Phase Equilibria and Salting Out of Butyric Acid in the Sodium Chloride - Water - Butyric Acid Ternary System
Phase equilibria in the water-butyric acid binary system in the range of -10÷0° C and in the sodium chloride-water-butyric acid ternary system in the range of 10.0÷60.0° C were studied using the visual polythermal method. The phase diagram of the water-butyric acid binary system at -9.5° C is characterized by eutectic equilibrium, the solid phases of which being ice and butyric acid crystals. The metastable delamination range was found on the ice crystallization field, bounded by a binodal curve with an upper critical solution temperature of -3.7 ° C. Sodium chloride was found to delaminate mixtures of water and butyric acid in a wide concentration range. The compositions of the solutions corresponding to the critical solubility points at several temperatures were determined. The isothermal phase diagrams of the ternary system at 10.0, 25.0, 40.0, and 60.0° C were plotted, and the distribution coefficients of butyric acid between the liquid phases of monotectic state were calculated. The salting-out effect of butyric acid from its aqueous solutions by sodium chloride was shown to decrease with increasing temperature. The concentration of butyric acid in the organic phase of monotectics at 20.0° C is 92 wt.% with a distribution coefficient of 61.3. Sodium chloride was established to be an effective salting-out agent of butyric acid from its aqueous solutions in the range of 10.0÷30.0° C and can be recommended for practical use.