SU888814A3 - Method of preparing dimethylterephthalate - Google Patents

Abstract

Prodn. of dimethyl terephthalate (I) by oxidn. of methyl p-toluate (II), opt. mixed with p-xylene (III), is carried out in the liq. phase at elevated pressure and temp. in the presence of a low-mol. aliphatic alcohol, using (gas contg.)O2 in the presence of oxidn. catalysts, followed by esterification of the acids formed with MeOH and sepn. of the esterification prods. The novelty is that, during oxidn., the liq. phase is treated with Me OH in an amt. insufficient for significant esterification, so that a MeOH concn. of 400-0000 (700-2000) ppm is maintained in this phase. Pref. oxidn. is carried out in stages in a series of oxidn. reactors and the MeOH concn. is controlled separately in each stage. (I) is used as raw material in the mfr. of fibre- and film-forming polyesters. No solvents or hydrocarbon cpds. are used and the amt. of volatile acids and of high boiling residues, which cannot be converted to (I) and (II), formed is less than usual, without the oxidn. of harmful amts. of MeOH.

Description

one

This invention relates to the field of organic synthesis, specifically to a process for the preparation of a dimethyl terephthalate chemical product.

A known method for producing terephthalic acid dimethyl ester involves oxidizing p-xylene and p-toluic acid methyl ester with oxygen-containing gas at elevated temperatures in the presence of u as a catalyst for cobalt or manganese salts, followed by separation of the product and recycling unreacted methyl ester p-toluenera: spots on the stage of oxidation - la

HMBflJ.

The disadvantage of this method is that the selectivity of the process is not high enough due to side reactions of the formation of formic and acetic acids 20 and carbon dioxide.

The closest in technical essence and the achieved result is a method for producing dimethyl terephthalate by oxidation of a mixture of p-xi-25

lol and p-toluic acid methyl ester with air at 150–170 ° C and atm pressure in the presence of a catalyst — a mixture of cobalt and manganese acetates followed by esterification of the resulting product with methanol 2.

The yield of the target product is 8k wt.%.

The disadvantage of this method is the relatively low selectivity of the process due to losses due to the formation of such by-products as formic acid, acetic acid and carbon dioxide, which leads to a decrease in the yield of the target product.

The purpose of the invention is to increase the yield of the target product.

Claims (2)

For this, according to the proposed method for the treatment of dimethyl terephthalate, by oxidizing a mixture of p-xylene and p-toluic acid methyl ester with air at 130-170 ° C and a pressure of 5-7 atm in the presence of a mixture of cobalt acetates and catalyst. as well as in the presence of methanol, in an amount of 0, 4% by weight of the reaction pass. The yield of the target product was 86.5% D. A distinctive feature of the process is to conduct oxidation in the presence of methanol, taking in an amount of 0, OA-0.4% by weight of the reaction mass, which allows an increase in the yield of the target product. Example 1. To obtain dimethyl terephthalate, an installation consisting of a three-stage reactor cascade is used to oxidize the starting components, a plate column for etherifying the oxidation product with methanol and devices for processing the esterification product. At the same time, 6.0 t / h of p-xylene, 6.5 g / h of p-toluic acid methyl ester, 6 tons / recirculated residue of the vacuum distillation of the esterification product, 4600 air and +0 l / h are fed into the first reactor of the three-stage cascade. solution of acetates of cobalt and manganese in acetic acid. This solution contains 30 g / l of cobalt and 3 g / l of manganese. In addition, 3,500 and 2,900 MV4 air is still supplied to the second and third reactors, and another 0.5 t / h of p-xylene is also fed to the third reactor. The oxidation process in the three reactors is carried out at 150, 1bO and 170 ° C, respectively, and a pressure of 5.6 and 7 atm in the presence of 0.12 liquid methanol fed to the bottom of each reactor. The acid number of the oxidation product of the three reactors is 120, 200 and 2bO (mg KOH / g) The oxidation product from the third reactor, containing 12.6 kg of methanol, is fed to the esterification with methanol at 250 ° C and a pressure of 20 atm to an acid number of 5 mg KOH, with 5 t / h of methanol being added at the esterification stage. The esterification product is subjected to vacuum distillation at a pressure of 200 mbar. The resulting dimethyl terephthalate is purified by recrystallization from methanol. The yield of dimethyl terephthalate is 86.5, calculated as p-xylene. The secondary vapor of the three-stage cascade reactors is combined, the aqueous phase of the condensate produced is condensed, 4 and the off-gas is analyzed for formic and acetic acid and carbon dioxide. The data on the quantitative content of the components, mmol, is given below: Formic acid 9g5 Acetic acid 4.3 Carbon dioxide 8.8 Total carbon loss28, i Equivalent saponification of condensate 760 meq. Example 2. The process is carried out according to Example 1, but the oxidation is carried out in the presence of 0, methanol by weight of the reaction mass, and the oxidation product containing 5.1 kg of methanol is esterified with methanol. The following results are obtained: dimethyl terephthalate yield 86.1 wt. in terms of p-xylene; carbon loss, mmol: a) 11.2 formic acid; b) 7.1 acetic acid; c) 12.5 carbon dioxide; d) 40.6 (total); equivalent of condensate saponification, mEq 815 Example 3 Example 1 is repeated, but the oxidation process is carried out in the presence of 0.41 methanol by weight of the reaction mass, and the oxidation product containing 52.8 kg of methanol is esterified with Methanol. The following results are obtained; the output of dimethyl terephthalate 86,8% in terms of p-xylene; carbon loss, mmol: a) 8.7 formic acid; b) 3.8 acetic acid; c) 7.9 carbon dioxide; d) 26.1 (total); equivalent of condensation atatolate, mg.equ. 745. Invention manganese, followed by esterification of the product obtained with methanol, is required in order to increase the yield of the target product, the oxidation is carried out in the presence of methanol, taken in an amount of 0.04S 0.4% of the weight of the reaction mixture. Sources of information taken into account in the examination of 888811 4 1. German patent ff, Clo 07 C 69/82, published. 1975. 2. Patent of the USSR No., class C. 07 C b9 / b2, published 1970 (prototype /