SU1065404A1 - Process for producing benzoic acid - Google Patents

Abstract

A method for producing benzoic acid, which consists in dissolving sodium benzoate or kgce in water, followed by processing the resulting aqueous solution, uses an acidic agent, characterized in that, in order to improve the quality of the target product, the treatment is initially activated coal, and then hydrochloric acid, of 10–15% volume concentration, taken in equimolar volume to sodium or potassium benzoate, with a molar ratio of sodium or potassium benzoate and water Is

Description

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SP

The invention relates to methods for producing particularly pure substances specifically to a method for obtaining beneric acid, which is used in thermochemistry as standard samples of transferring the size of a unit amount of heat from the State primary standard of a unit amount of heat joule to means of measuring 1st, 2nd digits and workers devices.

A known method of producing benzoic acid by the liquid oxidation of toluene with air oxygen at a pressure of 10 atm.

The disadvantage of this method is that the benzoic acid content in the target product does not exceed 99.5 mol.%.

The closest in technical .csmHocTH and effect achieved to the invention is a method for producing benzoic acid, which consists in dissolving potassium or sodium benzoate in water, the resulting aqueous solution is treated with Ba (OH) 2, adjusted to a concentration of 0.150-0.175 mol / l sodium benzoate or potassium benzoate (molar ratio of sodium benzoate or potassium water 1: (320-370), respectively) and pass it through a column containing n-cation resin grade KU-2. Get benzoic acid with the content of the main substance of 99.6-99.8 mol.% 2J.

The disadvantage of this method is With | e4 very poor quality of the target product,

The purpose of the invention is to improve the quality of benzoic acid.

The goal is achieved by the fact that according to the method for producing benzoic acid, which consists in dissolving sodium or potassium benzoate in water, the resulting aqueous solution is treated first with activated carbon, then with hydrochloric acid of 10-15% concentration, taken in an equimolar amount of sodium or potassium benzoate, with a molar ratio of sodium or potassium benzoate and water I: (35-40), followed by sublimation of the resulting benzoic acid at 95-127 s and a residual pressure of (5-7) YH3 mm Hg. Art.

The content of benzoic acid in the target product is 99.94-99.99 mol.%

The proposed method for the preparation of benzoic acid with the content of the main component not lower than J 99.94 mol.% Is worth of three main successive stages:

purification of an aqueous solution of bonzoate n; ltri or potassium with activated carbon from organic impurities in the molecular form;

converting benzoate ion to benzoic acid with hydrochloric acid and precipitating benzoic acid that does not contain organic impurities;

benzoic acid drying using vacuum sublimation.

The elimination of any of these stages does not allow to obtain a product of the required purity. For example, the elimination of the first stage results in the preservation in the final product of organic impurities that have a vapor pressure close to that of benzoic acid vapor. The exception stage vacuum sublimation leads to excessive moisture of the product. It is also not possible to change the sequence of stages: sodium or potassium benzoate cannot be subjected to sublimation due to low vapor pressure, and the precipitation of benzoic acid from the solution as a first stage makes it impossible to clean it of organic impurities by adsorption with activated carbon, since benzoic acid itself acid is sorbed on coal. Thus / only the sequence of operations described in the proposed method allows to obtain benzoic acid with the content of the main component not lower than 99.94 mol%

Example. Sodium benzoate with the content of the main substance of 98% in the amount of 1670 g (11.6 mol at room temperature is dissolved in 5000 g (277.8 mol) of water. In the solution filtered from organic impurities, 33 g (2.8 mol) of activated coal and stirred for 1.5 hours. To the clarified solution is poured 11, 6 mol HCE 15% concentration. The result is a mixture of benzoic acid, salt and water. The precipitate is separated (benzoic acid) and washed from the centrifuge speed of 1700 rpm with a diameter of 300 mm (increase in the number of revolutions The centrifuge or its diameter leads to a decrease in the product yield, as the substance is carried away.) At this stage of the cleaning process, the product yield is 1553 g (10.8 mol or 93%.

The resulting acid is subjected to sublimation at and at a pressure of 510 mm Hg. The yield on the main product is 80% (9.3 mol) OR 1336 g, the content of the basic substance is 99.95 mol .-%.

Examples 2-5. The conditions associated with sodium benzoate treatment with hydrochloric acid are treated. The process is carried out as in Example 1. A 10 L glass flask equipped with a stirrer is charged with 5000 g (277.8 mol) of distilled water and 1670 g (11.6 mol) of sodium benzoate (98% basic substance) are dissolved in it. ) with stirring for 0.5 h. After the indicated time has elapsed, the degree of dissolution of sodium benzoate is visually checked. Then, 33 g (2.8 mol) of activated carbon is added to the solution and the contents of the flask are stirred for 1.5 hours. After that, the vacuum is separated from the solution by filtration through a Büchner funnel under reduced pressure. To the clarified filtrate, 11.6 mol (423.4 g) of hydrochloric acid are poured in the amounts indicated in the table at a rate of 70 ml / min. The result is a slurry consisting of benzoic acid, table salt and water. Separation of benzoic acid and washing it until neutral with C is carried out in a centrifuge with a diameter of 300 mm at 1700 r / m with filtering material - lavsan. Then benzoic acid is dried at 60 ° C with a layer thickness of not more than 5 mm. sodium benzoate hydrochloric acid is presented in Table. As follows from the data of Table 1, the conversion of sodium benzoate to benzoic acid in an aqueous solution is best carried out under conditions where hydrochloric acid is used at the initial concentration of lO-lS vol ..% and at the molar ratio of sodium benzoate I to water 1: (35-40). P p and measures 6-13. Under the conditions of Example 1, benzoic acid was synthesized, but the sublimation process was carried out at a residual pressure of 7 x 10 mm Hg; at the temperature specified in table.2. The yield of the target product and the degree of its purity are presented in table 2. Example 14. The synthesis of benzoic acid is carried out under the conditions of Example 1, but potassium benzoate with the content of the main substance of 98% is used as the starting material. The yield and quality of the target product corresponds to the benzoic acid obtained in Example 1. As can be seen from the experimental studies cited, the most optimal conditions are. The process of purification by sublimation is the temperature range of 122-127 €. If the purification process is carried out at a lower temperature, the process speed is reduced, and at a higher temperature, thermal occurs: decomposition of the substance, the products of which i contaminate the target product. All studies on the dependence of the yield of a substance on the process temperature are carried out with residual; nominal pressure (5-7) mm Hg Under these conditions, the speed of the process is maximum, as it depends on the partial pressure of the substance to be purified. With a higher residual pressure, the speed of the process slows down dramatically, and the achievement of a lower residual pressure is associated with greater technical difficulties, which leads to a decrease in the economic performance of the proposed method. Thus, the proposed method makes it possible to increase the quality of the centrifugal product to 99.99 mol.% Of the content of the basic substance. Table li

table 2

Process temperature, C79 95

Bajo target product, g / h

2.37 4.47 5.64 6.97 8.68 Purification rate ,. mol% 99.99 99.99 99.98

104 112 120 122 125 .127

12.42 99, 98 99, & 99.95 99.94 99.95

Claims (1)

METHOD FOR PRODUCING BENZOIC ACID, which consists in dissolving sodium or potassium benzoate in water and then treating the resulting aqueous ⁴ solution, including? Tjeft using an acidic agent, characterized in that, in order to improve the quality of the target product., The treatment is carried out first with activated carbon, and then with hydrochloric acid of 10-15% volume concentration, taken in equimolar amount to sodium or potassium benzoate, with a molar ratio of sodium or potassium benzoate to water 1: (3.5-40), followed by sublimation of the obtained benzoic th acid at 95-127 ° C and a residual pressure of (5-7) * 10 * ³ mm Hg.