Identification of phenolic compounds and their fouling mechanisms in ion-exchange membranes used at an industrial scale for wine tartaric stabilization by electrodialysis

Organic fouling of ion-exchange membranes (IEMs) during electrodialysis (ED) treatments of food beverages is a serious problem encountered by both industry and research in this sector. Identification and characterization of foulants in membranes would lead to a better understanding of their fouling mechanisms and extend membrane lifetime. In this context, the aims of this study were to extract foulants from homogeneous CMX-Sb and AMX-Sb (cation- and anion-exchange membranes, respectively) used at an industrial scale for wine tartaric stabilization by an ED process, to identify the exact nature of fouled phenolic compounds, to explore the fouling mechanisms and to compare these results with those obtained using a synthetic model solution to simulate fouling by phenolic compounds. The phenolic foulants were successfully extracted using a mixture of four solvents (acetonitrile, methanol, isopropanol and ultra-pure water, each 25% (v/v)). Over 30 compounds were identified and quantified by specific Ultra- and High-Performance Liquid Chromatography methods. Analysis by attenuated total reflectance Fourier-transform infrared (ATR-FTIR) detected highly hydrated C=O, -COOH due to the accumulation of phenolic acids in particular, and phenolic compounds in used AMX-Sb (confirming the affinity of organic acids for anion-exchange membranes). It also showed the intensification of the bands that correspond to the stretching vibration of the C=C bonds in polyphenol aromatic rings, especially in used CMX-Sb. It was concluded that the interactions between phenolic compounds and polymer matrix were principally governed by the CH-n and n-n stacking of aromatic rings, electrostatic interactions with charged functional sites of the matrix and the establishment of hydrogen bonds between linked water in the membrane matrix and hydroxide or acid functions of the foulants. The identification and quantification of fouled phenolic compounds on IEMs after a 2000-h fouling simulation using a synthetic model solution confirmed these assumptions. The simulation also demonstrated that deposition of these phenolic compounds on the surface increased membrane hydrophobicity, and their accumulation into the polymer matrix decreased ion-exchange capacity, electrical conductivity and the volume fraction of the inter-gel solution of IEMs.