JPH0418882B2 - - 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 separating and obtaining a specific component from a raw material mixture containing the specific component. (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 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, crystallization generally completes 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 step. I'll keep it. By repeating the above steps, products are produced continuously. (Problems to be Solved by the Invention) As mentioned above, the pressure crystallization method is a batch process, and the time for one cycle is usually about 2 to 5 minutes, which is a short time. The time spent draining the liquid phase from the high-pressure container after pressure crystallization occupies most of the time. Therefore, when the product yield is low, the amount of liquid phase discharged from the high-pressure container becomes relatively large, the liquid discharge time becomes longer, and the time required for one cycle becomes longer. Production will be lower. Conversely, if the product yield is high,
The amount of liquid phase discharged is relatively small, the liquid discharge time is shortened, the time required for one cycle is also shortened, and the production amount per unit time is increased. For this reason, there has been a demand for measures to increase productivity when producing desired products from the same raw materials using the same pressure crystallizer. On the other hand, the purity required for a product varies depending on its purpose and use, but with the trend toward finer products, higher purity is increasingly required. For example, in the purification of intermediates, the higher the purity, the more
The amount of other raw materials, the amount of side reaction products, the amount of energy required for the reaction in the next step, etc. are reduced, which greatly affects the steps after the next step. The present invention has been made in view of the current situation, and is a method that improves the conventional pressure crystallization method from its operational aspects and can produce high-purity products with high yield and high productivity. It provides: (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 cools a liquid mixture consisting of two or more components containing a specific component to prepare a slurry containing 5 to 35% of crystals of the specific component, and places the slurry in a high-pressure container. and start adiabatic pressure crystallization in the container, until the temperature inside the container reaches a temperature that is equal to or higher than the melting point of the specific component at normal pressure and does not exceed 25°C higher than the melting point. The pressure crystallization is terminated at the point when
Next, the liquid phase is discharged to the outside of the container while maintaining the pressure inside the container, and then the solid inside the container is partially melted by an adiabatic drop in the liquid pressure inside the container, and the solid is squeezed and the melted liquid is discharged from the container. is discharged until the temperature and pressure inside the container reach a state corresponding to a predetermined liquid composition, and then the inside of the container is brought to normal pressure and a solid product of a specific component is taken out. be. The method according to the second aspect is the pressure crystallization method according to the first aspect, wherein the liquid mixture is obtained by completely melting solid raw materials in advance.
Further, the method according to the third aspect is the pressure crystallization method according to the first aspect, in which the liquid pressure in the container is adiabatically lowered continuously or intermittently. (Function) As described above, in the pressure crystallization method according to the present invention, first, a liquid mixture consisting of two or more components containing a specific component is cooled and adjusted to a slurry containing 5 to 35% of crystals of the specific component. Then, the slurry is supplied into a high-pressure container, and adiabatic pressure crystallization is performed within the container. In this way, the supplied slurry will definitely contain crystals of the specific component that will serve as seed crystals for pressure crystallization. Therefore, high pressure is not required for initial crystal formation during pressurized crystallization. In addition, it has become possible to cause crystal growth without primary nucleation,
Therefore, large crystals are easily formed without producing fine crystals, which facilitates solid-liquid separation after crystallization.
This results in high product yield and purity. Here, the content of specific component crystals in the above raw materials is set at 5 to 35% because if it is less than 5%, the amount of seed crystals is insufficient, causing primary nucleation and resulting in a low product yield. If it exceeds 35%, it will be difficult to supply the container, and since the amount of crystals produced during pressure crystallization will be low, the temperature rise due to the latent heat of solidification generated as solidification progresses will be low. This is because it becomes impossible to secure the pressure crystallization end temperature, which is a requirement described later. In addition, the reason why the liquid mixture is cooled to adjust the above content rate is to ensure that crystals of specific components (high-purity seed crystals) that do not contain impurities are generated, resulting in higher product purity. The purpose is to make it into something. If the original raw material to be subjected to pressure crystallization is a solid-liquid mixture containing solids (crystals) at room temperature, the liquid mixture to be subjected to such cooling must be prepared by completely melting the mixture. be. If it is a liquid at room temperature, it is the liquid itself. When the original raw material is a solid-liquid mixture at room temperature, the reason why it is completely melted and then cooled as described above even though it contains crystals is as follows. That is, since the crystals in the original raw material are not generated under controlled conditions, the crystals often contain impurities. Therefore, when the original raw material is supplied and crystallized under pressure, the crystals act as seed crystals, but
Impurities may remain in the product, resulting in a decrease in product purity. On the other hand, if the original raw material is melted and then cooled, crystals of the specific component (high-purity seed crystals) containing no impurities can be generated. Further, when the original raw material is solid at room temperature, the reason why it is cooled after completely melting is to generate high-purity seed crystals, as described above. Regarding cooling in this case, after melting, the material is cooled to a predetermined temperature, but this temperature is inevitably higher than room temperature. Next, when the temperature inside the container during the pressure crystallization reaches a temperature that is equal to or higher than the melting point of the specific component at normal pressure and does not exceed a temperature 25°C higher than the melting point, the pressure crystallization is carried out. I'm trying to finish it. This means that if the temperature inside the container at the end of pressure crystallization is below the melting point at normal pressure,
Partial melting of the solid, which is a requirement described later, is difficult to occur, and sweat cleaning becomes insufficient.If the temperature exceeds 25℃ higher than the melting point, the amount of partial melting of the solid increases, resulting in unnecessary melting of the solid. This is because the product yield becomes low. By the above-mentioned pressure crystallization, at the end of the crystallization,
A crystal grain group consisting mostly of specific components is generated. Next, since the liquid phase is discharged outside the container while maintaining the pressure inside the container, a lumpy solid is formed inside the container. Subsequently, the solid inside the container is partially melted by an adiabatic drop in the liquid pressure inside the container, and the solid is squeezed and the melted liquid is discharged outside the container, so that the solid product is washed by sweat and purified. It will be done. Incidentally, the above-mentioned partial melting of the solid occurs due to a decrease in pressure after completion of discharge. In other words, as solid-liquid separation progresses, the proportion of liquid phase in the container decreases, and as a result, even though the pressure acting on the raw material in the container from the pressure source remains constant,
The pressure of the liquid phase in the container begins to decrease, and the pressure of the discharged liquid begins to decrease accordingly. When the pressure begins to decrease in this manner, the equilibrium state within the container shifts to the low pressure side as the pressure decreases, resulting in partial melting of the crystals. Here, while causing this melting,
By squeezing out the solid phase (by squeezing out the liquid phase), the amount of residual liquid phase (containing impurities) is reduced and product purity is improved. In order to promote crystal cleaning by the melting and a relative reduction in the amount of impurities in the remaining liquid phase, it is necessary to gradually reduce the pressure acting on the liquid phase in the container. Methods for lowering the pressure inside the container include (a) a method of continuously lowering the pressure of the pressure source, and (b) a method of lowering the pressure of the pressure source in stages. (c) There is a method of naturally lowering the pressure of the pressure source while keeping it constant. In methods (a) and (c), the pressure inside the container decreases smoothly, so the equilibrium state also transitions smoothly,
High purity and high yield can be easily obtained. In method (b), the pressure inside the container drops rapidly in a stepwise manner, which gives a shock to the high-pressure container, which is not preferable.
Also, since squeezing depends on the pressure of the pressure source, (c)
The crystals will be squeezed with the highest compression pressure,
The product has a high solid phase density (low liquid phase content) and high purity. Reduced pressure sweating is highly dependent on the temperature after the pressure crystallization, and the sweating effect is small below the normal pressure melting point of the pure product. In addition, since the partial melting and squeezing and discharge of the melted liquid are performed until the temperature and pressure within the container reach a state corresponding to a predetermined liquid composition, unnecessary solid melting can be prevented, and therefore the product High yields can be obtained. In other words, as decompression sweat cleaning progresses, the pressure inside the container decreases, and the temperature inside the container gradually decreases due to latent heat of fusion (endotherm) due to crystal melting during adiabatic depressurization (the temperature of the drained liquid decreases). do). On the other hand, the liquid composition inside the container is such that the concentration of the target substance gradually increases with partial melting, and draining continues, and at the same time, the crystals are squeezed, so that the liquid phase at the grain boundaries is squeezed out of the container. It will happen. As a result of crystal squeezing, the solid phase fraction within the container gradually increases, and finally reaches a certain solid-liquid ratio determined by the squeezing conditions. When this state is reached, the purity of the product in the container is uniquely determined by the amount of the liquid phase containing impurities, since the crystal itself is a pure component. On the other hand, the impurity concentration in the liquid phase is uniquely determined by the temperature and pressure conditions inside the container. Therefore, if the temperature and pressure inside the container are known, the concentration of impurities in the liquid phase, that is, the purity of the product can be determined. Therefore, it is preferable in terms of product yield to prevent excess crystal melting and discharge of the melt, so when the liquid phase state (temperature, pressure) in the container reaches a state corresponding to a predetermined liquid composition, Immediately close the drain valve to finish draining. Therefore, high purity products can be obtained with high yield and high productivity. (Example) Cresol mixture (p-component 80%, m-component 20%
%) as a raw material, a pressure crystallization test was conducted with the goal of producing high-purity p-cresol with a purity of 99.5% or higher. Furthermore, the melting point of p-cresol at normal pressure is 35
It is ℃. The pressure crystallizer is similar to that shown in FIG. In the following, Tf is the raw material supply temperature (°C), Sf is the raw material slurry concentration (%), Pp is the compression pressure (Kgf/cm ² ),
Pc is the crystallization pressure (Kgf/cm ² ), Tc is the crystallization end temperature (°C), Te is the liquid phase discharge end temperature (°C), Pe is the liquid phase discharge end pressure (Kgf/cm ² ), and Xe is the liquid composition at the end of liquid phase discharge (: p-cresol concentration (%)),
Xp is product purity (%), Wp is product yield (product amount/
The amount of raw materials (%) was changed. After heating the raw material to completely melt it, it was cooled to Tf (°C) in a pre-crystallizer 7 to prepare a slurry containing Sf (%) of p-cresol crystals, and the slurry was supplied to the crystallization chamber 4. Next, the pressure was increased adiabatically to Pc (Kgf/cm ² ),
crystallized. After the pressure was increased, the temperature inside the crystallization chamber 4 rose, and when it reached Tc (°C), discharge of the liquid phase was started. This discharge was performed while maintaining the inside of the crystallization chamber 4 at Pc (Kgf/cm). Next, the piston pressure is Pc (Kg
By naturally lowering the liquid pressure in the crystallization chamber 4 while maintaining the temperature at a temperature of 1.5 f/cm ² ), vacuum sweat cleaning (squeezing of solids, partial melting, and discharge of the molten liquid) was performed. As the perspiration cleaning progressed, the pressure and temperature inside the crystallization chamber 4 gradually decreased. The temperature and pressure are Te (℃) and Pe
(Kgf/cm ² ), the drain valve was immediately closed to complete draining. The temperature and pressure at the end of the process are as follows:
The liquid in the crystallization chamber 4 corresponds to a predetermined composition of Xe (%). Next, the inside of the container was brought to normal pressure and the solid product was taken out. Purity of the obtained product (p-cresol) Xp
(%) and yield Wp (%) above Tf, Sf, Pc,
Pp, Tc, Te,

【table】

【table】

[Table] Shown in Tables 1 and 2 together with Pe and Xe. As can be seen from Tables 1 and 2, in Nos. 1 to 3, the raw material slurry concentration Sf was too high, so the amount of pressurized crystallization was relatively small, and therefore it was difficult to increase the purity of the mother liquor through sweat purification during the depressurization process. Yes, product purity Xp is difficult to achieve. Nos. 4, 6, 7, and 9 are methods according to the present invention, and compared to Nos. 5 and 8, the liquid composition Xe at the end of liquid phase discharge is set appropriately under other conditions. It shows that there is. In addition, No. 7 has a purity Xp of 99.7%.
Since this value is too high than the target value, the yield Wp is about 1% lower than that under other conditions. No. 11 has the highest purity Xp of 100%, but since the raw material slurry concentration Sf is 0, the yield Wp
is extremely low compared to those under other conditions. (Effects of the Invention) According to the pressure crystallization method according to the present invention, high product yield and product purity can be obtained.

[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
... Pre-crystallization can, 8... Raw material supply pump, 9, 13...
Piping, 10... pressure reduction mechanism, 11, 12, 16... valve,
14... Raw material tank, 15... Overflow pipe.

Claims (1)

[Scope of Claims] 1. A liquid mixture consisting of two or more components containing a specific component is cooled to prepare a slurry containing 5 to 35% of crystals of the specific component, and the slurry is supplied into a high-pressure container, When adiabatic pressure crystallization is started in the container, and the temperature inside the container reaches a temperature that is equal to or higher than the melting point of the specific component at normal pressure and does not exceed 25°C higher than the melting point. After completing the pressure crystallization, the liquid phase is discharged from the container while maintaining the pressure inside the container, and then the solid inside the container is partially melted by an adiabatic drop in the liquid pressure inside the container. After squeezing and discharging the melted liquid out of the container until the temperature and pressure inside the container reach a state corresponding to a predetermined liquid composition, the inside of the container is brought to normal pressure and the solid product of the specific component is taken out. A pressure crystallization method characterized by: 2. The pressure crystallization method according to claim 1, wherein the liquid mixture is obtained by completely melting solid raw materials in advance. 3. The pressure crystallization method according to claim 1, wherein the liquid pressure in the container is adiabatically lowered continuously or intermittently.