Styrene monomer composition, method for producing same, and method for producing recycled styrenic resin

Abstract

Recycled styrenic resin compositions obtained by polymerizing recycled styrene monomers produced using conventional methods had significantly lower mass average molecular weights than styrenic resin compositions obtained by polymerizing petroleum-derived styrene monomers. The purpose of the present invention is to provide a styrene monomer composition which contains: a recycled styrene monomer (A) derived from a thermal degradation product of a styrenic resin product; and a thermal degradation compound (B) that is a compound which is derived from the thermal degradation product of a styrenic resin product and which is different from the recycled styrene monomer (A). The boiling point of the thermal degradation compound (B) is 140-150°C. The content of the thermal degradation compound (B) is less than 2 parts by mass relative to 100 parts by mass of styrene monomers in the styrene monomer composition.

Description

Styrene monomer composition, its production method, and production method for recycled styrene resin

[0001] The present invention relates to a styrene monomer composition, a method for producing the same, and a method for producing a recycled styrene-based resin.

[0002] The environmental impact of plastic waste has increased in recent years, and recycling plastic waste is important for reducing waste and improving sustainability.

[0003] Styrene is widely used as a raw material for important plastic products such as polystyrene (PS), which is produced primarily by copolymerization of styrene alone or with other monomers.

[0004] Styrene is a chemically stable molecule, and obtaining high-quality recycled styrene requires removing impurities from discarded styrene-based resin compositions and optimizing reaction conditions, making effective recycling technically difficult.

[0005] Patent Document 1 discloses a method for recycling waste polystyrene products, which is characterized by including a step of subjecting the waste polystyrene products to thermal decomposition treatment to obtain recycled styrene monomer from the waste polystyrene.

[0006] WO2021 / 230312

[0007] However, when used waste polystyrene products are collected, some amount of other resins such as polyethylene and polypropylene are mixed in. In such cases, when recycled styrene monomer produced according to the method disclosed in Patent Document 1 is used, polystyrene (or styrene-based resin) with the desired mass average molecular weight cannot be obtained, and the mass average molecular weight may be significantly lower than when only petroleum-derived styrene monomer is used.

[0008] The present inventors have clarified that pyrolysis compounds derived from the pyrolysis products of styrene-based resin products reduce the mass-average molecular weight of styrene-based resin compositions. As a result of extensive research, they have succeeded in suppressing the reduction in the mass-average molecular weight of styrene-based resin compositions by appropriately controlling the concentration of pyrolysis compounds with boiling points close to that of styrene, thereby completing the present invention.

[0009] [1] An object of the present invention is to provide a styrene monomer composition comprising: a recycled styrene monomer (A) derived from a thermal decomposition product of a styrene-based resin product; and a thermal decomposition compound (B) derived from the thermal decomposition product of the styrene-based resin product and being a compound other than the recycled styrene monomer (A), wherein the boiling point of the thermal decomposition compound (B) is 140°C or higher and 150°C or lower, and the thermal decomposition compound (B) is contained in an amount of less than 2 parts by mass per 100 parts by mass of styrene monomer in the styrene monomer composition.

[0010] By using the present styrene monomer composition, the recycled styrene-based resin, which is a polymer thereof, can be prevented from decreasing in mass average molecular weight, as compared with conventional recycled styrene-based resins.

[0011] [2] In the styrene monomer composition according to [1], the styrene-based resin product may further contain an ethylene-based resin and / or a paraffin-based hydrocarbon.

[0012] [3] In the styrene monomer composition according to [1] or [2], the thermally decomposed compound (B) may contain at least one of a linear olefin and a linear diolefin having 9 or less carbon atoms.

[0013] [4] In the styrene monomer composition according to any one of [1] to [3], the thermally decomposable compound (B) may be at least one of 1-nonene and 1,8-nonadiene.

[0014] [5] The styrene monomer composition according to any one of [1] to [4] may further contain a petroleum-derived fresh styrene monomer (C).

[0015] [6] Another object of the present invention is to provide a recycled styrene-based resin, which is a polymer of the styrene monomer composition according to any one of [1] to [5].

[0016] The recycled styrene-based resin, which is a polymer of the present styrene monomer composition, can suppress the decrease in mass average molecular weight compared to conventional recycled styrene-based resins.

[0017] [7] Another object of the present invention is to provide a method for producing a recycled styrene-based resin, comprising a polymerization step of polymerizing the styrene monomer composition according to any one of [1] to [5].

[0018] By using this method, it is possible to produce a recycled styrene-based resin in which the decrease in mass average molecular weight is suppressed compared to conventional recycled styrene-based resins.

[0019] [8] Another object of the present invention is to provide a method for producing a styrene monomer composition, comprising an adjusting step of adjusting styrene monomer units in the styrene-based resin product to 85 parts by mass or more per 100 parts by mass of the styrene-based resin product before thermal decomposition of the styrene-based resin product, and obtaining the adjusted styrene-based resin product.

[0020] By using this method, it is possible to obtain a styrene-based resin product in which the styrene monomer units in the styrene-based resin product before thermal decomposition have been adjusted.

[0021] DEFINITIONS For convenience, certain terms used in this application are collected here. Unless defined otherwise, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The singular forms "a," "an," and "the" include plural references unless the context clearly dictates otherwise.

[0022] Although the numerical ranges and parameters set forth in the present invention are approximate, the numerical values ​​set forth in the specific examples are reported as precisely as possible. However, any numerical value inherently contains certain errors necessarily resulting from the standard deviation found in each test measurement. Also, as used herein, the term "about" generally means within ±10%, ±5%, ±1%, or ±0.5% of a given value or range. Alternatively, the term "about" means within an acceptable standard error as considered by one of ordinary skill in the art.

[0023] Hereinafter, embodiments of the present invention will be described. The following embodiments are merely examples, and the scope of the present invention is not limited to the following embodiments. Note that similar content will not be described again to avoid repetition.

[0024] <Styrene Monomer Composition> The styrene monomer composition contains recycled styrene monomer (A) and a thermally decomposed compound (B). The recycled styrene monomer (A) is derived from a thermal decomposition product of a styrene-based resin product. The thermally decomposed compound (B) is derived from a thermal decomposition product of a styrene-based resin product and is a compound other than the recycled styrene monomer (A). The styrene monomer composition can be used in bulk polymerization or solution polymerization, which are conventional methods for producing styrene-based resins, and can be used as a raw material for producing recycled styrene-based resins. The styrene monomer composition may further contain petroleum-derived styrene monomer (fresh styrene monomer (C)).

[0025] Here, the term "styrene resin product" refers to a resin product containing a styrene resin, and refers to a resin product manufactured using a styrene resin or partially using a styrene resin. The styrene resin product may be a styrene resin product that is no longer needed, regardless of whether it is usable or not (which may be referred to as a waste styrene resin product (or a waste styrene resin product)). The styrene resin product may have any shape, such as the shape when unused, the shape when used, or the shape when discarded, and may be partially missing or may be a crushed product. The styrene resin product includes the prepared styrene resin product described below.

[0026] <Recycled Styrene Monomer (A)> The recycled styrene monomer (A) is a styrene monomer (pyrolyzed styrene monomer) recovered from a pyrolysis product obtained by pyrolyzing a styrene-based resin product, and may be used in combination with a petroleum-derived styrene monomer (fresh styrene monomer (C)).

[0027] <Thermal Decomposition Compound (B)> The thermal decomposition compound (B) is an impurity other than thermally decomposed styrene monomer, which is recovered from a thermal decomposition product obtained by thermally decomposing a styrene-based resin product, and which has a boiling point of 140°C or higher and 150°C or lower (for example, an impurity having a boiling point within a range between any two values ​​selected from 140, 141, 142, 143, 144, 145, 146, 147, 148, 149, and 150°C).

[0028] The thermally decomposable compound (B) is contained in an amount of less than 2.0 parts by mass (e.g., less than 1.5 parts by mass, less than 1.0 part by mass, less than 0.5 parts by mass, and less than 0.1 parts by mass) relative to 100 parts by mass of the styrene monomer in the styrene monomer composition. In an embodiment, the thermally decomposable compound (B) is contained in an amount of 0.001 parts by mass or more and less than 2.0 parts by mass (e.g., 0.01 parts by mass or more and less than 2.0 parts by mass (e.g., less than 1.5 parts by mass, less than 1.0 part by mass, less than 0.5 parts by mass, and less than 0.1 parts by mass) relative to 100 parts by mass of the styrene monomer in the styrene monomer composition.

[0029] When the recycled styrene monomer (A) derived from the pyrolysis product of a styrene-based resin product and the fresh styrene monomer (C) are mixed, it is preferable to mix them so that the amount of the pyrolysis compound (B) is less than 2.0 parts by mass per 100 parts by mass of the styrene monomer in the styrene monomer composition, since this can suppress a decrease in the mass average molecular weight of the recycled styrene-based resin obtained by polymerizing the styrene monomer composition.

[0030] The styrene-based resin product may further contain a thermoplastic resin other than a styrene-based resin, and / or additives such as a paraffin-based hydrocarbon, an antioxidant, an antistatic agent, a lubricant, a mold release agent, and a hydrophilic additive. In an embodiment, the styrene-based resin product further contains an ethylene-based resin and / or a paraffin-based hydrocarbon.

[0031] In one embodiment, the thermally decomposed compound (B) includes at least one of a linear olefin and a linear diolefin having 9 or less carbon atoms. The thermally decomposed compound (B) is preferably removed from the recycled styrene monomer (A) in a distillation purification step in which the recycled styrene monomer (A) is recovered from the thermal decomposition product of a styrene-based resin product. However, the thermally decomposed compound (B) having a boiling point of 140°C or higher and 150°C or lower is difficult to remove from the styrene monomer, which has a boiling point close to the boiling point. In particular, the linear olefins and linear diolefins having 9 carbon atoms (e.g., 1-nonene and 1,8-nonadiene), which are decomposition products of ethylene-based resins and / or paraffinic hydrocarbons, have boiling points of 140°C or higher and 150°C or lower, and are difficult to remove from the styrene monomer.

[0032] When the olefin compound and diolefin compound are contained in an amount of 2 parts by mass or more per 100 parts by mass of styrene monomer in the styrene monomer composition, a chain transfer effect occurs when the styrene monomer composition is polymerized, and the mass average molecular weight of the recycled styrene-based resin is significantly reduced.

[0033] <Method for producing styrene monomer composition> The method for producing a styrene monomer composition of the present embodiment includes a mixing step of mixing fresh styrene monomer (C) with a mixture containing recycled styrene monomer (A) and a thermally decomposed compound (B) so that the amount of the thermally decomposed compound (B) is less than 2 parts by mass per 100 parts by mass of styrene monomer in the styrene monomer composition.

[0034] In the mixing step of this embodiment, the recycled styrene monomer (A) may be further mixed with a residual styrene monomer composition that has a different concentration of the thermally decomposed compound (B) and that remains without being involved in the polymerization in the polymerization step of polymerizing the styrene monomer composition.

[0035] The method for producing a styrene monomer composition of the present embodiment may also include an adjustment step (1) of adjusting the styrene monomer units in the styrene-based resin product to 85 parts by mass or more per 100 parts by mass of the styrene-based resin product before thermal decomposition of the styrene-based resin product, and obtaining the adjusted styrene-based resin product.

[0036] In one embodiment, the method for producing a styrene monomer composition further comprises a thermal decomposition step (2) of thermally decomposing the prepared styrene-based resin product to obtain a thermal decomposition product. In one embodiment, the method for producing a styrene monomer composition further comprises a distillation purification step (3) of distilling and purifying the thermal decomposition product. In one embodiment, the thermal decomposition product is oily (also referred to as pyrolysis oil).

[0037] Furthermore, in the above step (1) or (2), alkaline earth oxides and / or hydroxides, iron oxides, and / or aluminum oxides, etc. may be added to the styrene-based resin product or the prepared styrene-based resin product, as needed, thereby obtaining a pyrolysis product with low chlorine, nitrogen, and sulfur contents.

[0038] (Preparation Step (1)) In the preparation step (1), the preparation may be carried out by blending with polystyrene (GPPS) and / or a styrene-based resin product having a known styrene monomer unit concentration. The blending method is not particularly limited, and may be tumble blending or melt mixing.

[0039] By adjusting the styrene monomer units in the styrene-based resin product to 85 parts by mass or more per 100 parts by mass of the styrene-based resin product before thermally decomposing the styrene-based resin product, the amount of thermally decomposed compound (B) generated can be suppressed. Therefore, by feeding the styrene monomer composition to a polymerization plant for recycled styrene-based resin, the amount of unpolymerized compounds including the thermally decomposed compound (B) concentrated in the recovery tank of the plant can be suppressed, and a decrease in the mass average molecular weight of the recycled styrene-based resin after polymerization can be suppressed, which is preferable.

[0040] (Pyrolysis Step (2)) In the pyrolysis step (2) of pyrolyzing the prepared styrene-based resin product to obtain a pyrolysis product, for example, the prepared styrene-based resin product is preferably supplied to a pyrolysis furnace and heated to a temperature of 400 to 800°C in a non-oxidizing atmosphere. The non-oxidizing atmosphere is preferably an inert gas atmosphere such as nitrogen, water vapor, carbon dioxide, or argon, or a negative pressure atmosphere. The pyrolysis gas generated at this time is sent to a condenser and condensed to become pyrolysis oil (pyrolysis product), which is then sent to a distillation purification step (3) in which the pyrolysis oil is purified by distillation.

[0041] (Distillation purification step (3)) In the distillation purification step (3) for distilling and purifying the pyrolysis product, for example, it is preferable to use two distillation columns, and separate compounds having a boiling point lower than that of styrene in the first distillation column and compounds having a boiling point higher than that of styrene in the second distillation column.

[0042] <Recycled styrene-based resin> The recycled styrene-based resin is a polymer having styrene-based monomer units obtained by polymerizing a recycled styrene monomer composition. The recycled styrene-based resin preferably has more than 15% by mass and 100% by mass or less of styrene-based monomer units in 100% by mass of the polymer having styrene-based monomer units. In one aspect, the recycled styrene-based resin may be a polymer of a styrene-based monomer (styrene-based polymer). In one aspect, the recycled styrene-based resin may be a copolymer having styrene-based monomer units and (meth)acrylic monomer units (styrene-(meth)acrylic copolymer).

[0043] The styrene-based polymer may be a styrene-based monomer homopolymer obtained by polymerizing only one type of styrene-based monomer, or a copolymer obtained by polymerizing only two or more types of styrene-based monomer. Furthermore, the styrene-based polymer preferably contains 95% by mass or more of styrene-based monomer units, more preferably (substantially) 100% by mass, of the styrene-based polymer. The content of the styrene-based monomer units in 100% by mass of the styrene-based polymer is, for example, 95, 96, 97, 98, 99, 99.5, or 100% by mass, and may be within a range between any two of the values ​​exemplified here. Note that when two or more types of styrene-based monomer units are used, the content refers to the total mass. From the viewpoint of minimizing dimensional change, the styrene-based polymer is preferably a styrene homopolymer.

[0044] The (meth)acrylic monomer unit is a (meth)acrylic acid monomer unit or a (meth)acrylic acid ester monomer unit. The styrene-(meth)acrylic copolymer is a styrene-(meth)acrylic acid copolymer or a styrene-(meth)acrylic acid ester copolymer.

[0045] <Method for Producing Recycled Styrenic Resin> The method for producing a recycled styrene-based resin according to this embodiment includes a polymerization step of polymerizing the styrene monomer composition.

[0046] Polymerization methods for producing recycled styrene-based resins include known styrene polymerization methods such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization. From the standpoints of quality and productivity, bulk polymerization and solution polymerization are preferred, and continuous polymerization is preferred. Examples of solvents that can be used include alkylbenzenes such as benzene, toluene, ethylbenzene, and xylene, ketones such as acetone and methyl ethyl ketone, and aliphatic hydrocarbons such as hexane and cyclohexane.

[0047] During polymerization of the styrene monomer composition, polymerization aids such as a polymerization initiator, a chain transfer agent, a crosslinking agent, and other polymerization aids may be used as necessary. The polymerization initiator is preferably a radical polymerization initiator, and examples of the polymerization initiator include peroxyketals such as 1,1-di(t-butylperoxy)cyclohexane, 2,2-di(t-butylperoxy)butane, 2,2-di(4,4-di-t-butylperoxycyclohexyl)propane, and 1,1-di(t-amylperoxy)cyclohexane, hydroperoxides such as cumene hydroperoxide and t-butyl hydroperoxide, alkyl peroxides such as t-amylperoxyisononanoate, and dialkyl peroxides such as t-butylcumyl peroxide, di-t-butyl peroxide, dicumyl peroxide, and di-t-hexyl peroxide. Examples of the peroxides include peroxyesters such as t-butylperoxyacetate, t-butylperoxybenzoate, and t-butylperoxyisopropyl monocarbonate; peroxycarbonates such as t-butylperoxyisopropyl carbonate and polyether tetrakis(t-butylperoxycarbonate); N,N'-azobis(cyclohexane-1-carbonitrile), N,N'-azobis(2-methylbutyronitrile), N,N'-azobis(2,4-dimethylvaleronitrile), and N,N'-azobis[2-(hydroxymethyl)propionitrile]; and these may be used alone or in combination of two or more. Examples of chain transfer agents include aliphatic mercaptans such as n-dodecyl mercaptan and tert-dodecyl mercaptan, aromatic mercaptans, thiocarboxylic acids such as thioglycolic acid and mercaptopropionic acid, polyfunctional mercaptans in which the hydroxyl group of a polyhydric alcohol such as ethylene glycol, tetraethylene glycol, neopentyl glycol, trimethylolpropane, pentaerythritol, dipentaerythritol, tripentaerythritol, or sorbitol is esterified with thioglycolic acid or mercaptopropionic acid, pentaphenylethane, α-methylstyrene dimer, and terpinolene. Among these, aliphatic mercaptans, aromatic mercaptans, thiocarboxylic acids, and polyfunctional mercaptans are preferred from the viewpoint of ease of molecular weight adjustment.

[0048] In the case of continuous polymerization, recycled styrene-based resins can be produced by a method including a polymerization step, a devolatilization step, and a granulation step.

[0049] First, in the polymerization step, a known complete mixing tank type agitation tank or tower type reactor is used, and the polymerization reaction is controlled by adjusting the polymerization temperature etc. so as to achieve the target molecular weight, molecular weight distribution and reaction conversion rate.

[0050] The polymer solution containing the polymer that has left the polymerization process is transferred to the devolatilization process, where unreacted monomers and polymerization solvent are removed. The devolatilization process is composed of a vacuum devolatilization tank equipped with a heater or a devolatilization extruder equipped with a vent. The molten polymer that has left the devolatilization process is transferred to the granulation process. In the granulation process, the molten resin is extruded in the form of strands through a multi-hole die and processed into pellets using the cold cut method, the in-air hot cut method, or the underwater hot cut method.

[0051] The present invention will be described in more detail below with reference to examples, but these examples are merely illustrative and are not intended to limit the scope of the present invention.

[0052] Examples 1 to 6 and Comparative Examples 1 to 7 Styrene Monomer Compositions Styrene-based resin products containing various ratios of styrene-based resin and ethylene-based resin were prepared by tumble blending and thermally decomposed at approximately 550°C under a nitrogen atmosphere in accordance with the thermal decomposition apparatus described in JP 2021-134281 A. The resulting pyrolysis product was subjected to a distillation process, and the styrene monomer was separated and purified in a first distillation column and a second distillation column to recover a styrene monomer composition. Various styrene monomer compositions with different concentrations of the thermal decomposition compound (B) and fresh styrene monomer were mixed to achieve the composition ratios shown in Table 1. Recycled Styrene-Based Resins Recycled styrene-based resins were prepared under the conditions shown in Table 1 as follows. The first and second reactors, which were complete mixing stirred tanks, and the third reactor, a plug-flow reactor equipped with a static mixer, were connected in series to form a polymerization process, and styrene resins were produced under the conditions shown in Table 1. The volumes of the first reactor, second reactor, and third reactor were 39 liters, 39 liters, and 16 liters, respectively. A raw material solution was prepared using the raw material composition shown in Table 1, and the raw material solution was continuously supplied to the first reactor at the flow rate shown in Table 1. The polymerization initiator was added to the raw material solution at the inlet of the first reactor to achieve the addition concentration (concentration by mass relative to the total amount of raw material monomer (styrene)) shown in Table 1, and the mixture was mixed uniformly.

[0053] The polymerization initiators listed in Table 1 are as follows: Polymerization initiator: 2,2-di(4,4-t-butylperoxycyclohexyl)propane [Pertetra A manufactured by NOF Corporation]

[0054] In the third reactor, a temperature gradient was applied along the direction of flow, and the temperatures at the intermediate portion and outlet portion were adjusted to be those shown in Table 1. Subsequently, the polymer-containing solution continuously removed from the third reactor was introduced into a vacuum devolatilizer tank equipped with a preheater, which was configured of two stages in series, and the temperature of the preheater was adjusted to give a resin temperature shown in Table 1, and the pressure was adjusted to be that shown in Table 1, thereby separating unreacted styrene and ethylbenzene. The polymer was then extruded into strands through a multi-hole die, and the strands were cooled and cut by a cold-cut method to be pelletized.

[0055] <Weight Average Molecular Weight (Mw)> The weight average molecular weight (Mw) of the recycled styrene-based resin was measured using gel permeation chromatography (GPC) under the following conditions. The measurement results are shown in Table 1. GPC model: Shodex GPC-101 manufactured by Showa Denko K.K. Column: PLgel 10 μm MIXED-B manufactured by Polymer Laboratories, Inc. Mobile phase: tetrahydrofuran Sample concentration: 0.2 mass% Temperature: oven 40°C, injection port 35°C, detector 35°C Detector: differential refractometer The molecular weight was calculated as a polystyrene-equivalent molecular weight by calculating the molecular weight at each elution time from the elution curve of monodisperse polystyrene.

[0056] <Mw Decay Rate Compared to Example 1> The Mw ratio (%) compared to Example 1 was calculated by [Mw of each recycled styrene-based resin (×10 ４ ) / Mw of Example 1 (× 10 ４ ) ], and the Mw reduction rate (%) relative to Example 1 is calculated based on [100 - Mw ratio (%) relative to Example 1].

[0057]

[0058] When the thermally decomposed compound (B) was contained in an amount of less than 2 parts by mass relative to 100 parts by mass of the styrene monomer in the styrene monomer composition (Examples 2 to 5), the Mw decay rates of Examples 2 to 5 relative to Example 1 were at most 2.9%, which enabled the suppression of a decrease in the mass average molecular weight of the recycled styrene-based resin. On the other hand, when the thermally decomposed compound (B) was contained in an amount of 2 parts by mass or more relative to 100 parts by mass of the styrene monomer in the styrene monomer composition (Comparative Examples 1 to 7), the Mw decay rates of Comparative Examples 1 to 7 relative to Example 1 were at least 4.2%, which was larger than that of the Examples, and therefore the mass average molecular weight of the recycled styrene-based resin was significantly reduced.

Claims

1. A styrene monomer composition comprising: a recycled styrene monomer (A) derived from a thermal decomposition product of a styrene-based resin product; and a thermal decomposition compound (B) derived from the thermal decomposition product of the styrene-based resin product and being a compound other than the recycled styrene monomer (A), wherein the boiling point of the thermal decomposition compound (B) is 140°C or higher and 150°C or lower, and the styrene monomer composition contains less than 2 parts by mass of the thermal decomposition compound (B) per 100 parts by mass of styrene monomer in the styrene monomer composition.

2. The styrene monomer composition according to claim 1, wherein the styrene-based resin product further comprises an ethylene-based resin and / or a paraffin-based hydrocarbon.

3. The styrene monomer composition according to claim 1, wherein the thermally decomposed compound (B) contains at least one of a linear olefin and a linear diolefin having 9 or less carbon atoms.

4. The styrene monomer composition according to claim 1, wherein the thermally decomposable compound (B) is at least one of 1-nonene and 1,8-nonadiene.

5. The styrene monomer composition according to claim 1, further comprising petroleum-derived fresh styrene monomer (C).

6. A recycled styrene-based resin which is a polymer of the styrene monomer composition according to claim 1.

7. A method for producing a recycled styrene-based resin, comprising a polymerization step of polymerizing the styrene monomer composition according to claim 1.

8. A method for producing a styrene monomer composition, comprising an adjustment step of adjusting the styrene monomer units in the styrene resin product to 85 parts by mass or more per 100 parts by mass of the styrene resin product before thermally decomposing the styrene resin product, and obtaining the adjusted styrene resin product.

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