Thermodynamic Modeling of Antisolvent Crystallization of NaCl-Water-Ethanol System

Crystallization is extensively used in chemical processes such as purification, separation and other sequences in production operations. In antisolvent crystallization technique a second solvent which is known as antisolvent or precipitant, is added to the solution, causing the reduction of solute solubility in the primary solvent, so supersaturatuion is generated. In this study, the antisolvent crystallization system containing sodium chloride as solute, water as primary solvent and ethanol as the antisolvent was considered. Starting with a saturated solution of water-NaCl, by gradual addition of ethanol in a specific rate, the solubility of NaCl decreases. The system is electrolyte which usually deviates extremely from ideal solutions in terms of thermodynamic behavior. Thus, it is necessary to use models which consider the long range electrostatic interactions besides the short range ones. A thermodynamic model which can predict the behavior of the aqueous salt systems containing non-electrolytes was applied. This model consists of Gibbs energy function, which combines a Debye-Hückel term with the standard UNIQUAC model. Using Extended UNIQUAC model for the purpose of thermodynamic modeling, the solubility of NaCl in the water-ethanol mixture in different compositions with an acceptable error of 0.05% was calculated. The model parameters including volume, surface area and binary interaction parameters were modified by comparing the experimental and theoretical data of NaCl solubility in water-ethanol mixture. Afterwards, this thermodynamic solubility model was introduced to the kinetic modeling of antisolvent crystallization process using Population Balance Equation method. Using this method crystal size was determined by the numerical solution to the Population Balance Equation. In order to evaluate the model accuracy, antisolvent addition rates were changed and the results were compared with the experimental data, they were justifiable with them.

کلیدواژه ها:

Extended UNIQUAC ، Electrolyte ، Thermodynamic modeling ، Solubility ، Antisolvent Crystallization