, etc.).