Waste plastic recycling process

Abstract

The present invention provides a waste plastic recycling process and a method for preparing recyclable plastics comprising the same.

Description

Technical Field

[0001] This invention relates to waste plastic recycling processes, and more particularly, to chemical recycling processes for the utilization of waste plastics through recrystallization and adsorption purification.

[0002] This application claims priority and benefit to Korean Patent Application No. 10-2021-0080482, filed with the Korean Intellectual Property Office on June 22, 2021, the entire contents of which are incorporated herein by reference. Background Technology

[0003] Plastics are widely used in modern society because they are easy to process and their physical and chemical properties are easily altered. Although landfill and incineration are commonly used to dispose of discarded plastics, it is difficult for plastics to decompose naturally. This means that when plastics are landfilled, they may cause environmental problems such as water and soil pollution, and when incinerated, they may cause environmental problems such as air pollution.

[0004] To address these environmental problems, numerous studies have been conducted on the processing, purification, conversion, and recycling of waste plastics, and some recycling methods have been put into practical application. However, due to the high unit cost of plastics recovered through recycling methods and the inability to significantly improve plastic purity, recycled plastics cannot be used in many applications. Furthermore, the mixing of waste plastics of various colors makes it difficult to process and purify recycled plastics, resulting in difficulties in specifying desired physical and chemical properties and achieving desired colors.

[0005] Therefore, there is a continued need to research waste plastic recycling processes that can achieve the desired color while significantly improving the purity of recycled plastics. Summary of the Invention

[0006] Technical issues

[0007] This invention aims to solve the problems of waste plastic recycling processes in related fields, and to provide a waste plastic recycling process that can significantly improve the purity of recycled plastics using chemical purification methods.

[0008] Technical solution

[0009] An exemplary embodiment of the present invention provides a waste plastic recycling process, which includes: preparing a first solution by dissolving the waste plastic in an organic solvent;

[0010] Add an adsorbent to the first solution;

[0011] By adding 60 parts by weight or more of a compound with a Hansen solubility parameter (HSP) of 5 to 14 for polycarbonate based on the total weight of 100 parts by weight of the first solution, the plastic is recrystallized; and

[0012] Collect recrystallized plastic.

[0013] Another exemplary embodiment of the present invention provides a method for preparing recyclable plastics, the method comprising a recycling process for the waste plastics.

[0014] Beneficial effects

[0015] The waste plastic recycling process of this invention can significantly improve the purity of recycled plastics using chemical purification methods involving recrystallization and adsorbents. Furthermore, colorless recycled plastics can be obtained.

[0016] Furthermore, the waste plastic recycling process according to the present invention can shorten the process time by reducing the number of times organic solvent is added to one, compared with the existing method of adding organic solvent twice.

[0017] Furthermore, according to the waste plastic recycling process of the present invention, the optimal adsorption conditions can be set by diversifying the types of adsorbents introduced and adjusting their content, so that impurities in waste plastics can be effectively removed while maintaining the inherent properties of existing polycarbonate. Detailed Implementation

[0018] The following sections will describe specific exemplary implementations in more detail.

[0019] An exemplary embodiment of the present invention provides a waste plastic recycling process, which includes: preparing a first solution by dissolving the waste plastic in an organic solvent;

[0020] Add an adsorbent to the first solution;

[0021] By adding 60 parts by weight or more of a compound with a Hansen solubility parameter (HSP) of 5 to 14 for polycarbonate based on the total weight of 100 parts by weight of the first solution, the plastic is recrystallized; and

[0022] Collect recrystallized plastic.

[0023] This invention is a chemical waste plastic recycling method that utilizes chemical reactions to replace mechanical plastic recycling methods that rely on physical alterations to recycle waste plastics.

[0024] Specifically, the present invention has the following advantages: the purity of the plastic is higher than that obtained by chemical plastic recycling methods in related fields, and colorless recycled plastic can be obtained by applying an adsorption purification method using an adsorbent and recrystallization of the plastic. Colorless recycled plastic means recycled plastic that does not contain pigments or dyes. More specifically, the term "colorless" recycled plastic will be further illustrated by the spectrophotometer measurements described below.

[0025] More specifically, the waste plastic recycling process according to the present invention can obtain plastics with significantly improved purity by adding an adsorbent to a first solution for an initial adsorption purification process, and adding a compound with a Hansen solubility parameter (HSP) of 5 to 14 for polycarbonate in an amount of 60 parts by weight or more based on 100 parts by weight of the total weight of the first solution to subject the plastic to recrystallization.

[0026] In this case, when a compound with a Hansen solubility parameter (HSP) of 5 to 14 for polycarbonate is included in the above range based on the total weight of 100 parts by weight of the first solution, additives such as antioxidants or heat stabilizers can be effectively removed from the waste plastic, and recrystallized plastic can be obtained in high yield. However, when the compound is included in an amount of less than 60 parts by weight, recrystallization cannot be carried out, or impurities may be included in large quantities in the recrystallized plastic, and the yield is low.

[0027] Furthermore, the waste plastic recycling process according to the present invention can recycle pure polycarbonate by diversifying the types of adsorbents in the adsorption step and adjusting the ratios of various types to set optimal adsorption conditions, thereby removing impurities or other stabilizers, colorants, etc., present in the waste plastic while maintaining the inherent properties of the existing polycarbonate.

[0028] In one exemplary embodiment of the invention, plastic is a general term for an organic polymer material that is plastic and can be softened by heating and molded into any shape.

[0029] The plastic can be, for example, polycarbonate (PC), polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), or polyethylene terephthalate (PET), but is not limited to these.

[0030] In one exemplary embodiment of the present invention, waste plastic means waste generated after the use of plastic, and the waste can be any industrial waste, commercial waste or household waste, but is not limited to any instance.

[0031] In one exemplary embodiment of the present invention, the waste plastic can be waste polycarbonate.

[0032] In this specification, plastics recovered through waste plastic recycling processes are referred to as "recyclable plastics" or "recycled plastics".

[0033] In one exemplary embodiment of the invention, the weight-average molecular weight of the waste polycarbonate can be from 40,000 g / mol to 60,000 g / mol. The weight-average molecular weight (Mw) can be measured using gel permeation chromatography. Specifically, the weight-average molecular weight can be measured using a THF-GPC instrument on a PLgel Mixed Bx 2 column, in tetrahydrofuran (THF) solvent, at a flow rate of 1.0 mL / min and a temperature of 40°C.

[0034] In one exemplary embodiment of the present invention, the polydispersity index (PDI) of the waste polycarbonate can be from 1.7 to 3. Specifically, the polydispersity index of the waste polycarbonate can be from 1.8 to 3.

[0035] In one exemplary embodiment of the present invention, the melt flow rate (MFR) of the waste polycarbonate can be from 6 to 30. Specifically, the melt flow rate (MFR) of the waste polycarbonate can be from 10 to 28.

[0036] Melt flow rate was measured at 300°C using an apparatus manufactured by Toyoseki MFR with a weight of 1.2 kg, according to ASTM D1238-94A / ISO 1133 method.

[0037] When the waste polycarbonate of the present invention satisfies at least one of the above-mentioned weight-average molecular weight, polydispersity index and melt flow rate, the waste polycarbonate of the present invention is a waste plastic that can be appropriately used in the waste plastic recycling process according to the present invention.

[0038] In one exemplary embodiment of the present invention, the recrystallized plastic is polycarbonate.

[0039] Polycarbonate refers to polymers that contain carbonate bonds in their main chain, i.e., carbonate ester bonds.

[0040] In one exemplary embodiment of the invention, the organic solvent is a solvent based on cyclic ethers, a solvent based on linear or cyclic carbonates, or a hydrocarbon solvent having 1 to 8 carbon atoms containing one or more halogen atoms.

[0041] In one exemplary embodiment of this specification, the solvent based on the cyclic ether can be tetrahydrofuran.

[0042] In one exemplary embodiment of the present invention, the solvent based on linear carbonates may be dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethylpropyl carbonate (EPC), ethylmethyl carbonate (EMC), or methylpropyl carbonate (MPC), but is not limited thereto.

[0043] In one exemplary embodiment of the present invention, the solvent based on the cyclic carbonate can be ethyl carbonate (EC), propyl carbonate (PC), 1,2-butylene carbonate (BC), 2,3-butylene carbonate, 1,2-pentanediol carbonate, 2,3-pentanediol carbonate, vinylene carbonate (VC), vinyl ethylene carbonate, or fluoroethylene carbonate, but is not limited thereto. Preferably, the solvent based on the cyclic carbonate can be propylene carbonate.

[0044] In one exemplary embodiment of the present invention, the hydrocarbon solvent containing one or more halogen atoms and having 1 to 8 carbon atoms can be dichloromethane or dichloroethane, but is not limited thereto.

[0045] In one exemplary embodiment of the present invention, the organic solvent is preferably selected from one or more of tetrahydrofuran, propylene carbonate, methyl carbonate, and dichloroethane.

[0046] In one exemplary embodiment of the present invention, the organic solvent is tetrahydrofuran.

[0047] In one exemplary embodiment of the present invention, the organic solvent is propylene carbonate.

[0048] In one exemplary embodiment of the present invention, the organic solvent is methyl carbonate.

[0049] In one exemplary embodiment of the present invention, the organic solvent is dichloroethane.

[0050] In one exemplary embodiment of the present invention, the organic solvent is dichloromethane.

[0051] In one exemplary embodiment of the invention, waste plastic is included in an amount of 10 to 20 parts by weight, and organic solvent is included in an amount of 80 to 90 parts by weight, based on the total weight of 100 parts by weight of the first solution.

[0052] Specifically, based on the total weight of 100 parts by weight of the first solution, waste plastics are included in an amount of 13 to 20 parts by weight, and organic solvents are included in an amount of 83 to 90 parts by weight.

[0053] More specifically, based on the total weight of 100 parts by weight of the first solution, waste plastics are included in an amount of 14 to 16 parts by weight, and organic solvents are included in an amount of 84 to 86 parts by weight.

[0054] When waste plastics and organic solvents are contained in the first solution within the above-mentioned range, the waste plastics do not precipitate out, and the first solution can be prepared appropriately.

[0055] In one exemplary embodiment of the present invention, when preparing the first solution by dissolving waste plastic in an organic solvent, the waste plastic is dissolved in the organic solvent for 1 to 3 hours.

[0056] Specifically, the waste plastic is dissolved in an organic solvent for 1 hour and 30 minutes to 2 hours and 30 minutes, preferably 2 hours.

[0057] When waste plastics are dissolved in an organic solvent for 1 to 3 hours as described above, the waste plastics do not swell and melt on the surface of the organic solvent, but dissolve well in the organic solvent, so that a first solution can be prepared appropriately.

[0058] In one exemplary embodiment of the invention, the preparation of the first solution by dissolving waste plastic in an organic solvent can be carried out at room temperature. Specifically, the preparation of the first solution by dissolving waste polycarbonate in an organic solvent can be carried out at a temperature of 15°C to 25°C. When the waste plastic is dissolved in the organic solvent at a temperature of 15°C to 25°C as described above, the degree of vaporization of the organic solvent is low, allowing the desired first solution to be prepared without significantly altering the solution concentration.

[0059] In one exemplary embodiment of the invention, the first solution is further filtered after the first solution is prepared.

[0060] The first solution is filtered using a filter with a mesh structure having a maximum diameter of 0.45 μm or greater and 1 μm or smaller to remove insoluble additives and waste plastics contained in the first solution for various purposes, as well as other insoluble impurities, other polymers, etc.

[0061] Filters can be used without restriction, as long as they meet the above-mentioned maximum diameter range or are insoluble in organic solvents. For example, a filter can be made of polytetrafluoroethylene (PTFE) manufactured by STERLITECH with a maximum diameter of 0.45 μm.

[0062] When the filter meets the maximum diameter within the above range, it can effectively filter out insoluble additives and waste plastics that are present in the first solution dissolved for various purposes, as well as other insoluble impurities, other polymers, etc.

[0063] In this invention, after filtering the dissolved first solution, an adsorbent is added as described below.

[0064] Since additives may remain in the first solution after the first solution has been dissolved, waste plastics can be recycled into high-purity plastics through an adsorption purification process using an adsorbent.

[0065] Additives refer to organic and inorganic dyes or pigments, heat stabilizers, antioxidants, UV stabilizers, flame retardants, antistatic agents, impact modifiers, plasticizers, flow aids, etc., other than polymer compounds added during the preparation of plastics, and are not limited thereto. Additives can also refer to all additives used in the art for the preparation of plastics.

[0066] Antioxidants can be, for example, Irgafos antioxidants, and heat stabilizers can be, for example, Tinuvin heat stabilizers.

[0067] In one exemplary embodiment of the invention, adding the adsorbent to the first solution can be done by adding the adsorbent to the first solution and stirring the resulting mixture for 1 to 3 hours. Specifically, the mixture is stirred for 1 hour and 30 minutes to 2 hours and 30 minutes, preferably 2 hours.

[0068] In one exemplary embodiment of the invention, adding an adsorbent to the first solution and stirring the resulting mixture for 1 to 3 hours can be carried out at room temperature. Specifically, adding an adsorbent to the first solution and stirring the resulting mixture for 1 to 3 hours can be carried out at a temperature of 15°C to 25°C. When the solution is stirred at a temperature of 15°C to 25°C as described above, the degree of vaporization of the organic solvent is low, so that the concentration of the solution can be changed without significant change.

[0069] In one exemplary embodiment of the invention, the adsorbent is further removed after it has been added to the first solution.

[0070] The adsorbent is removed by using a filter with a mesh structure having a maximum diameter of 0.45 μm or larger and 1 μm or smaller.

[0071] Filters can be used without restriction, as long as they meet the above-mentioned maximum diameter range or are insoluble in organic solvents. For example, a filter can be made of polytetrafluoroethylene (PTFE) manufactured by STERLITECH with a maximum diameter of 0.45 μm.

[0072] When the filter meets the maximum diameter within the above range, the adsorbent can be effectively removed.

[0073] The mesh structure refers to the skeleton structure that forms the filter.

[0074] There are no particular restrictions on the shape of the mesh structure, and it can be used without limitation, as long as the maximum diameter is met.

[0075] The maximum diameter refers to the longest line segment connecting two points on the perimeter of the graph (forming various network structures) using a straight line passing through the center of the graph. The center of the graph can refer to the centroid.

[0076] As the adsorbent is removed, the additives remaining in the waste plastic contained in the first solution can be initially removed, thus further improving the purity of the recycled plastic.

[0077] In one exemplary embodiment of the present invention, the adsorbent is activated carbon; activated carbon pretreated with hydrochloric acid, sulfuric acid or phosphoric acid; acidic clay; diatomaceous earth; zeolite; silica gel; alumina; magnesium silicate (MgO3Si); ​​or ion exchange resin; or a combination thereof.

[0078] When the adsorbent is an adsorbent pretreated with an acid solution, the adsorbent can be modified to be polar and adsorb additives, and even when the adsorbent contains substituents such as hydroxyl (-OH) or carboxylic acid (-COOH), it can adsorb polar substituents of the additives.

[0079] In one exemplary embodiment of the present invention, the adsorbent may be activated carbon. The activated carbon may be activated charcoal powder from DUKSAN Science (CAS No. 7440-44-0), but is not limited thereto.

[0080] In one exemplary embodiment of the present invention, the activated carbon may be activated carbon pretreated with hydrochloric acid, sulfuric acid or phosphoric acid.

[0081] Pretreatment refers to contacting activated carbon with an acid solution, including hydrochloric acid, sulfuric acid, or phosphoric acid, followed by washing with distilled water to modify the surface of the activated carbon. The contact between activated carbon and the acid solution can be achieved by immersing the activated carbon in the acid solution or by passing the acid solution through the activated carbon. Specifically, activated carbon pretreated with hydrochloric acid, sulfuric acid, or phosphoric acid can be C4386 pretreated with hydrochloric acid or C5510 pretreated with sulfuric acid and phosphoric acid, purchased from Sigma-Aldrich.

[0082] In one exemplary embodiment of the invention, the activated carbon has a particle size of 100 mesh or smaller. Specifically, the activated carbon can have a particle size of 4 mesh or larger and 100 mesh or smaller. More specifically, the activated carbon can have a particle size of 4 mesh or larger and 12 mesh or smaller, 12 mesh or larger and 20 mesh or smaller, or 20 mesh or larger and 40 mesh or smaller. When the activated carbon meets the above particle size requirements, it can effectively adsorb additives. Activated carbon with a particle size of 100 mesh or smaller can be purchased from Sigma-Aldrich or DAEJUNG Chemicals & Metals.

[0083] In one exemplary embodiment of the invention, the adsorbent may be acidic clay. The acidic clay may be CAS number 68333-91-5 from DUKSAN COMPANY, but is not limited thereto.

[0084] In one exemplary embodiment of the present invention, the adsorbent is diatomaceous earth. The diatomaceous earth can be CAS number 68855-54-9 from Sigma-Aldrich. 545, but not limited to this.

[0085] In one exemplary embodiment of the present invention, the adsorbent may be zeolite. The zeolite may be CBV 5524G from Zeolyst, CAS No. 1318-02-1, but is not limited thereto.

[0086] In one exemplary embodiment of the invention, the adsorbent may be silica gel. The silica gel may be silica gel 60 from Merck, CAS number 7631-86-9, but is not limited thereto.

[0087] In one exemplary embodiment of the present invention, the adsorbent may be alumina. The alumina may be alkaline alumina powder from Baker CAS No. 1344-28-1, but is not limited thereto.

[0088] In one exemplary embodiment of the present invention, the adsorbent may be magnesium silicate (MgO3Si, Florisil). Magnesium silicate may be CAS No. 1343-88-0 from Sigma-Aldrich. But it is not limited to this.

[0089] In one exemplary embodiment of the present invention, the adsorbent may be an ion exchange resin. The ion exchange resin may be Amberlite IRC120H from Sigma-Aldrich, CAS No. 39389-20-3, but is not limited thereto.

[0090] In one exemplary embodiment of the invention, the adsorbent may be a combination of two or more of the following: activated carbon; activated carbon pretreated with hydrochloric acid, sulfuric acid or phosphoric acid; acidic clay; diatomaceous earth; zeolite; silica gel; alumina; magnesium silicate (MgO3Si); ​​and ion exchange resin.

[0091] In one exemplary embodiment of the invention, the adsorbent may be a combination selected from two or more of the following: activated carbon; acidic clay; silica gel; alumina; and magnesium silicate (MgO3Si).

[0092] In one exemplary embodiment of the invention, the adsorbent may be a combination of three or more of the following: activated carbon; acidic clay; silica gel; alumina; and magnesium silicate (MgO3Si).

[0093] In one exemplary embodiment of the present invention, the adsorbent may comprise activated carbon; acidic clay; and magnesium silicate (MgO3Si).

[0094] When an adsorbent contains two or more materials, the materials can be physically mixed and used.

[0095] In one exemplary embodiment of the present invention, the adsorbent may be composed of activated carbon, acidic clay and magnesium silicate (MgO3Si).

[0096] When the adsorbent contains activated carbon, acidic clay, and magnesium silicate (MgO3Si), impurities other than plastic dissolved in the first solution being filtered can be removed by adsorption via activated carbon and acidic clay, and the oxidized portion of the plastic can be selectively removed by magnesium silicate (MgO3Si).

[0097] In one exemplary embodiment of the invention, the adsorbent may be included in an amount of 0.5 parts by weight or more and 8 parts by weight or less, based on the total weight of 100 parts by weight of the first solution.

[0098] Specifically, based on the total weight of 100 parts by weight of the first solution, the adsorbent may be included in an amount of 0.5 parts by weight or more and 7 parts by weight or less.

[0099] More specifically, based on the total weight of 100 parts by weight of the first solution, the adsorbent may be included in an amount of 0.5 parts by weight or more and 6 parts by weight or less.

[0100] When the adsorbent is contained in the first solution within the above-mentioned range, it can effectively remove impurities remaining in the first solution while maintaining processability.

[0101] In one exemplary embodiment of the invention, the adsorbent is activated carbon, and based on the total weight of 100 parts by weight of the first solution, the adsorbent may be included in an amount of 0.5 parts by weight or more and 8 parts by weight or less.

[0102] In one exemplary embodiment of the invention, the adsorbent is activated carbon, and based on the total weight of 100 parts by weight of the first solution, the adsorbent may be included in an amount of 0.5 parts by weight or more and 6 parts by weight or less.

[0103] In one exemplary embodiment of the invention, the adsorbent is activated carbon, and based on the total weight of 100 parts by weight of the first solution, the adsorbent may be included in an amount of 1 part by weight or more and 5 parts by weight or less.

[0104] In one exemplary embodiment of the invention, the adsorbent is activated carbon, and based on the total weight of 100 parts by weight of the first solution, the adsorbent may be included in an amount of 1 part by weight or more and 4 parts by weight or less.

[0105] In one exemplary embodiment of the invention, the adsorbent is acidic clay, and based on the total weight of 100 parts by weight of the first solution, the adsorbent may be included in an amount of 0.5 parts by weight or more and 8 parts by weight or less.

[0106] In one exemplary embodiment of the invention, the adsorbent is acidic clay, and based on the total weight of 100 parts by weight of the first solution, the adsorbent may be included in an amount of 0.5 parts by weight or more and 6 parts by weight or less.

[0107] In one exemplary embodiment of the invention, the adsorbent is acidic clay, and based on the total weight of 100 parts by weight of the first solution, the adsorbent may be included in an amount of 1 part by weight or more and 5 parts by weight or less.

[0108] In one exemplary embodiment of the invention, the adsorbent is acidic clay, and based on the total weight of 100 parts by weight of the first solution, the adsorbent may be included in an amount of 1 part by weight or more and 4 parts by weight or less.

[0109] In one exemplary embodiment of the invention, the adsorbent is acidic clay, and based on the total weight of 100 parts by weight of the first solution, the adsorbent may be included in an amount of 1 part by weight or more and 3 parts by weight or less.

[0110] In one exemplary embodiment of the invention, the adsorbent is diatomaceous earth, and based on the total weight of 100 parts by weight of the first solution, the adsorbent may be included in an amount of 0.5 parts by weight or more and 8 parts by weight or less.

[0111] In one exemplary embodiment of the invention, the adsorbent is diatomaceous earth, and based on the total weight of 100 parts by weight of the first solution, the adsorbent may be included in an amount of 0.5 parts by weight or more and 6 parts by weight or less.

[0112] In one exemplary embodiment of the invention, the adsorbent is diatomaceous earth, and based on the total weight of 100 parts by weight of the first solution, the adsorbent may be included in an amount of 1 part by weight or more and 5 parts by weight or less.

[0113] In one exemplary embodiment of the invention, the adsorbent is diatomaceous earth, and based on the total weight of 100 parts by weight of the first solution, the adsorbent may be included in an amount of 1 part by weight or more and 4 parts by weight or less.

[0114] In one exemplary embodiment of the invention, the adsorbent is zeolite, and based on the total weight of 100 parts by weight of the first solution, the adsorbent may be included in an amount of 0.5 parts by weight or more and 8 parts by weight or less.

[0115] In one exemplary embodiment of the invention, the adsorbent is zeolite, and based on the total weight of 100 parts by weight of the first solution, the adsorbent may be included in an amount of 0.5 parts by weight or more and 6 parts by weight or less.

[0116] In one exemplary embodiment of the invention, the adsorbent is zeolite, and based on the total weight of 100 parts by weight of the first solution, the adsorbent may be included in an amount of 1 part by weight or more and 5 parts by weight or less.

[0117] In one exemplary embodiment of the invention, the adsorbent is zeolite, and based on the total weight of 100 parts by weight of the first solution, the adsorbent may be included in an amount of 1 part by weight or more and 4 parts by weight or less.

[0118] In one exemplary embodiment of the invention, the adsorbent is silica gel, and based on the total weight of 100 parts by weight of the first solution, the adsorbent may be included in an amount of 0.5 parts by weight or more and 8 parts by weight or less.

[0119] In one exemplary embodiment of the invention, the adsorbent is silica gel, and based on the total weight of 100 parts by weight of the first solution, the adsorbent may be included in an amount of 0.5 parts by weight or more and 6 parts by weight or less.

[0120] In one exemplary embodiment of the invention, the adsorbent is silica gel, and based on the total weight of 100 parts by weight of the first solution, the adsorbent may be included in an amount of 1 part by weight or more and 5 parts by weight or less.

[0121] In one exemplary embodiment of the invention, the adsorbent is silica gel, and based on the total weight of 100 parts by weight of the first solution, the adsorbent may be included in an amount of 1 part by weight or more and 4 parts by weight or less.

[0122] In one exemplary embodiment of the invention, the adsorbent is alumina, and based on the total weight of 100 parts by weight of the first solution, the adsorbent may be included in an amount of 0.5 parts by weight or more and 8 parts by weight or less.

[0123] In one exemplary embodiment of the invention, the adsorbent is alumina, and based on the total weight of 100 parts by weight of the first solution, the adsorbent may be included in an amount of 0.5 parts by weight or more and 6 parts by weight or less.

[0124] In one exemplary embodiment of the invention, the adsorbent is alumina, and based on the total weight of 100 parts by weight of the first solution, the adsorbent may be included in an amount of 1 part by weight or more and 5 parts by weight or less.

[0125] In one exemplary embodiment of the invention, the adsorbent is alumina, and based on the total weight of 100 parts by weight of the first solution, the adsorbent may be included in an amount of 1 part by weight or more and 4 parts by weight or less.

[0126] In one exemplary embodiment of the invention, the adsorbent is alumina, and based on the total weight of 100 parts by weight of the first solution, the adsorbent may be included in an amount of 2 parts by weight or more and 4 parts by weight or less.

[0127] In one exemplary embodiment of the invention, the adsorbent is magnesium silicate (MgO3Si), and based on the total weight of 100 parts by weight of the first solution, the adsorbent may be included in an amount of 0.5 parts by weight or more and 8 parts by weight or less.

[0128] In one exemplary embodiment of the invention, the adsorbent is magnesium silicate (MgO3Si), and based on the total weight of 100 parts by weight of the first solution, the adsorbent may be included in an amount of 0.5 parts by weight or more and 6 parts by weight or less.

[0129] In one exemplary embodiment of the invention, the adsorbent is magnesium silicate (MgO3Si), and based on the total weight of 100 parts by weight of the first solution, the adsorbent may be included in an amount of 1 part by weight or more and 5 parts by weight or less.

[0130] In one exemplary embodiment of the invention, the adsorbent is magnesium silicate (MgO3Si), and based on the total weight of 100 parts by weight of the first solution, the adsorbent may be included in an amount of 1 part by weight or more and 4 parts by weight or less.

[0131] In one exemplary embodiment of the invention, the adsorbent is magnesium silicate (MgO3Si), and based on the total weight of 100 parts by weight of the first solution, the adsorbent may be included in an amount of 0.5 parts by weight or more and 2 parts by weight or less.

[0132] In one exemplary embodiment of the invention, the adsorbent is an ion exchange resin, and based on the total weight of 100 parts by weight of the first solution, the adsorbent may be included in an amount of 0.5 parts by weight or more and 8 parts by weight or less.

[0133] In one exemplary embodiment of the invention, the adsorbent is an ion exchange resin, and based on the total weight of 100 parts by weight of the first solution, the adsorbent may be included in an amount of 0.5 parts by weight or more and 6 parts by weight or less.

[0134] In one exemplary embodiment of the invention, the adsorbent is an ion exchange resin, and based on the total weight of 100 parts by weight of the first solution, the adsorbent may be included in an amount of 1 part by weight or more and 5 parts by weight or less.

[0135] In one exemplary embodiment of the invention, the adsorbent is an ion exchange resin, and based on the total weight of 100 parts by weight of the first solution, the adsorbent may be included in an amount of 1 part by weight or more and 4 parts by weight or less.

[0136] In one exemplary embodiment of the present invention, based on the total weight of 100 parts by weight of the first solution, the adsorbent may comprise 0.5 to 3 parts by weight of activated carbon, 0.5 to 4 parts by weight of acidic clay, and 0.5 to 2 parts by weight of magnesium silicate (MgO3Si).

[0137] In one exemplary embodiment of the present invention, based on the total weight of 100 parts by weight of the first solution, the adsorbent may comprise 1 to 3 parts by weight of activated carbon, 1 to 4 parts by weight of acidic clay, and 0.5 to 1 part by weight of magnesium silicate (MgO3Si).

[0138] In one exemplary embodiment of the present invention, based on the total weight of 100 parts by weight of the first solution, the adsorbent may comprise 1 to 2 parts by weight of activated carbon, 1 to 3 parts by weight of acidic clay, and 0.5 to 1 part by weight of magnesium silicate (MgO3Si).

[0139] In one exemplary embodiment of the present invention, based on the total weight of 100 parts by weight of the first solution, the adsorbent may contain 2 parts by weight of activated carbon, 3 parts by weight of acidic clay and 1 part by weight of magnesium silicate (MgO3Si).

[0140] In one exemplary embodiment of the present invention, based on the total weight of 100 parts by weight of the first solution, the adsorbent may contain 1.5 parts by weight of activated carbon, 2 parts by weight of acidic clay and 0.5 parts by weight of magnesium silicate (MgO3Si).

[0141] In one exemplary embodiment of the present invention, based on the total weight of 100 parts by weight of the first solution, the adsorbent may contain 1 part by weight of activated carbon, 1 part by weight of acidic clay and 0.5 parts by weight of magnesium silicate (MgO3Si).

[0142] After removing the adsorbent, based on the total weight of 100 parts by weight of the first solution, a compound with a Hansen solubility parameter (HSP) of 5 to 14 for polycarbonate is added to the first solution to remove the additive contained in the first solution for a second time and to crystallize the polycarbonate.

[0143] That is, the additives are initially removed by the adsorbent mentioned above, and a compound with a Hansen solubility parameter (HSP) of 5 to 14 for polycarbonate is added to remove the additives a second time, so that waste plastics can be recycled into high-purity plastics.

[0144] In one exemplary embodiment of the invention, based on the total weight of 100 parts by weight of the first solution, a compound having a Hansen solubility parameter (HSP) of 5 to 14 for polycarbonate may be added to the first solution in an amount of 60 to 100 parts by weight.

[0145] When compounds with a Hansen solubility parameter (HSP) of 5 to 14 for polycarbonate are included in an amount of more than 100 parts by weight, the yield can be expected to be similar to that when the compounds are included in an amount of 60 to 100 parts by weight. However, this range of content may have an adverse effect on economic feasibility and processability because the effect is not significant and a large amount of solvent is used.

[0146] That is, considering economic feasibility, the addition of compounds with a Hansen solubility parameter (HSP) of 5 to 14 for polycarbonate in amounts of 60 to 100 parts by weight can be carried out under optimal addition conditions that can exhibit excellent effects.

[0147] In one exemplary embodiment of the invention, based on the total weight of 100 parts by weight of the first solution, a compound having a Hansen solubility parameter (HSP) of 5 to 14 for polycarbonate can be added to the first solution in an amount of 70 to 90 parts by weight.

[0148] In one exemplary embodiment of the invention, based on the total weight of 100 parts by weight of the first solution, a compound having a Hansen solubility parameter (HSP) of 5 to 14 for polycarbonate can be added to the first solution in an amount of 80 to 90 parts by weight.

[0149] In one exemplary embodiment of the invention, based on the total weight of 100 parts by weight of the first solution, a compound having a Hansen solubility parameter (HSP) of 5 to 14 for polycarbonate can be added to the first solution in an amount of 83 to 87 parts by weight.

[0150] In one exemplary embodiment of the invention, based on the total weight of 100 parts by weight of the first solution, a compound having a Hansen solubility parameter (HSP) of 5 to 14 for polycarbonate can be added to the first solution in an amount of 85 parts by weight.

[0151] In one exemplary embodiment of the invention, the compound having a Hansen solubility parameter (HSP) of 5 to 14 for polycarbonate is a hydrocarbon compound selected from one or more of the following: alcohols, ketones, ethers, cycloalkanes, esters, carboxylic acids, and nitriles.

[0152] Considering the degree of bonding of the internal materials of polycarbonate, the Hansen solubility parameter of polycarbonate can be specifically calculated from the nonpolar dispersion force, the dipole-dipole force due to the permanent dipole, and the hydrogen bonding force.

[0153] Specifically, compounds with a Hansen solubility parameter (HSP) of 5 to 14 for polycarbonates are hydrocarbon compounds having 1 to 10 carbon atoms selected from one or more of the following: alcohols, ketones, ethers, cycloalkanes, esters, carboxylic acids, and nitriles.

[0154] More specifically, compounds with a Hansen solubility parameter (HSP) of 5 to 14 for polycarbonates are hydrocarbon compounds having 1 to 5 carbon atoms selected from one or more of the following: alcohols, ketones, esters, and nitriles.

[0155] Preferably, the compound having a Hansen solubility parameter (HSP) of 5 to 14 for polycarbonate is ethanol, acetone, ethyl acetate, or acetonitrile.

[0156] In one exemplary embodiment of the invention, the compound having a Hansen solubility parameter (HSP) of 5 to 14 for polycarbonate is ethanol.

[0157] In one exemplary embodiment of the invention, the compound having a Hansen solubility parameter (HSP) of 5 to 14 for polycarbonate is acetone.

[0158] In one exemplary embodiment of the invention, the compound having a Hansen solubility parameter (HSP) of 5 to 14 for polycarbonate is ethyl acetate.

[0159] In one exemplary embodiment of the invention, the compound having a Hansen solubility parameter (HSP) of 5 to 14 for polycarbonate is acetonitrile.

[0160] In one exemplary embodiment of the invention, the weight percentage of waste plastic relative to the total weight of the first solution is 20% by weight or less, and the weight percentage of recrystallized plastic relative to the total weight of the first solution is 20% by weight or less.

[0161] In one exemplary embodiment of the invention, the weight percentage of waste plastic relative to the total weight of the first solution is 15% by weight or less, and the weight percentage of recrystallized plastic relative to the total weight of the first solution is 15% by weight or less.

[0162] The weight percentage of waste plastic relative to the total weight of the first solution can be 1% by weight or greater.

[0163] When the percentage concentration of waste plastics or recrystallized plastics meets the above range, the waste plastics or recrystallized plastics can be fully dissolved in the solvent to maintain an appropriate saturation state.

[0164] After adding a compound with a Hansen solubility parameter (HSP) of 5 to 14 for polycarbonate to the first solution, the polycarbonate is collected and recrystallized.

[0165] In one exemplary embodiment of the invention, the collection of recrystallized polycarbonate may further include: precipitating powdered or granular plastic from the recrystallized polycarbonate; and obtaining recycled plastic by processing the precipitate. There are no particular limitations on the precipitation and processing methods, and methods applicable in the art may be suitably employed.

[0166] Since the plastics recycled using the waste plastic recycling process of the present invention do not contain additives such as organic and inorganic dyes or pigments, the plastics can be colorless.

[0167] In one exemplary embodiment of the invention, based on the dL, da, db, and y values ​​measured by a spectrophotometer using dichloromethane in its pure solvent state, the dL, da, db, and y values ​​of a solution in which plastic recovered through a waste plastic recycling process is dissolved in dichloromethane solvent at a concentration of 5% by weight satisfy the following relational expression.

[0168] [Relational Expression]

[0169] |dL|<0.35, |da|<0.2, |db|<0.3, y<1.5

[0170] The spectrophotometer can be the X-rite Ci7600 color spectrophotometer.

[0171] Specifically, the relational expression refers to the difference between the reference value (0) and the dL, da, and db values ​​of the recycled plastic, wherein the dL, da, and db values ​​of dichloromethane in its pure solvent state, measured by a spectrophotometer, are set as the reference value (0), and the dL, da, and db values ​​of the recycled plastic are measured by a spectrophotometer. In the relational expression, y refers to the yellowness index.

[0172] Dichloromethane in its pure solvent state refers to dichloromethane that does not contain solute.

[0173] In this specification, when the values ​​of dL, da, db, and y measured by a spectrophotometer satisfy the relational expression, it can mean that the measured target (recycled plastic) is colorless and does not exhibit a specific color.

[0174] An exemplary embodiment of this specification provides a method for preparing recyclable plastics, the method comprising a recycling process for waste plastics.

[0175] In the method for preparing recyclable plastics, in addition to the recycling process of waste plastics, other processes required for preparing recyclable plastics may be used, and processes known in the art may be used as said processes.

[0176] Invention Embodiments

[0177] The invention will be illustrated in more detail below by way of examples. The invention is not limited to these examples, and various modifications can be made to the embodiments according to the invention, and these modifications should not be construed as limiting the scope of the invention to the examples described in detail below. The embodiments of the invention are provided to illustrate the invention more completely to those skilled in the art.

[0178] Examples 1 to 30.

[0179] To prepare a first solution of 100 parts by weight, 15 parts by weight of waste polycarbonate were added to 85 parts by weight of the organic solvent shown in Table 1 at room temperature and dissolved for 2 hours. Waste polycarbonate with a weight-average molecular weight of 40,000 g / mol to 60,000 g / mol, a polydispersity index (PDI) of 1.8 to 3, and a melt flow rate (MFR) of 10 to 28 was used.

[0180] After filtering the dissolved first solution using a polytetrafluoroethylene (PTFE) filter manufactured by STERLITECH with a mesh structure having a maximum diameter of 0.45 μm, activated carbon as an adsorbent as shown in Table 1 was added, and the resulting mixture was stirred for 2 hours.

[0181] After stirring, the adsorbent was removed using a polytetrafluoroethylene (PTFE) filter manufactured by STERLITECH, which has a mesh structure with a maximum diameter of 0.45 μm. Then, compounds with Hansen solubility parameters (HSP) of 5 to 14 for polycarbonate as listed in Table 1 were added, and the recrystallized polycarbonate was collected.

[0182] Comparative examples 1 to 6.

[0183] The experiment was conducted in the same manner as in the above examples, except that compounds and adsorbents with a Hansen solubility parameter (HSP) of 5 to 14 for polycarbonate were added in the amounts shown in Table 1 below.

[0184] [Table 1]

[0185]

[0186]

[0187] The specific adsorbents used are listed in Table 1.

[0188] - Activated charcoal: Activated charcoal powder from DUKSAN Science (CAS No. 7440-44-0)

[0189] - Acidic clay: CAS No. 68333-91-5 from DUKSAN Company

[0190] - Magnesium silicate: CAS No. 1343-88-0 from Sigma-Aldrich

[0191] - Silicone: 60g silicone from Merck, CAS number 7631-86-9

[0192] - Alumina: Alkaline alumina powder from Baker, CAS No. 1344-28-1

[0193] Experimental example.

[0194] After the plastic is precipitated from recrystallized plastic into a powder form, it is processed into pellets using an extruder to obtain recycled plastic.

[0195] The color of recycled plastics was measured under the following conditions and is shown in Table 2 below.

[0196] - Spectrophotometric measurement of recycled plastics: The difference between the reference value (0) and the dL, da, db and y values ​​measured using an X-rite Ci7600 color spectrophotometer are shown after setting the dL, da, db and y values ​​measured by first placing dichloromethane in pure solvent state into the measuring cuvette as the reference value (0).

[0197] [Table 2]

[0198]

[0199]

[0200] According to Table 2, in the case of embodiments 1 to 30 of the exemplary implementation of the present invention, it can be determined that the recycled plastic is colorless by the fact that the spectrophotometric measurement results in Table 2 satisfy the relational expression, indicating that additives such as organic and inorganic dyes or pigments have been removed and are not included.

[0201] Furthermore, in Examples 27 and 28, in which 110 parts by weight and 120 parts by weight of the compound having a Hansen solubility parameter (HSP) of 5 to 14 for polycarbonate were used, it was determined that the spectrophotometric measurements met the relational expression, but the difference in effect was not significant compared to the case where 60 parts by weight to 100 parts by weight of the compound were used.

[0202] Furthermore, in Comparative Example 1 in which no adsorbent was added, the recycled plastic was not colorless because the dL and db values ​​did not satisfy the relational expression, thus confirming that additives or impurities were contained in the recycled plastic.

[0203] Furthermore, in Comparative Examples 2 to 4, where 10 parts by weight, 20 parts by weight, and 30 parts by weight of compounds with a Hansen solubility parameter (HSP) of 5 to 14 for polycarbonate were used, the amount of the added compounds with a Hansen solubility parameter (HSP) of 5 to 14 for polycarbonate was so small that solids could not be obtained due to unsuccessful recrystallization of polycarbonate.

[0204] Furthermore, in Comparative Examples 5 and 6, in which 40 parts by weight and 50 parts by weight of compounds with Hansen solubility parameters (HSP) of 5 to 14 for polycarbonate were used, it was determined that the dL value did not satisfy the relational expression, thus indicating that the recycled plastic was not colorless, the yield of solids obtained was about half that of the yield of solids obtained in Comparative Example 1, and therefore it was not suitable for the process, and that additives or impurities were contained in the recycled plastic.

[0205] Therefore, it has been determined that recycled plastics with excellent purity can be obtained when the waste plastic recycling process according to the present invention is applied.

Claims

1. A waste plastic recycling process, comprising: The first solution is prepared by dissolving waste plastic in an organic solvent; Add an adsorbent to the first solution; By adding 60 to 100 parts by weight of a compound with a Hansen solubility parameter (HSP) of 5 to 14 for polycarbonate based on the total weight of 100 parts by weight of the first solution, the plastic is recrystallized; and Collect recrystallized plastic.

2. The recycling process according to claim 1 further includes filtering the dissolved first solution after preparing the first solution.

3. The recovery process according to claim 1 further includes removing the adsorbent after adding the adsorbent to the first solution.

4. The recycling process according to claim 1, wherein the recrystallized plastic is polycarbonate.

5. The recycling process according to claim 1, wherein the organic solvent is a solvent based on cyclic ethers, a solvent based on linear or cyclic carbonates, or a hydrocarbon solvent having 1 to 8 carbon atoms containing one or more halogen atoms.

6. The recycling process according to claim 1, wherein the compound having a Hansen solubility parameter (HSP) of 5 to 14 for polycarbonate is a hydrocarbon compound selected from one or more of the following: alcohols, ketones, ethers, cycloalkanes, esters, carboxylic acids, and nitriles.

7. The recovery process according to claim 1, wherein the adsorbent is activated carbon; activated carbon pretreated with hydrochloric acid, sulfuric acid or phosphoric acid; acidic clay; diatomaceous earth; zeolite; silica gel; alumina; magnesium silicate; or ion exchange resin; or a combination thereof.

8. The recycling process according to claim 1, wherein the adsorbent comprises activated carbon, acidic clay, and magnesium silicate.

9. The recovery process according to claim 1, wherein the adsorbent is added in an amount of 0.5 parts by weight or more and 8 parts by weight or less, based on the total weight of 100 parts by weight of the first solution.

10. The recycling process according to claim 8, wherein, based on the total weight of 100 parts by weight of the first solution, the adsorbent comprises 0.5 to 3 parts by weight of the activated carbon, 0.5 to 4 parts by weight of the acidic clay, and 0.5 to 2 parts by weight of the magnesium silicate.

11. The recycling process according to claim 1, wherein the waste plastic is included in an amount of 10 to 20 parts by weight based on the total weight of 100 parts by weight of the first solution, and the organic solvent is included in an amount of 80 to 90 parts by weight.

12. The recycling process according to claim 1, wherein the compound having a Hansen solubility parameter (HSP) of 5 to 14 for polycarbonate is included in an amount of 80 to 90 parts by weight, based on 100 parts by weight of the total weight of the first solution.

13. The recovery process according to claim 3, wherein the adsorbent is removed by using a filter comprising a mesh structure having a maximum diameter of 0.45 μm or greater and 1 μm or smaller.

14. The recycling process according to claim 1, wherein the weight percentage of the waste plastic relative to the total weight of the first solution is 20% by weight or less, and the weight percentage of the recrystallized plastic relative to the total weight of the first solution is 20% by weight or less.

15. A method for preparing recyclable plastic, the method comprising the recycling process according to any one of claims 1 to 14.

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