JPS6161841B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method in which a mixture of two or more substances is used as a raw material, brought into a solid-liquid coexistence state under pressure, and then separated into solid-liquid. Specifically, the present invention relates to a method for improving solid-liquid separation under high pressure.

[Prior Art] There are many methods known in chemical engineering for separating a mixture of two or more components (for example, specific component A and specific component B) into specific component A and specific component B, using a mixture as a raw material. . However, there are some mixtures, such as eutectic mixtures, which are difficult to separate by conventional means, and conventionally it has been mainstream to separate such mixtures by a crystallization method that uses temperature as a variable. However, this method has drawbacks such as difficulty in accurately controlling the temperature, lack of homogeneity due to the formation of a temperature gradient within the system, and long operation time. Based on the expectation that the above-mentioned drawbacks would be solved by making pressure a variable, we have conducted various researches and have made numerous inventions not only in principle but also in practical aspects.

By the way, as the practical use of crystallization methods that use pressure as a variable progresses, especially when it comes to the phase of deployment to large-scale equipment, problems that need to be solved have come to be seen here and there.One of them is high pressure. The problem is how to efficiently discharge the liquid phase from the solid-liquid mixture coexisting below to the outside of the system.

In the pressure crystallization separation method, a high-pressure container equipped with a filter on the wall is used, and the back side of the filter is communicated with the outside of the system under atmospheric pressure (however, in the process of forming a solid-liquid coexistence state, the communication is closed by valve operation). In many cases, a device (of course, this device can be implemented in various variations) is used which can be used to shut off the device. When a solid-liquid coexistence state is formed in the high-pressure container, for example, a solid phase mainly composed of specific component A and a liquid phase mainly composed of specific component B are obtained, the above-mentioned valve operation The mother liquid passage on the back side of the filter is opened, and the liquid phase in the high-pressure container is discharged to the outside of the system via the filter.

[Problem that the invention seeks to solve]

If we examine the progress of solid-liquid separation performed including the above steps in more detail, we can analyze it as follows.

(1) At the initial stage of liquid phase discharge, the liquid phase existing between each crystal grain dispersed in the system communicates with each other, moves to the filter surface, and then flows out through the filter. I will do it.

(2) When the pressure in the system decreases as the liquid phase flows out, the solid phase that has been formed melts and flows out together with the liquid phase that originally existed. Even during the operation of ), the pressure is applied within a range that does not cause a substantial drop in the pressure inside the high-pressure vessel. Specifically, the piston, which is the means for applying high pressure into the high-pressure container, is gradually lowered.

(3) As the liquid phase near the filter flows out, the distance between the crystals begins to narrow on the front surface of the filter, and as the liquid phase flows out less, solid phase compression begins as the piston descends. When such a state is reached, the liquid phase pressure on the back side of the filter and eventually on the front side of the filter begins to decrease, and the crystal surface near the filter partially melts and flows out. Of course, along with this pressure drop, the liquid in the center of the high-pressure container away from the filter also flows out.

(4) When the solid phase is further compressed and the liquid phase pressure near the filter section becomes even lower, the low-purity portion of the surface of the crystal near the filter will be melted and removed. As a result, it is highly purified and is in a state in which it will not melt even if the pressure is slightly reduced. Therefore, a liquid phase discharge passage in the vicinity of the filter is not secured, and a liquid phase containing a high concentration of impurities is left behind in the center of the high-pressure vessel, forming a state where it is trapped in the solid phase.

(5) Since it is not possible to visually determine that such a state has occurred, the liquid phase pressure in the filter section may be further lowered in order to further discharge the liquid phase. When the operation progress reaches this stage, even high-purity crystals near the filter may melt and flow out, reducing the yield of specific component A. Sometimes the cake-like crystals deposited near the filter may have holes, causing internal damage. There is a problem in that the liquid that has been trapped in the crystals is blown out all at once with some melting of the crystals, resulting in a decrease in yield.

Therefore, as equipment becomes larger and even higher-speed separation is desired, it is necessary to take some measures to solve the problems identified in the above (1) to (5). There is.

The present invention was made in consideration of such a situation, and an object of the present invention is to provide a means for improving solid-liquid separation under high pressure.

[Means for solving problems]

The solid-liquid separation method in the present invention is as follows (1)
The main point is that it includes the steps (5) to (5).

(1) The raw material mixture charged in the high-pressure container is
A step of forming a solid-liquid coexistence state in which a solid phase mainly containing the specific component and the remaining liquid phase are brought into a mixed state under pressure.

(2) A liquid phase-partial separation step in which a part of the liquid phase is discharged out of the high-pressure container until the pressure of the liquid phase in a solid-liquid coexistence state is lower than the pressure of the solid phase.

(3) A partial solid phase melting process in which the pressure inside the high-pressure vessel is lowered to melt part of the solid phase.

(4) A solid-liquid coexistence state reconstruction process in which the pressure inside the high-pressure vessel is increased again to form a new solid-liquid coexistence state.

(5) A remaining liquid phase separation step in which the remaining liquid phase is discharged out of the high-pressure container until the pressure of the liquid phase in the solid-liquid coexistence state described in the previous item 4 becomes lower than the pressure of the solid phase again.

[Effect]

FIG. 2 is an explanatory diagram showing the concept of the pressure crystallizer used in the present invention, in which 1 is the main body of the high-pressure container, 2 is the piston, 3 is the filter, 4 is the liquid phase discharge channel, and 5
indicates a pressure gauge, and 6 indicates a valve. FIG. 3 is a graph showing the pressure behavior when all steps of pressure crystallization are carried out within a short time using this apparatus. Each step in FIG. 3 is as described below.

O→A: Increase in crystals A→B: Initial overflow B→C: Initial compression C→D: Late compression However, the chain line after point B indicates the piston pressure, and the solid line after point B indicates the liquid side. The difference between the pressure shown by the chain line and the pressure shown by the solid line corresponds to the squeezing pressure as shown in the figure. In addition, in the process description above, the period A→B was expressed as the initial phase, but in reality, crystals may gradually increase even between A→B, and the initial phase is referred to as B. Sometimes it starts from a point. In any case, the details of the process may be subject to changes in the initial and later stages, changes due to addition of temperature control, etc., and should not be construed as limiting.

In this way, as the number of crystals increases, initial overflow, and initial compression proceed, a state of crystal accumulation is created on the front of the filter (4th stage).
figure). That is, as the solid-liquid coexistence state formation step and the liquid phase partial separation step proceed, a situation is created in which there is concern that the problems described in the section of problems to be solved may occur. Therefore, in the present invention, a solid phase partial melting step is started in which the pressure inside the high-pressure container is lowered and a portion of the solid phase is dissolved. Figure 1 shows the procedure of such an operation using pressure behavior.
In FIG. 1, the piston pressure is lowered at point F, and since the piston pressure and liquid phase pressure are the same between C and E (difference E=O), no squeezing phenomenon occurs. However, due to this operation, a part of the A crystal (specifically the surface part) melts,
In particular, fine crystals are preferentially melted and a state is formed in which the liquid phases communicate with each other.

B: As the amount of the liquid phase trapped in the cake-like solid phase inside the container increases, the liquid phase pressure increases, and this pressure causes the cake-like solid phase to become trapped. Therefore, communication between the liquid phases is further promoted.

C The surface of the cake is melted and the flowability of the liquid phase is further improved.

A phenomenon like this occurs. During this time, depending on the amount of melting of the solid phase, the discharge of the liquid phase may be continued or may be interrupted at any time.

In the present invention, the pressure inside the high-pressure container is increased again,
A solid-liquid coexistence state reconstruction process is started to form a new solid-liquid coexistence state. According to FIG. 1, this corresponds to the process from E to A', and in some cases, the process from A' to B' is included. In this process, the amount of crystals begins to increase again, but rather than generating new nuclei and growing, the existing crystals often continue to grow, so there are few fine grains formed and large crystals. only grows. In addition, since liquid with a high concentration of impurity components has penetrated between the cake lumps destroyed as described above, there is no risk of crystallization even if pressure is applied again, and there is no risk of crystallization between the cake lumps. There's no such thing as being locked up. FIG. 5 shows the state formed in this way, and the front surface of the filter 3 is provided with a flow path for the liquid phase.
Therefore, following the previous example, we perform the initial strain indicated by A'→B' and the initial squeeze indicated by B'→C'.
In this way, the remaining liquid phase separation step is carried out, and the third
A much better solid-liquid separation effect can be obtained than in the case shown in the figure.

However, if a higher separation effect is desired, the same procedure can be repeated further. That is, to explain according to Fig. 1, the pressing process (B'→
As C') progresses, when it becomes difficult to separate the liquid phase, the piston pressure is lowered in the direction of F'→E' to melt part of the crystals, and further in the direction of E'→A''. After repressurizing to , discharge the liquid phase in steps A″→B″ and then B″→C″.

〔Example〕

As we proceeded with solid-liquid separation in pressure crystallization according to Figure 1 above, we found that the squeezing pressure (difference between piston pressure and liquid pressure) between B' and C' was smaller than the squeezing pressure between B and C. Despite this, a considerable amount of liquid phase was able to flow out. Furthermore
Between B'' and C'', the liquid phase outflow amount decreased considerably, but the squeezing pressure further decreased. These facts, that is, the fact that as the number of repetitions increases, a sufficient amount of liquid phase can be discharged even when the squeezing pressure is low means that the discharged liquid phase pressure becomes higher if the piston pressure remains the same. means. That is, since the separation operation is performed on the higher pressure side, this corresponds to discharging a liquid phase with a higher impurity concentration, and extremely good results can be obtained in terms of recovery efficiency. In this sense, it is recommended to make the piston pressure as high as A, such as E→A' and E'→A'' in Figure 1, but for example, at the initial stage of B''→C'', After the compression is finished, the third
In order to prevent a decrease in the amount of discharged liquid when performing the latter stage of compression as shown in the figure, the piston pressure should be stopped rising again at about A, and after repeating it again, the pressure should be increased from A to D as shown in Figure 1. It is recommended to adopt the procedure of concluding with a late compression as shown below.

As described above, the present invention repeats the rise and fall of the piston pressure at least twice, or more if necessary, but in the embodiment, the liquid phase was discharged each time. However, it is also possible to disclose an operation in which the pressure is raised and lowered several times without discharging the liquid phase, and the microcrystals are completely disappeared by this repetition, and then the liquid phase is discharged.

〔Effect of the invention〕

Since the present invention is configured as described above, it is possible to avoid difficulty in draining the liquid phase during compression,
As a result of being able to efficiently discharge or separate the liquid phase with a high impurity concentration as a concentrated liquid, it has become possible to support larger pressure crystallizers and higher operating speeds.

Such an operation is particularly effective when the viscosity of the liquid to be separated is high or when the crystals obtained by pressurization are fine particles.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of pressure behavior in the implementation of the present invention, Fig. 2 is a conceptual diagram of an apparatus implementing the present invention, Fig. 3 is an explanatory diagram of pressure behavior in a general method, and Figs. 4 and 5 are front views of the filter. FIG. 2 is an explanatory diagram showing a solid-liquid coexistence state of 1... High pressure vessel body, 2... Piston, 3...
Filter, 4...Liquid phase discharge channel.

Claims (1)

[Claims] 1. In separating a specific component from a mixture, (1) the mixture raw material charged in a high-pressure container is
(2) forming a solid-liquid coexistence state in which the solid phase mainly containing the specific component and the remaining liquid phase are mixed under pressure; (2) the pressure of the liquid phase in the solid-liquid coexistence state is changed to (3) a liquid phase partial separation step in which the liquid phase is discharged out of the high-pressure container until the pressure drops below the applied pressure; and (3) a solid phase partial melting step in which the pressure inside the high-pressure container is lowered to melt a portion of the solid phase. (4) A solid-liquid coexistence state reconstruction step in which the pressure inside the high-pressure container is increased again to form a new solid-liquid coexistence state; and (5) the pressure of the liquid phase in the solid-liquid coexistence state described in the previous item 4. 1. A method for separating a liquid phase in pressure crystallization, comprising a step of separating a remaining liquid phase out of a high-pressure container until the pressure becomes lower than the pressure applied to a solid phase.