The method of separation of benzoic acid from the product of liquid-phase oxidation of toluene

 

The invention relates to an improved method of extraction of benzoic acid from the product of liquid-phase oxidation of toluene by distillation, which consists in the fact that the rectification is carried out at a column of the periodic operation at a pressure of 100 mm RT. Art. in which after separation of the first fraction from a mixture of toluene and benzaldehyde add azeotropic separating agent - ndimethylacetamide, with sequential selection of the second fraction from a mixture of ndimethylacetamide and diphenyl when reflux from 57 to 66, the temperature of the top of the column from 153,7 to 162oWith over 3.5 and 5.6 h, an intermediate fraction containing benzoic acid and ndimethylacetamide, from the cube column at a temperature of 154-186,2oWith that return columns in the cube along with supplied azeotropic separating agent for further acceleration, and a third fraction of benzoic acid at reflux the number from 0.8 to 1.2 for 5 to 5.5 hours, and the selected second fraction from a mixture of ndimethylacetamide and diphenyl extracted with water at a temperature of from 20 to 22oWith the receipt of diphenyl in the form of crystals and an aqueous solution of ndimethylacetamide with a further selection by the distillation of ndimethylacetamide returned to the process. The method allows to increase the yield of benzoic acid, with">

The invention relates to chemical technology, and in particular to methods for the separation of industrial mixtures containing benzoic acid, and can be used in the technology of basic organic synthesis.

Liquid-phase oxidation of toluene with oxygen of air to form a product containing the target component - benzoic acid (Bq) and the number of components, such as toluene, benzaldehyde, diphenyl, benzyl benzoate and other Selection Bq limited by the presence of azeotropic mixtures of BC and diphenyl with a minimum boiling point.

A known method of separation of benzoic acid from the product of liquid-phase oxidation of toluene by distillation in two columns of continuous action, with the first column at atmospheric pressure to produce distillate toluene, benzaldehyde and the azeotropic mixture of BC and diphenyl that is returned in the process of liquid-phase oxidation of toluene. VAT residue of the first column refer to the second column, where under vacuum allocate Bq. VAT residue of the second column, containing, in particular, Bq and benzyl benzoate is a waste production (see Nazimok C. F., Ovchinnikov C. I., Newton C. M. Liquid-phase oxidation of alkylaromatic hydrocarbons. M.: Chemistry, 1987, 260 S., S. 135).

Ostrava hardly separated azeotropic mixture of BC and diphenyl, and as residue of the second column.

The closest in technical essence and the achieved result of the present invention (the prototype) is a method of separation of benzoic acid from the product of liquid-phase oxidation of toluene by distillation in five columns of continuous operation. The product of liquid-phase oxidation of toluene sent in the first column, where at atmospheric pressure produce toluene and VAT residue is served in a rotary film evaporator, in which the bleaching and cleaning of resin and catalyst slurry raw Bq. While not evaporated part of that is waste, burn, and clarified crude Bq sent to the second column, where at a pressure of 30 mm RT. Art. produce a distillate containing the benzaldehyde and the azeotropic mixture of BC and diphenyl, which is directed in the third column, where at a pressure of 30 mm RT. senior separated into a distillate benzaldehyde and VAT residue is a waste product, is not subject to disposal. VAT residue of the second column serves on the power of the fourth column, where at a pressure of 30 mm RT. senior separated into a distillate Bq and VAT residue containing BC and benzyl benzoate, served in the fifth column, where the pressure of 20-30 mm RT. senior allocate extra the cube selected clarified benzyl benzoate (see Popov D. M., Pavlova, I. S. Chemistry and technology of organic synthesis products. Proceedings of GIAP.-1972, vol.XV.-155 C.).

The disadvantages of this process are the losses Bq due to the formation hardly separated azeotropic mixture of BC and diphenyl, which is the waste production; high energy costs, due to the complexity of the technological process of selection Bq in five columns.

The invention solves the problem of increasing the output Bq, lowering energy costs, more marketable products - diphenyl.

To obtain such a technical result in the proposed method of separation of benzoic acid from the product of liquid-phase oxidation of toluene rectification is carried out at a column of the periodic operation at a pressure of 100 mm RT. Art. in which after separation of the first fraction from a mixture of toluene and benzaldehyde add azeotropic separating agent - ndimethylacetamide with sequential selection of the second fraction from a mixture of ndimethylacetamide and diphenyl when reflux from 57 to 66, the temperature of the top of the column from 153 to 162oWith over 3.5 to 5.6 h and the third fraction from BK at reflux the number from 0.8 to 1.2 in the course of from 5.0 to 5.5 h, and the selected second fraction and the e crystals and an aqueous solution of ndimethylacetamide with a further selection by the distillation of ndimethylacetamide, returned in the process.

The increase in the output Bq provided with the exception of education in the process of rectification is hardly separated azeotropic mixture of BC and diphenyl due to add in a column of the periodic steps after extraction of the first fraction separating azeotropic agent ndimethylacetamide with the formation of the azeotropic mixture of ndimethylacetamide and diphenyl, and the most complete exhaustion of Bq from the cube of the column due to the concentration therein of the high-boiling components within five razgonom in the process.

The reduction in energy costs due to simplification of the technological process that allows complete selection Bq rectification in the same column of the periodic action.

Get more product - diphenyl provided by adding to the column of periodic action after extraction of the first fraction separating azeotropic agent ndimethylacetamide and selection of the second fraction from a mixture of ndimethylacetamide and diphenyl, extraction which allows water to obtain diphenyl.

The invention is illustrated by a drawing, which shows a selection scheme Bq of product liquid-phase oxidation of toluene (see drawing).

oWith independent temperature control circuit (not shown) for preventing crystallization in him Bq.

The product of liquid-phase oxidation of toluene F refer to the cube of the column 1 of the periodic actions. The disbursement of the first fraction1carried out at the exit of the column 1 to the operating mode due to the fact that the condensation of vapor fractions of D1from a mixture of toluene and benzaldehyde occurs at a temperature below the temperature of the reflux condenser. These conditions allow the first fraction of D1not in the reflux condenser of the column and the condenser (not shown), located after it cooled brine. The selected fraction of D1from a mixture of toluene and benzaldehyde return in the process of liquid-phase oxidation of toluene.

After separation of the first fraction of D1in the cube column 1 add azeotropic separating agent ndimethylacetamide in an amount corresponding to the composition of the ndimethylacetamide-diphenyl at a pressure of 100 mm RT. century, in particular in the range from 17.7 to 25.0 kg Application ndimethylacetamide fewer than 17.7 kg will result is consistent, as unreasonably increases the cost of the extractant and energy cost allocation ndimethylacetamide extraction.

Followed by a sequential selection of the second fraction of D2from a mixture of ndimethylacetamide and diphenyl and third fractions of D3- benzoic acid.

The selection of the second fraction of D2optimally carried out at reflux the number from 57 to 66, the temperature of the top of the column from 153.7 to 162.0oWith over 3.5 to 5.6 hours Allocation under reflux number less than 57, the temperature of the top of the column is less 153.7oWith in less than 3.5 hours will decrease the yield of the target Bq due to the formation hardly separated azeotropic mixture of BC and diphenyl, and at reflux more than 66, the temperature of the top of the column more 162.0oWith over 5.6 h to increasing energy costs and the duration of the allocation fraction, and the temperature of the top of the column is connected with the pressure, reflux ratio and depends on the composition of the vapor distillate.

For complete exhaustion of ndimethylacetamide from the cube columns 1 select the intermediate fraction containing ndimethylacetamide and BC, which return to the cube of the column 1 together with supplied azeotropic separating agent ndimethylacetamide subsequent rectification.

The allocation of third frisle less than 0.8 will deteriorate the quality of BC due to pollution benzyl benzoate, and at reflux more than 1.2 will increase the energy cost allocation Bq.

Selected second fraction of D2from a mixture of ndimethylacetamide and diphenyl after each pickup direct the holding tank (not shown), and then extracted with water at a temperature of from 20 to 22oWith the extractor 2 with obtaining diphenyl in the form of crystals and an aqueous solution of ndimethylacetamide. The temperature of extraction is equal 20-22oC is optimal, since under these conditions the solubility of ndimethylacetamide in water 97.5 g/100 ml, and the insoluble diphenyl (see Reference chemist. T2. -SPb, Goskomizdat, 1963, 1168 S., S. 453, 654).

Obtained in the form of crystals of diphenyl subjected to drying and stockpiling as additional marketable product that has the quality that meets the requirements of GOST 4254-87 "Diphenyl technical".

Of an aqueous solution of ndimethylacetamide distillation in distant cube 3 allocate ndimethylacetamide, which return in the process, directing in column 1 of the periodic steps in the subsequent distillation, and steam, which is condensed and cooled to a temperature of 20oWith directing the formed water in the extractor 2.

After holding the pickup VAT residue column 1 of the periodic action contains Bq and wysokosc the ez unload VAT residue. For each of the evaporating device number cube initial load of the column 1 is constant, but increases as the number of razgonom in each subsequent load changes the ratio of the components is determined by the reduction in the content of Bq and increase high-boiling components, in particular benzyl benzoate, the amount of which in the fifth rectification will be not less than 10 wt.% from VAT residue.

This VAT residue is the only production waste and sent for incineration.

Example 1 (the optimal values of the parameters - azeotropic separating agent ndimethylacetamide). The product of liquid-phase oxidation of toluene served in the cube column of the periodic actions in the number of 3900 kg composition: Bq - 94.20 wt. % toluene - 3.00 wt.%, the benzaldehyde - 0.60 wt.%, diphenyl - 0.20 wt.%, the benzyl benzoate - 2.00 wt.%. When the diameter of the column, equal to 400 mm, the amount of steam flow will be 8.0 KMOL/h Efficiency of the column is 30 theoretical plates, a pressure of 100 mm RT. Art. the temperature of the top of the column is equal to 125oC.

The disbursement of the first fraction from a mixture of toluene and benzaldehyde carried out at the exit of the column on the operating mode. At a pressure of 100 mm RT. senior pairs of toluene and benzaldehyde have a temperature equal to, respectively 51.5 him and the cooled brine. The first fraction is returned to the process of liquid-phase oxidation of toluene.

After extraction of the first fraction in the amount of 140 kg in the column remains in the mixture in an amount 3760 kg composition: Bq - 97.71 wt.%; diphenyl - 0.21 wt.%; the benzyl benzoate - 2.08 wt.%. Cube add columns separating azeotropic agent ndimethylacetamide in 20 kg. quantity of the mixture, then in Cuba columns will be 3780 kg composition: Bq - 97.19 wt.%; the ndimethylacetamide - 0.53 wt.%; diphenyl - 0.21 wt.%; the benzyl benzoate - 2.07 wt.%.

The selection of the second fraction from a mixture of ndimethylacetamide and diphenyl carried out at a temperature of the top of the column 153.7oWith the number 26 kg composition: ndimethylacetamide - 70.00 wt.%, diphenyl - 30.00 wt.%, reflux the number 60 for 3.9 hours

For complete exhaustion of ndimethylacetamide from the cube column at a temperature of from 155.0 to 186.2oWith select in the amount of 6.5 kg intermediate fraction from a mixture of ndimethylacetamide and BC, in which the content of Bq is 72.31 wt.%. The intermediate fraction is returned to the cube of the column together with supplied azeotropic separating agent ndimethylacetamide subsequent rectification.

The selection of the third fraction of the BC carried out at a temperature 186.2oWith, reflux 1 within 5.05 including the Number of Bq will be 3365 kg

Selected second practice the ndimethylacetamide extracted with water at a temperature of 20oWith the extractor. The amount of extractable mixture will be 130 kg, the amount of extractant (water) - 95 kg the result is a diphenyl in the form of crystals in the amount of 39 kg, which is dried and warehoused, as more marketable product that meets the requirements of GOST 4257-87 "Diphenyl technical and 186 kg of the extract is an aqueous solution of ndimethylacetamide, containing 51.05 wt.% water and 48.95 wt.% the ndimethylacetamide.

From 186 kg of an aqueous solution of ndimethylacetamide distillation in distant Cuba allocate ndimethylacetamide in the amount of 91 kg, which is sent to the column in the subsequent distillation, and steam, which is condensed and cooled to a temperature of 20oWith directing the formed water in the extractor.

After five razgonom output Bq will be 16825 kg or 96.3% of theoretically possible amount of waste equal to 380 kg or 2.10% of the total product of liquid-phase oxidation of toluene, the number of ndimethylacetamide, regenerated and returned to the process, will be 91 kg, and the obtained diphenyl - 39 kg

The total time of one pickup of the product liquid-phase oxidation of toluene will be 18.2 hours

Example 2 (lower bound parameters - azeotropic separating agent ndimethylacetamide). The product of liquid-phase oxidation of toluene is subjected to rectification by the use of the process and the disbursement of the first fraction from a mixture of toluene and benzaldehyde, but after extraction of the first fraction in the cube add columns separating azeotropic agent ndimethylacetamide in the amount of 17.7 kg quantity of the mixture, then in Cuba columns will be 3777.7 kg composition: Bq - 97.25% by weight, the ndimethylacetamide - 0.47 wt.%, diphenyl - 0.21 wt.%, the benzyl benzoate - 2.07 wt.%.

The selection of the second fraction from a mixture of ndimethylacetamide and diphenyl carried out at a temperature of the top of the column 162.0oWith the amount of 24.2 kg composition: ndimethylacetamide - 67.77 wt.%, diphenyl - 32.23 wt.%, reflux the number 66 for 5.6 hours

For complete exhaustion of ndimethylacetamide from the cube column at a temperature of from 163.0 to 186.2oWith select in the amount of 6.9 kg intermediate fraction from a mixture of ndimethylacetamide and BC, in which the content of Bq is 81.00 wt.%. The intermediate fraction is returned to the cube of the column together with supplied azeotropic separating agent ndimethylacetamide subsequent rectification.

The selection of the third fraction of BC is carried out at reflux the number 1 for 5.5 hours, the Number of Bq will be 3365 kg

Selected second fraction from a mixture of ndimethylacetamide and diphenyl after each pickup guide in cumulative capacity. Then extracted with water at a temperature of 20oWith the extractor. The amount of extractable mixture will be 121 kg, the amount of EC is more marketable product, meets the requirements of GOST 4254-87 "Diphenyl technical and 174 kg of the extract (aqueous solution of ndimethylacetamide, containing 52.88 wt.% water and 47.12 wt.% the ndimethylacetamide.

From 174 kg of an aqueous solution of ndimethylacetamide distillation in distant Cuba allocate ndimethylacetamide in the amount of 82 kg, which return in the process, sending a column in the subsequent distillation, and steam, which is condensed and cooled to a temperature of 20oWith directing the formed water in the extractor.

The output Bq after five razgonom similar to example 1. The concentration of high-boiling components (in particular benzyl benzoate) in Cuba columns is carried out as in example 1.

Example 3 (upper bound parameters - azeotropic separating agent ndimethylacetamide). The product of liquid-phase oxidation of toluene is subjected to rectification in the same way as in example 1, with the same number of the original product, options, columns, parameters of the process and highlight the first fractions of toluene and benzaldehyde. After separation of the toluene and benzaldehyde in the cube column serves separating azeotropic agent ndimethylacetamide in the amount of 25 kg quantity of the mixture, then in Cuba columns will be 3785 kg composition: Bq - 97.06 wt.%; the ndimethylacetamide - 0.66 mA is estlat at reflux 57, the temperature of the top of the column 154.0oWith the number of 31.3 kg composition: ndimethylacetamide - 75.08 wt.%; diphenyl - 24.92 wt.%; reflux the number 66 for 5.6 hours

For complete exhaustion of ndimethylacetamide from the cube column at a temperature of from 154.0 to 186.2oWith select in the amount of 5.2 kg intermediate fraction from a mixture of ndimethylacetamide and BC, in which the content of Bq is 71.15 wt.%. The intermediate fraction is returned to the cube of the column together with supplied azeotropic separating agent ndimethylacetamide subsequent rectification.

The selection of the third fraction of BC is carried out at reflux the number 1 for 5.5 hours, the Number of Bq will be 3365 kg

Selected second fraction from a mixture of ndimethylacetamide and diphenyl after each pickup guide in cumulative capacity. After the fifth pickup the ndimethylacetamide extracted with water at a temperature of 20oWith the extractor. The amount of extractable mixture will be 156.5 kg, the amount of extractant (water) - 130 kg the result is 39 kg of diphenyl in the form of crystals which are dried and warehoused as a more marketable product that meets the requirements of GOST 4254-87 "Diphenyl technical and 247.5 kg of the extract (aqueous solution of ndimethylacetamide, containing 52.52 wt.% water and 47.48 wt.% the ndimethylacetamide.

From 247.5 kg of an aqueous solution upravlja in the column for subsequent rectification, and steam, which is condensed and cooled to a temperature of 20oWith directing the formed water in the extractor.

The output Bq after five razgonom similar to example 1. The concentration of high-boiling components (in particular benzyl benzoate) in Cuba columns is carried out as in example 1.

Thus, the use of the present invention will increase the output Bq, reduce energy costs, to get a more marketable product - diphenyl, reduce emissions into the environment.

Claims

The method of separation of benzoic acid from the product of liquid-phase oxidation of toluene by distillation, characterized in that the distillation is carried out at a column of the periodic operation at a pressure of 100 mm RT. Art. in which after separation of the first fraction from a mixture of toluene and benzaldehyde add azeotropic separating agent - ndimethylacetamide, with sequential selection of the second fraction from a mixture of ndimethylacetamide and diphenyl when reflux from 57 to 66, the temperature of the top of the column from 153,7 to 162oWith over 3.5 and 5.6 h, an intermediate fraction containing benzoic acid and ndimethylacetamide, from the cube column at a temperature of 154-186,2oWith that return in kubanskiej acid at reflux the number from 0.8 to 1.2 for 5-5,5 h, moreover, the selected second fraction from a mixture of ndimethylacetamide and diphenyl extracted with water at a temperature of from 20 to 22oWith the receipt of diphenyl in the form of crystals and an aqueous solution of ndimethylacetamide with a further selection by the distillation of ndimethylacetamide returned to the process.

 

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EFFECT: improved preparing method.

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EFFECT: improved method of synthesis.

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EFFECT: improved method of synthesis.

5 ex

FIELD: organic chemistry, chemical technology.

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EFFECT: improved method of synthesis.

39 cl, 11 ex

FIELD: industrial organic synthesis.

SUBSTANCE: invention relates to a process for production of C2-C4-alkane into alkene and carboxylic acid and immediately using them in ester synthesis stage. According to invention, to produce alkyl carboxylate, in particular ethyl acetate, or alkenyl carboxylate, in particular vinyl acetate, stage wherein alkane is oxidized to corresponding alkene and carboxylic acid is combined with alkenyl carboxylate or alkyl carboxylate production stage. Process comprises contacting of alkane- and alkene-containing gas raw material with molecular oxygen and catalyst in the first oxidation reaction zone, catalyst being efficient in oxidation of alkane into corresponding alkene and carboxylic acid. In the second reaction zone, part of streams isolated in separation stage and enriched with alkene and carboxylic acid is brought into contact with at least one catalyst efficient to produce either alkyl carboxylate or alkenyl carboxylate in presence of oxygen-containing gas. For example, first product stream consists of ethylene and acetic acid with water admixture. In the second reaction zone, stream enriched with alkene and carboxylic acid comes into contact with oxygen, optionally in presence of additional amount of ethylene and/or acetic acid from the first product stream. As a result, second product stream comprising vinyl acetate, water, acetic acid, and optionally small amounts of carbon oxides is obtained. Second product stream is separated into fractions containing vinyl acetate and acetic acid, which are subjected to further purification. In a cycle wherein acetic acid from main fraction is regenerated, the latter is recycled to vinyl acetate stage in the second reaction zone.

EFFECT: improved economical efficiency of process.

36 cl, 1 dwg

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