Gas chromatography is widely used in petrochemical, scientific research and teaching, environmental monitoring, food and medicine safety, high purity gas industry, life science, forensic identification and other fields. Wuhan Tetworth Technology Co., Ltd. is located in Jiangxia District, Wuhan, China, specializing in the production of gas chromatographs. The main products include GC2030 series gas chromatograph analyzer, GC966 series online gas chromatograph, GC966 portable gas chromatograph and other related equipment. The following chromatographic technicians from Wuhan Tetworth Technology Co., Ltd. mainly introduce gas chromatographic analysis methods for oxygen-containing coalbed methane components.
The analysis of coalbed methane composition is very important for the exploitation and utilization of coalbed methane. The method for determining the composition of coalbed methane by gas chromatography is characterized by standard gas and quantitative by external standard method. The single gas path double column can be used to make the coalbed gas sample on two chromatographs of one chromatograph. Analysis, to achieve a single injection analysis of the main components of coalbed methane. Aiming at the influencing factors such as column temperature, injection temperature and carrier gas flow rate, relevant experimental research was carried out, and the repeatability of the method was also examined. The research results show that the method is easy to operate, accurate and shortens the analysis time.
Coalbed methane mining and utilization has received great attention, and the coalbed methane components should be analyzed and tested when utilized. Combined with the characteristics of coalbed methane, it is possible to study the appropriate coalbed methane utilization mode from the technical point of view and strengthen the resource utilization of coal mine methane drainage.
The coalbed methane components mainly include: CH4, O2, N2, and a small amount of CO2. It is difficult to accurately analyze all kinds of gases under one analysis condition, and only different components can be analyzed under several conditions. At present, the commonly used method is to complete the whole component analysis of coalbed methane by using two gas chromatographs. This method will increase the operating error of the system, especially for trace components, and the relative error is large. At the same time, because the analytical instrument is expensive, Increase equipment investment.
Based on the analysis of the gas chromatographic detection method, the single gas path double column method can be used to analyze the sample on two different chromatographic columns of one chromatograph to realize one injection and the main group of coalbed methane. Analyze the analysis to save analysis time and cost. The analysis and research on the analysis method of coalbed methane components were carried out through experiments, and the better analytical operating conditions were selected.
1 Experimental part
1.1 Instruments and samples
Gas chromatograph; high purity N2 (99.999%), high purity H2 (99.999%); sample gas is coalbed methane.
1.2 Choice of analytical methods
Gas chromatography is commonly used in the analysis and detection of gases. The shut-off valve is connected in the gas chromatograph gas flow process, and the two chromatographic columns are connected by a shut-off valve, and the main components of the oxygen-containing coalbed methane are measured by one chromatograph, which is easy to operate and saves cost. The analysis was performed by constant temperature operation, quantitative injection, qualitative analysis by standard method using standard gas, and quantitative analysis results by external standard method. The detector is a Thermal Conductivity Detector (TCD).
1.3 Analysis Process
Turn on the gas source, turn on the gas chromatograph and chromatographic workstation and set the parameters. After each parameter reaches the set value, use the quantitative tube to perform the analysis. After the analysis is completed, the column is aged, and the impurities in the column are discharged to prevent the accumulation of impurities from clogging the column and affecting the next test result. The aging condition of the 5A molecular sieve column is 25 mL/min, the column temperature is 270-320 °C, and the aging time is 6-8 h. The aging conditions of the TDX-01 column are column flow rate 25 mL/min, column temperature 260 °C, and aging time 6-8 h. The aging conditions of GDX-104 column are column flow rate 25 mL/min, column temperature 100 °C, and aging time 6-8 h. After the aging is finished, turn off the hot wire. After the temperature has dropped to normal temperature, turn off the gas chromatograph and turn off the carrier gas.
1.4 Experimental process
Firstly, the column temperature, injection temperature, detection temperature, carrier gas flow rate, and the influence of the column on the analysis results were investigated. After selecting the better operating conditions, standard samples with different volume fractions were prepared, and the analysis results were analyzed. And repeatability.
2 Analysis condition selection
1) Column temperature selection. Lower temperature facilitates separation of components, increases column selectivity, and improves column stability; while increasing column temperature reduces analysis time. It can be seen from the chromatograms at different column temperatures that the analysis time is longer when the column temperature is 40 °C, and the adhesion of different components occurs at 60 °C, which affects the accurate quantification. It is appropriate to consider the column temperature to choose 50 °C.
2) The choice of temperature detection. Increasing the detector temperature and hot wire temperature increases sensitivity, but causes the baseline to be unstable and the hot wire to burn out. Considering the sensitivity of the test and the protection of the detector, the hot wire temperature is set to 150 °C and the detector temperature is selected to be 100 °C.
3) Selection of injection temperature. The appropriate injection temperature should ensure that all components of the sample are completely vaporized at the moment of injection without causing decomposition of the sample. Generally, it is selected at the boiling point of the sample or slightly above the boiling point to ensure rapid and complete gasification of the sample. Considering that water vapor is contained in the coalbed methane, the injection temperature is selected to be 100 °C.
4) Selection of carrier gas flow rate. The separation effect of gas chromatography is related to the design of the column and the operating conditions, and the carrier gas flow rate will affect the separation efficiency of the column. When the carrier gas flow rate is low, the sample is seriously diffused, and the separation efficiency of the column is greatly reduced. When the carrier gas flow rate is high, the mass transfer resistance of the sample is large, and the column efficiency is also reduced. Therefore, the appropriate carrier gas flow rate should be selected. . Through analysis and comparison, when the carrier gas flow rate is 25 mL/min, the response value of CH4 is the most gao, and the peak area is the largest, indicating that the sensitivity of the instrument to be tested is better at this flow rate.
3 Conclusion
1) When the column temperature is 50 °C, the detector temperature is 100 °C, the injection temperature is 100 °C, and the carrier gas flow rate is 25 mL/min, the coalbed methane component separation effect is better.
2) The 5A molecular sieve column can achieve good separation of N2, O2 and CH4, but the adsorption of H2O should be prevented from deactivating during use. The column should be aged after the end of the test.
3) The selected chromatographic method has good linearity and repeatability, which can effectively save analysis time and cost.
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