JPH05186410A - Method for purifying crude acetonitrile by extraction with caustic alkali - Google Patents

Abstract

PURPOSE:To prevent containers or pipes in an extraction step from being clogged and provide stable operation by suppressing the formation of an insoluble substance in crude acetonitrile in bringing the crude acetonitrile into contact with an aqueous solution of an alkali metallic hydroxide, dehydrating and purifying the crude acetonitrile. CONSTITUTION:Crude acetonitrile containing water and acrolein cyanohydrin and/or methacrolein cyanohydrin is brought into contact with an aqueous solution of an alkali metallic hydroxide to obtain acetonitrile containing water in a smaller amount than that in the crude acetonitrile. In the process, one or more compounds selected from ammonia, amines and salts thereof in a molar amount of 1-15 times, preferably 2-5 times based on the acrolein cyanohydrin and/or methacrolein cyanohydrin contained in the crude acetonitrile are previously made to coexist in the crude acetonitrile to suppress the formation of polymeric substances sparingly soluble in the crude acetonitrile. Thereby, industrially stable and continuous operation can be performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for dehydrating and refining crude acetonitrile containing water, achlorene cyanohydrin or methachloren cyanohydrin.

[0002]

General industrial acetonitrile produced in the petrochemical industry is obtained as a by-product, for example, in the process for producing acrylonitrile or methacrylonitrile by catalytic ammoxidation of propylene or isobutylene with ammonia and oxygen. The crude acetonitrile obtained as this by-product has many impurities.

The following methods have been conventionally proposed for separating and purifying impurities according to the desired use of acetonitrile. As a method of obtaining anhydrous acetonitrile, a method of removing water as a ternary mixture of acetonitrile-benzene-water by adding benzene (Japanese Patent Publication No. 3649/1985).
0), a method of converting existing hydrogen cyanide and cyanohydrin into sodium cyanide with sodium hydroxide, and then reacting with ferrous sulfate to form sodium ferrocyanide and removing it (JP-B-47-35416, JP-B-47-35416). JP-B-45-36490), and a method of removing by treatment with formalin and an equimolar amount of hydrogen cyanide and cyanohydrin (JP-A-48-81816, JP-A-50-25527). Water, crude acetonitrile containing acrylonitrile, alkali metal and ammonium hydroxide, ammonia and aliphatic amine 10-
A method for recovering pure acetonitrile by fractional distillation of a reaction mixture reacted at a temperature of 100 ° C. (JP-A-56-54)
49) is known.

[0004]

All of these methods use a distillation method to remove a large amount of water in crude acetonitrile, but they are not necessarily satisfactory in terms of energy consumption and purity of the purified product. It's not something that goes by. There is also known a method of removing hydrogen cyanide and water by contacting crude acetonitrile containing water and hydrogen cyanide with concentrated caustic (Japanese Patent Application Laid-Open No. 57-32259). When this method was applied to crude acetonitrile containing hydrin, a polymer was produced, which adhered to the container or piping and became clogged, making continuous operation impossible.

[0005]

Means for Solving the Problems That is, the present invention is to reduce the amount of crude acetonitrile containing water and achlorene cyanohydrin or metachlorene cyanohydrin by contacting it with an aqueous alkali metal hydroxide solution, and reducing the amount compared with the crude acetonitrile. The method for purifying crude acetonitrile is characterized in that crude acetonitrile is allowed to coexist with one or more of ammonia, amine and salts thereof in advance when obtaining acetonitrile containing a specified amount of water. In carrying out the present invention, crude acetonitrile is a by-product of the catalytic ammoxidation of propylene or isobutylene with ammonia and oxygen, for example for the production of acrylonitrile or methacrylonitrile, which produces water and Widely applied to including.

The composition of crude acetonitrile is, for example, 30% to 15% of water and 50% to 70% of acetonitrile on a weight basis.
%, Acrolen cyanohydrin and / or methacroleen cyanohydrin of 0.1% to 5% are applied, but not limited to this range. The ammonia used in the method of the present invention is gaseous ammonia or aqueous ammonia and ammonium salts.

As the ammonium salt, an ammonium salt of an inorganic acid represented by ammonium carbonate, ammonium sulfate, ammonium dihydrogen phosphate, etc., and an organic acid ammonium salt represented by ammonium acetate, ammonium oxalate, etc. are used. The amines used in the method of the present invention are primary and secondary amines. For example, amines such as methylamine, dimethylamine, ethanolamine, ethylenediamine, morpholine, diethanolamine, piperazine and the like, carbonic acid, hydrochloric acid, nitric acid,
It is a salt with an inorganic acid such as sulfuric acid or an organic acid such as acetic acid or oxalic acid. In carrying out the present invention, the method of adding ammonia, amine and a salt thereof to crude acetonitrile is not particularly limited, but for example, in the case of amine, ammonia which is a gas at room temperature, a known gas introduction method is adopted to absorb the gas. They may be added or added as an aqueous solution. The amine used in the present invention may be a single liquid or a mixed liquid containing a combination of different amines. The amount of ammonia, amine and salts thereof to be added to the crude acetonitrile in the present invention is 1 to 15 times mol of the contained acrolen cyanohydrin and / or methacroleen cyanohydrin. It is preferably used in a molar amount of 2 to 5 times. The temperature at which the crude acetonitrile is added and mixed is not particularly limited, and it can be carried out over a wide range of temperatures.
It is usually carried out at 5 ° C to 40 ° C, but can be changed up to 82.5 ° C which is the boiling point of acetonitrile.

In the method of bringing the crude acetonitrile into contact with the aqueous alkali metal hydroxide solution according to the present invention, it is necessary to preliminarily allow one or more of ammonia, amine and salts thereof to coexist in the crude acetonitrile. At this time, the effect of preventing the formation of the polymer cannot be expected even if ammonia, amine and salts thereof are added after bringing the crude acetonitrile into contact with the alkali metal hydroxide aqueous solution.

Sodium hydroxide is used as the alkali metal hydroxide. Sodium hydroxide is usually sufficient for the practice of the present invention when used as an aqueous solution containing 25 to 60% by weight. Temperature to contact with caustic is 5 ℃ to 60 ℃
Perform in the temperature range. It is preferably carried out at 15 to 40 ° C.

[0010]

The present invention will be described in detail below with reference to examples. In the examples, “part” means “part by weight” and “%” means “% by weight”.

[0011]

Example 1 An aqueous solution of cyanohydrin-containing acetonitrile having the following composition was prepared, and this solution was designated as solution A. Concentrated ammonia water (ammonia content 28%) was added to 7.2 g (2.0% as ammonia) per 100 g of the liquid A.
g) Add, stir at room temperature for 10 minutes, then stir and contact with 50 parts of 50% aqueous sodium hydroxide solution at room temperature for about 5 minutes, and then allow this mixture to pass through a glass filter and allow to stand. The phases were placed and the phases were separated. About 68 parts of aqueous phase and 64 parts of organic phase were recovered. The organic phase had the following composition: The amount of polymer attached to the filter was a trace amount.

[0012]

[0013]

[Example 2] An aqueous acetonitrile solution containing cyanohydrin having the following composition was prepared, and this solution was designated as solution B. The same operation as in Example 1 was performed except that the above solution B was used.
There was a trace amount of polymer attached to the filter.

[0014]

Examples 3 to 7 To 100 g of the liquid A prepared in Example 1, an amine or amine salt was added in advance, and the mixture was stirred at room temperature for 1 hour.
After stirring for 5 minutes and allowing to stand for 1 hour, the mixed solution which was contacted with 30 g of 50% aqueous sodium hydroxide solution at room temperature for 10 minutes was filtered through a glass filter to separate the amount of polymer adhering to the filter. Was measured. For Examples 6 to 7, the same operation as in the above Example was performed except that the solution B prepared in Example 2 was used. The results are shown in Table 1.

[0015]

Comparative Example 1 100 g of the solution A prepared in Example 1 was shaken with 30 g of a 50% aqueous sodium hydroxide solution at room temperature for 5 minutes, and then concentrated ammonia water (ammonia content 28%) was added to the mixed solution. 7.2 g (as ammonia 2.
0 g) and stirred at room temperature for 10 minutes, and the mixture was filtered through a glass filter. The amount of polymer attached to the filter was 80 mg.

[0016]

Comparative Example 2 100 g of the solution A prepared in Example 1 was shaken with 30 g of a 50% aqueous sodium hydroxide solution at room temperature for 5 minutes, and the mixed solution was filtered through a glass filter. The deposit on the filter was 120 mg.

[0017]

[Table 1]

[0018]

According to the method of the present invention, when the crude acetonitrile and the aqueous solution of the alkali metal hydroxide are contacted with each other, one or more of ammonia, amine and salts thereof are added in advance to dissolve the crude acetonitrile in the crude acetonitrile. It is possible to suppress the generation of volatile substances, and to operate stably without clogging in containers and pipes during the extraction process. As described above, the crude acetonitrile dehydrated and concentrated by the method of the present invention can be carried out by a number of methods obvious to those skilled in the art including extraction and / or distillation with a conventionally known salt aqueous solution.

Claims (1)

[Claims] 1. A crude acetonitrile containing water and achlorencyanhydrin and / or methacroleencyanhydrin is contacted with an aqueous alkali metal hydroxide solution to obtain acetonitrile containing a reduced amount of water compared to the crude acetonitrile. In this case, a method for purifying crude acetonitrile is characterized in that crude acetonitrile is allowed to coexist with one or more of ammonia, amine and salts thereof in advance.