JP3233226B2 - Purification method of acrylonitrile - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for efficiently purifying acrylonitrile containing an acid as an impurity.
It is useful as a method for purifying acrylonitrile waste liquid generated after performing various synthetic reactions using acrylonitrile as a raw material or a solvent.

[0002]

2. Description of the Related Art Acrylonitrile is a highly toxic compound having a peculiar smell, and is a compound of various acrylamide derivatives represented by acrylamide or 2-acrylamide-2-methylpropanesulfonic acid, tert-butylacrylamide, diacetone acrylamide and the like. It is used as an important raw material for synthesis. When synthesizing some of these compounds, acrylonitrile is used in excess of the amount required as a raw material for synthesis, and an acid such as sulfuric acid is used as another raw material for synthesis or as a catalyst. When the target product is removed from the mixture, acrylonitrile containing an acid such as sulfuric acid or an organic acid as an impurity (hereinafter referred to as acrylonitrile waste liquid) remains. In order to dispose of such acrylonitrile waste liquid, a great deal of labor and equipment are required to reduce the toxicity of acrylonitrile and safely dispose it, and a waste liquid containing acrylonitrile at a high concentration that can be used as a synthesis raw material is required. Since discarding is not economically desirable, it is desired to reuse it as a raw material. However, when the acrylonitrile waste liquid is reused as a raw material without purification, the purity of the product is reduced.

[0003] As a method of recovering acrylonitrile purified from acrylonitrile waste liquid, Japanese Patent Application Laid-Open No. Hei 2-500
No. 188, acrylonitrile waste liquid is neutralized with a base in the presence of a very small amount of water to form a salt which is a hardly water-soluble solid, which is mechanically separated and removed by centrifugation, filtration, sedimentation, etc. After that, a method of purifying acrylonitrile thus roughly purified by distillation has been proposed. However, in the above-mentioned method, since the generated salt takes in a base and inhibits the progress of neutralization, there is a problem that a base more than the theoretical amount required for neutralization is required and the neutralization speed is slow. Also, depending on the base, the salt produced by neutralization is viscous and tends to adhere to the walls of the mixing tank, making continuous practice substantially difficult,
It will be implemented by a batch method. As a result, the equipment used for neutralization is increased in size, and at the time of distillation, the impurity components of acrylonitrile supplied to the distillation process vary, so that the operating conditions are constantly checked to maintain the optimum operating conditions, A problem arises that must be changed.

[0004] Therefore, there has been a demand for a purification method capable of efficiently removing an acid as an impurity from an acrylonitrile waste liquid.

[0005]

SUMMARY OF THE INVENTION The present invention provides a method for efficiently purifying an acrylonitrile waste liquid by neutralizing an acrylonitrile waste liquid containing an acid as an impurity and removing a generated neutralized salt. is there.

[0006]

Means for Solving the Problems As a result of intensive studies on the above problems, the present inventors have neutralized acrylonitrile waste liquid with an aqueous solution of a base in which a neutralization salt formed by the neutralization reaction is soluble in water, and Layer and an aqueous layer containing a neutralized salt, and by separating the formed acrylonitrile layer and the aqueous layer into liquids, the progress of neutralization is facilitated, and the separation of the generated neutralized salt is facilitated. They have found and completed the present invention.

That is, the present invention relates to a method of forming a water layer containing a water-soluble salt formed by a neutralization reaction of acrylonitrile containing an acid as an impurity with a base and water, and the acid in the acrylonitrile. A method for purifying acrylonitrile, comprising separating and removing the aqueous layer.

Hereinafter, the present invention will be described in more detail. The acid in the acrylonitrile waste liquid used in the present invention is not particularly limited, but is preferably one having a sulfonic acid group because it is easy to make the neutralized salt water-soluble, and specifically, for example, sulfuric acid and organic sulfone. Acids and the like.

The base used in the present invention is not particularly limited as long as a salt formed by a neutralization reaction with an acid in acrylonitrile is soluble in water. Preferred examples include ammonia, sodium hydroxide, potassium hydroxide, and the like. There are sodium carbonate and potassium carbonate. Among these bases, ammonia and sodium hydroxide are particularly preferable bases because they can be obtained at low cost and can efficiently neutralize the acid in acrylonitrile.

In the purification method of the present invention, a water-soluble neutralized salt formed by the neutralization reaction is added to the acrylonitrile layer in order to smoothly progress the neutralization reaction between the acid and the base, which are impurities in acrylonitrile. It is necessary to contact a sufficient amount of water with acrylonitrile to form an aqueous layer to be extracted into acrylonitrile.

The method of contacting the acrylonitrile waste liquid with the base and water is not particularly limited. For example, water is mixed with the acrylonitrile waste liquid after mixing the base or when mixing the base (A), or the acrylonitrile waste liquid and water are mixed. A base may be mixed with the mixed solution (B), or an aqueous solution of the base may be prepared in advance, and the aqueous solution of the base may be mixed with the acrylonitrile waste liquid (C). Among these methods, the method (C) is particularly efficient and preferred.

As described above, the aqueous base solution may be prepared before mixing with the waste acrylonitrile solution, or may be adjusted to a desired concentration by adding water when mixing the waste acrylonitrile solution with the base. Also in the case of, the preferred concentration of the base in the aqueous base solution consisting of the added base and water is
2 to 30% by weight. A particularly preferable concentration may be appropriately adjusted depending on the type of the base to be used. For example, when an aqueous ammonia solution is used, the concentration is 5 to 10 wt%, and when an aqueous sodium hydroxide solution is used, the concentration is 10 to 20 wt%. When neutralization is performed using a high-concentration aqueous base solution, the progress of the neutralization may be slow, and the neutralized salt may precipitate as a solid and not form an aqueous layer. Conversely, if neutralization is performed using a low-concentration aqueous base solution, the pH measurement value will not be stable, and it may be difficult to accurately determine the end point of the neutralization reaction.
The use amount of the base is most preferably equivalent to the acid in the acrylonitrile waste liquid, but if it is in the range of 0.9 to 1.1 times the corresponding amount, there is no problem and the effects of the present invention are exhibited. be able to. The time required for neutralization varies depending on the base used, but is usually 1 to 5 minutes. If acetic acid or organic sulfonic acid is present in the acrylonitrile waste liquid, neutralization is promoted, and the neutralization can be completed in a short time. The preferred addition ratio of acetic acid or organic sulfonic acid to be present in the acrylonitrile waste liquid is 0.01 to 100 parts by weight (hereinafter simply referred to as "parts") of the acrylonitrile waste liquid.
5 parts. If it is less than 0.01 part, it may be difficult to sufficiently exert the neutralization accelerating effect, and even if it is added in excess of 5 parts, the neutralization accelerating effect does not change much, and the acid impurity content is rather increased. Therefore, it is not preferable.

In order to efficiently contact the acrylonitrile waste liquid with the base and water, a mixing tank having a stirrer may be used, or a tubular mixer such as a static mixer may be used. By leaving the neutralized acrylonitrile waste liquid in this manner, an aqueous layer containing a water-soluble neutralized salt is formed below the acrylonitrile layer, and the liquid is separated into liquid to obtain acrylonitrile from which the acid has been removed. Can be.

The purification method of the present invention can be carried out in a continuous mode, if desired. For example, in a reactor having a stirrer and a pH electrode, an acrylonitrile waste liquid and a base aqueous solution are introduced, and after sufficient contact and neutralization thereof, the neutralized liquid is taken out to a stationary container, whereby an aqueous layer is formed. It can be separated into acrylonitrile layers.

The aqueous layer separated as described above can be directly supplied to a waste liquid combustion facility for combustion treatment. Further, after acrylonitrile contained in the aqueous layer is removed by distillation or the like, the components of the aqueous layer are removed. Can be treated in a wastewater treatment facility such as an activated sludge tank. The solubility of acrylonitrile in water at room temperature is about 7 wt%. However, when liquids are separated by the method of the present invention, the concentration of acrylonitrile in the aqueous layer slightly changes due to the effect of dissolved neutralizing salts. , 2
Another feature of the present invention is that the content of acrylonitrile is 3 wt%, and the loss of acrylonitrile due to disposal of the aqueous layer can be reduced.

[0016]

The acrylonitrile waste solution containing an acid is neutralized with a base in the presence of a small amount of water, and the precipitated salt is mechanically removed by centrifugation, filtration, sedimentation, or the like. Requires an equivalent or more base. This is because the neutralization reaction proceeds on the surface of the base solid, and the generated salt covers the surface of the base solid. As in the present invention, when water sufficient to form an aqueous layer is added together with a base that forms a water-soluble neutralized salt, the generated neutralized salt dissolves in the aqueous layer, and neutralization proceeds smoothly. Therefore, neutralization is completed with a molar equivalent of base. Further, by removing the aqueous layer containing the neutralized salt by liquid-liquid separation, a complicated mechanical operation such as centrifugal separation becomes unnecessary, and the removal of the neutralized salt becomes extremely easy.

[0017]

EXAMPLES The present invention will be specifically described below with reference to examples. Example 1 To 1000 g of acrylonitrile waste liquid containing 0.1 mol of organic sulfonic acid in which 0.2 mol of sulfuric acid and organic sulfonic acid having 4 to 7 carbon atoms are mixed, 106 g of 8 wt% ammonia aqueous solution (0.5 mol of ammonia ) Was added and the pH was measured with stirring. The pH stabilized at 5.8 after 30 seconds. When the stirring was stopped and the mixture was allowed to stand, it was separated into an acrylonitrile layer and an aqueous layer after about 10 seconds, and acrylonitrile 97 from which sulfuric acid and organic sulfonic acid had been removed by liquid-liquid separation.
5 g were obtained.

Example 2 15 wt.
Acrylonitrile waste liquid was neutralized in the same manner as in Example 1 except that 133 g of a 0.1% aqueous sodium hydroxide solution (0.5 mol of sodium hydroxide) was used. The pH stabilized at 5.5 after 3 minutes. When the stirring was stopped and the mixture was allowed to stand, about 15 seconds later, it separated into an acrylonitrile layer and an aqueous layer, and 955 g of acrylonitrile from which sulfuric acid and organic sulfonic acid had been removed by liquid-liquid separation.
I got

COMPARATIVE EXAMPLE 1 18.5 g of calcium hydroxide was added to an aqueous ammonia solution.
25 mol) and 30 g of water, except that an attempt was made to neutralize the acrylonitrile waste liquid in the same manner as in Example 1. However, although the pH value increased to 2.5 after 15 minutes, the pH value did not change and neutralization was continued. Could not finish in a short time.

Comparative Example 2 28.0 g of calcium hydroxide was added to an aqueous ammonia solution (0.
38 mol) and 30 g of water, except that the procedure was as in Example 1. The pH stabilized at 6.2 after 11 minutes. When the stirring was stopped and the mixture was allowed to stand, a part of the generated neutralized salt adhered to the wall of the mixing tank and did not settle.

Example 3 32 g of an 8 wt% aqueous ammonia solution was added to 1000 g of acrylonitrile waste liquid containing 1.3 wt% of sulfuric acid and 0.1 wt% of acetic acid, and the pH was measured with stirring. Stabilized at 5.8.

Example 4 To 1000 g of acrylonitrile waste liquid containing 1.3 wt% of sulfuric acid and 0.1 wt% of acetic acid, 40 g of a 15 wt% aqueous sodium hydroxide solution was added, and the pH was measured with stirring. Stabilized at 5.8.

Example 5 The present invention was continuously carried out using a glass reactor equipped with a stirrer and an inlet tube and an outlet tube. The reactor has an inlet tube for the acrylonitrile waste liquid and the aqueous ammonia solution and a pH electrode, and the residence time is 2 minutes. Acrylonitrile waste liquid 100 containing 0.1 mol of organic sulfonic acid mixed with 0.2 mol of sulfuric acid and organic sulfonic acid having 4 to 7 carbon atoms
The solution was supplied at a ratio of 106 parts of an 8 wt% ammonia aqueous solution to 0 parts, and the pH was measured while stirring. pH 5.5
It was stable in the range of 5.8, and the neutralized liquid flowed out in a state where the aqueous layer was uniformly dispersed. No precipitation of the neutralized salt in the reactor or adhesion to the vessel wall was observed. The effluent was allowed to stand to separate into an acrylonitrile layer and an aqueous layer. By liquid-liquid separation, 976 parts of acrylonitrile from which sulfuric acid and organic sulfonic acid had been removed were obtained with respect to 1000 parts of supplied acrylonitrile waste liquid.

[0024]

The purification method of the present invention makes it possible to easily purify acrylonitrile containing an acid. It can be carried out continuously if desired, and the amount of acrylonitrile lost during purification is extremely small. It has the feature of being in a small amount, and has an immeasurable effect on the world as an economical method for purifying acrylonitrile.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References Special Table Hei 2-500188 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C07C 253/34 C07C 255/08

Claims (1)

(57) [Claims] An acrylonitrile containing an acid as an impurity is brought into contact with a base and water to produce a water-soluble salt by a neutralization reaction between the base and the acid in acrylonitrile, and to form an aqueous layer containing the salt. A method for purifying acrylonitrile, comprising separating and removing the aqueous layer after formation.