Thermodynamics Research Center / ThermoML | Journal of Chemical and Engineering Data

ABSTRACT

The salt effect on the liquid-liquid equilibrium (LLE) for the water - ethylene glycol (EG) - ethylene glycol diacetate (EGDA) system was studied at 303.2K and 101.3kPa. The influence of different NaCl concentrations (0, 5, 15 and 20 wt %) and salt types (NaCl, CaCl2 and KCl) on the equilibrium systems was researched. The distribution coefficients and separation factors were calculated to evaluate the effect of the EG extraction. The results show that the addition of salt increases the two-phase region of the equilibrium system, and the order of effect of salt types is as follows: CaCl2 greater than NaCl greater than KCl. The reliability of the experimental data was validated by the Eisen-Joffe equation. NRTL model was applied to correlate the experimental data, the low values of MAD and RMSD confirmed the good correlation of the experimental results. 1. INTRODUCTION Ethylene glycol diacetate (EGDA), an environmental and efficient solvent, is widely used in the manufacture of paints, inks, adhesives and paint removers. 1,2 The production of EGDA is mainly performed by esterification of ethylene glycol (EG) and acetic acid under the action of acidic catalyst in industry at present. 3 This esterification reaction is a typical reversible reaction, so the unreacted EG in the reaction mixture can form azeotrope with EGDA, which makes it difficult separate by conventional distillation. Because of the wide application of high purity EGDA in industry, it is very important to separate the residual EG from the EGDA. Liquid-liquid extraction is considered as an effective separation process with low energy consumption, particularly suitable for the separation of azeotropic system.4 A liquid solution containing a solute in contact with another liquid solvent incompatible with the first one, solute transfers from the solution to the other solvent and reaches equilibrium in two immiscible solvents, finally.5 Liquid-liquid equilibrium for multicomponent systems is the theoretical basis of the extraction operation, and reliable liquid-liquid equilibrium data is essential for the selection of extractant, the design of an extraction process and the optimization of extraction equipment. In order to separate the EG-EGDA mixture system, toluene is a commonly used solvent at present. However, toluene, which is flammable and toxic, is not suitable for large-scale applications in industry due to its damage to human body and environment. Therefore, it is necessary to find another economic and environmental solvent to separate the EG-EGDA mixture system. Water is the most widely used solvent in industry because of its excellent properties of non-toxic, harmless, low price and easy to obtain. According to the relevant document,1 EG is easily soluble in water, EGDA is only partially soluble in water, and the solubility of EG in water is higher than that in EGDA. Thus, water is intended as a solvent for separating the EG-EGDA mixture system in this paper. The addition of salt into the mixture system will cause great changes in the composition and affect the liquid-liquid equilibrium.6-12 Salt mainly affects the solubility of organic components in aqueous-organic solvent mixtures.13 On the basis of the theory of "similarity and intermiscibility", in the presence of salt, the association of salt ions with water molecules changes