Highly Efficient and Solvent-Free Purification Technique and Model Study of Layer Melt Crystallization

Developing a green and sustainable technique seems necessary when facing an increase in the environmental burden. Layer melt crystallization (LMC) is recognized as an environmentally friendly separation technique because of its lower energy consumption and chemical waste emission. For the first time, this study applied LMC to prepare the high-purity isophthaloyl chloride (IPC), which is an important chemical intermediate in the synthesis of fibers. Under the optimal trajectory, the purity of IPC could improve from 97.811 to 99.381%, which reached the standard of subsequent production. Meanwhile, theoretical models were established and combined with the experimental results to visualize the crystallization and sweating processes. The fractal porosity model was used to describe the crystal layer structure, in which the pore structure could provide the adsorption sites for inclusion components and channels for the melt flow. Crystallization and sweating process kinetics models were established to explore the crystal layer growth and sweating melt flow characteristics. The distribution coefficient and the impurity removal rate were used to describe the separation efficiency. The interfacial solute distribution factor and the mass transfer coefficient were used to explore the solute and impurity distribution rules. The mechanisms of the mass flow were revealed. Finally, four different crystallizer structures were designed to intensify the heat and mass transfer, which significantly improved the separation efficiency.