389945 Preparation and Characterization of Sulphonated Poly(styrene- ethylene/butylene-styrene) Block Copolymer Membranes for Desalination By Pervaporation
Pervaporation is a potential low energy membrane technology. It has been extensively used for separation or concentration of mixtures of aqueous-organic or organic liquids. Using dense hydrophilic pervaporation membranes for desalination has been proved to be an efficient way to obtain potable water as it has the advantage of near 100% of salt rejection and energy consumption being independent of the feed salt concentration. The pervaporation of an aqueous salt solution can be regarded as separation of a pseudo-liquid mixture containing free water molecules and bulkier hydrated ions formed in solution upon dissociation of the salt in water. Not too many open literatures involved desalination by pervaporation. In this work, hydrophilic sulphonated poly(styrene-ethylene/butylene-styrene) (S-SEBS) triblock copolymer membranes based on poly(styrene-ethylene/butylene-styrene) (SEBS) thermoplastic elastomer were synthesized via chemically modiﬁed of grafting a sulfonic group into the polystyrene chain. A range of techniques such as FTIR, SEM, TGA were used to characterize the structure and properties of S-SEBS membranes. Results revealed that the sulfonate groups were grafted into the para-position of PS end-blocks successfully. Desulfonation was happened at around 200–300℃ proved by a weight loss in TGA curve, which indicated a good thermal stability of S-SEBS.
Taking advantages of the ion channel generated by phase separation due to thermodynamic incompatible of S-SEBS and its highly hydrophilic properties, S-SEBS membranes were ted for pervaporation of aqueous salt solution with NaCl concentrations of 1wt%-3wt% at temperatures 50-75 ℃, feed flow rate 16L/h and vacuum 0.095MPa. The salt rejection remained high (up to 99%) under all operating conditions because of the intimacy between water and sulfonate groups in S-SEBS membranes and the non volatilization of salt. The water flux of S-SEBS membranes increased with the increase of the sulfonated degree and feed temperature while the flux decreased with the increase of feed salt concentration. A high water flux of 22.87 kg/m2·h could be achieved when the sulfonated degree was 54.1% at the feed temperature of 65 ℃ and salt concentration of 1 wt%. The activation energy for water permeation was found to be 58.9 kJ/mol. In a word, the results indicated that the pervaporation process with S-SEBS membrane is a promising candidate for desalination.