JP2002003458A - Method for producing formamide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing formamide with small, amount of impurities in high yield. SOLUTION: Methyl formate and ammonia are continuously fed to a reaction vessel to react them, and the reaction liquid is fed to a separation column of low boiling materials to distil off the low boiling materials from the overhead. The bottom product is taken out from the bottom, and fed to a separation column of high boiling materials. The objective formamide is distilled off from the overhead and the high boiling materials are taken off from the bottom. Methanol is added to a part or the whole of the resultant high-boiling materials, and the high-boiling materials with the added methanol are recycled to the reaction vessel and/or the separation column of the low boiling materials.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing formamide.

[0002]

2. Description of the Related Art Formamide is an industrially useful substance used as a raw material for organic synthesis, a raw material for pharmaceuticals and a solvent.

[0003] Several processes for producing formamide from methyl formate and ammonia have been disclosed. For example, JP-A-3-68544 discloses a method for producing formamide from methyl formate and ammonia using a basic catalyst. However, this method has a problem that formamide is hydrolyzed and formic acid, ammonia or ammonium formate is by-produced.

JP-A-57-150648 discloses a method of continuously producing formamide from methyl formate and ammonia while recovering methanol as a by-product. However, reduction of diformamide is disclosed. There is no mention of any measures. JP-A-6-34060
No. 1 discloses a method of reducing formaldehyde by producing formamide in the presence of at least 20% by weight of alcohol based on methyl formate, but a large amount of alcohol as a by-product must be added. Not efficient. Japanese Patent Application Laid-Open No. H11-124359 discloses a method for producing formamide by circulating a high-boiling component extracted from the bottom of a high-boiling separation column in the presence of ammonia in the presence of formamide. However, this method of simply circulating a part or all of the high-boiling components inevitably causes accumulation of high-boiling components during long-term operation, which is undesirable because it causes coloring and blockage.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the conventional method and to provide a method for producing high-purity formamide in a high yield.

[0006]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that high-purity formamide can be produced by adding methanol to a high-boiling component extracted from the bottom of a high-boiling separation column. The present invention has been completed.

That is, the present invention provides a method for producing formamide by reacting methyl formate with ammonia.
1) Methyl formate and ammonia are continuously supplied to a reaction tank to cause a reaction. 2) The reaction liquid is supplied to a low-boiling separation column to distill low-boiling components from the top of the column. 3) Formamide was distilled off from the top of the high-boiling separation column, high-boiling components were extracted from the bottom of the column, methanol was added to the high-boiling components, and then methanol was added. High boiling components in the reactor and / or
Or a method for producing formamide which is circulated and supplied to a low-boiling separation column.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the production method of the present invention will be specifically described. The molar ratio between methyl formate and ammonia is in the range of 0.5 to 2.0, preferably 0.7 to 2.0.
To 1.5, more preferably 0.85 to 1.1.
Supply in the range of 5. When the molar ratio is more than 2.0 or less than 0.5, it is not efficient and is not preferred. The reaction temperature ranges from 10 to 60C, preferably from 30 to 50C. Further, there is no need to use a catalyst, and the reaction is carried out without a catalyst.

The reaction liquid extracted from the reaction tank is supplied to the middle stage of a low-boiling separation column, and is distilled under normal pressure at a bottom temperature of 60 to 120 ° C. A low-boiling component containing methanol and / or methyl formate as a main component is distilled from the top of the column, and if necessary, supplied to a methanol recovery column. A liquid containing formamide as a main component is withdrawn from the bottom of the column and sent to a high-boiling separation column.

In this case, two low-boiling separation columns may be set in series. At this time, the liquid extracted from the bottom of the first low-boiling separation column is supplied to the middle stage of the second low-boiling separation column. In the second low boiling separation column, the pressure is 0.1 to 30 kPa, and the top temperature is 0 to 40.
Distillation is carried out at a temperature of 90 ° C. and a bottom temperature of 90 to 140 ° C. A low-boiling component containing methanol and / or methyl formate as a main component is distilled off from the top of the column, and is optionally supplied to a methanol recovery column. A liquid containing formamide as a main component is withdrawn from the bottom of the column and sent to a high-boiling separation column. When the low-boiling fraction obtained from the top of the low-boiling separation tower is supplied to the methanol recovery tower, methyl formate is distilled from the top of the methanol recovery tower, and methanol is extracted from the bottom of the tower. The methanol extracted from the bottom of the methanol recovery tower is added to part or all of the high-boiling components extracted from the bottom of the high-boiling separation tower.

In the high boiling separation column, the pressure is 0.01 to 7 kPa,
Distillation is performed at a top temperature of 90 to 110 ° C. and a bottom temperature of 100 to 140 ° C. to distill formamide from the top of the column and to extract high boiling components from the bottom.

The high-boiling components extracted from the bottom of the column contain trace amounts of impurities such as diformamide. When high-boiling components are circulated and supplied in the presence of diformamide, a compound insoluble in formamide is generated due to the reaction of cyclization with diformamide and formamide, which causes blockage in piping and the like. In the present invention, diformamide is reduced by adding methanol. As the methanol, a new raw material, a reaction solution containing methanol, a distillate containing methanol, or methanol recovered from a methanol recovery tower can be used. Since diformamide and methanol react rapidly at room temperature, there is no need to use a catalyst.
-Diformamide can be reduced without by-producing impurities such as methylformamide. The compounds formed by the reaction between diformamide and methanol are formamide and methyl formate, and do not affect the quality of formamide. Mixing high boiling point with methanol is 20-14
It is desirable to carry out at 0 ° C., preferably at 20 to 100 ° C. The amount of methanol to be added is 1 to 50 moles, preferably 2 to 30 moles, based on the amount of diformamide formed.

As described above, methyl formate and ammonia are simultaneously fed and continuously reacted, unreacted raw materials and methanol are separated by distillation, and the product formamide is distilled off from the top of the high-boiling separation column to obtain a high-form product. Methanol is added to part or all of the high-boiling components including diformamide extracted from the bottom of the boiling separation column and circulated and supplied to the reaction tank or the low-boiling separation column, so that formamide with a low impurity content such as diformamide is obtained. Can be obtained stably in high yield.

[0014]

The present invention will now be described in more detail with reference to Examples, but it should not be construed that the invention is limited thereto. Example 1 200 kg of formamide was charged at 40 ° C. and normal pressure, and the reaction solution was supplied at 155 kg / h while continuously supplying 120 kg / h of methyl formate and 35 kg / h of ammonia (molar ratio of ammonia / methyl formate = 1.03). And extracted continuously. The composition of the reaction solution three days after the start of the reaction in a steady state was formamide 57.4%, methanol 40.9%, ammonia 0.9%, methyl formate 0.8%, and diformamide 10 ppm or less. Was not found. This reaction liquid and 32 kg / h of circulating raw materials (formamide 98%, methyl formate 0.5%, water 0.01%, ammonium formate 0.12%, diformamide 0.15% and methanol 1.2%) were mixed. Was supplied to the middle stage of the first low-boiling separation column at 187 kg / h. Normal pressure, overhead temperature 56
° C, the bottom temperature is kept at 110 ° C, a low-boiling component containing methanol as a main component is distilled off from the top of the column, and a liquid containing formamide as a main component is withdrawn from the bottom at 132 kg / h. Supplied. The pressure of the second low boiling separation column was 10.7 kP.
a, keeping the tower top temperature at 13 ° C. and the tower bottom temperature at 110 ° C., distilling off low-boiling components mainly composed of methanol from the column top, extracting a liquid mainly containing formamide from the column bottom at 125 kg / h, The mixture was fed to a high boiling separation column. The high boiling separation column was operated at a pressure of 1.3.
kPa, tower top temperature 110 ° C, tower bottom temperature 120 ° C,
The product formamide was withdrawn at 84 kg / h from the top. The composition of the product formamide is 99.9 formamide
%, Methanol 0.005%, methyl formate, formic acid and diformamide were all 10 ppm or less. High boiling components were extracted from the bottom of the column at 41 kg / h. The composition of the high boiling point was formamide 94%, water 0.01%, ammonium formate 0.15% and diformamide 4.3%). Of the high-boiling components, 31 kg / h was distilled off from the top of the second low-boiling separation column to recover methanol liquid (methanol 9 / h).
(9.1%, methyl formate 0.9%) was mixed at 1 kg / h to obtain a circulating raw material. After two weeks of continuous operation, there was no operation trouble and no coloring was observed in the product formamide.

Example 2 A reaction was carried out in the same manner as in Example 1 under the conditions shown in Table 1. The composition of the obtained product formamide was 99.9 formamide.
%, Methanol 0.005%, methyl formate, formic acid and diformamide were all 10 ppm or less. 2
After continuous operation for a week, there was no operation trouble, and no coloring was observed in the product formamide.

Comparative Example 1 A reaction was carried out under the same conditions as in Example 1 except that no recovered methanol was added to the circulating raw material. One week later, the high-boiling circulation pump was blocked by the black clay-like substance, and the operation had to be stopped.

[0017]

[Table 1]

[0018]

Industrial Applicability According to the present invention, formamide containing less impurities can be produced in a high yield, which is of great industrial significance.

Claims (1)

[Claims] 1. A method for producing formamide by reacting methyl formate with ammonia, wherein 1) methyl formate and ammonia are continuously supplied to a reaction vessel to cause a reaction, and 2) a reaction solution is supplied to a low-boiling separation column. To distill low boilers from the top of the column, extract bottoms from the bottom and supply it to the high-boiling separation column. 3) Distill formamide from the top of the high-boiling separation column and A method for producing formamide, comprising extracting a boiling point, adding methanol to part or all of the high boiling point, and circulating the high boiling point to which the methanol has been added to a reaction tank and / or a low boiling point separation column. Method.