JPH0779922B2 - Purification of substances using pressure crystallization - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for purifying a substance using a pressure crystallization method.

(Prior Art) The pressure crystallization method has great potential for application to a raw material system that is difficult to separate by the conventional distillation method or cooling crystallization method, that a high-purity product is easily obtained, and Since the yield is easy to obtain and the energy consumption is small, it is a separation and refining technique that has been attracting a great deal of attention with the recent finer chemical industry, and has been put into practical use.

An outline of such pressure crystallization method is, for example, Volume 50 of Chemical Industry (19
1986) Page 331 "Outline of pressure crystallization method and equipment". This will be described with reference to FIG. 1 (a diagram showing the concept of the process flow and the apparatus). The pressure vessel (1) is provided with a lid (lower lid) (2) below and the piston (5) is a hydraulic unit. It is provided so as to move up and down in the container (1) by the operation of (3), and the crystallization chamber (4) is provided in the pressure container (1) by the piston (5) and the lower lid (2). It is formed. The crystallization chamber (4) and the drainage tank (6) are connected by a pipe (9) via a pressure reducing mechanism (10) and a valve (11). The crystallization chamber (4) and the preliminary crystallization can (7) are connected by a pipe (13) via a raw material supply pump (8) and a valve (12).

In this apparatus, the raw material is fed from the raw material tank (14) to the preliminary crystallization can (7), where it is cooled to generate seed crystals for pressure crystallization. This is because when the raw material without containing seed crystals is subjected to pressure crystallization, the supersaturation pressure in pressure crystallization is generally relatively high, at several hundred atmospheres or higher, and high pressure is required for initial crystal formation. Because there is a risk that
When the liquid is supplied in a slurry state containing seed crystals, there is an advantage that not only is there no concern about such supersaturation pressure, but also crystal growth can be expected without generation of nuclei due to pressurization.

Next, the raw material is injected into the crystallization chamber (4) from the pipe (13) through the valve (12). When the crystallization chamber (4) is filled with the raw material, the liquid begins to flow out through the overflow pipe (15) having an opening at the tip of the piston. When this is detected, the valves (12) and (16) are closed. Pressurization by the piston (5) is started. When the raw material liquid is pressurized, crystallization of the specific substance in the raw material proceeds, and the inside of the crystallization chamber (4) is in a solid-liquid equilibrium state under high pressure. The solid formed at this time is generally an extremely high-purity substance. Although the temperature in the crystallization chamber (4) rises due to the latent heat of solidification generated with the progress of solidification, the pressure crystallization method generally does not perform cooling to prevent this temperature rise, and adiabatically applies it. The method of pressing is adopted. The ultimate temperature after the temperature is raised, that is, the solid-liquid separation start temperature affects the purity and yield of the product, and is adjusted by the liquid supply temperature in consideration of the specific heat of the raw material mixture and the latent heat of solidification.

Next, when the pressure is increased to a predetermined pressure, generally, a predetermined solid-liquid ratio (saturated state) is immediately reached. Therefore, as soon as this pressure is detected, the valve (11) is opened and the hydraulic unit (3) moves to the piston (5). When the piston continues to descend while the pressure acting on the) is maintained, the liquid phase is transferred from the crystallization chamber (4) to the drain tank (6) while the pressure inside the crystallization chamber (4) is kept constant. Is discharged. When the piston (5) is further continued to descend, the crystal grains in the crystallization chamber (4) are pressed and squeezed, and the residual liquid between the crystal grains is subjected to a so-called "squeeze action" and discharged to the drainage tank (6). To be done.

As the piston (5) is further lowered, the crystal grains are formed into one large lump solid product along the shape of the crystallization chamber (4). In this way, when the liquid is separated from the solid into almost the whole, the liquid phase pressure in the crystallization chamber (4) communicating with the drainage tank (6) under atmospheric pressure gradually decreases. The crystal surface is partially melted, a so-called "perspiration cleaning" is performed, and a lump solid product is purified.

When the pressure of the waste liquid discharged from the crystallization chamber (4) drops to a predetermined pressure, the lowering of the piston (5) is stopped, the ascent of the piston is started, and the high-pressure container (1) is also raised. The solid product is taken out of the container (1) while being placed on the lower lid (2). This is taken out by a product take-out device (not shown), the high-pressure container (1) is lowered and attached to the lower lid (2), and then the process of injecting the raw material is repeated and the same process is repeated. In addition, prior to the injection of raw materials, the residual liquid in the overflow pipe (15) is purged with a gas such as nitrogen gas that is inert to the product, and preparations for full liquid detection at the time of injection in the next process are made. Keep it.

By repeating the above steps, products are continuously produced.

(Problems to be Solved by the Invention) As described above, the conventional pressure crystallization method is to pressurize a raw material in a high-pressure vessel to cause crystallization to form a mixture in a solid-liquid coexisting state, and The liquid phase is discharged under pressure to perform solid-liquid separation,
Further, the mixture in the container (group of crystal grains containing residual liquid) is squeezed to form a solid product of the specific component in the container, and then the product is taken out.

FIG. 2 shows a schematic view of the state of a solid product obtained by such a pressure crystallization method. As shown in this figure, the liquid (18) (black part in the figure) is the crystal grain (17) inside the product.
It remains trapped between them. This residual liquid (18)
Since the raw material supplied has a composition that is uniquely determined by the operating conditions of each step of pressure crystallization, it necessarily contains components (impurities) other than the specific components. Therefore, the solid product cannot be a completely pure substance. In addition, since the product is a highly compressed mass, the crystal grains (17) have a strong bonding force, so that the residual liquid (18) in the product is large.
Is extremely difficult to remove and separate. Therefore, the conventional pressure crystallization method naturally has a limit to the purification of the product.
This is a very serious problem in the pressure crystallization method in which highly purified products are required.

A pressure crystallization method has also been proposed in which a part of the solid-liquid separation step is performed by using an enclosed gas or a supply gas in order to break the limit of the product purity. This method discharges the liquid phase component by replacing the liquid phase component with gas, and can reduce the amount of the residual liquid between the crystal grains. However, since this method requires the pressure to be in the range of several thousand to several hundreds of atmospheres, a high-pressure container having much higher pressure resistance than the conventional one is required, and therefore the shape of the high-pressure container is limited. There is a problem on the device such as. Although it can be performed at a lower pressure than this, in this case, since the liquid flow path length in the crystal group becomes large, the solid-liquid separation time becomes long, and as a result, the processing capacity decreases and the production amount Will be reduced. In addition, a gas blow-through phenomenon is likely to occur, resulting in a reduction in product purity.

The present invention has been made by paying attention to such a situation, and its object is to solve the above-mentioned problems of the conventional one, without increasing the pressure strength of the high-pressure container,
Another object of the present invention is to provide a method for purifying a substance using a pressure crystallization method which can break the limit of product purity in the conventional pressure crystallization method without causing a decrease in production amount.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a method for purifying a substance using a pressure crystallization method having the following constitution.

That is, the method according to the first aspect is a mixture in a solid-liquid coexisting state in which a raw material composed of two or more kinds of components including a specific component is supplied to a high-pressure container, and the raw material in the container is pressurized to cause crystallization. Then, the discharge of the liquid phase component to the outside of the high-pressure container under pressure is started, the discharge is stopped before the mixture in the high-pressure container is agglomerated, and then the mixture is taken out of the high-pressure container. A method for purifying a substance using a pressure crystallization method, which comprises subjecting the mixture outside the container to a separation treatment of a liquid phase to recover a solid of a specific component.

The method according to claim 2 is characterized in that after the liquid phase component of the mixture outside the high-pressure vessel is separated, solvent washing is further performed, and the solid of the specific component is recovered after the washing. A method for purifying a substance using the pressure crystallization method described in the item.

The method according to claim 3 is the pressure crystallization method according to claim 1 or 2, wherein the liquid phase component of the mixture outside the high-pressure container is separated by replacing the liquid phase component with a gas. Is a method for purifying a substance using.

The method according to claim 4 is a method for purifying a substance using the pressure crystallization method according to claim 3, wherein the substitution is performed by filtering the mixture outside the high-pressure vessel.

The method according to claim 5 is a method for purifying a substance using the pressure crystallization method according to claim 3, wherein the substitution is performed by subjecting the mixture outside the high-pressure vessel to a centrifugal separation treatment.

The method according to claim 6 is a method for purifying a substance using the pressure crystallization method according to claim 4, wherein the filtration is performed with a vacuum filter.

The method according to claim 7 is a method for purifying a substance using the pressure crystallization method according to claim 4, wherein the filtration is performed using a pressurized gas.

(Operation) In the pressure crystallization method according to the present invention, as described above, the raw material in the high-pressure vessel is pressure-crystallized to form a mixture in a solid-liquid coexisting state, and then the mixture is pressurized to the outside of the high-pressure vessel. The discharge of the liquid phase component is started, and the discharge is stopped before the mixture in the high-pressure container agglomerates. In this way, a part or most of the liquid phase is discharged to the outside of the high-pressure container, but the mixture in the high-pressure container after the discharge is not a solid mass but a slurry or soft one.

Then, the mixture in the high-pressure container is taken out of the high-pressure container. Since the mixture outside the high-pressure container is inevitably slurry-like or soft-like, the cohesive force between the crystals is weak, and therefore it is extremely easy to remove and separate the residual liquid in the mixture.

The mixture outside the container is subjected to a liquid phase component separation treatment to recover the solid of the specific component. Since the separation process of the liquid phase is performed outside the container in this way, it can be performed under atmospheric pressure, and therefore the most effective separation process can be selected without being limited to the mechanical squeeze separation method. Becomes Further, the above mixture is extremely easy to remove and separate the residual liquid as described above. Therefore, by this separation treatment, almost all of the liquid phase component can be separated and removed.
Therefore, the purity of the solid (product) of the specific component to be recovered can be increased, and the limit of product purity in the conventional pressure crystallization method can be overcome.

Further, in the method according to the second aspect, since the liquid phase component of the mixture outside the high-pressure vessel is separated, solvent washing is further performed, and the solid of the specific component is recovered after the washing. It becomes possible to more surely achieve high purity.

The method described above can be naturally performed without increasing the pressure resistance of the high-pressure container and without lowering the production amount.

In the method according to the present invention, the liquid phase component separation treatment of the mixture outside the high-pressure vessel can be performed by a method of replacing the liquid phase component with a gas, and the replacement method is preferable. This is because the substitution method can be carried out more easily than other methods, and the amount of liquid phase separated can be increased.

More specifically, the replacement may be performed by a filtration method or a centrifugal separation method.

This filtration method is preferably a method using a vacuum filter or a method using a pressurized gas. This is because the separation speed of the liquid phase component is increased and the production amount is improved. The choice between the two is determined by the crystal shape and size.

(Example) An example according to the present invention will be described. The pressure crystallizer used in the examples is a pilot plant of 1.5,
The configuration contents are the same as those described in FIG. 1 except for the scale (capacity).

Example 1 A cresol mixture (p-cresol 80%, balance m-cresol) was cooled to 15 ° C. in a preliminary crystallization can to form a slurry state, which was then injected into a high-pressure vessel (crystallization chamber), and then the vessel. The internal raw material was pressurized up to 1500 atm for crystallization. Continue pressure 15
Starting to discharge the liquid phase component outside the container while maintaining at 00 atm,
When half the liquid phase was discharged, the liquid phase discharge was stopped. Next, the pressure was reduced to atmospheric pressure, the mixture in the container (substantially slurry-like) was taken out of the container, transferred to a centrifuge, and subjected to a liquid phase separation treatment, and then the solid was recovered.

The obtained solid was p-cresol with a purity of 99.85%. This purity seems to be almost the same as the purity of 99.70% in the case of the conventional method (for example, Comparative Example 1 shown below), but in consideration of the difference in the purity range of this level, the above-mentioned purity increase is not observed. This is a very large effect and has a very great industrial significance.

Incidentally, in the above example, the liquid phase component discharge was stopped at the time when the mixture in the high pressure vessel was in a substantially slurry state, but the time when the mixture in the high pressure vessel became a soft solid cake in addition to this example, or Even if the discharge of the liquid phase component is stopped before the cake is formed, the same effect as in the above-described embodiment can be obtained.

Further, the separation treatment of the liquid phase was performed by a centrifuge,
In addition to this, the same effect as in the above embodiment can be obtained by the filtration method.

Further, the mixture taken out of the container was subjected to separation treatment of the liquid phase as it was, but when the mixture taken out of the container was a soft solid cake, a liquid having the same composition as the liquid phase in the mixture, Alternatively, if a liquid containing less impurities than that is added to form a slurry and then the separation process of the liquid phase is performed, the separation process becomes easy. Further, even when the mixture taken out of the container is in a substantially slurry form, it is easier to separate the liquid phase by separating the liquid phase after adding the same liquid as above to make the mixture more slurry. In these cases, the same effect as that of the above-mentioned embodiment can be obtained in terms of product purity.

Comparative Example 1 As in Example 1, the raw material was cooled to 15 ° C., poured into a high-pressure container, pressurized to 1500 atm, and then the liquid phase was discharged while maintaining this pressure to perform solid-liquid separation, followed by squeezing. Then, perspiration was performed under reduced pressure up to 600 atm, and the solid formed in the container was taken out.

The purity of the obtained solid was 99.70%.

(Effects of the Invention) According to the method for purifying a substance using the pressure crystallization method according to the present invention, without increasing the pressure resistance of the high-pressure vessel,
It is possible to break the limit of product purity in the conventional pressure crystallization method without causing a decrease in production amount.

[Brief description of drawings]

FIG. 1 is a diagram showing the concept of a process flow and a device relating to a conventional pressure crystallization method, and FIG. 2 is a schematic diagram relating to the state of a solid product obtained by the conventional pressure crystallization method. (1) …… Pressure vessel, (2) …… Lower lid (3) …… Hydraulic unit, (4) …… Crystallization chamber (5) …… Piston, (6) …… Drainage tank (7)… … Preliminary crystallization can, (8) …… Raw material supply pump (9) (13) …… Piping, (10) …… Decompression mechanism (11) (12) (16) …… Valve, (14) …… Raw material Tank (15) …… Overflow pipe, (17) …… Crystal grain (18) …… Residual liquid

Claims (7)

[Claims] 1. A raw material composed of two or more components including a specific component is supplied to a high-pressure vessel, and the raw material in the vessel is pressurized to cause crystallization to form a mixture in a solid-liquid coexisting state. The discharge of the liquid phase component outside the high-pressure container under pressure is started, the discharge is stopped before the mixture in the high-pressure container agglomerates, then the mixture is taken out of the high-pressure container, and the liquid phase is further added to the mixture outside the container. A method for purifying a substance using a pressure crystallization method, which comprises subjecting a solid component of a specific component to recovery by performing a separation treatment of minutes. 2. The pressure according to claim 1, wherein after the separation of the liquid phase of the mixture outside the high-pressure vessel, a solvent washing is further performed, and the solid of the specific component is recovered after the washing. Purification of substances using crystallization. 3. A substance using the pressure crystallization method according to claim 1 or 2, wherein the liquid phase component of the mixture outside the high-pressure vessel is separated by replacing the liquid phase component with a gas. Purification method. 4. A method for purifying a substance using a pressure crystallization method according to claim 3, wherein the substitution is carried out by filtering the mixture outside the high-pressure vessel. 5. The method for purifying a substance using the pressure crystallization method according to claim 3, wherein the substitution is performed by subjecting the mixture outside the high-pressure vessel to a centrifugal separation treatment. 6. The method for purifying a substance using the pressure crystallization method according to claim 4, wherein the filtration is performed by a vacuum filter. 7. The method for purifying a substance using the pressure crystallization method according to claim 4, wherein the filtration is performed using a pressurized gas.