Chemical treatment for improved performance of reverse osmosis membranes

摘要

A novel method of chemical treatment is described which causes a simultaneous improvement of flux and rejection of thin-film composite (TFC) reverse osmosis (RO) membranes. The water flux of CPA2 and SWC1 which are commercially important aromatic polyamide based TFC RO membranes has been shown to be increased significantly, without any loss of ion rejection, on short-term treatment with acids such as hydrofluoric and fluosilicic and alcohols like isopropanol. In most cases simultaneous increases in flux and rejection have been observed. Surface characterization studies by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and contact angle measurements reveal that limited hydrolysis and fluorination of the membrane skin seem to be responsible for such improvement in the membrane flux and rejection on treatment with hydrofluoric and fluosilicic acids. With isopropyl alcohol, partial dissolution coupled with surface tension driven collapse of pores in the membrane skin seem to be key factors which cause a simultaneous increase in flux and rejection. Therefore enhancement by short-term chemical treatment may be a very useful approach for the future development of RO membranes having higher flux and rejection.