Vinyl chloride product produced by ethylene method and trace impurity detection method

Abstract

The invention belongs to the technical field of analytical chemistry, and particularly relates to a vinyl chloride product produced by an ethylene method and a trace impurity detection method. According to the method disclosed by the invention, a vinyl chloride liquid sample is instantly and completely vaporized and integrally transferred to a gas chromatograph through flash evaporation sample injection, so that the liquid vinyl chloride sample is completely vaporized and integrally transferred; liquid vinyl chloride is subjected to flash evaporation and then enters a gas chromatography 1mL sample injection six-way valve, volume quantification is ensured, vinyl chloride and impurities are effectively separated through the separation effect of a gas chromatography column, only 1-3 characteristic ions of target impurities are monitored in an SIM mode through the advantages of high sensitivity and low detection limit of a quadrupole mass spectrometry detector, interference of other ions in a matrix is eliminated, and the detection accuracy of the target impurities is improved. The detection method has the advantages that the signal-to-noise ratio is greatly increased, high-sensitivity and high-selectivity quantitative analysis on trace and even trace (g / g level and even lower) impurities in vinyl chloride is realized, rapid screening of vinyl chloride products and identification of process abnormality are realized, and the detection method has universality.

Description

Technical Field

[0001] This invention belongs to the field of analytical chemistry technology, specifically relating to a method for detecting trace impurities in vinyl chloride products produced by the ethylene process. Background Technology

[0002] Vinyl chloride (VCM) is the monomer used to synthesize polyvinyl chloride (PVC), and industrially it is mainly produced through the calcium carbide process and the ethylene process (ethylene chlorination followed by cracking). The purity and impurity content of vinyl chloride are key indicators that determine the quality of PVC resin and its subsequent processing performance.

[0003] In the ethylene process for producing vinyl chloride, trace impurities may remain in the product due to incomplete reactions, side reactions, and the introduction of raw materials. These impurities mainly include unreacted raw materials (ethylene) and byproducts (acetylene, chloromethane, 1-butene, vinylacetylene, 1,3-butadiene, chloroethane, 2-butene, vinyl bromide, 1,1-dichloroethylene, trans-1,2-dichloroethylene, 1,1-dichloroethane, cis-1,2-dichloroethylene, 1,2-dichloroethane, etc.). The presence of these impurities not only affects the degree of polymerization and subsequent processing performance of polyvinyl chloride products but may also cause equipment corrosion and process safety hazards. Therefore, accurate detection of vinyl chloride products and impurities is a core element in ensuring production quality and optimizing the process.

[0004] The detection of vinyl chloride typically employs traditional gas chromatography, where the sample is vaporized and analyzed using a flame ionization detector. These methods have the following main drawbacks: First, there is sample introduction discrimination: In traditional methods, the sample is directly injected as a liquid or released directly into the gas chromatograph injection interface through a sampling cylinder. This has a significant sample introduction discrimination effect on vinyl chloride and impurities that are released instantaneously to atmospheric pressure and form a gas-liquid mixture, resulting in inaccurate quantification of the main components and impurities. Second, the sensitivity and anti-interference ability are poor: the main peak of vinyl chloride in the sample (content greater than 99.9%) is extremely high, and traditional methods have poor separation effect on impurities and high detection limits; Third, the qualitative ability is insufficient: traditional hydrogen flame ionization detectors cannot accurately identify unknown impurities. The accuracy of qualitative identification depends only on standard substances. They are not capable of identifying unknown impurities and are difficult to effectively separate and identify impurities with similar structures, such as isomers. Fourth, the methods have low sensitivity and high detection limits: traditional vinyl chloride detection methods have detection limits of 10-20 µg / g or higher, which cannot meet the detection requirements of high-end PVC production for trace impurities (µg / g or even lower).

[0005] Gas chromatography-quadrupole mass spectrometry (GC-MS) is currently the most advanced and popular detection method, but there are few reports on its application in detecting vinyl chloride products and trace impurities produced by the ethylene process. Therefore, there is an urgent need to develop an accurate, direct, and comprehensive method for analyzing the content of vinyl chloride products and trace impurities generated by the ethylene process. Summary of the Invention

[0006] The technical problem to be solved by this invention is to provide a method for detecting trace impurities in vinyl chloride products produced by the ethylene process. The method using flash injection-gas chromatography-quadrupole mass spectrometry provides a more comprehensive and superior analytical guarantee for the quality control and process optimization of vinyl chloride products produced by the ethylene process.

[0007] The technical solution adopted is as follows: A method for detecting trace impurities in vinyl chloride products produced by the ethylene process includes the following steps: S1. Sample flashing and injection: The liquid vinyl chloride sample is instantly vaporized through a flash injector, and the vaporized sample is transferred to the six-way gas injection valve of the gas chromatograph. S2. Gas chromatography separation: The sample enters the vaporization chamber through the six-way gas injection valve and then enters the chromatographic column for separation; S3. Mass spectrometry detection: The components separated by chromatography are sequentially introduced into a quadrupole mass spectrometer and ionized under an electron impact ionization source. The detection includes: (a) Using full scan mode, total ion chromatograms and mass spectra of each component were acquired for qualitative analysis; (b) Selected ion monitoring mode is used to monitor the characteristic ion signals of specific target impurities for quantitative analysis; S4. Data Processing: (a) Qualitative analysis: The mass spectra of each chromatographic peak in the total ion current chromatogram obtained in full scan mode are compared with the standard mass spectrum library, and the main peak of vinyl chloride and each impurity peak are qualitatively identified by combining the retention time of the standard. (b) Quantitative analysis: In selected ion monitoring mode, the external standard method is used to establish a standard working curve by analyzing the target impurity standard gas, and the concentration of the target impurity characteristic ion in the vinyl chloride sample is calculated based on the response value of the target impurity characteristic ion.

[0008] Preferably, before detection, the flash injector, gas chromatograph, and mass spectrometer are started sequentially, parameters are set and preheating is performed, the temperature of the flash injector is set to 100°C and preheated for at least 20 minutes; the flash injector is connected to the gas chromatograph inlet via a heated transmission line. Set the gas chromatograph injection port or vaporization chamber temperature to 200℃, the gas six-way valve temperature to 100℃, the transfer line temperature to 120~150℃, and the initial column temperature to 45℃. The ion source temperature of the quadrupole mass spectrometer was set to 200℃, and the interface temperature was set to 250℃.

[0009] Preferably, in step S1, after the sample is vaporized, the pipeline is first purged with the sample to remove the gas in the original pipeline; the sample purging time is 1 to 2 minutes.

[0010] Preferably, in step S2, the gas injection six-way valve is a 1mL gas injection six-way valve; the injection time is 1min, and the auxiliary carrier gas pressure of the gas six-way valve is set to 40.0kPa during injection.

[0011] Preferably, the chromatographic column is a capillary column filled with 100% divinylbenzene porous polymer, with dimensions of 30m × 0.32mm × 10μm; the column flow rate for chromatographic separation is 2 mL / min.

[0012] Preferably, during detection, the temperature program of the chromatographic column is as follows: initial temperature of 45°C held for 3 min, then increased to 180°C at a rate of 5°C / min and held for 10–15 min.

[0013] Preferably, in step S4, the electron energy of the ion source is 70 eV; the full scan mode has a scan quality range of m / z 35–400.

[0014] Preferably, in step S4, the qualitative analysis adopts a full scan mode, comparing the mass spectra of each chromatographic peak in the obtained total ion current chromatogram with standard mass spectrometry libraries such as NIST, and combining the retention times of the standards to qualitatively identify the vinyl chloride main peak and each impurity peak; the identified impurities include: ethylene, acetylene, ethane, propylene, chloromethane, propyne, vinyl chloride, isobutane, 1-butene, vinylacetylene, 1,3-butadiene, chloroethane, 1-butyne, 2-butene, vinyl bromide, 1,1-dichloroethylene, trans-1,2-dichloroethylene, 1,1-dichloroethane, cis-1,2-dichloroethylene, 1,2-dichloroethane, and 1,1,2-trichloroethane.

[0015] Preferably, in step S4, the quantitative analysis adopts selected ion monitoring mode and external standard method for quantification; a standard working curve is established for the standard gas containing the target impurity under the same analytical conditions as the sample, and its concentration in the sample is calculated based on the response value of the target analyte.

[0016] Preferably, the method for determining the limit of detection is as follows: using a mixed standard gas containing the target component with a concentration close to or equal to 5 times the expected limit of detection, the analysis is repeated 7 times under the exact same conditions as the sample analysis, and the concentration corresponding to the signal-to-noise ratio of 3 is taken as the limit of detection of the method.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The method of the present invention uses flash evaporation to make the liquid vinyl chloride sample instantly and completely vaporize and transfer to the gas chromatograph, ensuring that the liquid vinyl chloride sample is completely vaporized and transferred as a whole; after flash evaporation, the liquid vinyl chloride enters the 1mL injection six-way valve of the gas chromatograph. Combined with the accurate volume quantification of the gas injection six-way valve, the combination of flash vaporization and gas injection six-way valve eliminates the injection discrimination effect, making the composition of the gas sample entering the gas chromatograph highly consistent with the composition of the original liquid sample, ensuring the accuracy of qualitative and quantitative detection.

[0018] (2) This invention effectively separates vinyl chloride and impurities through gas chromatography column separation, and qualitatively identifies vinyl chloride and impurities through quadrupole mass spectrometry detector. It obtains rich fragment ion information through mass spectrometry, obtains clear information on unknown compounds, and can also identify isomers by directional retrieval of characteristic ion peaks of isomers.

[0019] (3) This invention utilizes the advantages of high sensitivity and low detection limit of quadrupole mass spectrometer to monitor only 1-3 characteristic ions of target impurities in SIM mode, eliminating interference from other ions in the matrix, greatly improving the signal-to-noise ratio, and achieving highly sensitive and selective quantitative analysis of trace or even ultra-trace levels (µg / g level or even lower) of impurities in vinyl chloride. It enables rapid screening and identification of process anomalies in vinyl chloride products, and allows for precise comparison of vinyl chloride from different batches and process sources, providing data support far exceeding traditional methods for production process optimization.

[0020] (4) The present invention establishes an ethylene method for vinyl chloride analysis. Flash evaporation injection-gas chromatography separation-quadrupole mass spectrometry detection is a complete technical solution. Its technical principle and framework can be extended to the full component analysis of other chemical products with similar physicochemical properties and analytical needs (such as butadiene), demonstrating good versatility and industry promotion value. Attached Figure Description

[0021] Figure 1 The chromatograms and mass spectra are those obtained in Example 1 of this invention.

[0022] Figure 2 Figure 1 shows the quantitative chromatograms of a typical impurity (chloromethane) in Example 1 of this invention; wherein, (a) is the quantitative chromatogram of characteristic ions of the impurity, and (b) is the calibration curve.

[0023] Figure 3 The chromatograms and mass spectra are for the detection in Example 1 of the present invention. Detailed Implementation

[0024] The accompanying drawings are for illustrative purposes only; some common knowledge or prior art may be omitted to better illustrate this embodiment. Unless otherwise specified, all instruments and materials used are available through conventional commercial channels.

[0025] The present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0026] Example 1 A method for detecting trace impurities in vinyl chloride products produced by the ethylene process involves first connecting the equipment. A flash sampler is connected to the gas chromatograph (GC) inlet via a heated transfer line, and the GC is connected to a quadrupole mass spectrometer (QMS). Before detection, the flash sampler, GC, and QMS are started sequentially, parameters are set, and preheating is performed. The flash sampler temperature is set to 100°C and preheated for 30 minutes. The GC inlet or vaporization chamber temperature is set to 200°C, the six-way gas valve temperature to 100°C, the transfer line temperature to 120°C, and the initial column temperature to 45°C.

[0027] The ion source temperature of the quadrupole mass spectrometer was set to 200℃, and the interface temperature was set to 250℃.

[0028] The detection method includes the following steps: S1. Sample flashing and injection: The liquid vinyl chloride sample is instantly vaporized through a flash injector, and the vaporized sample is used to purge the pipeline for 2 minutes to remove other gases in the pipeline; the vaporized sample is then transferred to the six-way gas injection valve of the gas chromatograph.

[0029] S2. Gas Chromatography Separation: The sample enters the vaporization chamber through the six-way gas injection valve and then enters the chromatographic column for separation. It is equipped with a 1 mL six-way injection valve, valve temperature 100℃, valve injection time 1 minute, and auxiliary carrier gas 40.0 kPa. The vaporization chamber temperature is 200℃. A 100% divinylbenzene porous polymer column (30 m * 0.32 mm * 10 μm) is used. The temperature program is 45℃ held for 3 min, then increased to 180℃ at 5℃ / min and held for 15 min. The column flow rate is 2 mL / min.

[0030] S3. Mass spectrometry detection and data processing: After chromatographic separation, each component sequentially enters a quadrupole mass spectrometer and is ionized under an electron impact ionization source. The detection includes: (a) Using full scan mode, total ion chromatograms and mass spectra of each component were acquired for qualitative analysis.

[0031] (b) Selected ion monitoring mode is used to monitor the characteristic ion signals of specific target impurities for quantitative analysis.

[0032] S4. Data Processing: (a) Qualitative Analysis: The mass spectra of each peak in the total ion current chromatogram obtained in full scan mode are compared with those in a standard mass spectrometry library. Combined with the retention times of the standards, the vinyl chloride main peak and various impurity peaks are qualitatively identified. The scan range is set to m / z 35-400. Based on the mass spectra generated by the instrument, the mass spectra are analyzed to identify characteristic ions, and then ions for SIM monitoring are screened and determined. Higher ion intensity results in better detection sensitivity. Using high abundance, high specificity, good stability, and moderate mass number as screening principles, 1-3 optimal characteristic ions are selected. The ion with the highest abundance and greatest stability is selected for precise quantification.

[0033] Select one or two additional characteristic ions. During sample analysis, only when the signal intensity ratio of these two or three ions matches that in the standard can it be confirmed that the detected signal does indeed come from the target impurity, rather than interference from other isotopes.

[0034] like Figure 1 , 2 As shown, the mass spectra of each peak in the obtained total ion current chromatogram (TIC) were compared with standard mass spectrometry libraries such as NIST. Based on the retention times of the standards, the main peak of vinyl chloride and various impurity peaks were qualitatively identified. For the ethylene process, the key impurities identified included, but were not limited to: ethylene, acetylene, ethane, propylene, chloromethane, propyne, vinyl chloride, isobutane, 1-butene, vinylacetylene, 1,3-butadiene, chloroethane, 1-butyne, 2-butene, vinyl bromide, 1,1-dichloroethylene, trans-1,2-dichloroethylene, 1,1-dichloroethane, cis-1,2-dichloroethylene, 1,2-dichloroethane, and 1,1,2-trichloroethane.

[0035] (b) Quantitative analysis: In selected ion monitoring mode, the external standard method is used to establish a standard working curve by analyzing the target impurity standard gas, and the concentration of the target impurity characteristic ion in the vinyl chloride sample is calculated based on the response value of the target impurity characteristic ion.

[0036] The external standard method was used for quantification. Standard gases containing the target impurities were purchased, and a standard working curve was established under the same analytical conditions as the sample. The concentration of the target analyte in the sample was calculated based on its response value.

[0037] (c) Calculation of the limit of detection (LOD): A certified mixed standard gas containing vinyl chloride and its impurities (ethylene, acetylene, ethane, propylene, chloromethane, propyne, vinyl chloride, isobutane, 1-butene, vinylacetylene, 1,3-butadiene, chloroethane, 1-butyne, 2-butene, vinyl bromide, 1,1-dichloroethylene, trans-1,2-dichloroethylene, 1,1-dichloroethane, cis-1,2-dichloroethylene, 1,2-dichloroethane, 1,1,2-trichloroethane) was used. The concentration of the standard gas was close to 5 times the expected detection limit of each component. The low-concentration mixed standard gas was analyzed 7 times in the same manner as the sample. The signal-to-noise ratio of each component was directly measured at concentrations close to the detection limit. The signal-to-noise ratio (S / N) = 3 was used as the criterion for determining the detection limit.

[0038] The limit of detection (LOD) is: LOD = Blank mean + 3 × Blank standard deviation.

[0039] When repeated measurements are performed on low-concentration standard samples, the following can be obtained: .

[0040] After 7 replicates at a 5-fold LOD concentration, the average signal-to-noise ratio (SNR) was approximately S / N ≈ 15. Generally, SNR is proportional to concentration; therefore, it can be deduced that: ; Where C is the concentration of the substance, the LOD of vinyl chloride and its various impurities can be calculated.

[0041] A 5x LOD ensures stable and measurable signal. The main purpose of the 7 repetitions is to evaluate the average value and standard deviation of the signal at that concentration and to calculate the average signal-to-noise ratio.

[0042] The detection limits of the method of the present invention for vinyl chloride and its main impurities are shown in Table 1.

[0043] Table 1 Characteristic monitoring ions and detection limits for each impurity As shown in Table 1, the detection limits for each impurity are as low as µg / g, indicating that the detection method of this invention, through precise instrument coupling and optimized parameters, achieves a complete process innovation from sample introduction and separation to detection. It can reliably detect and quantify impurities in vinyl chloride at levels as low as one part per million or even lower. It also meets the stringent requirements for impurity control in high-end polymerization-grade raw materials and has universal applicability.

[0044] Application Example 1 like Figure 3 As shown, a vinyl chloride sample produced by a factory was subjected to qualitative and quantitative analysis of impurities using the detection method of this invention and the conditions set by each instrument in Example 1.

[0045] The test results showed that acetylene was 0.2 µg / g, chloromethane was 33.4 µg / g, vinylacetylene was 3.2 µg / g, 1,3-butadiene was 1.2 µg / g, chloroethane was 28.5 µg / g, bromoethylene was 2.6 µg / g, and 1,1,2-trichloroethane was 1.8 µg / g.

[0046] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A method for detecting trace impurities in vinyl chloride products produced by the ethylene process, characterized in that, Includes the following steps: S1. Sample flashing and injection: The liquid vinyl chloride sample is vaporized through a flash injector, and the vaporized sample is transferred to the six-way gas injection valve of the gas chromatograph. S2. Gas chromatography separation: The sample enters the vaporization chamber through the six-way gas injection valve and then enters the chromatographic column for separation; S3. Mass spectrometry detection: The components separated by chromatography are sequentially introduced into a quadrupole mass spectrometer and ionized under an electron impact ionization source. The detection includes: (a) Using full scan mode, total ion chromatograms and mass spectra of each component were acquired for qualitative analysis; (b) Selected ion monitoring mode is used to monitor the characteristic ion signals of specific target impurities for quantitative analysis; S4. Data Processing: (a) Qualitative analysis: The mass spectra of each chromatographic peak in the total ion current chromatogram obtained in full scan mode are compared with the standard mass spectrum library, and the main peak of vinyl chloride and each impurity peak are qualitatively identified by combining the retention time of the standard. (b) Quantitative analysis: In selected ion monitoring mode, the external standard method is used to establish a standard working curve by analyzing the target impurity standard gas, and the concentration of the target impurity characteristic ion in the vinyl chloride sample is calculated based on the response value of the target impurity characteristic ion.

2. The method for detecting trace impurities in vinyl chloride products produced by the ethylene process according to claim 1, characterized in that, Before detection, start the flash injector, gas chromatograph, and quadrupole mass spectrometer in sequence, set the parameters and preheat them. Set the temperature of the flash injector to 100℃ and preheat it for at least 20 minutes. The flash injector is connected to the gas chromatograph inlet via a heated transfer line. Set the gas chromatograph injection port or vaporization chamber temperature to 200℃, the gas six-way valve temperature to 100℃, the transfer line temperature to 120~150℃, and the initial column temperature to 45℃. The ion source temperature of the quadrupole mass spectrometer was set to 200℃, and the interface temperature was set to 250℃.

3. The method for detecting trace impurities in vinyl chloride products produced by the ethylene process according to claim 1, characterized in that, In step S1, after the sample is vaporized, the pipeline is purged with the sample for 1 to 2 minutes.

4. The method for detecting trace impurities in vinyl chloride products produced by the ethylene process according to claim 1, characterized in that, In step S2, the gas injection six-way valve is a 1mL gas injection six-way valve; the injection time is 1min, and the auxiliary carrier gas pressure of the gas six-way valve is set to 40.0kPa during injection.

5. The method for detecting trace impurities in vinyl chloride products produced by the ethylene process according to claim 4, characterized in that, The chromatographic column is a capillary column packed with 100% divinylbenzene porous polymer, with dimensions of 30m × 0.32mm × 10μm; the column flow rate for chromatographic separation is 2 mL / min.

6. The method for detecting trace impurities in vinyl chloride products produced by the ethylene process according to claim 5, characterized in that, During detection, the column temperature program is as follows: initial temperature 45℃ held for 3 min, then increased to 180℃ at a rate of 5℃ / min and held for 10–15 min.

7. The method for detecting trace impurities in vinyl chloride products produced by the ethylene process according to claim 1, characterized in that, In step S4, the electron energy of the ion source is 70 eV; Full scan mode, scan quality range m / z 35-400.

8. The method for detecting trace impurities in vinyl chloride products produced by the ethylene process according to claim 1, characterized in that, In step S4, the qualitative analysis adopts full scan mode. The mass spectra of each chromatographic peak in the obtained total ion current chromatogram are compared with standard mass spectrometry libraries such as NIST. Combined with the retention time of the standard, the main peak of vinyl chloride and each impurity peak are qualitatively identified. The identified impurities include: ethylene, acetylene, ethane, propylene, chloromethane, propyne, vinyl chloride, isobutane, 1-butene, vinylacetylene, 1,3-butadiene, chloroethane, 1-butyne, 2-butene, vinyl bromide, 1,1-dichloroethylene, trans-1,2-dichloroethylene, 1,1-dichloroethane, cis-1,2-dichloroethylene, 1,2-dichloroethane, and 1,1,2-trichloroethane.

9. The method for detecting trace impurities in vinyl chloride products produced by the ethylene process according to claim 1, characterized in that, In step S4, the quantitative analysis adopts the selected ion monitoring mode and the external standard method is used for quantification; a standard working curve is established for the standard gas containing the target impurity under the same analytical conditions as the sample, and the concentration of the target analyte in the sample is calculated based on the response value of the target analyte.

10. The method for detecting trace impurities in vinyl chloride products produced by the ethylene process according to claim 1, characterized in that, The method for determining the limit of detection is as follows: using a mixed standard gas containing the target component with a concentration close to or equal to 5 times the expected limit of detection, the analysis is repeated 7 times under the exact same conditions as the sample analysis, and the concentration corresponding to the signal-to-noise ratio of 3 is taken as the limit of detection of the method.

Images