Crystallization Behavior of Hydroxypivalic Acid Neopentyl Glycol Ester

Achieving high-purity separation of hydroxypivalic acid neopentyl glycol ester (HPN) requires a detailed understanding of its crystallization behavior, thermodynamic phase relationships, and crystal morphology. Hydroxypivalic acid neopentyl glycol ester (HPN), a byproduct of neopentyl glycol (NPG) synthesis, contains residual NPG as a major impurity, rendering its purification challenging. In this study, the crystallization behavior and structural properties of HPN were systematically examined to establish an effective purification strategy. Solid-liquid equilibrium (SLE) data for the HPN-NPG, HPN-water system was experimentally obtained and thermodynamically modeled to identify favorable crystallization conditions. Molecular-level crystal morphology was investigated through the Bravais-Friedel-Donnay-Harker (BFDH) method and the attachment energy (AE) model, supported by X-ray diffraction (XRD) and optical microscopy. Furthermore, adsorption-annealing simulations were conducted to evaluate the influence of water and NPG on the crystal surface. The predicted morphology exhibited strong agreement with experimental observations, and both impurities were found to exert minimal impact on the dominant crystal habit. These findings provide an integrated thermodynamic and morphological framework for the design of high-purity crystallization processes of HPN.