JPH0640923B2 - Pressure cooling crystallization method and equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention provides an improved pressurization that allows a specific component to be crystallized and separated from a raw material mixture containing the specific component at a relatively low operating pressure and with good thermal efficiency. The present invention relates to a cooling crystallization method and a pressure cooling crystallization apparatus which is advantageously applied to this method.

[Conventional method] The pressure cooling crystallization method is a state in which a raw material composed of a liquid phase or a slurry containing a plurality of components is generally precooled and then introduced into a high-pressure container, and a mother liquor discharge pipeline is closed. Is a method of accelerating the crystallization of a specific component by applying a high pressure (for example, a high pressure exceeding 1000 atm). By this operation, a solid-liquid mixed state consisting of the crystal of the specific component and the residual liquid (mother liquor) is obtained. . At that time, the mother liquor discharge pipe line is closed and piston pressure is applied to the solid-liquid coexisting state, the mother liquor is discharged to the outside of the system through a filter, and the remaining solid phase is squeezed to further separate the solid-liquid. Is discharged, a high-purity specific component can be recovered.

For example, FIG. 3 is a conceptual diagram showing a conventional pressure crystallizer, in which a raw material mixture A is cooled to an appropriate temperature in a precooling tank 1 and then pressure crystallized from a slurry pump 2 through a raw material supply line L _1. It is sent into the high pressure chamber 4 of the analyzer 3. Then, the piston 5 is driven to pressurize the raw material in the high-pressure chamber 4 to increase or generate a specific component crystal in the raw material, and then the liquid phase component (mother liquor) is squeezed and discharged from the screen through the mother liquor discharge conduit L _2. After that, the crystals of the specific component remaining in the high pressure chamber 4 are then recovered. In the figure, V ₁ and V ₂ are open / close valves, N is a discharge nozzle, 6 is a drain tank, and 7 is a pressurizing unit.

The pressure crystallization method is shown below in the order of steps.

I: A step of closing the on-off valve V ₂ and opening the on-off valve V ₁ to supply the raw material mixture into the high pressure chamber 4, II: closing the on-off valve V ₁ and operating the piston 5 to apply high pressure to the raw material mixture To increase or generate crystals of a specific component, III: open the on-off valve V ₂ and discharge the mother liquor in the high-pressure chamber 4 through the screen, the mother liquor discharge conduit L ₂ and the discharge nozzle, IV: the piston 5 Step of squeezing and removing the mother liquor remaining in the high-pressure chamber 4 by operation, V: Step of opening the high-pressure chamber 4 and taking out crystals of a specific component.

After the step V is completed, the step I is returned to again, and by repeating this operation, the separation and recovery of the specific component are continuously performed. FIG. 4 conceptually shows the change with time of the operating pressure during the operation, and FIG. 5 similarly shows the relationship between the temperature and the pressure during the operation.

[Problems to be Solved by the Invention] In FIG. 5, a straight line W is a solid-liquid equilibrium line of a specific component (pure substance), a straight line X is a solid-liquid equilibrium line of a raw material mixture, and Y is a mother liquor separated by high-pressure crystallization. The isoconcentration line and Z are solid-liquid equilibrium lines of the eutectic mixture, respectively, and high-pressure crystallization separation is performed along the thick solid arrow.

That is, when the raw material mixture is precooled to point A and then pressurized,
Until the point B (intersection with the straight line X) is reached, the pressure rises rapidly with almost no temperature rise, but if the pressure exceeds the point B, heat is generated due to crystallization of a specific component. , As the pressure increases, a considerable temperature rise will be seen. In this example, the raw material mixture is pressurized to a pressure P to generate or increase crystals of the specific component, and then the mother liquor which has not been crystallized is filtered and discharged to recover the high-purity specific component. The temperature rises to T due to the heat generated by the crystallization of the specific component. In the conventional example, after this state is obtained, the on-off valve V ₂ (FIG. 3) is opened to discharge and remove the mother liquor, and further squeezing is performed to more completely remove the mother liquor. If it becomes lower than the straight line W, even the specific component crystallized in a polygonal manner is melted and discharged, resulting in a loss. Therefore, by adjusting the opening degree of the discharge nozzle N or cooling the operating pressure, -The temperature is controlled so that it does not fall below the straight line W.

As can be easily understood from this figure, the pressure for efficiently promoting the crystallization of the specific component rises sharply as the raw material temperature rises. Since the temperature of the raw material rises due to condensation as the temperature increases, the operating pressure must be increased accordingly. As a result, not only the pressure resistance design strength of the device and the piping line must be extremely high, but also the pressurizing performance of the pressurizing unit must be extremely large.
Equipment costs are skyrocketing. Moreover, in this method, the pressure difference between the pressure during crystallization separation and the pressure during depressurization (normal pressure) becomes very large, so that the amount of melting of the specific substance crystals generated in the final pressing step is large and the yield is reduced. There is also the problem of doing.

The inventors of the present invention have considered a method shown by a dashed arrow in FIG. 5 as a means for improving such problems. That is, the raw material mixture is pre-cooled to a temperature lower than that of the conventional method and A '
This is a method in which the temperature is lowered to a point and then pressure crystallization is carried out. In this method, the temperature (T ') after pressure crystallization can be kept low by the amount corresponding to the decrease in the pressure start temperature. As a result, as indicated by point D, the same crystallization efficiency can be obtained at a pressure P ', which is considerably lower than the above crystallization operation pressure P. Moreover, since the pressure difference between the pressure during crystallization separation and the pressure during depressurization can be suppressed to a small degree, it is also possible to suppress a decrease in the yield of crystals of the specific component.

However, in this method, the raw material mixture is changed from point A to A ′.
A large cooling device is required to cool to a point, especially when trying to cool to room temperature or below, a dedicated refrigeration device is required in addition to the normal water-cooled pre-cooling device, significantly increasing the initial cost and running cost. To be done. Moreover, if the amount of crystals in the raw material mixture may increase excessively in this cooling step, the pipe L ₁ for feeding to the high pressure chamber 4
In some cases, pipe clogging occurs in the inside, the on-off valve V ₁ , the slurry pump 2 and the like, and the operation becomes impossible.

The present invention has been made in view of such circumstances, and its object is to reduce the crystallization operation pressure by lowering the crystallization operation temperature, and further increase the load of refrigeration equipment and the like accompanying it. An object of the present invention is to provide a pressure-cooled crystallization method that does not cause pipe line clogging and the like, and an apparatus advantageously applied to the implementation of such a crystallization method.

[Means for Solving the Problems] The constitution of the crystallization method of the present invention which has been able to achieve the above object is as follows: I: pressurizing the temperature-controlled raw material mixture, II: the pressurized raw material mixture By cooling while passing through a high-pressure pipe kept at a temperature lower than the raw material temperature after pressurization, crystals of a specific component are generated or increased and injected into the solid-liquid separation device, and then solid-liquid coexistence Separation and discharge of mother liquor from the raw material mixture in a state through a filtration mechanism, III: Stop the supply of raw material to the solid-liquid separation device, and discharge the residual mother liquor at a lower pressure than the mother liquor separation and discharge step The method of the present invention is a device for pressure-cooling crystallization of a specific component from a raw material mixture containing the specific component, and a temperature control mechanism for the raw material mixture. Of the raw material mixture Increased pressure supply mechanism, high-pressure pipe for conveying the increased pressure raw material mixture while maintaining its pressure and cooling, solid-liquid separation device equipped with filtration separation mechanism, and mother liquor equipped with flow rate adjustment mechanism or pressure adjustment mechanism The gist of the present invention is that it is provided with a discharge pipe.

[Operations and Examples] The present inventors pay attention to the fact that the raw material mixture is heated to a considerably high temperature due to the compression heat and latent heat generated when the raw material mixture is pressurized as described with reference to FIG. It was thought that if a method of first applying pressure to raise the temperature and then cooling is adopted, there is a considerable temperature difference from the normal water temperature, and efficient cooling can be achieved even with water cooling.
That is, it is economical because there is no need to use a special refrigerating device or the like. The operation procedure will be described with reference to FIG. 5. As shown by the broken line arrow in FIG. 5, for example, in order to cool the raw material mixture at around room temperature to below room temperature (for example, below about 0 ° C.), it is necessary to set the temperature depending on the target temperature. A low-temperature refrigerant must be used, and the use of a refrigerating device is indispensable. However, if the raw material mixture heated to, for example, about 50 ° C. or more by pressurization is cooled to near normal temperature, industrial water at normal temperature is used. It should be possible to sufficiently fulfill the purpose of cooling by directly using the above.

Utilizing such an idea, the present inventors have considered a method of first pressurizing a raw material and then cooling it when the raw material temperature rises to some extent. That is, the solid line arrow in FIG. 1 shows changes in pressure and temperature when this method is adopted [the thin chain line arrow corresponds to the thick solid line arrow (conventional method) in FIG. 5], and the raw material mixture is When the pressure is applied from the point, the pressure rises and rises in the direction of the point C after passing the point B, but the pressure rises at the point C ', that is, when the pressure reaches P'and the temperature reaches the point T ". Then, the solution is cooled to point D, and at this point, crystallization is performed and then mother liquor is separated and squeezed off (for example, paraxylene: 90%, metaxylene: 10% from a raw material mixture Specific control conditions for separating and purifying xylene are as follows: A point: 8 ° C., 1 kgf / cm ² , B point: 12 ° C., 500 k
gf / cm ² , C point: 70 ° C, 3000 kgf / cm ² , C'point: 5
0 ℃, 1500kgf / cm ² , D point: 35 ℃, 1500kgf / c
m ² ), it is possible to obtain the same crystallization separation effect as the crystallization at the point C in the conventional method and the separation / squeezing of the mother liquor. It is possible to enjoy many effects such as reduction and improvement of cooling efficiency. However, it is a heavy burden on the equipment to be able to cool the entire crystallizer under pressure, and there is a risk of pipe clogging when attempting to supply a large amount of crystals to the high pressure chamber due to pressurization and cooling. Comes out.

From such a point, in the present invention, as described above, first, [I]
The temperature-controlled raw material mixture is pressurized. At this stage, a part of the specific component in the raw material mixture may or may not be crystallized, and it may be in a supersaturated state or an unsaturated state. [II] Then, the pressurized raw material mixture is cooled while being passed through a high-pressure pipe kept at a temperature lower than the raw material temperature after the pressurization to generate or increase crystals of a specific component to solidify. The method of injecting into the liquid separation device (that is, the high-pressure chamber) and separating the mother liquor and squeezing filtration is adopted in the same manner as in the conventional example. That is, the present invention employs a method of performing a rapid cooling step of crystal of a specific component in a high-speed transportation state under high pressure,
Compared with the case where crystallization is performed in a stationary state, the crystals are made finer and can be maintained in a slurry state with good fluidity, and the tube clogging phenomenon can be prevented as much as possible. Moreover, since the high-pressure pipe is usually formed to have a smaller diameter than the normal-pressure pipe, indirect cooling with cooling water or the like can be efficiently performed. In this way, the objectives of reducing operating pressure and temperature, preventing pressure drop and associated yield loss, simplifying cooling equipment and improving cooling efficiency can be achieved all at once without the problem of pipe clogging. .

FIG. 2 is a schematic flow chart illustrating an apparatus used for carrying out the above method. Since the structure of the crystallizer main body 3 and thereafter is substantially the same as the conventional example shown in FIG. 3, The same portions will be denoted by the same reference symbols and redundant description will be omitted. As is clear from the illustrated example, the present invention is characterized mainly in the steps of supplying the raw material mixture into the high-pressure chamber 4 of the crystallizer main body 3, and the raw material mixture A is first prepared in the precooling tank 1. After being cooled to near room temperature by a water cooling mechanism (not shown) or the like, it is fed to the raw material supply pipe L ₁ while being pressurized to a predetermined pressure by the high pressure pumps 8a and 8b. The pressure feeding process up to here is A → B in FIG.
→ Corresponds to the step C '. The figure shows an example in which two piston-type high-pressure pumps are installed side by side so that continuous operation can be performed by switching operation. It is also possible to adopt a structure for feeding, and it is of course possible to employ another high-pressure feeding mechanism such as a gear pump type. The raw material supply pipeline L ₁ after these high-pressure pumps 8a and 8b has a pressure resistant structure, and a cooling mechanism 9 is attached to the pipeline L ₁ immediately in front of the crystallizer main body 3, and the pressure rising in this portion The raw material mixture heated by is cooled. This cooling process is the first
This corresponds to the step C ′ → D in the figure. It is of course effective to use a bellows tube or a finned tube as the raw material supply pipeline for cooling to improve the cooling efficiency. It is also possible to use ammonia gas or the like as the refrigerant, but the most advantageous is cooling water in view of the gist of the present invention of simplification of the cooling equipment, and the raw material mixture flowing through the supply pipeline in the present invention is As described above, since the temperature is considerably high due to pressurization, ordinary industrial water or the like can be sufficiently cooled. Of course, ice water or the like can be used if necessary.

The raw material mixture pressurized and cooled in this way is controlled by the on-off valve V
₁ is sent to the high pressure chamber 4, the on-off valve V ₁ is continuously closed, the on-off valve V ₂ is opened, and after adjusting the opening degree of the discharge nozzle,
The mother liquor is separated and discharged through a screen (not shown). After that, when the pressure in the high-pressure chamber 4 becomes slightly lower than the above pressure, the piston 5 is actuated to squeeze, and the mother liquor adhering to the crystal surface in the high-pressure chamber 4 melts slightly from the surface layer due to the pressure reduction. Only the crystals of the high-purity specific component remain in the high-pressure chamber 4 after being squeezed out together with the specific component. Therefore, after that, the high-pressure chamber 4 may be opened to take out the cake-like specific component, or the high-pressure chamber 4 may be released and heated to once melt the crystal of the specific component, and then taken out through a separately provided discharge conduit.

As can be easily understood from the above description, in the present invention, basically, the crystallization operation pressure is secured by the high-pressure pumps 8a and 8b, and the crystallization operation temperature is secured by the cooling mechanism 9. No increase or decrease in temperature occurs in the main body 3, and the piston 5 is used only during compression. Therefore, when the content of the specific component in the raw material mixture is small (the amount of crystallization is relatively small with respect to the mother liquor), the raw material mixture is supplied into the high-pressure chamber 4 while being cooled under pressure, and continuously fed through the filter. If a certain amount of specific component crystals are accumulated in the high pressure chamber 4 and the process is moved to the squeeze separation step, the specific component crystal is taken out (that is, the number of times the high pressure chamber 4 is opened).
Is preferable and both productivity and operability can be improved, which is preferable. In this case, a pressure gauge P ₁ is provided on the raw material inlet side of the high pressure chamber 4, and a pressure gauge P ₂ is provided on the mother liquor outlet side, and these P ₁ and P ₂ are connected to the differential pressure sensor Q ₁ in advance. If an automatic control circuit is built up so as to start squeezing (that is, the operation of the piston 5) by detecting the accumulation of a predetermined amount of crystals in 4 by means of the differential pressure sensor Q ₁ , the accumulation of crystals It is possible to accurately control the setting of the pressing start time.

Further, when the mother liquor discharge side pipeline is released to the atmospheric pressure all at once in the final squeeze separation step, the effect of the release extends to the inside of the high pressure chamber 4 to increase the melting amount of the specific component crystal and reduce the recovery rate. Although there is a risk, if, for example, a means for disposing a plurality of pressure release nozzles in series in the mother liquor discharge side line is taken and the mother liquor discharge side is stepped down in the squeeze separation step, The melt squeezing loss of crystals of a specific component can be suppressed to a necessary minimum.

By the way, in the present invention, as described above, the method of cooling in a high-pressure fluidized state is adopted, and although pipe clogging due to crystallized substances is unlikely to occur, in the case where an overpressure or a supercooled state occurs during operation, the crystal is There is no risk of pipe clogging due to a sudden increase in the number of items, so it is always good to take measures that anticipate such a situation. From this point of view, in the example of FIG. 2, a mechanism capable of automatically detecting clogging of the raw material supply line is also added. That is, the pressure gauges Pa and Pb are provided on the raw material discharge side lines of the high pressure pumps 8a and 8b, respectively, and the pressure gauge P provided on the raw material inlet side line to the high pressure chamber 4 is provided.
₁ is utilized, and these Pa, Pb and P ₁ are connected to the differential pressure sensor Q.
₂ is connected and the pressure difference between the two is constantly detected. P
When the pipe clogging occurs in the raw material supply pipe L ₁ between a or Pb and P _1, the differential pressure detected by the differential pressure sensor Q ₂ increases rapidly. Therefore, by detecting this differential pressure, the pipe clogging is immediately eliminated. I can know. Therefore, when such a phenomenon occurs, the driving of the pressurizing pumps 8a and 8b is stopped to release the pressure in the raw material supply pipe L ₁ , or the inside of the cooling mechanism 9 is supplied with hot water or the like. within road _{L 1} heated, the conduit _{L 1}
If the crystals inside are melted, the tube clogging can be immediately eliminated.

[Effects of the Invention] The present invention is configured as described above, and the effects thereof are summarized as follows.

Since the method of cooling the raw material mixture while pressurizing it and raising the temperature is adopted, it is possible to cool efficiently even with cooling water at about room temperature, no special refrigeration equipment is required at all, and running costs are reduced. it can.

Since pressure crystallization can be performed at a relatively low temperature, it is not necessary to pressurize excessively, the pressure resistance strength of the entire equipment can be designed lower, and the equipment cost can be reduced and the operability and safety can be improved. it can.

It is possible to reduce pressure drops at the time of crystallization under pressure cooling and at the time of taking out under pressure release, and it is possible to suppress the melting loss of a specific component to a necessary minimum.

The features of the present invention described in the above 1 to 5 are exerted to the maximum extent in the pressure-cooled crystallization separation of the substance having a large temperature rise due to pressurization.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing changes in pressure and temperature when the method of the present invention is adopted, FIG. 2 is a schematic flow chart showing an embodiment of the present invention, FIG. 3 is a conceptual diagram showing a conventional method, and FIG. FIG. 5 is a graph showing changes in pressure with time when the conventional method is adopted, and FIG. 5 is an explanatory diagram showing changes in pressure and temperature when the conventional method and the improved method are adopted. 1: Pre-cooling tank, 2: Slurry pump 3: Pressure crystallizer main body, 4: High pressure chamber 5: Piston, 6: Mother liquor tank 7: Pressurizing unit, 8a, 8b: Pressurizing pump 9: Cooling mechanism, A: raw material mixture _{V 1,} V _2: off valves, N: the mother liquor discharge nozzle _{P 1, P 2, Pa,} Pb: pressure gauge _{Q 1,} Q _2: differential pressure sensor

Claims (6)

[Claims] 1. A step of pressurizing a temperature-controlled raw material mixture, II: cooling the pressurized raw material mixture while passing it through a high-pressure pipe kept at a temperature lower than the temperature of the raw material after the pressurization. By doing so, a step of generating or increasing crystals of a specific component and injecting it into the solid-liquid separation device, and then separating and discharging the mother liquor from the raw material mixture in the solid-liquid coexisting state through the filtration mechanism, III: solid-liquid separation And a step of discharging the residual mother liquor at a lower pressure than the step of separating and discharging the mother liquor, the pressure-cooled crystallization method for a specific substance. 2. The pressure-cooled crystallization method according to claim 1, wherein the pressurization of the raw material mixture, the injection into the solid-liquid separation device, and the separation of the mother liquor by the solid-liquid separation device are continuously performed. 3. The process according to claim 1 or 2, wherein in the step III, the crystals in the solid-liquid separation device are squeezed under pressure and the mother liquor is discharged continuously or stepwise under reduced pressure. Pressure cooling crystallization method. 4. An apparatus for crystallizing under pressure cooling of a specific component from a raw material mixture containing the specific component, comprising a temperature control mechanism for the raw material mixture, a pressure increasing supply mechanism for the raw material mixture, and a pressure increased raw material mixture. It is characterized by comprising a high-pressure pipe for conveying while maintaining its pressure and cooling, a solid-liquid separation device having a filtration separation mechanism, and a mother liquor discharge pipe having a flow rate adjustment mechanism or a pressure adjustment mechanism. Pressure cooling crystallizer. 5. A differential pressure sensor for detecting a differential pressure between a raw material inlet side pressure and a mother liquor outlet side pressure of the solid-liquid separation device, and at the time when the differential pressure detected by the sensor reaches a predetermined value, The pressure-cooled crystallization device according to claim 4, further comprising a mechanism for starting the pressing of the raw material in the solid-liquid separation device. 6. A pressure sensor for detecting a pressure difference between an outlet pressure of the pressure increasing mechanism and a raw material inlet side pressure of the solid-liquid separation device,
The pressure-cooled crystallization device according to claim 4 or 5, wherein clogging in the high-pressure pipe can be detected by a differential pressure detected by the sensor.