Detection system and method for gaseous components of the reaction for the production of dimeric phthalic anhydride by phenoxylation

Abstract

This invention relates to the field of detection, specifically to a detection system and method for gaseous components in the preparation of maleic anhydride by benzene oxidation. The system includes: a first analytical unit comprising a second switching valve, a second chromatographic column, a third switching valve, and a fourth switching valve connected in sequence; the second switching valve is connected to a first chromatographic column, and the third switching valve is connected to a third chromatographic column; a second analytical unit comprising the first switching valve, the fourth chromatographic column, and the fourth switching valve connected in sequence; and a detection device connected to the fourth switching valve via a pipeline for detecting gaseous components; the first and second switching valves are respectively connected to the analyte gas source and the carrier gas source. Using the system provided by this invention offers advantages such as simple qualitative analysis, good repeatability, and accurate quantitative analysis.

Description

Technical Field

[0001] This invention relates to the field of detection, specifically to a detection system and a method for detecting gaseous components in the preparation of maleic anhydride by benzene oxidation. Background Technology

[0002] Maleic anhydride, also known as maleic acid anhydride or dehydrated malic anhydride, is currently the world's third largest acid anhydride after phthalic anhydride and acetic anhydride. It is primarily used in the production of unsaturated polyester resins (UPR) and alkyd resins. In addition, it can be used to produce a range of important chemical products, including 1,4-butanediol (BDO), γ-butyrolactone (GBL), tetrahydrofuran (THF), maleic acid, fumaric acid, and tetrahydroanhydride.

[0003] The main process flow for producing maleic anhydride via benzene oxidation is as follows: benzene vapor and air (or oxygen) are mixed in a certain proportion, and then... n Under the action of an O-series catalyst, maleic anhydride mixture is generated in a fixed-bed reactor. After initial cooling by a gas cooler, some liquid crude maleic anhydride is captured in a partial condenser. The uncondensed gaseous maleic anhydride is absorbed by water or solvent and refined to obtain refined maleic anhydride. The liquid refined maleic anhydride is cooled and pressed into the finished product during the packaging process.

[0004] The main gaseous products of maleic anhydride production via benzene oxidation include CO, CO2, O2, N2, benzene, toluene, and maleic anhydride. Conventional monitoring of these gaseous products involves gas chromatography-thermal conductivity detector (GC-TDC). However, since the concentration of maleic anhydride in these products ranges from ppm to percentage, the biggest drawback of this method is the insufficient sensitivity of the TDC, making quantitative analysis of ppm-level products difficult. This requires multiple detectors and chromatographs, including TDC, flame ionization (FID), and nickel conversion furnaces. This approach is resource-intensive, time-consuming, and cumbersome. Furthermore, because TDC and FID are general-purpose detectors, separating polar and non-polar compounds in the reaction is challenging, necessitating the use of multiple columns. Qualitative analysis typically requires high-purity standards and the establishment of a standard curve using external standard methods, resulting in a lengthy testing cycle. GC-MS overcomes these shortcomings. Mass spectrometry (MS) offers high sensitivity to permanent gases and hydrocarbons, eliminating the need for high-purity standards for qualitative analysis. The selected ion mode of MS transforms it into a selective detector, significantly reducing the difficulty of separating permanent gases and hydrocarbons. Therefore, the use of gas chromatography-mass spectrometry (GC-MS) for quality control of the gas-phase reaction in the preparation of maleic anhydride by benzene oxidation is a very meaningful research work. Summary of the Invention

[0005] To address the above shortcomings of existing gas chromatography (TCD or FID) techniques for monitoring gaseous components in the benzene oxidation process for maleic anhydride production, this invention provides a detection system and method for gaseous components in the benzene oxidation process for maleic anhydride production. This system detects the contents of CO, CO2, O2, N2, benzene, toluene, and maleic anhydride in the reaction gas, offering advantages such as rapid detection, simple qualitative analysis, good repeatability, and accurate quantitative analysis.

[0006] To achieve the above objectives, a first aspect of the present invention provides a detection system for gaseous components in the benzene oxidation process for producing maleic anhydride, the system comprising:

[0007] The first analytical unit includes a second switching valve, a second chromatographic column, a third switching valve and a fourth switching valve connected in sequence. The second switching valve is connected to the first chromatographic column, and the third switching valve is connected to the third chromatographic column.

[0008] The second analytical unit includes a first switching valve, a fourth chromatographic column, and a fourth switching valve connected in sequence; and

[0009] The detection device, which is connected to the fourth switching valve via a pipeline, is used to detect gas phase components;

[0010] The first switching valve is connected to the gas source to be tested and the carrier gas source, the second switching valve is connected to the gas source to be tested and the carrier gas source, the first chromatographic column is used to separate O2+N2+CO, CO2 and benzene+toluene+maleic anhydride, the second chromatographic column is used to analyze CO2, the third chromatographic column is used to separate O2, N2 and CO, and the fourth chromatographic column is used to separate benzene, toluene and maleic anhydride.

[0011] A second aspect of the present invention provides a method for detecting gaseous components in the preparation of maleic anhydride by benzene oxidation, the method being carried out in the system described above, the method comprising:

[0012] The gas to be tested enters the system through a valve injection method, and the gas to be tested enters the first switching valve and the second switching valve respectively;

[0013] After the gas to be tested is separated by the first chromatographic column, O2+N2+CO, CO2, and benzene+toluene+maleic anhydride are obtained. Among them, benzene+toluene+maleic anhydride is backflushed out of the system. O2+N2+CO is then switched to the third chromatographic column for separation, and the separated O2, N2, and CO are then switched to the detection device for detection. CO2 is then switched to the second chromatographic column and then switched to the detection device for detection.

[0014] After the gas to be tested is separated by the fourth chromatographic column, benzene, toluene and maleic anhydride are obtained, and then the gas is switched to the detection device for detection.

[0015] Preferably, by controlling the switching sequence of the switching valves, the peak elution order of each component in the gas to be tested is controlled to be O2, N2, CO, CO2, benzene, toluene and maleic anhydride.

[0016] Using the method described in this invention within the system, the contents of CO, CO2, O2, N2, benzene, toluene, and maleic anhydride in the reaction gas phase can be determined simultaneously. The analysis process is completed within 7-15 minutes, providing a simple, rapid, and reliable analytical method for the gas phase components in the benzene oxidation process for producing maleic anhydride, which is beneficial for optimizing the reaction process conditions of the benzene oxidation process for producing maleic anhydride.

[0017] Moreover, the system provided by this invention has the advantages of simple qualitative analysis, good repeatability and accurate quantitative analysis, and the minimum detection limit of each component can be below 0.1 ppm. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the detection system for the gas phase components of the benzene oxidation method for producing maleic anhydride as described in this invention.

[0019] Figure 2 This is a gas chromatography-mass spectra of the gas-phase reaction products CO, CO2, O2, N2, benzene, toluene, and maleic anhydride described in Example 1 of this invention.

[0020] Explanation of reference numerals in the attached figures

[0021] 1. First switching valve; 2. Second switching valve; 3. Third switching valve; 4. Fourth switching valve; col1, First chromatographic column; col2, Second chromatographic column; col3, Third chromatographic column; col4, Fourth chromatographic column; 5. Detection device. Detailed Implementation

[0022] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0023] The first aspect of this invention provides a detection system for gaseous components in the benzene oxidation process for producing maleic anhydride, the system comprising:

[0024] The first analytical unit includes a second switching valve, a second chromatographic column, a third switching valve and a fourth switching valve connected in sequence. The second switching valve is connected to the first chromatographic column, and the third switching valve is connected to the third chromatographic column.

[0025] The second analytical unit includes a first switching valve, a fourth chromatographic column, and a fourth switching valve connected in sequence; and

[0026] The detection device, which is connected to the fourth switching valve via a pipeline, is used to detect gas phase components;

[0027] The first switching valve is connected to the gas source to be tested and the carrier gas source, the second switching valve is connected to the gas source to be tested and the carrier gas source, the first chromatographic column is used to separate O2+N2+CO, CO2 and benzene+toluene+maleic anhydride, the second chromatographic column is used to analyze CO2, the third chromatographic column is used to separate O2, N2 and CO, and the fourth chromatographic column is used to separate benzene, toluene and maleic anhydride.

[0028] Unless otherwise specified, all devices in this system are conventional devices. It should be understood that the system is also equipped with other conventional devices or pipelines, which can be configured as needed by those skilled in the art. Unless otherwise specified, connections are made according to conventional connection methods in the art, and will not be described in detail here.

[0029] For example, the system may also include an electronic flow control system for controlling flow and for pressure and / or flow compensation. Those skilled in the art can adjust its connection as needed, for example, it may be located between the first switching valve and the fourth chromatographic column, and / or between the second chromatographic column and the third switching valve.

[0030] Preferably, the first switching valve is a six-way valve, the second switching valve is a ten-way valve, the third switching valve is a six-way valve, and the fourth switching valve is a four-way valve.

[0031] Preferably, the stationary phase of the first chromatographic column is a polystyrene-based packing material, a polyvinylbenzene-based packing material, a polystyrene-divinylbenzene-based packing material, or a carbon molecular sieve packing material, more preferably a polystyrene-divinylbenzene-based packing material or a carbon molecular sieve packing material.

[0032] Among them, polystyrene fillers can be, for example, plot Q fillers or plot U fillers.

[0033] Among them, polyvinylbenzene fillers can be, for example, Chromosorb 101 filler or Chromosorb 102 filler.

[0034] Among them, polystyrene-divinylbenzene type fillers can be, for example, Porapak Q filler or Porapak S filler.

[0035] Among them, carbon molecular sieve packings can be, for example, Shincarbon packings or Carbon Sieve packings.

[0036] Preferably, the mesh size of the filler is 80-100 mesh.

[0037] Preferably, the first chromatographic column is a plot Q column, a Haysep Q column, or a Shincarbon column.

[0038] Preferably, the first chromatographic column has a length of 25-50m and a diameter of 0.25-0.32mm.

[0039] The stationary phase of the second chromatographic column is a polystyrene-based packing material, a polyvinylbenzene-based packing material, a polystyrene-divinylbenzene-based packing material, or a carbon molecular sieve packing material, preferably a polystyrene-divinylbenzene-based packing material or a carbon molecular sieve packing material.

[0040] Preferably, the mesh size of the filler is 80-100 mesh.

[0041] Preferably, the second chromatographic column is a plot Q column, a Haysep Q column, or a Shincarbon column.

[0042] Preferably, the second chromatographic column has a length of 25-50m and a diameter of 0.25-0.32mm.

[0043] The first chromatographic column and the second chromatographic column may be the same or different.

[0044] Preferably, the stationary phase of the third chromatographic column is a molecular sieve packing material, such as 5A molecular sieve packing material, more preferably MS5A packing material or Linden 5A packing material.

[0045] Preferably, the third chromatographic column is a 5A molecular sieve column. For example, it can be a 5A molecular sieve column purchased from Agilent Technologies.

[0046] Preferably, the mesh size of the filler is 80-100 mesh.

[0047] Preferably, the third chromatographic column has a length of 25-50m and a diameter of 0.25-0.32mm.

[0048] Preferably, the stationary phase of the fourth chromatographic column is a polyethylene glycol-based packing material.

[0049] Among them, polyethylene glycol fillers can be polyethylene glycol-10000 fillers or polyethylene glycol-20000 fillers, preferably polyethylene glycol-20000 fillers.

[0050] Preferably, the filler membrane thickness is 0.1-1 μm.

[0051] Preferably, the fourth chromatographic column is an Innowax column or a Stabilwax column.

[0052] The fourth chromatographic column has a length of 30-60m and a diameter of 0.25-0.32mm.

[0053] Preferably, port 1 of the first switching valve is connected to the vent valve, port 2 of the first switching valve is connected to port 9 of the second switching valve and / or the carrier gas source, a metering tube is provided between port 3 and port 6 of the first switching valve, port 4 of the first switching valve is connected to the fourth chromatographic column, and port 5 of the first switching valve is connected to the carrier gas source.

[0054] Preferably, a metering tube is provided between port 1 and port 8 of the second switching valve, a first chromatographic column is provided between port 2 and port 5 of the second switching valve, port 3 of the second switching valve is connected to a vent valve, ports 4 and 7 of the second switching valve are respectively connected to a carrier gas source, port 6 of the second switching valve is connected to a second chromatographic column, port 9 of the second switching valve is connected to port 2 of the first switching valve, and port 10 of the second switching valve is connected to the gas source to be tested.

[0055] Preferably, the No. 1 port of the third switching valve is closedly connected to the No. 6 port of the third switching valve, the No. 2 port of the third switching valve is connected to the No. 1 port of the fourth switching valve, a third chromatographic column is provided between the No. 3 port of the third switching valve and the No. 4 port of the third switching valve, and the No. 5 port of the third switching valve is connected to the second chromatographic column.

[0056] The closed connection method can be, for example, by connecting a damping valve between two interfaces.

[0057] Preferably, port 1 of the fourth switching valve is connected to port 2 of the third switching valve, port 2 of the fourth switching valve is connected to the mass spectrometer, port 3 of the fourth switching valve is connected to the fourth chromatographic column, and port 4 of the fourth switching valve is connected to the vent valve.

[0058] Those skilled in the art can select the appropriate size of the metering tube as needed, which will not be elaborated here.

[0059] Preferably, the detection device is a mass spectrometer.

[0060] A second aspect of the present invention provides a method for detecting gaseous components in the preparation of maleic anhydride by benzene oxidation, the method being carried out in the system described above, the method comprising:

[0061] The gas to be tested enters the system through a valve injection method, and the gas to be tested enters the first switching valve and the second switching valve respectively;

[0062] After the gas to be tested is separated by the first chromatographic column, O2+N2+CO, CO2, and benzene+toluene+maleic anhydride are obtained. Among them, benzene+toluene+maleic anhydride is backflushed out of the system. O2+N2+CO is then switched to the third chromatographic column for separation, and the separated O2, N2, and CO are then switched to the detection device for detection. CO2 is then switched to the second chromatographic column and then switched to the detection device for detection.

[0063] After the gas to be tested is separated by the fourth chromatographic column, benzene, toluene and maleic anhydride are obtained, and then the gas is switched to the detection device for detection.

[0064] Preferably, by controlling the switching sequence of the switching valves, the peak elution order of the components in the gas to be measured is controlled to be O2, N2, CO, CO2, benzene, toluene, and maleic anhydride, respectively. For example, the third, second, and fourth switching valves can be switched sequentially, so that the gases in the third, second, and fourth chromatographic columns enter the detection device for detection in sequence.

[0065] It should be understood that the switching time between valves should allow for complete elution of the analyte peak in the chromatographic column. The specific time will vary depending on the chromatographic conditions, and those skilled in the art can adjust it as needed.

[0066] Preferably, the chromatographic conditions include:

[0067] Temperature conditions: 40-150℃, constant temperature;

[0068] Carrier gas: helium or hydrogen.

[0069] Flow rate: 0.5-1.5 mL / min, constant flow rate;

[0070] Injection volume: 0.1 mL - 3 mL

[0071] Split ratio: 1:5-1:100.

[0072] Preferably, the detection is a quantitative detection, and the method uses external standard quantification. External standard quantification is a conventional method in the art and will not be described in detail here.

[0073] In this invention, unless otherwise specified, the proportions of each component are expressed by volume.

[0074] The present invention will be described in detail below through embodiments.

[0075] Reagents and medicines:

[0076] Standard gases: 1. O2 9.8%, N2 9.7%, CO 9.8%, CO2 9.9%, Benzene 0.7%, Toluene 0.5%, Maleic anhydride 0.2%, Helium (balanced)

[0077] 2. O2 100ppm, N2 100ppm, CO 100ppm, CO2 100ppm, benzene 10ppm, toluene 10ppm, maleic anhydride 10ppm, helium (balance).

[0078] In the following embodiments, the carrier gas is helium.

[0079] In the following examples, the reaction gas was taken from the maleic anhydride production reactor by benzene oxidation, and the reaction gas was introduced into the gas flow meter via a gas valve for gas chromatography-mass spectrometry (GC-MS) detection.

[0080] In the following examples, the chromatographic separation system was controlled and recorded using an Agilent 7890B / 5977B GC-MS system, and the control and recording of the chromatographic separation system were performed by a MassHunter workstation.

[0081] Specifically, the following embodiments are performed in the detection system described in this invention, such as... Figure 1 As shown:

[0082] The system includes: a first analytical unit comprising a second switching valve 2, a second chromatographic column col2, a third switching valve 3, and a fourth switching valve 4 connected in sequence; the second switching valve 2 is connected to the first chromatographic column col1, and the third switching valve 3 is connected to the third chromatographic column col3; a second analytical unit comprising a first switching valve 1, a fourth chromatographic column col4, and a fourth switching valve 4 connected in sequence; and a detection device connected to the fourth switching valve 4 via a pipeline for detecting gaseous components; wherein, the first switching valve 1 is connected to the analyte gas source and the carrier gas source, the second switching valve 2 is connected to the analyte gas source and the carrier gas source, the first chromatographic column col1 is used to separate O2+N2+CO, CO2, and benzene+toluene+maleic anhydride, the second chromatographic column col2 is used to analyze CO2, the third chromatographic column col3 is used to separate O2, N2, and CO, and the fourth chromatographic column col4 is used to separate benzene, toluene, and maleic anhydride. The first switching valve 1 is a six-way valve, the second switching valve 2 is a ten-way valve, the third switching valve 3 is a six-way valve, and the fourth switching valve 4 is a four-way valve.

[0083] Specifically, port 1 of the first switching valve 1 is connected to the vent valve, port 2 of the first switching valve 1 is connected to port 9 of the second switching valve 2 and / or the carrier gas source, a metering tube (25μL) is provided between port 3 and port 6 of the first switching valve 1, port 4 of the first switching valve 1 is connected to the fourth chromatographic column col4, and port 5 of the first switching valve 1 is connected to the carrier gas source.

[0084] A quantitative tube (500 μL) is installed between port 1 and port 8 of the second switching valve 2. A first chromatographic column col1 is installed between port 2 and port 5 of the second switching valve 2. Port 3 of the second switching valve 2 is connected to a vent valve. Ports 4 and 7 of the second switching valve 2 are respectively connected to a carrier gas source. Port 6 of the second switching valve 2 is connected to the second chromatographic column col2. Port 9 of the second switching valve 2 is connected to port 2 of the first switching valve 1. Port 10 of the second switching valve 2 is connected to the gas source to be tested.

[0085] A damping valve is connected between port 1 and port 6 of the third switching valve 3. Port 2 of the third switching valve 3 is connected to port 1 of the fourth switching valve 4. A third chromatographic column col3 is provided between port 3 and port 4 of the third switching valve 3. Port 5 of the third switching valve 3 is connected to the second chromatographic column col2.

[0086] The first port of the fourth switching valve 4 is connected to the second port of the third switching valve 3. The second port of the fourth switching valve 4 is connected to the mass spectrometer detector 5. The third port of the fourth switching valve 4 is connected to the fourth chromatographic column col4. The fourth port of the fourth switching valve 4 is connected to the vent valve.

[0087] Example 1: Selection of Chromatographic Conditions

[0088] Introduced gases: O2 100ppm, N2 100ppm, CO 100ppm, CO2 100ppm, benzene 10ppm, toluene 10ppm, maleic anhydride 10ppm, helium (equilibrium).

[0089] The first column (col1) and the second column (col2) were PlotQ columns purchased from Agilent Technologies, 25m × 0.25mm, with a packing mesh size of 80 / 100; the third column (col3) was a 5A molecular sieve column purchased from Agilent Technologies, 25m × 0.25mm, with a packing mesh size of 80 / 100; and the fourth column (col4) was an Innowax column purchased from Agilent Technologies, 30m × 0.25mm, with a film thickness of 7μm.

[0090] 1.1 Selection of valve switching time, column temperature, and carrier gas flow rate

[0091] Experiments were conducted with varying valve switching times and column temperatures, from low to high, and carrier gas flow rates, from slow to fast. The valve switching time was designed to ensure that the analytes (O2+N2+CO), (CO2), and (benzene+toluene+maleic anhydride) from the third, second, and fourth columns entered the mass spectrometer detector sequentially. The column temperature and carrier gas flow rate were designed to ensure baseline separation of CO, CO2, O2, N2, benzene, toluene, and maleic anhydride while simultaneously shortening the analysis time.

[0092] The results showed that a valve switching time of 1.2–7.6 min ensured that each component entered the detector sequentially without conflict. Baseline separation with a short separation time was achieved when the column temperature was within the range of 40℃–150℃ and the carrier gas flow rate was between 0.5–1.5 mL / min. The preferred conditions are shown in Table 1. Specifically, under condition 2, the gas chromatography-mass spectra of the reaction products CO, CO2, O2, N2, benzene, toluene, and maleic anhydride are shown in Table 1. Figure 1 .

[0093] Table 1

[0094] serial number Column temperature ℃ Flow rate mL / min Valve switching time (min) Condition 1 40 0.5 V1=0 V2=5.5 V3=3.2 V4=7.6 Condition 2 60 0.7 V1=0 V2=5.0 V3=3.0 V4=6.9 Condition 3 90 0.9 V1=0 V2=4.5 V3=2.7 V4=6.1 Condition 4 100 1.0 V1=0 V2=4.0 V3=2.3 V4=5.5 Condition 5 120 1.2 V1=0 V2=3.6 V3=2.0 V4=5.1 Condition 6 150 1.5 V1=0 V2=3.0 V3=1.8 V4=4.2

[0095] 1.2 Selection of Sample Injection Volume, Sample Concentration, and Split Ratio

[0096] In the benzene oxidation process for maleic anhydride production, the concentrations of CO, CO2, O2, N2, benzene, toluene, and maleic anhydride in the reaction gas vary considerably, requiring a wide linear range for the external standard curve in quantitative analysis. Experiments were conducted with varying sample injection volume, sample injection concentration, and chromatographic injection port split ratio from low to high, aiming for linear ranges of CO, CO2, O2, N2, benzene, toluene, and maleic anhydride between 10 ppm and 10%.

[0097] The results showed that the optimal sample injection volume was 0.1-3 mL and the split ratio was 1:5-1:100.

[0098] Example 2: Preparation of External Standard Curve (High Concentration)

[0099] A set of diluted helium gases (equilibrium) was prepared by diluting a standard gas with the following concentrations (O2 9.8%, N2 9.7%, CO 9.8%, CO2 9.9%, benzene 0.7%, toluene 0.5%, maleic anhydride 0.2%) at a 1:10 ratio. This yielded a set of diluted helium gases (equilibrium) with the following concentrations (O2 1.0%, N2 1.0%, CO 1.0%, CO2 1.0%, benzene 700 ppm, toluene 500 ppm, maleic anhydride 200 ppm). Both the standard and diluted gases were then injected chromatographically.

[0100] The first column (col1) and the second column (col2) were PlotQ columns purchased from Agilent Technologies, 25m × 0.25mm, with a packing mesh size of 80 / 100; the third column (col3) was a 5A molecular sieve column purchased from Agilent Technologies, 25m × 0.25mm, with a packing mesh size of 80 / 100; and the fourth column (col4) was an Innowax column purchased from Agilent Technologies, 30m × 0.25mm, with a film thickness of 7μm.

[0101] The conditions included: helium carrier gas, constant flow rate of 1.0 mL / min, constant column temperature of 90 °C, injection volume of 25 μL / 500 μL, and split ratio of 1:50.

[0102] Plotting concentration Y (%) against peak area C, the regression equation is:

[0103] Y O2 =1.52C O2 ×10 -6 R 2 =0.992

[0104] Y N2 =1.83C N2 ×10 -6 R 2 =0.998

[0105] Y CO =1.47C CO ×10 -6 R 2 =0.999

[0106] Y CO2 =1.30C CO2 ×10 -6 R 2 =0.993

[0107] Y 苯 =4.07C 苯 ×10 -7 R 2 =0.996

[0108] Y 甲苯 =5.15C 甲苯 ×10 -7 R 2 =0.995

[0109] Y 顺酐 =4.74C 顺酐 ×10 -7 R 2 =0.998

[0110] Example 3: Preparation of External Standard Curve (Low Concentration)

[0111] A set of standard gases with concentrations of 100 ppm O2, 100 ppm N2, 100 ppm CO, 100 ppm CO2, 10 ppm benzene, 10 ppm toluene, 10 ppm maleic anhydride, and helium (equilibrium) was diluted 1:10 using helium to obtain a set of diluted gases with concentrations of 10 ppm O2, 10 ppm N2, 10 ppm CO, 10 ppm CO2, 1 ppm benzene, 1 ppm toluene, 1 ppm maleic anhydride, and helium (equilibrium). Both the standard and diluted gases were then injected chromatographically.

[0112] The first column (col1) and the second column (col2) were Shincarbon columns purchased from Restek, 30m × 0.25mm, with a packing mesh size of 80 / 100; the third column (col3) was a 5A molecular sieve column purchased from Restek, 30m × 0.25mm, with a packing mesh size of 80 / 100; and the fourth column (col4) was a Stabilwax column purchased from Restek, 60m × 0.25mm, with a film thickness of 7μm.

[0113] Helium was used as the carrier gas, with a constant flow rate of 1.0 mL / min and a constant column temperature of 90 °C. The injection volumes were 25 μL / 500 μL, and the split ratio was 1:10. A plot of concentration Y (%) against peak area C was generated, and the regression equation was:

[0114] Y O2 =1.21C O2 ×10 -5 R 2 =0.991

[0115] Y N2 =1.47C N2 ×10 -5 R 2 =0.996

[0116] Y CO =1.90C CO ×10 -5 R 2 =0.990

[0117] Y CO2 =1.29C CO2 ×10 -5 R 2 =0.993

[0118] Y 苯 =7.86C 苯 ×10 -7 R 2 =0.999

[0119] Y 甲苯 =8.40C甲苯 ×10 -7 R 2 =0.998

[0120] Y 顺酐 =8.29C 顺酐 ×10 -7 R 2 =0.996

[0121] Example 4 Methodology Determination

[0122] 4.1 Accuracy

[0123] Different concentrations of standard gases, including CO, CO2, O2, N2, benzene, toluene, and maleic anhydride, were added to high-purity helium gas. Samples of known concentrations of CO, CO2, O2, N2, benzene, toluene, and maleic anhydride were obtained and analyzed by gas chromatography to obtain the corresponding chromatographic peak areas. The peak areas were then substituted into the regression equation of the external standard curves for high and low concentrations of CO, CO2, O2, N2, benzene, toluene, and maleic anhydride to calculate the content. The ratio of the added amount to the calculated amount was calculated to obtain the accuracy of the method. The results for Example 2 are shown in Table 2, and the results for Example 3 are shown in Table 3. The results indicate that the method described in this invention has good accuracy.

[0124] Table 2

[0125] Analyte <![CDATA[O2]]> <![CDATA[N2]]> CO <![CDATA[CO2]]> benzene Toluene maleic anhydride Added amount (ppm) 950 970 980 990 70 50 20 Calculated amount (ppm) 1040 1020 1070 980 69 47 22 Accuracy % 110 106 110 99 99 94 110

[0126] Table 3

[0127] Analyte <![CDATA[O2]]> <![CDATA[N2]]> CO <![CDATA[CO2]]> benzene Toluene maleic anhydride Added amount (ppm) 50 50 50 50 5 5 5 Calculated amount (ppm) 52 51 55 48 5.5 5.3 5.1 Accuracy % 104 102 110 96 110 106 102

[0128] 4.2 Precision

[0129] Sample gases from Examples 2 and 3 were measured six times under the same experimental conditions. The precision of the method was calculated using the ratio of the quantitative peak areas of CO, CO2, O2, N2, benzene, toluene, and maleic anhydride. The relative standard deviations (RSDs) for Examples 2 and 3 are shown in Table 4, indicating that the method described in this invention has good precision.

[0130] Table 4

[0131] RSD of analyte <![CDATA[O2]]> <![CDATA[N2]]> CO <![CDATA[CO2]]> benzene Toluene maleic anhydride Example 2 1.11％ 1.74％ 1.39％ 1.87％ 3.90％ 2.01％ 3.14％ Example 3 1.39％ 1.66％ 1.17％ 1.98％ 2.54％ 2.16％ 3.08％

[0132] 4.3 Limit of Detection

[0133] The limit of detection (LOD) is divided into qualitative and quantitative analysis LODs. Qualitative analysis LOD: The ratio of the analyte peak height to the average peak height of the noise baseline (S / N) is > 2.5. Quantitative analysis LOD: The ratio of the analyte peak height to the average peak height of the noise baseline (S / N) is > 5.0. The signal-to-noise ratio of the lowest concentration of dilution gas in Example 3 was calculated, as shown in Table 5. The results show that the qualitative detection limits for each component are all below 0.1 ppm.

[0134] Table 5

[0135] Analyte <![CDATA[O2]]> <![CDATA[N2]]> CO <![CDATA[CO2]]> benzene Toluene maleic anhydride Peak height 1250 1400 1680 1140 2080 2190 1890 noise 20 20 20 20 20 20 20 Qualitative limit ppm 0.08 0.07 0.06 0.10 0.05 0.05 0.06 Limit of Quantification (ppm) 0.04 0.03 0.03 0.05 0.02 0.02 0.03

[0136] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for detecting gaseous components in the preparation of maleic anhydride via benzene oxidation, characterized in that, The method is performed in a system comprising: The first analytical unit includes a second switching valve, a second chromatographic column, a third switching valve and a fourth switching valve connected in sequence. The second switching valve is connected to the first chromatographic column, and the third switching valve is connected to the third chromatographic column. The second analytical unit includes a first switching valve, a fourth chromatographic column, and a fourth switching valve connected in sequence. The detection device, which is connected to the fourth switching valve via a pipeline, is used to detect gas phase components; The first switching valve is connected to the gas source to be tested and the carrier gas source, the second switching valve is connected to the gas source to be tested and the carrier gas source, the first chromatographic column is used to separate O2+N2+CO, CO2 and benzene+toluene+maleic anhydride, the second chromatographic column is used to analyze CO2, the third chromatographic column is used to separate O2, N2 and CO, and the fourth chromatographic column is used to separate benzene, toluene and maleic anhydride. The method includes: The gas to be tested enters the system through a valve injection method, and the gas to be tested enters the first switching valve and the second switching valve respectively; After the gas to be tested is separated by the first chromatographic column, O2+N2+CO, CO2, and benzene+toluene+maleic anhydride are obtained. Among them, benzene+toluene+maleic anhydride is backflushed out of the system. O2+N2+CO is then switched to the third chromatographic column for separation, and the separated O2, N2, and CO are then switched to the detection device for detection. CO2 is then switched to the second chromatographic column and then switched to the detection device for detection. After the gas to be tested is separated by the fourth chromatographic column, benzene, toluene and maleic anhydride are obtained, and then the gas is switched to the detection device for detection. By controlling the switching sequence of the switching valves, the peak elution order of each component in the gas to be tested is controlled to be O2, N2, CO, CO2, benzene, toluene and maleic anhydride. Chromatographic conditions include: Temperature conditions: 40-150℃, constant temperature; Carrier gas: helium or hydrogen. Flow rate: 0.5 mL / min - 1.5 mL / min, constant flow rate; Injection volume: 0.1 mL - 3 mL Flow split ratio: 1:5-1:100; The stationary phase of the first chromatographic column is a polystyrene-divinylbenzene packing material or a carbon molecular sieve packing material; the stationary phase of the second chromatographic column is a polystyrene-divinylbenzene packing material or a carbon molecular sieve packing material; and the stationary phase of the third chromatographic column is a 5A molecular sieve packing material.

2. The method according to claim 1, wherein, The first switching valve is a six-way valve, the second switching valve is a ten-way valve, the third switching valve is a six-way valve, and the fourth switching valve is a four-way valve.

3. The method according to claim 1, wherein, The first chromatographic column is a plot Q column, a Haysep Q column, or a Shincarbon column; and / or The second chromatographic column is a plot Q column, a Haysep Q column, or a Shincarbon column; and / or The third chromatographic column is a 5A molecular sieve column; and / or The fourth chromatographic column is either an Innowax column or a Stabilwax column.

4. The method according to claim 1 or 3, wherein, The first chromatographic column has a length of 25-50 m, a diameter of 0.25-0.32 mm, and a packing material mesh size of 80-100 mesh; and / or The second chromatographic column has a length of 25-50 m, a diameter of 0.25-0.32 mm, and a packing material mesh size of 80-100 mesh; and / or The third chromatographic column has a length of 25-50 m, a diameter of 0.25-0.32 mm, and a packing material mesh size of 80-100 mesh; and / or The fourth chromatographic column has a length of 30-60m, a diameter of 0.25-0.32mm, and a packing membrane thickness of 0.1-1μm.

5. The method according to claim 1, wherein, The first switching valve's port 1 is connected to the vent valve, the first switching valve's port 2 is connected to the second switching valve's port 9, a metering tube is installed between the first switching valve's port 3 and port 6, the first switching valve's port 4 is connected to the fourth chromatographic column, and the first switching valve's port 5 is connected to the carrier gas source. A metering tube is installed between port 1 and port 8 of the second switching valve. A first chromatographic column is installed between port 2 and port 5 of the second switching valve. Port 3 of the second switching valve is connected to a vent valve. Ports 4 and 7 of the second switching valve are respectively connected to a carrier gas source. Port 6 of the second switching valve is connected to the second chromatographic column. Port 9 of the second switching valve is connected to port 2 of the first switching valve. Port 10 of the second switching valve is connected to the gas source to be tested. The third switching valve has a closed connection between port 1 and port 6, port 2 of the third switching valve is connected to port 1 of the fourth switching valve, a third chromatographic column is provided between port 3 and port 4 of the third switching valve, and port 5 of the third switching valve is connected to the second chromatographic column. The No. 1 port of the fourth switching valve is connected to the No. 2 port of the third switching valve, the No. 2 port of the fourth switching valve is connected to the mass spectrometer, the No. 3 port of the fourth switching valve is connected to the fourth chromatographic column, and the No. 4 port of the fourth switching valve is connected to the vent valve.

6. The method according to claim 1, wherein, The detection device is a mass spectrometer.

7. The method according to claim 1, wherein, The detection method is a quantitative detection method, which uses external standard quantification.

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