Method for detecting content of ethylene glycol in esterification wastewater

Abstract

The invention discloses a method for detecting the content of ethylene glycol in esterification wastewater, which comprises the following steps: performing closed hydrothermal separation treatment on wastewater to be detected to obtain a wastewater sample to be detected, and then detecting the content of ethylene glycol in the wastewater sample to be detected by adopting a gas chromatography quantitative analysis method. According to the method, high-risk chemicals are not used in the whole test process, new toxic substances and highly toxic products are not generated, the health of operators is not endangered, the method is safe and environment-friendly, and the used chemical reagents are low in safety control cost and risk. According to the method disclosed by the invention, the detection lower limit of the ethylene glycol content is 0.005%, the variation coefficient of the same sample to be detected is less than 1.0% according to the statistics of six test results, the deviation from the test result of a sodium arsenite chemical titration method is less than 0.05%, and the method has the characteristics of fine test precision, high result accuracy and good repeatability. According to the detection method disclosed by the invention, the test time consumption is only 1 / 3-1 / 4 of that of a sodium arsenite chemical titration method, so that the test efficiency and the timeliness of result feedback are greatly improved.

Description

Technical Field

[0001] The present invention relates to the field of chemical analysis and detection, and particularly relates to a method for detecting the content of ethylene glycol in esterification wastewater. Background Art

[0002] The content of ethylene glycol in the esterification wastewater during polyester production is an important indicator for measuring whether the process tower of the esterification system is operating normally. When the content of ethylene glycol in the esterification wastewater is too high, it not only increases the consumption of ethylene glycol during polyester production, but also causes a relatively high COD in the production wastewater, increasing the load of sewage treatment. This indicator has important reference value for enterprise production and environmental protection. Therefore, by measuring the content of ethylene glycol in the esterification wastewater, the operation condition of the process tower can be accurately judged, so as to achieve the purpose of reducing unit consumption and the load of sewage treatment.

[0003] At present, the titration method is used to test the content of ethylene glycol in the esterification wastewater during polyester production. Excessive periodic acid is used to oxidize ethylene glycol into formaldehyde. The remaining periodic acid can be reduced to iodate by potassium iodide, and the released equimolar iodine can be titrated with sodium arsenite standard solution (prepared by reacting arsenic trioxide with sodium hydroxide, arsenic trioxide is commonly known as arsenic, a highly toxic substance) using starch as an indicator in a sodium bicarbonate buffer solution. The content of ethylene glycol is calculated from the difference in the amount of sodium arsenite solution consumed in the sample and the blank test. The chemical reaction equations are as follows:

[0004] CH2OHCH2OH + HIO4 = 2HCHO + HIO3 + H2O

[0005] 2HIO4 + 14KI + 7H2SO4 = 7K2SO4 + 8H2O + 8I2

[0006] 2HIO3 + 10KI + 5H2SO4 = 5K2SO4 + 6H2O + 6I2

[0007]

[0008] In this method, the chemical reagent sodium arsenite is used. Sodium arsenite produces highly toxic arsenic trioxide when it encounters acid, posing a major drug safety risk. Therefore, it is of great significance to provide a safe and effective method for testing the content of ethylene glycol without using / producing highly toxic chemical reagents. Summary of the Invention

[0009] The technical problem to be solved by the present invention is to provide a method for detecting the content of ethylene glycol in esterification wastewater in view of the problems of generating highly toxic substances and major safety risks existing in the existing testing methods. This method uses gas chromatography, is easy to operate and detect, has low cost, low sample detection limit, high sample detection precision and accuracy.

[0010] To solve the above technical problems, the technical solution adopted by the present invention is: a method for detecting the content of ethylene glycol in esterification wastewater, and the method is as follows: First, the wastewater to be detected is subjected to closed hydrothermal separation treatment to obtain a wastewater sample to be detected, and then the content of ethylene glycol in the wastewater sample to be detected is detected by gas chromatography quantitative analysis method.

[0011] Preferably, the method of closed hydrothermal separation treatment is: placing the wastewater to be detected in a closed container, maintaining it at a temperature of 55 °C to 80 °C for 10 min to 30 min, and then cooling to room temperature to obtain a wastewater sample to be detected.

[0012] Preferably, the gas chromatography quantitative analysis method uses the internal standard method for detection, and the internal standard substance is 1,6 - hexanediol.

[0013] Preferably, the method for detecting the content of ethylene glycol in the esterification wastewater includes the following steps:

[0014] S1. Determine the correction factor K of ethylene glycol:

[0015] Mix a methanol solution of ethylene glycol (EG) with a known concentration and an internal standard solution with a known concentration to obtain a mixed solution. Inject the mixed solution into a gas chromatograph for testing. After the peaks appear and end, read the peak areas of the internal standard substance and ethylene glycol from the chromatogram, and calculate the correction factor K of ethylene glycol according to the following formula:

[0016]

[0017] In the formula: S EG is the peak area of ethylene glycol in the chromatogram, S NB is the peak area of the internal standard substance in the chromatogram, m EG is the mass of ethylene glycol in the injected mixed solution, m NB is the mass of the internal standard substance in the injected mixed solution;

[0018] S2. Perform closed hydrothermal separation treatment on the wastewater to be detected to obtain a wastewater sample to be detected:

[0019] S3. Detection of the wastewater to be detected:

[0020] S3 - 1. Accurately weigh a mass m of the wastewater to be detected and add it to a container, then pipette an internal standard solution with a known concentration and add it to the container, and shake well to obtain a mixed solution;

[0021] S3 - 2. Inject the mixed solution into a gas chromatograph for testing. After the peaks appear and end, read the peak area S' NB of the internal standard substance and the peak area S' EG of ethylene glycol, and calculate the content C EG of ethylene glycol in the wastewater to be detected according to the following formula:

[0022]

[0023] Preferably, the internal standard solution is a methanol solution of 1,6 - hexanediol.

[0024] Preferably, the concentration of the internal standard solution is 0.2 - 0.8 g / L.

[0025] Preferably, the chromatographic column is a strongly polar chromatographic column.

[0026] Preferably, the method for detecting the content of ethylene glycol in the esterification wastewater includes the following steps:

[0027] S1. Determine the correction factor K of ethylene glycol:

[0028] Accurately pipette 12.5 - 50 mL of a methanol solution of ethylene glycol with a concentration of 5 - 20 g / L and 2.5 - 10 mL of the internal standard solution into a glass sample bottle. The internal standard solution is a methanol solution of 1,6 - hexanediol with a concentration of 0.2 - 0.8 g / L. Tighten the bottle cap and shake well to obtain a mixed solution. Pipette 0.3 - 1.2 μL of this mixed solution into a gas chromatograph for injection testing. After the peaks have emerged, read the peak areas of the internal standard and ethylene glycol from the chromatogram, and calculate the correction factor K of ethylene glycol according to the following formula:

[0029]

[0030] In the formula: S EG is the peak area of ethylene glycol in the chromatogram, S NB is the peak area of the internal standard in the chromatogram, m EG is the mass of ethylene glycol in the injected mixed solution, m NB is the mass of the internal standard in the injected mixed solution;

[0031] S2. Closed hydrothermal dissociation treatment: Place the wastewater to be detected in a closed container, maintain it at a temperature of 55 °C - 80 °C for 10 min - 30 min, and then cool it to room temperature to obtain the wastewater sample to be measured;

[0032] S3. Detection of the wastewater to be measured:

[0033] S3 - 1. Accurately weigh 1 - 2 g of the wastewater to be detected and add it to a sample bottle, record the mass m, accurate to 0.0001 g, and then accurately pipette 2.5 - 10 mL of a methanol solution of 1,6 - hexanediol with a mass concentration of 0.2 - 0.8 g / L into the sample bottle, and shake well to obtain a mixed solution;

[0034] S3 - 2. Pipette 0.3 - 1.2 μL of the mixed solution into a gas chromatograph for injection testing. After the peaks have emerged, read the peak area S' of the internal standard NB and the peak area S' of ethylene glycol from the chromatogramEG , the ethylene glycol content C in the wastewater to be detected is calculated according to the following formula EG :

[0035]

[0036] Preferably, the method for detecting the ethylene glycol content in the esterification wastewater includes the following steps:

[0037] S1. Determine the ethylene glycol correction factor K:

[0038] Accurately pipette 25 mL of a methanol solution of ethylene glycol with a concentration of 10 g / L and 5 mL of an internal standard solution into a glass sample bottle using a pipette. The internal standard solution is a methanol solution of 1,6 - hexanediol with a concentration of 0.4 g / L. Tighten the bottle cap and shake well to obtain a mixed solution. Pipette 0.6 μL of this mixed solution into a gas chromatograph for injection testing; after the peaks have finished emerging, read the peak areas of the internal standard and ethylene glycol from the chromatogram, and calculate the ethylene glycol correction factor K according to the following formula:

[0039]

[0040] In the formula: S EG is the peak area of ethylene glycol in the chromatogram, S NB is the peak area of the internal standard in the chromatogram, m EG is the mass of ethylene glycol in the injected mixed solution, m NB is the mass of the internal standard in the injected mixed solution;

[0041] S2. Closed - hydrothermal detachment treatment: Place the wastewater to be detected in a closed container, maintain it at a temperature of 55 °C - 80 °C for 10 min - 30 min, and then cool it to room temperature to obtain a wastewater sample to be tested;

[0042] S3. Detection of the wastewater to be tested:

[0043] S3 - 1. Accurately weigh 1 - 2 g of the wastewater to be detected and add it to a sample bottle, record the mass m, accurate to 0.0001 g, and then accurately pipette 5 mL of a methanol solution of 1,6 - hexanediol with a mass concentration of 0.4 g / L into the sample bottle, and shake well to obtain a mixed solution;

[0044] S3 - 2. Pipette 0.6 μL of the mixed solution into a gas chromatograph for injection testing using a micro - syringe. After the peaks have finished emerging, read the peak area S' of the internal standard NB and the peak area S' of ethylene glycol EG , and calculate the ethylene glycol content C in the wastewater to be detected according to the following formula EG :

[0045]

[0046] Preferably, the detection parameters of the gas chromatograph are as follows:

[0047] 1) Column temperature: Programmed temperature increase is adopted. Specifically, the temperature is raised to 70 °C and held for 2 min, and then it is raised to 175 °C at a rate of 15 °C / min and held for 2 min.

[0048] 2) Detector temperature is 250 °C, and injector temperature is 250 °C.

[0049] 3) Flow rate of hydrogen needle valve is 30 ml / min, flow rate of air needle valve is 350 ml / min, and flow rate of nitrogen needle valve is 30 ml / min.

[0050] The beneficial effects of the present invention are as follows:

[0051] The present invention provides a method for detecting the content of ethylene glycol in esterification wastewater. This method does not use highly hazardous chemicals throughout the test, does not produce new toxic substances, has no highly toxic products, does not endanger the health of operators, is safe and environmentally friendly, and the cost and risk of safety control of the chemical reagents used are low.

[0052] In the method of the present invention, the lower limit of detection of ethylene glycol content is 0.005%. For the same sample to be tested, the coefficient of variation is < 1.0% based on the statistical results of 6 test results, and the deviation from the test results of the sodium arsenite chemical titration method is < 0.05%. It has the characteristics of fine test precision, high result accuracy, and good repeatability.

[0053] The test time (10 - 15 min) of the method for detecting the content of ethylene glycol provided by the present invention is only 1 / 3 - 1 / 4 of that of the sodium arsenite chemical titration method, greatly improving the test efficiency and the timeliness of result feedback. Description of the Drawings

[0054] Figure 1 The chromatogram obtained for determining the correction factor K in step S1 of Example 1;

[0055] Figure 2 The chromatogram of the sample obtained in the test example;

[0056] Figure 3 The chromatogram of the sample obtained in Comparative Example 2. Detailed Embodiments

[0057] The following further describes the present invention in detail with reference to embodiments, so that those skilled in the art can implement it according to the description in the specification.

[0058] It should be understood that the terms such as "having", "comprising", and "including" used herein do not exclude the presence or addition of one or more other elements or their combinations.

[0059] Unless otherwise specified, the test methods used in the following examples are all conventional methods. Unless otherwise specified, the materials and reagents used in the following examples can all be obtained through commercial channels. For those not specifying specific conditions in the following examples, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. For reagents or instruments without indicating the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0060] The present invention provides a method for detecting the content of ethylene glycol in esterification wastewater. The method is as follows: First, the wastewater to be detected is subjected to closed hydrothermal dissociation treatment to obtain a wastewater sample to be detected, and then the content of ethylene glycol in the wastewater sample to be detected is detected by gas chromatography quantitative analysis method; the internal standard method is adopted, the internal standard substance is 1,6 - hexanediol, and the chromatographic column is a strong polar chromatographic column. Specifically, it includes the following steps:

[0061] S1. Determine the ethylene glycol correction factor K:

[0062] Accurately pipette 12.5 - 50 mL of a methanol solution of ethylene glycol with a concentration of 5 - 20 g / L and 2.5 - 10 mL of an internal standard solution into a glass sample bottle. The internal standard solution is a methanol solution of 1,6 - hexanediol with a concentration of 0.2 - 0.8 g / L. Tighten the bottle cap and shake well to obtain a mixed solution. Pipette 0.3 - 1.2 μL of this mixed solution into a gas chromatograph for injection testing; after the peak emergence ends, read the peak areas of the internal standard substance and ethylene glycol from the chromatogram, and calculate the ethylene glycol correction factor K according to the following formula:

[0063]

[0064] In the formula: S EG is the peak area of ethylene glycol in the chromatogram, S NB is the peak area of the internal standard substance in the chromatogram, m EG is the mass of ethylene glycol in the injection mixed solution, m NB is the mass of the internal standard substance in the injection mixed solution.

[0065] S2. Closed hydrothermal dissociation treatment: Place the wastewater to be detected in a closed container, keep it at a temperature of 55°C to 80°C for 10 min to 30 min, and then cool it to room temperature to obtain a wastewater sample to be detected;

[0066] Acetaldehyde is produced during the polyester production process and exists in the esterification wastewater. When it reacts with ethylene glycol in the wastewater, a trace amount of the intermediate substance 2-methyl-1,3-dioxolane (2-MD, C4H8O3) is formed. When directly sampling the wastewater and testing it using a gas chromatograph (GC), due to the small amount of 2-methyl-1,3-dioxolane (2-MD) present, the detected content of ethylene glycol will be lower than the actual value (because the ethylene glycol that reacts with acetaldehyde to form the intermediate substance 2-methyl-1,3-dioxolane should also be counted as the ethylene glycol in the wastewater, but this part of ethylene glycol cannot be detected when directly using a gas chromatograph for testing, so the test value is lower than the actual value). The conventional sodium arsenite chemical titration method is a chemical reaction process, and sufficient chemical heat will be generated during the process, causing 2-methyl-1,3-dioxolane to decompose into ethylene glycol and acetaldehyde, thereby releasing the ethylene glycol in 2-methyl-1,3-dioxolane (2-MD) and enabling it to be detected; so this part of ethylene glycol will be counted into the total ethylene glycol content in the wastewater, that is, the ethylene glycol content determined by the sodium arsenite chemical titration method includes this part of ethylene glycol present in 2-methyl-1,3-dioxolane. Therefore, in the present invention, in order to ensure the detection of this part of ethylene glycol, the wastewater sample to be tested is first subjected to a closed hydrothermal dissociation treatment to release this part of ethylene glycol present in 2-methyl-1,3-dioxolane, thereby ensuring the detection accuracy. The reaction formula is as follows:

[0067]

[0068] S3. Detection of wastewater to be tested:

[0069] S3-1. Accurately weigh 1 - 2 g of the wastewater to be tested and add it to a sample bottle, record the mass m, accurate to 0.0001 g, and then accurately pipette 2.5 - 10 mL of a methanol solution of 1,6-hexanediol with a mass concentration of 0.2 - 0.8 g / L into the sample bottle, and shake well to obtain a mixed solution;

[0070] S3-2. Use a microsyringe to transfer 0.3 - 1.2 μL of the mixed solution into the gas chromatograph for injection testing. After the peak emergence ends, read the peak area S' of the internal standard substance from the chromatogram NB and the peak area S' of ethylene glycol EG , and calculate the ethylene glycol content C in the wastewater to be tested according to the following formula EG :

[0071]

[0072] In steps S1 and S3, the gas chromatograph detection parameters are:

[0073] 1) Column temperature: Programmed temperature rise is adopted. Specifically, the temperature is raised to 70 °C and held for 2 min, then it is raised to 175 °C at a rate of 15 °C / min and held for 2 min;

[0074] 2) The detector temperature is 250 °C and the injector temperature is 250 °C;

[0075] 3) The flow rate of the hydrogen needle valve is 30 ml / min, the flow rate of the air needle valve is 350 ml / min, and the flow rate of the nitrogen needle valve is 30 ml / min.

[0076] 4) Use a micro syringe to inject the mixed solution, and the injection volume is 0.6 μL;

[0077] 5) Adopt a strong polar chromatographic column, and the specifications are: 15 m × 0.32 mm × 0.25 μm (column length × column diameter × liquid film thickness).

[0078] The above is the general concept of the present invention. The following provides detailed examples and comparative examples on this basis to further illustrate the present invention.

[0079] Example 1

[0080] A method for detecting the content of ethylene glycol in esterification wastewater, the method comprising the following steps:

[0081] S1. Determine the ethylene glycol correction factor K:

[0082] Accurately pipette 25 mL of a methanol solution of ethylene glycol with a concentration of 10 g / L and 5 mL of an internal standard solution into a glass sample bottle using a pipette. The internal standard solution is a methanol solution of 1,6 - hexanediol with a concentration of 0.4 g / L. Tighten the bottle cap and shake well to obtain a mixed solution. Use a micro syringe to pipette 0.6 μL of this mixed solution into a gas chromatograph for injection testing; after the peaks have finished emerging, read the peak areas of the internal standard and ethylene glycol from the chromatogram, and calculate the ethylene glycol correction factor K according to the following formula:

[0083]

[0084] In the formula: S EG is the peak area of ethylene glycol in the chromatogram, S NB is the peak area of the internal standard in the chromatogram, m EG is the mass of ethylene glycol in the injected mixed solution, m NB is the mass of the internal standard in the injected mixed solution;

[0085] S2. Closed hydrothermal separation treatment: Place the wastewater to be detected in a closed container, keep it at a temperature of 65 °C for 20 min, and then cool it to room temperature to obtain the wastewater sample to be detected;

[0086] S3. Detection of the wastewater to be detected:

[0087] S3-1. Weigh accurately 1 - 2 g of the wastewater to be detected and add it to a sample bottle. Record the mass m, accurate to 0.0001 g. Then accurately pipette 5 mL of a methanol solution of 1,6 - hexanediol with a mass concentration of 0.4 g / L into the sample bottle and shake well to obtain a mixed solution.

[0088] S3-2. Use a micro - syringe to pipette 0.6 μL of the mixed solution into a gas chromatograph for injection testing. After the peak emergence ends, read the peak area S' of the internal standard from the chromatogram. NB and the peak area S' of ethylene glycol EG , and calculate the content C of ethylene glycol in the wastewater to be detected according to the following formula EG :

[0089]

[0090] Application effect test:

[0091] Test example: Use the esterification wastewater from the factory of Jiangsu Xuanda High - Molecular Materials Co., Ltd. as the wastewater to be detected, and detect the content of ethylene glycol in it by the method of Example 1.

[0092] For comparison, set Control Example 1 and Control Example 2 at the same time. Control Example 1 uses the traditional sodium arsenite chemical titration method for detection; the difference between the method used in Control Example 2 and that in Example 1 is that it does not include step S2, that is, directly test the wastewater to be detected using a gas chromatograph.

[0093] Refer to Figure 1 , which is the chromatogram obtained for determining the correction factor K in step S1 of Example 1. Refer to Figure 2 , which is the chromatogram of the sample obtained in the test example. Refer to Figure 3 , which is the chromatogram of the sample obtained in Control Example 2. The specific detection data of the test example and Control Examples 1 and 2 are shown in Table 1 below. The detection lower limit of the content of ethylene glycol in the method of the present invention is 0.005%. For the same sample to be detected, for the statistical results of 6 tests, the coefficient of variation of Example 1 < 1.0%, and the deviation from the test result of the sodium arsenite chemical titration method < 0.05%, having the characteristics of fine test precision, high result accuracy and good repeatability.

[0094] Table 1

[0095]

[0096] Although the embodiments of the present invention have been disclosed as above, it is not limited to only the applications listed in the specification and embodiments. It can be fully applied to various fields suitable for the present invention. For those familiar with the field, additional modifications can be easily made. Therefore, without departing from the general concept defined by the claims and the equivalent scope, the present invention is not limited to specific details.

Claims

1. A method for detecting the content of ethylene glycol in esterification wastewater, characterized in that: The method comprises the following steps: firstly subjecting the wastewater to be tested to a closed hydrothermal separation treatment to obtain a wastewater sample to be tested, and then using a gas chromatography quantitative analysis method to detect the ethylene glycol content in the wastewater sample to be tested.

2. The method for detecting the ethylene glycol content in esterification wastewater according to claim 1, characterized in that: The method of closed hydrothermal separation treatment is: place the wastewater to be tested in a closed container, keep it at a temperature of 55°C to 80°C for 10min to 30min, and then cool it to room temperature to obtain the wastewater sample to be tested.

3. The method for detecting the ethylene glycol content in esterification wastewater according to claim 2, characterized in that: The gas chromatography quantitative analysis method adopts the internal standard method for detection, and the internal standard is 1,6-hexanediol.

4. The method for detecting the ethylene glycol content in esterification wastewater according to claim 3, characterized in that: The method comprises the following steps: S1. Determination of ethylene glycol correction factor K: Take a methanol solution of ethylene glycol of known concentration and mix it with an internal standard solution of known concentration to obtain a mixed solution. Take the mixed solution and inject it into a gas chromatograph for testing. After the peak is finished, read the internal standard and ethylene glycol peak areas from the chromatogram, and calculate the ethylene glycol correction factor K according to the following formula: Where: S EG is the peak area of ​​ethylene glycol in the chromatogram, S NB is the peak area of ​​the internal standard in the chromatogram, m EG is the mass of ethylene glycol in the injected mixed solution, m NB is the mass of the internal standard in the injected mixed solution; S2. Perform a closed hydrothermal separation treatment on the wastewater to be tested to obtain a wastewater sample to be tested: S3. Wastewater testing: S3-1. Accurately weigh the wastewater to be tested with a mass m and add it into a container. Then pipette an internal standard solution with a known concentration into the container and shake well to obtain a mixed solution. S3-2, take the mixed liquid and add it to the gas chromatograph for sampling test, wait until the peak is finished, and read the peak area S' of the internal standard from the chromatogram. NB and the peak area of ​​ethylene glycol S' EG , calculate the ethylene glycol content C in the wastewater to be tested according to the following formula EG :

5. The method for detecting the ethylene glycol content in esterification wastewater according to claim 4, characterized in that: The internal standard solution was a methanol solution of 1,6-hexanediol.

6. The method for detecting the ethylene glycol content in esterification wastewater according to claim 4, characterized in that: The concentration of the internal standard solution is 0.2-0.8 g / L.

7. The method for detecting the ethylene glycol content in esterification wastewater according to claim 4, characterized in that: The chromatographic column is a highly polar chromatographic column.

8. The method for detecting the ethylene glycol content in esterification wastewater according to claim 4, characterized in that: The method comprises the following steps: S1. Determination of ethylene glycol correction factor K: Use a pipette to accurately transfer 12.5-50mL of 5-20g / L ethylene glycol methanol solution and 2.5-10mL of internal standard solution, add them into a glass sample bottle, the internal standard solution is 0.2-0.8g / L 1,6-hexanediol methanol solution, tighten the bottle cap and shake well to obtain a mixed solution, use a micro syringe to transfer 0.3-1.2μL of the mixed solution to the gas chromatograph for injection testing; after the peak is finished, read the internal standard and ethylene glycol peak areas from the chromatogram, and calculate the ethylene glycol correction factor K according to the following formula: Where: S EG is the peak area of ​​ethylene glycol in the chromatogram, S NB is the peak area of ​​the internal standard in the chromatogram, m EG is the mass of ethylene glycol in the injected mixed solution, m NB is the mass of the internal standard in the injected mixed solution; S2. Closed hydrothermal separation treatment: Place the wastewater to be tested in a closed container, keep it at a temperature of 55°C to 80°C for 10min to 30min, and then cool it to room temperature to obtain the wastewater sample to be tested; S3. Wastewater testing: S3-1. Accurately weigh 1-2g of the wastewater to be tested and add it to the sample bottle. Record the mass m to an accuracy of 0.0001g. Then accurately pipette 2.5-10mL of a methanol solution of 1,6-hexanediol with a mass concentration of 0.2-0.8g / L into the sample bottle and shake well to obtain a mixed solution. S3-2, use a microsyringe to transfer 0.3-1.2 μL of the mixed solution into the gas chromatograph for injection testing, wait for the peak to be eluted, and read the peak area S' of the internal standard from the chromatogram. NB and the peak area of ​​ethylene glycol S' EG , calculate the ethylene glycol content C in the wastewater to be tested according to the following formula EG :

9. The method for detecting the ethylene glycol content in esterification wastewater according to claim 4, characterized in that: The method comprises the following steps: S1. Determination of ethylene glycol correction factor K: Use a pipette to accurately transfer 25 mL of 10 g / L ethylene glycol methanol solution and 5 mL of internal standard solution, add them to a glass sample bottle, the internal standard solution is 0.4 g / L 1,6-hexanediol methanol solution, tighten the bottle cap and shake well to obtain a mixed solution, use a micro syringe to transfer 0.6 μL of the mixed solution to the gas chromatograph for injection testing; after the peak is finished, read the internal standard and ethylene glycol peak areas from the chromatogram, and calculate the ethylene glycol correction factor K according to the following formula: Where: S EG is the peak area of ​​ethylene glycol in the chromatogram, S NB is the peak area of ​​the internal standard in the chromatogram, m EG is the mass of ethylene glycol in the injected mixed solution, m NB is the mass of the internal standard in the injected mixed solution; S2. Closed hydrothermal separation treatment: Place the wastewater to be tested in a closed container, keep it at a temperature of 55°C to 80°C for 10min to 30min, and then cool it to room temperature to obtain the wastewater sample to be tested; S3. Wastewater testing: S3-1. Accurately weigh 1-2g of the wastewater to be tested and add it to the sample bottle. Record the mass m to an accuracy of 0.0001g. Then accurately pipette 5mL of a methanol solution of 1,6-hexanediol with a mass concentration of 0.4g / L into the sample bottle and shake well to obtain a mixed solution. S3-2, use a micro syringe to transfer 0.6 μL of the mixed solution into the gas chromatograph for injection testing, wait until the peak is finished, and read the peak area S' of the internal standard from the chromatogram. NB and the peak area of ​​ethylene glycol S' EG , calculate the ethylene glycol content C in the wastewater to be tested according to the following formula EG :

10. The method for detecting the ethylene glycol content in esterification wastewater according to claim 1, characterized in that: The gas chromatograph detection parameters are: 1) Column temperature: The temperature was raised to 70°C, maintained for 2 min, then raised to 175°C at a rate of 15°C / min, and maintained for 2 min; 2) The detector temperature is 250°C and the injector temperature is 250°C; 3) The flow rate of the hydrogen needle valve is 30 ml / min, the flow rate of the air needle valve is 350 ml / min, and the flow rate of the nitrogen needle valve is 30 ml / min.

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