Abstract:

Suspension crystallization coupled centrifugal separation can directly prepare polyester grade coal-to-ethylene glycol. Based on the narrow boiling, azeotropic and heat sensitive system formed by impurities and ethylene glycol in the production process of coal to ethylene glycol, compared with the traditional distillation purification, suspension crystallization has the advantages of low energy consumption, no solvent and environmental friendly, and can achieve the effect of energy saving and emission reduction under the purification system. The optimization of crystallization operation can provide a reference for suspension crystallization coupled centrifugal separation technology. The effects of seed addition, filter cake thickness, stirring intensity, programmed cooling and mother liquor circulation operation process on the purification effect were studied. The results show that the particle size distribution of crystals is affected by the amount of seed addition. The purity of the product can be improved by increasing the amount of seed added, and the distribution coefficient can be reduced by about 15.8%; Because crystal and sweat gas more fully contact, reduced cake thickness enhances sweating with a maximum reduction of 56.8% distribution coefficient; Stirring intensity directly affects mass and heat transfer. The higher the stirring intensity, the higher the purity of the product, but the yield decreased, and the maximum decrease in distribution coefficient and yield was 39.4% and 30.8%, respectively; Programmed cooling directly affects crystallization time. Due to the increase of crystallization time, the program cooling reduces the purity of the product; The recycling of mother liquor led to the increase of water content in the system, which reduced the degree of under cooling, but improved the purity of the product, and the distribution coefficient decreased by 72.0% when it was cycled for 7 times compared with the fresh mother liquor.

Key words: coal-to-ethylene glycol, polyester grade, suspension crystallization, process optimization