Drying method and system for fully biodegradable polyester chips

Abstract

The present invention belongs to the field of polyester chip drying, specifically to a method and system for drying fully biodegradable polyester chips. Specifically, the drying system includes a buffer silo, a dryer connected to the outlet of the buffer silo, a first air supply device for continuously supplying gas into the buffer silo, a second air supply device for continuously supplying gas into the dryer, and dew point testing equipment located at the outlet of the buffer silo and at the outlet of the dryer. The dryer is equipped with a dynamic component to keep the polyester chips in motion.

Description

Technical Field

[0001] The invention belongs to the field of polyester chip drying, and in particular relates to a drying method and system for fully biodegradable polyester chips. Background Art

[0002] Fully biodegradable polyester is an aliphatic polyester with a simple, regularly repeating ester bond structure. The presence of ester bonds in the molecular chain results in the presence of carboxyl and hydroxyl groups in fully biodegradable materials, making them particularly sensitive to water and heat. At high temperatures and in humid environments, moisture within the fully biodegradable polyester chips can cause hydrolysis, leading to molecular chain depolymerization and the formation of segments with terminal carboxyl and hydroxyl groups. As the fully biodegradable polyester approaches its glass transition temperature, its molecular weight decreases significantly with increasing hydrolysis time. If fully biodegradable polyester chips are packaged without drying, the moisture content in the chips directly affects the shelf life of the product and, consequently, the stability of downstream processing. Therefore, prior to packaging and for downstream melt processing, the chips must be thoroughly dried and the moisture content in the system strictly controlled to prevent excess moisture from causing hydrolysis during processing, which can lead to molecular chain breakage and a decrease in molecular weight, thus affecting the physical properties of the final product.

[0003] In the industrial production of fully biodegradable polyester, after polymerization, the pellets are typically sliced ​​using either air-cooled strands or underwater pelletizing. Air-cooled strands absorb moisture from the cooling air during the cooling process, resulting in a moisture content of approximately 0.06% for the pelletized pellets. Centrifugal dehydration is typically used after underwater pelletizing, resulting in a moisture content of approximately 0.2%. Regardless of the slicing method used, if the pellets are directly bagged and packaged, the moisture in the pellets can easily lead to hydrolysis.

[0004] The existing drying method, traditional hot air drying, takes a long time. Although it can reduce the moisture content of the output material to a predetermined value, hydrolysis reaction occurs during the drying process, and when the moisture content in the slices drops to a certain level in the later stage of drying, local condensation reaction is prone to occur. Therefore, there is an urgent need to provide a new drying method to improve the above problems. Summary of the Invention

[0005] The purpose of the present invention is to provide a method and system for drying fully biodegradable polyester chips.

[0006] According to a first aspect of the present invention, a drying system for polyester chips is provided, which includes a buffer silo, a dryer connected to the outlet of the buffer silo, a first air supply device for continuously introducing gas into the buffer silo, a second air supply device for continuously introducing gas into the dryer, and a dew point testing device arranged at the air outlet of the buffer silo and a dew point testing device arranged at the air outlet of the dryer. The dryer is provided with a dynamic component for keeping the polyester chips dynamic.

[0007] In one or more embodiments, the first air supply device includes a first heater connected to the air inlet of the buffer silo, and a first stirring assembly is provided in the buffer silo;

[0008] The second air supply device includes a second heater connected to the air inlet of the dryer.

[0009] In one or more embodiments, the dynamic component includes a hollow screw conveying shaft and a transmission device connected to the hollow screw conveying shaft, and the dryer is a single-shaft spiral stirring dryer, which includes a shell, at least one stage of the hollow screw conveying shaft disposed in the shell, and at least one transmission device disposed outside the shell, one transmission device is connected to one hollow screw conveying shaft, two adjacent hollow screw conveying shafts are separated by a partition, and the conveying directions of the two adjacent hollow screw conveying shafts are opposite, and an air-material channel is left between the partition and the shell;

[0010] The shaft body of the last-stage hollow spiral conveyor shaft is hollow inside and has air holes on its surface. One end of the shaft is connected to a rotary joint provided with an air inlet, and the other end is connected to the transmission device. The discharge port of the dryer is arranged below one end of the last-stage hollow spiral conveyor shaft close to the air inlet.

[0011] In one or more embodiments, the drying system further comprises a first gas purification circulation device for purifying and recycling the gas flowing out of the buffer silo;

[0012] The first gas purification circulation device includes a filter, and a first cooler, a first dehumidifier and a first fan connected to the filter in sequence. The air outlet of the cache silo is connected to the filter. An exhaust port is provided on the pipeline connecting the filter and the first cooler. The air outlet of the first fan is connected to the first air supply device.

[0013] In one or more embodiments, the drying system further comprises a second gas purification circulation device for purifying and recycling the gas flowing out of the dryer;

[0014] The second gas purification circulation device includes a cyclone separator, and a catalytic oxidizer, a second cooler, a second dehumidifier and a second fan connected to the cyclone separator in sequence. The air outlet of the dryer is connected to the cyclone separator, and the air outlet of the second fan is connected to the second air supply device.

[0015] In one or more embodiments, the drying system further comprises a cooling silo connected to the discharge port of the dryer, wherein a spiral coil is provided in the cooling silo, and a plurality of through holes are provided on the coil, one end of the coil is an air inlet end, and an air outlet is provided at the upper portion of the cooling silo;

[0016] The air outlet of the second fan is connected to the air inlet end of the coil, and the air outlet of the cooling silo is connected to the second air supply device.

[0017] The second aspect of the present invention provides a method for drying polyester chips using the drying system according to the first aspect of the present invention, the method comprising the steps of:

[0018] (1) In a buffer silo, a first hot air flow is used to pre-dehumidify the polyester chip raw material to obtain pre-dehumidified polyester chips;

[0019] (2) drying the pre-dehumidified polyester chips in a dryer using a second hot air flow to obtain dried polyester chips, wherein the drying temperature in the dryer is greater than the buffer temperature in the buffer silo;

[0020] The gas dew point temperature of the first hot air flow at the gas outlet of the buffer silo is ≤-10°C;

[0021] The gas dew point temperature of the second hot air flow at the gas outlet of the dryer is ≤-10°C.

[0022] In one or more embodiments, the buffer temperature in the buffer silo is 90-130°C.

[0023] In one or more embodiments, the buffering time in the buffer silo is 0.1 to 2 hours.

[0024] In one or more embodiments, the gas dew point temperature of the first hot gas flow at the gas outlet of the buffer silo is -40°C to -10°C.

[0025] In one or more embodiments, the gas dew point temperature of the first hot gas flow at the gas inlet of the buffer silo is ≤-40°C.

[0026] In one or more embodiments, the drying temperature in the dryer is 100°C to 200°C.

[0027] In one or more embodiments, the drying time in the dryer is 0.5 to 5 hours.

[0028] In one or more embodiments, the gas dew point temperature of the second hot gas flow at the gas outlet of the dryer is -40°C to -10°C.

[0029] In one or more embodiments, the gas dew point temperature of the second hot gas stream at the gas inlet of the dryer is ≤ -40°C.

[0030] In one or more embodiments, the particle size of the polyester chip raw material is ≥1.5 mm.

[0031] In one or more embodiments, the moisture content of the polyester chip raw material is 0.03 to 0.3 wt %.

[0032] In one or more embodiments, the polyester chip raw material has a melt index of 10 to 80 g / 10 min (230° C., 2.16 kg).

[0033] In one or more embodiments, the residual monomer content of the polyester chip raw material is 1 to 5 wt %.

[0034] In one or more embodiments, the moisture content of the dried polyester chips is < 0.008 wt%.

[0035] In one or more embodiments, the dried polyester chips have a melt index of 3 to 50 g / 10 min (230° C., 2.16 kg).

[0036] In one or more embodiments, the residual monomer content of the dried polyester chips is <1 wt%. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Schematic diagram of the drying system in one or more embodiments of the present invention; wherein 1-buffer silo, 11-first stirring assembly, 2-dryer, 3-cooling silo, 31-coil, 41-first cyclone separator, 42-second cyclone separator, 5-catalytic oxidizer, 61-first cooler, 62-second cooler, 71-first dehumidifier, 72-second dehumidifier, 81-first fan, 82-second fan, 91-first heater, 92-second heater, b-rotary valve, c-filter.

[0038] Figure 2 Schematic diagram of a single-axis spiral stirring dryer in one or more embodiments of the present invention; wherein 21 is a feed port, 22 is a discharge port, 23 is an air inlet, 24 is an air outlet, 25 is a rotary joint, 26 is a vent, and 27 is a transmission device.

[0039] Figure 3 Schematic diagram of a two-stage single-shaft spiral stirring dryer in one or more embodiments of the present invention; wherein 21'-feed port, 22'-discharge port, 23'-air inlet, 24'-air outlet, 25'-rotary joint, 26'-air vent, 27'-transmission device, 28'-partition, 29'-gas channel. DETAILED DESCRIPTION

[0040] To facilitate understanding of the features and effects of the present invention by those skilled in the art, the following provides a general description and definition of the terms and expressions used in the specification and claims. Unless otherwise indicated, all technical and scientific terms used herein have the ordinary meanings as understood by those skilled in the art regarding the present invention. In the event of conflict, the definitions in this specification shall prevail.

[0041] The theories or mechanisms described and disclosed herein, whether correct or incorrect, should not limit the scope of the present invention in any way, that is, the present invention can be implemented without being limited by any specific theory or mechanism.

[0042] Herein, “comprising,” “including,” “containing” and similar terms encompass the meanings of “consisting essentially of” and “consisting of,” for example, when “A comprises B and C” is disclosed herein, “A consists essentially of B and C” and “A consists of B and C” should be deemed to have been disclosed herein.

[0043] Throughout this document, all features, such as values, amounts, amounts, and concentrations, specified in numerical ranges or percentage ranges are provided for simplicity and convenience only. Accordingly, the description of numerical ranges or percentage ranges should be considered to encompass and specifically disclose all possible subranges and individual values ​​within those ranges (including integers and fractions).

[0044] In this document, unless otherwise specified, percentage refers to mass percentage and ratio refers to mass ratio.

[0045] Herein, when describing embodiments or examples, it should be understood that they are not intended to limit the present invention to these embodiments or examples. On the contrary, all alternatives, modifications and equivalents of the methods and materials described herein are encompassed within the scope defined by the claims.

[0046] In this document, for the sake of brevity, not all possible combinations of the various technical features in each embodiment or example are described. Therefore, as long as there are no contradictions in the combination of these technical features, the various technical features in each embodiment or example can be combined in any way, and all possible combinations should be considered to be within the scope of this specification.

[0047] In this article, the gas-to-material ratio refers to the ratio of gas to material entering the buffer silo or dryer. The gas-to-material ratio entering the buffer silo is the ratio of the volume of the first hot air flow entering the buffer silo to the mass of the polyester chips. The gas-to-material ratio entering the dryer is the ratio of the volume of the second hot air flow entering the dryer to the mass of the pre-dehumidified polyester chips. For example, 1:(50-150) L / g means 1 L of gas is passed through for every 50-150 g of material. The gas-to-material ratio entering the buffer silo or dryer can be adjusted based on the dew point temperature at the outlet of each device. A higher gas-to-material ratio results in lower water content in the gas at the outlet and a lower dew point temperature. Conversely, a lower gas-to-material ratio results in higher water content in the gas at the outlet and a higher dew point temperature. The dew point temperature at the outlet can be measured using a dew point meter. For example, the gas-to-material ratio entering the buffer silo can be 1:(50-150) L / g, such as 1:50 L / g, 1:110 L / g, 1:150 L / g, or a range between any two values. For another example, the gas-to-material ratio entering the dryer can be 1:(10-100) L / g, such as 1:20 L / g, 1:60 L / g, 1:80 L / g, or a range between any two values.

[0048] The invention provides a drying method, comprising pre-dehumidifying fully biodegradable polyester chips in a buffer silo and then placing them in a dryer for deep drying; wherein the polyester chips are dried by hot air convection both in the buffer silo and in the dryer, the buffer temperature in the buffer silo is 90-130°C, the buffer time is 0.1-2 hours, and the gas dew point temperature at the gas outlet of the buffer silo is not higher than -10°C; the drying temperature in the dryer is 100-200°C, the drying temperature in the dryer is higher than the buffer temperature in the buffer silo, the drying time is 0.5-5 hours, the gas dew point temperature at the gas outlet of the dryer is not higher than -10°C, and the dryer is provided with a dynamic component for keeping the polyester chips dynamic; furthermore, after drying, the material enters a cooling silo for cooling.

[0049] At higher temperatures, moisture in the environment (including some moisture released from the polyester chips) and moisture within the polyester chips can easily cause polyester hydrolysis. In the present invention, polyester chips flow in and out of the buffer silo, and gas flows in and out of the buffer silo. The temperature within the buffer silo is relatively low, and convection of hot air within the buffer silo can carry away some of the moisture released from the polyester chips. At the same time, the present invention also requires controlling the dew point temperature of the gas at the gas outlet of the buffer silo. The dew point temperature at the gas outlet can reflect the moisture content in the environment within the buffer silo. By maintaining the dew point temperature at the gas outlet below -10°C, the environment within the buffer silo is always kept at a low dew point temperature, which can prevent the moisture content in the buffer silo from being too high and reduce the occurrence of polyester hydrolysis.

[0050] Polyester chips that have been pre-dehumidified in the buffer silo are fed into the dryer for deep drying. The drying temperature in the dryer is higher than the buffer temperature in the buffer silo. Low-dew-point gas is continuously introduced into the dryer, and hot air convection can continuously remove unreacted monomers and oligomers in the polyester chips, as well as the moisture released from the polyester chips. During the drying process, the polyester chips remain dynamic due to the action of the dynamic components to avoid adhesion. Similarly, the gas dew point temperature at the dryer outlet must be controlled. The gas dew point temperature at the outlet reflects the moisture content in the dryer environment. By maintaining the gas dew point temperature at the outlet below -10°C, the moisture content in the dryer can be prevented from being too high, reducing the occurrence of polyester hydrolysis reactions.

[0051] Polyester chip drying system

[0052] like Figure 1 As shown, the present invention provides a polyester chip drying system, comprising a buffer silo 1, a dryer 2 connected to the discharge port of the buffer silo 1, a first air supply device for continuously supplying gas into the buffer silo 1, a second air supply device for continuously supplying gas into the dryer 2, and a dew point testing device arranged at the air outlet of the buffer silo 1 and a dew point testing device arranged at the air outlet of the dryer 2. The dryer 2 is provided with a dynamic component for keeping the polyester chips dynamic.

[0053] Buffer silo 1 is provided with a feed inlet, a discharge port, an air inlet, and an air outlet, and dryer 2 is provided with a feed inlet, a discharge port, an air inlet, and an air outlet. As a further preferred embodiment, dew point measurement equipment is provided at the air inlet of buffer silo 1 and the air inlet of dryer 2. Exemplarily, the dew point measurement equipment is an online dew point meter.

[0054] As a further preferred solution, a first stirring assembly 11 for dynamically pre-dehumidifying the material is provided in the buffer silo 1. The first stirring assembly 11 can be a stirring assembly commonly used in the art, and when the first stirring assembly 11 rotates, the material is turned upward. For example, the first stirring assembly 11 can be a paddle-type stirring assembly.

[0055] The first gas supply device includes a first heater 91, and the first heater 91 is connected to the air inlet of the cache silo 1. The second gas supply device includes a second heater 92, and the second heater 92 is connected to the air inlet of the dryer 2. Specifically, the first heater 91 is used to heat the gas entering the cache silo 1; the second heater 92 is used to heat the gas entering the dryer 2. In a preferred embodiment, an air volume control valve is provided on the pipeline connecting the first heater 91 and the cache silo 1, and / or on the pipeline connecting the second heater 92 and the dryer 2, and the gas flow entering the cache silo 1 and / or the dryer 2 is controlled by providing the air volume control valve.

[0056] In some embodiments, the inner wall of the dryer 2 shell is provided with an interlayer into which thermal oil is passed. The shell is provided with a thermal oil outlet and a thermal oil inlet. The outer surface of the dryer 2 shell is further wrapped with a thermal insulation material. The temperature of the thermal oil can be the same as or higher than the temperature of the gas entering the dryer 2, and preferably the same as the temperature of the gas entering the dryer 2.

[0057] In some embodiments, the drying system of the present invention further comprises a cooling silo 3 connected to the discharge port of the dryer 2. The cooling silo 3 is provided with a feed port and a discharge port. The discharge port of the dryer 2 is connected to the feed port of the cooling silo 3. The discharge port of the cooling silo 3 is the outlet for the dried material. The material dried by the dryer 2 first enters the cooling silo 3 and is then packaged after cooling.

[0058] Furthermore, a spiral coil 31 is provided in the cooling silo 3, and a plurality of through holes are provided on the coil 31. One end of the coil 31 is the air inlet end, and the other end of the coil 31 can be closed or open. An air outlet is provided at the upper part of the cooling silo 3.

[0059] Low-temperature, dry gas enters the coil 31 through the air inlet of the cooling silo 3 (i.e., the air inlet end of the coil 31), flows out of the coil 31 through the through hole, and then exchanges heat and further moisture with the material in the cooling silo 3, and then flows out through the air outlet at the top of the cooling silo 3. The gas flowing out of the cooling silo 3 has an extremely low water content and can also be mixed with the gas entering the buffer silo 1 from the gas inlet in the pipeline leading to the first heater 91, and then enter the first heater 91, realizing the recycling of the gas; and / or, it can be mixed with the gas entering the dryer 2 from the gas inlet in the pipeline leading to the second heater 92, and then enter the second heater 92, realizing the recycling of the gas.

[0060] When the drying system of the present invention dries the raw materials, the first airflow is heated to a set temperature in the first heater 91 and then enters the buffer silo 1. The second airflow is heated to a set temperature in the second heater 92 and then enters the dryer 2. The material enters the buffer silo 1 from the feed port of the buffer silo 1, is pre-dehumidified by the first airflow having a certain temperature through thermal convection, and is then discharged from the discharge port of the buffer silo 1 into the dryer 2. In the dryer 2, the material is further dried by the second airflow having a certain temperature through thermal convection, and is then discharged from the discharge port of the dryer 2. Preferably, the material discharged from the discharge port of the dryer 2 enters the cooling silo 3, is cooled and further dried in the cooling silo 3, and is then discharged from the discharge port of the cooling silo 3.

[0061] Furthermore, a first cyclone separator 41 is provided between the material raw material inlet of the polyester chips entering the drying system of the present invention and the buffer silo 1 .

[0062] Furthermore, a rotary valve b is provided on the pipe connecting the first cyclone separator 41 and the inlet of the cache silo 1, the pipe connecting the outlet of the cache silo 1 and the inlet of the dryer 2, the pipe connecting the outlet of the dryer 2 and the inlet of the cooling silo 3, and the pipe connecting the outlet of the cooling silo 3 and the outlet of the dried material. The rotary valve b can be used to adjust the flow direction and flow rate of the material.

[0063] Furthermore, the drying system of the present invention also includes a first gas purification and circulation device for purifying and recycling the gas flowing out of the buffer silo 1. The first gas purification and circulation device includes a filter c, and a first cooler 61, a first dehumidifier 71, and a first fan 81, which are sequentially connected to the filter c. The air outlet of the buffer silo 1 is connected to the filter c, and the air outlet of the first fan 81 is connected to the first heater 91. The pipeline connecting the filter c and the first cooler 61 is also provided with an exhaust port for allowing some moisture to exit the drying system.

[0064] In actual application, the gas discharged from the gas outlet of the buffer silo 1 enters the filter c, and after filtration, a small portion of the wet gas is separated and directly discharged from the drying system, and then enters the first cooler 61, is cooled in the first cooler 61, and then enters the first dehumidifier 71, is dehumidified in the first dehumidifier 71, and then enters the first fan 81. The gas flows out of the first fan 81 and enters the first heater 91. After being heated to a specific temperature by the first heater 91, it enters the buffer silo 1 through the air inlet of the buffer silo 1. The gas inlet for the fresh low dew point gas entering the buffer silo 1 can be set on the pipeline connecting the first dehumidifier 71 and the first fan 81, and can also be set on the pipeline connecting the first fan 81 and the first heater 91.

[0065] Furthermore, the drying system of the present invention also includes a second gas purification circulation device for purifying and recycling the gas flowing out of the dryer 2. The second gas purification circulation device includes a second cyclone separator 42, and a catalytic oxidizer 5, a second cooler 62, a second dehumidifier 72, and a second fan 82 connected in sequence to the second cyclone separator 42. The air outlet of the dryer 2 is connected to the second cyclone separator 42, and the air outlet of the second fan 82 is connected to the second heater 92. As a further preferred embodiment, the air outlet of the second fan 82 is connected to the air inlet end of the coil 31 in the cooling silo 3, and the air outlet at the upper end of the cooling silo 3 is connected to the second heater 92.

[0066] In actual application, the gas discharged from the air outlet of dryer 2 enters the second cyclone separator 42, where it is separated from entrained solid and liquid impurities (dust removal), then enters the catalytic oxidizer 5, where small organic molecule impurities are removed, then enters the second cooler 62, where it is cooled, then enters the second dehumidifier 72, where it is dehumidified, and then enters the second fan 82. After flowing out of the second fan 82, the gas enters the cooling silo 3, where it exchanges heat and moisture with the material, then enters the second heater 92, where it is heated to a specific temperature, and then enters the dryer 2 through the air inlet. The gas inlet for fresh low-dew-point gas entering the dryer 2 is provided in the pipeline connecting the air outlet of the cooling silo 3 and the second heater 92.

[0067] The first dehumidifier 71 and the second dehumidifier 72 may be dehumidifiers commonly used in the art. For example, the first dehumidifier 71 and the second dehumidifier 72 may dehumidify the gas through the molecular sieves contained therein.

[0068] In some embodiments, the cooling temperature in the first cooler 61 is ≤60°C, for example, 30-60°C or 40-50°C; the cooling temperature in the second cooler 62 is ≤60°C, for example, 30-60°C, 40-50°C. The cooling temperature in the first cooler 61 and the cooling temperature in the second cooler 62 may be the same or different.

[0069] In the above embodiment, the dynamic component of the dryer 2 can be a spiral conveying component, a stirring component, a vibration component, or a drum component. Specifically, the dryer 2 can be a vertical dryer or a horizontal dryer. Vertical dryers include but are not limited to vibrating countercurrent dryers, tower dryers with stirring components, and fluidized bed dryers with stirring components. By adopting a vibrating countercurrent dryer, the material is not prone to "bridging" or agglomeration in a spiral vibration environment. By providing a stirring component in a tower dryer or a fluidized bed dryer, the material can be kept dynamically dry during the drying process to prevent material adhesion. Horizontal dryers include but are not limited to single-axis spiral stirring dryers, double-axis spiral stirring dryers, multi-axis spiral stirring dryers, and drum dryers.

[0070] Within dryer 2, the gas flow direction is opposite to the material flow direction. For example, in a vertical dryer, low-dew-point hot gas enters through the air inlet at the bottom of the dryer, passes through the material layer, and flows in the opposite direction to the material to dry it, creating a "reciprocating motion" within the dryer. In a horizontal dryer, the material flows in a plug flow, and the main gas flow direction is opposite to the material conveying direction.

[0071] In some embodiments, the dynamic component includes a hollow screw conveying shaft and a transmission device connected to the hollow screw conveying shaft. The dryer 2 is a single-axis spiral stirring dryer, which includes a shell, at least one hollow screw conveying shaft arranged in the shell, and at least one transmission device arranged outside the shell. One transmission device is connected to one hollow screw conveying shaft. The two adjacent hollow screw conveying shafts are separated by a partition, and the conveying directions of the two adjacent hollow screw conveying shafts are opposite. An air material channel is left between the partition and the shell; the shaft body of the last-stage hollow screw conveying shaft is hollow inside and has air holes on the surface. One end of the shaft is connected to a rotary joint provided with an air inlet, and the other end is connected to the transmission device. The discharge port of the dryer is arranged below one end of the last-stage hollow screw conveying shaft near the air inlet.

[0072] The hollow spiral conveyor shaft includes a central shaft and conveying blades spirally wrapped around the central shaft. The transmission device drives the conveying blades to rotate by connecting to the central shaft, thereby promoting material transportation.

[0073] The gas enters the last stage hollow spiral conveyor shaft from the air inlet provided on the rotary joint, and flows out from the air vent of the last stage hollow spiral conveyor shaft into the shell to dry the material, and finally flows out from the air outlet of the single-axis spiral stirring dryer. The conveying direction of the material at the same stage in the shell is opposite to the mainstream flow direction of the gas.

[0074] Specifically, the single-shaft spiral stirring dryer can be a one-stage, two-stage or above single-shaft spiral stirring dryer. The number of hollow spiral conveying shafts and the number of transmission devices contained in the one-stage, two-stage or above single-shaft spiral stirring dryer are the same as its number of stages, and one transmission device is connected to one hollow spiral conveying shaft.

[0075] The structure of the first-stage single-axis spiral stirring dryer is as follows: Figure 2 The housing of the single-shaft spiral agitator dryer is provided with a feed inlet 21, a discharge inlet 22, and an air outlet 24. The feed inlet 21 and the air outlet 24 are located above the end of the hollow spiral conveyor shaft away from the air inlet 23, while the discharge inlet 22 is located below the end of the hollow spiral conveyor shaft near the air inlet 23. The central axis of the hollow spiral conveyor shaft is hollow and has a plurality of air vents 26 on its surface.

[0076] Material (e.g., polyester chips, fully biodegradable polyester chips) enters the single-shaft spiral agitator dryer through feed port 21 and exits through discharge port 22. Low-dew-point gas enters through inlet 23 of rotary joint 25 and exits through vents 26 on the hollow spiral conveyor shaft. It passes through the material layer within the spiral, exchanging heat and water with the material before being discharged through outlet 24. The material is conveyed in the opposite direction of the main gas flow. Driven by a transmission device 27, the hollow spiral conveyor shaft rotates, further driving the material. The material's interface is updated under the action of the hollow spiral conveyor shaft, and the material moves in a plug flow to prevent adhesion.

[0077] The structure of the two-stage or above single-shaft spiral stirring dryer is similar, such as Figure 3 As shown, taking a two-stage single-axis spiral stirring dryer as an example, each stage includes a hollow spiral conveying shaft and a transmission device 27'. The two-stage hollow spiral conveying shafts are stacked up and down and separated by a partition 28'. The conveying directions of the upper and lower hollow spiral conveying shafts are opposite. The starting end of the hollow spiral conveying shaft of the lower stage is located below the end of the hollow spiral conveying shaft of the upper stage, so that the conveying directions of the upper and lower materials are opposite; the channel formed between the partition 28' and the shell is the air channel 29', which is the discharge port of the upper-stage single-axis spiral stirring dryer and the feed port of the lower-stage single-axis spiral stirring dryer, and also the air outlet of the lower-stage single-axis spiral stirring dryer and the air inlet of the upper-stage single-axis spiral stirring dryer.

[0078] The air inlet 23' of the entire single-axis spiral stirring dryer is arranged on a rotary joint 25' connected to one end of the next-stage hollow spiral conveying shaft, and the discharge port 22' is arranged below the end of the next-stage hollow spiral conveying shaft close to the air inlet 23', that is, the discharge port 22' and the air inlet 23' are located on the same side of the single-axis spiral stirring dryer; the feed port 21' and the air outlet 24' are arranged above the previous-stage hollow spiral conveying shaft and on the same side as the discharge port 22' and the air inlet 23' (when the single-axis spiral stirring dryer is a 2N-stage single-axis spiral stirring dryer). Only the central axis of the next-stage hollow spiral conveying shaft is hollow and has a vent hole 26' on its surface. The gas in the next-stage hollow spiral conveying shaft is discharged from the vent hole 26' into the shell, passes through the material layer in the next-stage spiral to perform hydrothermal exchange with the material, and the exchanged gas enters the material layer in the previous-stage spiral through the gas-material channel 29' to perform hydrothermal exchange with the material, and is finally discharged from the gas outlet 24'. The material conveying direction of each stage is opposite to the mainstream flow direction of the gas.

[0079] Preferably, the diameter of the vent holes 26, 26' is 0.1-1 mm, preferably 0.4-0.6 mm or 0.2-0.8 mm.

[0080] Preferably, the gap between the portion of the hollow spiral conveying shaft closest to the housing and the housing is less than 1 mm.

[0081] Preferably, the spiral pitch of the hollow spiral conveying shaft is 100-500 mm, preferably 250-350 mm, for example 320 mm.

[0082] Drying method

[0083] The present invention provides a method for drying polyester chips, which uses the above drying system to dry the polyester chips. The method comprises the following steps:

[0084] (1) In a buffer silo, a first hot air flow is used to pre-dehumidify the polyester chip raw material to obtain pre-dehumidified polyester chips;

[0085] (2) drying the pre-dehumidified polyester chips in a dryer using a second hot air flow to obtain dried polyester chips, wherein the drying temperature in the dryer is greater than the buffer temperature in the buffer silo;

[0086] The gas dew point temperature of the first hot air flow at the gas outlet of the buffer silo is ≤-10°C;

[0087] The gas dew point temperature of the second hot air flow at the gas outlet of the dryer is ≤-10°C.

[0088] Preferably, in step (1), the gas dew point temperature of the first hot air flow at the gas outlet of the buffer silo is controlled to be -40°C to -10°C, for example, -40°C, -35°C, -30°C, or within a range consisting of any two values.

[0089] Furthermore, the gas dew point temperature of the first hot air flow at the air inlet of the buffer silo is ≤-40°C, such as -40°C, -45°C, -50°C, or within a range consisting of any two values.

[0090] In the present invention, the buffer temperature refers to the set temperature within the buffer silo, and the buffer time refers to the residence time of the material within the buffer silo. In some embodiments, the first hot air flow pre-dehumidifies the polyester chip raw material by convection. In some embodiments, the buffer temperature within the buffer silo is 90-130°C, preferably 90-120°C, 100-115°C, for example, 105°C. The buffer time within the buffer silo is 0.1-2 hours, preferably 0.5-1 hour.

[0091] In some embodiments, a first stirring assembly is provided within the buffer silo. The stirring mechanism of the first stirring assembly is to stir the material upward during rotation. For example, the first stirring assembly is a paddle-type stirring assembly. The stirring speed of the first stirring assembly is 5 to 50 rpm, preferably 10 to 25 rpm, 20 to 30 rpm, or 15 to 40 rpm.

[0092] In step (2), the gas dew point temperature of the second hot air flow at the outlet of the dryer is -40°C to -10°C, for example, -40°C, -20°C, -10°C, or within a range consisting of any two values.

[0093] Furthermore, the gas dew point temperature of the second hot air flow at the air inlet of the dryer is ≤-40°C, such as -40°C, -45°C, -50°C, or a range between any two values.

[0094] In step (2), the pre-dehumidified polyester chips are convectively dried using a second hot air flow. In the dryer, the drying temperature can be 100-200° C., for example, 120° C., 150° C., 180° C., or a range between any two values. The drying time in the dryer can be 0.5-5 hours, for example, 1 hour, 3 hours, 5 hours, or a range between any two values.

[0095] In a preferred embodiment, the dryer is the above-described single-shaft spiral agitator dryer. Preferably, the single-shaft spiral agitator dryer has a rotational speed of 2 to 50 rpm, preferably 5 to 30 rpm, for example 6 rpm. The material filling rate within the single-shaft spiral agitator dryer is 5 to 95%, preferably 40 to 85%, for example 60%.

[0096] The first hot air flow and the second hot air flow are each independently selected from one or more of air, nitrogen and an inert gas. Preferably, the first hot air flow and the second hot air flow are the same gas.

[0097] In some embodiments, the polyester chips are polyglycolic acid chips; preferably, the polyester chips are fully biodegradable polyglycolic acid chips. Polyglycolic acid chips are copolymers containing repeating units of glycolic acid.

[0098] In a preferred embodiment, the dried polyester chips are sent to a cooling silo for cooling. The temperature of the cooling silo can be ≤60°C, for example, 20°C, 40°C, 50°C, or between any two numerical values; preferably 30-60°C. Preferably, the temperature of the cooling silo is the same as the cooling temperature of the cooler 62.

[0099] In another preferred embodiment, the method includes conveying the pelletized polyester chips to a buffer silo in a low dew point environment. The low dew point environment has a gas dew point temperature of ≤ -30°C, such as -30°C, -40°C, -45°C, or a range between any two values.

[0100] The polyester chip raw material may have a particle size of ≥1.5 mm, preferably 1.5 to 6 mm or 2 to 6 mm. Furthermore, the polyester chip raw material may have a moisture content of 0.03 to 0.3 wt %. Furthermore, the polyester chip raw material may have a melt index of 10 to 80 g / 10 min (230° C., 2.16 kg). Furthermore, the polyester chip raw material may have a residual monomer content of 1 to 5 wt %.

[0101] The moisture content of the dried polyester chips may be less than 0.008 wt %. Furthermore, the melt index of the dried polyester chips may be 3 to 50 g / 10 min (230° C., 2.16 kg). Furthermore, the residual monomer content of the dried polyester chips may be less than 1 wt %.

[0102] The embodiments of the present invention have the following beneficial effects:

[0103] 1. Pre-dehumidify the polyester chip raw materials in the buffer silo and control the gas dew point temperature at the outlet of the buffer silo to solve the problem of material hydrolysis caused by storing polyester chips in the buffer silo before drying in industrial production.

[0104] 2. Add a stirring component to the buffer silo to prevent materials from sticking and bridging in the buffer silo.

[0105] 3. During the drying process, the polyester chips are dynamically dried to prevent adhesion. At the same time, the gas dew point temperature at the dryer outlet is controlled to prevent the chips from hydrolyzing during the drying process.

[0106] 4. The use of a single-shaft spiral agitator dryer creates plug flow within the dryer, enabling continuous production without mixed flow that could lead to uneven drying of the slices. This also allows for rapid renewal of the material-air contact surface, facilitating moisture removal. Existing hot air drying processes typically adjust process parameters based solely on whether the output moisture content meets standards, resulting in prolonged drying times and ignoring the adverse effects of ambient moisture on polyester materials during the drying process.

[0107] 5. Equipped with a gas purification and circulation device. The high-temperature gas discharged from the buffer silo is mainly water. After filtering, a portion is discharged, and the remaining portion is cooled and dehydrated. The purified gas can be reused. The high-temperature gas discharged from the dryer contains a small amount of monomers and oligomers. After passing through the catalytic oxidizer, the monomers and oligomers in the gas are completely removed. After cooling, the gas is dehydrated and purified, and can be reused. Furthermore, the purified gas first passes through the cooling silo to cool the material, which can increase the gas temperature and further save energy when the gas is recycled.

[0108] The present invention will be further described below in conjunction with specific examples. It should be understood that these examples are intended to illustrate the present invention only and are not intended to limit the scope of the invention. The experimental methods in the following examples, for which specific conditions are not specified, are generally based on conventional conditions or the conditions recommended by the manufacturer. Unless otherwise stated, percentages and parts are calculated by weight.

[0109] Test method:

[0110] 1. Moisture test

[0111] Refer to GB / T37191-2018 Determination of moisture content of raw rubber, Karl Fischer method.

[0112] 2. Melt index test

[0113] (1) Set the test temperature of the test instrument to 230°C and preheat the instrument; (2) Place 6-8 g of dry polymer into a barrel through a funnel and compact the material with a piston; (3) After heating for 4 min, cut a section every 10 seconds under a 2.16 kg weight, obtaining a total of ten sections; (4) Weigh the mass of each sample and calculate its MFR.

[0114] MFR = 600 W / t (g / 10 min), where W is the average mass of each sample segment and t is the time interval between each segment cutting.

[0115] 3. Particle size test

[0116] Place the particles in a 4-10 mesh sieve and use mechanical vibration or manual method to make the particles pass through the sieve until the desired particles are obtained.

[0117] 4. Residual monomer test

[0118] Take about 0.5g of sample and place it in a sealed container. Accurately add 15ml of hexafluoroisopropanol to dissolve it. After dissolution is complete, transfer the test solution to a 100ml round-bottom (flat-bottom) flask, add 15ml of hexafluoroisopropanol and brush it clean in a sealed container. Transfer it to the flask, accurately add 10ml of acetone, shake to precipitate the polymer, shake to dissolve, filter, and take the filtrate; take 1μL each of the above-mentioned reference solution and test solution, inject them into the gas chromatograph, record the chromatogram, and calculate the content of residual small molecules.

[0119] The raw materials of the following specific examples are: the particle size of the polyglycolic acid chips before entering the drying system is 2.8 mm, the moisture content is 0.2%, the melt index is 80 g / 10 min (230°C, 2.16 kg), the residual monomer is 3%, and the material density of the polyglycolic acid chips is 1.5 g / cm 3 , bulk density 1g / cm 3 .

[0120] In the embodiment, the tower dryer and the first-stage single-axis spiral stirring dryer are both non-standard customized, and the dew point testing equipment is a LY60SP intelligent dew point meter.

[0121] Example 1

[0122] use Figure 1 The drying system shown dries polyglycolic acid slices, wherein a paddle stirring assembly is provided in the buffer hopper 1, and the dryer 2 is specifically a one-stage single-axis spiral stirring dryer. The diameter of the vent hole of the hollow spiral conveying shaft is 0.5 mm, the spiral pitch of the hollow spiral conveying shaft is 320 mm, and the gap between the hollow spiral conveying shaft and the shell is 0.5 mm.

[0123] The gas entering the buffer silo is air, the gas dew point temperature at the buffer silo air inlet is -50°C, the buffer silo temperature is 120°C, the stirring speed is 12 rpm, the buffer time is 0.5h, the temperature of the cooler 61 is 40°C, and the gas dew point temperature at the buffer silo gas outlet is -25°C;

[0124] The gas entering the dryer is air, the gas dew point temperature at the dryer air inlet is -50°C, the temperature of the single-shaft spiral stirrer dryer is 190°C, the material filling rate in the dryer is 60%, the stirring rate is 6 rpm, the dryer jacket temperature is 190°C, the gas dew point temperature at the dryer gas outlet is -35°C, the drying time is 5h, the temperature of the cooler 62 is 40°C, and the temperature in the cooling silo is 60°C;

[0125] The moisture content of the polyester chips after drying was measured to be 0.0028 wt %, the melt index was 24 g / 10 min, and the residual monomer content was 0.3 wt %.

[0126] Example 2

[0127] The polyglycolic acid slices were dried using the same drying system as in Example 1.

[0128] The gas entering the buffer silo is air, the gas dew point temperature at the buffer silo air inlet is -50°C, the buffer silo temperature is 130°C, the stirring speed is 6 rpm, the buffer time is 0.1h, the temperature of the cooler 61 is 40°C, and the gas dew point temperature at the buffer silo gas outlet is -20°C;

[0129] The gas entering the dryer is air, the gas dew point temperature at the dryer air inlet is -50°C, the temperature of the single-shaft spiral stirring dryer is 180°C, the material filling rate in the dryer is 85%, the stirring rate is 10 rpm, the jacket temperature is 180°C, the gas dew point temperature at the dryer gas outlet is -20°C, the drying time is 4h, the temperature of the cooler 62 is 60°C, and the temperature in the cooling silo is 60°C;

[0130] The moisture content of the polyester chips after drying was measured to be 0.0035 wt %, the melt index was 31 g / 10 min, and the residual monomer content was 0.6 wt %.

[0131] Example 3

[0132] The polyglycolic acid slices were dried using the same drying system as in Example 1.

[0133] The gas entering the buffer silo is air, the gas dew point temperature at the buffer silo air inlet is -50°C, the buffer silo temperature is 90°C, the stirring speed is 20 rpm, the buffer time is 1 hour, the temperature of the cooler 61 is 40°C, and the gas dew point temperature at the buffer silo gas outlet is -10°C;

[0134] The gas entering the dryer is air, the gas dew point temperature at the dryer air inlet is -50°C, the temperature of the single-shaft spiral stirring dryer is 190°C, the material filling rate in the dryer is 70%, the stirring rate is 14 rpm, the jacket temperature is 190°C, the gas dew point temperature at the dryer gas outlet is -10°C, the drying time is 3h, the temperature of cooler 62 is 50°C, and the temperature in the cooling silo is 50°C;

[0135] The moisture content of the polyester chips after drying was measured to be 0.0041 wt %, the melt index was 38 g / 10 min, and the residual monomer content was 0.5 wt %.

[0136] Example 4

[0137] The polyglycolic acid slices were dried using the same drying system as in Example 1.

[0138] The gas entering the buffer silo is air, the gas dew point temperature at the buffer silo air inlet is -50°C, the buffer silo temperature is 100°C, the stirring speed is 20 rpm, the buffer time is 2h, the temperature of the cooler 61 is 50°C, and the gas dew point temperature at the buffer silo gas outlet is -20°C;

[0139] The gas entering the dryer is air, the gas dew point temperature at the dryer air inlet is -50°C, the temperature of the single-shaft spiral stirring dryer is 200°C, the material filling rate in the dryer is 40%, the stirring rate is 28 rpm, the jacket temperature is 200°C, the gas dew point temperature at the dryer gas outlet is -35°C, the drying time is 0.5h, the temperature of the cooler 62 is 60°C, and the temperature in the cooling silo is 60°C;

[0140] The moisture content of the polyester chips after drying was measured to be 0.0046 wt %, the melt index was 47 g / 10 min, and the residual monomer content was 0.9 wt %.

[0141] Example 5

[0142] use Figure 1 The drying system shown is used to dry polyglycolic acid chips, wherein the dryer 2 is specifically a tower dryer with a stirring component.

[0143] The gas entering the buffer silo is air, the gas dew point temperature at the buffer silo air inlet is -50°C, the buffer silo temperature is 120°C, the stirring speed is 10 rpm, the buffer time is 0.5h, the temperature of the cooler 61 is 50°C, and the gas dew point temperature at the buffer silo gas outlet is -20°C;

[0144] The gas entering the dryer is air, the dew point temperature of the gas at the dryer inlet is -50°C, the temperature of the vertical drying tower is 150°C, the material filling rate is 29%, the stirring rate is 20 rpm, the jacket temperature is 150°C, the dew point of the dryer gas outlet is -30°C, the drying time is 3h, the temperature of the cooler 62 is 60°C, and the temperature in the cooling silo is 60°C;

[0145] The moisture content of the polyester chips after drying was measured to be 0.0029 wt %, the melt index was 28 g / 10 min, and the residual monomer content was 0.4 wt %.

[0146] Example 6

[0147] The polyglycolic acid slices were dried using the same drying system as in Example 5.

[0148] The gas entering the buffer silo is air, the gas dew point temperature at the buffer silo air inlet is -50°C, the buffer silo temperature is 120°C, the stirring speed is 15 rpm, the buffer time is 0.2h, the temperature of the cooler 61 is 50°C, and the gas dew point temperature at the buffer silo gas outlet is -10°C;

[0149] The gas entering the dryer is air, the dew point temperature of the gas at the dryer inlet is -50°C, the temperature of the vertical drying tower is 140°C, the material filling rate is 48%, the stirring rate is 20 rpm, the jacket temperature is 140°C, the dew point of the dryer gas outlet is -30°C, the drying time is 5h, the temperature of the cooler 62 is 60°C, and the temperature in the cooling silo is 60°C;

[0150] The moisture content of the polyester chips after drying was measured to be 0.0038 wt %, the melt index was 41 g / 10 min, and the residual monomer content was 0.7 wt %.

[0151] Comparative Example 1

[0152] The polyglycolic acid chips were dried using the same drying system as in Example 1. The difference between this comparative example and Example 1 is that the gas-to-material ratio entering the buffer silo and the gas-to-material ratio entering the dryer are reduced, and the gas dew point temperature at the gas outlet of the buffer silo and the gas dew point temperature at the gas outlet of the dryer are both controlled at 0°C.

[0153] The moisture content of the polyester chips after drying was measured to be 0.0048 wt%, the melt index was 60 g / 10 min, and the residual monomer content was 1.3 wt%. Although the moisture content of the polyester chips after drying was below 0.005 wt%, the residual monomer test results and the melt index test results were significantly higher than the test results of Example 1.

[0154] Comparative Example 2

[0155] The polyglycolic acid slices were dried using the same drying system as in Example 1.

[0156] The buffer silo is only used for the intermediate buffering of incoming polyglycolic acid chips. No low dew point heating gas is passed through it. The stirring speed is 12 rpm and the buffering time is 0.5h.

[0157] The gas entering the dryer is air, the gas dew point temperature at the dryer air inlet is -50°C, the temperature of the single-shaft spiral stirrer dryer is 190°C, the material filling rate in the dryer is 60%, the stirring rate is 6 rpm, the dryer jacket temperature is 190°C, the gas dew point temperature at the dryer gas outlet is -35°C, the drying time is 5h, the temperature of the cooler 62 is 60°C, and the temperature in the cooling silo is 60°C;

[0158] The moisture content of the polyester chips after drying was measured to be 0.005 wt %, the melt index was 73 g / 10 min, and the residual monomer content was 1.43 wt %.

[0159] The difference between this comparative example and Example 1 is that the polyester chips are temporarily stored in a buffer silo, and the buffer silo does not pass low dew point heating gas for pre-dehydration. The chips are directly dried in the dryer. Although the moisture content of the polyester chips can be reduced to 0.005wt%, the residual monomer test results and the melt index test results are significantly higher than the test results of Example 1.

Claims

1. A polyester chip drying system, characterized in that: The drying system includes a buffer silo, a dryer connected to the outlet of the buffer silo, a first air supply device for continuously supplying gas into the buffer silo, a second air supply device for continuously supplying gas into the dryer, and a dew point testing device arranged at the air outlet of the buffer silo and a dew point testing device arranged at the air outlet of the dryer. The dryer is provided with a dynamic component for keeping the polyester chips dynamic.

2. The drying system according to claim 1, wherein: The first air supply device includes a first heater connected to the air inlet of the buffer silo, and a first stirring component is provided in the buffer silo; The second air supply device includes a second heater connected to the air inlet of the dryer.

3. The drying system according to claim 1, wherein: The dynamic component includes a hollow screw conveying shaft and a transmission device connected to the hollow screw conveying shaft. The dryer is a single-shaft spiral stirring dryer, which includes a shell, at least one stage of the hollow screw conveying shaft disposed in the shell, and at least one transmission device disposed outside the shell, one transmission device is connected to one hollow screw conveying shaft, two adjacent hollow screw conveying shafts are separated by a partition, and the conveying directions of the two adjacent hollow screw conveying shafts are opposite, and an air material channel is left between the partition and the shell; The shaft body of the last-stage hollow spiral conveyor shaft is hollow inside and has air holes on its surface. One end of the shaft is connected to a rotary joint provided with an air inlet, and the other end is connected to the transmission device. The discharge port of the dryer is arranged below one end of the last-stage hollow spiral conveyor shaft close to the air inlet.

4. The drying system according to any one of claims 1 to 3, characterized in that: The drying system further includes a first gas purification circulation device for purifying and recycling the gas flowing out of the buffer silo; The first gas purification circulation device includes a filter, and a first cooler, a first dehumidifier and a first fan connected to the filter in sequence. The air outlet of the cache silo is connected to the filter. An exhaust port is provided on the pipeline connecting the filter and the first cooler. The air outlet of the first fan is connected to the first air supply device.

5. The drying system according to any one of claims 1 to 3, characterized in that: The drying system further includes a second gas purification circulation device for purifying and recycling the gas flowing out of the dryer; The second gas purification circulation device includes a cyclone separator, and a catalytic oxidizer, a second cooler, a second dehumidifier and a second fan connected to the cyclone separator in sequence. The air outlet of the dryer is connected to the cyclone separator, and the air outlet of the second fan is connected to the second air supply device.

6. The drying system according to claim 5, characterized in that The drying system further comprises a cooling silo connected to the discharge port of the dryer, wherein a spiral coil is provided in the cooling silo, and a plurality of through holes are provided on the coil, one end of the coil is an air inlet end, and an air outlet is provided at the upper part of the cooling silo; The air outlet of the second fan is connected to the air inlet end of the coil, and the air outlet of the cooling silo is connected to the second air supply device.

7. A method for drying polyester chips using the drying system according to any one of claims 1 to 6, characterized in that: The method comprises the steps of: (1) In a buffer silo, a first hot air flow is used to pre-dehumidify the polyester chip raw material to obtain pre-dehumidified polyester chips; (2) drying the pre-dehumidified polyester chips in a dryer using a second hot air flow to obtain dried polyester chips, wherein the drying temperature in the dryer is greater than the buffer temperature in the buffer silo; The gas dew point temperature of the first hot air flow at the gas outlet of the buffer silo is ≤-10°C; The gas dew point temperature of the second hot air flow at the gas outlet of the dryer is ≤-10°C.

8. The method according to claim 7, wherein Step (1) has one or more of the following characteristics: The buffer temperature in the buffer silo is 90-130°C; The cache time in the cache silo is 0.1 to 2 hours; The gas dew point temperature of the first hot air flow at the gas outlet of the buffer silo is -40°C to -10°C; The gas dew point temperature of the first hot air flow at the air inlet of the buffer silo is ≤-40°C.

9. The method according to claim 7, wherein Step (2) has one or more of the following characteristics: The drying temperature in the dryer is 100°C to 200°C; The drying time in the dryer is 0.5 to 5 hours; The gas dew point temperature of the second hot air flow at the outlet of the dryer is -40°C to -10°C; The gas dew point temperature of the second hot air flow at the air inlet of the dryer is ≤-40°C.

10. The method according to any one of claims 7 to 9, wherein The polyester chip raw material has the following characteristics: The particle size of the polyester chip raw material is ≥1.5mm; The moisture content of the polyester chip raw material is 0.03-0.3wt%; The melt index of the polyester chip raw material is 10 to 80 g / 10 min (230° C., 2.16 kg); The residual monomer content of the polyester chip raw material is 1 to 5 wt%; And the dried polyester chips have the following characteristics: The moisture content of the dried polyester chips is less than 0.008 wt%; The melt index of the dried polyester chips is 3 to 50 g / 10 min (230°C, 2.16 kg); The residual monomer content of the dried polyester chips is less than 1 wt%.

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