JPH0794001B2 - Countercurrent melt cooling refining method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a countercurrent melt cooling and refining method for purifying one component from a crystal of a plurality of components by combining a cooling type crystallizer and a vertical melting and refining machine.

[0002]

2. Description of the Related Art When a pure component is to be obtained from a mixture of multi-component substances, there are unit operations such as a distillation method or an extraction method, but the former uses a large amount of heat energy and the latter requires an operation. It may be complicated and unsatisfactory in terms of purity. On the other hand, if the mixture is cooled to obtain pure crystals of the desired component A within a certain concentration range, a purification method by crystallization is possible.

That is, industrially, a substance of interest can be cooled to obtain a pure A component, which can be obtained by a solid-liquid separator. At this time, components other than the component A increase in the removed mother liquor. If it is attempted to recover the component A from this mother liquor,
It is necessary to cool at a temperature lower than the first crystallization temperature. For this reason, conventionally, (1) unit crystal tanks are simply arranged in multiple stages in series to form a continuous tank, or (2) a horizontal stirring crystal tank is continuously operated.

[0004]

In the case of the conventional multi-stage tank of the above (1), a method is adopted in which the temperature of each tank is sequentially lowered and the processing liquid is caused to flow along this flow. , In this method, the crystals and mother liquor are completely mixed in each crystal tank,
Since it moves together with the crystals produced in the next tank, the mother liquor with the highest concentration of the B component and the crystals of the A component coexist in the final tank, and therefore the A component is separated by the solid-liquid separation device. However, since the concentration of the B component in the mother liquor attached to the crystals is high, it is difficult to obtain a pure A component as a whole.

In a crystal facility using such a multi-stage tank, it is ideally desirable that the intended crystals of the A component and the mother liquor containing a large amount of the B component be countercurrent. The reason is that the amount of the B component attached to the crystals obtained from the first tank with the smallest B component is the smallest.

Many attempts have been made to make such a countercurrent method, and the simplest method among them is that the feed liquid flows into each tank by gravity, and the crystals obtained in each tank are This is a method in which the crystals are moved to the higher temperature side and the mother liquor is moved to the lower temperature side by treating with a solid-liquid separator provided between each tank. According to this method, the movement of the crystal and the mother liquor is surely countercurrent, the crystal comes into contact with the mother liquor having a large amount of the A component on the high temperature side, and the B component attached to the crystal is diluted by the high temperature mother liquor and reduced. Therefore, the most disadvantageous aspect is that it requires expensive solid-liquid separation equipment (filter, centrifuge, etc.) and its operating and maintenance costs are high.

On the other hand, in the above-mentioned conventional method (2), specifically, a ribbon blade is provided inside the horizontal jacketed crystal tank to continuously cool and generate the generated crystal in one direction. On the other hand, it is a method of continuously flowing the liquid countercurrently. However, in this method, crystals often float in the tank and are entrained in the liquid, and a countercurrent is not often generated. Further, in order to obtain a temperature difference per 1 ° C., a distance of about 2 m is required. Therefore, for example, if the difference between the melting temperature of the product and the crystal precipitation temperature on the low temperature side containing a large amount of impurities is large, the total horizontal length of the crystal tank will be considerably long, and not only will the installation space be large. , The movement of the crystal in the crystal tank,
The amount of movement differs at each position, and the cooled crystals and the flow of warm mother liquor are relatively unstable or the amount of precipitated crystals changes, which makes it difficult to achieve stable operation.

On the other hand, the crystals and mother liquor thus obtained are usually supplied to a vertical melting and refining machine, or the crystals are taken out by a centrifugal separator to obtain a product. In the case of the former, there are many cases in which continuous processing is possible by combining with a crystallizer, but with such a kind, there is no settling part (clarification part) of the liquid that moves to the low temperature side, so crystals are entrained. Separation efficiency is poor. In order to improve this point, it is necessary to provide a crystal settling section in the upper part of the refiner.

When the latter centrifuge is used,
The mother liquor adheres, and there is a limit to the purity of crystals that can be obtained by substitution and washing. The reason is that there are voids between the particles of the cake layer that have been dehydrated by centrifugal force, and since the voids have a gas present, there is a contact adhesion part between the particles, so when a cleaning liquid is applied, This is because the cleaning liquid is accelerated by the centrifugal force, so that the cleaning liquid passes through the surface of the particles having voids without sufficient contact, or the cleaning liquid does not sufficiently contact the contact portion. Therefore, in any case, in the case of crystallization, if the purity is to be increased, recrystallization must be performed a plurality of times, resulting in a significant increase in operating cost.

The present invention cleverly solves the problems of the conventional method. And the objective is to provide a refining method with a low equipment cost and high refining efficiency.

[0011]

According to the present invention for solving the above-mentioned problems, a vertical melting apparatus having a plurality of cooling type crystal tanks each having a refining section in an upper part and a refining section in an upper part and a heater in a lower part, respectively. Using equipment equipped with a purification tower, while supplying the raw materials to the crystallization tank, each of the crystallization tanks perform crystallization operation at a different temperature, the purification tower is the highest temperature of each crystallization operation temperature The crystals produced in the crystallizer operating at a higher temperature are guided to the refining section of the crystallizer where the crystallization operation is performed at a higher temperature, and the crystals produced in the crystallizer with the highest crystallization operation temperature are solid. It leads to the refining section of the purification tower through the liquid separation means, melts the crystals that move to the lower part of the purification tower by the heater at the lower part, takes out a part of the melt as a product, and refluxes the other part. It rises as a liquid and moves to the lower part After cleaning the crystals, the clearing liquid in the upper part of the purification tower and the crystallizing tank is transferred in order from the crystallizing tank with a higher crystallization operation temperature to the lower one, and the clearing liquid in the final low-temperature crystallizing tank is taken out of the system. Regarding the relationship between the produced crystals and the mother liquor in the melted mixture of the plurality of components, the purification of the crystals formed and the mother liquor between the upper and lower portions of the crystal tank and the upper and lower portions of the purification tower from the crystal tank is performed. The flow to the refining section of the tower and the flow from the upper refining section of the purification tower to the crystallizing tank have countercurrent relationships.

Here, solid-liquid separating means can be provided between a plurality of crystallizing tanks. The solid-liquid separation means is preferably a liquid cyclone.

[0013]

The present invention relates to the relationship between the produced crystals and the mother liquor in the molten mixture of the target components, and the flow of the produced crystals and the mother liquor between the upper and lower portions of the crystal tank and the upper and lower portions of the purification column. With respect to the flow of, the flow from the crystal tank to the refining section of the purification tower and the flow from the upper refining section of the purification tower to the crystal tank have countercurrent relations with each other, so equipment cost is reduced and high-purity crystals are obtained. Can be efficiently purified.

[0014]

The present invention will now be described by way of specific examples for achieving this object. The drawing shows one specific example,
Two crystallization tanks 1A and 1B are provided as crystallization tanks, and this is combined with the purification tower 2.

Each of the first and second crystallizing tanks 1A and 1B has refining portions 10A and 10B at the upper portion thereof, cooling jacket portions 12A and 12B through which a cooling medium 11 is passed are provided at the lower peripheral wall thereof, and inside thereof. Heat transfer surface scraping blades 14A, 14B are rotatably driven by the stirring drive devices 13A, 13B.

At the lower portion, a crystal slurry outlet 15 is provided.
The crystal slurry extracted from the crystal slurry withdrawal port 15B, which has A and 15B, is fed to the refining section 10A of the first crystal tank 1A by the slurry pump 16B and the crystal slurry withdrawal port 1
The crystal slurry from 5A is configured to be fed to the refining section 20 in the upper part of the purification tower 2 by the slurry pump 16A. In the lower part of the first crystal tank 1A, a molten mixture 17 of a plurality of components, for example, a eutectic system containing the components A and B, in which the crystallization temperature of the A component is high and the crystallization temperature of the mixture of the AB component is low, A supply port for the mixture is provided.

On the other hand, the refining tower 2 is of a vertical type, and has a refining section 20 above it. Further, the refining tower 2 has a refining principle known in, for example, Japanese Patent Publication No. 54-34705, except that it has a refining section 20 at the top. That is, a heater 22 through which a heat medium 21 such as steam is passed is provided in the lower part, and an agitator 2 for stabilizing the behavior of the crystal particle layer in a region below the refining part 20 is provided inside.
3 are arranged and can be operated by the drive motor 24. Further, a screen 25 is arranged in the lower part, and a part of the melt is extracted as a product 27 by a pump 26 while removing impurities here.

On the other hand, an overflow port 28 is formed in the upper part of the purification tower 2, and the clarified liquid is guided to the clarification part 10A of the first crystallization tank 1A by gravity by the pipe line 31, and the clarification part of the first crystallization tank 1A. An overflow port 18A is formed in 10A, and the clarified liquid flowing out from the overflow port 18A is supplied to the clarification section 10B of the second crystallization tank 1B by a conduit 32.
The clarified liquid from the overflow port 18B, which is guided by the above, is discharged to the outside of the system through the pipe line 33.

In the refining equipment thus constructed, the second
The crystallizing tank 1B, the first crystallizing tank 1A, and the refining tower 2 are sequentially operated at higher temperatures. In the example, the crystallization temperature of the second crystal tank 1B is 13 ° C., that of the first crystal tank 1A is 43 ° C., and in the refining tower 2, the upper portion thereof is 48 ° C. and the lower portion thereof is 53 ° C.

When the molten mixture 17 is supplied to the first crystal tank 1A, it is cooled by its scraping cooling surface and becomes supersaturated.
The supersaturated liquid comes into contact with already existing crystals to be produced and grown. The crystal slurry thus obtained is guided to the refining section 20 of the purification tower 2. Further, the crystal slurry obtained by the crystallization operation of the second crystal tank 1B is guided to the refining section 10A of the first crystal tank.

The following operations are carried out in the purification tower 2. That is, in the refining unit 20, the crystals and the mother liquor in the guided crystal slurry are dispersed by the rising mother liquor of high purity, diluted and washed, and then transferred to the lower crystal particle layer. In the crystal particle layer, the crystal slowly descends, and at the same time, the crystal surface is melted and washed while being in contact with the ascending molten reflux liquid, and at the same time, reaches the melting part of the heater 22 and is melted there, and part of the product 27 Is extracted as. The melt other than withdrawal becomes a reflux liquid, which rises in the column and is used for washing the falling crystals. Such an operation is continuously performed.

The clarified liquid diluted and clarified in the clarification section 20 of the purification tower 2 is returned to the first crystallization tank 1A for crystallization. Further, in the upper part of the first crystal tank 1A, the second crystal tank 1B is provided.
The crystal slurry derived from (1) is mixed with the mother liquor in the first crystal tank 1A to dilute and wash the crystals, and the purified crystals descend to the lower crystal generating portion. On the other hand, the mother liquor obtained under the precipitation conditions of the first crystal tank 1A is guided to the refining section 10B of the second crystal tank 1B because it is necessary to further lower the cooling temperature to recover the A component, and the second crystal tank A similar crystallization operation is performed in 1B. The final mother liquor containing a large amount of B component is taken out of the system through the conduit 33.

As described above, according to the method of the present invention, the crystals and the mother liquor are surely brought into countercurrent contact with each other, so that the purification efficiency is extremely high, and the solid-liquid separation device is not necessarily required. Costs and operating costs are reduced.

Further, in the present invention, in order to obtain a large temperature difference, and by reducing the amount of the mother liquor in the slurry that moves to the high temperature side, the countercurrent efficiency with the refining liquid that overflows countercurrently from the refining section on the high temperature side. A solid-liquid separation means is provided in order to increase the temperature. That is, in FIG. 1, reference numeral 50 is a liquid cyclone as the solid-liquid separating means.

The solid-liquid separating means may be a solid-liquid separating device such as a filter or a centrifuge, but a liquid cyclone is advantageous in terms of maintenance.

Further, in the crystallization tank, the refining section and the crystallization section may be separated by a partition wall or a partition. With this configuration, it is possible to prevent the crystallized substances from moving to the refining section. The supply position of the eutectic material as a raw material may be selected according to the supply concentration. High purity ones are supplied to the high temperature side crystal tank, and low purity ones are supplied to the low temperature side crystal tank. Further, in the case where the recrystallization is repeated to obtain the purity in the factory, the operation in the same equipment may be repeated a plurality of times. However, in the case of the method of the present invention, a highly pure product can be easily obtained, and thus it is not usually required.

Although the above example is an example in which two units are provided as the crystallization tank, the number of units may be further increased, or only one unit may be combined with the purification column. In short, the purity you are trying to obtain,
The radix of the crystallization tank is selected depending on how much the component A is to be recovered.

By the way, in the above description, it was mentioned that a solid-liquid separator may be provided.

When the solid-liquid separator is not provided, the crystal slurry moves from the crystallization section to the refining section at almost the same temperature, so that a temperature difference cannot be obtained between the crystal tanks and the purification tower. If you absolutely want to take the temperature difference, there is also a method of evaporating with an evaporator and transferring only crystals to the refining section, but in this case heat energy is required,
The mother liquor is wasted. Therefore, if it is necessary to obtain a temperature difference, a filter or a cyclone may be provided to transfer only the crystals to the refining section. When a filter is used, a maximum temperature difference of 30 ° C. and when a cyclone is used, a temperature difference of usually about 5 ° C. and a maximum of about 10 to 15 ° C. can be taken.
The mother liquor after separation, in the case of a filter, to the clarification section of the crystallization tank,
In the case of a cyclone, some crystals are entrained in the mother liquor, so it is desirable to return them to the lower part of the refining section or the crystallization section.

Next, examples will be shown. The PDCB (para-dichlorobenzene) has a device configuration similar to that of the above specific example.
Was purified. The crystal tank has a diameter of 600 mm and a height of 100
Cooling crystal tank with 0mm jacket, with a jacket height of 600mm, a liquid height of 900mm, and a liquid refining section of 300mm.
Two of these crystal vessels were arranged in series. Also 400m in diameter
A purification tower having a heater of m, height of 2000 mm, and an electric heating area of 0.2 m ^{2 at} the bottom was prepared. The heating area of the crystal tank is
A 1.14 ^2, also attached to the agitator was operated at 20rpm by 1.5 kW motor, and provided with a scraper blade capable Although Ri front scraping the lateral surface, and a structure having a draft tube in the center.

For such a device, PDCB 90%, ODCB (
An average of 100% of a mixture of 9% ortho-dichlorobenzene) and 1% MDCB (meta-dichlorobenzene).
It is supplied at a rate of kg / hr, the clarified liquid obtained from the upper part of the first tank is supplied to the second tank, the precipitated crystals are supplied to the upper part of the purification tower, and the product is taken out from the lower part of the purification tower and the The overflow liquid was returned to the first tank. In the second crystal tank, the overflow liquid from the first tank was received to crystallize PDCB, the obtained crystals were fed to the first tank, and the upper overflow liquid was taken out of the system.

The operating temperature conditions were 43 ° C. in the first tank, 13 ° C. in the second tank, 48 ° C. in the upper part of the purification tower, and 53 ° C. in the lower part. The product in the purification tower was extracted at 83 kg / hr, and the PDCB purity was 99.9%. The reflux amount in the purification tower is 25
It was ~ 30 kg / hr. Furthermore, the amount of crystals transferred from the second tank to the first tank is about 70 kg / hr, that from the first tank to the second tank is about 220 kg / hr, and the concentration of the overflow liquid from the second tank is
The PDCB was 40% and the recovery rate was 92.6%.

As in this embodiment, according to the method of the present invention,
Compared with the above-mentioned distillation method, the heat of fusion generally transferred to the lower part in the purification column is 1/10 to 1/5 of the latent heat of vaporization, and the boiling point is similar to that of the PDCB purification in the above-mentioned embodiment. Compared with the distillation method in the case of the system having the, the reflux ratio may be 1/10 to 1/100, so the steam consumption for heating is 1/10 or less, and the heat energy is extremely small.

Further, in the case of using a conventional crystallizer, if a high-purity product is to be obtained, a recrystallization method must be carried out 2-3 times, but as described above, a purity of 99.9% is 1%. It can be achieved by refining once, energy saving is possible, and the product loss was about 5% when the recrystallization operation was performed, whereas according to the method of the present invention, it was almost zero, and the recrystallization method was also used. However, the number of operators required was 2 to 3, but it was found that the present invention requires 0.5.

[0035]

As described above, according to the present invention, the facility cost and the operating cost can be reduced, and the operation with high purification efficiency can be performed.

[Brief description of drawings]

FIG. 1 is a flow sheet showing an example of the present invention.

FIG. 2 is a detailed view of a main part thereof.

[Explanation of symbols]

1A ... 1st crystal tank, 1B ... 2nd crystal tank, 2 ... Purification tower, 1
0A, 10B, 20 ... Clarifying section, 12A, 12B ... Cooling jacket, 14A, 14B ... Scraping blade, 17 ... Molten mixture, 22 ... Heater, 23 ... Stirrer, 27 ... Product, 50
… Hydrocyclone.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuto Nakamaru 2-17-15 Tsukushima, Chuo-ku, Tokyo Within Tsukishima Kikai Co., Ltd. (72) Koji Miwa 2-17-15 Tsukishima, Chuo-ku, Tokyo Tsukishima Machinery Co., Ltd. (56) Reference JP-A-57-99301 (JP, A) JP-B 53-9585 (JP, B2) JP-B 4-31721 (JP, B2)

Claims (3)

[Claims] 1. A crystallization tank equipped with a plurality of cooling type crystal tanks each having a refining section at the top and a vertical melting and refining tower having a refining section at the top and a heater at the bottom, respectively. While supplying the raw materials, each of the crystallizing tanks performs a crystallization operation at a different temperature, the refining tower is operated at a temperature higher than the highest temperature among the crystallization operating temperatures, and the crystals produced in the crystallizing tank are It is led to the refining section of the crystal tank where the crystallization operation is performed at a higher temperature, and the crystals produced in the crystal tank with the highest crystallization operation temperature are introduced to the refining section of the purification tower through the solid-liquid separation means for purification. The crystals that move to the lower part of the column are melted by the heater of the lower part, a part of the melt is taken out as a product, the other part is raised as reflux liquid, and the crystals that move to the lower part are washed. , Clearing liquid at the top of the purification tower and crystallizer The crystallization operation temperature is changed from a high-temperature crystallization tank to a low-temperature crystallization tank in this order, and the final low-temperature crystallization tank clarified liquid is taken out of the system. Regarding the flow of the produced crystals and the flow of the mother liquor between the upper and lower portions of the crystal tank and between the upper and lower portions of the purification tower, the flow from the crystal tank to the refining section of the purification tower and the crystals from the upper refining section of the purification tower A countercurrent melt cooling and refining method characterized by having countercurrent relationships in the flow to the tank. 2. The countercurrent melt cooling and refining method according to claim 2, further comprising solid-liquid separating means between a plurality of crystallizing tanks. 3. The countercurrent melt cooling and refining method according to claim 1, wherein the solid-liquid separating means is a liquid cyclone.