Device and method for preparing filter membrane substrate particle standard substance

Abstract

The present invention provides a device and method for preparing a standard substance for filter-based particulate matter, belonging to the technical field of standard substance measurement and detection. The device comprises an aerosol generator, wherein the air outlet of the aerosol generator is connected to the air inlet of a dryer, the air outlet of the dryer is connected to the air inlet of a two-stage mixer, the air outlet of the two-stage mixer is connected to the air inlet of a multi-stage aerosol diverter, the air outlet of the multi-stage aerosol diverter is connected to the air inlet of a filter membrane parallel sampler, the air outlet of the filter membrane parallel sampler is connected to the air inlet of a leak detector, the leak detector is further connected to a vacuum pump, and the aerosol generator, the two-stage mixer, the multi-stage aerosol diverter, the filter membrane parallel sampler, the leak detector, and the vacuum pump are all electrically connected to a computer control unit. The present invention can achieve rapid batch preparation of standard substances for filter-based particulate matter, the amount of particulate matter deposited on the filter membrane surface and the chemical composition can be controlled, and the mass of the loaded particulate matter has good consistency.

Description

Technical Field

[0001] The present invention relates to the technical field of standard substance metrology and detection, and in particular to a device and method for preparing a filter membrane substrate particle standard substance. Background Art

[0002] Monitoring atmospheric particulate matter pollution is a key task in environmental monitoring. Particulate matter composition measurement is a key foundation for pollutant source apportionment and causal analysis. Various manual and automated methods for component measurement, such as manual measurement of water-soluble ions, organic carbon / elemental carbon, and metal elements, and online measurement of organic carbon / elemental carbon and elemental analysis, all utilize membrane filters to collect and analyze atmospheric particulate matter. Particulate matter reference materials based on membrane filters are essential for instrument calibration and full-process verification.

[0003] Currently, particulate matter reference materials for filter membranes are primarily prepared by sampling environmental samples, such as SRM 2783 and RM 8785 developed by the U.S. National Institute of Standards and Technology (NIST) and ERM-CZ110 developed by the European Union. These filter membrane reference materials require lengthy sampling times and cannot guarantee similar sample amounts and chemical compositions between any two filter membranes. Each filter membrane must be individually calibrated, and the values ​​cannot be actively controlled. Furthermore, the sample volume carried by a single filter membrane is extremely small, resulting in significant uncertainty in weighing and chemical analysis results. Summary of the Invention

[0004] The purpose of the present invention is to provide a device and method for preparing filter membrane substrate particulate matter standard substances, which can realize the rapid batch preparation of filter membrane substrate particulate matter standard substances, the particle deposition amount and chemical composition on the filter membrane surface can be controlled, and the quality of the loaded particulate matter has good consistency.

[0005] To achieve the above-mentioned objectives, the present invention provides a device and method for preparing a filter membrane substrate particulate matter standard substance, comprising an aerosol generator, wherein the air outlet of the aerosol generator is connected to the air inlet of a dryer, the air outlet of the dryer is connected to the air inlet of a two-stage mixer, the air outlet of the two-stage mixer is connected to the air inlet of a multi-stage aerosol diverter, the air outlet of the multi-stage aerosol diverter is connected to the air inlet of a filter membrane parallel sampler, the air outlet of the filter membrane parallel sampler is connected to the air inlet of a leak detector, the leak detector is also connected to a vacuum pump, and the aerosol generator, two-stage mixer, multi-stage aerosol diverter, filter membrane parallel sampler, leak detector and vacuum pump are all electrically connected to a computer control unit.

[0006] Preferably, the two-stage mixer includes a first-stage mixer and a second-stage mixer, the air inlet of the first-stage mixer is connected to the air outlet of the dryer, the air inlet of the second-stage mixer is connected to the air outlet of the first-stage mixer, and the first-stage mixer is also connected to an electrostatic neutralizer.

[0007] Preferably, the outlet of the multi-stage aerosol diverter is divided into multiple paths, each of which is connected to a filter membrane parallel sampler.

[0008] Preferably, the aerosol splitter adopts a rotationally symmetrical structure to split one aerosol sample into multiple paths.

[0009] The present invention also provides a method for preparing a filter membrane substrate particle standard substance, comprising the following steps:

[0010] S1, aerosol generator generates aerosol to dryer;

[0011] S2, a dryer removes moisture from the aerosol to obtain a dried aerosol;

[0012] S3, the dried aerosol enters the first-stage mixer and mixes with the charged ion wind generated by the static neutralizer to remove the surface charge of the particles in the dried aerosol, thus obtaining an aerosol with static electricity removed;

[0013] S4, the aerosol after static electricity removal enters the second-stage mixer and is mixed with clean air to obtain an aerosol for preparing a standard substance;

[0014] S5. The aerosol used to prepare the standard substance enters the aerosol splitter to achieve aerosol diversion;

[0015] S6, the split aerosols enter different filter membrane parallel samplers respectively;

[0016] S7. The gas outlet of the membrane parallel sampler is connected to a leakage detector, and the measurement result of the leakage detector is transmitted to the computer control unit to determine whether the membrane parallel sampler is leaking.

[0017] The outlet of the leak detector is connected to a vacuum pump. When preparing standard substances, the computer control unit starts the vacuum pump to extract air and generate negative pressure, thereby driving the aerosol to pass through the filter membrane installed in the parallel sampler. The particles in the aerosol are retained by the filter membrane, and the gas is discharged through the vacuum pump.

[0018] Preferably, in step S6, the filter membrane parallel sampler is installed before use, and the installation steps are as follows:

[0019] The filter membranes were numbered and then placed in an environment with a temperature of 15-25°C and a humidity of 30-60% RH for 24 hours. During the placement process, the temperature fluctuation did not exceed ±1°C, and the humidity fluctuation did not exceed ±5% RH. Afterwards, they were weighed continuously at least 3 times every hour in the same environment using a balance, and the average value was calculated as the weighing result at that moment. The difference between the current weighing result and the weighing result 1 hour ago was within ±10 μg. The last weighing result was recorded as the mass of the filter membrane before sampling.

[0020] Preferably, in step S7, when it is determined that the membrane parallel sampler is leaking, the computer control unit controls the aerosol generator, the electrostatic neutralizer, the second-stage mixer, the membrane parallel sampler and the vacuum pump to shut down urgently.

[0021] When it is determined that there is no leakage in the membrane parallel sampler, the start and stop of the membrane parallel sampler can be controlled according to the preset sampling time or sampling volume, or manually

[0022] Therefore, the present invention adopts the above-mentioned device and method for preparing a filter membrane substrate particle standard substance, and the beneficial technical effects are as follows:

[0023] (1) Rapid batch preparation of standard particle materials on the filter membrane substrate is possible. The amount of particle deposition and chemical composition on the filter membrane surface can be controlled, and the mass of the loaded particles has good consistency.

[0024] (2) Using a two-stage mixer can add a particle size screening device between the first stage mixer and the second stage mixer, such as PM 2.5 Cutter or PM 10 Cutter, etc., to meet the needs of collecting aerosols of specific particle size. Since the particle screening device usually has a fixed working flow, such as the commonly used PM 2.5 Cutter and PM 10 The cutter's operating flow rate is 16.7 L / min. However, when batch-producing membrane-based particulate matter standards, multiple membrane samplers can be used simultaneously, resulting in a total sampling flow rate far exceeding 16.7 L / min. This presents a flow mismatch. This problem can be resolved by using a two-stage mixing system, ensuring an outlet flow rate of 16.7 L / min in the first stage, meeting the requirements of the particle screening device, while continuing to replenish clean air in the second stage to meet the requirements of membrane parallel sampling. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic diagram of the gas path structure of a filter membrane substrate particle standard substance preparation device of the present invention;

[0026] Figure 2 This is a schematic diagram of the circuit control structure of a filter membrane substrate particle standard substance preparation device of the present invention;

[0027] Figure 3 Schematic diagram of the rotational symmetry axis of the aerosol splitter;

[0028] Figure 4 This is a schematic diagram of the method of using the outlet part of the aerosol splitter; Figure 4 (a) means any two exits can be used; Figure 4 (b) in the figure has three exits that are rotationally symmetrical and can be used; Figure 4 (c) in the figure is rotationally symmetrical with four outlets and can be used; Figure 4 (d) The three exits do not form rotational symmetry and cannot be used;

[0029] Figure 5 This is a graph showing the consistency of 16-channel filter membrane sampling. DETAILED DESCRIPTION

[0030] The technical solution of the present invention is further described below with reference to the accompanying drawings and embodiments.

[0031] Unless otherwise defined, technical or scientific terms used in the present invention shall have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs.

[0032] Example 1

[0033] like Figure 1 The figure shows a schematic diagram of the air path structure of a filter membrane base particulate matter standard material preparation device of the present invention, which includes an aerosol generator, the air outlet of the aerosol generator is connected to the air inlet of the dryer, the air outlet of the dryer is connected to the air inlet of the two-stage mixer, the air outlet of the two-stage mixer is connected to the air inlet of the multi-stage aerosol diverter, the air outlet of the multi-stage aerosol diverter is connected to the air inlet of the filter membrane parallel sampler, the air outlet of the filter membrane parallel sampler is connected to the air inlet of the leak detector, and the leak detector is also connected to the vacuum pump.

[0034] Figure 2 This is a schematic diagram of the circuit control structure of a filter membrane-based particulate matter standard substance preparation device of the present invention. The aerosol generator, two-stage mixer, multi-stage aerosol diverter, filter membrane parallel sampler, leak detector and vacuum pump are all electrically connected to the computer control unit.

[0035] The functions of each component are described in detail below.

[0036] The aerosol generator can generate aerosol in the form of dry powder or liquid droplets, and has an air inlet pressure or flow control function. The air inlet pressure or flow of the aerosol generator can be adjusted using a computer control unit.

[0037] Dryers can remove water by diffusion drying or heating, converting liquid droplets into solid particles.

[0038] The dried aerosol enters the first-stage mixer, where it mixes with the charged ionized air generated by the static neutralizer, eliminating the surface charge on the particles in the aerosol. The de-staticized aerosol then enters the second-stage mixer, where it mixes with clean air to produce the aerosol used to prepare the standard substance.

[0039] The second-stage mixer features a clean air flow control function, allowing the clean air intake to be adjusted using a computer control unit. Furthermore, the second-stage mixer monitors temperature, humidity, and particulate matter concentration. The computer control unit collects temperature, humidity, and particulate matter concentration data within the second-stage mixer and adjusts the aerosol generator's operating parameters and the second-stage mixer's intake air volume based on the particulate matter concentration to maintain the aerosol sample concentration. The second-stage mixer has an exhaust port equipped with a high-efficiency filter cartridge. When the intake air flow exceeds the sampling flow, excess gas is discharged through the exhaust port. Therefore, there is no need to ensure that the sampling flow is completely consistent with the intake air flow during sampling.

[0040] The aerosol splitter uses a rotationally symmetrical structure to evenly divide one aerosol sample into multiple paths. The so-called rotationally symmetrical structure is characterized by: taking the straight line along the airflow direction of the inlet center as the rotational symmetry axis, the internal cavity of the aerosol splitter can completely overlap with the original cavity after rotating around the axis by a certain angle (greater than 0° and less than 360°), such as Figure 3 For an aerosol splitter with more than two outlets, not all outlets need to be used; that is, unused outlets can be closed by blocking them. Aerosol splitters can be used in cascades, with the outlet of the previous aerosol splitter connected to the inlet of the next aerosol splitter.

[0041] In order to ensure that the aerosol concentration at each outlet of the aerosol splitter is consistent, the following conditions should be met when using it: all outlets of a single aerosol splitter have the same flow rate, and when there are more than two outlets in use, each outlet should form a rotationally symmetrical structure, such as Figure 4 If multiple aerosol splitters are used in cascade, each aerosol splitter should meet the above conditions.

[0042] The membrane parallel sampler has a flow control function. The sampling flow rate can be set and the sampling start and stop can be controlled through the computer control unit, and the real-time flow rate and cumulative volume can be fed back to the computer control unit.

[0043] The leak detector uses a particle counting or mass concentration sensor module to measure the concentration of particulate matter in the gas after it passes through the filter membrane. A computer control unit collects the leak detector's measurement results and uses them to determine whether the filter parallel sampler is leaking. If a leak occurs, the computer control unit can control the aerosol generator, static neutralizer, second-stage mixer, filter parallel sampler, and vacuum pump to emergency shut down.

[0044] The present invention will be further described below through specific examples.

[0045] The present invention provides a filter membrane-based particle standard material preparation device comprising a computer control unit, an aerosol generator, a dryer, a first-stage mixing, an electrostatic neutralizer, a second-stage mixer, a multi-stage aerosol diverter, a filter membrane parallel sampler, a leak detector, and a vacuum pump. The multi-stage aerosol diverter is a two-stage cascade diversion device, each diverter having one inlet and four outlets. The four outlets of the first-stage diverter are respectively connected to the four inlets of the second-stage diverter, achieving an overall aerosol diversion effect of 1 to 16. There are a total of 16 filter membrane parallel samplers, which use a circular filter membrane with a diameter of 47 mm for sampling, and the sampling flow rate of a single unit is 10 L / min.

[0046] Before being installed in the parallel sampler, the filters were numbered and allowed to stand for 24 hours in an environment with a temperature of (20 ± 0.5)°C and a humidity of (50 ± 5)% RH. The filters were then weighed three times in the same environment at 1-hour intervals. The average of these three weighings was calculated as the current weighing result. This was repeated until the difference between the current weighing result and the one-hour previous weighing result was within ±10 μg. The final weighing result was recorded as the filter mass before sampling.

[0047] An aerosol generator based on the atomization principle and a sodium chloride aqueous solution were used to generate aerosols. The aerosol flow rate of the aerosol generator was adjusted to approximately 5 L / min, the neutralization flow rate of the electrostatic neutralizer was adjusted to 10 L / min, the clean air flow rate of the first-stage mixer was adjusted to 25 L / min, and the clean air flow rate of the second-stage mixer was adjusted to 125 L / min. The temperature, humidity, and particle concentration in the second-stage mixer were monitored. After the particle concentration in the second-stage mixer stabilized, the baseline fluctuation standard deviation of the leak detector was determined using the following method:

[0048] In this embodiment, the standard deviation of the leak detector's baseline fluctuation is calculated using the following method, although other calculation methods may be used as needed: Directly connect a clean air line to the leak detector's air inlet and purge it with clean air while simultaneously reading the leak detector's measurement results. Starting at 0 seconds of each minute, record one measurement result per second for 1 minute, obtaining 60 measurement results. Calculate the 1-minute average and standard deviation using the following formula.

[0049]

[0050]

[0051] The leak detector reading is considered stable when the difference between the average values ​​of the previous and next 2 minutes meets the following conditions:

[0052]

[0053] in, is the average value of the jth min; sj is the standard deviation of the jth min; i is the measurement result number within 1 minute; q ij is the i-th measurement result of the j-th min; is the average value of the j+1 minute; s j+1 is the standard deviation of the j+1 minute;

[0054] At this time, the measurement results were recorded continuously for 1 min, and the standard deviation was calculated as the baseline fluctuation standard deviation.

[0055] After completing the baseline fluctuation standard deviation measurement, connect the 16 outlets of the second-stage aerosol splitter to 16 parallel samplers. Connect the outlets of the parallel samplers to the inlet of the leak detector. Simultaneously initiate sampling using a computer control unit. Set the sampling time to 1 hour.

[0056] In this embodiment, the computer control unit reads the measurement results of the leak detector at 1-second intervals and compares them with the baseline results. When the particle concentration exceeds 10 times the standard deviation of the baseline fluctuation, the filter sampler is deemed to be leaking. If the measurement results indicate a leak for at least 5 consecutive seconds, the computer control unit stops aerosol generation and sampling, and a prompt is displayed on the software interface.

[0057] When the sampling time reaches the set time, the computer control unit simultaneously stops sampling from the 16 parallel samplers. Stop the aerosol generator, electrostatic neutralizer, first-stage mixer, and second-stage mixer, disconnect the parallel sampler and aerosol diverter, remove the filter membrane from the 16 parallel samplers, and place it in an environment with a temperature of (20±0.5)°C and a humidity of (50±5)% RH for 24 hours. Then, use a balance to weigh it three times every hour in the same environment. Calculate the average of the three weighings as the weighing result at that moment, until the difference between the current weighing result and the weighing result 1 hour ago is within ±10μg. Record the last weighing result as the mass of the filter membrane after sampling.

[0058] The mass difference before and after sampling of each filter membrane is calculated in turn, which is the mass of the particulate matter sample collected on the filter membrane surface. The results are shown in Table 1:

[0059] Table 1 Filter membrane sampling and weighing results

[0060] Filter membrane number Mass before sampling (μg) Mass after sampling (μg) Particle mass (μg) 1 1333526 1334992 1466 2 1365271 1366724 1453 3 1381695 1383154 1459 4 1354487 1355949 1462 5 1312528 1313983 1455 6 1346698 1348158 1460 7 1376658 1378117 1459 8 1360868 1362325 1457 9 1358086 1359548 1462 10 1377633 1379089 1456 11 1390028 1391486 1458 12 1375884 1377345 1461 13 1369790 1371253 1463 14 1378532 1379985 1453 15 1342077 1343528 1451 16 1333695 1335152 1457 average value / / 1458

[0061] From Table 1 and Figure 5 As can be seen, the particle mass collected by the 16 filter membranes is highly consistent. The maximum relative deviation between the particle mass collected on a single filter and the average of the 16 membranes is within ±0.6%, meeting the uniformity requirements for standard material values.

[0062] Therefore, the present invention adopts the above-mentioned filter membrane base particulate matter standard material preparation device and method, which can realize the rapid batch preparation of filter membrane base particulate matter standard material, the particulate matter deposition amount and chemical composition on the filter membrane surface can be controlled, and the quality of the loaded particulate matter has good consistency.

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A filter membrane substrate particle standard material preparation device, characterized in that: The device comprises an aerosol generator, wherein the air outlet of the aerosol generator is connected to the air inlet of a dryer, the air outlet of the dryer is connected to the air inlet of a two-stage mixer, the air outlet of the two-stage mixer is connected to the air inlet of a multi-stage aerosol diverter, the air outlet of the multi-stage aerosol diverter is connected to the air inlet of a membrane parallel sampler, the air outlet of the membrane parallel sampler is connected to the air inlet of a leak detector, the leak detector is further connected to a vacuum pump, and the aerosol generator, two-stage mixer, multi-stage aerosol diverter, membrane parallel sampler, leak detector and vacuum pump are all electrically connected to a computer control unit; The two-stage mixer includes a first-stage mixer and a second-stage mixer, the air inlet of the first-stage mixer is connected to the air outlet of the dryer, the air inlet of the second-stage mixer is connected to the air outlet of the first-stage mixer, and the first-stage mixer is further connected to a static neutralizer; The outlet of the multi-stage aerosol diverter is divided into multiple paths, each of which is connected to a filter membrane parallel sampler; The aerosol splitter uses a rotationally symmetrical structure to divide one aerosol sample into multiple paths. The following conditions should be met when used: all outlets of a single aerosol splitter have the same flow rate, and when there are more than two outlets in use, each outlet constitutes a rotationally symmetrical structure. If multiple aerosol splitters are used in cascade, each aerosol splitter should meet the above conditions.

2. A method for preparing a filter membrane substrate particle standard substance, characterized in that: The device for preparing a standard substance of a filter membrane substrate particle according to claim 1 comprises the following steps: S1, aerosol generator generates aerosol to dryer; S2, a dryer removes moisture from the aerosol to obtain a dried aerosol; S3, the dried aerosol enters the first-stage mixer and mixes with the charged ion wind generated by the static neutralizer to remove the surface charge of the particles in the dried aerosol, thus obtaining an aerosol with static electricity removed; S4, the aerosol after static electricity removal enters the second-stage mixer and is mixed with clean air to obtain an aerosol for preparing a standard substance; S5. The aerosol used to prepare the standard substance enters the aerosol splitter to achieve aerosol diversion; S6, the split aerosols enter different filter membrane parallel samplers respectively; S7. The gas outlet of the membrane parallel sampler is connected to a leakage detector, and the measurement result of the leakage detector is transmitted to the computer control unit to determine whether the membrane parallel sampler is leaking.

3. The method for preparing a filter membrane substrate particle standard substance according to claim 2, characterized in that: In step S6, the filter membrane parallel sampler is installed before use, and the installation steps are as follows: The filter membranes were numbered and then placed in an environment with a temperature of 15-25°C and a humidity of 30-60% RH for 24 hours. During the placement process, the temperature fluctuation did not exceed ±1°C, and the humidity fluctuation did not exceed ±5% RH. Afterwards, they were weighed continuously at least three times every hour in the same environment using a balance, and the average value was calculated as the weighing result at that moment. The difference between the current weighing result and the weighing result 1 hour ago was within ±10 μg. The last weighing result was recorded as the mass of the filter membrane before sampling.

4. The method for preparing a filter membrane substrate particle standard substance according to claim 2, characterized in that: In step S7, when it is determined that the membrane parallel sampler leaks, the computer control unit controls the aerosol generator, the electrostatic neutralizer, the second-stage mixer, the membrane parallel sampler and the vacuum pump to shut down urgently.

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