Method for preparing recycled polymers

Abstract

The present invention provides a method for preparing recycled polymers, the method comprising: (S1) a step for supplying cycloalkyl alkyl ether as a solvent to both a dissolution tank and a precipitation tank; (S2) a step for supplying a composite resin to the dissolution tank and then heating 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; (S3) a step for supplying the polymer solution to the precipitation tank, in which the solvent is maintained at the precipitation temperature, and precipitating the polymer included in the polymer solution to obtain a solution including a polymer precipitate; and (S4) a step for filtering the solution containing the polymer precipitate to obtain the 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. 10-2024-0030453, filed March 4, 2024, and Korean Patent Application No. 10-2025-0007711, filed January 20, 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 minimize the residual amount of solvent used 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] The problem to be solved in the present invention is to provide a method for producing a regenerated polymer that can minimize the energy consumed for solvent removal by using the same solvent during dissolution and recrystallization when recovering the polymer from waste resin and reducing the amount of solvent residue contained in the polymer precipitated by the recrystallization, in order to solve the problem mentioned in the background technology of the above invention.

[0011] According to one embodiment of the present invention for solving the above problems, the present invention provides a method for producing a regenerated polymer, comprising the steps of: (S1) supplying cycloalkyl alkyl ether as a solvent to a dissolution tank and a precipitation tank, respectively; (S2) supplying a composite resin to the dissolution tank and then heating it to a dissolution temperature, and dissolving a polymer contained in the composite resin while maintaining the dissolution tank at the dissolution temperature to obtain a polymer solution; (S3) supplying the polymer solution to the precipitation tank in which the solvent is maintained at a precipitation temperature to precipitate a polymer contained in the polymer solution to obtain a solution containing a polymer precipitate; and (S4) filtering the solution containing the polymer precipitate to obtain a polymer precipitate.

[0012] According to the present invention, by using cycloalkyl alkyl ether as the same solvent supplied to a dissolution tank and a sedimentation tank for recovering a polymer contained in a composite resin derived from waste resin, the polymer can be sufficiently dissolved in the dissolution tank at a high temperature equal to or higher than the boiling point of the solvent, and then the precipitation rate of the dissolved polymer can be improved in a sedimentation tank maintained at a low temperature. That is, the cycloalkyl alkyl ether has sufficient solubility in the polymer at a temperature near the boiling point, while its affinity for the polymer decreases at low temperatures, thereby providing an excellent polymer precipitation effect. In addition, the polymer precipitate obtained from the sedimentation tank has a low solvent residual amount, so that the energy consumed for solvent removal can be minimized.

[0013] Additionally, the present invention can reduce the energy consumed to lower the high-temperature polymer solution by performing the dissolution step and the recrystallization step of the polymer separately in a dissolution tank and a precipitation tank, respectively.

[0014] 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.

[0015] 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.

[0016] Hereinafter, the present invention will be described in more detail to help understand the present invention.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] For example, the composite resin may contain a polymer including polyethylene, polypropylene or a mixture thereof in an amount of 40 to 99 wt% or 40 to 80 wt% based on its weight.

[0021] The present invention is for selectively recovering a polymer contained in a composite resin as described above and manufacturing it as a regenerated polymer, and may first include a step (S1) of supplying cycloalkyl alkyl ether as a solvent to a dissolution tank and a precipitation tank, respectively.

[0022] The above cycloalkyl alkyl ether has characteristics such as low heat of vaporization, hydrophobicity, and chemical stability, and thus can be applied as a solvent in a wide range from low to high temperatures. In addition, it can have the function of selectively dissolving a polymer that needs to be dissolved for the production of a regenerated polymer from a composite resin derived from waste resin, and can have the function of further maximizing the precipitation ability in recrystallizing the dissolved polymer.

[0023] These cycloalkyl alkyl ethers can selectively dissolve target polymers at high temperatures and then increase the supersaturation over a wide temperature range when recrystallizing the dissolved polymer by lowering the temperature, thereby enhancing the rate at which polymer precipitates are formed.

[0024] Examples of cycloalkyl alkyl ethers usable in the present invention 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 ether ether, and cyclohexyl ether ether can be advantageously used because they exhibit particularly low affinity for polymers at low temperatures compared to their solubility at high temperatures.

[0025] In the present invention, by using a single solvent of cycloalkyl alkyl ether having the above-described characteristics for dissolving and recrystallizing a polymer contained in the composite resin, 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 the polymer and an antisolvent for precipitating the polymer can be overcome.

[0026] A method for producing a regenerated polymer according to one embodiment of the present invention may include a step (S2) of supplying the composite resin to a dissolution tank in which the cycloalkyl ether has been supplied in advance, 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.

[0027] 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 cycloalkyl alkyl ether solvent in the dissolution tank.

[0028] If necessary, the dissolution step in the dissolution tank may be performed under stirring to promote effective dispersion of the composite resin in the solvent and thus dissolution efficiency.

[0029] In one embodiment of the present invention, the dissolution temperature may be a temperature higher than the boiling point of the solvent, which is maintained to selectively dissolve the polymer in the dissolution tank. Here, the boiling point may refer to the boiling point at atmospheric pressure (1 atm).

[0030] In the above step S2, since the dissolution temperature is maintained at a temperature higher than the boiling point of the solvent, the pressure of the dissolution tank can be maintained higher than the atmospheric pressure in order to prevent vaporization of the solvent in the dissolution tank. At this time, in the process of raising the temperature of the dissolution tank to the dissolution temperature, the pressure condition of the dissolution tank may be to maintain atmospheric pressure until the boiling point of the solvent is reached, and pressurize to a pressure higher than the atmospheric pressure when the temperature higher than the boiling point of the solvent is reached. Since the boiling point of the solvent also increases when the pressure of the dissolution tank is increased, the solvent can be dissolved without vaporization even if the temperature is maintained higher than the boiling point of the solvent.

[0031] The pressure at the dissolution temperature in the dissolution tank may be atmospheric pressure to 3 bar. If the pressure in the dissolution tank is below atmospheric pressure, the solvent may vaporize and the polymer may not dissolve. If the pressure exceeds 3 bar, the dissolution effect due to pressurization may be minimal, resulting in reduced efficiency.

[0032] Specifically, the dissolution temperature may be between 90°C and 140°C. If the dissolution temperature is lower than 90°C, the temperature may be too low to sufficiently dissolve the polymer. In addition, if the dissolution temperature exceeds 140°C, excessive energy may be consumed to raise the temperature, and the dissolution efficiency of the polymer may decrease compared to the amount of energy consumed.

[0033] Since the above solvent has a relatively high boiling point, it can function as a solvent over a wide temperature range. That is, in the S2 step, the dissolution temperature is maintained high to maximize the solubility of the polymer, thereby dissolving the polymer, and by lowering the temperature of the polymer solution thus obtained, the polymer can be easily precipitated.

[0034] Meanwhile, if the dissolution temperature is lower than the boiling point of the solvent, the polymer may not be sufficiently dissolved, which may result in a decrease in the content of the polymer precipitated in the subsequent recrystallization step. If the dissolution temperature exceeds 10°C above the boiling point of the solvent, heat loss occurs, which is disadvantageous in terms of energy.

[0035] In addition, 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 solvent in the dissolution tank to the time the polymer is dissolved in the solvent. If the dissolution time is less than 120 minutes, the polymer may not be completely dissolved, and if it exceeds 300 minutes, the energy consumption may increase and the efficiency of obtaining the polymer may be low in comparison.

[0036] By controlling the dissolution temperature and dissolution time as described above, 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 solution. If 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. If 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.

[0037] Additionally, the polymer solution obtained from the dissolution tank may undergo a filtration process to remove insoluble substances that have not dissolved in the solvent. The filtration may be performed by one or more of filtration by filter, filtration by centrifugation, and filtration by sedimentation. For example, the polymer solution may be passed through a filter, such as a mesh strainer, to separate insoluble substances, and the filtrate containing the dissolved polymer may be used in a subsequent step.

[0038] 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 temperature of the solvent is maintained at a precipitation temperature, thereby precipitating the polymer contained in the polymer solution to obtain a solution containing a polymer precipitate.

[0039] In the present invention, in order to minimize the energy consumption required to lower the temperature for recrystallization of the high-temperature polymer solution, a separate precipitation tank, which is a different member from the dissolution tank that performs polymer dissolution, is used to perform recrystallization and precipitation of the polymer dissolved in the polymer solution.

[0040] Specifically, a precipitation step can be performed in which a cycloalkyl alkyl ether solvent is supplied in advance to the precipitation tank, the high-temperature polymer solution is added dropwise in the form of droplets while stirring is performed as needed, and the polymer dissolved in the polymer solution is recrystallized due to the temperature difference to form a precipitate. At this time, the greater the temperature difference between the precipitation tank temperature and the dissolution tank applied in the previous step, the greater the precipitation efficiency of the polymer can be increased.

[0041] To this end, in the present invention, as described above, cycloalkyl alkyl ether, which is a solvent applicable over a wide temperature range from high to low temperatures, is used in both the dissolution tank and the precipitation tank, while the dissolution tank is heated to a high temperature equal to or higher than the boiling point of the solvent, and the precipitation tank is maintained at a low temperature range including room temperature, thereby maximizing the precipitation efficiency of the polymer.

[0042] In one embodiment of the present invention, the precipitation temperature can be controlled to maintain a temperature 70 to 130°C lower than the dissolution temperature (i.e., dissolution temperature - 70 to 130°C), specifically, a temperature of dissolution temperature - 80 to 120°C, and more specifically, a temperature of dissolution temperature - 95 to 115°C. That is, since the dissolution tank is heated and the dissolution of the polymer is performed at a temperature equal to or higher than the boiling point of the solvent, the temperature of the polymer solution can be set to an upper limit, so that the precipitation efficiency due to the temperature difference can be improved by controlling the temperature of the precipitation tank into which the polymer solution is supplied based on the dissolution temperature. For example, the precipitation temperature, which is the temperature of the precipitation tank into which the polymer solution is dropped, can be in the range of -40°C to 70°C, -20°C to 50°C, or 0°C to 30°C. When the above precipitation temperature range is maintained, precipitation by recrystallization of the polymer can be facilitated because the temperature of the solvent in the precipitation tank is significantly lower than the temperature of the polymer solution obtained from the dissolution tank.

[0043] The cycloalkyl alkyl ether, which is a solvent used for dissolving and precipitating the polymer, may be a substance having low affinity for the polymer. However, when the temperature of the solvent is increased to the same level as the dissolution temperature, the affinity for the polymer increases, and the substance may be capable of dissolving the polymer. Therefore, in the present invention, by utilizing this characteristic, the temperature in the dissolution tank is increased to the same level as the dissolution temperature, the polymer is dissolved in the solvent, and the polymer solution is obtained, and the polymer solution is dropped into the precipitation tank at a low temperature to rapidly lower the temperature, thereby rapidly reducing the solubility of the solvent in the polymer, thereby inducing the polymer to recrystallize and precipitate at a rapid rate. Due to the rapid drop in temperature and the decrease in affinity for the solvent, the polymer dissolved in the polymer solution can rapidly form dense crystals. This may shorten the precipitation time of the polymer precipitate, while also obtaining a precipitate with a very low residual amount of the solvent contained in the polymer precipitate.

[0044] If the above precipitation temperature is below 0°C, a separate cooling device must be provided to control the temperature, which may increase energy consumption. If it exceeds 50°C, the precipitation ability of the cycloalkyl alkyl ether may decrease, which may slow down the precipitation speed of the polymer by recrystallization, and as a result, the yield of the final regenerated polymer may decrease.

[0045] Meanwhile, the volume of the solvent supplied to the sedimentation tank may be 0.5 to 10 times, specifically 2 to 8 times or 2 to 6 times, of the volume of the polymer solution. If the volume of the solvent in the sedimentation tank is less than 0.5 times that of the polymer solution, it may be difficult to sufficiently lower the temperature of the polymer solution, and thus the precipitation ability of the solvent for the dissolved polymer may not be sufficiently exerted. If it exceeds 10 times that of the polymer solution, the economic feasibility may be reduced due to excessive use of solvent.

[0046] 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.

[0047] In addition, a method for producing a regenerated polymer according to one embodiment of the present invention may include a step (S4) of obtaining a polymer precipitate by filtering a solution containing the polymer precipitate to separate a solvent in the solution.

[0048] The above filtration may be performed by one or more of filtration by reduced pressure, filtration by press, filtration by filter, filtration by centrifugation, and filtration by sedimentation. Among these, reduced pressure filtration and press filtration may be advantageously applied in terms of minimizing the amount of solvent residue contained in the polymer precipitate.

[0049] The polymer precipitate obtained through the above filtration may include polyethylene, polypropylene, or a mixture thereof. In addition, the polymer precipitate may include a solid content (polymer) of 40 to 80 wt% or 43 to 68 wt% based on the weight thereof. That is, the first residual solvent amount, which is the amount of residual solvent contained in the polymer precipitate, may be obtained by subtracting the content (weight) of the polymer (solid content) from the polymer precipitate, and the first residual solvent amount may be 20 to 60 wt% or 32 to 57 wt% based on the weight of the polymer precipitate. The polymer precipitate may be dried to obtain a regenerated polymer, but as the first residual solvent amount increases, excessive energy may be consumed in drying the polymer precipitate.

[0050] Additionally, the filtered polymer precipitate can be used as a regenerated polymer through a drying process.

[0051] 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.

[0052] The solvent separated through the above filtration and the residual solvent recovered by drying the polymer precipitate can be recovered and reused in the dissolution tank and sedimentation tank. In this case, the solvent recovered after use in the present invention is a single solvent, not a mixed solvent, and therefore can be reused immediately without a separate separation process such as fractional distillation. This simplifies the process and reduces costs, ensuring economic feasibility.

[0053] Additionally, according to one embodiment of the present invention, it may include a regenerated polymer manufactured by the method for manufacturing the regenerated polymer.

[0054] The above regenerated polymer may be a regenerated polymer obtained by dissolving and precipitating the above composite resin in a cycloalkyl alkyl ether, which is a solvent, according to a method for producing the above regenerated polymer, and then drying the same.

[0055] The above-mentioned regenerated polymer may be one in which the solvent has been completely removed through a drying process of the polymer precipitate obtained during the above-mentioned precipitation process. However, a trace amount of the solvent may remain during the drying process depending on the drying conditions, such as drying temperature, drying time, and type of dryer. Such residual amount may not affect the use of the regenerated polymer as a commercial product, and depending on the content, the solvent may be difficult to detect using conventional detection methods. However, if the solvent is detected, it can be known that the solvent was used during the manufacturing process of the regenerated polymer.

[0056] The second residual solvent amount, which is the amount of solvent remaining in the regenerated polymer, may not be detected (0 ppm) based on the weight of the regenerated polymer, or, if detected, may be 10 ppm to 5000 ppm, 10 ppm to 2000 ppm, or 800 ppm to 180 ppm. The second residual solvent amount of 0 ppm may mean that the solvent does not exist. The closer the second residual solvent amount is to 0 ppm, the better, and when the second residual solvent amount exceeds 5000 ppm, the physical properties and processability of the recovered regenerated polymer may deteriorate.

[0057] The solvent remaining in the above-mentioned regenerated polymer may be a cycloalkyl alkyl ether, which is a solvent used in the method for producing the above-mentioned regenerated polymer. Specifically, the solvent remaining in the above-mentioned regenerated polymer may include one or more 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.

[0058] 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.

[0059] Example 1:

[0060] Cyclopentyl methyl ether (CPME) (bp 106℃) was prepared as a solvent, 50 ml of CPME was supplied to the dissolution tank, and 200 ml of CPME was supplied to the precipitation tank.

[0061] A composite resin sample (6.45 g) containing 77.89 wt% polyethylene was supplied to the above-described dissolution tank, and the above-described dissolution tank was heated to dissolve the polyethylene contained in the composite resin at 110°C, which is higher than the boiling point of CPME, to obtain a polymer solution (solubility 6.7%). The dissolution was performed for 180 minutes under stirring.

[0062] 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 (CPME 200 ml) 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 CPME solvent in the sedimentation tank was four times the volume of the polymer solution added. In the sedimentation tank, a precipitate was formed as the high-temperature polymer solution (110°C) was recrystallized due to the temperature difference.

[0063] The solution in the above sedimentation tank was filtered under reduced pressure to obtain a polyethylene precipitate, and the CPME used for dissolution and precipitation was separated. The polyethylene precipitate was placed in a kneader reactor and dried at 120°C to separate the residual solvent. The dried polyethylene precipitate was used as a regenerated polymer. Meanwhile, the solvent separated by the filtering under reduced pressure and the kneader reactor was recovered and reused.

[0064] Example 2:

[0065] The same process as Example 1 was performed, except that the polyethylene included in the composite resin was dissolved in the above-mentioned dissolution tank at 106°C, the boiling point of CPME, to obtain a polymer solution.

[0066] Reference Example 1:

[0067] The same process as Example 1 was performed, except that the polyethylene included in the composite resin was dissolved in the above-mentioned dissolution tank at 100°C, which is lower than the boiling point of CPME, to obtain a polymer solution.

[0068] Reference Example 2:

[0069] The same process as Example 1 was performed, except that the polyethylene included in the composite resin was dissolved in the above-mentioned dissolution tank at 100°C, which is lower than the boiling point of CPME, to obtain a polymer solution, and the filtration method was changed to press filtration.

[0070] Example 3:

[0071] The same process as Example 1 was performed, except that the solvent supplied to the dissolution tank and the precipitation tank was replaced with cyclopentyl ethyl ether (CPEE) (bp 122°C) and the dissolution temperature or filtration method was changed to those shown in Table 1 below.

[0072] Example 4:

[0073] The same process as Example 1 was performed, except that the solvent supplied to the dissolution tank and the precipitation tank was replaced with cyclohexyl methyl ether (CHME) (bp 135°C) and the dissolution temperature or filtration method was changed to those shown in Table 1 below.

[0074] Comparative Examples 1 to 4:

[0075] The same process as Example 1 was performed, except that the solvent supplied to the dissolution tank and the sedimentation tank was replaced with methyl cyclohexane (MCH) (bp 101°C), and the dissolution temperature, the amount of solvent supplied to the sedimentation tank, or the filtration method were changed as shown in Table 1 below.

[0076] TSC (Dissolution Tank Sedimentation Tank Filtration) 2) (weight%)Solvent temperature(℃)Solubility 1)(Wt%)Pressure(bar)SolventTemperature(℃)Comparative Example 1MCH 50ml105102MCH 200ml25Filter paper5.0Comparative Example 2MCH 50ml1056.72MCH 150ml25Decompression18.4Comparative Example 3MCH 50ml1006.71MCH 150ml25Decompression32.3Comparative Example 4MCH 50ml956.71MCH 150ml25Decompression33.5Example 1CPME 50ml1106.72CPME 150ml25Decompression67.7Example 2CPME 50ml1066.71CPME 150ml25Decompression64.7Reference Example 1CPME 50ml1006.71CPME 150ml25vacuum13.6Reference Example 2 CPME 50ml1006.71 CPME 150ml25pressure11.0Example 3 CPEE 50ml1256.72 CPEE 150ml25vacuum45.8Example 4 CHME 50ml1406.72 CHME 150ml25vacuum43.71) Solubility represents the content of dissolved polymer based on the weight of the polymer solution.2) TSC (total solid content) represents the solid content of the polymer precipitate after filtration.

[0077] In the above Table 1, in Examples 1 to 4, in which CPME (bp 106°C), CPEE (bp 122°C), or CHME (bp 135°C) were used as solvents for dissolving and recrystallizing polyethylene, and the dissolution temperature was performed at a temperature higher than the boiling point of each, the solid content in the final obtained polymer precipitate increased as the temperature difference with the precipitation tank having a room temperature was maximized while sufficiently dissolving the polymer in the dissolution tank heated to a high temperature, while on the other hand, the amount of the first residual solvent contained in the polymer precipitate decreased. That is, the cycloalkyl alkyl ether had sufficient solubility in the polymer at a temperature higher than the boiling point, while its affinity for the polymer decreased at low temperatures, resulting in an excellent polymer precipitation effect. Accordingly, the polymer precipitate obtained in the precipitation tank had a low residual solvent content, which can minimize the energy consumed for solvent removal. Meanwhile, in the case of Reference Examples 1 and 2, since the dissolution step was performed at a temperature lower than the boiling point of CPME used as a solvent, the temperature difference with the sedimentation tank (25°C) decreased, and thus the solid content in the final obtained polymer sediment decreased.

[0078] Comparative Examples 1 to 4 used MCH (bp 101°C) as a solvent for dissolution and recrystallization. Even though the polymer was dissolved at a temperature near the boiling point of the solvent and then the precipitation step was performed, the solids content of the final polymer precipitate was low, resulting in a high amount of solvent residue. This indicates that although MCH has a superior solubility in polymers than CPME, its affinity for polymers at low temperatures is high, resulting in a lower polymer precipitation ability.

[0079] An experiment was conducted to detect the amount of solvent remaining in the regenerated polymer obtained in Examples 1 to 4 (second residual solvent amount).

[0080] The regenerated polymers obtained in Examples 1 to 4 were obtained by drying the polymer precipitate in a vacuum oven at 100°C for 12 hours.

[0081] 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 2.

[0082] Classification 2 Residual solvent amount (ppm) Example 1800 Example 2700 Example 31500 Example 41800

[0083] In Table 2, the residual amount (ppm) in Examples 1 to 4 represents the second residual solvent amount of the regenerated polymer obtained in each Example expressed in ppm (parts per million) based on the weight of the regenerated polymer. Referring to Table 2, it can be confirmed that only a very small amount of solvent remains in the regenerated polymer, ranging from 700 ppm to 1800 ppm. This value does 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) A step of supplying cycloalkyl alkyl ether as a solvent to each of a dissolution tank and a precipitation tank; (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 temperature of the solvent is maintained at the precipitation temperature, thereby precipitating the polymer contained in the polymer solution to obtain a solution containing a polymer precipitate; and (S4) A method for producing a regenerated polymer, comprising the step of filtering a solution containing the polymer precipitate to obtain the polymer precipitate.

2. In paragraph 1, The above composite resin is a method for producing a recycled polymer by washing, drying and crushing waste resin manufactured from a resin composition in which two or more polymers are blended or a single polymer containing an additive.

3. In paragraph 1, 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 having a melting temperature of 90°C to 140°C.

5. 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.

6. In paragraph 1, A method for producing a regenerated polymer, wherein the step (S2) further comprises performing filtration to remove insoluble matter from the polymer solution.

7. In paragraph 1, A method for producing a regenerated polymer, wherein the precipitation temperature is 70 to 130°C lower than the dissolution temperature.

8. In paragraph 1, A method for producing a regenerated polymer, wherein the above precipitation temperature is -40 to 70°C.

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

10. In paragraph 1, A method for producing a regenerated polymer, wherein the polymer precipitate contains 40 to 80 wt% of a polymer based on its weight.

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. A regenerated polymer containing cycloalkyl alkyl ether as a residual component.

13. In paragraph 12, A regenerated polymer comprising at least one selected from the group consisting of 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.

14. In paragraph 12, A regenerated polymer wherein the cycloalkyl alkyl ether remains in an amount of 10 ppm to 5000 ppm based on the weight of the regenerated polymer.