Refining system

Abstract

To provide a refining system that can refine substances by mild temperature control, and can reuse a solvent without using distillation.SOLUTION: A refining system, which refines a substance containing a target compound C by using a solvent which contains a component A and a component B and has a critical solution temperature, has: a first separation part which dissolves the substance in the solvent at a temperature T1, and separates components other than the target compound C that are contained in the substance; and a second separation part which changes a temperature of a solution, in which the target compound C is dissolved in the solvent, from the temperature T1 to a temperature T2, thereby causing phase change of the solvent and separating the target compound C from the solvent.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a purification system. [Background technology]

[0002] In recent years, there has been a demand for reuse in order to reduce the environmental load, and various techniques for separating components have been investigated.

[0003] For example, Patent Document 1 discloses "a method for purifying recycled polyethylene. In one embodiment, the method involves obtaining recycled polyethylene, contacting the recycled polyethylene with a first fluid solvent to produce extracted recycled polyethylene, and then dissolving the extracted recycled polyethylene in the solvent to produce a first solution comprising polyethylene. The first solution is precipitated and then filtered. A method for purifying recycled polyethylene is disclosed, which separates higher purity polyethylene from the resulting solution."

[0004] Furthermore, Patent Document 2 discloses a "method for reducing the volume of expanded polystyrene, characterized in that the expanded polystyrene is dissolved in a dissolving solvent selected from the group consisting of glycol ether acetate ester compounds, glycol ether compounds, acetylacetone, diethyl carbonate, and ethyl orthoformate." [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2021-527727 [Patent Document 2] Japanese Patent Application Publication No. 11-80418 Summary of the Invention [Problem to be solved by the invention]

[0006] Patent Document 1 describes how high-purity recycled polyethylene can be obtained by dissolving recovered polyethylene in a low-boiling point solvent under high-pressure conditions and separating it from impurities. By lowering the pressure after removing the impurities, it becomes possible to easily separate the low-boiling point solvent from the polyethylene. However, the method of Patent Document 1 requires treatment under high pressure conditions, which leads to increased equipment costs. In addition, the solvent after use is prone to vaporization under normal pressure, making it difficult to recover or reuse the solvent. In order to reduce recycling costs, a method that can be carried out under normal pressure and that allows efficient recovery and reuse of the solvent is required.

[0007] On the other hand, in Patent Document 2, it is said that polystyrene can be reused by dissolving it in a good solvent to reduce its volume and then reprecipitating it in a poor solvent. In addition, in Patent Document 2, the mixed solvent remaining after reprecipitation is separated by distillation and reused. However, the distillation method employed in Patent Document 2 is often used as a method for separating components from a mixed solvent, but it is known that the cost required for heating is high. A method for reusing the mixed solvent after reprecipitation at low cost is required.

[0008] Therefore, an object of the present disclosure is to provide a purification system that is capable of purifying a substance through mild temperature adjustment and that is capable of reusing a solvent without using distillation. [Means for solving the problem]

[0009] Means for solving the above problems include the following aspects. <1> A purification system for purifying a substance containing a target compound C using a solvent containing components A and B and having a critical solution temperature, a first separation section that dissolves the substance in the solvent at a temperature T1 and separates components contained in the substance other than the target compound C; a second separation section for changing a temperature of a solution in which the target compound C is dissolved in the solvent from the temperature T1 to a temperature T2, thereby causing a phase transition of the solvent and separating the target compound C from the solvent; A purification system comprising: <2> The solvent is in a phase-separated state at the temperature T1 and in a compatible state at the temperature T2, The target compound C is soluble in the component A at the temperature T1 and insoluble in the solvent at the temperature T2. <1> The purification system according to claim 1. <3> The specific gravity of the component A at the temperature T1 is lower than the specific gravity of the component B at the temperature T1, The specific gravity of the component B at the temperature T1 is equal to or greater than the specific gravity of the target compound C at the temperature T1. <2> The purification system according to claim 1. <4> The specific gravity of the component A at the temperature T1 is higher than the specific gravity of the component B at the temperature T1, The specific gravity of the component B at the temperature T1 is equal to or lower than the specific gravity of the target compound C at the temperature T1. <2> The purification system according to claim 1. <5> The solvent is in a compatible state at the temperature T1 and in a phase-separated state at the temperature T2, The target compound C is soluble in the solvent at the temperature T1 and insoluble in the component A and the component B at the temperature T2. <1> The purification system according to claim 1. <6> The component B includes ethylene carbonate. <1> ~ <5> 2. A purification system according to any one of claims 1 to 11. <7> The target compound C is a polyolefin resin, The component A includes aromatic hydrocarbons. <1> ~ <6> 2. A purification system according to any one of claims 1 to 11. Effect of the Invention

[0010] According to the present disclosure, it is possible to provide a purification system that is capable of purifying substances through mild temperature control and that allows for the reuse of solvents without the use of distillation. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a block diagram illustrating an example of a purification system of the present disclosure. [Diagram 2] FIG. 2 shows the miscibility and phase separation behavior of a two-component system. [Diagram 3] FIG. 3 is a diagram showing the relationship between the phase state of a solvent and the solubility. [Figure 4] FIG. 4 is a block diagram illustrating an example of a first separation unit according to the present disclosure. [Diagram 5] FIG. 5 is a block diagram illustrating an example of a second separation unit according to the present disclosure. [Figure 6] 6A and 6B are diagrams showing calculation results of energy consumption of the refining system, where Fig. 6(a) is a diagram showing calculation results of the refining system of Example 1, and Fig. 6(b) is a diagram showing results of the conventional refining system. [Figure 7] 7A and 7B are diagrams showing calculation results of energy consumption of the refining system, where Fig. 7(a) is a diagram showing calculation results of the refining system of Example 2, and Fig. 7(b) is a diagram showing results of the conventional refining system. [Figure 8] 8A and 8B are diagrams showing calculation results of energy consumption of the refining system, in which Fig. 8(a) shows the calculation results of the refining system of Example 3, and Fig. 8(b) shows the results of the conventional refining system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment that is an example of the present disclosure will be described. These descriptions and examples are merely illustrative of the embodiment, and are not intended to limit the scope of the invention. In the present specification, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range. In addition, in the present specification, the upper or lower limit of the numerical range may be replaced with a value shown in the examples.

[0013] In this specification, each component may contain multiple types of the corresponding substance. Furthermore, when referring to the amount of each component in a composition, if there are multiple substances corresponding to each component in the composition, unless otherwise specified, it means the total amount of those multiple substances present in the composition. Additionally, "normal temperature" means 25°C, and "normal pressure" means 1 atmosphere.

[0014] [Refining system (or refining method)] The purification system (or purification method, hereinafter the same) according to this embodiment is a purification system (or purification method) that purifies a substance containing a target compound C by using a solvent containing components A and B and having a critical solution temperature. Hereinafter, a solvent containing components A and B and having a critical solution temperature will be referred to as a "specific solvent", and a substance containing target compound C will be referred to as a "specific substance". Examples of specific substances include substances that contain target compound C and impurities that are components other than target compound C.

[0015] As shown in FIG. 1, the purification system (or purification method) according to this embodiment has a first separation section (or a first separation step) that dissolves a specific substance in a specific solvent at a temperature T1 and separates impurities, which are components other than a target compound C contained in the specific substance, and a second separation section (or a second separation step) that changes the temperature of the solution in which the target compound C is dissolved in the specific solvent from temperature T1 to temperature T2, thereby causing a phase transition of the specific solvent and separating the target compound C from the specific solvent.

[0016] As shown in FIG. 1, the specific solvent separated in the second separation section (or the second separation step) may be reused as a specific solvent for dissolving a specific substance in the first separation section (or the first separation step). In this embodiment, the specific substance is dissolved in a specific solvent containing components A and B in the first separation section (or the first separation step). Therefore, the specific solvent separated in the second separation section (or the second separation step) can be used as it is in the first separation section (or the first separation step), and a step for separating components A and B is not required, making it possible to reuse the specific solvent without using distillation.

[0017] The specific solvent is a mixed solvent that exhibits temperature-dependent phase separation behavior, and undergoes a phase transition at a critical solution temperature, which is a temperature between temperatures T1 and T2. For example, a mixed solvent that is in a phase-separated state at temperature T1 and a compatible state at temperature T2, or a compatible state at temperature T1 and a miscible state at temperature T2, can be mentioned. That is, in the specific solvent, component A and component B exhibit mutually separate behavior at temperature T1 and mutually miscible behavior at temperature T2, or exhibit mutually miscible behavior at temperature T1 and mutually miscible behavior at temperature T2.

[0018] As shown in Figure 2, the miscibility and phase separation behavior in a two-component system can be classified into (i) cases where UCST (Upper Critical Solution Temperature) type behavior is observed, (ii) cases where LCST (Lower Critical Solution Temperature) type behavior is observed, and (iii) cases where the critical temperature is not observed. The behavior of the specific solvent containing the above-mentioned components A and B corresponds to the behavior of FIG. 2(i) or FIG. 2(ii).

[0019] In this embodiment, the temperature of the specific solvent is changed from temperature T1 to temperature T2, whereby the specific solvent undergoes a phase transition and the solubility of the target compound C in the specific solvent changes. In this embodiment, the specific substance is purified by utilizing the change in solubility of the target compound C accompanying the phase transition of the specific solvent. Therefore, the temperature of the specific solvent may be changed from a temperature lower than the critical solution temperature to a temperature higher than the critical solution temperature, or from a temperature higher than the critical solution temperature to a temperature lower than the critical solution temperature, and the temperature difference between temperature T1 and temperature T2 may be small. Therefore, compared to, for example, a purification method that utilizes only the temperature dependence of solubility, a purification method that utilizes distillation, and the like, purification under normal pressure is possible, and purification of the substance is possible by mild temperature adjustment.

[0020] -First aspect- In the first embodiment, a specific solvent that is in a phase-separated state at a temperature T1 and in a compatible state at a temperature T2 is used as the specific solvent. In the first embodiment, the target compound C is soluble in at least component A among components A and B contained in the specific solvent in a phase-separated state at temperature T1, and is insoluble in the specific solvent in a compatible state at temperature T2. Note that the target compound C may be soluble or insoluble in component B contained in the specific solvent in a phase-separated state at temperature T1, and is preferably insoluble.

[0021] Here, when a target compound is "soluble" in a certain component, it means that when the target compound and a certain component are brought into contact with each other under certain temperature and pressure conditions, the two mix to form a uniform mixed system, and when a target compound is "insoluble" in a certain component, it means that when the target compound and a certain component are brought into contact with each other under certain temperature and pressure conditions, the two do not mix and remain in a non-uniform state. A specific example of the first aspect is shown in Figures 3(i) and (ii), in which "the compound is insoluble in a specific solvent when the specific solvent is in a homogeneous state, and is soluble in the high-density phase or the low-density phase in a phase-separated state."

[0022] In the embodiment shown in FIG. 3(i), among the components A and B constituting the specific solvent in a phase-separated state, the target compound C is soluble in the relatively high density phase (e.g., component A) and is insoluble in the relatively low density phase (e.g., component B). The target compound C is insoluble in the specific solvent in a compatible state (i.e., homogeneous state). Therefore, in the first separation section (or first separation step), the target compound C contained in the specific substance is dissolved in the high density phase (e.g., component A), and in the second separation section (or second separation step), the target compound C is separated from the compatible specific solvent.

[0023] As shown in FIG. 3(i), the target compound C is soluble in component A at temperature T1, and the specific gravity D of component A at temperature T1 is A1 is the specific gravity D of component B at temperature T1 B1 (i.e., component A is the high-density phase and component B is the low-density phase), the specific gravity D of the low-density phase B1 is the specific gravity D of the target compound C at temperature T1C1 The specific gravity of the low density phase is preferably less than or equal to D B1 is the specific gravity of the target compound, D C1 Below (i.e. D B1 ≦D C1 ) such that even when the specific solvent is allowed to stand, the target compound C can easily come into contact with the component A, and the target compound C can be easily dissolved in the component A.

[0024] In the embodiment shown in FIG. 3(ii), among components A and B constituting the specific solvent in a phase-separated state, the target compound C is soluble in the relatively low-density phase (e.g., component A) and is insoluble in the relatively high-density phase (e.g., component B). The target compound C is insoluble in the specific solvent in a compatible state (i.e., homogeneous state). Therefore, in the first separation section (or first separation step), the target compound C contained in the specific substance is dissolved in the low-density phase (e.g., component A), and in the second separation section (or second separation step), the target compound C is separated from the compatible specific solvent.

[0025] As shown in FIG. 3(ii), the target compound C is soluble in component A at temperature T1, and the specific gravity D of component A at temperature T1 is A1 is the specific gravity D of component B at temperature T1 B1 (i.e., component A is the low-density phase and component B is the high-density phase), the density of the high-density phase D B1 is the specific gravity D of the target compound C at temperature T1 C1 The specific gravity of the high density phase is preferably equal to or greater than D B1 is the specific gravity of the target compound, D C1 That's it (D B1 ≧D C1 ) such that even when the specific solvent is allowed to stand, the target compound C can easily come into contact with the component A, and the target compound C can be easily dissolved in the component A.

[0026] -Second aspect- In the second embodiment, a specific solvent that is in a compatible state at a temperature T1 and in a phase-separated state at a temperature T2 is used as the specific solvent. In the second embodiment, the target compound C is soluble in a specific solvent in a compatible state at a temperature T1, and is insoluble in the components A and B at a temperature T2.

[0027] A specific example of the second aspect is shown in FIG. 3(iii), in which the compound is soluble in a specific solvent in a homogeneous state and insoluble in both the high-density phase and the low-density phase in a phase-separated state.

[0028] In the embodiment shown in Fig. 3(iii), the target compound C is soluble in the specific solvent in a compatible state (i.e., homogeneous state), and is insoluble in both components A and B constituting the specific solvent in a phase-separated state. Therefore, in the first separation section (or the first separation step), the target compound C contained in the specific substance is dissolved in the specific solvent in a compatible state, and in the second separation section (or the second separation step), the target compound C is separated from the specific solvent in a phase-separated state (i.e., components A and B). In the embodiment shown in FIG. 3(iii), since the soluble phase is a homogeneous single phase, even if the specific solvent is allowed to stand, the target compound C can easily come into contact with the specific solvent, and the target compound C can easily be dissolved in the specific solvent.

[0029] The composition of the specific solvent containing component A and component B is determined depending on the type of target compound C contained in the specific substance. Hereinafter, as examples of the specific solvent and specific substance, components A and B contained in the specific solvent applied to the first embodiment, and target compound C and impurities contained in the specific substance will be described.

[0030] A liquid component is applied as component A. When component A is solid at room temperature, it may be liquefied by heating before use. Examples of component A include aromatic hydrocarbons, alcohols, esters, carbonates, ethers, ketones, halogenated hydrocarbons, amines, and sulfoxides. Examples of aromatic hydrocarbons include benzene, ethylbenzene, toluene, xylene, cumene, pseudocumene, and cymene. Examples of alcohols include aliphatic alcohols (methanol, ethanol, propanol, butanol, hexanol, etc.), aromatic alcohols (benzyl alcohol, etc.), and the like. Examples of the esters include aliphatic carboxylates (methyl acetate, ethyl acetate, butyl acetate, vinyl acetate, ethyl propionate, ethyl butyrate, etc.). Examples of carbonates include chain carbonates (dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, dipropyl carbonate, etc.) and cyclic carbonates (propylene carbonate, ethylene carbonate, butylene carbonate, etc.). Examples of the ethers include chain ethers (diethyl ether, ethyl propyl ether, ethyl isopropyl ether, etc.), and cyclic ethers (tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, etc.). Examples of the ketones include acetone, methyl ethyl ketone, pentanone, hexanone, heptanone, and cyclohexanone. Examples of halogenated hydrocarbons include dichloroethane and trichloromethane. Examples of the amines include N-methyl-2-pyrrolidone and N,N-dimethylformamide. The sulfoxides include dimethyl sulfoxide and the like.

[0031] A liquid component is applied as component B. When component B is a solid at room temperature, it may be liquefied by heating before use. Examples of component B include a component containing ethylene carbonate. In particular, ethylene carbonate has a highly symmetric molecular structure and strong intermolecular interactions, and in a mixed system, phase changes of miscibility and separation occur at relatively high temperatures. Due to the properties of ethylene carbonate, in a mixed system of ethylene carbonate and other components, each component can be easily separated by a mild cooling operation. In addition, ethylene carbonate is known as a highly polar solvent used in electrolytes, etc., and has the property of easily dissolving polar substances. Therefore, even in a mixed system of a polar solvent and a nonpolar solvent that does not originally contain ethylene carbonate, it is possible to separate the nonpolar solvent by extracting the polar solvent with ethylene carbonate, and then separate ethylene carbonate and the polar solvent by a cooling operation. Therefore, as component B, a component containing ethylene carbonate is preferable. When component B is a component containing ethylene carbonate, the content of ethylene carbonate in the entire component B is, for example, 80 mass% or more, and from the viewpoint of facilitating the phase change, it is preferably 90 mass% or more, and more preferably 95 mass% or more.

[0032] From the viewpoint of facilitating the phase transition of the specific solvent, the proportion of component A contained in the specific solvent is, for example, 10% by mass to 90% by mass, and preferably 20% by mass to 80% by mass, based on the total of components A and B.

[0033] A solid or liquid component can be used as the target compound C. From the viewpoint of ease of application of the purification system of this embodiment, the target compound C is preferably a solid. Examples of the target compound C include low molecular weight compounds, polymeric compounds not having a three-dimensional cross-linked structure, and inorganic compounds. Examples of the low molecular weight compounds include alcohols and aromatic derivatives. Examples of polymer compounds that do not have a three-dimensional cross-linked structure include polyolefin resins (polymers such as polypropylene, polyethylene, and cycloolefin), polystyrene resins, and rubbers (ethylene propylene rubber, etc.). Examples of the inorganic compounds include alkali metal salts and alkaline earth metal salts. The target compound C may be a single compound or a mixture of two or more compounds. The impurities that can be contained in the specific substance are not particularly limited, and examples thereof include compounds that differ in at least one of polarity and solubility from that of the target compound C. The impurities may be a single compound or a mixture of two or more compounds.

[0034] From the viewpoint of ease of application of the purification system of this embodiment, the target compound C is preferably a polyolefin resin. When target compound C is a polyolefin resin, it is preferred that component A contains aromatic hydrocarbons, and it is more preferred that component A contains aromatic hydrocarbons and component B contains ethylene carbonate.

[0035] When the target compound C is a polyolefin resin, component A is an aromatic hydrocarbon, and component B is ethylene carbonate, the amount of target compound C (i.e., polyolefins) added to 100 parts by mass of the specific solvent may be an amount according to the fluidity of the target compound C, and may be, for example, 0.1 to 100 parts by mass, preferably 1 to 10 parts by mass, and more preferably 1 to 5 parts by mass.

[0036] The purification system (or purification method) according to this embodiment will be described in detail below.

[0037] <First separation section (or first separation step)> In the first separation section (or first separation step), for example, as shown in FIG. 4, a specific substance containing a target compound C and an impurity is added to a specific solvent containing components A and B, and the mixture of the specific substance and the specific solvent is adjusted to a temperature T1. This causes the specific solvent to be in a soluble phase state, dissolving the target compound C in the specific solvent, and the liberated impurities are separated by a removal operation. As a result, a solution in which the target compound C is dissolved in the specific solvent is obtained.

[0038] The temperature T1 is not particularly limited as long as it is a temperature at which the specific solvent is in a soluble phase state. The temperature T1 is preferably a temperature at which the specific solvent is in a soluble phase state, the solubility of the target compound C is high, and the temperature is equal to or higher than the freezing point and equal to or lower than the boiling point of the specific solvent. When component A is aromatic hydrocarbons and component B is ethylene carbonate, the temperature T1 may be, for example, 25°C to 140°C. The operation of adjusting the mixture to temperature T1 may be a heating operation or a cooling operation.

[0039] The operation of removing impurities is carried out depending on the characteristics of the impurities to be removed. In addition to the operation using an adsorbent, the operation of removing impurities may include filtration, centrifugation, decantation, etc. Examples of the adsorbent include silica gel, zeolite, and activated carbon.

[0040] <Second separation section (or second separation process)> In the second separation section (or second separation step), for example, as shown in FIG. 5, the temperature of the solution (i.e., the solution in which the target compound C is dissolved in the specific solvent) obtained in the first separation section (or first separation step) is adjusted from temperature T1 to temperature T2. This causes the specific solvent to undergo a phase transition to a phase state (i.e., an insoluble phase state) different from that in the first separation section (or first separation step), thereby precipitating the target compound C, and the target compound C and the specific solvent are separated by a separation operation. As a result, the purified target compound C and the specific solvent are obtained, respectively.

[0041] The temperature T2 is not particularly limited as long as it is a temperature at which the specific solvent is in an insoluble phase state. When the critical solution temperature of the specific solvent is higher than the temperature T1, the specific solvent undergoes a phase transition by setting the temperature T2 to a temperature higher than the temperature T1. On the other hand, when the critical solution temperature of the specific solvent is lower than the temperature T1, the specific solvent undergoes a phase transition by setting the temperature T2 to a temperature lower than the temperature T1. For example, in the first embodiment (i.e., the embodiment in which the phase-separated state is a soluble phase state), when components A and B exhibit UCST behavior, the operation of adjusting the temperature of the solution from temperature T1 to temperature T2 in order to make temperature T2 higher than temperature T1 is a heating operation. On the other hand, when components A and B exhibit LCST behavior in the first embodiment, the operation of adjusting the temperature of the solution from temperature T1 to temperature T2 in order to make temperature T2 lower than temperature T1 is a cooling operation.

[0042] The temperature T2 is preferably a temperature at which the specific solvent is in an insoluble phase and is equal to or higher than the freezing point and equal to or lower than the boiling point of the specific solvent. When component A is an aromatic hydrocarbon and component B is ethylene carbonate, the temperature T2 is, for example, 60°C to 160°C. From the viewpoint of facilitating the phase transition, the difference (absolute value) between the temperatures T1 and T2 is, for example, 10° C. or more. From the viewpoint of purifying the specific substance by gentle temperature adjustment, the difference (absolute value) between the temperatures T1 and T2 is preferably 100° C. or less, and more preferably 50° C. or less.

[0043] The separation operation for separating the target compound C from the specific solvent is carried out depending on the properties of the target compound C and the specific solvent. Examples of the separation operation include filtration, centrifugation, decantation, and the like. EXAMPLES

[0044] The present disclosure will be described in more detail below with reference to examples, but the present disclosure is not limited to these examples. The examples were carried out under normal pressure and at room temperature of 25°C.

[0045] [Example 1 Reprecipitation test of polystyrene resin] An example will be described in which the purification system (and purification method) of the present disclosure is applied to the reprecipitation of polystyrene resin. 500 mg of polystyrene resin (an example of a specific substance) containing 20% ​​by mass of impurities (metal powder) was added at room temperature to 40 g of a solvent (an example of a specific solvent) containing xylene (an example of component A) and ethylene carbonate (an example of component B) in a mass ratio of 1:4. At room temperature, the solvent was liquid-liquid separated (i.e., in a phase-separated state), and the polystyrene resin immediately after being added to the solvent was located on the interface between the xylene and ethylene carbonate. The polystyrene resin then completely dissolved at room temperature. The polystyrene solution in which the polystyrene resin was dissolved in the solvent was subjected to a decantation treatment at room temperature to remove impurities. When the polystyrene solution from which the impurities had been removed was heated to 60°C and stirred, the solvent interface disappeared, the solution became homogeneous (i.e., compatible), and polystyrene resin (an example of target compound C) precipitated on the liquid surface. This polystyrene precipitate was collected and left to stand until the temperature of the remaining solvent returned to room temperature, resulting in liquid-liquid separation again.

[0046] When 400 mg of polystyrene resin was added to the solvent after purifying the polystyrene resin at room temperature, it dissolved completely. When the solution was heated to 60°C after removing the impurities, the solvent became homogeneous as in the first operation, and a polystyrene precipitate was generated. This confirmed that the solvent used in this test does not require component separation after operation and can be used repeatedly. The critical solution temperature of the above solvent is 35°C. In addition, in the phase-separated state of the above solvent, xylene is in the low-density phase and ethylene carbonate is in the high-density phase, polystyrene resin is soluble in xylene alone and insoluble in the above solvent in a homogeneous state, and the specific gravity of ethylene carbonate is equal to or greater than that of polystyrene resin. The yield of polystyrene precipitate recovered in both the first and second runs was 95% or more.

[0047] Next, the energy consumption per ton of polystyrene resin in the polystyrene resin reprecipitation process was calculated, taking into account the solvent recovery after reprecipitation. In addition to the reprecipitation flow according to the purification system (and purification method) of the present disclosure, a conventional reprecipitation flow using d-limonene and ethanol was also examined for comparison. In this calculation, the mass ratio of the mixed solvent of xylene and ethylene carbonate to polystyrene resin was 100 times, and that of d-limonene and ethanol was 50 times each, and the calculation was performed assuming that the thermal efficiency of each operation was 25% and the efficiency of the separation operation was 100%. The thermal properties of each substance were referenced from the values ​​listed in the NIST data book. Note that this calculation does not take into account the specific heat and heat of solution of polystyrene resin, or the heat of mixing of each solvent. The calculation results are shown in Figure 6. Figure 6(a) shows the calculation results of the reprecipitation flow in accordance with the purification system (and purification method) of the present disclosure, and Figure 6(b) shows the calculation results of the conventional reprecipitation flow. In Figure 6, "PS" stands for polystyrene resin. In this study, calculation results showed that while the energy consumption in the conventional method, which requires solvent reuse by distillation, is approximately 643 [GJ / ton-PS], it can be reduced to approximately 44 [GJ / ton-PS] by using the purification system (and purification method) of the present disclosure.

[0048] The conventional method involves the following steps: 1) dissolving polystyrene resin (PS) in d-limonene at 25°C, 2) adding ethanol to the polystyrene solution to precipitate and separate the polystyrene resin, and 3) separating the d-limonene and ethanol by distillation.

[0049] [Example 2 Reprecipitation test of polyethylene resin] An example will be described in which the purification system (and purification method) of the present disclosure is applied to the reprecipitation of a polyethylene resin. 125 mg of polyethylene resin (an example of a specific substance) containing 20% ​​by mass of impurities (metal powder) was added to 10 g of a solvent (an example of a specific solvent) containing pseudocumene (an example of component A) and ethylene carbonate (an example of component B) in a 1:1 mass ratio, and heated to 105°C. At 105°C, the solvent was in a liquid-liquid separation state (i.e., in a phase-separated state), and the polyethylene resin immediately after being added to the solvent was located on the interface between the pseudocumene and ethylene carbonate. The polyethylene resin then completely dissolved at 105°C. The polyethylene solution in which the polyethylene resin was dissolved in the solvent was subjected to decantation treatment at 105°C to remove impurities. When the polyethylene solution from which the impurities had been removed was heated to 140°C and stirred, the solvent interface disappeared, the solution became homogeneous (i.e., compatible), and polyethylene resin (an example of target compound C) precipitated on the liquid surface. This polyethylene precipitate was collected and left at room temperature until the remaining solvent was again in a liquid-liquid separation state.

[0050] When 100 mg of polyethylene resin was added to the solvent after purifying the polyethylene resin and heated to 105°C, it completely dissolved. When the solution temperature was raised to 140°C after removing the impurities, the solvent became homogeneous, as in the first operation, and a polyethylene precipitate was generated. This confirmed that the solvent used in this test does not require component separation after operation and can be used repeatedly. The critical solution temperature of the above solvent is 120°C. In addition, in the phase-separated state of the above solvent, pseudocumene is in the low-density phase and ethylene carbonate is in the high-density phase, polyethylene resin is soluble in pseudocumene alone but insoluble in the above solvent in a homogeneous state, and the specific gravity of ethylene carbonate is equal to or greater than that of polyethylene resin. The yield of polyethylene precipitate recovered in both the first and second runs was 75% or more.

[0051] As in Example 1, the energy consumption in the reprecipitation operation of the polyethylene resin was calculated. In addition to the reprecipitation flow according to the purification system (and purification method) of the present disclosure, a conventional reprecipitation flow using xylene and acetone was also examined for comparison. In this calculation, the mixed solvent of pseudocumene and ethylene carbonate was used at 100 times the mass ratio of the polyethylene resin, and xylene and acetone were used at 50 times the mass ratio of the polyethylene resin. The calculation results are shown in Figure 7. Figure 7(a) shows the calculation results of the reprecipitation flow in accordance with the purification system (and purification method) of the present disclosure, and Figure 7(b) shows the calculation results of the conventional reprecipitation flow. In Figure 7, "PE" represents polyethylene resin. In this study, calculation results showed that while the energy consumption in the conventional method, which requires solvent reuse by distillation, is approximately 465 [GJ / ton-PE], it can be reduced to approximately 132 [GJ / ton-PE] by using the purification system (and purification method) of the present disclosure.

[0052] Here, the conventional method was a system in which: 1) polyethylene resin (PE) was dissolved in xylene at 105°C, 2) the polyethylene solution was cooled to 40°C, 3) acetone at 40°C was added to the polyethylene solution to precipitate and separate the polyethylene resin, and 4) the xylene and acetone were separated by distillation.

[0053] [Example 3: Reprecipitation test of polypropylene resin] An example in which the purification system (and purification method) of the present disclosure is applied to the reprecipitation of a polypropylene resin will be described. 375 mg of polypropylene resin (an example of a specific substance) containing 20% ​​by mass of impurities (metal powder) was added to 30 g of a solvent (an example of a specific solvent) containing cymene (an example of component A) and ethylene carbonate (an example of component B) in a 1:1 mass ratio, and heated to 140°C. At 140°C, the solvent was separated into liquid and liquid (i.e., in a phase-separated state), and the polypropylene resin immediately after being added to the solvent was located on the interface between the cymene and ethylene carbonate. The polypropylene resin then completely dissolved at 140°C. The polypropylene solution in which the polypropylene resin was dissolved in the solvent was subjected to decantation treatment at 140°C to remove impurities. When the polypropylene solution from which the impurities had been removed was heated to 160°C and stirred, the solvent interface disappeared, the solution became homogeneous (i.e., compatible), and polypropylene resin (an example of target compound C) precipitated on the liquid surface. This polypropylene precipitate was collected and left at room temperature until the remaining solvent was again in a liquid-liquid separation state.

[0054] When 300 mg of polypropylene resin was added to the solvent after purifying the polypropylene resin and heated to 140°C, it completely dissolved. When the solution temperature was raised to 160°C after removing the impurities, the solvent became homogeneous as in the first operation, and a polypropylene precipitate was generated. This confirmed that the solvent used in this test does not require component separation after operation and can be used repeatedly. The critical solution temperature of the above solvent is 145°C. In addition, in the phase-separated state of the above solvent, cymene is in the low-density phase and ethylene carbonate is in the high-density phase, polypropylene resin is soluble in cymene alone but insoluble in the above solvent in a homogeneous state, and the specific gravity of ethylene carbonate is equal to or greater than that of polypropylene resin. The yield of polypropylene precipitate recovered in the first and second operations was 60% or more in both cases.

[0055] As in Example 1, the energy consumption in the reprecipitation operation of the polypropylene resin was calculated. In addition to the reprecipitation flow according to the purification system (and purification method) of the present disclosure, a conventional reprecipitation flow using xylene and acetone was also examined for comparison. In this calculation, the mixed solvent of cymene and ethylene carbonate was used 100 times, and xylene and acetone were used 50 times each in mass ratio relative to the polypropylene resin. The other conditions were the same as those in Examples 1 and 2. The calculation results are shown in Figure 8. Figure 8(a) shows the calculation results of the reprecipitation flow in accordance with the purification system (and purification method) of the present disclosure, and Figure 8(b) shows the calculation results of the conventional reprecipitation flow. In Figure 8, "PP" represents polypropylene resin. This time, the calculation results showed that while the energy consumption in the conventional method, which requires solvent reuse by distillation, is approximately 507 [GJ / ton-PP], it can be reduced to approximately 159 [GJ / ton-PP] by using the purification system (and purification method) of the present disclosure.

[0056] Here, the conventional method involves the following system: 1) dissolving polypropylene resin (PP) in xylene at 130°C, 2) cooling the polypropylene solution to 40°C, 3) adding acetone at 40°C to the polypropylene solution to precipitate and separate the polypropylene resin, and 4) separating the xylene and acetone by distillation.

[0057] From the above, it is understood that the purification system (and purification method) of this example makes it possible to purify resins in an energy-saving manner by gentle temperature adjustment under normal pressure without using distillation. It is also understood that the purification system (and purification method) of this embodiment makes it possible to reuse the solvent without using distillation.

[0058] Preferred aspects of the present disclosure are described below. <1> A purification system for purifying a substance containing a target compound C using a solvent containing components A and B and having a critical solution temperature, a first separation section that dissolves the substance in the solvent at a temperature T1 and separates components contained in the substance other than the target compound C; a second separation section for changing a temperature of a solution in which the target compound C is dissolved in the solvent from the temperature T1 to a temperature T2, thereby causing a phase transition of the solvent and separating the target compound C from the solvent; A purification system comprising: <2> The solvent is in a phase-separated state at the temperature T1 and in a compatible state at the temperature T2, The target compound C is soluble in the component A at the temperature T1 and insoluble in the solvent at the temperature T2. <1> The purification system according to claim 1. <3> The specific gravity of the component A at the temperature T1 is lower than the specific gravity of the component B at the temperature T1, The specific gravity of the component B at the temperature T1 is equal to or greater than the specific gravity of the target compound C at the temperature T1. <2> The purification system according to claim 1. <4> The specific gravity of the component A at the temperature T1 is higher than the specific gravity of the component B at the temperature T1, The specific gravity of the component B at the temperature T1 is equal to or lower than the specific gravity of the target compound C at the temperature T1. <2> The purification system according to claim 1. <5> The solvent is in a compatible state at the temperature T1 and in a phase-separated state at the temperature T2, The target compound C is soluble in the solvent at the temperature T1 and insoluble in the component A and the component B at the temperature T2. <1> The purification system according to claim 1. <6> The component B includes ethylene carbonate. <1> ~ <5> 2. A purification system according to any one of claims 1 to 11. <7> The target compound C is a polyolefin resin, The component A includes aromatic hydrocarbons. <1> ~ <6> 2. A purification system according to any one of claims 1 to 11.

Claims

1. A purification system for purifying a substance containing a target compound C by using a solvent containing components A and B and having a critical solution temperature, Temperature T １ a first separation section for dissolving the substance in the solvent and separating components contained in the substance other than the target compound C; The temperature of the solution in which the target compound C is dissolved in the solvent is set to the temperature T １ From temperature T ２ a second separation section for causing a phase transition of the solvent and separating the target compound C from the solvent; A purification system comprising:

2. The solvent is heated to a temperature T １ At the temperature T ２ In the above, The target compound C is at the temperature T １ and is soluble in component A at temperature T ２ 2. The purification system of claim 1, wherein the purification system is insoluble in the solvent.

3. The temperature T of the component A １ The specific gravity of the component B at the temperature T １ Lower than the specific gravity in The temperature T of the component B １ The specific gravity at the temperature T １ The purification system of claim 2, wherein the specific gravity is equal to or greater than that at

4. The temperature T of the component A １ The specific gravity of the component B at the temperature T １ Higher than the specific gravity in The temperature T of the component B １ The specific gravity at the temperature T １ 3. The purification system of claim 2, wherein the specific gravity is equal to or less than that at

5. The solvent is heated to a temperature T １ At the temperature T ２ In the phase-separated state, The target compound C is at the temperature T １ and is soluble in the solvent at the temperature T ２ 2. The purification system of claim 1, wherein the purification system is insoluble in component A and component B in a water-insoluble state.

6. The purification system according to any one of claims 1 to 5, wherein the component B comprises ethylene carbonate.

7. The target compound C is a polyolefin resin, 7. The purification system of claim 6, wherein component A comprises aromatic hydrocarbons.

Images