Synchronous monitoring system and method for non-methane total hydrocarbon and volatile organic compound components

Abstract

The invention discloses a synchronous monitoring system and method for non-methane total hydrocarbon and volatile organic compound components, and belongs to the technical field of environmental monitoring. Comprising an adsorption tube and a monitoring assembly, the adsorption tube is detachably connected with the monitoring assembly, the monitoring assembly comprises a focusing tube, a six-way valve, a four-way valve and a gas chromatograph, and the four-way valve and the six-way valve are each provided with an emptying flow path; the six-way valve is respectively communicated with the focusing tube and the capillary chromatography sampling assembly, and the capillary chromatography sampling assembly, the capillary chromatographic column and the mass spectrometry detector are sequentially communicated; a heating assembly is arranged outside the adsorption tube, a temperature control device is arranged outside the focusing tube, a thermal desorption temperature control area is arranged outside the focusing tube, the six-way valve and the four-way valve, and a column oven is arranged outside the capillary chromatographic column. Synchronous monitoring of non-methane hydrocarbon and VOCs components is achieved through the same monitoring assembly, the occupied space is reduced, the monitoring range is expanded, meanwhile, the sampling volume of the adsorption tube is flexible and controllable, and the sample preservation time is long.

Description

Technical Field

[0001] The invention belongs to the technical field of environmental monitoring, and in particular relates to a system and method for synchronously monitoring non-methane total hydrocarbons and volatile organic matter components. Background Art

[0002] Non-methane hydrocarbons (NMHC) refer to the general term for all hydrocarbons except methane. It is generally believed that it mainly includes components such as alkanes, alkenes, aromatic hydrocarbons and oxygenated hydrocarbons, and refers to hydrocarbon substances with C2-C12 (or C2-C8). Non-methane hydrocarbons are a type of atmospheric pollutants, and their existence is to describe and evaluate the pollution of environmental organic matter. According to "Direct Injection-Gas Chromatography for the Determination of Total Hydrocarbons, Methane and Non-methane Hydrocarbons in Ambient Air" (HJ 604-2017) and "Gas Chromatography for the Determination of Total Hydrocarbons, Methane and Non-methane Hydrocarbons in Waste Gas from Stationary Pollution Sources" (HJ 38-2017), total hydrocarbons refer to: the sum of gaseous organic compounds that respond on the hydrogen flame ionization detector of the gas chromatograph under the determination conditions specified in the standard; non-methane hydrocarbons refer to: the sum of other gaseous organic compounds after methane is deducted from the total hydrocarbons under the determination conditions specified in the standard.

[0003] There are three main methods for measuring non-methane total hydrocarbons: (1) subtraction method; (2) direct measurement method; (3) catalytic method. (Reference: Li Jia, Chen Yong, Zhang Yu, et al. Study on the correlation between volatile organic compounds and non-methane total hydrocarbons [J]. China Testing, 2019, 45(12):8. DOI:CNKI:SUN:SYCS.0.2019-12-013.) (1) Subtraction method: The sample is injected through a six-way valve + quantitative loop, and the contents of methane and total hydrocarbons are measured on the methane column and the total hydrocarbon column respectively. The difference between the two is NMHC. At the same time, the sample is replaced by hydrocarbon-free air, and the response value of oxygen on the total hydrocarbon column is measured to deduct the interference of oxygen in the sample on the determination of total hydrocarbons. This method complies with the requirements of analytical method standards HJ 38-2017, HJ 604-2017 and HJ 1332-2023.

[0004] (2) Direct measurement method: The sample is injected through a ten-port valve + quantitative loop, and the carrier gas carries the sample into the Porapak Q packed column for separation. After the oxygen and methane peaks appear, the valve is switched to backflush the remaining components into the FID to form a NMHC peak.

[0005] (3) Catalytic method: The gas sample enters the total hydrocarbon detection unit and the methane catalytic conversion unit respectively, and the total hydrocarbon and methane contents are measured by the hydrogen flame ionization detector (FID). The difference between the two is the NMHC content. This method meets the requirements of the analytical method standard HJ 1331-2023.

[0006] The above three methods all use direct injection through a quantitative loop, separation by gas chromatography, and determination by a hydrogen flame ionization detector (FID). The volume of the quantitative loop is generally 1 mL, without enrichment.

[0007] In the non-methane total hydrocarbon analysis method, there are the following problems: Most non-methane hydrocarbon monitoring is done by sampling on-site and then taking it back to the laboratory for analysis. The samples are collected by air bags, but the air bags have different degrees of adsorption for different VOCs components, which will cause the results to be low. Air bag sampling has a shelf life of only 48 hours, and samples need to be analyzed as quickly as possible, which places high demands on the timeliness of laboratory work; The detection limit of non-methane hydrocarbons is 0.07 mg / m 3 The lower limit of determination is 0.28 mg / m 3 , while the content of non-methane total hydrocarbons in the ambient air is low, with concentrations in some areas lower than 0.28 mg / m 3 , which is difficult to quantify accurately.

[0008] Volatile Organic Compounds (VOCs) are a class of organic compounds that exist in the air in the form of vapor at room temperature. The so-called VOCs components refer to the various material components belonging to VOCs, such as non-methane hydrocarbons, halogenated hydrocarbons, oxygen-containing organic compounds, sulfur-containing organic compounds, etc.

[0009] In the existing technology, non-methane total hydrocarbons and volatile organic compounds (VOCs) are collected and analyzed separately, while some non-standard applications use air bags to collect samples, which are fed into two chromatographic columns (or empty columns) by two quantitative loops to measure non-methane total hydrocarbons and VOCs components respectively. The equipment occupies a large space and has a small range of monitored components, making it impossible to use one device to simultaneously monitor non-methane total hydrocarbons and VOCs components. In addition, because the sample is injected using a quantitative loop (generally not more than 1mL; if it is too large, it exceeds the capacity of the chromatographic column and it is difficult to form a quantifiable chromatographic peak), there is no enrichment process, which makes the method detection limit of the VOCs component relatively high, resulting in the existing technology being only applicable to high-concentration samples.

[0010] On the other hand, when using the air bag method to collect samples for monitoring VOCs components, the adsorption losses of many substances are difficult to ignore. Therefore, in fact only some VOCs components can be analyzed by air bags.

[0011] Therefore, in certain application scenarios, a solution is needed that can achieve simultaneous monitoring of non-methane total hydrocarbons and VOCs components, while solving the above-mentioned problems related to collecting samples with air bags. Summary of the invention

[0012] The object of the present invention is to provide a system and method for synchronously monitoring non-methane total hydrocarbons and volatile organic components to solve the problems existing in the current background technology.

[0013] The objective of the present invention is achieved through the following technical solutions: A synchronous monitoring system for non-methane total hydrocarbons and volatile organic components, characterized in that: it comprises an adsorption tube and a monitoring component, the adsorption tube is detachably connected to the monitoring component, and the monitoring component comprises a focusing tube, a six-way valve, a four-way valve and a gas chromatograph; One end of the adsorption tube is connected to the inert gas source, and the other end of the adsorption tube is connected to the six-way valve and the four-way valve through a three-way connection, respectively, and the four-way valve and the six-way valve are both provided with an exhaust flow path; The gas chromatograph comprises a hydrogen flame ionization detector, an air inlet, a mass spectrometer, a capillary chromatographic injection assembly, and a capillary chromatographic column. The six-way valve is respectively connected to the focusing tube and the capillary chromatographic injection assembly, the capillary chromatographic injection assembly, the capillary chromatographic column, and the mass spectrometer are connected in sequence, and the four-way valve is respectively connected to the hydrogen flame ionization detector and the air inlet; A heating component is arranged outside the adsorption tube, a temperature control device is arranged outside the focusing tube, a thermal desorption temperature control area is arranged outside the focusing tube, the six-way valve and the four-way valve, and a column temperature box is arranged outside the capillary chromatographic column.

[0014] Furthermore, the capillary chromatographic injection assembly comprises an injection cavity, an injection gas carrier end and an exhaust end, wherein the injection gas carrier end is connected to the six-way valve, one end of the injection cavity is connected to the six-way valve, and the other end of the injection cavity is respectively connected to the capillary chromatographic column and the exhaust end. The injection gas carrier end and the exhaust end are both provided with an electronic flow control unit.

[0015] Furthermore, adsorbents with adsorption strengths from weak to strong are arranged on the adsorption tube from the sampling inlet end to the outlet end, and the adsorbents include Carbopack C, Carbopack B, and Carboxen 1003 in sequence; when the adsorption tube is used for sampling and preservation, removable seals are arranged at both ends of the adsorption tube, and after the adsorption tube is connected to the monitoring component, one end of the strong adsorbent of the adsorption tube is connected to the inert gas source, and a first electronic flow path controller is arranged between the inert gas source and the adsorption tube.

[0016] Furthermore, adsorbents with adsorption strengths from weak to strong are arranged in sequence in the focusing tube.

[0017] Furthermore, the air inlet end is provided with an electronic flow control unit of the same specification.

[0018] Furthermore, the exhaust flow paths of the four-way valve and the six-way valve are connected in parallel via an inert tee, a second electronic flow path controller is provided on the exhaust flow path of the six-way valve, and a damping member is provided on the exhaust flow path of the four-way valve.

[0019] The method for simultaneously monitoring non-methane total hydrocarbons and volatile organic components comprises the following steps: S1: One end of the adsorption tube is connected to an air pump and a flow control component. The airflow flows from the weak adsorbent end to the strong adsorbent end of the adsorption tube. Volatile organic compounds except methane are adsorbed by the adsorption tube, while inorganic compounds such as nitrogen and water will not be adsorbed. S2: The adsorption tube is sealed and stored; S3: The adsorption tube is connected to the monitoring component, and air is blown into the adsorption tube through an inert gas source. The trace methane, moisture and other impurities remaining in the adsorption tube are blown away by the inert gas source. The airflow through the adsorption tube is divided into two paths through a three-way valve, one path passes through a six-way valve and a focusing tube, and then is discharged from the corresponding exhaust flow path of the six-way valve, and the other path is discharged from the corresponding exhaust flow path through a four-way valve; at the same time, the temperature of the focusing tube is reduced to a set low temperature through a temperature control device; at the same time, the air inlet end is connected to a hydrogen flame ionization detector through a four-way valve and an inert gas is introduced; S4: The adsorption tube is heated to 330°C by a heating assembly. After desorption, the volatile organic matter in the adsorption tube flows into the six-way valve and the four-way valve respectively along with the inert gas. The gas flow flowing into the six-way valve flows in from the weak adsorbent end of the focusing tube and flows out from the strong adsorbent end, and then enters the exhaust flow path; at the same time, the four-way valve is switched, and the gas flow flowing into the four-way valve enters the hydrogen flame ionization detector to measure the response of non-methane total hydrocarbons; S5: The heating assembly stops heating, the inert gas source is turned off, the focusing tube is heated to 330°C by the temperature control device, and the six-way valve is switched so that the carrier gas at the carrier gas end of the injection port enters from the strong adsorbent end of the focusing tube, flows out from the weak adsorbent end of the focusing tube and enters one end of the injection cavity body, and then the gas flows out from the other end of the injection cavity body and enters the capillary column and the exhaust end respectively; S6: The temperature control device stops heating and switches the six-way valve. The carrier gas end of the injection port is connected to the injection port body through the six-way valve. The temperature of the capillary column is adjusted by a column oven to separate the volatile organic compounds in the capillary column and enter the mass spectrometer through the carrier gas to detect and analyze the components of the volatile organic compounds. At the same time, the adsorption tube is separated from the monitoring component, waiting for the injection and analysis of the next sample.

[0020] Further, in step S3, the flow rate of the inert gas introduced into the air inlet end is the same as the exhaust flow rate of the exhaust flow path corresponding to the four-way valve.

[0021] Furthermore, in step S5, the total flow rate and split ratio are set at the carrier gas end of the injection port. If the total amount of the sample is low, no split or a low split ratio is set; if the total amount of the sample is high, a high split ratio is set.

[0022] The beneficial effects of the present invention are: The same monitoring component is used to achieve simultaneous monitoring of non-methane total hydrocarbons and VOCs components, reducing space occupancy and expanding the monitoring range.

[0023] The optimized thermal desorption method has a high recovery rate and can be used for quantitative detection by drawing a working curve to ensure that the results are not too low. In addition, the adsorption tube samples have a longer shelf life, with an effective storage time of up to 7 days. At the same time, the sampling volume of the adsorption tube can be flexibly controlled and is not limited to the volume of the existing quantitative loop.

[0024] More volume can be collected through the adsorption tube. First, after enrichment, the lower limit of determination can be lowered, and samples with lower concentrations can be analyzed. Second, the representativeness of the sample can be improved. For example, it can be collected at a low flow rate for a long time to adapt to different sampling environments.

[0025] Introducing nitrogen into the monitoring component can not only balance the airflow in the monitoring system, but also blow away impurities such as moisture in the adsorption tube, as well as trace amounts of methane that may remain, thereby improving the accuracy of subsequent monitoring. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of S1 in the method for synchronously monitoring non-methane total hydrocarbons and volatile organic components of the present invention; Figure 2 Schematic diagram of S2 in the method for synchronously monitoring non-methane total hydrocarbons and volatile organic components of the present invention; Figure 3 Schematic diagram of S3 in the method for synchronously monitoring non-methane total hydrocarbons and volatile organic components of the present invention, wherein arrows in the figure represent the direction of airflow; Figure 4 Schematic diagram of S4 in the method for synchronously monitoring non-methane total hydrocarbons and volatile organic components of the present invention, wherein arrows in the figure represent the direction of airflow; Figure 5 Schematic diagram of S5 in the method for synchronously monitoring non-methane total hydrocarbons and volatile organic components of the present invention, wherein arrows in the figure represent the direction of airflow; Figure 6 Schematic diagram of S6 in the method for synchronously monitoring non-methane total hydrocarbons and volatile organic components of the present invention, wherein arrows in the figure represent the direction of airflow; In the figure, 1-adsorption tube, 111-seal, 2-focusing tube, 3-six-way valve, 4-four-way valve, 5-hydrogen flame ionization detector, 51-inlet end, 6-mass spectrometer detector, 7-capillary chromatography injection assembly, 71-injection port carrier gas end, 72-injection port body, 73-emptying end, 8-capillary chromatography column, 9-electronic flow control unit, 10-inert gas source, 11-first electronic flow path controller, 12-second electronic flow path controller, 13-damping element, 14-heating component, 15-temperature control device, 16-column oven, 17-thermal desorption temperature control area, 18-gas pump and flow controller component, 19-emptying flow path. DETAILED DESCRIPTION

[0027] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention. Example

[0028] like Figure 1-Figure 6 As shown, a non-methane total hydrocarbon and volatile organic component synchronous monitoring system, a non-methane total hydrocarbon and volatile organic component synchronous monitoring system, characterized in that: comprising an adsorption tube 1 and a monitoring component, the adsorption tube 1 and the monitoring component are detachably connected, and the monitoring component comprises a focusing tube 2, a six-way valve 3, a four-way valve 4 and a gas chromatograph; One end of the adsorption tube 1 is connected to the inert gas source 10, and the other end of the adsorption tube 1 is connected to the six-way valve 3 and the four-way valve 4 through three-way valves, respectively. Both the four-way valve 4 and the six-way valve 3 are provided with an exhaust flow path 19; The gas chromatograph comprises a hydrogen flame ionization detector 5, an air inlet end 51, a mass spectrometer detector 6, a capillary chromatographic injection assembly 7, and a capillary chromatographic column 8. The six-way valve 3 is respectively connected to the focusing tube 2 and the capillary chromatographic injection assembly 7, the capillary chromatographic injection assembly 7, the capillary chromatographic column 8, and the mass spectrometer detector 6 are sequentially connected, and the four-way valve 4 is respectively connected to the hydrogen flame ionization detector 5 and the air inlet end 51; The adsorption tube 1 is provided with a heating assembly 14 , the focusing tube 2 is provided with a temperature control device 15 , the focusing tube 2 , the six-way valve 3 and the four-way valve 4 are provided with a thermal desorption temperature control area 17 , and the capillary column 8 is provided with a column temperature box 16 .

[0029] Through the above technical scheme, the sample is collected through the adsorption tube 1, and a weak adsorbent and a strong adsorbent are set in the adsorption tube 1. Volatile organic compounds except methane are adsorbed by the adsorption tube 1, and inorganic compounds such as nitrogen and water are not adsorbed. The adsorption tube 1 after adsorption can be stored for a long time, and the subsequent component monitoring can be completed by connecting the adsorption tube 1 after adsorption to the monitoring component. During the monitoring process, one gas flow after thermal desorption of the adsorption tube 1 is introduced into the hydrogen flame ionization detector 5, and the response value of non-methane total hydrocarbons in the hydrogen flame ionization detector 5 can be measured. At the same time, another gas flow after thermal desorption of the adsorption tube 1 enters the focusing tube 2 for enrichment, and then desorbs in the focusing tube 2, and then enters the mass spectrometer detector 6 to measure the components of volatile organic compounds. That is, the synchronous monitoring of non-methane total hydrocarbons and VOCs components is achieved through a monitoring component.

[0030] Furthermore, the adsorption tube 1 is provided with adsorbents with adsorption strengths from weak to strong in sequence from the sampling inlet end to the outlet end.

[0031] Preferably, the adsorption tube 1 has an outer diameter of 6 mm, an inner diameter of 4 mm, and a length of 9 cm. The adsorbents from the sampling inlet to the outlet are Carbopack C, Carbopack B, and Carboxen 1003, respectively, with filling lengths of 1.5 cm, 1.5 cm, and 2 cm, respectively, and the mesh sizes are all 60-80 meshes. Carbopack C belongs to the graphitized carbon black category, is a weak adsorbent, with a specific surface area of ​​10m² / g, and mainly adsorbs larger molecular VOCs components with a boiling point of 100℃~250℃; Carbopack B belongs to the graphitized carbon black category, is a medium adsorbent, with a specific surface area of ​​100m² / g, and mainly adsorbs VOCs components with a boiling point of 40℃~100℃; Carboxen 1003 belongs to the carbon molecular sieve category, is a strong adsorbent, with a specific surface area of ​​1000m² / g, and mainly adsorbs volatile VOCs components with a boiling point of -100℃~40℃, including C2 (compounds with two carbon atoms), such as ethane, ethylene, acetylene, etc.

[0032] This type of carbon adsorbent has a high upper temperature tolerance (up to 400°C), can accept a higher desorption temperature, and has a longer effective life. Carboxen 1003 is a carbon molecular sieve with a clean background; compared to 5 A molecular sieves and Carbosieve S-III, it has a weaker water absorption capacity and can maintain a high adsorption rate in a high humidity environment.

[0033] Adsorption tube 1 (the above-mentioned combined adsorbent) has an adsorption rate of less than 5% for methane at a temperature of 0°C~25°C and normal pressure within a flow rate of 50mL / min. Its adsorption capacity for methane is weak. Even if there is a trace amount of adsorption, it can be blown off by the inert gas source 10 (nitrogen) at room temperature in the subsequent monitoring component. At the same time, the adsorption rate for C2 is higher than 80%, and the adsorption rate for C3 (compounds with three carbon atoms) is not less than 90%. The higher the molecular boiling point, the higher the adsorption rate is generally. After the collection is completed, if the adsorption tube is purged with high-purity nitrogen at a flow rate of 50mL / min for 1~3min, methane can be completely removed. At the same time, adsorption tube 1 cannot adsorb inorganic substances such as nitrogen and oxygen. At a desorption temperature of 330°C (rapid heating), adsorption tube 1 has a desorption efficiency of more than 95% for VOCs components of C2~C14.

[0034] By optimizing the components in adsorption tube 1, the monitoring system has a comprehensive recovery rate of more than 90% for most components from C2 to C14. Since this monitoring system uses standard gas injection to draw the working curve, even if the comprehensive recovery rate is lower than 90%, it can be accurately quantified because the standard gas has the same loss rate.

[0035] like Figure 1 As shown, when the adsorption tube 1 is sampling, the sampling outlet end is connected to the air pump and flow controller assembly 18, the flow rate of the sample collection is preferably 20~50mL / min, and the sampling volume is generally 5~300mL. Sampling is divided into ambient air and exhaust gas. When collecting ambient air, a PTFE filter membrane is set at the sampling inlet end of the adsorption tube 1 to filter particulate matter; when collecting exhaust gas, a glass wool filter head is set at the sampling inlet end of the adsorption tube 1.

[0036] When collecting samples, the temperature of the adsorption tube 1 should be close to that of the standard gas, and the temperature should be between 0℃ and 25℃. In general, the lower the temperature, the more conducive it is to adsorption, but if the temperature is below 0℃, the water in the sample will freeze, which may block the adsorption tube 1 or damage the graphitized carbon black. When collecting ambient air samples, if the adsorption tube 1 is not temperature controlled, even if the temperature is below 0℃, because the ambient air is also below 0℃, the water in the air is unsaturated at this temperature, and it is difficult for ice to form in the adsorption tube 1; but for exhaust gas, especially high-temperature and high-humidity exhaust gas, it is necessary to ensure that the temperature is between 0℃ and 25℃. The specific temperature control method is: if the sampling temperature is low, you can wrap the adsorption tube 1 with an insulation layer to keep it warm; if the temperature is high, you can cool the outside of the adsorption tube 1 with ice water.

[0037] like Figure 2 As shown, when the adsorption tube 1 is stored after sampling, removable sealing members 111 are provided at both ends of the adsorption tube 1. The adsorption tube 1 needs to be protected from light during storage and can be stored at room temperature or refrigerated.

[0038] Sampling through the adsorption tube 1 overcomes the shortcomings of air bag sampling in the background technology. After the adsorption tube 1 adsorbs the volatile organic components, it is equivalent to fixing the VOCs in the adsorption tube. Under sealing (even low temperature), the optimized thermal desorption method has a high recovery rate, and can be quantitatively analyzed by drawing a working curve, which can ensure that the result is not too low; in addition, the adsorption tube 1 has a longer storage time, which can be effectively preserved for up to 7 days; at the same time, the sampling volume of the adsorption tube 1 can be flexibly controlled, and is not limited to the existing quantitative ring quantification method, and more volume can be collected. Collecting more volume has two major advantages: first, after sample enrichment, the lower limit of determination can be lowered, and samples with lower concentrations can be analyzed; second, the representativeness of the sample can be improved, such as long-term collection at a low flow rate to adapt to different sampling environments.

[0039] like Figure 3 As shown, after the adsorption tube 1 is connected to the monitoring component, one end of the strong adsorbent of the adsorption tube 1 is connected to the inert gas source 10, and a first electronic flow path controller 11 is provided between the inert gas source 10 and the adsorption tube 1. The inert gas source 10 uses nitrogen. The introduction of nitrogen can not only balance the airflow rate in the monitoring system, but also blow away impurities such as moisture in the adsorption tube 1, as well as trace amounts of methane that may remain.

[0040] The specific flow rate and time of the balanced gas flow 1 can be optimized according to the conditions of the instrument. Generally speaking, the nitrogen flow rate through the adsorption tube 1 is 50 mL / min, and it is passed for 1 minute. In this step, the focusing tube 2 is kept at room temperature (the same temperature as the adsorption tube 1), and the impurities flowing out of the adsorption tube 1 cannot be adsorbed because the focusing tube 2 does not use a stronger adsorbent than the adsorption tube 1, but are discharged through the exhaust flow path 19.

[0041] Furthermore, adsorbents with adsorption strengths from weak to strong are sequentially arranged in the focusing tube 2 .

[0042] like Figure 3-6 As shown in the figure, the upper end of the focusing tube 2 is a weak adsorbent and the lower end is a strong adsorbent. The strong adsorbent of the focusing tube 2 should not be an adsorbent with a stronger adsorption capacity than the Carboxen 1003 in the adsorption tube 1, but Carboxen 1003 can be used. When the gas desorbed from the adsorption tube 1 is enriched, it is enriched from the weak adsorbent to the strong adsorbent; and when the focusing tube 2 is desorbed, it is desorbed from the strong adsorbent to the weak adsorbent. This can avoid the problem that the high-boiling point substance first contacts the strong adsorbent when the focusing tube 2 is desorbed, thereby causing "dead adsorption" and failing to desorb efficiently; at the same time, it can avoid the problem that the focusing tube 2 cannot desorb efficiently, because even if the medium and high boiling point substances are desorbed from the weak adsorbent, they may be adsorbed when they flow through the strong adsorbent.

[0043] The desorption temperature of adsorption tube 1 is preferably 330°C. However, due to the different specific materials of each adsorption tube 1 (such as stainless steel, quartz), the thickness has slight differences and can be adjusted appropriately. The heating rate of adsorption tube 1 and focusing tube 2 should be greater than 80°C / s, and the desorption gas flow should be appropriate to ensure that the target can be desorbed quickly, otherwise it will cause the chromatographic peak to become wider or even tailing, increasing the quantitative error. Generally speaking, the total flow rate during desorption of adsorption tube 1 should be 80~200mL / min; if the non-methane total hydrocarbon flow path has an inner diameter of 1mm, the flow rate of this flow path should be 10~20mL / min, if it is 2mm inner diameter, the flow rate should be 30~50mL / min; because the inner diameter of focusing tube 2 is generally 2mm, the flow rate of the flow path through focusing tube 2 should be 20~80mL / min. The higher the total flow rate of the inert gas source 10 is, the more conducive it is to the desorption of the substance in the adsorption tube 1 . However, an excessively high flow rate may lower the actual temperature and make the flow rates of the non-methane total hydrocarbons and VOCS component flow paths not in the appropriate range; while an excessively low flow rate is not conducive to the rapid desorption of the adsorption tube 1 .

[0044] The temperature of the focusing tube 2 is not controlled in the thermal desorption temperature control area 17, and the temperature control area of ​​the six-way valve 3 and the four-way valve 4 and their pipelines is constantly controlled by the thermal desorption temperature control area 17. A higher temperature is beneficial to reduce adsorption and prevent condensation. Generally, a temperature above 120°C is set to ensure that VOCs will not be lost when the airflow flows in this area.

[0045] The temperature of the focusing tube 2 varies in different steps. During focusing, it is generally below -20°C, and during desorption, it quickly rises to a high temperature of over 300°C. The function of focusing tube 2 is to gather the VOCs desorbed from the adsorption tube in a small area, and then quickly desorb them into the capillary column 8 to form a sharp chromatographic peak. It is smaller than the adsorption tube 1, has a faster temperature transfer, and requires a lower air flow rate for rapid desorption. If the adsorption tube 1 is directly desorbed into the capillary column 8, the chromatographic peak will easily become very wide, and the quantitative effect will be poor.

[0046] Furthermore, the capillary chromatography injection assembly 7 includes an injection cavity body 72, an injection gas carrier end 71 and an exhaust end 73, the injection gas carrier end 71 is connected to the six-way valve 3, one end of the injection cavity body 72 is connected to the six-way valve 3, and the other end of the injection cavity body 72 is respectively connected to the capillary chromatography column 8 and the exhaust end 73, and the injection gas carrier end 71 and the exhaust end 73 are both provided with an electronic flow control unit 9.

[0047] Through the above technical solution, the carrier gas is injected into the capillary chromatographic injection assembly 7 to drive the VOCs in the focusing tube 2 to enter the capillary chromatographic column 8 after thermal desorption, and then the VOCs components are analyzed by the mass spectrometer detector 6.

[0048] The injection cavity 72 is provided with the gas chromatograph, and has a liner therein, and is generally used for liquid sample injection. The injection cavity 72 in this embodiment can be replaced by an inert tee.

[0049] The function of the evacuation end 73 is to divert the flow. "Diverting" is a common function of gas chromatographs, which can make the target enter the capillary column 8 faster, reduce the residence time in the injection area, make the chromatographic peak sharper, and make the quantification more accurate. In this embodiment, it can make the target desorb from the focusing tube 2 to the capillary column 8 faster, making the peak sharper. For example: if the dead volume of the focusing tube 2 is 0.5mL, the inlet flow rate of the carrier gas end 71 of the injection port is 1mL / min, and diverting is not used (the evacuation end 73 is 0mL), then the time it takes to completely replace the dead volume of the focusing tube 2 is 0.5min, that is, the chromatographic peak width may be close to 0.5min, while the peak width of the gas chromatographic peak is generally within 10s. Therefore, the split mode is adopted. If the inlet flow rate of the carrier gas end 71 of the injection port is 4mL / min, the flow rate of the evacuation end 73 is 3mL / min, and the other 1mL of the target enters the capillary column 8 at a flow rate of 1mL / min, the dead volume time of the displacement focusing tube 2 becomes about 7s, and the chromatographic peak becomes narrow and sharp. Although the total amount of the target entering the capillary column is reduced, the sensitivity is often not worse than that without splitting because the chromatographic peak shape is good.

[0050] Furthermore, the air inlet end 51 is provided with an electronic flow control unit 9 of the same specification. The exhaust flow paths 19 provided in the four-way valve 4 and the six-way valve 3 are connected in parallel through an inert three-way connection, the exhaust flow path 19 of the six-way valve 3 is provided with a second electronic flow path controller 12, and the exhaust flow path 19 of the four-way valve 4 is provided with a damping member 13.

[0051] Through the above technical solution, the exhaust flow path 19 of the four-way valve 4 is provided with a damping member 13 for adjusting the exhaust flow rate. The damping value of the damping member 13 is similar to the damping value of the hydrogen flame ionization detector 5, ensuring that the flow rate entering the hydrogen flame ionization detector 5 is the same as the exhaust flow rate, thereby reducing the signal fluctuation of the hydrogen flame ionization detector 5. Figure 3 The gas flow into the hydrogen flame ionization detector 5 is similar to Figure 4 The flow rate (generally 10-20 mL / min) directly flowing into the hydrogen flame ionization detector 5 through the adsorption tube 1 after the switching of the middle four-way valve 4 is the same. This step is used to ensure that the flow rate entering the hydrogen flame ionization detector 5 is the same as the exhaust flow rate, thereby reducing the signal fluctuation of the hydrogen flame ionization detector 5.

[0052] The quantitative method of this monitoring system is to use standard gas to draw the working curve. The curve of VOCs components is drawn by the standard gas of the corresponding substance.

[0053] The non-methane total hydrocarbon curve can be drawn in two ways: 1. Using propane standard gas. The current analytical method standard (HJ 38-2017) uses methane to draw the curve, but the previous version of the analytical method standard (HJ / T 38-1999) uses propane. From the preparation instructions of the current standard, it can be seen that for non-methane total hydrocarbons, the response ratio of propane and methane with the same mole fraction is close to 3:1, which has an ideal quantitative relationship. The reason why propane is deleted from the standard gas component in the current standard is to make the standard gas more affordable. Therefore, propane standard gas can be used to draw the working curve. 2. Use mixed standard gas to draw. When the characteristic pollutants of the sample are clear and the monitoring unit focuses on these characteristic pollutants, the mixed standard gas of the characteristic pollutants can be used to draw the curve.

[0054] It is preferred to configure standard gases of different concentrations to draw the working curve, and the sampling volume of the standard gas is the same as the sampling volume of the sample.

[0055] Generally speaking, the quantitative range of mass spectrometry (MS) is two orders of magnitude, while that of hydrogen flame ionization detector (FID) can exceed six orders of magnitude. Therefore, when drawing curves, non-methane total hydrocarbons (quantified by FID) can be drawn as one curve, while component analysis (MS quantification) can be drawn as two or three working curves by adjusting the split ratio (low, high). It is particularly noted that when adjusting the split ratio, the split at the carrier gas end 71 of the injection port is adjusted first. If only adjusting the split at the carrier gas end 71 of the injection port cannot meet the situation, the split ratio between the adsorption tube 1 to the four-way valve 4 and to the six-way valve 3 can also be adjusted.

[0056] Mass spectrometry (MS) can be quantified by internal standard method or external standard method, and internal standard method is generally preferred. Addition of internal standard substance: After collecting standard gas or sample, before loading on the machine, the adsorption tube 1 quantitatively collects internal standard gas, or injects 1μL internal standard solution (methanol as solvent). The internal standard substance is added from the weak adsorbent end of the adsorption tube 1. Example

[0057] The method for simultaneously monitoring non-methane total hydrocarbons and volatile organic components comprises the following steps: S1: Figure 1 As shown. One end of the adsorption tube 1 is connected to an air pump and a flow control component, and the airflow flows from the weak adsorbent in the adsorption tube 1 to the strong adsorbent. Volatile organic matter other than methane is adsorbed by the adsorption tube 1, while inorganic matter such as nitrogen and water will not be adsorbed; S2: Figure 2 As shown. Adsorption tube 1 is sealed and stored away from light. It can be stored at room temperature or refrigerated; S3: Figure 3As shown. The adsorption tube 1 is connected to the monitoring component, and air is blown into the adsorption tube 1 through the inert gas source 10 (high-purity nitrogen). The trace methane, moisture and other impurities remaining in the adsorption tube 1 are blown away by the inert gas source 10. The airflow through the adsorption tube 1 is divided into two paths through the three-way valve, one path passes through the six-way valve 3 and the focusing tube 2 and then is discharged from the corresponding exhaust flow path 19 of the six-way valve 3, and the other path passes through the four-way valve 4 and is discharged from the corresponding exhaust flow path 19 of the four-way valve 4; at the same time, the temperature of the focusing tube 2 is reduced to the set low temperature through the temperature control device 15; at the same time, the air inlet end 51 is connected to the hydrogen flame ionization detector 5 through the four-way valve 4 and an inert gas is introduced; The airflow through the adsorption tube 1 is divided into two paths, one path enters the six-way valve 3, and the other path enters the four-way valve 4. Each path has a fixed flow rate, that is, the flow rate ratio of the two paths is fixed. After the airflow rate is balanced and constant for about 30 seconds, start the focusing tube 2 to cool down (semiconductor refrigeration can be used) and reduce it to the set low temperature (usually -30℃).

[0058] At the same time, the high-purity nitrogen gas inputted by the inert gas source 10 can not only stabilize the gas flow rate, but also blow away the impurities such as moisture in the adsorption tube 1, as well as the trace amount of methane that may remain. If it is judged that there are many impurities in the adsorption tube 1 according to the actual situation of the sample, a large amount of gas flow can be distributed to the four-way valve 4 for pre-cleaning the adsorption tube 1, and then adjusted to the predetermined gas flow of the four-way valve 4 and the six-way valve 3 after several tens of seconds.

[0059] Take the example of the air flow diversion through the adsorption tube 1: the total air flow is controlled to 100mL / min, the flow rate to the six-way valve 3 is 80mL / min, and the flow rate to the four-way valve 4 is 20mL / min. In this case, 80% of the gas sample actually enters the six-way valve 3 to complete the subsequent VOCs component analysis, and 20% is analyzed for non-methane total hydrocarbons. The air flow from the air inlet end 51 into the hydrogen flame ionization detector 5 is the same as the flow rate (generally 10~20mL / min) flowing into the hydrogen flame ionization detector 5 through the adsorption tube 1 when the four-way valve 4 is switched in the next step. This step is used to ensure that the flow rate entering the hydrogen flame ionization detector 5 is the same as the exhaust flow rate, reducing the signal fluctuation of the hydrogen flame ionization detector 5.

[0060] S4: Figure 4 As shown. The adsorption tube 1 is heated to 330°C by the heating component 14. After desorption, the volatile organic matter in the adsorption tube 1 flows into the six-way valve 3 and the four-way valve 4 respectively along with the inert gas. The gas flow flowing into the six-way valve 3 flows in from the weak adsorbent end of the focusing tube 2 and flows out from the strong adsorbent end, and then enters the exhaust flow path 19; at the same time, the four-way valve 4 is switched, and the gas flow flowing into the four-way valve 4 enters the hydrogen flame ionization detector 5 to measure the response of non-methane total hydrocarbons; The required heating rate of the adsorption tube 1 is greater than 80°C / s, and the heating component 14 can complete the heating by placing the heating block (pre-heated to 330°C) close to the adsorption tube 1; if the adsorption tube 1 is made of stainless steel, rapid heating can also be completed by powering both ends. The VOCs in the adsorption tube 1 are desorbed, one way passes through the six-way valve 3 to enter the refrigerated focusing tube 2 to be re-adsorbed, and the other way enters the hydrogen flame ionization detector 5 to measure the response of non-methane total hydrocarbons. This step generally lasts for 2-5 minutes. In this step, the carrier gas at the air inlet end 51 can be temporarily turned off to save carrier gas.

[0061] S5: Figure 5 As shown. Stop heating by the heating assembly 14, turn off the inert gas source 10, heat the focusing tube 2 to 330°C through the temperature control device 15, the temperature control device 15 heating rate is greater than 80°C / s, switch the six-way valve 3, so that the carrier gas at the carrier gas end 71 of the injection port enters from the strong adsorbent end of the focusing tube 2, flows out from the weak adsorbent end of the focusing tube 2 and enters one end of the injection cavity body 72, and then the gas flows out from the other end of the injection cavity body 72 and enters the capillary column 8 and the evacuation end 73 respectively. This step is generally maintained for 2 minutes; S6: Figure 6 As shown. The temperature control device 15 stops heating, the focusing tube 2 cools to room temperature, the six-way valve 3 is switched, the carrier gas end 71 of the injection port is connected to the injection port body 72 through the six-way valve 3, and the temperature of the capillary column 8 is adjusted by the column oven 16, so that the volatile organic matter is separated in the capillary column 8, and then enters the mass spectrometer detector 6 through the carrier gas to detect and analyze the components of the volatile organic matter; at the same time, the adsorption tube 1 is separated from the monitoring component, waiting for the next sample injection analysis.

[0062] The temperature rise of the column oven 16 represents "programmed temperature rise" in gas chromatography analysis, which is specifically a temperature rise program, such as maintaining at 40°C for 5 minutes, then increasing the temperature to 200°C at 10°C / min, maintaining for 5 minutes, to complete the entire analysis.

[0063] Furthermore, in step S5, the total flow rate and split ratio are set at the carrier gas end 71 of the injection port. If the total amount of the sample is low, no split or a low split ratio is set; if the total amount of the sample is high, a high split ratio is set.

[0064] The above is only a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications or environments, that is, on the basis of the scope of the concept described herein, through the above conception or directly through the technology or knowledge in the relevant field. The changes and modifications made by those skilled in the art do not deviate from the spirit and scope of the present invention, and should all belong to the protection scope of the claims attached to the present invention.

Claims

1. Synchronous monitoring system for non-methane total hydrocarbons and volatile organic components, characterized by: It comprises an adsorption tube (1) and a monitoring component, wherein the adsorption tube (1) is detachably connected to the monitoring component, and the monitoring component comprises a focusing tube (2), a six-way valve (3), a four-way valve (4) and a gas chromatograph; One end of the adsorption tube (1) is connected to the inert gas source (10), and the other end of the adsorption tube (1) is connected to the six-way valve (3) and the four-way valve (4) respectively through a three-way connection, and both the four-way valve (4) and the six-way valve (3) are provided with an exhaust flow path (19); The gas chromatograph comprises a hydrogen flame ionization detector (5), an air inlet end (51), a mass spectrometer detector (6), a capillary chromatographic injection assembly (7), and a capillary chromatographic column (8); the six-way valve (3) is respectively connected to the focusing tube (2) and the capillary chromatographic injection assembly (7); the capillary chromatographic injection assembly (7), the capillary chromatographic column (8), and the mass spectrometer detector (6) are sequentially connected; and the four-way valve (4) is respectively connected to the hydrogen flame ionization detector (5) and the air inlet end (51); The adsorption tube (1) is provided with a heating component (14) outside, the focusing tube (2) is provided with a temperature control device (15) outside, the focusing tube (2), the six-way valve (3) and the four-way valve (4) are provided with a thermal desorption temperature control area (17) outside, and the capillary chromatographic column (8) is provided with a column temperature box (16) outside.

2. The synchronous monitoring system for non-methane total hydrocarbons and volatile organic components according to claim 1, characterized in that: The capillary chromatographic injection assembly (7) comprises an injection cavity body (72), an injection gas carrier end (71) and an exhaust end (73); the injection gas carrier end (71) is connected to the six-way valve (3); one end of the injection cavity body (72) is connected to the six-way valve (3); the other end of the injection cavity body (72) is respectively connected to the capillary chromatographic column (8) and the exhaust end (73); and the injection gas carrier end (71) and the exhaust end (73) are both provided with an electronic flow control unit (9).

3. The synchronous monitoring system for non-methane total hydrocarbons and volatile organic components according to claim 2, characterized in that: The adsorption tube (1) is provided with adsorbents with adsorption strengths from weak to strong from the sampling inlet end to the outlet end, and the adsorbents include Carbopack C, Carbopack B, and Carboxen 1003 in sequence; when the adsorption tube (1) is sampled and the sample is stored, both ends of the adsorption tube (1) are provided with detachable sealing members (111); after the adsorption tube (1) is connected to the monitoring component, one end of the strong adsorbent of the adsorption tube (1) is connected to the inert gas source (10), and a first electronic flow controller (11) is provided between the inert gas source (10) and the adsorption tube (1).

4. The synchronous monitoring system for non-methane total hydrocarbons and volatile organic components according to claim 2, characterized in that: Adsorbents with adsorption strengths from weak to strong are arranged in sequence in the focusing tube (2).

5. The synchronous monitoring system for non-methane total hydrocarbons and volatile organic components according to claim 2, characterized in that: The air inlet end (51) is provided with an electronic flow control unit (9) of the same specification.

6. The synchronous monitoring system for non-methane total hydrocarbons and volatile organic components according to claim 2, characterized in that: The exhaust flow paths (19) provided on the four-way valve (4) and the six-way valve (3) are connected in parallel via an inert tee, the exhaust flow path (19) of the six-way valve (3) is provided with a second electronic flow controller (12), and the exhaust flow path (19) of the four-way valve (4) is provided with a damping member (13).

7. A method for synchronously monitoring non-methane total hydrocarbons and volatile organic components, according to the synchronous monitoring system for non-methane total hydrocarbons and volatile organic components according to any one of claims 3 to 6, characterized in that: The following steps are involved: S1: One end of the adsorption tube (1) is connected to an air pump and a flow control component, and the airflow flows from the weak adsorbent in the adsorption tube (1) to the strong adsorbent. Volatile organic matter other than methane is adsorbed by the adsorption tube (1), while nitrogen and water are not adsorbed; S2: The adsorption tube (1) is sealed and stored; S3: The adsorption tube (1) is connected to the monitoring component, and air is blown into the adsorption tube (1) through the inert gas source (10). The trace methane and water remaining in the adsorption tube (1) are blown away by the inert gas. The airflow through the adsorption tube (1) is divided into two paths through a three-way valve. One path passes through the six-way valve (3) and the focusing tube (2) and is then discharged from the exhaust flow path (19) corresponding to the six-way valve (3). The other path passes through the four-way valve (4) and is discharged from the corresponding exhaust flow path (19). At the same time, the temperature of the focusing tube (2) is reduced to -30°C through the temperature control device (15). At the same time, the air inlet end (51) is connected to the hydrogen flame ionization detector (5) through the four-way valve (4) and an inert gas is introduced. S4: The adsorption tube (1) is heated to 330° C. by a heating component (14), and the volatile organic matter in the adsorption tube (1) is desorbed and flows into the six-way valve (3) and the four-way valve (4) respectively along with the inert gas. The gas flow flowing into the six-way valve (3) flows into the weak adsorbent end of the focusing tube (2) and flows out from the strong adsorbent end, and then enters the exhaust flow path (19); at the same time, the four-way valve (4) is switched, and the gas flow flowing into the four-way valve (4) enters the hydrogen flame ionization detector (5) to measure the response of non-methane total hydrocarbons; S5: the heating component (14) stops heating, the inert gas source (10) is turned off, the focusing tube (2) is quickly heated to 330°C by the temperature control device (15), and the six-way valve (3) is switched so that the carrier gas at the carrier gas end (71) of the injection port enters from the strong adsorbent end of the focusing tube (2), flows out from the weak adsorbent end of the focusing tube (2), and enters one end of the injection cavity body (72), and then the gas flows out from the other end of the injection cavity body (72) and enters the capillary column (8) and the exhaust end (73) respectively; S6: The temperature control device (15) stops heating and switches the six-way valve (3). The carrier gas end (71) of the injection port is connected to the injection port body (72) through the six-way valve (3). The column temperature oven (16) is used to adjust the temperature of the capillary column (8) so that the volatile organic matter is separated in the capillary column (8) and then enters the mass spectrometer detector (6) through the carrier gas to detect and analyze the components of the volatile organic matter. At the same time, the adsorption tube (1) is separated from the monitoring component, waiting for the injection and analysis of the next sample.

8. The method for synchronously monitoring non-methane total hydrocarbons and volatile organic components according to claim 7, characterized in that: In step S3, the flow rate of the inert gas introduced into the gas inlet end (51) is the same as the exhaust flow rate of the exhaust flow path (19) corresponding to the four-way valve (4).

9. The method for synchronously monitoring non-methane total hydrocarbons and volatile organic components according to claim 7, characterized in that: In step S5, the total flow rate and split ratio are set at the carrier gas end (71) of the injection port. If the total amount of the sample is low, no split or a low split ratio is set; If the total sample volume is high, set a high split ratio.

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