Separation of phenols and their advanced oxidation intermediate products in aqueous solution by NF/RO membranes

The performance of nanofiltration and reverse osmosis membranes (NF-90 and TFC-HR) to retain the intermediate products of phenol chemical oxidation in aqueous solution was examined. Physical properties of the active layer of both membranes, such as roughness and hydrophobicity, were examined and pure water permeability was determined. Temporal evolution experiments of permeate relative flux and solute rejection were carried out for aqueous phenol, catechol, resorcinol, hydroquinone, malonic acid, oxalic acid, acetic acid, and formic acid. Physicochemical properties of solutes and membranes were used to analyse the filtration performance. NF-90 membrane exhibited lower relative fluxes for every solute than the corresponding to TFC-HR membrane. In addition, differences in flux decline between members of the same type of solute (aromatic and carboxylic) were also more evident for NF-90 membrane. At natural pH, rejection selectivity between phenolic solutes and dicarboxylic acids was higher for NF-90 membrane than for TFC-HR membrane. Except for oxalic acid, the sieving effect seems to be predominant over other mechanisms for the TFC-HR membrane; however, NF-90 rejection performance cannot be solely explained through steric hindrance interaction. In order to compare rejection selectivity between aromatic and carboxylic solutes of similar molecular weight at the same solution pH, performance of NF-90 membrane for dicarboxylic acids was investigated at solution pH higher than natural one. Experiments evidenced that selective separation between phenols and dicarboxylic acids can be achieved at solution pH around 5. (C) 2009 Elsevier B.V. All rights reserved.