| As an important intermediate,6-tert-butyl-m-cresol is widely used in the production of fine chemicals such as fragrances and pesticides.Chemical enterprises mainly use distillation method to separate 6-tert-butyl-m-cresol and 2-tert-butyl-p-cresol,but there are some shortcomings such as difficult separation,high energy consumption,low concentration,and so on.The use of crystallization purification has the advantages of no solvent added,small equipment size and so on.In this paper,the high efficiency separation of 6-tert-butyl-m-cresol and 2-tert-butyl-p-cresol was carried out by distillation melting crystallization coupling separation method,which has the advantages of low energy consumption and high purity.With the development of 6-tert-butyl-m-cresol in the application field,it is of great significance for the industrialization of 6-tert-butyl-m-cresol purification process.Firstly,it was found that the water content had a great influence on the crystallization process of 6-tert-butyl-m-cresol.It was found that there are two crystal forms of 6-tert-butylm-cresol,one is non-crystalline and the other is crystalline containing water.On this basis,the binary phase diagrams of aqueous system of 6-tert-butyl-m-cresol and 2-tert-butyl-p-cresol and anaqueous system of 6-tert-butyl-m-cresol and 2-tert-butyl-p-cresol were determined by dynamic method.The results show that the aqueous 6-tert-butyl-m-cresol and 2-tert-butyl-pcresol system is a low eutectic system,the lowest eutectic point is 14.69 ℃,and the molar percentage of aqueous 6-tert-butyl-m-cresol in the eutectic substance is 0.6001.The system of anhydrous 6-tert-butyl-m-cresol and 2-tert-butyl-p-cresol is also a low eutectic system.The lowest eutectic point is 12.65℃,and the molar percentage of anhydrous 6-tert-butyl-m-cresol in the eutectic substance is 0.7686.Secondly,two single crystals of anhydrous 6-tert-butyl-m-cresol and hydrated 6-tert-butylm-cresol were cultured,and the two single crystals were characterized by X-ray detection methods.According to the characterization,6-tert-butyl-m-cresol is quarter hydrate.On this basis,the Gaussian software is used to calculate the quantum chemistry of the two crystal structures of 6-tert-butyl-m-cresol with water and without water,and compare the difference of molecular vibration,energy and electrostatic potential between the two crystal types.According to the calculation of single point energy,the energy of the crystalline type is lower,indicating that the structure of the crystalline type is more stable.The 2D fingerprint in Hirshfeld surface was used to compare the interaction forces between the molecules in the two crystals.Through comparison,it was found that the O...H accounted for 3.1% and 2.4%,respectively.Finally,the purity of the product was 99.68% after purification of 48.91% 6-tert-butyl-mcresol by distillation,melting and crystallization coupling purification method.Firstly,the raw material of 6-tert-butyl-m-cresol with 48.91% content was purified to the mixture of 6-tertbutyl-m-cresol with 92.04% content and 2-tert-butyl-p-cresol with 6.01% content by vacuum distillation,and then the mixture was used as the raw material of static melting crystallization and dynamic melting crystallization.When static melting crystallization is adopted,the best cooling crystallization conditions are the cooling rate of 2 ℃/h,the crystallization end point temperature of 25 ℃,the better sweating conditions are the sweating heating rate of 1 ℃/h,the sweating end point temperature of 35 ℃,the purity of the product through static melting can reach 99.60%,the crystallization yield is 40.56%.Under stirring conditions,the optimal crystallization conditions are cooling rate of 1.5 ℃/h,crystallization end point temperature of25 ℃,stirring rate of 400 r/min,the purity of filtered crystal can reach 99.68%,crystallization yield is 48.90%.The results of static crystallization and dynamic crystallization showed that 6-tert-butylm-cresol was more suitable for purification by dynamic melting crystallization. |
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