Background and overview[1][2]
Trimethylbenzene is a colorless, flammable and volatile liquid. There are three isomers, namely mesitylene, mesitylene and mesitylene, with slightly different properties. They are all insoluble in water and soluble in alcohol, ether and benzene. Mainly used as chemical raw materials, solvents and paint thinners, it is slightly toxic. It can be slowly absorbed through the digestive tract, respiratory tract and skin. Oxidized in the body to phenolic and formic acid compounds. The former combines with sulfate radicals and a small amount with glucuronic acid radicals. The latter is mainly combined with glycine and excreted in the urine; a small amount is excreted unchanged through the lungs or kidneys. There have been no reports of occupational poisoning. When the concentration of this product mixture in the workshop air is 50 mg ~ 300 mg/m3, workers often have symptoms such as weakness, headache, dizziness, or reduced numbers of platelets and red blood cells, gum and nose bleeding, subcutaneous hematoma, etc. Asthmatic bronchitis may still be seen in those exposed to higher concentrations. Acute poisoning patients may experience symptoms such as central nervous system depression or loss of reflexes.
Apply[3-7]
Trimethylbenzene is mainly used as chemical raw materials, solvents and paint thinners. Examples of its applications are as follows:
1. Homogeneous oxidation of mesitylene to produce 3.5-dimethylbenzoic acid. It involves a method of producing crude 3.5-dimethylbenzoic acid through homogeneous oxidation using mesitylene as raw material, no solvent, only one catalyst, and direct air circulation. It is characterized by adding fresh mesitylene and catalyst into the tank and mixing them evenly before adding them to the oxidation tower, and then adding the recovered mesitylene and catalyst into the tank and mixing them evenly before use. When the fresh feed liquid is heated in the oxidation tower and compressed air is passed through to start the oxidation reaction, the recovered feed liquid is slowly added in batches. When the material liquid reaches a certain milliequivalent after several hours of oxidation, oxidize the liquid material, remove benzene, distillate and slice to obtain crude 3.5-dimethylbenzoic acid, or remove benzene and then cool and crystallize, and solid-liquid separation can obtain 3.5-dimethylbenzoic acid. Crude benzoic acid.
2. Fixed-bed gas-phase oxidation of trimellitic anhydride to produce trimellitic anhydride, which involves a manufacturing method of trimellitic anhydride. It mixes trimene, water vapor and air into a tubular reactor equipped with a vanadium-titanium fixed bed catalyst, so that trimene is oxidized into trimellitic anhydride; the reaction conditions are: water vapor and The feed volume ratio of mesitylene is 1:5~40, the catalyst load is 10~100g/L·h, the space velocity is 1000~10000L/L·h, and the reaction temperature is 350~450°C. The method for preparing trimellitic anhydride of the present invention has low equipment corrosion, simple process flow, and is easy to form industrial production.
3. The production of trimesic acid by air-liquid phase catalytic oxidation has the characteristics of low product cost and good product quality. The process is simple and the technology is mature. The conversion rate of mesitylene is 98.5-990‰. For mesitylene, the weight yield of trimesic acid is 115-120%. The invention uses mesitylene as raw material, air as oxidant, acetic acid as solvent, bromide as initiator, cobalt acetate as catalyzer, and manganese acetate as cocatalyst. The initiator bromide is tetrabromoethane or sodium bromide or ammonium bromide. Fine trimesic acid can be obtained by recrystallizing the crude trimesic acid obtained by oxidation with dilute acetic acid. After distillation, dilute acetic acid removes organic carboxylic acid and can be recycled.
4. The synthesis of trimethylhydroquinone from trimethylbenzene includes the following steps: using trimylene as raw material, through bromination reaction, oxidation reaction and reduction reaction, trimethylhydroquinone is finally prepared; the reaction equation is: This The invention uses cheap trimethylbenzene as the starting raw material, has a short process route and high yield. The bromine element can be completely recycled through recovery. It is a clean synthesis process that solves the shortage of intermediate cresol sources in the existing process and the problem of dimethylbenzene. There is a serious pollution problem in the toluene process.
5. Preparation of 5-tert-butyltrimethylbenzene. Using trimethylbenzene and tert-butane chloride as reactants, quaternary ammonium salt ionic liquid [Et3NHCl][AlCl3] as catalyst, the reaction temperature is 0~20℃, the reaction time is 3h~6h, tert-butane chloride The molar ratio to trithionine is 1:1~4:1, the mass ratio of ionic liquid to trithionine is 0.05:1~0.2:1, and the molar ratio of anion [AlCl3] and cation [Et3NHCl] of ionic liquid is 1.5:1~2.5:1. After the reaction, the ionic liquid catalyst can be reused after being directly stratified, which reduces the energy consumption of the post-treatment process and reduces the overall operating cost. Under optimized reaction conditions, the reaction conversion rate can reach 100% and the selectivity can reach 95%. The preparation process of the catalyst used in this method is simple and the raw materials are easily available.
Preparation [8-9]
Method 1: A method of cracking prolific trimethylbenzene using heavy aromatic hydrocarbon components such as C9 and above, including the following steps:
a) Heavy aromatic hydrocarbons and non-aromatic hydrocarbon raw materials are purified, mixed with hydrogen, heated to 200~400°C, and then entered into a fixed bed reactor equipped with a catalyst for reaction to generate aromatic hydrocarbons rich in trimethylbenzene and Reaction products of light alkane components;
b) The reaction product is condensed into a gas phase and a liquid phase. The gas phase product mainly contains low-carbon alkanes and hydrogen, and the liquid phase product contains non-aromatic hydrocarbons;
c) Liquid phase products containing non-aromatic hydrocarbons enter the middle of the stripping tower, liquefied gas is obtained from the top reflux tank, and carbon six and above components are obtained from the stripping tower still;
d) Materials with carbon six and above enter the BTX tower, the BTX products are obtained at the top of the tower, and the materials with carbon nine and above components are obtained from the tower kettle;
e) Materials with carbon nine and above components enter the middle of the trimethylbenzene tower, and high value-added mesitylene and mesitylene are obtained at the top of the tower.��Trimethylbenzene, the heavy C9 and trimethylbenzene fractions in the tower kettle are recycled heavy aromatic hydrocarbon materials, which are sent to the fixed bed reactor in step a) for reaction.
In the above technical solution, the catalyst can be a commonly used oxide catalyst, or a molecular sieve supported oxide catalyst. The preferred technical solution is that the catalyst contains a metal selected from Cu, Sn, Pb, Zn and Fe or at least one of the oxides.
Method 2: To purify trithionine from mixed C9 aromatic hydrocarbon solvent oil, place the mixed C9 aromatic hydrocarbon solvent oil in a reaction kettle, raise the temperature to 40~140°C, add the catalyst anhydrous aluminum trichloride, and stir evenly ;Pour in the alkylating agent C2~C5 olefins, perform an alkylation reaction, and alkylate the mesitylene in the raw material into alkyl mesitylene. During the reaction, the temperature is controlled at 40~140°C, and the alkylating agent After the introduction is completed, continue stirring; wash the alkylation liquid with water at 40~140°C, let it stand still, take the upper alkylation liquid, reflux, perform vacuum distillation of the alkylation liquid, and cut out the alkyl terephthalate. Toluene fraction; the alkyl mesitylene fraction cut out by distillation is subjected to dealkylation reaction under the action of catalyst M-H molecular sieve, the reaction temperature is 300~650°C; the dealkylation liquid is subjected to vacuum rectification or normal pressure rectification , to obtain high-purity trimethylbenzene with a purity of more than 92%. The advantage is that the purity of trimethylbenzene obtained is high and it can be produced continuously.
Main reference materials
[1] Health Dictionary Compound Dictionary
[2] CN02112544.9 Method for producing 3.5-dimethylbenzoic acid by homogeneous oxidation of mesitylene
[3] CN03111257.9 Method for producing trimellitic anhydride by gas phase oxidation of trimethylene in fixed bed
[4] CN01133428.2 Method for preparing trimesic acid by air-liquid phase catalytic oxidation of mesitylene
[5] CN201611001125.1 A method for synthesizing trimethylhydroquinone from trimethylbenzene
[6] CN201510574799.X A method for preparing 5-tert-butyltrimethylbenzene using an ionic liquid catalyst
[7] CN201210412533.1 Method for cracking C9 and above heavy aromatic hydrocarbon components to produce prolific trimethylbenzene
[8] CN200610047287.9 Method for purifying trimethylbenzene from mixed C9 aromatic hydrocarbon solvent oil
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