Process for producing styrene monomer

Abstract

The present disclosure provides a method for thermally decomposing a styrene dimer and / or a styrene trimer and converting a styrene monomer from the styrene dimer and / or the styrene trimer into a styrene monomer with a good yield.SOLUTION: The present disclosure relates to a method for producing a styrene monomer, including a first pyrolysis step of pyrolyzing a composition containing a styrene dimer and / or a styrene trimer under the following conditions (A) and (B) to prepare a first pyrolysis liquid containing a styrene monomer: (A) The thermal decomposition temperature is 300 °C or higher and lower than 700 °C, and (B) the thermal decomposition pressure is lower than the 66hPa super 1013hPa.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] Polystyrene (hereinafter abbreviated as PS) resin is a resin obtained by polymerizing styrene monomer. It is known that styrene oligomers such as styrene dimer and styrene trimer are often produced during the production process of PS resin. Patent Document 1 discloses that the presence of large amounts of styrene dimer or styrene trimer in PS resin reduces the heat resistance of the PS resin as a whole, causes defects such as volatilization and residue in the mold during injection molding, and transfer of the residual styrene dimer or styrene trimer to the molded product, and reduces productivity by increasing the frequency of mold cleaning. Meanwhile, Patent Document 2 discloses a technology for recovering styrene monomer by thermally decomposing a styrene-based resin. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2009-197105 [Patent Document 2] Patent Publication No. 2023-84584 Summary of the Invention [Problem to be solved by the invention]

[0004] However, Patent Document 1 merely shows that styrene dimer or styrene trimer is produced in the production process of PS resin, and does not disclose a technology for converting a composition containing styrene dimer and / or styrene trimer into styrene monomer. Furthermore, Patent Document 2 discloses a technology for recovering styrene monomer by thermally decomposing PS resin, but does not describe at all a technology for converting styrene dimer and / or styrene trimer into styrene monomer by thermally decomposing it. However, styrene dimers and styrene trimers are recognized as by-products in the production of PS resin, and a method for utilizing these styrene dimers and styrene trimers is desired. In addition, styrene dimers and styrene trimers are by-produced when PS resin is thermally decomposed to obtain styrene monomer.

[0005] Therefore, an object of the present disclosure is to provide a method for thermally decomposing styrene dimer and / or styrene trimer and converting the styrene dimer and / or styrene trimer into styrene monomer with high yield. [Means for solving the problem]

[0006] As a result of intensive research to solve the above-mentioned problems, the present inventors have found that styrene monomer can be obtained by thermally decomposing a styrene dimer and / or a styrene trimer or a composition containing them under specified conditions, and have thus completed the present invention.

[0007] That is, the present invention is as follows. [1] A method for producing a styrene monomer, comprising a first thermal decomposition step of thermally decomposing a composition containing a styrene dimer and / or a styrene trimer under the following conditions (A) and (B) to prepare a first thermal decomposition liquid containing a styrene monomer: (A) Thermal decomposition temperature is 300°C or more and less than 700°C, (B) Thermal decomposition pressure is greater than 66 hPa and less than 1013 hPa

[0008] [2] A second thermal decomposition step is carried out before the first thermal decomposition step, in which a polystyrene-based resin composition is thermally decomposed under the following conditions (X) and (Y) to prepare a second thermal decomposition liquid containing a styrene monomer; 2. The method for producing a styrene monomer according to claim 1, wherein the composition containing a styrene dimer and / or a styrene trimer is obtained from the second pyrolysis liquid. (X) Thermal decomposition temperature is 400°C or more and less than 1200°C; (Y) Thermal decomposition pressure is greater than 10 hPa and less than 300 hPa

[0009] [3] The method for producing a styrene monomer according to [1] or [2], further comprising a first distillation step of distilling the first pyrolysis liquid to separate it into a second fraction containing a styrene monomer and a first fraction having a lower styrene monomer concentration than the second fraction.

[0010] [4] The method for producing a styrene monomer according to [2], further comprising a second distillation step of distilling the second pyrolysis liquid to separate it into a fourth fraction containing styrene monomer and a third fraction having a lower styrene monomer concentration than the fourth fraction.

[0011] [5] The method for producing a styrene monomer according to [4], further comprising a third distillation step of distilling the fourth fraction 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.

[0012] [6] The method for producing a styrene monomer according to any one of [3] to [5], wherein the composition containing a styrene dimer and / or a styrene trimer is any one of the second pyrolysis liquid, the fourth fraction, and the sixth fraction.

[0013] [7] The method for producing a styrene monomer according to any one of [1] to [6], further comprising a recovery step of recovering the styrene monomer.

[0014] [8] The method for producing a styrene monomer according to any one of [1] to [7], wherein the first pyrolysis step further comprises a cooling step of cooling the gas containing the styrene monomer.

[0015] [9] The method for producing a styrene monomer according to any one of [1] to [8], wherein the total content of styrene dimer and / or styrene trimer contained in the composition is 10 mass% or more based on the total amount of the composition.

[0016]

[10] The method for producing a styrene monomer according to any one of [1] to [9], wherein the first thermal decomposition pressure is 100 hPa or more and 900 hPa or less.

[0017]

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

[10] , wherein the total content of styrene dimer, styrene trimer, styrene monomer, benzene, ethylbenzene, α-methylstyrene, and cumene present in the composition accounts for 60 mass% or more of the total amount of the composition.

[0018]

[12] The thermal decomposition step is a step of preparing a thermal decomposition liquid using a thermal decomposition catalyst, The method for producing a styrene monomer according to any one of [1] to

[10] , wherein the thermal decomposition catalyst is a compound containing any element classified in Periods 2 to 7 of Groups 1 to 17 of the Periodic Table, which elements have stable isotopes, and which exists as a solid at room temperature and normal pressure and has a decomposition temperature of 300°C or higher.

[0019]

[13] The method further comprises a first distillation step of distilling the first pyrolysis liquid to separate it into a second fraction containing styrene monomer and a first fraction having a lower styrene monomer concentration than the second fraction; The method for producing a styrene monomer according to [2], further comprising a recycling step of making the second fraction part of the second pyrolysis liquid. [Effects of the Invention]

[0020] According to the present disclosure, styrene monomer can be efficiently produced from a composition containing a styrene dimer and / or a styrene trimer. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is a flow diagram showing an example of the method for producing a styrene monomer according to this embodiment. [Figure 2] FIG. 2 is a flow diagram showing an example of a preferred method for producing a styrene monomer according to this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0022] 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. Unless otherwise specified below, pressure will be expressed as absolute pressure.

[0023] [Method of producing styrene monomer] The present disclosure relates to a method for producing a styrene monomer, comprising a first thermal decomposition step (S1) of thermally decomposing a composition containing a styrene dimer and / or a styrene trimer under the following conditions (A) and (B) to prepare a first thermal decomposition liquid containing a styrene monomer: (A) Thermal decomposition temperature is 300°C or more and less than 700°C, (B) Thermal decomposition pressure is greater than 66 hPa and less than 1013 hPa This allows efficient production of styrene monomer from a composition containing a styrene dimer and / or a styrene trimer. The composition containing a styrene dimer and / or a styrene trimer is a composition containing one or two members selected from the group consisting of a styrene dimer and a styrene trimer.

[0024] The method for producing a styrene monomer according to the present disclosure essentially includes a first pyrolysis step (S1). One preferred embodiment of the method for producing a styrene monomer according to the present disclosure will be described with reference to FIG. Dotted lines in the diagrams represent optional steps. Similarly, solid lines in the diagrams represent required steps.

[0025] As shown in FIG. 1, after a preparation step (S0) of preparing a composition containing styrene dimer and / or styrene trimer from a polystyrene resin composition containing a polystyrene resin is optionally performed, the composition containing styrene dimer and / or styrene trimer is subjected to a first thermal decomposition step (S1) to prepare a first thermal decomposition liquid. Next, if necessary, a first distillation step (S2) of distilling the first thermal decomposition liquid may be further included. The first distillation step (S2) separates the first fraction into a first fraction mainly composed of high-boiling components and a second fraction containing styrene monomer and having a lower boiling point than the first fraction. If necessary, a recycling step (S3) of converting the second fraction into a part of the composition containing styrene dimer and / or styrene trimer or a part of the second thermal decomposition liquid described below may be further included. The first pyrolysis step (S1), and the first distillation step (S2) and recycling step (S3), which are optionally included, will be described in detail below.

[0026] (First pyrolysis step (S1)) The method for producing a styrene monomer according to the present disclosure essentially includes a first thermal decomposition step (S1), which is a step of thermally decomposing a composition containing a styrene dimer and / or a styrene trimer under the above-described conditions (A) and (B) to prepare a first thermal decomposition liquid containing a styrene monomer. In the present embodiment, a method for thermally decomposing a composition containing a styrene dimer and / or a styrene trimer (hereinafter also simply referred to as a composition) includes a method of heating the composition to a temperature of 300° C. or higher and lower than 700° C. The pyrolysis furnace used for the pyrolysis is not particularly limited as long as it is a furnace equipped with a heating means and a pressure adjusting means, as will be described later.

[0027] In the first pyrolysis step (S1), the temperature at which the composition containing styrene dimer and / or styrene trimer is thermally decomposed (= pyrolysis temperature) may be, for example, a temperature range of 300°C or higher but lower than 700°C, preferably 350°C to 500°C, in which the composition is filled into a pyrolysis furnace. The temperature of the filled composition is about 20 to 300°C, more preferably 150 to 260°C. Alternatively, the first pyrolysis step (S1) may be performed by filling a preheated pyrolysis furnace with the composition. The temperature at which the pyrolysis furnace is preheated is about 300°C or higher but lower than 700°C, preferably 350 to 500°C, and the temperature of the filled fluid is about 20 to 300°C, more preferably 150 to 260°C. By setting the temperature range of the pyrolysis furnace, most of the generated pyrolysis vapor can be the pyrolysis product of styrene dimer and / or styrene trimer. Therefore, it is preferable to use a heating means described later to create an atmosphere with a temperature in the range of 300° C. or higher and lower than 700° C. It is possible to reduce the conversion of components other than styrene dimer and / or styrene trimer contained in the composition containing the raw material styrene dimer and / or styrene trimer into by-products that lead to a decrease in the yield of styrene monomer. Furthermore, since the decomposition of styrene dimer and / or styrene trimer occurs competitively with the vaporization of styrene dimer and / or styrene trimer, by setting the temperature range of the pyrolysis furnace as described above, it is possible to prevent the styrene dimer and / or styrene trimer from vaporizing before they are decomposed.

[0028] In the first pyrolysis step (S1), the pressure conditions (= pyrolysis pressure) for pyrolyzing the composition containing styrene dimer and / or styrene trimer are such that the composition containing styrene dimer and / or styrene trimer is pyrolyzed under an atmosphere of pressure greater than 66 hPa and less than 1013 hPa. Therefore, for example, it is preferable to use a pressure adjustment means described below to create an atmosphere of pressure greater than 66 hPa and less than 1000 hPa. The pyrolysis pressure may more preferably be 100 hPa or more and 900 hPa or less, even more preferably 200 hPa or more and 800 hPa or less, and even more preferably 300 hPa or more and 700 hPa or less. In this embodiment, for example, when the composition is decomposed in a pyrolysis furnace, the composition may be decomposed at a pressure of more than 66 hPa and less than 1013 hPa, preferably at a pressure of 100 hPa or more and 900 hPa or less, more preferably at a pressure of 200 hPa or more and 800 hPa or less, and even more preferably at a pressure of 300 hPa or more and 700 hPa or less. By setting the pressure of the pyrolysis furnace within the above range, most of the generated pyrolysis vapor can become pyrolysis products of styrene dimer and / or styrene trimer. Furthermore, it is possible to reduce the conversion of components other than styrene dimer and / or styrene trimer contained in the raw material styrene dimer and / or styrene trimer-containing composition into by-products that would lead to a decrease in the yield of styrene monomer. Furthermore, because the decomposition of styrene dimer and / or styrene trimer occurs competitively with the vaporization of styrene dimer and / or styrene trimer, setting the pressure of the pyrolysis furnace within the above range can prevent the styrene dimer and / or styrene trimer from vaporizing before they are decomposed.

[0029] The pyrolysis vapor generated in the first pyrolysis step (S1) may be cooled to a temperature between the boiling point of styrene monomer and 180°C, and the high-boiling components may be liquefied using a liquefaction device and dropped into the pyrolysis furnace again, returning the liquefied vapor to the pyrolysis furnace for another pyrolysis step. The pyrolysis vapor may also be liquefied by cooling using a liquefaction device to obtain a pyrolysis liquid. The cooling temperature is preferably between −30°C and the boiling point (Tsb) of styrene monomer (°C), more preferably −20°C to 80°C. In this case, a known liquefaction device may be used. Examples include various heat-removing solvents, including water, capable of cooling to the desired cooling temperature, and cooling tubes utilizing the heat-removing effect of heat-removing elements made of metals and various inorganic materials. If necessary, a reforming device for modifying the components of the pyrolysis vapor (e.g., dechlorination, adsorption of odorous and coloring components, removal of acidic or basic components, heat treatment, etc.) may be fluidly connected between the pyrolysis furnace and the liquefaction device. In this specification, "thermal decomposition" refers to chemical decomposition of organic substances by heating them in the absence of oxygen, etc. Furthermore, "rectification" refers to the separation of a mixture with multiple boiling points into multiple compounds by utilizing the difference in boiling points of each compound when the mixture is heated and then cooled.

[0030] <Pyrolysis furnace> The pyrolysis furnace used in the method for producing a styrene monomer of this embodiment is not particularly limited as long as it is a furnace that can thermally decompose a composition containing a styrene dimer and / or a styrene trimer under the conditions (A) and (B) and the conditions (X) and (Y). Therefore, a known pyrolysis furnace can be used as the pyrolysis furnace of this embodiment. However, heating in the pyrolysis furnace is preferably carried out in a reduced pressure environment or an atmosphere with a reduced oxygen concentration.

[0031] The configuration of the pyrolysis furnace is not particularly limited, and may be configured as, for example, a furnace equipped with an electric heating means, a kettle furnace, a tubular furnace, a hot-air furnace, a shaft furnace, a kiln furnace, a fluidized-bed furnace, or a gasification / reforming furnace. The pyrolysis furnace is preferably a kettle furnace or a tubular furnace. It is preferable to gasify the composition in a fluidized-bed furnace at a relatively low temperature and in a low-oxygen atmosphere, thereby decomposing the styrene dimer and / or styrene trimer in the composition into styrene monomer. More specifically, the composition is separated into a fraction (gas component) containing aromatic hydrocarbons such as styrene monomer and a residue containing solid-phase substances called char or tar and substances derived from impurities. The pyrolysis furnace of this embodiment is connected to a composition supply channel, and the composition can be introduced through the supply channel. If necessary, the composition supply channel may be equipped with an on-off valve that opens and closes to adjust the amount of composition supplied. Furthermore, the pyrolysis furnace may be connected to a transport channel for transporting a gas containing styrene monomer and a transport channel for transporting pyrolysis residue, and each of the transport channels may be equipped with an on-off valve for adjusting the transport rate. The composition can be supplied into the pyrolysis furnace through the composition supply channel by a pressure-transfer means such as a pump. For example, if the pressure-transfer means is a vacuum pump, the interior of the pyrolysis furnace can be maintained at a negative pressure and / or in a low-oxygen state, thereby preventing the composition and its decomposition products from unintentionally oxidizing under heating.

[0032] The pyrolysis furnace of this embodiment preferably includes a heating means and a pressure adjusting means. By using the heating means, the temperature inside the pyrolysis furnace can be increased within a predetermined range. The heating means may be configured as a heat exchanger. An example of the heating means is a heat exchanger configured as a heat transfer tube. In the example of a heat exchanger configured as a heat transfer tube, the temperature inside the pyrolysis furnace can be adjusted to a temperature range of 300°C or higher and lower than 700°C by the heat of the high-temperature gas passing through the heat transfer tube. The temperature of the gas passing through the heat transfer tube is preferably equal to or higher than the set value of the temperature inside the pyrolysis furnace described above, and can be, for example, 300°C or higher.

[0033] On the other hand, the pressure adjusting means is not particularly limited as long as it is a mechanism for adjusting the pressure inside the pyrolysis furnace, and specific examples include a pressure adjusting valve, a vacuum pump, and a pump for introducing an inert gas (e.g., nitrogen gas) into the pyrolysis furnace. The pressure adjusting means may further include a means for detecting the pressure inside the pyrolysis furnace and a means for adjusting the amount of the inert gas introduced according to the detected pressure, if necessary. By adopting the above-described configuration for the pressure adjusting means, the pressure condition for pyrolysis can be maintained at a pressure greater than 66 hPa and less than 1013 hPa.

[0034] The pyrolysis furnace of this embodiment preferably includes, for example, a pyrolysis furnace connected for introducing the fluid, a raw material supply pump for supplying 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 furnace. The fluid may be stored in a storage tank provided before being connected to the pyrolysis furnace. 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 polymerizable components contained in the pyrolysis liquid.

[0035] In this embodiment, the first pyrolysis step (S1) may prepare the first pyrolysis liquid using a pyrolysis catalyst. The pyrolysis catalyst is preferably a compound that contains any element classified in Periods 2 to 7 of Groups 1 to 17 of the Periodic Table, which has stable isotopes, exists as a solid at room temperature and pressure, and has a decomposition temperature of 300°C or higher. Examples of the thermal decomposition catalyst include BaO, TiO2, MgO, Al2O3, CaO, NiO, and Y2O3.

[0036] The first pyrolysis step (S1) of this embodiment may include a cooling step of cooling the gas containing styrene monomer. That is, when a composition containing styrene dimer and / or styrene trimer is pyrolyzed in the pyrolysis furnace, pyrolysis products can be fractionated into pyrolysis product gas, and fluid and solid matter remaining without being gasified. A cooling tower can then cool the fractionated pyrolysis product gas to prepare a first pyrolysis liquid. The fluid and solid matter remaining without being gasified can be disposed of or used as fuel. If necessary, the system may also include a compressor that compresses the cooled pyrolysis product gas to generate compressed gas, a second flow path that connects the cooling tower and the compressor and supplies the pyrolysis product gas from the cooling tower to the compressor, and a first flow path that connects the pyrolysis furnace and the compressor or connects the pyrolysis furnace and the second flow path and supplies the pyrolysis product gas from the pyrolysis furnace to the compressor or the second flow path. Specifically, the production apparatus used in the method for producing styrene monomer according to this embodiment preferably includes a pyrolysis furnace for pyrolyzing a composition containing styrene dimer and / or styrene trimer, and optionally a fractionation tower fluidly connected to the pyrolysis furnace for fractionating the pyrolysis product gas, the remaining ungasified liquid, and a solids, a cooling tower for cooling the pyrolysis product gas, and a distillation tower for distilling the pyrolysis product gas or the first pyrolysis liquid. If necessary, the apparatus may further include a compressor for compressing the cooled pyrolysis product gas and a distillation tower for distilling the compressed pyrolysis product gas or the first pyrolysis liquid. The distillation tower may also be comprised of a plurality of distillation towers. The cooling tower is a device for cooling the fractionated pyrolysis product gas, and a known cooling tower can be used. The cooling temperature in the cooling step is usually −30° C. or higher and 80° C. or lower. The compressor compresses the cooled pyrolysis product gas to generate compressed gas. As the compressor, a known compressor can be used, such as a centrifugal compressor, an axial compressor, or a reciprocating compressor. The distillation column can fractionate the produced compressed gas or first pyrolysis liquid into a second fraction containing styrene monomer (for example, a second fraction containing styrene monomer and low-boiling point components) and a first fraction having a lower styrene monomer concentration than the second fraction (for example, a first fraction having a higher boiling point than the second fraction). As the distillation column, a known distillation column can be used, for example, a plate column or a packed column.

[0037] <Preparation process (S0)> The method for producing a styrene monomer according to this embodiment may include a preparatory step (S0) as needed. More specifically, the method for producing a styrene monomer according to this embodiment may include a preparatory step (S0) for preparing a composition containing a styrene dimer and / or a styrene trimer, whereby a composition containing a styrene dimer and / or a styrene trimer is obtained. For example, a polystyrene-based resin composition may be subjected to a second pyrolysis step (S4) described below to produce a styrene dimer and / or a styrene trimer, or a method of blending a styrene dimer and / or a styrene trimer into a polystyrene-based resin composition may be included. Generally, when producing a styrene monomer by chemically recycling a polystyrene-based resin composition, pyrolysis (e.g., at 400 to 800°C) is performed. However, it has been confirmed that this pyrolysis produces styrene dimer and / or a styrene trimer, resulting in a problem of a reduced yield of the final styrene monomer. However, when the method for producing a styrene monomer according to this embodiment is included, the styrene dimer and / or a styrene trimer produced as a by-product in the pyrolysis can be effectively utilized to improve the yield of the final styrene monomer. Generally, whether the polystyrene resin composition is made from virgin material or recycled waste material, the content of styrene dimer and / or styrene trimer is low.

[0038] <First distillation step (S2)> The method for producing a styrene monomer of this embodiment may include a first distillation step (S2) as needed. More specifically, the method for producing a styrene monomer of this embodiment preferably includes a first distillation step (S2) of distilling the first pyrolysis liquid obtained in the first pyrolysis step (S1). Furthermore, when the first pyrolysis liquid is distilled in the first distillation step (S2), it is separated into a second fraction containing styrene monomer and low-boiling point components (for example, components with a boiling point of 50 to 200°C), and a first fraction containing a higher boiling point component than the second fraction (for example, components with a boiling point higher than that of the low-boiling point component). When the first pyrolysis liquid is distilled, styrene monomer is produced, and therefore, styrene monomer can be recovered in a higher yield or with a higher purity. The first fraction, which contains more high-boiling components than the second fraction (e.g., is mainly composed of high-boiling components), is discarded or used as fuel for the thermal decomposition process of the present invention (e.g., the first thermal decomposition process and / or the second thermal decomposition process). In the first distillation step (S2), a known distillation column can be used, for example, a plate column or a packed column. The first distillation step (S2) is preferably carried out in one or more stages using one or more distillation columns, and it is preferable to fill the interior of the one or more distillation columns with an inert gas (e.g., nitrogen, rare gas, etc.) from an inert gas supply source before starting up the distillation, and to replace the air inside the distillation column with the inert gas before distillation. The distillation temperature in the first distillation step (S2) is, for example, preferably in the range of 50 to 200° C., more preferably 50 to 150° C. For example, in the first distillation step (S2), when the second fraction is distilled in one stage of one distillation column, 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 first distillation step (for example, the pressure inside the distillation column) is preferably 10 to 100 Torr, more preferably 20 to 70 Torr.

[0039] <Recycling process (S3)> The method for producing a styrene monomer of this embodiment may include a recycling step (S3) as needed. More specifically, the method for producing a styrene monomer of this embodiment preferably includes a step of recycling the second fraction obtained in the first distillation step (S2) and / or a recycling step (S3) of recycling the first pyrolysis liquid. The recycling step (S3) is a step of making the second fraction part of a composition containing styrene dimer and / or styrene trimer, or part of a second thermal decomposition liquid described below, or a step of pumping part or all of the first thermal decomposition liquid by means of a pump or the like to make it part of the second thermal decomposition liquid. In other words, the recycling step (S3) is a step of mixing the second fraction obtained in the first distillation step (S2) or the first thermal decomposition liquid with a composition containing styrene dimer and / or styrene trimer, or mixing the second fraction with the second thermal decomposition liquid described below.

[0040] <Styrene monomer recovery process> The method for producing a styrene monomer according to the present embodiment may, if necessary, include a recovery step of recovering the styrene monomer. More specifically, the method includes a recovery step of recovering the styrene monomer from the first pyrolysis liquid prepared in the first pyrolysis step (S1). The phrase "recovering styrene monomer from the first pyrolysis liquid" includes recovering styrene monomer directly from the first pyrolysis liquid, and indirectly recovering styrene monomer by subjecting the first pyrolysis liquid to a first distillation step (S2) or the like in which the first pyrolysis liquid is distilled (including rectification). The first pyrolysis liquid may contain components produced by pyrolysis of a composition containing styrene dimer and / or styrene trimer, and may be subjected to preliminary pyrolysis before or during the recovery step. In addition, in the pyrolysis step and / or the recovery step, optional additional components may be added as necessary to suppress the polymerization reaction of the styrene monomer produced.

[0041] 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 distilling or fractionating the first pyrolysis liquid to separate 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 furnace and the fractionation column. In the recovery step, the material to be recovered may be the first pyrolysis liquid, the second fraction, or the fifth fraction described below. If necessary, the recovery step may include a measurement step in which quantitative analysis using GC-FID as described in the Examples is performed to measure the styrene monomer concentration, and the feasibility of recovery may be determined. In this case, the styrene monomer content of the entire material to be recovered may be 10% by mass or more, preferably 15% by mass or more, and more preferably 20% by mass or more. The material to be recovered may be shipped as a product.

[0042] (Composition containing styrene dimer and / or styrene trimer) The styrene dimer and / or styrene trimer-containing composition of this embodiment is not particularly limited as long as it contains styrene dimer and / or styrene trimer. For example, styrene dimer and / or styrene trimer produced during the production of a polystyrene-based resin containing a styrene polymer using a styrene monomer may be purified and separated for use, or may be synthesized and isolated by other methods for use. Alternatively, commercially available styrene dimer and / or styrene trimer may be used. Alternatively, the styrene dimer and / or styrene trimer-containing composition may be a thermal decomposition product of a polystyrene-based resin composition containing a polystyrene-based resin as a main component. Such polystyrene-based resin compositions include virgin polystyrene-based resin compositions and discarded polystyrene-based resin compositions (post-consumer and pre-consumer). Therefore, the styrene dimer and / or styrene trimer-containing composition may be a discarded polystyrene-based resin composition or a thermal decomposition product of the discarded polystyrene-based resin composition. Specifically, a polystyrene-based resin composition and / or a discarded polystyrene-based resin composition may be subjected to the second pyrolysis step (S4) described below to prepare a composition containing a styrene dimer and / or a styrene trimer.

[0043] Styrene dimer and / or styrene trimer obtained by purifying a product obtained by thermally decomposing a polystyrene resin containing a styrene polymer containing a styrene monomer unit may be used, or styrene dimer and / or styrene trimer synthesized or produced from a biomass source may be used. Furthermore, as long as the embodiment of the present invention is not impaired, a composition containing the above-mentioned styrene dimer and / or styrene trimer or a combination thereof mixed in any ratio may be used. Specifically, a polystyrene-based resin composition containing a polystyrene-based resin as a main component may be subjected to the second pyrolysis step (S4) described below to prepare a composition containing a styrene dimer and / or a styrene trimer. It is desirable to isolate the styrene dimer and / or the styrene trimer by a purification method such as distillation or to use one having a high mass% concentration. However, as described above, both the styrene dimer and / or the styrene trimer are obtained when producing a polystyrene resin composition containing a styrene polymer containing a styrene monomer unit or by thermally decomposing a polystyrene resin composition containing a styrene polymer containing a styrene monomer unit, and therefore are often obtained as a mixture. Since separation and purification of these require many facilities, steps, and energy, the styrene dimer and / or the styrene trimer or a combination thereof may be mixed in any ratio within a range that does not impair the embodiment of the present invention.

[0044] In the composition of this embodiment containing a styrene dimer and / or a styrene trimer, the total proportion of the styrene dimer and the styrene trimer is preferably greater than 10% by mass, more preferably greater than 20% by mass, even more preferably greater than 30% by mass, even more preferably greater than 40% by mass, and even more preferably greater than 65% by mass. The higher the total proportion, the higher the yield of styrene monomer upon thermal decomposition. Furthermore, the higher the total proportion, the less likely side reactions will occur due to other components in the composition used as a raw material during thermal decomposition, and the more likely it is that the generation of thermal decomposition residues that do not flow at room temperature and normal pressure will be suppressed, resulting in superior maintainability and reduced generation of industrial waste.

[0045] The total content (X) of the styrene dimer and / or styrene trimer contained in the composition and the styrene monomer, ethylbenzene, α-methylstyrene, and cumene contained as other components in the composition is more than 10% by mass, more preferably more than 30% by mass, even more preferably more than 60% by mass, even more preferably more than 65% by mass, and still more preferably more than 70% by mass. The higher the proportion of the total content (X), the higher the yield of styrene monomer obtained upon thermal decomposition.

[0046] A preferred embodiment of the composition containing a styrene dimer and / or a styrene trimer of the present embodiment essentially contains a styrene dimer and / or a styrene trimer, and the total content of the styrene dimer and the styrene trimer is preferably 10 to 100% by mass, more preferably 15 to 95% by mass, and even more preferably 20 to 90% by mass. When the composition containing a styrene dimer and / or a styrene trimer contains a styrene monomer, ethylbenzene, α-methylstyrene, and cumene, the total content of the styrene monomer, ethylbenzene, α-methylstyrene, and cumene is preferably 0 to 80 mass%, more preferably 1 to 70 mass%, and even more preferably 4 to 60 mass%.

[0047] In the composition containing the styrene dimer and / or styrene trimer, the content of the styrene dimer relative to the entire composition is preferably 0 to 100 mass%, more preferably 5 to 50 mass%, and even more preferably 10 to 30 mass%, and the content of the styrene trimer relative to the entire composition is preferably 0 to 100 mass%, more preferably 10 to 80 mass%, and even more preferably 20 to 70 mass%.

[0048] The components other than the total content (X) contained in the composition are characterized by having a boiling point of 200°C or higher at normal pressure or having 14 or more carbon atoms, excluding toluene, and their concentration by mass relative to the composition is preferably less than 50% by mass, more preferably less than 40% by mass, and even more preferably 30% by mass or less. When the content of the components other than X contained in the composition is within the above range, side reactions are less likely to occur, the yield of styrene monomer obtained upon thermal decomposition is improved, and the generation of thermal decomposition residue that does not flow at room temperature and normal pressure can be suppressed, resulting in excellent maintainability and suppression of industrial waste generation.

[0049] <Styrene dimer and / or styrene trimer> The styrene dimer of this embodiment is not particularly limited as long as it is a compound made from two styrene monomers as reaction raw materials. Examples of the styrene dimer of this embodiment include one or more compounds selected from the group consisting of compounds represented by the following general formulas (1-1) to (1-4), and mixtures of the compounds. The styrene trimer of this embodiment is not particularly limited as long as it is a compound made from three styrene monomers as reaction raw materials. Examples of the styrene dimer of this embodiment include one or more compounds selected from the group consisting of compounds represented by the following general formulas (2-1) to (2-4), and mixtures of the compounds.

[0050] Hereinafter, preferred embodiments of the styrene dimer and / or styrene trimer of this embodiment will be described. <<Styrene dimer>> The styrene dimer in this embodiment may be one or more compounds selected from the group consisting of compounds represented by the following general formulas (1-1) to (1-4), or a mixture thereof. In this embodiment, the styrene dimer is preferably represented by general formula (1-1) or (1-2), as this provides a high conversion rate to styrene monomer. The styrene dimer is more preferably represented by general formula (1-1). Furthermore, the styrene dimer may be one or more compounds selected from the group consisting of compounds represented by general formulas (1-1) to (1-4), or a mixture thereof, but from the viewpoint of the yield of styrene monomer obtained by thermal decomposition, it is preferred that the aromatic ring in each of general formulas (1-1) to (1-4) is unsubstituted. [ka] (In the above general formula (1-1), E 1 and E 2 may be the same or different and each represents a vinyl group, an acryloyl group, a methcroyl group, or an alkyl group having 1 to 10 carbon atoms; x1 and y1 each represent E 1 and E 2 represents the number of substituents on the aromatic ring, and is selected from integers of 0 to 5.1 and E 2 The substitution position of may be any position.) [ka] (In the above general formula (1-2), E 1 and E 2 may be the same or different and are a vinyl group, an acryloyl group, a methcroyl group, or an alkyl group having 1 to 10 carbon atoms; x2 and y2 may be the same or different; E 1 and E 2 represents the number of substituents on the aromatic ring, and is selected from integers of 0 to 5. 1 and E 2 The substitution position of may be any position.) [ka] (In the above general formula (1-3), E 1 and E 2 may be the same or different and are a vinyl group, an acryloyl group, a methcroyl group, or an alkyl group having 1 to 10 carbon atoms; x3 and y3 may be the same or different; E 1 and E 2 represents the number of substituents on the aromatic ring, and is selected from integers of 0 to 5. 1 and E 2 The substitution position of may be any position.) [ka] (In the above general formula (1-4), E 1 and E 2 may be the same or different and are a vinyl group, an acryloyl group, a methcroyl group, or an alkyl group having 1 to 10 carbon atoms; x4 and y4 may be the same or different and E 1 and E 2 represents the number of substituents on the aromatic ring, and is selected from integers of 0 to 5. 1 and E 2The substitution position of may be any position.)

[0051] <<Styrene trimer>> The styrene trimer in this embodiment may be one or more compounds selected from the group consisting of compounds represented by the following general formulas (2-1) to (2-4), or a mixture thereof. In this embodiment, the styrene trimer is preferably a compound represented by general formula (2-1) or (2-2), since the conversion rate to styrene monomer is high. The styrene trimer is more preferably a compound represented by general formula (2-1). Furthermore, the styrene trimer may be one or more compounds selected from the group consisting of compounds represented by general formulas (2-1) to (2-4), or a mixture thereof, but from the viewpoint of the yield of styrene monomer obtained by thermal decomposition, it is preferable that the aromatic ring in each of the general formulas (2-1) to (2-4) is unsubstituted. [ka] (In the above general formula (2-1), E 3 , E 4 , and E 5 may be the same or different and are a vinyl group, an acryloyl group, a methcroyl group, or an alkyl group having 1 to 10 carbon atoms. x4, y4, and z1 are each a group represented by E 3 , E 4 , and E 5 represents the number of substituents on the aromatic ring, and is selected from integers of 0 to 5. 3 , E 4 , and E 5 The substitution position of may be any position.) [ka] (In the above general formula (2-2), E 3 , E 4 , and E 5 may be the same or different and are a vinyl group, an acryloyl group, a methcroyl group, or an alkyl group having 1 to 10 carbon atoms. 4represents the number of substituents on the aromatic ring, and is selected from integers of 0 to 4; y5 and z2 are each E 3 and E 5 represents the number of substituents on the aromatic ring, and is selected from integers of 0 to 5. 3 , E 4 , and E 5 The substitution position of may be any position.) [ka] (In the above general formula (2-3), E 3 , E 4 , and E 5 may be the same or different and are each a vinyl group, an acryloyl group, a methcroyl group, or an alkyl group having 1 to 10 carbon atoms. x6, y6, and z3 are each E 3 , E 4 , and E 5 represents the number of substituents on the aromatic ring, and is selected from integers of 0 to 5. 3 , E 4 , and E 5 The substitution position of may be any position.) [ka] In the above general formula (2-4), E 3 , E 4 , and E 5 may be the same or different and are a vinyl group, an acryloyl group, a methcroyl group, or an alkyl group having 1 to 10 carbon atoms. 3 , E 4 , and E 5 represents the number of substituents on the aromatic ring, and is selected from integers of 0 to 5. 3 , E 4 , and E 5 The substitution position may be any position. The composition containing a styrene dimer and / or a styrene trimer of this embodiment preferably contains a compound represented by the general formula (1-1) and a compound represented by the general formula (2-1). Under the conditions (A) and (B) of the first thermal decomposition step (S1) of this embodiment, the compound represented by the general formula (1-1) and the compound represented by the general formula (2-1) tend to be efficiently decomposed into styrene monomers.

[0052] <<Polystyrene-based resin composition>> When a thermal decomposition product of a polystyrene-based resin composition is used as the composition containing a styrene dimer and / or a styrene trimer that serves as a raw material in the method for producing a styrene monomer of the present embodiment, the polystyrene-based resin composition contains a polystyrene-based resin as a main component. In this specification, "containing A as a main component" means that A is contained in an amount of 50 mass % or more based on the entire composition. The polystyrene-based resin may contain a styrene-based polymer containing a styrene monomer unit, and the content of the styrene-based polymer contained in the polystyrene-based resin used as the raw material for the pyrolysate is preferably 50% by mass or more, more preferably 60% by mass, even more preferably 70% by mass, and even more preferably 80% by mass, based on the total polystyrene-based resin. When the content of the styrene polymer contained in the polystyrene resin 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.

[0053] The polystyrene resin 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-spec pellets, etc. The styrene resin composition may also contain additives such as a phosphorus-based flame retardant, liquid paraffin, a stabilizer, or a colorant.

[0054] The polystyrene resin, the polystyrene resin composition, or the composition containing a styrene dimer and / or a styrene trimer may contain impurities. The impurities may include other resins that are substantially free of styrene monomer units, such as olefin resins, polyether resins, polyester resins, or polyamide resins. Products may also be laminated with these other resins, or 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, used in fiber-reinforced plastics. Metals, such as aluminum, iron, and stainless steel, may also be included. The amount of impurities contained in the polystyrene-based resin, the polystyrene-based resin composition, or the composition containing styrene dimer and / or styrene trimer used as a raw material is preferably 50% by mass or less, more preferably 40% by mass or less, even more preferably 30% by mass or less, and still more preferably 20% by mass or less, based on the total amount of the composition.

[0055] In particular, the use of post-consumer materials that generate residues upon thermal decomposition is beneficial for the styrene monomer production method of this embodiment. However, even if the polystyrene resin of this embodiment is a virgin polystyrene resin composition containing an unused styrene polymer, or a pre-consumer material such as a factory-recovered product, it may contain the above-mentioned additives or other resins or inorganic substances that are mixed in during processing. Therefore, the styrene monomer production method of this embodiment is beneficial 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.

[0056] <Styrene-based polymer> The polystyrene-based resin usable in this embodiment contains a styrene-based polymer containing a styrene monomer unit. The polystyrene-based resin or styrene-based polymer may be a used, discarded, or discarded material. The styrene-based polymer may contain a styrene monomer unit, and is preferably a polymer obtained by polymerizing a styrene monomer unit and, if necessary, one or more selected from other vinyl-based monomer units and rubber-like polymers copolymerizable with the styrene-based monomer. In other words, the styrene-based polymer contained in the polystyrene-based resin is preferably a polymer containing a styrene monomer unit, and more preferably a polymer that essentially contains a styrene monomer unit and optionally contains monomer units of other vinyl-based monomers and / or rubber-like polymers copolymerizable with the styrene-based monomer unit. The preferred form of the styrene-based polymer in this embodiment is not particularly limited, but specific examples include polystyrene, a rubber-modified styrene-based resin in which rubber polymer particles are dispersed in a polymer matrix containing a polystyrene-based polymer (such as polystyrene and / or polystyrene-unsaturated carboxylic acid polymer), and a styrene-based copolymer resin. The styrene polymer containing styrene monomer units contained in the polystyrene resin usable in this embodiment may have 50% by mass or more of styrene monomer units relative to the entire styrene polymer (100% by mass), preferably 60% by mass or more, and more preferably 70% by mass or more.

[0057] <Polystyrene> The polystyrene in this embodiment is a homopolymer of a styrene monomer or a copolymer obtained by polymerizing a styrene monomer and a styrene-based monomer, and a generally available one can be appropriately selected and used. Examples of the styrene-based monomer include, in addition to styrene, α-methylstyrene, α-methyl-p-methylstyrene, ο-methylstyrene, m-methylstyrene, p-methylstyrene, vinyltoluene, ethylstyrene, isobutylstyrene, and t-butylstyrene, and styrene derivatives such as bromostyrene and indene.

[0058] <Rubber-modified styrene resin> In this embodiment, the rubber-modified styrene-based resin is a resin in which rubber-like polymer particles are dispersed in a polystyrene or styrene-based copolymer matrix phase, and has a sea-island structure in which the matrix phase is a sea phase and the rubber-like polymer particles (=rubber-like polymer particles) are island phases. The rubber-modified styrene-based resin can be produced by polymerizing a styrene-based monomer (and an unsaturated carboxylic acid-based monomer added as needed) in the presence of the rubber-like polymer. The unsaturated carboxylic acid monomer includes a (meth)acrylic acid monomer and a (meth)acrylic acid ester monomer.

[0059] 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-based 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.

[0060] 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. As the polybutadiene, both high-cis polybutadiene with a high cis content and low-cis polybutadiene with a low cis content can be used. Furthermore, the structure of the styrene-butadiene copolymer can be either a random structure or a block structure. One or more of these rubbery polymers (a) can be used. Furthermore, saturated rubber obtained by hydrogenating butadiene rubber can also be used.

[0061] 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).

[0062] The content of the rubber-like polymer in the rubber-modified styrene-based resin is preferably 3 to 20% by mass, more preferably 5 to 15% by mass, based on 100% by mass of the total amount of the rubber-modified styrene-based resin. If the content of the rubber-like polymer in the rubber-modified styrene-based resin is less than 3% by mass, the impact resistance of the styrene-based resin may decrease. If the content of the rubber-like polymer exceeds 20% by mass, the flame retardancy may decrease. 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.

[0063] 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, more preferably 0.8 to 3.5 μm, from the viewpoint of impact resistance and flame retardancy.

[0064] <Styrene copolymer resin> In the present embodiment, the styrene copolymer resin is a resin containing a styrene monomer unit and another monomer copolymerizable with the styrene monomer (for example, an unsaturated carboxylic acid monomer unit). For example, when the other monomer is an unsaturated carboxylic acid monomer unit, the styrene copolymer resin according to the present invention preferably has a styrene monomer unit content of 69 to 98% by mass, more preferably 74 to 96% by mass, and even more preferably 77 to 92% by mass, when the total content of the styrene monomer unit and the unsaturated carboxylic acid monomer unit is taken as 100% by mass.

[0065] The unsaturated carboxylic acid monomer in this embodiment includes unsaturated carboxylic acid monomers and unsaturated carboxylic acid ester monomers.

[0066] The unsaturated carboxylic acid monomer constituting the styrene copolymer resin of the present embodiment is not particularly limited, but examples thereof include methacrylic acid, acrylic acid, maleic anhydride, maleic acid, fumaric acid, and itaconic acid.

[0067] The unsaturated carboxylic acid ester monomer constituting the styrene copolymer resin of this embodiment is not particularly limited, but examples thereof include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, and cyclohexyl (meth)acrylate. As the (meth)acrylic acid ester monomer, methyl (meth)acrylate is preferred because it has little effect on the deterioration of heat resistance. These unsaturated carboxylic acid ester monomers can be used alone or in combination of two or more.

[0068] 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.

[0069] <Optional addition ingredients> In addition to the above components, the styrene-based resin composition of the present embodiment may optionally contain conventionally known additives, processing aids, and other optional additives, as long as the effects of the present invention are not impaired. Examples of these additives and processing aids include antioxidants, weathering agents, lubricants, antistatic agents, and fillers.

[0070] Examples of the antioxidant include phenolic compounds, phosphorus compounds, and thioether compounds.

[0071] As the weatherproofing agent, an ultraviolet absorber or the like can be used.

[0072] As the lubricant, fatty acid amides, fatty acid esters, fatty acids, fatty acid metal salts, etc. can be used.

[0073] As the antistatic agent, cationic, anionic, nonionic, amphoteric, fatty acid partial esters such as glycerin fatty acid monoesters, etc. can be used.

[0074] Examples of the filler that can be used include talc, calcium carbonate, barium sulfate, carbon fiber, glass fiber, cellulose fiber, mica, wollastonite, and whisker.

[0075] In addition to the additives and processing aids described above, the mixture 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 optional components such as additives and processing aids in the mixture may be 0.05 to 5% by mass.

[0076] [Preferable method for producing styrene monomer] The method for producing a styrene monomer according to the present disclosure essentially includes a first pyrolysis step (S1). A preferred embodiment of the method for producing a styrene monomer according to the present disclosure will be described in its entirety with reference to Fig. 2, and then each step will be described in detail below.

[0077] As shown in Figure 2, the method for producing styrene monomer of the present disclosure may include a raw material preparation step (P1) before the first pyrolysis step (S1) and the second pyrolysis step (S4), in which a polystyrene-based resin composition is prepared by, for example, recovering waste plastics (post-consumer products) and recycling them as a polystyrene-based resin composition, or by recovering pre-consumer products (e.g., scraps from manufacturing) and recycling them as a polystyrene-based resin composition. If necessary, a second pyrolysis step (S4) is then performed, in which the polystyrene-based resin composition is pyrolyzed under the following conditions (X) and (Y) and cooled under known cooling conditions to prepare a second pyrolysis liquid. If necessary, a second distillation step (S5) may be performed, in which the second pyrolysis liquid is distilled to separate it into a fourth fraction containing styrene monomer and high-boiling components with a boiling point higher than that of styrene monomer at room temperature and normal pressure, and a third fraction containing low-boiling components with a boiling point lower than that of styrene monomer at room temperature and normal pressure. If necessary, a third distillation step (S6) may be carried out in which the fourth fraction is distilled to separate it into a fifth fraction mainly composed of styrene monomer and a sixth fraction mainly composed of high-boiling components having a boiling point higher than that of styrene monomer under the room temperature and normal pressure conditions. On the other hand, as shown in FIG. 2, when the second distillation step (S5) is not carried out, the second thermal decomposition liquid corresponds to the sixth fraction. Similarly, when the third distillation step (S6) is not carried out, the fourth fraction corresponds to the sixth fraction. The sixth fraction corresponds to the composition containing styrene dimer and / or styrene trimer of this embodiment. By subjecting the polystyrene resin composition to the second pyrolysis step (S4), the amount of styrene dimer and / or styrene trimer produced in the system increases. Furthermore, by subjecting the polystyrene resin composition to the second distillation step (S5) and / or the third distillation step (S6), the amount of styrene dimer and / or styrene trimer can be concentrated, resulting in the recovery of styrene monomer in a higher yield and with a higher purity.

[0078] The second pyrolysis liquid, the fourth fraction, the sixth fraction, or a polystyrene resin composition containing styrene dimer and / or styrene trimer corresponds to the composition containing styrene dimer and / or styrene trimer of this embodiment. Therefore, a first pyrolysis step (S1) or (S4) is performed in which any of these is pyrolyzed under the following conditions (A) and (B) and cooled under known cooling conditions to prepare a first pyrolysis liquid. If necessary, a first distillation step (S2) may be performed in which the first pyrolysis liquid is distilled to separate it into a second fraction containing styrene monomer and low-boiling components and a first fraction containing higher-boiling components than the second fraction. If necessary, a recycling step (S3) may be performed in which the second fraction is used as part of the second pyrolysis liquid (or the second fraction is mixed with the second pyrolysis liquid) to increase the yield of styrene monomer.

[0079] The amount of styrene monomer in the second pyrolysis liquid or the second fraction is analyzed as necessary, and if it is confirmed that the styrene monomer has a desired purity or higher, a recovery step is carried out in which the second pyrolysis liquid or the second fraction is recovered as styrene monomer.

[0080] The preparation step (S0) of this embodiment includes one or more steps selected from the group consisting of a second pyrolysis step (S4), a second distillation step (S5), and a third distillation step (S6).

[0081] Each step will be explained in detail below. (Preparation process (P)) The method for producing a styrene monomer according to the present disclosure preferably includes a raw material preparation step (P) of preparing a polystyrene-based resin composition. Examples of the raw material preparation process (P) include a process of collecting styrene resin-containing waste plastics (post-consumer products) generated from the market or consumers and recycling them as a composition containing styrene dimer and / or styrene trimer, and / or a process (P1) of collecting products (pre-consumer products) that have not yet been distributed to consumers or the market, such as scraps from manufacturing, and recycling them as a polystyrene resin composition. The raw material preparation process (P1) for preparing a polystyrene-based resin composition from post-consumer and / or pre-consumer products preferably includes a crushing process for crushing styrene-based resin-containing waste plastics, a washing process for washing the crushed waste plastics, or a sorting process for sorting the crushed waste plastics. On the other hand, the raw material preparation step (P2) of preparing a polystyrene-based resin composition from materials such as virgin pellets preferably includes a crushing step of crushing virgin materials containing a styrene-based resin.

[0082] <Crushing process> The shredding process involves using a known shredder to shred waste plastics containing styrene resins or virgin materials containing styrene resins, thereby obtaining shredded waste plastics containing styrene resins or virgin materials containing styrene resins. The maximum length of the shredded material is approximately 0.5 cm or more, preferably 0.5 to 5.0 cm. For example, the shredded material (shredder dust) can be transported to the next process using a conveyor such as a screw conveyor.

[0083] In the shredding process, the size of the shredded material is particularly suitable for removing foreign matter such as metals or soil attached to the shredded material in an optional subsequent washing process, thereby improving the efficiency of sorting in an optional sorting process. If necessary, before and / or after the shredding process, the waste plastic containing a styrene-based resin or the virgin material containing a styrene-based resin may be dissolved in a solvent to separate it into a component soluble in the solvent and a component insoluble or poorly soluble in the solvent, and the component dissolved in the solvent may be devolatilized and used in the next process. If necessary, manual sorting or dry sorting may be performed before the shredding process. The manual sorting is a manual process of removing metals, glass, inorganic materials, paper, wood chips, etc. from scrapped automobiles, scrapped home appliances, scrapped building materials, scrapped plastic containers, etc. In manual sorting, in order to prevent problems in the subsequent processes, for example, a person can manually remove items other than those to be recovered while observing with the naked eye on a belt conveyor. The removed items are treated as residue. Metals or glass may be used as recycled materials as they are. The dry sorting may be carried out using an optical sorter, a sieve sorter, or an air sorter, or a magnetic sorter. The sorting using an optical sorter or an air sorter can employ a known method, for example, by analyzing the wavelength of near-infrared light to recognize a specific material, and then blowing the material away with an air nozzle to separate it.

[0084] <Sorting process> The sorting step is a step of separating a resin component containing a styrene-based resin from a metal, an inorganic substance, or soil and sand from the crushed waste plastic containing a styrene-based resin, and removing the metal, inorganic substance, or soil and sand. Examples of the sorting step include a dry sorting step using a magnetic separator or a sieve separator, and a gravity separation step described below. Note that if there is no need to recover magnetic materials such as iron, the metal, inorganic substance, or soil and sand may be separated from the crushed material using a sieve separator. The sorting step uses a sieve sorter to separate metals, inorganic matter, or soil and sand from the crushed waste plastic containing styrene-based resin, and recover the metals, inorganic matter, or soil and sand as residue. The sieve sorter can be an eddy current sorter that uses eddy currents generated by a rotating magnetic field and magnetic field interactions to throw non-magnetic materials (aluminum, copper, etc.) forward, or a dry gravity sorter that uses a tilted plate with openings that is vibrated from below while being blown with air.

[0085] The crushed styrene-based resin-containing waste plastics treated in the sorting step are preferably subjected to dry sorting using an optical sorting machine, a wind sorting machine, or manual sorting, as necessary, to sort and remove metals, soil, glass, and other impurities contained in the crushed material, thereby further removing impurities such as metals, inorganic matter, and soil.

[0086] <Gravity sorting process> The gravity separation step is a step of separating the crushed waste plastic containing a styrene resin into floating matter and sediment. In the gravity separation step, the floating matter is used as a raw material (= a composition containing a styrene dimer and / or a styrene trimer) in the styrene monomer production method of the present embodiment, and the floating matter is separated into floating matter and sediment. 3 This is a sorting process in which the materials are sorted into floating and sinking materials in a liquid tank containing a liquid such as a solvent containing water, an aqueous solution, or oil; or a heavy liquid containing salt, ferrochrome, potassium nitrate, or the like. The gravity separation process can remove metals, inorganic matter, soil, sand, etc., as well as mainly halogenated resins, polyester resins, etc., from the crushed waste plastics containing styrene-based resins. The halogenated resins include vinyl chloride-based resins and bromine-based resins. By performing a washing process before the gravity separation process, the crushed waste plastics containing styrene-based resins can be made wettable, thereby shortening the sorting time and improving the sorting accuracy. For the crushed waste plastics containing styrene-based resins, a solvent or heavy liquid with a specific gravity of approximately 0.9 to 1.5 is used. Since the specific gravity of halogen-based resins (e.g., PVC resins) is 1.3 to 1.4, a specific gravity is used to separate the halogen-based resins. The heavy liquid is prepared using salt, ferrochrome, potassium nitrate, etc. In the gravity separation step, the solvent can be adjusted appropriately to have a specific gravity of 0.9 to 1.5 depending on the specific gravity of the material to be removed. The liquid tank used in the gravity separation process can be a treatment device equipped with a plurality of paddles attached to the top surface and a spiral discharger attached to the bottom of the box-shaped sorting liquid tank to discharge the settled crushed material.

[0087] In the gravity separation step, gravity separation is performed using a heavy liquid to separate the materials into floating matter and sediment, which are then recovered. The floating matter from the gravity separation step may be further subjected to manual separation.

[0088] <Cleaning process> The washing step is a step of washing the crushed waste plastic containing the styrene-based resin to remove dirt adhering to the crushed material. In the washing step, the crushed styrene resin-containing waste plastic may be washed and simultaneously crushed into small pieces having a size of 5 cm or less, preferably about 1 cm.

[0089] <Second pyrolysis step (S4)> The method for producing a styrene monomer according to the present disclosure optionally includes a second thermal decomposition step (S4). The second thermal decomposition step (S4) is a step for preparing a composition containing a styrene dimer and / or a styrene trimer, in which a polystyrene-based resin composition is thermally decomposed under the above conditions (X) and (Y) to prepare a second thermal decomposition liquid containing a styrene monomer. In the present embodiment, the method for thermally decomposing the polystyrene-based resin composition may be a method for heating the polystyrene-based resin composition to a temperature of 400° C. or higher but lower than 1200° C. The pyrolysis furnace used for the pyrolysis is not particularly limited as long as it is a furnace equipped with the heating means and pressure adjusting means described in the section <First pyrolysis step (S1)> above.

[0090] In the second pyrolysis step (S4), the temperature at which the polystyrene-based resin composition is pyrolyzed (= pyrolysis temperature) may be, for example, in a pyrolysis furnace after the composition is filled, and then the polystyrene-based resin composition is heated in a temperature range of 400°C or higher and lower than 1200°C, preferably 420°C to 800°C, and more preferably 450°C to 600°C. In this case, the temperature of the polystyrene-based resin composition to be filled is about 20 to 300°C, and more preferably 150 to 260°C. Alternatively, the second pyrolysis step (S4) may be performed by filling a preheated pyrolysis furnace with the polystyrene-based resin composition. In this case, the temperature to which the pyrolysis furnace is preheated is about 400°C or higher and lower than 1200°C, preferably 420 to 800°C, and more preferably 450°C to 600°C. The temperature of the fluid to be filled is about 20 to 300°C, and more preferably 150 to 260°C. By setting the temperature of the pyrolysis furnace within the above range, most of the generated pyrolysis vapor can become the pyrolysis products of the polystyrene-based resin composition. Therefore, it is preferable to use the heating means described in the above section <First pyrolysis step (S1)> to create an atmosphere with a temperature in the range of 400°C or higher and lower than 1200°C. It is possible to reduce the conversion of components contained in the raw material polystyrene resin composition into by-products that would lead to a decrease in the yield of styrene monomer.

[0091] In the second pyrolysis step (S4), the pressure conditions (= pyrolysis pressure) for pyrolyzing the polystyrene-based resin composition are such that the polystyrene-based resin composition is pyrolyzed under an atmosphere of pressure greater than 10 hPa and less than 300 hPa. Therefore, for example, it is preferable to use the pressure adjusting means described in the above section <First pyrolysis step (S1)> to create an atmosphere of pressure greater than 11 hPa and less than 250 hPa. The pyrolysis pressure is more preferably 12 hPa or more and 200 hPa or less, even more preferably 14 hPa or more and 150 hPa or less, and even more preferably 15 hPa or more and 100 hPa or less. In this embodiment, for example, when the composition is decomposed in a pyrolysis furnace, the composition may be decomposed at a pressure of more than 10 hPa and less than 300 hPa, preferably at a pressure of 11 hPa or more and 250 hPa or less, more preferably at a pressure of 12 hPa or more and 200 hPa or less, and even more preferably at a pressure of 14 hPa or more and 150 hPa or less. By setting the pressure in the pyrolysis furnace within the above range, most of the generated pyrolysis vapor can become pyrolysis products of the polystyrene-based resin composition, and it is possible to reduce the conversion of components of the raw material polystyrene-based resin composition into by-products that would lead to a decrease in the yield of styrene monomer.

[0092] The pyrolysis vapor generated in the second pyrolysis step (S4) may be cooled to a temperature between the boiling point of the styrene monomer and 180°C, and the high-boiling components may be liquefied using a liquefaction device and dropped again into the pyrolysis furnace, returning the liquefied vapor to the pyrolysis furnace and conducting the pyrolysis step again. The pyrolysis vapor generated may also be liquefied by cooling using a liquefaction device to obtain a second pyrolysis liquid. The cooling temperature is preferably between -30°C and the boiling point Tsb (°C) of the styrene monomer, more preferably between -20°C and 80°C. In this case, a known liquefaction device may be used. Examples of suitable liquefaction devices include various heat-removing solvents, including water, capable of cooling to the desired cooling temperature, and cooling tubes utilizing the heat-removing effect of heat-removing elements made of metals and various inorganic materials. 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 furnace and the liquefaction device.

[0093] In this embodiment, the second pyrolysis step (S4) may prepare the second pyrolysis liquid using a pyrolysis catalyst. The pyrolysis catalyst is preferably a compound that contains any element classified in Periods 2 to 7 of Groups 1 to 17 of the Periodic Table, which has stable isotopes, exists as a solid at room temperature and pressure, and has a decomposition temperature of 300°C or higher. Examples of the pyrolysis catalyst include BaO, TiO, MgO, AlO, CaO, NiO, and YO.

[0094] The second pyrolysis step (S4) of this embodiment may include a cooling step of cooling the gas containing styrene monomer. That is, when a composition containing a polystyrene-based resin composition is pyrolyzed in the pyrolysis furnace, pyrolysis products can be fractionated into pyrolysis product gas, a fluid remaining without being gasified, and the solid fraction. A cooling tower can be used to cool the fractionated pyrolysis product gas, preparing a first pyrolysis liquid. The fluid remaining without being gasified and the solid fraction can be disposed of or used as fuel. If necessary, the system may also include a compressor that compresses the cooled pyrolysis product gas to generate compressed gas, a second flow path that connects the cooling tower and the compressor and supplies the pyrolysis product gas from the cooling tower to the compressor, and a first flow path that connects the pyrolysis furnace and the compressor or connects the pyrolysis furnace and the second flow path and supplies the pyrolysis product gas from the pyrolysis furnace to the compressor or the second flow path. Specifically, the production apparatus used in the method for producing a styrene monomer of this embodiment preferably includes a pyrolysis furnace for pyrolyzing a polystyrene resin composition, and optionally a fractionation tower fluidly connected to the pyrolysis furnace for fractionating the pyrolysis product gas, the fluid remaining ungasified, and the solid component, and a cooling tower for cooling the pyrolysis product gas. If necessary, the production apparatus may further include a compressor for compressing the cooled pyrolysis product gas, and a distillation tower for distilling the compressed pyrolysis product gas or the second pyrolysis liquid. The distillation tower may also be comprised of a plurality of distillation towers. The cooling tower is a device for cooling the fractionated pyrolysis product gas, and a known cooling tower can be used. The cooling temperature in the cooling step is usually −30° C. or higher and 80° C. or lower. The compressor compresses the cooled pyrolysis product gas to generate compressed gas. As the compressor, a known compressor can be used, such as a centrifugal compressor, an axial compressor, or a reciprocating compressor. The distillation column distills the produced compressed gas or the second pyrolysis liquid into a third fraction containing styrene monomer and low-boiling components, and a fourth fraction having a boiling point higher than that of the third fraction. As the distillation column, a known distillation column can be used, for example, a plate column or a packed column.

[0095] (Second distillation step (S5)) The method for producing a styrene monomer of this embodiment may optionally include a second distillation step (S5). The second distillation step (S5) 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 (S5) is, for example, preferably in the range of 50 to 200° C., more preferably 50 to 150° C. For example, when the second pyrolysis liquid is distilled in one stage using one distillation column in the second distillation step (S5), the distillation temperature in the one stage of distillation is, for example, in the range of 50 to 200° C., preferably 50 to 150° C. The pressure of the distillation atmosphere in the second distillation step (S5) (for example, the pressure inside the distillation column) is preferably 10 to 100 Torr, more preferably 20 to 70 Torr. When the second pyrolysis liquid is distilled under the above distillation conditions, it is separated into a fourth fraction (so-called high-boiling components) containing styrene monomer and styrene dimer and / or styrene trimer, and a third fraction (so-called low-boiling components) having a lower styrene monomer concentration than the fourth fraction. It is preferable that the difference between the styrene monomer concentration in the fourth fraction and the styrene monomer concentration in the third fraction is approximately twice or more the styrene monomer concentration in the fourth fraction compared to the styrene monomer concentration in the third fraction. For example, in the second distillation step (S5), when the second 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 and / or styrene dimer / trimer, etc. become high-boiling components. In the second distillation step, a polymerization inhibitor may be used to prevent polymerization of styrene monomer. This allows the second pyrolysis liquid to be separated into a fourth fraction containing styrene monomer and high-boiling components, and a fifth fraction containing lower-boiling components than the fourth fraction, thereby producing high-purity styrene monomer.

[0096] (Third distillation step (S6)) The method for producing a styrene monomer of this embodiment may optionally include a third distillation step (S6). The third distillation step (S6) 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 third distillation step (S6) is, for example, preferably in the range of 50 to 200° C., more preferably 50 to 150° C. For example, in the third distillation step (S6), when the fourth fraction is distilled in one stage of one distillation column, 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 third distillation step (for example, the pressure inside the distillation column) is preferably 10 to 100 Torr, more preferably 20 to 70 Torr. When the fourth fraction is distilled under the above distillation conditions, it is separated into a sixth fraction (so-called high-boiling components) containing styrene dimer and / or styrene trimer, and a fifth fraction (so-called low-boiling components) having a higher styrene monomer concentration than the sixth 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. For example, in the third distillation step (S6), 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 third distillation step (S6), a polymerization inhibitor may be used to prevent polymerization of the styrene monomer. Since the fifth fraction is the fraction with the highest purity of styrene monomer, it is preferable to recover the fifth fraction as styrene monomer. As a result, the fourth fraction is separated into a fifth fraction mainly composed of styrene monomer and a sixth fraction mainly composed of components with a higher boiling point than the fifth fraction, thereby enabling the production of styrene monomer in high yield.

[0097] The composition containing the styrene dimer and / or styrene trimer of this embodiment can be prepared by the second pyrolysis step (S4), the second distillation step (S5), and / or the third distillation step (S6). The composition containing the styrene dimer and / or styrene trimer can then be subjected to the first pyrolysis step (S1) to produce styrene monomer. [Example]

[0098] [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.

[0099] <Pyrolysis experiment> Although the pyrolysis experiment was carried out using a small reactor for simple experiments, there are no particular limitations on the size of the equipment as long as it does not deviate from the purpose of carrying out the desired experiment. A stainless steel reactor is placed inside the cast-in heater, a stainless steel cover with a branch pipe attached, and the bolts tightened with a wrench. A dedicated adapter with an O-ring is attached to the branch pipe, and a glass Liebig condenser, a distillation adapter with a vacuum hose attachment, and a pyrolysis liquid recovery flask are attached, each coated with silicone grease. A three-way stopcock is attached to the vacuum hose attachment, and a nitrogen balloon and vacuum pump are connected. Temperatures are monitored using thermocouples installed inside the cast-in heater and the vessel. A refrigerant is pumped at -10°C, the pressure is set with a vacuum pump, and the output of the cast-in heater is adjusted. A composition containing styrene dimer and styrene trimer is charged into the stainless steel reactor at the desired filling temperature, thermally decomposed at each temperature, and liquefied in the Liebig condenser through which the refrigerant is introduced, resulting in the recovery of the first pyrolysis liquid in the pyrolysis flask.

[0100] The materials used in the examples and comparative examples are as follows. <Benzene> Benzene (CAS No. 71-43-2) purchased from Tokyo Chemical Industry Co., Ltd. was used as is. <Toluene> Toluene (CAS No. 108-88-3) purchased from Tokyo Chemical Industry Co., Ltd. was used as is. <Ethylbenzene> Ethylbenzene (CAS No. 100-41-4) purchased from Tokyo Chemical Industry Co., Ltd. was used as is. <Styrene monomer> Styrene (CAS No. 100-42-5) purchased from Tokyo Chemical Industry Co., Ltd. was used, with the stabilizer TBC removed immediately before use. <α-methylstyrene> α-Methylstyrene (CAS No. 98-83-9) purchased from Tokyo Chemical Industry Co., Ltd. was used, with the stabilizer TBC removed immediately before use. <Kumen> Cumene (CAS No. 98-82-8) purchased from Tokyo Chemical Industry Co., Ltd. was used as is.

[0101] <Styrene dimer> Styrene dimer was prepared from polystyrene resin. <<Styrene dimer (1-1) (compound represented by general formula (1-1) (provided that, in said general formula (1-1), x1 = 0 and y1 = 0)>> 2,4-Diphenyl-1-butene (CAS No. 16606-47-6) purchased from Fujifilm Wako Pure Chemical Industries, Ltd. was used as is.

[0102] <Styrene trimer> Styrene trimers were prepared from polystyrene resins. <Styrene trimer (2-1), (a compound represented by general formula (2-1) (provided that in the general formula (1-1) x4 = y4 = z1 = 0)> 1,3-Diphenylpropane (CAS No. 1081-75-0) purchased from Tokyo Chemical Industry Co., Ltd. was used as is.

[0103] <Styrene trimer (2-4), a compound represented by general formula (2-4) (wherein, in said general formula (2-4), x7, y7 and z4=0)> 1,3,5-Triphenylbenzene (CAS No. 612-71-5) purchased from Tokyo Chemical Industry Co., Ltd. was used as is.

[0104] <Preparation of Composition (1) Containing Styrene Dimer and / or Styrene Trimer> GPPS680, a GPPS (polystyrene) manufactured by PS Japan Co., Ltd., is loaded into a stainless steel reaction vessel, placed inside a cast-in heater, and a stainless steel cover with a branch pipe is attached and bolted down with a wrench. A dedicated adapter with an O-ring is attached to the branch pipe, and a glass Liebig condenser, a distillation adapter with a pressure-reducing hose attachment branch, and a pyrolysis liquid recovery flask are attached, each coated with silicone grease. A three-way stopcock is attached to the pressure-reducing hose attachment branch, and a nitrogen balloon and vacuum pump are connected. Temperature is monitored using thermocouples installed inside the cast-in heater and vessel. The refrigerant was pumped at -10°C, the vacuum pump was set to 34 hPa to reduce pressure, the output of the cast-in heater was adjusted, and pyrolysis was carried out at 450°C. The refrigerant was then introduced into a Liebig condenser, and the resulting mixture was liquefied in a flask to prepare a second pyrolysis liquid. The second pyrolysis liquid was heated at 13 hPa from 50°C to 80°C in 5°C increments every 5 minutes using a rotary evaporator, and the low-boiling components (second fraction) were distilled off. The concentrated liquid remaining in the flask was composition (1) containing styrene dimer and / or styrene trimer. Table 1-1 shows the results of GC-FID analysis of composition (1) containing styrene dimer and / or styrene trimer used in each example, with quantitative analysis of styrene dimer (1-1), styrene trimer (2-1), toluene, styrene monomer, benzene, ethylbenzene, α-methylstyrene, and cumene in composition (1). Although quantitative analysis was not possible, molecular ion peaks that are thought to be derived from any of styrene dimers (1-1), (1-2), (1-3), and (1-4) and styrene trimers (2-1), (2-2), (2-3), and (2-4) were detected in the composition (1) by GC-MS analysis. Therefore, it is considered that the composition (1) also contains components that could not be quantified by GC-FID analysis.

[0105] <Preparation of Composition (2) Containing Styrene Dimer and / or Styrene Trimer> GPPS680, a GPPS manufactured by PS Japan Co., Ltd., is loaded into a stainless steel reaction vessel, placed inside a cast-in heater, and a stainless steel cover with a branch pipe is attached and bolted down with a wrench. A dedicated adapter with an O-ring is attached to the branch pipe, and a glass Liebig condenser, a distillation adapter with a pressure-reducing hose attachment branch, and a pyrolysis liquid recovery flask are attached, each coated with silicone grease. A three-way stopcock is attached to the pressure-reducing hose attachment branch, and a nitrogen balloon and vacuum pump are connected. Temperature is monitored using thermocouples installed inside the cast-in heater and vessel. The refrigerant is pumped at -10°C, the vacuum pump is set to 34 hPa to reduce the pressure, the output of the cast-in heater is adjusted, thermal decomposition is carried out at 450°C, and the refrigerant is liquefied in a Liebig condenser to prepare a second thermal decomposition liquid in a flask. The prepared second thermal decomposition liquid is a composition (2) containing styrene dimer and / or styrene trimer, characterized by containing a large amount of styrene monomer. In addition, composition (2) was also subjected to GC-FID analysis in the same manner as composition (1), and the styrene dimer (1-1), styrene trimer (2-1), toluene, styrene monomer, benzene, ethylbenzene, α-methylstyrene, and cumene in composition (1) were quantitatively analyzed. Although quantitative analysis was not possible, molecular ion peaks that are thought to be derived from any of styrene dimers (1-1), (1-2), (1-3), and (1-4) and styrene trimers (2-1), (2-2), (2-3), and (2-4) were detected in the composition (2) by GC-MS analysis. Therefore, it is considered that the composition (2) also contains components that could not be quantified by GC-FID analysis.

[0106] <GC-MS analysis of decomposition liquid> [GC / MS analysis] The compositions containing styrene dimer and styrene trimer, which are the raw materials charged in the styrene monomer production method, and the pyrolysis liquids obtained in the Examples and Comparative Examples were analyzed by preparing methyl ethyl ketone solutions and using GC / MS Agilent 7890 and Agilent 5975 under the following conditions. Column HP-5MS (L 30m, ID 0.250mm, Film 0.25μm) Carrier Helium Detector: MSD EI ionization method Oven temperature: 40℃ (5min hold) → 20℃ / min → 320℃ (10min hold) ·Inlet temperature 250℃ Transfer temperature: 320℃ ·Mass range m / z 10-800 Injection mode: Splitless ·Injection volume 1μL Measurement mode SIM

[0107] <GC-FID analysis of decomposition liquid> [GC-FID analysis] The compositions containing styrene dimer and styrene trimer, which are the raw materials charged in the styrene monomer production method, and the pyrolysis liquids obtained in the examples and comparative examples were analyzed by preparing methyl ethyl ketone solutions and using a GC-FID Agilent 8860 under the following conditions. Column HP-5MS (L 30m, ID 0.250mm, Film 0.25μm) Carrier Helium Detector: FID Oven temperature: 40℃ (5min hold) → 20℃ / min → 320℃ (10min hold) ·Inlet temperature 250℃ Injection mode: Splitless ·Injection volume 1μL

[0108] [Quantitative analysis using GC-FID] The compositions containing styrene dimer and styrene trimer, which are the raw materials used in the styrene monomer production process, and the pyrolysis liquids obtained in the Examples and Comparative Examples were analyzed by preparing methyl ethyl ketone solutions and conducting the GC-FID analysis under the above-mentioned conditions. Quantitative analysis was carried out by the absolute calibration curve method, in which standard samples purchased from a reagent manufacturer were dissolved in methyl ethyl ketone at arbitrary concentrations and a calibration curve was prepared.

[0109] <Styrene monomer yield> The yield of styrene monomer was calculated using the following formulas (1) to (4). [Number 1] (X)=(Y)·(A) Equation (1) (B)=(Y)·(E) Equation (2) (F)=(B)-(X) Equation (3) Styrene monomer yield (%) = [(F)] / [(Y)-(X)]·100 Equation (4) (In the above formulas (1) to (4), (X) represents the mass (g) of styrene monomer in the composition containing styrene dimer and / or styrene trimer, (Y) represents the mass (g) of the composition containing styrene dimer and / or styrene trimer, (A) represents the styrene monomer concentration (% by mass) in the composition containing styrene dimer and / or styrene trimer, (B) represents the weight (g) of styrene monomer in the second pyrolysis liquid, (E) represents the styrene monomer concentration (% by mass) in the second pyrolysis liquid, and (F) represents the increase in the amount of styrene monomer before and after the first pyrolysis (g).)

[0110] "Examples 1 to 16" The first pyrolysis step (S1) was carried out using a prepared composition containing styrene dimer and / or styrene trimer under the pyrolysis conditions shown in the Examples of Table 1-1. A first pyrolysis liquid was prepared by condensing the gas generated by the first pyrolysis step (S1) in a cooling tube cooled to -10°C. The first pyrolysis liquid was then analyzed by GC-FID, and the styrene monomer concentration (mass%) and styrene monomer yield in the first pyrolysis liquid are shown in the Examples of Table 1-1.

[0111] "Comparative Examples 1 to 4" A pyrolysis step was carried out using the prepared composition containing styrene dimer and / or styrene trimer under the pyrolysis conditions shown in the comparative examples in Table 1-2. The gas generated by the pyrolysis was condensed in a cooling tube cooled to -10°C to obtain a pyrolysis liquid. The pyrolysis liquid was then analyzed by GC-FID, and the styrene monomer concentration (mass%) in the pyrolysis liquid and the styrene monomer yield are shown in the comparative examples in Table 1-1.

[0112] [Table 1-1] [Table 1-2]

Claims

1. A method for producing a styrene monomer, comprising: a first thermal decomposition step of thermally decomposing a composition containing a styrene dimer and / or a styrene trimer under the following conditions (A) and (B) to prepare a first thermal decomposition liquid containing a styrene monomer: (A) a thermal decomposition temperature of 300°C or higher and lower than 700°C; (B) Thermal decomposition pressure is greater than 66 hPa and less than 1013 hPa

2. a second thermal decomposition step in which the polystyrene-based resin composition is thermally decomposed under the following conditions (X) and (Y) to prepare a second thermal decomposition liquid containing a styrene monomer is carried out before the first thermal decomposition step; The method for producing a styrene monomer according to claim 1, wherein the composition containing a styrene dimer and / or a styrene trimer is obtained from the second pyrolysis liquid. (X) a thermal decomposition temperature of 400°C or more and less than 1200°C; (Y) Thermal decomposition pressure is greater than 10 hPa and less than 300 hPa

3. 3. The method for producing a styrene monomer according to claim 1 or 2, further comprising a first distillation step of distilling the first pyrolysis liquid to separate it into a second fraction containing a styrene monomer and a first fraction having a styrene monomer concentration lower than that of the second fraction.

4. 3. The method for producing a styrene monomer according to claim 2, further comprising a second distillation step of distilling the second pyrolysis liquid to separate it into a fourth fraction containing a styrene monomer and a third fraction having a styrene monomer concentration lower than that of the fourth fraction.

5. 5. The method for producing a styrene monomer according to claim 4, further comprising a third distillation step of distilling the fourth fraction 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.

6. The method for producing a styrene monomer according to any one of claims 3 to 5, wherein the composition containing a styrene dimer and / or a styrene trimer is any one of the second thermal decomposition liquid, the fourth fraction, and the sixth fraction.

7. The method for producing a styrene monomer according to any one of claims 1 to 5, further comprising a recovery step of recovering the styrene monomer.

8. 2. The method for producing a styrene monomer according to claim 1, wherein the first pyrolysis step further comprises a cooling step of cooling the gas containing the styrene monomer.

9. 2. The method for producing a styrene monomer according to claim 1, wherein the total content of the styrene dimer and / or styrene trimer contained in the composition is 10 mass% or more based on the total amount of the composition.

10. The method for producing a styrene monomer according to claim 1, wherein the first thermal decomposition pressure is 100 hPa or more and 900 hPa or less.

11. 2. The method for producing a styrene monomer according to claim 1, wherein the total content of styrene dimer, styrene trimer, styrene monomer, benzene, ethylbenzene, α-methylstyrene, and cumene present in the composition is 60 mass% or more based on the total amount of the composition.

12. The first pyrolysis step is a step of preparing a first pyrolysis liquid using a pyrolysis catalyst, 2. The method for producing a styrene monomer according to claim 1, wherein the thermal decomposition catalyst is a compound containing any one of elements classified in Periods 2 to 7 of Groups 1 to 17 of the Periodic Table, which elements have stable isotopes, which exists as a solid at room temperature and normal pressure, and which has a decomposition temperature of 300°C or higher.

13. The method further comprises a first distillation step of distilling the first pyrolysis liquid to separate it into a second fraction containing styrene monomer and a first fraction having a lower styrene monomer concentration than the second fraction, The method for producing a styrene monomer according to claim 2, further comprising a recycling step of making the second fraction part of the second pyrolysis liquid.

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