| Thymol(5-methyl-2-isopropylphenol)is a spice widely used in fine chemical products in the fields of essence,medicine and food.According to literature reports,most chemical enterprises mainly use phenol and isopropyl to catalyze the synthesis of thymol.However,this synthesis method produces a large number of by-products,among which there are two main components with higher content: m-thymol(5-methyl-3-isopropylphenol)and p-thymol(3-methyl-4-isopropylphenol).This article studies the application of separation and purification processes for thymol and its isomers in industrial production processes,as well as the development of thymol hydrogenation catalysts.1.Separation and purification of thymol raw material using distillation melting crystallization coupling technology.Separation and purification of industrial thymol raw materials using distillation melting crystallization coupling technology.Preliminary separation was carried out through vacuum distillation method,and the contents of the three fractions after vacuum distillation reached75.11%,71.32%,and 73.62%,respectively(thymol,meta thymol,para thymol,in the same order below).Melt crystallization of crude products separated by distillation.Static melting crystallization,the content of the three target products reached 99.11%,99.19%,and 99.04%,respectively,with yields of 41.23%,39.85%,and 42.28%;Dynamic melting crystallization,the content of the three target products reached 99.72%,99.83%,and 99.51%,respectively,with yields of 51.03%,49.11%,and 48.37%.By comparing and using dynamic melting crystallization for purification,it is more efficient to obtain pure products.2.Study on the catalytic performance of Ni/X system catalyst for the hydrogenation of thymol to menthol.Through experiments,it has been proven that doping nickel oxide and cerium oxide in a certain proportion can significantly improve the conversion and selectivity of thymol hydrogenation reaction,and reduce the proportion of impurities in the hydrogenation reaction.At a reaction temperature of 190 ℃,a reaction pressure of 6 MPa,a reaction time of 6 hours,and a stirring speed of 500 r/min,Ni4/Ce1 can achieve the optimal effect.The conversion rate of thymol is close to 100%,the selectivity of DL menthol reaches 56.3%,and the impurities are only 0.4%.According to the characterization experiment,adding a certain amount of cerium oxide to the highly active nickel oxide can significantly improve its particle Dispersity,increase its specific surface area,pore volume,pore size and other structural parameters,increase the adsorption and desorption efficiency of reactants,and increase the reaction efficiency.After stability evaluation experiments,the catalyst still maintains good catalytic performance,proving that this type of catalyst is not prone to poisoning and deactivation during long-term reaction processes,and has certain industrial application value.3.Study on the catalytic performance of Co/X system catalyst for the hydrogenation of thymol to menthol.Experiments have shown that the mixture of cobalt oxide and neodymium oxide can reduce impurities in the hydrogenation reaction,while improving the conversion and selectivity of thymol hydrogenation reaction.At a reaction temperature of 190 ℃,a reaction pressure of 6 MPa,a reaction time of 6 hours,and a stirring speed of 500 r/min,Co4/Nd1 can achieve the optimal effect.The conversion rate of thymol is close to 100%,the selectivity of DL menthol is 55.4%,and the impurity content is 0.7%.Through characterization experiments,it was found that the dense cobalt oxide particles were not conducive to the reaction.The addition of neodymium oxide improved the Dispersity of the catalyst system and improved the structure,which was conducive to the hydrogenation of thymol and reduced the generation of impurities.After stability tests,it still maintains excellent catalytic performance,proving that this type of catalyst is not prone to poisoning and deactivation in long-term reactions,and has certain industrial application value. |
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