A diffusion tube based on 3D printing, an atmospheric active gas collection device and a sampling method thereof

Abstract

The present invention provides a diffusion tube based on 3D printing, an atmospheric active gas collection device and a method for using the same. The diffusion tube is a 3D printed diffusion tube having a structure of multiple single tubes in parallel; the length of the diffusion tube is more than 4 cm. In this application, 3D printing technology is used to obtain a diffusion tube of a certain length of metal or other materials, which overcomes the problems of fragility, unreliable glue dispensing and limited length processing of traditional glass diffusion tubes. The present application can achieve the purpose of completely collecting active gas samples at high sampling flow rates by increasing gas flow channels and extending the length of the diffusion tube, providing an analytical basis for subsequent sample isotope analysis. The present invention meets the needs of scientific researchers to completely collect atmospheric samples at high flow rates in clean areas such as the polar regions, or at low flow rates in areas with a high degree of pollution, and because the sampling is fast, high-resolution sampling can be performed, thereby achieving the purpose of studying the source and transformation mechanism of pollutant gases in the atmosphere by isotope means.

Description

Technical Field

[0001] The present invention relates to the fields of atmospheric chemistry, air pollution and gas isotope analysis technology, and in particular to a diffusion tube based on 3D printing, an atmospheric active gas collection device and a sampling method thereof. Background Art

[0002] Nitrates, sulfates and ammonium salts are important components of haze pollution. These pollutants mainly come from NO2 emitted by human activities or natural processes. x (NO+NO2), HONO, SO2, NH3 and other reactive gases. Effectively collecting these gases and conducting isotopic analysis on them is of great significance for understanding the sources and generation mechanisms of key pollutants in haze, as well as the corresponding changes in the atmospheric oxidation environment caused by the emission of these reactive gases, and can also provide a scientific basis for the formulation of emission reduction policies.

[0003] However, these polluted gases are generally more active, and it is difficult to separate and effectively collect them on site, especially for isotope analysis, which requires solving the problems of large collection volume and background interference. At present, the main gas collection methods are divided into two categories: active sampling and passive sampling. The passive sampling method has the problems of excessive background interference due to the long collection time and the collection efficiency cannot be guaranteed, so the active sampling method is more commonly used. The most common active sampling method is: preparing a chemical coating on the inner wall of a borosilicate glass diffusion tube, adsorbing the target sample gas and converting it into stable chemical components, and then extracting these chemical components for isotope analysis.

[0004] Traditional diffusers include single diffusers and annular diffusers. Single diffusers are only suitable for situations with high pollutant gas concentrations and low sampling flow rates (such as around 1L / min) because they only have one gas flow channel and are limited in design length. Annular diffusers can be designed with multiple gas flow channels, so they can collect gas at higher sampling flow rates (such as around 10L / min) while ensuring collection efficiency. However, the internal pipes of the annular diffusers currently on the market are basically bonded with glass glue. The chemical coating attached to the inner wall of the diffuser will corrode the glass glue, causing the internal glass pipe to separate and fall off. Therefore, this type of diffuser is not only expensive, but also has a short service life.

[0005] In addition to human activity areas, plateaus, ocean boundary layers, and polar regions that are less affected by human activities are NO xThe information on the sources and transformation mechanisms of gases such as HONO, SO2 and NH3 is also very important, which can provide the circulation process of these gases without human interference and evaluate the impact of human activity emissions on the global atmospheric environment. However, in remote areas, the concentration of these pollutants is very low (as low as ppt), so in order to collect enough samples for isotope analysis, it is necessary to increase the sampling flow rate and sampling time, but this will affect the collection efficiency and amplify the background interference.

[0006] In summary, the diffusion tubes currently available on the market cannot meet the researchers' goal of quickly collecting atmospheric samples while ensuring collection efficiency. Summary of the invention

[0007] In view of this, the present application provides a 3D printed diffusion tube, an atmospheric active gas collection device and a sampling method thereof. The atmospheric active gas collection device provided in the present application uses the diffusion tube as the main body. The collection device is used for sampling. Under the premise of ensuring the collection efficiency, it can meet the researchers' needs for collecting precursor gases of particulate pollutants in various situations such as outdoor or indoor areas, areas with severe air pollution and clean areas (plateaus or polar regions), thereby providing a basis for subsequent concentration and isotope analysis.

[0008] The present invention provides a diffuser tube based on 3D printing, wherein the diffuser tube is a diffuser tube formed by 3D printing and has a structure of multiple single tubes in parallel; and the length of the diffuser tube is more than 4 cm.

[0009] Preferably, the diffuser is a cylindrical diffuser, and the material of the diffuser is one or more of metal, ceramic and plastic; more than 50 parallel single tubes of equal size are evenly distributed inside the diffuser, and the single tubes are symmetrical structures.

[0010] Preferably, a chemical coating for collecting active gas is attached to the inner wall of the diffusion tube.

[0011] The present invention provides an atmospheric active gas collection device, comprising: a sleeve with a diffusion tube sleeved inside; the diffusion tube is the diffusion tube based on 3D printing, and is attached with a chemical coating.

[0012] Preferably, the sleeve is made of plastic or metal; the sleeve includes a laminar flow section, a diffusion tube sampling section, and a transition section from the air inlet end to the air outlet end.

[0013] Preferably, the diffusion tube sampling section is provided with one or more diffusion tubes.

[0014] Preferably, the air inlet end of the casing is also connected to a single-channel or multi-channel filter membrane and / or a flow control meter; the air outlet end of the casing is also connected to a pump.

[0015] Preferably, the sleeve in the atmospheric active gas collection device is connected to the outside using a 1 / 4 PFA tube or a 3 / 8 PFA tube.

[0016] The present invention provides a method for sampling atmospheric active gases, comprising the following steps:

[0017] A diffusion tube with a chemical coating attached to the inner wall is provided, wherein the diffusion tube is a diffusion tube formed by 3D printing, and the diffusion tube has a structure of multiple single tubes in parallel; the length of the diffusion tube is more than 4 cm;

[0018] The diffusion tube with the chemical coating attached to the inner wall is used to collect active gas in the atmospheric environment to obtain the target gas sample.

[0019] Preferably, the type of active gas in the atmospheric environment is selected from one or more of NO, NO2, HONO, SO2, HNO3 and NH3; the concentration range of active gas in the atmospheric environment is ppt level to ppm level; the sampling flow rate in the atmospheric environment is 0.1L / min to 60L / min.

[0020] Compared with the prior art, the present application provides a 3D printed diffusion tube, and the diffusion tube is used as the main part of the sampling device; the length of the diffusion tube is more than 4 cm. In the present application, a diffusion tube of a certain length of metal material (it can also be ceramic or plastic) is obtained by 3D printing technology, which overcomes the problems of fragility, unreliable glue dispensing and limited length processing of traditional glass diffusion tubes. The present application can achieve the purpose of completely collecting active gas samples at high sampling flow rates by increasing the gas flow channel and extending the length of the diffusion tube. Therefore, the present invention meets the needs of scientific researchers to completely collect atmospheric samples under high flow rates in clean areas such as polar regions, plateaus, and marine boundary layers, or low flow rates in areas with high pollution levels such as cities, industries, and agriculture, and because the sampling speed is fast, high-resolution sampling can be performed, thereby achieving the purpose of studying the source and transformation mechanism of these polluting gases in the atmosphere by isotope means. In addition, the device is portable, not easy to damage, has a long service life, and is suitable for indoor and outdoor atmospheric sampling. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A three-dimensional schematic diagram of a 3D printed stainless steel diffusion tube provided in Example 1;

[0022] Figure 2 for Figure 1 A schematic cross-sectional view of

[0023] Figure 3 is a flow chart of the collection device in Example 2;

[0024] Figure 4The absorption results of outdoor NO2 gas by the 3D printed stainless steel diffusion tube at different sampling flow rates in Example 2. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] The present invention provides a diffuser tube based on 3D printing, wherein the diffuser tube is a diffuser tube formed by 3D printing and has a structure of multiple single tubes in parallel; and the length of the diffuser tube is more than 4 cm.

[0027] By using the diffusion tube provided in this application to construct an atmospheric sampling device and collect active gases, atmospheric samples can be collected quickly with high collection efficiency. This can meet the researchers' needs for collecting precursor gases of particulate pollutants in various situations, such as outdoors or indoors, in areas with severe air pollution and in clean areas (plateaus or polar regions), and facilitate subsequent concentration and isotope analysis.

[0028] The present invention mainly adopts 3D printing technology and uses plastic materials such as metals, ceramics or plastics as printing raw materials to design a new type of honeycomb diffuser. That is, the diffuser described in the present application is a diffuser formed by 3D printing, and is a honeycomb structure with multiple single tubes in parallel.

[0029] 3D printing technologies that can be used to directly shape and manufacture metal functional parts include: selective laser sintering (SLS), selective laser melting (SLM), etc. SLM technology is developed on the basis of SLS, and the basic principles of the two are similar. SLM technology completely melts the metal powder and directly forms metal parts. In an embodiment of the present invention, the diffuser is formed by laser selective melting; the laser selective melting forming technology (i.e. the above-mentioned SLM technology) is one of the most common technologies in metal 3D printing. It uses a fine focused spot to quickly melt prefabricated metal powder, with a scanning speed of up to 1000mm / s and a laser power of about 250W. Workpieces of any shape and complete metallurgical bonding can be directly obtained.

[0030] After the diffusion tube in the embodiment of the present invention is printed, the workpiece is preferably annealed in a vacuum furnace with a vacuum of ≤0.01 bar and a temperature of 1050-1100°C for 1-2 hours to eliminate residual stress in the steel part, stabilize the size, and reduce the probability of deformation and cracking.

[0031] In an embodiment of the present invention, the material of the diffusion tube may be metals such as stainless steel and nickel alloy, or ceramics, plastics, etc. In an embodiment of the present invention, stainless steel is preferably used as raw material to prepare a stainless steel diffusion tube; not only is the material property stable, but it can also meet the needs of subsequent applications. Limited by the current 3D printing technology and the properties of the material itself, the diffusion tube sample is printed with polytetrafluoroethylene material, and the surface is not smooth and in a thin layer, which will affect the adhesion of the subsequent chemical coating on the surface; the photosensitive resin material contains a photosensitizer, and this type of substance has relatively high chemical activity, which will produce active intermediates and easily react with external chemical substances. After testing, the 3D sample printed with the photosensitive resin is placed in a NO2 absorption liquid, and the sample is completely damaged after two days. In some embodiments of the present invention, after screening, the 316L stainless steel material has stable chemical properties and is not easily corroded. After being prepared into a diffusion tube, the surface is relatively smooth, and the subsequent purging and polishing can achieve the purpose of preparing the coating and then using it.

[0032] The diffuser tube of the present invention may be a cylindrical long tube or other types of tubes. The diffuser tube is formed of multiple parallel single tubes in one piece, with a length of more than 4 cm, which is a honeycomb diffuser tube. The diffuser tube has a special structure to achieve a specific surface area, meeting the requirements of subsequent sampling flow rate and adsorption efficiency. The diffuser tube in the preferred embodiment of the present invention is a 3D-printed honeycomb stainless steel diffuser tube. No adhesive or physical model is required during the molding process. Not only does it have a long service life, but the length and other dimensions can be flexibly designed, which is convenient for its use in an atmospheric background environment.

[0033] In a preferred embodiment of the present application, more than 50 single tubes are evenly distributed inside the diffusion tube, and the single tubes can be symmetrical structures such as circular or hexagonal; for example, more than 200 parallel single tubes of equal size are evenly distributed, and the length can be 5cm to 20cm. In addition, a chemical coating can be attached to the inner wall of the diffusion tube to collect active gases. The present application is conducive to completely collecting sample gas at a higher sampling flow rate by increasing the gas flow channel and extending the length of the diffusion tube.

[0034] As for the specific specifications and dimensions of the diffusion tube, for the determination of the isotopic characteristic values ​​of active gases, the collection efficiency of the sample gas needs to reach more than 95%, otherwise the isotope fractionation during the collection process will cause a significant deviation between the analysis results and the source characteristic values. Therefore, the size design of the diffusion tube is calculated based on the altitude and temperature of the sampling site, the target gas concentration, the required amount of sample analysis, and the sampling time interval (whether high-resolution sampling is used). For example, the honeycomb stainless steel diffusion tube is a cylinder with a length of 15 cm and a cross-sectional diameter of 74 mm. 439 regular hexagonal holes with a side length of 1.5 mm are distributed inside the cylinder as sampling gas flow channels, and each regular hexagon is spaced 0.5 mm apart; the diffusion tube can meet the needs of researchers in the Nam Co area at an altitude of 5,000 meters, and collect samples of nitrogen oxides with an average concentration of 100 ppt alternating day and night, thereby meeting the needs of researchers for isotope analysis.

[0035] For areas with lower or higher concentrations of active gases, the design of the diffusion tube is not limited to the above-mentioned form. For example, for areas with lower concentrations, the length or diameter of the column can be increased according to local sampling conditions; for areas with higher concentrations of polluted gases, the diffusion tube can be printed into a more portable style. Therefore, when the diffusion tube of the present invention is prepared using 3D printing technology, the form and size of the diffusion tube can be flexibly designed according to the sampling conditions and sampling scheme, through the calculation of the preliminary collection efficiency, etc.

[0036] In addition, depending on the diffusion tube coating chemistry, it can be applied to a variety of applications including NO x , HONO, NH3, SO2 and other active gases are collected. In the embodiment of the present application, the diffusion tube can be coated with a chemical coating by an impregnation method; when preparing the coating, it should be ensured that each small hole in the diffusion tube is infiltrated with the coating liquid, and after the infiltration is completed, it can be purged with an inert gas until the coating is dry.

[0037] NOx emitted by human activities or natural processes x (NO+NO2), HONO, SO2, NH3 and other reactive gases will lead to the formation of nitrates, sulfates and ammonium salts, which are particulate pollutants in haze. At present, for severely polluted areas with high trace gas concentrations, single diffusers, annular diffusers and glass honeycomb diffusers can be used to achieve the collection purpose. However, for clean air areas such as the polar regions, plateaus and marine boundary layers, the concentrations of these pollutants are basically in the ppt level. To meet the demand for 50nmol isotope sample analysis, traditional diffusers are limited by glass processing technology, and the specifications and dimensions such as aperture and number of holes cannot meet the requirements of fast and efficient sampling. They are only suitable for low flow rate sampling under high pollution concentrations. Therefore, there is currently no sampling device on the market for the rapid and complete collection of trace gases in atmospheric background areas. At present, for NO in polar, plateau and marine boundary layer areas, there is no sampling device on the market for the rapid and complete collection of trace gases in atmospheric background areas. xThere are almost no research reports on the isotopic characteristic values ​​of trace gases such as SO2, NH3, and HONO. There are few studies reporting on the isotopic characteristic values ​​of trace gas emission sources in the atmospheric background areas. Obtaining data on the isotopic characteristic values ​​of trace gas emission sources in the background areas is crucial for researchers to use isotope methods to analyze the sources of particulate matter in polluted areas and to better understand the contribution of pollution sources to emissions in polluted areas.

[0038] Based on this, an embodiment of the present invention discloses an atmospheric active gas collection device suitable for isotope analysis, which is also called a sampling device, a sampler, etc. The atmospheric active gas collection device comprises: a sleeve with a diffusion tube inside; the diffusion tube is the diffusion tube based on 3D printing described above, and a chemical coating is attached to the inner wall.

[0039] Accordingly, an embodiment of the present invention provides a method for sampling atmospheric active gases, comprising the following steps: providing a diffusion tube with a chemical coating attached to the inner wall, wherein the diffusion tube is a 3D printed diffusion tube, and the diffusion tube has a structure of multiple single tubes in parallel; the length of the diffusion tube is more than 4 cm; using the diffusion tube with a chemical coating attached to the inner wall, active gases are collected in an atmospheric environment to obtain a target gas sample.

[0040] In an embodiment of the present invention, the sampling device is suitable for complete collection of trace gases in various situations such as polluted areas and clean air areas. For example, the concentration range of active gases in the atmospheric environment is ppt to ppb, and in some cases (such as boiler emissions, vehicle exhaust pipes, chimneys, etc.), it can reach ppm; the sampling flow rate in the atmospheric environment can be 0.1L / min to 60L / min, and the specific sampling flow rate can be calculated based on the sampling time, the altitude and temperature of the sampling location, the amount required to analyze a single sample, the target gas concentration, the adsorption rate, etc. For urban areas with a high degree of air pollution (the concentration of active gases in the atmosphere in polluted areas is ppb (~10^10molecules / cm 3 )), only a section of the diffusion tube is placed in the casing to complete sample collection at a lower flow rate, which can be used for urban pollutant gas emission sources such as coal-fired power plants and automobile exhaust emissions of NO x , NH3, SO2 concentration analysis and isotope analysis, providing sample collection devices for urban pollution source emission investigations.

[0041] For clean air areas (low concentration of active gases (ppt level ~ 10^7 molecules / cm 3) areas), where sampling is required at a higher flow rate, two sections of diffusion tubes can be placed, the first section is used to collect samples, and the second section is used to detect whether the collection is complete (if the collection efficiency does not reach more than 95%, the isotope fractionation during the collection process will affect the final measured isotope data). It can be used to collect NH3 emitted by farm animals, NO in the atmospheric background of polar plateau areas x , HONO collection and NO collection emitted from soil, providing a sample collection method for establishing an inventory of isotopic characteristic values ​​of trace gas emission sources in low-pollution areas.

[0042] In addition, due to the fast sampling speed, the sampling device described in the embodiment of the present invention can perform high-resolution sampling, and can use isotope methods to study the rapid transformation mechanism of these pollutant gases in the atmosphere. For example, the generation pathways of nitric acid are different under light conditions during the day and lightless conditions at night. By performing high-resolution sampling during the day and at night, analyzing the concentration and isotope values ​​of the final product nitrate and its precursor NO2, it is helpful to better understand the generation and transformation mechanism of nitrate.

[0043] Specifically, the main components of the atmospheric sampling device provided by the embodiment of the present invention include: the above-mentioned 3D-printed honeycomb stainless steel diffusion tube (disposed in a resin sleeve), a pump, a flow meter, a filter membrane clamp and a filter membrane; the connection order from left to right is filter membrane clamp and filter membrane → flow meter → diffusion tube → pump.

[0044] In the embodiment of the present application, the main body of the sampling device is a honeycomb stainless steel diffusion tube, and the size specifications and other contents are as described above. The stainless steel diffusion tube can be placed in a polytetrafluoroethylene sleeve, which mainly supports the diffusion tube. It can also be made of other chemically resistant resin materials or metals such as stainless steel and aluminum. One end of the sleeve is the air inlet end, and a 5cm polytetrafluoroethylene laminar flow section is preferably set. The laminar flow distance is long enough to ensure that the sampling airflow enters the diffusion tube smoothly. The air outlet end is also provided with a 5cm polytetrafluoroethylene transition section to prevent the air extraction port from being too close to the diffusion tube, resulting in the airflow passing only from the center of the diffusion tube. In some embodiments of the present invention, two sections of stainless steel diffusion tubes can be placed in the polytetrafluoroethylene sleeve. Generally speaking, the section near the air inlet is used to collect the target gas, and the second section is used to detect whether the gas is completely collected. The two sections of the diffusion tube can be separated by a polytetrafluoroethylene spacer, which is made of polytetrafluoroethylene material to ensure chemical corrosion resistance and will not interfere with sampling.

[0045] Preferably, a single-channel or multi-channel filter membrane (pre-filter membrane) is also connected to the air inlet end of the sleeve, that is, a filter membrane is arranged in the front section of the sampling device, and the filter membrane can be fixed by setting a filter membrane clamp, which is mainly used to remove existing particulate components in the air and gaseous components that interfere with the analysis results. In an embodiment of the present invention, the sampled airflow can remove particulate matter or other substances after passing through the filter membrane, thereby avoiding the interference of nitric acid, sulfuric acid or ammonium in the particulate matter on the diffusion tube gas sampling. The target sample gas is absorbed in the form of ions when passing through a stainless steel diffusion tube prepared with a specific chemical coating. When collecting the target gas, the pre-filter membrane in the gas path can simultaneously collect the reaction end products of these target gases in the atmosphere, such as nitric acid (NO x product), sulfuric acid (product of SO2), NH4 + By combining the concentration and isotope analysis results of particulate matter adsorbed by the filter membrane and the collected gas, the isotope effects of these substances in the atmospheric reaction process can be studied, providing basic data for tracing the emission sources of atmospheric pollutants by isotope means.

[0046] In addition, the air inlet end of the sleeve can also be connected to a flow control meter (referred to as flow meter); the air outlet end of the resin sleeve is also connected to a pump (such as a vacuum pump). In the embodiment of the present invention, the 3D printing technology using stainless steel as raw material is already very mature in the market, and the remaining components such as pumps, flow meters, filter membrane clips, etc. are also instruments and consumables that are often needed in laboratories. Therefore, there is no difficulty in making and purchasing components in this sampling device. In an embodiment of the present invention, the various components of the sampling device are connected by a PFA tube. In urban areas with a high degree of pollution, the sampling flow rate requirement is low, and a 1 / 4 PFA connection (inner diameter 4.35 mm, outer diameter 6.35 mm) can be used; in clean air areas such as polar plateaus with high sampling flow rate requirements, a 3 / 8 PFA tube connection (inner diameter 6.35 mm, outer diameter 9.53 mm) can be used to avoid limiting the increase in the sampling flow rate due to the thin tube diameter.

[0047] Before collecting the sample gas, the specific embodiment of the present invention rinses the diffusion tube with ultrapure water and methanol three times (at least 15 mL each time), and after rinsing, the diffusion tube is purged with ultrapure nitrogen until it is dry; then the prepared coating liquid is used to rinse the diffusion tube three times (at least 15 mL each time), and when preparing the coating, it should be ensured that each small hole in the diffusion tube is infiltrated with the coating liquid; after infiltration, the diffusion tube is purged with 1L / min ultrapure nitrogen for 20 minutes until the coating is dry. In the embodiments of the present invention, the target gas collected is different, and the types of filter membranes and chemical coatings required for the sampling device are different. The specific methods are listed as follows:

[0048] NO x(NO+NO2): Two filter membranes are placed in front of the diffusion tube, namely polytetrafluoroethylene filter membrane and nylon filter membrane, to remove particulate nitric acid and gaseous nitric acid; a mixed solution of potassium hydroxide, guaiacol and methanol can be used as a coating material for the diffusion tube, and the coating can selectively absorb NO2 to NO2 - (NO is not absorbed); if NO needs to be collected at the same time, CrO3 solid oxidant can be added to the front end of the diffusion tube. CrO3 oxidant can oxidize NO into NO2, so as to achieve the purpose of collecting NO and NO2 at the same time. If NO and NO2 need to be collected separately, CrO3 solid oxidant can be added between the two diffusion tubes. The first diffusion tube selectively collects NO2, and the second one collects the oxidized NO.

[0049] HONO: Add polytetrafluoroethylene filter membrane and nylon filter membrane to remove particulate nitric acid and gaseous nitric acid. The coating of the two diffusion tubes is prepared by a mixed solution of Na2CO3, glycerol and methanol. Both HONO and NO2 will be absorbed by the coating to become NO2 - However, HONO is completely collected in the first diffusion tube, and the second diffusion tube only absorbs a part of the interfering substance NO2. Experiments have shown that NO2 is evenly distributed in the two diffusion tubes. Therefore, the NO2 reduced by NO2 in the second diffusion tube can be used. - The concentration and isotope value of HONO are used to correct the influence of NO2 in the first diffusion tube on the determination of HONO concentration and isotope value.

[0050] NH3: Add polytetrafluoroethylene filter membrane and nylon filter membrane to remove particulate matter (NH4 + 、NO3 - etc.) and gaseous nitric acid, the diffusion tube coating is prepared from a mixed solution of citric acid, glycerol, methanol and ultrapure water; NH3 is absorbed as NH4 + Afterwards, it is oxidized to NO2 by alkaline hypobromite solution. - , and then perform isotope analysis.

[0051] SO2: A glass fiber filter is added to remove particulate sulfate, and the diffusion tube coating is prepared from sodium hydroxide and hydrogen peroxide solution; this coating can absorb SO2 into SO4 2- .

[0052] After sampling, the embodiment of the present invention can rinse the diffusion tube with ultrapure water (at least 15 mL each time, rinse three times), and store the eluent in a freezer at -20°C for subsequent concentration and isotope analysis. Then repeat the diffusion tube cleaning step, and after the diffusion tube is dried, seal both ends to avoid contamination and keep it for the next use.

[0053] By preparing a specific chemical coating on the inner wall of the diffusion tube, the sampling device of the present invention can complete the collection of various atmospheric trace gases. Among them, one or two filter membranes can be added to the front end of the airflow entering the diffusion tube to remove interfering substances that affect the analysis of the collected samples. The device can meet the needs of researchers to completely collect various trace gases in clean atmospheric background areas, and provide a basis for the subsequent analysis of the isotopic characteristic values ​​of various pollutant gas emission sources.

[0054] In order to further understand the present application, the 3D printing-based diffusion tube, atmospheric active gas collection device and method provided by the present application are specifically described below in combination with the embodiments. However, it should be understood that these embodiments are implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operation processes are given only to further illustrate the features and advantages of the present invention, rather than to limit the claims of the present invention, and the protection scope of the present invention is not limited to the following embodiments.

[0055] Example 1

[0056] The prefabricated metal powder (316L stainless steel material) is quickly melted using a fine focused spot, with a scanning speed of 1000 mm / s and a laser power of about 250 W, to directly obtain a honeycomb diffusion tube workpiece with complete metallurgical bonding.

[0057] After printing, annealing treatment is performed in a vacuum furnace with a vacuum of ≤0.01 bar and a temperature of 1050-1100°C for 1-2 hours to obtain a finished stainless steel diffusion tube.

[0058] Figure 1 A three-dimensional schematic diagram of a 3D printed stainless steel diffusion tube provided in Example 1; Figure 2 for Figure 1 The cross-sectional diagram of the prepared stainless steel diffusion tube is a cylinder with a height of 15 cm and a cross-sectional diameter of 74 mm (effective diameter is 70 mm, and wall thickness is 4 mm). 439 regular hexagonal small hole single tubes with a side length of 1.5 mm are distributed inside the cylinder as sampling gas flow channels, and each regular hexagon is spaced 0.5 mm apart.

[0059] Example 2

[0060] with NO x Taking (NO+NO2) gas collection as an example, the complete use process of the atmospheric sampling device is as follows:

[0061] 1) Diffusion tube cleaning:

[0062] The diffusion tube prepared in Example 1 was rinsed with ultrapure water and methanol three times (15 mL each time). After rinsing, the diffusion tube was purged with ultrapure nitrogen until dry. Both ends of the diffusion tube were wrapped with tin foil and placed securely for use.

[0063] 2) Preparation of diffusion tube chemical coating:

[0064] The NO2 absorbing coating liquid is prepared from a methanol solution containing 10 wt% potassium hydroxide and 25 wt% guaiacol. The coating can selectively absorb NO2 to NO2 - (does not absorb NO).

[0065] The prepared coating liquid was taken to rinse the diffusion tube three times (15 mL each time) so that each small hole in the diffusion tube was infiltrated with the coating liquid; after infiltration, the diffusion tube was purged with 1 L / min ultrapure nitrogen for 20 minutes until the coating was dry, thereby obtaining a diffusion tube with a chemical coating attached to the inner wall.

[0066] 3) Sampling device construction:

[0067] Two filters are placed in front of the diffusion tube, namely 1.0μm polytetrafluoroethylene filter membrane and 1.0μm nylon filter membrane. Put the prepared coating diffusion tube into the polytetrafluoroethylene sleeve, and then Figure 3 Flowchart shown, connect the gas path. Figure 3 In the figure, 1 is a vacuum pump; 2 is a polytetrafluoroethylene sleeve; 3 is a 3D-printed stainless steel diffusion tube, which has two sections and the same length parameters; 4 is a polytetrafluoroethylene septum; 5 is a polytetrafluoroethylene 5cm laminar flow section and transition section; 6 is a flow control meter; 7 is a filter membrane clamp and a filter membrane, which has two sections. The connection order is: pump → diffusion tube → flow meter → filter membrane clamp and filter membrane, connected with 3 / 8 PFA tube (inner diameter 6.35mm, outer diameter 9.53mm).

[0068] 4) Sampling efficiency:

[0069] The constructed sampling device is used to collect active gases; at a sampling flow rate of 60L / min, the theoretical collection efficiency of the sampling device for NO2 gas can still reach 99.99%.

[0070] The required isotope analysis amount for a single sample is 50 nmol. For atmospheric background areas such as Nam Co, where the NO2 concentration is at the order of 100 ppt, a sampling flow rate of 60 L / min is required to collect enough samples for isotope analysis in 5.5 hours of sampling; for urban areas with high air pollution such as Beijing, where the NO2 concentration is around 30 ppb, the required sample volume can be collected in 0.68 hours of sampling even at a sampling flow rate of 1 L / min.

[0071] Actual adsorption efficiency test: In polluted and clean areas, the sampling flow rate requirement is generally 1-20L / min. The adsorption efficiency of the device under this sampling flow rate range is as follows: Figure 4 shown. Figure 4The blue, yellow, green and red lines represent the NO2 concentration levels (below the detection line) of the outdoor atmosphere in Hefei after passing through the constructed sampling device (only one section of diffusion tube is placed) at four sampling flow rates of 1.5L / min, 5L / min, 15L / min and 20L / min, respectively. The purple line represents the NO2 concentration in the outdoor atmosphere in Hefei (the average value is 9.13ppb). Figure 4 As shown in the figure, under the set sampling flow rate variation of 1.5L / min to 20L / min, after the ambient atmosphere passes through the diffusion tube, the NO2 concentration level drops below the detection line, achieving the purpose of complete absorption, which is consistent with the theoretical calculation efficiency result.

[0072] The NO2 concentration level in the ambient atmosphere of clean areas is basically at the ppt level. Compared with urban areas with greater pollution and higher NO2 concentration, NO2 is more easily absorbed. Therefore, this experiment verifies that at a flow rate of 1.5 to 20 L / min, the diffuser device can completely absorb the ambient atmospheric NO2. Controlled by the experimental gas line connection resistance, the laboratory pump can only reach a maximum flow rate of 20 L / min. The absorption efficiency of the diffuser at a higher flow rate needs to be verified by a pump with a higher power.

[0073] 5) Diffusion tube rinsing and filter membrane storage:

[0074] After sampling, rinse the diffusion tube with ultrapure water (15 mL each time, three times), and store the eluent in a -20°C freezer for subsequent concentration and isotope analysis. Repeat the diffusion tube cleaning steps to prepare for the next sampling.

[0075] After sampling, take out the filter from the filter holder, wrap it in aluminum foil, seal it in a tight bag, mark the sampling date and store it in a -20°C freezer for subsequent concentration and isotope analysis.

[0076] By combining the concentration and isotope analysis results of particulate matter adsorbed by the filter membrane and collected gases, the isotope effects of these substances in the atmospheric reaction process can be studied, providing basic data for tracing the emission sources of atmospheric pollutants using isotope methods.

[0077] The invention meets the needs of scientific researchers to completely collect atmospheric samples at high flow rates in clean areas such as polar regions and plateaus or at low flow rates in areas with high pollution levels. Due to the fast sampling speed, high-resolution sampling can be performed, and the isotope principle can be used to study the rapid generation and transformation mechanism of these polluting gases in the atmosphere. In addition, the device is portable, not easy to damage, has a long service life, and is suitable for indoor and outdoor atmospheric sampling.

[0078] The above descriptions are only preferred embodiments of the present invention. It should be pointed out that professionals in this technical field can implement various modifications to these embodiments without departing from the technical principles of the present invention, and these modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A diffusion tube based on 3D printing, characterized in that: The diffuser is a diffuser formed by 3D printing, and has a structure of multiple single tubes in parallel; the length of the diffuser is more than 4 cm; the diffuser is a cylindrical diffuser, and the material of the diffuser is one or more of metal, ceramic and plastic; more than 50 parallel single tubes of equal size are evenly distributed inside the diffuser, and the single tubes are symmetrical structures; the inner wall of the diffuser is attached with a chemical coating for collecting active gases.

2. An atmospheric active gas collection device, comprising: A sleeve having a diffusion tube inside; the diffusion tube is the 3D printing-based diffusion tube as described in claim 1.

3. The atmospheric active gas collection device according to claim 2, characterized in that: The sleeve is made of plastic or metal; the sleeve includes a laminar flow section, a diffusion tube sampling section, and a transition section from the air inlet end to the air outlet end.

4. The atmospheric active gas collection device according to claim 3, characterized in that: The diffusion tube sampling section is provided with one or more diffusion tube sections.

5. The atmospheric active gas collection device according to any one of claims 2 to 4, characterized in that: The air inlet end of the sleeve is also connected to a single-channel or multi-channel filter membrane and / or a flow control meter; the air outlet end of the sleeve is also connected to a pump.

6. The atmospheric active gas collection device according to claim 5, characterized in that: The sleeve in the atmospheric active gas collection device is connected to the outside by a 1 / 4 PFA tube or a 3 / 8 PFA tube.

7. A method for sampling atmospheric active gases, comprising the following steps: A diffusion tube with a chemical coating attached to the inner wall is provided, the diffusion tube is a 3D printed diffusion tube, the diffusion tube has a structure of multiple single tubes in parallel; the diffusion tube is more than 4 cm long; the diffusion tube is a cylindrical diffusion tube, and the diffusion tube material is one or more of metal, ceramic and plastic; more than 50 parallel single tubes of equal size are evenly distributed inside the diffusion tube, and the single tube is a symmetrical structure; the inner wall of the diffusion tube is attached with a chemical coating for collecting active gas; The diffusion tube with the chemical coating attached to the inner wall is used to collect active gas in the atmospheric environment to obtain the target gas sample.

8. The sampling method according to claim 7, characterized in that: The type of active gas in the atmospheric environment is selected from one or more of NO, NO2, HONO, SO2, HNO3 and NH3, and the concentration range is ppt level to ppm level; the sampling flow rate in the atmospheric environment is 0.1L / min to 60L / min.

Images