KR102525838B1 - Method for Recovering Styrene Monomer from Waste Polystyrene - Google Patents

Abstract

The present invention relates to a method for recovering styrene monomer from waste polystyrene, and more particularly, by depolymerizing waste polystyrene using an environmentally friendly solvent and a potassium-containing carbonate depolymerization catalyst, thereby recovering ethylbenzene as a by-product in the recovery process of styrene monomer. The present invention relates to a method for recovering styrene monomer from waste polystyrene capable of recovering styrene monomer in high yield by suppressing the production of the like.

Description

Method for recovering styrene monomer from waste polystyrene {Method for Recovering Styrene Monomer from Waste Polystyrene}

The present invention relates to a method for recovering styrene monomer from waste polystyrene, and more particularly, to a method for recovering styrene monomer by depolymerizing waste polystyrene in the presence of a catalyst, wherein by-products generated by side reactions are suppressed to obtain high yield and high purity It relates to a method for recovering styrene monomer from waste polystyrene, characterized in that styrene monomer is recovered.

Along with industrial development, a large amount of plastic is being used all over the world, and Korea produced more than 7 million tons of general-purpose plastic products last year, becoming the world's fourth largest plastic producer. However, plastics are discarded in large quantities after use, causing many environmental problems. Although waste plastics are currently mainly disposed of by landfill, they have a long biodegradation time in soil and cause serious environmental problems due to the lack of landfills.

Although various methods have been proposed for the treatment of waste plastics, the method of reusing them as fuel oil and raw materials with added value rather than simple physical addition or processing is considered the most desirable method in terms of environmental problems and economics. Recycling methods of waste plastics are divided into a method of recycling raw plastics as they are or after processing (material recycle), a method of recovering chemicals such as thermal recycling (thermal recycle) such as incineration, and a method of recovering chemicals such as resin raw materials (chemical recycle).

In the case of the physical recycling method, it is mainly recycled for the production of recycled resin, lightweight concrete, adhesive manufacturing, etc., but as a physical recycling method, its added value is very low, and it cannot be recycled after several physical regenerations, so a large amount of waste polystyrene is eventually Occurs. In addition, a large amount of contaminated waste polystyrene discharged as agricultural and fishery products market or construction waste is not clean compared to other waste polystyrene, so it is difficult to use it as a physical recycling method.

Moreover, a large amount of contaminated waste polystyrene has a volume about 50 times larger than that of other waste polystyrene, so physical recycling is difficult, so it is disposed of by landfill or incineration. However, the incineration method has a problem of causing environmental problems such as dioxin generation.

Accordingly, a chemical regeneration method is attracting attention, and the recovery technology of styrene, a monomer from waste polystyrene, was first tried by Nishizaki et al. in 1997, and about 50% of the monomer was recovered from polystyrene by thermal decomposition at 733 K. reported. Based on this technology, in order to increase the yield of styrene monomer, many researchers have studied the influence of various catalysts and many catalysts have been developed.

As a method for recovering styrene monomer using the catalyst, a technique for recovering styrene monomer using a metal oxide such as highly acidic Co ₃ O ₄ , Fe ₂ O ₃ , Cr ₂ O ₃ , or CuO as a catalyst (non-patented Document 0001), a technology for recovering styrene monomer using a sulfate catalyst (Patent Documents 0001 and 0002), a two-way catalyst technology prepared by supporting a metal oxide as a main catalyst and a basic catalyst as a cocatalyst on silica and alumina, respectively (Patent Documents 0001 and 0002) 0003) have been suggested.

However, when metal oxides such as Co ₃ O ₄ , Fe ₂ O ₃ , Cr ₂ O ₃ , and CuO, which are highly acidic, are used as catalysts as in Non-Patent Document 0001, polystyrene single (CC) bonds are cleaved to form carcinogens. A carboanion is generated, and styrene is separated in a chain, and the thermal decomposition reaction proceeds. However, since the carbocation is unstable due to a lack of two electrons, it causes side reactions such as attacking the surrounding benzene ring, resulting in the yield of styrene monomer. I had a problem with this falling off.

On the other hand, when a basic catalyst such as BaO, K ₂ O, MgO, ZnO, or CaO or a sulfate catalyst is used, it satisfies the octet law to generate a stable carboanion without electron deficiency and chain Although the thermal decomposition reaction proceeds with the separation of styrene, there is a problem in that the selectivity of the styrene monomer is lowered by increasing ethylbenzene or alpha methyl styrene as a by-product.

In particular, ethylbenzene has a similar boiling point to styrene monomer, which is the final target material, and thus has a great impact on economic feasibility as the cost required for separating commercially available high-purity (>99.6%) styrene monomer increases.

Therefore, there is a need for a new recovery method for recovering styrene as a monomer from waste polystyrene in high yield/purity.

Japanese Patent Laid-Open No. 2001-294708 (Publication date: 2001.10.23) Korean Patent Publication No. 2001-87093 (published date: 2001.09.15) Korean Patent Publication No. 2003-0081717 (published date: 2003.10.22)

Ind. Eng. Res., Vol. 34, no. 12, 1995, 4519

The main object of the present invention is to solve the above-mentioned problems, and to suppress the production of ethylbenzene, alphamethylstyrene, benzene, toluene, etc. generated as a side reaction in the conventional waste polystyrene recovery process to recover styrene monomer in high yield is to provide a way

Among them, it is intended to increase the ease of separation of styrene monomer from depolymerization products of waste polystyrene by suppressing generation of ethylbenzene, which has a similar boiling point to that of styrene monomer and is difficult to separate.

In order to achieve the above object, one embodiment of the present invention is (a) adding at least one solvent selected from tetrahydrofuran and methyltetrahydrofuran and at least one depolymerization catalyst selected from potassium carbonate and potassium hydrogen carbonate to waste polystyrene. adding to obtain a mixture in which polystyrene is dissolved; (b) separating and recovering the solvent by distilling the polystyrene-dissolved mixture; and (c) depolymerizing the mixture recovered from solvent separation obtained in step (b) to obtain a product containing styrene monomer, wherein the product for styrene monomer (SM) in the product obtained in step (c) Provided is a method for recovering styrene monomer from waste polystyrene, characterized in that the weight ratio (SM/EB) of ethylbenzene (EB) is 80 or more.

In a preferred embodiment of the present invention, in step (a), tetrahydrofuran and/or methyltetrahydrofuran may be added in an amount of 100 parts by weight to 200 parts by weight based on 100 parts by weight of waste polystyrene.

In a preferred embodiment of the present invention, step (a) may be performed at room temperature and pressure.

In a preferred embodiment of the present invention, the distillation in step (b) may be performed at 80 °C to 250 °C.

In a preferred embodiment of the present invention, the depolymerization in step (c) may be performed at 200 °C to 600 °C.

In a preferred embodiment of the present invention, in step (c), potassium carbonate and/or potassium hydrogen carbonate may be present in an amount of 1 to 10 parts by weight based on 100 parts by weight of waste polystyrene.

In a preferred embodiment of the present invention, tetrahydrofuran and/or methyltetrahydrofuran, which are solvents separated in step (b), may be reused for dissolving waste polystyrene in step (a).

The method for recovering styrene monomer from waste polystyrene of the present invention depolymerizes polystyrene with a combination of a specific solvent and a specific catalyst, thereby suppressing the production of ethylbenzene, etc., which is produced as a by-product in the recovery process of styrene monomer, and thereby recovering the recovered styrene monomer. yield can be increased.

In addition, since the solvent used in the present invention is an eco-friendly solvent with a low boiling point, environmental pollution caused by the use of conventional toxic organic solvents such as toluene is prevented and recovery costs for solvent reuse are reduced.

1 is a schematic process diagram showing a method for recovering styrene monomer from waste polystyrene according to an embodiment of the present invention.
Figure 2 is a graph showing the yield of products produced in Examples 1 and 2 and Comparative Examples 1 to 5 according to the present invention.
3 is a graph showing the weight ratio of ethylbenzene to styrene monomer produced in Examples 1 and 2 and Comparative Examples 1 to 5 according to the present invention.
4 shows K ₂ CO ₃ in a pristine state and This is a graph of XRD measurement results of K ₂ CO ₃ obtained after solvent evaporation in a mixture prepared by dissolving 5 g of K ₂ CO ₃ in 100 ml of THF and 100 ml of toluene, respectively.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In general, the nomenclatures used herein are those well known and commonly used in the art.

When it is said that a certain part "includes" a certain component throughout the present specification, it means that it may further include other components without excluding other components unless otherwise stated.

'Waste polystyrene' described in this specification means to include discarded polystyrene after being used in various industrial fields, and may be applied regardless of their shape, use, and the like.

'Atmospheric temperature' described herein may be 20 ± 10 °C as a normal atmospheric temperature, and 'atmospheric pressure' means a normal atmospheric pressure.

Terms such as 'include', 'include' or 'has' described in this specification refer to the presence of features, values, steps, operations, components, parts, or combinations thereof described in the specification. It does not rule out the possibility that other features, figures, steps, operations, components, parts, or combinations thereof may exist or be added that have not been described.

(a) obtaining a polystyrene-dissolved mixture by adding at least one solvent selected from tetrahydrofuran and methyltetrahydrofuran and at least one depolymerization catalyst selected from potassium carbonate and potassium hydrogen carbonate to waste polystyrene; (b) separating and recovering the solvent by distilling the polystyrene-dissolved mixture; and (c) depolymerizing the mixture recovered from solvent separation obtained in step (b) to obtain a product containing styrene monomer, wherein the product for styrene monomer (SM) in the product obtained in step (c) It relates to a method for recovering styrene monomer from waste polystyrene, characterized in that the weight ratio (SM/EB) of ethylbenzene (EB) is 80 or more. In addition, the yield of styrene monomer by the method according to the present invention exceeds 70 wt%.

More specifically, the method for recovering styrene monomer according to an embodiment of the present invention is a combination of tetrahydrofuran and/or methyltetrahydrofuran, which are eco-friendly solvents derived from biomass, and potassium carbonate and/or potassium hydrogen carbonate, which are depolymerization catalysts, to obtain polystyrene. By depolymerizing the styrene monomer, the yield of recovered styrene monomer can be increased by suppressing the production of ethylbenzene, etc., which is produced as a by-product in the recovery process of styrene monomer, and at the same time, when the waste polystyrene is dissolved, a depolymerization catalyst is added simultaneously with the solvent to obtain waste polystyrene. By dissolving, the efficiency of depolymerization of waste polystyrene can be increased by uniform dispersion of the depolymerization catalyst in the solvent phase.

Hereinafter, a preferred embodiment of a method for recovering styrene monomer from waste polystyrene according to the present invention will be described in detail with reference to the accompanying drawings.

1 is a schematic process diagram showing a method for recovering styrene monomer from waste polystyrene according to an embodiment of the present invention.

Referring to FIG. 1, in the method for recovering styrene monomer from waste polystyrene according to an embodiment of the present invention, first, tetrahydrofuran and/or methyltetrahydrofuran and potassium carbonate and/or potassium hydrogen carbonate are added to waste polystyrene at room temperature and pressure. was added and stirred to obtain a mixture in which polystyrene was dissolved [step (a)].

In the present invention, tetrahydrofuran (THF), methyltetrahydrofuran (MTHF), and mixtures thereof are used as solvents for dissolving waste polystyrene.

While tetrahydrofuran (THF) and methyltetrahydrofuran (MTHF) have high solubility in polystyrene, they have low solubility in other synthetic resins such as polypropylene and polyethylene, do not ignite, have high vaporization points, and are bio It is manufactured in a mass and has very eco-friendly properties, so it can completely dissolve waste polystyrene in a short time even under normal temperature and pressure without changing the physical properties of polystyrene itself, improving volume reduction efficiency.

In addition, there may be toluene, styrene, benzene, xylene, limonene, etc. as solvents capable of dissolving conventional polystyrene, but their solubility in polystyrene is low, and they are highly toxic to the human body, so there may be problems from an environmental point of view. However, since the boiling point is almost similar to that of the styrene monomer, as the amount thereof increases, the cost required for separation of the styrene monomer increases, which affects economic feasibility.

Accordingly, in the present invention, by dissolving waste polystyrene using tetrahydrofuran, methyltetrahydrofuran, and mixtures thereof, waste polystyrene can be completely dissolved in a short time even at room temperature and normal pressure to improve volume reduction efficiency, and the solvent has a high vaporization point. In the collection process, it is possible to prevent environmental pollution and solvent loss due to natural evaporation, and also to increase the ease of work processes such as solvent recovery, which will be described later.

The tetrahydrofuran and/or methyltetrahydrofuran may be added in an amount of 100 parts by weight to 200 parts by weight based on 100 parts by weight of waste polystyrene. If the amount of tetrahydrofuran and/or methyltetrahydrofuran is less than 100 parts by weight based on 100 parts by weight of waste polystyrene, the reduction in polystyrene may not be sufficient, and if it exceeds 200 parts by weight, the recovery cost of the solvent may increase. .

On the other hand, potassium carbonate (K ₂ CO ₃ ) and/or potassium hydrogen carbonate (KHCO ₃ ) is a thermal decomposition catalyst that promotes a thermal decomposition reaction, and since it is stable at high temperatures, the catalyst stability is high and recovery is easy.

In addition, the potassium carbonate (K ₂ CO ₃ ) and/or potassium hydrogen carbonate (KHCO ₃ ) are added to polystyrene at the same time as tetrahydrofuran and/or methyltetrahydrofuran when polystyrene is dissolved. Therefore, the aggregation of the catalyst can be prevented, and the polystyrene depolymerization efficiency can be improved as it is uniformly dispersed in tetrahydrofuran and/or methyltetrahydrofuran together with polystyrene.

In this case, the potassium carbonate (K ₂ CO ₃ ) and/or potassium hydrogen carbonate (KHCO ₃ ) may be present in an amount of 1 to 10 parts by weight based on 100 parts by weight of the waste polystyrene. When the potassium carbonate (K ₂ CO ₃ ) and/or potassium hydrogen carbonate (KHCO ₃ ) is present in less than 1 part by weight based on 100 parts by weight of waste polystyrene, the reactivity is greatly reduced and the amount of ethylbenzene is greatly increased. may occur, and when it exceeds 10 parts by weight, there may be a problem in that the cost increases without a difference in reactivity.

The mixture to which tetrahydrofuran and/or methyltetrahydrofuran and potassium carbonate (K ₂ CO ₃ ) and/or potassium hydrogen carbonate (KHCO ₃ ) are added may be stirred at room temperature and normal pressure to dissolve waste polystyrene. At this time, when the waste polystyrene is completely dissolved in the solvent, it is allowed to stand temporarily to precipitate foreign substances such as flame retardants, binders, and coatings other than polystyrene contained in the waste polystyrene, and the precipitated foreign substances can be filtered and removed from the mixture.

On the other hand, in the recovery method of styrene monomer according to an embodiment of the present invention, vinyl, paper, wood chips, food scraps, small stones, etc. attached to the waste polystyrene by a method such as washing the waste polystyrene before the step (a). The method may further include removing impurities from and pulverizing the waste polystyrene into a size suitable for dissolution. At this time, the waste polystyrene to be pulverized may be pulverized to an average particle size of 1.0 cm to 10 cm, which is a size suitable for dissolution.

Then, the polystyrene-dissolved mixture obtained by adding tetrahydrofuran and/or methyltetrahydrofuran and potassium carbonate (K ₂ CO ₃ ) and/or potassium hydrogen carbonate (KHCO ₃ ) is decomposed at the reaction temperature or undergoes a catalytic reaction. Since it can be inhibited, it is distilled to separate and recover the solvent, tetrahydrofuran and/or methyltetrahydrofuran [step (b)].

The distillation may be performed at 80 °C to 250 °C under normal pressure using a conventional distiller. If distillation is performed at less than 80 ° C, tetrahydrofuran and / or methyltetrahydrofuran are not properly separated and recovered from the mixture in which polystyrene is dissolved, and if the temperature exceeds 250 ° C, solvent recovery is difficult due to thermal decomposition of the solvent. Problems may arise.

The separated and recovered tetrahydrofuran and/or methyltetrahydrofuran can be reused for dissolving waste polystyrene in step (a).

Thereafter, the mixture in which tetrahydrofuran and/or methyltetrahydrofuran are separated and polystyrene is dissolved is subjected to depolymerization in the presence of potassium carbonate (K ₂ CO ₃ ) and/or potassium hydrogen carbonate (KHCO ₃ ) to obtain styrene monomer. A contained product is obtained [step (c)].

The depolymerization may be performed at 200 °C to 600 °C for 0.5 to 5 hours. If the depolymerization temperature is less than 200 ° C, depolymerization does not occur and the reactivity may be greatly reduced, and if it exceeds 600 ° C, the amount of benzene and toluene is greatly increased due to the cracking reaction, and the amount of styrene monomer produced is greatly reduced. This may cause a problem that dimers and trimers with high boiling points may be mixed in the product. In addition, when the depolymerization time is less than 0.5 hours, the reaction time is not sufficient, so the recovery of styrene monomer is small. When the depolymerization time exceeds 5 hours, the amount of ethylbenzene increases significantly and energy consumption increases, resulting in reduced productivity. may occur.

Thereafter, the product obtained from the depolymerization reaction may be collected and recovered by cooling. At this time, the cooling method used in the art such as an indirect cooling method or a direct cooling method in which the refrigerant is compressed and evaporated and the collected product is cooled using the evaporation heat of the refrigerant may be used without limitation.

The product obtained in the depolymerization reaction contains not only styrene monomer (SM), which is the final target component, but also ethylbenzene (EB), toluene, cumene, alpha methylstyrene, etc. High boiling point materials and depolymerization reaction residues are generated. These residues not only hinder the depolymerization reaction, but also reduce the yield of styrene monomer, and conventionally, the yield of styrene monomer is reduced during long-term operation.

Therefore, in the method for recovering styrene monomer according to the present invention, the yield of styrene monomer, the final target component, can be recovered by 70% or more by dissolving and depolymerizing waste polystyrene using a potassium-containing carbonate catalyst together with an environmentally friendly solvent, and ethyl Ethylbenzene (EB), toluene, cumene, and alpha methylstyrene can be recovered with a yield of 3.5% or less, respectively. In particular, in the method for recovering styrene monomer according to the present invention, the weight ratio (SM/EB) of styrene monomer (SM) to ethylbenzene (EB) can be set to 80 or more, preferably 84 or more.

That is, the method for recovering styrene monomer according to the present invention is a separation process for recovering the final styrene monomer by suppressing the production of ethylbenzene, alphamethylstyrene, toluene, particularly ethylbenzene, which are produced as side reactions in the conventional styrene monomer recovery process. can facilitate

Hereinafter, the present invention will be described in more detail through specific examples. The following examples are merely examples to aid understanding of the present invention, and the scope of the present invention is not limited thereto.

<Example 1>

After putting 60 g of pulverized waste polystyrene in a reactor that can be opened and closed at room temperature, 100 g of tetrahydrofuran and 3 g of potassium carbonate (K ₂ CO ₃ ) (Sigma-aldrich, ACS reagent > 99%) as a catalyst were added thereto, The mixture was added and stirred at room temperature and pressure for 10 minutes to dissolve waste polystyrene and disperse the catalyst. The mixture in which the waste polystyrene was dissolved was distilled at 200° C. for 30 minutes to separate tetrahydrofuran. Thereafter, the temperature was raised to 375 °C, and the depolymerization reaction was performed at this temperature for 1 hour. The product decomposed by the depolymerization reaction was obtained by liquefying in a condenser, and the obtained product was obtained by GC equipped with a capillary column (HP-5, 30 m × 0.32 mm × 1.0 μm, crosslinked 5% PH ME Siloxane). It was measured using /FID (Youngrin Instruments), and the results are shown in Table 1, FIGS. 1 and 2.

<Example 2>

Depolymerization of waste polystyrene was performed in the same manner as in Example 1 to obtain a product, but potassium hydrogen carbonate (KHCO ₃ ) was used as a catalyst (Sigma-aldrich, ACS reagent > 99.7%) instead of potassium carbonate (K ₂ CO ₃ ). Depolymerization was performed by adding 3 g, and the obtained product was measured in the same manner as in Example 1, and the results are shown in Table 1 and FIGS. 1 and 2.

<Comparative Example 1>

Depolymerization of waste polystyrene was performed in the same manner as in Example 1 to obtain a product, but depolymerization was performed without introducing a catalyst, and the obtained product was measured in the same manner as in Example 1, and the results are shown in Table 1 and FIG. 1. and shown in FIG. 2 .

<Comparative Example 2>

Depolymerization of waste polystyrene was carried out in the same manner as in Example 1 to obtain a product, but 3 g of barium oxide (BaO) (Sigma-aldrich, CS reagent > 97%) instead of potassium carbonate (K ₂ CO ₃ ) as a catalyst was added to perform depolymerization, and the obtained product was measured in the same manner as in Example 1, and the results are shown in Table 1 and FIGS. 1 and 2.

<Comparative Example 3>

Depolymerization of waste polystyrene was performed in the same manner as in Example 1 to obtain a product, but depolymerization was performed by adding 3 g of calcium oxide (CaO) instead of potassium carbonate (K ₂ CO ₃ ) as a catalyst. was measured in the same manner as in Example 1, and the results are shown in Table 1, FIGS. 1 and 2.

<Comparative Example 4>

Depolymerization of waste polystyrene was performed in the same manner as in Example 1 to obtain a product, but depolymerization was performed by adding 3 g of strontium oxide (SrO) instead of potassium carbonate (K ₂ CO ₃ ) as a catalyst. was measured in the same manner as in Example 1, and the results are shown in Table 1, FIGS. 1 and 2.

<Comparative Example 5>

Depolymerization of waste polystyrene was performed in the same manner as in Example 1 to obtain a product, but depolymerization was performed by adding 3 g of KNO ₃ instead of potassium carbonate (K ₂ CO ₃ ) as a catalyst. It was measured in the same way as in 1, and the results are shown in Table 1, FIGS. 1 and 2.

<Comparative Example 6>

Waste polystyrene was depolymerized in the same manner as in Example 1 to obtain a product, but depolymerization was performed using toluene instead of tetrahydrofuran as a solvent, and the obtained product was measured in the same manner as in Example 1 to obtain a product. The results are shown in Table 1, FIGS. 1 and 2.

[Table 1]

As shown in Table 1, FIGS. 1 and 2, in the case of Examples 1 and 2, the yield of styrene monomer (SM) was higher than that of Comparative Examples 1 to 6, while the side reaction product ethylbenzene , EB), toluene, cumene, and alpha methylstyrene (a-MS) yields were found to be low. In particular, in Examples 1 and 2, the yield of styrene monomer (SM) was 70 wt% or more, and the weight ratio of styrene monomer (SM) to ethylbenzene (EB) was 84 or more.

Comparing Examples 1 and 2 with Comparative Examples 1 to 5, it was found that the presence or absence of a catalyst or the type of catalyst has a great relationship with the yield of styrene monomer (SM) and the amount of side reaction products generated. In particular, even when the same potassium salt was used, a large difference in activity was shown depending on the type of anion, and the carbonate (CO ₃ ^2- ) or bicarbonate (HCO ₃ ^- ) form had a high yield of styrene monomer (SM) and ethylbenzene. By-products such as (EB) appeared low.

In addition, when comparing the results of Example 1 and Comparative Example 6, even if the type of catalyst is the same, the type of solvent that dissolves waste styrene is also related to the yield of final styrene monomer and the amount of side reaction products. . Comparative Example 6 uses toluene, which is widely used as a solvent for reducing waste styrene, as a solvent, and Example 1 uses THF as a solvent. When toluene is used as a solvent, the yield of styrene monomer is 62.3 wt% As a result, it was only about 88 wt% when THF was used as a solvent, and the yield of ethylbenzene was high.

In order to confirm the cause of this difference in activity, _a mixture prepared by dissolving 5 g of pristine K ₂ CO ₃ and K _{2 CO 3 in} 100 ml of THF and 100 ml of toluene, respectively, was prepared. After stirring for 24 hours, the solvent was evaporated at 120 °C for 12 hours, and K ₂ CO ₃ obtained was analyzed by XRD (Rigaku Ultima IV), and the results are shown in FIG. 4 .

Referring to FIG. 4, after dissolving in THF and toluene, K ₂ CO ₃ shows a change in overall crystallinity compared to pristine K ₂ CO ₃ , but in particular, in the case of toluene, the peak at 2theta = 32.5 degrees is large. As the peak at 2theta = 31.6 degrees decreases, it shows greater stability in THF than in toluene and less tendency to phase transformation, and the K ₂ CO ₃ structure in THF solution than in toluene. was confirmed to be stable.

Therefore, as in the present invention, when waste polystyrene is depolymerized with a combination of a solvent and a catalyst in which at least one of THF and MTHF is selected as the solvent and at least one of K ₂ CO ₃ and KHCO ₃ is selected as the depolymerization catalyst, the depolymerization styrene monomer can be recovered in high yield, and the production of ethylbenzene, which has a boiling point similar to that of styrene monomer, can be suppressed, thereby reducing the cost in the product separation process. It was found that the efficiency could be greatly improved.

Although the preferred embodiment of the present invention has been described above, the present invention is not limited thereto, and it is possible to make various modifications and practice within the scope of the claims and the detailed description of the invention and the accompanying drawings, and this is also the present invention. It is natural to fall within the scope of

Claims (7)

(a) obtaining a polystyrene-dissolved mixture by adding at least one solvent selected from tetrahydrofuran and methyltetrahydrofuran and at least one depolymerization catalyst selected from potassium carbonate and potassium hydrogen carbonate to waste polystyrene;
(b) separating and recovering the solvent by distilling the polystyrene-dissolved mixture; and
(c) depolymerizing the mixture recovered from solvent separation obtained in step (b) to obtain a product containing styrene monomer;
A method for recovering styrene monomer from waste polystyrene, characterized in that the weight ratio (SM/EB) of ethylbenzene (EB) to styrene monomer (SM) in the product obtained in step (c) is 80 or more.
According to claim 1,
In the step (a), tetrahydrofuran and/or methyltetrahydrofuran are added in an amount of 100 parts by weight to 200 parts by weight based on 100 parts by weight of the waste polystyrene.
According to claim 1,
Step (a) is a method for recovering a styrene monomer from waste polystyrene, characterized in that carried out at room temperature and pressure.
According to claim 1,
A method for recovering styrene monomer from waste polystyrene, characterized in that the distillation in step (b) is performed at 80 ° C. to 250 ° C.
According to claim 1,
The method for recovering styrene monomer from waste polystyrene, characterized in that the depolymerization in step (c) is performed at 200 ° C to 600 ° C.
According to claim 1,
In the step (c), potassium carbonate and / or potassium hydrogen carbonate is present in an amount of 1 part by weight to 10 parts by weight based on 100 parts by weight of the waste polystyrene.
According to claim 1,
A method for recovering styrene monomer from waste polystyrene, characterized in that the solvent separated in step (b) is reused for dissolving waste polystyrene in step (a).

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