JPH0770079A - Method for recovering 1,3-dimethyl-2-imidazolidinone - Google Patents

Abstract

PURPOSE:To provide a method for recovering 1,3-dimethyl-2-imidazolidinone by a simple operation efficiently and in high recovery ratio. CONSTITUTION:In distilling and purifying hydrous 1,3-dimethyl-2-imidazolidinone, a solvent to form an azeotropic composition with water is added to 1,3- dimethyl-2-imidazolidinone and a distillation column having two or more theoretical stages is used. A distilled liquid is separated into a water phase and an oil phase, the water phase is removed out of the system and the oil phase is returned to the top of the distillation column and dehydrated and distilled. After distillation of water is completed, the solvent added by ordinary distillation operation is distilled and removed and 1,3-dimethyl-2-imidazolidinone is next distilled to recover 1,3-dimethyl-2-imidazolidinone.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recovering DMI from a solution of water-containing 1,3-dimethyl-2-imidazolidinone (hereinafter abbreviated as DMI) after a chemical reaction or the like.

More specifically, a solvent for forming an azeotropic composition is added to water-containing DMI and distilled using a distillation column having several stages, and water is distilled out of the system together with the added solvent. Relates to a method for recovering DMI, which comprises returning the solvent from the top of a distillation column into the system, distilling off the added solvent, and distilling DMI off.

[0003]

2. Description of the Related Art DMI is used as a solvent in a wide range of fields because it has excellent dissolving power and stability for various inorganic and organic compounds.

However, since DMI has a strong hygroscopic property, DMI
When using as a solvent, when recovering and reusing,
Often it is necessary to remove water. Especially when using DMI as a solvent in a chemical reaction, DM with a low water content
Quality of I is often required.

On the other hand, since DMI and water can be mixed at an arbitrary ratio, a method of discharging the reaction liquid containing DMI to water after completion of the reaction and separating DMI and inorganic salts to the water phase side is often used. Yes, it becomes more difficult to collect.

The present invention relates to DM used in such a reaction.
The present invention relates to a method for recovering DMI from solution I by a simple operation using a simple device, efficiently and with a high recovery rate.

Conventionally, in order to remove water from hydrous DMI to obtain DMI, a method of directly distilling and purifying using a distillation column having 10 or more stages has been generally used.

[0008]

However, in the conventional method, in order to ensure the quality of the recovered DMI having a water content of 300 ppm or less, it is necessary to set the reflux ratio to 5 or more in a distillation column having 10 or more plates. There is.

Therefore, the construction cost of the distillation apparatus is high, the operation management is complicated, and the DMI loss is large in order to reduce the water content, so that it is not satisfactory in the industrial implementation. It was

[0010]

Means for Solving the Problems The inventors of the present invention have made earnest studies in order to solve the above problems, and finally arrived at the present invention.

That is, according to the present invention, a solvent for forming an azeotropic composition with water is added to water-containing DMI, and the mixture is distilled using a distillation column having several stages, and water is distilled out of the system together with the added solvent. Then, the solvent is returned from the top of the distillation column into the system, and the added solvent is distilled off, and then DMI is distilled off.

The present invention is suitable for recovering DMI from hydrous DMI used for reaction, extraction, purification by recrystallization and the like. The number of stages of the distillation column used in the present invention is suitably 2 to 5, preferably 2 to 3. The simple distillation does not sufficiently exhibit the above effect, and even if the number of stages is 5 or more, the distillation effect does not change, the construction cost is only increased, and it is economically disadvantageous.

Any solvent having a boiling point lower than that of DMI can be used as a solvent for forming an azeotropic composition with water used in the present invention. Examples of such a solvent include toluene,
Aromatic compounds such as benzene, m-xylene, styrene, ethylbenzene, cyclohexane, n-hexane,
Aliphatic hydrocarbon compounds such as heptane, octane and dodecane, dichloromethane, 1,2-dichloroethane,
Chlorine-based compounds such as 1,2-dichloroethylene and chlorobenzene may be used.

The amount of the solvent added is 30 to 300 parts by weight, preferably 50 to 20 parts by weight, relative to 100 parts by weight of DMI.
0 parts by weight is suitable. If the amount is less than 30 parts by weight, the above effects of the present invention cannot be sufficiently obtained. Further, even if it is more than 300 parts by weight, the effect does not change and the amount of distillation treatment increases, which is economically disadvantageous.

The addition amount of the above-mentioned solvent indicates the ratio in batch distillation. At the time of continuous distillation, the solvent is first charged to the distillation pot in the above proportion, and it is not necessary to add the solvent to DMI continuously supplied later. Although the same effect can be obtained by batch distillation or continuous distillation, continuous distillation is preferable because the amount of total solvent added is small.

The distillation can be carried out under either normal pressure or reduced pressure. The preferred embodiments of the present invention are as follows. a) Water-containing DMI and the above-mentioned solvent are added in the above-mentioned proportions, and distilled using a distillation column having the above-mentioned number of plates. Discharge to the outside of the system. b) The solvent is recycled from the top of the distillation column back into the system. c) After the completion of dehydration, the added solvent is distilled off. d) Next, DMI is distilled off to obtain DMI.

As described above, according to the present invention, when the added solvent is returned to the system, it is simply returned to the top of the distillation column to prevent DMI from distilling and reduce the number of distillation columns to several stages.

Further, unlike the conventional method, it is not necessary to build a tower of 10 stages or more and to set a large reflux ratio, the construction cost of the distillation apparatus can be kept low, and the distillation operation is simple. Moreover, DMI can be collected efficiently, which is very useful.

By recovering DMI by the method of the present invention, a DMI recovery rate of 90% or more can be achieved, and the DMI loss is reduced as compared with the conventional method.

[0020]

EXAMPLES In order to describe the present invention more specifically, examples and comparative examples will be described below, but the present invention is not limited to these examples. Example 1 FIG. 1 shows a schematic diagram of an apparatus for carrying out the present invention. DMI4
DMI was recovered from a DMI containing 2.6% by weight of water.
Water-containing DMI 140kg, azeotropic solvent toluene 100kg
Is charged in the distiller 1 in the figure. Further hydrous DMI580
kg is continuously fed at a rate of 50 l / hr during dehydration. The azeotropic liquid of toluene and water is distilled off under normal pressure. The distillate is left to stand in the separator of 4 and separated into water and toluene, the water in the lower layer is discharged, and the toluene in the upper layer returns to the top of 2 due to overflow. Dehydration is continued even after the supply of the raw materials is stopped, and the completion of dehydration is confirmed by the tower top temperature reaching the boiling point of toluene. 383.3 kg of water was distilled off. Then, toluene is distilled off under a reduced pressure of 100 mmHg.
71.1 kg of toluene was distilled off. When the distillation of toluene has stopped, the degree of vacuum is set to 30 mmHg and the distillate is cut during this period. First distillation cut 56.5 kg. The temperature is further raised and DMI is distilled off at 120 ° C. As a result, 254.6 kg of DMI having a water content of 300 ppm was obtained. The DMI recovery rate is 83.0% because there is 0.1% DMI in the waste water, 9.0% in toluene, and 7.9% in the bottom of the kettle. When the residual loss is recovered in the next batch, the recovery rate is improved to 99.0%.

Comparative Example 1 Water-containing DMI was directly distilled using a column corresponding to 10 plates to separate water and DMI. DMI 35.9 of the same type as in Example 1
DMI was recovered from DMI containing water by weight. 111
Charge 22.8 g of water-containing DMI and add 61% of water as the first distillation.
92.9 g was distilled. All was distilled off when the first distillation was cut. Further, 194.2 g of middle distillate was distilled out. The reflux ratio was 5 at the time of middle distillation. The middle distillate contains 98.6% by weight of DMI, which is a loss of 4.8% relative to the charge. As a result, the DMI that can be recovered as the main distillate is 3223.7.
The recovery rate is 80.7%, and when the middle distillate is recovered in the next batch, the recovery rate becomes 85.5%. The water content in the obtained DMI is 400 ppm.

[0022]

As is apparent from the examples, the method of the present invention can recover and purify DMI efficiently with a simple operation of returning the distilling solvent from the top of the distillation column into the system. , Unlike the conventional method, it is not necessary to build a tower of 10 stages or more, and it is possible to distill with several distillation columns, the construction cost of the distillation apparatus can be kept low, and the distillation of DMI to water is further reduced. And a recovery rate of 90% or more can be achieved.

[Brief description of drawings]

FIG. 1 is a schematic view of a distillation / purification device used in Example 1 of the present invention.

[Explanation of symbols]

 1. Distiller 2. Distillation tower 3. Condenser 4. Separator

Claims (1)

[Claims] 1. When distilling and refining hydrous 1,3-dimethyl-2-imidazolidinone, a solvent that forms an azeotropic composition with water is added, and distillation is performed using a distillation column having two or more theoretical plates. The resulting liquid is separated into an aqueous phase and an oil phase, the aqueous phase is removed from the system, the oil phase is returned to the top of the distillation column for dehydration distillation, and is added by a normal distillation operation after the completion of water distillation. The method for recovering 1,3-dimethyl-2-imidazolidinone, which comprises distilling and removing the above-mentioned solvent and further distilling 1,3-dimethyl-2-imidazolidinone.