Solid–Liquid Equilibrium Solubility Measurement and Thermodynamic Model Evaluation of Hexahydro-1,3,5-Trinitro-1,3,5-Triazine (RDX) in Nitric Acid + Acetic Acid Binary Mixed Solvents

The solubility of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in nitric acid + acetic acid Binary mixed solvents was systematically determined using the gravimetric method over the temperature range from 283.15 K to 323.15 K at atmospheric pressure. The experimental results show that the solubility of RDX in mixed solvents increases with temperature. To enhance the applicability of the solubility data, the experimental results were correlated using four thermodynamic models: the modified Apelblat model, the van’t Hoff model, the CNIBS/R–K model, and the Jouyban-Acree model. The correlation performance of each model was evaluated using relative deviation, average relative deviation, root-mean-square deviation, and the squared correlation coefficient. The results demonstrate that all models exhibit satisfactory correlation accuracy in the selected solvent system, with the modified Apelblat model showing the best performance. This study provides important fundamental data for solvent selection and crystallization-process design of RDX.