Method for preparing regenerated polymer

Abstract

The present invention provides a method for preparing a regenerated polymer, the method comprising: preparing a mixed solvent comprising a first solvent and a second solvent, and supplying the mixed solvent to a dissolving tank and a precipitation tank, respectively; supplying the composite resin to the dissolving tank and dissolving the resin to obtain a dissolved mixture; filtering the dissolved mixture to obtain a polymer solution; and supplying the polymer solution to a precipitation tank and recrystallizing to obtain a precipitation mixture comprising the regenerated polymer.

Description

[0001] Cross - reference to related applications

[0002] This application claims the priority benefits of Korean Patent Application No. 10 - 2023 - 0059632, filed on May 9, 2023, and Korean Patent Application No. 10 - 2024 - 0055992, filed on April 26, 2024, the entire contents of which are incorporated herein by reference as part of the specification. Technical field

[0003] The present invention relates to a method for preparing a recycled polymer, and more particularly, to a method for preparing a recycled polymer from a composite resin using a mixed solvent. Background art

[0004] Recently, due to the development of resin materials having physical properties required for various uses and purposes, the use of polymer materials such as resins or plastics has increased. Generally, a large amount of energy is used from crude oil collection to manufacturing of resins or plastics, and a large amount of carbon is emitted during the process. In addition, when the final product is discarded and the resins or plastics included in the product are also discarded, it causes environmental pollution and the social cost of its treatment. Therefore, in order to reduce energy consumption, reduce carbon emissions, and prevent environmental pollution, it is necessary to recycle waste resins.

[0005] Herein, the waste resin can be a resin of a composite material or a resin of a single resin. The resin of the composite material is difficult to be recycled in the state of a blend of two or more resins, and the single resin is also difficult to be recycled because the single resin contains additives (such as plasticizers, fillers, flame retardants, stabilizers, fillers, foaming agents, viscosity reducers, colorants, and heat stabilizers) for imparting required physical properties during the manufacture of the single resin.

[0006] Therefore, in order to obtain a recycled polymer from waste resins, conventionally, the recycled polymer is obtained by selectively dissolving the polymer contained in the waste resin in a good solvent to obtain a polymer solution, and evaporating the good solvent contained in the polymer solution or contacting the polymer solution with an anti - solvent for recrystallization.

[0007] However, when evaporating the good solvent contained in the polymer solution, the thermal energy for removing the good solvent contained in the polymer solution is excessively increased. At the same time, recrystallization by contacting the polymer solution with an anti - solvent may make it difficult to recycle the remaining residual solvent after obtaining the recycled polymer recrystallized in the anti - solvent, and it is not economically preferable because a separate process for separating the residual solvent into a good solvent and an anti - solvent is also required.

[0008] Related technical literature

[0009] Patent Document

[0010] (Patent Document 1) Korean Patent Publication No. 2022-0170372 Summary of the Invention

[0011] Technical Problem

[0012] In order to solve the problems mentioned in the background art, an object of the present invention is to provide a method for preparing a recycled polymer, which can recycle the polymer from waste resin by recovering the mixed solvent from the precipitated mixture without separate separation.

[0013] Technical Solution

[0014] In general, a method for preparing a recycled polymer includes: preparing a mixed solvent containing a first solvent and a second solvent, and supplying the mixed solvent to each of a dissolution tank and a precipitation tank; supplying a composite resin to the dissolution tank and dissolving the resin to obtain a dissolved mixture; filtering the dissolved mixture to obtain a polymer solution; and supplying the polymer solution to the precipitation tank and performing recrystallization to obtain a precipitated mixture containing the recycled polymer.

[0015] Advantageous Effects

[0016] According to the method for preparing a recycled polymer, a mixed solvent including a first solvent and a second solvent is used. The first solvent is excellent in dissolving the polymer, and the second solvent is easy to recrystallize the dissolved polymer. Thus, the mixed solvent can simultaneously serve as a dissolution solvent for dissolving the polymer and a precipitation solvent for recrystallizing the dissolved polymer.

[0017] In addition, the weight ratio between the first solvent and the second solvent in the mixed solvent is controlled, so that depending on the temperature control of the mixed solvent, the function of the mixed solvent as a dissolution solvent or a precipitation solvent is maximized, and moreover, it also has a process advantage.

[0018] Specifically, the mixed solvent is recovered from the precipitated mixture obtained from the precipitation tank, and it can be directly supplied to the dissolution tank or the precipitation tank without separate separation and regeneration. Therefore, the process can be more simplified and the process cost can be reduced, so it may be preferable from an economic point of view. Detailed Description of the Invention

[0019] The terms and words used in the description and claims of the present invention should not be construed as having a general or dictionary meaning, but should be construed as having a meaning and concept that satisfy the technical idea of the present invention based on the principle that the inventor can appropriately define the terms in order to describe their own invention in the best mode.

[0020] In the following, the present invention will be described in more detail to better understand the present invention.

[0021] A method for preparing a recycled polymer according to an exemplary embodiment of the present invention may include: preparing a mixed solvent including a first solvent and a second solvent, and supplying the mixed solvent to each of a dissolution tank and a precipitation tank; supplying a composite resin to the dissolution tank and dissolving the resin to obtain a dissolved mixture; filtering the dissolved mixture to obtain a polymer solution; and supplying the polymer solution to the precipitation tank and performing recrystallization to obtain a precipitated mixture including the recycled polymer.

[0022] First, in a method for preparing a recycled polymer according to an exemplary embodiment of the present invention, a mixed solvent including a first solvent and a second solvent is prepared, and the mixed solvent is supplied to each of a dissolution tank and a precipitation tank.

[0023] The first solvent is a solvent that can more easily dissolve the polymer to be dissolved in the present invention, and may have a function of maximizing the dissolution ability of the dissolved polymer. Herein, the dissolution ability may refer to the degree or ability to selectively dissolve the polymer contained in the composite resin. That is, the first solvent may be a solvent that performs the function of dissolving only the polymer required for preparing the recycled polymer among the polymers contained in the composite resin. Herein, the polymer may be one or more of polyethylene and polypropylene, as described below.

[0024] More specifically, the first solvent may be an aromatic solvent, and may be one or more of o-xylene, m-xylene, p-xylene, and toluene. Preferably, the first solvent may be toluene. The first solvent may be a solvent having such a property that it has a maximized dissolution ability for the polymer within a certain temperature range, but the dissolution ability for the polymer decreases at temperatures outside the certain temperature range. Among them, the certain temperature range may be 80°C to 130°C. That is, the first solvent has a maximized dissolution ability for polyethylene and polypropylene within the range of 80°C to 130°C, but has a relatively reduced dissolution ability for the polymer at a temperature lower than 80°C, for example.

[0025] Meanwhile, the second solvent is a solvent that can recrystallize the polymer in the polymer solution obtained by filtering the dissolved mixture in which the composite resin is dissolved, and may have a function of maximizing the precipitation ability of the dissolved polymer to recrystallize. Herein, the precipitation ability may refer to the degree or ability to recrystallize the polymer (dissolved polymer) in the polymer solution.

[0026] Meanwhile, the second solvent also functions as a dissolving solvent for dissolving the polymer, but the ability of the second solvent to dissolve the polymer is lower than that of the first solvent. Therefore, even within the temperature range where the second solvent functions as a dissolving solvent, the dissolving ability of the first solvent can be higher than that of the second solvent. However, when the second solvent is mixed with the first solvent in a certain ratio and used as a dissolving solvent at a temperature of 80 °C or higher, it can exhibit a significantly higher dissolving ability than when the first solvent is used alone as a dissolving solvent. Among them, the certain ratio, that is, the weight ratio of the first solvent to the second solvent can be from 1:9 to 5:5. Generally, when using a mixed solvent containing two or more solvents, the solubility of the main body to be dissolved can vary according to the weight ratio of the solvents included in the mixed solvent. In the present invention, when using a mixed solvent in which the first solvent and the second solvent are mixed in a certain ratio, the solubility of the polymer can be maximized compared to a single solvent.

[0027] More specifically, the second solvent can be an aliphatic solvent, specifically, one or more of isooctane, n-decane, n-octane, and methylcyclohexane. Preferably, the second solvent can be methylcyclohexane. The second solvent can be a solvent with such characteristics that it has a precipitation ability for the dissolved polymer maximized within a certain temperature range, but the precipitation ability for the dissolved polymer decreases at temperatures outside the certain temperature range. Among them, the certain temperature range can be from 0 °C to 50 °C. That is, the second solvent of the present invention can have a maximized precipitation ability for the dissolved polymer within the temperature range of 0 °C to 50 °C, but can have a relatively reduced precipitation ability for the dissolved polymer at temperatures above 50 °C, for example.

[0028] The mixed solvent of the present invention can include a first solvent and a second solvent. Therefore, even when using the same mixed solvent to dissolve the polymer and recrystallize the dissolved polymer, the mixed solvent can have both a maximized dissolving function for the polymer and a maximized recrystallization function for the dissolved polymer.

[0029] Meanwhile, conventionally, a polymer to be obtained is dissolved in a dissolution tank including a good solvent to obtain a polymer solution, and the polymer solution is supplied to a precipitation tank including an anti-solvent and recrystallized to obtain a regenerated polymer. Among them, the good solvent and the anti-solvent are different solvents from each other, and the polymer may have solubility in the good solvent and insolubility in the anti-solvent. In this case, after obtaining the regenerated polymer as the target product, a separate process for separating the recovered solvent into the good solvent and the anti-solvent again, such as a distillation process, is required. Therefore, the amount of energy used in the distillation process may increase, which may not be preferable from an economic perspective. In addition, depending on the types of the good solvent and the anti-solvent used, it may be difficult to separate the good solvent and the anti-solvent from the recovered solvent, and thus it is difficult to regenerate the recovered solvent even using a separate process.

[0030] Therefore, in order to improve the above situation, a mixed solvent including a first solvent and a second solvent can be used in the present invention. That is, the solvent in the dissolution tank for dissolution and the precipitation tank for recrystallization can be the same as the mixed solvent. Different from the previous situation where it was crucial to separate the recovered solvent to regenerate the good solvent and the anti-solvent, since the same mixed solvent is used in the present invention, the solvent can be regenerated without using a separate process for separating the recovered mixed solvent.

[0031] According to an exemplary embodiment of the present invention, the weight ratio of the first solvent and the second solvent in the prepared mixed solvent can be from 1:9 to 5:5, specifically from 2:8 to 4:6. When the weight ratio of the mixed solvent is within this range, the first solvent and the second solvent are in a state of being mixed in an optimal ratio in the mixed solvent. Specifically, although the same mixed solvent is used for dissolution in the dissolution tank and recrystallization in the precipitation tank, the dissolution of the polymer and the recrystallization of the dissolved polymer can be maximized by controlling the weight ratio of the mixed solvent, the temperature of the mixed solvent in the dissolution tank, and the temperature of the mixed solvent in the precipitation tank.

[0032] Specifically, when the weight ratio of the first solvent and the second solvent in the mixed solvent is greater than 5:5, the content of the second solvent, which plays an important role in the recrystallization carried out in the precipitation tank, is reduced, so that the recrystallization of the dissolved polymer cannot be fully carried out. Therefore, the yield of the regenerated polymer obtained in the present invention may be reduced. When the weight ratio of the first solvent and the second solvent in the mixed solvent is less than 1:9, it may be difficult to maximize the dissolution ability of the first solvent in the mixed solvent, and thus it is difficult to achieve the desired level in the present invention when dissolving the polymer in the mixed solvent.

[0033] Next, the method for preparing a regenerated polymer according to an exemplary embodiment of the present invention may include supplying a composite resin to a dissolution tank and dissolving the resin to obtain a dissolved mixture.

[0034] The composite resin is derived from waste resin and can be obtained by pretreating the waste resin. The waste resin can be recovered from various products molded using the resin or its composition or from its use, regardless of whether it is hard or soft. In addition, the composite resin obtained by pretreating the waste resin can be a single type of polymer containing additives or a resin composition in which two or more polymers are blended. Meanwhile, pretreatment refers to the entire process of treating the waste resin into a state suitable for the method of applying the recycled polymer of the present invention. For example, the pretreatment can be a process of washing the waste resin with a solvent such as water to remove relatively large foreign matters such as dust, drying, and pulverizing.

[0035] The composite resin is not particularly limited. However, for example, when pretreating a film-shaped waste resin to obtain a composite resin, the ratio of the area of the composite resin to the thickness of the composite resin can be from 1000:1 to 10:1, from 500:1 to 100:1, or from 300:1 to 200:1. When the ratio of the area of the composite resin to the thickness of the composite resin is less than 10:1, too much energy may be used in the pretreatment process of the waste resin to prepare such a composite resin. When the ratio of the area of the composite resin to the thickness of the composite resin is greater than 1000:1, the size of the composite resin is large, so it may take too much time to supply the composite resin to the dissolution tank and dissolve the resin.

[0036] Meanwhile, in order to prepare the recycled polymer described in the present invention, the polymer included in the composite resin can be one or more of polyethylene and polypropylene. The polyethylene can include high-density polyethylene (HDPE), low-density polyethylene (LDPE), and linear low-density polyethylene (LLDPE), depending on its density. The content of the polymer in the composite resin can be from 50% by weight to 90% by weight.

[0037] In the present invention, in order to obtain the recycled polymer from the composite resin, the composite resin can be brought into contact with a mixed solvent in a dissolution tank to dissolve the polymer. Here, the dissolution of the polymer can be carried out while stirring the mixed solvent in the dissolution tank. Thus, by bringing the composite resin into contact with the mixed solvent under stirring of the mixed solvent, the composite resin is dispersed in the mixed solvent, making it easier for the polymer to dissolve. Therefore, a dissolved mixture including the polymer dissolved by the mixed solvent in the dissolution tank can be obtained, and the dissolved mixture can also include insoluble matters that are not soluble in the mixed solvent.

[0038] Specifically, during the polymer dissolution process, the temperature of the mixed solvent in the dissolution tank can be 80°C to 130°C, 80°C to 120°C, or 80°C to 100°C. By dissolving the polymer using the mixed solvent at a temperature within this range, the dissolving ability of the first solvent included in the mixed solvent can be maximized. Specifically, although the second solvent included in the mixed solvent can also dissolve the polymer, compared with the function of the second solvent to dissolve the polymer within this temperature range, the function of the first solvent as the dissolving solvent can be maximized. Therefore, when dissolving the polymer in the mixed solvent within the above temperature range, the weight ratio between the first solvent and the second solvent included in the mixed solvent can play an important role.

[0039] Specifically, when the temperature of the mixed solvent in the dissolution tank is lower than 80°C, it is difficult for the polymer to be fully dissolved in the mixed solvent, so the yield of the regenerated polymer obtained in the present invention may decrease. When the temperature of the mixed solvent in the dissolution tank is higher than 130°C, the temperature of the mixed solvent is too high, such that other polymers can be dissolved together with the polymer to be dissolved in the present invention, and the purity of the finally obtained regenerated polymer may decrease.

[0040] The time for supplying the composite resin to the dissolution tank and dissolving the polymer can be 120 to 300 minutes. This time can refer to the time from the node when the composite resin contacts the mixed solvent in the dissolution tank to the node when the polymer is dissolved in the mixed solvent in the dissolution tank.

[0041] Subsequently, in the present invention, the dissolved mixture can be filtered to obtain a polymer solution. The dissolved mixture may contain insoluble substances as described above, and the dissolved mixture can be filtered to separate the dissolved mixture into insoluble substances and a polymer solution. Here, the insoluble substances can be the components included in the composite resin that are not dissolved in the mixed solvent. Meanwhile, the polymer solution can be the filtrate containing the dissolved polymer, in a state where the insoluble substances are separated from the dissolved mixture. Specifically, the polymer solution can include the mixed solvent and the polymer dissolved in the mixed solvent.

[0042] When separating the dissolved mixture into insoluble substances and a polymer solution, filtration can be performed in which the dissolved mixture is filtered. The separation by filtration can be carried out by, for example, one or more of filtering with a filter, centrifugal filtration, and sedimentation filtration. In the present invention, the separation into insoluble substances and a polymer solution can be performed by filtering with a filter, and as an example, a mesh filter can be used as the filter to perform the operation. The dissolved mixture is filtered by filtration to separate out the insoluble substances, thereby obtaining a polymer solution.

[0043] Meanwhile, the content of the dissolved polymer contained in the polymer solution obtained by filtering the dissolved mixture may be 1 wt% or more, 5 wt% or more, or 8 wt% or more, and 20 wt% or less, 15 wt% or less, or 13 wt% or less. When the content of the dissolved polymer contained in the polymer solution (i.e., the concentration of the polymer solution) is less than 1 wt%, since the concentration of the polymer in the polymer solution is low, the amount of the regenerated polymer produced may be reduced. When the concentration of the polymer solution is greater than 20 wt%, the viscosity of the dissolved mixture increases significantly, and it is difficult to separate the insoluble matter and the polymer solution from the dissolved mixture.

[0044] The method for preparing a regenerated polymer according to an exemplary embodiment of the present invention may include supplying a polymer solution to a precipitation tank and performing recrystallization to obtain a precipitation mixture including the regenerated polymer.

[0045] That is, in the present invention, a dissolution tank for dissolving a polymer and a separate precipitation tank as another component are used to perform recrystallization and precipitation of the polymer dissolved in the polymer solution. Therefore, the energy consumption required to cool the polymer solution at a high temperature for recrystallization is reduced, and the yield of the finally obtained regenerated polymer can be increased.

[0046] Specifically, the method of supplying the polymer solution to the precipitation tank may be performed by dropping the polymer solution in the form of droplets into a mixed solvent, and the mixed solvent may be in a stirred state. Therefore, the polymer present in the state dissolved in the polymer solution, that is, the dissolved polymer, can be recrystallized and precipitated in the mixed solvent in the precipitation tank, and this can be the regenerated polymer of the present invention. Therefore, a precipitation mixture including the regenerated polymer can be obtained by recrystallization performed in the precipitation tank, and the precipitation mixture may further include the mixed solvent in the precipitation tank and the mixed solvent contained in the polymer solution.

[0047] According to the present invention, the recovered polymer may be one or more of polyethylene and polypropylene.

[0048] Meanwhile, the mass of the mixed solvent supplied to the precipitation tank may be 2 to 10 times, specifically 2 to 8 times, or 2 to 6 times the mass of the polymer solution supplied to the precipitation tank. When the mass of the mixed solvent supplied to the precipitation tank is less than twice the mass of the polymer solution supplied to the precipitation tank, although the temperature of the mixed solvent in the precipitation tank is controlled, it may be difficult for the mixed solvent to fully exhibit the precipitation ability for the dissolved polymer. When the mass of the mixed solvent supplied to the precipitation tank is greater than 10 times the mass of the polymer solution supplied to the precipitation tank, the amount of the mixed solvent used in the precipitation tank increases excessively, which may not be preferred from an economic perspective.

[0049] In addition, the temperature of the mixed solvent in the precipitation tank into which the polymer solution is introduced may be 0°C to 50°C, 0°C to 30°C, or 10°C to 20°C. When recrystallization is carried out in the mixed solvent at a temperature within this range, the temperature of the mixed solvent in the precipitation tank is lower than the temperature of the mixed solvent in the dissolution tank. Therefore, recrystallization of the dissolved polymer can be easily carried out. In addition, when recrystallization is carried out, when using the mixed solvent at a temperature within the above range, the dissolving ability of the first solvent contained in the mixed solvent can be reduced, and the precipitation ability of the second solvent can be enhanced. Therefore, the precipitation ability of the second solvent depending on the temperature may play a more important role within the above temperature range.

[0050] Specifically, when the temperature of the mixed solvent in the precipitation tank is lower than 0°C, a separate cooling device should be provided to control the temperature. Therefore, energy consumption may increase. When the temperature of the mixed solvent in the precipitation tank is higher than 50°C, the precipitation ability of the second solvent in the mixed solvent is reduced. Therefore, it may be difficult to recrystallize the dissolved polymer and the recrystallization rate may also be reduced. As a result, the yield of the polymer recovered in the present invention may be reduced.

[0051] According to an exemplary embodiment of the present invention, the preparation of the mixed solvent including the first solvent and the second solvent may include recovering the mixed solvent from the precipitated mixture. The step of recovering the mixed solvent from the precipitated mixture may be a series of processes for recovering the mixed solvent contained in the precipitated mixture to regenerate the mixed solvent.

[0052] According to the present invention, fractionation is not involved in recovering the mixed solvent from the precipitated mixture. Fractionation is distillation carried out to separate a liquid mixture including two or more liquids into each liquid. And since a mixed solvent is used in the present invention, fractionation may not be involved when recovering the mixed solvent. Specifically, since a mixed solvent including the first solvent and the second solvent is used in the present invention to dissolve the polymer and recrystallize the dissolved polymer, it is not necessary to separate the mixed solvent into the first solvent and the second solvent.

[0053] Specifically, recovering the mixed solvent from the precipitation mixture can be carried out by including separating the regenerated polymer and the mixed solvent and drying the separated regenerated polymer.

[0054] First, the separation into the regenerated polymer and the mixed solvent may refer to the process of separating the precipitated mixture into the regenerated polymer and the mixed solvent. More specifically, the separation into the regenerated polymer and the mixed solvent can be carried out in the same manner as the filtration of the above-mentioned dissolved mixture. Thus, by way of example, the process of separating into the regenerated polymer and the mixed solvent can be carried out by filtering the precipitated mixture with a filter. Therefore, the target product (regenerated polymer) can be obtained through the process of separating into the regenerated polymer and the mixed solvent, and the mixed solvent used during this process can be recovered and regenerated.

[0055] Meanwhile, the drying of the separated regenerated polymer can be carried out by drying the regenerated polymer separated from the process of separating into the regenerated polymer and the mixed solvent to finally obtain the regenerated polymer. Specifically, although the regenerated polymer and the mixed solvent are separated in the above-mentioned separation into the regenerated polymer and the mixed solvent, some of the mixed solvent may remain in the chains of the separated regenerated polymer. That is, the separated regenerated polymer may contain residual mixed solvent. Based on 100% by weight of the separated regenerated polymer, the content of the mixed solvent remaining in the separated regenerated polymer can be from 30% to 200% by weight. Therefore, in order to separate and recover the solvent remaining in the separated regenerated polymer, the drying of the separated regenerated polymer can be carried out. The drying can be carried out by heating with hot air or under hot conditions and is carried out in a fluidized drying device. The fluidized drying device can be a device that dries the object to be dried by the flow of hot air or the device, for example, it can be a kneader. When drying is carried out in a kneader reactor, a separate solvent recovery device for recovering the remaining mixed solvent from the separated regenerated polymer can be connected to the kneader reactor. Thus, the remaining mixed solvent can be further recovered by drying, and the regenerated polymer after drying the remaining mixed solvent can be obtained with high purity.

[0056] Therefore, the mixed solvent is recovered by the separation into the regenerated polymer and the mixed solvent and the drying of the separated regenerated polymer, and then regenerated, thereby minimizing the amount of the mixed solvent lost in this process, and the amount of fresh first solvent and / or second solvent used to supplement the loss can be very small.

[0057] According to an exemplary embodiment of the present invention, the weight ratio between the first solvent and the second solvent in the prepared mixed solvent may be the same as the weight ratio between the first solvent and the second solvent in the recovered mixed solvent. Specifically, since most of the mixed solvent in the present invention is recovered by filtration, and the remaining mixed solvent in the separated regenerated polymer is recovered by drying, without performing a separate fractionation process to recover the mixed solvent from the precipitate mixture, the weight ratio can be kept the same. Therefore, the recovered mixed solvent can be supplied to the dissolution tank and the precipitation tank and recycled.

[0058] Meanwhile, when a good solvent is used in dissolution and an anti-solvent is used in recrystallization as before, a separate fractionation process for separating the good solvent and the anti-solvent from the recovered solvent after finally obtaining the regenerated polymer (such as a distillation column) needs to be provided. However, since the separation in the dissolution tank is not precise, when some of the anti-solvent is supplied to the dissolution tank together with the good solvent separated from the distillation column to perform dissolution, the solubility of the polymer may be significantly reduced only when some of the anti-solvent is supplied to the dissolution tank.

[0059] From this perspective, in the present invention, a mixed solvent having a controlled weight ratio between a first solvent and a second solvent functions at the temperature for performing polymer dissolution and the temperature for performing polymer recrystallization, thereby reusing the recovered mixed solvent without separate separation, while obtaining a regenerated polymer at a yield similar to the conventional yield. Therefore, the present invention can simplify process equipment and is preferable in terms of energy use.

[0060] Hereinafter, the present invention will be described in more detail by way of examples. However, the following examples are for illustrative purposes of the present invention, and it is obvious to those skilled in the art that various modifications and changes can be made without departing from the scope and spirit of the present invention, and the scope of the present invention is not limited thereto.

[0061] Example 1

[0062] Prepare a mixed solvent in which a first solvent (toluene) and a second solvent (methylcyclohexane) are mixed at a weight ratio of 3:7. Supply 20 ml of the mixed solvent to a dissolution tank at 100 °C, and supply 100 ml of the mixed solvent to a precipitation tank at 20 °C.

[0063] Supply a composite resin sample (6.45 g) containing 77.89 wt% polyethylene to the dissolution tank and dissolve it with stirring for 180 minutes to obtain a dissolved mixture.

[0064] Thereafter, filter the dissolved mixture with a mesh filter to obtain a polymer solution from which insoluble matters are separated. At this time, the concentration of the polymer solution is 20 wt%.

[0065] Subsequently, supply the polymer solution to the precipitation tank in which the mixed solvent is stirred. At this time, the polymer solution is added dropwise at an addition rate of 5 ml / min. At this time, the mass of the mixed solvent supplied to the precipitation tank is 4 times the total mass of the polymer solution to be added to the precipitation tank. Therefore, the polyethylene dissolved in the polymer solution recrystallizes in the mixed solvent in the precipitation tank. Finally, a precipitation mixture including the regenerated polymer (polyethylene) is obtained.

[0066] The precipitated mixture is added to a mesh filter and separated into a recycled polymer (polyethylene) and a mixed solvent. The separated recycled polymer (polyethylene) is added to a kneader reactor and dried at 120 °C to separate the remaining mixed solvent in the separated recycled polymer (polyethylene), and finally a recycled polymer is obtained. At the same time, the mixed solvent separated from the mesh filter and the kneader reactor is recovered and recycled.

[0067] Example 2

[0068] A recycled polymer is prepared in the same manner as in Example 1, except that a mixed solvent in which the first solvent and the second solvent are mixed at a weight ratio of 5:5 is used.

[0069] Example 3

[0070] A recycled polymer is prepared in the same manner as in Example 1, except that a mixed solvent in which the first solvent and the second solvent are mixed at a weight ratio of 1:9 is used.

[0071] Comparative Example 1

[0072] A recycled polymer is prepared in the same manner as in Example 1, except that toluene is used as a single solvent instead of a mixed solvent, 20 ml of toluene is supplied to the dissolution tank at 100 °C, and 100 ml of toluene at 20 °C is supplied to the precipitation tank.

[0073] Comparative Example 2

[0074] A recycled polymer is prepared in the same manner as in Example 1, except that methylcyclohexane (MCH) is used as a single solvent instead of a mixed solvent, 20 ml of MCH is supplied to the dissolution tank at 100 °C, and 100 ml of MCH at 20 °C is supplied to the precipitation tank.

[0075] Comparative Example 3

[0076] A mixed solvent is prepared in which the first solvent (toluene) and the second solvent (methylcyclohexane) are mixed at a weight ratio of 3:7. 20 ml of the mixed solvent is supplied to the dissolution tank at 100 °C.

[0077] 6.45 g of a composite resin sample containing 77.89 wt% polyethylene is supplied to the dissolution tank and dissolved for 180 minutes with stirring to obtain a dissolved mixture.

[0078] Thereafter, the dissolved mixture is filtered through a mesh filter to obtain a polymer solution from which insoluble matters are separated. At this time, the concentration of the polymer solution is 20 wt%.

[0079] The polymer solution is cooled from 100 °C to 20 °C, causing the polyethylene dissolved in the polymer solution to recrystallize. Finally, a precipitate mixture containing the recycled polymer (polyethylene) is obtained.

[0080] The precipitated mixture is added to a mesh filter and separated into the recycled polymer (polyethylene) and the mixed solvent. The separated recycled polymer (polyethylene) is added to a kneader reactor and dried at 120 °C to separate the remaining mixed solvent in the separated recycled polymer (polyethylene), and finally the recycled polymer is obtained.

[0081] Table 1 below shows the yields of the finally obtained recycled polymers in the examples and comparative examples.

[0082] [Table 1]

[0083]

[0084] It is confirmed from Table 1 that the yield of the recycled polymer in the examples is significantly higher than that in the comparative examples. Therefore, it is confirmed that by using a mixed solvent including a first solvent with excellent dissolution properties and a second solvent that is easy to recrystallize, the role of the mixed solvent in the dissolution and recrystallization processes is maximized, and the amount of the finally obtained recycled polymer increases.

[0085] In Comparative Example 1 where only the first solvent (toluene) is used instead of the mixed solvent as in the examples, it is difficult to perform recrystallization well by recrystallizing the dissolved polymer using only the first solvent alone, and thus the yield of the finally recycled polymer is the lowest.

[0086] In Comparative Example 2, only the second solvent (methylcyclohexane) is used as a single solvent. Compared with Comparative Example 1 where only the first solvent is used, the amount of the recrystallized recycled polymer is increased by using the second solvent that is easy to recrystallize, but compared with the examples using the mixed solvent, the yield of the recycled polymer is significantly reduced.

[0087] In Comparative Example 3, the polymer solution obtained by dissolving the polymer in the mixed solvent as in Example 1 is not added dropwise to the precipitation tank, but the polymer solution itself is cooled as it is. During the recrystallization process, crystal particles are finely formed, making it difficult to separate the polymer crystals and the solvent, and thus the yield of the finally recycled polymer is reduced. In addition, during the process of cooling the polymer solution at a high temperature (100 °C) obtained in the dissolution step to 20 °C, the energy consumption increases.

Claims

1. A method for preparing a recycled polymer, the method comprising: preparing a mixed solvent comprising a first solvent and a second solvent, and supplying the mixed solvent to each of a dissolution tank and a precipitation tank; supplying a composite resin to the dissolution tank and dissolving the resin to obtain a dissolved mixture; filtering the dissolved mixture to obtain a polymer solution; and The polymer solution is supplied to the precipitation tank and recrystallized to obtain a mixture containing a precipitate of a regenerated polymer.

2. The method for preparing a recycled polymer according to claim 1, wherein: The recycled polymer is one or more of polyethylene and polypropylene.

3. The method for preparing a recycled polymer according to claim 1, wherein: The temperature of the mixed solvent in the dissolution tank is 80°C to 130°C, and the temperature of the mixed solvent in the precipitation tank is 0°C to 50°C.

4. The method for preparing a recycled polymer according to claim 1, wherein: The first solvent includes one or more of o-xylene, m-xylene, p-xylene and toluene, and the second solvent includes one or more of isooctane, n-decane, n-octane and methylcyclohexane.

5. The method for preparing a recycled polymer according to claim 1, wherein: The weight ratio of the first solvent to the second solvent in the prepared mixed solvent is 1:9 to 5:

5.

6. The method for preparing a recycled polymer according to claim 1, wherein: The first solvent is toluene, and the second solvent is methylcyclohexane.

7. The method for preparing a recycled polymer according to claim 1, wherein: In the polymer solution obtained by filtering the dissolved mixture, the content of the dissolved polymer is 1 wt % to 20 wt %.

8. The method for preparing a recycled polymer according to claim 1, wherein: The mass of the mixed solvent supplied to the precipitation tank is 2 to 10 times the mass of the polymer solution supplied to the precipitation tank.

9. The method for preparing a recycled polymer according to claim 1, wherein: The step of preparing a mixed solvent comprising a first solvent and a second solvent includes recovering the mixed solvent from the precipitated mixture.

10. The method for preparing a recycled polymer according to claim 9, wherein: The step of recovering the mixed solvent from the precipitated mixture is performed by comprising separating the regenerated polymer and the mixed solvent and drying the separated regenerated polymer.

11. The method for preparing a recycled polymer according to claim 9, wherein: The step of recovering the mixed solvent from the precipitated mixture does not involve fractional distillation.

12. The method for preparing a recycled polymer according to claim 9, wherein: The weight ratio of the first solvent to the second solvent in the prepared mixed solvent is the same as the weight ratio of the first solvent to the second solvent in the recovered mixed solvent.

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