A recycling method of polystyrene plastic

Abstract

The application relates to the polystyrene waste treatment technical field, in particular to a polystyrene plastic recycling method.The polystyrene plastic recycling method comprises the following steps: under the conditions of 200-270 DEG C and 5-15 MPa air pressure, polystyrene waste and near-critical water are mixed, stirring is carried out to perform swelling and depolymerization reaction, a depolymerization system is obtained, a surfactant and a foaming agent are added into the depolymerization system, stirring and mixing are carried out, and a reshaping system is obtained.The reshaping system is cooled, pressure is released and foamed, polystyrene is separated out, and cooling and shaping are carried out, and regenerated polystyrene material is obtained.The method uses near-critical water as a reaction medium, energy consumption is low or there is no solvent pollution, the performance of the regenerated polystyrene material is close to or better than that of virgin material, and the process is simple and easy to popularize in industry.

Description

Technical Field

[0001] This application relates to the field of polystyrene waste treatment technology, and in particular to a method for recycling and regenerating polystyrene plastics. Background Technology

[0002] Polystyrene (PS), a widely used plastic material, has always presented a challenge in environmental protection with its waste disposal. Common polystyrene recycling technologies currently include pyrolysis, solvent dissolution, extrusion regeneration, and catalytic degradation.

[0003] Thermal pyrolysis decomposes waste polystyrene at high temperatures of 600-900℃, producing combustible gas, liquid oil, and solid char. It cannot directly regenerate polystyrene, is energy-intensive, and easily generates harmful gases. Solvent dissolution typically uses large amounts of organic solvents, leading to difficulties in solvent recovery and purification, and significant environmental pollution risks. Extrusion regeneration involves heating and melting polystyrene waste, then extruding and cutting it into granular polystyrene particles, but the performance of polystyrene degrades significantly. Catalytic degradation degrades polystyrene waste into inorganic substances through processes such as addition, substitution, and electron transfer between free radicals and polystyrene. While it can lower the reaction temperature, the catalyst is expensive and prone to deactivation. These drawbacks limit the large-scale application of these recycling methods. Summary of the Invention

[0004] To address the aforementioned issues, this solution provides a method for recycling and regenerating polystyrene plastics. This method involves swelling and depolymerizing waste polystyrene in near-critical water, then adding surfactants and foaming agents after the chain segments have expanded. Through physical and chemical actions, the polystyrene structure is reshaped, restoring or improving its performance.

[0005] A method for recycling polystyrene plastic includes: mixing polystyrene waste with near-critical water under conditions of 200-270°C and 5-15 MPa pressure, stirring to induce swelling and depolymerization reactions to obtain a depolymerization system; adding a surfactant and a foaming agent to the depolymerization system, stirring and mixing to obtain a remolding system; cooling the remolding system, depressurizing and foaming to separate the polystyrene, cooling and molding to obtain recycled polystyrene material.

[0006] By employing the above technical solution, polystyrene is in a viscous flow state at temperatures of 200-270℃. Near-critical water, with its extremely high diffusion coefficient and strong mass transfer capacity, allows it to permeate polystyrene, weakening interchain forces. Polystyrene swells in this near-critical water and, under stirring, disperses within it. Under the high temperature and pressure environment of near-critical water, water molecules act as nucleophiles, directly attacking carbon atoms in the polystyrene backbone, causing partial chain hydrolysis and breakage, generating active ends (such as carboxyl groups, hydroxyl groups, and free radicals), and producing lower molecular weight segments. This causes the entangled molecular chains affecting the performance of polystyrene waste to unravel, resulting in a depolymerized system. After depolymerization, surfactants and blowing agents are added. Surfactants reduce interfacial tension, making it easier for the aqueous and polystyrene phases to mix uniformly. When the system cools or pressure is released, the blowing agent decomposes to produce gas, which permeates and disperses between the chain segments. Surfactants stabilize the bubbles generated by the blowing agent, preventing them from coalescing and breaking, thus contributing to the formation of a uniform and fine cell structure. PS segments encapsulate these bubbles and are "frozen" during the cooling process, forming a stable three-dimensional porous network structure, thus achieving reshaping and enhancing performance compared to polystyrene waste.

[0007] In this method, the mass ratio of polystyrene waste to water can be 1:(5~20), but is not limited to this. Before mixing the polystyrene waste with near-critical water, the waste polystyrene can be cleaned and then crushed to a particle size of less than 5mm to increase the swelling and depolymerization rate of the polystyrene waste.

[0008] A preferred embodiment of the polystyrene recycling method is to add p-toluenesulfonic acid when mixing polystyrene waste with near-critical water, such that the concentration of p-toluenesulfonic acid in the near-critical water is 0.5~2g / L; after the swelling and depolymerization reactions are completed, alkali is added to make the water in the depolymerization system neutral.

[0009] By employing the above technical solution, p-toluenesulfonic acid further attacks the tangled molecular chains, enhancing the depolymerization degree of polystyrene and facilitating better reshaping of polystyrene plastics. The alkali can be sodium carbonate, sodium bicarbonate, or calcium hydroxide.

[0010] A preferred embodiment of the polystyrene plastic recycling method is to add a chain extender before adding the surfactant and the foaming agent, and then stir the reaction; the chain extender is 1,4-butanediol diglycidyl ether, and the amount added is 1~3 wt% of the polystyrene waste.

[0011] By employing the above technical solution, the polystyrene molecular chains swell and depolymerize in the high-temperature, high-pressure, and highly reactive environment provided by near-critical water. Near-critical water permeates between PS segments, acting as a plasticizer, widening the interchain spacing, weakening interchain forces, and causing hydrolytic breakage of some chains, generating active ends (such as carboxyl groups, hydroxyl groups, and free radicals), resulting in segments with lower molecular weights. The epoxy groups at both ends of 1,4-butanediol diglycidyl ether can react with the active ends (such as carboxyl groups, hydroxyl groups, and free radicals) of the two polystyrene molecular chains generated by depolymerization, allowing the two broken polystyrene molecular chains to reconnect, ensuring sufficient chain length for subsequent remodeling to guarantee strength.

[0012] A preferred embodiment of the polystyrene plastic recycling method is as follows: after adding the chain extender and stirring to react, and before adding the surfactant and the foaming agent, a grafting modifier is added and stirred to react; the grafting modifier is glutaric anhydride, and the amount added is 2-4 wt% of the polystyrene waste.

[0013] By adopting the above technical solution, glutaric anhydride reacts with the polystyrene backbone at high temperature, grafting long-chain alkyl and carboxyl groups onto the backbone, thereby increasing surface polarity and improving the hydrophobicity of polystyrene. This greatly enhances its compatibility with fillers or other polymers in the original polystyrene waste, thus achieving performance reshaping and improvement.

[0014] A preferred embodiment of the polystyrene recycling method is as follows: the polystyrene waste and near-critical water are stirred and reacted for 30 to 120 minutes; the chain extender is added and stirred and reacted for 20 to 30 minutes; the grafting modifier is added and stirred and reacted for 20 to 30 minutes; and the surfactant and foaming agent are added and stirred and mixed for 10 to 30 minutes.

[0015] By adopting the above technical solution, polystyrene waste reacts with near-critical water, the entangled chains affecting performance are dispersed, some chains break, the chain extender reconnects the stretched broken chains, the graft modifier enhances the surface polarity of polystyrene and improves the compatibility of polystyrene with fillers, the surfactant enhances the compatibility of the polystyrene phase and the aqueous phase, the foaming agent generates bubbles, and the surfactant can stabilize the bubbles generated by the foaming agent to form a uniform and dense cell structure, thus achieving reshaping.

[0016] A preferred embodiment of the polystyrene recycling method is that the surfactant is sodium dodecylbenzenesulfonate or sodium dodecyl p-toluenesulfonate, and the amount of surfactant added is 1 to 5 wt% of the polystyrene waste.

[0017] By adopting the above technical solution, the surfactant not only makes it easier to mix the aqueous phase and the polystyrene phase evenly, but also improves the compatibility between the filler and the polystyrene.

[0018] A preferred embodiment of the polystyrene plastic recycling method is that the foaming agent is azodicarbonamide or azobisisobutyronitrile, and the amount of foaming agent added is 0.5~3wt% of the polystyrene waste.

[0019] By adopting the above technical solution, the foaming agent generates bubbles under appropriate temperature and pressure. The bubbles are wrapped between polystyrene chains, which helps to reshape the properties of polystyrene.

[0020] A preferred embodiment of the method for recycling and regenerating polystyrene plastic is to cool the remodeling system to 150~180°C and then depressurize it to atmospheric pressure within 1 minute to allow it to foam.

[0021] By adopting the above technical solution, polystyrene remains in a plastic state at 150~180℃, and this temperature is the foaming temperature of the foaming agent. The gas dispersed in the polystyrene melt expands rapidly due to the sudden pressure drop, forming a uniform microporous structure. This process completes the foaming. The polystyrene melt containing the foaming agent encapsulates the expanded bubbles. Subsequently, the depressurized hot material is transferred to a mold and cooled to room temperature under a certain pressure, thus forming a stable three-dimensional porous structure and obtaining the final shaped product.

[0022] The polystyrene recycling method provided in this solution achieves the following technical advantages compared to some current technologies: 1) Utilizing near-critical water as the reaction medium results in low energy consumption or no solvent pollution; 2) The properties of recycled polystyrene materials are close to or better than those of virgin materials; 3) The process is simple and easy to promote industrially. Attached Figure Description

[0023] Figure 1 This is a flowchart of Example 1. Detailed Implementation

[0024] The technical solutions in the embodiments are described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the following embodiments, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0025] The following examples and comparative examples use the same polystyrene waste. Example 1

[0026] A method for recycling and regenerating polystyrene plastic, such as Figure 1 Production will proceed according to the following steps.

[0027] S1: Take polystyrene waste, wash it, and crush it into particles with a diameter of about 3mm.

[0028] S2: Add 1 kg of crushed polystyrene and 10 L of water to a high-pressure reactor, start stirring, heat to 235 °C, and increase the pressure to 10 MPa. Maintain this condition for 75 minutes to carry out swelling and depolymerization reactions, and obtain a depolymerization system.

[0029] S3: Continue to add 30g sodium dodecylbenzenesulfonate (surfactant) and 15g azodicarbonamide (foaming agent) to the depolymerization system at 235℃ and 10MPa, and stir for 20 minutes to obtain the remodeling system.

[0030] S4: Cool the remolding system to 165°C, and then depressurize it to atmospheric pressure within 1 minute. This causes the compressed bubbles generated by the decomposition of the foaming agent to expand rapidly and be encapsulated in polystyrene, thus achieving foaming and forming a closed-cell structure with fine pore size and uniform distribution.

[0031] S5: The foamed hot material is discharged from the high-pressure reactor, the polystyrene is separated, dried with hot air and kept at 135°C, transferred to a molding mold preheated to 100°C, molded, cooled and cured, demolded, and recycled polystyrene material is obtained. Example 2

[0032] A method for recycling polystyrene plastic, the only difference from Example 1, is that when mixing polystyrene waste with near-critical water, 10g of p-toluenesulfonic acid is added to the high-pressure reactor, and after addition, the concentration of p-toluenesulfonic acid in the near-critical water is 1g / L; the swelling and depolymerization reaction time is reduced to 40 minutes, and after the reaction is completed, sodium carbonate aqueous solution is added until the depolymerization system is neutral. Example 3

[0033] A method for recycling polystyrene plastic, differing from Example 1 in that 20 g of 1,4-butanediol diglycidyl ether (chain extender) is added to the remodeling system before the addition of surfactant and foaming agent, and the reaction is stirred for 25 minutes. This reaction is also carried out at 235°C and 10 MPa. Example 4

[0034] A method for recycling polystyrene plastic, differing only from Example 3, is provided in that, after adding the chain extender and stirring the reaction, and before adding the surfactant and foaming agent, 30g of glutaric anhydride (grafting modifier) ​​is added, and the reaction is stirred for 25 minutes. This reaction is also carried out at 235°C and 10MPa. Example 5

[0035] A method for recycling polystyrene plastic is disclosed, comprising the following steps. This embodiment is derived from Embodiment 1 by combining the different steps of Embodiments 2-4.

[0036] S1: Take polystyrene waste, wash it, and crush it into particles with a diameter of about 3mm.

[0037] S2: Add 1 kg of crushed polystyrene, 10 g of p-toluenesulfonic acid, and 10 L of water to a high-pressure reactor. Start stirring, raise the temperature to 235 °C, and increase the pressure to 10 MPa. Maintain these conditions for 40 minutes to allow for swelling and depolymerization reactions, obtaining a depolymerized system. Add sodium carbonate aqueous solution until the water in the depolymerized system is neutral. The reaction time in this step can be adjusted according to the properties of the polystyrene waste.

[0038] S3: Continue to add 20g of 1,4-butanediol diglycidyl ether (chain extender) to the high-pressure reactor at 235℃ and 10MPa, and stir for 25 minutes.

[0039] S4: Continue to add 30g of glutaric anhydride (grafting modifier) ​​to the high-pressure reactor at 235℃ and 10MPa, and stir for 25 minutes.

[0040] S5: Continue at 235℃ and 10MPa, add 30g sodium dodecylbenzenesulfonate (surfactant) and 15g azodicarbonamide (foaming agent) to the depolymerization system, stir for 20 minutes to obtain the remodeling system.

[0041] S6: Cool the remolding system to 165°C, and then depressurize it to atmospheric pressure within 1 minute. This causes the compressed bubbles generated by the decomposition of the foaming agent to expand rapidly and be encapsulated in polystyrene, thus achieving foaming and forming a closed-cell structure with fine pore size and uniform distribution.

[0042] S7: The foamed hot material is discharged from the high-pressure reactor, the polystyrene is separated, dried with hot air and kept at 135°C, transferred to a molding mold preheated to 100°C, molded, cooled and cured, demolded, and recycled polystyrene material is obtained. Example 6

[0043] A method for recycling polystyrene plastic, comprising the following steps:

[0044] S1: Take polystyrene waste, wash it, and crush it into particles with a diameter of about 3mm.

[0045] S2: Add 1 kg of crushed polystyrene, 1 g of p-toluenesulfonic acid, and 5 L of water to a high-pressure reactor. Start stirring, raise the temperature to 200°C, and increase the pressure to 5 MPa. Maintain these conditions for 40 minutes to allow for swelling and depolymerization reactions, resulting in a depolymerized system. Add sodium carbonate aqueous solution until the water in the depolymerized system is neutral. The reaction time in this step can be adjusted according to the properties of the polystyrene waste.

[0046] S3: Continue to add 10g of 1,4-butanediol diglycidyl ether (chain extender) to the high-pressure reactor at 200℃ and 5MPa, and stir for 20 minutes.

[0047] S4: Continue to add 20g of glutaric anhydride (grafting modifier) ​​to the high-pressure reactor at 200℃ and 5MPa, and stir for 20 minutes.

[0048] S5: Continue to add 10g sodium dodecyl p-toluenesulfonate (surfactant) and 5g azobisisobutyronitrile (foaming agent) to the depolymerization system at 200℃ and 5MPa, and stir for 10 minutes to obtain the remodeling system.

[0049] S6: Cool the remolding system to 150°C, and then depressurize it to atmospheric pressure within 1 minute. This causes the compressed bubbles generated by the decomposition of the foaming agent to expand rapidly and be encapsulated in polystyrene, thus achieving foaming and forming a closed-cell structure with fine pore size and uniform distribution.

[0050] S7: The foamed hot material is discharged from the high-pressure reactor, the polystyrene is separated, dried with hot air and kept at 120°C, transferred to a molding die preheated to 100°C, molded, cooled and cured, and demolded to obtain recycled polystyrene material. Example 7

[0051] A method for recycling polystyrene plastic, comprising the following steps:

[0052] S1: Take polystyrene waste, wash it, and crush it into particles with a diameter of about 3mm.

[0053] S2: Add 1 kg of crushed polystyrene, 40 g of p-toluenesulfonic acid, and 20 L of water to a high-pressure reactor. Start stirring, raise the temperature to 270 °C, and increase the pressure to 15 MPa. Maintain these conditions for 40 minutes to allow for swelling and depolymerization reactions, resulting in a depolymerized system. Add sodium carbonate aqueous solution until the water in the depolymerized system is neutral. The reaction time in this step can be adjusted according to the properties of the polystyrene waste.

[0054] S3: Continue to add 30g of 1,4-butanediol diglycidyl ether (chain extender) to the high-pressure reactor at 270℃ and 15MPa, and stir for 30 minutes.

[0055] S4: Continue to add 40g of glutaric anhydride (grafting modifier) ​​to the high-pressure reactor at 270℃ and 15MPa, and stir for 30 minutes.

[0056] S5: Continue to add 50g sodium dodecyl p-toluenesulfonate (surfactant) and 30g azodicarbonamide (foaming agent) to the depolymerization system at 270℃ and 15MPa, and stir for 30 minutes to obtain the remodeling system.

[0057] S6: Cool the remolding system to 180°C, and then depressurize it to atmospheric pressure within 1 minute. This causes the compressed bubbles generated by the decomposition of the foaming agent to expand rapidly and be encapsulated in polystyrene, thus achieving foaming and forming a closed-cell structure with fine pore size and uniform distribution.

[0058] S7: The foamed hot material is discharged from the high-pressure reactor, the polystyrene is separated, dried with hot air and kept at 150°C, transferred to a molding mold preheated to 100°C, molded, cooled and cured, demolded, and recycled polystyrene material is obtained.

[0059] Comparative Example 1 A method for recycling polystyrene plastic, the only difference from Example 1, is that the gas pressure and water temperature inside the high-pressure reactor are different in steps S2 and S3. In this comparative example, the water inside the high-pressure reactor is heated to 380°C and the gas pressure is increased to 23 MPa to generate supercritical water. Under these conditions, the reactions in steps S2 and S3 of Example 1 are carried out, and finally recycled polystyrene material is obtained.

[0060] Comparative Example 2 A method for recycling polystyrene plastic, differing from Example 1 only in that the gas pressure and water temperature inside the high-pressure reactor are different in steps S2 and S3, and the reaction time is reduced. In this comparative example, the water in the high-pressure reactor is heated to 380°C and the gas pressure is increased to 23 MPa to generate supercritical water. Under these conditions, the reactions in steps S2 and S3 of Example 1 are carried out, but the reaction time in step S2 is reduced from 75 minutes to 30 minutes, and the reaction time in step S3 is reduced from 20 minutes to 10 minutes, finally yielding recycled polystyrene material.

[0061] Experimental Example 1 The properties of polystyrene before and after recycling are shown in Table 1.

[0062] Table 1 Properties of polystyrene before and after recycling

[0063] In Table 1, PDI = Mw / Mn. The larger the PDI, the wider the molecular weight distribution, indicating a greater difference in molecular chain size within the sample.

[0064] Analysis of the data in Table 1 shows that after recycling in each embodiment, the polystyrene waste exhibits enhanced strength and toughness, and a more balanced molecular weight distribution. Comparative Example 1, which uses supercritical water at higher temperatures and pressures to treat the polystyrene waste, yields a product with slightly enhanced strength and toughness, but both are significantly weaker than the products treated in each embodiment. Furthermore, while the molecular weight distribution of the product in Comparative Example 1 is slightly improved compared to the waste, it is still inferior to the products in the embodiments. This is because Comparative Example 1 uses supercritical water to swell and depolymerize the polystyrene waste, resulting in excessive depolymerization of the polystyrene and a significant reduction in its molecular weight, leading to a significant decrease in the performance of the recycled product compared to the embodiments. Comparative Example 2, despite reducing the processing time compared to Comparative Example 1, does not show significant improvement in strength, toughness, or molecular weight distribution.

[0065] Compared to Example 1, Example 2 uses p-toluenesulfonic acid to accelerate the de-entanglement of polystyrene molecules, which helps to restore the physicochemical properties of polystyrene.

[0066] Compared to Example 1, Example 3 added 1,4-butanediol diglycidyl ether to connect the depolymerized polystyrene segments, which increased the molecular weight and made the molecular weight distribution more uniform, thereby improving the strength and toughness of the recycled polystyrene.

[0067] Compared to Example 3, Example 4 involved adding 1,4-butanediol diglycidyl ether for chain extension, followed by grafting glutaric anhydride onto the polystyrene backbone, which increased the molecular weight and crosslinking density, resulting in improved strength and toughness of the recycled polystyrene.

[0068] Compared to Example 1, Example 5 uses p-toluenesulfonic acid to accelerate the depolymerization of polystyrene molecular entanglement, which helps to restore the physicochemical properties of polystyrene. 1,4-Butanediol diglycidyl ether is added to connect the depolymerized polystyrene segments. Glutaric anhydride is added to graft onto the polystyrene backbone, which increases the molecular weight and makes the molecular weight distribution more uniform, thereby increasing the crosslinking density. The strength and toughness of the recycled polystyrene are significantly improved.

[0069] Compared to Example 5, Examples 6 and 7 adjusted the proportions of each raw material. Compared to Example 1, the molecular weight was increased and the molecular weight distribution was more uniform, which increased the crosslinking density and significantly improved the strength and toughness of the recycled polystyrene.

[0070] The polystyrene recycling method described in this application does not use organic solvents to dissolve polystyrene waste, making it more environmentally friendly and cost-effective. The performance of the recycled material is superior to that of the polystyrene waste, and is close to or better than that of newly prepared polystyrene plastic. This method is simple and easy to industrialize.

[0071] Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for recycling and regenerating polystyrene plastic, characterized in that, include: Under the conditions of 200~270℃ and 5~15MPa pressure: polystyrene waste and near-critical water are mixed and stirred to carry out swelling and depolymerization reactions to obtain a depolymerization system. Surfactant and foaming agent are added to the depolymerization system and stirred to obtain a remolding system. The remodeling system is cooled, depressurized and foamed to separate polystyrene, and then cooled and molded to obtain recycled polystyrene material; Before adding the surfactant and the foaming agent, a chain extender is also added and the mixture is stirred to react; the chain extender is 1,4-butanediol diglycidyl ether, and the amount added is 1-3 wt% of the polystyrene waste. When polystyrene waste is mixed with near-critical water, p-toluenesulfonic acid is also added. After the addition, the concentration of p-toluenesulfonic acid in the near-critical water is 0.5~2g / L. After the swelling and depolymerization reactions are completed, alkali is added to make the water in the depolymerization system neutral. After adding the chain extender and stirring to react, and before adding the surfactant and the foaming agent, a graft modifier is added and stirred to react; the graft modifier is glutaric anhydride, and the amount added is 2-4 wt% of the polystyrene waste.

2. The method for recycling and regenerating polystyrene plastic according to claim 1, characterized in that, The stirring reaction time for the polystyrene waste and near-critical water is 30-120 minutes; the stirring reaction time for adding the chain extender is 20-30 minutes; the stirring reaction time for adding the graft modifier is 20-30 minutes; and the stirring and mixing time for adding the surfactant and foaming agent is 10-30 minutes.

3. The method for recycling and regenerating polystyrene plastic according to claim 1, characterized in that, The surfactant is sodium dodecylbenzenesulfonate or sodium dodecyl p-toluenesulfonate, and the amount of surfactant added is 1-5 wt% of the polystyrene waste.

4. The method for recycling and regenerating polystyrene plastic according to claim 1, characterized in that, The foaming agent is azodicarbonamide or azobisisobutyronitrile, and the amount of foaming agent added is 0.5~3wt% of polystyrene waste.

5. The method for recycling and regenerating polystyrene plastic according to claim 1, characterized in that, The remodeling system is cooled to 150-180°C and then depressurized to atmospheric pressure within 1 minute to allow it to foam.

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