JPH0770036A - Purification of acrylonitrile - Google Patents

Abstract

PURPOSE:To efficiently purify an acrylonitrile recovered from a reactional system, esp. recovered acrylonitrile containing acids as impurities. CONSTITUTION:This purification can be accomplished by distilling an acrylonitrile recovered from a reactional system in an inert gas atmosphere containing 0.1-11vol.% of oxygen. By this method, the purification can be performed without the need for any expensive apparatus efficiently in a simple operation and in high recovery rate, even at relatively high temperatures.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for efficiently purifying acrylonitrile recovered from a reaction system, and more particularly to a method suitable for purifying acrylonitrile containing an acid as an impurity recovered from a reaction system. .

[0002]

BACKGROUND OF THE INVENTION Acrylonitrile is a highly toxic compound having a peculiar odor.
Acrylamido-2-methylpropanesulfonic acid, tert
-Used as an important raw material for the synthesis of various acrylamide derivatives represented by butyl acrylamide and diacetone acrylamide.

When synthesizing these compounds, acrylonitrile is often used in excess of the required amount as a synthetic raw material, and when an acid such as sulfuric acid is used in the other synthetic raw material or a catalyst for these synthetic reactions, By removing the target product from the reaction mixture after completion of the reaction, it is recovered as acrylonitrile containing an acid such as sulfuric acid or an organic acid as an impurity.

[0004] It is economically problematic to discard a recovery liquid containing acrylonitrile which can be used as a synthetic raw material at a high concentration, and the disposal of acrylonitrile reduces the toxicity of acrylonitrile and is safe. Since a great deal of labor and equipment are required for the waste treatment, it is strongly desired to provide a means for purifying the recovered liquid containing acrylonitrile in order to reuse it as a raw material.

[0005] As a method for purifying acrylonitrile recovered from the reaction system, for example, in Japanese Patent Publication No. 2-500188, a very small amount of water, which is a catalytic amount, is allowed to exist to neutralize acrylonitrile with a base to make it poorly water-soluble. A method is disclosed in which acrylonitrile is primarily purified by separating and removing a salt which is a solid, and the acrylonitrile is distilled under vacuum.

However, in the above-mentioned method, the primary purified acrylonitrile containing some impurities is used in a heat exchanger (under vacuum, at 172 ° F. or lower) and a thin film evaporator (under vacuum, at a temperature higher than the melting point of the substance). It is said that it must be handled at a relatively low temperature (172 ° F or less), but it is somewhat lower than that, for example 75 ° C.
Even when distilled at a heating temperature above (167 ° F),
Acrylonitrile may polymerize due to impurities remaining in acrylonitrile. To avoid this, for example, if the vacuum degree is about 320 mmHg, cooling water or brine is supplied to the condenser of the evaporator. The system is required, the apparatus is expensive, and the recovery rate of acrylonitrile is low, which is not an industrially advantageous method.

[0007]

DISCLOSURE OF THE INVENTION The present inventors have succeeded in efficient and high recovery of acrylonitrile recovered from a reaction system by a simple operation even at a relatively high temperature without using an expensive apparatus. The present invention has been completed by earnestly studying the method of purification by.

[0008]

According to the first aspect of the present invention, acrylonitrile recovered from a reaction system is mixed with oxygen at 0.1 vo
A method for purifying acrylonitrile, which comprises distilling in an inert gas atmosphere containing 1% to 11% by volume.

The second aspect of the present invention is to recover from the reaction system,
A method for purifying acrylonitrile, which comprises distilling acrylonitrile containing an acid as an impurity in an inert gas atmosphere containing 0.1 vol% to 11 vol% oxygen.

In a third aspect of the present invention, acrylonitrile containing an acid as an impurity recovered from the reaction system is brought into contact with a base and water, and the base is neutralized with the acid in the acrylonitrile to give water. After a soluble salt is formed and an aqueous layer containing the soluble salt is formed, the aqueous layer is separated and removed for primary purification, and oxygen is added in an amount of 0.1 vol% to 1%.
A method for purifying acrylonitrile, which comprises distilling the above-mentioned primary purified acrylonitrile in an inert gas atmosphere containing 1 vol%.

The recovered acrylonitrile targeted in the present invention is not particularly limited, and is acrylonitrile recovered from the reaction system after carrying out various synthetic reactions using acrylonitrile as a raw material or a solvent. Preferably, acrylonitrile recovered from the reaction system and containing an acid as an impurity, for example, acrylonitrile recovered from the synthesis of 2-acrylamido-2-methylpropanesulfonic acid, more preferably an acid as the impurity. Is an acrylonitrile after neutralizing acrylonitrile containing and separating the produced salt, particularly preferably, by contacting acrylonitrile containing an acid as an impurity recovered from the reaction system with a base and water, A water-soluble salt is produced by a neutralization reaction between the base and the acid in the acrylonitrile, and a water layer containing the salt is formed, and then the water layer is separated and removed to perform primary purification of acrylonitrile (hereinafter, referred to as Primary purified acrylonitrile)).

[0012] Acrylonitrile containing an acid as an impurity recovered from the reaction system has a high risk of causing a polymerization reaction during its distillation, and is suitable as an object of the present invention as described above. The present invention is effective when applied to.

The third invention, which is directed to the primary purified acrylonitrile, will be described in more detail below. In the acrylonitrile containing an acid as an impurity recovered from the reaction system, the acid is not particularly limited, but since it is particularly easy to make the neutralized salt water-soluble, the sulfonic acid group is Those having are suitable, and specific examples thereof include sulfuric acid and organic sulfonic acid.

The base for converting the acid into a neutral salt is not particularly limited, but a base forming a water-soluble salt by a neutralization reaction of acrylonitrile with an acid is particularly preferable. Examples include ammonia, sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate and the like. 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 primary purification of the above-mentioned recovered acrylonitrile, in order to smoothly proceed the neutralization reaction between the base and the acid which is an impurity in the acrylonitrile, a water-soluble salt produced by the neutralization reaction is added to the acrylonitrile layer. A sufficient amount of water must be contacted with the acrylonitrile to form an aqueous layer for extraction to the outside.

The contacting method is not particularly limited. For example, acrylonitrile may be mixed with water after or at the time of mixing the base, or a mixture of acrylonitrile and water may be mixed with the base in advance. It is also possible to prepare an aqueous solution and mix this aqueous solution of the base with the recovered acrylonitrile. Among these methods, the method using an aqueous base solution is particularly efficient and preferable.

The aqueous base solution may be prepared as described above before mixing with acrylonitrile, or may be prepared to have a desired concentration by adding water when mixing acrylonitrile and a base. Also, the preferred concentration of the base in the aqueous base solution consisting of the added base and water is 2 to 3
It is 0 wt%. A particularly preferable concentration may be appropriately adjusted depending on the type of base used, and is, for example, 5 to 10 wt% when an aqueous ammonia solution is used and 10 to 20 wt% when an aqueous sodium hydroxide solution is used.

If neutralization is performed using a high-concentration aqueous base solution, the progress of neutralization may be slow and the neutralized salt may precipitate as a solid. On the other hand, if neutralization is performed using a low-concentration aqueous base solution, the measured pH value may not be stable, and it may be difficult to accurately determine the end point of the neutralization reaction.

The amount of the base used for the neutralization reaction of acrylonitrile with an acid is most preferably equivalent to the acid in the acrylonitrile, but if it is in the range of 0.9 to 1.1 times the corresponding amount. , Can be fully effective.
The time required for neutralization varies depending on the base used, but is usually 1 to 5 minutes.

In a recovered acrylonitrile containing sulfuric acid as an acid, such as acrylonitrile recovered from a synthetic system of 2-acrylamido-2-methylpropanesulfonic acid, when an organic acid such as acetic acid or organic sulfonic acid coexists, a base is formed. Neutralization at the time of addition is promoted, and the neutralization can be completed in a short time. The preferable addition amount of the acid coexisting in acrylonitrile is 0.01 to 5 parts by weight per 100 parts by weight of acrylonitrile. If it is less than 0.01 part by weight, it may be difficult to sufficiently exert the neutralization promoting effect, and if it is added in excess of 5 parts by weight, the neutralization promoting effect does not change so much and the acid content is rather high. This is not preferable because it causes an inconvenience such as an increase in the required base amount.

In order to bring the recovered acrylonitrile containing an acid into contact with the base and water efficiently, a mixing tank having a stirrer may be used, or a tubular mixer such as a static mixer may be used. Good. By allowing the thus neutralized acrylonitrile to stand, an aqueous layer containing a water-soluble neutralizing salt is formed under the acrylonitrile layer,
By separating this from liquid, primary purified acrylonitrile from which the acid has been removed can be obtained.

The above method can be carried out in a continuous mode if desired. For example, in a reactor having a stirrer and a pH electrode, an acid-containing acrylonitrile and a base aqueous solution are introduced, these are sufficiently contacted and neutralized, and then the neutralized solution is transferred to a stationary container to form an aqueous layer. And acrylonitrile layer can be separated.

The water layer separated as described above can be directly supplied to a waste liquid combustion facility for combustion treatment, and after removing acrylonitrile contained in the water layer by distillation or the like, the components of the water layer are removed. Can also be treated in a wastewater treatment facility such as an activated sludge tank. Although the solubility of acrylonitrile in water is about 7 wt% at room temperature, when liquid-liquid separation is carried out by the method of the present invention, the concentration of acrylonitrile in the water layer slightly changes due to the influence of the dissolved neutralizing salt. , 2
It is 3 wt% and the loss of acrylonitrile due to the discard of the aqueous layer can be reduced.

In the present invention, the distillation of the recovered acrylonitrile is carried out in an inert gas atmosphere containing 0.1 vol% to 11 vol% of oxygen.

The content of oxygen in the inert gas is 0.
If it is less than 1 vol%, a polymer of acrylonitrile is produced, and if it exceeds 11 vol%, it may be a roaring mixture with acrylonitrile, which is not safe. The lower limit of the preferable oxygen content is 1 vol%.

Examples of the inert gas include nitrogen, helium, argon and the like, and nitrogen gas is particularly preferable in terms of price and the like. To mix a certain amount of oxygen with an inert gas,
It is preferable to mix the inert gas and air so that the oxygen has a predetermined content.

The method of introducing the atmospheric gas into the distillation system is not particularly limited, and for example, it may be introduced directly into the distillation vessel or may be an indirect method via a circulation pump or the like.

In the present invention, the heating temperature during distillation is 60.
℃ ~ 100 ℃ is preferable, more preferably 75 ℃ ~ 90
C., particularly preferably 80 to 90.degree. 60
If the temperature is lower than 100 ° C, the recovery rate of acrylonitrile may decrease, and if the temperature exceeds 100 ° C, a polymer may be produced.

The pressure in the present invention is preferably 330 Torr to normal pressure, more preferably 370 Torr to normal pressure. Also, for the condenser, cold water, for example, 15
It suffices to pass tap water of about ℃ to room temperature, especially about room temperature.

[0030]

EXAMPLES The present invention will be described more specifically with reference to Examples and Comparative Examples. Example 1 0.0 in which various organic sulfonic acids having 4 to 7 carbon atoms are mixed
8 wt.% In 500 g of acrylonitrile-containing recovery liquid containing 5 mol of organic sulfonic acid and 0.1 mol of sulfuric acid
% Aqueous ammonia solution 53 g (0.25 mol of ammonia)
Was added, and the mixture was stirred, stood still, and separated to obtain 490 g of primary purified acrylonitrile as an organic layer.

This layer was placed in a 1 liter distillation vessel,
Heat the distillation vessel to 85 ° C in an oil bath and use a condenser that passes tap water at 25 ° C, and add 7 vol% to the liquid phase.
Nitrogen containing oxygen was aerated at a flow rate of 20 liters / hour for 5 hours while performing distillation at normal pressure to recover 450 g of acrylonitrile. No polymer was observed in the analysis by high performance liquid chromatography of the liquid phase portion remaining in the container after completion of the distillation.

Example 2 Primary purified acrylonitrile 4 obtained in the same manner as in Example 1
90 g was placed in a 1-liter distillation vessel, the distillation vessel was heated to 80 ° C. in an oil bath, and a condenser in which tap water at 25 ° C. was passed was used to add nitrogen containing 3 vol% oxygen to the liquid phase part. While aerating at a flow rate of 10 liters / hour for 5 hours, distillation was performed at 400 Torr to recover 440 g of acrylonitrile. No polymer was observed in the analysis by high performance liquid chromatography of the liquid phase portion remaining in the container after completion of the distillation.

Example 3 480 g of primary purified acrylonitrile was obtained in the same manner as in Example 1 except that 133 g of a 15 wt% sodium hydroxide aqueous solution (0.5 mol of sodium hydroxide) was used as the basic aqueous solution instead of the ammonia aqueous solution.

The liquid was placed in a 1-liter distillation vessel,
The distillation vessel was heated to 75 ° C in an oil bath, and 10 vo was added to the gas phase using a condenser that passed cold tap water at 15 ° C.
Nitrogen containing 1% oxygen was aerated at a flow rate of 20 liters / hour for 5 hours while performing distillation at 350 Torr to recover 435 g of acrylonitrile. No polymer was observed in the analysis by high performance liquid chromatography of the liquid phase portion remaining in the container after completion of the distillation.

Comparative Example 1 Primary purified acrylonitrile 4 obtained in the same manner as in Example 1
90g was put in a 1 liter distillation vessel, the distillation vessel was heated to 85 ° C in an oil bath, and a condenser that passed 25 ° C tap water was used. Distillation was carried out at atmospheric pressure while aerating for a period of time to recover 415 g of acrylonitrile. 2 hours after the start of distillation, white turbidity occurred in the liquid phase, and the liquid phase remaining in the vessel after the distillation (including white turbidity) was analyzed by high performance liquid chromatography and infrared absorption analysis to confirm the polymer of acrylonitrile. did.

Comparative Example 2 Primary purified acrylonitrile 4 obtained in the same manner as in Example 1
90 g was put in a 1 liter distillation vessel, the distillation vessel was heated to 70 ° C. in an oil bath, and a condenser which passed through tap water at 25 ° C. was used. When distillation was carried out at 250 Torr while aerating for a time, only 400 g of acrylonitrile could be recovered. No polymer was observed in the analysis by high performance liquid chromatography of the liquid phase portion remaining in the container after completion of the distillation.

Comparative Example 3 Primary purified acrylonitrile 4 obtained in the same manner as in Example 3
80 g was placed in a 1-liter distillation container, the distillation container was heated to 75 ° C. in an oil bath, and a condenser that passed cold tap water at 15 ° C. was used.
When it was distilled at 350 Torr while aerating at a flow rate of 5 hours, only 405 g of acrylonitrile could be recovered. 3 hours after the start of distillation, white turbidity was observed in the liquid phase part, and the liquid phase part (including white turbidity) remaining in the container after the distillation was analyzed by high performance liquid chromatography and infrared absorption analysis to confirm the polymer of acrylonitrile. did.

Comparative Example 4 Primary purified acrylonitrile 4 obtained in the same manner as in Example 3
80 g was placed in a 1-liter distillation vessel, the distillation vessel was heated to 65 ° C. in an oil bath, and a condenser that passed cold tap water at 15 ° C. was used, and 20 liters of nitrogen was added to the gas phase portion.
When it was distilled at 250 Torr while aerating at a flow rate of 5 hours, only 390 g of acrylonitrile could be recovered. No polymer was observed in the analysis by high performance liquid chromatography of the liquid phase portion remaining in the container after completion of the distillation.

Comparative Example 5 480 g of acrylonitrile layer obtained in the same manner as in Example 3
In a 1-liter distillation container, heat the distillation container to 65 ° C. in an oil bath, and use a condenser through which a refrigerant of −5 ° C. is passed, and use nitrogen in the gas phase at a flow rate of 20 liters / hour. When the mixture was distilled at 250 Torr while aerating for a period of time, 435 g of acrylonitrile was recovered. No polymer was observed in the analysis by high performance liquid chromatography of the liquid phase portion remaining in the vessel after completion of the distillation.

[0040]

EFFECTS OF THE INVENTION According to the present invention, acrylonitrile recovered from a reaction system can be efficiently and highly recovered with a simple operation even at a relatively high temperature without using an expensive apparatus. As a result, there are immeasurable effects on the industry as an economical refining method.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Teruo Yoshida 1-1 Funami-cho, Minato-ku, Nagoya, Aichi Toagosei Chemical Industry Co., Ltd. Nagoya Research Institute

Claims (3)

[Claims] 1. A method for purifying acrylonitrile, which comprises distilling acrylonitrile recovered from a reaction system in an inert gas atmosphere containing 0.1 vol% to 11 vol% oxygen. 2. Acrylonitrile containing an acid as an impurity, which is recovered from the reaction system, is mixed with oxygen at 0.1 vol% to
A method for purifying acrylonitrile, which comprises distilling in an inert gas atmosphere containing 11 vol%. 3. A water-soluble salt is produced by contacting acrylonitrile, which contains an acid as an impurity, recovered from the reaction system with a base and water to neutralize the base and the acid in the acrylonitrile. After forming an aqueous layer containing this, the aqueous layer is separated and removed for primary purification, and the primary purified acrylonitrile is distilled in an inert gas atmosphere containing 0.1 vol% to 11 vol% oxygen. A method for purifying acrylonitrile, which comprises: