Feasibility of several commercial membranes to recover valuable phenolic compounds from extracts of wet olive pomace through organic-solvent nanofiltration

Abstract

Organic-solvent nanofiltration (OSN) has been applied to purify and fractionate the phenolic compounds present in wet olive pomace, which is the main by-product of olive mills. Nine commercial OSN membranes have been tested: DuraMem® 150, DuraMem® 300, DuraMem® 500, PuraMem® 600 (Evonik), NFS, NFX (Synder), oNF-1 and oNF-2 (Borsig) and NF270 (FilmTec). Their stability in ethanol/water 50:50 (v/v) and their effectiveness to treat a model solution of a solvent-based extract of wet olive pomace have been studied. To that end, a METcell cross-flow system (Evonik) has been utilized. DuraMem® 500, NFX and NF270 membranes displayed satisfactory values of permeate flux (10–100 L·h−1·m−2) compared to the other tested membranes. Measurements of the contact angle of the membranes after their conditioning and after the nanofiltration process allowed the comprehension of the interaction between the ethanol/water 50:50 (v/v) solution and the membrane. The solvent contact angle was also examined. AFM was employed to understand the modification of membrane morphology. To characterize the samples, liquid chromatography coupled to mass spectrometry (and/or refractive index detector) was employed. The selected membranes exhibited low rejection values for the aimed phenolic compounds (less than 10 % for hydroxytyrosol) and high rejection (50–100 %) of the undesired compounds, such as sugars and organic acids. Therefore, the purification of the target phenolic compounds was accomplished.