Method for producing recycled polyester using recycled dimethyl terephthalate (DMT) and recycled ethylene glycol (EG) produced by low-temperature methanolysis depolymerization technology

Abstract

In a method for manufacturing recycled polyester using waste polyester, A raw material input step of introducing recycled dimethyl terephthalate (DMT) and recycled ethylene glycol (EG), produced by low-temperature methanolysis-based depolymerization technology, into a reactor in a molar ratio of 1.0:1.0 to 2.2; an ester exchange reaction step of raising the internal temperature of the reactor to 210–260°C and the external temperature to 280–320°C to produce recycled bis-2-hydroxyethylene terephthalate (BHET), and introducing 100–600 ppm of zinc acetate (ZnAC) as a catalyst relative to the weight of recycled dimethyl terephthalate; and introducing 10–400 ppm of a metal catalyst selected from titanium (Ti), antimony (Sb), and germanium (Ge), and trimethyl phosphate (TMP) as a heat stabilizer to the produced recycled bis-2-hydroxyethylene terephthalate (BHET). The present invention provides a method for manufacturing recycled polyester using waste polyester, characterized by comprising a condensation polymerization reaction step in which 200~900 ppm, 5~25 wt% of ethylene glycol (EG) BHET by weight is added and reacted, and a recycled polyester chip manufacturing step. According to the method for manufacturing recycled polyester of the present invention, all colorless and colored waste polyester generated domestically can be depolymerized into monomers without distinguishing between grades, and recycled polyester with excellent physical properties can be manufactured. In addition, the waste polyester manufacturing method according to the present invention can be utilized for various purposes as an eco-friendly product capable of significantly reducing carbon emissions.

Description

Technology Field

[0001] The present invention relates to a method for producing recycled polyethylene terephthalate (hereinafter referred to as ‘PET’) by subjecting recycled dimethyl terephthalate (hereinafter referred to as ‘DMT’) obtained by depolymerizing polyester waste and recycled ethylene glycol (hereinafter referred to as ‘EG’) to an ester exchange reaction and a condensation polymerization reaction. Background Technology

[0002] With the recent development of the plastics industry leading to a proliferation of plastic products, waste disposal is emerging as a major environmental issue.

[0003] Plastics have high utility in various fields such as films, beverage bottles, and fibers, and are widely used in large quantities. However, the recovery rate for the reuse of waste plastics remains at approximately 25% globally, and the remaining unrecovered resources are disposed of through methods such as incineration or landfilling. This is analyzed to cause not only environmental pollution but also significant economic losses due to the final disposal of usable resources.

[0004] According to the Ministry of Environment's Resource Circulation Information System, the amount of waste textiles generated at industrial sites nationwide recently reached 1,239 tons per day. This figure was recorded in 2018 and is about six times higher than the 224 tons generated in 2017. Of the total 1,239 tons of waste textiles generated in 2018, 67 tons were incinerated and 18 tons were landfilled, leaving the fate of the remaining waste textiles unknown.

[0005] Over the past 15 years, clothing production has more than doubled, and there is a forecast that demand for textiles will increase by 84% over the next 20 years. This is because, along with the growth of the so-called fast fashion industry, prices for clothing products are falling every year and consumption is occurring in shorter cycles.

[0006] The severity of waste fibers is less known than that of waste plastics, and experts and environmental groups agree that the problems associated with waste fibers must be recognized and resolved. Furthermore, as the market share of recycled PET in the PET market—one of the synthetic fibers that accounts for 60% of the total fiber market—increased by approximately 6% from 8% in 2007 to 14% as of 2017, the demand for sustainable fibers is steadily increasing.

[0007] Since solidified polyester is unstable to heat, it is almost impossible to reuse it after melting it at a temperature above its melting point, so the waste must be recovered at a lower temperature. Processes for recovering waste polyester include a process for recovering raw materials such as terephthalate acid (TPA), dimethyl terephthalate (DMT), and ethylene glycol (EG) through depolymerization of waste polyester using catalysts, and a process for manufacturing the intermediate product bis-2-hydroxyethyl terephthalate (BHET).

[0008] Depolymerization pathways applied industrially for polyester recycling include hydrolysis, glycolysis, methanolysis, and ammonolysis, and various chemical depolymerization methods are widely used, ranging from complex processes that combine these to leverage the advantages of each process.

[0009] Glycolysis is a depolymerization reaction in which glycol is added as a reactant. The most common example of glycolysis is the process of producing bis(2-hydroxyethyl) terephthalate (BHET) by adding an excess amount of ethylene glycol, one of the monomer raw materials. Since ethylene glycol, which is one of the raw materials for the synthesis of polyethylene terephthalate (PET) polymers, is used as a reactant, the products produced by the depolymerization reaction have a chemical structure in which ethylene glycol is already bonded to both ends of the terephthalate. Therefore, replacing only a portion of the raw materials in the existing condensation process using terephthalic acid can lead to very favorable results in terms of reaction kinetics.

[0010] Glycolysis is generally performed under reflux conditions of the reactant glycol, but there is a problem in that the product purity may be low and it is difficult to separate the final product, the monomer, from the reactant with high purity or high yield because the rate of decomposition from oligomer to monomer is slow and the equilibrium between compounds is reached even if the reaction time is delayed.

[0011] The methanolysis process is one of the processes that has been widely applied in actual commercial processes in the past, ranging from global chemical companies to small and medium-sized plastics industries. Theoretically, through the above process, dimethyl terephthalate (DMT) is obtained as the final monomer product, and as the transesterification reaction proceeds, ethylene glycol (EG) equivalent to the number of moles of decomposed terephthalate can be liberated.

[0012] Registered Patent No. 10-2462599 discloses a method for producing DMT and EG through a low-temperature methanolisis process for treating waste polyester in a mixture containing methanol, calcium carbonate (K2CO3) and a polar aprotic solvent.

[0013] The present invention aims to provide a method for producing recycled polyester through ester exchange reaction and condensation polymerization reaction using recycled DMT and recycled EG obtained in this way. Prior art literature

[0014] Registered Patent No. 10-2462599 (Published Nov. 03, 2022) Published Patent No. 10-2023-0068533 (Published May 18, 2023) Published Patent No. 10-2023-0132222 (Published Sep. 15, 2023) The problem to be solved

[0015] The present invention aims to provide a recycled polyester resin with excellent physical properties and appearance by using recycled dimethyl terephthalate (DMT) and recycled ethylene glycol (EG), obtained by a method of depolymerizing a polymer containing an ester functional group, which significantly reduces energy consumption because production is possible under conditions requiring no energy usage or only relatively low heat from the reaction to the product purification, through an ester exchange reaction and a condensation polymerization reaction. means of solving the problem

[0016] To solve the above problem, the present invention provides a method for manufacturing recycled polyester using waste polyester, comprising: a raw material input step of introducing recycled dimethyl terephthalate (DMT) and recycled ethylene glycol (EG), produced by low-temperature methanolysis-based depolymerization technology, into a reactor in a molar ratio of 1.0 : 1.0 to 2.2; an ester exchange reaction step of raising the internal temperature of the reactor to 210~260℃ and the external temperature to 280~320℃ to produce recycled bis-2-hydroxyethylene terephthalate (BHET), and introducing zinc acetate (ZnAC) as a catalyst at a ratio of 100~600 ppm relative to the weight of recycled dimethyl terephthalate; and introducing a metal catalyst selected from titanium (Ti), antimony (Sb), and germanium (Ge) at a ratio of 10~400 ppm to the produced recycled bis-2-hydroxyethylene terephthalate (BHET). The present invention provides a method for manufacturing recycled polyester using waste polyester, characterized by comprising a condensation polymerization reaction step in which 200 to 900 ppm of trimethyl phosphate (TMP) and 5 to 25 wt% of ethylene glycol (EG) are added as heat stabilizers relative to the weight of the manufactured recycled BHET and reacted, and a recycled polyester chip manufacturing step.

[0017] In one embodiment of the present invention, the ester exchange reaction step may comprise a first heating step of heating the input raw material to an internal reactor temperature of 150°C and an external temperature of 100°C to 180°C within 1 to 2 hours, a second heating step of heating the internal reactor temperature from 150°C to 170°C to 200°C at a heating rate of 0.1 to 3.0°C / min, a first holding step of maintaining the internal reactor temperature at 170°C to 200°C for 30 to 60 minutes, a third heating step of heating the internal reactor temperature from 170°C to 200°C to 210°C to 260°C at a heating rate of 0.1 to 3.0°C / min, and a second holding step of maintaining the temperature at 210°C to 260°C for 30 to 60 minutes.

[0018] In addition, the condensation polymerization reaction step is characterized by increasing the internal temperature of the reactor from 210 to 260°C to 260 to 310°C at a heating rate of 0.1 to 3.0°C / min, and carrying out the reaction for 150 to 180 minutes under a vacuum state of a final pressure of 0.1 to 0.5 Torr.

[0019] Meanwhile, the above condensation polymerization reaction step is characterized by having a cold trap of -30.0 to -60.0℃ so that unreacted ethylene glycol is solidified and removed inside.

[0020] The above-mentioned recycled polyester chip manufacturing step is characterized by manufacturing by extruding the recycled polyester inside the reactor into water using nitrogen pressure and cutting it. Effects of the invention

[0021] According to the method for manufacturing recycled polyester of the present invention, all colorless and colored waste polyester generated domestically can be depolymerized into monomers without distinguishing between grades, and recycled polyester with excellent physical properties can be manufactured.

[0022] In addition, the waste polyester manufacturing method according to the present invention can be utilized for various purposes as an eco-friendly product capable of significantly reducing carbon emissions. Brief explanation of the drawing

[0023] Figure 1 is a schematic diagram of a recycled polyester manufacturing process according to the present invention. Specific details for implementing the invention

[0024] The present invention will be explained in more detail below through examples and experimental examples. However, these examples are intended only to aid in understanding the invention and do not limit the scope of the invention in any way.

[0025] A method for manufacturing recycled polyester using waste polyester according to one embodiment of the present invention comprises: a raw material input step of introducing recycled dimethyl terephthalate (DMT) and recycled ethylene glycol (EG), produced by low-temperature methanolysis-based depolymerization technology, into a reactor in a molar ratio of 1.0 : 1.0 to 2.2; and an ester exchange reaction step of raising the internal temperature of the reactor to 210~260℃ and the external temperature to 280~320℃ to produce recycled bis-2-hydroxyethylene terephthalate (BHET), and introducing zinc acetate (ZnAC) as a catalyst at a ratio of 100~600 ppm relative to the weight of recycled dimethyl terephthalate. The method is characterized by comprising: a condensation polymerization reaction step in which 10 to 400 ppm of a metal catalyst selected from titanium (Ti), antimony (Sb), and germanium (Ge), 200 to 900 ppm of trimethylphosphate (TMP) as a heat stabilizer, and 5 to 25 wt% of ethylene glycol (EG) relative to the weight of the prepared recycled BHET are added to the above-mentioned recycled bis-2-hydroxyethylene terephthalate (BHET) and reacted; and a recycled polyester chip manufacturing step.

[0026] First, recycled dimethyl terephthalate (DMT) and recycled ethylene glycol (EG), which are used as raw materials, are obtained by low-temperature methanolysis-based depolymerization. They are recovered by depolymerizing methanol and calcium carbonate at a temperature of 25°C using them as catalysts.

[0027] Recycled dimethyl terephthalate (DMT) and recycled ethylene glycol (EG) are introduced into a reactor in a molar ratio of 1.0:1.0 to 2.2. The composition of the monomers affects the ester exchange reaction rate, the purity of bis-2-hydroxyethylene terephthalate (BHET), and the viscosity of the final product. Therefore, if less than 1.0 mole of recycled ethylene glycol is mixed with 1 mole of recycled dimethyl terephthalate (DMT), unreacted residual monomers remain in the ester exchange reaction, and if it exceeds 2.2 moles, the reaction time becomes longer and the amount of residual impurities increases, causing the intrinsic viscosity of the final product to decrease.

[0028] After the raw materials are introduced into the reactor, zinc acetate (ZnAC) can be introduced as a catalyst at a concentration of 100 to 600 ppm relative to the weight of recycled dimethyl terephthalate (DMT). After the introduction of the raw materials is finished, the reactor is sealed, and while rotating the internal stirrer at 60 to 100 rpm, the internal temperature of the reactor is raised from room temperature to 230°C through sequential heating and holding stages, and the ester exchange reaction is performed for a processing time of 3 to 5 hours.

[0029] If the temperature is rapidly increased at the beginning of the ester exchange reaction, a large amount of DMT and EG are released, and the reaction does not proceed sufficiently; if the time for increasing the temperature is too long, methanol is not sufficiently extracted, and the viscosity decreases during the condensation polymerization reaction stage.

[0030] In the ester exchange reaction step, the stirrer inside the reactor is stirred at 60 to 100 rpm, and the temperature is initially raised to 150°C. In the second heating step, which reaches 170 to 200°C from 150°C, if the temperature is raised at a rate exceeding 3.0°C / min, DMT and EG are discharged at the initial heating stage, preventing the ester exchange reaction from occurring sufficiently; if the heating rate is too slow at less than 0.1°C, the processing time increases excessively and methanol is not completely extracted.

[0031] Once the second heating step is completed, the reactor internal temperature is maintained at 170–200°C for 30–60 minutes to allow the ester exchange reaction to proceed sufficiently. At this time, the completeness of the ester exchange reaction can be determined by checking the amount of methanol discharged; when the amount of methanol discharged relative to the amount of DMT input reaches a molar ratio of 1.0:1.8 to 2.0 molar, the ester exchange reaction can be considered complete.

[0032] Once the first holding stage is completed, the internal temperature of the reactor is raised from 170–200°C to 210–260°C at a rate of 0.1–3.0°C / min in a third raising stage, and the ester exchange reaction is completed through a second holding stage at 210–260°C for 30–60 minutes. When the temperature is raised to 210–260°C, unreacted EG vaporizes and is removed to the outside. During the second holding time at 210–260°C, if no methanol is released and the vaporization of EG does not proceed further, the ester exchange reaction is terminated and recycled bis-2-hydroxyethylene terephthalate (BHET) is formed.

[0033] After the ester exchange reaction is completed, a condensation polymerization reaction step using recycled bis-2-hydroxyethylene terephthalate (BHET) is carried out. This step involves adding 10 to 400 ppm of a metal catalyst selected from titanium (Ti), antimony (Sb), and germanium (Ge), 200 to 900 ppm of trimethylphosphate (TMP) as a heat stabilizer, and 5 to 25 wt% of ethylene glycol (EG) relative to the weight of the prepared recycled BHET to the recycled bis-2-hydroxyethylene terephthalate (BHET) and reacting them.

[0034] The metal catalyst is intended to promote the condensation polymerization reaction and may be one or more selected from TiO2, Sb2O3, and GeO2. It would be more preferable to use GeO2.

[0035] It is preferable to add a metal catalyst at 265°C in an amount of 10 to 400 ppm based on bis-2-hydroxyethyl terephthalate.

[0036] In addition, trimethyl phosphate (TMP) may be added for the thermal stability of bis-2-hydroxyethyl terephthalate (BHET). It is preferable to add 200 to 900 ppm of trimethyl phosphate (TMP) based on bis-2-hydroxyethyl terephthalate (BHET) at 260°C.

[0037] Meanwhile, to promote heating, 5 to 25 wt% of the weight of recycled BHET produced by ethylene glycol (EG) based on bis-2-hydroxyethyl terephthalate is added and reacted, and to prevent color change due to oxidation of the reaction product, nitrogen is continuously supplied into the reactor while oxygen is discharged, and the reactor stirring speed and stirrer torque are controlled so that the target intrinsic viscosity (IV) becomes 0.3 to 0.9 dl / g.

[0038] Since BHET begins to melt at 230°C or higher, the temperature is increased from 210–260°C to 260–310°C while rotating the stirrer at 30 to 120 rpm, and the condensation polymerization reaction is carried out for 150 to 180 minutes under reduced pressure of 0.1–0.5 Torr. At this time, the heating rate is increased at 0.1–3.0°C / min.

[0039] In the condensation polymerization step, unreacted EG and heating EG are removed as byproducts by condensing in a Cold Trap with a temperature of -30.0 to -60.0°C, thereby preventing a decrease in the physical properties of the recycled polyester produced. After reaching a temperature of 260°C to 310°C, the condensation polymerization reaction step of the recycled polyester is completed by controlling the current load of the stirrer and the intrinsic viscosity (IV) of the recycled polyester produced while adjusting the rotation speed of the stirrer to 20 to 100 rpm for 150 to 180 minutes.

[0040] When the above condensation polymerization reaction is completed, the vacuum state of the reactor is released and stirring is terminated. High-pressure nitrogen is supplied, and using that pressure, the reaction product, recycled polyester, is extruded into a water bath containing cold water and cut into a uniform length to produce recycled polyester chips.

[0041] Specific embodiments and experimental examples according to the present invention will be described below. The following embodiments are provided merely as examples to aid in understanding the present invention, and the technical scope of the present invention is not limited thereby.

[0042] Recycled polyester chips were prepared using recycled dimethyl terephthalate (DMT) and recycled ethylene glycol (EG) produced using low-temperature methanolis-based depolymerization technology according to an example and a comparative example of one embodiment of the present invention, and their physical properties were compared.

[0043] [Example]

[0044] <Example 1>

[0045] Recycled DMT and recycled EG were added in a molar ratio of 1:1.3, and the ester exchange reaction was carried out with varying zinc acetate (ZnAC) levels of 100–600 ppm, temperature and maintenance conditions, and the rotation speed of the stirrer. The reaction was determined to have ended when no more methanol was discharged, and the reaction conditions and manufacturing process status were compared and shown in [Table 1] while producing recycled bis-2-hydroxyethylene terephthalate (BHET).

[0046] [Table 1]

[0047]

[0048] In Example 1-1, where the temperature was rapidly increased from 150°C to 170–200°C, it was confirmed that a large amount of DMT and EG were released externally during the initial temperature increase, resulting in insufficient ester exchange reaction. In Example 1-2, where the temperature was increased from 170–200°C to 210–260°C at a relatively slow rate, it was confirmed that 100% of methanol was not extracted, causing the viscosity to drop below the target level in the subsequent condensation polymerization step. It was confirmed that the temperature increase rates for steps 1, 2, and 3, as well as the holding temperatures and times for the first and second stages, in Example 1-3 were the most desirable.

[0049] <Example 2>

[0050] 200 ppm of GeO2 was added as a metal catalyst to recycled bis-2-hydroxyethylene terephthalate (BHET) prepared under the conditions of Examples 1-3, and 300-900 ppm of trimethylphosphate (TMP) and 5-25 wt% of ethylene glycol relative to the weight of the BHET being prepared were added to the reactor. While raising the internal temperature of the reactor to 230°C, stirring was performed without operating the stirrer in Examples 2-1 and 2-4, while increasing the rotation speed of the stirrer to 60 rpm in Example 2-2 and to 100 rpm in Example 2-3. While applying a vacuum to the inside of the reactor at 210-260°C, the temperature was raised from 260°C to 310°C with varying rates and times for each example.

[0051] Finally, the holding time was varied for each example at a temperature of 260–310°C, and the rotation speed of the stirrer was changed from 30 rpm in Example 2-1 and 60 rpm to 20 rpm after 3 hours of reaction in Example 2-2, from 100 rpm to 50 rpm after 2 hours of reaction in Example 2-3, and from 100 rpm to 90 rpm, 40 rpm, and 30 rpm in Example 2-4. The intrinsic viscosity (IV) and color (L value) of the recycled polyester chips produced and the current load of the stirrer were compared and are shown in [Table 2].

[0052] The intrinsic viscosity (IV) of the recycled polyester chips manufactured above was measured by a conventional method, and the color of the recycled polyester chips was measured using a CR-310 colorimeter according to the ASTM D6290 method L* value.

[0053] [Table 2]

[0054]

[0055] In Example 2-1, the intrinsic viscosity of the final reactant was low, the color was poor, and bubbles were generated during the condensation polymerization reaction step. In Example 2-2, carbonization occurred during the reaction process due to excessive reaction time, and the current value was high at 0.17–0.16 due to increased load on the stirrer, indicating poor process workability. In Example 2-3, the intrinsic viscosity was poor at 0.40, and the color value was also low at 39.84, which was determined to be due to carbonization caused by the addition of 300 ppm of trimethylphosphate (TMP). In Example 2-4, where the initial rotation speed of the stirrer was sequentially reduced from 100 rpm to 30 rpm, the intrinsic viscosity, color, and current load were confirmed to be the best at 0.09–0.11 mA.

Claims

Claim 1 A method for manufacturing recycled polyester using waste polyester, comprising: a raw material input step of introducing recycled dimethyl terephthalate (DMT) and recycled ethylene glycol (EG), produced by low-temperature methanolysis-based depolymerization technology, into a reactor in a molar ratio of 1.0 : 1.0 to 2.2; an ester exchange reaction step of raising the internal temperature of the reactor to 230°C and the external temperature to 300°C to produce recycled bis-2-hydroxyethylene terephthalate (BHET), and introducing zinc acetate (ZnAC) as a catalyst at a ratio of 100 to 600 ppm relative to the weight of recycled dimethyl terephthalate; and to the recycled bis-2-hydroxyethylene terephthalate (BHET) produced above, introducing 200 ppm of germanium oxide (GeO2) catalyst, 200 to 900 ppm of trimethyl phosphate (TMP) as a heat stabilizer, and ethylene The method comprises a condensation polymerization reaction step in which 5 to 25 wt% of glycol (EG) is added relative to the weight of the manufactured recycled BHET and reacted; and a recycled polyester chip manufacturing step, wherein the ester exchange reaction step comprises: a first heating step in which the added raw material is heated to an internal reactor temperature of 150°C and an external temperature of 180°C within 1 to 2 hours; a second heating step in which the internal reactor temperature is heated from 150°C to 185°C at a heating rate of 0.1 to 3.0°C / min; a first holding step in which the internal reactor temperature is maintained at 185°C for 30 to 60 minutes, and maintained until the molar ratio of methanol outflow to the amount of recycled dimethyl terephthalate (DMT) added becomes 1.0 : 1.8 to 2.0; and a third heating step in which the internal reactor temperature is heated from 185°C to 230°C at a heating rate of 0.1 to 3.0°C / min. A method for manufacturing recycled polyester using waste polyester, characterized by comprising a second holding step of maintaining at a temperature of 230℃ for 30 minutes. Claim 2 delete Claim 3 A method for manufacturing recycled polyester using waste polyester according to claim 1, wherein the condensation polymerization reaction step is performed under conditions in which the internal temperature of the reactor is raised from 230℃ to 280℃ at a heating rate of 0.1 to 3.0℃ / min, and for 160 minutes in a vacuum state with a final pressure of 0.1 to 0.5 Torr, and the speed of the stirrer is adjusted stepwise from 100 rpm to 90, 40, and 30 rpm. Claim 4 A method for manufacturing recycled polyester using waste polyester according to claim 1, wherein the condensation polymerization reaction step is provided with a cold trap of -30.0 to -60.0℃ so that unreacted ethylene glycol is condensed and removed inside. Claim 5 A method for manufacturing recycled polyester using waste polyester according to claim 1, wherein the recycled polyester chip manufacturing step is characterized by extruding recycled polyester inside a reactor into water using nitrogen pressure and cutting to manufacture.

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