Study On The Separation Of Mixed Dichlorotoluene By Vacuum Extraction And Distillation And The Preparation Of 2,6-dichlorotoluene By Isomerization

Dichlorotoluenes are important fine chemical intermediates.They are widely used in many fields such as pesticides,pharmaceuticals,dyes,photosensitive materials and have a very broad development prospect.The traditional industrial preparation of 2,6dichlorotoluene will produce a large amount of 2,4-dichlorobenzene and 2,5dichlorotoluene,which greatly reduces the yield of 2,6-dichlorotoluene.What's more,the isomers' boiling points are very close,so it is difficult to separate the dichlorotoluenes mixture by ordinary distillation method.This paper summarized the properties,synthesis routes and application status of 2,4-dichlorotoluene,2,5-dichlorotoluene and 2,6-dichlorotoluene.The separation methods of dichlorotoluenes mixture were summarized in this paper.So reduced pressure extractive distillation was proposed to separate the dichlorotoluenes mixture.In addition,this paper studied the isomerization of the 2,5-dichlorobenzene because of it's lower utility value.Six solvents were selected from twelve major types of solvents by referring to the literatures and the solvent handbook.The single-stage extraction of raw materials in the six solvents was simulated by Aspen Plus software.At the same time,the vapor-liquid equilibrium data of raw materials in different solvents were experimentally determined by single-stage vapor-liquid equilibration devices.And the relative volatilities of different components were calculated.Combined with the simulation data and experimental results,the optimum extractant for the separation of dichlorobenzenes mixrure was determined.The reduced pressure extractive distillation and solvent recovery column were simulated by Aspen Plus.Firstly,the number of theoretical plates,solvent ratio,reflux ratio,bottom product quantity and feed position of reduced pressure extractive column were optimized by single factor rotation method and orthogonal experiment analysis.And based on the simulation data,confirmatory experiment was carried out,the mass fraction and yield of 2,4-dichlorobenzene reached 77.68%and 78.12%,respectively.And 2,6-dichlorobenzene reached 1.13%.Secondly,the number of theoretical plates,reflux ratio,and feed position of solvent recovery column were optimized by single factor rotation method.And under the optimal conditions,the mass fraction and yield of solvent were both 99.99%.This paper can provide theoretical basis for the further research.H? zeolite was selected as the catalyst for the isomerization of 2,5-dichlorotoluene.The tubular reactor was used to study the catalytic performance of H? zeolite.The effects of reaction temperature,WHSV and reaction pressure were investigated.Under the optimal conditions,the conversion of 2,5-dichlorotoluene was 23.56%,and the selectivity of 2,6-dichlorotoluene was 23.21%.H? zeolite was modified by pure NaOH solution,NaOH and tetrabutylammonium hydroxide(TBAOH)mixed alkali solution,respectively.And the samples' acidity and pore structure were characterized by XRD,N2 adsorption,X-ray fluorescence,TEM,FT-IR and Py-IR.The effects of different modified solutions on the acidity,pore structure and isomerization catalytic properties of H? zeolite were studied.The results showed that the pore structure and acid center content of H? zeolite can be modified by the modification of both alkali solutions.And the conversion of 2,5-dichlorotoluene and 2,6-dichlorotoluene's selectivity can be improved.By comparison,the sample which was modified by NaOH and TBAOH mixed alkali solution existed more homogeneously microporous-mesoporous structures because TBAOH can better maintain the H? zeolite's crystallinity and skeletal structure.And it had better stability during the isomerization reaction.