JPS6048205B2 - Separation method for eutectic mixtures - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for crystallizing and separating a specific component or concentrating another specific component from a multi-component liquid phase eutectic mixture that mutually forms intermolecular compounds, and in particular to a method for crystallizing and separating a specific component or concentrating another specific component. This paper relates to a new separation method that utilizes the phenomenon that point composition changes due to pressure changes.

For example, a eutectic mixture has a solid-liquid equilibrium state (X
e indicates the eutectic point composition) and the solid-liquid equilibrium state (Xe, , Xe) as shown in Figure 2.

Although it is known that the latter shows a eutectic point composition, it is possible to obtain a specific composition from a eutectic mixture having two (or three or more) eutectic point compositions (hereinafter simply referred to as eutectic points). : The separation and recovery rate is considered to be low. In other words, Figure 2 is
Phase diagram of a eutectic mixture in which A and B form a certain kind of compound AB (e.g. addition compound, hydrate, etc.: intermolecular compound referred to in the present invention) in a coexistence system of specific component A (!1.B) The dashed line in the figure is an equilibrium state diagram assuming that no intermolecular compound AB is formed, and Xe is the virtual eutectic point at that time. When cooled, if the intermolecular compound AB is not formed, A component equivalent to the maximum (Xa-X.) will be crystallized, but if the intermolecular compound Tsukuda is formed, Only the A component corresponding to the maximum (Xa-Xel) is crystallized, and the A component corresponding to (Xe, -Xe) cannot be crystallized and separated.Therefore, as for the B component, sufficient concentration is required. Furthermore, as shown in Figure 3, if the mixed composition X of the starting stock solution b is between the eutectic point X., and XAB (XAB is the composition of the intermolecular compound), then (X., -X,,) is only separated by crystallization, and it becomes impossible to separate and recover the pure A component.In other words, the composition ratio between the eutectic points Xel and Xe2 is different from conventional separation. However, when a eutectic mixture forms an intermolecular compound as described above, the composition range between the eutectic points Xe and Xe (region where crystallization cannot be separated) is generally wide. Therefore, it is desired to establish a technology that can crystallize and separate specific components in high yield even from such a J-type mixed system. Various studies have been conducted in an attempt to provide a method for crystallizing or concentrating specific components in high yields even from eutectic mixtures, especially those having composition ratios within the region where crystallization cannot be separated under normal pressure. I've been piling it up.

As a result, we found a new fact that the eutectic point of a eutectic mixture changes significantly with changes in pressure, and that it is possible to utilize this new fact to change the However, they discovered that specific components can be crystallized and separated or concentrated in high yield, and have successfully completed the present invention. That is, the configuration of the separation method according to the present invention is to utilize the phenomenon that the eutectic point between an intermolecular compound and each specific component fluctuates due to changes in pressure, and to generate a compound having a composition ratio within the region where crystallization cannot be separated. It involves crystallizing and separating a specific component from a crystalline mixture. More specifically, the eutectic mixture is cooled under high pressure or further pressurized to crystallize intermolecular compounds or specific components. ,
The gist lies in concentrating or separating one specific component and concentrating the other specific component.

In addition, in the present invention, by combining crystallization under high pressure and crystallization under low pressure (including normal pressure), either the intermolecular compound or the specific component is crystallized under each pressure. Also provided are methods for solidifying and separating specific components or increasing the concentration of other specific components. In the present invention, when one of the intermolecular compounds or a specific component is crystallized and separated from a multicomponent eutectic mixture that forms intermolecular compounds under normal pressure, the mixture is pressurized and the eutectic composition is formed under high pressure. The specific component whose ratio increases is brought into a solid-liquid coexistence state at a temperature and pressure that allows it to be concentrated in the liquid phase more than the eutectic composition under atmospheric pressure, and one of the intermolecular compounds or the specific component from the coexistence phase is made into a solid. It is characterized by the effective use of the basic idea of separating and separating, and this basic idea itself was quantitatively confirmed for the first time by the inventors.

The present invention will be explained below using an example in which it is applied to crystallization separation of a P- and m-cresol mixture, but the present invention is not limited thereto. It can be applied to the crystallization separation of any eutectic mixture that moves.

The solid-liquid equilibrium phase diagram of P- and m-cresol at normal pressure is known, and as shown in Figure 4, m-isomer/p-isomer = about 2/
1 (67/33) to form an intermolecular compound W. The m-isomer/p-isomer has two eutectic points Em and Ep at compositions of approximately 89/11 and 42/58. However, the inventors have confirmed through experiments that this phase diagram changes considerably under high pressure, especially when the eutectic point Ep is m-isomer/p-isomer = 42/58 at normal pressure. It was found that the composition shifted to 52/48 (Epl5OO) at a pressure of 15 and to 60/40 (E.3OOO) at a pressure of 30. Moreover, at an even higher pressure F, intermolecular compounds disappear, and it is finally possible to handle the system as a simple eutectic system of p- and n-forms. ．． However, in the case of cresol, the pressure required to form a simple eutectic system is even higher, at 5000 k
Since it reaches more than 9/c, it is not necessarily economically advantageous to treat it as a simple eutectic system. Therefore, one advantageous method is to perform treatment in the region where intermolecular compounds exist. That is, for example, the composition of the stock solution corresponds to point C (m-isomer/p-isomer=B4O/6
In the case of the mixture 0), as is clear from the analysis of Figure 4, it is possible to crystallize and separate a small amount of p-isomer even at 1 atm (42-40) (42 x 100 = 4.8% of the stock solution). ).

However, the composition of the stock solution is equivalent to point d (m-isomer/p-isomer 1 = 50/5
0), at 1 atm, m-isomer/p-isomer = 42/5
Although only a eutectic composition liquid of 8 and an intermolecular compound of 67/33 were obtained, it was not possible to crystallize and separate the p-isomer alone, and the concentration of the m-isomer in the residual liquid could not be increased satisfactorily. However, this increases the pressure in the separation system. As a result of the fluctuation of the eutectic point Ep as shown in Figure 4, at 1500 (52-50) atmospheric pressure, it becomes x100 = 4% of the stock solution, and at 300 olfactory pressure, it
0)×100=17% of the p-isomer can be isolated by crystallization alone.

“According to the present invention, the eutectic mixture in the vicinity of the composition of intermolecular compounds, which was conventionally considered impossible to separate at normal pressure, can be separated by increasing the pressure during crystallization. The recovery rate of the components can be greatly increased.Moreover, by increasing the crystallization recovery rate of the p-isomer in the example shown in Figure 4, the concentration of the m-isomer in the residual liquid will also inevitably increase. , we have shown an example where the eutectic point moves in the direction toward the intermolecular compound composition under high pressure, but for example, as shown in Figure 5, the eutectic point moves in the direction away from the intermolecular compound composition. Even in such cases, the features of the present invention can be effectively utilized.

That is, Figure 5 is a phase diagram of a eutectic mixture in which specific components X and Y form an intermolecular compound W', which exhibits two eutectic points Ex' and EY' at normal pressure. When attempting to crystallize and separate a mixture of composition h at normal pressure, the eutectic point EY'
Only a mixture having a composition corresponding to , and a small amount of intermolecular compound W can be obtained, and there is a limit to increasing the x concentration in the crystallized product or the Y concentration in the residual liquid. However, when the pressure '[ of this mixed system is increased, the eutectic point becomes the intermolecular compound composition W'
Since they move in the direction of Ex and EY away from the The Y concentration is also increased to a composition corresponding to EY. Therefore, using intermolecular compounds as raw materials, known separation methods such as ?
If one of the specific components is recovered by a method of forming and separating an adduct, a 5-adsorption method, a 6-sulfonation method, etc., the recovery rate of the specific component can be greatly increased. As described above, in the present invention, even if a purified product of a specific component cannot be obtained by itself, the concentration of the specific component can be greatly increased compared to the conventional method, so it can be used in conjunction with other separation methods. The combination can significantly increase the recovery rate of specific components. In the above description, the operation of cooling under high pressure was described, but the same result can be obtained by further increasing the pressure under high pressure. As mentioned above, the present invention utilizes the phenomenon that the eutectic point moves by increasing the pressure during crystallization,
It is characterized by an increased crystallization recovery rate or concentration rate of specific components, which makes it possible to separate specific components even from eutectic mixtures that cannot be separated by crystallization under normal pressure. The effect becomes more apparent as the pressure increases.

Considering practical application on an industrial scale, it may be difficult to use extremely high pressure equipment, so it is important to consider how to increase separation efficiency at a practical pressure.
This is extremely important for further enhancing the effectiveness and effectiveness of the present invention.
The second method provided by the present invention takes into consideration the above points, and is designed to maximize separation efficiency by repeatedly performing crystallization under high pressure and crystallization under low pressure. I have to. For example, when a m-, p-fu mixed cresol is used as a eutectic mixture and is repeatedly crystallized by setting the high pressure treatment to 30 atm and the low pressure treatment to 1 atm, the stock solution composition c (m-body / p-isomer = 45/55) mixture at 3
When gradually cooled at 0 beating pressure, the p-isomer in the mixture gradually crystallizes along the 5 liquidus line at 30 beating pressure, reaching the eutectic point Ep3O.
O. (60-45)
. ×100=25% pure p-isomer crystallizes. When the crystals, that is, the p-form, are removed from this system, the composition of the remaining liquid is estimated to be mo-form/p-form = 60/40 from the eutectic point of EplOO. When this residual liquid is then returned to 1 atm and cooled, crystallization occurs along the solid-liquid equilibrium line at 1 atm, but the eutectic point at 1 atm is E.
Since it is moving to l, in this process m-isomer/p-isomer''-6
7/33 composition σ] Intermolecular compounds gradually crystallize, Ep
, the solid phase consists of about 72% (67-4
2×100) and the liquid phase of m-isomer/p-isomer'-42/58 about 2r
% (100-72) of solid-liquid coexistence state is obtained. Therefore, when the liquid phase, which removes the solid phase (intermolecular compounds) from this coexisting phase, is crystallized again at 30 stroke pressure, Ep, and Ep3O are formed.
It is possible to crystallize and separate the p-isomer corresponding to the compositional difference of OO as a pure product. By repeating this operation and successively recovering the precipitated p-isomer and intermolecular compounds, the recovery rate of p-isomer can be greatly improved, and along with this, the concentration of m-isomer in the residual liquid can be dramatically increased. It became a matter of fact. Even in the case of a eutectic mixture with a relatively wide intermolecular compound composition range (distance between each eutectic point) at 1 atm, specific components can be extracted by combining high-pressure and low-pressure crystallization. In addition to further increasing the crystallization recovery rate of , it has become possible to dramatically increase the concentration of other specific components or intermolecular compounds. Note that the order of the high and low pressure repeated treatments is not particularly limited, and either high or low pressure may be performed first, but especially when the stock solution composition is at the eutectic point EM. ．． ．． O and E
pl. When the concentration is between O, it is preferable to first process at low pressure to increase the concentration of p-isomer, and then crystallize and collect the p-isomer at high pressure.
The above explanation took the case of m-, p-cresol mixture as an example, but the point is that crystallization of all eutectic mixtures whose eutectic point changes depending on pressure Applicable to separation.

Furthermore, Fig. 7 shows an example of application to a eutectic mixture in which the distance between each eutectic point expands by increasing the pressure (corresponding to Fig. 5), and the repeated crystallization method described above has this property. The same method as Z can also be applied to the separation and purification of specific components from mixtures. For example, the stock solution (composition h) is first maintained at high pressure and cooled to reach the eutectic point EY at high pressure. Then, the intermolecular compound W in the stock solution crystallizes, and the concentration of the specific component Y (G) in the remaining solution is increased to a concentration corresponding to EY. Then, when the pressure is returned to low and it is cooled for 3 times, the Y component in the remaining liquid gradually crystallizes until it reaches the low pressure side eutectic point EY', and at the same time, the concentration of the X component in the remaining liquid is increased. Therefore, repeat this operation,
By repeating the crystallization removal of intermolecular compounds at high pressure (increasing the concentration of Y component in the residual liquid) and the crystallization of Y4r component at low pressure (repeated operations along the arrows in Figure 7), the Y component in the mixture is removed. It is possible to obtain as much pure product as possible, and to maximize the concentration of the remaining component X.
In addition, a typical example of an intermolecular compound is a racemic compound of optical isomers, and the eutectic point of many of these types of optical isomer mixture systems fluctuates considerably due to changes in pressure.

Even from this type of mixture whose composition is within the range where crystallization cannot be separated (for example, one synthesized in a non-synthetic manner), the specific component can be efficiently crystallized and separated. Although the above explanation mainly focused on the case where the pressure is changed, there is a fixed relationship between the pressure and temperature during transformation, and when carrying out the present invention, it is necessary to set an appropriate temperature corresponding to the pressure. Should.

The relationship between pressure and temperature when crystallizing and separating an m-, p-cresol mixture has already been illustrated in FIG. 4, but it will be slightly supplemented with FIG. Figure 8 shows the p-g form of cresol, m/P
Ep shows the solid-liquid equilibrium lines of the eutectic composition of the p-form and the w-form, respectively. For example, when the starting composition is pure p-isomer, it is solid on the high-pressure/low-temperature side of the solid-liquid equilibrium line of p-isomer, and is liquid on the low-pressure/high-temperature side. Therefore, in order to crystallize pure p-isomer under high pressure, it is necessary to set a temperature corresponding to the pressure. Of course, the same applies to m-form, w-form and eutectic. In other words, whether at high pressure or low pressure, the temperature required to crystallize a specific component and bring the composition concentration in the liquid phase to a predetermined value is uniquely determined from the unique phase diagram determined by the type of mixture. Therefore, temperature control as well as pressure control are naturally essential requirements for the crystallization method operation in the present invention. However, since the relationship between these temperatures and pressures is unique to the substances and mixtures to be separated, in order to carry out the present invention, a solid-liquid equilibrium phase diagram (a function of temperature and mixture composition) when the pressure is changed is required. ) is preferably created experimentally in advance, and the optimal separation operating conditions are determined based on this phase diagram. To explain further based on the experimental results, in Fig. 8, the solid-liquid equilibrium of a liquid with a composition equivalent to the eutectic composition (P = 58%) between P and W bodies under atmospheric pressure is as shown in the figure. Indicated by a dashed line. Furthermore, under high pressure, a eutectic having a composition different from the above-mentioned eutectic composition is formed, and its solid-liquid equilibrium relationship is shown as an Ep form in the figure. From this figure, if each is conveniently approximated by a straight line, the liquid equilibrium line at P = 58% is P
=41(T-3.3)...P, and that of the eutectic can be approximately expressed as P =69(T-3.3)...(2).

Therefore, in the present invention, it is important to apply a pressure equal to or higher than formula (1) in order to achieve sufficient precipitation of crystals.

However, under high pressure, even if a pressure equal to or higher than formula (2) is applied, the so-called eutectic supersaturation state may occur, and eutectic may not occur, so crystallization must be completed under pressure equal to or higher than formula (2). is even more effective in terms of P-body recovery. Furthermore, the above explanation is based on crystallization under atmospheric pressure, and has been explained for convenience as a crystallization method in which cooling is performed under high pressure. However, as is clear from FIG. 8, specific components or molecules are The intermediate compound may be solidified and crystallized, or it may be crystallized while applying pressure at an arbitrary pressure rate and increasing the temperature accordingly.

Selection of temperature and pressure under which solid and liquid are separated is extremely important, but the selection is left to the discretion of the person implementing the present invention. However, it is most preferable to proceed with crystallization by pressurizing the stock solution, which is maintained at a temperature lower than the temperature in the state to be separated under high pressure, so that the solid-liquid state is formed at an elevated temperature. This is a separation method that can improve productivity. As a further supplement, in the above explanation, for convenience, it was explained that solid-liquid separation occurs at the eutectic point, regardless of whether the pressure is low or high, but industrially, it is not necessary to completely coincide with the eutectic point, and the crystallization The present invention has its own meaning in utilizing fluctuations due to pressure in the non-separable region.
Further, in the above description, a case has been described in which the separated liquid phase is repeatedly subjected to crystallization operations, but the present invention naturally includes the use of the separated liquid phase mixed with the raw material to be used next. By the way, a technique of employing high pressure for crystallization separation of a eutectic mixture is disclosed, for example, in Japanese Patent Application Laid-Open No. 51-8227.

However, as stated in the lower right column of the same publication, page (3) (page 161), "crystallization under normal pressure or sweating crystallization method results in poor crystal shape. The separation and purification of high-purity meta or vala-cresol, which could not be achieved due to the adhesion of mother liquor, can now be carried out efficiently by crystallizing under high pressure and separating the solid and liquid. The main purpose is to improve the crystal shape and prevent the adhesion of mother liquor. ``Moreover, on page (2) of the same publication (page 160 of the combined edition), the 10th to 2nd digits in the lower right column say, ``By the way... in the case of pressurization, both pressure and temperature act. Therefore, the eutectic point does not necessarily match the eutectic point under normal pressure, and although it does not vary greatly, it may differ slightly from that under normal pressure.Therefore, the meta and bulk composition ratios also "It may change as the eutectic point moves depending on conditions such as pressure and temperature," and although it is recognized that the eutectic point moves slightly due to pressure changes, there is no fact that this has been quantitatively confirmed. Furthermore, there is no recognition of the fact that fluctuations in the eutectic point composition due to pressure are large enough to have a significant effect on the crystallization recovery rate of specific compounds, and even more so, there is no recognition that pressure is a factor in improving the crystallization recovery rate. There are no recognized facts.
These points are explained in the same publication, which actively excludes composition ratios sandwiched between two eutectic points.
page (page 160 of the combined book)
” It is clear from this. However, as is clear from the explanation below in Figure 3, the basis of the present invention lies in the quantitative confirmation of the fact that the eutectic composition fluctuates widely due to changes in pressure, and by utilizing this fact. Even from a eutectic mixture with a composition ratio that was considered impossible to separate under normal pressure, it has been possible to crystallize and separate specific components, or to significantly improve the separation and recovery rate. In particular, the second configuration of the present invention utilizes the difference in eutectic point composition between high pressure and low pressure,
Crystallization of a specific component or intermolecular compound at high pressure and crystallization of an intermolecular compound or specific component at low pressure are repeated, and the concentration of the specific component in the liquid phase is increased by crystallization of the intermolecular compound, and then the specific component is identified again. The main feature is that the components are crystallized, and these structures are based on an original idea of the present invention, which has never been considered in the prior art, let alone in the above-mentioned published publications. The above explanation is based on 2 for the sake of brevity.
Although this study focused on component eutectic systems, even if it is a three-component system or a multi-component system with more than one component, if one or more of the two components forms an intermolecular compound, The same effects as above can be obtained.

The present invention is roughly configured as described above, and can enjoy various benefits as shown below.

1. Employing a crystallization method under high pressure, specific components can be recovered in high yield even from eutectic mixtures that cannot be separated by crystallization under normal pressure.

2. It can be applied to the separation of any eutectic mixture whose eutectic point composition changes depending on pressure, so its range of application is extremely wide.

3 It is effective not only for the separation and purification of specific components, but also as a method for concentrating specific components, so it can also be used as a secondary treatment method for other separation methods (adduct formation separation method, adsorption separation method, sulfonation separation method, etc.) I can use it.

4. With the improvement of the separation and recovery rate of specific components, the concentration of other specific components will also be dramatically increased.

5. By adopting a method of repeating high-pressure and low-pressure crystallization operations, it is possible to further enhance the crystallization recovery effect of specific components and the concentration effect of other specific components.

[Brief explanation of the drawing]

FIG. 1 is an example of a phase diagram of a eutectic mixture having one eutectic point, and FIGS. 2 and 3 are examples of a phase diagram of a eutectic mixture that forms an intermolecular compound and exhibits two eutectic points.

Claims (1)

[Scope of Claims] 1. From a multi-component eutectic mixture in which two specific components form an intermolecular compound, and in which the intermolecular compound or the specific component cannot be crystallized and separated in the phase diagram under atmospheric pressure, When separating an intermolecular compound or a specific component, the mixture is pressurized or under high pressure by utilizing the phenomenon that the eutectic point composition of the intermolecular compound and each specific component that constitutes it fluctuates under high pressure. A compound characterized by concentrating or separating one specific component and concentrating the other specific component to a level higher than the eutectic composition under atmospheric pressure by cooling and crystallizing an intermolecular compound or a specific component. Separation method for crystalline mixtures. 2 In claim 1, two specific components A
, B form an intermolecular compound under atmospheric pressure, a eutectic point composition AP of the intermolecular compound and the specific component A, a eutectic point composition BP of the intermolecular compound and the specific component B, and A separation method applied to a eutectic mixture in which at least one of the eutectic point compositions AP and BP moves in a direction closer to an intermolecular compound composition in response to an increase in pressure. 3. The separation method according to claim 2, wherein specific components A and B are m-cresol and p-cresol. 4. The separation method according to claim 2, wherein specific components A and B are optical isomers of d-form and l-form. 5 In claim 1, two specific components A
, B form an intermolecular compound under atmospheric pressure, and a eutectic point composition AP of the intermolecular compound and the specific component A, and a eutectic point composition BP of the intermolecular compound and the specific component B are formed, respectively,
Moreover, the separation method is applicable to a eutectic mixture in which at least one of the eutectic point compositions AP and BP moves in a direction away from the intermolecular compound composition in response to an increase in pressure. 6. When separating a specific component from a multi-component eutectic mixture in which two specific components form an intermolecular compound and in which the intermolecular compound or the specific component cannot be separated by crystallization in the phase diagram under atmospheric pressure, Utilizing the phenomenon that the eutectic point composition of an intermolecular compound and each specific component that constitutes it fluctuates under high pressure, by combining the crystallization operation under high pressure and the crystallization operation under low pressure, Either the intermolecular compound or the specific component is crystallized under the following steps, the intermolecular compound or the specific component is solidified and separated, and the specific component or other specific component is converted to a eutectic composition under low pressure or a eutectic composition under high pressure. A method for separating eutectic mixtures characterized by concentration exceeding the crystal composition.