Process for preparing regenerated polymers

Abstract

Provided is a method for preparing a regenerated polymer, comprising: (S1) supplying a mixed solvent of a first solvent comprising a C3-8 alkyl acetate and a second solvent of a non-aromatic cyclic hydrocarbon to a dissolving tank and a precipitation tank, respectively; (S2) supplying a composite resin to the dissolving tank, heating to a dissolving temperature, and dissolving a polymer contained in the composite resin while maintaining the dissolving tank at the dissolving temperature to obtain a polymer solution; (S3) supplying the polymer solution into the precipitation tank, maintaining the mixed solvent in the precipitation tank at a precipitation temperature, and precipitating the polymer contained in the polymer solution to obtain a solution containing a polymer precipitate having a spherical shape; and (S4) press-filtering the solution containing the polymer precipitate having a spherical shape to obtain the polymer precipitate.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to Korean Patent Application No. 10-2024-0030461, filed on March 4, 2024, and Korean Patent Application No. 10-2025-0006126, filed on January 15, 2025, the entire contents of which are incorporated herein by reference as a part of the specification. Technical Field

[0003] This disclosure relates to a method for preparing a recycled polymer, and more specifically, to a method for preparing a recycled polymer in which an economical physical filtration process can be applied by controlling the shape of the precipitate when recovering the polymer from waste resin. Background Technology

[0004] Recently, the use of polymer materials such as resins or plastics has been increasing due to the development of resin materials with physical properties required for various uses and purposes. Typically, resins or plastics are manufactured using a large amount of energy collected from crude oil, and a significant amount of carbon is emitted in the process. Furthermore, environmental pollution and the social costs of disposal arise when the final product is discarded along with the resins or plastics contained within it. Therefore, it is necessary to recycle waste resins to reduce energy consumption, carbon emissions, and prevent environmental pollution.

[0005] Meanwhile, the waste resin can be either resin from composite materials or single resin. The resin from composite materials is in a blend of two or more resins, and because single resins contain additives (such as plasticizers, fillers, flame retardants, stabilizers, fillers, foaming agents, viscosity reducers, colorants, and heat stabilizers) used to impart the desired physical properties, it may be difficult to regenerate single resins by physical methods.

[0006] Therefore, methods for recovering and regenerating polymers from waste resins using chemical methods are underway. For example, polymers contained in waste resins are selectively dissolved in a good solvent to obtain a polymer solution, and the good solvent contained in the polymer solution is evaporated or the polymer solution is contacted with an antisolvent to recrystallize the solution, thereby preparing a regenerated polymer.

[0007] Because the recycling technique recovers the polymer without decomposing it through dissolution and recrystallization, while maintaining its physical properties by increasing the polymer's purity, it reduces carbon emissions. However, since the good solvent for dissolving the polymer and the antisolvent for precipitating the polymer are mixed, the two solvents used should be separated so that they can be reused later.

[0008] Therefore, to avoid using antisolvents in the recrystallization step, methods for precipitating polymers by lowering the temperature of the solvent dissolved in the polymer have recently attracted attention. However, since polymers precipitated by self-cooling of the polymer solution contain a large amount of solvent, an additional process of removing the solvent by evaporation is involved, which consumes a significant amount of energy.

[0009] Furthermore, the precipitated polymer crystals are mostly in powder form, and when the polymer precipitated in powder form exists in solution as a slurry, the filtration step used for solvent separation requires energy-intensive vacuum filtration, and it is difficult to apply simple and economical squeezing or pressing. Summary of the Invention

[0010] Technical issues

[0011] In order to address the problems mentioned in the background art, one object of the present invention is to provide a method for preparing recycled polymers, wherein when recovering polymers from waste resins, an economical physical filtration process can be applied to the method by controlling the shape of the precipitate.

[0012] Technical solution

[0013] In one general aspect, a method for preparing a recycled polymer includes: (S1) dissolving C, a component containing acetic acid. 3-8 A mixture of a first solvent of alkyl esters and a second solvent of non-aromatic cyclic hydrocarbons is supplied to a dissolving tank and a precipitation tank, respectively; (S2) a composite resin is supplied to the dissolving tank, heated to a dissolving temperature, and the polymer contained in the composite resin is dissolved while the dissolving tank is maintained at the dissolving temperature to obtain a polymer solution; (S3) the polymer solution is supplied to the precipitation tank, the mixed solvent in the precipitation tank is maintained at a precipitation temperature, and the polymer contained in the polymer solution is precipitated to obtain a solution containing polymer precipitates having a spherical shape; and (S4) the solution containing polymer precipitates having a spherical shape is pressure filtered to obtain a polymer precipitate.

[0014] Beneficial effects

[0015] According to the present invention, a mixed solvent is used as the same solvent supplied to the dissolving tank and the settling tank, the mixed solvent comprising acetic acid C, which is conducive to polymer precipitation. 3-8A first solvent containing alkyl esters and a second solvent containing non-aromatic cyclic hydrocarbons with higher polymer solubility than the first solvent are used. The dissolving and settling tanks are used to recover polymers contained in composite resins derived from waste resins. The mixed solvents are heated in the dissolving tank to a dissolution temperature (equal to or above the boiling point) to fully dissolve the polymer. The polymer dissolved in the settling tank, maintained at a low temperature, is then rapidly crystallized to form spherical precipitates. The solution containing polymer precipitates with spherical shapes can be physically pressure filtered in a subsequent filtration step, such as by squeezing or pressurizing, reducing energy consumption compared to conventional filtration under reduced pressure.

[0016] In addition, by performing the polymer dissolution and recrystallization steps separately in the dissolution tank and the precipitation tank, the present invention can reduce the energy consumed in lowering the temperature of the polymer solution at high temperature before adding the polymer solution to the precipitation tank.

[0017] Furthermore, since the same solvent is supplied to both the dissolving and settling tanks, any remaining solvent after obtaining the final polymer precipitate can be directly reused in both tanks without a separate separation process. This simplifies the process and reduces costs, which is economically advantageous. Detailed Implementation

[0018] The terms and words used in the specification and claims of this invention should not be construed as having a general or dictionary meaning, but should be interpreted as having a meaning and concept that satisfies the technical concept of the invention, based on the principle that the inventors are able to properly define the concepts of the terms in order to best describe their own invention.

[0019] The invention will be described in more detail below for a better understanding.

[0020] A method for preparing a regenerated polymer according to an exemplary embodiment of the present invention may include (S1) supplying the same solvent to a dissolving tank and a precipitation tank; (S2) dissolving the polymer contained in the composite resin; (S3) precipitating the dissolved polymer by recrystallization; and (S4) obtaining a polymer precipitate.

[0021] The composite resin used in this invention is derived from waste resin and can be obtained by pretreating waste resin. Waste resin can be recycled from various products molded using the resin or its composition, or from its applications, regardless of whether it is hard or soft. Furthermore, the composite resin obtained by pretreating waste resin can be a single type of polymer containing additives, or a resin composition made by mixing two or more polymers. Pretreating refers to the entire process of treating the waste resin to a state suitable for use in the preparation method of the recycled polymer of this invention. For example, pretreating can be a process of washing the waste resin with a solvent such as water to remove relatively large foreign matter such as dust, drying, and pulverizing. Pulverizing is advantageously performed so that the dried waste resin has a uniform size, for example, 1 mm to 5 cm. When the size of the pulverized resin is less than 1 mm, it is difficult to handle due to the generation of dust, and when the size is greater than 5 cm, it takes a long time to dissolve it during polymer recycling.

[0022] The pretreated composite resin may include polymers such as polyethylene, polypropylene, or mixtures thereof, and the polymers can be recycled from the composite resin and used as recycled resins. Polyethylene is classified according to density into high-density polyethylene (HDPE), medium-density polyethylene (MDPE), low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), ultra-low-density polyethylene (VLDPE), etc., and can be used after appropriate selection based on the properties of the composite resin.

[0023] For example, based on the weight of the composite resin, the composite resin may include 50 to 90% by weight of a polymer, including polyethylene, polypropylene, or mixtures thereof.

[0024] The present invention aims to selectively recover the polymer contained in the above-mentioned composite resin to prepare a recycled polymer, and a method for preparing a recycled polymer according to an exemplary embodiment of the present invention may include, firstly: (S1) dissolving C containing acetic acid... 3-8 The first solvent of alkyl esters and the second solvent of non-aromatic cyclic hydrocarbons are mixed solvents supplied to the dissolving tank and the precipitation tank, respectively.

[0025] Acetic acid C used as the first solvent 3-8 Alkyl esters can dissolve polymers, but they have a stronger tendency to induce recrystallization of dissolved polymers. Therefore, when using acetic acid alone... 3-8 When alkyl esters are used as solvents, they have low solubility for polymers such as polyethylene or polypropylene and may not be able to dissolve the polymer well. Instead, they are used with a second solvent that has high solubility for the polymer to ensure excellent dissolving ability, thereby having the effect of rapidly precipitating the polymer during the precipitation process after selectively dissolving the polymer from the composite resin.

[0026] However, when using acetic acid C 3-8 When solvents other than alkyl esters, such as alcohols, are used as the primary solvent, the polymer does not dissolve completely, and the yield of the regenerated polymer may be reduced. Alcohols are unsuitable for dissolving polymers such as polyethylene or polypropylene because they have poor solubility, which is not improved even by heating.

[0027] In an exemplary embodiment of the present invention, the first solvent may include one or more selected from n-butyl acetate, tert-butyl acetate, isopropyl acetate, amyl acetate, and n-hexyl acetate. Among these, n-butyl acetate is more advantageously used because it exhibits good solubility in polymers and excellent precipitation properties.

[0028] Simultaneously, the non-aromatic cyclic hydrocarbons used as the second solvent exhibit excellent solubility for the polymer and can compensate for the insufficient solubility of the first solvent before mixing. Therefore, the mixed solvent containing the first and second solvents exhibits excellent solubility for the polymer and allows the dissolved polymer to recrystallize advantageously for forming polymer precipitates. The second solvent may have low solubility for the polymer at low temperatures, such as room temperature, but can exhibit increased solubility at temperatures close to the boiling point of the second solvent. Therefore, in this invention, utilizing this property, the polymer contained in the composite resin can be dissolved by maintaining the temperature of the mixed solvent close to the boiling point of the second solvent.

[0029] However, when aromatic solvents are used as a second solvent, dissolving the polymer is not a problem due to their excellent solubility. However, because aromatic solvents have poor recrystallization ability, the polymer may not precipitate completely during the precipitation process. Furthermore, because aromatic solvents have a very high affinity for polymers, the polymer may precipitate in the form of gels rather than particles. These gel-form precipitates contain a high solvent content, potentially requiring more energy to dry.

[0030] In an exemplary embodiment of the present invention, the second solvent may include one or more selected from methylcyclohexane and cycloalkyl ethers. Cycloalkyl ethers are preferred.

[0031] Cycloalkyl ethers possess properties such as relatively high boiling points, low melting points, low heats of vaporization, hydrophobicity, and chemical stability. In this text, boiling point may refer to the boiling point at atmospheric pressure (1 atm). In particular, due to their relatively high boiling points, cycloalkyl ethers can be used as solvents across a wide range of temperatures, from low to high. Therefore, by using cycloalkyl ethers as a second solvent, the polymer to be dissolved can be selectively dissolved to prepare recycled polymers from composite resins derived from waste resins, and the precipitation ability of the mixed solvent with the first solvent can be improved during the subsequent precipitation step when recrystallizing the dissolved polymer.

[0032] For example, cycloalkyl ethers can have boiling points above 100°C. Such high boiling points mean that cycloalkyl ethers have a wide temperature range, allowing a second solvent to be heated to a high temperature to selectively dissolve the target polymer, and then the temperature to be lowered to recrystallize the dissolved polymer. This can improve the rate of polymer precipitation by increasing supersaturation at low temperatures.

[0033] Specific examples of cycloalkyl alkyl ethers may include one or more selected from cyclopentylmethyl ether, cyclopentylethyl ether, cyclopentylpropyl ether, cyclopentylisopropyl ether, cyclopentyl tert-butyl ether, cyclohexylmethyl ether, cyclohexylethyl ether, cyclohexylpropyl ether, cyclohexylisopropyl ether, and cyclohexyl tert-butyl ether. Cyclopentylmethyl ether, cyclopentylethyl ether, and cyclohexylethyl ether are advantageously used because they exhibit excellent solubility at high temperatures and low affinity for polymers at low temperatures.

[0034] Furthermore, in an exemplary embodiment of the present invention, the mixed solvent may refer to a solvent in which a first solvent and a second solvent are mixed. In the mixed solvent, the first solvent and the second solvent can maintain their respective properties of polymer dissolution and precipitation. Specifically, the first solvent has poor dissolving power for the polymer, but can have excellent ability to recrystallize and precipitate the polymer at low temperatures, and can retain this property in the mixed solvent. Furthermore, although the second solvent has poor dissolving power for the polymer at low temperatures, it can have improved polymer dissolution power, and can retain this property even in the mixed solvent. Therefore, by creating an environment that maximizes the respective properties of the first solvent and the second solvent, polymers can be effectively dissolved and precipitated.

[0035] In one exemplary embodiment of the invention, the mixed solvent can be a mixture of a first solvent and a second solvent with a volume ratio of 2:1 to 5:1, specifically 2:1 to 4:1. When the mixed solvent meeting this ratio is supplied to the dissolving tank and the settling tank respectively, the precipitation capacity of the polymer after dissolution and recrystallization is maximized, thereby improving the polymer recovery rate. When the volume ratio of the first solvent and the second solvent is less than 2:1, no precipitation effect caused by the first solvent occurs, allowing the polymer to precipitate in powder form. When the volume ratio is greater than 5:1, no polymer dissolution effect caused by the second solvent is observed, making it possible for the polymer to not dissolve completely.

[0036] Therefore, in this invention, a mixed solvent containing a first solvent and a second solvent is supplied as the same solvent to both the dissolution tank for polymer dissolution and the precipitation tank for recrystallization. This overcomes the disadvantages of conventional techniques that involve separation processes for later reuse due to the mixing of two different solvents, namely a good solvent for dissolving the polymer and an anti-solvent for precipitating the polymer.

[0037] A method for preparing a recycled polymer according to an exemplary embodiment of the present invention may include: (S2) supplying a composite resin to a dissolving tank, heating it to a dissolving temperature, and dissolving the polymer contained in the composite resin while maintaining the dissolving tank at the dissolving temperature to obtain a polymer solution.

[0038] Specifically, the polymer solution can be obtained by contacting the composite resin with a mixture of a first solvent and a second solvent in a dissolving tank to selectively dissolve the target polymer to be recycled, such as polyethylene, polypropylene, or a mixture thereof.

[0039] If necessary, the dissolution step in the dissolving tank can be carried out under stirring in order to effectively disperse the composite resin in the mixed solvent and improve the resulting dissolution efficiency.

[0040] In one exemplary embodiment of the present invention, the dissolution temperature may be a temperature maintained for selectively dissolving the polymer in the dissolution tank. That is, (S2) may involve supplying the composite resin to the dissolution tank, heating it until the temperature of the dissolution tank reaches the dissolution temperature, and dissolving the polymer contained in the composite resin while maintaining the dissolution temperature.

[0041] Meanwhile, the dissolution temperature can be a temperature corresponding to "high temperature", at which the solubility of the polymer in the second solvent in the mixed solvent is improved.

[0042] In this paper, pressurized conditions may be required in the dissolving tank to maintain the dissolution temperature, and the pressure in the dissolving tank can range from atmospheric pressure to 3 bar. When the pressure in the dissolving tank is less than atmospheric pressure, the temperature of the mixed solvent does not rise sufficiently, so the polymer may not dissolve. When the pressure is greater than 3 bar, excessive energy is consumed to increase the pressure, but the dissolution efficiency of the polymer decreases accordingly, and therefore, the process efficiency may deteriorate.

[0043] Specifically, the dissolution temperature can be between 100°C and 150°C. When the dissolution temperature is below 100°C, the second solvent does not reach the temperature required to enhance the solubility of the polymer, and the polymer may not dissolve sufficiently. Furthermore, when the dissolution temperature is above 150°C, the second solvent exceeds the point where the polymer's solubility is maximized; therefore, the polymer's dissolution efficiency decreases, and excessive energy may be consumed to raise the temperature.

[0044] Additionally, the dissolution time in the dissolving tank can range from 120 to 300 minutes. Dissolution time refers to the time from the point when the composite resin comes into contact with the mixed solvent in the dissolving tank until the polymer dissolves in the mixed solvent. When the dissolution time is less than 120 minutes, the polymer may not dissolve sufficiently, and when the dissolution time is greater than 300 minutes, excessive energy may be consumed to maintain the dissolution temperature.

[0045] By adjusting the dissolution temperature and time, the polymer solution obtained in the dissolution tank can meet a predetermined polymer concentration range. For example, based on the weight of the polymer solution, the polymer content contained in the polymer solution can be 1% or more by weight, 5% or more by weight, or 8% or more and 20% or less by weight, 15% or less by weight, or 13% or less by weight. When the polymer content dissolved in the polymer solution is less than 1% by weight, the amount of regenerated polymer finally prepared may be reduced. When the polymer content dissolved in the polymer solution is greater than 20% by weight, the viscosity increases, making it potentially difficult to separate the dissolved polymer from the insoluble substances.

[0046] Furthermore, the polymer solution obtained in the dissolving tank can be filtered to remove insoluble substances that are not dissolved in the mixed solvent. Filtration can be performed by one or more of filter filtration, centrifugal filtration, and sedimentation filtration. As an example, when performing a filter filtration method, the polymer is passed through a filter such as a screen filter to separate insoluble substances from the polymer solution, and the filtrate containing the dissolved polymer can be used for subsequent steps.

[0047] Furthermore, a method for preparing a regenerated polymer according to an exemplary embodiment of the present invention may include: (S3) supplying a polymer solution to a precipitation tank, wherein a mixed solvent is maintained at a precipitation temperature, and causing the polymer contained in the polymer solution to precipitate, thereby obtaining a solution containing polymer precipitates having a spherical shape.

[0048] In this invention, the polymer dissolved in the polymer solution is recrystallized by lowering the temperature of the polymer solution at a high temperature, and in order to minimize the energy consumption required to lower the temperature of the polymer solution, the recrystallization and precipitation of the polymer dissolved in the polymer solution are carried out at a low temperature using a separate precipitation tank, which is a component other than the dissolution tank that is kept at a high temperature.

[0049] Specifically, if necessary, a precipitation step can be performed with a mixture of the first and second solvents pre-supplied to the precipitation tank. During this process, a high-temperature polymer solution is added dropwise while stirring, causing the polymer dissolved in the solution to recrystallize and form a precipitate due to the temperature difference. Here, the greater the difference between the precipitation temperature of the precipitation tank and the dissolution temperature of the dissolving tank used in the previous step, the higher the polymer precipitation efficiency can be.

[0050] Therefore, in this invention, while using a mixture of the first solvent and the second solvent in the dissolving tank and the settling tank as described above, the temperature of the dissolving tank is heated to a high dissolving temperature to maximize the dissolving capacity of the mixed solvent, thereby dissolving the polymer in the dissolving tank, and the settling temperature is maintained in a low temperature range including room temperature (25°C) for precipitation, thereby maximizing the settling efficiency of the polymer in the settling tank.

[0051] In one exemplary embodiment of the invention, the precipitation temperature is the temperature of the mixed solvent used to precipitate the polymer in the precipitation tank, and can be controlled to be maintained at a temperature 40°C to 120°C lower than the dissolution temperature (i.e., dissolution temperature minus (40°C to 120°C)), specifically, a temperature 60°C to 100°C lower than the dissolution temperature (i.e., dissolution temperature minus (60°C to 100°C)). That is, since the upper limit of the polymer solution temperature can be determined by the boiling point of the mixed solvent in the dissolution tank, the precipitation temperature can be controlled based on the dissolution temperature of the dissolution tank.

[0052] Specifically, the precipitation temperature of the precipitation tank, where the polymer solution is added dropwise, can be within the range of 5°C to 50°C, 5°C to 30°C, or 10°C to 25°C. When this temperature range is maintained, the temperature of the solvent in the precipitation tank is significantly lower than the temperature of the polymer solution obtained in the dissolution tank, thus allowing for easy precipitation via polymer recrystallization. When the precipitation temperature is below 5°C, a separate cooling device should be provided to control the temperature, which may increase energy consumption. Furthermore, when the precipitation temperature is above 50°C, the precipitation capacity of the mixed solvent decreases, thereby reducing the precipitation rate and speed of the polymer by recrystallization, resulting in a decrease in the efficiency of preparing the final regenerated polymer.

[0053] In addition, the first solvent in the mixed solvent supplied to the settling tank can cause rapid crystallization of the polymer dissolved in the polymer solution to form spherical precipitates.

[0054] The precipitation temperature in the settling tank can be a temperature that further enhances the settling ability of the first solvent, which has excellent settling power. Furthermore, the settling temperature remains relatively low compared to the dissolution temperature, and this can be a temperature at which the solubility of the polymer is significantly reduced due to the properties of the second solvent. The process of forming a precipitate utilizing such properties can be achieved by adding the polymer solution obtained in the dissolution tank, where the polymer solution has maximized solubility for the second solvent according to the dissolution temperature, dropwise to a settling tank at a temperature that maintains the maximum settling power of both the first and second solvents, thereby rapidly lowering the temperature and causing the polymer to recrystallize and precipitate quickly. During this process, the polymer dissolved in the polymer solution can rapidly form dense crystals, resulting in the formation of spherical polymer precipitates.

[0055] Spherical precipitates can have an average diameter ranging from 500 μm to 5000 μm. When the average diameter of the spherical precipitates is less than 500 μm, a finer filter than a conventional filter should be used in the subsequent pressure filtration process, or other filtration methods requiring high energy should be employed, thus potentially increasing process costs. Furthermore, when the average diameter of the spherical precipitates is greater than 5000 μm, the precipitate size is too large, and therefore, solvent removal may not be effective during pressure filtration.

[0056] When the dissolution and precipitation of the polymer do not meet the above conditions, the polymer may not precipitate as spherical particles, and may precipitate, for example, as a powder. When the polymer precipitates as a powder, the crystals of the polymer precipitate do not form densely, so the mixed solvent may be largely contained in the polymer precipitate, and pressure filtration may not be applicable in subsequent filtration steps. Compared with other filtration methods, pressure filtration is a simple and low-cost method for filtering large amounts of precipitate, and the application of pressure filtration can reduce process costs. When applied to large quantities in a process, the process reduction effect may be even greater.

[0057] Solutions containing polymer precipitates with spherical shapes can be physically pressure filtered in subsequent filtration steps, such as by squeezing or pressurizing, which reduces energy consumption compared to conventional vacuum filtration. Specifically, pressure filtration is performed by adding the polymer precipitate to a filter, compressing the precipitate, and discharging the solvent contained within it. However, since vacuum filtration involves reducing the pressure in a container holding the polymer precipitate, a separate vacuum pump is required, and a filter is necessary to discharge the solvent during depressurization; therefore, the filter may become clogged or require periodic replacement. Because pressure filtration requires no separate auxiliary equipment other than the filter and eliminates the need to replace components such as filters, it is convenient to operate and reduces process costs.

[0058] In one exemplary embodiment of the present invention, the amount of mixed solvent in the precipitation tank can be 0.5 to 10 times the volume of the polymer solution to be precipitated, specifically 2 to 8 times, or 2 to 6 times. When the amount of mixed solvent in the precipitation tank is less than 0.5 times the volume of the polymer solution, it may be difficult to fully demonstrate the solvent's ability to precipitate the dissolved polymer, while when the amount is greater than 10 times the volume of the polymer solution, economic feasibility may be reduced due to excessive use of solvent.

[0059] Since the polymer precipitate formed in the settling tank exists in a state of mixture with the solvent contained in the added polymer solution and the solvent pre-supplied in the settling tank, a process is required to separate the polymer precipitate from the solvent used.

[0060] Therefore, the solution in the filtration sedimentation tank is filtered to separate the solvent in the solution, thereby obtaining a solid polymer precipitate (S4).

[0061] As described above, since the solution in the settling tank contains polymer precipitates with spherical shapes, physical pressure filtration can be performed in the filtration step.

[0062] For example, pressure filtration can be performed by supplying a solution containing polymer precipitates with spherical shapes to a squeeze or pressure filtration device and applying pressure of 0.1 MPa to 3 MPa or 0.5 MPa to 1.5 MPa, from which a polymer precipitate with the solvent separated can be obtained.

[0063] Because pressure filtration can separate spherical polymer precipitates and liquid solvents using a simple method of physical force, it reduces energy consumption compared to vacuum filtration, which is applied to powdered polymer precipitates in conventional methods. Furthermore, pressure filtration reduces the amount of residual solvent contained in the polymer precipitate compared to vacuum filtration.

[0064] The polymer precipitate obtained by pressure filtration may include polyethylene, polypropylene, or mixtures thereof. Furthermore, based on the weight of the polymer precipitate, the polymer precipitate may contain 19% to 80% by weight or 19% to 37% by weight of solids. That is, based on the weight of the polymer precipitate, the residual solvent content 1, which is the amount of residual solvent contained in the polymer precipitate, may be 81% to 20% by weight or 81% to 63% by weight. When the polymer precipitate is dried to remove the solvent contained in the polymer precipitate, a regenerated polymer can be obtained. However, as the residual solvent content 1 increases, more energy is consumed in removing the solvent; therefore, process costs may increase and process efficiency may decrease.

[0065] Furthermore, the filtered polymer precipitate can be used commercially as a regenerated polymer after the drying process.

[0066] For example, the drying of polymer precipitates can be carried out by heating with hot air or by heat conduction, and can be done, for example, using a flow drying apparatus such as a kneader reactor. In the flow drying apparatus, a separate solvent recovery unit can be connected for recovering residual solvent removed from the polymer precipitates, and the polymer precipitates dried in this unit can be used as regenerated polymer.

[0067] Solvents separated by filtration and residual solvents recovered by drying polymer precipitates can be recycled and reused in dissolving and settling tanks. In this study, since the recovered solvents have the same composition as the initially used mixed solvents, they can be directly reused without separate separation processes such as fractionation. Therefore, process simplification and cost reduction are achieved to ensure economic viability.

[0068] Furthermore, according to an exemplary embodiment of the present invention, the present invention may include a regenerated polymer prepared by the method for preparing the regenerated polymer.

[0069] The recycled polymer can be obtained by dissolving a composite resin in a mixture of a first solvent and a second solvent according to a method for preparing the recycled polymer, followed by precipitation and drying. After drying the polymer precipitate obtained during the precipitation process, the mixed solvent can be completely removed from the recycled polymer. However, depending on drying conditions such as drying temperature, drying time, and drying method, a small amount of mixed solvent may sometimes remain in the recycled polymer. Depending on the content, such residual amount may be at a level that does not affect the use of the recycled polymer as a product, and may be to a degree that makes it difficult to detect the mixed solvent using conventional detection methods. However, when the mixed solvent is detected, it indicates that the mixed solvent was used in the preparation of the recycled polymer.

[0070] The first solvent and the second solvent can be detected by the amount of mixed solvent remaining in the regenerated polymer, respectively. The amount of the first solvent remaining in the regenerated polymer can be expressed as residual solvent amount 2-1, and the amount of the second solvent remaining in the regenerated polymer can be expressed as residual solvent amount 2-2. Residual solvent amount 2-1 can be undetectable (0 ppm), or if detected, it can be from 10 ppm to 3000 ppm or from 10 ppm to 100 ppm based on the weight of the regenerated polymer. Furthermore, residual solvent amount 2-2 can be undetectable (0 ppm), or if detected, it can be from 10 ppm to 3000 ppm or from 10 ppm to 1500 ppm based on the weight of the regenerated polymer. Residual solvent amounts 2-1 and 2-2 being 0 ppm can mean that either the first solvent or the second solvent is absent. Preferably, residual solvent amounts 2-1 and 2-2 are close to 0 ppm, and when they are greater than 3000 ppm, the physical properties and processability of the recovered regenerated polymer may deteriorate.

[0071] The mixed solvent remaining in the regenerated polymer is the solvent used in the method for preparing the regenerated polymer, and may contain acetic acid C. 3-8 The first solvent is an alkyl ester, and the second solvent is a non-aromatic cyclic hydrocarbon. Specifically, the first solvent of the mixed solvent remaining in the regenerated polymer can be one or more selected from n-butyl acetate, tert-butyl acetate, isopropyl acetate, amyl acetate, and n-hexyl acetate. Additionally, specifically, the second solvent of the mixed solvent remaining in the regenerated polymer can be one or more selected from methylcyclohexane and cycloalkyl ethers. More specifically, the cycloalkyl ether in the second solvent can include one or more selected from cyclopentylmethyl ether, cyclopentylethyl ether, cyclopentylpropyl ether, cyclopentylisopropyl ether, cyclopentyltert-butyl ether, cyclohexylmethyl ether, cyclohexylethyl ether, cyclohexylpropyl ether, cyclohexylisopropyl ether, and cyclohexyltert-butyl ether.

[0072] The invention will be described in more detail below by way of examples. However, the following examples are provided to illustrate the invention, and it will be apparent to those skilled in the art that various modifications and changes can be made without departing from the scope and spirit of the invention, and the scope of the invention is not limited thereto.

[0073] Example 1:

[0074] A mixed solvent was prepared, wherein n-butyl acetate (n-BuAc) as the first solvent and methylcyclohexane (MCH) as the second solvent were mixed in a volume ratio of 2:1. 75 ml of the mixed solvent was supplied to a dissolving tank, and 225 ml of the mixed solvent was supplied to a precipitation tank.

[0075] A composite resin sample (6.45 g) containing 77.89 wt% polyethylene was supplied to a dissolving tank, which was then heated to 125 °C. At this temperature, the mixed solvent was boiled to obtain a polymer solution containing polyethylene dissolved in the composite resin (solubility: 6.7 wt%). Dissolution was carried out for 180 minutes with stirring.

[0076] The polymer solution was filtered through a screen filter to separate insoluble matter, and stirred while simultaneously being added dropwise to a settling tank (mixed solvent: 225 mL) at room temperature (25 °C) at a rate of 5 mL / min. The amount of polymer solution added was adjusted so that the volume of the mixed solvent was four times the volume of the polymer solution added to the settling tank. The polymer solution was then recrystallized at a high temperature (125 °C) to form spherical precipitates in the settling tank.

[0077] The solution from the settling tank is fed to a filter press and filtered at 1 MPa to obtain a polyethylene precipitate. The mixed solvent used to dissolve the precipitate is separated. The polyethylene precipitate is added to a kneader reactor and dried at 120°C to separate residual solvent. The dried polyethylene precipitate is used as a recycled polymer. Simultaneously, the solvent separated from the filter press and kneader reactors is recovered and reused.

[0078] See Examples 1-1 and 1-2:

[0079] Except for the changes in the temperature of the sedimentation tank and the filtration method as shown in Table 1 below, the process is the same as in Example 1.

[0080] Example 2 and Reference Example 2:

[0081] Except for changes to the mixing ratio of the first and second solvents, the conditions of the dissolving tank and the settling tank, or the filtration method as shown in Table 1 below, the process is the same as in Example 1.

[0082] Examples 3 to 5 and Reference Examples 3 and 4:

[0083] The process was carried out in the same manner as in Example 1, except that n-butyl acetate (n-BuAc) was used as the first solvent and cyclopentyl methyl ether (CPME) was used as the second solvent, and the mixing ratio of the two solvents, the conditions of the dissolving tank and the settling tank, or the filtration method were changed as shown in Table 1 below.

[0084] Comparative Examples 1 to 8:

[0085] Except for replacing the solvent supplied to the dissolving tank and the settling tank with a single solvent of methylcyclohexane (MCH) or cyclopentylmethyl ether (CPME) (Comparative Examples 1 to 5), or replacing butanol with a mixed solvent of methylcyclohexane or cyclopentylmethyl ether (Comparative Examples 6 to 8), and changing the conditions of the dissolving tank and the settling tank and the filtration method as shown in Table 1 below, the process was carried out in the same manner as in Example 1.

[0086] [Table 1]

[0087]

[0088] In Table 1, in the embodiments, a mixed solvent of a first solvent (n-BuAc) and a second solvent (MCH or CPME) is used in each of the dissolving tank and the settling tank. In the dissolving tank, the mixed solvent is heated to the boiling point to fully dissolve the polymer. Then, in the settling tank, which is maintained at a lower temperature than the dissolving tank, the dissolved polymer is rapidly crystallized by the action of the first solvent to form spherical precipitates. The solution containing the polymer precipitates with spherical shapes is then pressure filtered in a pressure filtration device.

[0089] However, in Comparative Examples 1 to 5, which used a single solvent, the same solubility as in the Examples was observed, but rapid crystallization as in the Examples was not achieved in the settling tank, resulting in the polymer precipitate forming in powder form rather than spherical form. Furthermore, the polymer precipitate was filtered under reduced pressure to obtain regenerated polymer. When the powder-shaped polymer precipitate was filtered using the pressure filter apparatus of Comparative Examples 1 to 5, the powder particles were too small, causing them to pass through the filter of the filter apparatus along with the solvent, and proper filtration was not achieved.

[0090] In Comparative Examples 6 to 8, experiments were conducted using mixed solvents with compositions different from those of the present invention. In Comparative Examples 6 and 7, cycloalkyl alkyl ethers were used as the second solvent, but butanol was used instead of acetic acid C. 3-8 Alkyl esters were used as the first solvent, and further experiments could not be conducted because the polymer did not dissolve sufficiently in the dissolution tank. In Comparative Example 8, acetic acid C was used. 3-8 Alkyl esters were used as the first solvent, and xylene, an aromatic cyclic hydrocarbon, was used as the second solvent. The polymer was fully dissolved in the dissolving tank, but xylene's dissolving power was too great, so precipitation did not occur well. Furthermore, in Comparative Example 8, the precipitate formed as a powder, and like Comparative Examples 1 to 5, it could not be filtered by pressure.

[0091] This indicates that, in this invention, the polymer is dissolved and precipitated by a first solvent and a second solvent, and the polymer forms spherical shapes, thereby allowing the use of pressure filtration, which can further reduce process costs and improve the efficiency of the process for preparing regenerated polymers.

[0092] Table 2 below shows that in the examples and reference examples, the polymer precipitate is formed into a spherical shape, but the yield of the regenerated polymer can be changed when the filtration method is changed.

[0093] [Table 2]

[0094]

[0095] Referring to Table 2, the polymer precipitates formed in the examples and reference examples are all spherical in shape. However, when pressure filtration was used in the examples, an increase in the yield of the regenerated polymer was observed. This indicates that when filtering polymer precipitates with a spherical shape under reduced pressure, the mixed solvent cannot be sufficiently removed in terms of the relatively large spherical particles. This suggests that, given the nature of such a spherical shape, pressure filtration, which consumes relatively less energy, is more preferable in the method for preparing regenerated polymers according to the invention, thereby increasing the yield of recycled polymers. Therefore, it is more efficient and economical than conventional processes.

[0096] Next, the polymer precipitates obtained in Examples 1 to 5 were dried in a vacuum oven at 100°C for 12 hours to obtain regenerated polymers.

[0097] The amount of solvent in the regenerated polymer was measured using liquid chromatography (LC) equipment, and the measured amount of the second residual solvent is shown in Table 3.

[0098] [Table 3]

[0099]

[0100] In Table 2, the residual amounts (ppm) in Examples 1 to 4 are the second residual solvent amounts of the recovered polymer obtained in each example, shown as parts per million (ppm) relative to the weight of the recovered polymer.

[0101] Referring to Table 3, the first solvent in the regenerated polymer is approximately 70 ppm to 100 ppm, and the second solvent is 160 ppm to 1300 ppm, and it is confirmed that both solvents remain in very small amounts. These values ​​have no impact on the physical properties or processability of the regenerated polymer when used. However, since the solvents used to prepare the regenerated polymer are detected, they can be used as indicators to determine the solvents used in preparing the regenerated polymer.

Claims

1. A method for preparing a recycled polymer, the method comprising: (S1) will contain acetic acid C 3-8 The first solvent of alkyl esters and the second solvent of non-aromatic cyclic hydrocarbons are respectively supplied to the dissolving tank and the precipitation tank; (S2) The composite resin is supplied to the dissolving tank, heated to the dissolving temperature, and the polymer contained in the composite resin is dissolved while the dissolving tank is maintained at the dissolving temperature to obtain a polymer solution; (S3) The polymer solution is supplied to the precipitation tank, the mixed solvent in the precipitation tank is maintained at the precipitation temperature, and the polymer contained in the polymer solution is precipitated to obtain a solution containing polymer precipitates having a spherical shape; and (S4) Filter the solution containing polymer precipitates with spherical shapes to obtain polymer precipitates.

2. The method for preparing recycled polymer according to claim 1, wherein, The first solvent includes one or more selected from n-butyl acetate, tert-butyl acetate, isopropyl acetate, amyl acetate, and n-hexyl acetate. The second solvent includes one or more selected from methylcyclohexane and cycloalkyl ethers.

3. The method for preparing a recycled polymer according to claim 3, wherein, The cycloalkyl alkyl ethers include one or more selected from cyclopentyl methyl ether, cyclopentyl ethyl ether, cyclopentyl propyl ether, cyclopentyl isopropyl ether, cyclopentyl tert-butyl ether, cyclohexyl methyl ether, cyclohexyl ethyl ether, cyclohexyl propyl ether, cyclohexyl isopropyl ether, and cyclohexyl tert-butyl ether.

4. The method for preparing a recycled polymer according to claim 1, wherein, The first solvent and the second solvent are mixed in a volume ratio of 2:1 to 5:

1.

5. The method for preparing a recycled polymer according to claim 1, wherein, The melting temperature is 100°C to 140°C.

6. The method for preparing a recycled polymer according to claim 1, wherein, Based on the weight of the polymer solution, the polymer solution contains 1% to 20% by weight of the polymer.

7. The method for preparing a recycled polymer according to claim 1, wherein, The precipitation temperature is 40°C to 120°C lower than the dissolution temperature.

8. The method for preparing a recycled polymer according to claim 1, wherein, The precipitation temperature is between 5°C and 50°C.

9. The method for preparing a recycled polymer according to claim 1, wherein, The volume of the mixed solvent supplied to the precipitation tank is 0.5 to 10 times the volume of the polymer solution.

10. The method for preparing a recycled polymer according to claim 1, wherein, The pressure filtration is performed by squeezing or applying pressure.

11. The method for preparing a recycled polymer according to claim 1, wherein, The polymer precipitate includes polymers selected from polyethylene, polypropylene, or mixtures thereof.

12. The method for preparing a recycled polymer according to claim 1, wherein, The average diameter of the polymer precipitate is between 500 μm and 5000 μm.

13. A recycled polymer containing residual components, wherein, The residual components include acetic acid C. 3-8 Alkyl esters and one or more selected from methylcyclohexane and cycloalkyl alkyl ethers.

14. The recycled polymer according to claim 13, wherein, Acetic acid C 3-8 Alkyl esters are selected from one or more of n-butyl acetate, tert-butyl acetate, isopropyl acetate, amyl acetate, and n-hexyl acetate, and The cycloalkyl alkyl ether is selected from one or more of cyclopentylmethyl ether, cyclopentylethyl ether, cyclopentylpropyl ether, cyclopentylisopropyl ether, cyclopentyltert-butyl ether, cyclohexylmethyl ether, cyclohexylethyl ether, cyclohexylpropyl ether, cyclohexylisopropyl ether, and cyclohexyltert-butyl ether.

15. The recycled polymer according to claim 13, wherein the acetic acid C 3-8 The alkyl ester content is from 10 ppm to 3000 ppm, and the content of one or more selected from methylcyclohexane and cycloalkyl alkyl ethers is from 10 ppm to 3000 ppm.

Images