Application of polymeric membranes for the purification of solutions containing cationic surfactants

The aim of the study was to examine physicochemical properties of three cationic surfactants and to evaluate the effectiveness of their removal with the use of polymeric membranes. The experiments were performed in a laboratory scale set-up with the use of Microdyn-Nadir^® nanofiltration and ultrafiltration membranes. Cetrimonium bromide (CTAB), benzalkonium chloride (BAC) and Tequat LC90i (TEAQ) were chosen for the test. In the experiments, surfactant solutions in a wide range of concentration were treated (50-3,000 mg L^-1). The experimental research included evaluation of the effect of membrane type and solution parameters (surfactant type and concentration, presence of inorganic compounds) on the process efficiency (retention coefficient and permeate flux). It was shown that surfactant removal by means of the pressure-driven membrane processes is an extensive issue and its efficiency depends on many factors. Ultrafiltration and nanofiltration membranes proved to be usable in CTAB removal (separation exceeded 90%); however, the process effectiveness was affected by surfactant concentration, membrane polymer type and membrane pore size. Separation obtained for BAC was on the lower level - the use of nanofiltration membranes brought maximum retention of 70%. TEAQ separation was very high and reached 100% with the use of ultrafiltration membranes. Mineral salt addition led to significant drop in surfactant retention.