Method for producing styrene monomer

Abstract

To provide a styrene monomer production method that prevents decrease in styrene yield per unit time.SOLUTION: The present disclosure provides a method for producing styrene monomer, comprising: a mixed-solution preparation step of preparing a mixed solution by mixing a styrene resin composition containing a styrene-based polymer having styrene monomer units with a solvent; a purification step of purifying the mixed solution by purification means; a devolatilization step of devolatilizing the purified mixed solution into a fluid; and a first pyrolysis step of thermally decomposing the fluid to produced a first pyrolysis liquid.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a process for producing styrene monomer. [Background technology]

[0002] In response to the recent trend toward the SDGs, there is a demand for technologies to recycle plastic materials such as polystyrene resin. Among these, two methods of recycling polystyrene resin that are attracting attention are mechanical recycling, which aims to reuse polystyrene resin without first returning it to styrene monomer, and chemical recycling, which returns polystyrene resin to styrene monomer first.

[0003] Known mechanical recycling of polystyrene resins is a technique described, for example, in Patent Document 1. Patent Document 1 discloses a technique in which polystyrene resin waste is dissolved in a good solvent such as cymene, p-xylene, toluene, or ethylbenzene, insoluble matter is removed, and then the resulting solution is mixed with a poor solvent such as heptane to precipitate and recover the polystyrene resin components. Furthermore, Patent Document 2 discloses a technology for recovering polystyrene resin without reducing the molecular weight of polystyrene waste by dissolving polystyrene waste in limonene or an organic solvent with a boiling point of less than 200°C, removing insoluble matter, and then vacuum heating and devolatilizing the solution.

[0004] Meanwhile, regarding chemical recycling of polystyrene resin, for example, a technology described in Patent Document 3 is known. Patent Document 3 discloses a technology in which waste polystyrene resin is thermally melted to produce molten polystyrene resin, which is introduced into a tubular pyrolysis device and further pyrolyzed at high heat to obtain styrene monomer.

[0005] Similarly, Patent Document 4 discloses a technique for obtaining styrene monomer by thermally melting polystyrene resin at high temperatures using a twin-screw extruder and then thermally decomposing the resin. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2023 / 082009 [Patent Document 2] Japanese Patent Application Laid-Open No. 2000-334738 [Patent Document 3] Japanese Patent Application Laid-Open No. 2001-40136 [Patent Document 4] Patent Publication No. 2021-134281 Summary of the Invention [Problem to be solved by the invention]

[0007] The conventional mechanical recycling technology for styrene resin described above involves first dissolving polystyrene waste using two or more organic solvents to remove foreign matter, and then precipitating or devolatilizing using a poor solvent to recover high-quality recycled polystyrene resin. However, it has been confirmed that the purity of recycled polystyrene resin is insufficient depending on the intended use, such as when recycled polystyrene resin is used for food hygiene purposes. Therefore, depending on the intended use, it is currently required to remove impurities in accordance with various standards.

[0008] Furthermore, all of the above-mentioned conventional chemical recycling technologies for styrene resins involve a step of thermally decomposing polystyrene waste, and the current situation is that it is virtually impossible to avoid the thermal decomposition step when converting polymers into monomers by chemical recycling. Therefore, Patent Documents 3 and 4 disclose mechanisms for removing the thermal decomposition residue or solid residue generated during thermal decomposition. However, polystyrene waste is generally not composed solely of pure polystyrene resin, and may inevitably contain inorganic substances such as metal powder as well as other resins, such as polyolefin resins used in packaging, etc. Furthermore, in the reduction process of polystyrene waste to styrene monomer through thermal decomposition, it has been confirmed that the other resins and inorganic substances exhibit decomposition behavior different from that of polystyrene resin, and therefore do not simply become pyrolysis residue. Specifically, it was confirmed that, since the gas produced by pyrolysis produces a low-fluidity liquid or solid at a temperature lower than the pyrolysis temperature, in addition to the pyrolysis residue containing carbides and inorganic substances produced during pyrolysis, new problems arise, such as blockage of the pyrolysis equipment or the piping connecting each equipment, or a decrease in the continuous operability of the pyrolysis process. Therefore, an object of the present disclosure is to suppress a decrease in the amount of styrene produced per average operating hour during long-term operation. [Means for solving the problem]

[0009] As a result of intensive research into solving the above-mentioned problems, the present inventors have found that by converting a styrene-based resin composition containing a styrene-based polymer containing styrene monomer units into a mixed liquid by adding a solvent, and then purifying and devolatilizing the mixed liquid to obtain a fluid, a first pyrolysis liquid can be obtained, which makes it possible to suppress clogging of piping due to residues generated in the pyrolysis step or gases produced by pyrolysis, and also to suppress a reduction in the amount of styrene produced over the average operating time during long-term operation, and have completed the present invention.

[0010] That is, the present disclosure is as follows. [1] a mixed solution preparation step of preparing a mixed solution by mixing a styrene-based resin composition containing a styrene-based polymer including a styrene monomer unit with a solvent; a purification step of purifying the mixture by a purification means; a devolatilization step of devolatilizing the purified mixture to form a fluid; a first pyrolysis step of pyrolyzing the fluid to produce a first pyrolysis liquid containing styrene monomer; A method for producing styrene monomer, comprising:

[0011] [2] The method for producing a styrene monomer according to [1], further comprising a recovery step of distilling the first pyrolysis liquid to recover the styrene monomer.

[0012] [3] The method for producing a styrene monomer according to [1], wherein the solvent is one or more selected from the group consisting of toluene, methyl ethyl ketone, and ethylbenzene.

[0013] [4] The method for producing a styrene monomer according to any one of [1] to [3], wherein the fluid contains the styrene polymer in an amount of 10% by mass or more and 100% by mass or less relative to 100% by mass of the total amount of the fluid.

[0014] [5] The method for producing a styrene monomer according to any one of [1] to [4], wherein the purified mixture contains the styrene polymer in an amount of 5% by mass or more and 100% by mass or less, relative to 100% by mass of the total amount of the purified mixture.

[0015] [6] The method for producing a styrene monomer according to any one of [1] to [5], wherein the mixed liquid contains the styrene polymer in an amount of 5% by mass or more relative to 100% by mass of the total amount of the mixed liquid.

[0016] [7] The method for producing a styrene monomer according to any one of [1] to [6], wherein the temperature of the atmosphere in which the styrene-based resin composition and the solvent are mixed in the mixed solution preparation step is 0°C or higher.

[0017] [8] The method for producing a styrene monomer according to any one of [1] to [7], wherein the devolatilization step is carried out under reduced pressure.

[0018] [9] The method for producing a styrene monomer according to any one of [1] to [8], wherein the first pyrolysis step is carried out under reduced pressure.

[0019]

[10] The method for producing a styrene monomer according to any one of [1] to [9], further comprising an analysis step of analyzing the first pyrolysis liquid.

[0020]

[11] The method for producing a styrene monomer according to any one of [1] to

[10] , characterized in that in the first pyrolysis step, pyrolysis vapor containing the styrene monomer is cooled to form a first pyrolysis liquid.

[0021]

[12] The method for producing a styrene monomer according to any one of [1] to

[11] , wherein the styrene-based resin composition contains 20% by mass or less of impurities.

[0022]

[13] The method for producing a styrene monomer according to any one of [1] to

[12] , further comprising a second pyrolysis step of distilling the first pyrolysis liquid to separate it into a first fraction containing styrene monomer and a second fraction having a lower styrene monomer concentration than the first fraction, separating the first fraction into a third fraction having a higher styrene monomer concentration than the first fraction and a fourth fraction having a lower styrene monomer concentration than the first fraction, and then pyrolyzing the fourth fraction again to produce a second pyrolysis liquid.

[0023]

[14] The method for producing a styrene monomer according to

[13] , further comprising a recycling step of distilling the second pyrolysis liquid to separate it into a fifth fraction containing styrene monomer and a sixth fraction having a lower styrene monomer concentration than the fifth fraction, and then recovering the styrene monomer from the fifth fraction.

[0024]

[15] The method for producing a styrene monomer according to

[14] , wherein the recycling step further comprises a step (I) of recovering styrene monomer from the fifth fraction as part of the first pyrolysis liquid, and a step (II) of distilling the fifth fraction separately from the first pyrolysis liquid to recover styrene monomer.

[0025]

[16] The method for producing a styrene monomer according to any one of [1] to

[15] , wherein the first pyrolysis step is a step of heating the fluid to obtain pyrolysis vapor containing a styrene monomer, and then cooling the pyrolysis vapor to produce the first pyrolysis liquid, and the concentration of adhesion-inducing substances contained in the first pyrolysis liquid is less than 0.2 mass%.

[0026]

[17] The method for producing a styrene monomer according to any one of [1] to

[16] , wherein the devolatilization step is a step of devolatilizing the mixed liquid to form the fluid using a flash drum, a flash tank polymer heater, a twin-screw devolatilizer, a thin-film evaporator, or an extruder.

[0027]

[18] The method for producing a styrene monomer according to any one of [1] to

[17] , wherein the purification means is one or more means selected from the group consisting of filtration, decantation, centrifugation, centrifugal sedimentation, a screw decanter, a strainer, a screen mesh, or a filter.

[0028]

[19] The method for producing a styrene monomer according to any one of [1] to

[18] , wherein the purification means is a purification mechanism combining centrifugation and filtration. [Effects of the Invention]

[0029] According to the present disclosure, it is possible to provide a method for suppressing a decrease in the amount of styrene produced per average operating hour during long-term operation. According to the present disclosure, a method can be provided that contributes to extending continuous operation time. According to the present disclosure, it is possible to provide a method that reduces by-products in the pyrolysis liquid obtained in the pyrolysis step, reduces the load on the subsequent distillation step, and allows continuous operation without complicated maintenance. [Brief explanation of the drawings]

[0030] [Figure 1] FIG. 1 is a flow diagram showing an example of a method for producing a styrene monomer from a styrene-based resin composition according to this embodiment. [Figure 2] FIG. 2 is a flow diagram showing another example of the method for producing a styrene monomer from a styrene-based resin composition according to this embodiment. [Figure 3] FIG. 3 is a schematic diagram showing an example of a thermal decomposition apparatus used in the method for producing a styrene monomer from a styrene-based resin composition according to this embodiment. [Figure 4] FIG. 4 is a flow diagram showing another example of the method for producing a styrene monomer from a styrene-based resin composition according to this embodiment. [Figure 5] FIG. 5 is a schematic diagram showing an example of a styrene monomer production apparatus according to this embodiment. [Figure 6] Fig. 6 is a photograph showing the state of the connection part C1P, which is a glass tube, immediately before the production of styrene monomer when styrene monomer is produced using an apparatus in which the thermal decomposition apparatus 10 and the liquefaction apparatus L of Fig. 3 are connected via the connection part C1P. More specifically, Fig. 6 is a photograph showing the state of the connection part C1P, which is a glass tube, immediately before the production of styrene monomer in Comparative Example 5. [Figure 7] FIG. 7 is a photograph showing the state of the connection part C1P, which is a glass tube, during the production of styrene monomer in Comparative Example 5 when styrene monomer is produced using an apparatus in which the thermal decomposition apparatus 10 of FIG. 3 and the liquefaction apparatus L are connected via the connection part C1P. [Figure 8] FIG. 8 is a photograph showing the state of the connection part C1P, which is a glass tube, immediately after the production of styrene monomer in Comparative Example 5, when styrene monomer is produced using an apparatus in which the thermal decomposition apparatus 10 of FIG. 3 and the liquefaction apparatus L are connected via the connection part C1P. DETAILED DESCRIPTION OF THE INVENTION

[0031] Below, we will explain in detail the form for implementing the present invention (hereinafter referred to as the ``present embodiment''), but the present invention is not limited to the following description and can be implemented in various modifications within the scope of its gist.

[0032] [Method of producing styrene monomer] The method for producing a styrene monomer according to the present disclosure is a method for thermally decomposing a styrene-based resin composition containing a styrene-based polymer containing styrene monomer units. The styrene-based polymer may be a resin containing styrene monomer units that has been used, discarded, or is to be discarded. That is, the method for producing a styrene monomer according to this embodiment includes a mixed solution preparation step of preparing a mixed solution by mixing a styrene-based resin composition with a solvent, a purification step of purifying the mixed solution using a purification means, a devolatilization step of devolatilizing the purified mixed solution to form a fluid, and a first pyrolysis step of pyrolyzing the fluid to produce a first pyrolysis liquid containing styrene monomer. This makes it possible to suppress factors that reduce the continuous operability of the pyrolysis process, such as blockage of the pyrolysis equipment or the piping connecting each equipment, as well as pyrolysis residues containing carbides and inorganic substances that are generated during pyrolysis. Preferably, the method for producing a styrene monomer further comprises a recovery step of distilling the first pyrolysis liquid to recover the styrene monomer, thereby producing a highly pure styrene monomer. Hereinafter, the entire method for producing a styrene monomer of this embodiment will be described with reference to Figures 1 and 2, and then each of steps (S1) to (S10) will be described in detail. In addition, as an example of a preferred embodiment of the method for producing a styrene monomer of this embodiment, a flow chart shown in Figure 4 is shown.

[0033] Fig. 1 is a flow diagram showing an example of a method for producing a styrene monomer from a styrene-based resin composition according to this embodiment. More specifically, Fig. 1 shows a mixed solution preparation step (S1) of preparing a mixed solution by mixing a raw material styrene-based resin composition with a solvent, a purification step (S2) of purifying the mixed solution to concentrate the styrene polymer contained in the mixed solution, a devolatilization step (S3) of devolatilizing the purified mixed solution to prepare a fluid by distilling off a certain amount of the solvent, a first pyrolysis step (S4) of thermally decomposing the fluid to produce a first pyrolysis liquid containing a styrene monomer, and an optional recovery step (S5) of recovering the styrene monomer from the first pyrolysis liquid.

[0034] FIG. 2 is a flow diagram showing another example of the method for producing a styrene monomer from a styrene-based resin composition according to this embodiment. More specifically, in FIG. 2 , there are shown a mixed solution preparation step (S1) of preparing a mixed solution by mixing a styrene-based resin composition as a raw material with a solvent, a purification step (S2) of purifying the mixed solution to concentrate the styrene-based polymer contained in the mixed solution, a devolatilization step (S3) of devolatilizing the purified mixed solution to prepare a fluid by distilling off a certain amount of the solvent, a first pyrolysis step (S4) of thermally decomposing the fluid to produce a first pyrolysis solution containing styrene monomer, an optionally provided first distillation step (S6) of distilling the first pyrolysis solution to separate it into a first fraction containing styrene monomer and a second fraction having a lower styrene monomer concentration than the first fraction, and an optionally provided first distillation step (S7) of distilling the first pyrolysis solution to separate it into a first fraction containing styrene monomer and a second fraction having a lower styrene monomer concentration than the first fraction. The process includes a second distillation step (S7) in which the first fraction is distilled to separate it again into a third fraction containing styrene monomer and a fourth fraction having a lower styrene monomer concentration than the third fraction, a second thermal decomposition step (S8) in which the fourth fraction is thermally decomposed again to produce a second thermal decomposition liquid, an optional third distillation step (S9) in which the second thermal decomposition liquid is distilled to separate it into a fifth fraction containing styrene monomer and a sixth fraction having a lower styrene monomer concentration than the fifth fraction, an optional recycling step (S10) in which styrene monomer is recovered from the fifth fraction, and an optional recovery step (S5) in which styrene monomer is recovered from the first thermal decomposition liquid.

[0035] FIG. 4 is a flow chart showing another example of a method for producing styrene monomer from a styrene-based resin composition according to the present embodiment. More specifically, FIG. 4 shows a preparation step for preparing a raw material styrene-based resin composition; a mixed solution preparation step (S1) for blending the raw material styrene-based resin composition with a solvent to prepare a mixed solution; a purification step (S2) for purifying the mixed solution to concentrate the styrene-based polymer contained in the mixed solution and removing impurities contained in the raw material styrene-based resin composition; a devolatilization step (S3) for devolatilizing the purified mixed solution to prepare a fluid by distilling off a certain amount of the solvent; a first pyrolysis step (S4) for thermally decomposing the fluid to produce a first pyrolysis liquid containing styrene monomer; and an optional recovery step (S5) for recovering the styrene monomer from the first pyrolysis liquid. The method may also include a step of recovering the solvent distilled off from the purified mixed solution in the devolatilization step (S3) and purifying the solvent by distillation (i.e., a solvent recovery and purification step). The recycled solvent purified in the solvent recovery and purification step may be reused in the mixed solution preparation step (S1). Also, the residue other than the purified recycled solvent obtained in the solvent recovery and purification step may be blown down and used as fuel in the first pyrolysis step (S4). Furthermore, the light fraction or heavy fraction (light or heavy oil), which is a component other than the styrene monomer obtained in the recovery step (S5), may be used as fuel in the first thermal cracking step (S4), which is expected to improve the yield of the obtained styrene monomer. Each step will be described below.

[0036] (Mixture preparation process: S1) The method for producing a styrene monomer according to the present embodiment includes a step of preparing a mixed solution by mixing a styrene-based resin composition with a solvent, which has the effect of concentrating the styrene-based polymer by utilizing the solubility of the solvent.

[0037] <Solvent> The solvent of the present embodiment preferably dissolves the styrene polymer in the styrene resin composition. This allows separation into a component containing the styrene polymer that is soluble in the solvent and a component that is insoluble or poorly soluble in the solvent. As a result, the styrene polymer can be concentrated. In this embodiment, the solubility parameter (SP value (cal / cm 3 ) 1 / 2 ) is preferably 8.0 or more and less than 11.0, more preferably 8.3 or more and less than 10.5, and even more preferably 8.6 or more and less than 10.0. When the solubility parameter of the solvent is within the above range, it becomes easy to selectively dissolve styrene polymers (for example, polystyrene, styrene-(meth)acrylic acid copolymers, etc.). Preferred solvents in this embodiment include the following solvents. In this case, the number in parentheses indicates the SP value of the corresponding solvent. The solvent is preferably an organic solvent, and specifically, the organic solvent may be one or more solvents selected from the group consisting of acetone (9.9), chloroform (9.3), methyl ethyl ketone (9.3), benzene (9.2), tetrahydrofuran (9.1), toluene (8.9), ethylbenzene (8.8), and styrene (9.3). The solvent may be a single solvent or a mixed solvent of two or more solvents.

[0038] The solubility parameter (SP value) defined in this embodiment is calculated using a function of cohesive energy density shown in the following formula (1). SP value ((cal / cm 3 ) 1 / 2 )=(△E / V) 1 / 2 (1) (In the above formula (1), ΔE represents the intermolecular cohesive energy (heat of vaporization), V represents the total volume of the mixed liquid, and ΔE / V represents the cohesive energy density.) The change in heat quantity due to mixing, ΔHm, is expressed by the following formula (2) using the SP value. △Hm=V(δ1-δ2)·Φ1·Φ2 (2) (In the above formula (2), δ1 represents the SP value of the solvent, δ2 represents the SP value of the solute, Φ1 represents the volume fraction of the solvent, and Φ2 represents the volume fraction of the solute.) According to the above formulas (1) and (2), the closer the values ​​of δ1 and δ2 are, the smaller ΔHm becomes and the smaller the Gibbs free energy becomes, so that substances with a small difference in SP value have a high affinity with each other. The above SP values ​​are SP values ​​obtained using the Hilderbrand method (including the Hansen method), and were obtained by reference to literature values ​​("Polymer Handbook 4th Edition," "J. Brandrup, E. H. Immergut, E. A. Grulke," Wiley-Interscience).

[0039] The solvent in this embodiment is preferably an organic solvent, and may be a mixed solvent of two or more organic solvents. Each component constituting the organic solvent preferably has 8 or less carbon atoms, and more preferably has 1 to 8 carbon atoms. By making the number of carbon atoms in the organic solvent 8 or less, it is possible to prevent the boiling point of the solvent itself from becoming high while ensuring the solubility of the styrene-based polymer, and also to keep the amount of solvent remaining in the fluid low in the devolatilization step in which a purified mixed liquid containing the styrene-based polymer is devolatilized to form the fluid. In addition, the number of carbon atoms is 1 or more and 8 or less, and the solubility parameter (SP value (cal / cm 3 ) 1 / 2 By using an organic solvent in which the solubility (kJ / kcal) of each component in the organic solvent is 8.0 or more and less than 11.0, selective separation of the styrene-based polymer and / or styrene monomer from the impurities and / or adhesion-inducing substances described below can be promoted by utilizing the difference in solubility of each component in the organic solvent.

[0040] The content of the solvent in this embodiment is preferably 5 to 95 mass % of the entire mixed liquid, more preferably 35 to 90 mass %, and even more preferably 50 to 80 mass %. When the amount of the solvent mixed is within the above range, the mixture is easily separated into a component containing the styrene polymer that dissolves in the solvent and components other than the above component.

[0041] <Styrene-based resin composition> The styrene-based resin composition used in the method for producing a styrene monomer of the present embodiment may contain a styrene-based polymer containing a styrene monomer unit, and the lower limit of the content of the styrene-based polymer contained in the styrene-based resin composition used as a raw material in the method for producing a styrene monomer may be preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, and still more preferably 80% by mass or more, based on the entire styrene-based resin composition. On the other hand, the upper limit of the content of the styrene polymer can be 50 mass %, 60 mass %, 70 mass %, 80 mass %, or 100 mass % or less based on the entire styrene resin composition. When the content of the styrene polymer contained in the styrene resin composition is within the above range, the yield of the pyrolysis liquid generated in the pyrolysis step described below increases, thereby increasing the yield of the styrene monomer in the recovery step.

[0042] The styrene-based resin composition of the present embodiment includes used, discarded, or to-be-discarded materials, pre-consumer materials such as factory-collected products, post-consumer materials such as market-collected products, long-term inventory pellets, off-specification pellets, etc. The styrene-based resin composition may also contain additives such as a phosphorus-based flame retardant, liquid paraffin, a stabilizer, or a colorant.

[0043] The styrene-based resin composition may contain impurities. It is preferable that the styrene-based resin composition of this embodiment is a used, discarded, or discarded material, i.e., the styrene-based resin composition is a recycled polystyrene-based resin composition. When the styrene-based resin composition of this embodiment is a recycled polystyrene-based resin composition, the styrene-based resin composition may contain impurities as contaminants derived from recycling. The impurities may include, for example, resins other than styrene-based polymers (e.g., olefin resins such as polyethylene-based resins and polypropylene-based resins), inorganic substances (e.g., metal powder or silica), pigments, dyes, fine particles, deposits, or foreign matter. More specifically, the term "impurities" as used herein may include other resins that are substantially free of styrene monomer units, such as olefin resins, polyether resins, polyester resins, or polyamide resins. The term may also refer to products in which these other resins are laminated, or to mixed resins in which other resins, such as olefin resins, polyether resins, polyester resins, or polyamide resins, are mixed with styrene polymers containing styrene monomer units. Another aspect of the styrene resin composition of this embodiment may be a composition in which celluloses, such as paper (e.g., paper labels), thermosetting resins, such as phenolic resins, polyurethane resins, epoxy resins, and melamine resins, are mixed with styrene polymers containing styrene monomer units. Furthermore, the styrene resin composition may contain inorganic materials, such as silicate minerals, such as talc, glass, or fillers, such as carbon fiber, glass fiber, or cellulose fiber, which are used in fiber-reinforced plastics. Metals, such as aluminum, iron, and stainless steel, may also be included. The upper limit of the amount of impurities contained in the styrene-based resin composition used as a raw material in the production method of styrene monomer is preferably 50% by mass or less, more preferably 40% by mass or less, even more preferably 30% by mass or less, and even more preferably 20% by mass or less, based on the entire styrene-based resin composition. The lower limit of the amount of impurities contained in the styrene-based resin composition is preferably 0% by mass or more, and more preferably more than 0% by mass, based on the entire styrene-based resin composition.

[0044] In particular, in the method for producing styrene monomer of this embodiment, it is advantageous to use a post-consumer material that generates residues upon thermal decomposition. However, even if the styrene resin composition of this embodiment is a virgin polystyrene resin composition containing an unused styrene polymer, or a pre-consumer material such as a recycled product from a factory, it may contain the above-mentioned additives or other resins or inorganic substances mixed in during processing. Therefore, the method for producing styrene monomer of this embodiment is advantageous as a method that can produce styrene monomer from these virgin polystyrene resin compositions or pre-consumer materials while suppressing the generation of thermal decomposition residues.

[0045] <<Styrene-based polymer>> The styrene-based resin composition usable in this embodiment contains a styrene-based polymer containing a styrene monomer unit. The styrene-based resin composition or the styrene-based polymer may be a used, discarded, or discarded material. The styrene-based polymer may contain a styrene monomer unit. Preferably, the styrene-based polymer is a polymer obtained by polymerizing a styrene monomer unit and, if necessary, one or more selected from other vinyl-based monomer units and rubbery polymers copolymerizable with the styrene monomer. In other words, the styrene-based polymer contained in the styrene-based resin composition is preferably a polymer containing a styrene monomer unit, and more preferably a polymer essentially containing a styrene monomer unit and optionally containing other vinyl-based monomers and / or rubbery polymer monomer units copolymerizable with the styrene monomer unit. The preferred form of the styrene-based polymer in this embodiment is not particularly limited, but specific examples include rubber-modified styrene-based resins in which rubbery polymer particles are dispersed in a polymer matrix containing polystyrene, a polystyrene-based polymer (such as polystyrene and / or polystyrene-unsaturated carboxylic acid polymer), and a styrene-based copolymer resin.

[0046] In the styrene polymer contained in the styrene resin composition usable in this embodiment, the lower limit of the content of styrene monomer units relative to the entire styrene polymer (100% by mass) is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more. On the other hand, the upper limit of the content of styrene monomer units can be 50%, 60%, 70%, 80%, or 100% by mass.

[0047] -polystyrene- In this embodiment, polystyrene refers to a polymer containing styrene monomer units and, if necessary, other styrene-based monomer units. Monomers constituting the polystyrene include, in addition to styrene, other styrene-based monomers as optional components. Examples of other styrene-based monomers include α-methylstyrene, α-methyl-p-methylstyrene, ο-methylstyrene, m-methylstyrene, p-methylstyrene, vinyltoluene, ethylstyrene, isobutylstyrene, and t-butylstyrene, as well as styrene derivatives such as bromostyrene and indene. These monomers can be used alone or in combination. While polystyrene may contain further monomer units other than the above-mentioned monomer units as long as the effects of the present invention are not impaired, it typically consists of styrene monomer units.

[0048] -Rubber-modified styrene resin- In this embodiment, the rubber-modified styrene-based resin is a resin in which rubbery polymer particles are dispersed in a styrene-based polymer (e.g., polystyrene) as a matrix phase, and has a sea-island structure in which the matrix phase is a sea phase and the rubbery polymer particles (=rubber-like polymer particles) are island phases. The rubber-modified styrene-based resin can be produced by polymerizing styrene monomer (and other styrene-based monomers and unsaturated carboxylic acid-based monomers, which are added as needed) in the presence of the rubbery polymer. The unsaturated carboxylic acid monomers include (meth)acrylic acid monomers and (meth)acrylic acid ester monomers.

[0049] The styrene monomer and other styrene monomers added as needed that constitute the rubber-modified styrene resin of this embodiment are the same as the styrene monomer of the polystyrene described above, and therefore will not be described here.

[0050] The rubbery polymer particles contained in the rubber-modified styrene-based resin of this embodiment may, for example, contain a resin containing styrene monomer units obtained from the above-mentioned styrene monomer inside the rubbery polymer particle, and / or may have a resin containing styrene monomer units grafted onto the surface of the rubbery polymer particle. More specifically, the rubbery polymer particles may also include a form in which polystyrene and / or polystyrene-unsaturated carboxylic acid polymers are contained inside. Similarly, polystyrene and / or polystyrene-unsaturated carboxylic acid polymers may be grafted onto the surface of the rubbery polymer particle.

[0051] Examples of the rubbery polymer that can be used include rubber components such as polybutadiene, polyisoprene, natural rubber, polychloroprene, styrene-butadiene copolymer, and acrylonitrile-butadiene copolymer. Among these, polybutadiene or styrene-butadiene copolymer is preferred as the rubbery polymer. Both high-cis polybutadiene with a high cis content and low-cis polybutadiene with a low cis content can be used as the polybutadiene. Furthermore, both random and block structures can be used as the structure of the styrene-butadiene copolymer. One or more of these rubbery polymers can be used. Saturated rubber obtained by hydrogenating butadiene rubber can also be used.

[0052] Examples of such rubber-modified styrene resins include HIPS (high impact polystyrene), ABS resin (acrylonitrile-butadiene-styrene copolymer), AAS resin (acrylonitrile-acrylic rubber-styrene copolymer), and AES resin (acrylonitrile-ethylene propylene rubber-styrene copolymer).

[0053] When the rubber-modified styrene resin is a HIPS resin, the particularly preferred rubber polymer is a high-cis polybutadiene having 90 mol % or more of cis-1,4 bonds, preferably having 6 mol % or less, and particularly preferably having 3 mol % or less, of vinyl-1,2 bonds.

[0054] The content of isomers having a cis-1,4 structure, a trans-1,4 structure, or a vinyl-1,2 structure as structural unit isomers of the high-cis polybutadiene can be measured using an infrared spectrophotometer and calculated by processing the data by the Morello method.

[0055] The high-cis polybutadiene can be easily obtained by a known production method, for example, by polymerizing 1,3-butadiene using a catalyst containing an organoaluminum compound and a cobalt or nickel compound.

[0056] The content of the rubber-like polymer contained in the rubber-modified styrene-based resin is preferably 3 to 20 mass %, more preferably 5 to 15 mass %, relative to 100 mass % of the total amount of the rubber-modified styrene-based resin. In the present disclosure, the content of the rubber-like polymer contained in the rubber-modified styrene-based resin is a value calculated using pyrolysis gas chromatography.

[0057] The average particle size of the rubber-like polymer particles contained in the rubber-modified styrene-based resin is preferably 0.5 to 4.0 μm, and more preferably 0.8 to 3.5 μm. In the present disclosure, the average particle size of the rubber-like polymer particles contained in the rubber-modified styrene-based resin is measured by the following method. An ultrathin section with a thickness of 75 nm is prepared from a rubber-modified styrene-based resin stained with osmium tetroxide, and a photograph is taken at a magnification of 10,000 times using an electron microscope. In the photograph, the black-stained particles are the rubber-like polymer (a). From the photograph, the following mathematical formula (N1): [Number 1] Average particle diameter=ΣniDri 3 / ΣniDri2 (N1) (In the above formula (N1), ni is the number of rubber-like polymer particles having a particle diameter Dri, and the particle diameter Dri is the particle diameter calculated as a circle-equivalent diameter from the area of ​​the particle in the photograph.) The area-average particle diameter is calculated by the above equation, and is taken as the average particle diameter of the rubber-like polymer particles. This measurement is carried out by scanning a photograph at a resolution of 200 dpi and using particle analysis software of an image analyzer IP-1000 (manufactured by Asahi Kasei Corporation).

[0058] The reduced viscosity of the rubber-modified styrene-based resin (which is an index of the molecular weight of the rubber-modified styrene-based resin) is preferably in the range of 0.50 to 0.85 dL / g, and more preferably in the range of 0.55 to 0.80 dL / g. In the present disclosure, the reduced viscosity of the rubber-modified styrene-based resin is a value measured in a toluene solution at 30° C. and a concentration of 0.5 g / dL.

[0059] -Styrene copolymer resin- In this embodiment, the styrene copolymer resin is a resin containing a styrene monomer unit and an unsaturated carboxylic acid monomer unit copolymerizable with the styrene monomer. When the total content of the styrene monomer unit and the unsaturated carboxylic acid monomer unit in the styrene copolymer resin according to this embodiment is taken as 100% by mass, the content of the styrene monomer unit is preferably 69 to 98% by mass, more preferably 74 to 96% by mass, and even more preferably 77 to 92% by mass. The unsaturated carboxylic acid monomer in this embodiment includes unsaturated carboxylic acid monomers (for example, (meth)acrylic acid monomers) and unsaturated carboxylic acid ester monomers (for example, (meth)acrylic acid ester monomers).

[0060] In the styrene-based copolymer resin of the present embodiment, when the total content of styrene monomer units, unsaturated carboxylic acid monomer units, and unsaturated carboxylic acid ester monomer units in the styrene-based copolymer resin is taken as 100% by mass, the content of unsaturated carboxylic acid monomer units is preferably 2 to 16% by mass, more preferably 4 to 14% by mass, and even more preferably 8 to 13% by mass.

[0061] In this embodiment, when the total content of the styrene monomer units, unsaturated carboxylic acid monomer units, and unsaturated carboxylic acid ester monomer units is taken as 100% by mass, the content of the unsaturated carboxylic acid ester monomer units is preferably 0 to 15% by mass, more preferably 1 to 12% by mass, and even more preferably 2 to 10% by mass.

[0062] In the present embodiment, the contents of the styrene monomer unit, the unsaturated carboxylic acid monomer unit (for example, methacrylic acid monomer unit), and the unsaturated carboxylic acid ester monomer unit (for example, methyl methacrylate monomer unit) in the styrene copolymer resin can be determined by proton nuclear magnetic resonance ( 1 It can be calculated from the integral ratio of the spectrum measured by a H-NMR spectrometer.

[0063] In the present embodiment, the styrene copolymer resin may further contain monomer units other than the styrene monomer unit and an unsaturated carboxylic acid monomer (e.g., an unsaturated carboxylic acid monomer unit and an unsaturated carboxylic acid ester monomer unit), which are examples of other monomers, to the extent that the effects of the present invention are not impaired. However, the styrene copolymer resin in the present invention is preferably typically composed of a styrene monomer unit, an unsaturated carboxylic acid monomer unit, and / or an unsaturated carboxylic acid ester monomer unit.

[0064] The styrene copolymer resin of the present embodiment may contain other styrene monomers in addition to the styrene monomer.

[0065] The unsaturated carboxylic acid monomer constituting the styrene-based copolymer resin of the present embodiment is not particularly limited, but examples thereof include (meth)acrylic acid (methacrylic acid and / or acrylic acid), maleic anhydride, maleic acid, fumaric acid, and itaconic acid.

[0066] The unsaturated carboxylic acid ester monomer constituting the styrene copolymer resin of this embodiment is not particularly limited, but examples thereof include (meth)acrylic acid esters (e.g., methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, cyclohexyl (meth)acrylate), etc. These unsaturated carboxylic acid ester monomers may be used alone or in combination of two or more.

[0067] Suitable styrene copolymer resins for this embodiment include styrene-methacrylic acid copolymer, styrene-methyl methacrylate copolymer, styrene-methacrylic acid-methyl methacrylate copolymer, styrene-acrylic acid copolymer, styrene-methyl acrylate copolymer, styrene-acrylic acid-methyl acrylate copolymer, styrene-methyl methacrylate-butyl methacrylate copolymer, styrene-butyl methacrylate copolymer, and styrene-maleic anhydride copolymer.

[0068] In this embodiment, the weight average molecular weight (Mw) of the styrene copolymer resin is preferably 100,000 to 350,000, more preferably 120,000 to 300,000, and even more preferably 140,000 to 240,000. The weight average molecular weight (Mw) is a value obtained by gel permeation chromatography in terms of standard polystyrene.

[0069] In the present embodiment, the polymerization method for the styrene-based polymer resin is not particularly limited, but for example, bulk polymerization or solution polymerization can be suitably adopted as a radical polymerization method. The polymerization method mainly comprises a polymerization step of polymerizing polymerization raw materials (monomer components) and a devolatilization step of removing volatile components such as unreacted monomers and polymerization solvent from the polymerization product.

[0070] -Optional addition ingredients- In addition to the styrene polymer and any impurities contained as needed, the styrene resin composition of the present embodiment may contain optional additives such as conventionally known additives and processing aids, as needed, within the range that does not impair the effects of the present invention. Examples of these additives and processing aids include antioxidants, weathering agents, lubricants, antistatic agents, and fillers.

[0071] Examples of the antioxidant include phenolic compounds, phosphorus compounds, and thioether compounds. As the weatherproofing agent, an ultraviolet absorber or the like can be used. As the lubricant, fatty acid amides, fatty acid esters, fatty acids, fatty acid metal salts, etc. can be used. As the antistatic agent, cationic, anionic, nonionic, amphoteric, fatty acid partial esters such as glycerin fatty acid monoesters, etc. can be used. Examples of the filler that can be used include talc, calcium carbonate, barium sulfate, carbon fiber, glass fiber, cellulose fiber, mica, wollastonite, and whisker.

[0072] In addition to the additives and processing aids described above, the styrene-based resin composition of this embodiment may contain optional components such as antiblocking agents, colorants, antiblooming agents, surface treatment agents, antibacterial agents, and anti-seizure agents (such as silicone oils described in JP 2009-120717 A, monoamide compounds of higher aliphatic carboxylic acids, and monoester compounds obtained by reacting higher aliphatic carboxylic acids with monohydric to trihydric alcohol compounds). The total content of the optional components, such as the additives and processing aids, in the styrene-based resin composition may be preferably 0% to 6% by mass, more preferably 0.05 to 5% by mass.

[0073] <Preferred embodiment of styrene-based resin composition> A preferred embodiment of the styrene-based resin composition used as a raw material in the method for producing a styrene monomer of the present embodiment may be a recycled styrene-based resin composition containing a styrene-based polymer, in which the total content of the styrene-based polymer and any additional components is 50 to 100 mass% and the content of impurities is 1 to 30 mass% relative to the entire styrene-based resin composition, and the styrene-based resin composition is a used, discarded, or recycled discarded styrene-based resin composition. By using a recycled styrene-based resin composition containing a used, discarded, or recycled discarded styrene-based polymer as a raw material in the production method, it is possible to reduce the environmental load.

[0074] <Preferred embodiment of the mixed liquid> In a preferred embodiment of the mixed liquid obtained by the mixed liquid preparation step of the present embodiment, the total content of the styrene polymer, solvent, and optional added components is preferably 50 to 100% by mass, more preferably 50% by mass or more and less than 100% by mass, relative to the entire mixed liquid, and the content of impurities is preferably 0 to 30% by mass, more preferably more than 0% by mass and 10% by mass or less.

[0075] <Mixing or kneading conditions in the mixed liquid preparation step> The mixed solution in the present embodiment may contain a styrene-based resin composition containing a styrene-based polymer including a styrene monomer unit and a solvent, and the dispersion state of the solvent in the styrene-based resin composition is not particularly limited. Pre-mixing may be performed using a known mixing mechanism or kneading mechanism before or during the purification step described below. The mixing or kneading mechanism for mixing the styrene-based resin composition and the solvent is not particularly limited, and a method that uniformly mixes the components in the mixed solution is preferred, and melt mixing or melt kneading may be used as necessary. Specific examples of the mixing or kneading mechanism include a magnetic stirrer, a three-one motor, a single-screw extruder, a twin-screw extruder, a screw-type extruder, an open roll, a kneader, a Banbury mixer, and an internal mixer. The mixing or kneading time in the mixed solution preparation step is preferably about 1 to 240 minutes, more preferably 1 to 120 minutes, even more preferably 2 to 120 minutes, and even more preferably 5 to 120 minutes. The temperature of the mixing atmosphere in the mixed solution preparation step is preferably 0 to 260°C, more preferably 10 to 100°C, and even more preferably 20 to 80°C. Furthermore, during mixing, the pressure inside the mixing mechanism (or mixing device) is preferably such that the pressure difference between atmospheric pressure and the pressure inside is within ±500 hPa, more preferably within ±300 hPa. If necessary, the inside of the mixing mechanism (or mixing device) can be purged with an inert gas. Specific examples of the inert gas include nitrogen gas, argon gas, and carbon dioxide gas.

[0076] <Preparation process> The method for producing a styrene monomer according to the present disclosure may include, for example, a preparation step of preparing a raw material styrene resin composition prior to the mixed solution preparation step. Examples of the preparation step include a step of collecting styrene resin-containing waste plastics (post-consumer products) generated from the market or consumers and recycling them as the raw material styrene resin composition (post-consumer), and / or a step of collecting products (pre-consumer products) before distribution to consumers or the market, such as scraps during production, and recycling them as the raw material styrene resin composition (pre-consumer). The preparation process for preparing a styrene-based resin composition from post-consumer products and / or pre-consumer products preferably includes a crushing process for crushing styrene-based resin-containing waste plastics, a cleaning process for cleaning the crushed waste plastics, or a sorting process for sorting the crushed waste plastics. On the other hand, the preparation step for preparing a styrene-based resin composition from a material such as pre-consumer virgin pellets preferably includes a crushing step of crushing a styrene-based resin-containing virgin material.

[0077] (Purification process: S2) The method for producing a styrene monomer according to the present embodiment includes a purification step of purifying the mixed liquid prepared in the mixed liquid preparation step by a purification means, which has the effect of removing impurities that may be mixed into the mixed liquid. Furthermore, the term "purification" as used herein refers to a process in which contaminants such as impurities and contaminants derived from the styrene-based resin composition are removed, so that the concentration of the styrene-based polymer contained in the mixed liquid after the purification step is higher than the concentration of the styrene-based polymer contained in the mixed liquid before the purification step. The purification means in this embodiment is not particularly limited as long as it is an apparatus that can be used for the mixed liquid, and a known purification mechanism may be used to perform preliminary purification before or while performing the devolatilization step described below. The purification mechanism is not particularly limited, and is preferably a means by which each component in the mixed liquid is purified uniformly. Specific examples of the purification mechanism include filtration, decantation, centrifugation, centrifugal sedimentation, a screw decanter, a strainer, a screen mesh, or a filter. The purification mechanism may be a single mechanism or a combination of two or more mechanisms. Among these, a purification mechanism that can perform continuous processing (e.g., centrifugation, filtration, a screw decanter, a strainer, a screen mesh, or a filter) is preferred, and a purification mechanism that combines centrifugation and filtration is more preferred. This allows for the removal of impurities that may be mixed into the mixed liquid by centrifugation, thereby improving the time efficiency of filtration (e.g., processing speed). The time required for purification, from the time the mixed liquid is introduced into the purification means to the time the purified mixed liquid is obtained through the purification means, is preferably about 1 second to 240 minutes.

[0078] The centrifugation used in this embodiment preferably uses a centrifugal separator. The centrifugal separator is a device that has a rotor (basket) therein with holes or slits in the side, and generates centrifugal force as the rotor rotates to separate solids from liquids or substances with different specific gravities. The centrifuge preferably performs centrifugation at a centripetal acceleration in the range of 200 to 20,000 G. The rotor preferably has a cross-sectional shape in the vertical direction including its rotation axis that is substantially cylindrical or substantially truncated cone. Aggregates with low specific gravity contained in the mixed liquid are supplied to the inside of the rotor of the centrifuge and centrifuged, and become floating components that collect on the side closer to the rotation axis of the rotor and are separated from the remaining mixed liquid. The centrifuge is preferably, for example, a disk centrifuge or a screw de-counter.

[0079] In this embodiment, in order to efficiently remove impurities that may be mixed into the mixed liquid, a filter (for example, a bag made of nonwoven fabric or resin sheet, etc.) as described below may be provided along the inner wall of the rotor of the centrifuge. By providing a bag made of nonwoven fabric or resin sheet along the inner wall of the rotor, the effects of both centrifugal sedimentation and centrifugal filtration can be achieved, and therefore impurities and the like that have accumulated inside the rotor can be removed to the outside of the rotor together with the filter and the bag made of nonwoven fabric or resin sheet.

[0080] The filtration used in this embodiment is preferably filtration using a filter. The filter may contain a filter aid on the filter surface and / or inside the filter. From the viewpoint of reducing scratches and particles, the mesh size of the filter is preferably 1 / 10 or less of the average particle size of the filter aid, more preferably 1 / 20 or less, and even more preferably 1 / 30 or less. From the viewpoint of preventing leakage of the aid, the upper limit of the mesh size of the filter is preferably 10 μm or less, more preferably 5 μm or less, and even more preferably 3 μm or less. Furthermore, from the viewpoint of improving the liquid passage speed of the filter, the lower limit of the mesh size of the filter is preferably 0.1 μm or more, more preferably 0.2 μm or more, and even more preferably 0.3 μm or more. Examples of the filter material include filter paper, plastics such as polyethylene, polypropylene, polyethersulfone, polyphenylene sulfide, cellulose acetate, nylon, polycarbonate, and Teflon (registered trademark), ceramics, and metal mesh. The shape of the filter is not particularly limited, but from the viewpoint of ease of handling and reduction of scratches and particles, a sheet type, a cylindrical type, a disc type, or a folded type is preferred. The conditions for filtration using the filter are not particularly limited, but from the viewpoint of improving filtration accuracy and productivity, the differential pressure during filtration is preferably 0.008 to 10 MPa, more preferably 0.05 to 1 MPa. From the viewpoint of improving filtration accuracy and productivity, the number of filter stages is preferably 1 to 5, more preferably 1 to 3. From the viewpoint of improving filtration accuracy and productivity, the filtration rate is preferably 0.1 L / (min m 2 ) or more, preferably 5 L / (min m 2 )That's all.

[0081] In addition, when a filter cloth is used as a filter, the air permeability of the filter is set to 1 to 3000 cm 3 / cm 2 min or less can be used, and 1 over 3000 cm 3 / cm 2 Less than 20 min is preferable, and 2500 cm 3 / cm 2 Less than 1 min is more preferable. The material of the filter cloth is preferably a metal, nylon, fluororesin (such as polytetrafluoroethylene), PPS, PAEK (polyarylene ether ketone), polyester, polypropylene, or polyethylene, which has low solubility in the solvent (for example, 100 parts by mass of solvent is added to 1 part by weight of filter cloth, the filter cloth is immersed at 40°C for 1 hour, solid-liquid separation is performed, the filter cloth is recovered as a solid, and the filter cloth is vacuum-dried at an ambient temperature of 100°C for 1 hour; the weight changes by less than 10% compared to the weight of the original filter cloth), and more preferably stainless steel, nylon, fluororesin (such as polytetrafluoroethylene), PPS, or PAEK. The filter cloth may be woven in the form of a plain weave, a twill weave (also called a diagonal weave), or a satin weave, with a twill weave being preferred.

[0082] In the purified mixed liquid obtained through the purification means, the content of the styrene polymer in the mixed liquid is preferably 5% by mass or more and 100% by mass or less, more preferably 5% by mass or more and 50% by mass or less, based on the total amount of the purified mixed liquid. Furthermore, in the purified mixture obtained through the purification means, the content of impurities in the mixture is preferably 30% by mass or less, more preferably 20% by mass or less, based on the total mass of the purified mixture. The content of impurities in the purified mixture is the value obtained by subtracting the total content of the styrene polymer and the solvent from the total content of the mixture. The purified mixture may also contain other resins that do not substantially contain styrene monomer units, such as olefin-based resins, polyether-based resins, polyester-based resins, or polyamide-based resins.

[0083] In the purification step or purification means of this embodiment, if necessary, an auxiliary agent (so-called filter aid) for improving purification efficiency, such as diatomaceous earth, perlite, powdered silica, powdered activated carbon, or aluminum silicate, may be added to the mixed solution prepared in the mixed solution preparation step. These auxiliary agents not only improve the efficiency of removing impurities (e.g., pigments, other resins, and other inorganic substances) or fine particles that are difficult to remove without the auxiliary agent, but also contribute to the removal and / or reduction of undesired chemical substances from the mixed solution during the production and recovery of styrene monomer through chemical and / or physical adsorption by the auxiliary agent, or through inclusion and / or support by aggregates of the auxiliary agent. Here, inclusion and / or support by aggregates of the auxiliary agent from the mixed solution includes the effect of creating a situation in which specific components in the mixed solution are surrounded by aggregates of auxiliary agent particles, preventing their diffusion into the mixed solution. The auxiliary is preferably granular. In this case, the volume average particle diameter (D50) of the auxiliary is, for example, preferably 5 μm to 100 μm, more preferably 10 μm to 50 μm. The particle size distribution of the average particle diameter (D50) of the auxiliary was measured using a laser diffraction particle size distribution analyzer (manufactured by Shimadzu Corporation, trade name "SALD-2300"), and the volume average particle diameter D50 was calculated from the 50% value of the obtained particle size distribution.

[0084] The amount of the auxiliary agent added to the purification means is preferably 50% by mass or less, more preferably 0.001% by mass to 45% by mass or less, and even more preferably 0.1% by mass to 30% by mass, based on the total weight of the mixture. The amount of the auxiliary agent added to the purification means is preferably 100% by mass or less, more preferably 0.01% by mass to 50% by mass or less, and even more preferably 0.1% by mass to 40% by mass, based on the total weight of the impurities in the mixture.

[0085] The auxiliary may be added by adding the auxiliary described below to the mixing or kneading in the mixed solution preparation step, as in the so-called body feed method. Alternatively, the auxiliary may be added to the mixed solution purified by the purification means. In this case, the method for mixing the auxiliary to be added to the mixed solution and the method for mixing the mixed solution containing the auxiliary are not particularly limited, and a method that uniformly mixes the components in the mixed solution is preferred, and melt mixing or melt kneading may be used as necessary. Specific examples of the mixing or kneading mechanism include a magnetic stirrer, a three-one motor, a single-screw extruder, a twin-screw extruder, a screw-type extruder, an open roll, a kneader, a Banbury mixer, and an internal mixer. The time for mixing or kneading the purified mixture with the auxiliary is preferably about 1 to 240 minutes, more preferably 1 to 120 minutes, even more preferably 2 to 120 minutes, and even more preferably 5 to 120 minutes. The temperature at which the purified mixture containing the auxiliary is mixed or kneaded is preferably 0 to 260°C, more preferably 10 to 100°C, and even more preferably 20 to 80°C. Furthermore, during mixing, the pressure inside the mixing mechanism (or mixing device) is preferably such that the pressure difference between atmospheric pressure and the pressure inside the mixing mechanism (or mixing device) is within ±500 hPa, more preferably within ±300 hPa. If necessary, the inside of the mixing mechanism (or mixing device) can be purged with an inert gas. Specific examples of the inert gas include nitrogen gas, argon gas, and carbon dioxide gas. Alternatively, the auxiliary agent may be added by first applying the auxiliary agent or a dispersion of the auxiliary agent to the interior or exterior surface of the refining mechanism, and then contacting the mixture to perform purification. The dispersion liquid is preferably a substance that is liquid at room temperature and normal pressure and that helps to uniformly disperse the auxiliary agent. The dispersion liquid is preferably selected from the solvents of this embodiment, and examples of the solvent include one or more solvents selected from the group consisting of acetone, chloroform, methyl ethyl ketone, benzene, tetrahydrofuran, toluene, ethylbenzene, and styrene. The solvent may be a single solvent or a mixed solvent of two or more solvents. In this case, specific examples of the purification mechanism include filtration, decantation, centrifugation, centrifugal sedimentation, a screw decanter, a filter, etc. The time required for purification, from the time when the mixed liquid is introduced into the purification means to which the auxiliary agent or a dispersion of the auxiliary agent has been applied in advance inside the purification mechanism or on the outer surface of the purification mechanism, to the time when the purified mixed liquid is obtained through the purification means, is preferably, for example, about 1 second to 240 minutes.

[0086] (Devolatilization process: S3) The method for producing a styrene monomer according to the present embodiment includes a devolatilization step in which solvent components (including the solvent and the solvent contained in the raw material styrene-based resin composition) contained in the mixed liquid purified in the purification step are devolatilized to form a fluid. This has the effect of volatilizing low molecular weight components and distilling off the solvent. In this specification, the product obtained by subjecting the purified mixed liquid to the devolatilization step is referred to as a fluid. The devolatilization step in this embodiment is not particularly limited as long as it is a step using an apparatus that can be adapted to the mixed liquid, and a known devolatilization apparatus may be used to perform preliminary devolatilization before or during the thermal decomposition step described below. The devolatilization step is not particularly limited, and it is preferable that the volatile components in the purified mixed liquid are uniformly removed. Specific examples of the devolatilization step that can be used include a conventional devolatilization device such as a flash drum, a flash tank polymer heater, a twin-screw devolatilizer, a thin-film evaporator, or an extruder. Among these, a devolatilization device with a small retention area is preferred. The temperature of the devolatilization treatment in the devolatilization step (for example, the temperature inside the devolatilizer) is usually about 100 to 280° C., more preferably 190 to 260° C. The pressure of the devolatilization treatment (for example, the pressure inside the devolatilizer) is usually about 0.13 to 5.0 kPa, preferably 0.13 to 4.5 kPa, more preferably 0.13 to 4.0 kPa. Preferred examples of the devolatilization step in this embodiment include a method of removing volatile components by reducing the pressure inside a devolatilization apparatus while heating the purified mixed solution at 100 to 280°C in the devolatilization apparatus, and a method of removing volatile components through an extruder or the like designed for the purpose of devolatilization.

[0087] For example, if the viscosity of the fluid needs to be adjusted, the fluid may contain the solvent remaining as a result of the devolatilization step, or the viscosity may be adjusted by adding a separate solvent using the mixing mechanism or kneading mechanism described above. In this case, the solvent to be added separately may be preheated, and the temperature of the prepared fluid is about 50 to 280°C, and more preferably 190 to 260°C.

[0088] In the fluid, the content of the solvent in the fluid is preferably 90% by mass or less, more preferably 50% by mass or less, based on the total mass of the fluid. Furthermore, in the fluid, the content of the styrene polymer in the fluid is preferably 10% by mass or more and 100% by mass or less, more preferably 50% by mass or more and 100% by mass or less, based on the entire fluid. The content of impurities that may be contained in the fluid obtained through the devolatilization step is determined by subtracting the total content of the styrene polymer and the solvent from the content of the fluid.

[0089] <Solvent recovery and purification process> The method for producing a styrene monomer according to this embodiment may optionally include a step of recovering the solvent component distilled off from the purified mixed solution in the devolatilization step (S3) and purifying the solvent by distillation (=solvent recovery and purification step). The solvent purified in the solvent recovery and purification step (=so-called recycled solvent) may be reused in the mixed solution preparation step (S1). Furthermore, the residue other than the purified recycled solvent obtained in the solvent recovery and purification step may be blown down and used as fuel for the first pyrolysis step (S4). The distillation method can be carried out under known distillation conditions according to the type of solvent used.

[0090] (1st pyrolysis step: S4) The method for producing a styrene monomer according to the present embodiment includes a first pyrolysis step in which the fluid prepared in the devolatilization step is pyrolyzed, whereby a fluid containing a high concentration of a styrene-based polymer is used, and the styrene-based polymer is thermally decomposed into a high-concentration styrene monomer. The fluid may contain a styrene-based resin composition containing a styrene-based polymer containing styrene monomer units, and may be subjected to preliminary pyrolysis before or during the first pyrolysis step. Furthermore, the optional additive components may be added to the fluid before and / or during the pyrolysis step, as necessary. In the fluid, the content of the styrene polymer in the fluid is preferably 10% by mass or more and 100% by mass or less, more preferably 50% by mass or more and 100% by mass or less, based on the total mass of the fluid. In the present embodiment, a method for thermally decomposing a fluid may involve, for example, filling a thermal decomposition apparatus with the fluid and then heating the fluid in an atmosphere (e.g., the temperature inside the thermal decomposition apparatus) at a temperature of 400 to 800°C, preferably 450 to 600°C, and more preferably 450 to 580°C. The temperature of the fluid to be filled is about 50 to 280°C, more preferably 190 to 260°C. Furthermore, the first thermal decomposition step may involve filling a preheated thermal decomposition apparatus with the fluid. When the thermal decomposition apparatus is preheated, the temperature inside the thermal decomposition apparatus is about 400 to 800°C, preferably 450 to 600°C, and the temperature of the fluid to be filled is about 50 to 280°C, more preferably 190 to 260°C. Since the thermal decomposition temperature of styrene-based polymers (e.g., polystyrene, rubber-modified polystyrene-based resins, and styrene-based copolymer resins) is approximately 330 to 380°C, by setting the temperature range of the thermal decomposition apparatus as described above, most of the generated thermal decomposition vapor can be the thermal decomposition products of the styrene-based polymer. Furthermore, by subjecting the fluid to this first thermal decomposition step, other resins such as polyolefin-based resins that may be contained in the styrene-based resin composition containing the raw material styrene-based polymer containing styrene monomer units can be removed.

[0091] In this embodiment, the first pyrolysis step can be carried out under reduced pressure or normal pressure, but is preferably carried out under reduced pressure. Specifically, the reaction pressure in the first pyrolysis step is preferably 1 to 100 kPa, more preferably 2 to 50 kPa, and even more preferably 3 to 30 kPa. The first pyrolysis step must be carried out at a temperature at which the material is heated and evaporated to form a vaporized raw material. Therefore, carrying out the first pyrolysis step under reduced pressure has the effect of suppressing the generation of by-products during decomposition.

[0092] The pyrolysis device of this embodiment can be a known pyrolysis device. For example, the pyrolysis device of this embodiment includes a pyrolysis device connected to introduce the fluid, a raw material supply pump that supplies the fluid, and a heating mechanism (such as a hot plate, an electric heating wire, or a hot air oven) provided on the periphery of the pyrolysis device. The fluid may be stored in a storage tank provided before being connected to the pyrolysis device. The pyrolysis method used in the first pyrolysis step is not particularly limited, and any known method can be used. For example, general pyrolysis methods such as an externally heated rotary kiln pyrolysis device or a fluidized bed pyrolysis device can be used. Furthermore, if necessary, a polymerization inhibitor may be intermittently or continuously supplied using a device for supplying a polymerization inhibitor to suppress the polymerization reaction of the polymerizable components contained in the pyrolysis liquid.

[0093] An example of the pyrolysis device in this embodiment is the device shown in FIG. That is, the pyrolysis device 10 has a cylindrical pyrolysis section 1 having an opening 2 and an outlet 3 at each end, and a pyrolysis furnace 5 surrounding the pyrolysis section 1. The outlet 3 is fluidly connected to a liquefaction device L that cools the pyrolysis vapor via a connection part C1P (for example, a tubular body such as a glass tube). In one example of the pyrolysis furnace 5 shown in FIG. 3, the pyrolysis furnace 5 (more specifically, the wall of the pyrolysis furnace 5) covers the tubular pyrolysis section 1, and a cavity is formed between the pyrolysis furnace wall and the tubular pyrolysis section 1, with various heating means installed within the cavity. Examples of the heating means include a heating means that supplies a heat medium (heating gas) into the cavity of the pyrolysis furnace 5 to heat the tubular pyrolysis section 1 and control the temperature within a predetermined range. The inlet for the heat medium (heating gas) sent into the cavity of the pyrolysis furnace 5 is preferably located near the opening 2 through which the fluid is supplied. This increases the ambient temperature to which the resin composition supplied to the pyrolysis section 1 from the opening can be exposed, allowing for a rapid temperature rise, which is preferable from the viewpoint of suppressing the generation of pyrolysis residue. When a fluid is supplied to opening 2 from opening 2, the raw material composition moves along the process flow path direction (arrow direction) inside cylindrical pyrolysis section 1 heated by pyrolysis furnace 5, and is converted into pyrolysis vapor. The pyrolysis vapor obtained by pyrolyzing the raw material composition is then circulated from outlet 3 through connection section C1P (e.g., a tubular body) to liquefaction device L, which cools the pyrolysis vapor and prepares a (first) pyrolysis liquid. Furthermore, in the pyrolysis device 10 of this embodiment, in order to adjust the amount of pyrolysis steam generated inside the cylindrical pyrolysis section 1 and discharge it to the outside, the cylindrical pyrolysis section 1 may be provided with a vent hole (not shown) and a pipe through which the pyrolysis steam flowing out from the vent hole (not shown) can pass. The pipe may extend, for example, to the vicinity of the outlet 3 of the pyrolysis section 1. As a result, the pyrolysis steam flowing out from the vent hole (not shown) can be collected, as necessary, through the pipe equipped with a valve or the like. In this specification, the term "thermal decomposition" refers to chemical decomposition of organic matter by heating it in the absence of oxygen or the like.

[0094] In the first pyrolysis step, the fluid can be heated to generate a first pyrolysis liquid. More specifically, in the first pyrolysis step, it is preferable to cool pyrolysis vapor containing styrene monomer to produce the first pyrolysis liquid. Specifically, pyrolysis vapor generated by heating the fluid in the pyrolysis device is cooled to generate the first pyrolysis liquid containing styrene monomer. The temperature at which the pyrolysis vapor is cooled is preferably −30° C. or higher and the boiling point T of styrene monomer. sb The temperature is preferably (°C) or lower, and more preferably -20°C to 80°C. This allows for the effective removal of low-boiling-point monomers, which are decomposition products of other resins such as polyolefin resins that may be contained in the styrene-based resin composition, since olefin-based hydrocarbon compounds (e.g., ethylene and propylene) having a boiling point of -30°C or less are not liquefied or are hardly liquefied. sb The fraction below (°C) may be stored separately and used as a combustion feedstock for the thermal cracking device. Furthermore, the pyrolysis vapor generated by heating the fluid in the first pyrolysis step has a boiling point T sb The high-boiling point components of the first pyrolysis liquid cooled to a temperature of 100°C or higher and 450°C or lower may be liquefied by a liquefaction device and dropped again into the pyrolysis device, whereby the pyrolysis step may be carried out again. In addition, the generated pyrolysis vapor may be liquefied by a liquefaction device and dropped again into the pyrolysis device, whereby the pyrolysis step may be carried out again. sb The pyrolysis liquid may be liquefied by cooling to a temperature of (°C) in a liquefaction device and obtained as part of the second pyrolysis liquid described below. The method for cooling the pyrolysis vapor preferably uses a liquefaction device. Any known liquefaction device can be used as the liquefaction device. Examples of such devices include various heat-removing solvents, including water, that can be cooled to the desired cooling temperature, and cooling tubes that utilize the heat-removing effect of heat-removing elements made of metals and various other inorganic materials. Furthermore, if necessary, a reforming device for reforming the components of the pyrolysis vapor (including, for example, dechlorination, adsorption of odorous or coloring components, removal of acidic or basic components, heat treatment, etc.) may be fluidly connected between the pyrolysis device and the liquefaction device. If necessary, an analysis step may be provided for analyzing the first pyrolyzed liquid, which may include evaluating the styrene monomer concentration in the first pyrolyzed liquid, the temperature of the first pyrolyzed liquid, the viscosity of the first pyrolyzed liquid, and other properties of the first pyrolyzed liquid.

[0095] <Cooling pipe deposits> When examining the styrene monomer production method of this embodiment, it was confirmed that deposits may occur on the cooling pipes during cooling in the first pyrolysis step. The presence of such deposits on the cooling pipes reduces the thermal efficiency of the pyrolysis apparatus, which in turn reduces the pyrolysis efficiency, potentially leading to blockage of piping and a reduction in throughput. Furthermore, when the pyrolysis vapor generated during the pyrolysis of the fluid in the first pyrolysis step is cooled to obtain the first pyrolysis liquid, the deposits may reduce the cooling efficiency. In the method for producing a styrene monomer according to the present embodiment, the amount of impurities contained in the fluid that reaches the first pyrolysis step is generally reduced, which is thought to reduce the amount of material adhering to the cooling pipes.

[0096] In this embodiment, the first pyrolysis step preferably involves heating a fluid to obtain pyrolysis vapor containing styrene monomer, and then cooling the pyrolysis vapor using a liquefaction device to generate a first pyrolysis liquid. More specifically, the pyrolysis vapor containing styrene monomer, which is generated by heating a fluid at a predetermined temperature and a predetermined pressure using a pyrolysis device, is cooled to generate a first pyrolysis liquid containing styrene monomer. The temperature at which the pyrolysis vapor is cooled is not less than -30°C and not more than the boiling point T of styrene monomer. sb The temperature is preferably (°C) or lower, and more preferably -20°C to 80°C. For example, when the thermal decomposition apparatus shown in FIG. 3 is used for the first thermal decomposition step, the outlet 3 is fluidly connected to the liquefaction apparatus. Therefore, when the pyrolysis vapor containing the generated styrene monomer is injected into the liquefaction apparatus, deposits may form on the inside of the pipes (also referred to as cooling pipes or heat exchanger inner walls) in the liquefaction apparatus, extending from the connecting portion (so-called connecting pipe) fluidly connecting the thermal decomposition apparatus and the liquefaction apparatus (see FIG. 7 or FIG. 8). Upon examining the deposits, it was found that when the amount of a specific component (hereinafter referred to as an "adhesion inducer") contained in the resulting first thermal decomposition liquid is high, the amount of deposits on the inner walls of the cooling pipes or heat exchangers (including the pipes in the liquefaction apparatus extending from the connecting portion fluidly connecting the thermal decomposition apparatus and the liquefaction apparatus) increases. It was also confirmed that the amount of deposit inducers and deposits on the inner walls of the cooling pipes or heat exchangers can be reduced by adjusting the type of solvent used and the purification process conditions to specific conditions.

[0097] More specifically, when styrene monomer of this embodiment is produced using a thermal cracking apparatus 10 shown in FIG. 3 and a liquefaction apparatus L connected via a connecting part C1P (glass tube) connecting the thermal cracking section 1 of the thermal cracking apparatus 10, as can be seen from the image in FIG. 6, the connecting part C1P (glass tube) was transparent immediately before the start of the first thermal cracking step. However, as the thermal cracking operation was carried out, the connecting part C1P (glass tube) became cloudy, and a thin film of milky white deposit was observed on the inner wall of the connecting part C1P (see FIG. 7). Furthermore, as the thermal cracking operation was carried out, it was confirmed that a black substance Res had adhered to the entire inner wall of the connecting part C1P and the liquefaction apparatus L, and that they were close to clogging (see FIG. 8).

[0098] In this embodiment, the first pyrolysis process is a process in which the fluid is heated to obtain pyrolysis vapor containing styrene monomer, and then the pyrolysis vapor is cooled to produce the first pyrolysis liquid, and it is preferable that the concentration of adhesion-inducing substances contained in the first pyrolysis liquid is less than 0.2 mass%. As described above, while investigating the deposits on the inner wall surfaces of the cooling pipes or heat exchangers, a certain correlation was confirmed between the amount of deposits on the inner wall surfaces of the cooling pipes or heat exchangers and the amount of deposits contained in the first pyrolysis liquid. However, by reducing the concentration of the deposit inducer contained in the first pyrolysis liquid to less than 0.2 mass%, the amount of deposits on the inner wall surfaces of the cooling pipes or heat exchangers can be reduced. Furthermore, as shown in the examples and comparative examples described below, when the concentration of the deposit inducer contained in the first pyrolysis liquid is less than 0.2 mass%, the glass tube at the connecting portion C1P remains transparent, as shown in the image in Figure 6, and no thin, milky-white deposits were observed on the inner wall of the cooling pipes or heat exchangers. On the other hand, when the concentration of the deposit inducer contained in the first pyrolysis liquid is 0.2 mass% or more, the glass tube at the connecting portion C1P becomes cloudy, as shown in Figure 7, or a thin, milky-white deposit was observed on the inner wall of the cooling pipes or heat exchangers. When the operation was continued with the deposits remaining on the inner walls, it was confirmed that the black substance Res had adhered to the entire inner walls of the connecting portion C1P and the liquefaction device L, causing blockage. The concentration of adhesion inducers contained in the first pyrolysis liquid may be 0 to less than 0.2 mass% relative to the total first pyrolysis liquid, preferably greater than 0 mass% and less than 0.19 mass%, and more preferably greater than 0 mass% and less than 0.18 mass%. In particular, it is preferable from the viewpoint of long-term operation that the amount of adhesion-inducing substances in the first pyrolysis liquid is less than 0.2 mass %.

[0099] In this specification, the term "adhesion inducers" refers to substances that are largely comprised of thermal decomposition components of impurities, and may be inorganic salts (particularly those containing elements from periods 2 to 5 of the elements of groups 1 to 17 of the periodic table) or low-molecular-weight organic compounds having a melting point of 100°C or less and a molecular weight (or number-average molecular weight) of 10 to 1000 (particularly those having a melting point of 40°C or less as a single compound), or resins such as polyethylene, polypropylene, polyacetal (particularly polyoxymethylene), polyamide (particularly polyamide 6, polyamide 66), polyvinyl chloride, polyester (particularly polyethylene terephthalate, polybutylene terephthalate), polyether, polyphenylene ether (particularly modified polyphenylene ether), and particularly resins having a weight-average molecular weight (Mw) of less than 100,000.

[0100] (Recovery process: S5) The method for producing a styrene monomer according to the present embodiment preferably includes, as necessary, a recovery step of recovering the styrene monomer from the first pyrolysis liquid containing the styrene monomer prepared in the first pyrolysis step. As a result, styrene monomer is recovered via the pyrolysis liquid from which impurities and low-volatile substances (solvents, olefinic hydrocarbon compounds, etc.) have been removed in the devolatilization step. Furthermore, the recovery step is more preferably a step of recovering styrene monomer from the first pyrolysis liquid containing styrene monomer by distillation. In other words, for example, the recovery step is preferably a distillation recovery step of recovering styrene monomer from the first pyrolysis liquid containing styrene monomer by distillation. The distillation recovery step is preferably carried out in two or more stages using two or more distillation columns. Furthermore, it is preferable that these two or more distillation columns are filled with an inert gas (e.g., nitrogen, rare gas, etc.) from an inert gas supply source, and distillation is carried out by replacing the air inside the distillation column with the inert gas. The distillation temperature in the distillation recovery step is, for example, preferably in the range of 50 to 200° C., more preferably 50 to 150° C. For example, when the first thermally decomposed liquid is distilled in two stages using two distillation columns in the distillation recovery step, the distillation temperature in the first of the two stages is, for example, preferably in the range of 50 to 200° C., preferably 50 to 150° C. The distillation temperature in the second of the two stages is, for example, preferably in the range of 50 to 200° C., preferably 50 to 150° C. The pressure of the distillation atmosphere in the distillation recovery step (for example, the pressure inside the distillation column) is preferably 10 to 70 Torr, more preferably 20 to 60 Torr. When the first pyrolysis liquid is distilled under the above distillation conditions, it is separated into a fraction containing a high concentration of styrene monomer (so-called light components) and a fraction having a lower concentration of styrene monomer than the first pyrolysis liquid (so-called heavy components). For example, in the distillation recovery step, when the first pyrolysis liquid is distilled in two stages using two distillation columns, components with low boiling points (e.g., containing toluene) become light components in the first distillation column, and components with high boiling points (e.g., containing styrene monomer) become heavy components. After venting the light components, the heavy components are preferably distilled again in a second distillation column to separate them into a fraction containing a high concentration of styrene monomer and a fraction having a lower styrene monomer concentration than the first fraction, thereby recovering styrene monomer. In addition, a polymerization inhibitor may be used in the distillation recovery step to prevent polymerization of styrene monomer.

[0101] The first pyrolysis liquid may contain styrene monomer, and may be subjected to preliminary pyrolysis before or during the recovery step. Furthermore, during the first pyrolysis step and / or during the recovery step after the first pyrolysis step, optional additives may be added to the fluid as necessary to suppress the polymerization reaction of the styrene monomer produced.

[0102] In this embodiment, a known recovery method can be used as a method for recovering styrene monomer. For example, the first pyrolysis liquid may be fluidly connected to a fractionation column capable of fractionating the first pyrolysis liquid and separating low-boiling components such as benzene or toluene from crude styrene monomer (styrene monomer having a purity of 90% or less). Furthermore, the fractionation column may be fluidly connected to a distillation column that fractionates the crude styrene monomer in order to increase the purity of the separated crude styrene monomer. If necessary, a dechlorination device that dechlorinates components in the pyrolysis liquid may be fluidly connected between the pyrolysis device and the fractionation column.

[0103] (1st distillation step (S6)) In the method for producing styrene monomer of this embodiment, it is preferable to, as necessary, distill the first pyrolysis liquid to separate it into a first fraction containing styrene monomer and a second fraction having a lower styrene monomer concentration than the first fraction. This makes it possible to recover the second fraction containing a low concentration of styrene monomer, or to recover the first fraction containing styrene monomer, styrene dimer, and styrene trimer at high concentrations from the second fraction. Since it is possible to recover a fraction containing a high concentration of styrene monomer, the yield of styrene monomer can be improved. That is, when the styrene-based resin composition is thermally decomposed in the first thermal decomposition step, styrene dimer, styrene trimer, etc. may be contained as by-products in the first thermal decomposition liquid. Therefore, if these styrene dimer and styrene trimer can be effectively utilized, the yield of styrene monomer can be improved. Distillation using a distillation column is preferred as a method for distilling the first pyrolysis liquid to separate it into a first fraction containing styrene monomer, styrene dimer, and styrene trimer and a second fraction having a lower styrene monomer concentration than the first fraction. Therefore, the method for producing a styrene monomer of this embodiment preferably includes, as necessary, a first distillation step in which the first pyrolysis liquid is distilled to separate it into a first fraction containing styrene monomer, styrene dimer, and styrene trimer, and a second fraction having a lower styrene monomer concentration than the first fraction.

[0104] The first distillation step is preferably carried out in one or more stages using one or more distillation columns, and is preferably carried out by filling the one or more distillation columns with an inert gas (e.g., nitrogen, rare gas, etc.) from an inert gas supply source and replacing the air inside the distillation column with the inert gas. The distillation temperature in the first distillation step is, for example, preferably in the range of 50 to 200° C., more preferably 50 to 150° C. For example, when the first pyrolysis liquid is distilled in one stage using one distillation column in the first distillation step, the distillation temperature in the one stage is, for example, preferably in the range of 50 to 200° C., more preferably 50 to 150° C. The pressure of the distillation atmosphere in the first distillation step (for example, the pressure inside the distillation column) is preferably 10 to 70 Torr, more preferably 20 to 60 Torr. When the first pyrolysis liquid is distilled under the above distillation conditions, it is separated into a first fraction (so-called high-boiling components) containing styrene monomer, styrene dimer, and styrene trimer, and a second fraction (so-called low-boiling components) having a lower styrene monomer concentration than the first fraction. It is preferable that the difference between the styrene monomer concentration in the first fraction and the styrene monomer concentration in the second fraction is approximately twice or more the styrene monomer concentration in the first fraction relative to the styrene monomer concentration in the second fraction. For example, in the first distillation step, when the first pyrolysis liquid is distilled in one stage using one distillation column, components with low boiling points (toluene, etc.) become low-boiling components in the distillation column, and styrene monomer, styrene dimer / trimer, etc. become high-boiling components. In the first distillation step, a polymerization inhibitor may be used to prevent polymerization of styrene monomer.

[0105] (Second distillation step (S7)) In the method for producing styrene monomer according to this embodiment, it is preferable to, as necessary, distill the first fraction to separate it into a third fraction containing styrene monomer and a fourth fraction having a lower styrene monomer concentration than the third fraction. This allows styrene monomer to be recovered from the third fraction containing a high concentration of styrene monomer. Alternatively, a fourth fraction containing a high concentration of styrene dimer and styrene trimer can be recovered from the third fraction. This allows a fraction containing a high concentration of styrene monomer to be recovered, thereby improving the yield of styrene monomer. Furthermore, when the styrene-based resin composition is thermally decomposed in the first thermal decomposition step, styrene dimer, styrene trimer, and the like may also be contained as by-products in the first thermal decomposition liquid. Therefore, if these styrene dimers and styrene trimers can be effectively utilized, the yield of styrene monomer can be improved. As a method for distilling the first fraction to separate it into a fourth fraction containing styrene dimer and styrene trimer and a third fraction having a higher styrene monomer concentration than the fourth fraction, distillation using a distillation column is preferred. Therefore, the method for producing a styrene monomer of the present embodiment preferably includes, as necessary, a second distillation step in which the first fraction is distilled to separate the first fraction into a fourth fraction containing styrene dimer and styrene trimer and a third fraction having a higher styrene monomer concentration than the fourth fraction.

[0106] The second distillation step is preferably carried out in one or more stages using one or more distillation columns, and is preferably carried out by filling the one or more distillation columns with an inert gas (e.g., nitrogen, rare gas, etc.) from an inert gas supply source and replacing the air inside the distillation column with the inert gas. The distillation temperature in the second distillation step is, for example, preferably in the range of 50 to 200° C., more preferably 50 to 150° C. For example, when the fourth fraction is distilled in one stage of one distillation column in the second distillation step, the distillation temperature in the one stage is, for example, preferably in the range of 50 to 200° C., preferably 50 to 150° C. The pressure of the distillation atmosphere in the second distillation step (for example, the pressure inside the distillation column) is preferably 10 to 70 Torr, more preferably 20 to 60 Torr. When the first fraction is distilled under the above distillation conditions, it is separated into a fourth fraction (so-called high-boiling components) containing styrene dimers and styrene trimers, and a third fraction (so-called low-boiling components) having a higher styrene monomer concentration than the first fraction. It is preferable that the difference between the styrene monomer concentration in the third fraction and the styrene monomer concentration in the fourth fraction is approximately twice or more the styrene monomer concentration in the third fraction relative to the styrene monomer concentration in the fourth fraction. For example, in the second distillation step, when the fourth fraction is distilled in one stage using one distillation column, components with low boiling points (such as styrene monomer) become low-boiling components in the distillation column, and styrene dimers, trimers, etc. become high-boiling components. In the second distillation step, a polymerization inhibitor may be used to prevent polymerization of the styrene monomer. Since the fraction with the highest purity of styrene monomer is the third fraction, it is preferable to recover the third fraction as styrene monomer.

[0107] (Second pyrolysis step (S8)) The method for producing a styrene monomer according to the present embodiment preferably further includes a second pyrolysis step of pyrolyzing the fourth fraction again to produce a second pyrolysis liquid, as required, whereby the fourth fraction containing styrene dimer and styrene trimer is pyrolyzed to further produce styrene monomer, thereby improving the yield of styrene monomer. In this embodiment, the method for thermally decomposing the fourth fraction may be, for example, a second thermal decomposition step in which the fourth fraction is loaded into a thermal decomposition apparatus and then heated in an atmosphere (e.g., the temperature inside the thermal decomposition apparatus) at a temperature of 300 to 700°C, preferably 320 to 600°C, and more preferably 350 to 500°C. In this case, the temperature of the loaded fourth fraction is about 0 to 300°C, preferably 25 to 280°C, more preferably 25 to 250°C, and even more preferably 25 to 150°C. Furthermore, the second thermal decomposition step in which the fourth fraction is loaded into a preheated thermal decomposition apparatus may be performed. In this case, when the thermal cracker is preheated, the temperature inside the thermal cracker is 300 to 700°C, preferably 320 to 600°C, and more preferably 350 to 500°C. The temperature of the fourth fraction to be charged is about 0 to 300°C, preferably 25 to 280°C, more preferably 25 to 250°C, and even more preferably 25 to 150°C. Since the thermal decomposition temperature at atmospheric pressure of the styrene dimer and styrene trimer contained in the fourth fraction is approximately 200 to 700°C, by setting the temperature range of the thermal cracker as described above, most of the generated thermal decomposition vapor can become the thermal decomposition products of styrene dimer and styrene trimer. This can improve the yield of styrene monomer.

[0108] In this embodiment, the second pyrolysis step can be carried out under reduced pressure or normal pressure, but is preferably carried out under reduced pressure. Specifically, the reaction pressure in the second pyrolysis step is preferably 1 to 202 kPa, more preferably 7 to 101 kPa, even more preferably 20 to 101 kPa, and even more preferably 20 to 80 kPa. The second pyrolysis step must be carried out at a temperature at which the raw material is vaporized by heating, and therefore, by carrying out the step under reduced pressure, the amount of by-products produced by decomposition can be reduced. Also, in the second pyrolysis step, when the fourth fraction is heated to produce the second pyrolysis liquid, it is preferable to cool the pyrolysis vapor to produce the second pyrolysis liquid. Specifically, the pyrolysis vapor generated by heating the fourth fraction in the pyrolysis device is cooled to produce the second pyrolysis liquid containing styrene monomer. The temperature to which the pyrolysis vapor is cooled is preferably from -30°C to the boiling point Tsb (°C) of styrene monomer, and more preferably from -20°C to 80°C. The cooling can be carried out by a known method, similar to that in the first pyrolysis step.

[0109] (Third distillation step (S9)) In the method for producing a styrene monomer of this embodiment, it is preferable to distill the second pyrolysis liquid, if necessary, to separate it into a fifth fraction containing a styrene monomer and a sixth fraction having a lower styrene monomer concentration than the fifth fraction, thereby improving the yield of styrene monomer. As a method for distilling the second pyrolysis liquid to separate it into a fifth fraction containing styrene monomer and a sixth fraction having a lower styrene monomer concentration than the fifth fraction, distillation using a distillation column is preferred. Therefore, the method for producing styrene monomer of this embodiment preferably includes, as necessary, a third distillation step in which the second pyrolysis liquid is distilled to separate it into a fifth fraction containing styrene monomer and a sixth fraction having a lower styrene monomer concentration than the fifth fraction. The third distillation step is preferably carried out at least once in one or more distillation columns (i.e., one or more stages of distillation). The distillation column is preferably filled with an inert gas (e.g., nitrogen, rare gas, etc.) from an inert gas supply source, and the air inside the distillation column is preferably replaced with the inert gas. The distillation temperature in the third distillation step is, for example, preferably in the range of 50 to 200°C, more preferably 50 to 150°C. The pressure of the distillation atmosphere in the third distillation step (for example, the pressure inside the distillation column) is preferably 8 to 70 Torr, more preferably 9 to 60 Torr. When the second pyrolysis liquid is distilled under the above distillation conditions, it is separated into a fifth fraction (so-called low-boiling point components) containing styrene monomer and a sixth fraction (so-called high-boiling point components) having a lower styrene monomer concentration than the fifth fraction. The difference between the styrene monomer concentration in the fifth fraction and the styrene monomer concentration in the sixth fraction is preferably such that the styrene monomer concentration in the fifth fraction is approximately twice or more the styrene monomer concentration in the sixth fraction. In the third distillation step, a polymerization inhibitor may also be used to prevent polymerization of the styrene monomer.

[0110] (Recycling process (S10)) The method for producing a styrene monomer according to the present embodiment preferably further includes a recycling step of recovering styrene monomer from the fifth fraction, as necessary, thereby improving the yield of styrene monomer. The recycling step is preferably, for example, a step (I) of recovering styrene monomer from the fifth fraction as part of the first pyrolysis liquid, and a step (II) of distilling the fifth fraction separately from the first pyrolysis liquid to recover styrene monomer. For the step (I) of recovering styrene monomer from the fifth fraction as part of the first thermally decomposed liquid, the contents of the above section (Recovery step: S5) are incorporated by reference. In addition, for the step (II) of distilling the fifth fraction separately from the first thermal decomposition liquid to recover styrene monomer, the contents of the above (First distillation step: S6) and / or (Second distillation step: S7) / or (Third distillation step: S9) sections are incorporated herein by reference.

[0111] (Styrene monomer manufacturing equipment) The present disclosure relates to a styrene monomer production apparatus including a dissolver for preparing a mixed liquid by mixing a styrene-based resin composition containing a styrene-based polymer including styrene monomer units with a solvent, a purification means for purifying the mixed liquid, a devolatilizer for devolatilizing the purified mixed liquid to form a fluid, a pyrolysis apparatus for thermally decomposing the fluid, and a liquefaction apparatus for cooling the pyrolysis vapor obtained by the pyrolysis apparatus to produce a first pyrolysis liquid. An example of an apparatus for producing a styrene monomer will be described below with reference to Fig. 5. Fig. 5 shows an apparatus equipped with the method for producing a styrene monomer according to this embodiment. Specifically, the styrene monomer production apparatus of this embodiment is an apparatus fluidly connected to a dissolver 15, which is a recessed vessel filled with and mixed with the raw material styrene resin composition 12, a filter aid 13 that is added as needed, and a solvent 11, a purification means 17 that purifies the mixed liquid prepared by the dissolver 15, a devolatilizer 20 that devolatilizes the mixed liquid purified by the purification means 17 to prepare a fluid, a pyrolysis apparatus 10 (Figure 3) that pyrolyzes the fluid, and a liquefaction apparatus L (Figure 3) that cools the pyrolysis vapor obtained by the pyrolysis apparatus 10 (Figure 3) to produce a first pyrolysis liquid.

[0112] An example of the production of styrene monomer using the styrene monomer production apparatus is as follows. The raw material styrene resin composition 12 and the filter aid 13, which is added as needed, are filled into a dissolver 15, which is a vessel with a recess, via a hopper 14. The solvent 11 is also filled into the dissolver 15, which is a vessel with a recess. The dissolver 15 is fitted with a rotating shaft S, which has an agitator blade attached to one end of the rotating shaft, and a motor (M) serving as a power source, attached to the other end of the rotating shaft. As a result, as the rotating shaft S rotates, a mixture of the raw material styrene resin composition 12, the filter aid 13, which is added as needed, and the solvent 11 is prepared in the dissolver 15. The dissolver 15 is also fluidly connected to a purification means 17 via a tube attached to the bottom or side of the dissolver 15, and the mixture prepared in the dissolver 15 is pumped to the purification means 17 by a pump 16. The purification means 17 can be, for example, a centrifuge with a filter installed inside the rotor. As a result, impurities in the mixed liquid are removed and discharged to the outside as an impurity cake 18. Meanwhile, the mixed liquid from which the impurities have been removed is filled into tank 19. Then, since tank 19 is fluidly connected to volatilizer 20 via a pipe attached to tank 19, the purified mixed liquid filled into tank 19 is pumped to volatilizer 20 by pump 16. Thereafter, the solvent and the like are distilled off by volatilizer 20 to produce a fluid. Then, the fluid is pumped to, for example, a thermal decomposition apparatus shown in FIG. 3, where a first thermal decomposition step (S4) and a recovery step (S5) of recovering styrene monomer from the first thermal decomposition liquid are carried out. [Example]

[0113] [Measurement and evaluation methods] The physical properties of the resin compositions obtained in the examples and comparative examples were measured and evaluated according to the following methods.

[0114] <Method for evaluating solvents in the mixed solution preparation process> The solubility of the styrene resin composition in the solvent used in the mixed solution preparation process of this embodiment can be evaluated using GPPS pellets. 1.0 g of GPPS pellets and a solvent at a predetermined mass % concentration were added to a 100 mL screw vial using various solvents. The mixture was then mixed and liquefied on a shaker at 25°C for 1 hour. If solids with a long side of 5 mm or more remained, the mixture was evaluated as "unsuitable for mixed liquefaction" ("x"). If no solids with a long side of 5 mm or more remained, the mixture was evaluated as "suitable for mixed liquefaction" ("o"). Table 1-1 shows the solvent type, mass %, and whether or not the mixture could be mixed and liquefied.

[0115] <Pyrolysis apparatus and procedures used in the examples and comparative examples> "Examples 1 to 21" In Examples 1 to 21 and Comparative Examples 1 to 5, pyrolysis experiments were carried out using a small reactor (small laboratory pyrolysis device) for simple experiments, but the size of the equipment is not particularly limited as long as it does not deviate from the purpose of conducting the desired experiment. Specifically, it is as follows. A styrene-based resin composition containing a styrene-based polymer containing styrene monomer units was placed in a SUS reactor and placed inside a cast-in heater. A SUS cover with a branch pipe was attached and bolted with a wrench. A dedicated adapter with an O-ring was then attached to the branch pipe. A glass Liebig condenser, a distillation adapter with a pressure-reducing hose attachment, and a pyrolysis liquid recovery flask were attached, each coated with silicone grease. A three-way stopcock was then attached to the pressure-reducing hose attachment, and a nitrogen balloon and vacuum pump were connected. Temperatures were monitored using thermocouples installed inside the cast-in heater and the vessel. The refrigerant was pumped in at -10°C, the vacuum pump was set to 34 hPa, and the output of the cast-in heater was adjusted. The pyrolysis was carried out at 450°C, and the pyrolysis liquid was recovered in a pyrolysis flask by liquefaction in the Liebig condenser into which the refrigerant had flowed.

[0116] <Residue rate> The residue ratio (A) in the method for producing a styrene monomer according to the present embodiment can be calculated from the crude residue ratio (B), which is calculated from the weight ratio of the styrene resin composition charged into a pyrolysis apparatus to the solid matter remaining after pyrolysis, the thermal weight loss ratio (C) measured under a nitrogen atmosphere, and the thermal weight loss ratio (D) measured under an air atmosphere. The residue ratio (A), crude residue ratio (B), thermal weight loss ratio (C), and thermal weight loss ratio (D) are expressed by the following equations: In this case, a residue rate (A) of 0.4% or less is considered "excellent," and a rate of 0.35% or less is considered "good." If the residue rate (A) is greater than 0.5%, the thermal efficiency of the pyrolysis apparatus will decrease, which may result in a decrease in pyrolysis efficiency, blockage of piping, and a decrease in throughput. If the weight of the solid matter remaining after the pyrolysis of the charged styrene-based resin composition is zero, the crude residue rate (B) will be zero, and the thermal weight loss rate (C) and the thermal weight loss rate (D) will also be considered to be zero. Residue rate (A) = (crude residue rate (B) × (thermogravimetric decrease rate (C) - thermogravimetric decrease rate (D)) + crude residue (B) × (thermogravimetric decrease rate (D)) / 100

[0117] <Thermogravimetric reduction rate (%)> The thermal weight loss rate (%) was measured using a Shimadzu TGA apparatus (TGA-50) with a TA60-WS. A 10 mg sample of the crude residue obtained in the pyrolysis experiment was placed in a deep-bottom aluminum pan. The temperature was increased from 25°C to 550°C at a rate of 20°C / min under a 20 mL / min nitrogen or dry air flow, and the temperature was measured according to a program that held the temperature at 550°C for 60 minutes. The thermal weight loss rates (C) and (D) were calculated from the difference between the weight at 25°C (the starting point of the measurement) and the weight at 550°C (the end point of the measurement, which was the 60-minute holding point after the heating program). Thermal weight loss rate (C)% = "Remaining weight in the deep-bottom aluminum pan after measurement under nitrogen conditions" / "Weight of sample weighed in the deep-bottom aluminum pan before measurement" x 100 Thermal weight loss rate (D) % = "remaining weight in the deep-bottom aluminum pan after measurement under air conditions" / "weight of the sample weighed in the deep-bottom aluminum pan before measurement" x 100

[0118] <Method for evaluating adhesions> The first pyrolysis step in this example involves purifying a mixture of a styrene-based resin composition containing a styrene-based polymer containing styrene monomer units and a solvent, devolatilizing the resulting fluid, heating the resulting fluid to obtain pyrolysis vapor containing styrene monomer, and then cooling the pyrolysis vapor to produce a first pyrolysis liquid. In this process, cases where a thick deposit was observed on the heat exchanger inner wall surface (the so-called cooling pipe surface) of the liquefaction device that cools the pyrolysis vapor were marked with an × (e.g., the state in FIG. 8), cases where a small amount of thin-film deposit was observed were marked with a △ (e.g., the state in FIG. 7), and cases where no deposit was observed were marked with an ◯ (e.g., the state in FIG. 6). The presence or absence of deposits is recorded in Tables 1-2 to 1-5. If there is any deposit on the cooling pipe, the thermal efficiency of the pyrolysis device will decrease, which may result in a decrease in the pyrolysis efficiency of the entire device, leading to blockage of the pipes, etc., and a decrease in the throughput. Furthermore, when the pyrolysis vapor generated during the pyrolysis of the fluid in the first pyrolysis step is cooled to obtain the first pyrolysis liquid, the deposit may decrease the cooling efficiency.

[0119] <Method for quantifying adhesion inducers in the first pyrolysis liquid> In the present examples and comparative examples, the adhesion inducers in the first pyrolysis liquid were quantified by the following procedure. The first pyrolysis liquid obtained in the pyrolysis experiment of a styrene-based resin composition was heated for 30 minutes so that the internal temperature of the first pyrolysis liquid reached 60°C. Then, 10 g of the heated first pyrolysis liquid was extracted and weighed, and the liquid was cooled at 0°C in a refrigerator for 1 hour. The cooled liquid was recovered by vacuum filtration using a PTFE membrane filter (T100A047A) manufactured by Toyo Roshi Kaisha, Ltd., and the filtrate was subsequently washed with MEK (1 mL) cooled to 0°C. The washed filtrate was dried in a vacuum dryer at 60°C for 30 minutes, and the dry weight of the filtrate was weighed. The mass concentration of the adhesion inducer was calculated from the dry weight ratio of 10 g of the weighed first pyrolysis liquid to the filtrate.

[0120] Furthermore, while examining the deposits on the heat exchanger inner wall surface (the so-called cooling pipe surface), a certain correlation was confirmed with the components (=deposition inducers) contained in the first pyrolysis liquid. When the amount of adhesion inducers in the first pyrolysis liquid obtained in the first pyrolysis step was 0 to less than 0.2 wt%, no adhesion was observed on the liquefaction device that cools the pyrolysis vapor immediately after the first pyrolysis liquid was produced. On the other hand, when the amount of adhesion inducers in the first pyrolysis liquid was 0.2 wt% or more but less than 0.45 wt%, a thin film of adhesion was confirmed on the heat exchange inner wall surface of the liquefaction device that cools the pyrolysis vapor immediately after the first pyrolysis liquid was produced. Furthermore, when the amount of adhesion inducers in the first pyrolysis liquid was 0.45 wt% or more, clear adhesion was observed.

[0121] Furthermore, in the first pyrolysis step, a fluid is heated to obtain pyrolysis vapor containing styrene monomer, and then the first pyrolysis liquid generation step by cooling the pyrolysis vapor is operated continuously for one week without disassembly or cleaning. When thick deposits were found on the surface of the heat exchange inner wall of the liquefaction device that cools the pyrolysis vapor, they were marked with an X, when a small amount of thin-film deposits were found, they were marked with a △, and when no deposits were found, they were marked with an ◯. These are shown in Tables 1-2 to 1-5 as the items indicating the presence or absence of deposits (after one week of operation). When the first pyrolysis step was operated continuously for one week without disassembly and cleaning, if the amount of adhesion inducers in the first pyrolysis liquid was 0 to less than 0.15 wt%, no adhesion was observed on the liquefaction device that cooled the pyrolysis vapor in the step of producing the first pyrolysis liquid. However, if the amount of adhesion inducers in the first pyrolysis liquid was 0.15 wt% or more but less than 0.35 wt%, thin-film adhesion was confirmed on the heat exchange inner wall surface of the liquefaction device that cooled the pyrolysis vapor in the step of producing the first pyrolysis liquid. Furthermore, if the amount of adhesion inducers in the first pyrolysis liquid was 0.35 wt% or more, clear adhesion was observed.

[0122] The materials used in the examples and comparative examples are as follows. <gpps> We used 680, a GPPS manufactured by PS Japan Co., Ltd. <Post-consumer material: Polystyrene material A> The styrene resin composition used was collected from home appliances. The weight average molecular weight (Mw) was 110,000. <Recovered and sorted material: Polystyrene material B> The styrene resin composition was selected as polystyrene from waste plastics collected under the Container Recycling Law. The weight-average molecular weight (Mw) was 110,000. <Recovered and sorted material: Polystyrene material C> The styrene resin composition was selected from recycled waste plastics and classified as polystyrene. The weight average molecular weight (Mw) was 100,000. <Recovered and sorted material: Polystyrene material D> The styrene resin composition was selected from recycled waste plastics and classified as polystyrene. The weight average molecular weight (Mw) was 105,000. <Polyethylene> Braskem SGF4960 was used. <Polypropylene> MA3 manufactured by Japan Polypropylene Corporation was used.

[0123] Example 1 A mixed liquid was prepared by adding GPPS (99 parts by mass) and polyethylene (1 part by mass) to toluene to a concentration of 10% by mass (solids concentration) and stirring. Next, the mixed liquid was suction filtered using a Kiriyama funnel and Kiriyama filter paper 5B to purify the mixed liquid. The purified mixed liquid was then devolatilized in a vacuum dryer at 160°C and 40 hPa to obtain fluid (1). The devolatilized and recovered fluid (1) was subjected to thermal decomposition at 450°C and 34 hPa, and the gas containing styrene monomer generated by the thermal decomposition was condensed in a cooling tube cooled to -10°C to obtain a first thermal decomposition liquid (1) containing styrene monomer. The crude residue rate (B), weight loss rate (C), and weight loss rate (D) in the vessel used for pyrolysis, as well as the residue rate (A) calculated from these, are shown in Table 1-2.

[0124] Example 2 A mixed liquid was prepared by adding GPPS (99 parts by mass) and polypropylene (1 part by mass) to toluene to a concentration of 10% by mass (solids concentration) and stirring. The mixed liquid was then purified by suction filtration using a Kiriyama funnel and Kiriyama filter paper 5B. The purified mixed liquid was then devolatilized in a vacuum dryer at 160°C and 40 hPa to obtain fluid (2). Fluid (2) recovered after devolatilization was pyrolyzed at 450°C and 34 hPa, and the gas generated by pyrolysis was condensed in a cooling tube cooled to -10°C to obtain a first pyrolyzed liquid (2). The crude residue rate (B) in the vessel used for pyrolysis, the weight loss rates (C) and (D), and the residue rate (A) calculated from these are shown in Table 1-2.

[0125] Example 3 A mixed liquid was prepared by adding GPPS (99 parts by mass) and talc (1 part by mass) to toluene to a concentration of 10% by mass (solids concentration) and stirring. The mixed liquid was then purified by suction filtration using a Kiriyama funnel and Kiriyama filter paper 5B. The purified mixed liquid was then devolatilized in a vacuum dryer at 160°C and 40 hPa to obtain fluid (3). The devolatilized and recovered fluid (3) was subjected to thermal decomposition at 450°C and 34 hPa, and the gas generated by the thermal decomposition was condensed in a cooling tube cooled to -10°C to obtain a first thermal decomposition liquid (3). The crude residue rate (B) in the vessel used for pyrolysis, the weight loss rates (C) and (D), and the residue rate (A) calculated from these are shown in Table 1-2.

[0126] Example 4 A mixed solution was prepared by adding methyl ethyl ketone to GPPS (99 parts by mass) and talc (1 part by mass) to a concentration of 10% by mass (solids concentration) and stirring. The mixed solution was then purified by suction filtration using a Kiriyama funnel and Kiriyama filter paper 5B. The purified mixed solution was then devolatilized in a vacuum dryer at 160°C and 40 hPa to obtain fluid (4). The devolatilized and recovered fluid (4) was subjected to thermal decomposition at 450°C and 34 hPa, and the gas generated by the thermal decomposition was condensed in a cooling tube cooled to -10°C to obtain a first thermal decomposition liquid (4). The crude residue rate (B), weight loss rates (C) and (D) in the vessel used for thermal decomposition, and the residue rate (A) calculated from these are shown in Table 1-2.

[0127] Example 5 A mixture of polystyrene material A (100 parts by mass) and toluene was added to a concentration of 10% by mass (solids concentration) and stirred to prepare a liquid mixture. The resulting slurry was purified by suction filtration using a Kiriyama funnel and Kiriyama filter paper 5B. The purified slurry was then devolatilized in a vacuum dryer at 160 °C and 40 hPa to obtain fluid (5). The devolatilized and recovered fluid (4) was pyrolyzed at 450 °C and 34 hPa, and the gas generated by pyrolysis was condensed in a cooling tube cooled to -10 °C to obtain a first pyrolysis liquid (5). The crude residue rate (B) in the vessel used for decomposition, the weight loss rates (C) and (D) analyzed by TGA analysis, and the residue rate (A) calculated from these are shown in Table 1-2.

[0128] Example 6 Toluene was added to polystyrene material B (100 parts by mass) to a concentration of 10% by mass, and the mixture was stirred to prepare a mixed solution. The slurry was then purified by suction filtration using a Kiriyama funnel and Kiriyama filter paper 5B. The purified slurry was then devolatilized in a vacuum dryer at 160 °C and 40 hPa to obtain fluid (6). The devolatilized and recovered fluid (6) was subjected to thermal decomposition at 450 °C and 34 hPa, and the gas generated by thermal decomposition was condensed in a cooling tube cooled to -10 °C to obtain a first thermal decomposition liquid (6). The crude residue rate (B), weight loss rates (C) and (D) in the vessel used for decomposition, and the residue rate (A) calculated from these are shown in Table 1-2.

[0129] Example 7 A mixture of polystyrene material B (100 parts by mass) and MEK was added to a concentration of 10% by mass and stirred to prepare a liquid mixture. The mixture was then suction filtered using a Kiriyama funnel and Kiriyama filter paper 5B to purify the slurry. The purified slurry was then devolatilized in a vacuum dryer at 160°C and 40 hPa to obtain fluid (7). The recovered fluid (7) was then pyrolyzed at 450°C and 34 hPa, and the gas generated by pyrolysis was condensed in a cooling tube cooled to -10°C to obtain a first pyrolysis liquid (7). The crude residue rate (B), weight loss rates (C) and (D) in the vessel used for decomposition, and the residue rate (A) calculated from these are shown in Table 1-2.

[0130] Example 8 A mixed solution was prepared by adding toluene to polystyrene material B (100 parts by mass) to a concentration of 10% by mass and stirring. Radiolite #100 (diatomaceous earth) manufactured by Showa Chemical Industry Co., Ltd. was added at 4% by mass based on the weight of the mixed solution and stirred to obtain a diatomaceous earth-containing mixed solution. The diatomaceous earth-containing mixed solution was purified by suction filtration using a Kiriyama funnel and Kiriyama filter paper 5B. The purified diatomaceous earth-containing mixed solution was then devolatilized in a vacuum dryer at 160°C and 40 hPa to obtain fluid (8). The devolatilized and recovered fluid (8) was thermally decomposed at 450°C and 34 hPa, and the gas generated by thermal decomposition was condensed in a cooling tube cooled to -10°C to obtain a first pyrolysis liquid (8). The crude residue rate (B), weight loss rates (C) and (D) in the vessel used for decomposition, and the residue rate (A) calculated from these are shown in Table 1-2.

[0131] Example 9 A mixed solution was prepared by adding MEK to 100 parts by weight of polystyrene material B to a concentration of 10% by weight and stirring. Radiolite #100 (diatomaceous earth) manufactured by Showa Chemical Industry Co., Ltd. was added at 4% by weight based on the weight of the mixed solution and stirred to obtain a diatomaceous earth-containing mixed solution. The diatomaceous earth-containing mixed solution was purified by suction filtration using a Kiriyama funnel and Kiriyama filter paper 5B. The purified diatomaceous earth-containing mixed solution was then devolatilized in a vacuum dryer at 160°C and 40 hPa to obtain fluid (9). The devolatilized and recovered fluid (9) was thermally decomposed at 450°C and 34 hPa, and the gas generated by thermal decomposition was condensed in a cooling tube cooled to -10°C to obtain a first pyrolysis liquid (9). The crude residue rate (B), weight loss rates (C) and (D) in the vessel used for decomposition, and the residue rate (A) calculated from these are shown in Table 1-2.

[0132] Example 10 A mixed liquid was prepared by adding ethylbenzene to GPPS (99 parts by mass) and polyethylene (1 part by mass) to a concentration of 10% by mass (solids concentration) and stirring. The mixed liquid was then suction filtered using a Kiriyama funnel and Kiriyama filter paper 5B to purify the mixed liquid. The purified mixed liquid was then devolatilized in a vacuum dryer at 160°C and 40 hPa to obtain a fluid (10). The devolatilized and recovered fluid (10) was subjected to thermal decomposition at 450°C and 34 hPa, and the gas containing styrene monomer generated by the thermal decomposition was condensed in a cooling tube cooled to -10°C to obtain a first thermal decomposition liquid (10) containing styrene monomer. The crude residue rate (B), weight loss rate (C), and weight loss rate (D) in the vessel used for pyrolysis, as well as the residue rate (A) calculated from these, are shown in Table 1-3.

[0133] Example 11 A mixed liquid was prepared by adding ethylbenzene to GPPS (99 parts by mass) and polypropylene (1 part by mass) to a concentration of 10% by mass (solids concentration) and stirring. The mixed liquid was then purified by suction filtration using a Kiriyama funnel and Kiriyama filter paper 5B. The purified mixed liquid was then devolatilized in a vacuum dryer at 160°C and 40 hPa to obtain a fluid (11). The fluid (11) recovered after devolatilization was subjected to thermal decomposition at 450°C and 34 hPa, and the gas generated by the thermal decomposition was condensed in a cooling tube cooled to -10°C to obtain a first thermal decomposition liquid (11). The crude residue rate (B) in the vessel used for pyrolysis, the weight loss rates (C) and (D), and the residue rate (A) calculated from these are shown in Table 1-3.

[0134] Example 12 A mixed liquid was prepared by adding ethylbenzene to GPPS (99 parts by mass) and talc (1 part by mass) to a concentration of 10% by mass (solids concentration) and stirring. The mixed liquid was then purified by suction filtration using a Kiriyama funnel and Kiriyama filter paper 5B. The purified mixed liquid was then devolatilized in a vacuum dryer at 160°C and 40 hPa to obtain fluid (12). The recovered fluid (12) was subjected to thermal decomposition at 450°C and 34 hPa, and the gas generated by the thermal decomposition was condensed in a cooling tube cooled to -10°C to obtain a first thermal decomposition liquid (12). The crude residue rate (B) in the vessel used for pyrolysis, the weight loss rates (C) and (D), and the residue rate (A) calculated from these are shown in Table 1-3.

[0135] Example 13 A mixed solution was prepared by adding ethylbenzene to polystyrene material A (100 parts by mass) to a concentration of 10% by mass (solids concentration) and stirring. The mixed solution was purified by suction filtration using a Kiriyama funnel and Kiriyama filter paper 5B. The purified mixed solution was then devolatilized in a vacuum dryer at 160 °C and 40 hPa to obtain fluid (13). The recovered fluid (13) was subjected to thermal decomposition at 450 °C and 34 hPa, and the gas generated by thermal decomposition was condensed in a cooling tube cooled to -10 °C to obtain a first thermal decomposition liquid (13). The crude residue rate (B) in the vessel used for decomposition, the weight loss rates (C) and (D) analyzed by TGA analysis, and the residue rate (A) calculated from these are shown in Table 1-3.

[0136] Example 14 A mixed solution was prepared by adding ethylbenzene to polystyrene material B (100 parts by mass) to a concentration of 10% by mass and stirring. The mixed solution was then purified by suction filtration using a Kiriyama funnel and Kiriyama filter paper 5B. The purified slurry was then devolatilized in a vacuum dryer at 160°C and 40 hPa to obtain fluid (14). The recovered fluid (14) was subjected to thermal decomposition at 450°C and 34 hPa, and the gas generated by thermal decomposition was condensed in a cooling tube cooled to -10°C to obtain a first thermal decomposition liquid (14). The crude residue rate (B), weight loss rates (C) and (D) in the vessel used for decomposition, and the residue rate (A) calculated from these are shown in Table 1-3.

[0137] Example 15 A mixed solution was prepared by adding ethylbenzene to 100 parts by weight of polystyrene material B to a concentration of 10% by weight and stirring. Radiolite #100 (diatomaceous earth) manufactured by Showa Chemical Industry Co., Ltd. was added at 4% by weight based on the weight of the mixed solution and stirred to obtain a diatomaceous earth-containing mixed solution. The diatomaceous earth-containing mixed solution was purified by suction filtration using a Kiriyama funnel and Kiriyama filter paper 5B. The purified diatomaceous earth-containing mixed solution was then devolatilized in a vacuum dryer at 160°C and 40 hPa to obtain fluid (15). The devolatilized and recovered fluid (15) was pyrolyzed at 450°C and 34 hPa, and the gas generated by pyrolysis was condensed in a cooling tube cooled to -10°C to obtain a first pyrolysis liquid (15). The crude residue rate (B), weight loss rates (C) and (D) in the vessel used for decomposition, and the residue rate (A) calculated from these are shown in Table 1-3.

[0138] Example 16 A mixed solution was prepared by adding ethylbenzene to polystyrene material C (100 parts by mass) to a concentration of 10% by mass and stirring. The mixed solution was then purified by suction filtration using a Kiriyama funnel and Kiriyama filter paper 5B. The purified mixed solution was then devolatilized in a vacuum dryer at 160°C and 40 hPa to obtain fluid (16). The recovered fluid (16) was subjected to thermal decomposition at 450°C and 34 hPa, and the gas generated by thermal decomposition was condensed in a cooling tube cooled to -10°C to obtain a decomposition solution. The crude residue rate (B), weight loss rates (C) and (D) in the vessel used for decomposition, and the residue rate (A) calculated from these are shown in Table 1-4.

[0139] Example 17 A mixed solution was prepared by adding ethylbenzene to 100 parts by weight of polystyrene material C to a concentration of 10% by weight and stirring. Radiolite #100 (diatomaceous earth) manufactured by Showa Chemical Industry Co., Ltd. was added at 4% by weight based on the weight of the mixed solution and stirred to obtain a diatomaceous earth-containing mixed solution. The diatomaceous earth-containing mixed solution was purified by suction filtration using a Kiriyama funnel and Kiriyama filter paper 5B. The purified diatomaceous earth-containing mixed solution was then devolatilized in a vacuum dryer at 160°C and 40 hPa to obtain fluid (17). The devolatilized and recovered fluid (17) was thermally decomposed at 450°C and 34 hPa. The gas generated by thermal decomposition was condensed in a cooling tube cooled to -10°C to obtain a decomposed solution. The crude residue rate (B), weight loss rates (C) and (D) in the vessel used for decomposition, and the residue rate (A) calculated from these are shown in Table 1-4.

[0140] Example 18 A mixed solution was prepared by adding ethylbenzene to polystyrene material D (100 parts by mass) to a concentration of 10% by mass and stirring. The mixed solution was then purified by suction filtration using a Kiriyama funnel and Kiriyama filter paper 5B. The purified mixed solution was then devolatilized in a vacuum dryer at 160°C and 40 hPa to obtain fluid (18). The recovered fluid (18) was subjected to thermal decomposition at 450°C and 34 hPa, and the gas generated by thermal decomposition was condensed in a cooling tube cooled to -10°C to obtain a decomposition solution. The crude residue rate (B), weight loss rates (C) and (D) in the vessel used for decomposition, and the residue rate (A) calculated from these are shown in Table 1-4.

[0141] Example 19 A mixed solution was prepared by adding ethylbenzene to 100 parts by weight of polystyrene material D to a concentration of 10% by weight and stirring. Radiolite #100 (diatomaceous earth) manufactured by Showa Chemical Industry Co., Ltd. was added at 4% by weight based on the weight of the mixed solution and stirred to obtain a diatomaceous earth-containing mixed solution. The diatomaceous earth-containing mixed solution was purified by suction filtration using a Kiriyama funnel and Kiriyama filter paper 5B. The purified diatomaceous earth-containing mixed solution was then devolatilized in a vacuum dryer at 160°C and 40 hPa to obtain fluid (19). The devolatilized and recovered fluid (19) was thermally decomposed at 450°C and 34 hPa, and the gas generated by thermal decomposition was condensed in a cooling tube cooled to -10°C to obtain a decomposed solution. The crude residue rate (B), weight loss rates (C) and (D) in the vessel used for decomposition, and the residue rate (A) calculated from these are shown in Table 1-4.

[0142] Example 20 A mixed liquid was prepared by adding styrene monomer to GPPS (99 parts by mass) and polyethylene (1 part by mass) to a concentration of 10% by mass (solids concentration) and stirring. Next, the mixed liquid was suction filtered using a Kiriyama funnel and Kiriyama filter paper 5B to purify the mixed liquid. The purified mixed liquid was then devolatilized in a vacuum dryer at 160°C and 40 hPa to obtain a fluid (20). The devolatilized and recovered fluid (20) was pyrolyzed at 450°C and 34 hPa, and the gas containing styrene monomer generated by the pyrolysis was condensed in a cooling tube cooled to -10°C to obtain a first pyrolysis liquid (20) containing styrene monomer. The crude residue rate (B), weight loss rate (C), and weight loss rate (D) in the vessel used for pyrolysis, as well as the residue rate (A) calculated from these, are shown in Table 1-4.

[0143] Example 21 A mixed liquid was prepared by adding styrene monomer to GPPS (99 parts by mass) and polypropylene (1 part by mass) to a concentration of 10% by mass (solids concentration) and stirring. The mixed liquid was then purified by suction filtration using a Kiriyama funnel and Kiriyama filter paper 5B. The purified mixed liquid was then devolatilized in a vacuum dryer at 160°C and 40 hPa to obtain a fluid (21). The devolatilized and recovered fluid (21) was subjected to thermal decomposition at 450°C and 34 hPa, and the gas generated by the thermal decomposition was condensed in a cooling tube cooled to -10°C to obtain a first thermal decomposition liquid (21). The crude residue rate (B) in the vessel used for pyrolysis, the weight loss rates (C) and (D), and the residue rate (A) calculated from these are shown in Table 1-4.

[0144] Example 22 A mixed liquid was prepared by adding styrene monomer to GPPS (99 parts by mass) and talc (1 part by mass) to a concentration of 10% by mass (solids concentration) and stirring. The mixed liquid was then purified by suction filtration using a Kiriyama funnel and Kiriyama filter paper 5B. The purified mixed liquid was then devolatilized in a vacuum dryer at 160°C and 40 hPa to obtain a fluid (22). The recovered fluid (22) was subjected to thermal decomposition at 450°C and 34 hPa, and the gas generated by the thermal decomposition was condensed in a cooling tube cooled to -10°C to obtain a first thermal decomposition liquid (22). The crude residue rate (B) in the vessel used for pyrolysis, the weight loss rates (C) and (D), and the residue rate (A) calculated from these are shown in Table 1-4.

[0145] Example 23 A mixed solution was prepared by adding styrene monomer to polystyrene material A (100 parts by mass) to a concentration of 10% by mass (solids concentration) and stirring. The mixed solution was purified by suction filtration using a Kiriyama funnel and Kiriyama filter paper 5B. The purified mixed solution was then devolatilized in a vacuum dryer at 160°C and 40 hPa to obtain fluid (23). The recovered fluid (23) was subjected to thermal decomposition at 450°C and 34 hPa, and the gas generated by the first thermal decomposition (23) was condensed in a cooling tube cooled to -10°C to obtain first thermal decomposition liquid (23). The crude residue rate (B) in the vessel used for decomposition, the weight loss rates (C) and (D) analyzed by TGA analysis, and the residue rate (A) calculated from these are shown in Table 1-4.

[0146] Example 24 A mixed solution was prepared by adding styrene monomer to polystyrene material B (100 parts by mass) to a concentration of 10% by mass and stirring. The mixed solution was then purified by suction filtration using a Kiriyama funnel and Kiriyama filter paper 5B. The purified mixed solution was then devolatilized in a vacuum dryer at 160°C and 40 hPa to obtain fluid (24). The recovered fluid (24) was subjected to thermal decomposition at 450°C and 34 hPa, and the gas generated by thermal decomposition was condensed in a cooling tube cooled to -10°C to obtain a first thermal decomposition liquid (24). The crude residue rate (B), weight loss rates (C) and (D) in the vessel used for decomposition, and the residue rate (A) calculated from these are shown in Table 1-4.

[0147] Example 25 A mixed solution was prepared by adding styrene monomer to polystyrene material B (100 parts by mass) to a concentration of 10% by mass and stirring. Radiolite #100 (diatomaceous earth) manufactured by Showa Chemical Industry Co., Ltd. was added at 4% by mass based on the weight of the mixed solution and stirred to obtain a diatomaceous earth-containing mixed solution. The diatomaceous earth-containing mixed solution was purified by suction filtration using a Kiriyama funnel and Kiriyama filter paper 5B. The purified diatomaceous earth-containing mixed solution was then devolatilized in a vacuum dryer at 160°C and 40 hPa to obtain fluid (25). The devolatilized and recovered fluid (25) was thermally decomposed at 450°C and 34 hPa, and the gas generated by thermal decomposition was condensed in a cooling tube cooled to -10°C to obtain a first pyrolysis liquid (25). The crude residue rate (B), weight loss rates (C) and (D) in the vessel used for decomposition, and the residue rate (A) calculated from these are shown in Table 1-2.

[0148] Example 26 A mixed solution was prepared by adding styrene monomer to polystyrene material C (100 parts by mass) to a concentration of 10% by mass and stirring. The mixed solution was then purified by suction filtration using a Kiriyama funnel and Kiriyama filter paper 5B. The purified mixed solution was then devolatilized in a vacuum dryer at 160°C and 40 hPa to obtain fluid (26). The recovered fluid (26) was subjected to thermal decomposition at 450°C and 34 hPa, and the gas generated by thermal decomposition was condensed in a cooling tube cooled to -10°C to obtain a first thermal decomposition liquid (26). The crude residue rate (B), weight loss rates (C) and (D) in the vessel used for decomposition, and the residue rate (A) calculated from these are shown in Table 1-2.

[0149] Example 27 A mixed solution was prepared by adding styrene monomer to polystyrene material C (100 parts by mass) to a concentration of 10% by mass and stirring. Radiolite #100 (diatomaceous earth) manufactured by Showa Chemical Industry Co., Ltd. was added at 4% by mass based on the weight of the slurry and stirred to obtain a diatomaceous earth-containing mixed solution. The diatomaceous earth-containing mixed solution was purified by suction filtration using a Kiriyama funnel and Kiriyama filter paper 5B. The purified mixed solution was then devolatilized in a vacuum dryer at 160°C and 40 hPa to obtain fluid (27). The recovered fluid (27) was thermally decomposed at 450°C and 34 hPa. The gas generated by thermal decomposition was condensed in a cooling tube cooled to -10°C to obtain a first pyrolysis liquid (27). The crude residue rate (B), weight loss rates (C) and (D) in the vessel used for decomposition, and the residue rate (A) calculated from these are shown in Table 1-2.

[0150] Example 28 A mixed solution was prepared by adding styrene monomer to polystyrene material D (100 parts by mass) to a concentration of 10% by mass and stirring. The mixed solution was then purified by suction filtration using a Kiriyama funnel and Kiriyama filter paper 5B. The purified mixed solution was then devolatilized in a vacuum dryer at 160°C and 40 hPa to obtain fluid (28). The recovered fluid (28) was subjected to thermal decomposition at 450°C and 34 hPa, and the gas generated by thermal decomposition was condensed in a cooling tube cooled to -10°C to obtain a first thermal decomposition liquid (28). The crude residue rate (B), weight loss rates (C) and (D) in the vessel used for decomposition, and the residue rate (A) calculated from these are shown in Table 1-2.

[0151] Example 29 A mixed solution was prepared by adding styrene monomer to 100 parts by weight of polystyrene material D to a concentration of 10% by weight and stirring. Radiolite #100 (diatomaceous earth) manufactured by Showa Chemical Industry Co., Ltd. was added at 4% by weight based on the weight of the mixed solution and stirred to obtain a diatomaceous earth-containing mixed solution. The diatomaceous earth-containing mixed solution was purified by suction filtration using a Kiriyama funnel and Kiriyama filter paper 5B. The purified diatomaceous earth-containing mixed solution was then devolatilized in a vacuum dryer at 160°C and 40 hPa to obtain fluid (29). The devolatilized and recovered fluid (29) was pyrolyzed at 450°C and 34 hPa. The gas generated by pyrolysis was condensed in a cooling tube cooled to -10°C to obtain a first pyrolysis liquid (29). The crude residue rate (B), weight loss rates (C) and (D) in the vessel used for decomposition, and the residue rate (A) calculated from these are shown in Table 1-2.

[0152] "Example 30" A mixed solution was prepared by adding styrene monomer to polystyrene material B (100 parts by mass) to a concentration of 10% by mass and stirring, and Radiolite #100 (diatomaceous earth) manufactured by Showa Chemical Industry Co., Ltd. was added in an amount of 4% by mass based on the weight of the slurry and stirred to prepare a mixed solution containing diatomaceous earth. 3 / cm 2 The diatomaceous earth-containing mixture was purified by pressure filtration with nitrogen at 0.2 MPa using a 2 / 2 twill nylon filter cloth with a flow rate of 1.5 min. The purified diatomaceous earth-containing mixture was then devolatilized at 160°C and 40 hPa to obtain fluid (30). The recovered fluid (30) was pyrolyzed at 450°C and 34 hPa using the pyrolysis apparatus shown in Figure 3, and the gas generated by pyrolysis was condensed in a cooling tube cooled to -10°C to obtain first pyrolysis liquid (30). The crude residue rate (B) and weight loss rates (C and D) in the decomposition apparatus were calculated to give a residue rate (A) of 0.35%, and the content of adhesion-inducing substances in the first pyrolysis liquid was 0.02 wt%. Then, the first pyrolysis liquid (30) was distilled under conditions of 60°C and 53 Torr as a first distillation step, and the obtained second fraction was distilled under conditions of 100°C and 22 Torr as a second distillation step, thereby obtaining styrene monomer as a third fraction. The total yield of styrene monomer recovered by distillation in the above process was 55%.

[0153] Example 31 A mixed solution was prepared by adding ethylbenzene to polystyrene material D (100 parts by mass) to a concentration of 10% by mass and stirring. 3 / cm 2 The mixture was purified by pressure filtration with nitrogen at 0.2 MPa using a 2 / 2 twill nylon filter cloth with a flow rate of 1.5 min. The purified mixture was then devolatilized at 160°C and 40 hPa to obtain a fluid (31). The fluid (31) recovered by devolatilization was pyrolyzed at 450°C and 34 hPa using the pyrolysis apparatus shown in Figure 3, and the gas generated by pyrolysis was condensed in a cooling tube cooled to -10°C to obtain a first pyrolysis liquid (31). The crude residue rate (B) and weight loss rates (C and D) in the apparatus used for the decomposition were calculated to give a residue rate (A) of 0.34%, and the content of adhesion-inducing substances in the first pyrolysis liquid was 0.02 wt%.

[0154] Example 32 A mixed solution was prepared by adding GPPS (99 parts by mass) and polyethylene (1 part by mass) to toluene to a concentration of 10% by mass (solids concentration) and stirring. The mixed solution was then purified by pressure filtration with nitrogen at 0.2 MPa using a pressure filter and a nylon 2 / 2 twill filter cloth with an air permeability of 1000 cm³ / cm²·min. The purified mixed solution was then devolatilized at 160°C and 40 hPa to obtain fluid (32). Fluid (32) recovered by devolatilization was pyrolyzed at 450°C and 34 hPa using the pyrolysis apparatus shown in Figure 3. The gas generated by pyrolysis was condensed in a cooling tube cooled to -10°C to obtain a first pyrolysis solution (32). The crude residue rate (B), weight loss rates (C) and (D) in the decomposition apparatus, and the residue rate (A) calculated from these were 0.05%, and the content of adhesion-inducing substances in the first pyrolysis solution was 0.01 wt%.

[0155] Example 33 A mixed solution was prepared by adding ethylbenzene to polystyrene material B (100 parts by mass) to a concentration of 10% by mass and stirring, and Radiolite #100 (diatomaceous earth) manufactured by Showa Chemical Industry Co., Ltd. was added in an amount of 4% by mass based on the weight of the mixed solution and stirred to obtain a mixed solution containing diatomaceous earth. 3 / cm 2 The diatomaceous earth-containing mixture was purified by pressure filtration with nitrogen at 0.2 MPa using a 2 / 2 twill nylon filter cloth with a capacity of 1.5 min. The purified diatomaceous earth-containing mixture was then devolatilized at 160°C and 40 hPa to obtain a fluid (33). The fluid (15) recovered by devolatilization was then subjected to a first pyrolysis step using the pyrolysis apparatus shown in FIG. 3 at 450°C and 34 hPa to pyrolyze the recovered fluid (15). The gas generated by pyrolysis was condensed in a cooling tube cooled to -10°C to obtain a first pyrolysis liquid (33). The first pyrolysis liquid (33) was then distilled at 60°C and 53 Torr in the first distillation step, and the resulting second fraction was distilled at 100°C and 22 Torr in the second distillation step to obtain styrene monomer as the third fraction. Meanwhile, the fourth fraction (excluding the third fraction) was subjected to the second pyrolysis step. Specifically, a stainless steel reactor filled with the fourth fraction was placed in a cast-in heater, and a stainless steel cover with a branch pipe was attached and bolted with a wrench. A dedicated adapter with an O-ring was attached to the branch pipe, and a condenser, a distillation adapter with a pressure-reducing hose attachment branch, and a receiver for collecting the pyrolysis liquid were attached, each coated with silicone grease. A three-way stopcock was then attached to the pressure-reducing hose attachment branch, and a nitrogen balloon and a vacuum pump were connected. Temperatures were monitored using thermocouples installed in the cast-in heater and the vessel. The refrigerant was pumped at -10°C, the vacuum pump was set to 700 hPa to reduce the pressure, the output of the cast-in heater was adjusted, and the second pyrolysis step was carried out at 450°C. The refrigerant was then liquefied in a condenser into which it flowed, to prepare a second pyrolysis liquid in a receiving container. The prepared second pyrolysis liquid was heated in a distiller from 50°C to 80°C at 13 hPa in 5°C increments every 5 minutes, and the light boiling fraction (fifth fraction) was distilled off. Meanwhile, the heavy boiling fraction (sixth fraction) was discharged to the outside. The light boiling fraction (fifth fraction) was recycled by adding it to the first pyrolysis liquid as necessary. The crude residue rate (B) and weight loss rates (C) and (D) in the equipment container used for decomposition, and the residue rate (A) calculated from these, were 0.05%, and the content of adhesion-inducing substances in the first pyrolysis liquid was 0.01 wt%. The total yield of styrene monomer recovered by distillation in the above process was 70%.

[0156] (Comparative Example 1) A mixture of GPPS (99 parts by mass) and polyethylene (1 part by mass) was prepared and, without dissolving in a solvent and without undergoing a purification process or a devolatilization process, thermally decomposed at 450°C and 34 hPa, and the gas generated by the decomposition was condensed in a cooling tube cooled to -10°C to obtain a decomposition liquid. The crude residue rate (B), weight loss rates (C) and (D) in the vessel used for the decomposition, and the residue rate (A) calculated from these are shown in Table 1-2.

[0157] (Comparative Example 2) A mixture of GPPS (99 parts by mass) and polypropylene (1 part by mass) was prepared, and without dissolving it in a solvent, and without undergoing a purification process or a devolatilization process, it was thermally decomposed at 450°C and 34 hPa, and the gas generated by the decomposition was condensed in a cooling tube cooled to -10°C to obtain a decomposition liquid. The crude residue rate (B), weight loss rates (C) and (D) in the vessel used for the decomposition, and the residue rate (A) calculated from these are shown in Table 1-2.

[0158] (Comparative Example 3) GPPS (99 parts by mass) and talc (1 part by mass) were mixed and thermally decomposed at 450°C and 34 hPa without undergoing a purification or devolatilization process, and the decomposition liquid was obtained by condensing the gas generated by the decomposition in a cooling tube cooled to -10°C. The crude residue rate (B) and weight loss rates (C and (D) in the vessel used for the decomposition, as well as the residue rate (A) calculated from these, are shown in Table 1-2.

[0159] Comparative Example 4 Polystyrene material A (100 parts by mass) was pyrolyzed at 450°C and 34 hPa without dissolving it in a solvent and without undergoing a purification or devolatilization process, and a decomposition liquid was obtained by condensing the gas generated by the decomposition in a cooling tube cooled to -10°C. The crude residue rate (B) in the vessel used for the decomposition, the analyzed weight loss rates (C) and (D), and the residue rate (A) calculated from these are shown in Table 1-2.

[0160] (Comparative Example 5) Similar to the styrene monomer production apparatus used in Examples 30 to 33, styrene monomer was produced using an apparatus in which the thermal decomposition apparatus 10 and liquefaction apparatus L shown in FIG. 3 were connected. Polystyrene material B (100 parts by mass) was pyrolyzed at 450°C and 34 hPa without being dissolved in a solvent and without undergoing a purification process or a devolatilization process. The gas generated by the decomposition was condensed in a liquefaction apparatus cooled to -10°C to obtain a decomposition liquid. The crude residue rate (B), weight loss rates (C) and (D) in the vessel used for the decomposition, and the residue rate (A) calculated from these are shown in Table 1-2.

[0161] FIG. 6 shows the state of the connection part C1P, which is the glass tube in Comparative Example 5, immediately before styrene monomer production. FIG. 7 shows the state of the connection part C1P, which is the glass tube during styrene monomer production. FIG. 8 shows the state of the connection part C1P, which is the glass tube, immediately after styrene monomer production. FIGS. 6 to 8 are photographs showing the state of the glass tube over time. These photographs confirm that the transparent glass tube gradually becomes cloudy with a thin film of milky white deposits, and that ultimately, a black substance Res adheres to the entire inner wall of the connection part C1P and the liquefaction device L, causing blockage.

[0162] (Comparative Example 6) A mixture of GPPS (90 parts by mass) and polystyrene material B (10 parts by mass) was pyrolyzed at 450°C and 34 hPa without dissolving in a solvent and without undergoing a purification or devolatilization process, and a decomposition liquid was obtained by condensing the gas generated by the decomposition in a cooling tube cooled to -10°C. The crude residue rate (B) and weight loss rates (C and D) in the vessel used for the decomposition, as well as the residue rate (A) calculated from these, are shown in Table 1-2.

[0163] (Comparative Example 7) A mixture of GPPS (75 parts by mass) and polystyrene material B (25 parts by mass) was pyrolyzed at 450°C and 34 hPa without dissolving in a solvent and without undergoing a purification or devolatilization process, and a decomposition liquid was obtained by condensing the gas generated by the decomposition in a cooling tube cooled to -10°C. The crude residue rate (B) and weight loss rates (C and D) in the vessel used for the decomposition, as well as the residue rate (A) calculated from these, are shown in Table 1-2.

[0164] (Comparative Example 8) A mixture of GPPS (50 parts by mass) and polystyrene material B (50 parts by mass) was pyrolyzed at 450°C and 34 hPa without dissolving in a solvent and without undergoing a purification process or a devolatilization process, and a decomposition liquid was obtained by condensing the gas generated by the decomposition in a cooling tube cooled to -10°C. The crude residue rate (B) and weight loss rates (C and D) in the vessel used for the decomposition, as well as the residue rate (A) calculated from these, are shown in Table 1-2.

[0165] (Comparative Example 9) A mixture of GPPS (30 parts by mass) and polystyrene material B (70 parts by mass) was pyrolyzed at 450°C and 34 hPa without dissolving in a solvent and without undergoing a purification process or a devolatilization process, and a decomposition liquid was obtained by condensing the gas generated by the decomposition in a cooling tube cooled to -10°C. The crude residue rate (B) and weight loss rates (C and (D) in the vessel used for the decomposition, as well as the residue rate (A) calculated from these, are shown in Table 1-2.

[0166] (Comparative Example 10) A mixture of GPPS (15 parts by mass) and polystyrene material B (85 parts by mass) was pyrolyzed at 450°C and 34 hPa without dissolving in a solvent and without undergoing a purification process or a devolatilization process, and a decomposition liquid was obtained by condensing the gas generated by the decomposition in a cooling tube cooled to -10°C. The crude residue rate (B) and weight loss rates (C and D) in the vessel used for the decomposition, as well as the residue rate (A) calculated from these, are shown in Table 1-2.

[0167] [Table 1-1]

[0168] [Table 1-2]

[0169] [Table 1-3]

[0170] [Table 1-4]

[0171] [Table 1-5]

[0172] From the experimental results in Tables 1-2 to 1-5, it was confirmed that the method for producing styrene monomer of this example reduces deposits on the inner walls of the cooling pipes or heat exchangers, or reduces residues, compared with the production method of the comparative example. Therefore, it is considered that the clogging of pipes by residues generated by pyrolysis or gas generated by pyrolysis can be suppressed, and therefore the reduction in the amount of styrene produced per unit time can be suppressed.< / gpps>

Claims

1. a mixed solution preparation step of preparing a mixed solution by mixing a styrene-based resin composition containing a styrene-based polymer including a styrene monomer unit with a solvent; a purification step of purifying the mixture by a purification means; a devolatilization step of devolatilizing the purified mixture to form a fluid; a first pyrolysis step of pyrolyzing the fluid to produce a first pyrolysis liquid; A method for producing styrene monomer, comprising:

2. 2. The method for producing a styrene monomer according to claim 1, further comprising a recovery step of distilling the first pyrolysis liquid to recover the styrene monomer.

3. 2. The method for producing a styrene monomer according to claim 1, wherein the solvent is one or more selected from the group consisting of toluene, methyl ethyl ketone, and ethylbenzene.

4. 2. The method for producing a styrene monomer according to claim 1, wherein the fluid contains the styrene polymer in an amount of 10% by mass or more and 100% by mass or less relative to 100% by mass of the total amount of the fluid.

5. 3. The method for producing a styrene monomer according to claim 1, wherein the purified mixture contains the styrene polymer in an amount of 5% by mass or more and 100% by mass or less, relative to 100% by mass of the total amount of the purified mixture.

6. 3. The method for producing a styrene monomer according to claim 1, wherein the mixed solution contains the styrene polymer in an amount of 5% by mass or more relative to 100% by mass of the total amount of the mixed solution.

7. 3. The method for producing a styrene monomer according to claim 1, wherein the temperature of the atmosphere in which the styrene-based resin composition and the solvent are mixed in the mixed solution preparation step is 0°C or higher.

8. The method for producing a styrene monomer according to claim 1 or 2, wherein the devolatilization step is carried out under reduced pressure.

9. 3. The method for producing a styrene monomer according to claim 1, wherein the first pyrolysis step is carried out under reduced pressure.

10. The method for producing a styrene monomer according to claim 1 or 2, further comprising an analysis step of analyzing the first pyrolysis liquid.

11. 3. The method for producing a styrene monomer according to claim 1, wherein the pyrolysis vapor containing the styrene monomer in the first pyrolysis step is cooled to form a first pyrolysis liquid.

12. The method for producing a styrene monomer according to claim 1 or 2, wherein the styrene-based resin composition contains 20% by mass or less of impurities.

13. 3. The method for producing a styrene monomer according to claim 1 or 2, further comprising a second thermal decomposition step of distilling the first thermal decomposition liquid to separate it into a first fraction containing styrene monomer and a second fraction having a lower styrene monomer concentration than the first fraction, separating the first fraction into a third fraction having a higher styrene monomer concentration than the first fraction and a fourth fraction having a lower styrene monomer concentration than the first fraction, and then thermally decomposing the fourth fraction again to produce a second thermal decomposition liquid.

14. 14. The method for producing a styrene monomer according to claim 13, further comprising a recycling step of distilling the second pyrolysis liquid to separate it into a fifth fraction containing a styrene monomer and a sixth fraction having a styrene monomer concentration lower than that of the fifth fraction, and then recovering the styrene monomer from the fifth fraction.

15. 15. The method for producing a styrene monomer according to claim 14, wherein the recycling step further comprises: a step (I) of recovering styrene monomer from the fifth fraction as part of the first thermally decomposed liquid; and a step (II) of distilling the fifth fraction separately from the first thermally decomposed liquid to recover styrene monomer.

16. 2. The method for producing a styrene monomer according to claim 1, wherein the first pyrolysis step is a step of heating the fluid to obtain pyrolysis vapor containing a styrene monomer, and then cooling the pyrolysis vapor to produce the first pyrolysis liquid, and a concentration of an adhesion-inducing substance contained in the first pyrolysis liquid is less than 0.2 mass%.

17. 2. The method for producing a styrene monomer according to claim 1, wherein the devolatilization step is a step of devolatilizing the mixed liquid to form the fluid using a flash drum, a flash tank polymer heater, a twin-screw devolatilizer, a thin-film evaporator, or an extruder.

18. 2. The method for producing a styrene monomer according to claim 1, wherein the purification means is one or more means selected from the group consisting of filtration, decantation, centrifugation, centrifugal sedimentation, a screw decanter, a strainer, a screen mesh, and a filter.

19. 19. The method for producing a styrene monomer according to claim 18, wherein the purification means is a purification mechanism that combines centrifugation and filtration.

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