Research Journal of Applied Sciences, Engineering and Technology 96-98, 2011 ISSN: 2040-7467 © Maxwell Scientific Organization, 2011 Received: November 17, 2010 Accepted: December 18, 2010 Published: February 20, 2011 Corresponding Author: G. Khayati, Department of Chemical Engineering, Technical Faculty, Guilan University, Rasht, 419961- 3769, Iran 96 Liquid-Liquid Equilibria of Aqueous Two-phase Systems Containing Polyethylene Glycol 4000 and Two Different Salts of Ammonium G. Khayati, A. Daghbandan, H. Gilvari and N. Pheyz-Sani Department of Chemical Engineering, Technical Faculty, Guilan University, Rasht, 419961-3769, Iran Abstract: The aim of this study was to survey on phase diagrams and Liquid-Liquid Equilibrium (LLE) data of the aqueous PEG 4000 - (NH 4 ) 2 HPO 4 and PEG 4000 - (NH 4 ) 2 SO 4 systems experimentally at 298.15 K. The salting-out effect was also discussed on the basis of the Gibbs free energy of hydration of ions. The experimental binodal data were satisfactorily correlated with the Merchuk equation. Tie line compositions were correlated using the Othmer-Tobias and Bancroft equations, and the parameters have also reported. Good agreement was obtained with the experimental data with the model equations. Key words: Liquid_liquid equilibrium, polyethylene glycol 4000, salts of ammonium INTRODUCTION Presently, industrial demands and economic downstream processes for extraction and purification of biomolecules with high yield purity of the product are growing fast (Haghtalab and Joda, 2009; Amaresh et al., 2008). The Aqueous Two Phase System (ATPS) provides a powerful method to separating mixtures of biomolecules by extraction in down stream processing. Aqueous two-phase systems are formed by soluble polymers in water by using two polymers or an inorganic salt and a polymer (Albertsson, 1971). Using ATPS as a practical process allows one to integrate clarification, concentrating, and partial purification of biomolecules in one step. Also polymer-salt aqueous two- phase systems have several advantages such as low price, low viscosity, and short time for phase separation. One of the major polymers for this purpose is Polyethylene Glycol (PEG), which is a nontoxic, inflammable and low in cost (Imani et al., 2009). Aqueous Two-Phase Systems (ATPSs) can be applied successfully for the separation of biological materials, dyes, drug molecules, proteins, and nucleic acid (Azevedo et al., 2009; Da Silva and Meirelles, 2000; Karakatsanis and Liakopoulou- Kyriakides, 2007). On the other hand, a liquid-liquid extraction process requires knowledge of the phase behavior of the system for engineering design and process optimization. This work is devoted to obtaining LLE data for aqueous PEG 4000 - (NH 4 ) 2 HPO 4 and PEG 4000 - (NH 4 ) 2 SO 4 systems at 298.15 K. Suitable equations were used to correlate the binodal and the tie-line data for the investigated systems. MATERIALS AND METHODS Materials: The salts and other chemicals used were of analytical grade. The salts were dried in an oven at about 393.15Kfor 24 h before use. All chemicals were used without further purification. Apparatus and procedure: The experimental apparatus employed is essentially similar to the one used previously (Khayati et al., 2009). The bimodal curves were determined by a titration method. A salt solution of known concentration was titrated with the polymer solution or vise versa, until the solution turned turbid; which indicated the formation of two liquid phases. In accordance to with the amount titrant added until turbidity was observed. The composition of the mixture was determined by mass using an analytical balance with a precision of ± 0.0001 g. For the determination of the tie- lines, feed samples were prepared by mixing appropriate amounts of polymer, salt and water in the vessel. The thermostat was set at a desired temperature, and the sample was stirred for 2-3 h. Then the mixture was allowed to settle for 24 h. Portions of solutions in both phases were taken out carefully for analysis. The concentration of PEG was determined by refractive index measurements at 298.15K using a Kruss Abbe refractometer AR3D. Since the refractive index of phase samples depends on PEG and salt concentration, calibration plots of refractive index versus polymer concentration were prepared for different concentration of salt (Cheluget et al., 1994). The relation between the refractive index, n D , and the mass fractions of polymer, w 1 and w 2 salt, is given by: