JPH02157003A - Method for purifying substances by pressure crystallization process - Google Patents

Abstract

PURPOSE:To raise the purity of products by taking a mixture out of a high pressure vessel and effecting thereafter the separation of liquid phase therefrom. CONSTITUTION:A mixture of cresol (80% p-cresol, remainder being m-cresol) is cooled to 15 deg.C in a preliminary crystallization tank to form it into a slurry, which slurry is then fed into a high pressure vessel so as to be pressurized up to 1,500atm. to effect crystallization, following which its liquid phase is discharged under 1,500atm. to the outside until half of the liquid has been discharged, whereupon the discharge of liquid phase is stopped and the pressure in the vessel is reduced to atmospheric pressure, whereby the mixture in the vessel(nearly a slurry) is taken out of the vessel to be transferred to a centrifuge, where the liquid phase is separated and thereafter the solids are recovered. The solids thus obtained are p-cresol of 99.85% purity.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a method for purifying substances using pressure crystallization.

(Conventional technology) Pressure crystallization has great potential for application to raw material systems that are difficult to separate using conventional distillation or cooling crystallization, is easy to obtain high-purity products, and has high Due to its easy yield and low energy consumption, it is a separation and purification technology that has been attracting a lot of attention as the chemical industry has become increasingly refined in recent years, and has been put into practical use.

An overview of this pressure crystallization method can be found, for example, in Kagaku Kogyo Volume 50 (
(1986), p. 331, "Outline of pressure crystallization method and apparatus". To explain this using Figure 1 (a diagram showing the process flow and the concept of the device), the pressure vessel (1)
A lid body (lower lid) (2) is provided below, and a piston (5) is provided to move up and down within the container (1) by the operation of a hydraulic unit (3). (
5) and the lower lid (2) form a crystallization chamber (4) within the pressure vessel (1). This crystallization chamber (4) and the drain tank (
6) is connected by a pipe (9) via a pressure reducing mechanism 00) and a valve (11). Further, the crystallization chamber (4) and the pre-crystallizer (7) are connected via a raw material supply pump (8) and a valve (03) via a pipe (03).

In this apparatus, raw materials are fed from a raw material tank 04 to a pre-crystallizer (7), where they are cooled to produce seed crystals for pressure crystallization. This is because when raw materials without seed crystals are subjected to pressure crystallization, the supersaturation pressure is generally relatively high, typically several hundred atmospheres or more, and high pressure is required for initial crystal formation. This is because there is a risk that the slurry containing seed crystals will be supplied, which has the advantage that not only is there no need to worry about such supersaturation pressure, but crystal growth can be expected without nucleation due to pressurization.

Next, the raw material is passed from pipe 03) to valve 02) into the crystallization chamber (
4) Inject. When the crystallization chamber (4) is filled with raw materials,
An overflow pipe (15) with an opening at the tip of the piston
As the liquid begins to flow out through valve 02, this is detected and valve 02 is opened.
), 06) are closed and pressurization by the piston (5) is started. When the raw material liquid is pressurized, crystallization of a specific substance in the raw material progresses, and the inside of the crystallization chamber (4) becomes in a solid-liquid equilibrium state under high pressure. The solid produced at this time is generally a substance of extremely high purity. Note that the temperature inside the crystallization chamber (4) rises due to the latent heat of solidification generated as assimilation progresses, but in the pressure crystallization method, cooling is generally not performed to prevent this temperature rise, and instead an adiabatic A method of applying pressure is adopted. The temperature reached after the temperature rise, that is, the temperature at which solid-liquid separation starts, affects the purity and yield of the product, so this is adjusted by the temperature of the supplied liquid, taking into consideration the specific heat, latent heat of assimilation, etc. of the raw material mixture.

Next, when the pressure is increased to a predetermined pressure, the predetermined solid-liquid ratio (saturation state) is immediately reached. ), the pressure inside the crystallization chamber (4) remains constant and the liquid phase flows from the crystallization chamber (4) to the drain tank (6).
) is discharged. Further, as the piston (5) continues to descend, the crystal grains in the crystallization chamber (4) are compressed and the remaining liquid between the crystal grains is discharged into the drain tank (6) through the so-called "squeezing action". be done.

As the piston (5) continues to descend further, the crystal grains are formed into one large lumpy solid product along the shape of the crystallization chamber (4). When the liquid is almost completely separated from the solid in this way, the liquid phase pressure in the crystallization chamber (4) communicating with the drain tank (6) under atmospheric pressure gradually decreases. , the crystal surface is partially melted, a so-called "sweating wash" is carried out, and the bulk solid product is purified.

When the pressure of the waste liquid discharged from the crystallization chamber (4) decreases to a predetermined pressure, the piston (5) stops descending, and at the same time the piston begins to rise, the high pressure container (1) also rises. , the solid product is removed from the container (1) while being placed on the lower lid (2). This is the product removal device (
(not shown), lower the high-pressure container (1) and attach it to the lower lid (2), and then return to the raw material injection process.
The same process will be repeated. Before injecting the raw material, purge the remaining liquid in the overflow pipe θω with a gas inert to the product, such as nitrogen gas, to prepare for full liquid detection during injection in the next process. I'll keep it.

By repeating the above steps, products are produced continuously.

(Problems to be Solved by the Invention) As described above, in the conventional pressure crystallization method, raw materials are pressurized in a high-pressure container to crystallize to form a solid-liquid mixture, and then The liquid phase is discharged under pressure and solid-liquid separation is carried out.
Furthermore, by squeezing the mixture (crystal grains containing residual liquid) in the container, a solid product of specific components is formed in the container, and then the product is taken out.

A schematic diagram of the state of a solid product obtained by such a pressure crystallization method is shown in FIG. As shown in this figure, the liquid 08) (black portion in the figure) remains trapped between the crystal grains 09 inside the product.

This residual liquid 08) has a composition uniquely determined by the supplied raw materials and the operating conditions of each step of pressure crystallization, and therefore inevitably contains components (impurities) other than the specific components. Therefore, solid products cannot be completely pure substances. Furthermore, since the product is a highly compressed mass, the bonding force between the crystal grain surfaces is strong, and therefore it is extremely difficult to remove and separate the residual liquid θB) in the product. Therefore, conventional pressure crystallization methods naturally have limitations in achieving high purity products. This is an extremely serious problem in pressure crystallization methods that require extremely high product purity.

In order to overcome the above-mentioned product purity limit, a pressure crystallization method has also been proposed in which part of the solid-liquid separation step is performed using an enclosed gas or a supplied gas. This method discharges the liquid phase by replacing it with gas, thereby reducing the amount of liquid remaining between the crystal grains. However, this method requires a pressure of several hundred to several thousand atmospheres, which requires a high-pressure container with much higher pressure resistance than conventional methods, and this also limits the shape of the high-pressure container. There are problems with the equipment, such as Note that it is possible to perform the process at a lower pressure than this, but in this case, the length of the liquid flow path in the crystal group increases, so the solid-liquid separation time becomes longer, resulting in a decrease in processing capacity and production volume. This will lead to a decrease in In addition, gas blowing tends to cause phenomena, resulting in a decrease in product purity.

The present invention has been made with attention to these circumstances, and its purpose is to solve the above-mentioned problems of the conventional ones, and to improve the pressure resistance of the high-pressure container without requiring -H.
Another object of the present invention is to provide a method for purifying a substance using pressure crystallization, which can overcome the limits of product purity in conventional pressure crystallization without reducing production.

(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 configuration.

That is, the method according to the first claim provides ``2 containing a specific component.
A raw material consisting of more than one component is supplied to a high-pressure container, and the raw material in the container is pressurized to crystallize it into a mixture in a solid-liquid coexistence state, and then the liquid phase is transferred to the outside of the high-pressure container under pressure. start discharging, stop the discharging before the mixture in the high-pressure container becomes agglomerated, and then take out the mixture outside the high-pressure container,
This is a substance purification method using a pressure crystallization method, which is characterized in that the mixture outside the container is subjected to a liquid phase separation treatment and solids of specific components are recovered.

The method according to claim 2 is characterized in that after the liquid phase of the mixture outside the high-pressure container is separated, solvent washing is further performed, and solids of specific components are recovered after the washing. It is a method of purifying substances.

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

The method according to the fourth aspect is a method for purifying a substance using the pressure crystallization method according to the third aspect, in which the substitution is performed by filtering the mixture outside the high-pressure container.

The method according to claim 5 is a method for purifying a substance using the pressure crystallization method according to claim 3, in which the substitution is performed by centrifuging the mixture outside the high-pressure container.

The method according to claim 6 is a method for purifying a substance using the pressure crystallization method according to claim 4, in which the filtration is performed using 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, in which the filtration is performed using pressurized gas.

(Function) As explained above, in the pressure crystallization method according to the present invention, the raw material in the high-pressure container is crystallized under pressure to form a mixture in a solid-liquid coexistence state, and then the material is transferred under pressure to the outside of the high-pressure container. The liquid phase of the container is started to be discharged, and the discharge is stopped before the mixture in the high-pressure container becomes lumpy. In this way, 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 becomes a slurry or a soft material.

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 necessarily in the form of a slurry or a soft substance, the bonding 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 separation treatment to recover the solids of specific components. Since the liquid phase separation process is performed outside the container, it can be performed under atmospheric pressure, and is therefore not limited to mechanical compression separation methods.
It becomes possible to select the most effective separation process. Further, as mentioned above, the residual liquid of the above mixture is extremely easy to remove and separate. Therefore, this separation process makes it possible to separate and remove almost all of the liquid phase. Therefore,
The purity of the solid (product) of the specific component to be recovered can be increased,
It becomes possible to overcome the limits of product purity in conventional pressure crystallization methods.

Furthermore, in the method according to the second claim, after the liquid phase of the mixture outside the high-pressure container is separated, solvent washing is further performed, and solids of specific components are recovered after the washing. High purity can be achieved more reliably.

Naturally, the method described above can be carried out without requiring an increase in the pressure resistance of the high-pressure container and without causing a decrease in production.

In the method according to the present invention, the separation treatment for the liquid phase of the mixture outside the high-pressure container can be carried out by a method of replacing the liquid phase with a gas, and it is preferable to use this replacement method. This is because the substitution method is easier to implement than other methods and can increase the amount of liquid phase separated.

More specifically, the above substitution may be performed by a filtration method or a centrifugation method.

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

(Example) An example according to the present invention will be described. The pressure crystallizer used in the examples is a 1.52 pilot plant, and its configuration is the same as that described in FIG. 1 above, except for the scale (capacity).

1 lid ±1 cresol mixture (p-cresol 80χ, remainder m-
Cresol) was cooled to 15°C in a pre-crystallizer to form a slurry state, and poured into a high-pressure container (crystallization chamber), and the raw material in the container was pressurized to 1500 atmospheres to crystallize. Subsequently, while maintaining the pressure at 1500 atm, discharging the liquid phase to the outside of the container was started, and when half of the liquid phase was discharged, discharging the liquid phase was stopped. Next, the pressure was reduced to atmospheric pressure, and the mixture in the container (substantially in the form of slurry) was taken out of the container, transferred to a centrifuge, and subjected to liquid phase separation treatment, after which solids were collected.

The obtained solid was p-cresol with a purity of 99.85χ. This purity does not seem to be much different from the purity of 99.70χ obtained by the conventional method (for example, Comparative Example 1 shown below), but considering the difference in this level of purity range, the above purity increase This is an extremely large effect and has extremely great industrial significance.

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

In addition, the liquid phase was separated using a centrifuge.
In addition, the same effects as in the above embodiment can be obtained by using a filtration method.

Furthermore, the mixture taken out of the container was directly subjected to a separation treatment for the liquid phase, but if the mixture taken out of the container was a soft solid cake, a liquid having the same composition as the legal phase in the mixture, Alternatively, if a liquid containing less impurities is added to form a slurry and then the liquid phase is separated, the separation becomes easier. Further, even if the mixture taken out of the container is in the form of a slurry, it is easier to separate the mixture by adding a liquid in the same manner as described above to form a slurry and then separating the liquid phase. In the case of Gore et al., the same effect as in the above example can be obtained regarding product purity.

-Same as in Example I, the raw material was cooled to 15°C, poured into a high-pressure container, pressurized to 1500 atm, and continued to maintain this pressure while discharging the liquid phase to separate solid and liquid. After that, squeeze
After sweating under reduced pressure to 600 atmospheres, the solid formed in the container was taken out.

The purity of the obtained solid was 99.70χ.

(Effects of the Invention) According to the method for refining a substance using the pressure crystallization method according to the present invention, it is possible to eliminate the conventional pressure It will be possible to overcome the limits of product purity in crystallization methods.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a process flow and the concept of an apparatus related to a conventional pressure crystallization method, and FIG. 2 is a schematic diagram regarding 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) - Pre-crystallizer (
8) - Raw material supply pump (9) flush piping 0 ports) - pressure reduction mechanism (II) Q2106) - one valve
En - Raw material tank 0ω - Overflow pipe θ Kerr grain 08) - Residual liquid Patent applicant Kobe Steel Seikagaku Co., Ltd. Patent attorney Akira Zenshi -

Claims (7)

[Claims] (1) A raw material consisting of two or more components including a specific component is supplied to a high-pressure container, and the raw material in the container is pressurized to crystallize it into a mixture in a solid-liquid coexistence state. Start discharging the liquid phase to the outside of the high-pressure vessel, stop the discharge before the mixture inside the high-pressure vessel becomes agglomerated, then take out the mixture outside the high-pressure vessel, and add the liquid phase to the mixture outside the vessel. A method for purifying substances using pressure crystallization, which is characterized by performing separation treatment and recovering solid components of specific components. (2) Pressure crystallization according to claim 1, characterized in that after the liquid phase of the mixture outside the high-pressure container is separated, solvent washing is further performed, and solids of specific components are recovered after the washing. A method for purifying substances using a method. (3) Purification of the substance using the pressure crystallization method according to claim 1 or 2, in which the separation treatment of the liquid phase of the mixture outside the high-pressure container is performed by replacing the liquid phase with gas. Law. (4) A method for purifying a substance using a pressure crystallization method according to claim 3, wherein the substitution is performed by filtering the mixture outside the high-pressure container. (5) A method for purifying a substance using a pressure crystallization method according to claim 3, wherein the substitution is performed by centrifuging the mixture outside the high-pressure container. (6) A method for purifying a substance using a pressure crystallization method according to claim 4, wherein the filtration is performed using a vacuum filter. (7) A method for purifying a substance using a pressure crystallization method according to claim 4, wherein the filtration is performed using pressurized gas.