CaSO4 SOLUBILITY IN WATER-ETHANOL MIXTURES IN THE PRESENCE 1 OF SODIUM CHLORIDE AT 25°C. APPLICATION TO A REVERSE OSMOSIS

1 OF SODIUM CHLORIDE AT 25°C. APPLICATION TO A REVERSE OSMOSIS 2 PROCESS. 3 V.Gomis*, M.D. Saquete, J. García-Cano 4 Departamento de Ingeniería Química, Universidad de Alicante, Apartado 99, E-03080 5 Alicante, Spain. Phone: +34 965 90 38 67 Fax: +34 965 90 38 26. 6 e-mail: [email protected] 7 8 9 10 Abstract 11 Nowadays, the most common way to desalinate seawater is by reverse osmosis. As the 12 degree of conversion during this process increases more freshwater is recovered from 13 the feedwater. As a result, the salt concentration in the feed increases up to a point 14 where the solubility limit could be reached. Experimentally, it is known that adding an 15 organic substance such as ethanol to salty water induces salt precipitation. This work 16 investigated the solid-liquid equilibrium of the system water-ethanol-NaCl-CaSO4 at 17 25°C. Results show that as the ethanol content is increased CaSO4 solubility decreases. 18 On the other hand, brine from the reverse osmosis plant at the University of Alicante 19 was treated with ethanol to precipitate calcium sulfate and produce brine containing less 20 calcium and sulfate. The treated brine was analyzed and its calcium content was 21 compared with the predicted value based on the experimental data. The results suggest 22 that it is possible to use ethanol to precipitate the salts from brine in order to obtain a 23 higher degree of conversion in a reverse osmosis process. The obvious limitation of the 24 method is the cost of recovering the ethanol by separation. 25