Role of surfactants in cleaning of PVDF ultrafiltration membranes fouled by emulsified cutting oil

Abstract

Chemical cleaning with anionic, cationic and non-ionic surfactants was studied for polyvinylidene (PVDF) hollow fiber ultrafiltration (UF) membranes irreversibly fouled by cutting fluid with anionic emulsifiers. The membrane cleaning efficiency of the surfactants was determined by pure water permeability and the results are in agreement with morphological observations of the membrane surfaces and molecular vibrational analyses. The anionic surfactants sodium dodecyl sulfate (SDS) and sodium dodecylbenzene sulphonate (SDBS), showed better cleaning through the combined effect of electrostatic repulsion with emulsified oil particles and re-emulsification of the oil layer. Inclusion of the phenyl group in the dodecyl sulfate anion had a significant role in cleaning. Molecular vibrational analyses indicated a higher presence of residual surfactant on the membranes after cleaning with cationic (cetyltrimethylammonium bromide (CTAB)) and non-ionic (Tween 85 (T-85)) surfactants, which also resulted in higher apparent hydrophilicity of the membrane surface. Alkalizing the anionic surfactant solution improved cleaning efficiency, but had no significant effect for cationic and non-ionic surfactants. The effect of surfactant concentration and ionic strength on cleaning efficacy was analyzed for SDBS. As mass transport increased, higher cleaning efficacy was observed at higher SDBS concentration. The cleaning efficacy of SDBS was also influenced to varying degrees by solution pH and ionic strength.