Highly Selective and Sustainable Purification of Aromatic Isomers: Multistage Melt Crystallization Kinetics, Pore Architecture, and Separation Mechanisms for High-Purity Durene Production

Abstract A solvent-free multistage purification route integrating simple distillation, two-stage suspension melt crystallization, and post-crystallization sweating was established for durene recovery from mixed aromatics. Through systematic parameter optimization, the integrated process achieved final product purity exceeding 99%. X-ray diffraction (XRD) and FT-IR revealed stage-dependent preferred orientation without polymorphic transformation, indicating that primary crystallization yielded fine, randomly oriented crystallites, while secondary crystallization favored low-energy facets with improved crystalline coherence. Kinetic analysis revealed distinct growth behaviors, with primary crystallization exhibiting interface-controlled growth characteristics and strong sensitivity to supercooling (exponent 36.89), whereas secondary crystallization showed a substantially weaker dependence (exponent 9.17) with increased diffusion/mass-transfer influence; sweating was governed by pore-mediated transport. Pore structure analysis established direct links between crystallization history and sweating effectiveness: primary crystallization formed a high-porosity disordered network, secondary crystallization restructured it into a more compact regular packed structure, and sweating further optimized pore architecture. Increasing crystallization temperature reduced impurity incorporation via slower growth and enhanced back-diffusion; increasing sweating temperature intensified selective melt drainage, decreasing the distribution coefficient (0.60 → 0.43) and yield (0.92 → 0.73) while increasing the mass-transfer coefficient (0.25 → 0.80). Secondary crystallization outperformed primary crystallization in both purity and yield, attributable to higher feed purity and recrystallization benefits. The established kinetics–pore structure–separation performance framework provides quantitative guidance for designing green, highly selective purification processes for aromatic isomer systems.