VOCs efficient enrichment device based on electric field guidance and use method thereof

Abstract

The invention provides a VOCs efficient enrichment device based on electric field guidance and a use method thereof, and relates to the technical field of atmospheric organic matter detection, the VOCs efficient enrichment device comprises a pre-enrichment component used for pre-treating and enriching low-concentration target VOCs in the atmosphere; the pre-enrichment component comprises an enrichment gas circuit, a sample introduction gas circuit and a driving gas circuit; the enrichment gas circuit comprises a VOCs enrichment device, the VOCs enrichment device can selectively and directionally adsorb VOCs molecules with different polarities by dynamically adjusting the intensity and frequency of an electric field, the enrichment efficiency of the device is remarkably improved, and the application range is widened. Compared with a traditional VOCs enrichment method, the device effectively solves the problem that the selective adsorption capacity is limited in a complex component gas environment, and overcomes the limitation that the same adsorbent is insufficient in universality in different application scenes. The device and the method have the advantages that efficient enrichment of VOCs is realized through assistance of the electric field, and the device and the method are particularly suitable for rapid enrichment and subsequent detection of various VOCs in a complex gas environment.

Description

Technical Field

[0001] The present invention belongs to the technical field of atmospheric organic matter detection, and specifically relates to a high-efficiency VOCs enrichment device based on electric field guidance and its usage method. Background Art

[0002] Volatile Organic Compounds (VOCs) widely exist in the atmosphere, and their sources include natural and anthropogenic factors. Industrial emissions are the main anthropogenic source. With the development of industry, the emissions of VOCs continue to increase. Many VOCs have unpleasant odors and are difficult to degrade. Some substances have teratogenic, carcinogenic, and mutagenic effects. For example, long-term exposure to benzene, toluene, etc. can lead to neurosis, heart disease, and even leukemia. VOCs can also cause photochemical smog, secondary aerosols, and haze weather. Therefore, it is crucial to monitor their types and contents.

[0003] There are many types of VOCs in the atmosphere. Due to their different chemical properties and environmental conditions, the concentration range of VOCs in the atmosphere is from one part per trillion (ppt v ) to one part per million (ppm v ). Currently, the commonly used method for capturing trace VOCs in the atmosphere at home and abroad is the adsorption enrichment method, and usually combined with cryogenic freezing method to improve the sensitivity and accuracy of monitoring. Currently, this technology is widely used. For example: the VOCs enrichment means used in the volatile organic compound adsorption and concentration sampling device mentioned in the paper "Development of a New Type of Volatile Organic Compound Adsorption and Concentration Online Monitoring System" and the thermal desorption instruments of patents CN115980378B and CN110646549B. The present invention solves the problems of limited selective adsorption ability of traditional VOCs enrichment methods for VOCs in complex gases and insufficient adaptability of the same adsorbent in different application scenarios by introducing electric field regulation technology into the above methods. When using the existing technology to process complex sample gases (such as multi-component VOCs), there will be a situation of competitive adsorption of non-target molecules, resulting in a decrease in the enrichment efficiency of target molecules. In contrast, the present invention realizes the selective directional adsorption of different polar VOCs molecules by dynamically adjusting the electric field strength and frequency, significantly improving the enrichment efficiency. The precise regulation of the electric field enhances the enrichment ability of target molecules, enabling efficient and accurate enrichment even in a complex gas environment. This innovation effectively solves the adaptability and selectivity problems of traditional adsorption enrichment methods in multi-component gases, improving the accuracy and sensitivity of subsequent VOCs detection. Summary of the Invention

[0004] (I) Technical Problems to be Solved

[0005] In view of the deficiencies in the prior art, the present invention provides a VOCs efficient enrichment device based on electric field guidance and a method of using the same, which solves the problems raised in the above background technology.

[0006] (II) Technical solution

[0007] The atmospheric online enrichment sampling device provided in the present application realizes the selective directional adsorption of VOCs molecules of different polarities by dynamically adjusting the electric field strength and frequency. The advantage of this device lies in its efficient VOCs enrichment ability, which is particularly suitable for multi-component VOCs detection in complex gas environments. By precisely controlling the response mode of the electric field, not only the enrichment effect on the target molecules is enhanced, but also the enrichment efficiency is greatly improved, so that the device can show excellent adaptability in the monitoring of different types of VOCs. It ensures that the detection device used in conjunction with it can provide high-sensitivity and high-precision real-time data in atmospheric pollution monitoring, and meets the needs of synchronous monitoring of VOCs with complex components.

[0008] In order to achieve the above technical objectives, the technical solution adopted by the present invention is:

[0009] A VOCs efficient enrichment device based on electric field guidance, comprising:

[0010] Pre-enrichment components are used to pre-treat and enrich low-concentration VOCs in the atmosphere so that the VOCs concentration can reach the detection limit of the detection device;

[0011] The pre-enrichment component includes an enrichment gas path, a sample injection gas path and a drive gas path;

[0012] The enrichment gas circuit includes a pneumatic six-way valve, a quantitative ring, a vacuum pump, and a particulate filter, a Nafion gas drying tube, a first three-way solenoid valve, an electromagnetic pulse valve, a VOCs enricher, and a first pressure controller connected in sequence. The pneumatic six-way valve is connected to the outlet of the first pressure controller, the inlet and outlet of the quantitative ring, and the inlet of the vacuum pump. Through the coordinated work of multiple components, efficient gas collection and concentration are achieved. Its main function is to remove solid particles and moisture from the sample gas, ensure the efficiency of the adsorbent in enriching VOCs and extend its service life; at the same time, it creates negative pressure to promote the sample gas to flow through the VOCs enricher, concentrate low-concentration VOCs, and improve the analytical detection limit of the detection device;

[0013] The sample injection gas path includes a nitrogen supply end and a second pressure controller. The nitrogen supply end, the second pressure controller, and the pneumatic six-way valve are connected in sequence. The pneumatic six-way valve enables the carrier gas to flow through the enrichment gas path by controlling the gas path mode, and sends the enriched target VOCs substance into the detection device. Its function is to stably input the enriched and concentrated sample gas into the detection device. By maintaining the pressure at the sample outlet of the enrichment device to be greater than or equal to the pressure at the sample injection port of the detection device, it prevents the situation where the target substance cannot enter the detection device and the carrier gas in the gas path of the detection device is sucked back into the enrichment device. At the same time, this gas path can flexibly switch the gas path direction, blow out the enriched target substance from the enrichment gas path with the carrier gas, and efficiently transmit it to the detection device;

[0014] The drive gas path includes a third pressure controller and a second three-way solenoid valve. The intake end of the third pressure controller is connected to the nitrogen supply end, and the outlet end of the second three-way solenoid valve is connected to the drive gas intake end of the pneumatic six-way valve. Its function is to control the on-off of the drive gas entering the pneumatic six-way valve to control the mode switching of the pneumatic six-way valve. The pressure controller is used to maintain the pressure of the drive gas within a suitable range, which not only meets the switching condition of the drive gas pressure but also prevents excessive pressure from damaging the pneumatic six-way valve. The switching of the three-way solenoid valve passage can instantaneously discharge the gas accumulated at the drive port, achieving the purpose of instantaneously switching the gas path mode of the device to optimize the enrichment performance and response speed of the entire device.

[0015] Preferably, the VOCs enricher includes a cryogenic adsorption component, an electric field adsorption component, and a temperature control component.

[0016] The cryogenic adsorption component includes a quartz adsorption tube filled with an adsorbent and straight-through adapters connected to both ends of the quartz adsorption tube. The straight-through adapters are used to connect the quartz adsorption tube to the electromagnetic pulse valve and the first pressure controller. A fluororubber gasket seal is installed inside the passage at the end where the straight-through adapter is connected to the quartz adsorption tube.

[0017] The electric field adsorption component includes a cylindrical ring electrode and a cylindrical conductive rod. The cylindrical ring electrode is closely attached to the inner wall of the quartz adsorption tube, and the cylindrical conductive rod is located at the center of the adsorbent layer.

[0018] The temperature control component includes an electric heating wire, a semiconductor refrigeration sheet, a heat conduction sheath, and a radiator. The electric heating wire is wound around the outside of the quartz adsorption tube. The heat conduction sheath is composed of a metal sheet with two parallel grooves and a hollow semi-cylindrical metal sheet. The electric heating wire and the quartz adsorption tube are placed in the heat conduction sheath. The semiconductor refrigeration sheet is closely attached to the lower part of the heat conduction sheath, and the radiator is placed below the semiconductor refrigeration sheet.

[0019] When the cylindrical ring electrode and the cylindrical conductive rod are energized, a radial electric field is generated between the two to achieve the directional adsorption of target VOCs molecules.

[0020] The electric field adsorption component can perform dynamic electric field regulation. By dynamically regulating the electric field strength and frequency, VOCs molecules with different polarities can respond to the electric field in different ways, thus achieving selective capture.

[0021] Preferably, the generation and regulation of the electric field are achieved through the cooperation of a power supply and a frequency converter to optimize the adsorption effect of VOCs. The power supply provides adjustable voltage and current to control the electric field strength, and its output range is usually from 1 kV / cm to 10 kV / cm, which can ensure the stable operation of the system and continuously generate the required electric field. The frequency converter controls the alternating speed of the electric field by adjusting the current frequency input to the electric field generation device to achieve dynamic adjustment of the frequency.

[0022] VOCs molecules with different polarities have different response forms to the electric field. The electric field frequency is optimized for different types of VOCs. High-frequency electric fields (>100 kHz) are mainly used for selectively adsorbing polar VOCs molecules; medium and low-frequency electric fields (<100 kHz) are used for selectively adsorbing weakly polar and non-polar VOCs.

[0023] Furthermore, by real-time monitoring the VOCs concentration, the control system can dynamically adjust the electric field strength according to the sensor feedback. A higher-intensity electric field (5 - 10 kV / cm) is used in a low-concentration VOCs environment, while a lower-intensity electric field (1 - 5 kV / cm) is used in a high-concentration VOCs environment to reduce the collision and repulsion interference between molecules to ensure the best enrichment effect.

[0024] Preferably, the arrangement of the adsorbent in the quartz adsorption tube is divided into a front section, a middle section, and a rear section. The front section is filled with non-polar VOCs adsorption filler, the middle section is filled with transitional adsorption filler that has an adsorption effect on both polar and non-polar VOCs, and the rear section is filled with polar VOCs adsorption filler.

[0025] Preferably, the quartz adsorption tube is divided into multiple temperature control regions, and the temperature of each region is independently set according to the characteristics of the filler and the condensation characteristics of the target compound. The number of temperature control regions corresponds to the number of filler types.

[0026] Furthermore, the front section area is mainly used for adsorbing non-polar VOCs, and the temperature is set relatively high, generally 0 to -5 °C. This is to prevent non-polar molecules from prematurely condensing on the adsorption tube wall before contacting the adsorbent at too low a temperature and to enhance the adsorption capacity of the adsorbent for these molecules, ensuring efficient enrichment. The temperature in the middle section area is moderate, generally -5 to -15 °C, which can not only effectively adsorb polar VOCs but also enrich a certain amount of non-polar VOCs. The temperature control design in this area ensures good adsorption efficiency for various gas components, especially suitable for mixed gases with complex compositions. The rear section area is used for adsorbing polar VOCs, and the temperature is set relatively low, generally -15 to -30 °C, to promote the enrichment of target polar molecules at low temperatures and enhance the interaction force between molecules and the adsorbent surface, improving the adsorption efficiency.

[0027] Preferably, the first pressure controller and the electromagnetic pulse valve cooperate with the electric field adsorption component to control the contact time between VOCs molecules and the adsorbent using pulsed airflow.

[0028] Preferably, the period and flow rate of the pulsed airflow are optimized according to the characteristics of different VOCs and the frequency intensity of the electric field.

[0029] Furthermore, for polar VOCs, when using a high-frequency electric field, the pulsed airflow period is shorter (5 - 50 ms) and the flow rate is smaller (10 - 50 mL / s). For weakly polar VOCs, when using a medium-frequency electric field, the pulsed airflow period is moderate (50 - 200 ms) and the flow rate is moderate (50 - 150 mL / s). Non-polar VOCs are suitable for a low-frequency electric field, with a long pulsed airflow period (200 - 500 ms) and a large flow rate (150 - 300 mL / s).

[0030] Furthermore, the pre-enrichment component further includes a temperature sensor, which is arranged on the heating wire and used to monitor the real-time temperature of the heating wire.

[0031] Preferably, the pneumatic six-way valve has six air holes, which are respectively marked as the first to the sixth air holes; the first air hole is connected to the output end of the first pressure controller, the second air hole is connected to the input end of the quantitative loop, the third air hole is connected to the detection device, the fourth air hole is connected to the output end of the second pressure controller, the fifth air hole is connected to the output end of the quantitative loop, and the sixth air hole is connected to the input end of the vacuum pump.

[0032] The pneumatic six-way valve has two gas path modes, a and b;

[0033] When the pneumatic six-way valve is in state a, the first air hole is communicated with the sixth air hole, the second air hole is communicated with the third air hole, and the fourth air hole is communicated with the fifth air hole;

[0034] When the pneumatic six-way valve is in state b, the first air hole communicates with the second air hole, the third air hole communicates with the fourth air hole, and the fifth air hole communicates with the sixth air hole.

[0035] The three-way solenoid valve has two gas path modes, a and b;

[0036] When the three-way solenoid valve is in state a, the A and E air holes communicate, and the P air hole does not form a gas path with any of the A or E air holes;

[0037] When the three-way solenoid valve is in state b, the A and P air holes communicate, and the E air hole does not form a gas path with any of the A or P air holes.

[0038] A method of using a VOCs high-efficiency enrichment device based on electric field guidance, which is used for the injection of VOCs gas cryogenic concentration and thermal desorption, includes the following steps:

[0039] 1) Heating and purging: By heating the VOCs enricher and flowing the purging gas, it helps to desorb and remove impurities in the adsorption tube. The purging gas passes through the quartz adsorption tube, pressure controller and vacuum pump, and discharges the impurity gas into the atmosphere to ensure the system is clean and returns to normal working state. This process avoids the interference of residual substances from the previous enrichment on subsequent detections;

[0040] 2) Cooling: By switching the VOCs enricher from the heating mode to the refrigeration mode and continuously introducing the purging gas, the temperature control regions of the quartz adsorption tube gradually decrease to the target temperature. This process helps to enhance the condensation and adsorption efficiency of the target substances under low-temperature conditions and complete the preparation for subsequent sample gas collection;

[0041] 3) Sampling: Turn on the electric field adsorption component and the vacuum pump, suck the sample gas, make it pass through the VOCs enricher, and finally discharge it into the atmosphere. In the VOCs enricher, the low temperature promotes the preliminary enrichment of the target substances, and at the same time the electric field enhances the binding force between the molecules and the adsorption material through directional adsorption, further improving the enrichment efficiency. This step combines cryogenic enrichment and electric field adsorption to achieve efficient sampling and enrichment of the target substances;

[0042] 4) Injection: Turn off the electric field adsorption component and the vacuum pump and switch the VOCs enricher to the heating mode. After a period of time, the purging gas starts to flow in and clean the quartz adsorption tube. The purging process helps to release the adsorbed target substances into the detection device for subsequent analysis or processing.

[0043] Among them, in Step 1 during heating and purging, the purging gas flow rate is 5 - 10 mL / min, the heating temperature is 300 - 400 °C, and the duration is 5 - 10 min; in Step 2 during cooling, the purging gas flow rate is 5 - 10 mL / min; in Step 3, the sampling duration is 5 - 20 min; in Step 4 during injection, the temperature is heated to above 360 °C and maintained for 30 - 150 s before purging, and the purging time is 20 - 30 s.

[0044] Beneficial effects

[0045] The present invention provides a high - efficiency VOCs enrichment device based on electric - field guidance and its usage method, having the following beneficial effects:

[0046] 1. By dynamically adjusting the intensity and frequency of the electric field, the present application realizes the selective directional adsorption of VOCs molecules with different polarities, significantly improving the enrichment efficiency and adaptability. By precisely controlling the electric field, not only the selective enrichment of the target substance is enhanced, but also the application range is broadened, especially suitable for the detection of multi - component VOCs sample gases.

[0047] 2. By dividing the quartz adsorption tube into multiple sections and using different types of adsorption fillers according to the characteristics of different VOCs, the present application realizes the high - efficiency enrichment of polar and non - polar VOCs. At the same time, the temperature of each temperature - control region is independently set to maximize the adsorption efficiency of different fillers, and precise regulation is carried out according to the condensation characteristics of different target compounds, thereby improving the overall enrichment efficiency of the device and expanding the applicable range.

[0048] 3. By using pulsed airflow to adjust the contact time between VOCs molecules and the adsorbent, the present application optimizes the adsorption process. Pulsed airflow control can precisely adjust the gas flow rate and the contact time between VOCs and the adsorbent, enhance the interaction between the target VOCs and the adsorbent, improve the enrichment efficiency, and at the same time avoid adsorption failure or efficiency decline caused by too long or too short contact time. Description of the drawings

[0049] Figure 1 It is a schematic diagram of the high - efficiency VOCs enrichment device and the gas - path flow of the present invention;

[0050] Figure 2 It is a schematic diagram of the straight - through adapter in the high - efficiency VOCs enrichment device of the present invention;

[0051] Figure 3 It is a schematic diagram of the VOCs enricher in the high - efficiency VOCs enrichment device of the present invention;

[0052] Figure 4 It is a schematic diagram of the electric - field - guided molecular dipole moment rotation in the high - efficiency VOCs enrichment device of the present invention;

[0053] Figure 5Comparison chart of test results of the VOCs high-efficiency enrichment device of the present invention using different electric field frequencies;

[0054] Figure 6 Comparison chart of test results of the VOCs high-efficiency enrichment device of the present invention with the electric field turned on and off;

[0055] Figure 7 Schematic flow chart of the operation of the VOCs high-efficiency enrichment device of the present invention.

[0056] The names of the reference numerals in the figure are as follows: 1. Nitrogen supply end; 2. Particle filter; 3. Nafion gas drying tube; 4. First three-way solenoid valve; 5. Electromagnetic pulse valve; 6. VOCs enricher; 7. First pressure controller; 8. Second pressure controller; 9. Pneumatic six-way valve; 10. Quantitative loop; 11. Vacuum pump; 12. Third pressure controller; 13. Second three-way solenoid valve; 14. Power supply; 15. Frequency converter; 16. Lower computer; 17. Interface interaction module; 18. Fluororubber gasket seal; 19. Metal ferrule; 20. Straight-through adapter; 21. Quartz adsorption tube; 22. Electric heating wire; 23. Heat conduction sheath; 24. Temperature sensor; 25. Semiconductor refrigeration chip; 26. Radiator; 27. Cylindrical ring electrode; 28. Cylindrical conductive rod. Detailed implementation manners

[0057] The following are only the preferred implementation manners of the present invention, and the protection scope is not limited to this embodiment. All technical solutions belonging to the present invention should fall within the protection scope of the present invention. At the same time, it should be pointed out that for those of ordinary skill in the art in the technical field, several improvements and retouches made without departing from the principle of the present invention should also be regarded as within the protection scope of the present invention.

[0058] A VOCs high-efficiency enrichment device based on electric field guidance, comprising:

[0059] A pre-enrichment component for pre-treating and enriching low-concentration VOCs in the atmosphere so that the concentration of VOCs can reach the detection limit of the detection device.

[0060] Refer to the appendix Figure 1 As shown, the pre-enrichment component includes an enrichment gas path, a sampling gas path and a driving gas path.

[0061] The enrichment gas path includes a particulate filter 2, a Nafion gas dryer 3, a pneumatic six-way valve 9, a first pressure controller 7, a first three-way solenoid valve 4, an electromagnetic pulse valve 5, a sampling loop 10, a vacuum pump 11, and a VOCs enricher 6, and is constructed as follows: First, the inlet end of the particulate filter 2 is connected to ambient air, and a high-efficiency filter medium is used to remove solid particles with a diameter greater than 2 μm, thereby ensuring the purity of the sample gas entering the system. The outlet end of the particulate filter 2 is connected to the Nafion gas dryer 3, which effectively removes moisture in the air through membrane technology, keeps the gas dry, and avoids interference with subsequent analysis.

[0062] Next, the outlet end of the Nafion gas dryer 3 is connected to the first three-way solenoid valve 4, which switches the gas path channel according to the control signal, enabling the gas flowing through the VOCs enricher 6 to switch between the carrier gas and the sample gas. The outlet end of the first three-way solenoid valve 4 is connected to the inlet end of the electromagnetic pulse valve 5. The electromagnetic pulse valve 5 controls the sample gas to flow through the adsorbent in the VOCs enricher 6 in the form of a pulsed gas flow. The outlet end of the electromagnetic pulse valve 5 is connected to the inlet end of the VOCs enricher 6. The VOCs enricher 6 is equipped with an electric field adsorption component and a specific adsorption material to efficiently adsorb the target substance and achieve a high-fold concentration effect.

[0063] In addition, the outlet end of the VOCs enricher 6 is connected to the inlet end of the first pressure controller 7. The first pressure controller 7 adjusts the gas pressure to ensure the stability and accuracy of the gas flow rate during the enrichment process. Finally, the pneumatic six-way valve 9 is connected to the outlet end of the first pressure controller 7, the inlet and outlet ends of the sampling loop 10, and the inlet end of the vacuum pump 11, and can flexibly switch the gas flow path to ensure that the high-concentration target substance flowing out of the VOCs enricher 6 can flow into the sampling loop 10, and the gas exceeding the volume upper limit of the sampling loop 10 will be discharged into the atmosphere.

[0064] The sampling gas path includes a nitrogen supply end 1, a second pressure controller 8, and a pneumatic six-way valve 9, and is constructed as follows: First, the inlet end of the second pressure controller 8 is connected to the nitrogen supply end 1 to provide a stable source of carrier gas. This pressure controller is used to precisely adjust the pressure of the carrier gas to ensure that the carrier gas reaches the pressure set at the inlet of the detection device when entering the detection device, avoiding pressure imbalance at the inlet of the detection device.

[0065] One end of the pneumatic six-way valve 9 is connected to the inlet of the detection device. After the gas path mode is switched, the carrier gas flows through the sampling loop 10 and accurately sends the high-concentration target substance inside to the detection device for analysis. The entire sampling gas path system ensures the efficient transmission of the sample gas and the accuracy of the analysis process by real-time monitoring of the gas flow rate and pressure. The sampling gas path designed in this way is more flexible and efficient when transporting the sample gas, and can adjust the sampling time and sampling volume according to needs to meet different experimental requirements.

[0066] The described drive gas path includes a third pressure controller 12, a second three-way solenoid valve 13, and a pneumatic six-way valve 9, configured as follows: First, the intake end of the third pressure controller 12 is connected to the nitrogen supply end 1 to provide a stable source of drive gas. The main function of this pressure controller is to regulate the pressure of the drive gas to ensure that the pressure of the drive gas entering the pneumatic six-way valve 9 meets the requirements for switching the gas path of the six-way valve, and at the same time prevent damage to the six-way valve due to excessive drive gas pressure.

[0067] Second, the outlet end of the third pressure controller 12 is connected to the intake end of the second three-way solenoid valve 13. The regulated drive gas will first flow into the second three-way solenoid valve 13 before entering the six-way valve. The function of this solenoid valve is to switch the flow path of the gas according to the control signal. Its outlet end is connected to the drive gas intake end of the six-way valve, controlling the drive gas to enter the six-way valve or allowing the drive gas in the six-way valve to be discharged from the orifice in the second three-way valve 13 to achieve the switching of the gas path state of the six-way valve.

[0068] Through such a design, the entire drive gas path can ensure the rapid switching of the device gas path under different working processes, thereby improving the overall performance and efficiency of the system.

[0069] In some embodiments of the present application, the particulate filter 2 is made of silanized 316L stainless steel, with a cylindrical outer shell, an outer diameter of 15 mm, an inner diameter of 10 mm, an inner filter disc with a diameter of 10 mm and a thickness of 1.7 mm, and an effective pore diameter of the filter disc of 2 μm.

[0070] In some embodiments of the present application, the wall thickness and tube length of the Nafion gas drying tube 3 are adjusted according to the change in ambient humidity to improve the efficiency of removing moisture from the gas.

[0071] Low humidity (≤30% RH): Use a shorter Nafion tube (10 - 20 cm) and a thinner membrane (70 - 150 μm) to reduce the water exchange time and avoid excessive drying of the gas.

[0072] Medium humidity (30% - 70% RH): Use a medium-length Nafion tube (20 - 50 cm) and a moderate membrane thickness (150 - 200 μm) to balance the gas drying efficiency and flow rate and ensure effective removal of moisture.

[0073] High humidity (≥70% RH): Use a longer Nafion tube (50 - 100 cm) and a thicker membrane (200 - 300 μm) to provide a larger moisture transfer area and time to enhance the dehumidification ability and prevent excessive humidity from affecting subsequent detection or processing.

[0074] In addition, in a high-humidity environment (> 90% RH), multiple Nafion tubes can be connected in series or desiccants can be added to assist in dehumidification (such as combined with silica gel or molecular sieve) to improve the moisture removal efficiency.

[0075] In some embodiments of the present application, the adjustment range set by the pressure controller is designed to adapt to the requirements of different gas flow rates to ensure the stability of the gas flow rate during the enrichment process; the accuracy is designed to be able to achieve the required gas pressure control accuracy to meet the specific requirements of the detection device for the sample gas pressure.

[0076] Refer to the attached Figure 2 , Figure 3 As shown, the VOCs enricher 6 includes a cryo-adsorption component, an electric field adsorption component, and a temperature control component.

[0077] The cryo-adsorption component includes a quartz adsorption tube 21 filled with a specific adsorbent, aiming to efficiently enrich the target substance. Both ends of the quartz adsorption tube 21 are connected with straight-through adapters 20, and the straight-through adapters 20 are used to connect the quartz adsorption tube 21 with the electromagnetic pulse valve 5 and the first pressure controller 7. In order to enhance the connection reliability, a fluororubber gasket seal ring 18 is arranged at the end of the channel inside the straight-through adapter 20, and this seal ring can effectively prevent gas leakage. In addition, the fluororubber material has good corrosion resistance and high-temperature resistance, and can adapt to different working environments and conditions. At the same time, a metal ferrule 19 is installed on the fluororubber gasket seal ring 18 to play a role in fixing the position of the seal ring.

[0078] The arrangement of the adsorbent in the quartz adsorption tube 21 is divided into a front section, a middle section, and a rear section. Among them, the front section is filled with non-polar VOCs adsorption filler, the middle section is filled with a transition adsorption filler that has an adsorption effect on both polar and non-polar VOCs, and the rear section is filled with polar VOCs adsorption filler. The specific filler arrangement and sequence setting consider the physical and chemical properties of different adsorbents and their adsorption performance for different types of VOCs molecules.

[0079] In some embodiments of the present application, the front section is filled with carbon molecular sieve, which is mainly used to enrich non-polar VOCs molecules. Its microporous structure can further enhance the adsorption ability of weakly polar or neutral molecules under the action of an electric field, realizing the preliminary screening of non-polar molecules. Activated carbon is used in the middle section, which has a high specific surface area and a wide pore size distribution, can effectively capture non-polar or weakly polar VOCs in the air flow, and efficiently filter out interfering molecules with larger molecular weights, ensuring that the adsorption process in the subsequent stage is more specific. Functionalized activated carbon is used as the adsorbent in the rear section. By introducing polar groups through surface chemical modification, the adsorption ability for polar VOCs (such as alcohols, aldehydes, ketones, etc.) is enhanced. At the same time, the action of the electric field can further improve its adsorption efficiency, promote the electrostatic attraction between the surface polar groups and VOCs molecules, and enhance the adsorption efficiency.

[0080] The electric field adsorption component includes a cylindrical ring-shaped electrode 27 and a cylindrical conductive rod 28. The cylindrical ring-shaped electrode 27 is closely attached to the inner wall of the quartz adsorption tube 21 to form a uniform annular electric field region; the cylindrical conductive rod 28 is located at the center of the adsorbent layer to ensure the uniform distribution of the electric field within the adsorption tube. This electric field adsorption component performs directional adsorption and selective adsorption on VOCs molecules in the gas through the action of the electric field. By adjusting the intensity and frequency of the electric field, the efficiency of the electric field for adsorbing VOCs is dynamically optimized, and the enrichment effect on VOCs is improved.

[0081] In this application, the lengths of the cylindrical ring-shaped electrode 27 and the cylindrical conductive rod 28 should be designed according to the size of the adsorption tube, covering at least the entire effective adsorption region of the adsorption tube to form a uniform electric field in the adsorption layer.

[0082] The materials of the cylindrical ring-shaped electrode 27 and the cylindrical conductive rod 28 are selected from one of the three conductors: platinum, copper, or stainless steel. The thickness of the copper electrode can be selected from 1 to 2 mm. Because of its good conductivity, it can provide good electric field uniformity. The platinum electrode can be selected from 0.5 to 1 mm, which is suitable for high-precision and high-stability applications. Since the stainless steel electrode has poor conductivity, it needs to be thickened to 2 to 3 mm to avoid excessive concentration of the electric field on the electrode surface, resulting in too high local electric field intensity, which will affect the electric field uniformity and may cause electrode breakdown or damage.

[0083] The outside of the cylindrical ring-shaped electrode 27 and the cylindrical conductive rod 28 is wrapped with a ceramic insulation layer as a physical barrier to prevent the adsorbent from contacting the electrode and causing a short circuit. The electrical insulation characteristics on the electrode surface ensure the normal distribution of the electric field and the distribution pattern of the electric field intensity between the electrodes.

[0084] The electrical connection of the electric field adsorption component should be connected to an external power supply through a suitable connector (such as a conductive metal wire or a welded connection). A wire hole is reserved on the quartz adsorption tube 21 and the wire is fixed by quartz fusion. A ceramic sleeve is selected as the wire outer shell to avoid melting the wire outer shell during fusion. After fusion, the quartz adsorption tube 21 can ensure airtightness.

[0085] The adjustment of the power supply 14 and the frequency converter 15 can control the intensity and frequency of the electric field, thereby optimizing the adsorption effect of VOCs.

[0086] The generation and adjustment of the electric field are jointly completed by two core components: the power supply 14 and the frequency converter 15. First, the power supply 14 is responsible for providing the required voltage and current output to control the intensity of the electric field. The adjustment of the electric field intensity mainly depends on the output power of the power supply 14. Generally, the electric field intensity can be achieved by adjusting the output voltage of the power supply 14. Secondly, the function of the frequency converter 15 is to adjust the frequency of the electric field. The frequency converter 15 adjusts the alternating speed of the electric field by changing the current frequency input to the electric field generating device.

[0087] Under the action of a variable-frequency electric field, the change in the electric field frequency affects the enrichment effect of VOCs molecules. When the electric field frequency is higher than a certain value, the force between polar molecules and the adsorbent weakens because the rotational motion of their dipole moments cannot keep up with the change of the electric field in time. Non-polar molecules generate instantaneous dipole moments through induced polarization in the electric field, and the instantaneous dipole moments also rotate with the change of the electric field direction. Excessively high electric field frequency will also cause the change of instantaneous dipole moments to fail to keep up with the electric field. This phenomenon can be used to achieve selective adsorption of VOCs molecules. The influence of the frequency of the variable-frequency electric field on the adsorption of VOCs molecules can be judged by the electric field frequency (f) and the relaxation time (τ) of the molecules:

[0088] When f is much lower than 1 / τ, the dipole moments of polar molecules and the instantaneous dipole moments of non-polar molecules can follow the change of the electric field, which can enhance the interaction between molecules and the adsorbent and improve the adsorption capacity; when f is close to or exceeds 1 / τ, the dipole moments of polar molecules and the instantaneous dipole moments of non-polar molecules cannot follow the change of the electric field, which usually reduces the adsorption capacity of molecules and even promotes the desorption of molecules from the adsorbent.

[0089] This application simultaneously uses an electrostatic field and a variable-frequency electric field to enrich VOCs molecules with different polarities.

[0090] Refer to the appendix Figure 4 As shown, under the action of the electrostatic field, the direction of the dipole moment of polar molecules has a tendency to turn towards the external electric field, and the larger the electric field strength, the smaller the angle between the direction of the dipole moment and the direction of the electric field. The change in the arrangement direction of polar molecules can guide them to move towards the surface of the adsorption material in a directional manner, come into contact with the adsorption sites, and enhance the force between the molecules and the adsorption material (such as van der Waals force, hydrogen bond or electrostatic attraction). The electrostatic field can also induce non-polar VOCs molecules to form instantaneous dipole moments, enhance the force between them and the surface of the adsorption material, and improve the adsorption efficiency. Adjusting the electrostatic field strength can effectively promote the adsorption behavior of polar and non-polar VOCs.

[0091] The variable-frequency electric field realizes the selective enrichment of VOCs molecules by adjusting the frequency. When the frequency of the variable-frequency electric field is low, both polar and non-polar molecules can move directionally following the electric field. However, when the electric field frequency is close to or exceeds the relaxation time of the molecules, the dipole moments of the molecules will not be able to change synchronously with the electric field. By adjusting the frequency of the electric field to be close to or exceed the relaxation time of a certain type of molecule, the adsorption of this type of molecule can be reduced, thereby achieving differential enrichment. The variable-frequency electric field adjusts and optimizes the adsorption process, improves the selective adsorption effect of target molecules, enhances the applicability of the system in different environments, reduces the interference of non-target molecules, and enhances the enrichment performance of the system.

[0092] The variable-frequency electric field of the present application has two modes: low frequency and high frequency. Among them, the low-frequency electric field is for the adsorption of non-polar VOCs, and the high-frequency electric field is for the adsorption of polar VOCs.

[0093] Polar molecules have a permanent dipole moment and will quickly adjust their orientation to align with the electric field direction under the action of an external electric field, which results in a relatively short relaxation time for polar molecules. The low-frequency electric field can provide sufficient time for the dipole moment of polar molecules to continuously align with the electric field direction, so polar molecules can stably respond to the electric field. This stable response can promote the affinity between polar VOCs molecules and the adsorbent and improve their adsorption capacity.

[0094] Non-polar molecules themselves do not have a permanent dipole moment, but when exposed to an electric field, they can undergo induced polarization through the displacement of the electron cloud. Since its polarization response is achieved through the deformation of the electron cloud rather than direct dipole deflection, the speed of this change is usually slower than the orientation polarization of polar molecules, resulting in a relatively longer relaxation time for non-polar molecules compared to polar molecules. This means that when the change period of the electric field approaches the relaxation time of polar molecules, the adsorption effect of non-polar molecules will decline first.

[0095] In the present application, the dynamic switching between the electrostatic field and the variable-frequency electric field, as well as the electric field strength and frequency, can be determined according to the gas components to be monitored or the required capture effect. For example, the concentration of VOCs, molecular characteristics (such as polarity, molecular weight, etc.).

[0096] The concentration of VOCs has an important influence on the selection of the electric field type. Different concentrations of VOCs may require different electric field strengths to achieve more effective capture and separation. Under low-concentration conditions, the number of VOCs molecules is small, and the probability of approaching the adsorbent by relying on gas flow transportation is low. Therefore, a higher electric field strength (such as 5 - 10 kV / cm) is required to provide a stronger driving force to promote the directional migration of molecules towards the adsorption surface and improve the capture efficiency, especially for low-polarity or non-polar molecules. On the contrary, under high-concentration conditions, the higher molecular density has enhanced the transportation efficiency towards the adsorbent surface. An overly strong electric field may cause some polar or easily polarizable VOCs molecules to carry a higher charge under the action of the strong electric field, resulting in mutual repulsion between molecules, making it difficult for them to stably adsorb on the surface and even possibly being carried away by the gas flow again, which instead affects the adsorption efficiency. Therefore, a relatively low electric field strength (such as 1 - 5 kV / cm) is usually adopted to optimize the adsorption process. The specific implementation can refer to the following steps:

[0097] Use sensors to monitor the concentration of VOCs in real time. The sensors can be chemical sensors, optical sensors, electrochemical sensors, etc., and appropriate sensors are selected according to specific application requirements. Set a threshold value. When the concentration of VOCs is lower than this value, the system automatically switches to the low-intensity electric field mode; when the concentration is higher, it switches to the high-intensity electric field mode. The selection of the specific threshold value can be determined through experimental data or can be adjusted dynamically. Through the output signal of the sensor, the control system can adjust the electric field type according to the concentration change. For example, digital signal processing (DSP) or a microcontroller (MCU) is used to receive the concentration data in real time and issue commands to adjust the electric field intensity.

[0098] The frequency adjustment of the variable-frequency electric field plays an important role in the capture of different types of VOCs. High-frequency electric fields (>100 kHz) are suitable for capturing polar VOCs, which can provide enough time for the dipole moment of polar molecules to align with the electric field direction, thereby enhancing the adsorption force between the molecules and the adsorption material. Medium- and low-frequency electric fields (<100 kHz) are suitable for weakly polar and non-polar VOCs. Through the action of the alternating electric field, the induced polarization effect of non-polar molecules can be promoted, enhancing their adsorption ability.

[0099] Different types of VOCs have different response abilities to the electric field, which is closely related to molecular structure, dipole moment, and polarization effect. In order to achieve the enrichment of different VOCs, the frequency range can be determined according to these characteristics. The following is the frequency range adjustment corresponding to each type of VOC.

[0100] Polar VOCs (such as alcohols, phenols, acids, etc.) have a significant dipole moment. The low-frequency electric field can provide enough time for the dipole moment of these molecules to align with the electric field direction, thereby enhancing the adsorption effect. However, at low-frequency electric fields, weakly polar and non-polar molecules will also move with the electric field. In order to adsorb only polar VOCs, the electric field frequency should be increased. Frequency range: 100 kHz - 1 MHz.

[0101] Weakly polar VOCs (such as ketones, amines, etc.) have a relatively small dipole moment, but still have a certain polarity. The low-frequency electric field can moderately guide the direction of the dipole moment of these molecules. However, compared with polar VOCs, they are more suitable for enrichment in medium- to high-frequency electric fields. Frequency range: 10 - 100 kHz. In this frequency range, the electric field can slightly affect the dipole moment of weakly polar molecules, making the weakly polar molecules align with the electric field to a certain extent, while not promoting the adsorption of non-polar molecules.

[0102] Non-polar VOCs (such as alkanes, aromatic hydrocarbons, alkenes, etc.) usually lack a dipole moment. The electric field enhances the interaction between the molecules and the adsorption surface through the induced polarization effect. Excessive electric field frequency will weaken the induced polarization effect. Frequency range: 1 - 10 kHz.

[0103] The temperature control component includes a heating wire 22, a semiconductor refrigeration sheet 25, a heat conduction sheath 23, and a radiator 26. The heating wire 22 is wound around the outside of the quartz adsorption tube 21 to provide the required heating function. The heat conduction sheath 23 is composed of a metal sheet with two parallel grooves and a hollow semi-cylindrical metal sheet, aiming to enhance the heat conduction efficiency and enable the heat generated by the heating wire 22 to be more effectively transferred to the adsorbent inside the quartz adsorption tube 21. Both the heating wire 22 and the quartz adsorption tube 21 are placed in the heat conduction sheath 23 to ensure the concentration and uniform distribution of heat. The semiconductor refrigeration sheet 25 is closely attached to the lower part of the heat conduction sheath 23 to lower the temperature of the gas and prevent the adsorption effect from being affected by overheating. The radiator 26 is arranged below the semiconductor refrigeration sheet 25 to play an auxiliary heat dissipation role, ensuring that the refrigeration sheet can work continuously and effectively and maintaining the required low temperature state.

[0104] The quartz adsorption tube 21 is divided into multiple temperature control regions, and the temperature of each region is independently set according to the characteristics of the filler and the condensation characteristics of the target compound. The number of temperature control regions corresponds to the number of filler types, ensuring that the adsorption performance of each filler can exert its maximum efficiency at the most suitable temperature.

[0105] Specifically, the design of the temperature control region follows the following principles:

[0106] Front section region: This region is mainly for the adsorption of non-polar VOCs, and the temperature is set relatively high, generally 0–-5°C. This is to prevent polar molecules from prematurely condensing on the adsorption tube wall due to low temperature before contacting the adsorbent, and at the same time, this temperature range enhances the adsorption ability of the adsorbent to non-polar molecules. The adsorbent usually uses carbon molecular sieve or other materials with strong selectivity for non-polar VOCs.

[0107] Middle section region: The temperature in this region is moderate, generally -5 to -15°C. It can not only effectively adsorb polar VOCs but also capture a certain amount of non-polar VOCs. In this temperature range, polar VOCs can be effectively enriched, and at the same time, non-polar VOCs that were not completely intercepted in the front section can still be adsorbed. The temperature control design in this region ensures a high adsorption efficiency for various VOCs, especially when dealing with mixed gases with complex compositions, and can achieve a good enrichment effect. The adsorption material usually selects activated carbon because of its large specific surface area and good adsorption characteristics, which can provide appropriate selectivity between VOCs with different polarities.

[0108] Rear section area: Used for adsorbing polar VOCs. The temperature in this area is set relatively low, generally -15 to -30 °C, to promote the enrichment of target polar molecules at a lower temperature, enhance the interaction force with the adsorbent surface, and improve the adsorption efficiency. To enhance the selectivity for polar VOCs, functionalized activated carbon or adsorbents containing polar groups are usually used to ensure the preferential capture ability of the adsorption material for polar molecules and reduce the interference of non-polar VOCs.

[0109] The temperature control area is equipped with an independent heating wire 22, a semiconductor refrigeration chip 25, and a heat conduction sheath 23, and the coordinated work of these parts ensures temperature stability. The design of the temperature control component aims to avoid mutual interference between regions by precisely controlling the temperature of each region.

[0110] To avoid mutual temperature interference between the temperature control areas, an independent temperature control circuit, physical isolation design, and sensor feedback control strategy are adopted. The heating wire 22 and the semiconductor refrigeration chip 25 in each temperature control area are equipped with independent control circuits to ensure independent adjustment of their respective heating and refrigeration powers and avoid mutual interference. Physical isolation is achieved between the heat conduction sheaths 23 by using high-efficiency thermal insulation materials such as aluminum silicate fiber to prevent the mutual influence of temperature changes. At the same time, each area is equipped with a temperature sensor 24 to monitor the temperature in real time and precisely adjust the heating and refrigeration processes through feedback signals.

[0111] The temperature sensor 24 uses a high-temperature resistant adhesive to fix the thermocouple on the heating wire 22 to monitor the real-time temperature of the heating wire 22 and avoid delays in the sensor reading the temperature caused by non-direct contact, especially when the heating wire 22 rapidly heats up.

[0112] In the system design of this application, the use of pulsed airflow plays an important role in controlling the contact time between VOCs molecules and the adsorbent. The pulsed airflow helps the VOCs molecules maintain the optimal contact time with the adsorbent surface through periodic airflow changes, thereby ensuring that the directional adsorption effect generated by the electric field can be fully exerted. The pulsed airflow adjusts the contact speed and frequency of the molecules with the adsorbent, which helps to improve the adsorption efficiency of the molecules.

[0113] The pulsed airflow causes fluctuations in the gas flow rate within a short period through periodic changes at specific frequencies and time intervals. These periodic changes precisely regulate the contact time between VOCs molecules and the adsorbent surface, not only avoiding insufficient adsorption caused by too fast flow but also avoiding the condensation of VOCs before contacting the adsorbent due to too slow flow.

[0114] To match the electric field type and the adsorption mechanism of VOCs molecules, the period and flow rate settings of the pulsed airflow need to be optimized according to the molecular characteristics of different VOCs and the frequency of the electric field used to improve the effect during the adsorption process.

[0115] Polar VOCs are suitable for enrichment under high-frequency electric fields (100 kHz to 1 MHz). At this time, the pulse gas flow period should be short (5 to 50 ms), the flow rate should be small (10 to 50 mL / s), and the slower flow rate provides enough time for VOCs molecules to move to the surface of the adsorbent and bind to the adsorbent through dipole-dipole interactions or electrostatic attraction.

[0116] Weakly polar VOCs have a small dipole moment and are suitable for trapping under medium-frequency electric fields (10 kHz to 100 kHz). At this time, the pulse gas flow period can be set to be moderate (50 to 200 ms), and the flow rate is moderate (50 to 150 mL / s), ensuring that the molecules can maintain a polarized state at a higher frequency, while avoiding the condensation of VOCs molecules on the adsorption tube wall or the decrease in adsorption efficiency due to too low a flow rate.

[0117] For non-polar VOCs, since they mainly respond to low-frequency electric fields (1 kHz to 10 kHz) through induced polarization, the pulse gas flow period should be long (200 to 500 ms), and the flow rate should be large (150 to 300 mL / s). Since the polarization response of non-polar molecules is slow, more molecule-surface contacts must be made to enhance adsorption. Therefore, a higher flow rate is adopted to increase the contact opportunity between molecules and the surface of the adsorbent and reduce the condensation effect that may be brought about by a low flow rate.

[0118] Assuming that the electric field frequency has been determined, the gas flow pulse period can be adjusted according to the electric field frequency to ensure that the gas flow period matches the electric field frequency. Each period of the pulse gas flow is greater than one action period of the electric field, so that the VOCs within each pulse period can be effectively regulated by the electric field. During each gas flow pulse period, the contact time between VOCs molecules and the surface of the adsorbent is precisely regulated, and the electric field can also act on the molecules at the same moment, promoting molecular polarization and orientation, increasing the attraction between the molecules and the surface of the adsorption material, and thus enhancing the adsorption effect.

[0119] In one embodiment of the present application, a microcontroller (MCU) or a digital signal processor (DSP) is used to control the electromagnetic pulse valve 5. The control system will adjust the on-off period of the gas flow in real time according to the calculated pulse period to synchronize the gas flow pulse period with the electric field action period. In addition, the flow rate of the gas flow is monitored in real time through a flow sensor, and the microcontroller will adjust the working state of the first pressure controller 7 according to the target flow rate, so as to maintain the stability and flow accuracy of the gas flow.

[0120] Further, the pneumatic six-way valve 9 has six air holes, namely, the first, second, third, fourth, fifth, and sixth air holes. The first air hole is connected to the output end of the first pressure controller 7, the second air hole is connected to the input end of the quantitative loop 10, the third air hole is connected to the detection device, the fourth air hole is connected to the output end of the second pressure controller 8, the fifth air hole is connected to the output end of the quantitative loop 10, and the sixth air hole is connected to the input end of the vacuum pump 11. The pneumatic six-way valve 9 has two gas path modes, namely, mode a and mode b. In state a, the first air hole communicates with the sixth air hole, the second air hole communicates with the third air hole, and the fourth air hole communicates with the fifth air hole. In state b, the first air hole communicates with the second air hole, the third air hole communicates with the fourth air hole, and the fifth air hole communicates with the sixth air hole. In addition, the three-way solenoid valve also has two gas path modes, namely, mode a and mode b. In state a, the A air hole communicates with the E air hole, and the P air hole does not form a gas path with any of the A or E air holes. In state b, the A air hole communicates with the P air hole, and the E air hole does not form a gas path with any of the A or P air holes.

[0121] Refer to the attached Figure 7 As shown, the device further includes an integrated control system, which is used to control the temperature, gas flow rate, electric field strength, frequency and mode of the entire device, as well as the gas path switching and on / off. The integrated control system includes a lower computer 16 and an interface interaction module 17. The first three-way solenoid valve 4, electromagnetic pulse valve 5, VOCs enricher 6, first pressure controller 7, second pressure controller 8, vacuum pump 11, third pressure controller 12, second three-way solenoid valve 13, power supply 14, and frequency converter 15 are respectively electrically connected to the lower computer 16. The integrated control system includes a temperature control system, a flow control system, a gas path switching system, an electric field control system, and an interaction control system.

[0122] The temperature control system includes a heating module for the VOCs enricher 6, which is responsible for controlling the heating rate and the maximum temperature of the heating wire 22 in the VOCs enricher 6, and a refrigeration module for the VOCs enricher 6, which is responsible for controlling the cooling rate and the minimum temperature of the semiconductor refrigeration chip 25 in the VOCs enricher 6.

[0123] The flow control system includes a gas dynamic pressure regulating module, which is responsible for regulating the flow rates of the carrier gas and the sample gas passing through the quartz adsorption tube 21; a pulsed gas flow generation module, which is responsible for controlling the sample gas to enter the quartz adsorption tube in the form of a pulsed gas flow and controlling the pulse period of the gas flow; and an injection pressure regulating module, which is responsible for regulating the pressure of the enriched sample gas when it enters the detection device.

[0124] The gas path switching system includes a sample loading switching module, which is responsible for switching the flow of the carrier gas and the sample gas in the quartz adsorption tube 21, and a gas path state switching module, which is responsible for switching the two gas path states of the pneumatic six-way valve 9.

[0125] The electric field control system includes an electric field intensity adjustment module responsible for controlling the intensity of the electric field generated by the electric field adsorption component; an electric field frequency adjustment module responsible for controlling the frequency of the electric field generated by the electric field adsorption component; and an electric field mode switching module for controlling the switching of the electric field mode generated by the electric field adsorption component between an electrostatic field and a variable-frequency electric field.

[0126] The interaction control system includes an interface interaction module 17 responsible for the display and input of set parameters and real-time parameter transmission to the lower computer 16; and an interaction control module responsible for receiving instructions and converting the instructions into control signals executable by the lower computer 16, thereby realizing the real-time monitoring and adjustment of the system.

[0127] The present invention also includes a method for using a VOCs high-efficiency enrichment device based on electric field guidance, comprising the following steps:

[0128] 1) Heating and purging: First, switch the pneumatic six-way valve 9 to the b state, and the first three-way solenoid valve 4 is also switched to the b state. The system enters the heating mode, with a heating temperature of 300 - 400 °C and a duration of 5 - 10 min. In this mode, the purging gas will flow in from the P air hole of the first three-way solenoid valve 4 and flow through the quartz adsorption tube 21 through the gas path system. The flow rate of the purging gas is 5 - 10 mL / min. The purging gas passing through the quartz adsorption tube 21 will carry the impurities in the adsorption tube and flow out from the VOCs enricher 5. Thereafter, the purging gas will continue to flow along the gas path, pass through the first pressure controller 7, the metering loop 10, the vacuum pump 11, and finally be discharged into the atmosphere. During this process, the impurities in the quartz adsorption tube 21 are effectively removed, preparing for the subsequent cooling process to ensure no residual impurities in the subsequent operations of the system.

[0129] 2) Cooling: Once the heating and purging process is completed, the system will switch to the cooling mode. At this time, the heating module of the VOCs enricher 6 will be turned off, and the refrigeration module will be started. During the cooling process, the purging gas continues to be introduced through the adsorption tube, and the gas flow direction in the system remains unchanged, with a flow rate of 5 - 10 mL / min. As time goes by, the temperature control component in the system starts to function, gradually reducing the temperature of each temperature control area of the quartz adsorption tube 21 to the set target value. At this time, the adsorbent in the quartz adsorption tube 21 is gradually cooled to an ideal state, ensuring that the quartz adsorption tube 21 is in a suitable low-temperature condition before the sampling process starts, so as to maximize the enrichment efficiency of the target substance.

[0130] 3) Sampling: After the cooling process is completed, the system enters the sampling stage, and the sampling duration is 5 - 20 min. First, the first three-way solenoid valve 4 will switch to state a, and at the same time, the electric field adsorption component and the vacuum pump 11 are started. The operation of the vacuum pump 11 guides the sampled gas to flow into the system through the E air hole of the first three-way solenoid valve 4 and flow out from the A air hole. The sampled gas will pass through the quartz adsorption tube 21 to enrich the target substance, continue to flow along the gas path, pass through the first pressure controller 7, the quantitative loop 10 and the vacuum pump 11, and finally be discharged into the atmosphere. During this process, the vacuum pump 11 continuously operates to ensure the stable flow of the sampled gas, effectively adsorbing and enriching the target substance from the sampled gas.

[0131] 4) Injection: After the sampling process is completed, the system will turn off the electric field adsorption component and the vacuum pump 11, and switch the refrigeration mode of the VOCs enricher 6 to the heating mode, heating the temperature of the quartz adsorption tube 21 to above 360 °C. In the heating mode, the target substance in the quartz adsorption tube 21 is gradually released during the heating process. The heating process lasts for 30 - 150 s to ensure that all the target substances in the adsorption tube can be effectively released. Then, the first three-way solenoid valve 4 switches back to state b, and the purge gas flows in through the P air hole of the first three-way solenoid valve 4 and purges through the adsorption tube. The purge time is 20 - 30 s. The purge gas carries the released target substance and flows out of the adsorption tube, passes through the gas path system, including the first pressure controller 7, the quantitative loop 10, the vacuum pump 11, and is finally discharged into the atmosphere. After a period of purging, the pneumatic six-way valve 9 switches back to state a, and the carrier gas flowing out from the outlet end of the second pressure controller 8 sends the target substance in the quantitative loop 10 into the detection device for analysis.

[0132] Using the above VOCs high-efficiency enrichment device, usage method and operating conditions, the following experimental analysis is carried out:

[0133] 1. Comparison of the enrichment effect of electric field frequency on non-polar molecules

[0134] Using a 2L Teflon gas sampling bag, inject a 5 ppb benzene series standard gas (including benzene, toluene, ethylbenzene, m-xylene, o-xylene) into the device to test the influence of different electric field frequencies on the enrichment effect of non-polar substances. During two injections, the electric field frequencies are 2 kHz and 10 kHz respectively. Other conditions are the same, the electric field intensity is 7 kV / cm, the injection time is 900 s, the refrigeration temperatures of each temperature control area of the adsorption tube are 0 °C, -10 °C, -20 °C, the injection pulse period is 300 ms, the injection flow rate is 200 mL / s, and the heating temperature is 360 °C.

[0135] Refer to the appendix Figure 5As shown in the figure, it can be seen that the enrichment effect is better at an electric field frequency of 2 kHz than at 10 kHz. With the assistance of an electric field at a frequency of 2 kHz, the peak heights and peak areas of the five benzene series substances in the detection results are relatively large. This shows that a low-frequency electric field is suitable for non-polar substances such as benzene series substances.

[0136] 2. On-site Application and Precision Verification of the Device

[0137] To verify the feasibility of the device for detecting on-site samples, 2 L of Teflon gas sampling bags were used to collect ambient air samples in a petrochemical park and sent back to the laboratory for analysis. In the laboratory, the device was used as the front injection system of a gas chromatography-mass spectrometer. The parameters of the high-efficiency VOCs enrichment device were set as follows: electric field strength 8 kV / cm, electric field frequency 2.3 kHz, injection time 600 s, the refrigeration temperatures of each temperature control area of the adsorption tube were -2 °C, -11 °C, and -23 °C respectively, injection pulse period 330 ms, injection flow rate 260 mL / s, and heating temperature 360 °C. Then, the electric field in the high-efficiency VOCs enrichment device was turned off and injection was carried out again.

[0138] Refer to the appendix Figure 6 As shown, the enrichment effects of the device with the electric field on and off were compared. When the electric field of the device was on, the peak areas and peak heights of non-polar substances such as hexamethyldisiloxane, benzene, toluene, m-xylene, and p-xylene all increased significantly. The detection results under the two experimental conditions are shown in the following table.

[0139] Table 1 Influence of the Electric Field Switch in the High-Efficiency VOCs Enrichment Device on the Enrichment Effect

[0140]

[0141]

[0142] The device was combined with a portable gas chromatography-photoionization detector to detect the ambient air at the nitrochlorobenzene production device in the petrochemical park. Five parallel tests were carried out on the air sample, and the test results of the main substances benzene and chlorobenzene in the sample are shown in the following table.

[0143] Table 2 Results of Detecting On-Site Samples by the High-Efficiency VOCs Enrichment Device

[0144]

[0145] The test results show that the device and the supporting usage method can be used in on-site detection, and the precision of the detection results can also meet the usage requirements.

[0146] Although embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. An efficient VOCs enrichment device based on electric field guidance, characterized in that: It includes a pre-enrichment component, which is used for pre-treating and enriching low-concentration VOCs in the atmosphere so that the VOCs concentration can reach the detection limit of the detection device; The pre-enrichment component includes an enrichment gas path, a sampling gas path and a driving gas path; The enrichment gas path is used for filtering and drying the sample gas and enriching the target substances in the sample gas. The enrichment gas path includes a pneumatic six-way valve (9), a quantitative loop (10), a vacuum pump (11), and a particulate filter (2), a Nafion gas drying tube (3), a first three-way solenoid valve (4), an electromagnetic pulse valve (5), a VOCs enricher (6), and a first pressure controller (7) connected in sequence. The pneumatic six-way valve (9) is connected to the outlet end of the first pressure controller (7), the inlet and outlet ends of the quantitative loop (10), and the inlet end of the vacuum pump (11); The sampling gas path includes a nitrogen supply end (1) and a second pressure controller (8). The nitrogen supply end (1), the second pressure controller (8), and the pneumatic six-way valve (9) are connected in sequence. The pneumatic six-way valve (9) controls the gas path mode to allow the carrier gas to flow through the enrichment gas path and send the enriched target VOCs substance into the detection device; The driving gas path includes a third pressure controller (12) and a second three-way solenoid valve (13) connected in sequence. The inlet end of the third pressure controller (12) is connected to the nitrogen supply end (1), and the outlet end of the second three-way solenoid valve (13) is connected to the driving gas inlet end of the pneumatic six-way valve (9).

2. The high-efficiency VOCs enrichment device based on electric field guidance according to claim 1, characterized in that: The VOCs enricher (6) includes a cryogenic adsorption component, an electric field adsorption component, and a temperature control component; The cryogenic adsorption component includes a quartz adsorption tube (21) filled with an adsorbent and a straight-through adapter (20) connected to both ends of the quartz adsorption tube (21). The straight-through adapter (20) is used to connect the quartz adsorption tube (21) with the electromagnetic pulse valve (5) and the first pressure controller (7). A fluororubber gasket seal (18) is installed inside the passage of the straight-through adapter (20) connecting the quartz adsorption tube (21); The electric field adsorption component can perform dynamic electric field adjustment. By dynamically adjusting the electric field strength and frequency, VOCs molecules with different polarities respond to the electric field in different ways, thereby achieving selective capture. The electric field adsorption component includes a cylindrical ring electrode (27) and a cylindrical conductive rod (28). The cylindrical ring electrode (27) is closely attached to the inner wall of the quartz adsorption tube (21), and the cylindrical conductive rod (28) is located at the center of the adsorbent layer; The temperature control component includes an electric heating wire (22), a semiconductor refrigeration sheet (25), a heat conduction sheath (23), and a radiator (26). The electric heating wire (22) is wound around the outer side of the quartz adsorption tube (21). The heat conduction sheath (23) is composed of a metal sheet with two parallel grooves and a hollow semi-cylindrical metal sheet. The electric heating wire (22) and the quartz adsorption tube (21) are placed in the heat conduction sheath (23). The semiconductor refrigeration sheet (25) is closely attached to the lower part of the heat conduction sheath (23), and the radiator (26) is arranged below the semiconductor refrigeration sheet (21).

3. The high-efficiency VOCs enrichment device based on electric field guidance according to claim 2, characterized in that: Optimize the electric field frequency for different types of VOCs; a high-frequency electric field (>100 kHz) is used to selectively adsorb polar VOCs molecules; a medium-low frequency electric field (<100 kHz) is used to selectively adsorb weakly polar and non-polar VOCs; By real-time monitoring of the VOCs concentration, the control system can dynamically adjust the electric field intensity according to the sensor feedback. A higher-intensity electric field (5 - 10 kV / cm) is used in a low-concentration VOCs environment, while a lower-intensity electric field (1 - 5 kV / cm) is used in a high-concentration VOCs environment.

4. An efficient VOCs enrichment device based on electric field guidance according to claim 2, characterized in that: The packing of the adsorbent in the quartz adsorption tube (21) is divided into a front section, a middle section, and a rear section. The front section is filled with non-polar VOCs adsorption packing, the middle section is filled with transitional adsorption packing that has an adsorption effect on both polar and non-polar VOCs, and the rear section is filled with polar VOCs adsorption packing.

5. The highly efficient VOCs enrichment device based on electric field guidance according to claim 2, wherein: The quartz adsorption tube (21) is divided into multiple temperature control regions, and the temperature of each region is independently set according to the characteristics of the packing and the condensation characteristics of the target compound. The number of temperature control regions corresponds to the number of packing types; The front section region is used to adsorb non-polar VOCs, and the temperature is set relatively high, at 0 to -5 °C; the middle section region has a moderate temperature, at -5 to -15 °C; the rear section region is used to adsorb polar VOCs, and the temperature is set relatively low, at -15 to -30 °C.

6. The high-efficiency VOCs enrichment device based on electric field guidance according to claim 2, wherein: The first pressure controller (7) cooperates with the electromagnetic pulse valve (5) to act on the electric field adsorption component, and uses pulsed air flow to control the contact time between VOCs molecules and the adsorbent.

7. The highly efficient VOCs enrichment device based on electric field guidance according to claim 1, wherein: The pneumatic six-way valve (9) has six air holes. The first air hole is connected to the output end of the first pressure controller (7), the second air hole is connected to the input end of the quantitative loop (10), the third air hole is connected to the detection device, the fourth air hole is connected to the output end of the second pressure controller (8), the fifth air hole is connected to the output end of the quantitative loop (10), and the sixth air hole is connected to the input end of the vacuum pump (11); The pneumatic six-way valve (9) has two gas path modes, a and b; When the pneumatic six-way valve (9) is in the a state, the first air hole is communicated with the sixth air hole, the second air hole is communicated with the third air hole, and the fourth air hole is communicated with the fifth air hole; When the pneumatic six-way valve (9) is in the b state, the first air hole is communicated with the second air hole, the third air hole is communicated with the fourth air hole, and the fifth air hole is communicated with the sixth air hole; The first three-way solenoid valve (4) and the second three-way solenoid valve (13) have two gas path modes, a and b; When the first three-way solenoid valve (4) and the second three-way solenoid valve (13) are in state a, the A and E air holes are communicated, and the P air hole does not form an air path with any of the A or E air holes; When the first three-way solenoid valve (4) and the second three-way solenoid valve (13) are in state b, the A and P air holes are communicated, and the E air hole does not form an air path with any of the A or P air holes.

8. A method for using an efficient VOCs enrichment device guided by an electric field, which is used for sample injection in the cryogenic concentration and thermal desorption of VOCs gas. This method for using adopts the efficient VOCs enrichment device described in any one of claims 1-7, and is characterized in that: The usage method includes the following steps: Step 1: Heating and purging. Switch the pneumatic six-way valve (9) to state b, switch the first three-way solenoid valve (4) to state b, and the VOCs enricher (6) enters the heating mode. The purging gas flows in from the P air hole of the first three-way solenoid valve (4) and flows out from the A air hole of the first three-way solenoid valve (4). The purging gas sequentially passes through the quartz adsorption tube (21), the first pressure controller (7), the quantitative loop (10), the vacuum pump (11), and finally the purging gas and the impurity gas in the gas path system are discharged into the atmosphere from the output port of the vacuum pump (11); Step 2: Cooling. Switch the heating mode of the VOCs enricher (6) to the refrigeration mode, and continuously introduce the purging gas until the temperature control regions of the quartz adsorption tube (21) drop to the target temperature; Step 3: Sampling. Switch the first three-way solenoid valve (4) to state a, start the electric field adsorption component and the vacuum pump (11). The sample gas flows in from the E air hole of the first three-way solenoid valve (4) and flows out from the A air hole. The sample gas sequentially passes through the electromagnetic pulse valve (5), the quartz adsorption tube (21), the first pressure controller (7), the quantitative loop (10), the vacuum pump (11), and finally is discharged into the atmosphere from the output port of the vacuum pump (11); Step 4: Injection. Close the electric field adsorption component and the vacuum pump (11), switch the refrigeration mode of the VOCs enricher (6) to the heating mode. After a period of time, switch the first three-way solenoid valve (4) to state b. The purging gas flows in from the P air hole of the first three-way solenoid valve (4) and flows out from the A air hole. After purging for a period of time, switch the pneumatic six-way valve (9) to state a.

9. The usage method of an efficient VOCs enrichment device based on electric field guidance according to claim 8, characterized in that: In step 1, during heating and purging, the flow rate of the purging gas is 5 - 10 mL / min, the heating temperature is 300 - 400 °C, and the duration is 5 - 10 min; In step 2, during cooling, the flow rate of the purging gas is 5 - 10 mL / min; In step 3, the sampling duration is 5 - 20 min; In step 4, during injection, heat the temperature to above 360 °C and maintain it for 30 - 150 s before purging, and the purging time is 20 - 30 s.

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