JPH0417682B2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a pressure crystallization method, and in particular, to improving the durability of a high-pressure container, relaxing its design standards, or reducing liquid phase discharge. This invention relates to a pressure crystallization method that reduces the energy required.

(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 It is a separation and purification technology that has been attracting a lot of attention as the chemical industry has become more sophisticated in recent years because of its easy yield and low energy consumption.

The outline of such pressure crystallization method can be found, for example, in the chemical industry.
Volume 50 (1986) Page 331 "Overview of pressure crystallization method and equipment"
It is described in. This will be explained with reference to FIG. 1 (a diagram showing the process flow and the concept of the device). The piston 5 and the lower lid 2 form a crystallization chamber 4 within the pressure vessel 1 . The crystallization chamber 4 and the drain tank 6 are connected by a pipe 9 via a pressure reducing mechanism 10 and a valve 11. Further, the crystallization chamber 4 and the pre-crystallizer 7 are connected by a pipe 13 via a raw material supply pump 8 and a valve 12.

In this apparatus, raw materials are fed from a tank 14 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 injected into the crystallization chamber 4 from the pipe 13 via 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, so this is detected, the valves 12 and 16 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 enters 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 solidification progresses, but in the pressure crystallization method, generally, cooling is not performed to prevent this temperature rise, but the pressure is applied adiabatically. will be adopted. The temperature reached after the temperature rise, that is, the solid-liquid separation start temperature, affects the purity and yield of the product, so these are adjusted by the liquid supply temperature in consideration of the specific heat, latent heat of solidification, etc. of the raw material mixture.

Next, when the pressure is increased to a predetermined pressure, generally the predetermined solid-liquid ratio (saturation state) is immediately reached, so as soon as this pressure is detected, the valve 11 is opened.
When the piston continues to descend while maintaining the pressure acting on the piston 5 from the hydraulic unit 3, the liquid phase is discharged from the crystallization chamber 4 to the drain tank 6 while the pressure inside the crystallization chamber 4 is maintained constant. be done. 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".

As the piston 5 continues to descend further, the crystal grain group forms 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, which is connected to the drain tank 6 under atmospheric pressure, gradually decreases, so that the crystal surface Partial melting and so-called "sweating washing" takes place and purification of the bulk solid product takes place.

When the pressure of the liquid discharged from the crystallization chamber 4 drops to a predetermined pressure, the piston 5 stops descending, and at the same time the piston starts rising, the high-pressure container 1 also rises, and the solid product is removed from the bottom lid. 2 is taken out from the container 1. 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 the process returns to the raw material injection process and the same process is repeated. Prior to the injection of raw materials, the residual liquid in the overflow pipe 15 described above is purged 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.

(Problem to be solved by the invention) As stated above, the conventional pressure crystallization method
Pressurizing the mixture supplied to a high-pressure container to achieve a predetermined solid-liquid coexistence state, and then pressurizing and discharging the liquid phase into the container to form a solid product of a specific component in the container; The product is taken out from the container. At this time, it is assumed that the temperature and composition of the mixture in the high-pressure container are always uniform, and that it immediately shifts to a new solid-liquid equilibrium state in response to changes in pressure conditions. Therefore, the operation is performed with the applied pressure for precipitating crystals (hereinafter referred to as crystallization pressure) equal to the applied force maintained while discharging the liquid phase (hereinafter referred to as separation pressure). These pressures are important factors that are used as design standards for high-pressure vessels and the like. That is, the high-pressure container is manufactured to ensure a predetermined durability corresponding to the time for which the crystallization pressure value and the separation pressure value are maintained. Also,
The hydraulic unit is selected to ensure separation pressure and mother liquor discharge rate.

However, in general material systems, there is a metastable region between the stable region where crystals always dissolve and the unstable region where new crystals precipitate, even in equilibrium theory. Precipitation is actually a mass transfer of specific components between the solution and the crystal surface, and since it involves issues such as diffusion rate, it takes a certain amount of time to reach a true equilibrium state. In other words, the mixture in the high-pressure container is not necessarily homogeneous because the microscopically non-uniform state continues, and the density of the crystals is generally higher than the density of the mother liquor, causing precipitation of the crystals in the mother liquor. Not maintained.

Considering this point of view, the conventional pressure crystallization method, which is based on the premise that the mixture in a high-pressure container immediately shifts to a new solid-liquid equilibrium state in response to changes in its pressure conditions, does not suffer from the phenomenon described above. etc., should be reviewed based on actual behavior. It is hoped that the optimal pressure conditions will be clarified and that high-pressure containers will be designed and operated. For example, it is not necessarily necessary to operate with the crystallization pressure and separation pressure being equal, and it is conceivable that the separation pressure can be lowered. If the separation pressure can be lowered, not only can the durability of the high-pressure container be improved or its design standards can be relaxed, but also the energy required for discharging the liquid phase can be reduced.

The present invention has been made based on this idea, and an object of the present invention is to provide a pressure crystallization method that can lower the separation pressure without significantly reducing product purity and yield.

(Means for Solving the Problems) In order to achieve the above problems, the present invention provides a pressure crystallization method having the following configuration. That is, the pressure crystallization method according to the first claim supplies a mixture of two or more components including a specific component to a high-pressure container, and pressurizes the mixture to a predetermined crystallization pressure in the container. Crystallizes specific components to form a solid-liquid coexistence state,
In a pressure crystallization method in which a solid product of a specific component is formed in the container by subsequently discharging the liquid phase out of the container under pressure, and the product is taken out from the container, after the pressure crystallization. First, without discharging the liquid phase, the pressure inside the high-pressure container is lowered to a draining start pressure that is lower than the crystallization pressure and is set to a degree of vacuum that does not melt the crystals generated by the pressurized crystallization. This is a pressure crystallization method characterized in that the continuous discharge of the liquid phase component is started after that.
Further, in the pressure crystallization method according to the second claim, after the solid-liquid coexistence state is established and before the discharge of the liquid phase component is started, the pressure in the high-pressure container is reduced to below the crystallization pressure, and the discharged liquid is The pressure crystallization method according to claim 1, wherein the pressure is maintained at a pressure higher than the starting pressure for a predetermined period of time.

(Function) As explained above, in the pressure crystallization method according to the present invention, the liquid phase component is discharged at a pressure lower than the pressure required to achieve a solid-liquid coexistence state. Although the separation pressure is lower than the crystallization pressure in this way, pressure crystallization can be performed without significantly reducing product purity and yield. The reason for this will be explained below.

That is, after achieving a solid-liquid coexistence state, the density of the generated crystals is greater than the density of the mother liquor, and the crystals settle in the mother liquor, resulting in separation of the solid and liquid.
The crystals produced by pressure crystallization are relatively large and have a high sedimentation rate, so they are separated into solid and liquid in a short time. The separated solid-liquid is separated into a solid-phase concentrated portion and an upper clear portion, each in a state of solid-liquid equilibrium. The mass transfer in this state is only due to the mixing phenomenon, which takes an extremely long time, such as diffusion, because there is no stirring in the high-pressure container. Therefore, even if the pressure inside the high-pressure container is reduced, the change in the solid-liquid ratio of the entire system is extremely small. Therefore, even if the separation pressure is lower than the pressure required to achieve a solid-liquid coexistence state, the change in the solid-liquid ratio of the entire system is extremely small, and therefore the product purity and yield do not decrease much. .

In the above, the higher the degree of solid-liquid separation, that is, the more completely the solid-liquid is separated, the smaller the change in solid-liquid ratio when the separation pressure is lowered, and the smaller the degree of decrease in product purity and yield. Become. Also, the separation pressure can be lowered. Therefore, it is desirable to increase the degree of solid-liquid separation before starting to discharge the liquid phase component.

Therefore, in the present invention, while the solid-liquid is separated in the high-pressure container after the solid-liquid coexistence state is established, the pressure is lower than the pressure required to achieve the solid-liquid coexistence state, and higher than the pressure applied to discharge the liquid phase component. After the pressure inside the high-pressure container is maintained at a pressure of , the discharge of the liquid phase is started. This pressure holding allows for a more complete separation of solid and liquid during this time.

Here, the longer the pressure is maintained, the higher the degree of solid-liquid separation becomes, which means that the separation pressure can be lowered. That is, when the separation pressure is lowered, the degree of reduction in product purity and yield is reduced.
Therefore, the longer the pressure holding time, the better.

Note that when the liquid phase is discharged, when the liquid phase (clarified liquid) passes through the solid phase concentrated portion, the separated solid and liquid are remixed. If the degree of remixing is large, the degree of solid-liquid separation will decrease and the degree of product purity and yield will decrease, so it is desirable to reduce the degree of remixing. To do this, a pipe (piping A) that connects to a filter placed at the top of the high-pressure container that can come into contact with only the clarified liquid, as a liquid phase discharge pipe,
Piping (piping B) that connects to filters placed in other parts is provided to provide two or more systems of liquid phase discharge piping. It is preferable to discharge at least most of the clarified liquid via the former pipe (piping A).

As described above, the present invention enables pressure crystallization without significantly reducing product purity and yield even when the separation pressure is lower than the crystallization pressure.

(Example) An example according to the present invention is based on the operation results of a pressure crystallization pilot plant with an internal capacity of 1.5,
This will be explained in comparison with a comparative example. The configuration of this plant is the same as that shown in FIG.

Comparative Example 1 Cresol mixture (p-component 80%, m-component 20%
%) to 15℃ to form a slurry, supply it to a pressure crystallizer, increase the pressure adiabatically to a crystallization pressure of 1500 atm, crystallize, and then separate this pressure (1500 atm). While maintaining the pressure, the liquid phase was discharged for solid-liquid separation, and the pressure was then lowered to 600 atm to perform vacuum sweating to obtain a product. The yield of the obtained product was 35.3% and the purity was 99.7%.

The operating methods of the following Comparative Examples and Examples are based on Comparative Example 1, and the values of crystallization pressure, separation pressure, and start point of liquid phase discharge are different, but other points are different. is the same as Comparative Example 1.

Comparative Example 2 Both the crystallization pressure and separation pressure were 1800 atm. The liquid phase discharge was started immediately after crystallization, as in Comparative Example 1. As a result, the yield of the product obtained was 37.3
%, and the purity was 99.8%. The yield increased by about 6% and the purity increased by 0.1%.

Comparative Example 3 Both the crystallization pressure and separation pressure were 1200 atm. The liquid phase discharge starts immediately after crystallization. As a result, the yield of the obtained product was 32.3% and the purity was 99.6%
It was hot. The yield decreased by about 9% and the purity decreased by 0.1%.

Example 1 The crystallization pressure was 1800 atm and the separation pressure was 1500 atm. The starting point of liquid phase discharge was the same as in Comparative Example 1.
Immediately after crystallization. The yield of the resulting product is
The purity was 99.7%. The yield is increased by about 2% compared to Comparative Example 1, and the purity is approximately the same.
In addition, compared to Comparative Example 2, the yield was about 4%, and the purity was
They decreased by only 0.1% each.

Example 2 The crystallization pressure was 1500 atm and the separation pressure was 1200 atm. The starting point of liquid phase discharge was the same as in Comparative Example 1.
Immediately after crystallization. As a result, the yield of the obtained product was 33.3% and the purity was 99.6%. The yield is increased by about 3% compared to Comparative Example 3, and the purity is approximately the same. Note that, compared to Comparative Example 1, the yield was reduced by about 6% and the purity was reduced by 0.1%.

Example 3 The crystallization pressure was 1800 atm and the separation pressure was 1500 atm. Unlike Comparative Example 1, the liquid phase discharge was started after the temperature was maintained at 1800 atmospheres for 5 seconds after crystallization.
As a result, the yield of the obtained product was 36.7%, and the purity was
It was 99.8%. Compared to Comparative Example 1, the yield is about 4
% and purity increased by 0.1% each. This shows that even though the time maintained at a pressure higher than the separation pressure is extremely short, the extent to which the yield is improved is relatively large.

Furthermore, compared to Comparative Example 2, the yield was only reduced by about 2%, and the purity was approximately the same. this is,
This shows that even if the separation pressure is lowered, the product yield does not decrease much and the purity does not change.

Example 4 The crystallization pressure was 1500 atm and the separation pressure was 1200 atm. The start point of liquid phase discharge is 1500 for 5 seconds after crystallization.
After being maintained at atmospheric pressure. As a result, the yield of the obtained product was 34.3% and the purity was 99.8%. Compared to Comparative Example 3, the yield increased by about 6% and the purity increased by 0.1%.

Moreover, compared to Comparative Example 2, the yield is reduced by about 3%, and the purity is approximately the same. This indicates that even if the separation pressure is reduced, the product yield does not decrease significantly.

(Effects of the Invention) According to the pressure crystallization method according to the present invention, the separation pressure can be lowered without significantly reducing product purity and yield. The durability of a high-pressure container is a function of the pressure value and time applied to the high-pressure container, and most of the time during which pressure is applied is the time during which liquid phase components are discharged by separation pressure. Therefore, not only can the durability of the high-pressure container be improved or its design criteria relaxed, but also the energy required for discharging the liquid phase can be reduced.

Furthermore, in cases where the separation pressure is limited in the already manufactured high-pressure vessels etc. due to their durability, it is also possible to improve the product purity and yield.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a process flow and a concept of an apparatus related to a pressure crystallization method. 1...Pressure vessel, 2...Lower lid, 3...Hydraulic unit, 4...Crystallization chamber, 5...Piston, 6...Drainage tank, 7...Preliminary crystallizer, 8...Raw material supply Pump, 9, 13, 24... Piping, 10... Pressure reduction mechanism, 11, 12, 16, 23... Valve, 14... Raw material tank, 15... Overflow pipe, 17...
Crusher, 18, 19... Conveyor, 20... 1st
Raw material mixing can, 21... Second raw material mixing can, 22...
transfer pump.

Claims (1)

[Claims] 1. A mixture of two or more components containing a specific component is supplied to a high-pressure container, and the mixture is pressurized in the container to a predetermined crystallization pressure to crystallize the specific component. Pressure crystallization in which a solid-liquid coexistence state is formed, and then the liquid phase is discharged out of the container under pressure to form a solid product of a specific component in the container, and the product is removed from the container. In the method, after the pressure crystallization, first, draining is started at a degree of vacuum set to a degree lower than the crystallization pressure without discharging the liquid phase and not melting the crystals generated by the pressure crystallization. A pressure crystallization method characterized by lowering the internal pressure of a high-pressure container to a pressure level, and then starting continuous discharge of a liquid phase component. 2. After the solid-liquid coexistence state is established and before the start of discharging the liquid phase, the pressure inside the high-pressure container is maintained at a pressure below the crystallization pressure and above the discharge start pressure for a predetermined period of time. The pressure crystallization method according to claim 1.