A complex solvent and method for dissolving sea-floated polystyrene foam

Abstract

This application relates to the field of marine-drifted polystyrene foam remediation technology, specifically disclosing a composite solvent and method for dissolving marine-drifted polystyrene foam. The composite solvent comprises the following components by mass percentage: 70%–79% main solvent, 12%–20% demulsifier, 6%–9% water-soluble shielding salt additive, and 1%–3% amphiphilic encapsulating agent; the main solvent is a mixture of sec-butyl acetate and isoamyl 2-methylbutyrate. The main solvent rapidly dissolves polystyrene, the demulsifier prevents the main solvent from emulsifying upon contact with water, the shielding salt additive complexes salt ions and enters the aqueous phase to prevent salt ions from mixing into the polystyrene, and the encapsulating agent encapsulates solid impurities and enters the aqueous phase to prevent solid impurities from mixing into the polystyrene. The synergistic effect of the four components allows the composite solvent to directly treat marine-drifted polystyrene foam with high water and high salt content, and the recycled material meets product performance requirements.

Description

Technical Field

[0001] This application relates to the field of marine polystyrene foam remediation technology, specifically disclosing a composite solvent and method for dissolving marine polystyrene foam. Background Technology

[0002] Polystyrene foam is widely used in marine aquaculture and other fields due to its lightweight, strength, and corrosion resistance. The current problem is that large quantities of discarded polystyrene foam products are scattered in the marine environment, forming marine debris. Polystyrene foam is not easily decomposed or degraded by microorganisms in the marine environment, posing a long-term threat to the marine ecosystem and biosecurity.

[0003] Currently, the recycling of marine-drifted polystyrene foam is mainly divided into three categories: physical recycling, pyrolysis / pyrolysis, and solvent recycling.

[0004] Physical recycling methods (such as melt granulation and cold pressing for volume reduction) have relatively simple processes. However, when dealing with marine foam with high water and salt content, the seawater and salt that have seeped into the pores inside the foam are difficult to remove completely by simple washing. Ultimately, the salt and impurities will remain in the recycled material, causing the recycled product to become brittle, discolored, and have reduced mechanical properties, thus failing to meet the quality requirements of recycled plastics.

[0005] Pyrolysis / cracking can convert polystyrene into styrene monomers and fuel oil, but it requires large equipment investments, harsh reaction conditions (usually above 400-600℃), high energy consumption, and the products are complex and require further refining. If polystyrene foam containing brominated flame retardants is pyrolyzed, highly toxic substances such as brominated dioxins may also be generated.

[0006] Solvent recovery utilizes the solubility of polystyrene in specific organic solvents, achieving recycling through a process of dissolution and distillation. This method can operate at room temperature or lower, consumes less energy than pyrolysis, and yields high-purity recycled polystyrene, making it considered one of the most promising technologies for recycling waste polystyrene. However, current solvent recovery technologies primarily target land-based waste foam, facing the following prominent challenges when processing marine-sourced polystyrene foam.

[0007] (1) The solvent system lacks water resistance design and is prone to emulsification failure upon contact with water. Almost all of the relevant solvents are lipophilic organic solvents, which are immiscible with the seawater absorbed by the polystyrene foam. During the stirring and dissolution process, a large amount of water (with a water content of up to 20%~60%) brought in by the sea foam is broken into tiny droplets by mechanical force and dispersed in the organic phase, forming a stable emulsion. The formation of the emulsion layer makes it difficult to separate the two phases, and a large amount of water phase is coated in the polymer solution, which leads to increased energy consumption for subsequent evaporation and difficulty in solvent recovery.

[0008] (2) Salt accumulates in the organic phase, resulting in excessive salt content in the recycled material. Conventional solvents do not have the ability to adsorb or shield salt ions. Some of the salts (NaCl, MgCl2, etc.) attached to marine foam migrate to the organic phase during the dissolution process. When the solvent is recovered by distillation, all the non-volatile salts remain in the recycled polystyrene, causing the performance of the recycled plastic to fail to meet the relevant requirements.

[0009] (3) Solid impurities mixed into recycled materials affect product quality. Marine foam often has solid impurities such as fine mud and sand particles, algae fragments, and shell fragments attached to its surface. These impurities will mix into the polymer solution and eventually remain in the recycled materials, reducing product performance. Summary of the Invention

[0010] To address the challenges of high water content, high salt content, and numerous attached impurities in marine-drifted polystyrene foam, conventional methods for recovering marine-drifted polystyrene foam involve emulsifying the organic solvents upon contact with water, resulting in high residual salt and solid impurities in the recovered polystyrene. This application provides a composite solvent system that is room-temperature soluble, salt-resistant, and water-resistant, along with a matching dissolution method, enabling rapid dissolution and high-purity regeneration of marine-drifted polystyrene foam.

[0011] In the first aspect, this application proposes a composite solvent for dissolving marine-drifted polystyrene foam, and adopts the following technical solution.

[0012] A composite solvent for dissolving marine-drifted polystyrene foam comprises the following components by mass percentage: 70%~79% main solvent, 12%~20% demulsifier, 6%~9% water-soluble shielding salt additive, and 1%~3% amphiphilic encapsulating and solidifying agent; wherein the main solvent is a mixture of sec-butyl acetate and isoamyl 2-methylbutyrate.

[0013] By employing the above technical solution, the main solvent rapidly dissolves polystyrene, the demulsifier prevents the main solvent from emulsifying upon contact with water, the salt-shielding agent complexes salt ions and allows them to enter the aqueous phase, preventing salt ions from mixing into the polystyrene, and the solidification agent encapsulates solid impurities and allows them to enter the aqueous phase, preventing solid impurities from mixing into the polystyrene. The synergistic effect of these four components allows the composite solvent to directly treat marine-drifted polystyrene foam with high water and salt content. Using this composite solvent, the foam can be rapidly dissolved at room temperature, and salt and impurities are effectively shielded or dispersed. The ash content of the recycled polystyrene is ≤1wt%, meeting the requirements of GB / T 40006.6-2021 Recycled Plastics - Part 6: Polystyrene (PS) and Impact-Resistant Polystyrene (PS-I) Materials.

[0014] Preferably, in the main solvent, the mass ratio of sec-butyl acetate to isoamyl 2-methylbutyrate is (50~55):(20~24).

[0015] By adopting the above technical solution, sec-butyl acetate dissolves polystyrene quickly but is prone to emulsification in water, while isoamyl 2-methylbutyrate has slightly weaker dissolving ability but good water resistance. The combination of the two maintains rapid dissolution and enhances the solvent's tolerance to water, reducing solvent emulsification loss.

[0016] Preferably, the demulsifier is dimethyl carbonate or ethyl methyl carbonate.

[0017] By adopting the above technical solution, dimethyl carbonate or ethyl methyl carbonate forms hydrogen bonds with water molecules through its own carbonyl oxygen, binding trace water molecules near the interface instead of entering the organic phase, thus playing a demulsifying role. After the demulsifier adsorbs water molecules, it sinks into the aqueous phase. Therefore, the demulsifier can reduce the turbidity of the composite solvent caused by water, making the composite solvent water resistant.

[0018] Preferably, the shielding salt additive is triethylene glycol dimethyl ether or N,N-dimethylformamide.

[0019] By adopting the above technical solution, triethylene glycol dimethyl ether reacts with Na through multiple ether oxygen atoms. + Mg 2+ Ca 2+ Through multi-point coordination, N,N-dimethylformamide forms strong coordination bonds with salt ions via carbonyl oxygen. Water-soluble triethylene glycol dimethyl ether or N,N-dimethylformamide forms a solvation shell to shield against salt ion interference. The coordination product dissolves in the aqueous phase, thus preventing salt ions from impairing the solubility of the main solvent, resulting in a salt-resistant composite solvent. Salt molecules essentially do not enter the main solvent, therefore, salt remains virtually non-existent in recycled polystyrene.

[0020] Preferably, the encapsulating agent is castor oil polyoxyethylene ether EL-20 or castor oil polyoxyethylene ether EL-40.

[0021] By adopting the above technical solutions, castor oil polyoxyethylene ether EL-20 and castor oil polyoxyethylene ether EL-40 have hydrophobic and hydrophilic chains. The hydrophobic chains are adsorbed on the surface of solid particles such as mud, algae, etc., while the hydrophilic chains enter the aqueous phase and sink into the aqueous phase under the action of gravity, thereby basically avoiding the mixing of solid particles such as mud, algae, etc. into polystyrene.

[0022] Secondly, this application proposes a method for dissolving marine-drifted polystyrene foam, and adopts the following technical solution.

[0023] A method for dissolving marine-drifted polystyrene foam, comprising using the aforementioned composite solvent for dissolving marine-drifted polystyrene foam to treat the foam; the method for dissolving marine-drifted polystyrene foam includes: S1, the main solvent, the demulsifier, the shielding salt additive and the encapsulating solidifying agent are mixed and stirred evenly according to the ratio to obtain a homogeneous composite solvent for dissolving marine-drifted polystyrene foam; S2, add the marine-drifted polystyrene foam into the composite solvent that dissolves the marine-drifted polystyrene foam to obtain an undissolved system; S3, under normal temperature and pressure conditions, the undissolved system is stirred to dissolve the marine-drifted polystyrene foam, thus obtaining a dissolved system; S4, let stand, the dissolution system is divided into two layers: the lower layer is an aqueous phase containing the shielding salt ion encapsulated by the shielding salt auxiliaries and the solid impurity encapsulating agent encapsulated by the solid impurity, and the upper layer is an organic phase containing the main solvent and polystyrene; S5, collect the upper layer and filter to remove suspended impurities; S6, the filtered organic phase is evaporated to recover the solvent, the solvent is condensed and recycled, and the residue after evaporation is polystyrene.

[0024] By employing the above technical solution, this method achieves high efficiency in dissolving polystyrene. After dissolution and settling, the polystyrene separates into layers, with all salts and solid impurities remaining in the lower aqueous phase, without contaminating the upper organic phase. The demulsifier's demulsification function primarily occurs at the oil-water interface, strongly adsorbing and disrupting the hydrogen bond network between water molecules, reducing interfacial film strength, lowering oil-water interfacial tension, promoting water droplet coalescence, and achieving rapid oil-water separation. The water droplets can then settle into the aqueous phase along with the coalescing droplets.

[0025] Preferably, in step S2, the ratio of the mass of the marine-drifted polystyrene foam to the volume of the composite solvent used to dissolve the marine-drifted polystyrene foam is 1 kg: (8~12) L.

[0026] By adopting the above technical solution, at this ratio, the solvent can completely dissolve the foam within 8 to 12 minutes. The amount of solvent used is moderate, which can reduce the energy consumption of recycling.

[0027] Preferably, the evaporation in step S6 is carried out at 60°C to 80°C and a pressure of 1 kPa to 5 kPa.

[0028] By adopting the above technical solution, the boiling point of the solvent is significantly reduced under reduced pressure, and it can evaporate under mild conditions of 60℃~80℃, thus avoiding the thermal degradation of polystyrene.

[0029] In summary, the composite solvent and method for dissolving marine-drifted polystyrene foam of this application have the following beneficial effects: This composite solvent achieves rapid dissolution and stratification of marine-drifted polystyrene foam under aqueous conditions through the synergistic effect of the demulsifier and the main solvent, without forming a stable emulsion, thus ensuring complete separation of the aqueous and organic phases.

[0030] This composite solvent effectively prevents salt ions from interfering with the dissolution process by shielding the coordination and complexation of salt additives, and the salt residue of recycled polystyrene meets relevant requirements.

[0031] This composite solvent encapsulates solid impurities such as mud, sand, and algae in the lower aqueous phase by encapsulating them with a solidifying agent, thus ensuring a clear and pure polymer solution.

[0032] This composite solvent can directly treat marine-sourced waste polystyrene foam with a water content of about 30wt% and a salt content of about 10wt%. It can work efficiently at room temperature (10~40℃) and normal pressure, and complete the foam dissolution in 8~12 minutes. The energy consumption is much lower than that of the pyrolysis method. Moreover, the solvent can be distilled and recycled, with a recovery rate of over 92%. Attached Figure Description

[0033] Figure 1 This is a flowchart of Example 1. Detailed Implementation

[0034] 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. Example 1

[0035] A method for dissolving marine-drifted polystyrene foam, reference Figure 1 This includes the following steps.

[0036] S1, Solvent preparation: sec-butyl acetate, isoamyl 2-methylbutyrate, dimethyl carbonate, triethylene glycol dimethyl ether, and castor oil polyoxyethylene ether EL-20 are added to a dissolving vessel in a mass ratio of 53:22:16:7:2 and stirred and mixed evenly at room temperature to obtain a uniform and transparent composite solvent for dissolving marine-drifted polystyrene foam.

[0037] S2, Feeding: Add the collected marine-drifted polystyrene foam with a moisture content of 33wt% and a salt content of 10.5wt% into the composite solvent. The solid-liquid ratio is 1kg marine-drifted polystyrene foam: 10L composite solvent.

[0038] S3, rapid dissolution at room temperature: Under normal temperature and pressure conditions, turn on the stirrer, turn on the speed at 100 r / min, stir for 10 min, and the polystyrene foam will dissolve.

[0039] S4, Impurity Removal and Separation: Stop stirring and let stand for 5 minutes. The system naturally separates into two layers: a lower aqueous phase and an upper organic phase. The aqueous phase contains dimethyl carbonate, as well as complexes containing salt ions encapsulated by triethylene glycol dimethyl ether, and inclusions of solid impurities such as silt and algae encapsulated by castor oil polyoxyethylene ether EL-20. The upper layer is a clear polystyrene polymer solution containing sec-butyl acetate, isoamyl 2-methylbutyrate, and polystyrene.

[0040] S5, Separation: The upper organic phase is collected by discharging the material from the bottom of the vessel. The organic phase is then filtered through a 300-mesh filter to remove suspended solid impurities.

[0041] S6, Solvent Recovery and Polymer Regeneration: The filtered organic phase is introduced into a vacuum distillation unit to evaporate and recover the composite solvent at 70°C and 3 kPa. The solvent recovery rate is 93.5%, and the water content of the recovered solvent is 0.12 wt%. The distilled solvent is condensed and recycled to S1 for reuse. The distillation residue is high-purity recycled polystyrene with an ash content of 0.15 wt%, which can be directly granulated and reused. Example 2

[0042] A method for dissolving marine-drifted polystyrene foam. The difference between this embodiment and Embodiment 1 lies in the solvent ratio, solid-liquid ratio, and evaporation parameters. This embodiment includes the following steps.

[0043] S1, Solvent preparation: Add sec-butyl acetate, isoamyl 2-methylbutyrate, dimethyl carbonate, triethylene glycol dimethyl ether, and castor oil polyoxyethylene ether EL-20 into a dissolving vessel at a mass ratio of 55:24:12:6:3, and stir and mix evenly at room temperature to obtain a uniform and transparent composite solvent for dissolving marine-drifted polystyrene foam.

[0044] S2, Feeding: Add the collected marine-drifted polystyrene foam with a moisture content of 33wt% and a salt content of 10.5wt% into the composite solvent. The solid-liquid ratio is 1kg marine-drifted polystyrene foam: 8L composite solvent.

[0045] S3, rapid dissolution at room temperature: Under normal temperature and pressure conditions, turn on the stirrer, turn on the speed at 100 r / min, stir for 10 min, and the polystyrene foam will dissolve.

[0046] S4, Impurity Removal and Separation: Stop stirring and let stand for 5 minutes. The system naturally separates into two layers: a lower aqueous phase and an upper organic phase. The aqueous phase contains dimethyl carbonate, as well as complexes containing salt ions encapsulated by triethylene glycol dimethyl ether, and inclusions of solid impurities such as silt and algae encapsulated by castor oil polyoxyethylene ether EL-20. The upper layer is a clear polystyrene polymer solution containing sec-butyl acetate, isoamyl 2-methylbutyrate, and polystyrene.

[0047] S5, Separation: The upper organic phase is collected by discharging the material from the bottom of the vessel. The organic phase is then filtered through a 300-mesh filter to remove suspended solid impurities.

[0048] S6, Solvent Recovery and Polymer Regeneration: The filtered organic phase is introduced into a vacuum distillation unit to evaporate and recover the composite solvent at 60°C and 1 kPa. The solvent recovery rate is 92.8%, and the water content of the recovered solvent is 0.10 wt%. The distilled solvent is condensed and recycled to S1 for reuse. The distillation residue is high-purity recycled polystyrene with an ash content of 0.18 wt%, which can be directly granulated and reused. Example 3

[0049] A method for dissolving marine-drifted polystyrene foam. The difference between this embodiment and Embodiment 1 lies in the solvent ratio, solid-liquid ratio, and evaporation parameters. This embodiment includes the following steps.

[0050] S1, Solvent preparation: Add sec-butyl acetate, isoamyl 2-methylbutyrate, dimethyl carbonate, triethylene glycol dimethyl ether, and castor oil polyoxyethylene ether EL-20 into a dissolving vessel at a mass ratio of 50:20:20:9:1, and stir and mix evenly at room temperature to obtain a uniform and transparent composite solvent for dissolving marine-drifted polystyrene foam.

[0051] S2, Feeding: Add the collected marine-drifted polystyrene foam with a moisture content of 33wt% and a salt content of 10.5wt% into the composite solvent. The solid-liquid ratio is 1kg marine-drifted polystyrene foam: 12L composite solvent.

[0052] S3, rapid dissolution at room temperature: Under normal temperature and pressure conditions, turn on the stirrer, turn on the speed at 100 r / min, stir for 10 min, and the polystyrene foam will dissolve.

[0053] S4, Impurity Removal and Separation: Stop stirring and let stand for 5 minutes. The system naturally separates into two layers: a lower aqueous phase and an upper organic phase. The aqueous phase contains dimethyl carbonate, as well as complexes containing salt ions encapsulated by triethylene glycol dimethyl ether, and inclusions of solid impurities such as silt and algae encapsulated by castor oil polyoxyethylene ether EL-20. The upper layer is a clear polystyrene polymer solution containing sec-butyl acetate, isoamyl 2-methylbutyrate, and polystyrene.

[0054] S5, Separation: The upper organic phase is collected by discharging the material from the bottom of the vessel. The organic phase is then filtered through a 300-mesh filter to remove suspended solid impurities.

[0055] S6, Solvent Recovery and Polymer Regeneration: The filtered organic phase is introduced into a vacuum distillation unit to evaporate and recover the composite solvent at 80℃ and 5kPa. The solvent recovery rate is 93.1%, and the water content of the recovered solvent is 0.13wt%. The distilled solvent is condensed and recycled to S1 for reuse. The distillation residue is high-purity recycled polystyrene with an ash content of 0.20wt%, which can be directly granulated and reused. Example 4

[0056] A method for dissolving marine-drifted polystyrene foam. The difference between this embodiment and Embodiment 1 is the type of solvent. This embodiment includes the following steps.

[0057] S1, Solvent preparation: sec-butyl acetate, isoamyl 2-methylbutyrate, ethyl methyl carbonate, N,N-dimethylformamide, and castor oil polyoxyethylene ether EL-40 are added to a dissolving vessel in a mass ratio of 53:22:16:7:2 and stirred and mixed evenly at room temperature to obtain a uniform and transparent composite solvent for dissolving marine-drifted polystyrene foam.

[0058] S2, Feeding: Add the collected marine-drifted polystyrene foam with a moisture content of 33wt% and a salt content of 10.5wt% into the composite solvent. The solid-liquid ratio is 1kg marine-drifted polystyrene foam: 10L composite solvent.

[0059] S3, rapid dissolution at room temperature: Under normal temperature and pressure conditions, turn on the stirrer, turn on the speed at 100 r / min, stir for 10 min, and the polystyrene foam will dissolve.

[0060] S4, Impurity Removal and Separation: Stop stirring and let stand for 5 minutes. The system naturally separates into two layers: a lower aqueous phase and an upper organic phase. The aqueous phase contains ethyl methyl carbonate, as well as complexes containing N,N-dimethylformamide encapsulating salt ions, and castor oil polyoxyethylene ether EL-40 encapsulating solid impurities such as silt and algae. The upper layer is a clear polystyrene polymer solution containing sec-butyl acetate, isoamyl 2-methylbutyrate, and polystyrene.

[0061] S5, Separation: The upper organic phase is collected by discharging the material from the bottom of the vessel. The organic phase is then filtered through a 300-mesh filter to remove suspended solid impurities.

[0062] S6, Solvent Recovery and Polymer Regeneration: The filtered organic phase is introduced into a vacuum distillation unit, where the composite solvent is evaporated and recovered at 70°C and 3 kPa. The solvent recovery rate is 92.4%, and the water content of the recovered solvent is 0.15 wt%. The distilled solvent is condensed and recycled to S1 for reuse. The distillation residue is high-purity recycled polystyrene with an ash content of 0.22 wt%, which can be directly granulated and reused.

[0063] Comparative Example 1 A method for dissolving marine-drifted polystyrene foam, which differs from Example 1 in that it uses an equal mass of d-limonene instead of a mixture of sec-butyl acetate and isoamyl 2-methylbutyrate, specifically including the following steps.

[0064] S1, Solvent preparation: d-limonene, dimethyl carbonate, triethylene glycol dimethyl ether, and castor oil polyoxyethylene ether EL-20 are added to a dissolving vessel in a mass ratio of 75:16:7:2 and stirred and mixed evenly at room temperature to obtain a uniform and transparent composite solvent for dissolving marine-drifted polystyrene foam.

[0065] S2, Feeding: Add the collected marine-drifted polystyrene foam with a moisture content of 33wt% and a salt content of 10.5wt% into the composite solvent. The solid-liquid ratio is 1kg marine-drifted polystyrene foam: 10L composite solvent.

[0066] S3, rapid dissolution at room temperature: Under normal temperature and pressure conditions, turn on the stirrer, turn on the speed at 100 r / min, stir for 10 min, and the polystyrene foam will dissolve.

[0067] S4, Impurity Removal and Layering: After stopping stirring and allowing it to stand, the system fails to separate into layers, forming a stable milky white emulsion with no clear interface. Even after standing for 30 minutes, it remains turbid. This is because the extreme hydrophobicity of d-limonene causes a stable interfacial film to form at the oil-water interface, making it difficult for water droplets to coalesce and settle into a clear aqueous phase. The stabilization mechanism far exceeds the ability of the demulsifier dimethyl carbonate to balance the emulsion; the water is broken down into tiny droplets and maintained in an emulsified state.

[0068] S5, Separation: Since there was no stratification, centrifugation was performed at 4000 rpm for 10 min to obtain a small amount of supernatant (containing the organic phase of polystyrene) and a large amount of lower emulsion.

[0069] S6, Solvent Recovery and Polymer Regeneration: The supernatant after centrifugation was evaporated and the composite solvent was recovered at 70°C and 3 kPa. The solvent recovery rate was 23.9%, and the water content of the recovered solvent was as high as 5.2 wt%. The distillation residue was recycled polystyrene with an ash content of 2.43 wt%.

[0070] Comparative Example 2 A method for dissolving marine-drifted polystyrene foam, which differs from Example 1 in that it uses sec-butyl acetate alone instead of an equal mass mixture of sec-butyl acetate and isoamyl 2-methylbutyrate. This comparative example specifically includes the following steps.

[0071] S1, Solvent preparation: Add sec-butyl acetate, dimethyl carbonate, triethylene glycol dimethyl ether, and castor oil polyoxyethylene ether EL-20 into a dissolving vessel at a mass ratio of 75:16:7:2, and stir and mix evenly at room temperature to obtain a uniform and transparent composite solvent for dissolving marine-drifted polystyrene foam.

[0072] S2, Feeding: Add the collected marine-drifted polystyrene foam with a moisture content of 33wt% and a salt content of 10.5wt% into the composite solvent. The solid-liquid ratio is 1kg marine-drifted polystyrene foam: 10L composite solvent.

[0073] S3, rapid dissolution at room temperature: Under normal temperature and pressure conditions, turn on the stirrer, turn on the speed at 100 r / min, stir for 10 min, and the polystyrene foam will dissolve.

[0074] S4, Impurity Removal and Layering: Stop stirring and let stand for 30 minutes. The system mainly consists of two layers: a lower aqueous phase and an upper organic phase, with an emulsion layer between them. The interface is not as clear as in Example 1. Although pure sec-butyl acetate has strong solubility for polystyrene, its water resistance is not strong enough, lacking the water resistance regulating effect of isoamyl 2-methylbutyrate. Even with the demulsifier dimethyl carbonate, it cannot prevent sec-butyl acetate and water from dispersing and forming an emulsion layer. The emulsion layer also contains a small amount of solid impurities, which will reduce the recovery rate of sec-butyl acetate. The aqueous phase contains dimethyl carbonate, as well as triethylene glycol dimethyl ether complexes encapsulating salt ions, and castor oil polyoxyethylene ether EL-20 encapsulating solid impurities such as mud and algae. The upper layer is a polystyrene polymer solution containing sec-butyl acetate and polystyrene.

[0075] S5, Separation: The upper organic phase is collected by discharging the material from the bottom of the vessel. The organic phase is then filtered through a 300-mesh filter to remove suspended solid impurities.

[0076] S6, Solvent Recovery and Polymer Regeneration: The filtered organic phase is introduced into a vacuum distillation unit, and the composite solvent is evaporated and recovered at 70°C and 3 kPa. The solvent recovery rate is 81.4%, and the water content of the recovered solvent is 2.3 wt%. The distillation residue is high-purity recycled polystyrene with an ash content of 0.28 wt%, which can be directly granulated and reused.

[0077] Comparative Example 3 A method for dissolving marine-drifted polystyrene foam, which differs from Example 1 in that it does not contain the demulsifier dimethyl carbonate, specifically includes the following steps.

[0078] S1, Solvent preparation: sec-butyl acetate, isoamyl 2-methylbutyrate, triethylene glycol dimethyl ether, and castor oil polyoxyethylene ether EL-20 are added to a dissolving vessel in a mass ratio of 53:22:7:2 and stirred and mixed evenly at room temperature to obtain a uniform and transparent composite solvent for dissolving marine-drifted polystyrene foam.

[0079] S2, Feeding: Add the collected marine-drifted polystyrene foam with a moisture content of 33wt% and a salt content of 10.5wt% into the composite solvent. The solid-liquid ratio is 1kg marine-drifted polystyrene foam: 10L composite solvent.

[0080] S3, rapid dissolution at room temperature: Under normal temperature and pressure conditions, turn on the stirrer, turn on the speed at 100 r / min, stir for 10 min, and the polystyrene foam will dissolve.

[0081] S4, Impurity Removal and Separation: After stopping stirring and letting stand for 30 minutes, the system still presents a stable emulsion and cannot be clearly separated into layers.

[0082] S5, Separation: Since there was no stratification, centrifugation at 4000 rpm for 10 min was performed to obtain a small amount of supernatant (containing the organic phase of polystyrene) and a large amount of lower emulsion. Centrifugation was performed again, and the supernatant organic phase was collected. The organic phase was then filtered through a 300-mesh filter to remove suspended solid impurities.

[0083] S6, Solvent Recovery and Polymer Regeneration: The filtered organic phase is introduced into a vacuum distillation apparatus to evaporate and recover the composite solvent at 70°C and 3 kPa. The solvent recovery rate is 30.8%, and the water content of the recovered solvent is as high as 2.6 wt%. The ash content of the distillation residue is 1.74 wt%.

[0084] Comparative Example 4 A method for dissolving marine-drifted polystyrene foam, which differs from Example 1 in that it does not contain the shielding salt additive triethylene glycol dimethyl ether, specifically includes the following steps.

[0085] S1, Solvent preparation: Add sec-butyl acetate, isoamyl 2-methylbutyrate, dimethyl carbonate, and castor oil polyoxyethylene ether EL-20 into a dissolving vessel at a mass ratio of 53:22:16:2, and stir and mix evenly at room temperature to obtain a uniform and transparent composite solvent for dissolving marine-drifted polystyrene foam.

[0086] S2, Feeding: Add the collected marine-drifted polystyrene foam with a moisture content of 33wt% and a salt content of 10.5wt% into the composite solvent. The solid-liquid ratio is 1kg marine-drifted polystyrene foam: 10L composite solvent.

[0087] S3, rapid dissolution at room temperature: Under normal temperature and pressure conditions, turn on the stirrer, turn on the speed at 100 r / min, stir for 10 min, and the polystyrene foam will dissolve.

[0088] S4, Impurity Removal and Separation: Stop stirring and let stand for 5 minutes. The system will naturally separate into two layers: the lower layer is the aqueous phase and the upper layer is the organic phase.

[0089] S5, Separation: The upper organic phase is collected by discharging the material from the bottom of the vessel. The organic phase is then filtered through a 300-mesh filter to remove suspended solid impurities.

[0090] S6, Solvent Recovery and Polymer Regeneration: The filtered organic phase is introduced into a vacuum distillation apparatus to evaporate and recover the composite solvent at 70°C and 3 kPa. The solvent recovery rate is 92.3%, and the water content of the recovered solvent is 0.26 wt%. The distillation residue is recycled polystyrene with an ash content as high as 2.76 wt%.

[0091] Comparative Example 5 A method for dissolving marine-drifted polystyrene foam, which differs from Example 1 in that it does not contain the encapsulating solidifying agent castor oil polyoxyethylene ether EL-20, specifically includes the following steps.

[0092] S1, Solvent preparation: Add sec-butyl acetate, isoamyl 2-methylbutyrate, dimethyl carbonate, and triethylene glycol dimethyl ether into a dissolving vessel at a mass ratio of 53:22:16:7, and stir and mix evenly at room temperature to obtain a uniform and transparent composite solvent for dissolving marine-drifted polystyrene foam.

[0093] S2, Feeding: Add the collected marine-drifted polystyrene foam with a moisture content of 33wt% and a salt content of 10.5wt% into the composite solvent. The solid-liquid ratio is 1kg marine-drifted polystyrene foam: 10L composite solvent.

[0094] S3, rapid dissolution at room temperature: Under normal temperature and pressure conditions, turn on the stirrer, turn on the speed at 100 r / min, stir for 10 min, and the polystyrene foam will dissolve.

[0095] S4, Impurity Removal and Separation: Stop stirring and let stand for 5 minutes. The system naturally separates into two layers: a lower aqueous phase and an upper organic phase. Fine suspended solid particles are visible in the organic phase.

[0096] S5, Separation: The upper organic phase is collected by discharging the material from the bottom of the vessel. The organic phase is then filtered through a 300-mesh filter to remove suspended solid impurities. The filtration speed is significantly slower than in Example 1.

[0097] S6, Solvent Recovery and Polymer Regeneration: The filtered organic phase is introduced into a vacuum distillation apparatus to evaporate and recover the composite solvent at 70°C and 3 kPa. The solvent recovery rate is 92.1%, and the water content of the recovered solvent is 0.38 wt%. The distilled solvent is condensed and recycled to S1 for reuse. The distillation residue is recycled polystyrene with an ash content of 1.95 wt%.

[0098] Experimental Example 1 Recycled polystyrene prepared in Examples 1-4 and Comparative Examples 1-5, along with the same batch of marine-drifted polystyrene foam raw materials used in each example and comparative example, were heated to 240℃ to melt and then used to prepare samples for tensile strength, elongation at break, and impact strength tests. The tensile strength and elongation at break tests were performed according to GB / T 1040.2-2022 "Determination of Tensile Properties of Plastics". The impact strength test was performed according to GB / T 1043.1-2008 "Determination of Impact Properties of Simply Supported Beams of Plastics". The test results are shown in Table 1 below.

[0099] Table 1. Statistics of Polystyrene Performance Test Data Sample Ash content (wt%) Tensile strength (MPa) Elongation at break (%) <![CDATA[Impact strength (kJ / m 2 )]]> Example 1 0.15 41.9 3.3 2.5 Example 2 0.18 41.1 3.4 2.4 Example 3 0.20 41.5 3.2 2.3 Example 4 0.22 40.8 3.1 2.3 Comparative Example 1 2.43 22.3 2.3 1.5 Comparative Example 2 0.28 38.7 3.0 2.1 Comparative Example 3 1.74 26.4 2.8 1.9 Comparative Example 4 2.76 20.8 1.9 1.3 Comparative Example 5 1.95 25.1 2.5 1.8 raw material 14.39 16.4 0.6 0.5 Table 1 shows that the untreated marine-drifted polystyrene foam raw material has an ash content as high as 14.39% (mainly composed of salt and inorganic impurities such as silt), a tensile strength of only 16.4 MPa, an elongation at break of 0.6%, and an impact strength of 0.5 kJ / m. 2 This indicates that marine-drifted polystyrene foam suffers from severe pollution due to long-term immersion in the ocean, resulting in poor mechanical properties and making it unsuitable for direct resource utilization.

[0100] The recycled polystyrene in Examples 1-4 has an ash content of 0.15%~0.22%, meeting the requirement of ≤1wt% ash content in GB / T 40006.6-2021 Recycled Plastics - Part 6: Polystyrene (PS) and Impact-Resistant Polystyrene (PS-I) Materials. Its tensile strength, elongation at break, and impact strength reach or approach typical values ​​for virgin polystyrene. This indicates that the composite solvent system in these examples achieves efficient impurity removal from raw materials and high-purity product regeneration through multiple synergistic effects, including demulsification, shielding of salt ions, and encapsulation of solid impurities.

[0101] In Comparative Example 1, the main solvent, a mixture of sec-butyl acetate and isoamyl 2-methylbutyrate, was replaced with d-limonene, which resulted in severe emulsification after stirring and dissolving the raw materials, high salt residue in the recycled material, and a significant decrease in mechanical properties.

[0102] In Comparative Example 2, the main solvent was replaced with pure sec-butyl acetate. After stirring and dissolving the raw materials, an emulsion layer was present at the interface between the aqueous and organic phases, resulting in slightly lower mechanical properties of the recycled material compared to Example 1. This is because isoamyl 2-methylbutyrate in Example 1 effectively locks the demulsifier dimethyl carbonate on the aqueous phase side, thereby significantly reducing the possibility of fine water droplets entering the organic phase and ensuring the performance of the recycled material.

[0103] In Comparative Example 3, the composite solvent dimethyl carbonate without demulsifier emulsifier emulsified the system after stirring and dissolving the raw materials, making it difficult to separate into layers. Impurities mixed into the recycled materials led to the deterioration of the recycled materials' performance.

[0104] In Comparative Example 4, the composite solvent without shielding salt additive triethylene glycol dimethyl ether, after stirring and dissolving the raw materials, could not shield the salt and a large amount remained in the recycled material, resulting in the most serious ash content exceeding the standard and a significant decrease in product performance.

[0105] In Comparative Example 5, the composite solvent without encapsulating solid impurities, castor oil polyoxyethylene ether EL-20, resulted in solid impurities being mixed into the organic phase after the raw materials were stirred and dissolved, leading to higher ash content and decreased mechanical properties in the recycled material.

[0106] The composite solvent of this application consists of four functional components: the main solvent is a mixture of sec-butyl acetate and isoamyl 2-methylbutyrate, which utilizes the complementary structure of diester molecules to impart certain water resistance properties to the system while maintaining rapid dissolution of polystyrene; the demulsifier is made of dimethyl carbonate, diethyl carbonate, or methyl ethyl carbonate, which adsorbs onto the oil-water interface through its amphiphilic molecular structure, significantly reducing interfacial tension, promoting the coalescence of tiny water droplets, and preventing the formation of an emulsion layer; the salt shielding agent is made of triethylene glycol dimethyl ether or N,N-dimethylformamide, whose ether oxygen atom or carbonyl oxygen can form a coordination complex with salt ions in the solution, shielding the salt ions outside the organic phase, preventing them from interfering with the dissolution process of the main solvent, and reducing the salt residue in the recycled material; the solid impurity encapsulating agent is made of castor oil polyoxyethylene ether EL-20 or EL-40, whose amphiphilic structure can adsorb onto the surface of solid impurities, encapsulating and dispersing them in the aqueous phase, so that solid impurities no longer mix into the polymer solution, reducing the solid impurity residue in the recycled material.

[0107] Comparative Examples 1-5 each lacked one key component, resulting in increased ash content and decreased mechanical properties in the recycled materials. Examples 1-4 of this application can purify highly polluting marine-drifted polystyrene foam into high-purity recycled polystyrene, achieving mechanical properties comparable to conventional polystyrene and meeting the performance requirements of recycled materials. The results of the examples and comparative examples demonstrate that the four functional components of the composite solvent in this application synergistically enhance solvent recovery rate and the performance of recycled polystyrene during the dissolution and regeneration processes.

[0108] The technical solution of this application solves the problems of system emulsification, solvent deactivation, salt residue and impurity mixing in the process of recycling marine waste polystyrene foam, and provides a brand-new technical path for high-purity, low-emission and high-efficiency recycling of marine waste foam plastics.

[0109] 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 complex solvent for dissolving sea-surface floating polystyrene foam, characterized by comprising The composition comprises the following components by mass percentage: a main solvent 70-79%, a demulsifier 12-20%, a water-soluble shielding salt additive 6-9%, and an amphiphilic wrapping solid impurity agent 1-3%; the main solvent is a mixture of sec-butyl acetate and isoamyl 2-methylbutyrate.

2. The complex solvent for dissolving sea-swept polystyrene foam according to claim 1, wherein In the main solvent, the mass ratio of sec-butyl acetate to isoamyl 2-methylbutyrate is (50-55):(20-24).

3. The complex solvent for dissolving sea-swept polystyrene foam according to claim 1, wherein The demulsifier is dimethyl carbonate or methyl ethyl carbonate.

4. The complex solvent for dissolving sea-swept polystyrene foam according to claim 1, wherein The shielding salt additive is triethylene glycol dimethyl ether or N,N-dimethylformamide.

5. The complex solvent for dissolving sea-swept polystyrene foam according to claim 1, wherein The wrapping solid impurity agent is castor oil polyoxyethylene ether EL-20 or castor oil polyoxyethylene ether EL-40.

6. A method of dissolving a sea-floated polystyrene foam, characterized by, The method for dissolving sea-rafted polystyrene foam comprises the following steps: S1, mixing the main solvent, the demulsifier, the shielding salt additive, and the wrapping solid impurity agent according to the proportion, and stirring uniformly to obtain the complex solvent for dissolving sea-rafted polystyrene foam in a uniform phase; S2, putting the sea-rafted polystyrene foam into the complex solvent for dissolving sea-rafted polystyrene foam to obtain an unsolved system; S3, stirring the unsolved system under normal temperature and pressure to dissolve the sea-rafted polystyrene foam and obtain a dissolved system; S4, standing, and the dissolved system is divided into two layers: the lower layer is an aqueous phase containing the shielding salt additive wrapped salt ions and the wrapping solid impurity agent, and the upper layer is an organic phase containing the main solvent and polystyrene; S5, collecting the upper layer and filtering to remove suspended impurities; S6, evaporating the filtered organic phase to recover the solvent, and the solvent is recycled after condensation, and the residue after evaporation is polystyrene.

7. The method of dissolving sea-floated polystyrene foam according to claim 6, characterized in that, In step S2, the mass ratio of the sea-rafted polystyrene foam to the volume of the complex solvent for dissolving sea-rafted polystyrene foam is 1 kg:(8-12) L.

8. The method of dissolving sea-floated polystyrene foam according to claim 6, wherein The evaporation in step S6 is carried out at 60-80℃ and 1-5 kPa.

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