On-line continuous flow analysis and extraction device and method for methane carbon isotope composition in gas

Abstract

The present invention belongs to the technical field of determination of carbon isotope composition of methane in gas, and specifically discloses an online continuous flow extraction device for methane in gas and a carbon isotope composition analysis method, the device comprises a first six-way valve, a plurality of helium inlets connected to the first six-way valve, a second six-way valve connected to the first six-way valve, a helium inlet connected to the second six-way valve, a carbon dioxide collection pipe connected to the second six-way valve, a single-opening quartz tube connected to the second six-way valve, and a stable isotope mass spectrometer connected to the second six-way valve, the method is as follows: step 1, gas sample loading; step 2, back-blowing to degas, exhaust the air in the pipes at both ends of the gas collection pipe; step 3, oxidation, purification and collection of methane in the gas; step 4, carbon dioxide sublimation injection; step 5, methane carbon isotope determination. The present invention solves the problems of excessive consumption of sample preparation gas for offline pretreatment, cumbersome operation process and low efficiency.

Description

Technical Field

[0001] The invention belongs to the technical field of measuring carbon isotope composition of methane in gas, and specifically relates to an online continuous flow extraction device for methane in gas and a carbon isotope composition analysis method. Background Art

[0002] Methane is chemically active and can strongly absorb infrared light waves from the surface, causing the surface and near-ground atmospheric temperatures to increase. It is known as the second largest greenhouse gas after carbon dioxide. By directly or indirectly obtaining methane carbon isotope analysis data, the microenvironmental mechanisms and relative contribution rates of methane production, transmission and release can be revealed, providing important information on methane sources and sinks and atmospheric concentration changes. In addition, the carbon isotope composition of methane can be used to track the gas sources of natural gas hydrates and gas reservoirs in the basin and study their causal mechanisms. At present, the main methods for testing the carbon isotope composition of methane are offline dual-channel testing, gas chromatography-mass spectrometry and laser absorption spectroscopy, but these analysis methods have certain defects when testing the carbon isotope composition of methane.

[0003] The offline two-way test method generally connects a container containing about 50L of air to an offline vacuum system. After the vacuum is drawn, alcohol and dry ice are used to condense water vapor in the air, CO2 and N2O are frozen with liquid nitrogen, and CH4 and other gases that cannot be condensed by liquid nitrogen are passed through a high-temperature oxidation furnace to react to generate CO2 and H2O. The generated CO2 is separated and purified and frozen and collected by a sample collection tube, and the mass spectrometer's two-way test of its carbon isotope composition. The two-way method requires too much sample gas, resulting in a cumbersome purification process, consuming a large amount of alcohol, dry ice and liquid nitrogen, and high analysis costs and low efficiency.

[0004] The gas chromatography-mass spectrometry method uses a gas injection needle to inhale a certain volume of gas, and injects the sample into the syringe of the gas chromatograph. Driven by the high-purity He gas flow, the gas sample enters the chromatographic column at a certain temperature for separation. The O2 in the gas is absorbed by the reduction furnace, and CH4 is separated from other gases and oxidized in a high-temperature combustion furnace to generate CO2 and H2O. After water is removed by a water trap, the gas mass spectrometer measures the carbon isotope composition. For samples with a methane content of more than 10%, this method can obtain good results, but for samples with a methane content of ppm, which exceeds the detection limit of the gas chromatography-mass spectrometry, its carbon isotope composition cannot be tested.

[0005] Laser absorption spectroscopy uses the characteristic that the trace gas to be measured absorbs the laser of the wavelength at a specific wavelength, and uses the laser scanning driving current to obtain 13 CH4 and 12The absorption spectrum of CH4 is simulated by software to obtain the direct absorption spectrum at room temperature, one atmosphere and 5% water vapor interference. From the simulation results, the intensity of the selected absorption spectrum and the wave number difference between them can be obtained. 12 The gas spectrum of CH4 is relatively independent, but the current laser cannot 13 The three absorption lines corresponding to CH4 are effectively separated, and the absorption intensity is the sum of the three intensities. Therefore, the accuracy of laser absorption spectroscopy in testing the carbon isotope composition of methane is not high. Summary of the invention

[0006] The purpose of the present invention is to provide an online continuous flow analysis and extraction device and method for methane isotope composition in gas, which solves the problems of excessive consumption of offline pre-treatment sample preparation gas, complicated operation process and low efficiency, and makes up for the shortcomings that gas chromatography-mass spectrometry cannot test low-content methane carbon isotope composition and laser absorption spectroscopy technology has low analysis accuracy.

[0007] A technical solution to achieve the purpose of the present invention: an online continuous flow analysis and extraction device for methane carbon isotope composition in gas, the device comprising a first six-way valve, a plurality of helium inlets connected to the first six-way valve, a second six-way valve connected to the first six-way valve, a helium inlet connected to the second six-way valve, a carbon dioxide collection pipe connected to the second six-way valve, a single-opening quartz tube connected to the second six-way valve, and a stable isotope mass spectrometer connected to the second six-way valve, wherein the helium inlets connected to the first six-way valve include a first helium inlet, a second helium inlet, A third helium gas inlet, a gas collecting pipe, a first water trap, and a first carbon dioxide trap are sequentially arranged between the first helium gas inlet and the first six-way valve, and a second water trap and a gas injection needle are sequentially arranged between the third helium gas inlet and the first six-way valve; the helium gas inlet connected to the second six-way valve includes a fourth helium gas inlet, a fourth water trap is arranged between the fourth helium gas inlet and the second six-way valve, a second carbon dioxide trap is arranged between the second six-way valve and the single-opening quartz tube, and a cold trap, a reaction tube filled with copper oxide, and a third water trap are sequentially arranged between the second six-way valve and the first six-way valve.

[0008] A gas collection pipe air inlet valve and a gas collection pipe air outlet valve are respectively provided at both ends of the gas collection pipe. The gas collection pipe air inlet valve is connected to the first helium air inlet, and the gas collection pipe air outlet valve is connected to the inlet of the first water trap.

[0009] A first valve is provided between the gas collection pipe air inlet valve and the first helium air inlet.

[0010] A second valve is provided between the gas collection pipe gas outlet valve and the inlet of the first water trap.

[0011] The gas sampling needle is installed in a sample tube with a sealing cover.

[0012] The second helium inlet is communicated with the sixth port of the first six-way valve, the sixth port of the first six-way valve is communicated with the first port of the first six-way valve, the first port of the first six-way valve and the second port of the first six-way valve form a loop through a pipeline, and a third valve is provided on the pipeline through the loop.

[0013] The cold trap is placed in the first liquid nitrogen cup.

[0014] The copper oxide filled reaction tube is placed in a temperature-controlled heating furnace.

[0015] The carbon dioxide collection tube is placed in the second liquid nitrogen cup.

[0016] A gas conversion interface Conflo is provided between the second six-way valve and the stable isotope mass spectrometer.

[0017] A method for online continuous flow analysis and extraction of carbon isotope composition of methane in gas, the method specifically comprising the following steps:

[0018] Step 1, gas sampling;

[0019] Step 2: Back-blowing to remove air and exhaust the air in the pipes at both ends of the gas collection pipe;

[0020] Step 3, oxidation, purification and collection of methane in the gas;

[0021] Step 4, carbon dioxide sublimation injection;

[0022] Step 5: Determination of methane carbon isotope.

[0023] The specific steps of step 1 are as follows:

[0024] Step 1.1, setting the helium flow rate at the helium inlet;

[0025] Step 1.2: Adjust the first six-way valve and the second six-way valve to the sample collection mode, and connect the two ends of the gas collection tube to complete the gas sampling.

[0026] In the step 1.1, the flow rates of helium introduced into the first helium inlet, the second helium inlet, the third helium inlet and the fourth helium inlet are set to be the same.

[0027] The specific steps of step 2 are as follows: switch the first six-way valve to connect the fifth port with the sixth port, open the first valve and the second valve at the same time, close the inlet valve of the gas collection pipe and the outlet valve of the gas collection pipe, and the helium flows from the second helium inlet through the first six-way valve, the first carbon dioxide trap, the first water trap and the second valve into the air.

[0028] The specific steps of step 3 are as follows:

[0029] Step 3.1, oxidizing all the methane gas into CO2 and H2O;

[0030] Step 3.2, switch the first six-way valve to the gas methane collection mode, open the valve of the gas collection pipe, and close other valves;

[0031] Step 3.3, after the helium passes through the valve of the gas collection pipe, the water and CO2 in the helium gas are adsorbed, and other gases enter the cold trap through the first six-way valve and are condensed, collected, oxidized, absorbed, condensed and enriched.

[0032] The specific steps of step 3.1 are as follows: pour liquid nitrogen into the first liquid nitrogen cup and the second liquid nitrogen cup, completely condense N2O in the gas and completely collect CO2 in the cold trap and the carbon dioxide collection tube, and heat the temperature-controlled heating furnace to convert all methane gas into CO2 and H2O.

[0033] The specific steps of step 3.3 are as follows: the helium from the first helium inlet passes through the gas collecting tube, the helium and water in the gas are adsorbed by the first water trap, CO2 is adsorbed by the first carbon dioxide trap, N2O is condensed and collected by the cold trap, CH4 is oxidized to generate CO2 and H2O when passing through the reaction tube filled with copper oxide, H2O is absorbed by the third water trap, CO2 reaches the carbon dioxide collecting tube filled with nickel wire through the second six-way valve, and CO2 is condensed and enriched.

[0034] The specific steps of step 4 are as follows:

[0035] Step 4.1, set the second six-way valve to the methane injection mode, and the gas is discharged into the air after coming out of the second six-way valve;

[0036] Step 4.2, the helium is adsorbed and dried by the fourth water trap and enters the carbon dioxide collection pipe through the second six-way valve, and the CO2 in the carbon dioxide collection pipe sublimates into gas;

[0037] Step 4.3, CO2 gas enters the stable isotope mass spectrometer through the second six-way valve and the gas conversion interface Conflo to complete the carbon dioxide sampling.

[0038] The specific steps of step 4.2 are as follows: the helium from the fourth helium inlet enters the fourth water trap, the water in the helium is adsorbed, the helium is dried and enters the carbon dioxide collection tube filled with nickel wire through the second six-way valve, the second liquid nitrogen cup is withdrawn, the carbon dioxide collection tube is rapidly heated, and the solid CO2 attached to the nickel wire and the inner wall of the stainless steel tube is sublimated into gas.

[0039] The specific steps of step 5 are as follows:

[0040] Step 5.1, close the third valve, and the helium from the second helium inlet and the third helium inlet enters the pipeline, so that the entire pipeline is protected by high-purity helium;

[0041] Step 5.2, adding carbonate solid standard substance and liquid phosphoric acid into the sample tube 13 with a sealing cover to produce carbon dioxide gas;

[0042] Step 5.3, the standard CO2 gas is taken out from the sample tube with a sealed cover by helium, enters the first six-way valve, the cold trap, the reaction tube filled with copper oxide, the third water trap, the second six-way valve, and is collected by the carbon dioxide collection tube for the determination of methane carbon isotope composition.

[0043] The beneficial technical effects of the present invention are:

[0044] (1) The present invention connects an online continuous flow methane injection device, a standard carbon dioxide gas injection device and a carbon dioxide purification and collection device to a stable isotope mass spectrometer to achieve online injection, purification, high-temperature oxidation of methane gas, online collection of carbon dioxide gas and online testing of carbon dioxide carbon isotopes.

[0045] (2) The present invention can conveniently switch to the purification, collection and carbon isotope composition testing of standard carbon dioxide gas through the six-way valve.

[0046] (3) The carriers of the four channels of methane collection, standard carbon dioxide gas collection, back-blowing helium and isotope mass spectrometer in the present invention are all 99.999% high-purity helium, and the helium flow rate is controlled at 90 mL / min. The helium is adsorbed and dried by a water trap filled with magnesium perchlorate to reduce the interference of trace water vapor in the carrier gas on the stable isotope mass spectrometer.

[0047] (4) The methane-containing gas in the present invention is purified by adsorbing water by a water trap and adsorbing CO2 by a carbon dioxide trap, and then reacts with an oxidant in an oxidation furnace to generate CO2 and H2O. After the water is adsorbed, the CO2 is frozen and collected by liquid nitrogen, and the liquid nitrogen is removed to release the CO2 and enter a stable isotope mass spectrometer. The advantage of this device is that different volumes of inlet gas are used according to the different methane contents, thereby meeting the analysis of methane gas with different content ranges. The volume of the gas collection tube can be as small as 0.01 mL, while normal air requires 100 mL. The methane content ranges from 2 ppm to 20,000 ppm. The amount of gas required for the offline dual-path method is 50 L, which greatly reduces the sample amount and also makes up for the detection limit of the gas chromatography.

[0048] (5) The present invention selects gas collection tubes of different volumes according to the analysis needs. After being connected to the system, an online continuous flow sampling method using helium as the carrier gas is used. The sample is collected for 10 minutes to ensure that the gas in the gas collection tube is completely purged out. H2O in the gas is adsorbed by the water trap of magnesium perchlorate, CO2 is adsorbed by the carbon dioxide trap reaction, CH4 reacts with copper oxide in a 650°C oxidation furnace to generate CO2 and H2O, H2O is adsorbed by the water trap of magnesium perchlorate, CO2 is placed in a sample collection tube filled with nickel wire in liquid nitrogen for freezing and enrichment, and other gases that cannot be frozen by liquid nitrogen are directly discharged into the air to reduce damage to the stable isotope mass spectrometer. The role of the nickel wire is to prevent the generation of CO2 ice particles and to accelerate the release rate of CO2 after withdrawing liquid nitrogen. The released CO2 is diluted by the gas conversion interface Conflo and then enters the mass spectrometer to test the carbon isotope composition. This method is online enrichment, the experiment is simple and convenient, and more than 20 samples can be processed per day, greatly improving the experimental efficiency.

[0049] (6) The gas outlet stainless steel pipe for collecting gas samples in the present invention is placed at the bottom of a single-opening quartz tube. The single opening faces downward because the density of helium is much smaller than that of air, which better protects the pipeline and reduces the back suction of air. The carbon dioxide trap is filled with sodium hydroxide particles to effectively prevent the adsorption of carbon dioxide in the air during the back suction.

[0050] (7) In the gas methane online extraction device of the present invention, both ends of the sample collection tube are connected by 1 / 4 inch detachable quick connectors, sealed by O-type fluororubber sealing rings, the six-way valve is sealed by a tetrafluoroethylene gasket, and the rest are sealed by metal sealing gaskets. Under the protection of high-purity helium, the entire system is isolated from the air at room temperature without being affected. Methane or carbon dioxide gas passes through the entire system in a state of no dead volume, and condensation and distillation will not occur due to adsorption.

[0051] (7) The present invention solves the technical difficulty of online methane carbon isotope determination. Since gas is difficult to preserve and gas isotope standards are not as stable as solid standards, there are almost no methane carbon isotope standards. The six-way valve can be used to insert the injection needle into an empty sample tube in a pending state before the standard gas is introduced. The six-way valve is filled with helium to reduce the interference of the standard gas on the test results during collection. The standard carbon dioxide gas sample preparation method is to fill a 12mL sample tube with a sealing gasket with helium, add 10μg carbonate solid standard and 2 drops of 100% liquid phosphoric acid, react at room temperature and leave for more than 4h, directly insert the injection needle into the sample tube, collect carbon dioxide gas and inject for testing. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 This is a schematic structural diagram of an online continuous flow analysis and extraction device for the carbon isotope composition of methane in gas provided by the present invention.

[0053] In the figure:

[0054] 1 is the first helium inlet, 2 is the first valve;

[0055] 3 is a gas collecting pipe, 3-1 is a gas inlet valve of the gas collecting pipe, and 3-2 is a gas outlet valve of the gas collecting pipe;

[0056] 4 is the second valve, 5 is the first water trap, and 6 is the first carbon dioxide trap;

[0057] 7 is a first six-way valve, 7-1 is a first port of the first six-way valve, 7-2 is a second port of the first six-way valve, 7-3 is a third port of the first six-way valve, 7-4 is a fourth port of the first six-way valve, 7-5 is a fifth port of the first six-way valve, and 7-6 is a sixth port of the first six-way valve;

[0058] 8 is a third valve, 9 is a second helium inlet, 10 is a third helium inlet, 11 is a second water trap, 12 is a gas injection needle, 13 is a sample tube with a sealing cover, 14 is a cold trap, 15 is a first liquid nitrogen cup, 16 is a reaction tube filled with copper oxide, 17 is a temperature-controlled heating furnace, and 18 is a third water trap;

[0059] 19 is a second six-way valve, 19-1 is a first port of the second six-way valve, 19-2 is a second port of the second six-way valve, 19-3 is a third port of the second six-way valve, 19-4 is a fourth port of the second six-way valve, 19-5 is a fifth port of the second six-way valve, and 19-6 is a sixth port of the second six-way valve;

[0060] 20 is a second carbon dioxide trap, 21 is a single-opening quartz tube, 22 is a carbon dioxide collecting tube, 23 is a second liquid nitrogen cup, 24 is a fourth water trap, 25 is a fourth helium inlet, 26 is a gas conversion interface Conflo, and 27 is a stable isotope mass spectrometer. DETAILED DESCRIPTION

[0061] The present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0062] like Figure 1As shown, an online continuous flow analysis and extraction device for carbon isotope composition of methane in gas of this embodiment comprises a first helium inlet 1, a second helium inlet 9, a third helium inlet 10, a fourth helium inlet 25, a first valve 2, a second valve 4, a third valve 8, a gas collecting tube 3, a first water trap 5, a second water trap 11, a third water trap 18, a fourth water trap 24, a first carbon dioxide trap 6, a second carbon dioxide trap 20, a first six-way valve 7, a second six-way valve 19, a single-opening quartz tube 21, a gas injection needle 12, a sample tube with a sealing cover 13, a cold trap 14, a first liquid nitrogen cup 15, a second liquid nitrogen cup 23, a reaction tube filled with copper oxide 16, a temperature-controlled heating furnace 17, a carbon dioxide collection tube filled with nickel wire 22, a gas conversion interface Conflo 26 and a stable isotope mass spectrometer 27.

[0063] The first helium inlet 1 is connected to the inlet valve 3-1 of the gas collection pipe 3 through a pipeline, and the first valve 2 is provided on the pipeline; the outlet valve 3-2 of the gas collection pipe 3 is connected to the inlet of the first water trap 5 through a pipeline, and the second valve 4 is provided on the pipeline; the outlet of the first water trap 5 is connected to the inlet of the first carbon dioxide trap 6 through a pipeline, and the outlet of the first carbon dioxide trap 6 is connected to the fifth port 7-5 of the first six-way valve 7 through a pipeline. The first helium inlet 1 can be emptied from the first valve 2, or it can be connected to the fifth port 7-5 of the first six-way valve 7 through the inlet valve 3-1 of the gas collection pipe 3, the outlet valve 3-2 of the gas collection pipe 3, the first water trap 5, the first carbon dioxide trap 6 in sequence; the second valve 4 is the outlet for helium backblowing;

[0064] The second helium inlet 9 is communicated with the sixth port 7-6 of the first six-way valve 7 through a pipeline, and the sixth port 7-6 of the first six-way valve 7 is communicated with the first port 7-1 of the first six-way valve 7 through a pipeline. The first port 7-1 of the first six-way valve 7 and the second port 7-2 of the first six-way valve 7 form a loop through a pipeline, and the third valve 8 is arranged on the pipeline of the loop. The second helium inlet 9 passes through the sixth port 7-6 of the first six-way valve 7, and comes out of the first port 7-1 of the first six-way valve 7 and is emptied by the third valve 8.

[0065] The third helium inlet 10 is connected to the third port 7-3 of the first six-way valve 7 via the second water trap 11, the gas injection needle 12, and the sample tube with a sealing cover 13. The third helium inlet 10 is connected to the inlet of the second water trap 11 through a pipeline, and is connected to the outlet of the second water trap 11 through pipelines, one end of the gas injection needle 12, and the third port 7-3 of the first six-way valve 7, respectively, and the other end of the gas injection needle 12 is placed in the sample tube with a sealing cover 13.

[0066] The fourth port 7-4 of the first six-way valve 7 is connected to the first port 19-1 of the second six-way valve 19 via the cold trap 14, the reaction tube 16 filled with copper oxide, and the third water trap 18. The fourth port 7-4 of the first six-way valve 7 is connected to the inlet of the cold trap 14 through a pipeline, the outlet of the cold trap 14 is connected to the inlet of the reaction tube 16 filled with copper oxide through a pipeline, the outlet of the reaction tube 16 filled with copper oxide is connected to the inlet of the third water trap 18 through a pipeline, and the outlet of the third water trap 18 is connected to the first port 19-1 of the second six-way valve 19 through a pipeline.

[0067] The fourth helium inlet 25 is communicated with the inlet of the fourth water trap 24 through a pipeline, and the outlet of the fourth water trap 24 is communicated with the fourth port 19 - 4 of the second six-way valve 19 through a pipeline.

[0068] Both ends of the carbon dioxide collection pipe 22 are connected to the second port 19 - 2 and the fifth port 19 - 5 of the second six-way valve 19 through pipelines, respectively.

[0069] The stable isotope mass spectrometer 27 is connected to the third port 19-3 of the second six-way valve 19 via the gas conversion interface Conflo 26, the third port 19-3 of the second six-way valve 19 is connected to the inlet of the gas conversion interface Conflo 26 through a pipeline, and the outlet of the gas conversion interface Conflo 26 is connected to the stable isotope mass spectrometer 27 through a pipeline.

[0070] The injection needle 12 is inserted into the sample tube 13 with a sealing cover, the cold trap 14 is placed in the first liquid nitrogen cup 15, and the reaction tube 16 filled with copper oxide is nested in the groove of the temperature-controlled heating furnace 17; the outlet pipe of the carbon dioxide trap 20 is placed at the bottom of the inverted single-opening quartz tube 21, and the inlet of the carbon dioxide trap 20 is connected to the sixth port 19-6 of the second six-way valve 19 through a pipeline; the carbon dioxide collection tube 22 filled with nickel wire is placed in the second liquid nitrogen cup 23.

[0071] In this embodiment, the purity of the helium gas flowing through the first helium gas inlet 1, the second helium gas inlet 9, the third helium gas inlet 10, and the fourth helium gas inlet 25 is 99.999%.

[0072] In this embodiment, the connecting pipelines between the components are all made of stainless steel tubes with an outer diameter of 1 / 16 inch, except for the gas outlet end of the injection needle 12 which is a 1 / 32 inch quartz tube.

[0073] In this embodiment, when the first valve 2 and the second valve 4 are in operation, the air at both ends of the gas collecting pipe 3 is purged after the gas collecting pipe 3 is installed.

[0074] In this embodiment, the gas collection pipe 3 has an inlet valve 3 - 1 and an outlet valve 3 - 2 which are both 1 / 4 inch pipes and are sealed by O-type fluoro rubber ring gaskets.

[0075] In this embodiment, the first water trap 5, the second water trap 11, the third water trap 18, and the fourth water trap 24 can effectively absorb moisture in the gas.

[0076] In this embodiment, the first carbon dioxide trap 6 can completely adsorb CO2 gas in the gas.

[0077] In this embodiment, the third valve 8 is closed, and when the gas injection needle 12 is exposed to the air, the second helium inlet 9 serves as the backflush gas for the gas injection needle 12 .

[0078] In this embodiment, the second carbon dioxide trap 20 and the single-opening quartz tube 21 are used to prevent the back-absorption of carbon dioxide in the air when the liquid nitrogen is used to freeze and collect the sample.

[0079] In this embodiment, the injection needle 12 is inserted into the sample tube 13 with a sealing cover, and the gas is discharged from the bottom pipe port and inlet from the middle pipe port.

[0080] In this embodiment, the copper oxide filled reaction tube 16 can completely oxidize the passing methane into CO2 and H2O without any residue, and the operating temperature of the temperature controlled heating furnace 17 is 800°C.

[0081] In this embodiment, the carbon dioxide collection tube 22 filled with nickel wire is composed of a 1 / 16 inch stainless steel tube filled with nickel wire, which can prevent the generation of CO2 ice particles during liquid nitrogen freezing and accelerate the release rate of CO2 after withdrawing liquid nitrogen.

[0082] like Figure 1 As shown, an online continuous flow analysis and extraction method for methane carbon isotope composition in gas, the method specifically comprises the following steps:

[0083] Step 1: Gas sampling

[0084] Step 1.1: Set the helium flow rate at the helium inlet

[0085] Helium is introduced into the first helium inlet 1, the second helium inlet 9, the third helium inlet 10 and the fourth helium inlet 25, and the flow rate is set to 90 mL / min.

[0086] Step 1.2: Adjust the first six-way valve 7 and the second six-way valve 19 to the sample collection mode, and connect the two ends of the gas collection tube 3 to complete the gas sampling.

[0087] Adjust the first six-way valve 7 to the sample collection mode, that is, the first port 7-1, the third port 7-3 and the fifth port 7-5 of the first six-way valve 7 are used as air inlets, and the second port 7-2, the fourth port 7-4 and the sixth port 7-6 of the first six-way valve 7 are used as air outlets.

[0088] Adjust the second six-way valve 19 to the sample collection mode, that is, the first port 19-1 of the second six-way valve 19, the fourth port 19-4 of the second six-way valve 19, and the fifth port 19-5 of the second six-way valve 19 are used as air inlets, and the second port 19-2 of the second six-way valve 19, the third port 19-3 of the second six-way valve 19, and the sixth port 19-6 of the second six-way valve 19 are used as air outlets.

[0089] Connect the two ends of the gas collecting pipe 3 through a detachable joint.

[0090] Step 2: Backflush to remove air and exhaust the air in the pipes at both ends of the gas collection pipe 3.

[0091] Switch the first six-way valve 7 to connect the fifth port 7-5 with the sixth port 7-6, and open the first valve 2 and the second valve 4 at the same time. The helium flows from the second helium port 9 through the sixth port 7-6, the fifth port 7-5, the first carbon dioxide trap 6, the first water trap 5 and the second valve 4 of the first six-way valve 7 and is discharged into the air. At this time, the two valves of the gas collecting pipe 3, the gas inlet valve 3-1 of the gas collecting pipe and the gas outlet valve 3-2 of the gas collecting pipe are in a closed state for 10 minutes. The purpose is to exhaust the air in the pipes at both ends of the gas collecting pipe 3 and reduce the interference with the test of the carbon isotope composition of methane in the gas.

[0092] Step 3: Oxidation, purification and collection of methane in gas

[0093] Step 3.1: Oxidize all methane gas to CO2 and H2O

[0094] After degassing is completed, the cold trap 14 is placed in the first liquid nitrogen cup 15 and the carbon dioxide collection tube 22 is placed in the second liquid nitrogen cup 23, and liquid nitrogen is poured into the first liquid nitrogen cup 15 and the second liquid nitrogen cup 23, and left to stand for 2 minutes, in order to freeze the temperature of the cold trap 14 and the carbon dioxide collection tube 22 low enough to completely condense the N2O in the gas and completely collect the CO2. The temperature of the temperature-controlled heating furnace 17 is set to 800°C to ensure that all the methane gas passing through is converted into CO2 and H2O.

[0095] Step 3.2: Switch the first six-way valve 7 to the gas methane collection mode, open the valve of the gas collection pipe 3, and close other valves.

[0096] Switch the first six-way valve 7 to the gas methane collection mode, that is, the first port 7-1 of the first six-way valve 7, the third port 7-3 of the first six-way valve 7, and the fifth port 7-5 of the first six-way valve 7 are used as air inlets, and the second port 7-2 of the first six-way valve 7, the fourth port 7-4 of the first six-way valve 7, and the sixth port 7-6 of the first six-way valve 7 are used as air outlets.

[0097] At the same time, the first valve 2 and the second valve 4 are closed, and the gas inlet valve 3-1 of the gas collecting pipe and the gas outlet valve 3-2 of the gas collecting pipe are opened.

[0098] Step 3.3: After the helium passes through the valve of the gas collection pipe, the water and CO2 in the helium gas are adsorbed, and other gases enter the cold trap 14 through the first six-way valve 7 and are condensed, collected, oxidized, absorbed, condensed and enriched.

[0099] The helium from the first helium inlet 1 passes through the gas collection pipe inlet valve 3-1, and the gas in the gas collection pipe 3 is brought out by the helium from the gas collection pipe outlet valve 3-2; the helium and the water in the gas are adsorbed by the first water trap 5, and CO2 is adsorbed by the first carbon dioxide trap 6; other gases enter the fifth port 7-5 of the first six-way valve 7, and flow out from the fourth port 7-4 of the first six-way valve 7 into the cold trap 14, N2O is condensed and collected, and CH4 and other gases are oxidized when passing through the 650°C filled copper oxide reaction tube 16 CO2 and H2O are generated; H2O is absorbed by the third water trap 18, CO2 and other gases enter the first port 19-1 of the second six-way valve 19, and come out from the second port 19-2 of the second six-way valve 19 to reach the carbon dioxide collection pipe 22 filled with nickel wire; CO2 is condensed and enriched, and other gases that are not easily condensed by liquid nitrogen enter the fifth port 19-5 of the second six-way valve 19, come out from the sixth port 19-6 of the second six-way valve 19, enter the second carbon dioxide trap 20, and then reach the bottom of the second single-opening quartz tube 21 for emptying.

[0100] Step 4: Carbon dioxide sublimation injection

[0101] Step 4.1: Set the second six-way valve 19 to the methane injection mode, and the gas is discharged into the air after coming out of the second six-way valve 19.

[0102] The second six-way valve 19 is set to the methane injection mode, that is, the first port 19-1, the fourth port 19-4, and the fifth port 19-5 of the second six-way valve 19 are used as the inlet, and the second port 19-2, the third port 19-3, and the sixth port 19-6 of the second six-way valve 19 are used as the outlet. The gas entering the first port 19-1 of the second six-way valve 19 is discharged into the air after exiting the sixth port 19-6 of the second six-way valve 19.

[0103] Step 4.2: Helium is adsorbed and dried by the fourth water trap 24 and enters the carbon dioxide collection pipe 22 through the second six-way valve 19. The CO2 in the carbon dioxide collection pipe 22 sublimates into gas.

[0104] The helium from the fourth helium inlet 25 enters the fourth water trap 24, water in the helium is adsorbed, and after being dried, the helium enters the fourth port 19-4 of the second six-way valve 19 through a 1 / 16-inch stainless steel pipe, and then comes out from the fifth port 19-5 of the second six-way valve 19 and enters the carbon dioxide collection tube 22 filled with nickel wire at about -196°C. The second liquid nitrogen cup 23 is withdrawn, and the carbon dioxide collection tube 22 filled with nickel wire at -196°C is rapidly heated, and the solid CO2 attached to the nickel wire and the inner wall of the stainless steel tube is rapidly sublimated into gas in a short time.

[0105] Step 4.3, CO2 gas enters the stable isotope mass spectrometer 27 through the second six-way valve 19 and the gas conversion interface Conflo 26 to complete the carbon dioxide injection

[0106] Driven by helium, CO2 gas enters the second port 19-2 of the second six-way valve 19, and then exits from the third port 19-3 of the second six-way valve 19 and enters the gas conversion interface Conflo 26. Finally, the pure CO2 sample and the reference gas enter the stable isotope mass spectrometer 27 through two quartz capillaries, and the δ 13 C(‰) value.

[0107] Step 5: Methane carbon isotope determination

[0108] Step 5.1, close the third valve 8, and the helium from the second helium inlet 9 and the third helium inlet 10 enters the pipeline, so that the entire pipeline is protected by high-purity helium.

[0109] Before the gas injection needle 12 is inserted into the sample tube 13 with a standard sealing cover, the third valve 8 is closed, and the helium from the second helium gas inlet 9 passes through the sixth port 7-6 of the first six-way valve 7 and the first port 7-1 of the first six-way valve 7 in sequence, and the helium from the third helium gas inlet 10 passes through the second water trap 11, the gas injection needle 12, and the third port 7-3 of the first six-way valve 7 of the sample tube 13 with a sealing cover in sequence, and the entire pipeline is protected by high-purity helium.

[0110] Step 5.2: Add carbonate solid standard substance and liquid phosphoric acid to the sample tube 13 with a sealed cover to produce carbon dioxide gas.

[0111] In order to solve the problem of accurate determination of carbon isotope composition of methane, solid carbonate standard is used to prepare carbon dioxide gas. The method is to load 10 μg of carbonate solid standard material into a 12 mL sample tube 13 with a sealed cover and tighten the cover, then use a gas injection needle 12 to pierce the sample tube 13 with a sealed cover and purge for 10 minutes. The sample tube 13 with a sealed cover is completely filled with high-purity helium. Use an extremely fine acid needle to pierce the sealing gasket of the sample tube 13 with a sealed cover and then add 2 drops of 100% liquid phosphoric acid. The reaction is balanced at 25°C for more than 4 hours for use.

[0112] Step 5.3: The standard CO2 gas is taken out of the sample tube 13 with a sealed cover by the helium gas, enters the first six-way valve 7, the cold trap 14, the copper oxide reaction tube 16, the third water trap 18, the second six-way valve 19, and is collected by the carbon dioxide collection tube 22 for the determination of the methane carbon isotope composition.

[0113] The cold trap 14 is removed from the first liquid nitrogen cup 15, and the carbon dioxide collection tube 22 is placed in the second liquid nitrogen cup 23 and poured with liquid nitrogen, and left to stand for 2 minutes. The gas injection needle 12 is inserted into the standard sealed cover sample tube 13 and the first six-way valve 7 is switched, and the third port 7-3 of the first six-way valve 7 is connected with the fourth port 7-4. The standard CO2 gas is taken out of the sealed cover sample tube 13 by helium, enters the third port 7-3 of the first six-way valve 7, and passes through the cold trap 14, the copper oxide reaction tube 16, and the third water trap 18 after coming out of the fourth port 7-4. Enter the first port 19-1 of the second six-way valve 19, and the second port 19-2 of the second six-way valve 19 is collected by the carbon dioxide collection tube 22 filled with nickel wire, and carbon dioxide sublimation sampling is performed. The carbon dioxide sublimation sampling is the same as step 4.

[0114] By repeating this step, the carbon isotope composition of CO2 gas generated by different solid carbonate standards can be tested. A linear equation is established for multiple standards, which can be used for numerical correction of the carbon isotope composition of methane in the gas, thereby achieving accurate determination of the carbon isotope composition of methane in the gas.

[0115] The present invention is described in detail above with reference to the accompanying drawings and embodiments, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge of ordinary technicians in the field without departing from the purpose of the present invention. The contents not described in detail in the present invention can adopt the existing technology.

Claims

1. An online continuous flow analysis and extraction device for methane carbon isotope composition in gas, characterized in that: The device comprises a first six-way valve (7), a plurality of helium gas inlets connected to the first six-way valve (7), a second six-way valve (19) connected to the first six-way valve (7), a helium gas inlet connected to the second six-way valve (19), a carbon dioxide collection pipe (22) connected to the second six-way valve (19), a single-opening quartz pipe (21) connected to the second six-way valve (19), and a stable isotope mass spectrometer (27) connected to the second six-way valve (19); the helium gas inlets connected to the first six-way valve (7) comprise a first helium gas inlet (1), a second helium gas inlet (9), and a third helium gas inlet (10); a gas collection pipe (3), a first water trap (5), and a first carbon dioxide trap (6) are provided in sequence between the first helium gas inlet (1) and the first six-way valve (7); and a gas collection pipe (3), a first water trap (5), and a first carbon dioxide trap (6) are provided in sequence between the third helium gas inlet (10) and the first six-way valve (7). A second water trap (11) and a gas injection needle (12) are provided; a gas collection tube air inlet valve (3-1) and a gas collection tube air outlet valve (3-2) are respectively provided at both ends of the gas collection tube (3); the gas collection tube air inlet valve (3-1) is connected to the first helium air inlet (1), and the gas collection tube air outlet valve (3-2) is connected to the inlet of the first water trap (5); the helium air inlet connected to the second six-way valve (19) includes a fourth helium air inlet (25); a fourth water trap (24) is provided between the fourth helium air inlet (25) and the second six-way valve (19); a second carbon dioxide trap (20) is provided between the second six-way valve (19) and the single-opening quartz tube (21); and a cold trap (14), a reaction tube filled with copper oxide (16), and a third water trap (18) are provided in sequence between the second six-way valve (19) and the first six-way valve (7).

2. The on-line continuous flow analysis and extraction device for methane carbon isotope composition in gas according to claim 1, characterized in that: A first valve (2) is provided between the gas collection pipe inlet valve (3-1) and the first helium inlet (1).

3. The on-line continuous flow analysis and extraction device for methane carbon isotope composition in gas according to claim 2, characterized in that: A second valve (4) is provided between the gas collection pipe outlet valve (3-2) and the inlet of the first water trap (5).

4. The on-line continuous flow analysis and extraction device for methane carbon isotope composition in gas according to claim 3, characterized in that: The gas sampling needle (12) is installed in a sample tube (13) with a sealing cover.

5. The on-line continuous flow analysis and extraction device for methane carbon isotope composition in gas according to claim 4, characterized in that: The second helium inlet (9) is communicated with the sixth port (7-6) of the first six-way valve (7), the sixth port (7-6) of the first six-way valve (7) is communicated with the first port (7-1) of the first six-way valve (7), the first port (7-1) of the first six-way valve (7) and the second port (7-2) of the first six-way valve (7) form a loop through a pipeline, and a third valve (8) is provided on the pipeline of the loop.

6. The on-line continuous flow analysis and extraction device for methane carbon isotope composition in gas according to claim 5, characterized in that: The cold trap (14) is placed in the first liquid nitrogen cup (15).

7. The on-line continuous flow analysis and extraction device for methane carbon isotope composition in gas according to claim 6, characterized in that: The copper oxide filled reaction tube (16) is placed in a temperature-controlled heating furnace (17).

8. The on-line continuous flow analysis and extraction device for methane carbon isotope composition in gas according to claim 7, characterized in that: The carbon dioxide collection tube (22) is placed in the second liquid nitrogen cup (23).

9. The on-line continuous flow analysis and extraction device for methane carbon isotope composition in gas according to claim 8, characterized in that: A gas conversion interface Conflo (26) is provided between the second six-way valve (19) and the stable isotope mass spectrometer (27).

10. A method for performing on-line continuous flow analysis and extraction of carbon isotope composition of methane in gas using the on-line continuous flow analysis and extraction device for carbon isotope composition of methane in gas according to any one of claims 1 to 9, characterized in that: The method specifically comprises the following steps: Step 1, gas sampling; the specific steps of step 1 are as follows: Step 1.1, setting the helium flow rate at the helium inlet; Step 1.2, adjusting the first six-way valve (7) and the second six-way valve (19) to the sample collection mode, and connecting the two ends of the gas collection tube (3) to complete the gas sampling; Step 2, back-blowing to remove gas, and exhausting the air in the pipes at both ends of the gas collection pipe (3); the specific steps of step 2 are as follows: switching the first six-way valve (7) to connect the fifth port (7-5) with the sixth port (7-6), opening the first valve (2) and the second valve (4) at the same time, closing the gas inlet valve (3-1) and the gas outlet valve (3-2) of the gas collection pipe, and the helium flows from the second helium inlet (9) through the first six-way valve (7), the first carbon dioxide trap (6), the first water trap (5) and the second valve (4) to be discharged into the air; Step 3, oxidation, purification and collection of methane in the gas; the specific steps of step 3 are as follows: Step 3.1, oxidizing all the methane gas into CO2 and H2O; Step 3.2, switch the first six-way valve (7) to the gas methane collection mode, open the valve of the gas collection pipe (3), and close the other valves; Step 3.3, after the helium passes through the valve of the gas collection pipe, water and CO2 in the helium gas are adsorbed, and other gases enter the cold trap (14) through the first six-way valve (7) and are condensed, collected, oxidized, absorbed, condensed and enriched; Step 4, carbon dioxide sublimation injection; the specific steps of step 4 are as follows: Step 4.1, setting the second six-way valve (19) to a methane injection mode, and exhausting the gas from the second six-way valve (19) into the air; Step 4.2, the helium is adsorbed and dried by the fourth water trap (24) and enters the carbon dioxide collection pipe (22) through the second six-way valve (19), and the CO2 in the carbon dioxide collection pipe (22) is sublimated into gas; Step 4.3, the CO2 gas enters the stable isotope mass spectrometer (27) through the second six-way valve (19) and the gas conversion interface Conflo (26), completing the carbon dioxide sampling; Step 5, methane carbon isotope determination; the specific steps of step 5 are as follows: Step 5.1, closing the third valve (8), allowing the helium from the second helium inlet (9) and the third helium inlet (10) to enter the pipeline, so that the entire pipeline is protected by high-purity helium; Step 5.2, adding carbonate solid standard substance and liquid phosphoric acid into the sample tube with a sealing cover (13) to produce carbon dioxide gas; Step 5.3, the standard CO2 gas is carried out from the sample tube with a sealed cover (13) by the helium gas, enters the first six-way valve (7), the cold trap (14), the reaction tube filled with copper oxide (16), the third water trap (18), the second six-way valve (19), and is collected by the carbon dioxide collection tube (22) for the determination of the methane carbon isotope composition.

11. The method for online continuous flow analysis and extraction of carbon isotope composition of methane in gas according to claim 10, characterized in that: In the step 1.1, the flow rates of helium introduced into the first helium inlet (1), the second helium inlet (9), the third helium inlet (10) and the fourth helium inlet (25) are set to be the same.

12. The method for online continuous flow analysis and extraction of carbon isotope composition of methane in gas according to claim 11, characterized in that: The specific steps of step 3.1 are as follows: pouring liquid nitrogen into the first liquid nitrogen cup (15) and the second liquid nitrogen cup (23), completely condensing N2O in the gas and completely collecting CO2 in the cold trap (14) and the carbon dioxide collection tube (22), and heating the temperature-controlled heating furnace (17) so that the methane gas is completely converted into CO2 and H2O.

13. The method for online continuous flow analysis and extraction of carbon isotope composition of methane in gas according to claim 12, characterized in that: The specific steps of step 3.3 are as follows: the helium from the first helium inlet (1) passes through the gas collection tube (3), the helium and water in the gas are adsorbed by the first water trap (5), CO2 is adsorbed by the first carbon dioxide trap (6), N2O is condensed and collected by the cold trap (14), CH4 is oxidized to generate CO2 and H2O when passing through the copper oxide filled reaction tube (16), H2O is absorbed by the third water trap (18), CO2 passes through the second six-way valve (19) to reach the carbon dioxide collection tube (22) filled with nickel wire, and CO2 is condensed and enriched.

14. The method for online continuous flow analysis and extraction of carbon isotope composition of methane in gas according to claim 13, characterized in that: The specific steps of step 4.2 are as follows: the helium from the fourth helium inlet (25) enters the fourth water trap (24), water in the helium is adsorbed, the helium is dried and enters the carbon dioxide collection tube (22) filled with nickel wire through the second six-way valve (19), the second liquid nitrogen cup (23) is withdrawn, the carbon dioxide collection tube (22) is rapidly heated, and the solid CO2 attached to the nickel wire and the inner wall of the stainless steel tube is sublimated into gas.

Images