JP3238185B2 - Indirect cooling crystallization with scraping - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for crystallizing a target substance from a liquid containing a plurality of components by indirectly cooling the wall of a crystallization tank with a refrigerant and scraping off the crystals deposited on the inner wall. It relates to a preparative indirect cooling crystallization method.

[0002]

2. Description of the Related Art The cooling crystallization method includes a crystallization method in which a cooling surface is not used by utilizing latent heat of evaporation, such as a direct refrigerant injection method in which a refrigerant is directly blown into a liquid to be treated and an adiabatic cooling method. As described above, there is a scraping type indirect cooling crystallization method.

[0003] The scraping-type indirect cooling crystallization method is often used when the former two cannot be used, and a coolant is passed through a jacket or a cooling element to indirectly cool and crystallize a processing liquid.

[0004] In this case, since crystals are precipitated on the cooling surface,
The heat transfer coefficient decreases. In order to prevent this, a method of heating and dissolving the crystals attached to the cooling inner wall surface after the crystallization operation is completed or a method of continuously scraping the crystals attached to the cooling surface with a scraper or the like is adopted.

[0005] However, even in the method of continuously scraping the crystals adhered to the cooling surface, depending on the handling system, a large scraping force is required, so that a scraper of a type directly in contact with the cooling surface (generally a type pressed by a spring).
Has many problems such as a decrease in heat transfer coefficient, wear and tear of the scraper, and a clearance between the cooling surface and the scraper is secured, and the scraper is often of a fixed type.

[0006]

However, in this case, since a crystal layer having a thickness equivalent to the clearance is always adhered to the cooling surface, the heat transfer coefficient is extremely low and the crystallization tank used is very large. It is not economical.

[0007] In order to reduce the adhesion to the cooling surface, a method of reducing the temperature difference between the processing liquid (processed material) and the refrigerant is often used, but also in this case, the heat transfer area increases, and Crystal attachment cannot be completely prevented.

In general, when the concentration of a target component (a component to be crystallized) in a treated substance increases, the tendency of adhesion increases, and especially when the target component concentration becomes 70 to 80%, the scraping performance starts to decrease. , 90-95% or more, the content is remarkably reduced, and the direct scraping method often cannot be scraped.

Accordingly, a main object of the present invention is to improve the scraping performance in the scraping indirect cooling crystallization method.

[0010]

In order to crystallize the target substance from a liquid containing a plurality of components, the wall of the crystallization tank is cooled indirectly with a refrigerant, and the crystals deposited on the inner wall are scraped. In the crystallization operation, the crystallization operation is performed in a state where the purity of the crystal is not substantially reduced and the third component having solubility is added to the liquid to be treated, and the crystallization operation is performed on the inner wall surface of the crystallization layer.
Crystals that are to be scraped off and then the third component is separated from the crystals.
It can be solved by separating .

[0011]

According to the present invention, surprisingly, the addition of a third component, which does not substantially reduce the purity of the crystal and is soluble in the liquid to be treated, as described in the examples described below, The performance is dramatically improved.

To explain the present invention in more detail, in order to obtain a high-purity target component by crystallization, it is important to carry out the crystallization operation in the highest possible concentration region. This is for minimizing the residual amount of impurities remaining in the adhered liquid in the solid-liquid separation operation performed after the crystallization operation. However, as described above, even if the crystallization operation at a high concentration cannot be performed or is possible due to a problem on the scraping, the result is very inefficient, and as a result, it is possible to achieve high-purity crystallization. Often not.

In order to solve this problem, a third component which is inactive with respect to the processing substance, that is, a substance other than the target component originally contained in the processing substance is preferably added in a range of 1 to 10%. It was found that the adhesion of the target component to the cooling surface and the adhesion strength were significantly reduced.
This is presumed to be due to the fact that the third component added between the crystals attached to the cooling surface or between the crystal grains is mixed, thereby weakening the bonding force between the crystals or the crystal and the cooling surface.

[0014] More utilizing this property, be of any system, it is possible to crystallize while maintaining high heat transfer coefficient without lowering the scraping performance.

Since the addition of the third component remains as an impurity in the separated crystal, it is seemingly inconsistent with obtaining a high-purity crystal. Therefore, it is considered that there was no idea of the present invention. Can be However,
By selecting a substance having a very high relative volatility to the target component as the third component, after crystal separation, dissolve the crystal and remove the third component by a simple distillation or evaporation operation, or dry as a solid crystal It can be removed by evaporation in the process.

Thus, by adding the third component, the adhered crystals can be easily scraped off, so that a high heat transfer coefficient (200 to 1000 kal / m ² Hr ° C.) can be maintained.
The crystallization equipment is also compact. Further, since the scraper can be easily scraped , the life of the scraper is prolonged, the equipment cost and the maintenance cost are significantly reduced, and an economical crystallization process can be realized.

FIG. 1 shows a typical example of the crystallization apparatus used in the present invention. 1 is a crystallization tank, around which a cooling jacket 2
The coolant 3 is supplied to the cooling jacket 2, and the wall of the crystallization tank 1 is indirectly cooled by the coolant 3 in order to crystallize the target substance from the feed liquid 4 containing a plurality of components. ing. In the crystallization tank 1, a plurality of scraping blades 6 are provided in the height direction rotated by the drive motor 5.

The crystals precipitated on the inner wall surface are scraped off by the scraping blades 6.

In the present invention, the crystallization operation is carried out before or after supplying the third component which does not substantially lower the purity of the crystal and is soluble in the liquid to be treated, to or from the crystallization tank 1. Add before starting.

As the third component, one that does not substantially lower the purity of the crystal and has solubility in the liquid to be treated is used. The solubility includes those having complete solubility and those having partial solubility. Usually, it is preferable that the third component is inert to any of the components of the liquid to be treated. Further, it is desired that the third component does not affect processes before and after the crystallization operation process.

The crystallization tank 1 according to the present invention can be combined with other processes. For example, in FIG. 2, a plurality of, for example, two crystallization tanks 1A and 1B are provided.
0 is combined. That is, the feed solution 4 is supplied to the first crystallization tank 1A, where it is cooled and crystallized, and the crystallization slurry is separated directly or as necessary by a solid-liquid separation such as a cyclone through a conduit 11 as shown in FIG. The rich slurry is supplied to the upper part of the melting and refining tower 10. The melting and refining tower 10 has a stirrer 10a, a lower portion has a melting and heating means 10b such as a heater, and a lower and lower portion melts and heats the crystal by the melting and heating means 10b. An upward flow is given as a reflux liquid to wash the crystals moving downward. This enhances the purification effect. In addition, the melting and refining tower 10
The mother liquor is washed out by the clarified liquid on the upper part of the first crystallization tank, and the mother liquor is supplied to the first crystallization tank 1A through the return path 12, and the first crystallization tank 1A
Is supplied to the second crystallization tank 1B through the supply path 13,
Similarly, cooling crystallization is performed. The clarified liquid in the second crystallization tank 1B is supplied to the distillation column 15 via the supply path 14, the mother liquor is discharged from the lower part thereof together with the third component, and the vapor accompanying the distillation is converted into a liquid by the condenser 16 in the first crystallization tank 1B. 1A. Therefore, the equipment component denoted by reference numeral 17 constitutes the third component separation / recovery step.

FIG. 3 is similar to the example of FIG. 2, in which the crystal slurry from the first crystallization tank 1A is separated by a solid-liquid separator 20, and the filtrate is subjected to the third component separation and recovery step 1 described above.
7 and, on the other hand, the vapor generated when the crystal fraction separated by the solid-liquid separator 20 is dried by the dryer 21 is condensed by the condenser 22, and this liquid is combined with the liquid from the separation / recovery step 17 to obtain the first liquid. It is supplied to the crystallization tank 1A. The portion including the condenser 22 constitutes a separation / recovery step 23 for two or three components.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described to clarify the effects. (Example 1) A scraping cooling crystallization operation of cooling an aqueous solution containing fruit juice and sugar and separating water as ice was carried out by adding ethyl alcohol as a third component and changing the sugar concentration. An ethylene glycol aqueous solution at −20 ° C. was passed through a cooling jacket as a cooling medium to cool. In each operation,
The scraping performance was evaluated. Table 1 shows the results.

[0024]

[Table 1]

Example 2 Table 2 shows the results of the same evaluation performed by adding benzene as a third component to paradichlorobenzene.

[0026]

[Table 2]

(Example 3) The same evaluation was performed by adding water as the third component to caprolactam, and the results are shown in Table 3.

[0028]

[Table 3]

Example 4 Methyl methacrylate (M
Table 4 shows the results of the same evaluation performed by adding methanol as the third component to AA).

[0030]

[Table 4]

[0031]

As described above, according to the present invention, the scraping performance can be enhanced in the scraping type indirect cooling crystallization method. As a result, the size of the crystallization tank can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a cooling crystallization tank according to the present invention.

FIG. 2 is a flow sheet of a first example in combination with another device.

FIG. 3 is a flow sheet of a second example in combination with another device.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Hideki Suda 2-17-15 Tsukuda, Chuo-ku, Tokyo Inside Tsukishima Kikai Co., Ltd. (56) References JP-A-62-65702 (JP, A) International Publication 90 / 9372 (WO, A1) (58) Fields investigated (Int. Cl. ⁷ , DB name) B01D ^9/ 00-9/04

Claims (2)

(57) [Claims] 1. A crystallization operation in which a wall of a crystallization tank is indirectly cooled by a refrigerant and a crystal deposited on an inner wall is scraped in order to crystallize a target substance from a liquid containing a plurality of components. rows crystallization operation in a state of purity without substantial reduction, and the addition of a third component having a solubility in processing liquid
The crystals precipitated on the inner wall surface of the crystallization layer are scraped off and
And after that, a third component is separated from the crystals by a scraping-type indirect cooling crystallization method. 2. The method according to claim 1, wherein said third component is inert to any of the components of the liquid to be treated.