A carbon dioxide concentration measuring device and method based on microwave sensing

Abstract

The present invention provides a carbon dioxide concentration measuring device and method based on microwave sensing. By using a liquid organic amine carbon dioxide absorbent to replace the solid state gas sensitive material, the influence of humidity on detection can be avoided, the regeneration process of the gas sensitive material by heating or chemical treatment can be eliminated, and there is no need to replace the gas sensitive material coated on the microwave sensor, which can be recycled. In addition, by circulating the liquid organic amine in the system multiple times to react with carbon dioxide, the detection limit of the carbon dioxide measuring device can reach the ppm level.

Description

Technical Field

[0001] The present invention belongs to the field of carbon dioxide concentration measurement, and in particular relates to a device and method for measuring carbon dioxide concentration based on microwave sensing. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] CO2 is one of the main greenhouse gases in the atmosphere. The increase in its concentration will lead to global warming, which will in turn cause various environmental problems. Detecting CO2 concentration is of great significance in many aspects such as environmental protection, health and safety, industrial production, and agricultural development.

[0004] At present, the commonly used CO2 gas detection technologies include infrared absorption type, electrochemical type, thermal conduction type, etc. Infrared absorption type CO2 sensor detects CO2 concentration by using the absorption of infrared light of a specific wavelength by CO2 molecules. Its disadvantages are that changes in temperature and humidity will interfere with the transmission and absorption of infrared light, resulting in measurement errors; it will be affected by light source interference; and it is usually more expensive than other types of sensors. Electrochemical type CO2 sensor is based on the electrochemical reaction of CO2 molecules on the electrode, causing a change in potential difference, which is converted into an electrical signal related to CO2 concentration. Its disadvantage is that it is affected by environmental conditions, and changes in temperature, humidity and air pressure affect its accuracy and stability; the sensing element usually has a certain service life, and its performance will gradually decrease over time. Thermal conduction type CO2 sensor uses the fact that gas will take away the heat of the heating element, measures the temperature change to determine the thermal conductivity of the gas, and thus infers the concentration of CO2. Its disadvantages are that the heating element needs to consume energy, resulting in high power consumption; CO2 has a low thermal conductivity, so the response speed is slow; the result is greatly affected by the ambient temperature.

[0005] As a new type of sensing technology, microwave gas sensors have the advantages of strong adaptability, high precision, portability, and easy integration, and can effectively make up for the limitations of traditional sensors. Microwave gas sensors mainly allow the gas to be measured to flow through the surface of the gas-sensitive material loaded on the sensor. After the gas molecules are adsorbed by the gas-sensitive material, the dielectric constant of the gas-sensitive material changes, thereby changing the resonance frequency of the microwave resonator. The change in the resonance frequency is positively correlated with the concentration of the gas to be measured by the gas-sensitive material. However, current microwave sensors are easily affected by environmental factors. In particular, changes in temperature and humidity may interfere with the accuracy of measurement results. In addition, after the gas adsorption of the sensor gas-sensitive material reaches saturation, the sensor needs to be regenerated for reuse, which involves additional steps such as heating or chemical treatment to remove the adsorbed gas, and these regeneration steps increase the complexity of operation. In terms of repeatability, current microwave sensors also have certain limitations. After being used for a period of time, it is usually necessary to replace the gas-sensitive material of the sensor to restore its initial state. Summary of the Invention

[0006] To solve the above problems, the present invention proposes a device and method for measuring carbon dioxide concentration based on microwave sensing. By using a liquid organic amine carbon dioxide absorbent to replace the above-mentioned solid gas-sensitive material, the influence of humidity on detection can be avoided, the regeneration process of the gas-sensitive material by heating or chemical treatment can be eliminated, and it is not necessary to replace the gas-sensitive material coated on the microwave sensor, and it can be recycled.

[0007] According to some embodiments, the present invention adopts the following technical solutions:

[0008] A device for measuring carbon dioxide concentration based on microwave sensing, comprising a carbon dioxide supply mechanism, a first microfluidic chip, a second microfluidic chip, a microwave microfluidic chip, a vector network analysis unit, a container, and a pump, wherein:

[0009] The carbon dioxide supply mechanism is used to supply the carbon dioxide gas to be detected therein to the first microfluidic chip through a first pipeline;

[0010] The first pipeline is connected to a second pipeline. The second pipeline is arranged at the front end of the inlet of the first microfluidic chip and is connected to the pump. The pump is used to send the organic amine solution contained in the container into the second pipeline;

[0011] In the first microfluidic chip, the organic amine solution reacts with carbon dioxide. The solution after the reaction and the unreacted gas flow into the second microfluidic chip. The second microfluidic chip is connected to the microwave microfluidic chip. The microwave microfluidic chip is used to receive the solution flowing out of the second microfluidic chip and transport it back to the container through a pipeline;

[0012] The vector network analysis unit is used to test the solution in the microwave microfluidic chip, and determine the concentration of carbon dioxide according to the change of the scattering parameters obtained from the test.

[0013] As an alternative embodiment, the microwave microfluidic chip is arranged in a temperature control system, and the temperature control system controls the temperature of the microwave microfluidic chip at a set temperature.

[0014] As an alternative embodiment, the microwave microfluidic chip includes two layers, the lower layer is a microwave resonator, and the upper layer is PDMS with channels.

[0015] As an alternative embodiment, the first microfluidic chip includes two layers, the lower layer is glass, and the upper layer is PDMS with channels, forming upper and lower cavities.

[0016] As an alternative embodiment, the second microfluidic chip includes three layers, the bottom layer is glass, the middle layer is PDMS with channels, forming upper and lower cavities, and the upper layer is a gas diffusion layer.

[0017] As a further aspect, the diffusion layer is a carbon paper diffusion layer.

[0018] As a further aspect, the unreacted gas in the second microfluidic chip is released from the diffusion layer.

[0019] As a further aspect, the channels are all microfluidic channels with a plurality of bending portions.

[0020] As an alternative embodiment, the pump is a peristaltic pump.

[0021] As an alternative embodiment, the carbon dioxide supply mechanism includes a gas cylinder and a pressure pump. The gas cylinder is used to store carbon dioxide gas, and the pressure pump is used to supply the stored carbon dioxide gas to the first pipeline.

[0022] A gas concentration measuring device based on microwave sensing, comprising a gas supply mechanism, a first microfluidic chip, a second microfluidic chip, a microwave microfluidic chip, a vector network analysis unit, a container and a pump, wherein:

[0023] The gas supply mechanism is used to supply the gas to be detected therein to the first microfluidic chip through the first pipeline;

[0024] The first pipeline is connected to a second pipeline. The second pipeline is arranged at the front end of the inlet of the first microfluidic chip and is connected to the pump. The pump is used to send the solution contained in the container into the second pipeline;

[0025] In the first microfluidic chip, a reaction occurs between the solution and the gas. After the reaction, the solution and the unreacted gas flow into the second microfluidic chip. The second microfluidic chip is connected to a microwave microfluidic chip, which is used to receive the solution flowing out of the second microfluidic chip and transport it back to the container through a pipeline.

[0026] The vector network analysis unit is used to test the solution in the microwave microfluidic chip and determine the concentration of the target gas according to the change in the scattering parameters obtained from the test.

[0027] The working method based on the above device includes the following steps:

[0028] The carbon dioxide gas to be tested enters the first microfluidic chip through the carbon dioxide supply mechanism. At the same time, the organic amine solution in the container is pumped into the first microfluidic chip and reacts with the carbon dioxide gas. After the reaction, the solution and the unreacted gas flow through the second microfluidic chip, and carbon dioxide bubbles are released from the carbon paper diffusion layer.

[0029] The solution flows into the microwave microfluidic chip. According to the different dielectric constants of the solution after the reaction of CO2 with different concentrations of organic amine, the vector network analysis unit tests the change in the scattering parameters. The scattering parameters correspond one-to-one with the concentration of carbon dioxide, so as to obtain the carbon dioxide concentration.

[0030] The organic amine solution that has reacted with the carbon dioxide gas returns to the container and is pumped to the first microfluidic chip again to react with the carbon dioxide gas, and the cycle continues.

[0031] As a further step, for the measurement result during cyclic measurement, when the vector network analysis unit processes the measurement data, it determines the concentration of carbon dioxide according to the number of cycles and the change value of the microwave signal.

[0032] As a further step, when detecting the carbon dioxide gas concentration in the environment, the air in the environment is pumped into the first microfluidic chip through a vacuum pump or a micro peristaltic pump.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] 1. The reaction between carbon dioxide and the organic amine absorbent in the microchannel is beneficial to the mass transfer of CO2 in the organic amine solution, enabling CO2 with extremely low concentration to fully contact and react completely with the organic amine, thereby reducing the detection limit.

[0035] 2. One end of the peristaltic pump is connected to the system inlet to pump the organic amine into the system to react with CO2, and the other end is connected to the system outlet to pump the reacted organic amine back into the system to react with CO2 again, thereby further reducing the CO2 detection limit and achieving the detection of several ppm of CO2.

[0036] 3. The reacted organic amine solution and the excess gas pass through a device equipped with a gas diffusion layer, which allows the excess gas to escape, thereby avoiding the influence of gas flow and pressure on the subsequent microwave detection.

[0037] 4. The peristaltic pump for organic amine transfer is not directly connected to the detection module, thus avoiding the influence of the vibration caused by the pump on the microwave detection.

[0038] 5. By replacing different absorption solutions and gases, the device of the present invention can also be used to detect other gases.

[0039] To make the above objects, features, and advantages of the present invention more apparent and understandable, the following specific preferred embodiments are given, in conjunction with the accompanying drawings, and are described in detail as follows. Description of the Drawings

[0040] The specification drawings forming a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments and descriptions thereof of the present invention are used to explain the present invention and do not constitute an improper limitation of the present invention.

[0041] Figure 1 It is a schematic diagram of the device structure of this embodiment. Detailed Description of the Invention

[0042] The present invention will be further described below in conjunction with the drawings and embodiments.

[0043] It should be noted that the following detailed descriptions are all illustrative and are intended to provide a further description of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0044] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0045] Without conflict, the embodiments in this application and the features in the embodiments can be combined with each other.

[0046] Embodiment 1

[0047] A circulation device for detecting the CO2 concentration in a gas cylinder or the environment, as Figure 1 shown, includes a carbon dioxide supply mechanism 1, a first microfluidic chip 2, a second microfluidic chip 3, a microwave microfluidic chip 4, a vector network analysis unit 6, a container 7, and a peristaltic pump 8, wherein:

[0048] The carbon dioxide supply mechanism 1 is used to supply the carbon dioxide gas to be detected therein to the first microfluidic chip 2 through the first pipeline;

[0049] The first pipeline is communicated with a second pipeline. The second pipeline is arranged at the front end of the inlet of the first microfluidic chip 2 and is connected to a peristaltic pump 8. The peristaltic pump 8 is used to send the organic amine solution (such as aqueous ethanolamine solution) contained in the container 7 into the second pipeline;

[0050] In the first microfluidic chip 2, the organic amine solution reacts with carbon dioxide. The solution after the reaction and the unreacted gas flow into the second microfluidic chip 3. The second microfluidic chip 3 is connected to a microwave microfluidic chip 4. The microwave microfluidic chip 4 is used to receive the solution flowing out of the second microfluidic chip 3 and convey it back to the container 7 through a pipeline;

[0051] The vector network analysis unit 6, which is a vector network analyzer or nanoVNA or liteVNA, is used to test the solution in the microwave microfluidic chip 4 and determine the concentration of carbon dioxide according to the change of the scattering parameters obtained by the test.

[0052] In this embodiment, the microwave microfluidic chip 4 is arranged in the temperature control system 5. The temperature control system 5 controls the temperature of the microwave microfluidic chip 4 at a set temperature. The temperature control system 5 has or is connected to a temperature controller.

[0053] In this embodiment, the microwave microfluidic chip 4 includes two layers. The lower layer is a microwave resonator, and the upper layer is PDMS with channels.

[0054] The first microfluidic chip 2 includes two layers. The lower layer is glass, and the upper layer is PDMS with channels, forming upper and lower cavities.

[0055] The second microfluidic chip 3 includes three layers. The bottom layer is glass, the middle layer is PDMS with channels, forming upper and lower cavities, and the upper layer is a carbon paper diffusion layer or other gas diffusion layer materials.

[0056] The unreacted gas in the second microfluidic chip is released from the diffusion layer.

[0057] As Figure 1 shown, the channels are all microfluidic channels with multiple bending parts.

[0058] When the above device detects the CO2 concentration in the gas cylinder, the gas enters the first microfluidic chip 2 through the pressure pump; when detecting the CO2 concentration in the environment, the air in the environment is pumped into the first microfluidic chip 2 by the vacuum pump or the micro peristaltic pump. At the same time, the organic amine solution in the container 7 is pumped into the first microfluidic chip 2 by the peristaltic pump 8 and reacts with the CO2 bubbles. The solution after the reaction and the unreacted gas flow through the second microfluidic chip 3, and the CO2 bubbles are released from the carbon paper diffusion layer. Subsequently, the solution flows into the microwave microfluidic chip 4. According to the different dielectric constants of the solution after the reaction of CO2 with different concentrations and the organic amine, the vector network analyzer 6 is used to test the change of the scattering parameters in the circuit. The scattering parameters correspond one by one to the concentration of CO2, so as to obtain the CO2 concentration. The temperature control system 5 controls the temperature of the microwave microfluidic chip 4 at a stable temperature to ensure that the microwave detection process is not affected by temperature changes. Finally, the organic amine solution after reacting with CO2 returns to the container 7 and is pumped to the first microfluidic chip 2 again by the peristaltic pump 8 to react with CO2, and the cycle continues in turn.

[0059] A certain amount of organic amine solution can react with CO2 multiple times. According to the change amount of the VNA microwave signal when cycling a certain number of times, the concentration of CO2 is determined. When the CO2 concentration is very low, the organic amine needs to be cycled multiple times to produce an observable change in the VNA microwave signal. However, this recycling mechanism of the organic amine enables the detection limit of this CO2 detection system to reach several or even 1 ppm.

[0060] In this embodiment, according to the different dielectric constants after the reaction of CO2 with different concentrations and the gas-sensitive material. The vector network analyzer emits microwaves in a certain frequency range to the microwave gas sensor. When the dielectric constant of the gas-sensitive material changes, the scattering parameters of the microwave gas sensor also change.

[0061] A series of experiments can be carried out in advance, including using the vector network analyzer to test the scattering parameters in the circuit at different CO2 concentrations and establishing the corresponding relationship between the scattering parameters and the CO2 concentration.

[0062] When adding CO2 with an unknown concentration, by observing the value of the scattering parameter on the vector network analyzer, the concentration of CO2 can be determined.

[0063] Embodiment 2

[0064] A gas concentration measuring device based on microwave detection, including a gas supply mechanism, a first microfluidic chip, a second microfluidic chip, a microwave microfluidic chip, a vector network analysis unit, a container and a pump, wherein:

[0065] The gas supply mechanism is used to supply the gas to be detected therein to the first microfluidic chip through the first pipeline;

[0066] The first pipeline is connected to a second pipeline. The second pipeline is arranged at the front end of the inlet of the first microfluidic chip and is connected to a pump. The pump is used to send the solution contained in the container into the second pipeline;

[0067] In the first microfluidic chip, the solution reacts with the gas. After the reaction, the solution and the unreacted gas flow into the second microfluidic chip. The second microfluidic chip is connected to a microwave microfluidic chip. The microwave microfluidic chip is used to receive the solution flowing out of the second microfluidic chip and transport it back to the container through a pipeline;

[0068] The vector network analysis unit is used to test the solution in the microwave microfluidic chip and determine the concentration of the target gas according to the change of the scattering parameters obtained from the test.

[0069] The solution and the target gas in the container of the device can react or be adapted to each other.

[0070] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made by those skilled in the art without creative labor within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A carbon dioxide concentration measuring device based on microwave sensing, characterized in that, It includes a carbon dioxide supply mechanism, a first microfluidic chip, a second microfluidic chip, a microwave microfluidic chip, a vector network analysis unit, a container and a pump, where: The carbon dioxide supply mechanism is used to supply the carbon dioxide gas to be detected therein to the first microfluidic chip through a first pipeline; The first pipeline is connected to a second pipeline. The second pipeline is arranged at the front end of the inlet of the first microfluidic chip and is connected to the pump. The pump is used to send the organic amine solution contained in the container into the second pipeline; When the carbon dioxide gas to be tested enters the first microfluidic chip through the carbon dioxide supply mechanism, the organic amine solution in the container is pumped into the first microfluidic chip and reacts with the carbon dioxide gas. The solution after the reaction and the unreacted gas flow through the second microfluidic chip, and carbon dioxide bubbles are released from the carbon paper diffusion layer; Inside the first microfluidic chip, the organic amine solution reacts with carbon dioxide. The solution after the reaction and the unreacted gas flow into the second microfluidic chip. The second microfluidic chip is connected to the microwave microfluidic chip. The microwave microfluidic chip is used to receive the solution flowing out of the second microfluidic chip and transport it back to the container through a pipeline; When the solution flows into the microwave microfluidic chip, according to the different dielectric constants of the solution after the reaction of CO2 with different concentrations of organic amine, the vector network analysis unit is used to test the change of the scattering parameter. The scattering parameter corresponds to the concentration of carbon dioxide one by one, so as to obtain the carbon dioxide concentration; The vector network analysis unit is used to test the solution in the microwave microfluidic chip and determine the concentration of carbon dioxide according to the change of the scattering parameter obtained by the test; The organic amine solution after reacting with the carbon dioxide gas returns to the container and is pumped to the first microfluidic chip again to react with the carbon dioxide gas, and the cycle continues.

2. The carbon dioxide concentration measuring device based on microwave sensing according to claim 1, characterized in that, The microwave microfluidic chip is arranged in a temperature control system, and the temperature control system controls the temperature of the microwave microfluidic chip at a set temperature; 3. The carbon dioxide concentration measuring device based on microwave sensing according to claim 1, characterized in that, The microwave microfluidic chip includes two layers. The lower layer is a microwave resonator, and the upper layer is PDMS with channels; The first microfluidic chip includes two layers. The lower layer is glass, and the upper layer is PDMS with channels, forming upper and lower cavities; The second microfluidic chip includes three layers. The bottom layer is glass, the middle layer is PDMS with channels, forming upper and lower cavities, and the upper layer is a diffusion layer; 4. The carbon dioxide concentration measurement device based on microwave sensing according to claim 3, characterized in that, The diffusion layer is a carbon paper diffusion layer; The unreacted gas in the second microfluidic chip is released from the diffusion layer; 5. The carbon dioxide concentration measuring device based on microwave sensing according to claim 4, characterized in that, The channels are all microfluidic channels with multiple bending parts; 6. The carbon dioxide concentration measuring device based on microwave sensing according to claim 1, characterized in that, The carbon dioxide supply mechanism includes a gas cylinder and a pressure pump. The gas cylinder is used to store carbon dioxide gas, and the pressure pump is used to supply the stored carbon dioxide gas to the first pipeline; 7. The carbon dioxide concentration measuring device based on microwave sensing according to claim 1, characterized in that, If it is the measurement result during cyclic measurement, when the vector network analysis unit processes the measurement data, it determines the concentration of carbon dioxide according to the number of cycles and the numerical value of the change of the microwave signal; 8. The carbon dioxide concentration measuring device based on microwave sensing according to claim 1, characterized in that, When detecting the concentration of carbon dioxide gas in the environment, the air in the environment is pumped into the first microfluidic chip by a vacuum pump or a micro peristaltic pump.

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