Study On Crystallization Process Of Bis(2-hydroxyethyl) Terephthalate

Bis(2-hydroxyethyl)terephthalate(BHET)has good chemical properties.BHET is widely used to synthesize a variety of unsaturated polyester resins.The purity and quality of BHET have a great influence on the quality of subsequent products.However,the current research on BHET is mostly about the conversion rate of reactants,the yield of BHET and the reaction kinetics,and there are few studies on the purification of BHET.Therefore,this article studies the crystallization process of ethylene terephthalate.This paper uses XRD,FT-IR,DSC and 1H NMR to characterize BHET drugs,to ensure that BHET has not undergone chemical changes and to obtain the basic information of crystals.This paper determined the solubility of BHET in 16 pure solvents from 283.15 K to 323.15 K.The solubility of BHET is positively correlated with temperature.At 303.15 K,the order of solubility is:cyclohexanone>alcohols and 2-butanone>acetonitrile>esters.These two models(simplified Apelblat equation and Van't Hoff equation)have a good fitting effect on the experimental data.At the same time,?Hsol??Ssol??Gsol??H and ?TS during the dissolution of BHET in the 16 solvents selected are calculated.Use Materials Studio software for molecular simulation to calculate the thermodynamic properties of the mixture.Optimize the molecular structure of BHET and each solvent in the Focus module to get the lowest energy structure.The Blends module is used to calculate the Chi parameters and mixing energy of BHET and solvent at different temperatures.It was found that the Chi parameter and the mixing energy decreased with the increase of temperature and were close to a straight line,indicating that the solubility of BHET in the solvents increased with the increase of temperature.At the same time,using the Reflex module in the Materials Studio software to obtain the unit cell parameters of the crystal and the optimized unit cell,and then used the BFDH model,AE model and EM model in the Morphology module to predict the BHET crystal habit.It is found that the crystal habit obtained by the AE model is the most consistent with the crystal habit obtained by experiment.In this paper,we study the cooling crystallization process of BHET in ethanol solution.The width of metastable zone of BHET in ethanol solution was measured.The best cooling crystallization process condition for obtaining BHET in ethanol solution is adding 1%seed crystal at 35?,keeping the cooling rate at 2?/5min,stirring rate at 150 rpm,and cooling to 10? for 2 h.The crystals of the obtained product are complete and in good consistency,the purity has been significantly improved to 98.5%,and the product yield is 79.43%.The research of this subject provides a certain theoretical guidance significance and potential practical value for BHET separation and purification and industrial production.