CN106769929B - Atmospheric gaseous nitric acid online measurement method and device based on flow injection analysis - Google Patents
Atmospheric gaseous nitric acid online measurement method and device based on flow injection analysis Download PDFInfo
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Abstract
The invention discloses an atmospheric gaseous nitric acid online measurement method and a measurement device based on flow injection analysis, which are characterized in that based on the flow injection analysis, a wet chemical method and spectroscopy are combined, based on a cadmium column reduction principle, gaseous nitric acid is reduced into nitrous acid, a national standard method for detecting nitrite by using Gris-Sattman colorimetric is applied, the nitrite is continuously collected by using Gris reagent based on the flow injection method, the nitrite is transmitted by a peristaltic pump, the collected gas sample is subjected to colorimetric analysis by combining a long-optical-path liquid core optical fiber, and gaseous nitrous acid signals in the atmosphere are deducted, so that the determination of the concentration of the gaseous nitric acid in the atmosphere is realized. The device at least comprises a sampling unit, a gas/liquid transmission unit and a detection unit. The scheme of the invention has the characteristics of low detection limit, high sensitivity, high space-time resolution, high stability, low interference and low cost.
Description
Technical Field
The invention relates to an atmospheric quality detection technology, in particular to an atmospheric gaseous nitric acid online measurement method and device based on flow injection analysis.
Background
Gaseous nitric acid plays an important role in atmospheric chemistry, its existence involving numerous daytime and nighttime atmospheric chemical processes as a final store of active nitrogen compounds that can carry out long-distance transport of pollution; the number concentration of the cloud drops can be increased, so that the average size of the cloud drops is reduced, and the reflectivity of the cloud is increased; as a sink of OH radicals and a potential source of gaseous nitrous acid, it has a significant impact, directly or indirectly, on atmospheric oxidising and self-cleaning capabilities. Atmospheric pollution such as acid rain, photochemical smog, condensation of polar advection layer cloud and ozone depletion has important relation with gaseous nitric acid.
Since the first detection of gaseous nitric acid in 1980, techniques and methods for detecting gaseous nitric acid have been gradually developed and perfected. However, because of the easy adsorption, low concentration, large interference of the nitrogen-containing compound to the nitrogen-containing compound, and the like, accurate measurement of the gaseous nitric acid is always in a bottleneck period, and the low detection limit, the high sensitivity, the wider detection range, the low interference and the like become important performance indexes of the gaseous nitric acid measuring instrument.
The existing measuring method of gaseous nitric acid is mainly divided into an optical method and a wet chemical method, and the spectrum method is generally poor in detection limit and basically not suitable for cleaner areas; whereas the existing wet chemical methods generally have poor selectivity. Therefore, a gaseous nitric acid accurate online detection method simultaneously meeting the double requirements of field observation and laboratory research is lacking at present.
Disclosure of Invention
In order to overcome the defects in the prior art, the invention provides the online measurement method and the online measurement device for the gaseous nitric acid, which are used for measuring the concentration of the gaseous nitric acid in the atmosphere based on flow injection analysis by adopting a wet chemical method, and have the characteristics of low detection limit, high sensitivity, high space-time resolution, high stability, low interference and low cost.
The principle of the invention is as follows: because gaseous nitric acid in the atmosphere is easy to adsorb and has low concentration, and the measurement is easy to be interfered by other substances, the detection limit, the sensitivity, the response time and the interference of the nitric acid measuring instrument become important factors influencing the measurement accuracy. The invention is based on the cadmium column reduction principle, reduces gaseous nitric acid into nitrous acid, applies the national standard method of the Gris-Sartzmann colorimetric detection of nitrite, continuously collects nitrite by using Gris reagent based on the flow injection method, transmits the nitrite by a peristaltic pump, performs colorimetric analysis on the collected gas sample by combining a long-optical-path liquid core optical fiber, deducts gaseous nitrous acid signals in the atmosphere, and further realizes the indirect online measurement of gaseous nitric acid with high precision, high time resolution and high accuracy.
The technical scheme provided by the invention is as follows:
the on-line measuring method for the gaseous nitric acid in the atmosphere based on the flow injection analysis comprises the following steps:
1) Based on the cadmium column reduction principle, reducing gaseous nitric acid into nitrous acid; the method specifically comprises the following steps:
11 Collecting HNO by a spiral tube sampler 3 And then collect HNO 3 Is transferred into a cadmium column by a peristaltic pump;
12 The cadmium column has high reduction efficiency after pretreatment, and nitrate ions in the solution flowing through the cadmium column are reduced into nitrite ions;
2) The method for detecting nitrite by using the Grignard-Sartzmann colorimetric method adopts a flow injection method, and continuously collects nitrite by using Grignard reagent; the method specifically comprises the following steps:
21 The solution passing through the cadmium column becomes a solution containing nitrite ions, and the solution is transmitted into a first three-way mixing cavity through a peristaltic pump by a filter membrane;
22 The absorption liquid and the dyeing liquid are conveyed to a second three-way mixing cavity by a peristaltic pump to be mixed, and the absorption liquid and the dyeing liquid are the Grignard reagent;
23 The mixed solution in the second three-way mixing cavity enters the first three-way mixing cavity through a 1/16 tetrafluoro pipe and is mixed with the nitrite ion-containing solution in the step 21), and the mixed solution is azo dye;
24 Azo dye in the first three-way mixing cavity is continuously conveyed into the long-optical-path liquid core optical fiber for detection through the peristaltic pump;
3) Transmitting by peristaltic pump, and carrying out colorimetric analysis on the collected gas sample by combining with long-optical-path liquid core optical fiber;
4) The computer program obtains the measuring signal, and the signal is a signal of gaseous nitric acid and gaseous nitrous acid together; and simultaneously measuring and obtaining gaseous nitrous acid signals in the atmosphere (obtained by detecting a gaseous nitrous acid signal measuring instrument), and subtracting the gaseous nitrous acid signals in the atmosphere through a computer program to obtain the concentration of the gaseous nitrous acid in the atmosphere, thereby realizing the high-precision high-time-resolution high-accuracy indirect online measurement of the gaseous nitric acid.
The gaseous nitrous acid signal in the atmosphere is detected by a gaseous nitrous acid signal measuring instrument in the atmosphere, specifically, the signal of the gaseous nitrous acid and the gaseous nitrous acid is detected by one gaseous nitrous acid measuring instrument in the atmosphere, and the gaseous nitrous acid signal in the atmosphere is detected by another gaseous nitrous acid signal measuring instrument in the atmosphere, and the gaseous nitrous acid signal in the atmosphere can be detected by a method described in literature (Liu Y, lu K, dong H, et al, in situ monitoring of atmospheric nitrous acid based on multi-pumping flow system and liquid waveguide capillary cell [ J ]. Journal of Environmental Sciences,2016, 43:273-284); in the existing method, gaseous nitrous acid signal measurement specifically captures gaseous nitrous acid in the atmosphere through a Gris reagent to form a diazonium dye, then an absorption spectrum of the diazonium dye is obtained through a liquid core optical fiber, and a liquid marking of the instrument for nitrous acid is obtained through preparation of nitrite liquid marks with different concentrations, wherein the marking is a linear relation between a spectrum absorption signal and an actual corresponding nitrite ion in nitrous acid measurement of the gaseous nitrous acid signal measurement instrument. And (3) respectively making standard curves of nitrate and nitrite for the gaseous nitric acid measuring instrument to obtain the linear relation between the two ion concentrations and instrument signals. The absorption signal obtained by the computer program in the gaseous nitric acid measuring instrument is the signal of gaseous nitric acid and gaseous nitrous acid together. The two instruments (a gaseous nitric acid measuring instrument and a gaseous nitrous acid signal measuring instrument) are used for measuring simultaneously, the concentrations of gaseous nitrous acid are equal, the concentrations of nitrite are equal, the nitrite concentration obtained in the gaseous nitrous acid measuring device is converted into a nitrite signal converted by gaseous nitrous acid in the gaseous nitric acid device according to the linear relation between the absorption signal and the nitrite ion concentration, the nitrite signal is subtracted from the total signal, the rest signal is the nitrite signal converted by the gaseous nitric acid, the corresponding nitric acid concentration is obtained according to the standard curve converted by the nitric acid into nitrite, and then the gaseous nitric acid concentration under experimental conditions is obtained through temperature, pressure, gas and liquid flow rate correction.
In order to realize the online detection of the gaseous nitric acid, the invention develops a device for online detection of the gaseous nitric acid by a wet chemical method, and the device at least comprises a sampling unit, a gas/liquid transmission unit and a detection unit; the sampling unit includes: a spiral tube sampler; the gas/liquid transfer unit includes: diaphragm pump, buffer solution, absorption solution, dyeing solution, mass flowmeter, drying tube, safety bottle, peristaltic pump, cadmium column, three-way mixing cavity, bubble remover, filter membrane, bubble removing tube, multiple 1/4 inch tetrafluoro tubes, 1/16 inch tetrafluoro tube and 1/16 inch PEEK tube; the detection unit includes: the LED light source, the spectrometer, the optical fiber, the long optical path liquid core optical fiber, the notebook computer, the driving power circuit and the USB connecting wire. The spiral tube sampler is a single-channel spiral tube sampler and is provided with a gas inlet, a gas outlet, a liquid inlet, a liquid outlet, a water bath water inlet and a water bath water outlet; the peristaltic pump comprises a plurality of channels, wherein each channel in the peristaltic pump uses a peristaltic tube, and the peristaltic tube comprises a liquid inlet and a liquid outlet; the cadmium column, the filter membrane and the bubble remover all comprise a liquid inlet end and a liquid outlet end; the three-way mixing cavity comprises a first three-way mixing cavity and a second three-way mixing cavity; the spectrometer comprises a signal receiving end and a signal output end; the gas inlet of the spiral tube sampler is connected with the gas sampling tube, and the gas outlet of the spiral tube sampler is connected with the safety bottle through a 1/4 inch tetrafluoro tube; the safety bottle is communicated with the drying pipe through a 1/4 inch tetrafluoro pipe; the drying pipe is connected with the mass flowmeter through a 1/4 inch tetrafluoro pipe; the mass flowmeter is connected with the diaphragm pump through a 1/4 inch tetrafluoro pipe; the liquid inlet of the spiral tube sampler is connected with the liquid outlet of the peristaltic pump, and the liquid inlet of the peristaltic pump is connected with the buffer solution through a 1/16 inch tetrafluoro tube; the liquid outlet of the spiral pipe sampler is connected with the liquid inlet of the peristaltic pump, the liquid outlet of the peristaltic pump is connected with the liquid inlet end of the bubble remover, the liquid outlet end of the bubble remover is connected with the liquid inlet of the peristaltic pump, the liquid outlet of the peristaltic pump is connected with the liquid inlet end of the cadmium column, the liquid outlet end of the cadmium column is connected with the liquid inlet end of the filter membrane, and the liquid outlet end of the filter membrane is connected with the first end of the first three-way mixing cavity; the second end of the first three-way mixing cavity is connected with the third end of the second three-way mixing cavity, the first end of the second three-way mixing cavity is connected with the liquid outlet of the peristaltic pump, the liquid inlet of the peristaltic pump is connected with the absorption liquid R1, the second end of the second three-way mixing cavity is connected with the liquid outlet of the peristaltic pump, and the liquid inlet of the peristaltic pump is connected with the dyeing liquid R2; the third end of the first three-way mixing cavity is connected with the liquid inlet end of the bubble remover through a 1/16 inch PEEK pipe; the liquid outlet end of the bubble removing device is connected with the liquid inlet of the peristaltic pump through a 1/16 inch PEEK pipe, the liquid outlet of the peristaltic pump is connected with the liquid inlet end of the bubble removing pipe through a 1/16 inch PEEK pipe, the liquid outlet end of the bubble removing pipe is connected with the liquid inlet end of the filter membrane through a 1/16 inch PEEK pipe, the liquid outlet end of the filter membrane is connected with the liquid inlet end of the long-optical-path liquid core optical fiber through a 1/16 inch PEEK pipe, and the liquid outlet end of the long-optical-path liquid core optical fiber discharges waste liquid into a waste liquid barrel through a 1/16 inch tetrafluoro pipe; the LED light source is connected with the long-optical-path liquid core optical fiber light source inlet through the optical fiber; the optical signal receiving end of the spectrometer is connected with the long-optical-path liquid core optical fiber light source outlet through the optical fiber; and the signal output end of the spectrometer is connected with the notebook computer through the USB connecting wire.
Aiming at the online detection device of the gaseous nitric acid, the drying pipes are divided into two parts, wherein the first part is filled with silica gel, the second part is filled with active carbon, and gas passing through the safety bottle firstly passes through the drying pipe filled with the silica gel and then enters the drying pipe filled with the active carbon through a section of 1/4 inch tetrafluoro pipe; in the embodiment of the invention, the peristaltic pump uses 6 channels in total and is connected with a power supply.
When the detection device for online measurement of gaseous nitric acid works, the spiral tube sampler is heated by adopting a water bath at 20 ℃; a1/16 inch PEEK tube about 3 meters forward of the bubble trap inlet end was thermostatically heated (50 ℃.+ -. 1 ℃) using a heating fitting.
When the device for online measurement of gaseous nitric acid works, the spiral tube sampler is heated in a water bath, so that the spiral tube sampler has stable absorption efficiency, and the measurement accuracy of the gaseous nitric acid is improved. By heating the PEEK tube with constant temperature of 3 meters, the probability of bubble generation can be reduced, the reaction rate of the solution containing nitrite ions, the mixed solution of the absorption solution and the dyeing solution can be accelerated, the dyeing time can be shortened and stabilized, and the dyeing solution entering LWCC can be kept in the same dyeing degree state. The sampling gas flow is accurately controlled through the mass flowmeter (the air outlet of the spiral pipe sampling port is indirectly connected with the mass flowmeter), the buffer liquid flow entering the spiral pipe sampler is accurately controlled through the peristaltic pump (the buffer liquid is connected with the spiral pipe liquid inlet through the peristaltic pump), so that the sampling efficiency in the spiral pipe sampler is guaranteed, meanwhile, water vapor and acid vapor in sampling tail gas are removed through arrangement of double drying pipes (the silica gel drying pipe and the active carbon drying pipe are used together as described above), and harm of discharged tail gas to a human body is reduced while the mass flowmeter is protected. The two tee joint mixing cavities are used for mixing the absorption liquid and the dyeing liquid respectively, and the solution containing nitrite ions is mixed with the mixed liquid to provide places, and the inside of the tee joint mixing cavities adopts a liquid drop collision and mixing mode, so that the uniformity of the solution mixing can be ensured, and the mixing time can be shortened. The use of the filter membrane, the bubble remover and the bubble removing pipe ensures that no bubble and no particle with the particle size larger than 1um exist in the liquid entering the long-optical-path liquid-core optical fiber, so that the stable and real absorption spectrum can be obtained, the use damage of the long-optical-path liquid-core optical fiber can be reduced, and the later maintenance cost can be reduced.
In detection, the spiral tube sampler is designed into a glass sampler with 10 winding turns, 2cm winding diameter and 2mm winding tube diameter, and HNO is improved through high winding turns 3 The residence time in the spiral tube improves the absorption efficiency; cadmium column treatment is carried out by filling cadmium particles by using a tetrafluoro tube, and utilizing HCI and NH 4 CI flushing improves the reduction efficiency of cadmium particles, is simple and convenient to operate, convenient to replace and low in cost, and is suitable for field observation; preparing low-concentration absorption liquid (R1) and dyeing liquid (R2), wherein 1g of sulfanilamide+10ml of HCl is adopted for dissolving 1L of pure water, and 0.02g of naphthalene ethylenediamine hydrochloride is adopted for dissolving 1L of pure water for preparing R2, so that the concentration of the solution is greatly reduced, and the damage of acid volatilization to the instrument and surrounding facilities is reduced; the mixed solution tube is constantly heated (50 ℃), so that the solution reaction time is shortened, the response time of the instrument is shortened, the solution color reaction is stable under the constant temperature condition, and the stable sensitivity of the instrument is ensured.
Compared with the prior art, the invention has the beneficial effects that:
the invention provides an atmospheric gaseous nitric acid on-line measuring method and device based on flow injection analysis, which are used for measuring the concentration of gaseous nitric acid in the atmosphere by combining a wet chemical method and a spectroscopy method, and have the characteristics of low detection limit, high sensitivity, high space-time resolution, high stability, low interference and low cost. Specifically, the technical scheme of the invention has the advantages that:
firstly, a modular design is adopted to divide a measurement system into an absorption unit, a transmission reaction unit and a detection unit, and the invented technical framework has good stability and expansibility;
the invention combines the spiral tube sampler and the peristaltic pump, thereby realizing the full-automatic flow injection analysis of the gas sample;
thirdly, the self-made cadmium column is adopted, so that nitric acid can be reduced into nitrous acid, the reduction efficiency is stable, and the cost is low;
fourthly, by combining with an instrument for measuring the gaseous nitrous acid by a double-channel spiral pipe sampling-flow injection analysis method, the dynamic correction of original gaseous nitrous acid in air and measurement interference is realized, and the accurate measurement of the gaseous nitrous acid is realized;
5. the filter membrane and the bubble remover are used together, so that the diameter of particles contained in the liquid entering the long-optical-path liquid-core optical fiber is ensured to be smaller than 1um, the damage to the long-optical-path liquid-core optical fiber is reduced, the probability of bubbles occurring in the liquid entering the long-optical-path liquid-core optical fiber is reduced, and the quality of detection data is ensured;
6. the PEEK three-way mixing cavity is used for mixing the absorption liquid and the dyeing liquid, and the three-way cavity utilizes a liquid drop collision and mixing mode on the basis of corrosion resistance, so that the liquid mixing uniformity is improved on the basis of shortening the mixing time;
7. the invention adopts the long-optical-path liquid core optical fiber as the colorimetric pool, and the length of the built-in liquid core optical fiber is changed to meet the measurement requirements of different gaseous nitric acid concentrations;
8. the LED light source is adopted, the wavelength can cover 400-700nm, and the measurement requirements of different research purposes can be met;
9. the online measurement gaseous nitric acid technology of the invention belongs to single-point sampling (high spatial resolution), high time resolution, high sensitivity, dynamic deduction of measurement interference, good system stability, low cost and simple and convenient starting and maintenance.
Drawings
FIG. 1 is a block diagram of a detection device according to an embodiment of the present invention;
wherein, 1-sampling unit; 2-a gas/liquid transfer unit; 3-a detection unit; the gas/liquid transfer unit 2 includes: 2-1-safety bottle, 2-drying pipe, 2-3-mass flowmeter, 2-4-diaphragm pump, 2-5-peristaltic pump, 2-6-buffer solution, 2-7-absorption solution R1, 2-8-dyeing solution R2, 2-9-1-mixing cavity, 2-9-2-second mixing cavity, 2-10-cadmium column, 2-11-1-first filter head, 2-11-2-second filter head, 2-12-foam remover, 2-13-foam remover, 2-14-foam removing pipe, 2-15-20deg.C water bath box; wherein peristaltic pump 2-5 comprises: 2-5-1-peristaltic pump No. 1, 2-5-2-peristaltic pump No. 2, 2-5-3-peristaltic pump No. 3, 2-5-4-peristaltic pump No. 4, 2-5-peristaltic pump No. 5, 2-5-6-peristaltic pump No. 6; the detection unit 3 includes: 3-1-long optical path liquid core optical fiber, 3-2-spectrometer, 3-400-700 nm light source, 3-4-computer and 3-5-waste liquid bottle.
FIG. 2 is a block diagram of a single channel spiral tube sampler in a detection device sampling unit provided by an embodiment of the present invention;
wherein, (a) is a side view of the spiral tube sampler; (b) a front view of the spiral tube sampler; 1-1 is an atmospheric air inlet 6mm;1-2 is buffer liquid inlet with inner diameter of 2mm;1-3 is a thermostatic water bath water inlet and outlet, and the inner diameter is 6mm;1-4 is the air outlet 6mm;1-5 is HNO-absorbed 3 The inner diameter of the buffer liquid outlet is 2mm; the spiral tube is wound for 10 turns, and the winding diameter is 2cm.
FIG. 3 is a block diagram of a bubble remover in a gas/liquid transmission unit of a detection device according to an embodiment of the present invention;
wherein 2-12-1 is a liquid inlet; 2-12-2 is a gas outlet; 2-12-3 is a waste liquid outlet; 2-12-4 is a liquid outlet.
FIG. 4 is a schematic diagram of a cadmium column of a detection device according to an embodiment of the present invention;
wherein 4-1 is a filling isolation part; 4-2 is a part with glass wool filled at two ends; the entire cadmium column was 3cm long with an outer diameter of 1/16 inch.
Fig. 5 is a flow chart of the steps of the detection method of the present invention.
FIG. 6 is a block diagram of a data processing flow of a detection method in an embodiment of the invention.
Detailed Description
The invention is further described by way of examples in the following with reference to the accompanying drawings, but in no way limit the scope of the invention.
The invention provides an atmospheric gaseous nitric acid on-line measuring method and device based on flow injection analysis, which are used for measuring the concentration of gaseous nitric acid in the atmosphere by combining a wet chemical method and a spectroscopy based on the flow injection analysis, and have the characteristics of low detection limit, high sensitivity, high space-time resolution, high stability, low interference and low cost. Fig. 1 is a block diagram of a measuring device according to an embodiment of the present invention, and fig. 5 is a flow chart of steps of an atmospheric gaseous nitric acid online measurement method based on flow injection analysis according to the present invention, where the measuring device according to fig. 1 is used to measure the concentration of gaseous nitric acid in the atmosphere by using the atmospheric gaseous nitric acid online measurement method based on flow injection analysis, and specifically includes the following steps:
1) Based on the cadmium column reduction principle, reducing gaseous nitric acid into nitrous acid; the method specifically comprises the following steps:
11 Collecting HNO by a spiral tube sampler 3 And then collect HNO 3 Is transferred into a cadmium column 2-10 by a peristaltic pump 2-5;
12 The cadmium column 2-10 has high reduction efficiency after pretreatment, and nitrate ions in the solution flowing through the cadmium column are reduced into nitrite ions;
2) The method for detecting nitrite by using the Grignard-Sartzmann colorimetric method adopts a flow injection method, and continuously collects nitrite by using Grignard reagent; the method specifically comprises the following steps:
21 The solution passing through the cadmium column 2-10 becomes a solution containing nitrite ions, and the solution passes through the filter head 2-11-1 and enters the three-way mixing cavity 2-9-1;
22 The absorption liquid 2-7 and the dyeing liquid 2-8 are conveyed to the three-way mixing cavity 2-9-2 by the peristaltic pump 2-5 to be mixed, and the absorption liquid 2-7 and the dyeing liquid 2-8 are the Gris reagent;
23 The mixed solution in the three-way mixing cavity 2-9-2 enters the three-way mixing cavity 2-9-1 and is mixed with the solution containing nitrite ions in the step 21), and the mixed solution is azo dye;
24 Azo dye in the three-way mixing cavity 2-9-1 is continuously conveyed into a 3-1 long optical path liquid core optical fiber for detection through a peristaltic pump 2-5;
3) Transmitting through peristaltic pump 2-5, and carrying out colorimetric analysis on the collected gas sample by combining long-optical-path liquid core optical fiber;
4) Gaseous nitrous acid signals in the atmosphere are deducted, and the concentration of the gaseous nitrous acid in the atmosphere is calculated through a computer program, so that the high-precision high-time-resolution high-accuracy indirect online measurement of the gaseous nitric acid is realized.
The gaseous nitrous acid signal in the atmosphere is detected by a gaseous nitrous acid signal measuring instrument in the atmosphere, specifically, the signal of the gaseous nitrous acid and the gaseous nitrous acid is detected by one gaseous nitrous acid measuring instrument in the atmosphere, and the gaseous nitrous acid signal in the atmosphere is detected by another gaseous nitrous acid signal measuring instrument in the atmosphere, and the gaseous nitrous acid signal in the atmosphere can be detected by a method described in literature (Liu Y, lu K, dong H, et al, in situ monitoring of atmospheric nitrous acid based on multi-pumping flow system and liquid waveguide capillary cell [ J ]. Journal of Environmental Sciences,2016, 43:273-284); in the existing method, gaseous nitrous acid signal measurement specifically captures gaseous nitrous acid in the atmosphere through a Gris reagent to form a diazonium dye, then an absorption spectrum of the diazonium dye is obtained through a liquid core optical fiber, and a liquid marking of the instrument for nitrous acid is obtained through preparation of nitrite liquid marks with different concentrations, wherein the marking is a linear relation between a spectrum absorption signal and an actual corresponding nitrite ion in nitrous acid measurement of the gaseous nitrous acid signal measurement instrument. And (3) respectively making standard curves of nitrate and nitrite for the gaseous nitric acid measuring instrument to obtain the linear relation between the two ion concentrations and instrument signals. The absorption signal obtained by the computer program in the gaseous nitric acid measuring instrument is the signal of gaseous nitric acid and gaseous nitrous acid together. The two instruments (a gaseous nitric acid measuring instrument and a gaseous nitrous acid signal measuring instrument) are used for measuring simultaneously, the concentrations of gaseous nitrous acid are equal, the concentrations of nitrite are equal, the nitrite concentration obtained in the gaseous nitrous acid measuring device is converted into a nitrite signal converted by gaseous nitrous acid in the gaseous nitric acid device according to the linear relation between the absorption signal and the nitrite ion concentration, the nitrite signal is subtracted from the total signal, the rest signal is the nitrite signal converted by the gaseous nitric acid, the corresponding nitric acid concentration is obtained according to the standard curve converted by the nitric acid into nitrite, and then the gaseous nitric acid concentration under experimental conditions is obtained through temperature, pressure, gas and liquid flow rate correction.
In order to realize the online detection of the gaseous nitric acid, the invention develops a device for online detection of the gaseous nitric acid by a wet chemical method. FIG. 1 is a schematic structural view of an embodiment of a detection device. As shown in fig. 1, the whole instrument comprises three parts, namely a sampling unit 1, a gas/liquid transmission unit 2, and a detection unit 3. The sampling unit 1 is the single-channel spiral pipe sampler; the 2-1 safety bottle in the gas/liquid transmission unit 2 is connected with the gas outlet end of the single-channel spiral tube sampler of the sampling unit 1, the gas inlet end of the 2-2 drying tube is connected with the 2-1 safety bottle, the gas outlet end of the 2-2 drying tube is connected with the gas inlet end of the 2-3 mass flowmeter, and the 2-3 mass flowmeter is connected with the gas inlet end of the 2-4 sampling pump; 2-6 is buffer solution, is connected with a liquid inlet end of a No. 6 pump in a 2-5 peristaltic pump, a liquid outlet end of a No. 6 pump in the 2-5 peristaltic pump is connected with a liquid inlet of a single-channel spiral pipe sampler in a sampling unit 1, 2-7 is R1, is connected with a liquid inlet end of a No. 2 pump in the 2-5 peristaltic pump, a liquid outlet end is connected with a first end of a 2-9-2 three-way mixing cavity, 2-8 is R2, is connected with a liquid inlet end of a No. 1 pump in the 2-5 peristaltic pump, a liquid outlet end is connected with a second end of the 2-9-2 three-way mixing cavity, a third end of the 2-9-2 three-way mixing cavity is connected with a second end of the 2-9-1 three-way mixing cavity, a liquid inlet end of a No. 4 pump in the 2-5 peristaltic pump is connected with a liquid outlet end of a bubble remover 2-13, a liquid inlet end of the 2-13 bubble remover is connected with a liquid outlet end of a No. 3 pump, the liquid inlet end of the No. 3 pump is connected with the liquid outlet of the single-channel spiral tube sampler in the sampling unit 1, the liquid outlet end of the No. 4 pump is connected with the liquid inlet end of the 2-10 cadmium column, the liquid outlet end of the 2-10 cadmium column is connected with the liquid inlet end of the 2-11-1 filter head, the liquid outlet end of the 2-11-1 filter head is connected with the first end of the 2-9-1 three-way mixing cavity, the third end of the 2-9-1 three-way mixing cavity is connected with the liquid inlet end of the 2-12 bubble remover, a heater is used for heating a tetrafluoro tube between the third end of the 2-9-1 three-way mixing cavity and the liquid inlet end of the 2-12 bubble remover at a constant temperature of 50 ℃, the liquid inlet end of the No. 5 pump in the 2-5 peristaltic pump is connected with the liquid outlet end of the 2-12 bubble remover, the liquid outlet end of the No. 5 pump in the 2-5 peristaltic pump is connected with the liquid inlet end of the 2-14 bubble remover, the liquid outlet end of the 2-14 bubble removing pipe is connected with the liquid inlet end of the 2-11-2 filter head, and the liquid outlet end of the 2-11-2 filter head is connected with the liquid inlet end of the 3-1 long optical path liquid core optical fiber in the detection unit 3; one end of the 3-1 long-path liquid core optical fiber is connected with the 3-3LED through the optical fiber, the other end of the 3-1 long-path liquid core optical fiber is connected with the 3-2 spectrometer through the optical fiber, and the 3-2 spectrometer is connected with the 3-4 computer through a USB connecting wire.
As shown in FIG. 2, the standard of a spiral tube of the single-channel spiral tube sampler in the sampling unit 1 is that the winding diameter is 2cm, the spiral tube is wound ten times anticlockwise, the inner diameter of the spiral tube is 2mm, the outer diameters of a 1-1 sampling gas port and a 1-4 tail gas outlet are 6mm,1-2 is a liquid inlet end, 1-5 is a liquid outlet end, the outer diameters are 4mm, the inner diameters are 2mm, and 1-3 is a constant temperature water inlet and outlet end.
Referring to fig. 3, the bubble remover structure in the gas/liquid transfer unit 2 is 2-12-1 is a mixed liquid inlet, 2-12-2 is an exhaust port, 2-12-3 is a waste liquid outlet, 2-12-4 is a liquid outlet, and the liquid discharged from 2-12-4 enters the LWCC for detection.
As shown in fig. 4, the gas/liquid transfer unit 2 is a self-made cadmium column. The raw material is cadmium particles, the filling method is to fill the cadmium particles into a 1/4 inch tetrafluoro tube, the length is about 30mm, the two ends are filled with glass wool, the tube is washed by water for several times, and the tetrafluoro joint is used as the joint. 4-1 is cadmium particles, 4-2 is glass wool, and the glass wool has the function of preventing the cadmium particles from entering a pipeline to cause blockage.
The drying pipe 2-2 in the gas/liquid transmission unit 2 is filled with silica gel in the first part for removing water vapor in the tail gas, and is filled with activated carbon in the second part for removing hydrochloric acid in the tail gas. 2-3 mass flowmeter sampling range is the mass flowmeter of 2slm, and 2-4 sampling pump is the diaphragm pump. 2-15 is constant temperature water bath for providing constant temperature condition for the sampling unit 1, the temperature set value is 20 ℃ during sampling, and the water bath liquid is water. The 2-6 buffer solution is an ammonium chloride solution with pH=8.5 (+ -0.1), the 2-7 absorption solution is a mixed solution of sulfanilamide and hydrochloric acid, and the 2-8 dyeing solution is a naphthalene ethylenediamine hydrochloride solution.
The connecting optical fiber used in the detection unit 3 is an optical fiber with a core diameter of 400 um.
For the connecting pipelines in the device, wherein all the gas connecting pipelines are 1/4 inch tetrafluoro pipes; in the liquid connecting pipeline, except for the liquid connecting pipeline from the third end of the three-way mixing cavity 2-9-1 to the liquid core optical fiber with long optical path, a 1/16 inch PEEK pipe is adopted, so that the probability of generating bubbles in the transportation of the liquid pipeline is reduced; the remaining liquid connection lines were all 1/16 inch tetrafluoro tubes.
Brief description of the invention in operation workflow, as shown in figure 1, 2-6 buffer solution is pumped into the front end liquid inlet of a single spiral pipe sampler in a sampling unit 1, such as 1-2 in figure 2, by a No. 6 pump in a 2-5 peristaltic pump, gaseous nitric acid and gaseous nitrous acid in gas passing through the air inlet of the spiral pipe sampler 1-1 in figure 2 are absorbed by the buffer solution in the spiral pipe, then liquid enters the bubble remover by a front end liquid outlet of 1-5 in figure 2 through a No. 3 pump in figure 1-5 and then enters a cadmium column through a No. 4 pump, nitrate ion-containing solution is reduced into nitrite ions through a 2-10 cadmium column, then the liquid enters the first end of a 2-9-1 three-way mixing cavity through the filtering action of a 2-11-1 filter head, simultaneously, 2-7 absorption liquid (R1) and 2-8 dyeing liquid (R2) are pumped into two ends of a 2-9-2 tee mixing cavity through a No. 2 pump and a No. 1 pump of a 2-5 peristaltic pump respectively, a third end of the 2-9-2 tee mixing cavity is connected with a second end of the 2-9-1 tee mixing cavity, the mixed liquid of the two ends is discharged through a third end of the 2-9-1 tee mixing cavity, a PEEK pipe which is heated at constant temperature enters a bubble remover through a 2-12-1 in a graph in FIG. 3, primarily bubble-removed liquid is discharged through a 2-12-4, the discharged liquid enters a 2-14 bubble removing pipe through a No. 5 pump of the 2-5 for secondary bubble removal and a 2-11-2 um tetrafluoro filtering membrane connected with the bubble removing pipe enters a 3-1 long optical path liquid core optical fiber in a detection unit 3, the light source 3-3 is connected with the optical path inlet of the 3-1 long optical path liquid core optical fiber through an optical fiber, the 3-2 spectrometer (Ocean Optics USB 2000+) is connected with the optical path outlet of the 3-1 long optical path liquid core optical fiber through an optical fiber, the detected waste liquid is discharged, and the detection signal of the 3-2 spectrometer is recorded in a 3-4 computer through a USB connecting wire and waits for data analysis.
In the application of the invention, the data signal is stored in a computer and stored as the light intensity of the corresponding wavelength, the required absorption wavelength (550 nm or 580nm, depending on the concentration of gaseous nitric acid in the environment at the moment) and the reference wavelength (650 nm) are selected. The signal is the total signal of nitrous acid obtained by reducing gaseous nitric acid in air and the original gaseous nitrous acid in air. The signal of the original gaseous nitrous acid in the air is subtracted to obtain the liquid phase concentration of the gaseous nitrous acid in the air through the standard curve formulas of absorbance, nitrate and nitrite, and then the gaseous nitric acid concentration in corresponding time is obtained through temperature, liquid flow rate, gas flow rate and pressure correction, and the processing process is referred to in fig. 4.
It should be noted that the purpose of the disclosed embodiments is to aid further understanding of the present invention, but those skilled in the art will appreciate that: various alternatives and modifications are possible without departing from the spirit and scope of the invention and the appended claims. Therefore, the invention should not be limited to the disclosed embodiments, but rather the scope of the invention is defined by the appended claims.
Claims (8)
1. The on-line measuring method for the gaseous nitric acid in the atmosphere based on the flow injection analysis comprises the following steps:
1) Reducing gaseous nitric acid into nitrous acid by adopting a cadmium column reduction method; specifically comprises the steps 11) to 12):
11 Collecting HNO by a spiral tube sampler 3 Then will catch HNO 3 Is transferred into a cadmium column by a peristaltic pump;
12 The cadmium column has high reduction efficiency after pretreatment, and nitrate ions in the solution flowing through the cadmium column are reduced into nitrite ions; the solution passing through the cadmium column becomes a solution containing nitrite ions;
2) The method for detecting nitrite by using the Grignard-Sartzmann colorimetric method adopts a flow injection method, and continuously collects nitrite by using Grignard reagent; specifically comprising the steps 21) to 24):
21 Conveying the solution containing nitrite ions passing through the cadmium column into a first three-way mixing cavity by a peristaltic pump;
22 Conveying the absorption liquid and the dyeing liquid to a second three-way mixing cavity by a peristaltic pump for mixing, wherein the absorption liquid and the dyeing liquid are the Gris reagent;
23 The mixed solution in the second three-way mixing cavity enters the first three-way mixing cavity and is mixed with the nitrite ion-containing solution in the step 21), and the mixed solution is azo dye;
24 Continuously conveying azo dye in the first three-way mixing cavity into the long-path liquid core optical fiber by a peristaltic pump for detection;
3) Transmitting by peristaltic pump, and carrying out colorimetric analysis on the collected gas sample by combining with long-optical-path liquid core optical fiber;
4) The computer program obtains a measuring signal which is a signal of gaseous nitric acid and gaseous nitrous acid together; and meanwhile, gaseous nitrous acid signals in the atmosphere are obtained by measuring by a gaseous nitrous acid signal measuring instrument, and the gaseous nitrous acid signals in the atmosphere are subtracted by a computer program to obtain the concentration of the gaseous nitrous acid in the atmosphere, so that the high-precision high-time-resolution high-accuracy indirect online measurement of the gaseous nitric acid is realized.
2. The method for the on-line measurement of atmospheric gaseous nitric acid according to claim 1, wherein step 11) is performed by heating the spiral tube sampler in a water bath at 20 ℃.
3. The online measurement method of atmospheric gaseous nitric acid according to claim 1, wherein in the step 2), the third end of the first three-way mixing cavity is specifically connected with the liquid inlet end of the bubble removing device through a 1/16 inch PEEK tube; the liquid outlet end of the bubble removing device is connected with the liquid inlet of the peristaltic pump through a 1/16 inch PEEK pipe, and the liquid outlet of the peristaltic pump is connected with the liquid inlet end of the bubble removing pipe through a 1/16 inch PEEK pipe; and heating the 1/16 inch PEEK tube about three meters in front of the liquid inlet end of the bubble remover at constant temperature by using a heating accessory, and accelerating the reaction rate of the nitrite ion-containing solution and the mixed solution of the absorption liquid and the dyeing liquid, so that the dyeing solutions entering the long-optical-path liquid core optical fiber are all kept in the same dyeing degree state.
4. The method for online measurement of atmospheric gaseous nitric acid according to claim 1, wherein the first three-way mixing cavity and the second three-way mixing cavity are in a liquid drop collision and mixing mode.
5. The on-line measuring method of atmospheric gaseous nitric acid according to claim 1, wherein the spiral tube sampler winds a glass sampler with a pipe diameter of 2mm, the winding number of turns is 10, the winding diameter is 2cm, and HNO is improved by high winding number of turns 3 The residence time in the spiral tube improves the absorption efficiency.
6. The method for online measurement of atmospheric gaseous nitric acid according to claim 1, wherein the cadmium column is filled with cadmium particles by using a tetrafluoro tube, and HCI and NH are utilized 4 CI flushing improves the reduction efficiency of cadmium particles.
7. The method for online measurement of atmospheric gaseous nitric acid according to claim 1, wherein the absorbing solution and the staining solution in step 2) are prepared low-concentration solutions; the absorption liquid is dissolved in 1L of pure water by adopting 1g of sulfanilamide plus 10ml of HCl; the dyeing liquid is prepared by dissolving 0.02g of naphthalene ethylenediamine hydrochloride in 1L of pure water.
8. An on-line measuring device for atmospheric gaseous nitric acid is adopted to realize the measurement of the concentration of the gaseous nitric acid in the atmosphere based on flow injection analysis; the device at least comprises a sampling unit, a gas/liquid transmission unit and a detection unit;
the sampling unit comprises a spiral tube sampler;
the gas/liquid transmission unit comprises a mass flowmeter, a diaphragm pump, a drying pipe, a safety bottle, a peristaltic pump, a cadmium column, a three-way mixing cavity, a bubble remover, a filter membrane, a bubble removing pipe, buffer solution, absorption liquid, dyeing liquid, a plurality of 1/4 inch tetrafluoro pipes, 1/16 inch tetrafluoro pipes and 1/16 inch PEEK pipes;
the detection unit comprises an LED light source, a spectrometer, an optical fiber, a long-optical-path liquid core optical fiber, a notebook computer, a driving power circuit and a USB connecting wire;
the spiral tube sampler is a single-channel spiral tube sampler and is provided with a gas inlet, a gas outlet, a liquid inlet, a liquid outlet, a water bath water inlet and a water bath water outlet; the peristaltic pump comprises a plurality of channels, and each channel uses a peristaltic tube comprising a liquid inlet and a liquid outlet; the cadmium column, the filter membrane and the bubble remover all comprise a liquid inlet end and a liquid outlet end; the three-way mixing cavity comprises a first three-way mixing cavity and a second three-way mixing cavity; the spectrometer comprises a signal receiving end and a signal output end;
the gas inlet of the spiral tube sampler is connected with the gas sampling tube, and the gas outlet of the spiral tube sampler is connected with the safety bottle; the drying pipe is connected with the mass flowmeter; the mass flowmeter is connected with the diaphragm pump; the liquid inlet of the spiral tube sampler is connected with the liquid outlet of a No. 6 pump of the peristaltic pump; the buffer solution is connected with liquid inlet through a No. 6 pump liquid inlet of the peristaltic pump; the absorption liquid is connected with a liquid inlet end of a No. 2 pump in the peristaltic pump, and a liquid outlet end of a No. 2 pump in the peristaltic pump is connected with a first end of a second three-way mixing cavity; the dyeing liquid is connected with a liquid inlet end of a No. 1 pump in the peristaltic pump, and a liquid outlet end of a No. 1 pump in the peristaltic pump is connected with a second end of the second three-way mixing cavity; the third end of the second three-way mixing cavity is connected with the second end of the first three-way mixing cavity; the liquid inlet end of the No. 3 pump of the peristaltic pump is connected with the liquid outlet of the spiral tube sampler; the liquid outlet end of the No. 3 pump is connected with the liquid inlet end of the bubble remover, and the liquid outlet end of the bubble remover is connected with the liquid inlet of the No. 4 pump of the peristaltic pump; the liquid outlet end of the No. 4 pump is connected with the liquid inlet end of the cadmium column, the liquid outlet end of the cadmium column is connected with the liquid inlet end of the filter membrane, the liquid outlet end of the filter membrane is connected with the first end of the first three-way mixing cavity, the third end of the first three-way mixing cavity is connected with the liquid inlet end of the bubble removing device, the liquid outlet end of the bubble removing device is connected with the liquid inlet end of the No. 5 pump in the peristaltic pump, the liquid outlet end of the No. 5 pump in the peristaltic pump is connected with the liquid inlet end of the bubble removing pipe, the liquid outlet end of the bubble removing pipe is connected with the liquid inlet end of the filter membrane, the liquid outlet end of the filter membrane is connected with the liquid inlet end of the long-optical-path liquid core optical fiber, and the liquid outlet end of the long-path liquid core optical fiber discharges waste liquid into the waste liquid barrel; the LED light source is connected with the long-optical-path liquid core optical fiber light source inlet through an optical fiber; the optical signal receiving end of the spectrometer is connected with the long-optical-path liquid core optical fiber light source outlet through the optical fiber; the signal output end of the spectrometer is connected with the notebook computer through the USB connecting wire;
all gas connection pipelines in the device are tetrafluoro pipes with the diameter of 1/4 inch; the liquid connection pipeline comprises a 1/16 inch PEEK pipe and a 1/16 inch tetrafluoro pipe; the liquid connecting pipeline from the third liquid outlet of the first three-way mixing cavity to the liquid inlet of the long-optical-path liquid core optical fiber adopts a 1/16 inch PEEK pipe, and the liquid connecting pipelines of the rest parts are all 1/16 inch tetrafluoro pipes; the drying pipes are divided into two, the first drying pipe is filled with silica gel, and the second drying pipe is filled with activated carbon; the gas passing through the safety bottle first passes through the first drying tube and then enters the second drying tube.
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| CN111562257B (en) * | 2020-06-22 | 2024-06-18 | 北京大学 | On-line detection method and device for ultralow-concentration ammonia gas content |
| CN114166920B (en) * | 2020-08-19 | 2023-09-01 | 香港理工大学深圳研究院 | Method and system for measuring concentration of gaseous nitrous acid in ambient atmosphere |
| CN114755388A (en) * | 2022-06-15 | 2022-07-15 | 自然资源部第二海洋研究所 | Spiral copper-cadmium reduction device and method for seawater nitrate online analysis |
| CN115575340B (en) * | 2022-11-08 | 2023-03-10 | 杭州谱育科技发展有限公司 | Absorbance detection device and method |
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