SU432124A1 - METHOD OF OBTAINING AROMATIC DICARBONIC ACID - Google Patents

Description

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This invention relates to a process for the preparation of aromatic dicarboxylic acids, e.g., terephthalic or 2,6-naphthalane dicarboxylic, from alkyl derivatives of the benzene or naphthalene series (toluene or p-methylnaphthalene). These acids are the starting monomers for the production of heat-resistant and high-strength materials and polyester fibers.

A known method for producing alkaline salts of aromatic dicarboxylic acids is as follows.

The initial alkaline salt of monocarboxylic acid is prepared by neutralization of benzoic acid with caustic potassium or potassium in dilute aqueous solutions (20%). The aqueous solution is evaporated, potassium benzoate is dried to dryness and, in the presence of a catalyst, cadmium oxide or cadmium iodide is heated to 450 ° C for 6 hours. The reaction product is boiled with water and then acidified to give 40.3% of terephthalic acid.

However, according to this method, the yield of the target product is low, since in the preparation of alkaline salts, such as benzoic or p-naphthoic acids, all impurities of these acids, even in micro-amounts, are converted into benzoate or naphthoate potassium at the time of evaporation of the solution, which greatly slows down the reaction disproportionation.

In addition, to carry out the disproportionation process, it is necessary that the benzoate or potassium naphthoate be free of moisture, therefore the aqueous solutions are evaporated and the resulting salts are dried to dryness. This stage requires a lot of heat, since it is necessary to evaporate 4 tons of water per I t of TPA.

The aim of the proposed method is to increase the yield of the target product, simplify the process of its preparation and, in addition, make the process more economical. To achieve this goal, a solution of monocarboxylic acid in an organic solvent, such as alcohol, acetone, is treated with a solution of caustic potash in methyl or ethyl alcohol. The resulting alkali salt precipitate is filtered off, dried and heated in the presence of a catalyst, followed by isolation of the 1M dicarboxylic acid by known methods. The essence of the proposed method is that, for example, benzoic or p-naphthoic acid, obtained by oxidizing toluene or 2-methylnaphthalene with air in an acetic acid medium in the presence of cobalt acetate and sodium bromide, is dissolved without prior purification in an organic solvent,

for example, alcohol, acetone, etc .; the resulting solution is neutralized with an alcoholic solution of potassium hydroxide. The precipitate of potassium benzoate or potassium naphthoate is filtered off and dried. After rectification, organic solvents from the mother liquor are returned to the stage of dissolution of monocarbonate acid and potassium hydroxide, and the mixture of alkali salt and catalyst is heated to a temperature of 450 ° C in a CO2 atmosphere for one hour. Terephthalic or 2,6-naphthalene dicarboxylic acid is recovered from the reaction mixture in a yield of 95 or 70%, respectively.

The proposed method reduces the cost of, for example, terephthalic acid, as this method uses cheese, i.e., crude benzoic or p-naphthoic acid, and using an organic solvent to prepare alkaline salts of monocarboxylic acids eliminates the laborious stage of evaporation of large amounts of water, costly heat. Using organic solvents instead of water, high-purity alkaline salts are obtained, since impurities of benvoic and p-naphthoic acids (e.g. benzaldehyde, diphenyl, esters of acids, p-naphthaldehyde, p-methylnaphthalene and resinous substances) are well soluble in organic solvents such as ethyl or methyl alcohol, acetone and others. The alkaline salt precipitate is filtered off, and impurities remain in the mother liquor.

Since the purity of the initial salt obtained (benzoate or potassium naphthoate) in the proposed method is higher (the color of the aqueous solution of the potassium salt of 2-naphthoic acid, determined on the SF-4A spectrophotometer at a wavelength of 450 nm is 3-9) aqueous solutions (the color of the aqueous solution of the potassium salt of 2-naphthoic acid, determined under the same conditions, is 30.7), therefore, an increase in the yield of the alkaline salt of dicarboxylic acid is achieved during disproportionation.

So, for example, in the implementation of potassium benzoate disproportionation, obtained by neutralization of crude benzoic acid in an aqueous medium followed by evaporation, the yield of potassium terephthalate does not reach 70%. The use of potassium benzoate obtained from the same crude benzoic acid, but by the method with an organic solvent, makes it possible to increase the yield of potassium terephthalate up to 95%.

The proposed method, by replacing water with an organic solvent, makes it possible to combine three major stages — purification of benzoic acid, obtaining potassium benzoate and evaporation of the aqueous solution — in one stage.

Example 1. 351.7 g of toluene, 1.4 g of cobalt stearate, 0.05 g of sodium bromide are charged to a bubbling type reactor. Oxidation

carried out at a pressure of 10 atm and a temperature of 180 ° C for 4 hours. The air flow rate is 180 kg / h. After separation of the reaction products, 249.75 g of unreacted toluene and 127.5 g of benzoic acid containing (%): the basic substance 98.7, benzaldehyde 0.6, diphenyl 0.2, and esters 0.1 were obtained.

The benzoic acid is dissolved in 238 ml of 96% ethyl waste at 50 ° C. A solution of benzoic acid is poured into a solution of 6.8 g of KOH (85%) in 240 ml of 96% ethyl alcohol. The precipitated potassium benzoate is filtered off and then dried. 155.5 g of potassium benzoate unmixed with 4.8 g of CdO and pelletized (diameter and height of tablets 5 mm). 155 g of the tablet mixture is heated in a disproportionation reactor at 440-450 ° C for one hour under a pressure of carbon dioxide of 10 atm. 130 g of disproportionation products with a potassium terephthalate content of 83% are obtained. The yield of potassium terephthalate, calculated on the potassium benzoate loaded, is 95% of the theoretical value.

The total yield of potassium terephthalate, calculated on toluene converted, is 80.2%.

Example 2. In the oxidation process, benzoic acid is obtained, containing (%): the main substance 95.3, benzaldehyde 2.8, diphenyl 0.5, resinous products 1.2.

130 g of benzoic acid of the indicated composition are dissolved with stirring and 40 ° C in 250 ml of acetone.

In the resulting solution load 4 g of activated carbon brand KAD. After stirring for 20 minutes, the activated carbon is filtered off. A solution of benzoic acid in acetone is poured to a solution of 68.5 g of KOH (basic substance content 85%) in 255 ml of ethanol. The mixture is stirred for 40 minutes. The potassium benzoate precipitate is filtered, dried to constant weight at 120 ° C. 148.0 g of potassium benzoate are thoroughly mixed with 4.6 g of cadmium oxide and, after tableting, the disproportionation is heated in the reactor for 1 hour at 450 ° C and a pressure of 10 atm. 131 g of disproportionation products with a potassium terephthalate content of 80.5% were obtained. Potassium terephthalate yield is 94.2% of theoretical.

Example 3. 74.5 g of 2-naphthoic acid obtained by oxidation of 2-methylnaphthalene with atmospheric oxygen in an environment of 98% acetic acid in the presence of cobalt acetate and sodium bromide at 120-125 ° C and a pressure of 20 atm, with a content of the main substance 98 , 4%, is dissolved with stirring in 685 ml of ethanol at 40-50 ° C. To the solution was added 20 g of KAD-Milled activated carbon.

After stirring for 20 minutes, the carbon is filtered off, and the alcoholic solution of 2-naphthoic acid is poured, while stirring, to a solution of 27.5 g of 85% KOH in 80 ml of ethyl alcohol. The precipitate of the potassium salt of 2-naphthoic acid is filtered off and dried at 120 ° C.

The resulting potassium salt of 2-naphthoic acid in the amount of 74.7 g is mixed with 3.9 g of the catalyst CdJ2, the mixture is tableted and placed in a disproportionation reactor. In the reactor, the mixture is incubated for 1 hour at 450 ° C and a pressure of COz 40 atm. At the end of the reaction, 55.7 g of disproportionation products containing 64.5% of 2,6-naphthalene dicarboxylic acid dipotassium salt are discharged from the reactor, which corresponds to a yield of 70.5%.

Example 4. 35 g of p-naphthoic acid, obtained as in the previous experiment by oxidation of 2-methylnaphthalene with the content of the main substance of 98.33%, is dissolved in 344 g of acetone at 25-30 ° C. The acetone solution of 2-naphthoic acid is clarified with activated carbon and 12.9 g of 85% KOH in 30 g of ethanol are added to the solution. The precipitate of the potassium salt of 2-naphthoic acid is filtered off, washed with 30 ml of acetone and dried. 39.8 g of potassium salt of 2-naphthoic acid are obtained, which is mixed with 2.1 g of CdJg catalyst and disproportionated at 400-450 ° C under C02 pressure of 20-40 atm for 1 hour. Upon completion of the reaction receive

27.65 g of disproportionation products with a content of 66.8% of the dipotassium salt of 2.6 naphthalene dicarboxylic acid, which corresponds to the yield of 2,6-naphthalene dicarboxylic acid, calculated on the loaded 2-naphthoic acid potassium salt, 67%.

Subject invention

Claims (2)

1. A method for producing aromatic dicarboxylic acids, such as terephthalic, 2.6 naphthalene dicarboxylic, by neutralizing an aromatic monocarboxylic acid obtained by oxidation of an alkyl substituted aromatic hydrocarbon, an aqueous solution of potassium hydroxide or potash, followed by evaporation of the solution of the potassium salt of an aromatic monocarboxylic acid or potash followed by evaporation; the presence of a catalyst and the isolation of the target product by known methods, characterized in that, in order to increase the yield of the product and uggroscheni process, an aromatic monocarboxylic acid taken as a solution in an organic solvent, and neutralization are an alcoholic solution of potassium hydroxide or gyutisha followed filtratsnsG) oszdkg ka.pievoy salts of aromatic monocarboxylic acids. 2. The method according to claim 1, wherein that as the organic solvent using methyl alcohol, ethyl alcohol, acetone.