JP2000218101A - Crystallization method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the liquid content of wet cake by a method in which when slurry comprising mother liquor and a solute is circulated to an original container through following containers in turn to be crystallized while the slurry is mixed with a solution of a higher temperature and a higher concentration than those of the mother liquor. SOLUTION: A crystallizer is formed by connecting a container K1, a slurry circulating pump P, and an externally circulating heat exchanger E with piping A, B, C. After the slurry of the container K1 obtained by cooling crystallization is transferred to following containers in turn while being mixed with a solution or a fusing liquid which is a solute having a higher temperature and a higher concentration than those of the mother liquor in the container K1, the slurry is circulated to the container K1. The temperature of the slurry in the following containers is made lower by 0.2-20 deg.C, preferably 0.5-5 deg.C, than that of the slurry in the container K1 in turn. In this way, the liquid content of web cake obtained by filtering the slurry obtained by crystallization is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crystallization method. The present invention also relates to a method of crystallization by adding a high-concentration solute solution or a solute melt and circulating the slurry in the container to the first container via the second and subsequent containers.

[0002]

2. Description of the Related Art In a batch crystallization method using a crystallizer, a slurry comprising pyromellitic acid as a solute and dilute nitric acid as a solvent is gradually cooled from 100 ° C. to 40 ° C. in the crystallizer. And the cooling step is stopped when the mother liquor temperature reaches 40 ° C., and the cooling is stopped at 80 ° C. (before the precipitated crystals are completely dissolved).
A crystallization method and the like are known, which include three steps of a temperature raising step of raising the temperature to 80 ° C. and a final temperature lowering step of gradually cooling the temperature from 80 ° C. to 20 ° C.

[0003]

However, in the above-mentioned known method, the crystal growth is insufficient, and fine crystals generated by stirring or the like remain as they are. Therefore, the slurry obtained by this method is filtered. However, there is a problem that the liquid content in the obtained wet cake increases, and the purity of the product obtained by drying the wet cake decreases. Also, in the cooling step, when scaling occurs on the cooling heat transfer surface, the crystallizing pot or the like cannot be cooled to a predetermined temperature based on a decrease in the overall heat transfer coefficient due to the occurrence of the scaling,
There is a problem that the production capacity is significantly reduced.

[0004]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, using at least two containers, a slurry comprising a mother liquor and a solute in the first container was stirred under stirring. While adding a solute solution or solute melt at a higher temperature and higher concentration than the mother liquor in the first container, the slurry in the container is circulated to the first container via the second and subsequent containers, The inventors have found that the above problem can be solved by sequentially lowering the crystallization temperature in the second and subsequent vessels than the crystallization temperature in the first vessel, and completed the present invention. That is,
The present invention uses at least two containers and adds a solution of a solute or a melt of a solute having a higher temperature and a higher concentration than the mother liquor in the first container to a slurry composed of the mother liquor and the solute in the first container while stirring. And circulating the slurry in the container to the first container via the second and subsequent containers for crystallization, wherein the crystallization temperature in the second and subsequent containers is controlled by the crystallization in the first container. It is intended to provide a crystallization method characterized by sequentially lowering the temperature. Hereinafter, the present invention will be described in detail.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The crystallization method of the present invention is carried out in a batch system, and the first vessel (K ₁ ) usually has an agitator inside, and a cooling or heating vessel on the outer wall of the vessel. The one having a jacket for conducting the refrigerant or the heat medium is preferable. Like the first container (K ₁ ), the second and subsequent containers (K ₂ , K ₃ ,..., K _i ) have a stirrer inside, and have an outer wall of the container for cooling or heating. It may have a jacket for conducting a refrigerant or a heat medium, but a heat exchanger is more preferable. The present invention relates to a container (K) as shown in FIG.
₁ ) A slurry circulating pump (P) and an external circulating heat exchanger (E) are connected in a crystallizer connected in a loop by pipes (A, B, C).

In the crystallization method of the present invention, the first container (K
The slurry of ₁ ) is usually obtained by completely dissolving a solute in a solvent and then cooling and crystallizing. The combination of the solute and the solvent at the time of this cooling crystallization is not particularly limited, and may be any combination of organic substances, inorganic substances, and an organic substance and an inorganic substance. When the heat exchange capacity of the container is relatively small, a combination of organic substances having a small specific heat of the mother liquor is preferable. In particular, when the slurry to be charged in the first container is subjected to a crystallization method in which a temperature lowering step and a temperature increasing step are alternately performed as described below, the solute is often insoluble in an organic solvent when the solute is an inorganic substance. The solvent becomes an aqueous medium (water or a solution of water and an inorganic substance, or a solution of an organic solvent miscible with water and water), and the specific heat of the mother liquor increases. A combination of organic substances that can be switched quickly is preferable.

According to the crystallization method of the present invention, the slurry in the first vessel (K ₁ ) obtained by cooling crystallization is heated under stirring with a solute having a higher temperature and a higher concentration than the mother liquor in the first vessel K ₁ . while adding melted liquid solution or solute, the slurry in the vessel K ₁ is transferred to a vessel K ₂ later, can be performed by circulating the transport slurry to the vessel K _1. Transfer to the container K slurry vessel K ₂ later in _1, for example, it can be conducted using a slurry circulation pump (P) or the like.

The amount of the solute solution having a higher temperature and a higher concentration than the melt or the mother liquor in the container K ₁ per unit time is as follows:
It may be an amount enough to dissolve during the fine crystals generated by mechanical friction stir slurry and during transport from staying in the container K _1, the addition of large quantities too short, other than microcrystalline It is not preferable because the solute is dissolved. Slurry was transferred to the vessel K ₂ and later, the mother liquor temperature in said vessel is kept sequentially lower than the mother liquor temperature in the vessel K _1, the container K _2, K _3, staying in · · · K _i A solute crystal grows with a relatively large crystal as a nucleus from which fine crystals have been removed. That is, when the slurry is in the containers K ₁ , K ₂ , K ₃ ,
... while circulating in K _i, larger average particle diameter, and the range of particle size distribution is obtained slurry containing small crystals.

[0009] In the crystallization method of the present invention, a slurry of the first in one container K _1, melt liquid or container K ₁ of solutes to be added to
The ratio of the solute solution with higher temperature and higher concentration than the mother liquor in
The slurry in ₁ is not particularly limited as long as it can be stirred, but is preferably in a weight ratio of 1: 5 to 5:
1, and more preferably in the range of 1: 4 to 4: 1. In crystallization method of the present invention, the slurry temperature in the vessel K _1, the slurry is kept lower than the temperature to completely dissolve in the container, preferably slurry temperature 10 ° C. than the temperature at which the slurry is completely dissolved The temperature is lower than the above, more preferably the temperature lower than 20 ° C. Further, slurry temperature of the vessel K ₂ later, sequentially, than the slurry temperature in K _1, preferably a 0.2 to 20 ° C. lower temperature, more preferably, is 0.5 to 5 ° C. lower temperature .

[0010] The first cooling crystallization to obtain a slurry of the container K ₁ of the foregoing, for example, as described in JP 62-247802 and JP-slowly cooled slurry in the crystallization析釜A cooling step of crystallizing a part of the solute,
Stop cooling when the slurry temperature drops to some extent,
It may be performed by a known method including a temperature raising step of raising the temperature to a temperature before the precipitated crystals are completely dissolved, and a final temperature lowering step of gradually cooling from the temperature to the final temperature, Preferably, as described in the application specification of Japanese Patent Application No. 10-109255, the temperature of the slurry is lowered and the temperature of the slurry is reduced until a part of the solute is crystallized until the crystallization is completed. Step and a series of operations including a temperature raising step of raising the slurry temperature a plurality of times until the precipitated crystals are completely dissolved after the step, further including a final temperature lowering step, and The minimum value of the slurry temperature in the temperature lowering step and the maximum value of the slurry temperature in the temperature raising step are each sequentially reduced by a batch cooling crystallization method. The resulting temperature drop and temperature rise step in multiple repeating crystallization method, as the first slurry container K _1, for example, moderate melting point organic phosphorus compound is 85 ° C. or less and (solute) to the compound Boiling point indicating the solubility of
Those obtained from the following combinations of lower alkyl acetates (solvents) are preferred.

[0011] When performing a crystallization repeated several times and then decreased and heated in steps in container K _1, 1-time cooling step,
This is performed in order to obtain a slurry by cooling a solution in which the solute is completely dissolved in the solvent (the solution temperature at this time is assumed to be T ₀ ° C) to precipitate a part of the solute as crystals. The cooling rate is
The temperature is appropriately set according to the combination of the solute and the solvent, but the range of about 1 to 100 ° C. per hour is preferable industrially.
Further, it is preferable to minimize the difference (ΔT) between the mother liquor temperature and the refrigerant temperature from the viewpoint of avoiding scaling. Industrially, it is more preferably 5 ° C or lower, particularly preferably 3 ° C or lower.

The switching from the cooling step to the first heating step preferably reaches a mother liquor temperature about 10 ° C. lower than the slurry temperature (T ₁ ° C.) at which part of the solute began to precipitate as crystals. Time point, more preferably about 7 ° C. above T ₁ ° C.
When a low slurry temperature is reached, particularly preferably T ₁
The point in time when the slurry temperature reaches 1 to 5 ° C lower than 0 ° C can be used as a standard. The slurry temperature at the time of switching from the first temperature lowering step to the first temperature raising step is set to T ₂ ° C. The highest slurry temperature (referred to as T ₃ ° C) in the first heating step is lower than the above-mentioned T ₀ ° C, preferably T ₁ ° C. When the mother liquor temperature reaches T ₃ ° C, a heat-retaining step at the same temperature may be added if necessary.
The heat retention time in this step is preferably 5 to 30 minutes, more preferably 15 to 30 minutes. After the end of this step, the first series of operations ends.

[0013] When the first series of operations is completed, cooling is started. The cooling rate in the second cooling step is the same as that in the first cooling step. Lowest slurry temperature in the second cooling process (T ₄ ° C)
Is a temperature lower than the above T ₂ ° C, and preferably T ₄
° C. is 2 to 8 ° C. temperature lower than T ₂ ° C..

When the slurry temperature reaches T ₄ ° C, a second heating step is performed. Best slurry temperature T ₅ ° C. At this time, the a temperature lower than T ₃ ° C., preferably from 1 to 8 ° C. lower temperature than T ₃ ° C.. After the second temperature raising step, a temperature keeping step at T ₅ ° C may be inserted as necessary. The warming time is the same as in the first series of operations.

After the end of the second series of operations, a third series of operations is preferably performed. Note that if the assumed T ₆ ° C. The slurry temperature at the time of switching from the third cooling step to the third heating step, the T ₆ ° C. is the temperature lower than the T ₄ ° C., preferably, T ₆ ° C is 2 more than T ₄ ° C
８8 ° C. lower temperature. Assuming that the highest slurry temperature in the third heating step is T ₇ ° C, T ₇ ° C is lower than T ₅ ° C, and preferably T ₇ ° C is T ₅ ° C.
The temperature is 1 to 8C lower than C. In the third series of operations, if necessary, a step of keeping the temperature at T ₇ ° C may be included. The heat retention time is the same as in the first and second times. When performing the fourth and subsequent series of operations, the operations are performed according to the second to third series of operations.

Then, a final temperature lowering step is performed. The minimum slurry temperature at this time is defined as T _i ° C.

[0017]

According to the present invention, the wet cake obtained by filtering the slurry obtained by crystallization has a small liquid content, and the purity of the product can be improved. In addition, scaling during crystallization can be easily removed, the overall heat transfer coefficient of the cooling heat transfer surface increases, and the production capacity can be greatly improved.

[0018]

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. In the examples, parts and% are parts by weight and% by weight, respectively.

Reference Example 1 Crystallization was carried out under the following conditions using a crystallizer equipped with a crystallizer made of glass lining, a circulation pump and an external heat exchanger made of stainless steel as shown in FIG. Solute: N-acetyl O, S-dimethylphosphoramidothioate 100 parts Solvent: ethyl acetate 185 parts Solution temperature T ₀ : 40 ° C Slurry capacity / crystallizer capacity: 0.83 ΔT (difference between slurry temperature and refrigerant temperature ): 2 to 3 ° C. (constant during the crystallization operation) Crystal precipitation temperature T ₁ : 35 ° C. Number of series of operations: 4 times Slurry temperature T ₂ : 32 ° C. (minimum temperature in the first cooling step) Slurry temperature T ₃ : 35 ° C (the highest temperature in the second heating step) Slurry temperature T ₄ : 29 ° C (the lowest temperature in the second cooling step) Slurry temperature T ₅ : 33 ° C (the highest temperature in the second heating step) Slurry Temperature T ₆ : 26 ° C. (minimum temperature in the third cooling step) Slurry temperature T ₇ : 28 ° C. (maximum temperature in the third heating step) Slurry temperature T ₈ : 20 ° C. (minimum temperature in the fourth cooling step) ) slurry temperature T _9: 22 Slurry temperature T _i (the maximum temperature in the fourth heating step): 12 to 13 ° C. (lowest temperature in the final cooling step)

A part of the obtained slurry was subjected to solid-liquid separation with a small centrifugal filter (6 inches; centrifugal effect was 350 G), and the liquid content and average particle size of the wet cake were determined.
% And 450 μm. The overall heat transfer coefficient on the cooling surface of the external circulation heat exchanger is 460 Kcal / m ² · Hr · ° C.
Met. Similarly, when the liquid content and the average particle size of the wet cake were determined when the number of operations in the series was set to three times, they were 6.2% and 430 μm, respectively. When the liquid content and the average particle size were determined, each was about 7%.
And 370 μm. The overall heat transfer coefficient on the cooling surface of the external circulating heat exchanger is 380 Kcal / m ² · Hr · ° C. when the number of operations is three, and 170 Kcal / m ² when the number of operations is ^two.・ Hr · ° C.

Example 1 A slurry obtained by crystallization according to the above-mentioned crystallization method using 84 parts of N-acetyl O, S-dimethylphosphoramidothioate and 440 parts of ethyl acetate was applied to the apparatus shown in FIG. from crystallization析釜K _0, was transferred into the vessel K ₁ of the apparatus of FIG. The slurry temperature at this time was 14 ° C. A part of the slurry was subjected to solid-liquid separation with a small centrifugal filter (4 inches, rotation speed 2500 per minute), and the liquid content of the wet cake was determined to be 5.9.
%Met.

Next, from the storage tank M of a solution having a higher temperature and a higher concentration than the mother liquor in the container (crystallizer) K ₁ , to the crystallizer K ₁ via the pipe H, to 50 ° C. with stirring. Warm N-
Acetyl O, S-dimethyl phosphoramidothioate
A solution of 1150 parts of ethyl acetate 1920 parts slurry temperature of crystallization析釜K in ₁ was added dropwise over a period of 2 hours so as to maintain the 13 to 16 ° C., added dropwise simultaneously with the start of the circulating slurry by circulation pump I let it. Temperature of crystallization析釜K in ₁ when the steady state was 14 ° C.. After the completion of the dropping of the solution, a part of the slurry was subjected to solid-liquid separation using the small centrifugal filter, and the liquid content of the wet cake was determined to be 4.8%.

[Brief description of the drawings]

FIG. 1 shows an apparatus used in Reference Example 1.

FIG. 2 shows an apparatus used in Example 1.

[Explanation of symbols]

K ₁ first container, K _2, K _3, · ·, K _i containers of the second and subsequent, storage tanks M melting solution, A, B, C, H piping, pump P circulates E external heat exchanger K ₀ Crystallization pot

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yujiro Kiyoshima 2200 Tsuruzaki, Oita-shi, Oita F-term in Sumitomo Chemical Co., Ltd. (Reference) 4H050 AA02 AD15 BB17 BC50 BC51

Claims (7)

[Claims] 1. Using at least two containers, a solution of a solute or a molten solution of a solute having a higher temperature and a higher concentration than the mother liquor in the first container is added to a slurry comprising the mother liquor and the solute in the first container under stirring. A method in which the slurry in the vessel is circulated to the first vessel via the second and subsequent vessels while adding, and the crystallization temperature in the second and subsequent vessels is reduced by the crystallization temperature in the first vessel. A crystallization method characterized by sequentially lowering the crystallization temperature. 2. The method according to claim 1, wherein the second and subsequent vessels are heat exchangers. 3. The method according to claim 1, wherein the difference between the crystallization temperatures in the first and second and subsequent vessels is in the range of 0.2 to 20 ° C. 4. The method according to claim 3, wherein the difference between the crystallization temperatures in the first and second and subsequent vessels is in the range of 0.5 to 5 ° C. 5. A temperature decreasing step of lowering the temperature of the slurry and causing a part of the solute to crystallize before the slurry comprising the mother liquor and the solute in the first container starts cooling and completes crystallization;
After this step, a series of operations including a temperature raising step of raising the slurry temperature is performed a plurality of times until the precipitated crystals are completely dissolved, and further includes a final temperature lowering step, and each time and a final temperature lowering step The method according to any one of claims 1 to 4, wherein the minimum value of the slurry temperature and the maximum value of the slurry temperature in the temperature raising step are obtained by a batch cooling crystallization method in which the respective values are sequentially decreased. 6. The method according to claim 5, wherein a series of operations including a temperature lowering step and a temperature raising step is performed three times or more. 7. The method according to claim 1, wherein the solute is an organic phosphorus compound and the solvent is a lower alkyl acetate.