Method for oxidizing and decarburizing waste fan blade

Abstract

The application provides a waste wind turbine blade oxidation decarburization method, which comprises the following steps: crushing and drying the waste wind turbine blade; heating to 300-400 DEG C in a first atmosphere to preliminarily remove volatile organic compounds from the resin, and performing the first-stage oxidation on the surface of the glass fiber; heating to 500-600 DEG C in a second atmosphere to promote the conversion of long-chain carbon structures in the resin into short-chain hydrocarbons and further remove residual volatile organic compounds; heating to 650-750 DEG C in a third atmosphere, keeping for 1-1.5 h, and completing the oxidation removal of the residual carbon elements in the resin, and performing the second-stage oxidation on the surface of the glass fiber; adding a catalyst to catalyze the carbon-carbon bond in the resin; and separating and recycling the gaseous product, the solid product and the liquid product. Through the process innovation of gradient temperature oxidation, selective decarburization and catalyst assistance, the problems of carbon resource waste, fiber damage, high pollution and high energy consumption in the related oxidation decarburization are solved.

Description

Technical Field

[0001] This application relates to the field of decommissioned wind turbine blade treatment technology, and in particular to a method for oxidizing and decarbonizing waste wind turbine blades. Background Technology

[0002] With the rapid development of wind power technology, a large number of wind turbines have been installed and put into use. However, wind turbine blades are usually made of composite materials, which have extremely high durability and strength. This makes retired wind turbine blades difficult to degrade and recycle, posing an environmental problem. Currently, the main methods for handling retired wind turbine blades include landfill, mechanical recycling, and oxidative decarbonization treatment.

[0003] However, these methods all have their own drawbacks. For example, landfilling consumes a large amount of land resources, and the degradation cycle of composite materials exceeds 50 years, further consuming land resources and potentially causing the leachate of harmful substances. Mechanical recycling only recovers glass fibers for use as cement additives or in low-performance products, without effectively treating the resin matrix, resulting in insufficient resource utilization (fiber recovery rate is about 20%-30%, resin utilization rate is close to 0). Oxidative decarbonization mainly uses high-temperature air incineration (800-1000℃, oxygen concentration 21%) to release heat and decompose carbon elements through complete oxidation of the resin. However, this process requires continuous energy supply to maintain the high temperature, and glass fibers are easily broken in a strong oxidizing environment (surface oxidation rate > 0.5 mm / h). The product contains only low-calorific-value ash (calorific value < 5 MJ / kg), which has no economic value. Therefore, traditional oxidative decarbonization methods suffer from carbon resource waste, fiber damage, high pollution, and high energy consumption. Summary of the Invention

[0004] This application aims to at least partially address one of the technical problems in related technologies. Therefore, the purpose of this application is to propose a method for the oxidative decarbonization of waste wind turbine blades. This application solves the problems of carbon resource waste, fiber damage, high pollution, and high energy consumption associated with related oxidative decarbonization processes through process innovations such as gradient temperature controlled oxidation, selective decarbonization, and catalyst assistance.

[0005] To achieve the above objectives, a method for oxidative decarbonization of waste wind turbine blades is proposed according to the first aspect of this application, comprising the following steps; The discarded wind turbine blades are crushed, the metal parts are removed, and then dried. In a first atmosphere, the resin is heated to 300-400°C at a heating rate of 5-10°C / min to initially desorb volatile organic compounds, while the glass fiber surface undergoes a first-stage oxidation. In a second atmosphere, the resin is heated to 500-600°C at a heating rate of 3-5°C / min to promote the conversion of long-chain carbon structures in the resin into short-chain hydrocarbons and further remove residual volatile organic compounds. In a third atmosphere, the resin is heated to 650-750°C at a heating rate not exceeding 2°C / min and held for 1-1.5 hours to complete the oxidative removal of residual carbon elements in the resin, while the glass fiber surface undergoes a second-stage oxidation. A catalyst is added to catalytically break the carbon-carbon bonds in the resin; Gaseous products, solid products and liquid products are separated and recovered separately.

[0006] In some embodiments, the discarded wind turbine blades are broken into fragments with a diameter of 5-8 cm; And / or, the crushed waste fan blades are subjected to screening and magnetic separation to remove metal parts; And / or, the metal components include bolts and sensors; And / or, the crushed waste fan blades are dried with hot air at a temperature of 80-100℃ and a humidity of <10%.

[0007] In some embodiments, the first atmosphere is a nitrogen-oxygen mixture atmosphere with an oxygen concentration of 5%-10%; And / or, the second atmosphere is a nitrogen-oxygen mixture atmosphere with an oxygen concentration of 15%-20%; And / or, the third atmosphere is a nitrogen-oxygen mixture atmosphere with an oxygen concentration of 25%-30%.

[0008] In some embodiments, during the first oxidation stage, the thickness of the oxide layer on the glass fiber surface is ≤0.1mm; And / or, in the second oxidation stage, the thickness of the oxide layer on the surface of the glass fiber is 0.3-0.5 mm; and the strength of the glass fiber is ≥2500 MPa.

[0009] In some embodiments, the volatile organic compound comprises styrene monomer, which is initially desorbed from the resin in a yield of 5%-8%.

[0010] In some embodiments, the catalyst has a particle size ≤0.5 mm and the active material includes transition metal oxides Fe2O3 or CuO, with the loading of the transition metal oxides being 5%-10% based on the catalyst.

[0011] In some embodiments, the short-chain hydrocarbons include methane and ethylene.

[0012] In some embodiments, the gaseous products are recovered by condensation separation at a temperature not exceeding 150°C, and the remaining CO2 and N2 are compressed and reserved at a pressure not less than 1 MPa.

[0013] In some embodiments, the solid product is the residual glass fiber, which is acid-washed with 1%-3% hydrochloric acid at a temperature not exceeding 80°C, wherein the glass fiber recovery rate is ≥80% and the strength retention rate is ≥70%.

[0014] In some embodiments, the liquid product is an organic mixture obtained by condensing the volatile organic compound, wherein the purity of styrene is ≥60%, and it is then distilled for later use.

[0015] Compared with existing technologies, this application has the following advantages: (1) Gradient temperature control oxidation: The oxidation process is divided into three stages: low temperature (300-400℃), medium temperature (500-600℃), and high temperature (650-750℃). By controlling the oxygen concentration and heating rate in stages, the energy consumption for complete oxidation of the resin is reduced, while some carbon structure (such as carbon black precursor) is retained. (2) Selective decarbonization technology: Add transition metal oxide catalysts, such as Fe2O3 and CuO, to the oxidation reactor to selectively promote the conversion of long-chain carbon structures in the resin to short-chain hydrocarbons (such as methane and ethylene) or high-purity carbon black, and inhibit the reaction pathway of complete oxidation to CO2 (the catalyst can reduce the activation energy by about 30%-50%). (3) Glass fiber protection mechanism: By controlling the oxygen concentration and reaction time, the thickness of the oxide layer on the glass fiber surface is controlled at 0.3-0.5 mm, so that the oxidation rate of the glass fiber surface is reduced to 0.1-0.3 mm / h, while retaining the fiber strength (breaking strength ≥2500 MPa), which can be used as a reinforcing material for secondary use.

[0016] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0017] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein: Figure 1 This is a flowchart of a method for oxidizing and decarbonizing waste wind turbine blades according to an embodiment of this application. Detailed Implementation

[0018] Embodiments of this application are described in detail below. Examples of these embodiments are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application. Rather, embodiments of this application include all variations, modifications, and equivalents falling within the spirit and scope of the appended claims.

[0019] This application proposes improvements to the following related technologies: With the rapid development of wind power generation technology, a large number of wind turbine generators have been installed and put into use. However, wind turbine blades are usually made of composite materials, which have extremely high durability and strength, making retired wind turbine blades difficult to degrade and recycle, thus becoming an environmental problem. Currently, the main methods for treating retired wind turbine blades include landfill, mechanical recycling, and oxidative decarbonization treatment.

[0020] However, these methods all have their own drawbacks. For example, landfilling consumes a large amount of land resources, and the degradation cycle of composite materials exceeds 50 years, further consuming land resources and potentially leaching harmful substances. Mechanical recycling only recovers glass fibers for use as cement additives or low-performance products, without effectively treating the resin matrix, resulting in insufficient resource utilization (fiber recovery rate is about 20%-30%, resin utilization rate is close to 0). Oxidative decarbonization mainly uses high-temperature air incineration (800-1000℃, oxygen concentration 21%) to release heat and decompose carbon elements through complete oxidation of the resin. However, this process requires continuous energy supply to maintain the high temperature, and glass fibers are easily broken in a strong oxidizing environment (surface oxidation rate > 0.5 mm / h), and the product contains only low-calorific-value ash (calorific value < 5 MJ / kg), which has no economic value. Similar technology: The closest existing technology is the high-temperature air oxidation decarbonization method, whose process flow is as follows: Pretreatment: The blades are broken into 5-10cm fragments, and metal parts are removed; Oxidation reaction: In an air atmosphere (oxygen concentration 21%), use natural gas as fuel to heat to 800-1000℃ and maintain for 1-2 hours to completely oxidize the resin; Product separation: The residue (glass fiber) after oxidation is screened and used as a low-value building material, while the gaseous products (CO2, NO) are separated. x (etc.) need to be purified by the exhaust gas treatment system.

[0021] Therefore, traditional oxidative decarbonization methods result in the complete loss of carbon resources. The carbon elements in the resin matrix are completely oxidized to CO2 at high temperatures, failing to be converted into recyclable carbon materials (such as carbon black and gaseous hydrocarbons), leading to low resource utilization. Furthermore, under strong oxidizing conditions, the oxide layer thickness on the glass fiber surface reaches 0.8-1.2 mm (the surface oxidation rate under traditional processes is 0.5-0.8 mm / h), causing a decrease in fiber strength (breaking strength drops from ≥3500 MPa of the original material to <2000 MPa), making it unsuitable for high-performance composite materials. The poor quality of recycled glass fiber is due to the following reasons: multi-stage exhaust gas treatment equipment (such as denitrification, dust removal, and dioxin adsorption) is required, which increases the cost of processing each ton of blades by 150-300 yuan. Pollutant control costs are high. Finally, in the unit processing energy consumption, natural gas consumption accounts for more than 70% (about 600-900 kWh / t), and the thermal energy utilization rate is low (only 35%-45%). The energy dependence on fossil fuels does not meet the "dual carbon" target. Therefore, the oxidation decarbonization treatment method in related technologies has problems of carbon resource waste, fiber damage, high pollution and high energy consumption.

[0022] To achieve the above objectives, a method for oxidative decarburization of waste wind turbine blades is proposed according to the first aspect of this application, such as... Figure 1 This includes the following steps; S1: Crush the discarded fan blades, remove the metal parts, and dry them; S2: In the first atmosphere, heat to 300-400℃ at a heating rate of 5-10℃ / min to initially desorb volatile organic compounds from the resin, while the glass fiber surface undergoes the first stage of oxidation; in the second atmosphere, heat to 500-600℃ at a heating rate of 3-5℃ / min to promote the conversion of long-chain carbon structures in the resin into short-chain hydrocarbons and further remove residual volatile organic compounds; in the third atmosphere, heat to 650-750℃ at a heating rate not exceeding 2℃ / min and maintain for 1-1.5h to complete the oxidation and removal of residual carbon elements in the resin, while the glass fiber surface undergoes the second stage of oxidation. S3: Add a catalyst to catalyze the cracking of carbon-carbon bonds in the resin; S4: Gaseous products, solid products and liquid products are separated and recovered separately.

[0023] In step S1, the waste wind turbine blades are crushed into fragments with a diameter of 5-8 cm. The crushed waste wind turbine blades are then screened and magnetically separated to remove metal parts, including bolts, sensors, etc. After screening and magnetic separation, the wind turbine blades are dried with hot air at a temperature of 80-100℃ and a humidity of <10% to remove adsorbed water from the surface of the wind turbine blades and prevent moisture from reducing reaction efficiency during oxidation.

[0024] In step S2, the fan blades treated in step S1 are placed in an oxidation reactor and heated to 300-400°C at a heating rate of 5-10°C / min in a first atmosphere to allow the resin to initially desorb volatile organic compounds (VOCs). Simultaneously, the glass fiber surface undergoes a first-stage oxidation process. The first atmosphere is a nitrogen-oxygen mixture with an oxygen concentration of 5%-10%. The VOCs include styrene monomer, with a yield of 5%-8% during the initial resin desorption. During this first-stage oxidation, the oxide layer thickness on the glass fiber surface is ≤0.1mm.

[0025] After the wind turbine blades decompose at a low temperature of 300-400℃, they are heated to 500-600℃ in a second atmosphere at a heating rate of 3-5℃ / min. This second atmosphere is a nitrogen-oxygen mixture with an oxygen concentration of 15%-20%. This process promotes the conversion of long-chain carbon structures in the resin to short-chain hydrocarbons, including methane and ethylene, and further removes residual volatile organic compounds. During this process, the yield of volatile organic compounds is approximately 20%-30%, and the calorific value of the gaseous products increases to 20-25 MJ / m³. 3 .

[0026] After the wind turbine blades undergo decomposition in the intermediate temperature range of 500-600℃, they are heated to 650-750℃ in a third atmosphere at a heating rate not exceeding 2℃ / min. This third atmosphere is a nitrogen-oxygen mixture with an oxygen concentration of 25%-30%. During this process, the wind turbine blades are maintained at 650-750℃ for 1-1.5 hours to complete the oxidation and removal of residual carbon elements in the resin. Simultaneously, a second stage of oxidation occurs on the glass fiber surface. During this process, the oxide layer thickness on the glass fiber surface is 0.3-0.5 mm, and the strength of the glass fiber is ≥2500 MPa. CO2 emissions are reduced to 60%-70% of those in related technologies.

[0027] In S3, a catalyst is added to assist in the decarburization of the pyrolysis wind turbine blades. For example, the catalyst is incorporated into the inner wall of the oxidation reactor or into the fragments of the wind turbine blades to assist in the decarburization process. The catalyst has a particle size ≤0.5mm, and its active material includes transition metal oxides Fe2O3 or CuO. Based on the catalyst, the loading of transition metal oxides is 5%-10%. This catalyst catalyzes the cracking of carbon-carbon bonds in the resin, increasing the yield of short-chain hydrocarbons and reducing coke residue. After catalytic cracking, the activation energy in the resin decreases by approximately 30%-50%, the yield of short-chain hydrocarbons increases from 5%-10% to 15%-25%, and the coke residue decreases from 10%-15% to ≤5%.

[0028] In step S4, the gaseous, solid, and liquid products of the resin after catalytic cracking in step S3 are separated and recovered. The gaseous products are condensed and separated at a temperature not exceeding 150°C to recover short-chain hydrocarbons, such as methane and ethylene. The remaining CO2 and N2 are compressed under a pressure not less than 1 MPa for later use; for example, compressed CO2 can be used for carbon sequestration, or compressed N2 can be used for industrial oxygen production. The solid product is residual glass fiber, which is acid-washed with 1%-3% hydrochloric acid at a temperature not exceeding 80°C. The glass fiber recovery rate is ≥80%, and the strength retention rate is ≥70%. The recovered glass fiber can be used as a reinforcing phase in recycled composite materials. The liquid product is a mixture of volatile organic compounds obtained by condensation, in which the purity of styrene is ≥60%. After distillation, it can be used as a chemical raw material.

[0029] Therefore, this application protects the glass fiber structure while ensuring the resin decarbonization efficiency by gradient temperature control and segmented oxygen concentration regulation; and introduces a transition metal oxide catalyst to selectively cleave the carbon structure of the resin and improve the yield of high value-added products.

[0030] To facilitate a further understanding of this application, the solutions described below are further described in conjunction with embodiments. Those skilled in the art will understand that the embodiments described in this application are only some examples, and any other suitable specific embodiments are within the scope of this application.

[0031] Example 1 This embodiment proposes a method for oxidative decarbonization of waste wind turbine blades. The process and control parameters are as follows: the waste wind turbine blades are crushed into fragments with a diameter of 8cm, and the metal parts of the crushed waste wind turbine blades are removed and then dried.

[0032] The wind turbine blades were placed in an oxidation reactor and heated to 400°C at a rate of 10°C / min under a nitrogen-oxygen mixed atmosphere with an oxygen concentration of 5%. Simultaneously, the glass fiber surface underwent a first-stage oxidation, resulting in an oxide layer thickness ≤0.1 mm. Then, under a nitrogen-oxygen mixed atmosphere with an oxygen concentration of 15%, the temperature was increased to 500°C at a rate of 5°C / min to promote the conversion of long-chain carbon structures in the resin to short-chain hydrocarbons and further remove residual volatile organic compounds. Finally, under a nitrogen-oxygen mixed atmosphere with an oxygen concentration of 25%, the temperature was increased to 650°C at a rate of 1°C / min and held for 1 hour to complete the oxidation and removal of remaining carbon elements in the resin. Simultaneously, a second-stage oxidation process was performed on the glass fiber surface, resulting in an oxide layer thickness of 0.3 mm and a glass fiber strength ≥2500 MPa. Then, a catalyst with a particle size of 0.5 mm is added to the inner wall of the oxidation reactor. The active material is Fe2O3 with a loading of 10%. Finally, the gaseous product, solid product and liquid product are separated and recovered respectively.

[0033] Example 2 This embodiment proposes a method for the oxidative decarbonization of waste wind turbine blades. The process and control parameters differ from Embodiment 1 as follows: The wind turbine blades are placed in an oxidation reactor and heated to 300°C at a heating rate of 5°C / min under a nitrogen-oxygen mixed atmosphere with an oxygen concentration of 10%. Simultaneously, the glass fiber surface undergoes a first-stage oxidation process, resulting in an oxide layer thickness ≤0.1 mm. Then, under a nitrogen-oxygen mixed atmosphere with an oxygen concentration of 20%, the temperature is increased to 600°C at a heating rate of 3°C / min to promote the conversion of long-chain carbon structures in the resin to short-chain hydrocarbons and further remove residual volatile organic compounds. Finally, under a nitrogen-oxygen mixed atmosphere with an oxygen concentration of 30%, the temperature is increased to 750°C at a heating rate of 2°C / min and maintained for 1 hour.

[0034] Example 3 This embodiment proposes a method for the oxidative decarbonization of waste wind turbine blades. The process and control parameters differ from Embodiment 1 as follows: The wind turbine blades are placed in an oxidation reactor and heated to 350°C at a heating rate of 7°C / min under a nitrogen-oxygen mixed atmosphere with an oxygen concentration of 8%. Simultaneously, the glass fiber surface undergoes a first-stage oxidation process, resulting in an oxide layer thickness ≤0.1 mm. Then, under a nitrogen-oxygen mixed atmosphere with an oxygen concentration of 18%, the blades are heated to 550°C at a heating rate of 4°C / min to promote the conversion of long-chain carbon structures in the resin to short-chain hydrocarbons and further remove residual volatile organic compounds. Finally, under a nitrogen-oxygen mixed atmosphere with an oxygen concentration of 28%, the blades are heated to 700°C at a heating rate of 1°C / min and held for 1 hour.

[0035] Example 4 This embodiment proposes a method for oxidative decarbonization of waste wind turbine blades. The process and control parameters are different from those in Embodiment 1 as follows: a catalyst with a particle size of 0.5 mm is then added to the inner wall of the oxidation reactor. The active material is copper oxide with a loading of 5%. Finally, the gaseous product, solid product and liquid product are separated and recovered respectively.

[0036] Experimental Example The gaseous, solid, and liquid products obtained in each embodiment were separated and recovered. The gaseous products were condensed at 150°C to recover short-chain hydrocarbons, such as methane and ethylene. The remaining CO2 and N2 were compressed under a pressure of not less than 1 MPa for later use. The solid product was residual glass fiber, which was acid-washed with 1% hydrochloric acid at 60°C. The glass fiber recovery rate and strength retention rate were statistically analyzed, with a glass fiber recovery rate ≥80% and a strength retention rate ≥70%. The liquid product was a mixture of volatile organic compounds obtained by condensation. The purity of styrene in the organic mixture was statistically analyzed, showing a styrene purity ≥60%.

[0037] In the description of this application, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Furthermore, in the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0038] Any process or method described in the flowchart or otherwise herein can be understood as representing a module, segment, or portion of code comprising one or more executable instructions for implementing a particular logical function or process, and the scope of the preferred embodiments of this application includes additional implementations in which functions may be performed not in the order shown or discussed, including substantially simultaneously or in reverse order depending on the function involved, as will be understood by those skilled in the art to which embodiments of this application pertain.

[0039] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0040] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A method for oxidative decarburization of waste wind turbine blades, characterized in that, Includes the following steps; The discarded wind turbine blades are crushed, the metal parts are removed, and then dried. In a first atmosphere, the resin is heated to 300-400°C at a heating rate of 5-10°C / min to initially desorb volatile organic compounds, while the glass fiber surface undergoes a first-stage oxidation. In a second atmosphere, the resin is heated to 500-600°C at a heating rate of 3-5°C / min to promote the conversion of long-chain carbon structures in the resin into short-chain hydrocarbons and further remove residual volatile organic compounds. In a third atmosphere, the resin is heated to 650-750°C at a heating rate not exceeding 2°C / min and held for 1-1.5 hours to complete the oxidative removal of residual carbon elements in the resin, while the glass fiber surface undergoes a second-stage oxidation. A catalyst is added to catalytically break the carbon-carbon bonds in the resin; Gaseous products, solid products and liquid products are separated and recovered separately.

2. The method according to claim 1, characterized in that, The discarded wind turbine blades were broken into fragments with a diameter of 5-8 cm; And / or, the crushed waste fan blades are subjected to screening and magnetic separation to remove metal parts; And / or, the metal components include bolts and sensors; And / or, the crushed waste fan blades are dried with hot air at a temperature of 80-100℃ and a humidity of <10%.

3. The method according to claim 1 or 2, characterized in that, The first atmosphere is a nitrogen-oxygen mixture atmosphere with an oxygen concentration of 5%-10%; And / or, the second atmosphere is a nitrogen-oxygen mixture atmosphere with an oxygen concentration of 15%-20%; And / or, the third atmosphere is a nitrogen-oxygen mixture atmosphere with an oxygen concentration of 25%-30%.

4. The method according to claim 1, characterized in that, In the first oxidation stage, the thickness of the oxide layer on the glass fiber surface is ≤0.1mm; And / or, in the second oxidation stage, the thickness of the oxide layer on the surface of the glass fiber is 0.3-0.5 mm; and the strength of the glass fiber is ≥2500 MPa.

5. The method according to claim 1, characterized in that, The volatile organic compounds include styrene monomers, which are initially desorbed from the resin in a yield of 5%-8%.

6. The method according to claim 1, characterized in that, The catalyst has a particle size ≤0.5mm and the active material includes transition metal oxides Fe2O3 or CuO. Based on the catalyst, the loading of the transition metal oxide is 5%-10%.

7. The method according to claim 1, characterized in that, The short-chain hydrocarbons include methane and ethylene.

8. The method according to claim 1, characterized in that, The gaseous products are recovered by condensation separation at a temperature not exceeding 150°C. The remaining CO2 and N2 are compressed and kept for later use under a pressure not less than 1 MPa.

9. The method according to claim 1 or 4, characterized in that, The solid product is the residual glass fiber, which is acid-washed with 1%-3% hydrochloric acid at a temperature not exceeding 80°C. The glass fiber recovery rate is ≥80% and the strength retention rate is ≥70%.

10. The method according to claim 5, characterized in that, The liquid product is a mixture of volatile organic compounds obtained by condensing the organic compounds, wherein the purity of styrene is ≥60%, and it is then distilled for later use.

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