Novel solvent exchange cum immersion precipitation technique for the preparation of asymmetric polymeric membrane

A technique named ''solvent exchange cum immersion precipitation'' (SELF) has been developed for the preparation of integrally skinned asymmetric polyamide types of membranes for reverse osmosis (RO) applications. This involves ambient temperature operation and eliminates various problems encountered in conventional polyamide membrane preparation involving evaporation of high boiling point solvents such as dimethyl acetamide, dimethyl sulfoxide, n-methyl pyrrolidone, etc., from polymer casting solution film at elevated temperature and reduced pressure. This SEIP technique involves the following four steps. 1. Preparation of polymer solution using the appropriate solvent, additive and composition. 2. xchange of high boiling point solvent from the surface of the casting solution film with a more volatile non-solvent. 3. Evaporation of part of exchanged solvent at ambient temperature. 4. Coagulation of the film in demineralized water. In this paper, the preparation of polyetheramide hydrazide (PEAH) membranes using the above technique has been described. Different parameters involved in the preparation of these membranes such as selection of additive, choice of exchange solvent, casting solution composition, exchange solvent, exchange and evaporation time, etc., have been evaluated. The effect of all these parameters on RO properties of these membranes such as solute rejection and water permeation rate under sea water test conditions are presented. The basic difference and advantages of the SEIP technique over the conventional elevated temperature technique are highlighted.