Experimental Investigation into Suspension Crystallization Refining of Coal-to-Ethylene Glycol

Suspension crystallization coupled with centrifugal separation can be used to refine polyester-grade coal-to-ethylene glycol. Compared with the traditional distillation purification, suspension crystallization has the advantages of low energy consumption, no need for solvents and environmental friendliness. It is particularly effective in reducing energy consumption and emissions when purifying the narrow-boiling, azeotropic and heat-sensitive systems formed by impurities and ethylene glycol during the coal-to-ethylene glycol production process. To optimize the operation process of suspension crystallization for coal-to-ethylene glycol and provide a reference for the development of coupled centrifugal separation technology, this paper investigated the effects of seed dosage, filter cake thickness, stirring intensity, programmed cooling and mother liquid circulation operation process on the purification efficiency. The results show that seed dosage affects crystal size distribution, and that increasing the dosage may improve the product purity, with the effective distribution coefficient decreasing by 15.8%. Reducing the filter cake thickness allows for more sufficient contact between crystals and sweating gas, thus enhancing the sweating effect and resulting in a maximum reduction of 56.8% in the effective distribution coefficient. Stirring intensity directly affects mass and heat transfer. Higher stirring intensity leads to higher product purity but lower yield, with maximum decreases in the effective distribution coefficient and the yield of 39.4% and 30.8%, respectively. Programmed cooling directly affects crystallization time. A slower cooling rate prolongs the crystallization time but reduces product purity. Mother liquid recycling increases the water content in the system, reduces the degree of supercooling, and thereby improves product purity. Compared with fresh mother liquid, the mother liquid cycled for 7 times leads to an effective distribution coefficient decrease by 72.0%.