JPH072713B2 - Pyridine base separation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention provides a method for cooling a given pyridine base and another pyridine base from a mixture containing a plurality of pyridine bases forming a eutectic crystal by a cooling crystallization separation method. Well on how to separate.

[Prior Art] Pyridine bases, which are industrially important as raw materials or solvents for pharmaceuticals and agricultural chemicals, are obtained by fractional distillation of tar or synthesis from acetaldehyde and formaldehyde and ammonia.

[Problems to be Solved by the Invention] However, since the pyridine base thus obtained is a mixture of several pyridine bases, it is necessary to separate them from each other. Generally, it is separated and purified by distillation, but in this method, it is extremely difficult to separate a mixture containing two or more kinds of compounds having close boiling points, such as 3-picoline, 4-picoline and 2,6-lutidine. It is difficult and requires a large amount of energy to force the separation. Furthermore, the recovery rate will be low, and the cost will be high in this respect as well.

Further, US Pat. No. 2,402,158 proposes a cooling crystallization separation method of pyridine base. Since most of the mixture of pyridine bases forms a eutectic in the range of 0 to -50 ° C, this method is a method of performing crystallization operation at a temperature higher than the eutectic temperature for separation.

For example, 3-picoline 74% (wt%, the same below) and 4
In the case of a mixture with 26% picoline, when the crystallization operation is performed up to an approximate eutectic temperature of -37.4 ° C, the obtained crystal is 3-picoline, and the mother liquor has an approximate eutectic composition of 3-picoline 59. % And 4-picoline 41%. Therefore, although a part of the predetermined pyridine base is obtained by this method, the predetermined pyridine base having a eutectic composition or more remains in the mother liquor, and the recovery rate of the predetermined pyridine base is low. Further, this known technique does not disclose a method of cooling and crystallizing and separating substantially any pyridine base from a mother liquor having a eutectic composition.

In view of such circumstances, the present invention has been made to obtain a method for efficiently separating a predetermined pyridine base from a mixture containing a plurality of pyridine bases.

[Means for Solving the Problems] In the present invention, when a predetermined pyridine base is cooled and separated from a mixture containing a plurality of pyridine bases forming a eutectic crystal, a pyridine base other than the predetermined pyridine base is separated. Adjust the stirring rate and cooling rate so that the spontaneous generation temperature of the crystal nuclei is lower than the eutectic temperature by 10 ℃ or more.
A method for separating a pyridine base, which comprises cooling the mixture to a temperature lower than 10 ° C. or higher and higher than the spontaneous generation temperature to crystallize and separate a predetermined pyridine base. Thus, even though the crystallization temperature of the predetermined pyridine base becomes lower than the eutectic temperature in the crystallization operation, the predetermined pyridine base continues to be selectively precipitated, while the predetermined pyridine base of the mother liquor It was made because it was found that the content rate was lower than the eutectic composition, and thus the recovery rate of a given pyridine base was improved.

When separating a given pyridine base from a mixture forming a eutectic, it is common knowledge that if the crystallization temperature is lower than the eutectic temperature, eutectic crystals will precipitate and all of the mixture will solidify. The operation is performed above the eutectic temperature.
However, the present inventors have succeeded in improving the recovery rate of a predetermined pyridine base by adjusting the stirring rate and the cooling rate as described above and performing the crystallization operation below the eutectic temperature. According to the method of the present invention, it is possible to recover a predetermined pyridine base from a mixture of eutectic compositions, and also to recover a predetermined pyridine base from a mixture having a lower content of the predetermined pyridine base than the eutectic composition. Can be done. When the method of the present invention is carried out on a mixture of almost two components (meaning a mixture mainly composed of two components and may contain a small amount of other components, the same applies hereinafter), the obtained mother liquor is obtained. Contains a pyridine base other than the predetermined pyridine base in a larger amount than the eutectic composition, and is a mixture having a composition that facilitates selective precipitation of the pyridine base other than the predetermined pyridine base.
Then, when the method of the present invention and / or the conventional method are subsequently repeated, it becomes possible to almost completely separate the respective components despite the formation of the eutectic.

Examples Specific examples of the pyridine base used in the present invention include, for example, 3-picoline, 4-picoline, 2,6-lutidine and 2-picoline.
Examples thereof include, but are not limited to, picoline, 2-ethylpyridine, pyridine and the like.

In the present invention, a predetermined pyridine base is separated from a mixture containing a plurality of pyridine bases forming a eutectic by a cooling crystallization separation method.

Specific examples of the mixture containing a plurality of pyridine bases forming a eutectic include at least two or more pyridine bases selected from the group consisting of 3-picoline, 4-picoline, and 2,6-lutidine. However, it is not limited thereto.

The predetermined pyridine base referred to in the present specification means a pyridine base separated by a crystallization separation method by cooling a mixture containing a plurality of pyridine bases forming a eutectic crystal,
Even in the same mixed system, the predetermined pyridine base may be different depending on the ratio of the pyridine base contained in the mixture.

In the present invention, when a predetermined pyridine base is cooled and crystallized from a mixture containing a plurality of pyridine bases forming a eutectic crystal, the spontaneous generation temperature of the crystal nuclei of the pyridine base other than the predetermined pyridine base is controlled. The stirring speed and cooling rate were adjusted so that the temperature was lower than the crystallization temperature by 10 ° C or more, and the mixture was cooled to a temperature lower than the eutectic temperature by 10 ° C or higher and higher than the spontaneous generation temperature to give a predetermined pyridine base. Separate by crystallization.

The spontaneous generation temperature of crystal nuclei of a pyridine base other than the predetermined pyridine base means that when the mixture is cooled in a static state or a dynamic state such as under stirring, the pyridine base other than the predetermined pyridine base is It is the temperature at which crystal nuclei start to form.

Further, the eutectic temperature is a temperature at which all the mixture solidifies when the mixture forming the eutectic is carefully cooled by a method such as high-speed stirring so as not to be overcooled, and under constant pressure, depending on the kind of the mixture. It is an inherent temperature that is determined.

The spontaneous generation temperature of crystal nuclei of a pyridine base other than the predetermined pyridine base can be adjusted by adjusting the stirring rate and cooling rate of a liquid containing a mixture containing a plurality of pyridine bases forming a eutectic. . That is, when the stirring speed is slowed down, the temperature is lowered, and when the cooling speed is increased, the temperature is lowered. Therefore, this is similar to the case of the spontaneous generation temperature of crystal nuclei when crystallizing a solute from a solution at a general crystallization temperature. Further, it is considered that the temperature increases as the volume of the mixture increases, but even if the volume increases or decreases, the stirring rate and the cooling rate may be adjusted to suit the volume.

The cooling rate is related to the stirring rate, and is preferably as high as possible in order to prevent spontaneous generation of crystal nuclei of a component which is not desired to be crystallized. Usually, the cooling rate is adjusted so that the crystallization operation is completed in 0.5 to 3 hours. The stirring speed is preferably as low as possible for the same reason as above.

In the present invention, the spontaneous generation temperature is 10 ° C higher than the eutectic temperature.
The mixture is cooled to a temperature lower than the eutectic temperature and 10 ° C. lower than the eutectic temperature and higher than the spontaneous generation temperature.
When the temperature can be lowered to less than 0 ° C or the mixture is cooled to such a temperature, the recovery rate of a given pyridine base is slightly improved as compared with the conventional method, which is one of the objects of the present invention. It becomes extremely difficult to separately collect each pyridine base from a mixture composed of two components of the pyridine base.

The stirring rate and cooling rate were adjusted so that the spontaneous generation temperature was lower than the eutectic temperature by 10 ° C.
When the mixture is cooled to a temperature lower by 0 ° C. and higher than the spontaneous generation temperature to crystallize and separate the predetermined pyridine base, a seed crystal of the predetermined pyridine base may be added for the crystallization separation.

The size and amount of the seed crystal of the predetermined pyridine base are not particularly limited, and about 0.1% is sufficient with respect to the weight of the predetermined pyridine base in the mixture.

If desired, a solvent may be used in the method of the present invention.

Examples of such a solvent include benzene, toluene and cyclohexane. The amount of the solvent used is usually in the range of 0 to 0.2 times the weight of the pyridine base.

Next, a mixture of 3-pyricon and 4-pyricon will be described as an example.

The present inventors have conducted experiments to investigate the relationship between the composition and the spontaneous generation temperature of crystal nuclei when the mixture is cooled. For example, a mixture made of 3-picoline and 4-picoline is placed in one glass container, and the stirring speed is 435 rpm and the cooling speed is 0.5 ° C /
Table 1 shows the relationship when measured under different conditions. As a reference, Table 1 also shows the temperature at which solidification is started as described in US Pat. No. 2,402,158.

In Table 1, the content of 3-picoline in the mixture is 80%
In this case, 3-picoline crystal nuclei were generated early, and 3
-When the picoline content is 40% and 20%, 4-picoline crystal nuclei are generated first, and the 3-picoline content is
In the case of 59%, crystal nuclei of 3-picoline and / or 4-picoline are initially generated.

As can be seen from Table 1, in the case of a mixture of 3-picoline 59% which is a eutectic composition, the initial generation temperature of crystal nuclei is -73 ° C, which is 3 ° C as compared with the case of U.S. Pat. No. 2402158.
It is 5.6 ℃ lower. If the stirring speed and the cooling speed are adjusted, that is, if the stirring speed is slowed, the cooling speed is increased, or both are combined, the difference becomes larger. The greater the difference, the more effective the method of the present invention. In addition, in the mixture system of 3-picoline and 4-picoline, 3-picoline 80% and 40%
In the case of the mixture of the above, from the initial generation temperature of the crystal nuclei of 3-picoline and 4-picoline, respectively, it is more preferable to use 3-picoline as the predetermined pyridine base in the former and 4-picoline as the predetermined pyridine base in the latter. It turns out to be easy.

The method of the present invention was applied to 3-picoline 59% and 4-picoline 41
% Eutectic composition mixture, 4-picoline is cooled and separated by crystallization.

The mixture was cooled by adjusting the stirring rate and cooling rate so that the spontaneous generation of 3-picoline crystal nuclei was 10 ° C. or more lower than the eutectic temperature, and was below the eutectic temperature. At this point seed crystals of 4-picoline are added. The addition of this seed crystal initiates the crystallization of 4-picoline in the saturated or supersaturated mixture. Then, when the solid-liquid is separated by cooling just before the temperature at which 3-picoline crystal nuclei are spontaneously generated, 4-picoline crystals are obtained,
On the other hand, 3-picoline is concentrated in the mother liquor. When the solid-liquid was separated by cooling to -65 ° C by this method, the crystal composition was 3-
Picoline 37.7%, 4-picoline 62.3% with a mother liquor composition of 3-
It becomes 76.3% of picoline and 24.7% of 4-picoline. That is, 4-picoline was crystallized from the eutectic composition raw material, while the mother liquor had an increased 3-picoline content.
Pure 4-picoline cannot be obtained because the adhering mother liquor always remains in the crystals and the mother liquor is taken in.

Since the mother liquor obtained here has a higher content of 3-picoline than the eutectic composition, it is easy to crystallize 3-picoline by cooling crystallization, and it is necessary to particularly utilize the method of the present invention. Alternatively, 3-picoline may be crystallized by a conventional method so that the mother liquor composition becomes approximately a eutectic composition. Then, 4-picoline and 3-picoline can be almost completely separated by repeating crystallization separation of 4-picoline and 3-picoline alternately.

Further, in the above example, the seed crystal was added, but it is not always necessary to add the seed crystal depending on the composition of the raw material. The necessity of seed crystal is determined by the spontaneous generation temperature of the crystal nuclei of each of the component desired to be crystallized and the component not desired to be crystallized. For example, if the component desired to be crystallized is higher than the other components at the crystal nucleus generation temperature, the seed crystal is not necessary. When crystallizing 4-picoline from a mixture of 3-picoline and 4-picoline, a seed crystal of 4-picoline is necessary for a eutectic composition and a mixture having a lower content of 4-picoline than the eutectic composition. However, when the content of 4-picoline is higher than the eutectic composition, the seed crystal of 4-picoline is not particularly necessary. When 2,6-lutidine is crystallized from a mixture of 2,6-lutidine and 3-picoline, a eutectic composition does not require a seed crystal.

When the method of the present invention is carried out by a single crystallization separation operation as described above, the content of the predetermined pyridine base remaining in the solution can be made considerably lower than the eutectic composition. More pyridine bases are recovered than before.
Further, in the case of a mixture of two components, the components for precipitating crystals are alternately repeated and only when the method of the present invention is used or when the method of the present invention and the conventional technique are combined to perform crystallization separation several times, respectively. It is also possible to almost completely separate the components of. If it is necessary to recover high-purity components, the crystals obtained by the method of the present invention and the mother liquor can be highly purified by known continuous column crystallization operations.

Among the pyridine bases, the method of the present invention is
It is particularly effective for the fractional recovery of the respective pyridine bases from a mixture containing -picoline, 4-picoline and 2,6-lutidine.

Next, the method of the present invention will be described based on examples.

Example 1 100 g of mixed picoline containing 59% 3-picoline and 41% 4-picoline was placed in a glass flask, and the rotation speed was 435 rpm.
Cooling was started with stirring. When the internal temperature reached −40 ° C., seed crystals of pre-crystallized 4-picoline were reduced to about 0.
1 g was added and the mixture was cooled to -65 ° C at a cooling rate of 0.5 ° C for 1 minute to precipitate crystals. The crystals were filtered off, and the obtained crystals and the filtrate were analyzed by gas chromatography.

Similarly, the crystals and filtrate obtained by cooling to -60 ° C were analyzed. The results are shown in Table 2.

According to U.S. Pat. No. 2,402,158, the eutectic composition of 3-picoline and 4-picoline is 59% 3-picoline and 41% 4-picoline as described above, and the eutectic temperature is -37.4 ° C. .

Example 2 100 g of mixed picoline containing 59% of 3-picoline and 41% of 4-picoline and 11 g of toluene were placed in a glass flask, and cooling was started while stirring at a rotation speed of 435 rpm. When the internal temperature reached 45 ° C, about 0.1 g of 4-picoline seed crystal was added, and cooled to -72 ° C at a cooling rate of 0.5 ° C for 1 minute,
Crystals were precipitated. The crystals were filtered off, and 35 g of crystals and the filtrate 7
It was 6g.

When the obtained crystals and the filtrate were analyzed, the content of 4-picoline in the crystals (based on picolines) was 74.5%, and the content of 4-picoline in the filtrate was 26.9%.

Example 3 200% mixed solution of 55% 3-picoline and 45% 2,6-lutidine
g was put in a glass flask, and cooling was started while stirring at a rotation speed of 435 rpm. It cooled at the cooling rate of 0.5 degreeC for 1 minute after the internal temperature became -40 degreeC. Crystals precipitated when the temperature reached −59 ° C. The internal temperature rose temporarily due to the heat of crystallization, and then it was aged at -59 ° C for 1 hour. The precipitated crystals were separated by filtration to obtain 64.6 g of crystals and 135.4 g of filtrate.

When the obtained crystals and the filtrate were analyzed by gas chromatography, the content of 3-picoline in the crystals was 35.5%, and the content of 3-picoline in the filtrate was 64.9%.

According to US Pat. No. 2,402,158, the eutectic composition of 3-picoline and 2,6-lutidine is 3-picoline 52
%, 2,6-lutidine 48%, and the eutectic temperature is -39.4 ° C.

EFFECTS OF THE INVENTION By using the method of the present invention, each pyridine base can be separated and recovered from a mixture of pyridine bases with a small amount of energy. Moreover, 3-picoline that forms a eutectic, which has a boiling point close to that which was impossible to separate and purify by conventional distillation,
Each compound can be separated and recovered from the mixture containing 4-picoline and 2,6-lutidine by a cooling crystallization separation method. Therefore, the method of the present invention is an industrially extremely advantageous method for separating pyridine bases. Further, by combining several cooling crystallization separation operations, each pyridine base can be separated almost completely.

Claims (3)

[Claims] 1. A method for coordinating the spontaneous generation temperature of a crystal nucleus of a pyridine base other than a predetermined pyridine base during cooling crystallization separation of a predetermined pyridine base from a mixture containing a plurality of pyricin bases forming a eutectic. The stirring rate and cooling rate were adjusted so that the temperature was lower than the crystallization temperature by 10 ° C or more, and the mixture was cooled to a temperature lower than the eutectic temperature by 10 ° C or higher and higher than the spontaneous generation temperature to obtain a predetermined pyridine. A method for separating a pyridine base, which comprises separating the base by crystallization. 2. A stirring rate and a cooling rate are adjusted so that the spontaneous generation temperature of crystal nuclei of a pyridine base other than a predetermined pyridine base is 10 ° C. or more lower than the eutectic temperature, and 10 ° C. is higher than the eutectic temperature. A seed crystal of a predetermined pyridine base is added when the mixture is cooled to a temperature lower than the above and higher than the spontaneous generation temperature to crystallize and separate the predetermined pyridine base. Separation method described in paragraph. 3. A plurality of pyridine bases are 3-picoline, 4-
The separation method according to claim 1, which is at least two kinds of pyridine bases selected from the group consisting of picoline and 2,6-lutidine.