Selective Regulation And Separation Of Cresol Tert-butylation Products

Among the phenolic compounds in coal tar,cresol monomer and its tert-butyl substituent have high added value.The boiling points of m-cresol and p-cresol are almost the same and it is difficult to separate by rectification.However,the difference in boiling point between the alkylated products is large and easy to separate.In the traditional alkylation process,cresol is dialkylphenol,and after rectification,the alkyl group is removed to obtain the corresponding cresol product.From the perspective of economy,a variety of fine chemicals help to reduce the cost of the separation process.Based on the understanding of the alkylation process,this study regulates the product composition by changing the reaction rate: promoting the formation of p-cresol disubstituted and reducing the reaction of m-cresol.In this study m-cresol and p-cresol were used as raw materials to carry out tert-butylation of m-p-cresol with concentrated sulfuric acid as catalyst.The main factors affecting the conversion of reactants,product yield and selectivity were studied,based on the selectivity and yield of the target product 2,6-di-tert-butyl-4-methylphenol(BHT)and 2,4-di-tert-butyl-5-methylphenol(DMC),the experimental system was determined.The optimum conditions for the tert-butylation reaction of mixed cresols;the thermal-related parameters of the m-cresol and p-cresol tert-butylation reaction were calculated,which provided a theoretical basis for the subsequent selective control of the product;inhibiting the tert-butylation reaction of m-cresol,adjusting the main components of the product to BHT,6-tert-butyl-m-cresol(6-T-M)and unreacted m-cresol;Ultraviolet spectrophotometer was used to preliminarily explain the action mechanism of solvent in the process of tert-butylation of para-cresol;the cresol product is isolated from the light component of Xinjiang Hami low-temperature pyrolysis oil(<325 °C),and the target product is obtained through the alkylation process.(m-cresol and BHT).The main conclusions and results are as follows:1.The optimum conditions for the tert-butylation of m-cresol and p-cresol is: temperature:60 °C,time:90 min,airspeed of isobutylene:11.76(g·min-1,mass airspeed),the conversion of cresol is 100%,under this condition;the selectivity of 2-tert-butyl-4-methylphenol(2-T-P)is 0,the selectivity of 6-T-M is 3.80%,the selectivity of BHT is 97.35%,the selectivity of DMC is 92.31%.2.The equilibrium constant of the first tert-butylation reaction of m-cresol and p-cresol is same,and the equilibrium constant of the second step is quite different.3.The conversion rate of m-cresol and p-cresol decreased by 42.41% and 1.07% respectively under the influence of solvent dichloromethane.The reaction rate increased,the time of each product was advanced,and the products were mainly 6-T-M and BHT.The content of DMC was decreased obviously,the yield of DMC is essentially zero,and the regulation of the product is achieved.4.The ultraviolet spectrum of the results showed that the solvent influence the peak shape,peak position and peak intensity of ultraviolet absorption peak of phenolic compounds.According to the Solvent effect coefficient,m-cresol and 6-T-M between solvent and solvent effect than BHT and 2-T-P,this is the preliminary experimental result of DMC is not the main cause of generation.5.Taking the light component(<325 °C)of Xinjiang Hami low temperature pyrolysis oil as raw material(containing phenol content 28 wt%,GC-MS),the phenolic compound obtained after alkali-washing accounts for 19.84 wt% of total tar.After phenol rectification and refining,the fractions of 185-190 °C and 190-195 °C were collected(the cresol content was 75.62 wt% and 79.68 wt%,respectively),and then purified by distillation to obtain a purity of 94.10%.Mixed cresol(containing a small amount of o-cresol and xylenol),the by-products after the tert-butylation reaction are 2,4-dimethyl-6-tert-butylphenol,4-tert-butyl-2,6-Diisopropylphenol and 2,4,6-tri-tert-butylphenol.The fraction of m-cresol was 97.71%,the purity was 75.21%,the yield of the raw material mixed cresol intermediate cresol was 96.93%,the purity was 97.35%,and the BHT yield was 92.17.%,purity 100%,m-cresol and BHT can be directly exported as products.The optimized process compared with the traditional process to reduce energy consumption part of tert-butyl reaction part.Compared with the traditional technology can reduce energy consumption by 14.54%.