Method for detecting methane and non-methane total hydrocarbons in a gas

Abstract

The application provides a detection method of methane and non-methane total hydrocarbon in gas, and relates to the technical field of gas component detection and analysis. The detection method first enriches the sample gas to be detected by using an enrichment tube, then sequentially performs first desorption and second desorption, separates methane and non-methane total hydrocarbon from the enrichment tube, and then respectively detects the content of methane and non-methane total hydrocarbon; wherein the elution volume of the first desorption is greater than the elution volume of methane under the same desorption temperature and filler mass conditions, and is less than the elution volume of ethane under the same desorption temperature and filler mass conditions. The application can realize the measurement of methane and non-methane total hydrocarbon by using only one enrichment tube and one sampling cycle through the secondary desorption mode, and effectively avoids the loss of low-carbon hydrocarbon such as ethane in the separation process compared with the existing method for measuring methane and non-methane total hydrocarbon by using a PQ column and a methane quantitative ring.

Description

Technical Field

[0001] This invention relates to the field of gas composition detection and analysis technology, and in particular to a method for detecting methane and non-methane total hydrocarbons in a gas. Background Technology

[0002] Methane is one of the gases that contribute to the atmospheric greenhouse effect. NMHC refers to all hydrocarbons other than methane, mainly including alkanes, alkenes, aromatic hydrocarbons, and oxygenated hydrocarbons. Non-methane total hydrocarbons can, to a certain extent, provide a simple and intuitive characterization of VOCs pollution levels.

[0003] Currently, the detection of methane and non-methane total hydrocarbons mainly falls into two categories: stationary pollution sources and ambient air. For monitoring non-methane total hydrocarbon emissions from stationary pollution sources and ambient air, gas chromatography-flame ionization detector (GC-FID) is the primary method for detection and analysis. The main detection methods currently include indirect and direct methods.

[0004] Indirect method: Two separate chromatographic columns are used to determine the content of total hydrocarbons and methane (calculated as carbon). The difference between the two values ​​is the content of non-methane total hydrocarbons (indirect method). Direct method: Methane is separated from total hydrocarbons through chromatographic column separation, valve switching, backflushing, etc., allowing non-methane total hydrocarbons to elute as separate peaks for direct concentration determination. Currently, the detection of exhaust gas from stationary pollution sources mainly uses the indirect method, while ambient air monitoring mainly uses the direct method.

[0005] However, in existing direct methods for determining non-methane total hydrocarbons, methane is retained to a certain extent due to the properties of the packing material in the enrichment tube. This methane residue causes measurement deviations in non-methane total hydrocarbons. Often, a pre-column is added after the enrichment tube, using a gradient temperature increase to separate methane and non-methane total hydrocarbons. This method prolongs the analysis cycle and cannot achieve rapid analysis. Furthermore, it places high demands on the instrument.

[0006] Furthermore, due to the retention effect of the enrichment tube on methane, it cannot be connected in series with the methane quantitative loop for quantitative methane analysis. Typically, a separate methane quantitative loop and a PQ column are required for methane determination, necessitating two injections, resulting in a complex flow path and a long analysis cycle.

[0007] In view of this, the present invention is hereby proposed. Summary of the Invention

[0008] The purpose of this invention is to provide a method for detecting methane and non-methane total hydrocarbons in a gas. This method, through a two-stage desorption process, allows for the measurement of methane and non-methane total hydrocarbons in a single sampling cycle using only one enrichment tube. Compared to existing methods that utilize PQ columns and methane quantitative loops for methane and non-methane total hydrocarbon measurement, the analytical flow path is simpler, and the loss of low-carbon hydrocarbons such as ethane during separation is effectively avoided, resulting in more accurate measurement results.

[0009] This invention provides a method for detecting methane and non-methane total hydrocarbons in a gas, the method comprising the following steps:

[0010] The sample gas was enriched using an enrichment tube, followed by a first and second analysis to separate methane and non-methane total hydrocarbons from the enrichment tube, and then the contents of methane and non-methane total hydrocarbons were detected.

[0011] The elution volume of the first analysis is greater than the elution volume of methane under the same analysis temperature and packing mass conditions, but less than the elution volume of ethane under the same analysis temperature and packing mass conditions.

[0012] Furthermore, the elution volume curve of the methane is as follows:

[0013] Q1=(-0.01068+0.15092×0.98002 T )×m, where: Q1 is the elution volume of methane in L, T is the elution temperature in °C, and m is the mass of the packing material in g.

[0014] Furthermore, the elution volume curve of the ethane is as follows:

[0015] Q2=(0.06362+1.92566×0.97546 T )×m, where: Q2 is the elution volume of ethane (L), T is the elution temperature (°C), and m is the mass of the packing material (g).

[0016] Furthermore, the filler for the enrichment tube is Carbosieve SⅢ.

[0017] Furthermore, the enrichment tube enriches the sample gas at a temperature of -10℃ to 40℃.

[0018] Furthermore, the temperature for the first analysis is 0–60°C;

[0019] Furthermore, the temperature for the second analysis is 150–300°C;

[0020] Furthermore, the detection involves quantitative analysis of the swept methane or non-methane total hydrocarbons using a flame ionization detector.

[0021] Furthermore, the detection method includes the following steps:

[0022] (a) The sample gas to be tested is passed into the enrichment tube for sampling, and the temperature of the enrichment tube during the sampling process is -10℃~40℃;

[0023] (b) After sampling, the enrichment tube is heated to 0-60℃ for the first analysis. Under the action of carrier gas, methane is separated from the enrichment tube. Then, the sample is injected into the flame ionization detector to perform quantitative analysis of the swept methane and measure the methane content.

[0024] The elution volume of the first analysis is greater than the elution volume of methane under the temperature and packing mass conditions of the first analysis, but less than the elution volume of ethane under the temperature and packing mass conditions of the first analysis.

[0025] (c) The enrichment tube after the first analysis is heated to 150-300℃ for a second analysis. Under the action of the carrier gas, the non-methane total hydrocarbons are separated from the enrichment tube. Then, the sample is injected into the flame ionization detector to perform quantitative analysis on the swept methane and measure the content of non-methane total hydrocarbons.

[0026] Furthermore, in step (c), the heating rate of the enrichment tube after the first analysis and before the second analysis is 10–70 °C / s.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] This invention provides a method for detecting methane and non-methane total hydrocarbons in a gas. The method first enriches the sample gas using an enrichment tube, then performs a first and second elution to separate methane and non-methane total hydrocarbons from the enrichment tube, respectively. The contents of methane and non-methane total hydrocarbons are then detected. The elution volume of the first elution is greater than the elution volume of methane under the same elution temperature and packing mass, but less than the elution volume of ethane under the same elution temperature and packing mass. This application, through a two-stage desorption method, can measure methane and non-methane total hydrocarbons in a single sampling cycle using only one enrichment tube. Compared to existing methods using PQ columns and methane quantitative loops for measuring methane and non-methane total hydrocarbons, the analytical flow path is simpler, and the loss of low-carbon hydrocarbons such as ethane during separation is effectively avoided, resulting in more accurate measurement results. Attached Figure Description

[0029] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0030] Figure 1 The elution volume curve of methane on Carbosieve SⅢ provided for this invention;

[0031] Figure 2 Elution volume curve of ethane on Carbosieve SⅢ provided for the present invention. Detailed Implementation

[0032] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] According to one aspect of the present invention, a method for detecting methane and non-methane total hydrocarbons in a gas, the detection method comprising the following steps:

[0034] The sample gas was enriched using an enrichment tube, followed by a first and second analysis to separate methane and non-methane total hydrocarbons from the enrichment tube, and then the contents of methane and non-methane total hydrocarbons were detected.

[0035] The elution volume of the first analysis is greater than the elution volume of methane under the same analysis temperature and packing mass conditions, but less than the elution volume of ethane under the same analysis temperature and packing mass conditions.

[0036] This invention provides a method for detecting methane and non-methane total hydrocarbons in a gas. The method first enriches the sample gas using an enrichment tube, then performs a first and second elution to separate methane and non-methane total hydrocarbons from the enrichment tube, respectively. The contents of methane and non-methane total hydrocarbons are then detected. The elution volume of the first elution is greater than the elution volume of methane under the same elution temperature and packing mass, but less than the elution volume of ethane under the same elution temperature and packing mass. This application, through a two-stage desorption method, can measure methane and non-methane total hydrocarbons in a single sampling cycle using only one enrichment tube. Compared to existing methods using PQ columns and methane quantitative loops for measuring methane and non-methane total hydrocarbons, the analytical flow path is simpler, and the loss of low-carbon hydrocarbons such as ethane during separation is effectively avoided, resulting in more accurate measurement results.

[0037] It should be noted that the approach for separating methane and non-methane total hydrocarbons from the enrichment tube in this application is as follows:

[0038] 1. Determine the elution volume profile for methane:

[0039] Figure 1 The elution volume curve of methane on Carbosieve SⅢ is shown.

[0040] The elution volume of methane was measured at 0℃, 20℃, 40℃, 60℃, 80℃, and 100℃ respectively. Based on a reference point, a fitting curve of the elution volume versus temperature was plotted. The fitting model with the smallest residual was selected. The fitting curves are shown below:

[0041] The elution volume curve for methane is: Q1 = (-0.01068 + 0.15092 × 0.98002) T )×m;

[0042] In the formula, T is the temperature in °C, and m is the mass of the packing material in g.

[0043] 2. Determine the elution volume profile of ethane, the non-methane total hydrocarbon component that is most easily eluted:

[0044] Figure 2 The elution volume curve of ethane on Carbosieve SⅢ is shown.

[0045] The elution volume curve for ethane is: Q2 = (0.06362 + 1.92566 × 0.97546) T )×m;

[0046] In the formula, T is the temperature in °C, and m is the mass of the packing material in g.

[0047] Therefore, as long as the most easily eluted non-methane hydrocarbon component (ethane) is not eluted, it can be considered that there is no loss of non-methane hydrocarbons. In other words, as long as the elution volume Q of the enrichment tube is maintained in the order Q1(methane) < Q < Q2(ethane), methane elution can be completed and measured. After the methane measurement is complete, the enrichment tube is subjected to a second heating desorption process to determine the non-methane hydrocarbons.

[0048] In a preferred embodiment of the present invention, the filler of the enrichment tube is Carbosieve SⅢ.

[0049] It should be noted that the current non-methane total hydrocarbon enrichment tubes use Tenax GR and Carbosieve SⅢ type dual-packing enrichment tubes. Among them, the Carbosieve SⅢ type packing is mainly used to adsorb low-carbon components, but it also has a certain retention effect on methane. This application is based on this point and designs a new application mode.

[0050] In a preferred embodiment of the present invention, the enrichment tube enriches the sample gas at a temperature of -10°C to 40°C.

[0051] As a preferred implementation, in sampling mode, the enrichment tube is kept at a low temperature (-10℃ to 40℃), and the sample gas gradually enters the enrichment tube, where non-methane total hydrocarbons and some methane in the sample gas are retained on the enrichment tube.

[0052] In a preferred embodiment of the present invention, the temperature of the first analysis is 0 to 60°C;

[0053] As a preferred embodiment, at the temperature of the first analysis (0-60°C), the enrichment tube has a strong retention effect on non-methane total hydrocarbons, and by controlling the size of the purging volume, it is ensured that methane can be completely purged at this temperature and purging volume, without any loss of non-methane total hydrocarbons.

[0054] In a preferred embodiment of the present invention, the temperature of the second analysis is 150–300°C;

[0055] As a preferred embodiment, at the temperature of the second analysis (150-300°C), the remaining non-methane total hydrocarbons in the enrichment tube enter the detector for quantitative analysis under the action of the carrier gas, realizing the measurement of methane and non-methane total hydrocarbons in a single sampling.

[0056] In a preferred embodiment of the present invention, the detection is performed by using a flame ionization detector to quantitatively analyze the swept methane or non-methane total hydrocarbons.

[0057] In a preferred embodiment of the present invention, the detection method includes the following steps:

[0058] (a) The sample gas to be tested is passed into the enrichment tube for sampling, and the temperature of the enrichment tube during the sampling process is -10℃~40℃;

[0059] (b) After sampling, the enrichment tube is heated to 0-60℃ for the first analysis. Under the action of carrier gas, methane is separated from the enrichment tube. Then, the sample is injected into the flame ionization detector to perform quantitative analysis of the swept methane and measure the methane content.

[0060] The elution volume of the first analysis is greater than the elution volume of methane under the temperature and packing mass conditions of the first analysis, but less than the elution volume of ethane under the temperature and packing mass conditions of the first analysis.

[0061] (c) The enrichment tube after the first analysis is heated to 150-300℃ for a second analysis. Under the action of the carrier gas, the non-methane total hydrocarbons are separated from the enrichment tube. Then, the sample is injected into the flame ionization detector to perform quantitative analysis on the swept methane and measure the content of non-methane total hydrocarbons.

[0062] In the preferred embodiment described above, the heating rate of the enrichment tube after the first analysis and before the second analysis in step (c) is 10–70 °C / s.

[0063] As a preferred implementation method, the faster the heating rate during secondary analysis, the better the peak shape of the FID detector; conversely, a slow heating rate will result in peak tailing. A heating rate between 10 and 70°C / s, or a heating rate greater than 10°C / s, will provide a peak shape that meets detection requirements.

[0064] The technical solution of the present invention will be further described below with reference to the embodiments.

[0065] Example 1

[0066] A method for detecting methane and non-methane total hydrocarbons, the method comprising the following steps:

[0067] (a) The sample gas to be tested is passed into the enrichment tube for sampling. During the sampling process, the temperature of the enrichment tube is -10℃, the sampling flow rate is 20ml / min, and the sampling volume is 50ml.

[0068] The filler in the enrichment tube is Carbosieve SⅢ, with a mass of 0.05g;

[0069] (b) After sampling, the enrichment tube is connected to the carrier gas path with a carrier gas flow rate of 20 ml / min. At this time, the enrichment tube is simultaneously heated to the first desorption temperature of 0℃. At this time, the methane in the enrichment tube is desorbed from the enrichment tube under the action of the carrier gas. Then, the sample is injected into the flame ionization detector to perform quantitative analysis on the swept methane and measure the methane content.

[0070] The elution volume of the first analysis is greater than the elution volume of methane under the temperature and packing mass conditions of the first analysis, but less than the elution volume of ethane under the temperature and packing mass conditions of the first analysis.

[0071] (c) The enrichment tube after the first analysis is heated to 150°C for a second analysis. Under the action of the carrier gas, the non-methane total hydrocarbons are separated from the enrichment tube. Then, the sample is injected into the flame ionization detector to perform quantitative analysis on the swept methane and measure the content of non-methane total hydrocarbons.

[0072] Example 2

[0073] A method for detecting methane and non-methane total hydrocarbons, the method comprising the following steps:

[0074] (a) The sample gas to be tested is passed into the enrichment tube for sampling. During the sampling process, the temperature of the enrichment tube is 40°C, the sampling flow rate is 20ml / min, and the sampling volume is 50ml.

[0075] The filler in the enrichment tube is Carbosieve SⅢ, with a mass of 0.05g;

[0076] (b) After sampling, the enrichment tube is connected to the carrier gas path with a carrier gas flow rate of 20 ml / min. At this time, the enrichment tube is simultaneously heated to the first desorption temperature of 60°C. At this time, the methane in the enrichment tube is desorbed from the enrichment tube under the action of the carrier gas. Then, the sample is injected into the flame ionization detector to perform quantitative analysis on the swept methane and measure the methane content.

[0077] The elution volume of the first analysis is greater than the elution volume of methane under the temperature and packing mass conditions of the first analysis, but less than the elution volume of ethane under the temperature and packing mass conditions of the first analysis.

[0078] (c) The enrichment tube after the first analysis is heated to 300℃ for a second analysis. Under the action of the carrier gas, the non-methane total hydrocarbons are separated from the enrichment tube. Then, the sample is injected into the flame ionization detector to perform quantitative analysis on the swept methane and measure the content of non-methane total hydrocarbons.

[0079] Example 3

[0080] A method for detecting methane and non-methane total hydrocarbons, the method comprising the following steps:

[0081] (a) The sample gas to be tested is passed into the enrichment tube for sampling. During the sampling process, the temperature of the enrichment tube is -20℃, the sampling flow rate is 20ml / min, and the sampling volume is 50ml.

[0082] The filler in the enrichment tube is Carbosieve SⅢ, with a mass of 0.03g;

[0083] (b) After sampling, the enrichment tube is connected to the carrier gas path with a carrier gas flow rate of 20 ml / min. At this time, the enrichment tube is simultaneously heated to the first desorption temperature of 20°C and the elution volume is 20 ml. At this time, the methane in the enrichment tube is desorbed from the enrichment tube under the action of the carrier gas. Then, the sample is injected into the flame ionization detector to perform quantitative analysis on the swept methane and measure the methane content.

[0084] Note: At this time, the elution volume of methane is Q1 = 2.7 ml, and the elution volume of ethane is Q2 = 37 ml. Therefore, by determining the elution volume to be within the range of 2.7 to 37 ml, the purpose of eluting and separating methane and non-methane total hydrocarbons can be achieved.

[0085] (c) The enrichment tube after the first analysis is heated to 160℃ for a second analysis. Under the action of the carrier gas, the non-methane total hydrocarbons are separated from the enrichment tube. Then, the sample is injected into the flame ionization detector to perform quantitative analysis on the swept methane and measure the content of non-methane total hydrocarbons.

[0086] Example 4

[0087] A method for detecting methane and non-methane total hydrocarbons, the method comprising the following steps:

[0088] (a) The sample gas to be tested is passed into the enrichment tube for sampling. During the sampling process, the temperature of the enrichment tube is -20℃, the sampling flow rate is 20ml / min, and the sampling volume is 50ml.

[0089] The filler in the enrichment tube is Carbosieve SⅢ, with a mass of 0.05g;

[0090] (b) After sampling, the enrichment tube is connected to the carrier gas path with a carrier gas flow rate of 20 ml / min. At this time, the enrichment tube is simultaneously heated to the first desorption temperature of 40°C. At this time, the methane in the enrichment tube is desorbed from the enrichment tube under the action of the carrier gas. Then, the sample is injected into the flame ionization detector to perform quantitative analysis on the swept methane and measure the methane content.

[0091] Note: At this time, the elution volume of methane is Q1 = 2.8 ml, and the elution volume of ethane is Q2 = 39 ml. Therefore, by determining the elution volume to be within the range of 2.8 to 39 ml, the purpose of eluting and separating methane and non-methane total hydrocarbons can be achieved.

[0092] (c) The enrichment tube after the first analysis is heated to 300℃ for a second analysis. Under the action of the carrier gas, the non-methane total hydrocarbons are separated from the enrichment tube. Then, the sample is injected into the flame ionization detector to perform quantitative analysis on the swept methane and measure the content of non-methane total hydrocarbons.

[0093] In summary, the present invention provides a method for detecting methane and non-methane total hydrocarbons in a gas. Through a two-stage desorption process, it enables the measurement of methane and non-methane total hydrocarbons in a single sampling cycle using only one enrichment tube. Compared to existing methods that utilize PQ columns and methane quantitative loops for methane and non-methane total hydrocarbon measurement, the analytical flow path is simpler, and it effectively avoids the loss of low-carbon hydrocarbons such as ethane during separation, resulting in more accurate measurement results.

[0094] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for detecting methane and non-methane total hydrocarbons in a gas, characterized by, The detection method comprises the following steps: The enrichment tube is used to enrich the sample gas, and then the first resolution and the second resolution are sequentially performed to resolve and separate methane and non-methane total hydrocarbon from the enrichment tube, and then the contents of the methane and the non-methane total hydrocarbon are detected respectively; The elution volume of the first resolution is greater than the elution volume of methane under the same resolution temperature and filler mass conditions, and is less than the elution volume of ethane under the same resolution temperature and filler mass conditions; The filler of the enrichment tube is Carbosieve SIII, the enrichment temperature of the enrichment tube is-10℃-40℃, the first resolution temperature is 0-60℃, and the second resolution temperature is 150-300℃; The elution volume curve of the methane is: Q1= (-0.01068+0.15092x0.98002 T ) x m, wherein: Q1 is the elution volume of methane L, T is the elution temperature ℃, and m is the mass of the filler g. The elution volume curve for ethane is: Q2 = (0.06362 + 1.92566 x 0.97546 T ) x m, where Q2 is the elution volume of ethane in L, T is the elution temperature in °C, and m is the mass of the packing in g.

2. The method of claim 1, wherein, The detection is quantitative analysis of the swept methane or non-methane total hydrocarbon by using a flame ionization detector.

3. The method for detecting methane and non-methane total hydrocarbons in a gas according to claim 1, characterized in that, The detection method comprises the following steps: (a) The sample gas is introduced into the enrichment tube for sampling, and the sampling temperature of the enrichment tube is-10℃-40℃; (b) The enrichment tube after sampling is heated to 0-60℃ for the first resolution, methane is separated from the enrichment tube under the action of the carrier gas, then the sample is introduced into a flame ionization detector for quantitative analysis of the swept methane, and the methane content is measured; The elution volume of the first resolution is greater than the elution volume of methane under the same resolution temperature and filler mass conditions, and is less than the elution volume of ethane under the same resolution temperature and filler mass conditions; (c) The enrichment tube after the first resolution is heated to 150-300℃ for the second resolution, non-methane total hydrocarbon is separated from the enrichment tube under the action of the carrier gas, then the sample is introduced into a flame ionization detector for quantitative analysis of the swept methane, and the non-methane total hydrocarbon content is measured.

4. The method for detecting methane and non-methane total hydrocarbons in a gas according to claim 3, wherein In step (c), the heating speed of the enrichment tube after the first resolution and before the second resolution is 10-70℃ / s.

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