Method for preparing polystyrene powder by recovering waste polystyrene foam plastic with water-soluble organic solvent

Abstract

The invention discloses a method for preparing polystyrene powder by recovering waste polystyrene foam plastic by using a water-soluble organic solvent, which comprises the following steps: S1, dissolving the waste polystyrene foam plastic by using the water-soluble organic solvent to obtain a solution I; s2, aging the solution I, and filtering to remove insoluble impurities in the solution I to obtain a transparent solution II; s3, slowly adding the solution II obtained in the step S2 into deionized water, and slowly separating out polystyrene; adding all the solution II into deionized water, stirring until polystyrene is completely separated out, and filtering to obtain polystyrene powder; and S4, cleaning, drying, crushing and sieving the polystyrene powder obtained in the step S3, and then recovering. The method disclosed by the invention is simple in process, and high-temperature melting of PS for granulation and recovery is not needed; impurities are easy to remove, and pure PS powder can be obtained; and in the recovery process, no pollutant is discharged, dangerous chemicals are not used, and the process is safe and environmentally friendly.

Description

Technical Field

[0001] The invention relates to the field of recycling of waste plastics, in particular to a method for preparing polystyrene powder by recycling waste polystyrene foam plastics with a water-soluble organic solvent. Background Art

[0002] Polystyrene (PS) is a polymer formed by the polymerization of styrene monomers. By adding a foaming agent, it can be made into polystyrene foam plastics. This material has the advantages of acid and alkali resistance, light weight, low water absorption, good cushioning and shock resistance, heat insulation, sound insulation and thermal insulation performance, and is widely used in packaging materials, insulation boards, sound insulation boards and other fields. However, while polystyrene materials bring convenience to life, the discarded foam plastics after use are difficult to degrade and are called white foam garbage. If they cannot be effectively treated, they will become an important source of pollution to the ecological environment.

[0003] Currently, plastic waste disposal is a serious environmental problem worldwide. The three main ways to manage urban domestic waste are landfill, incineration and recycling. Due to the difficulty of plastic degradation, landfill is unsustainable; incineration produces toxic gases and causes air pollution. Both methods have more disadvantages than advantages. Therefore, the recycling or degradation of plastic waste is increasingly valued.

[0004] Since polystyrene is a thermoplastic, the current mainstream recycling method is hot melt recycling. This method needs to be carried out at high temperatures. On the one hand, there is a problem of toxic waste gas emissions. On the other hand, high temperatures will cause the degree of polymerization of polystyrene to decrease, affecting its quality. In addition, the high temperature process consumes a lot of energy. Therefore, the method of using solvent dissolution and then precipitation has attracted widespread attention.

[0005] As a non-polar thermoplastic organic polymer, polystyrene has a high solubility in non-polar organic solvents. Currently, a variety of organic solvents have been reported, but they are all non-water-soluble solvents, such as aromatic solvents (benzene, toluene, etc.), esters, ketones, halogenated hydrocarbons and limonene (orange peel oil).

[0006] For example, the journal article "Solvent Method for Recycling Waste Polystyrene Foam Plastics" (Plastics Science and Technology, 2010, 38(12): 69-73) uses dibutyl acetate and xylene as solvents; "Research on the Process of Recycling Polystyrene Foam Plastics by Solvent Method" (Modern Chemical Industry, 2012, 32(10): 43-45) uses toluene and ethylene dichloride as solvents; Polystyvert uses natural solvents to recycle polystyrene (Petrochemical Applications, 2020, 39: 90), using para-isopropyltoluene as solvent.

[0007] Monographs such as "Polymer Recycling - Science, Technology and Application" (Chemical Industry Press, 2004, P209-211) use limonene as solvent; "Preparation and Classification of Waste Plastic Recycling" (Chemical Industry Press, second edition, 2012, P204-215) uses aromatic benzene solvents.

[0008] Degree theses such as "Research on the Recycling and Modification of Polystyrene Foam Plastics" (PhD dissertation of Northeastern University, 2006) use cyclohexene as solvent; "Research on the Recovery of Waste Polystyrene Foam Plastics with Natural Solvents" (Master's thesis of Tianjin Institute of Light Industry, 2001) uses limonene as solvent; "Research on the Recovery of Polystyrene Waste by Aqueous Suspension Functionalized Granulation" (Master's thesis of Wuhan University of Technology, 2022) uses dichloromethane as solvent.

[0009] Patents such as CN1160728A "Method for Recycling Waste Polystyrene Foam Plastics" adopts limonene as solvent; CN103122074A "An Environmentally Friendly Method for Recycling Polystyrene Foam Plastics" adopts ethyl acetate as solvent and ethanol as precipitant; CN103224646A "New Process for Recycling Waste Polystyrene Foam Plastics" adopts mixed aromatic solvents and halogenated hydrocarbons as solvents; CN105087167A "Process for Extracting Volatile Oil from Citrus Peel and Method for Recycling Foam Plastics Using Volatile Oil" adopts limonene as solvent; CN101367956B "Method for Recycling Polystyrene Foam Plastics Using Methyl Esterification Products of Vegetable Oils and Fats as Volume Reducing Agents" adopts methyl esterification products of vegetable oils and fats as solvents.

[0010] However, aromatic solvents, halogenated hydrocarbons, cyclohexene, esters and ketones among these organic solvents are not only flammable and explosive hazardous chemicals, but also highly toxic, which limits their application. Although limonene is less toxic, it is mainly extracted from orange peels, which is expensive and economically unfeasible for recycling waste plastics. Although there have been related reports 20 to 30 years ago, it is still limited to experimental research and has not yet been applied on a large scale.

[0011] In summary, the current recycling methods of waste polystyrene foam plastics still have many drawbacks. Summary of the invention

[0012] The purpose of the present invention is to provide a method for preparing polystyrene powder by recycling waste polystyrene foam plastics with water-soluble organic solvents, so as to solve the environmental, safety and economic problems involved in the current high-temperature hot-melt recycling of waste PS foam plastics and the dissolution and recycling of waste PS foam plastics with non-water-soluble organic solvents.

[0013] To achieve the above object, the present invention provides a method for preparing polystyrene powder by recycling waste polystyrene foam plastics using a water-soluble organic solvent, comprising the following steps:

[0014] S1, dissolving waste polystyrene foam plastics using a water-soluble organic solvent to obtain solution I;

[0015] S2, aging solution I and filtering to remove insoluble impurities therein to obtain a transparent solution II;

[0016] S3, slowly adding the solution II obtained in step S2 into deionized water, and polystyrene slowly precipitates; adding all of the solution II into the deionized water, stirring until all of the polystyrene is precipitated, and filtering to obtain polystyrene powder;

[0017] S4. The polystyrene powder obtained in step S3 is recovered after being washed, dried, crushed and sieved.

[0018] Preferably, the water-soluble organic solvent is N-methylpyrrolidone.

[0019] Preferably, the mass ratio of the water-soluble organic solvent to the waste polystyrene foam plastic is 4-10:1-3.

[0020] Preferably, in step S2, the aging time of solution I is 30 to 60 minutes.

[0021] Preferably, in step S3, the mass ratio of the deionized water to solution II is 1 to 3:1.

[0022] Preferably, in step S3, the stirring time is 10 to 30 minutes.

[0023] Preferably, in step S4, the cleaning is performed using deionized water.

[0024] Preferably, in step S4, the drying condition is 60° C. for 6 to 8 hours.

[0025] Preferably, in step S4, the crushing particle size is ≥ 200 mesh.

[0026] Preferably, in step S3, the filtrate obtained by filtration is distilled under reduced pressure at 90° C. to remove water and recover the water-soluble organic solvent.

[0027] Therefore, the method of preparing polystyrene powder by recycling waste polystyrene foam plastics with a water-soluble organic solvent has the following beneficial effects:

[0028] (1) The water-soluble organic solvent NMP used in the present invention is not a hazardous chemical, and does not require a special hazardous chemical transport vehicle for transportation. Therefore, it can be transported to a waste foam plastic recycling point, and the foam plastic can be dissolved before transportation, thereby solving the transportation difficulty of the large foam plastic volume;

[0029] (2) NMP has a boiling point of 202°C and a melting point of -24°C. Therefore, except for a few cases where the temperature is below -24°C, it is liquid at normal room temperature. Therefore, the operation process of recycling waste polystyrene foam plastics can be carried out at room temperature without heating, which is very safe and convenient.

[0030] (3) Waste foam plastics are very difficult to clean due to their large volume. Moreover, foam plastics are often stuck with tapes as packaging materials, and it takes a lot of manpower to separate these tapes. When NMP is used to dissolve waste foam plastics, polystyrene is dissolved to form a solution, while the dirt on the foam plastics and the tape material are not dissolved. They can be easily precipitated and filtered to obtain a clean polystyrene solution.

[0031] (4) Adding a solution of polystyrene dissolved in NMP to deionized water, water has no affinity with polystyrene, and a powdery PS solid can be obtained. The precipitated PS powdery solid is filtered to obtain PS solid powder. The PS solid powder is dried and crushed to obtain PS powder with a small particle size of more than 200 meshes;

[0032] Compared with the existing method of using non-water-soluble organic solvents to precipitate PS, the present invention uses water-soluble organic solvents, which is safer;

[0033] Compared with the precipitation of PS by distilling organic solvents, since organic solvents have good affinity with PS, the precipitated PS is usually in a gel state. The gel PS is hard after drying and is difficult to crush to obtain small-size PS powder with a mesh size greater than 100 mesh. It usually needs to be re-granulated at high temperature, and the added alcohol is usually a flammable and explosive hazardous chemical.

[0034] (5) After adding water, the filtrate of PS precipitation is an aqueous solution of NMP. Since the boiling point of NMP is 202°C, which is much higher than 100°C of water, the water can be dried out of the liquid at a temperature slightly higher than 100°C to obtain NMP for reuse, or the water can be removed by vacuum distillation to obtain NMP for reuse.

[0035] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative labor.

[0037] Figure 1This is a picture of using water-soluble organic solvent NMP to dissolve waste PS foam plastics and then adding water to precipitate PS powder;

[0038] Figure 2 This is a picture of solid PS powder obtained by dissolving waste PS foam plastic with water-soluble organic solvent NMP, adding water to precipitate PS powder, and filtering it;

[0039] Figure 3 The waste PS foam plastics were dissolved by water-soluble organic solvent NMP, and then water was added to precipitate, dry and crush to obtain 200 mesh PS powder.

[0040] Figure 4 This is a photo of using the non-water-soluble organic solvent limonene to dissolve waste PS foam plastic and then adding ethanol to precipitate PS gel solid. DETAILED DESCRIPTION

[0041] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0042] In order to make the purpose, technical scheme and advantages of the present application clearer, more thorough and more complete, the technical scheme of the present invention is clearly and completely described below through the accompanying drawings and examples. The following detailed descriptions are all descriptions of the embodiments, and are intended to provide further detailed descriptions of the present invention. Unless otherwise specified, all technical terms used in the present invention have the same meaning as those generally understood by those skilled in the art to which the present application belongs.

[0043] The instruments, equipment, reagents and materials used in the examples were all obtained through commercial channels.

[0044] Embodiment 1

[0045] A method for preparing polystyrene powder by recycling waste polystyrene foam plastics using a water-soluble organic solvent comprises the following steps:

[0046] S1. Weigh 80 g of water-soluble organic solvent N-methylpyrrolidone (NMP), add 20 g of waste PS foam plastic, stir to dissolve the PS foam plastic, and form solution I.

[0047] S2. Aging solution I for 30 minutes, filtering to remove insoluble impurities therein, and obtaining a transparent solution II.

[0048] S3. Weigh 80 g of deionized water and slowly add Solution II into the deionized water under stirring. During the addition process, solid PS powder slowly precipitates. Figure 1 shown.

[0049] S4. After all the solution II is added to the deionized water, continue stirring for 10 minutes and then filter. The resulting powder is as follows: Figure 2The powder obtained by filtration was washed with deionized water, dried in an oven at 60°C for 6 hours, crushed, and passed through a 200-mesh sieve to obtain a 200-mesh PS powder, as shown. Figure 3 shown.

[0050] The weight of PS powder is 19.2g. Since the weight of waste PS foam plastic added is 20g, the recovery rate of PS can reach 96%. Since the waste PS contains a small amount of impurities, the recovery rate of PS is higher than 96%.

[0051] The filtrate obtained by filtration was distilled under reduced pressure at 90°C to remove water, thereby obtaining 76 g of NMP with a recovery rate of 95%, which can be recycled.

[0052] Embodiment 2

[0053] A method for preparing polystyrene powder by recycling waste polystyrene foam plastics using a water-soluble organic solvent comprises the following steps:

[0054] S1. Weigh 100 g of water-soluble organic solvent NMP, add 30 g of waste PS foam plastic, stir to dissolve the PS foam plastic, and form solution I.

[0055] S2. Aging solution I for 50 minutes, filtering to remove insoluble impurities therein, and obtaining a transparent solution II.

[0056] S3. Weigh 150 g of deionized water and slowly add Solution II into the deionized water under stirring. During the addition process, solid PS powder slowly precipitates.

[0057] S4. After all of Solution II is added to the deionized water, continue stirring for 20 minutes, then filter, wash the resulting filter cake with deionized water, place it in an oven at 60°C for 8 hours, crush the filter cake, and pass it through a 200-mesh sieve to obtain a 200-mesh PS powder.

[0058] The weight of PS powder is 28.5g. Since the weight of waste PS foam plastic added is 30g, the recovery rate of PS can reach 95%. Since the waste PS contains a small amount of impurities, the recovery rate of PS is higher than 95%.

[0059] The filtrate obtained by filtration was distilled under reduced pressure at 90°C to remove water, thereby obtaining 92 g of NMP with a recovery rate of 92%, which can be recycled.

[0060] Embodiment 3

[0061] A method for preparing polystyrene powder by recycling waste polystyrene foam plastics using a water-soluble organic solvent comprises the following steps:

[0062] S1. Weigh 150 g of water-soluble organic solvent NMP, add 30 g of waste PS foam plastic, stir to dissolve the PS foam plastic, and form solution I.

[0063] S2. Aging solution I for 60 minutes, filtering to remove insoluble impurities therein, and obtaining a transparent solution II.

[0064] S3. Weigh 300 g of deionized water and slowly add Solution II into the deionized water under stirring. During the addition process, solid PS powder slowly precipitates.

[0065] S4. After all of Solution II is added to the deionized water, continue stirring for 30 minutes, then filter, wash the resulting filter cake with deionized water, place it in an oven at 60°C for 8 hours, crush the filter cake, and pass it through a 200-mesh sieve to obtain a 200-mesh PS powder.

[0066] The weight of PS powder is 29.1g. Since the weight of waste PS foam plastic added is 30g, the recovery rate of PS can reach 97%. Since the waste PS contains a small amount of impurities, the recovery rate of PS is higher than 97%.

[0067] The filtrate obtained by filtration was distilled under reduced pressure at 90°C to remove water, thereby obtaining 138 g of NMP with a recovery rate of 92%, which can be recycled.

[0068] Comparative Example 1

[0069] Use limonene to dissolve waste polystyrene foam plastics, and then add ethanol to the solution to precipitate polystyrene gel solids as follows:

[0070] S1. Weigh 100 g of limonene, add 20 g of waste PS foam plastic, stir to dissolve the PS foam plastic, and form solution I.

[0071] S2. Aging solution I for 60 minutes, filtering to remove insoluble impurities therein, and obtaining a transparent solution II.

[0072] S3. Weigh 100g of anhydrous ethanol and slowly add solution II to the anhydrous ethanol under stirring. During the addition process, gel-like PS solids slowly precipitate. The precipitation photo is shown in the figure below. Figure 4 shown.

[0073] This gel-like PS solid is extremely viscous and needs to be placed in an oven at 60°C and dried for at least 10 hours to obtain hard solid particles. However, due to its extremely high hardness, it is difficult to further crush it into powder.

[0074] Therefore, the method for preparing polystyrene powder by recycling waste polystyrene foam plastics with a water-soluble organic solvent has a simple process flow, does not need to melt PS at a high temperature for granulation recovery, and the impurities in the process are easily removed to obtain pure PS powder; the recycling process has no pollutant emissions, does not use hazardous chemicals, and the overall process is safe and environmentally friendly.

[0075] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for preparing polystyrene powder by recycling waste polystyrene foam plastics using a water-soluble organic solvent, characterized in that: The steps include: S1, dissolving waste polystyrene foam plastics using a water-soluble organic solvent to obtain solution I; S2, aging solution I and filtering to remove insoluble impurities therein to obtain a transparent solution II; S3, slowly adding the solution II obtained in step S2 into deionized water, and polystyrene slowly precipitates; adding all of the solution II into the deionized water, stirring until all of the polystyrene is precipitated, and filtering to obtain polystyrene powder; S4. The polystyrene powder obtained in step S3 is recovered after being washed, dried, crushed and sieved.

2. The method for preparing polystyrene powder by recycling waste polystyrene foam plastics with a water-soluble organic solvent according to claim 1, characterized in that: The water-soluble organic solvent is N-methylpyrrolidone.

3. The method for preparing polystyrene powder by recycling waste polystyrene foam plastics with a water-soluble organic solvent according to claim 1, characterized in that: The mass ratio of the water-soluble organic solvent to the waste polystyrene foam plastic is 4-10:1-3.

4. The method for preparing polystyrene powder by recycling waste polystyrene foam plastics with a water-soluble organic solvent according to claim 1, characterized in that: In step S2, the aging time of the solution I is 30 to 60 minutes.

5. The method for preparing polystyrene powder by recycling waste polystyrene foam plastics with a water-soluble organic solvent according to claim 1, characterized in that: In step S3, the mass ratio of the deionized water to solution II is 1 to 3:

1.

6. The method for preparing polystyrene powder by recycling waste polystyrene foam plastics with a water-soluble organic solvent according to claim 1, characterized in that: In step S3, the stirring time is 10 to 30 minutes.

7. The method for preparing polystyrene powder by recycling waste polystyrene foam plastics with a water-soluble organic solvent according to claim 1, characterized in that: In step S4, the cleaning is performed by using deionized water.

8. The method for preparing polystyrene powder by recycling waste polystyrene foam plastics with a water-soluble organic solvent according to claim 1, characterized in that: In step S4, the drying condition is 60° C. for 6 to 8 hours.

9. The method for preparing polystyrene powder by recycling waste polystyrene foam plastics with a water-soluble organic solvent according to claim 1, characterized in that: In step S4, the crushing particle size is ≥ 200 mesh.

10. The method for preparing polystyrene powder by recycling waste polystyrene foam plastics with a water-soluble organic solvent according to claim 1, characterized in that: In step S3, the filtrate obtained by filtration is subjected to reduced pressure distillation at 90° C. to remove water and recover the water-soluble organic solvent.

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