How to recycle polyester materials

Abstract

PURPOSE: To provide a recycling method of a polyester material.SOLUTION: A recycling method of a polyester material includes steps of: fragmentation and cleaning a polyester material, followed by drying by using a microwave drying processing, melting and extruding the dried polyester material, and conducting melting filtration in a manner that a flow direction of the melting polyester material becomes a tangent angle to a surface of a filter, cooling the filtered polyester material, and pelletizing.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for recycling materials, and in particular to a method for recycling polyester materials. [Background technology]

[0002] Conventional mechanical recycling methods for waste polyester (polyethylene terephthalate, PET) involve comminutement (crushing PET bottles and film products, shredding textiles, etc.), washing, drying, melting, and extrusion, followed by melt filtration and granulation to obtain recycled PET (r-PET).

[0003] In the mechanical recycling process of PET, the drying and filtration processes are crucial, affecting quality (color, impurity content, intrinsic viscosity (IV)) and process efficiency (volume, pressure drop). Conventional technologies use hot air drying and static filters to filter impurities. However, drying waste PET using hot air is limited by the tendency for debris and fragments to adhere and agglomerate. Some PET contains residual moisture, which can cause degradation (IV drop) and poor color when extruded at high temperatures. When impurities are filtered using static mechanisms, the flow direction of molten PET is perpendicular to the filter surface, making the filter pores prone to clogging with impurities (solids). This increases pressure, leading to deformation and damage to the filter pores. Failure to filter impurities affects quality and, therefore, downstream processability. These two drawbacks impact downstream processability. In particular, when processing PET into PET bottles, insufficient IV results in residual impurities and excessive yellowing. The residual impurities make the spinning more susceptible to thread breakage, thereby affecting the spinning process. [Prior art document] [Patent documents] [Patent Document 1] U.S. Patent Publication No. 2021 / 0178638 [Patent Document 2] U.S. Patent Publication No. 2023 / 0104902 [Patent Document 3] European Patent No. 3778165 [Patent Document 4] International Publication No. 2017 / 092071 [Patent Document 5] International Publication No. 2018 / 077476

[0004] Based on the above, developing methods for recycling polyester materials to improve their subsequent processability is currently an important research topic. Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention provides a method for recycling polyester materials that can improve downstream processability, increasing the quality and process efficiency of recycled PET. [Means for solving the problem]

[0006] The method for recycling polyester materials of the present invention includes the following steps: first, the polyester material is comminuted and washed, and then dried using a microwave drying process; then, the dried polyester material is melted and extruded, and melt-filtered such that the flow direction of the molten polyester material is at a tangential angle to the surface of the filter; then, the molten and filtered polyester material is cooled and pelletized.

[0007] In one embodiment of the present invention, after being comminuted and washed, the polyester material is first dried using a hot air drying process and then dried using a microwave drying process.

[0008] In one embodiment of the present invention, the drying temperature in the hot air drying process is 40° C. to 150° C., the drying time is 5 minutes to 80 minutes, and the air speed is 1 m / s to 50 m / s.

[0009] In one embodiment of the present invention, the size of the polyester material after being comminuted is 5 x 5 cm 2 is less than.

[0010] In one embodiment of the present invention, the drying temperature in the microwave drying process is 30° C. to 125° C., the drying time is 0.1 minutes to 5 minutes, and the microwave output is 1 kW to 100 kW.

[0011] In one embodiment of the present invention, the moisture content of the polyester material after drying in a microwave drying process is less than 1,000 ppm (0.1%).

[0012] In one embodiment of the present invention, the temperature at which the melt extrusion is carried out is 220°C to 300°C.

[0013] In one embodiment of the present invention, the temperature at which the melt filtration is carried out is 230°C to 290°C.

[0014] In one embodiment of the present invention, the pore size of the filter pores is 10 μm to 100 μm.

[0015] In one embodiment of the present invention, the tangential velocity of the flow of the molten polyester material and the filter holes of the filter is 10 m / min to 200 m / min.

[0016] In one embodiment of the present invention, the pressure at which the filtration is carried out is between 10 bar and 100 bar.

[0017] In one embodiment of the present invention, the filtered polyester material is cooled to a temperature of between 30°C and 90°C.

[0018] In one embodiment of the present invention, the recycled polyester material has an intrinsic viscosity (IV) of 0.45 dl / g to 1.30 dl / g, and the reduction in intrinsic viscosity (IV) is less than 0.06 dl / g.

[0019] In one embodiment of the invention, the filter is mesh woven or laser drilled.

[0020] In one embodiment of the invention, the flow direction of the polyester material is at a tangential angle to the surface of the filter, and the filter is fixed so that the flow of polyester material flows over the side, and the flow of polyester material is in tangential contact with the filter.

[0021] In one embodiment of the present invention, the flow direction of the polyester material is at a tangential angle to the surface of the filter, and the filter employs a rotating method to bring the flow of polyester material into tangential contact with the filter.

[0022] In one embodiment of the present invention, the flow rate of the polyester material flowing through the filter pores of the filter is 0.1 m / min to 10 m / min. [Effects of the Invention]

[0023] As described above, the present invention provides a method for recycling polyester materials. By using a permeable and directional microwave drying process, the uniformity of drying can be improved, and moisture content can be evenly reduced to the required standard, eliminating any undried areas. Furthermore, the polyester material recycling method of the present invention also uses a dynamic melt filtering mechanism, which forces the PET flow direction to contact the filter surface at a tangential angle, preventing the molten PET from flowing perpendicular to the filter surface. Pressure forces the clean PET melt to flow through the filter holes, allowing solid impurities to be discharged to the outside without directly clogging the filter holes. DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, embodiments of the present invention will be described in detail, but these embodiments are merely examples and do not limit the present invention.

[0025] In this specification, ranges expressed as "one value to another value" are general expressions to avoid listing all the values ​​within the range. Thus, the description of a particular numerical range covers any numerical value within that numerical range and any smaller numerical range defined by that numerical value, and is the same as if any numerical value and smaller numerical range described above were specified in this specification.

[0026] The present invention provides a method for recycling polyester material, which includes the steps of: first, comminute and wash the polyester material, and then dry it using a microwave drying process; then, melt the dried polyester material, extrude it, and filter it so that the flow direction of the molten polyester material is at a tangential angle to the surface of the filter; then, cool the filtered polyester material, and pelletize it.

[0027] In this embodiment, the polyester material is, for example, a discarded polyester material, which may include discarded PET bottles, discarded film products, or discarded textiles, but the present invention is not limited thereto. The impurity content is less than 3 wt%, and the impurities may include sand, iron, PE, PP, PVC, nylon, etc. In the process of breaking down the polyester material, for example, the PET bottles and film products are crushed, and the textiles are shredded. The size of the polyester material after breaking down is, for example, 5 x 5 cm. 2 Less than 3 x 3 cm, preferably 2 is less than.

[0028] In this embodiment, a microwave drying process is used for drying. The drying temperature in the microwave drying process may be, for example, 30°C to 125°C, and preferably 40°C to 105°C. The drying time may be, for example, 0.1 to 5 minutes, and preferably 0.5 to 3 minutes. The microwave output may be, for example, 1 kW to 100 kW, and preferably 2 kW to 50 kW. After the polyester material is fragmented and washed, it can be dried using a hot air drying process in pre-treatment, and then dried using a microwave drying process in post-treatment. The drying temperature in the hot air drying process may be, for example, 40°C to 150°C, and preferably 50°C to 125°C. The drying time may be, for example, 5 to 80 minutes, and preferably 10 to 60 minutes. The air speed may be, for example, 1 m / s to 50 m / s, and preferably 2 m / s to 30 m / s. The microwave drying process can effectively control the moisture content, and the moisture content of the polyester material after drying by the microwave drying process can be, for example, less than 1000 ppm (0.1%), preferably less than 500 ppm (0.05%).

[0029] In this embodiment, the dried polyester material is melted and extruded, and the melt extrusion temperature may be, for example, 220°C to 300°C, and preferably 210°C to 290°C.

[0030] In this embodiment, melt filtration is performed using a dynamic filtration mechanism, with the flow direction of the molten polyester material forming a tangential angle with the filter surface. For example, if the filter is moving or rotating, the molten polyester material enters the filter directly, while if the filter is stationary, the molten polyester material enters at a lateral angle. Both of these methods maintain the flow direction of the molten polyester material at a tangential angle with the filter surface, preventing it from becoming perpendicular. In this way, clean molten polyester material flows through the filter holes, allowing solid impurities to be discharged to the outside without directly clogging the filter holes. The filtration temperature may be, for example, 230°C to 290°C, preferably 210°C to 290°C. The tangential velocity of the flow of the molten polyester material relative to the filter holes may be, for example, 10 m / min to 200 m / min, preferably 15 m / min to 150 m / min. The flow rate of the polyester material flowing through the filter holes is 0.1 m / min to 10 m / min, preferably 0.2 m / min to 10 m / min. The pressure used for filtration may be, for example, 10 bar to 100 bar, preferably 20 bar to 80 bar. The pore size of the filter pores may be, for example, 10 μm to 100 μm, preferably 20 μm to 80 μm. For example, mesh weaving or laser drilling can be used to achieve the required pore size. The flow direction of the molten polyester material is tangential to the filter surface. The filter can be fixed so that the polyester material flows from the side, bringing the flow into tangential contact with the filter, or a rotating filter can be used to bring the flow into tangential contact with the filter, thereby improving the efficiency and quality of melt filtration.

[0031] In this embodiment, the filtered polyester material is cooled to a temperature of 30° C. to 90° C., preferably 40° C. to 80° C. The intrinsic viscosity (IV) of the recycled polyester material is, for example, greater than 0.45 dL / g to 1.30 dL / g, and the reduction in intrinsic viscosity (IV) is, for example, less than 0.06 dL / g.

[0032] The above-mentioned method for recycling polyester materials of the present invention will be described in detail below with reference to experimental examples, although the present invention is not limited to these examples. Experimental Example Example 1

[0033] Recycled PET bottles were crushed (3 x 3 cm 2 After washing, 100.3 kg of PET bottle fragments were obtained. The IV was 0.81 dl / g, the moisture content was 4,800 ppm, and the content of impurities such as sand and PP was 0.2%. The fragments were dried for 15 minutes using hot air at 105°C at a speed of 10 m / s, followed by 10 minutes in a 36 kW microwave dryer. The moisture content of randomly sampled PET bottle fragments was 210 ± 40 ppm, with an average of 198 ppm. The fragments were then extruded at 250°C using an extruder and melt-filtered using a rotary filter. The filter pores were 50 μm in diameter. The tangential velocity of the flow through the filter was 20 m / s. The flow velocity through the filter pores was 0.8 m / s. The pressure was increased from 50 to 51 bar (50 → 51 bar). The filtered PET resin was cooled to 60°C with cooling water at 25°C and pelletized using a pelletizer. The obtained r-PET resin pellets weighed 99.5 kg (yield 99.5%) and had an IV of 0.79, resulting in a decrease in IV (ΔIV) of 0.02. Examples 2 to 6

[0034] The specifications of the feed material, drying conditions, and filter conditions were changed, but the rest were the same as in Example 1. The test data are shown in Table 1.

[0035] As can be seen from Table 1, microwave drying of bottle pieces effectively reduces moisture and improves drying uniformity. Effective moisture control effectively improves the specifications of the PET feedstock. The PET resin flows tangentially across the filter surface, ensuring stable process pressure. This improves filtration system efficiency and prevents clogging. Stable operation allows for a yield of over 99.0%, ensuring consistent quality.

[0036] [Table 1] Comparative Example 1

[0037] Recycled PET bottles were crushed (3 x 3 cm 2 After washing, 100.3 kg of PET bottle fragments were obtained. The IV was 0.81 dl / g, the moisture content was 0.1% (1000 ppm), and the content of impurities such as sand and PP was 0.2%. They were dried for 30 minutes using hot air at 105°C at a speed of 10 m / s. The moisture content of randomly sampled PET bottle fragments was 8,500 ± 4,300 ppm, with an average of 8,310 ppm. They were then extruded at 250°C using an extruder and filtered using a fixed filter. The filter pores were 50 μm in diameter. The flow was perpendicular to the contact surface of the filter. The flow velocity through the filter pores was 0.8 m / s. The pressure was 50–67 bar. The filtered PET resin was cooled to 60°C using cooling water at 25°C and pelletized using a pelletizer. The obtained r-PET resin pellets were 93.7 kg (yield 93.7%), had an IV of 0.72, and the decrease in IV (ΔIV) was as high as 0.09. Comparative Examples 2 to 6

[0038] The specifications of the feed material, drying conditions, and filter conditions were changed, but the rest were the same as in Comparative Example 1. The test data are shown in Table 2. As can be seen from Table 2, the bottle pieces were dried using only hot air. Drying has limitations that affect uniformity and cannot effectively control moisture, resulting in a lower specification of the PET feed material. The PET resin flows vertically across the filter surface, and the process pressure continues to increase. The filtration system is prone to clogging and cannot operate stably. The yield is less than 97.0%, and the IV reduction (ΔIV) is greater than 0.06, resulting in a decrease in quality stability and a smooth process.

[0039] [Table 2]

[0040] As described above, the present invention provides a method for recycling polyester materials. By using a permeable and directional microwave drying process, the uniformity of drying can be improved, and moisture content can be evenly reduced to the required standard, eliminating any undried areas. Furthermore, the polyester material recycling method of the present invention also uses a dynamic melt filtration mechanism, which forces the PET flow direction to contact the filter surface at a tangential angle, preventing the molten PET from flowing perpendicular to the filter surface. Pressure forces clean PET melt to flow through the filter holes, allowing solid impurities to be discharged without directly clogging the filter holes. The present invention primarily aims to effectively control the moisture content of raw materials (feedstock), effectively improving the specifications of PET feedstock and maintaining the stability of the filtration system during the process. This improves the efficiency of the filtration system, avoiding clogging and achieving consistent quality, significantly improving the smoothness of production line operation and effectively reducing energy consumption. [Industrial Applicability]

[0041] The method for recycling polyester materials of the present invention can be applied to the field of waste PET recycling.

Claims

1. drying the polyester material using a microwave drying process after the polyester material has been comminuted and washed; the dried polyester material is melted and extruded, and then filtered so that the flow direction of the molten polyester material forms a tangential angle with the surface of a filter; cooling and pelletizing the filtered polyester material; 1. A method for recycling polyester materials comprising:

2. 2. The method for recycling polyester materials according to claim 1, wherein after the polyester materials are shredded and washed, the polyester materials are first dried using a hot air drying process, and then dried using the microwave drying process.

3. 3. The method for recycling polyester materials according to claim 2, wherein the drying temperature in the hot air drying process is 40°C to 150°C, the drying time is 5 minutes to 80 minutes, and the air speed is 1 m / s to 50 m / s.

4. The size of the polyester material after being divided is 5 x 5 cm ２ 2. The method for recycling polyester material according to claim 1, wherein the polyester content is less than 100%.

5. 2. The method for recycling polyester materials according to claim 1, wherein the drying temperature in the microwave drying process is 30°C to 125°C, the drying time is 0.1 minutes to 5 minutes, and the microwave power is 1 kW to 100 kW.

6. 2. The method for recycling polyester material according to claim 1, wherein the moisture content of the polyester material after drying by the microwave drying process is less than 1,000 ppm.

7. 2. The method for recycling polyester materials according to claim 1, wherein the melt extrusion is carried out at a temperature of 220°C to 300°C.

8. 2. The method for recycling polyester materials according to claim 1, wherein the filtration is carried out at a temperature of 230°C to 290°C.

9. 2. The method for recycling polyester materials according to claim 1, wherein the filter has pores with a diameter of 10 μm to 100 μm.

10. 2. The method for recycling polyester materials according to claim 1, wherein the tangential velocity of the flow of the molten polyester material and the filter holes of the filter is 10 m / min to 200 m / min.

11. 2. The method for recycling polyester materials according to claim 1, wherein the pressure for carrying out the filtration is from 10 bar to 100 bar.

12. 2. The method for recycling polyester material according to claim 1, wherein the filtered polyester material is cooled to a temperature of 30°C to 90°C.

13. 2. The method for recycling polyester materials according to claim 1, wherein the recycled polyester material has an intrinsic viscosity (IV) of 0.45 dL / g to 1.30 dL / g, and the reduction in intrinsic viscosity (IV) is less than 0.06 dL / g.

14. 10. The method for recycling polyester material according to claim 1, wherein the filter uses a mesh weave or laser perforation.

15. 2. The method for recycling polyester material according to claim 1, wherein the flow direction of the polyester material is at a tangential angle to the surface of the filter, the filter is fixed so that the flow of the polyester material flows from the side, and the flow of the polyester material comes into tangential contact with the filter.

16. 2. The method for recycling polyester material according to claim 1, wherein the flow direction of the polyester material is at a tangential angle with respect to the surface of the filter, and the filter is rotated to bring the flow of the polyester material into tangential contact with the filter.

17. 2. The method for recycling polyester materials according to claim 1, wherein the flow rate of the polyester material flowing through the filter holes of the filter is 0.1 m / min to 10 m / min.

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