JPH0356761B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a pressure crystallization method, and more particularly to a pressure crystallization method for a material system with a low crystal growth rate.

(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.

An overview of such a pressure crystallization method is described, for example, in "Summary of Pressure Crystallization Method and Apparatus", p. 331, Volume 50 of Kagaku Kogaku (1986). To explain this with reference to FIG. 1 (a diagram showing the process flow and the concept of the device), the pressure vessel 1 has a lid body (lower lid) 2 at the bottom.
A piston 5 is provided to move up and down within the container 1 by the operation of the hydraulic unit 3, and a crystallization chamber 4 is formed within the pressure container 1 by the piston 5 and the lower lid 2. be done. 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. Also, crystallization chamber 4
The pre-crystallizer 7 includes a raw material supply pump 8 and a valve 22.
They are connected via piping 13.

In this apparatus, raw materials are fed from a raw material 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.

Next, when the pressure is increased to a predetermined pressure, the precipitation is generally completed immediately and a predetermined solid-liquid ratio (saturation state) is reached, so as soon as this pressure is detected, the valve 11 is opened and solid-liquid separation begins. do. Then, with the valve 11 open, the piston 5 is transferred from the hydraulic unit 3.
When the piston continues to descend while maintaining the pressure acting on the crystallization chamber 4, the liquid phase is discharged from the crystallization chamber 4 to the drain tank 6 while the pressure within the crystallization chamber 4 is maintained constant. 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, 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, 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.

(Problems to be Solved by the Invention) However, in the conventional pressure crystallization method, the actually obtained product yield may be lower than the expected product yield. As a result of various studies aimed at improving this yield, it was found that this decrease in yield is particularly remarkable in material systems with low crystal growth rates. It was also confirmed that the lower the crystal growth rate, the greater the decrease in yield. As described above, the conventional pressure crystallization method has a problem in that the product yield is low in material systems with a low crystal growth rate.

The present invention was made in view of these circumstances, and its purpose is to provide a pressure crystallizer that can improve the product yield when pressure crystallizing a material system (raw material) with a low crystal growth rate. The purpose of this study is to provide an analysis method.

(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 method of the first claim supplies a liquid or slurry raw material into a high-pressure container, pressurizes the raw material to a predetermined pressure in the container to crystallize it, and then converts the liquid phase portion into the liquid under pressure. In a pressure crystallization method in which a crystallized substance is obtained by discharging the liquid out of the container and separating the solid and liquid, the predetermined pressure is maintained at the predetermined pressure, and the amount of crystal formation reaches the predetermined amount while the pressure is maintained. This pressure crystallization method is characterized in that the solid-liquid separation is started after detecting. The method according to the second claim is the pressure crystallization method according to the first claim, which detects that the amount of crystal formation has reached a predetermined amount by detecting that the temperature inside the high-pressure container has reached a preset value. It's a method. The method according to the third aspect detects the difference between the temperature of the raw material to be fed into the high-pressure container and the temperature inside the high-pressure container after pressurization to determine the amount of temperature increase, and the amount of temperature increase is adjusted to a preset value. The pressure crystallization method according to claim 1, wherein the arrival of the predetermined amount of crystal production is detected by detecting that the amount of crystal production has reached the predetermined amount. The method of claim 4 uses a high-pressure container having a pressurizing piston, detects the displacement of the piston after pressurization, and detects that the displacement reaches a preset value, thereby generating the crystals. The pressure crystallization method according to claim 1, wherein reaching a predetermined amount is detected. Fifth
The method according to claim 4 includes detecting that the amount of crystal formation has reached a predetermined amount by detecting that the displacement of the piston after reaching the predetermined pressure has reached a preset value. This is the pressure crystallization method described. Further, the method according to claim 6 is characterized in that after reaching the predetermined pressure, the pressure is maintained for a predetermined period of time, and then the solid-liquid separation is started. A pressure crystallization method according to the claims.

(Operations and Examples) Based on the results of an investigation into the causes of low product yields in material systems with low crystal growth rates, explanations will be given below.

FIG. 2 shows the relationship between the time after pressurization (horizontal axis: t) and the internal pressure and temperature of the high-pressure container (vertical axis: P, T). In this example, the pressure is increased until it reaches a predetermined pressure Pe, and then the pressure Pe is maintained. In the figure, P indicates the pressure, Ta indicates the temperature in the case of material system A with a high crystal growth rate, and Tb indicates the temperature in the case of material system B with a low crystal growth rate.

As can be seen from this figure, when the pressure P reaches the predetermined pressure Pe after t ₁ second, in the case of the material system A, the temperature increase ends almost at the same time, and the temperature Ta reaches the maximum temperature Te. However, in the case of material system B, the predetermined pressure Pe
Even if it reaches t, it is still in the transition period of temperature increase and reaches the maximum temperature Te ₂ seconds after t.

This crystal temperature is due to latent heat of solidification generated as precipitation progresses. Therefore, in the case of material system B, even if the predetermined pressure Pe is reached, crystallization is still in progress. Therefore, if solid-liquid separation is started immediately after the predetermined pressure Pe is reached, solid-liquid separation will occur before crystallization is completed, resulting in a low product yield. This is the reason why product yields are low in conventional pressure crystallization methods for material systems with low crystal growth rates.

That is, in the conventional method, as soon as a predetermined pressure is reached, the valve 11 is opened, the liquid phase is discharged out of the container, and solid-liquid separation is started. Therefore, in the case of a material system with a high crystal growth rate, crystallization is completed as soon as the predetermined pressure is reached, so even if solid-liquid separation is started immediately after the predetermined pressure is reached, the desired product yield can be obtained.
However, in the case of a material system with a low crystal growth rate, crystallization is not yet complete even when the predetermined pressure is reached.
Solid-liquid separation occurs before crystallization is completed. This results in a low product yield.

In order to improve this product yield, solid-liquid separation may be started after the amount of crystal formation reaches a predetermined amount while maintaining the pressure at a predetermined pressure Pe. At this time, if solid-liquid separation is started t ₂ seconds after reaching the maximum temperature Te, the highest product yield can be obtained.

Therefore, as explained above, in the pressure crystallization method according to the present invention, after the raw material reaches a predetermined pressure in a high-pressure container, it is maintained at that pressure, and while the pressure is maintained, the amount of crystal formation reaches a predetermined amount. After detecting that the solid-liquid separation has been reached, the solid-liquid separation is started. In this way, even in the case of a material system with a low crystal growth rate, a high product yield can be achieved.

The above crystal formation amount has reached the specified amount (hereinafter,
A specific method for detecting the arrival of a predetermined amount will be described below.

As mentioned above, since the temperature increase is due to the latent heat of solidification generated as crystallization progresses, there is a close relationship between the temperature and the amount of crystal formation. Therefore, by determining this relationship in advance, setting a temperature corresponding to a predetermined amount of crystal formation based on it, and detecting that the set value has been reached, it is possible to detect that the predetermined amount has been reached.

Incidentally, the relationship between temperature and the amount of crystal formation varies depending on the crystallization start temperature, that is, the raw material supply temperature. It should be considered that this temperature may sometimes fluctuate by about 1°C due to various factors. Therefore,
By detecting the difference between the temperature of the raw material fed into the high-pressure container and the temperature inside the high-pressure container after pressurization to determine the amount of temperature increase, and detecting that the amount of temperature increase has reached a preset value. , it is more desirable to detect when a predetermined amount has been reached. Note that this temperature increase amount is indicated by ΔT in FIG.

In addition, as mentioned above, in order to obtain the highest product yield, it is sufficient to start solid-liquid separation after reaching the maximum temperature Te, but if it takes a long time to reach the maximum temperature Te, , the time required for one cycle (from raw material supply to product removal) becomes longer;
Production volume per unit time decreases. Therefore, in such a case, considering the balance between product yield and production amount, it is recommended to start solid-liquid separation when a certain temperature or amount of temperature increase is reached, for example, after time t ₃ seconds. is preferred.

Figure 3 shows the time after pressurization (horizontal axis: t), the pressure inside the high-pressure container, and the displacement of the piston (vertical axis: P,
shows the relationship with L). In the figure, P indicates the pressure, La indicates the piston displacement in the case of the material system A with a high crystal growth rate, and Lb indicates the piston displacement in the case of the material system B with the low crystal growth rate.

As can be seen from this figure, when the pressure P reaches the predetermined pressure Pe after t ₁ second, the piston displacement La in the case of the material system A reaches a constant value Le (maximum value) almost at the same time. However, in the case of material system B, the predetermined pressure Pe
Even if it reaches , it is still in the transition period of piston displacement, and reaches a constant value Le after t ₂ seconds.

This piston displacement is due to volume reduction accompanying crystallization. Therefore, in the case of material system B, even if the predetermined pressure Pe is reached, crystallization is still in progress.

As mentioned above, there is a close relationship between the piston displacement and the amount of crystal formation. Therefore, find this relationship in advance,
Based on this, the piston displacement corresponding to a predetermined amount of crystal production is set, and by detecting that the set value has been reached, it is possible to detect that the predetermined amount has been reached.

Incidentally, the relationship between the piston displacement and the amount of crystal formation differs depending on the piston position at the time of starting crystallization. This piston position varies depending on various factors and should be considered to be subject to some variation.
Therefore, it is preferable to detect that the predetermined amount has been reached by detecting that the displacement of the piston after reaching the predetermined pressure has reached a preset value. still,
This transition is indicated by ΔL in FIG.

In addition, in order to obtain the highest product yield, solid-liquid separation should be started after the piston displacement reaches a constant value Le or ΔL corresponding to Le, but it takes a long time to reach these values. In cases where it is necessary,
Production volume per unit time decreases. Therefore, in such a case, considering the balance between product yield and production amount, it is preferable to start solid-liquid separation when the piston reaches a certain level of displacement, for example, when the displacement Lf is reached.

In addition, as is clear from Figures 2 and 3, the time t, which is the common coordinate axis in Figures 2 and 3, is managed, and when the time reaches _t2 or _t3 , the solid-liquid It is also possible to initiate a separation.

(Effects of the Invention) According to the pressure crystallization method according to the present invention, when pressure crystallizing a material system (raw material) with a low crystal growth rate,
The product yield is improved and the desired high product yield can be obtained.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the process flow and the concept of the apparatus related to the pressure crystallization method, and Fig. 2 shows the time after pressurization (horizontal axis: t) and the pressure and temperature inside the high-pressure vessel (vertical axis: P, Figure 3 is a diagram showing the relationship with T).
FIG. 3 is a diagram showing the relationship between time after pressurization (horizontal axis: t), pressure inside the high-pressure container, and displacement of the piston (vertical axis: P, L). 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... Piping, 10... Pressure reduction mechanism, 1
1, 12, 16... Valve, 14... Raw material tank, 1
5...Overflow pipe.

Claims (1)

[Claims] 1. Supplying a liquid or slurry raw material into a high-pressure container, pressurizing the raw material to a predetermined pressure in the container to crystallize it, and then expelling the liquid phase from the container under pressure. In a pressure crystallization method in which a crystallized substance is obtained by discharging and separating solid and liquid, the pressure is maintained after reaching the predetermined pressure, and it is detected that the amount of crystal formation has reached a predetermined amount while the pressure is maintained. A pressure crystallization method characterized in that the solid-liquid separation is started after the solid-liquid separation is performed. 2. The pressure crystallization method according to claim 1, wherein reaching a predetermined amount of crystal formation is detected by detecting that the temperature inside the high-pressure container has reached a preset value. 3. Detecting the difference between the temperature of the raw material fed into the high-pressure container and the temperature inside the high-pressure container after pressurization to determine the amount of temperature increase, and detecting that the amount of temperature increase has reached a preset value. 2. The pressure crystallization method according to claim 1, wherein said method detects whether said crystal production amount reaches a predetermined amount. 4 Using a high-pressure container having a pressurizing piston, detecting the displacement of the piston after pressurization, and detecting that the displacement has reached a preset value, thereby detecting that the amount of crystal formation has reached a predetermined amount. The pressure crystallization method according to claim 1, which comprises: 5. The pressure crystallizer according to claim 4, wherein reaching the predetermined amount of crystal formation is detected by detecting that the displacement of the piston after reaching the predetermined pressure has reached a preset value. Method. 6. The pressure crystallization method according to claim 1 or 3, wherein after reaching the predetermined pressure, the pressure is maintained for a predetermined period of time, and then the solid-liquid separation is started. .