Performance enhancement of thin film composite reverse osmosis membranes by chemical surface modification

Protic acids, including hydrofluoric, hydrochloric, sulfuric, phosphoric and nitric acids, are studied as hydrophilizing agents for modifying the surfaces of thin film composite (TFC) reverse osmosis membranes. HR95PP, TFCL-LP and HR98PP (SW30HR) membranes on exposure to various concentrations of these acids increase in flux up to an order of magnitude without any loss in ion-rejection. The flux enhancement is about an order of magnitude in HR98PP (SW30HR) and a factor of two in high flux HR95PP membranes. In case of TFCL-LP membranes it is about 40%. Hydrofluoric (HF) and hydrochloric acids consistently increase the flux with no loss in ion rejection. The other protic acids cause an increase in flux with a decrease in rejection.; Surface characterization with contact angle measurements indicate an increase in hydrophilicity of the membrane surface. The microscopic studies like SEM and AFM show a significant change in the surface morphology of the membranes. The X-ray photoelectron spectroscopy studies show a change in the surface chemistry of the membranes also. At solvatable sites along the polymer chain, reactions causing partial hydrolysis may be responsible for the increase in hydrophilicity resulting in the observed flux increase. Exposure to mild solvents like methanol, ethanol and 2-propanol (isopropyl alcohol, IPA) and solvents like dimethyl acetamide and acetone also increases the flux with no loss in rejection; in fact a significant increase in rejection is obtained in some cases. Selective dissolution and elimination of defects probably are responsible for the increased rates of transport.; This method of treatment with protic acids and alcohols could be used as a viable post fabrication method in developing high flux and high rejection membranes of the future.; The dynamic studies using HF and fluosilicic acid (FSA) as feed solutions indicate that HF permeates through the membranes and FSA is rejected by the membranes. Therefore, these reverse osmosis membranes can be used for reprocessing and reusing HF from the spent microelectronic etching solutions. HF can be selectively recycled from a complex multicomponent mixtures containing various acids like nitric, sulfuric, hydrochloric and phosphoric acids; a complex waste mixture containing these acids is usually generated by most of integrated circuit (IC) fabrication laboratories. Based on the experimental results a system/prototype that can recover about 90% of HF as ultrapure product has been designed.