Impurity removal process for nylon 66 melt

Abstract

The invention discloses a nylon 66 melt impurity removal process which comprises the steps of raw material pretreatment, solvent extraction, airflow impurity removal, catalyst impurity removal, vacuum degassing, centrifugal separation, physical filtration, removal of tiny solid impurities in a melt through a filter screen, cooling and quality detection. Impurities in the nylon 66 melt are comprehensively removed in a physical mode, a chemical mode and other modes, low-molecular-weight impurities, oxides, unreacted monomers and catalyst residues in the nylon 66 melt can be remarkably removed, and the purity of the melt is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of nylon 66 production, and in particular relates to a nylon 66 melt impurity removal process. Background Art

[0002] Nylon 66 (poly(hexamethylene adipamide)) is a high-performance material widely used in the field of engineering plastics. It has excellent mechanical strength, thermal stability, chemical resistance and wear resistance. It is widely used in many fields such as automotive parts, electronic appliances, industrial machinery and consumer products. However, in the production process of nylon 66, due to the complexity of the chemical reaction, a small amount of unreacted raw materials, catalysts, solvents and low molecular weight compounds may remain in the melt. These impurities will not only affect the performance of nylon 66, but also produce bubbles or discoloration during subsequent processing, reducing the reliability and appearance quality of the material. In addition, the residue of volatile impurities such as moisture may cause nylon 66 to degrade during high-temperature processing, further affecting its physical properties.

[0003] In order to improve the quality of nylon 66, impurity removal processes are usually used to remove impurities in the melt to ensure its purity. At present, commonly used impurity removal technologies include solvent extraction, airflow impurity removal, vacuum degassing, etc. However, a single impurity removal method is often difficult to completely remove various impurities and cannot achieve the desired effect. Some traditional impurity removal processes are also prone to damage the melt structure during operation, resulting in a decrease in the performance of nylon 66. Therefore, developing a systematic, multi-level impurity removal process to comprehensively remove impurities in the nylon 66 melt through physical, chemical and other methods has become the key to ensuring the high purity and high performance of nylon 66. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a nylon 66 melt impurity removal process.

[0005] The technical solution provided by the present invention is as follows:

[0006] A nylon 66 melt impurity removal process comprises the following steps:

[0007] S1: Raw material pretreatment, drying the nylon 66 raw material, removing surface moisture and other volatile impurities, and heating the dried nylon 66 raw material to a molten state;

[0008] S2: solvent extraction, adding solvent to the melt, selectively dissolving low molecular weight substances, solvent and unreacted raw materials, and removing the solvent and dissolved impurities by separation methods;

[0009] S3: Airflow removal, which guides the melt through high-temperature airflow to remove volatile impurities;

[0010] S4: Catalyst impurity removal, adding catalyst to the melt to promote the reaction of oxides and impurities to form insoluble matter, which is then removed by filtration or centrifugation;

[0011] S5: Vacuum degassing, exposing the melt to a vacuum environment to remove gas impurities and moisture;

[0012] S6: physical filtration, removing tiny solid impurities in the melt through the filter;

[0013] S7: centrifugal separation: centrifuging the melt to further remove solid impurities;

[0014] S8: cooling, cooling the melt after impurities removal;

[0015] S9: Quality inspection: perform quality inspection on the melt after impurities removal to ensure its purity and performance.

[0016] In a preferred embodiment, the following steps are included:

[0017] S1: Raw material pretreatment: vacuum drying or hot air drying is used to dry the nylon 66 raw material for 6-8 hours at a drying temperature of 80°C-100°C to remove surface moisture and other volatile impurities, and the dried nylon 66 raw material is heated to a molten state at a heating temperature of 260°C-270°C;

[0018] S2: Solvent extraction, adding solvent to the melt, reacting for 20-30 minutes, selectively dissolving low molecular weight substances, solvents and unreacted raw materials, the extraction temperature is 60°C-80°C, and removing the solvent and dissolved impurities by separation method;

[0019] S3: Airflow impurity removal, the melt is guided by high-temperature airflow for 10-15 minutes, and the volatile impurities therein are removed under the conditions of gas temperature of 200℃-250℃ and gas flow rate of 5-10L / min;

[0020] S4: Catalyst impurity removal: adding catalyst to the melt, reacting at a reaction temperature of 220°C-250°C for 10-20 minutes to promote the reaction of oxides and impurities to form insoluble matter, which is then removed by filtration or centrifugal separation;

[0021] S5: Vacuum degassing: expose the melt to a vacuum environment with a vacuum degree of 0.1Mpa and a temperature of 220℃-240℃ for 15-30min to remove gas impurities and moisture;

[0022] S6: Physical filtration, at a temperature of 200℃-220℃, tiny solid impurities in the melt are removed through a filter;

[0023] S7: Centrifugal separation: centrifuge the melt for 10-20 min at a centrifugal speed of 5000-10000 rpm and a temperature of 180°C-200°C to further remove solid impurities;

[0024] S8: Cooling, cooling the melt after impurity removal, so that the nylon 66 after impurity removal is gradually cooled to room temperature, and the cooling rate is within 10°C / min;

[0025] S9: Quality inspection, quality inspection of the melt after impurity removal, including infrared spectroscopy analysis, which is used to detect residual organic impurities; thermogravimetric analysis, which is used to detect the thermal stability and impurity content of the melt; viscosity test, which is used to measure the fluidity of the melt to ensure that it meets the processing requirements.

[0026] In a preferred embodiment, the solvent is an alcohol solvent or a ketone solvent.

[0027] In a preferred embodiment, the gas used for airflow impurity removal is high-temperature nitrogen.

[0028] In a preferred embodiment, the catalyst is an aluminum salt, a titanium salt or a combination thereof.

[0029] In a preferred embodiment, the filter screen is a ceramic membrane or a metal mesh membrane with a filtration accuracy of 0.5-5 microns.

[0030] In a preferred embodiment, in step S9, the infrared spectrum analysis step is:

[0031] S911: Take nylon 66 melt and make a film or sheet sample after cooling it to room temperature;

[0032] S912: The sample was scanned in the wave number range of 4000-400cm-1, the resolution was set to 4cm-1, and the number of scans was 32 times;

[0033] S913: Analyze infrared absorption peaks to ensure that impurity characteristic peaks are below the detection limit.

[0034] In a preferred embodiment, in step S9, the step of thermogravimetric analysis is:

[0035] S921: Weigh 10-20 mg of sample and heat from room temperature to 500°C at a heating rate of 10°C / min, using nitrogen or air as the protective gas at a flow rate of 20-40 mL / min;

[0036] S922: Detect the weight loss rate to ensure that the weight loss rate before 200°C is less than 0.1%.

[0037] In summary, the beneficial effects of the present invention are:

[0038] (1) The impurity removal process of the present invention can significantly remove low molecular weight impurities, oxides, unreacted monomers and catalyst residues in the nylon 66 melt, and improve the purity of the melt. The process steps of solvent extraction, airflow impurity removal, catalyst reaction, vacuum degassing and high-efficiency filtration are adopted to further ensure the comprehensive removal of impurities, which not only improves the physical strength, mechanical properties and dimensional stability of nylon 66, but also enhances its heat resistance and chemical resistance, so that it can still maintain excellent performance under high temperature and corrosive environment. In addition, the process can avoid structural damage to the nylon 66 melt during the impurity removal process, ensure the molecular chain integrity of the material, and thus improve the service life and reliability of the product.

[0039] (2) The quality detection of the present invention can effectively detect organic impurities and low molecular weight substances in nylon 66 melt through the combination of FTIR and TGA to ensure the removal effect. FTIR is mainly used for qualitative and quantitative analysis of organic impurities, while TGA provides thermal stability data of impurities. The combination of the two provides a comprehensive detection basis for the quality of nylon 66 melt. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is the FTIR spectrum of nylon 66 after impurity removal;

[0041] Figure 2 This is the TGA thermogravimetric curve of nylon 66 after impurities removal. DETAILED DESCRIPTION

[0042] In order to deepen the understanding of the present invention, the present invention will be further described in detail below in conjunction with examples. The following examples are only used to explain the present invention and do not constitute a limitation on the scope of protection of the present invention.

[0043] Example 1

[0044] This embodiment provides an efficient nylon 66 melt impurity removal process, which aims to effectively remove low molecular weight impurities, oxides, residual catalysts and other substances in the melt that may affect product performance, thereby improving the physical, mechanical and chemical properties of nylon 66. The following is a specific implementation of the process, including detailed parameters and process control instructions for each step.

[0045] Step S1: Raw material pretreatment

[0046] First, the raw materials are pretreated. A small amount of moisture, unreacted monomers, catalysts and other volatile components may remain in the nylon 66 raw materials. These impurities will further affect the purity of the melt during the melting process. Through pretreatment, the moisture and most volatile impurities in the raw materials are removed. At the same time, the dried nylon 66 raw materials are melted evenly to provide an ideal fluidity and dispersion environment for subsequent impurity removal operations.

[0047] First, select nylon 66 raw materials, put them into a vacuum drying oven, set the temperature to 80℃-100℃, control the vacuum degree at 0.08Mpa, and dry them for 6-8 hours to ensure that the moisture content drops below 0.1%. After the raw materials are dried, they are placed in a closed environment for use to avoid moisture absorption again.

[0048] During the above process, a vacuum environment must be ensured to prevent moisture in the air from entering the drying oven. At the same time, the moisture content of the raw materials should be checked in a timely manner to ensure that it meets the standards.

[0049] The pretreated nylon 66 raw material is fed into the melting kettle, the initial temperature is set at 250°C, and the temperature is gradually raised to 260°C-270°C. The melting temperature is maintained within this range to ensure that the nylon 66 raw material is melted evenly and reaches a melt state with good fluidity. The melting time is controlled within 30-60 minutes to ensure that there are no solid particles in the melt and a uniform fluid state is formed.

[0050] Avoid excessive heating during the melting process to prevent degradation of the nylon 66 molecular chain and resulting in performance degradation. At the same time, nitrogen can be appropriately added as a protective gas to reduce the generation of oxides.

[0051] Step S2: Solvent Extraction

[0052] The low molecular weight organic impurities in nylon 66 melt are removed by the dissolution and extraction of solvents. Specifically:

[0053] Select a suitable solvent (such as ethanol, isopropanol or acetone) and add it into the molten nylon 66 melt at 5%-10% of the melt mass.

[0054] After the solvent is added, the temperature is controlled within the range of 60°C-80°C, and a stirring device is used to continuously mix for 20-30 minutes to ensure that the solvent is fully in contact with the impurities. After the reaction is completed, the melt is sent to a centrifugal separation device and centrifuged at a speed of 5000-8000 rpm to remove the solvent and the impurities brought out by it. In this embodiment, the device is a solvent extraction device or a mixer.

[0055] It should be noted that the solvent selection needs to be adjusted according to the properties of the impurities. Generally speaking, low molecular weight impurities have good solubility in polar solvents. At the same time, the control of extraction temperature and time is key to avoid mutual dissolution of nylon 66 and solvent. When selecting a solvent, it is necessary to ensure that its solubility in nylon 66 is low and it is only used to extract impurities without dissolving the nylon 66 body. Control the speed and time during centrifugation to avoid too fast heat loss of the melt and cause solidification.

[0056] Step S3: Airflow impurity removal

[0057] After solvent extraction and impurity removal, airflow impurity removal technology is used to remove volatile impurities in the melt, including residual solvents and a small amount of gas. Specifically:

[0058] The melt is passed into the airflow impurity removal device and treated with nitrogen. The temperature is controlled at 200℃-250℃ and the nitrogen flow rate is controlled at 5-10L / min. The treatment time is 10-15 minutes to ensure that the gas fully contacts the melt and removes volatile impurities.

[0059] Too high air flow velocity may cause melt temperature fluctuations, while too low air flow velocity will affect the impurity removal effect, so the flow rate needs to be kept constant. To ensure the treatment effect, multi-stage air flow impurity removal equipment can be used.

[0060] Nitrogen or other inert gases must be used during the airflow removal process to prevent the melt from being oxidized, and the equipment must be sealed to prevent air from entering.

[0061] Step S4: Catalyst impurity removal

[0062] Use catalysts to accelerate the decomposition reaction of impurities to remove impurities that are difficult to volatilize. Specifically:

[0063] A catalyst (such as aluminum trichloride or titanium tetrachloride) is selected and added to the melt at 0.01%-0.1% of the melt mass, and the melt is heated to 220°C-250°C and kept reacting for 10-20 minutes to allow the catalyst to fully contact with the impurities and produce volatile substances. The reaction product is removed through a high-temperature reactor.

[0064] The amount of catalyst should be appropriate. Too much may cause incomplete reaction and residual catalyst may also affect the performance of nylon 66.

[0065] Step S5: Vacuum degassing

[0066] Vacuum degassing is used to remove residual solvents, gases and other volatile impurities to improve the purity of the melt. Specifically:

[0067] Place the melt in a vacuum degassing furnace, heat to 220℃-240℃, control the vacuum degree below 0.1Mpa, maintain for 15-30 minutes, and gradually remove the residual gas in the melt.

[0068] It should be noted that the degassing temperature must be strictly controlled to prevent the melt from being oxidized or decomposed due to excessive temperature. At the same time, the stability of the vacuum degree is the key, and the airtightness of the degassing environment should be maintained.

[0069] Step S6: Physical filtration

[0070] Physical filtration is used to remove solid impurities in the melt, including incompletely reacted particles, tiny solid particles, etc. Specifically:

[0071] Use ceramic membrane or metal mesh membrane for high temperature filtration, the filter mesh aperture is 0.5-5 microns, the temperature is controlled at 200℃-220℃, and the filter device is filtered layer by layer to remove fine particles. The filtration accuracy is adjusted according to the required purity, and the filter mesh aperture of about 0.5 microns is usually the best. At the same time, the temperature of the filtration equipment is kept constant to avoid solidification of the melt.

[0072] Step S7: Centrifugal separation

[0073] Centrifugal separation is used to further remove higher density solid impurities to ensure the purity of the final product, specifically:

[0074] The filtered melt is placed in a high-temperature centrifugal device, the centrifugal speed is controlled at 5000-10,000rpm, and the temperature is set at 180℃-200℃. The processing time is 10-20 minutes, and the centrifugal force is used to separate the density impurities in the melt.

[0075] The centrifugal speed should be set according to the particle size of the impurities. Usually, high-density impurities are suitable for higher speeds. Similarly, the equipment temperature should be maintained during the centrifugation process to avoid melt solidification.

[0076] Step S8: Cooling

[0077] This step is to avoid thermal stress caused by rapid cooling of the melt and ensure that the melt is uniform and stable. Specifically:

[0078] After the melt is cleaned, it is cooled to room temperature and treated with cooling water or cooling air flow. The cooling speed should be properly controlled to avoid uneven internal stress caused by rapid cooling, and the cooling rate should be controlled within 10℃ / min.

[0079] Example 2

[0080] This embodiment provides a quality detection method for nylon 66 after impurity removal, which includes infrared spectroscopy analysis for detecting residual organic impurities; thermogravimetric analysis for detecting the thermal stability and impurity content of the melt; and viscosity detection for measuring the fluidity of the melt to ensure that it meets the processing requirements, wherein:

[0081] 1. Infrared spectroscopy analysis (FTIR)

[0082] It is used to qualitatively and quantitatively analyze organic impurities in nylon 66 melt and detect whether there are low molecular weight compounds or residual solvents that have not been completely removed. Specifically:

[0083] Take a small amount of nylon 66 melt, wait for it to cool to room temperature, and then make a film or sheet sample.

[0084] Instrument settings: Scan in the wave number range of 4000-400cm-1 to capture the characteristic peaks of the nylon 66 molecular structure and possible impurity peaks;

[0085] The resolution is set to 4cm-1, ensuring high sensitivity detection of trace impurities. ;

[0086] The scanning number was 32 times to enhance the signal-to-noise ratio and improve the spectrum quality.

[0087] Background correction: Use blank samples or pure nylon 66 samples for background correction to remove environmental noise interference.

[0088] Test scan: Place the sample in the FTIR instrument for scanning to obtain its infrared absorption spectrum.

[0089] Spectral analysis: Identify the characteristic peaks of nylon 66 (such as the characteristic peaks of functional groups such as NH, C=O, CN, etc.), and compare them with the spectrum of standard nylon 66; check whether there are characteristic peaks of impurities, especially the absorption peaks of low molecular weight substances and solvents (such as CH, OH stretching vibration peaks).

[0090] Quantitative analysis: Use the internal standard method or standard curve method to quantify the impurity content to ensure that the impurity content is lower than the limit required by the process.

[0091] The nylon 66 obtained in Example 1 after impurity removal was analyzed by infrared spectroscopy. The characteristic peak of impurities in the infrared spectrum was lower than the detection limit, and the impurity content was lower than 0.1%, which met the requirements.

[0092] For specific FTIR spectra, please refer to Figure 1 Its main characteristic peaks are at 3300cm-1 (NH stretching vibration), 1630cm-1 (C=O stretching vibration) and 1540cm-1 (NH bending vibration). These peaks reflect the molecular structure of nylon 66. In the spectrum of the treated nylon 66 sample, the lower intensity of C=O and NH peaks indicates that the impurity content is reduced. In addition, the CH vibration peak is significantly weakened, indicating that low molecular weight impurities have been removed.

[0093] 2. Thermogravimetric analysis (TGA)

[0094] It is used to evaluate the thermal stability and impurity content of nylon 66 melt, and to determine the content of impurities, volatile components or low molecular weight substances through the weight loss of the sample.

[0095] Weigh 10-20 mg of nylon 66 sample and place it in the TGA sample pan.

[0096] Instrument Setup:

[0097] Heating program: from room temperature to 500°C, heating rate is 10°C / MIN;

[0098] Atmosphere: Nitrogen; Nitrogen is usually used to exclude oxygen interference and ensure that only the decomposition or volatilization of impurities is detected.

[0099] Flow rate: 20-40mL / min, to ensure a stable test environment.

[0100] Test progress: Start heating up, and TGA records the weight change of the sample as the temperature changes.

[0101] Analytical data: Obtain thermogravimetric curves and analyze the thermal decomposition and volatilization behavior of samples.

[0102] Pay attention to the starting weight loss temperature and total weight loss rate of the thermogravimetric curve. Low molecular weight impurities or residual solvents generally lose weight at lower temperatures, while nylon 66 decomposes at higher temperatures.

[0103] Calculate the impurity content: Quantify the impurity content through the total weight loss value and weight loss temperature range to ensure the impurity removal effect.

[0104] Thermogravimetric analysis was used to analyze the nylon 66 obtained in Example 1 after the impurities were removed. The weight loss rate before 200°C was less than 0.1% (low-temperature weight loss generally represents the volatile impurity content), and the total weight loss rate met the process requirements, ensuring the thermal stability of the melt.

[0105] For specific TGA thermogravimetric curve, please refer to Figure 2 , which shows the effect of temperature on the weight of nylon 66, with two main weight loss stages at 100°C to 200°C (moisture or volatile impurities) and 350°C to 400°C (material decomposition). After the impurity removal treatment, the amplitude of the first weight loss stage should be significantly reduced, indicating the removal effect of impurities.

[0106] The combination of FTIR and TGA can effectively detect organic impurities and low molecular weight substances in nylon 66 melt to ensure the removal effect. FTIR is mainly used for qualitative and quantitative analysis of organic impurities, while TGA provides thermal stability data of impurities. The combination of the two provides a comprehensive detection basis for the quality of nylon 66 melt.

[0107] It should be noted that the implementation methods not shown or described in the drawings or the main text of the specification are all forms known to ordinary technicians in the relevant technical field and are not described in detail. In addition, the above definitions of each element and method are not limited to the various specific structures, shapes or methods mentioned in the embodiments.

[0108] It should also be noted that the directional terms mentioned in the embodiments, such as "up", "down", "front", "back", "left", "right", "inside", "outside", etc., are only for reference to the directions of the drawings and are not intended to limit the scope of protection of this application.

[0109] The above description shows and describes the preferred embodiments of the present invention. As mentioned above, it should be understood that the present invention is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be modified within the scope of the invention concept described herein through the above teachings or the technology or knowledge of the relevant field. The changes and modifications made by those skilled in the art do not depart from the spirit and scope of the present invention, and should be within the scope of protection of the claims attached to the present invention.

Claims

1. A nylon 66 melt impurity removal process, characterized in that: The following steps are involved: S1: Raw material pretreatment, drying the nylon 66 raw material, removing surface moisture and other volatile impurities, and heating the dried nylon 66 raw material to a molten state; S2: solvent extraction, adding solvent to the melt, selectively dissolving low molecular weight substances, solvent and unreacted raw materials, and removing the solvent and dissolved impurities by separation methods; S3: Airflow removal, which guides the melt through high-temperature airflow to remove volatile impurities; S4: Catalyst impurity removal, adding catalyst to the melt to promote the reaction of oxides and impurities to form insoluble matter, which is then removed by filtration or centrifugation; S5: Vacuum degassing, exposing the melt to a vacuum environment to remove gas impurities and moisture; S6: physical filtration, removing tiny solid impurities in the melt through the filter; S7: centrifugal separation: centrifuging the melt to further remove solid impurities; S8: cooling, cooling the melt after impurities are removed; S9: Quality inspection: perform quality inspection on the melt after impurities removal to ensure its purity and performance.

2. The nylon 66 melt impurity removal process according to claim 1, characterized in that: The following steps are involved: S1: Raw material pretreatment: vacuum drying or hot air drying is used to dry the nylon 66 raw material for 6-8 hours at a drying temperature of 80°C-100°C to remove surface moisture and other volatile impurities, and the dried nylon 66 raw material is heated to a molten state at a heating temperature of 260°C-270°C; S2: Solvent extraction, adding solvent to the melt, reacting for 20-30 minutes, selectively dissolving low molecular weight substances, solvents and unreacted raw materials, the extraction temperature is 60°C-80°C, and removing the solvent and dissolved impurities by separation method; S3: Airflow impurity removal, the melt is guided by high-temperature airflow for 10-15 minutes, and the volatile impurities therein are removed under the conditions of gas temperature of 200℃-250℃ and gas flow rate of 5-10L / min; S4: Catalyst impurity removal: adding catalyst to the melt, reacting at a reaction temperature of 220°C-250°C for 10-20 minutes to promote the reaction of oxides and impurities to form insoluble matter, which is then removed by filtration or centrifugal separation; S5: Vacuum degassing, exposing the melt to a vacuum environment with a vacuum degree of 220°C-240°C for 15-30 minutes to remove gas impurities and moisture; S6: Physical filtration, at a temperature of 200℃-220℃, tiny solid impurities in the melt are removed through a filter; S7: Centrifugal separation: centrifuge the melt for 10-20 min at a centrifugal speed of 5000-10000 rpm and a temperature of 180°C-200°C to further remove solid impurities; S8: Cooling, cooling the melt after impurity removal, so that the nylon 66 after impurity removal is gradually cooled to room temperature, and the cooling rate is within 10°C / min; S9: Quality inspection, quality inspection of the melt after impurity removal, including infrared spectroscopy analysis, which is used to detect residual organic impurities; Thermogravimetric analysis is used to detect the thermal stability and impurity content of the melt; viscosity testing is used to measure the fluidity of the melt to ensure that it meets processing requirements.

3. The nylon 66 melt impurity removal process according to claim 2, characterized in that: The solvent is an alcohol solvent or a ketone solvent.

4. The nylon 66 melt impurity removal process according to claim 2, characterized in that: The gas used for the airflow impurity removal is high-temperature nitrogen.

5. The nylon 66 melt impurity removal process according to claim 2, characterized in that: The catalyst is an aluminum salt, a titanium salt or a combination thereof.

6. The nylon 66 melt impurity removal process according to claim 2, characterized in that: The filter screen is a ceramic membrane or a metal mesh membrane, and the filtering accuracy is 0.5-5 microns.

7. The nylon 66 melt impurity removal process according to claim 2, characterized in that: In step S9, the infrared spectrum analysis step is: S911: Take nylon 66 melt and make a film or sheet sample after cooling it to room temperature; S912: The sample was scanned in the wave number range of 4000-400cm-1, the resolution was set to 4cm-1, and the number of scans was 32 times; S913: Analyze infrared absorption peaks to ensure that impurity characteristic peaks are below the detection limit.

8. The nylon 66 melt impurity removal process according to claim 2, characterized in that: In step S9, the steps of thermogravimetric analysis are: S921: Weigh 10-20 mg of sample and heat from room temperature to 500°C at a heating rate of 10°C / min, using nitrogen or air as the protective gas at a flow rate of 20-40 mL / min; S922: Detect the weight loss rate to ensure that the weight loss rate before 200°C is less than 0.1%.

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