JPH02193967A - Recovery of pyridine - Google Patents

Abstract

PURPOSE:To recover pyridine from waste liquid on commercial base in high efficiency by using a neutralization step of acetic acid, etc., with an inorganic alkali salt, an azeotropic distillation step of pyridine and water, a salting-out step of pyridine in the azeotropic distillate and a distillation step of the salting- out product. CONSTITUTION:Pyridine having high quality and suitable for the use as a reaction medium or raw material for pharmaceuticals is recovered in high recovery from a waste liquid containing at least pyridine, acetic acid or acetic anhydride, organic silicon compound and inert organic solvent by using the following steps; (a) a neutralization step of acetic acid or acetic anhydride with an inorganic alkali salt, (b) a distillation step to perform azeotropic distillation of pyridine and water and separate the organic solvent (e.g. toluene) or an organic base compound from pyridine, (c) a salting-out step to separate pyridine and water by the conventional salting-out process of pyridine in the above azeotropic distillate and (d) a distillation step to purify the above salting-out product composed mainly of pyridine. The recovery can be further improved by returning the fraction other than the objective product to each step.

Description

[Detailed description of the invention] <Industrial application field> The present invention relates to a method for recovering pyridine.

More specifically, the present invention relates to a method for recovering pyridine with increased recovery rate and improved quality by combining a plurality of steps.

According to the present invention, it is possible to efficiently recover pyridine on a commercial basis.

Pyridine has generally been separated from coal tar and produced as a product, but various studies have also been conducted on synthetic methods.

Among these, a method in which ammonia is reacted with acetaldehyde alone or together with formaldehyde is known as an effective production method.

Pyridine is used as a pharmaceutical agent (sulfonamides, antihistamines), a sedative, a vulcanization accelerator, a drug activator, an alcohol denaturant, and a solvent for anhydrous metal salts.

In addition, in recent years, it has often been used as a reaction mediator and raw material for pharmaceuticals.

For example, as disclosed in JP-A No. 62-238353, substituted pyridine is used as a reaction mediator in the synthesis of 4-acetoxy-3-hydroxy superkerazetidin-2-one derivatives, which are intermediates for penem antibiotics. is used as.

When these reaction mediators are used as pharmaceutical raw materials, the required quality of pyridine is an extremely low water content.

The reason is that many of these reactions are performed in non-aqueous systems.

Specifically, a water content of 0.1% or less is desired, and a purity of 99% or more is required in order to introduce substituents into pyridine with good yield.

For example, 4-acetoxy-3-hydroxyethylazetidin-2-one derivative 'Ml method
258353), the typical substances and composition of the waste liquid discharged are 50% pyridine and 30% nitric anhydride.
, other organic solvents, and 20% organic oxygen compounds.

In this WA production, pyridine only serves as a reaction mediator, and lysine is hardly consumed during the reaction.

That is, the amount of waste liquid generated is approximately twice the amount of pyridine used in the production.

Even if this WfaM is disposed of by means such as incineration, N.
There is also a risk that this will lead to pollution problems due to restrictions on the amount of oxygen.

In addition, since it contains nitric acid or nitric anhydride, if there is a waste liquid with a high water content, it is undesirable for safety to mix with waste liquid of alcohol-based organic substances that have hydroxyl groups that react with nitric acid or nitric anhydride, and must be incinerated separately. This causes the inconvenience of not being able to do so.

In addition, the cost of incineration is also extra.

On the other hand, the market price of pyridine is 900 to 1.50 per kg.
0 yen (September 1985 - 9987 chemical products),
It is not a good idea to incinerate waste liquid and purchase new one.

Therefore, it is more cost-effective to recover pyridine from the waste liquid and recycle it (prior art).

Conventional collection techniques include the following:

■A method of distillation separation without any treatment. ■A method of neutralizing nitric anhydride, then salting it out, and distilling off pyridine from the oxidized organic layer.■A method of distilling nitric acid anhydride into nitric acid and azeotropic distillation of water. There is a method in which pyridine is azeotropically distilled as an agent, the retained water fraction is salted, and pyridine is separated by distillation from the retained organic layer.

<Problems to be Solved by the Invention> However, each of the above methods has the following drawbacks.

That is, in method (2), if a substance having a boiling point close to that of pyridine (for example, toluene) is present, the recovery rate will be low.

In the method (2), as in the case (2), many organic substances are present in the pyridine, which causes a decrease in the recovery rate.

In method (2), since acetic acid is present as acetic acid, in normal distillation, acetic acid is mixed in the pyridine aqueous solution, leading to a decrease in recovery rate. will also become more extreme, leading to an increase in collection costs.

These methods ① to ③ cause a decrease in recovery rate, and are far from being useful methods.

Therefore, there is a strong need for a method for efficiently recovering pyridine on a commercial basis.

Therefore, as a result of intensive study, the present inventor has completed the present invention.

<Structure of the Invention> That is, the present invention provides the following steps. At least pyridine, nitric acid or nitric anhydride, an organic oxygen compound, and an inert organic solvent. ``Method for recovering pyridine from waste liquid containing pyridine''.

Next, the present invention will be explained in detail.

As mentioned above, the substances and composition contained in the waste liquid targeted by the pyridine recovery method of the present invention are approximately 50% pyridine, 30% acetic acid or acetic anhydride, and 20% other active organic solvents and organic chlorine compounds. be.

Among the above, the inert organic solvent containing about 20% together with the organic chlorine compound is JP-A No. 62-258353.
As described in the publication, these include halogen solvents such as ethylene chloride and carbon chloride, fatty acid hydrocarbons such as n-hexane, aromatic acid hydrocarbons such as toluene, and ethyl acetate.

Examples of organic chlorine compounds include silanes, silanols, and siloxanes having C1 to C6 lower alkyl groups, such as tert-butyldimethylsilane or silanol, (or siloxane) isopropyldimethylsilane (or silanol or siloxane), and trimethylsilane. (Mana is silanol or siloxane, etc.)

When this waste liquid is distilled as in method (2), the top of the column becomes closed in a short time.

This is presumed to be due to the azeotropy or modification of pyridine in the waste liquid and other contained substances and organic chlorine compounds, which precipitate in the reflux section at the top of the column.

In addition, the boiling point of the substance contained in the waste liquid is toluene 110
．． The boiling point difference between pyridine and pyridine is extremely small, and the azeotropic temperature of toluene and pyridine is 110°C. ℃, and the disadvantage is that the loss of pyridine in this azeotrope increases in proportion to the weight of toluene.

Therefore, it is necessary to remove these substances that have a boiling point close to that of pyridine by some kind of treatment, and as a result of intensive study, we decided to incorporate these processes into a neutralization process, azeotropic process, salt folding process, and finally a product distillation process. I had to go through it.

In addition, if you are trying to separate substances with similar boiling points by distillation, it is usually necessary to use a column series of 50 or more stages, refluxing, 10 to 2
0 I need more than that.

However, according to the present invention, the number of column plates is 20 or more.
Pyridine of the required quality can be recovered under the conditions of 40 stages and a reflux ratio of 1 to 5.

More specifically, the acetic acid or anhydride used in the present invention can recover quality pyridine with a water content of 0.1% or less and a purity of 99% or more at a recovery rate of 85-87 at a column number of 20 to 30 plates and a reflux ratio of 1 to 5. The inorganic alkali salt used to neutralize acetic acid is an inorganic alkali metal or alkaline earth metal salt such as sodium hydroxide, carlum hydroxide, calcium aquaculture, barium aquaculture, sodium carbonate, potassium carbonate, and uranium carbonate.

When these inorganic alkali salts are used as neutralizing agents, 10
Used as an aqueous solution of ~50% waste liquid.

The temperature in the neutralization step is not particularly important, but it is between 20 and 50°C.
It is preferable in terms of equipment to control the addition rate of the neutralizing agent so that it falls within the range of .

Also, neutralization produces neutralized salt, but the precipitation of this neutralized salt is undesirable in terms of equipment and operation. It is desirable to add hydrogen in advance.

However, considering the size of the device, the neutralization is 30~
It is better to use a 50% aqueous solution of an inorganic alkali salt and then supplement by dissolving the salt or sequentially adding water as an azeotropic agent.

Next is the step of azeotropically distilling pyridine, etc. (azeotropic distillation step), and this operation is carried out under normal pressure with a column grade of 20 to 40 plates, a distillation ratio of 1 to 5, and a distillation temperature of 94 to 100°C at the top of the column. fraction is obtained as a fraction of pyridine water.

This process is useful for separating pyridine from organic solvents such as toluene or organic chlorine compounds.

This is a salting process in which an azeotropic fraction of pyridine and water is separated into pyridine and water, and as a salting agent, known hydrochloric acid can be used.

For example, sodium chloride, potassium chloride, calcium chloride, ammonium chloride, sodium sulfate, ammonium sulfate, magnesium sulfate, sodium acetate, sodium hydroxide, potassium hydroxide, etc., but more preferably a medium such as sodium hydroxide. It is a salt that can also be used as a Japanese additive.

The amount of salt-folding agent used is 20-45% by weight based on the azeotropic fraction of pyridine and water (obtained at an azeotropic temperature of 94-100°C).
It is.

The pyridine layer obtained by salting contains 2 to 15% water, which is charged into a product distillation column and distilled under normal pressure.

As the product distillation column, a multi-hole column or a bubble bell column having 20 to 40 plates can be used, but a perforated plate column is preferable.

Fractions are divided into fractions that are azeotropic with water, pyridine fractions with a purity of 97% or less, and product fractions, depending on the top temperature range or purity.

The reflux ratio is set in the range of 1 to 5, but the reflux ratio may be reduced stepwise in consideration of the properties of the fraction and the required product quality.

Furthermore, it is possible to improve the recovery rate by returning the fractions other than the product to the previous process.

The recovered pyridine obtained by distillation for commercialization satisfies the required qualities of less than 0.1% water content and more than 99% purity.

On the other hand, the quality and recovery rate of recovered pyridine performed by conventional techniques do not satisfy the required quality as shown in the attached table, and the recovery rate is also inferior.

The reason for this is, as mentioned above, that in the normal distillation of method (1), the precipitate appears in the reflux section (condenser) at the top of the column, and at the same time the fraction is colored reddish-brown, and the fraction also contains (anhydrous) acetic acid. Contains.

■In the method that involves the steps of neutralization, salting, and distillation for product production, organic chlorine compounds, etc., are not separated sufficiently, which reduces the purity of the product.

Furthermore, in the method that goes through the steps of hydration, azeotropic distillation, salting, and product distillation, the presence of acetic acid in the liquid charged to the azeotropic distillation step (pyridine and water in the azeotropic distillation step) The retention rate of the distillate deteriorates, leading to a decrease in the recovery rate of the product.

Therefore, the pyridine products obtained by these methods cannot be said to be useful in terms of purity and recovery rate.

The recovery method of the present invention is a useful method that satisfies the quality required for a reaction mediator, that is, water content is 0.1% or less, purity is 99% or more, and the yield is also 85%.

The present invention will be described in detail below with reference to Examples and Comparative Examples, but the Examples are not limited.

"Example 1" Pyridine 51%, acetic anhydride 32%, others (toluene,
1,000 g of a liquid containing 17% (organic chlorine compounds, etc.) (hereinafter referred to as the charging liquid) was charged into a flask with a charging tube equipped with a stirrer and a reflux condenser, and was heated over 1.5 hours with 3,550 g of a 10% aqueous sodium hydroxide solution. After neutralization, fractional distillation was carried out in a 20-stage old sieve column with a constant decrease of R/D = 3, and pyridine-
1420 g of a water fraction (94-100°C) was obtained.

This was placed in a separatory funnel equipped with a stirrer, 740 g of solid sodium hydroxide was gradually added, and the mixture was salted.

480 g of the obtained salt fraction was fractionally distilled in a 20-stage Oldershaw tower under normal pressure at R/D = 5 (extraction rate 90%) to obtain 341 g of pyridine product (recovery rate 67%).

"Example-2" 1000g of the preparation liquid was mixed with 48% sodium hydroxide aqueous solution 60g
Neutralize with 0 g, feed water sequentially, perform azeotropic distillation,
Below, perform the same operation as in "Example-1" to obtain pyridine product 3.
40 g was obtained (recovery rate 67%).

“Example-3” (Operating conditions of the device are the same as Example-2) Charge liquid 1000
The lower layer water (containing 40% sodium hydroxide) from the salting process was used as a neutralizing agent, and 80 g of the pyridine fraction obtained as a product in the product distillation was recycled to the product distillation process.

As a result, the recovery rate was 75 to obtain 385 g of product pyridine.
%).

"Example-4" The same procedure as Example-3 was carried out, except that the amount of salt-folding agent used was 20% (based on pyridine water), and the pyridine water fraction kept in the product distillation process was recycled. .

As a result, 433 g of pyridine product was obtained (recovery rate: 85%).
).

"Comparative Example-1" 1000 g of the charging liquid was fractionated in a 20-stage all-Gusho tower at constant reduction and R/D = 5, but a precipitate appeared around the front of the double spinning, and the fraction was colored reddish brown.

The fraction contained acetic anhydride, making it impossible to recover pyridine using this method.

rComparative Example-2 1000g of the charging liquid was put into a flask equipped with a stirrer and a reflux condenser, and after neutralization with 1065g of 40% sodium hydroxide aqueous solution, 200g of sodium chloride was added and salted, and 630g of the salt-folded product was added. Obtained.

This solution was fractionally distilled (using a 20-stage Oldershaw column) under the same conditions as in Example to obtain 281 g of pyridine product (recovery rate 55%).

"Comparative Example-3" 1000 g of the charging liquid was charged into a flask equipped with a charging port, a stirrer, and a reflux condenser, 910 g of water was gradually added dropwise, and acetic anhydride was leveled out. Under the same method conditions as Example-1, Azeotropic distillation, salting, and product distillation were carried out.
%) Obtained 190g of pyridine product (recovery rate 37%) Procedural amendment (voluntary)

Claims (1)

[Claims] (a) A step of neutralizing nitric acid or nitric anhydride with an inorganic alkali salt (b) A distillation step of azeotropically distilling pyridine and water (c) A step of salting out pyridine in the azeotrope (d) )
A method for recovering pyridine from a waste liquid containing at least pyridine, nitric acid or nitric anhydride, an organic oxygen compound, and an inert organic solvent, the method comprising a distillation step for commercializing the above-mentioned salt-folded product mainly containing pyridine. .