Polyethylene naphthalate melt polycondensation devolatilization quality detection auxiliary device and method

Abstract

The present application relates to the technical field of polyester detection technology synthesized by melt polycondensation method, and particularly relates to a polyethylene naphthalate melt polycondensation devolatilization quality detection auxiliary device and method, which is characterized in that a parallel branch is designed on the basis of the original experimental device, the flow direction of the by-product ethylene glycol devolatilized by valve control is designed without affecting the normal polymerization experiment; the high-temperature ethylene glycol gas subsequently flowing out is forcedly cooled to liquid in the double-circle coil pipe, finally the ethylene glycol is flushed out by the solvent injected through the flushing valve, and the mixture is collected in the collection tank and subjected to quantitative analysis, so as to obtain the devolatilization quality of ethylene glycol per unit time, and further realize the polyethylene naphthalate melt polycondensation devolatilization quality detection, and solve the problem that the volatile by-product ethylene glycol molecule is difficult to be liquefied under the conditions of high temperature and high vacuum in the polyethylene naphthalate melt polycondensation process, resulting in poor accuracy of devolatilization quality monitoring.

Description

Technical Field

[0001] This invention relates to the field of polyester detection technology via melt polycondensation, specifically to an auxiliary device and method for detecting the devolatilization quality of polyethylene naphthalate via melt polycondensation. Background Technology

[0002] Polyethylene naphthalate (PEN), as a high-performance polyester material, stands out among many high-performance materials due to its unique molecular structure. PEN is prepared primarily from dimethyl 2,6-naphthalenedicarboxylate (NDC) and ethylene glycol. The rigid naphthalene ring structure in its molecular backbone endows the molecular chain with a high degree of planarity and strong rigidity. This special structural characteristic gives PEN excellent thermal stability, high mechanical strength, excellent gas barrier properties, and optical properties, making it one of the key raw materials in cutting-edge fields such as new energy vehicles and flexible electronics, with a very broad application prospect.

[0003] Currently, PEN resin is mainly synthesized via melt polycondensation, which offers advantages such as continuous production and high efficiency. In the synthesis process, the polycondensation reaction of the intermediate ethylene glycol 2,6-naphthalenedicarboxylate (BHEN) under a dual-catalyst system is a crucial step. This reaction requires high temperature (260-320℃) and high vacuum (<100Pa) conditions (often equipped with a vacuum pump). Deviation is an important phenomenon during the reaction. Deviation refers to the process by which volatile substances (such as small molecule byproducts and unreacted monomers) escape from the liquid phase into the gas phase in the reaction system. Accurately detecting the devolatilization quality is crucial for understanding the progress of the reaction, controlling reaction conditions, and optimizing the production process. By monitoring the devolatilization quality, the changes in the content of volatile substances in the reaction system can be monitored in real time, determining whether the reaction has reached equilibrium. This allows for timely adjustments to parameters such as reaction temperature and vacuum level, ensuring the reaction proceeds in the expected direction and improving the product quality and production efficiency of PEN.

[0004] However, due to the unique characteristics of the PEN melt polycondensation reaction, conventional detection techniques and equipment often fail to function properly under high temperature and high vacuum conditions. On one hand, the gases released during the reaction are difficult to liquefy, making traditional detection methods based on gas liquefaction collection and analysis often ineffective in capturing all volatile substances, thus hindering effective devolatilization detection and leading to significant deviations in the results. On the other hand, conventional optical gas detection instruments are typically designed for ambient temperature and pressure environments; their sensors and optical systems are easily damaged under high temperature and high vacuum conditions, resulting in inaccurate results or even failure to perform detection. Therefore, under current technological conditions, once the PEN melt polycondensation reaction begins, researchers find it difficult to directly and accurately understand the actual progress of the reaction, posing significant challenges to their research.

[0005] Therefore, the existing lack of devolatilization quality monitoring data in the PEN resin melt polycondensation process makes reaction control difficult, process adjustments are blind and uncertain, affecting product quality control, leading to unstable product quality, and hindering the further development and application of PEN materials. Summary of the Invention

[0006] To address the problem of accurately detecting the devolatilization quality during the melt polycondensation of polyethylene naphthalate (PEN) in existing technologies, this invention provides an auxiliary device and method for detecting the devolatilization quality of PEN melt polycondensation.

[0007] To achieve the above objectives, the present invention employs the following technical solution: The present invention provides an auxiliary device for detecting the quality of melt polycondensation and devolatilization of polyethylene naphthalate, comprising a first three-way valve disposed between the melt polycondensation reactor and a vacuum pump, wherein the first three-way valve is sequentially connected to a flushing valve, a heat exchanger and a second three-way valve; the second three-way valve is connected to the vacuum pump and a first collection tank.

[0008] Optionally, a first ball valve is provided between the first three-way valve and the vacuum pump.

[0009] Optionally, a first needle valve is provided between the first ball valve and the vacuum pump.

[0010] Optionally, a third three-way valve is provided between the first needle valve and the first ball valve, and the third three-way valve is connected to a second collection tank.

[0011] Optionally, a second ball valve is provided between the flushing valve and the heat exchanger.

[0012] Optionally, the flushing valve includes a fourth three-way valve disposed between the first three-way valve and the heat exchanger, the fourth three-way valve being connected to a third ball valve.

[0013] Optionally, a second needle valve is provided between the second three-way valve and the vacuum pump.

[0014] Optionally, a shut-off valve is provided between the second needle valve and the vacuum pump.

[0015] Optionally, the heat exchanger is a double-coil heat exchanger, the outlet of the heat exchanger is equipped with a thermocouple or a thermometer, and the heat exchange medium inside the heat exchanger is a cold trap.

[0016] The present invention also provides a method for detecting the melt polycondensation devolatilization quality of polyethylene naphthalate using the above-mentioned detection auxiliary device, comprising: Block the connection between the first three-way valve and the vacuum pump side, and at the same time connect the first three-way valve, the flushing valve, the heat exchanger and the second three-way valve, so that the molten polycondensation and devolatilization material of polyethylene naphthalate per unit time enters the heat exchanger and is forced to be cooled into a liquid state and stays in the heat exchanger. The connection between the first three-way valve and the flushing valve is blocked, while the first three-way valve and the vacuum pump are connected. Solvent is injected through the flushing valve to flush the liquid polyethylene naphthalate melt polycondensation devolatilization material remaining in the heat exchanger into the first collection tank for collection. Quantitative analysis was performed on the melt polycondensation devolatilization material of liquid polyethylene naphthalate collected in the first collection tank to obtain the quality test results of melt polycondensation devolatilization of polyethylene naphthalate.

[0017] Compared with the prior art, the present invention has the following beneficial effects: This invention provides an auxiliary device for detecting the devolatilization quality of polyethylene naphthalate (PEG) melt polycondensation. Through a parallel bypass design and valve control, this device achieves precise collection of ethylene glycol gas devolatilized per unit time without interfering with the normal operation of the main reactor. For the first time, it directly obtains ethylene glycol quality data at the experimental level, providing direct data support for monitoring the experimental process. It enables online detection of the polymerization process, suitable for continuous industrial production. It allows for periodic or real-time detection during continuous operation of the polymerization equipment without affecting the normal operation of the main reactor, eliminating the need for downtime sampling and significantly reducing labor and time costs. This device is suitable for industrial continuous production equipment, enabling dynamic monitoring of byproduct devolatilization behavior during polymerization, providing data support for online adjustment of process parameters and quality control. The device has a simple structure, requiring only the addition of a parallel branch, valves, and a double-coil heat exchanger to the existing polymerization unit. It requires no complex instruments or special testing equipment, resulting in low modification costs and easy operation. This design is easy to promote and apply, with good engineering feasibility and scale-up prospects. It is not only applicable to the melt polycondensation process of PEN, but its design concept and method are also applicable to polycondensation reactions under other high temperature and high vacuum conditions (such as polyester systems such as PET, PTT, and PBT). It has good versatility and promotion value.

[0018] This invention also provides a method for detecting the devolatilization quality of polyethylene naphthalate melt polycondensation using the aforementioned detection auxiliary device. This method selectively introduces devolatilized substances into the heat exchanger branch by switching the first three-way valve, while maintaining the connection between the main line and the vacuum pump. Without affecting the vacuum level and polymerization process within the reactor, it achieves independent collection of devolatilized substances per unit time, realizing truly online, uninterrupted detection. This provides a reliable basis for the kinetic study of the melt polycondensation process and industrial process control, and has significant practical value for the optimization and quality control of polyester synthesis processes. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of an auxiliary device for detecting the quality of melt polycondensation and devolatilization of polyethylene naphthalate according to the present invention.

[0020] Figure 2 This is a flowchart of a method for detecting the quality of melt polycondensation and devolatilization of polyethylene naphthalate according to the present invention.

[0021] Among them, 1-melt polycondensation reactor, 2-first three-way valve, 3-first ball valve, 4-third three-way valve, 5-second collection tank, 6-first needle valve, 7-flushing valve, 8-second ball valve, 9-heat exchanger, 10-second three-way valve, 11-first collection tank, 12-second needle valve, 13-stop valve, 14-vacuum pump, 15-double coil, 16-fourth three-way valve, 17-third ball valve. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0023] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0024] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0025] In the description of the embodiments of the present invention, it should be noted that if terms such as "upper," "lower," "horizontal," or "inner" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of the invention is in use, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. Furthermore, terms such as "first" and "second" are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0026] Furthermore, the use of the term "horizontal" does not imply that the component must be absolutely horizontal, but rather that it can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0027] In the description of the embodiments of the present invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in the present invention according to the specific circumstances.

[0028] The present invention will be further described in detail below with reference to specific embodiments. These descriptions are for explanation purposes only and are not intended to limit the scope of the invention.

[0029] See Figure 1 The present invention discloses an auxiliary device for detecting the quality of melt polycondensation devolatilization of polyethylene naphthalate, comprising a first three-way valve 2, a first ball valve 3, a third three-way valve 4 and a first needle valve 6 disposed between the melt polycondensation reactor 1 and the vacuum pump 14; The first three-way valve 2 is sequentially connected to a flushing valve 7, a second ball valve 8, a heat exchanger 9, a second three-way valve 10, a second needle valve 12, and a shut-off valve 13. The shut-off valve 13 is connected to a vacuum pump 14, and the second three-way valve 10 is connected to a first collection tank 11. The flushing valve 7 includes a fourth three-way valve 16 and a third ball valve 17. The fourth three-way valve 16 is disposed between the first three-way valve 2 and the second ball valve 8, and is connected to the third ball valve 17. The heat exchanger 9 is a heat exchanger with a built-in double coil 15. The outlet of the heat exchanger 9 is equipped with a thermocouple or a thermometer. The heat exchange medium inside the heat exchanger 9 is a cold trap.

[0030] The first ball valve 3 and the first needle valve 6 are main control valves. During normal polymerization experiments, the first ball valve 3 is fully open, which facilitates opening the path for ethylene glycol devolatilization. The function of the first needle valve 6 is to prevent non-gaseous components from being drawn out and blocking the pipeline due to excessive valve opening when adjusting the vacuum level using a vacuum pump. Similarly, the functions of the second ball valve 8 and the second needle valve 12 are the same as those of the first ball valve 3 and the first needle valve 6, which are to prevent non-gaseous components from being drawn out and blocking the pipeline due to excessive valve opening when adjusting the vacuum level using a vacuum pump. The flushing valve 7 is a combination of the fourth three-way valve 16 and the third ball valve 17. During use, the fourth three-way valve 16 is injected with solvent to flush out the devolatilized ethylene glycol, which is then collected in the first collection tank 11. The stop valve 13 is added to the branch to prevent the condensate in the branch from being drawn out after the vacuum pump is turned on, thus affecting the accuracy of the monitoring. The heat exchanger 9, with its built-in double-coil 15, significantly increases the heat exchange area and improves heat exchange efficiency. A thermocouple or thermometer is installed at the outlet of the heat exchanger 9 to detect its outlet temperature. In actual use, the outlet temperature of the heat exchanger 9 should be below 20°C to ensure that all the deashed material is forcibly cooled into a liquid state. The actual mass flow rate of ethylene glycol gas per unit time is less than or equal to the maximum condensation capacity of the heat exchanger 9 under this operating condition. The actual ethylene glycol volatilization rate is approximately 0.0005–0.0012 g / s (i.e., 0.03–0.07 g / min), which is very small. For the aforementioned double-coil 15 (with double-diameter spirals and a large area), under cooling in a cold trap (such as an ice-water bath or lower temperature), its maximum condensation capacity is far higher than this value (typically exceeding 0.1 g / s).

[0031] The bypass design employs a parallel branch design, where the designed parallel branch operates under the same temperature and pressure as the original system, ensuring the polymerization reaction continues to function normally under high temperature and low vacuum. The high-temperature ethylene glycol gas (devolve product from the melt polycondensation of polyethylene naphthalate) is generated during the polycondensation reaction in melt polycondensation reactor 1. The gas temperature is typically 130℃-200℃, and the system vacuum is generally less than 100Pa absolute pressure.

[0032] When rinsing with solvent, the solvent should generally be one with low viscosity, no reaction with the volatilized ethylene glycol, and stable chemical properties. Among these, anhydrous ethanol, a commonly used laboratory solvent, is preferred.

[0033] See Figure 2 The present invention also provides a method for detecting the melt polycondensation devolatilization quality of polyethylene naphthalate using the above-mentioned detection auxiliary device, comprising: S1: Block the connection between the first three-way valve 2 and the vacuum pump 14 side, while simultaneously connecting the first three-way valve 2, flushing valve 7, heat exchanger 9, and second three-way valve 10, so that the molten polycondensation and devolatilization material of polyethylene naphthalate per unit time enters the heat exchanger 9 and is forcibly cooled into a liquid state and remains in the heat exchanger 9. Specifically: Close the first ball valve 3 and the first needle valve 6, and open the second ball valve 8 and the second needle valve 12. This allows the high-temperature ethylene glycol gas, which is the melted polycondensation and devolvation material of polyethylene naphthalate, to flow to the heat exchanger 9 under the drive of the pressure difference, and to be forcibly cooled into a liquid and remain in the double coil 15 in a very short time.

[0034] S2: Block the connection between the first three-way valve 2 and the flushing valve 7, while connecting the first three-way valve 2 and the vacuum pump 14, and injecting solvent through the flushing valve 7 to flush the liquid polyethylene naphthalate melt polycondensation devolatilization material remaining in the heat exchanger 9 into the first collection tank 11 for collection, specifically: Open the first ball valve 3 and the first needle valve 6, close the second ball valve 8 and the second needle valve 12, open the flushing valve 7, and inject a certain amount of solvent into it. A liquid column is stably formed in the double-coil tube 15, and the liquid column is collected in the first collection tank 11 by pressure difference. The flushing solvent is generally selected to be a solvent with low viscosity, no reaction with the volatilized ethylene glycol, and stable chemical properties. Among them, anhydrous ethanol, a commonly used solvent in the laboratory, is preferred. A liquid column is stably formed in the double-coil tube 15. The amount of solvent injected should generally fill the tube radially to prevent ethylene glycol residue on the tube wall, which would affect the detection accuracy. Quantitative analysis is carried out using quantitative nuclear magnetic resonance analysis to accurately determine the target ethylene glycol content.

[0035] S3: Quantitative analysis was performed on the melt polycondensation devolatilization material collected in the first collection tank 11 to obtain the melt polycondensation devolatilization quality test results of polyethylene naphthalate, specifically: The concentration of ethylene glycol in the melt condensation and devolatilization of liquid polyethylene naphthalate was quantitatively analyzed using the nuclear magnetic resonance internal standard method, and the mass of ethylene glycol was then calculated.

[0036] The method for detecting the mass of the byproduct ethylene glycol per unit time during melt polymerization is as follows: The mass of the condensate per unit time was accurately weighed using an analytical balance; the content of ethylene glycol in the condensate was determined using a nuclear magnetic resonance spectrometer; and a stopwatch timer was used for timing.

[0037] By collecting volatile components per unit time, a correlation was established between the mass of ethylene glycol released and the molecular weight of the melt. The molecular weight was calculated and predicted. Comparison with the molecular weight of PEN melt sampled at the same time point revealed that the predicted molecular weight basically corresponded to the measured molecular weight. This indicates that the monitoring device described in this invention can accurately reflect the specific changes in the molecular weight within the system. Experimental data are shown in the table below: Reaction time (min) Condensate mass (within 5 minutes) Calculate molecular weight Measured molecular weight 180 0.67 3200 3809 210 0.68 5800 5986 240 0.54 8900 10370 270 0.53 12200 13450 300 0.45 15800 16643 330 0.40 18200 19877 360 0.28 22000 23280 The technical solution of the present invention will be described in detail below through specific embodiments: This experiment synthesized polyethylene naphthalate (PEN) resin using melt polycondensation. Dimethyl 2,6-naphthalenedicarboxylate (NDC, 183.49 g) and ethylene glycol (EG, 116.51 g) were used as the main reaction substrates, zinc acetate (73.3 mg) as the catalyst, and B225 (a mixture of antioxidants 1010 and 168 in equal mass ratio, 91.8 mg) as an antioxidant auxiliary.

[0038] Example 1 Three hours into the melt polycondensation reaction, the valve was switched to allow ethylene glycol gas to bypass the reaction, and the gas was collected for 10 minutes. The gas temperature was 150°C, and the vacuum degree was 500 Pa. After cooling through a double-coil tube, 40 g of anhydrous ethanol was injected for rinsing. The collected liquid was subjected to nuclear magnetic resonance analysis, and the mass of ethylene glycol was determined to be 0.67 g.

[0039] Example 2 The reaction proceeded for 3.5 hours, then a bypass was used to collect the gas for 10 minutes at a temperature of 132°C and a vacuum of 550 Pa. After cooling, anhydrous ethanol was injected, and NMR analysis showed that the mass of ethylene glycol was 0.68 g.

[0040] Example 3 The reaction proceeded for 4 hours, then a bypass was used to collect the gas for 10 minutes at a temperature of 136°C and a vacuum of 500 Pa. After cooling, anhydrous ethanol was injected, and NMR analysis showed that the mass of ethylene glycol was 0.54 g.

[0041] Example 4 The reaction proceeded for 4.5 hours, then a bypass was used to collect the gas for 10 minutes at a temperature of 135°C and a vacuum of 550 Pa. After cooling, anhydrous ethanol was injected, and NMR analysis showed that the mass of ethylene glycol was 0.53 g.

[0042] Example 5 The reaction proceeded for 5 hours, then a bypass was used to collect the gas for 10 minutes at a temperature of 130°C and a vacuum of 530 Pa. After cooling, anhydrous ethanol was injected, and NMR analysis showed that the mass of ethylene glycol was 0.45 g.

[0043] Example 6 The reaction proceeded for 5.5 hours, then a bypass was used to collect the gas for 10 minutes at a temperature of 110°C and a vacuum of 550 Pa. After cooling, anhydrous ethanol was injected, and NMR analysis showed that the mass of ethylene glycol was 0.40 g.

[0044] Example 7 The reaction proceeded for 6 hours, then a bypass was used to collect the gas for 10 minutes at a temperature of 90°C and a vacuum of 500 Pa. After cooling, anhydrous ethanol was injected, and NMR analysis showed that the mass of ethylene glycol was 0.28 g.

[0045] Comparative Example 1 Without a bypass, ethylene glycol gas is collected directly through the main pipeline. However, due to large pressure fluctuations in the main pipeline, the polymerization reaction is interrupted during the collection process, making it impossible to obtain effective data.

[0046] Comparative Example 2 The bypass valve was poorly designed, causing gas leakage during switching. The vacuum level rose to 800 Pa, the polymerization reaction stopped, and ethylene glycol could not be collected.

[0047] Comparative Example 3 Without using the double-coil 15, and only using straight tube cooling, the ethylene glycol gas could not be completely liquefied, resulting in low collection efficiency and a measured ethylene glycol mass of only 0.05g.

[0048] Comparative Example 4 Water was used as the rinsing solvent, which reacted with ethylene glycol, causing severe interference with the NMR spectrum and making quantitative analysis impossible.

[0049] Comparative Example 5 Quantitative analysis using nuclear magnetic resonance was not employed; the mass of the condensate was measured using only the weighing method, yielding a mass of 0.50 g. However, this condensate contained moisture and other volatiles, resulting in a significant error.

[0050] As demonstrated in Examples 1-7 and Comparative Examples 1-5, the method of this invention can stably collect ethylene glycol gas volatilized under high temperature and low vacuum conditions without interfering with the polymerization reaction. The mass of ethylene glycol per unit time can be accurately obtained through efficient cooling in a double-coil system, solvent washing, and quantitative NMR analysis. Inappropriate bypass design, insufficient cooling, improper solvent selection, or inaccurate analytical methods can all lead to data distortion or reaction interruption. This invention provides reliable data support for kinetic modeling and reactor design in melt polycondensation processes.

[0051] The above description is merely a preferred embodiment of the present invention and is not intended to limit the technical solution of the present invention in any way. Those skilled in the art should understand that, without departing from the spirit and principles of the present invention, the technical solution can be modified and replaced in several simple ways, and these modifications and replacements are all within the scope of protection covered by the claims.

Claims

1. An auxiliary device for detecting the quality of melt polycondensation and devolatilization of polyethylene naphthalate, characterized in that, It includes a first three-way valve (2) disposed between the melt polycondensation reactor (1) and the vacuum pump (14), the first three-way valve (2) being connected in sequence to a flushing valve (7), a heat exchanger (9) and a second three-way valve (10); the second three-way valve (10) is connected to the vacuum pump (14) and to a first collection tank (11).

2. The auxiliary device for detecting the quality of melt polycondensation and devolatilization of polyethylene naphthalate according to claim 1, characterized in that, A first ball valve (3) is provided between the first three-way valve (2) and the vacuum pump (14).

3. The auxiliary device for detecting the quality of melt polycondensation and devolatilization of polyethylene naphthalate according to claim 2, characterized in that, A first needle valve (6) is provided between the first ball valve (3) and the vacuum pump (14).

4. The auxiliary device for detecting the quality of melt polycondensation and devolatilization of polyethylene naphthalate according to claim 3, characterized in that, A third three-way valve (4) is provided between the first needle valve (6) and the first ball valve (3), and the third three-way valve (4) is connected to a second collection tank (5).

5. The auxiliary device for detecting the melt polycondensation and devolatilization quality of polyethylene naphthalate according to claim 1, characterized in that, A second ball valve (8) is provided between the flushing valve (7) and the heat exchanger (9).

6. The auxiliary device for detecting the quality of melt polycondensation and devolatilization of polyethylene naphthalate according to claim 1, characterized in that, The flushing valve (7) includes a fourth three-way valve (16) disposed between the first three-way valve (2) and the heat exchanger (9), and the fourth three-way valve (16) is connected to a third ball valve (17).

7. The auxiliary device for detecting the quality of melt polycondensation and devolatilization of polyethylene naphthalate according to claim 1, characterized in that, A second needle valve (12) is provided between the second three-way valve (10) and the vacuum pump (14).

8. The auxiliary device for detecting the quality of melt polycondensation and devolatilization of polyethylene naphthalate according to claim 8, characterized in that, A shut-off valve (13) is provided between the second needle valve (12) and the vacuum pump (14).

9. The auxiliary device for detecting the quality of melt polycondensation and devolatilization of polyethylene naphthalate according to claim 1, characterized in that, The heat exchanger (9) is a heat exchanger with a built-in double coil (15). The outlet of the heat exchanger (9) is equipped with a thermocouple or a thermometer. The heat exchange medium inside the heat exchanger (9) is a cold trap.

10. A method for detecting the melt polycondensation devolatilization quality of polyethylene naphthalate using the detection auxiliary device according to any one of claims 1-9, characterized in that, include: Block the connection between the first three-way valve (2) and the vacuum pump (14) side, and simultaneously connect the first three-way valve (2), flushing valve (7), heat exchanger (9) and second three-way valve (10) so that the molten polynaphthalene glycol ester devolve material per unit time enters the heat exchanger (9) and is forced to cool into a liquid state and remain in the heat exchanger (9); Block the connection between the first three-way valve (2) and the flushing valve (7) on one side, and connect the first three-way valve (2) and the vacuum pump (14) at the same time. Then, inject solvent through the flushing valve (7) to flush the liquid polyethylene naphthalate melt polycondensation devolatilization material remaining in the heat exchanger (9) into the first collection tank (11) for collection. The melt polycondensation and devolatilization of liquid polyethylene naphthalate collected in the first collection tank (11) was quantitatively analyzed to obtain the quality test results of melt polycondensation and devolatilization of polyethylene naphthalate.

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