Thermodynamics, Solubility, and Crystallization of 1,5-Pentylenediamine Hydrochloride in Mixed Solvent Systems

The properties of 1,5-pentylenediamine hydrochloride (PDAH), a precursor of biobased pentamethylene diisocyanate (PDI), have a key influence on the PDI quality. In this study, the thermodynamics, solubility, and crystallization of PDAH in ethanol-water mixed solutions (0-100 wt % ethanol) were investigated. First, the solubility was investigated at 273.15-323.15 K by a solvent evaporation method and characterized using the Apelblat, polynomial empirical, λh, and the modified van’t Hoff-Jouyban-Acree equations. The activity coefficient increased with decreasing polarity and decreasing temperature. Thermodynamic analysis shows that dissolution is always spontaneous if the solution is not saturated. The surface tension and surface entropy factor increased with decreasing polarity and decreasing temperature. Finally, the crystallization of PDAH in an ethanol-water solution was studied by comparing cooling crystallization, antisolvent crystallization, and three combined cooling and antisolvent crystallization processes. The best crystallization process was found to be antisolvent, followed by cooling crystallization, with a 66.72% one-time yield and 99% purity. This study provides an important reference for the crystallization separation of other biobased products.