CN111551643A - Method and system for detecting carbon-containing compound based on catalytic conversion technology - Google Patents
Method and system for detecting carbon-containing compound based on catalytic conversion technology Download PDFInfo
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Abstract
The invention relates to a method and a system for detecting carbon-containing compounds based on a catalytic conversion technology. The method comprises the following steps: (1) carrying out catalytic oxidation combustion on a sample to be detected in the presence of oxygen to generate carbon dioxide; (2) carrying out catalytic hydrogenation reduction on the carbon dioxide generated in the step (1) in the presence of hydrogen to generate methane; (3) detecting the methane generated in the step (2) by a hydrogen flame ionization detector. The method and system provided by the invention uses catalytic oxidative combustion and catalysisThe hydrogenation reduction technology indirectly realizes the detection of trace or trace carbon-containing compounds by using a hydrogen flame ionization detector and can simultaneously detect CO and CO2And organic substances, particularly formaldehyde, formic acid, formamide and the like which are difficult to detect by a conventional method, have relatively high detection sensitivity.
Description
The application is a divisional application of a patent application with the application date of 2018, 2 and 8, and the application number of 201810127070.1, and the name of the patent application is 'method and system for detecting carbon-containing compounds based on catalytic conversion technology'.
Technical Field
The invention relates to detection of carbon-containing compounds, in particular to a method and a system for detecting carbon-containing compounds based on a catalytic conversion technology.
Background
The carbon-containing compounds in the atmospheric environment mainly include carbon oxides and hydrocarbons, and the carbon oxides mainly include carbon monoxide (CO) and carbon dioxide (CO)2) The hydrocarbon, i.e., organic substance, mainly includes saturated hydrocarbons, unsaturated hydrocarbons, and oxygen-containing hydrocarbons, such as aldehydes, ketones, alcohols, acids, ethers, esters, and the like.
At present, no ideal measurement method exists for oxygen-containing hydrocarbons, which are important in atmospheric Volatile Organic Compounds (VOCs), mostly have high reactivity and can participate in atmospheric photochemical reaction. Studies have demonstrated that many oxygen-containing hydrocarbons can cause significant harm to human health. For example, formaldehyde is one of the best known carcinogenic teratogenic air pollutants, and the long-term low-concentration formaldehyde contact can cause the hypofunction and the pathological changes of human bodies; formamide has been classified by the eu chemical administration as a substance with reproductive toxicity and is listed by eu related regulations as a high interest substance candidate list. Such oxygen-containing organic substances are generally detected by colorimetry, photometry, chemical titration, or the like. However, the methods have complicated pretreatment, use more chemical products, and have large errors and low sensitivity in many measurement methods.
The Flame Ionization Detector (FID) is one of the most commonly used detectors in gas chromatography instruments, not only has high sensitivity and a relatively wide linear range for most organic substances, but also has low cost and simple operation and maintenance, and has been rapidly and widely used since 1958, and thus becomes a powerful tool for analyzing organic compounds. The inner flame of the hydrogen flame ionization detector is hydrogen-rich flame, and the outer flame is oxygen-rich flame. In the lower part of the flame, the hydrogen atoms diffusing inwards from the combustion zone have a high flux, and the hydrocarbons first undergo a thermal hydrogenolysis reaction to form a mixture of methane, ethylene and acetylene. These non-methane hydrocarbons then react with hydrogen atoms and are further hydrogenated to saturated hydrocarbons. At temperatures below 600 c, the c-c bond is broken and eventually all of the carbon is converted to methane, the most basic, common response unit, and then undergoes an ionization process to produce a signal. The reaction formula of the ionization process is as follows:
CH+O——→CHO++e-。
therefore, the response obtained by such detectors is generally proportional to the number of carbon atoms in the component being measured, and has an equimolar response to carbon, also referred to as an "isocarbon response". However, if the molecules of the organic components to be detected contain unsaturated bonds or other heteroatom functional groups (such as nitrogen, phosphorus, sulfur, halogen and the like), the response value of the detector can be affected. Particularly low carbon oxygen-containing organic compounds such as formaldehyde, formic acid, formamide, etc., have little or no response, and the hydrogen flame ionization detector has no response at all to carbon-containing inorganic compounds such as carbon monoxide and carbon dioxide.
In the prior art, a hydrogen flame ionization detector is also adopted to detect trace CO and CO2Usually, CO and CO are firstly added2Hydrogenation reduction to CH4. The method mainly comprises the steps that carrier gas with a sample is separated by a chromatographic column, and then mixed with hydrogen to enter a methane converter, and CO are carried out2The samples are catalytically hydrogenated to methane in a reformer at a temperature of about 350 ℃ and then detected by a hydrogen flame ionization detector, and CO in ppm and below can be easily analyzed2. However, the method can only realize the analysis of part of the oxygen-containing organic matters. When metal (Pd, Pt, Ru, Rh, Ni-Al, etc.) is used for catalytic hydrogenation reductionWhen the catalyst is used, only aldehyde groups and carbonyl groups can be hydrogenated and reduced into corresponding alcohol, and hydride ions are added instead of hydrogen atoms; the carbon-oxygen double bond in the carboxyl group and the ester group generally cannot undergo addition reaction unless a strong reducing agent such as lithium aluminum hydride (LiAlH) is used4) And the like. However, lithium aluminum hydride is flammable and explosive, and is decomposed explosively when it meets water, which makes it difficult to put it into practical use. Thus, many acids and esters (such as formic acid) cannot be measured by this method.
In addition, oxygen-containing compounds are detected using an oxygen selective flame ionization detector (OFID). The main method is that the components of the sample separated by the chromatographic column are firstly put into a cracking furnace to carry out cracking reaction at the temperature of more than 1000 ℃, the hydrocarbon is converted into hydrogen and carbon, the oxygen atoms in the oxygen-containing compound are converted into CO, and then the CO enters a methane converter to generate methane, and then the methane enters a FID to be detected. The cracking reactor in the cracking furnace is a spiral platinum/rhodium capillary fixed on an insulating frame, and is directly heated to 1000-1400 ℃ by a low-voltage power supply. Under these conditions, the cracking reaction takes place as follows:
a thin carbon layer formed after the reaction was attached to the inner wall of the platinum/rhodium capillary.
The methanation reactor in the methane converter is a short alumina PLOT (porous layer open tubular column) glass capillary tube, the inner wall of which adsorbs nickel catalyst and is directly inserted into the base of the common FID, and hydrogen is introduced and the temperature is kept at 350 ℃. The CO formed in the cracking furnace is converted here into methane:
since the mechanism of the OFID response is well-defined, one CO molecule can be generated by having one oxygen atom in the molecule. Therefore, the weight response value can be obtained by calculating the proportion of the molecular weight of CO in the molecular weight of the organic matter. The response of OFID is proportional to the percentage of oxygen in the compound, i.e., there is an equimolar response to oxygenIt is a selective detector which can only analyze oxygen-containing organic substances well, but has no response to oxygen-free organic substances such as saturated hydrocarbons and unsaturated hydrocarbons. Moreover, the operation condition is harsh, after the cracking reaction occurs, a thin layer of carbon is generated on the inner wall of the platinum/rhodium capillary tube, the carbon layer is helpful for the cracking reaction and inhibits the hydrocarbon response, so a large amount of hydrocarbon which is injected frequently is needed to generate carbon deposit or a proper amount of oxygen or air is injected to combust the carbon deposit to generate CO2And removing the excessive carbon deposition, thereby ensuring the proper carbon layer thickness. In addition, the higher the temperature of the cracking furnace, the higher the cracking rate, the higher the detection sensitivity, but too high a temperature may result in a reduction in the life of the cracking element of the reactor; if the gas path contains a trace amount of O2、H2O、CO、CO2And the like, which interfere with the analysis of the oxygenates and can consume carbon deposits, while releasing heat in large quantities to damage the cracking element. Moreover, the presence of these substances can cause the background noise of the instrument to rise and the baseline to be unstable. Therefore, the carrier gas and hydrogen gas are subjected to strict purification treatment, and the system is required to be absolutely sealed without any leakage.
Disclosure of Invention
The invention aims to provide a method and a system for indirectly detecting carbon-containing compounds by using a hydrogen flame ionization detector by using the technologies of catalytic oxidation combustion and catalytic hydrogenation reduction.
The invention provides a method for detecting carbon-containing compounds based on a catalytic conversion technology, which comprises the following steps:
(1) and (3) carrying out catalytic oxidation combustion on the sample to be detected in the presence of oxygen to generate carbon dioxide.
(2) And (2) carrying out catalytic hydrogenation reduction on the carbon dioxide generated in the step (1) in the presence of hydrogen to generate methane.
(3) Detecting the methane generated in the step (2) by a hydrogen flame ionization detector.
Preferably, the method according to the preceding, wherein the hydrogen flame ionization detector in step (3) burns the hydrogen used from the hydrogen remaining after the catalytic hydrogenation in step (2).
More preferably, the method according to the foregoing, wherein the step (3) comprises mixing hydrogen gas and tail-blown air, flowing out of a nozzle of the hydrogen flame ionization detector with the methane to be detected, and combusting in air around the nozzle; the volume flow ratio of the hydrogen to the tail blowing air is preferably (0.8-1.1): 1.
preferably, the method according to the foregoing, wherein before step (1), further comprising: and separating the sample by a chromatographic column to obtain the sample to be detected. And performing enrichment-thermal desorption treatment on the sample to obtain the sample to be detected, wherein the enrichment-thermal desorption treatment is to enrich the sample to be detected in the sample through the adsorbent in the adsorption tube, and then obtain the sample to be detected through high-temperature desorption.
Or preferably, according to the aforementioned method, wherein the combustion in step (1) is flameless combustion, the combustion temperature being 390 ℃ and above.
More preferably, the method according to the preceding, wherein the sample to be detected is selected from CO, CO2And one or more of an organic, preferably selected from one or more of formaldehyde, formamide, and formic acid.
The invention also provides a system for detecting carbon-containing compounds by adopting any one of the methods, wherein the method comprises the following steps: the device comprises an oxygen pipeline, a sample pipeline, a hydrogen pipeline, an air pipeline, a catalytic oxidation furnace, a methane reforming furnace and a hydrogen flame ionization detector; the sample pipeline, the catalytic oxidation furnace, the methane converter and the hydrogen flame ionization detector are sequentially connected; the oxygen pipeline is positioned in front of the catalytic oxidation furnace and is communicated with the sample pipeline; the hydrogen pipeline is positioned between the catalytic oxidation furnace and the methane reformer and is communicated with a pipeline connecting the catalytic oxidation furnace and the methane reformer; the air pipeline is communicated with the hydrogen flame ionization detector.
Preferably, according to the foregoing system, wherein the air line is divided into two paths, one path is communicated with the hydrogen flame ionization detector, and the other path is communicated with a line connecting the methane reformer and the hydrogen flame ionization detector.
Preferably, the system according to the foregoing, further comprising: the sample outlet of the first chromatographic column is connected with the sample inlet of the sample pipeline; and the sample outlet of the adsorption column is connected with the sample inlet of the first chromatographic column.
More preferably, the system according to the foregoing, further comprising: the device comprises a carbon oxide pipeline and a second chromatographic column, wherein a sample outlet of the second chromatographic column is connected with the carbon oxide pipeline, and the carbon oxide pipeline is communicated with a pipeline connecting the catalytic oxidation furnace and the methane conversion furnace.
The method and the system provided by the invention indirectly realize the detection of trace or trace carbon-containing compounds by using a hydrogen flame ionization detector by using the technologies of catalytic oxidation combustion and catalytic hydrogenation reduction, and can simultaneously detect CO and CO2And organic substances, particularly formaldehyde, formic acid, formamide and the like which are difficult to detect by a conventional method, have relatively high detection sensitivity.
Because the first-stage reaction adopts a catalytic oxidation method, both hydrocarbons and oxygen-containing hydrocarbons can be reacted and converted into carbon dioxide, the types of the measured substances are wider than those of the two methods introduced in the background art; in addition, the catalytic oxidation can burn some harmful substances, and the possibility of poisoning of a catalyst (a nickel catalyst and the like) in the methanation furnace is reduced.
All these compounds produce responses that are only related to the quality of the carbon element, using catalytic oxidative combustion and catalytic hydrogenation reduction techniques, such as formaldehyde, formic acid, formamide, etc. with the same sensitivity as methane. Since this method has an "isocarbon response" to both hydrocarbons and oxygenated hydrocarbons, only one of these compounds needs to be calibrated to allow quantitative analysis of the other compounds. Particularly, it is very useful under the condition that the standard sample is difficult to obtain, for example, formaldehyde is easy to undergo polymerization and oxidation reaction by thermal and photochemical processes, so that the preparation and preservation of the standard gas are quite difficult. The formaldehyde can be easily quantitatively analyzed by only using methane as a standard sample as measured by a catalytic oxidation combustion and catalytic hydrogenation reduction method.
The temperature of the catalytic oxidation furnace in the system is far lower than that of the cracking furnace, carbon deposition is not generated, the service life of working elements is prolonged, the operation condition is relatively simple, and the damage of impurities such as oxygen is avoided; the temperatures of two catalytic reactions of the catalytic oxidation furnace and the methane converter are the same, so that the integrated design can be realized, and the miniaturization of instruments is facilitated; the catalytic oxidation furnace has low cost and is easy to popularize and use.
The hydrogen flame ionization detector in the method and the system adopts a premixing-diffusion flame mode, so that the sensitivity of compound measurement is improved. The conventional hydrogen flame ionization detector works in a mode of adopting hydrogen-oxygen diffusion flame with nitrogen as carrier gas, wherein the inner flame is hydrogen-rich flame, and the outer flame is oxygen-rich flame. Higher oxyhydrogen flame temperature can lead to the increase of ion recombination effect, and reduce the response value of signals. In the method and the system, tail-blown air is adopted, so that on one hand, the linear speed of the outlet of the nozzle can be increased, the peak shape is improved, on the other hand, oxygen required by the reaction can be provided from the inside of the flame, the ionization efficiency is enhanced, nitrogen required by the dilution temperature is provided, and the ion recombination effect is reduced, so that the response value is greatly improved.
Drawings
FIG. 1 is a block diagram of a system for detecting carbon-containing compounds in accordance with an embodiment of the present invention;
FIG. 2 is a block diagram of a system for detecting carbon-containing compounds in accordance with another embodiment of the present invention;
FIG. 3 is a test spectrum of example 1; and
FIG. 4 is a test spectrum of example 2.
Reference numerals:
10. catalytic oxidation furnace, 20, methane reformer, 30, hydrogen flame ionization detector, 31, nozzle of hydrogen flame ionization detector, 40, first chromatographic column, 50, second chromatographic column, 1, sample pipeline, 2, oxygen pipeline, 3, hydrogen pipeline, 4, air pipeline, 5 carbon oxide pipeline.
Detailed Description
The following detailed description of the present invention, taken in conjunction with the accompanying drawings and examples, is provided to enable the invention and its various aspects and advantages to be better understood. However, the specific embodiments and examples described below are for illustrative purposes only and are not limiting of the invention.
As shown in fig. 1, the present invention provides a method and system for detecting carbon-containing compounds, the system comprising: a catalytic oxidation furnace 10, a methane reformer 20 and a hydrogen flame ionization detector 30 connected in sequence; further comprising: a sample pipeline 1, an oxygen pipeline 2, a hydrogen pipeline 3 and an air pipeline 4; the sample pipeline 1 is communicated with the oxygen pipeline 2 and then connected with the catalytic oxidation furnace 10, and the hydrogen pipeline 3 is positioned between the catalytic oxidation furnace 10 and the methane reformer 20 and communicated with a pipeline connecting the catalytic oxidation furnace 10 and the methane reformer 20; the air line 4 communicates with a hydrogen flame ionization detector 30.
Firstly, a sample to be detected is catalyzed, oxidized and combusted in the presence of oxygen to generate carbon dioxide; wherein, the sample to be detected enters the reaction chamber of the catalytic oxidation furnace 10 for catalytic oxidation reaction after being mixed with air or oxygen from the oxygen pipeline 2 through the sample pipeline 1. In some embodiments, the temperature of the reaction chamber is maintained above 400 ℃, and the sample to be tested is subjected to flameless combustion under the action of a noble metal catalyst such as platinum, palladium, ruthenium and the like in the reaction chamber. The air or oxygen flow in the oxygen line 2 is adjusted to supplement the excess oxygen so that the carbon-containing compounds in the sample to be tested are almost completely converted into carbon dioxide and water, and the conversion rate exceeds 99%.
In the catalytic oxidation furnace 10, the reactions that take place are as follows:
From the above reaction formula, all that can be completely combusted to produce CO2The carbon-containing compound (2) can be used as a sample to be detected of the system. Specifically can be CO or CO2And organic substances (such as formaldehyde, formamide, and formic acid). Overcomes the defect of single type of sample which can be detected in the prior art, has relatively simple operation condition and is not afraid of the harm of impurities such as oxygen and the like. The temperature of the catalytic oxidation furnace is far lower than that of the cracking furnace, carbon deposition is not generated, and the service life of a working element is prolonged. In addition, the catalytic oxidation can burn some harmful substances, and the possibility of poisoning of a catalyst (a nickel catalyst and the like) in the methanation furnace is reduced.
Then, the generated carbon dioxide is subjected to catalytic hydrogenation reduction in the presence of hydrogen to generate methane; specifically, the generated carbon dioxide, water and residual oxygen flow out of the catalytic oxidation furnace 10, are mixed with hydrogen from the hydrogen line 3, and then enter the reaction chamber of the methane reformer 20 for catalytic hydrogenation. In some embodiments, the temperature of the reaction chamber is maintained above 350 ℃, and the carbon dioxide and the remaining oxygen undergo a hydrogenation reduction reaction over a catalyst (typically a nickel catalyst) in the reaction chamber. The hydrogen flow in the hydrogen line 3 is adjusted to make up for excess hydrogen so that the remaining oxygen forms water and carbon dioxide is almost completely converted to methane with a conversion of over 99%.
In the methane reformer 20, the reactions that take place are as follows:
therefore, the detected sample is subjected to two-step reaction of catalytic oxidation and catalytic hydrogenation reduction, and carbon elements in the detected sample are completely converted into methane, so that in the subsequent step, the content of the detected sample can be calculated only by detecting the methane quantity. In addition, since the temperatures of the two catalytic reactions occurring in the catalytic oxidation furnace 10 and the methane reformer 20 are the same, they can be integrally designed, which is advantageous for downsizing the apparatus.
Next, the methane produced in the step is detected by a hydrogen flame ionization detector. The generated methane and water and the remaining hydrogen gas flow out of the methane reformer 20 and then enter the hydrogen flame ionization detector 30 for detection. The hydrogen flame ionization detector does not respond to water and only detects the signal of methane, thereby detecting carbon-containing compounds.
Therefore, the response value obtained by the hydrogen flame ionization detector in the system is only in direct proportion to the number of carbon atoms in the detected sample, and even unsaturated hydrocarbons or oxygen-containing hydrocarbons (such as formaldehyde, formamide, formic acid and the like) can realize true 'equal carbon response', namely, the response value obtained by the hydrogen flame ionization detector has equal molar response with the carbon in the detected sample.
Because the system has equal carbon response to hydrocarbon or oxygenated hydrocarbon, only one of the compounds needs to be calibrated, and other compounds can be quantitatively analyzed. The method is particularly useful under the condition that standard samples are difficult to obtain, for example, formaldehyde is easy to undergo polymerization and oxidation reactions through thermal and photochemical processes, so that the preparation and the storage of the standard gas are quite difficult, the standard gas is measured through a catalytic oxidation combustion method and a catalytic hydrogenation reduction method, and the formaldehyde can be easily quantitatively analyzed by only using the standard samples such as methane and the like.
In one embodiment, the air line 4 is split into two paths, one path communicating with the hydrogen flame ionization detector 30, the air from this path acting as a combustion supporting gas supplied around the nozzle 31 of the hydrogen flame ionization detector; the other path is communicated with a pipeline connecting the methane reformer 20 and the hydrogen flame ionization detector 30, and the air therein is used as tail blowing air. The air line 4 may be divided into two lines by a tee.
The residual hydrogen from the methane reformer 20 is mixed directly as combustion gas with the tail-blown air from the air line 4, carrying the measured methane and water out of the nozzle 31 of the hydrogen flame ionization detector, forming a premixed-diffusion flame. The tail blowing air can increase the linear speed of the outlet of the nozzle and improve the peak shape, and can provide oxygen required by reaction from the inside of the flame, thereby enhancing the ionization efficiency, providing nitrogen required by dilution temperature and reducing the ion recombination effect, thereby greatly improving the response value. Flame in this manner provides a several fold increase in methane response. However, if the flame is diluted too deeply, the temperature drops too low, which in turn causes a decrease in the response value, and therefore the volume flow ratio of hydrogen to tail-blown air is about (0.8 to 1.1): 1. most preferably 1: 1.
in one embodiment, the system further comprises: and a sample outlet of the first chromatographic column 40 is connected with a sample inlet of the sample pipeline 1. An adsorption column (not shown in the figure), wherein a sample outlet of the adsorption column is connected with a sample inlet of the first chromatographic column.
The sample is separated by the first chromatographic column 40 to obtain the sample to be detected. If the concentration of the sample to be detected in the total sample is low, the sample to be detected can be obtained by performing enrichment-thermal desorption treatment on the sample by adopting an adsorption column, the sample to be detected in the sample is enriched by the adsorbent in the adsorption tube, and the sample to be detected is obtained by high-temperature desorption. For example, when the system provided by the invention is used for detecting the total hydrocarbon content in the atmosphere, if the concentration of carbon monoxide or carbon dioxide is higher or the concentration of total hydrocarbons is lower, the adsorption column is used for carrying out enrichment-thermal desorption treatment on the sample, organic matters are firstly enriched by using a solid adsorbent in the adsorption tube, permanent gases including CO and CO2 are not retained in the adsorption tube, then the organic matter sample is released from the adsorbent through high temperature, and then the organic matter sample enters the total hydrocarbon chromatographic column for separation to obtain the sample to be detected.
As shown in fig. 2, in one embodiment, the system further comprises: the carbon oxide pipeline 5 and the second chromatographic column 50, the sample outlet of the second chromatographic column 50 is connected with the carbon oxide pipeline 5, and the carbon oxide pipeline 5 is communicated with the pipeline connecting the catalytic oxidation furnace and the methane converter.
When detecting carbon oxide and/or methane, the sample to be detected can be separated through the second chromatographic column 50, and the separated sample to be detected is mixed with hydrogen from the hydrogen pipeline 3 through the carbon oxide pipeline 5 and then enters the methane converter 20 for catalytic hydrogenation reaction to generate methane and water. The generated methane and water and the remaining hydrogen gas flow out of the methane reformer 20 and then enter the hydrogen flame ionization detector 30 for detection.
In summary, the present invention provides a method for detecting carbon-containing compounds using the above system, which comprises:
(1) and (3) carrying out catalytic oxidation combustion on the sample to be detected in the presence of oxygen to generate carbon dioxide. In some embodiments, the combustion in step (1) is flameless combustion, with a combustion temperature of 390 ℃ and above. The catalyst may be specifically selected from one or more of platinum, palladium and ruthenium. The combustion temperature is preferably 390-450 ℃.
(2) And (2) carrying out catalytic hydrogenation reduction on the carbon dioxide generated in the step (1) in the presence of hydrogen to generate methane. The catalyst may specifically be a nickel catalyst. The catalytic hydrogenation reaction temperature is preferably 350-450 ℃.
(3) Detecting the methane generated in the step (2) by a hydrogen flame ionization detector. In some embodiments, the hydrogen flame ionization detector combusts hydrogen gas used from the hydrogen gas remaining after the catalytic hydrogenation of step (2). The step (3) may specifically include mixing hydrogen with tail-blown air, then carrying the methane to be detected to flow out from a nozzle of the hydrogen flame ionization detector, and combusting in air around the nozzle. The volume flow ratio of the hydrogen to the tail blowing air is preferably (0.8-1.1): 1.
in one embodiment, step (1) is preceded by: and separating the sample by a chromatographic column to obtain the sample to be detected. If the concentration of the sample to be detected in the total sample is low, the sample can also be subjected to enrichment-thermal desorption treatment to obtain the sample to be detected, the enrichment-thermal desorption treatment is to enrich the sample to be detected in the sample through the adsorbent in the adsorption tube, and then the sample to be detected is obtained through high-temperature desorption.
In one embodiment, the sample to be tested is selected from CO, CO2And an organic substance, preferably one or more selected from the group consisting of formaldehyde, formamide, and formic acid.
The total hydrocarbon and the non-methane total hydrocarbon are important parts in the current environmental monitoring, the popularization and the realization of the existing method are not easy, the content of the total hydrocarbon requires to directly measure the response value of the FID detector, and because the response factors of the measured organic matters of each instrument are different, even if the same instrument is used, when the chromatographic condition is changed, the response factors of each organic matter are different, and the uniform comparison result is difficult to achieve.
The method and the system provided by the invention can be used for detecting total hydrocarbons and non-methane total hydrocarbons.
The method is divided into two parts of detection and analysis. The first part is that the sample is not separated by a total hydrocarbon chromatographic column (namely a first chromatographic column), and the content of total carbon is measured; the other part is separated into CO and CO respectively through a separation column (namely a second chromatographic column)2And methane, to measure CO and CO respectively2And the carbon content of methane. Using the total carbon content to subtract CO and CO2The carbon content can obtain the content of total hydrocarbon, and then the carbon content of methane is subtracted to obtain the content of non-methane total hydrocarbon.
Wherein, the total hydrocarbon chromatographic column can be selected from non-separation column with length of about 1m and inner diameter of about 2mm, and is filled with 60-80 mesh 6201 red carrier or silanized glass microsphere carrier, or can be selected from hollow column and other equivalent columns; CO, CO2The methane column can be carbon molecular sieve column with length of about 40cm and inner diameter of 2mm, and is filled with 40-60 mesh TDX-01 carbon molecular sieve or other equivalent columns.
The catalytic oxidation chamber in the catalytic oxidation furnace is a stainless steel column with a length of about 20cm and an inner diameter of 3mm, and is filled with a 40-60 mesh palladium-6201 catalyst.
Preparation of palladium-6201 catalyst: taking a certain amount of palladium chloride (PdCl)2) It is dissolved in deionized water under acidic conditions, preferably in an amount to immerse a red 6201 diatomaceous earth-type support (40-60 mesh). Standing for 2h, evaporating to dryness under gentle stirring, placing into U-shaped tube, placing in heating furnace, introducing air at 100 deg.C, oven drying for 30min, heating to 500 deg.C, igniting for 4h, cooling to 400 deg.C, replacing with nitrogen for 10min, and introducing hydrogen to reduce for 9 h. Then, the mixture was replaced with nitrogen for 10 min. Thus obtaining the black brown palladium-6201 catalyst.
The methanation chamber in the methane conversion furnace adopts a stainless steel column with the length of about 20cm and the inner diameter of 3mm, and is filled with a nickel-based catalyst with the size of 40-60 meshes, and the nickel-based catalyst is sold by mainstream manufacturers of chromatographic instruments such as Agilent, Shimadzu and the like.
Example 1
In the embodiment, the method and the system provided by the invention are adopted to detect the mixed gas of formaldehyde, methane and carbon dioxide.
Detection of formaldehyde in air is a practical example. The air generally contains 380ppm of CO2And 1.76ppm methane, the three components often need to be tested separately in the detection of formaldehyde.
Using the mode of operation of fig. 1, wherein the first chromatographic column is a stainless steel chromatographic column with stationary phase of Hayesep Q80-100 mesh, length of 2m, and inner diameter of 1/8 inches, and the sample is separated at room temperature of about 20 ℃;
the catalytic oxidation column (namely the catalytic oxidation furnace) adopts a stainless steel column with the length of about 20cm and the inner diameter of 3mm, and is filled with 40-60 mesh palladium-6201 catalyst, the methane conversion column (namely the methane conversion furnace) adopts a stainless steel column with the length of about 20cm and the inner diameter of 3mm, is filled with 40-60 mesh nickel catalyst, is respectively arranged in two U-shaped grooves of the same heating aluminum block, and is filled with glass heat-insulating cotton in a heat-insulating box, the temperature of the two reaction chambers is the same, and is controlled at 400 ℃;
high-purity nitrogen is used as carrier gas to enter a first chromatographic column, the flow rate is 25mL/min, the flow rate of oxygen supplemented by an oxygen pipeline 2 is 0.5mL/min, the flow rate of hydrogen supplemented by a hydrogen pipeline 3 is 50mL/min, the flow rate of one air pipeline 4 used as supplementary air is 50mL/min, the flow rate of the other air pipeline used as combustion-supporting gas is 500mL/min, and the flow rates of all gases are controlled by a Mass Flow Controller (MFC);
the sample gas adopts two kinds of steel cylinder standard gas of methane and formaldehyde with the ordered nominal values of 100ppm, according to the proportion of 1: diluting the mixture into standard gas of methane and formaldehyde with concentration of 50ppm at a ratio of 1, and analyzing by using a six-way valve quantitative tube with sample volume of 1mL to obtain a test spectrogram as shown in FIG. 3.
The results of the test were that the retention time of formaldehyde was 1.03 minutes, the retention time of methane was 1.67 minutes, and the residual carbon dioxide peak retention time was 4.07 minutes. The peak area of formaldehyde was 114.60pA · s and the peak area of methane was 122.12pA · s by chromatographic integration, giving a response factor of formaldehyde to methane of 0.94, very close to 1, and therefore methane can be used as the calibration gas in practical applications. The peak height of formaldehyde is 18.43pA, and the noise of the instrument system is 0.08pA, and the detection limit of the method can be calculated according to the concentration or the content of the substance to be detected corresponding to 2 times of the noise as a detection limit value. In fact, these parameter conditions are related to factors such as the performance structure of the detector, the type of the chromatographic column, and the like, and the obtained detection limit may be lower, and these data of this embodiment are only used as references.
Example 2
In this embodiment, formic acid is detected by the method and system provided by the present invention.
The working mode of fig. 1 was used, wherein the first chromatographic column was a solution of MXT-624 stainless steel capillary column of length 30m, internal diameter 0.53mm, film thickness 3um, and the sample was isolated at room temperature around 20 ℃;
the catalytic oxidation column (namely the catalytic oxidation furnace) adopts a stainless steel column with the length of about 20cm and the inner diameter of 3mm, and is filled with 40-60 mesh palladium-6201 catalyst, the methane conversion column (namely the methane conversion furnace) adopts a stainless steel column with the length of about 20cm and the inner diameter of 3mm, is filled with 40-60 mesh nickel catalyst, is respectively arranged in two U-shaped grooves of the same heating aluminum block, and is filled with glass heat-insulating cotton in a heat-insulating box, the temperature of the two reaction chambers is the same, and is controlled at 400 ℃;
high-purity nitrogen is used as carrier gas to enter a first chromatographic column, the flow rate is 20mL/min, the flow rate of oxygen supplemented by an oxygen pipeline 2 is 0.5mL/min, the flow rate of hydrogen supplemented by a hydrogen pipeline 3 is 50mL/min, the flow rate of one air pipeline 4 used as supplementary air is 50mL/min, the flow rate of the other air pipeline used as combustion-supporting gas is 500mL/min, and the flow rates of all gases are controlled by a Mass Flow Controller (MFC);
a method for manually preparing formic acid sample gas by using a needle cylinder comprises the steps of firstly extracting high-purity nitrogen from the needle cylinder by 100mL scales, then analyzing pure formic acid liquid by 0.234uL by using a micro-injector, slowly injecting the pure formic acid liquid into the needle cylinder with 100mL of nitrogen, preparing the formic acid sample gas with the concentration of 1000ppm, adopting a six-way valve quantitative tube for sample injection analysis, and obtaining a test spectrogram as shown in figure 4 by the sample injection amount of 1mL
The test results show that the retention time of the combined peaks of methane, carbon dioxide and the like is 0.90 minutes, and the retention time of formic acid is 4.99 minutes. The peak height of formic acid is 159.31pA, the noise of an instrument system is 0.08pA, and the detection limit of the method can be calculated to be 1.01ppm according to the concentration or the content of the substance to be detected corresponding to 2 times of the noise. In fact, these parameter conditions are related to factors such as the performance structure of the detector, the type of the chromatographic column, and the like, and the obtained detection limit may be lower, and these data of this embodiment are only used as references.
Finally, it should be noted that: it should be understood that the above examples are only for clearly illustrating the present invention and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications of the invention may be made without departing from the scope of the invention.
Claims (6)
1. A method for detecting carbon-containing compounds based on catalytic conversion technology, comprising:
(1) carrying out catalytic oxidation combustion on a sample to be detected in the presence of oxygen to generate carbon dioxide;
(2) carrying out catalytic hydrogenation reduction on the carbon dioxide generated in the step (1) in the presence of hydrogen to generate methane;
(3) detecting the methane generated in the step (2) by a hydrogen flame ionization detector.
2. The method of claim 1, wherein the hydrogen flame ionization detector in step (3) combusts hydrogen gas from hydrogen gas remaining after the catalytic hydrogenation in step (2).
3. The method of claim 2, wherein step (3) comprises mixing hydrogen gas and tail-blown air, flowing out of a nozzle of the hydrogen flame ionization detector with the methane to be detected, and combusting in air around the nozzle; the volume flow ratio of the hydrogen to the tail blowing air is preferably (0.8-1.1): 1.
4. the method of claim 1, further comprising, prior to step (1):
separating the sample by a chromatographic column to obtain a sample to be detected;
and performing enrichment-thermal desorption treatment on the sample to obtain the sample to be detected, wherein the enrichment-thermal desorption treatment is to enrich the sample to be detected in the sample through the adsorbent in the adsorption tube, and then obtain the sample to be detected through high-temperature desorption.
5. The method according to claim 1, wherein the combustion in step (1) is flameless combustion at a combustion temperature of 390 ℃ and above.
6. The method according to any one of claims 1 to 5, wherein the sample to be tested is selected from the group consisting of CO, CO2And one or more of an organic, preferably selected from one or more of formaldehyde, formamide, and formic acid.
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| CN110411973B (en) * | 2019-08-30 | 2021-12-17 | 中国科学院大学 | Method for detecting concentration of non-methane total hydrocarbons in gas |
| WO2021042351A1 (en) * | 2019-09-06 | 2021-03-11 | 暨南大学 | System and method for quantification of gas concentration on basis of catalytic conversion |
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