CS277227B6 - A process for obtaining arylamine from distillation residues after distillation or rectification of aryl isocyanates - Google Patents

Abstract

The distillation residue is subjected to decomposition with water at a temperature of 120 to 300 °C, optionally in the presence of acid or base, and the resulting arylamine is separated by distillation or rectification.

Description

The invention relates to a process for recovering arylamine from distillation residues after distillation or rectification of aryl isocyanates.

Aryl isocyanate is prepared by phosgenation of arylamine to give aryl carbamoyl chloride and decomposition to ryl isocyanate and hydrogen chloride. The preparation is usually carried out in an organic inert solvent such as toluene, chlorobenzene, xelene, so that the product in the first phase is a solution of aryl isocyanates in an organic inert solvent. For some other uses of aryl isocyanates in the chemical industry, distillation or rectification is required. The distillation product is a solution of aryl isocyanates in an organic inert solvent, the rectification product is an isolated aryl isocyanate. The advantage of obtaining isolated or distilled aryl isocyanates is, in addition to the improved quality of aryl isocyanates, the removal of small amounts of reaction off-gases, such as phosgene and hydrogen chloride, the presence of which in aryl isocyanates is unacceptable for some applications. The disadvantage of preparing distilled or rectified aryl isocyanates is the relatively low yield, which is usually 85 to 95% in the laboratory per aryl isocyanate used. This is due to the formation of high molecular weight substances in the boiler during distillation or rectification under reduced pressure. The distillation residue also contains by-products from phosgenation reactions. Isolation and disposal of very unpleasant distillation residues from distillation or rectification is difficult.

These disadvantages are largely eliminated by the process for treating distillation residues after distillation or rectification of aryl isocyanates prepared by phosgenation of the arylamine according to the invention. The essence consists in that the distillation residue after distillation or rectification of aryl isocyanates is hydrolyzed with water or an aqueous solution of acids such as hydrochloric, sulfuric, phosphoric or bases such as sodium, potassium, calcium hydroxide, at a temperature of 120 to

300 ° C to arylamine.

The decomposition reactions must be carried out in the presence of an amount of water which ensures the quantitative hydrolysis of the organic substances contained in the distillation residues to arylamine and carbon dioxide. The maximum amount of water is not limited except for the size of the reactor used. Water can also be used in the form of chemically or crystalline bound water-containing compounds, for example sodium carbonate decahydrate. The distillation residues can be used as such or in a mixture with an inert solvent. By the above-mentioned process, arylamine can be obtained not only from distillation residues from the current production, but also from distillation residues stored for a long time. After dewatering, the crude amine can be used as a valuable raw material in the chemical industry, for example again for the preparation of aryl isocyanates. It is far more advantageous to carry out the distillation or rectification of the crude arylamine. By choosing the rectification conditions, arylamine can be obtained in different quality depending on the requirements. The quality of the arylamine obtained is also affected by the quality of the starting arylamine used to prepare the arylamine. Distillation residues from the distillation or rectification of arylamine represent significantly lower amounts than the original residues from the distillation or rectification of aryl isocyanates. The reaction gas, which consists predominantly of non-toxic carbon dioxide, can optionally be collected, for example, in an absorption column which is sparged with sodium hydroxide solution. By discharging the reaction off-gas already during the reaction, it can be achieved

CS 277227 Ββ significant pressure drop during the reaction. Wastewater after obtaining crude arylamine can be used as a feedstock for other operations. To further illustrate the invention, the following examples are provided.

Example 1 - Preparation of m-tolyl isocyanate and m-toluidine

From a total batch of 10,920 g of a 40% solution of m-toluidine in chlorobenzene and 36,000 g of a 21% solution of phosgene, a total of 28,030 g of an 18.4% solution of m-tolyl isocyanate in chlorobenzene was prepared in a cascade of three stirred reaction flasks. yield 95% of theory on m-toluidine. The preparation of m-tolyl isocyanate was carried out under the following conditions: m-toluidine solution feed rate 364 g / h phosgene solution feed rate 1,200 g / h reaction flask temperature I (volume 0.25 L) 25-30 ° C reaction flask temperature II (volume 0.51) 80 to 85 ° C temperature in reaction flask III (volume 61) 130 ° C

In reaction flask I, the reaction mixture was stirred vigorously to ensure a smooth outflow of the reaction mixture. Reactors I and II operated continuously. After filling the reaction flask III, the dosing was stopped and excess phosgene and part of the chlorobenzene were distilled off from the reaction mixture. From the prepared m-tolyl isocyanate solution, it was first distilled off at a pressure of 1.33 via a rectification column with an efficiency of 10 theoretical plates. 10 ⁴ Pa and a temperature of 70 to 71 ° C at the top of the column and a reflux ratio L / D of 1: 1 chlorobenzene. After distilling off the chlorobenzene fraction, it was 2.7. At 10 Pa and 83 ° C and a L / D reflux ratio of 3: 1, pure m-tolyl isocyanate was distilled off. The rectification was terminated when m-tolyl isocyanate had stopped distilling. After completion of the rectification and aeration of the apparatus, the distillation residue was discharged from the boiler of the rectification column. A total of 4,540 g of isolated m-tolyl isocyanate with a content of 99.8% and 889 g of hot liquid was obtained, after cooling of the solid distillation residue. The distillation residue from the preparation of the isolated m-tolyl isocyanate was transferred to a pressure reactor, where 1,600 g of water had previously been introduced. After closing the reactor, the reaction mixture was heated to 185 ° C, where it was stirred for 2.5 hours. By venting the reaction off-gases during the reaction, a pressure of 2.5 MPa was maintained in the reactor. Then the reaction mixture was uniformly cooled to about 20 ° C. After separating the organic and aqueous layers in a separator, a total of 954 g of organic layer containing the remaining part of the non-separated water and 1190 g of aqueous layer was obtained, which was used as a feed in the following experiments. The crude arylamine-amine layer was charged to a distillation flask from which 15 theoretical efficiency was passed through a column

Excess water is distilled off on the floor and then at a pressure of 2.7. 10 Pa and a temperature of 100 ° C at the top of the column and a reflux ratio of about 2: 1, towards the end up to 10: 1, first 15 g of wet distillation precursor and then 585 g of m-toluidine with a content of 99.7% were obtained, with a content of 0 , 2% p-toluidine and 0.30% o-toluidine. Further, 176 g of a liquid distillation residue was obtained after cooling. A total of 4,368 g of m-toluidine, 4,540 g of isolated m-tolyl isocyanate and 585 g of m-toluidine were therefore obtained, which was used again to prepare a further 606 g of m-tolyl isocyanate.

Example 2 - Preparation of isolated m-tolyl isocyanate and m-toluidine

The preparation procedure was similar to Example 1, except that a solution of m-tolyl isocyanate in chlorobenzene was distilled off from the obtained solution of m-tolyl isocyanate in chlorobenzene on a continuously operating vacuum evaporator. Chlorobenzene was distilled off from this solution on another continuously operating column with an efficiency of 30 theoretical plates. The isolated m-tolyl isocyanate was obtained by continuous sampling from a column reboiler.

M-toluidine feed (99.9%) 4,700 g phosgene feed (100%) 8,640 g isolated m-tolyl isocyanate obtained 5,340 g m-tolyl isocyanate content 99.9% obtained distillation residues510 g water feed to pressure reactor heating time 180 ° C exposure time at 180 ° C maximum pressure in the reactor. Aqueous phase separation method A process for obtaining pure m-toluidine Pure m-toluidine with a content of 99.8% is obtained.

900 g

1.5 h, 1.5 h

6.1 MPa distilled off at a pressure of 8.0. 10 ³ Pa rectification at a pressure of 2.7. 10 ³ Pa

362 g

Example 3 - Preparation of isolated m-tolyl isocyanate and m-toluidine

7,000 g of water were added to the distillation residue from the rectification of m-tolyl isocyanate in an amount of 883 g, and after hydrolysis, m-toluidine was distilled off from a steam reactor. 605 g of m-toluidine with a content of 98.1% were obtained.

Example 4 - Preparation of isolated 3-chloro-4-tolyl isocyanate and 2-chloro-4-aminotoluene

From 1,000 g of distillation residues after rectification of 3-chloro-4-tolylisocyanate and 500 g of 10% sodium hydroxide solution, crude 2-chloro-hydride was prepared by hydrolysis at 190 ° C and 2.9 MPa for 3.5 hours. chloro-4-aminotoluene 19 g of distillation precursor containing predominantly p-toluidine and further 625 g of 2-chloro-4-aminotoluene containing 99.7%. Rectification was performed on a column with an efficiency of 10 theoretical plates at a pressure of 3.3. 10 ³ Pa and a vapor temperature at the top of the column of 133 to 134 ° C. The distillate was collected at a reflux ratio of L / D 5: 1.

The quality of the obtained 2-chloro-4-aminotoluene was as follows:

2-chloro-4-aminotoluene content diazotically: 99.7% p-toluidine content by gas chromatography: 0.2%

freezing point: 23 ° C water content: traces

From 600 g of the 2-chloro-4-aminotoluene thus obtained, 652 g of 3-chloro-4-tolyl isocyanate was further prepared in the form of a 17.1% solution in chlorobenzene. .

Example 5 - Preparation of m-toluidine from distillation residues after m-tolyl isocyanate

The procedure was the same as in Example 1, except that the decomposition of the distillation residues was carried out at a temperature of 125 to 135 ° C in the presence of 400 g of chlorobenzene and hydrochloric acid. The exposure time was 49 hours. Made in ampoules. A total of 1,600 g of 10% hydrochloric acid was added to 903 g of distillation residues. After hydrolysis and rectification, a total of 579 g of m-toluidine with a content of 99.8% was obtained.

Example 6 - Preparation of isolated m-tolyl isocyanate and m-toluidine

Decomposition of the distillation residues was performed by heating a mixture of water and distillation residues to 300 ° C, at which point the reaction mixture was exposed for 0.3 hours. After hydrolysis and rectification, 582 g of a major portion of m-toluidine with a content of 99.9% were obtained from 881 g of distillation residue.

Example 7 - Preparation of isolated m-tolyl isocyanate and m-toluidine

The procedure was similar to Example 1 except that the decomposition of the distillation residues was carried out for 7 hours at a temperature of 160 to 170 ° C. From 899 g of distillation residues, 598 g of m-toluidine with a content of 98.7% were obtained after hydrolysis and simple distillation under reduced pressure.

Example 8 - Preparation of 4-isopropylphenylisocyanate and 4-isopropylphenylamine

A total of 1,146 g of 100% 4-isopropylphenylisocyanate in the form of a 25% solution in chlorobenzene was prepared from 1000 g of 4-isopropylphenylamine in the form of a 30% solution in chlorobenzene and 1,480 g of phosgene in the form of a 20% solution in chlorobenzene.

4-Isopropylphenyl isocyanate with chlorobenzene was distilled off from the above solution on a vacuum evaporator. A total of 1,031 g of 100% 4-isopropylphenylisocyanate was obtained in the form of a 27.1% solution. Next, 165 g of distillation residue was obtained, which was charged with water to the autoclave. An additional 20 g of water was charged to the autoclave. After closing the autoclave, the mixture was heated to 190 ° C, at which point the reaction mixture was stirred for 0.5 hours. The pressure in the reactor was maintained at 2.9 MPa during the thermal exposure by discharging the reaction off-gas. Then, the reaction mixture was gradually cooled to 20 ° C. From the crude 4-isopropylphenylamine thus obtained, water was pressurized under distillation

O

5.33. 10 Pa and a vapor temperature at the top of the column with an efficiency of 20 theoretical plates distilled off at a reflux ratio L / D 5: 1 of about 10 g of distillation precursor, which was submitted as a batch to the next experiment for 4-isopropylphenylamine and 105 g of 4-isopropylphenylamine of the following quality. with a content of 99.8%. Furthermore, about 20 g of distillation residue were obtained.

Claims (1)

PATENT CLAIMS Process for obtaining arylamine from distillation residues after distillation or rectification of an aryl isocyanate prepared by phosgenation technology from arylamine, characterized in that the distillation residue after distillation or rectification of aryl isocyanate is hydrolyzed with water or aqueous acid, hydrochloric, sulfuric, phosphoric or basic hydroxides such as sodium, potassium hydroxide , calcium at a temperature of 120 to 300 ° C to an arylamine, which is subsequently purified by distillation or rectification.