Method for preparing recycled polymer

Abstract

The present invention provides a method for preparing a recycled polymer, comprising the steps of: (S1) supplying a mixed solvent including a first solvent of C3-8 alkyl acetate and a second solvent of a non-aromatic cyclic hydrocarbon to each of a dissolution tank and a precipitation tank; (S2) supplying a composite resin to the dissolution tank, heating the dissolution tank to a dissolution temperature, and, while maintaining the dissolution tank at the dissolution temperature, dissolving a polymer included in the composite resin to obtain a polymer solution; (S3) supplying the polymer solution to the precipitation tank in which the mixed solvent is maintained at a precipitation temperature, and precipitating the polymer included in the polymer solution to obtain a solution including a spherical polymer precipitate; and (S4) performing compression filtration on the solution including the spherical polymer precipitate to obtain a polymer precipitate.

Description

Method for producing regenerated polymers

[0001] Cross-citation with related applications

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

[0003] Technology field

[0004] The present invention relates to a method for producing a regenerated polymer, and more particularly, to a method for producing a regenerated polymer that can apply an economical physical filtration process by controlling the shape of a sediment when recovering a polymer from waste resin.

[0005] Recently, the use of polymer materials such as resins and plastics has increased as resin materials with the properties required for various applications and purposes have been developed. Generally, resins and plastics consume significant energy from crude oil extraction to manufacturing, and the process emits significant amounts of carbon. Furthermore, when the resin or plastic contained in the final product is discarded, it also causes environmental pollution and incurs social costs for its disposal. Therefore, recycling waste resins is essential to reduce energy consumption, carbon emissions, and prevent environmental pollution.

[0006] Meanwhile, waste resin may be a composite resin or a single resin. The composite resin is a blend of two or more resins, and in the case of a single resin, it may be difficult to recycle physically due to the additives (plasticizers, fillers, flame retardants, stabilizers, filling agents, foaming agents, viscosity-reducing agents, colorants, and heat stabilizers) used to impart desired properties.

[0007] Accordingly, methods are being implemented to chemically recover and recycle polymers from waste resin. For example, a polymer contained in waste resin can be selectively dissolved in a good solvent to obtain a polymer solution, and a recycled polymer can be produced by evaporating the good solvent contained in the polymer solution or by contacting the polymer solution with an antisolvent to recrystallize it.

[0008] This recycling technique, based on dissolution and recrystallization, offers the advantage of reducing carbon emissions by increasing the purity of the polymer, maintaining its physical properties, and recovering it without decomposition. However, because the polymer-dissolving solvent and the precipitating antisolvent are mixed, the two solvents must be separated for future reuse.

[0009] Accordingly, to avoid the use of an antisolvent during the recrystallization step, a method of precipitating the polymer by lowering the temperature of the solution in which the polymer is dissolved has recently been gaining attention. However, the polymer precipitated by self-cooling of the polymer solution contains a large amount of solvent, requiring an additional process of evaporating and removing the solvent, which consumes a significant amount of energy.

[0010] In addition, most of the crystals of the above-mentioned precipitated polymer are in powder form, and when such powder-form precipitated polymer exists in a slurry state in a solvent, energy-intensive depressurized filtration is required in the filtration step for solvent separation, and it is difficult to apply simple and economical squeezing or pressing.

[0011] The problem to be solved in the present invention is to provide a method for producing a regenerated polymer that can apply an economical physical filtration process by controlling the shape of the sediment when recovering the polymer from waste resin in order to solve the problem mentioned in the background technology of the above invention.

[0012] According to one embodiment of the present invention for solving the above problem, the present invention (S1) comprises a dissolution tank and a sedimentation tank C 3-8 A method for producing a regenerated polymer is provided, comprising: (S2) a step of supplying a mixed solvent including a first solvent of alkyl acetate and a second solvent of non-aromatic cyclic hydrocarbon; (S3) a step of supplying a composite resin to the dissolution tank and then heating the composite resin to a dissolution temperature, and dissolving a polymer included in the composite resin while maintaining the dissolution tank at the dissolution temperature to obtain a polymer solution; (S4) a step of supplying the polymer solution to the precipitation tank in which the mixed solvent is maintained at a precipitation temperature, and precipitating the polymer included in the polymer solution to obtain a solution including a spherical polymer precipitate; and (S4) a step of squeezing and filtering the solution including the spherical polymer precipitate to obtain a polymer precipitate.

[0013] According to the present invention, C, which is advantageous for precipitation of polymers, is supplied as the same solvent to the dissolution tank and the precipitation tank for recovering polymers contained in composite resins derived from waste resins. 3-8 A mixed solvent comprising a first solvent of alkyl acetate and a second solvent of a non-aromatic cyclic hydrocarbon having a higher solubility of the polymer than the first solvent is used, and the mixed solvent is heated in the dissolution tank to a dissolution temperature higher than the boiling point to sufficiently dissolve the polymer, and then rapid crystallization of the dissolved polymer is induced in a precipitation tank maintained at a low temperature to form a spherical precipitate. The solution containing such a spherical polymer precipitate can be subjected to physical compression filtration, such as squeezing or pressing, in a subsequent filtration step, thereby reducing energy consumption compared to conventional vacuum filtration.

[0014] In addition, the present invention can reduce the energy consumed to lower the temperature of the high-temperature polymer solution before introducing it into the precipitation tank by separately performing the dissolution step and the recrystallization step of the polymer in the dissolution tank and the precipitation tank, respectively.

[0015] Additionally, by supplying the same solvent to the dissolution tank and precipitation tank, the remaining solvent after obtaining the final polymer precipitate can be reused directly in the dissolution tank and precipitation tank without a separate separation process. This simplifies the process and reduces costs, resulting in economic benefits.

[0016] The terms or words used in the description and claims of the present invention should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

[0017] Hereinafter, the present invention will be described in more detail to help understand the present invention.

[0018] A method for producing a regenerated polymer according to one embodiment of the present invention may include a step (S1) of supplying the same solvent to a dissolution tank and a precipitation tank, a step (S2) of dissolving a polymer included in a composite resin, a step (S3) of precipitating the dissolved polymer by recrystallization, and a step (S4) of obtaining a polymer precipitate.

[0019] The composite resin used in the present invention is derived from waste resin and may be obtained by pretreating the waste resin. The waste resin, regardless of whether it is hard or soft, can be recovered from various products or uses molded using the resin or its composition. Furthermore, the composite resin obtained by pretreating the waste resin may be a single type of polymer containing an additive, or may be a resin composition blended with two or more polymers. Meanwhile, the pretreatment refers to an entire process of treating the waste resin to a state suitable for application to the method for producing the recycled polymer of the present invention. For example, the pretreatment may be a process of first washing the waste resin with a solvent such as water to remove relatively large foreign substances such as dust, drying, and then pulverizing. The pulverization is advantageously performed so that the dried waste resin is uniformly and consistently sized, for example, 1 mm to 5 cm. If the pulverized resin has a size less than 1 mm, handling is difficult due to the generation of dust, and if it exceeds 5 cm, the polymer recovery process takes a long time to dissolve.

[0020] The composite resin that has undergone such pretreatment may include a polymer such as polyethylene, polypropylene, or a mixture thereof, and the polymer can be recovered from the composite resin and used as a recycled resin. The polyethylene is classified into HDPE (high-density polyethylene), MDPE (medium-density polyethylene), LDPE (low-density polyethylene), LLDPE (linear low-density polyethylene), VLDPE (ultra-low-density polyethylene), etc., depending on its density, and can be appropriately selected and used depending on the characteristics of the composite resin.

[0021] For example, the composite resin may contain a polymer including polyethylene, polypropylene or a mixture thereof in an amount of 50 to 90 wt% based on its weight.

[0022] The present invention is to selectively recover the polymer contained in the composite resin as described above and manufacture it as a regenerated polymer. The method for manufacturing a regenerated polymer according to one embodiment of the present invention comprises first adding C to a dissolution tank and a sedimentation tank. 3-8 It may include a step (S1) of supplying a mixed solvent including a first solvent of alkyl acetate and a second solvent of non-aromatic cyclic hydrocarbon.

[0023] C used as the first solvent 3-8 Alkyl acetate may have the ability to dissolve polymers, but it may have a superior ability to precipitate, which induces recrystallization of the dissolved polymer. Therefore, as a solvent, the above C 3-8 When alkyl acetate is used alone, it may not dissolve well in polymers such as polyethylene or polypropylene due to its low solubility in the polymer. However, when used together with a second solvent having a higher solubility in the polymer, it can secure excellent dissolving ability, thereby selectively dissolving the polymer from the composite resin and then rapidly precipitating the polymer during the precipitation process.

[0024] On the other hand, C as the first solvent 3-8 When using solvents other than alkyl acetate, such as alcohol, the polymer may not be completely dissolved, thus reducing the yield of the regenerated polymer. Alcohols have very poor solubility for polymers such as polyethylene or polypropylene, and this does not improve even when the temperature is increased, making them unsuitable as solvents for dissolving the polymer.

[0025] In one embodiment of the present invention, the first solvent may include at least one selected from n-butyl acetate, t-butyl acetate, isopropyl acetate, pentyl acetate, and n-hexyl acetate. Among these, n-butyl acetate may be more advantageously used because it exhibits good solubility in polymers and excellent precipitation characteristics.

[0026] Meanwhile, the non-aromatic cyclic hydrocarbon used as the second solvent exhibits excellent solubility in the polymer, and thus can compensate for the insufficient solubility of the first solvent described above in the mixed solvent. Therefore, the mixed solvent including the first solvent and the second solvent can advantageously function to exhibit excellent dissolving ability in the polymer and to recrystallize the dissolved polymer to form a polymer precipitate. The second solvent may have low solubility in the polymer at a low temperature such as room temperature, but may have an increased solubility in the polymer at a temperature close to the boiling point of the second solvent. Therefore, in the present invention, by utilizing this characteristic, the temperature of the mixed solvent can be maintained at a temperature close to the boiling point of the second solvent, thereby dissolving the polymer included in the composite resin.

[0027] On the other hand, when an aromatic solvent is used as the second solvent, since the aromatic solvent has very good solubility in the polymer, dissolution of the polymer is not a problem, but since the recrystallization ability is low, a problem may occur in which the polymer is not completely precipitated during the precipitation process. In addition, since the aromatic solvent has very high affinity for the polymer, the polymer may be precipitated in a gel-like form rather than a particle form during the precipitation step. Since such a gel-like precipitate contains a high content of solvent, more energy may be consumed when drying the precipitate.

[0028] In one embodiment of the present invention, the second solvent may include at least one selected from methylcyclohexane and a cycloalkyl alkyl ether. Among these, the cycloalkyl alkyl ether may be preferably used.

[0029] The above cycloalkyl alkyl ether has the characteristics of a relatively high boiling point, a low melting point, a low heat of vaporization, hydrophobicity, chemical stability, etc. Here, the boiling point may mean the boiling point at atmospheric pressure (1 atm). In particular, the cycloalkyl alkyl ether has a relatively high boiling point, so that it can be applied as a solvent in a wide range from low to high temperatures. Therefore, by using the cycloalkyl alkyl ether as the second solvent, it is possible to selectively dissolve a polymer that needs to be dissolved for the production of a recycled polymer from a composite resin derived from waste resin, and in the subsequent precipitation step, when recrystallizing the dissolved polymer, the precipitation ability of the mixed solvent together with the first solvent can be improved.

[0030] For example, the cycloalkyl alkyl ether may have a boiling point exceeding 100°C, and this high boiling point may mean that the second solvent has a wide temperature range that allows for selectively dissolving the target polymer by heating it to a high temperature and then lowering the temperature to perform recrystallization of the dissolved polymer, and this can be used to increase the supersaturation at low temperatures, thereby improving the rate at which a polymer precipitate is formed.

[0031] Specific examples of such cycloalkyl alkyl ethers may include at least one selected from cyclopentyl methyl ether, cyclopentyl ethyl ether, cyclopentyl propyl ether, cyclopentyl isopropyl ether, cyclopentyl t-butyl ether, cyclohexyl methyl ether, cyclohexyl ethyl ether, cyclohexyl propyl ether, cyclohexyl isopropyl ether, and cyclohexyl t-butyl ether. Among these, cyclopentyl methyl ether, cyclopentyl ethyl ether, and cyclohexyl ethyl ether can be advantageously used because they exhibit excellent solubility in polymers at high temperatures and low affinity at low temperatures.

[0032] In addition, in one embodiment of the present invention, the mixed solvent may refer to a solvent in which the first solvent and the second solvent are mixed. In the mixed solvent, the first solvent and the second solvent may maintain their respective characteristics for dissolving and precipitating the polymer. Specifically, the first solvent may have a low dissolving ability for the polymer, but an excellent ability to recrystallize and precipitate the polymer at a low temperature, and this characteristic may be maintained within the mixed solvent. In addition, the second solvent may have a low dissolving ability for the polymer at a low temperature, but an improved ability to dissolve the polymer at a high temperature, and this characteristic may be maintained within the mixed solvent. Therefore, by creating an environment in the dissolution tank and the precipitation tank that can maximize the characteristics of each of the first solvent and the second solvent, the polymer can be efficiently dissolved and precipitated.

[0033] In one embodiment of the present invention, the mixed solvent may be a mixture of the first solvent and the second solvent in a volume ratio of 2:1 to 5:1, specifically, a volume ratio of 2:1 to 4:1, and when a mixed solvent satisfying this ratio is supplied to a dissolution tank and a precipitation tank, respectively, the precipitation ability to dissolve the polymer and then recrystallize it can be maximized, thereby improving the recovery rate of the polymer. When the volume ratio of the first solvent and the second solvent is less than 2:1, the precipitation effect due to the first solvent does not appear, and thus the polymer may be precipitated in a powder form, and when it exceeds 5:1, the polymer dissolution effect due to the second solvent does not appear, and thus the polymer may not be completely dissolved.

[0034] In this way, in the present invention, a mixed solvent including the first solvent and the second solvent as the same solvent is supplied to a dissolution tank that performs polymer dissolution and a precipitation tank that performs recrystallization, thereby overcoming the disadvantage of the prior art in which a separation process was required for later reuse due to mixing of two different solvents by using a good solvent for dissolving a polymer and an antisolvent for precipitation.

[0035] A method for producing a regenerated polymer according to one embodiment of the present invention may include a step (S2) of supplying a composite resin to the dissolution tank, heating the composite resin to a dissolution temperature, and dissolving the polymer contained in the composite resin while maintaining the dissolution tank at the dissolution temperature to obtain a polymer solution.

[0036] Specifically, a polymer solution can be obtained by selectively dissolving a target polymer to be recovered, such as polyethylene, polypropylene, or a mixture thereof, by contacting the composite resin with a mixed solvent of a first solvent and a second solvent in the dissolution tank.

[0037] If necessary, the dissolution step in the dissolution tank may be performed under stirring to promote effective dispersion of the composite resin in the mixed solvent and thus dissolution efficiency.

[0038] In one embodiment of the present invention, the dissolution temperature may be a temperature maintained in the dissolution tank to selectively dissolve the polymer. In other words, the step S2 may be to supply the composite resin to the dissolution tank, heat the dissolution tank until the temperature reaches the dissolution temperature, and dissolve the polymer contained in the composite resin while maintaining the dissolution temperature.

[0039] Meanwhile, the above dissolution temperature may be a temperature corresponding to 'high temperature', which is a temperature at which the solubility of the second solvent in the polymer in the mixed solvent is improved.

[0040] At this time, pressurized conditions may be required to maintain the dissolution temperature in the dissolution tank, and the pressure of the dissolution tank may be atmospheric pressure to 3 bar. If the pressure in the dissolution tank is below atmospheric pressure, the temperature of the mixed solvent may not rise sufficiently, and the polymer may not dissolve. If it exceeds 3 bar, excessive energy is consumed to increase the pressure, and the dissolution efficiency of the polymer may decrease in comparison, which may lower the process efficiency.

[0041] Also, specifically, the dissolution temperature may be a temperature of 100 to 150°C. When the dissolution temperature is less than 100°C, the second solvent may not reach a temperature at which its solubility in the polymer is enhanced, and thus the polymer may not be sufficiently dissolved. In addition, when the dissolution temperature exceeds 150°C, the second solvent may exceed the point at which its solubility in the polymer is maximized, and thus the dissolution efficiency in the polymer may be reduced and excessive energy may be consumed to increase the temperature.

[0042] Additionally, the dissolution time in the dissolution tank may be performed for 120 to 300 minutes. The dissolution time may refer to the time from the time the composite resin is brought into contact with the mixed solvent in the dissolution tank to the time the polymer is dissolved in the mixed solvent. If the dissolution time is less than 120 minutes, the polymer may not be sufficiently dissolved, and if it exceeds 300 minutes, excessive energy may be consumed to maintain the dissolution temperature.

[0043] By controlling the above dissolution temperature and dissolution time, the polymer solution obtained from the dissolution tank can satisfy a predetermined range of polymer concentration. For example, the content of the polymer contained in the polymer solution 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, based on the weight of the polymer solution. When the content of the dissolved polymer in the polymer solution is less than 1 wt%, the amount of the final produced regenerated polymer may decrease. When the content of the dissolved polymer in the polymer solution exceeds 20 wt%, the viscosity may increase, making it difficult to separate the dissolved polymer from the insoluble matter.

[0044] Additionally, the polymer solution obtained from the dissolution tank may undergo a filtration process to remove insoluble substances that are not dissolved in the mixed solvent. The filtration may be performed by one or more of filtration by filter, filtration by centrifugation, and filtration by sedimentation. For example, when filtration by filter is performed, the polymer solution is passed through a filter, such as a mesh strainer, to separate insoluble substances from the polymer solution, and the filtrate containing the dissolved polymer may be used in a subsequent step.

[0045] In addition, a method for producing a regenerated polymer according to one embodiment of the present invention may include a step (S3) of supplying the polymer solution to the precipitation tank in which the mixed solvent is maintained at a precipitation temperature, thereby precipitating the polymer contained in the polymer solution to obtain a solution containing a spherical polymer precipitate.

[0046] In the present invention, the temperature of a high-temperature polymer solution is lowered to recrystallize a polymer dissolved in the polymer solution, and in order to minimize the energy consumption required to lower the temperature of the polymer solution, a separate precipitation tank, which is a different member from the dissolution tank maintained at a high temperature, is used to perform recrystallization and precipitation of a polymer dissolved in the polymer solution at a low temperature.

[0047] Specifically, a precipitation step can be performed in which a high-temperature polymer solution is added dropwise in the form of droplets while stirring is performed as needed in a state in which the mixed solvent in which the first solvent and the second solvent are mixed is previously supplied to the precipitation tank, thereby forming a precipitate as the polymer dissolved in the polymer solution recrystallizes due to the temperature difference. At this time, the greater the difference between the precipitation temperature of the precipitation tank and the dissolution temperature applied in the previous step, the greater the precipitation efficiency of the polymer can be increased.

[0048] To this end, the present invention uses the mixed solvent in which the first solvent and the second solvent are mixed in the dissolution tank and the precipitation tank as described above, and in the dissolution tank, the temperature of the dissolution tank is heated to the dissolution temperature, which is a high temperature, to dissolve the polymer in order to maximize the dissolution ability of the mixed solvent, and in the precipitation tank, the precipitation temperature is maintained in a low temperature range including room temperature (25°C) to perform precipitation, thereby maximizing the precipitation efficiency of the polymer.

[0049] In one embodiment of the present invention, the precipitation temperature is the temperature of the mixed solvent maintained in the precipitation tank to precipitate the polymer, and can be controlled to maintain a temperature 40 to 120°C lower than the dissolution temperature (i.e., the dissolution temperature -40 to -120°C), specifically, a temperature 60 to 100°C lower than the dissolution temperature (i.e., the dissolution temperature -60 to -100°C). That is, since the temperature of the polymer solution can have an upper limit value depending on 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.

[0050] Specifically, the precipitation temperature of the precipitation tank into which the polymer solution is dropped may be in the range of 5°C to 50°C, 5°C to 30°C, or 10°C to 25°C. When the temperature range is maintained, since the temperature of the solvent in the precipitation tank is significantly lower than the temperature of the polymer solution obtained from the dissolution tank, precipitation by recrystallization of the polymer may be facilitated. When the precipitation temperature is lower than 5°C, a separate cooling device must be provided to control the temperature, which may increase energy usage. In addition, when the precipitation temperature exceeds 50°C, the precipitation ability of the mixed solvent may decrease, so that the precipitation speed and precipitation rate of the polymer by recrystallization may decrease, and as a result, the efficiency of producing the final recycled polymer may decrease.

[0051] In addition, the first solvent among the mixed solvents supplied into the sedimentation tank can induce rapid crystallization of the polymer dissolved in the polymer solution to form a spherical sediment.

[0052] The precipitation temperature in the above-described sedimentation tank may be a temperature at which the precipitation ability of the first solvent having excellent precipitation ability is further enhanced. In addition, the precipitation temperature is maintained at a relatively low temperature compared to the dissolution temperature, and this may be a temperature at which the solubility for the polymer is significantly reduced depending on the characteristics of the second solvent. The process of forming the precipitate by utilizing these characteristics may be such that, in a state where the dissolution ability of the polymer solution obtained from the dissolution tank for the second solvent is maximized depending on the dissolution temperature, the polymer solution is dropped into the precipitation tank at which the precipitation abilities of the first and second solvents are maximized, thereby rapidly lowering the temperature, thereby inducing the polymer to rapidly recrystallize and precipitate. In this process, the polymer dissolved in the polymer solution can rapidly form dense crystals, and as a result, the polymer precipitate can be formed in the above-described spherical shape.

[0053] The above spherical precipitate may have an average diameter of 500 μm to 5,000 μm. If the average diameter of the spherical precipitate is less than 500 μm, the subsequent press filtration process may require the use of a finer filter than a typical filter or other high-energy filtration methods, which may increase process costs. In addition, if the average diameter of the spherical precipitate exceeds 5,000 μm, the solvent may not be efficiently removed during the press filtration process due to the precipitate being too large.

[0054] If the dissolution and precipitation of the polymer do not satisfy the above conditions, the polymer may not be precipitated in the spherical shape, and the polymer may be precipitated in the form of, for example, powder. If the polymer is precipitated in the form of powder, the crystals of the polymer precipitate may not be formed densely, so that a large amount of the mixed solvent may be included in the polymer precipitate, and pressure filtration may not be applied in the subsequent filtration step. The pressure filtration is a method that can filter a large amount of precipitate in a simple manner and at a low cost compared to other filtration methods, and thus the process cost can be reduced by applying the pressure filtration. The effect of this process reduction can be even greater when applied to a large-scale process.

[0055] Solutions containing such spherical polymer precipitates can be subjected to physical compression filtration, such as squeezing or pressing, in the subsequent filtration step, thereby reducing energy consumption compared to conventional vacuum filtration. Specifically, the compression filtration can be performed by placing the polymer precipitate in a filter and squeezing it to discharge the solvent contained in the polymer precipitate. On the other hand, vacuum filtration is performed by reducing the pressure of a container containing the polymer precipitate, so a separate vacuum decompression pump is required, and a filter capable of discharging the solvent during decompression is essential, which entails problems such as filter clogging or periodic replacement. The compression filtration does not require any separate auxiliary equipment other than the filter, and does not cause the problem of replacing parts such as filters, so it is convenient to operate and can reduce process costs.

[0056] In one embodiment of the present invention, the amount of the mixed solvent in the sedimentation tank may be 0.5 to 10 times, specifically 2 to 8 times or 2 to 6 times, the volume of the polymer solution to be precipitated. If the amount of the mixed solvent in the sedimentation tank is less than 0.5 times that of the polymer solution, it may be difficult to sufficiently exhibit the precipitation ability of the solvent for the dissolved polymer, and if it exceeds 10 times that of the polymer solution, the economic feasibility may be reduced due to excessive use of the solvent.

[0057] Since the polymer precipitate formed in the above sedimentation tank exists mixed with the solvent contained in the introduced polymer solution and the solvent supplied in advance into the sedimentation tank, a process of separating the polymer precipitate from the used solvent is required.

[0058] Accordingly, the solution in the sedimentation tank is filtered to separate the solvent in the solution, thereby obtaining a polymer precipitate of solid content (S4).

[0059] As described above, since the solution in the sedimentation tank contains spherical polymer precipitates, physical compression filtration can be performed in the filtration step.

[0060] For example, the above compression filtration can be performed by supplying a solution containing a spherical polymer precipitate to a squeezing or pressing filter and applying a pressure of 0.1 to 3 MPa or 0.5 to 1.5 MPa, thereby obtaining a solvent-separated polymer precipitate.

[0061] This compression filtration method utilizes simple physical force to separate spherical polymer precipitates from liquid solvents, thereby reducing energy consumption compared to the conventional vacuum filtration method applied to powdery polymer precipitates. Furthermore, compared to vacuum filtration, the compression filtration method can reduce the amount of residual solvent contained in the filtered polymer precipitate.

[0062] The polymer precipitate obtained through the above compression filtration may include polyethylene, polypropylene, or a mixture thereof. In addition, the polymer precipitate may include a solid content of 19 to 80 wt% or 19 to 37 wt% based on the weight of the polymer precipitate. That is, the first residual solvent amount, which is the amount of residual solvent contained in the polymer precipitate, may be 81 to 20 wt% or 81 to 63 wt% based on the weight of the polymer precipitate. When the polymer precipitate is dried to remove the solvent contained in the polymer precipitate, the regenerated polymer can be obtained. However, as the amount of the first residual solvent increases, a lot of energy is consumed to remove it, which may increase the process cost and decrease the process efficiency.

[0063] Additionally, the filtered polymer precipitate can be commercialized as a regenerated polymer through a drying process.

[0064] For example, drying of the polymer precipitate can be performed by heating with hot air or heat conduction, and can be performed using a fluidized bed drying device such as a kneader reactor. A separate solvent recovery device can be connected to the fluidized bed drying device to recover residual solvent removed from the polymer precipitate, and the polymer precipitate dried in the device can be used as a regenerated polymer.

[0065] The solvent separated through the above filtration process and the residual solvent recovered by drying the polymer precipitate can be recovered and reused in the dissolution tank and sedimentation tank. Since the recovered solvent has the same composition as the initially used mixed solvent, it can be reused immediately without a separate separation process such as fractional distillation. This simplifies the process and reduces costs, ensuring economic feasibility.

[0066] Additionally, according to one embodiment of the present invention, the present invention may include a regenerated polymer manufactured by the method for manufacturing the regenerated polymer.

[0067] The above-mentioned regenerated polymer may be a regenerated polymer obtained by dissolving and precipitating the composite resin in a mixed solvent of the first solvent and the second solvent according to the method for producing the regenerated polymer, and then drying the same. The regenerated polymer may be one in which the mixed solvent is completely removed through a drying process of the polymer precipitate obtained in the precipitation process. However, depending on the drying conditions such as drying temperature, drying time, and drying method, the mixed solvent may remain in the regenerated polymer in a trace amount. Such residual amount may be at a level that does not affect the use of the regenerated polymer as a product, and depending on the content, it may be difficult to detect the mixed solvent using a conventional detection method. However, if the mixed solvent is detected, it can be known that the mixed solvent was used in the process of producing the regenerated polymer.

[0068] The amount of the mixed solvent remaining in the regenerated polymer may be expressed as a first solvent and a second solvent, respectively. The amount of the first solvent remaining in the regenerated polymer may be expressed as a 2-1 residual solvent amount, and the amount of the second solvent remaining in the regenerated polymer may be expressed as a 2-2 residual solvent amount. Based on the weight of the regenerated polymer, the 2-1 residual solvent amount may not be detected (0 ppm), or, if detected, may be 10 ppm to 3000 ppm or 10 ppm to 100 ppm. In addition, based on the weight of the regenerated polymer, the 2-2 residual solvent amount may not be detected (0 ppm), or, if detected, may be 10 ppm to 3000 ppm or 10 ppm to 1500 ppm. The 2-1 and 2-2 residual solvent amounts of 0 ppm may mean that the first solvent or the second solvent is not present. The closer the amount of residual solvent in the above-mentioned 2-1 and 2-2 is to 0 ppm, the better. If it exceeds 3000 ppm, the physical properties and processability of the recovered regenerated polymer may deteriorate.

[0069] The mixed solvent remaining in the above regenerated polymer is the solvent used in the method for producing the above regenerated polymer. 3-8It may include a first solvent of alkyl acetate and a second solvent of non-aromatic cyclic hydrocarbon. Specifically, the first solvent among the mixed solvents remaining in the regenerated polymer may be at least one selected from n-butyl acetate, t-butyl acetate, isopropyl acetate, pentyl acetate, and n-hexyl acetate. In addition, specifically, the second solvent among the mixed solvents remaining in the regenerated polymer may be at least one selected from methylcyclohexane and cycloalkyl alkyl ether. More specifically, the cycloalkyl alkyl ether among the second solvents may include at least one selected from cyclopentyl methyl ether, cyclopentyl ethyl ether, cyclopentyl propyl ether, cyclopentyl isopropyl ether, cyclopentyl t-butyl ether, cyclohexyl methyl ether, cyclohexyl ethyl ether, cyclohexyl propyl ether, cyclohexyl isopropyl ether, and cyclohexyl t-butyl ether.

[0070] Hereinafter, the present invention will be described in more detail by way of examples. However, the following examples are intended to illustrate the present invention, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope and technical spirit of the present invention, and the scope of the present invention is not limited to these examples alone.

[0071] Example 1:

[0072] A mixed solvent was prepared in which n-butyl acetate (n-BuAc) as the first solvent and methyl cyclohexane (MCH) as the second solvent were mixed in a volume ratio of 2:1. 75 ml of the mixed solvent was supplied to the dissolution tank, and 225 ml of the mixed solvent was supplied to the precipitation tank.

[0073] A composite resin sample (6.45 g) containing 77.89 wt% of polyethylene was supplied to the above-described dissolution tank, and the above-described dissolution tank was heated to 125°C, at which the mixed solvent boils, to obtain a polymer solution (solubility 6.7%) in which the polyethylene contained in the above-described composite resin was dissolved. The dissolution was performed for 180 minutes under stirring.

[0074] The polymer solution was filtered through a mesh strainer to separate insoluble matter, and then the polymer solution was added dropwise to a sedimentation tank (225 ml of mixed solvent) at room temperature (25°C) at a rate of 5 ml / min while stirring. The amount of polymer solution added was adjusted so that the amount of mixed solvent in the sedimentation tank was four times the volume of the polymer solution added. In the sedimentation tank, the high-temperature polymer solution (125°C) was recrystallized due to the temperature difference, forming a spherical sediment.

[0075] The solution in the above sedimentation tank was fed to a press filter and subjected to compression filtration at a pressure of 1 MPa to obtain a polyethylene precipitate, and the mixed solvent used for dissolution and precipitation was separated. The polyethylene precipitate was then fed to a kneader reactor and dried at 120°C to separate the residual solvent, and the dried polyethylene precipitate was used as a regenerated polymer. Meanwhile, the solvent separated from the compression filtration and kneader reactor was recovered and reused.

[0076] Reference examples 1-1 and 1-2:

[0077] The same process as Example 1 was performed, except that the temperature of the sedimentation tank or the filtration method was changed as shown in Table 1 below.

[0078] Example 2 and Reference Example 2:

[0079] The same process as Example 1 was performed, except that the mixing ratio of the first solvent and the second solvent, the conditions of the dissolution tank and the sedimentation tank, or the filtration method were changed to those shown in Table 1 below.

[0080] Examples 3 to 5 and Reference Examples 3 to 4:

[0081] The same process as Example 1 was performed, 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 dissolution tank and the precipitation tank, or the filtration method were changed to those shown in Table 1 below.

[0082] Comparative Examples 1 to 8:

[0083] The same process as Example 1 was performed, except that the solvent supplied to the dissolution tank and the sedimentation tank was replaced with a single solvent of methyl cyclohexane (MCH) or cyclopentyl methyl ether (CPME) (Comparative Examples 1 to 5) or a mixed solvent of butanol and methylcyclohexane or cyclopentyl methyl ether (Comparative Examples 6 to 8), and the conditions of the dissolution tank and the sedimentation tank and the filtration method were changed to those shown in Table 1 below.

[0084] Solvent typeDissolution tankSedimentation tankSediment shapeFiltration methodRemarksSolvent (ml)Temperature (℃)Solubility 1)(Wt%) Solvent (ml) Temperature (℃) Comparative Example 1 MCH (single) 50 100 102 00 25 Powder Filter paper Comparative Example 2 MCH (single) 50 110 6.7 15 0 25 Powder Decompression Comparative Example 3 MCH (single) 50 105 6.7 15 0 25 Powder Decompression Comparative Example 4 MCH (single) 50 100 6.7 15 0 25 Powder Decompression Comparative Example 5 CPME (single) 50 110 6.7 15 0 25 Powder Decompression Comparative Example 6 Butanol:MCH (3:1 v / v) 50 125-----Insoluble Comparative Example 7 Butanol:CPME (3:1 v / v) 50 125-----Insoluble Comparative Example 8 n-BuAc:Xylene (3:1 v / v)501256.715025 Powder Decompression Example 1 n-BuAc:MCH (2:1 v / v)501256.715025 Spherical Press Example 2 n-BuAc:MCH (3:1 v / v)501256.715025 Spherical Press Example 3 n-BuAc:CPME (2:1 v / v)501256.715025 Spherical Press Example 4 n-BuAc:CPME (3:1 v / v)501256.715025 Spherical Press Example 5 n-BuAc:CPME (4:1 v / v)501256.715025 Spherical Press 1) Solubility refers to the content of dissolved polymer based on the weight of the polymer solution.

[0085] In the above Table 1, in the examples, a mixed solvent of a first solvent (n-BuAc) and a second solvent (MCH or CPME) was used in each of the dissolution tank and the sedimentation tank, and the polymer was sufficiently dissolved by heating to the boiling point of the mixed solvent in the dissolution tank. Then, in the sedimentation tank maintained at a lower temperature than the dissolution tank, rapid crystallization of the dissolved polymer was induced due to the influence of the first solvent, thereby forming a spherical precipitate. The solution containing such a spherical polymer precipitate was filtered by pressing using a press filter. On the other hand, in Comparative Examples 1 to 5 using a single solvent, the same solubility as in the examples was observed in the dissolution tank, but rapid crystallization as in the examples did not occur in the sedimentation tank, so that the polymer precipitate was formed in a powder shape rather than a spherical shape. The polymer precipitate was filtered under reduced pressure to obtain a regenerated polymer. In Comparative Examples 1 to 5, when the powder-shaped polymer precipitate was filtered using a press filter, the powder-shaped particles were too small to pass through the filter of the press filter together with the solvent, so that proper filtration was not performed.

[0086] In Comparative Examples 6 to 8, experiments were conducted using a mixed solvent having a different composition from the mixed solvent of the present invention. In Comparative Examples 6 and 7, cycloalkyl alkyl ether was used as the second solvent, but C was used as the first solvent. 3-8 Butanol, not alkyl acetate, was used, and the polymer was not sufficiently dissolved in the dissolution tank, making subsequent experiments impossible. In Comparative Example 8, the first solvent was C 3-8 Although alkyl acetate was used, xylene, an aromatic cyclic hydrocarbon, was used as a second solvent, and although the polymer was sufficiently dissolved in the dissolution tank, the dissolving capacity of xylene was excessive, so precipitation did not occur smoothly. In addition, in Comparative Example 8, the precipitate was precipitated in a powder form, and press filtration could not be performed as in Comparative Examples 1 to 5.

[0087] This shows that the method of compression filtration, which is a method that can save process costs by forming the polymer into a spherical shape through dissolution and precipitation of the polymer by the first solvent and the second solvent in the present invention, can be used, and the efficiency of the process for manufacturing a regenerated polymer can be increased.

[0088] Table 2 below shows the results showing that although the shape of the polymer precipitate in the examples and reference examples was formed in a spherical shape, the yield of the regenerated polymer may vary when the filtration method is changed.

[0089] Solvent type, sediment shape, filtration method, TSC 2) (Wt%)Example 1n-BuAc:MCH (2:1 v / v) Old press 19.2Reference Example 1-1n-BuAc:MCH (2:1 v / v) Old decompression 11.8Reference Example 1-2n-BuAc:MCH (2:1 v / v) Old decompression 9.8Example 2n-BuAc:MCH (3:1 v / v) Old press 28.8Reference Example 2n-BuAc:MCH (3:1 v / v) Old decompression 13.2Example 3n-BuAc:CPME (2:1 v / v) Old press 32.4Reference Example 3n-BuAc:CPME (2:1 v / v) Old decompression 9.0Example 4n-BuAc:CPME (3:1 v / v) Old press 28.0Reference Example 4n-BuAc:CPME (3:1 v / v) Spherical pressure relief 11.6 Example 5 n-BuAc:CPME (4:1 v / v) Spherical press 36.52) TSC (total solid content) represents the solid content of the polymer precipitate after filtration.

[0090] Referring to Table 2, the shape of the polymer precipitate formed in the examples and reference examples is the same as a spherical shape, but it can be confirmed that the yield of the regenerated polymer increases when filtering using press filtration in the examples. This shows that when performing reduced pressure filtration on the spherical polymer precipitate in the examples, the mixed solvent cannot be sufficiently removed from the spherical shape having relatively large particles. This characteristic of the spherical shape rather shows that it is more preferable to perform compression filtration such as press filtration, which consumes relatively little energy, in the method for producing the regenerated polymer according to the present invention, and this can also improve the yield of the regenerated polymer, showing that it is more efficient and economical than the conventional process. Next, the polymer precipitates obtained in Examples 1 to 5 were dried in a vacuum oven at 100°C for 12 hours to obtain the regenerated polymer.

[0091] The amount of solvent contained in the above regenerated polymer was measured using LC (Liquid Chromatography) equipment, and the measured amount of the second residual solvent is shown in Table 3.

[0092] Classification 2 Residual solvent amount (ppm) First solvent Second solvent Example 1 BuOAc, 100 MCH, 300 Example 2 BuOAc, 100 MCH, 200 Example 3 BuOAc, 80 CPME, 1300 Example 4 BuOAc, 70 CPME, 1500 Example 5 BuOAc, 70 CPME, 160

[0093] In Table 2, the residual amount (ppm) in Examples 1 to 4 is expressed as ppm (parts per million) based on the weight of the regenerated polymer, which represents the amount of the second residual solvent in the regenerated polymer obtained in each Example. Referring to Table 3, it can be confirmed that the first solvent in the regenerated polymer is approximately 70 ppm to 100 ppm, and the second solvent is approximately 160 ppm to 1300 ppm, indicating that only very small amounts of both solvents remain. These values ​​do not affect the physical properties or processability of the regenerated polymer at all. However, since the solvent used in the production of the regenerated polymer is detected, it can be used as an indicator to know which solvent was used in the production of the regenerated polymer.

Claims

1. (S1) C in the dissolution tank and sedimentation tank 3-8 A step of supplying a mixed solvent comprising a first solvent of alkyl acetate and a second solvent of non-aromatic cyclic hydrocarbon; (S2) A step of supplying a composite resin to the dissolution tank, heating the composite resin to a dissolution temperature, and dissolving the polymer contained in the composite resin while maintaining the dissolution tank at the dissolution temperature to obtain a polymer solution; (S3) a step of supplying the polymer solution to the precipitation tank where the mixed solvent is maintained at a precipitation temperature, and precipitating the polymer contained in the polymer solution to obtain a solution containing a spherical polymer precipitate; and (S4) A method for producing a regenerated polymer, comprising the step of obtaining a polymer precipitate by squeezing and filtering a solution containing the above spherical polymer precipitate.

2. In paragraph 1, The first solvent comprises at least one selected from n-butyl acetate, t-butyl acetate, isopropyl acetate, pentyl acetate and n-hexyl acetate, A method for producing a regenerated polymer, wherein the second solvent comprises at least one selected from methylcyclohexane and cycloalkyl alkyl ether.

3. In paragraph 3, A method for producing a regenerated polymer, wherein the cycloalkyl alkyl ether comprises at least one selected from cyclopentyl methyl ether, cyclopentyl ethyl ether, cyclopentyl propyl ether, cyclopentyl isopropyl ether, cyclopentyl t-butyl ether, cyclohexyl methyl ether, cyclohexyl ethyl ether, cyclohexyl propyl ether, cyclohexyl isopropyl ether, and cyclohexyl t-butyl ether.

4. In paragraph 1, A method for producing a regenerated polymer, wherein the first solvent and the second solvent are mixed in a volume ratio of 2:1 to 5:

1.

5. In paragraph 1, A method for producing a regenerated polymer having a melting temperature of 100 to 140°C.

6. In paragraph 1, A method for producing a regenerated polymer, wherein the polymer solution contains 1 to 20 wt% of a polymer based on the weight thereof.

7. In paragraph 1, A method for producing a regenerated polymer, wherein the precipitation temperature is maintained at a temperature 40 to 120°C lower than the dissolution temperature.

8. In paragraph 1, A method for producing a regenerated polymer, wherein the above precipitation temperature is 5 to 50°C.

9. In paragraph 1, A method for producing a regenerated polymer, wherein the volume of the mixed solvent supplied to the above sedimentation tank is 0.5 to 10 times the volume of the above polymer solution.

10. In paragraph 1, The above compression filtration is a method for producing a regenerated polymer, which is performed by squeezing or pressing.

11. In paragraph 1, A method for producing a recycled polymer, wherein the polymer precipitate comprises a polymer selected from polyethylene, polypropylene and mixtures thereof.

12. In paragraph 1, A method for producing a regenerated polymer, wherein the polymer precipitate has an average diameter of 500 μm to 5000 μm. 13.C 3-8 alkyl acetate, and A regenerated polymer comprising at least one residual component selected from methylcyclohexane and cycloalkyl alkyl ether.

14. In paragraph 13, C above 3-8 The alkyl acetate is at least one selected from n-butyl acetate, t-butyl acetate, isopropyl acetate, pentyl acetate and n-hexyl acetate, The above cycloalkyl alkyl ether is at least one selected from cyclopentyl methyl ether, cyclopentyl ethyl ether, cyclopentyl propyl ether, cyclopentyl isopropyl ether, cyclopentyl t-butyl ether, cyclohexyl methyl ether, cyclohexyl ethyl ether, cyclohexyl propyl ether, cyclohexyl isopropyl ether and cyclohexyl t-butyl ether.

15. In paragraph 13, C above 3-8 Containing 10 ppm to 3000 ppm of alkyl acetate, A regenerated polymer comprising 10 ppm to 3000 ppm of at least one selected from the group consisting of methylcyclohexane and cycloalkyl alkyl ether.