Thermodynamic properties of 3-chlorophthalic anhydride and 4-chlorophthalic anhydride and their application for purification method development.

Development and design of crystallization process strongly depend on accurate solid-liquid equilibrium data. In this paper, the solubility of 3-chlorophthalic anhydride and 4-chlorophthalic anhydride in methyl acetate + cyclohexane binary solvent mixtures was determined from T = (283.15 to 328.15) K by gravimetric method under atmospheric pressure. The results show that the solubility of 3-chlorophthalic anhydride and 4-chlorophthalic anhydride increases with the increasing of temperature at constant solvent composition. At fixed temperature, the solubility of 3-chlorophthalic anhydride increases with mole fraction of methyl acetate increasing. Nevertheless, the solubility of 4-chlorophthalic anhydride displays a maximum with the solvent composition changing. To extend the applicability range of the solubility data, experimental solubility data in binary solvent mixtures was correlated by the modified Apelblat equation, the CNIBS/R-K equation and the Jouyban-Acree equation. It is found that the correlated data is in good agreement with the experimental data. The metastable zone width (MSZW) of 3-chlorophthalic anhydride and 4-chlorophthalic anhydride were also determined by the polythermal method at three different cooling rates. Finally, the cooling crystallization process of 3-chlorophthalic anhydride was designed to separate and purify 3-chlorophthalic anhydride according to its solubility and MSZW data. [ABSTRACT FROM AUTHOR]