Perstraction of phenolic compounds via nonporous PEBA membranes

Abstract

This study deals with removal of phenolic compounds from water by perstraction, and poly(ether-b-amide) (PEBA) membranes were selected because of their excellent permeability to phenolics. The permeability, diffusivity and solubility of model phenolic compounds (including the simplest phenol (PhOH), 4-methylphenol (MePhOH), 4-nitrophenol (O2NPhOH) and 4-chlorophenol (ClPhOH)) in the membrane were investigated. The membrane showed a permeability in the order of ClPhOH > MePhOH > O2NPhOH > PhOH, while the diffusivity followed the order of PhOH > MePhOH > O2NPhOH > ClPhOH. Based on the resistance-in-series model, the mass transfer characteristics of the liquid/membrane/liquid perstraction system was analyzed, and the individual mass transfer resistances from the various steps of the perstraction process were estimated. It was revealed that the membrane resistance was significant, and the mass transfer resistance at the downstream side of the membrane as a result of phenol desorption from the membrane and boundary layer effects was not negligible. While the strong affinity between PEBA and phenolics was responsible for the good phenol permeability in the membrane, it also resulted in a high resistance to phenol desorption from the membrane. The use of an alkaline stripping agent can effectively enhance phenol removal from water by reducing the mass transfer resistances of the liquid boundary layers and phenol desorption at the downstream side of the membrane. For a given phenolic compound, the enhancement in mass transfer rate was affected by the alkaline concentration, and the enhancement was particularly significant when thin membranes were used.