The Optimization Of Synthesis Process Of 4-chloro-2-methyl Phenoxyacetic Acid

O-Methylphenoxyacetic acid is an important chemical.It is an important raw material for the preparation of various medicines,pesticides,fuels,etc.Its chlorinated product,2-methyl-4-chlorophenoxyacetic acid(It’s called 2-methylene 4-chloro)is one of the most widely used herbicides in the world.The effectiveness and safety of2-methyl-4-chlorine makes such pesticides irreplaceable.Industrially,the method for synthesizing 2-methyl-4-chloride is mainly the Williamson ether synthesis method,which is divided into two processes: first chlorination condensation and first condensation and chlorination.For the former,the conversion of the raw material o-cresol is low,the selectivity of the chlorination process is poor,and toxic substances such as chlorophenols and dioxins which are difficult to separate are produced,so that the yield of2-methyl-4-chloro is very low.In the latter case,the hydrolysis of chloroacetic acid leads to low conversion of o-cresol and low reaction yield.In order to avoid the problem of chloroacetic acid hydrolysis and low conversion of o-cresol,the plant uses de-phenolization and stripping of phenol.The method,but has the disadvantages of long reaction time,unstable product purity,large discharge of phenol-containing wastewater,high pollution environment,high energy consumption,etc.;and easy chlorination in the process of chlorine,and the chlorination end point is difficult to judge,resulting in more impurities.Chloride,such as 2-methyl-4,6-dichlorophenoxyacetic acid,for this reason,we urgently need to optimize the existing production process for the production of2-methyl-4-chloride,to promote cost reduction,emission reduction,and environmental protection.And improving economic efficiency are all important.In this thesis,water is used as the reaction solvent for homogeneous reaction.The50% sodium chloroacetate aqueous solution is directly charged into the o-cresol sodium system.The optimum reaction conditions are obtained after optimization of o-methylphenoxyacetic acid: molar ratio of reaction materials Cresol: chloroacetic acid:sodium hydroxide=1:1:2,reaction temperature 110 ℃,reaction time 3 h;water as acidifying solvent,water: mass ratio of reaction liquid 0.6,acidified pH 2,crystallization temperature 5 ℃,the average yield(in terms of o-cresol)was 87.7 %,which was 2 %higher than the workshop process,reducing production costs and energy consumption.During the condensation process of o-methylphenoxyacetic acid,the raw material o-cresol does not completely react,and a large amount of phenol-containing wastewateris produced.In this paper,using Aspen Plus process simulation software,the ortho-cresol/water solution was subjected to pressure swing double column rectification,and the design process was optimized.The recovery rate of o-cresol was 97.9 %.The purified o-cresol is recycled as a raw material,and the rectified water is used as a reaction ingredient,thereby improving resource utilization and reducing waste water discharge.Aiming at the phenomenon of perchlorination in the preparation of2-methyl-4-chloride by post-chlorination,this paper uses a purity of 95%o-methylphenoxyacetic acid as raw material,and chlorine gas as a chlorinating reagent,and carried out a series of single factor experiment optimization.The reaction conditions are as follows: mass ratio o-methylphenoxyacetic acid: dichloroethane: water = 1:2.6:3,reaction temperature is 65 ℃,the rate of chlorine gas is controlled at 0.5 g/min,and the measurement method of weight gain of the reaction liquid is adopted.When the amount of chlorine gas reaches the theoretical amount,the excess is 3 %~4 %,then the dichloroethane phase is filtered while hot,the crystal is slowly cooled,the crystallization temperature is 0 ℃,the crystallization time is 1 h,and the purity of the2-methyl-4-chloride is 95.2 %,the yield reached 85.3 %,which reduced the occurrence of chlorine.The characteristics of this paper are to improve the yield,reduce the amount of wastewater,improve the utilization of o-cresol and reduce the phenomenon of perchlorination.Through this series of process optimization,a simpler,more efficient and environmentally friendly synthesis method has been established.