CN111905534A

CN111905534A - Method for researching degradation efficiency of low-temperature plasma on volatile organic pollutants

Info

Publication number: CN111905534A
Application number: CN202010864253.9A
Authority: CN
Inventors: 俞元春; 曹毅; 俞菲; 潘畅; 万京林; 戴阳
Original assignee: Nanjing Suman Plasma Technology Co ltd; Nanjing Forestry University
Current assignee: Nanjing Suman Plasma Technology Co ltd; Nanjing Forestry University
Priority date: 2020-08-25
Filing date: 2020-08-25
Publication date: 2020-11-10

Abstract

The invention discloses a method for researching the degradation efficiency of volatile organic pollutants by low-temperature plasma, which researches styrene, m-xylene and mixed gas of styrene and m-xylene by adopting a low-temperature plasma purification device in a coaxial double-dielectric barrier discharge form, respectively researches the influence of different discharge voltages, inlet gas flow, inlet gas concentration and duty ratio on the removal rate and energy efficiency of the organic pollutants, explores the feasibility of simultaneously degrading the organic pollutants by the plasma, and lays a theoretical foundation for further industrial application of the plasma; further, analyzing the reaction product and researching a corresponding reaction mechanism; in addition, a preliminary expansion experiment is carried out on the m-xylene, and compared with the degradation performance under the laboratory condition, the method is more suitable for industrial treatment of practical application.

Description

Method for researching degradation efficiency of low-temperature plasma on volatile organic pollutants

Technical Field

The invention relates to the technical field of degradation of volatile organic pollutants, in particular to a method for researching the degradation efficiency of low-temperature plasma on volatile organic pollutants.

Background

Human beings cannot survive in the atmosphere. Fresh clean air is one of the important prerequisites for healthy human life. However, due to the rapid advance of urbanization and the rapid development of global economy in recent years, the population is growing explosively, a series of environmental pollution problems are also raised, and the problem of air pollution is more serious. The appearance of large-area haze weather in 2013 early in China arouses wide attention to the problem of air pollution in China, so that people can be more aware of the necessity of treating the air pollution at the present stage. According to the relevant data, the problem of atmospheric pollution is increasingly severe in China in recent years, and the research on the treatment of atmospheric environmental pollution is urgent. Among all the atmospheric pollutants, volatile organic pollutants (VOCs) are the most threatening, and not only do VOCs have primary pollution and are discharged into the atmosphere to generate a large amount of active radicals, but also can cause secondary pollution. Benzene series including organic waste gases containing VOCs such as styrene, meta-xylene and the like are released in the processes of production of a plurality of raw materials in chemical industry, synthesis of medical drugs, printing process and the like. It is shown by the relevant data that VOCs have been referred to as the current third atmospheric pollutants following SOX, NOX. At present, the pollution of the VOCs to the atmospheric environment not only seriously damages the current ecological environment, but also seriously damages the health of human beings, so that the research on the purification technology of the VOCs is of great significance.

In recent years, people pay more and more attention to the discharge problem of VOCs and research on VOCs purification technology, but because China has rapid industrial development in recent years, the discharge amount of VOCs per year is more and more, the current treatment situation is still not optimistic, and data shows that the total discharge amount of VOCs in China is more than 2500 million tons in 2020 according to the current development trend if no effective measures are taken. Therefore, the pollution problem of the VOCs in China is more and more severe, and the research on the treatment of the VOCs and the purification technology of the VOCs is not slow. At present, the purification technologies of VOCs are various and roughly divided into two categories, namely traditional purification technologies and novel purification technologies. The traditional purification technology is to remove VOCs by using a more traditional method, mainly comprising a combustion method, an absorption method, an adsorption method, a condensation method and the like, the novel purification technology is a new treatment technology appearing in recent years, and comprises a membrane separation method, a biological method, a photocatalytic degradation method, a low-temperature plasma technology and the like, but still has a plurality of problems to be further researched: (1) at present, most of the organic waste gases in industrial practical application are the mixture of various VOCs, and for the application of plasma industrialization, the research on the degradation of various mixed gaseous pollutants is necessary; (2) some harmful byproducts are generated when the VOCs are degraded by the plasma, and the reaction mechanism of degrading the VOCS by the plasma is not particularly clear at present, so that the reaction mechanism of degrading the VOCs by the plasma is still to be studied more deeply; (3) at present, most researches are limited to laboratory stages, and industrial experiments which are more suitable for practical application are rarely researched; (4) the problem of energy consumption of plasma is a big problem, but the influence factors on energy efficiency are not clear at present, so how to improve the energy utilization rate is a key problem to be researched next.

Disclosure of Invention

Aiming at the existing problems, the invention aims to provide a method for researching the degradation efficiency of low-temperature plasma on volatile organic pollutants, which lays a theoretical foundation for further industrial application of the plasma through researching the influence of different discharge voltages, air inlet flow, air inlet concentration and duty ratio on the removal rate and energy efficiency of the volatile organic pollutants, and simultaneously analyzes reaction products and researches corresponding reaction mechanisms.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

the method for researching the degradation efficiency of the low-temperature plasma on the volatile organic pollutants is characterized by comprising the following steps of S1: assembling each part of the laboratory low-temperature plasma degradation system;

s2: checking the air tightness of the low-temperature plasma degradation system;

s3: distributing gas until the inlet and the outlet of the reactor reach the same gas concentration and keep relatively stable;

s4: changing the electrical parameters and the gas parameters of the reactor, sampling and analyzing the gas at the outlet of the reactor when the gas concentration is relatively stable, and measuring the degradation rate, the energy efficiency and the degradation products of the low-temperature plasma on the volatile organic pollutants;

s5: repeating the steps, changing different electrical parameters and gas parameters, and researching the influence of other single factors on the degradation of volatile organic pollutants by the low-temperature plasma;

s6: assembling the low-temperature plasma degradation system for the amplification experiment, repeating the steps S2-S5, and carrying out the research of the amplification experiment.

Further, the volatile organic pollutant is styrene or m-xylene or mixed gas of styrene and m-xylene.

Further, the electrical parameters described in steps S4 and S5 include discharge voltage, discharge current, and power supply duty ratio, and the gas parameters include intake air flow rate and intake air concentration.

Further, the degradation rate of the volatile organic pollutants by the low temperature plasma in step S4 is determined by the following formula

The energy efficiency is determined by the formula

In the formula, eta is the degradation rate of volatile organic pollutants; c₀Of volatile organic pollutantsAn initial concentration; c₁Is the concentration of the volatile organic pollutants after reaction; energy efficiency as volatile organic pollutants; m is the molecular weight of the volatile organic pollutants; v is the velocity of the gas; p is the discharge power.

Further, the determination of the degradation product in step S4 includes determination of a gaseous product and a solid product.

Further, the laboratory low-temperature plasma degradation system in step S1 includes a gas distribution system, a reactor, a power supply system, and an analysis and test system; the gas distribution system for preparing gas is connected with the inlet of the reactor, the power supply system provides power for the reactor, the analysis test system comprises an electrical parameter test system and a gas parameter test system, the electrical parameter test system is electrically connected with the power supply system, and the gas parameter test system tests the parameters of the gas at the inlet and the outlet of the reactor.

Further, the air distribution system comprises a dry air compression bottle, a glass rotameter, a volatile organic pollutant generation bottle and a mixing bottle; the air in the dry air compression bottle and the volatile organic pollutants in the volatile organic pollutants generating bottle are mixed and diluted in the mixing bottle and then are introduced into the reactor, and the glass rotameter is connected to the dry air compression bottle and the volatile organic pollutants generating bottle and is used for controlling the flow of mixed air and organic pollutants.

Further, the expanded experimental low-temperature plasma degradation system in the step S6 includes a pulse high-voltage power supply system, a reactor, a fan and an analysis test system; the fan used for preparing gas is communicated with the inlet of the reactor, and the pulse high-voltage power supply system is electrically connected with the reactor; the analysis test system comprises an electrical parameter test system and a gas parameter test system, the electrical parameter test system is electrically connected with the pulse high-voltage power supply system, and the gas parameter test system tests parameters of gas at an inlet and an outlet of the reactor.

Further, the reactor comprises more than one low-temperature plasma reactor, and a plurality of low-temperature plasma reactors are connected in parallel.

The invention has the beneficial effects that:

1. the method takes styrene, m-xylene and mixed gas of styrene and m-xylene as research objects, researches the influence of different discharge voltages, inlet gas flow, inlet gas concentration and duty ratio on the degradation rate and energy efficiency of the plasma for degrading the volatile organic pollutants, analyzes degradation products, and researches the reaction mechanism of the low-temperature plasma for degrading the volatile organic pollutants;

2. according to the invention, 45 reactors under laboratory conditions are connected in parallel, a preliminary amplification test is carried out on the reactors, the influence of different discharge currents, air inlet flow, air inlet concentration and duty ratio on the removal rate of the m-xylene is researched, and a theoretical basis is laid for the application of plasma industrialization.

Drawings

Fig. 1 is a schematic structural diagram of a low-temperature plasma degradation system used in one embodiment to another embodiment of the present invention;

fig. 2 is a schematic diagram illustrating a connection between a discharge voltage and a current detection circuit according to a first embodiment to a third embodiment of the invention;

FIG. 3 is an exemplary graph of the output U, I-t curve of the oscilloscope during discharge voltage measurement according to the present invention;

FIG. 4 is an exemplary graph of a styrene standard curve fitted for VOCs concentration determination according to the present invention;

FIG. 5 is a schematic diagram of the Lissajous figure detection circuit of the present invention;

FIG. 6 is an illustration of a schematic representation of Lissajous on an oscilloscope according to the present invention;

FIG. 7 is a schematic diagram of Lissajous in Origin according to the present invention;

FIG. 8 is a graph showing the effect of discharge voltage on the styrene degradation rate and energy efficiency in a first embodiment of the present invention;

FIG. 9 is a graph showing the effect of power supply duty cycle on styrene degradation rate and energy efficiency in a first embodiment of the present invention;

FIG. 10 is a graph showing the effect of gas concentration on the rate of styrene degradation and energy efficiency in one example of the present invention;

FIG. 11 is a graph showing the effect of gas flow on the styrene degradation rate and energy efficiency in the first example of the present invention;

FIG. 12 is a GC-MS diagram of the gaseous products of the low temperature plasma degradation of styrene in accordance with one embodiment of the present invention;

FIG. 13 is a graph showing the effect of discharge voltage on meta-xylene degradation rate and energy efficiency in the second embodiment of the present invention;

FIG. 14 is a graph showing the effect of power supply duty cycle on meta-xylene degradation rate and energy efficiency in a second embodiment of the present invention;

FIG. 15 is a graph showing the effect of gas concentration on meta-xylene degradation rate and energy efficiency in example two of the present invention;

FIG. 16 is a graph showing the influence of gas flow on meta-xylene degradation rate and energy efficiency in example two of the present invention;

FIG. 17 is a GC-MS diagram of the gaseous products of the low temperature plasma degradation of meta-xylene in example two of the present invention;

FIG. 18 is a graph showing the effect of discharge voltage on the degradation rate of styrene-m-xylene mixed gas and single-species gas in the third example of the present invention;

FIG. 19 is a graph showing the effect of the concentration of gases on the degradation rate of the mixed gases of styrene and metaxylene and the degradation rate of a single gas in the third embodiment of the present invention;

FIG. 20 is a graph showing the effect of gas flow on the degradation rate of styrene-m-xylene mixed gas and single-species gas in the third example of the present invention;

FIG. 21 is a GC-MS diagram of a solid product of a mixed gas of low-temperature plasma degraded styrene and meta-xylene in the third embodiment of the present invention;

FIG. 22 is a schematic structural diagram of a low temperature plasma degradation system used in the fourth embodiment of the present invention;

FIG. 23 is a graph showing the effect of discharge current on the degradation rate of metaxylene and ozone concentration in the fourth example of the present invention;

FIG. 24 is a comparative histogram of ozone concentration with and without meta-xylene in example four of the present invention;

FIG. 25 is a graph showing the influence of gas flow on the meta-xylene degradation rate and ozone concentration in the fourth example of the present invention;

FIG. 26 is a graph showing the influence of the gas concentration on the meta-xylene degradation rate and the ozone concentration in the fourth example of the present invention;

wherein: 1-dry air compression bottle, 2-glass rotameter, 3-volatile organic pollutant generation bottle, 4-mixing bottle, 5-reactor, 6-high voltage power supply, 7-voltage regulator, A-reactor inlet, B-reactor outlet, 81-pulse high voltage power supply, 82-power control console, 821-power switch, 822-voltage detection interface, 823-current detection interface, 824-frequency converter, 825-main machine, 9-plasma reactor, 91-air inlet, 92-air outlet, 93-air inlet sampling valve, 94-air outlet sampling valve, 95-high voltage input end and 10-fan.

Detailed Description

In order to make those skilled in the art better understand the technical solution of the present invention, the following further describes the technical solution of the present invention with reference to the drawings and the specific embodiments.

The first embodiment is as follows:

the research method for degrading the volatile organic pollutant styrene by the low-temperature plasma comprises the following steps:

1. assembling a laboratory low-temperature plasma degradation system;

specifically, the laboratory low-temperature plasma degradation system is shown in the attached figure 1 and comprises a gas distribution system, a reactor, a power supply system and an analysis test system;

the air distribution system comprises a dry air compression bottle 1, a glass rotameter 2, a volatile organic pollutant generation bottle 3 and a mixing bottle 4; the air in the dry air compression bottle 1 and the volatile organic pollutants in the volatile organic pollutants generating bottle 3 are mixed and diluted in the mixing bottle 4 and then are introduced into the reactor 5, the glass rotameter 2 is connected to the dry air compression bottle 1 and the volatile organic pollutants generating bottle 3, two readings are provided on the glass rotameter 2, namely the total gas flow and the pollutant gas flow, and the flow of the mixed air and the organic pollutants is controlled by controlling the glass rotameter 2;

the reactor 5 adopts a coaxial double-medium barrier discharge reactor;

the power supply system comprises a high-voltage power supply 6 and a voltage regulator 7, wherein the high-voltage power supply 6 adopts a pulse modulation power supply produced by Nanjing Suman plasma technology Limited, the model of the power supply is CTP-2000K/P, the voltage adjustable range is adjustable from 0kV to 40kV, the central frequency is 1kHz to 100kHz, the adjustable frequency range is about 30 percent of the central frequency, the duty ratio is 0 to 100, and electrical parameter signals are recorded by an oscilloscope; the high-voltage power supply 6 is electrically connected with the reactor 5, the pressure regulator 7 is electrically connected with the high-voltage power supply 6, and the pressure regulator 7 regulates the discharge voltage of the high-voltage power supply 6;

the analysis test system comprises an electrical parameter test system and a gas parameter test system, and the electrical parameter test is realized by using a American national Taike TDS2014 type oscilloscope and a P6015A type high-voltage probe to detect the output waveform of the power supply. The testing of gas parameters is mainly divided into the determination of gas concentration and the analysis of products. The VOCs concentration is mainly measured by sampling gas before and after discharge and then detecting the gas concentration before and after reaction through a gas chromatograph; the ozone concentration is mainly detected by a portable ozone detector. The analysis of the products was mainly carried out by analyzing the kinds of the reaction products by using a Trace-DSQ single quadrupole gas chromatograph-mass spectrometer (GC-MS) of Thermo Fisher, USA.

2. Checking the air tightness of the low-temperature plasma degradation system;

3. distributing gas until the inlet and the outlet of the reactor reach the same gas concentration and keep relatively stable;

specifically, the invention adopts a bubbling method to distribute gas, simulates waste gas and uses a small amount of N₂The volatile organic pollutants are introduced into a volatile organic pollutants generating bottle 3 arranged in the thermostatic water bath, and because the temperature has certain influence on the concentration of the VOCs, the VOCs are placed in the thermostatic water bath at 22 ℃, the VOCs carrying certain concentration and the other path of air from the dry air compression bottle 1 are mixed and diluted in a mixing bottle and are mixed with the air to react with the thermostatic water bath at 22 ℃,because it is more consistent with industrial practice. The mixed simulated waste gas finally enters a coaxial double-dielectric barrier discharge plasma reactor.

4. Changing the electrical parameters and the gas parameters of the reactor, sampling and analyzing the gas at the outlet of the reactor when the gas concentration is relatively stable, and measuring the degradation rate, the energy efficiency and the degradation products of the low-temperature plasma on the volatile organic pollutants;

wherein the electrical parameters include discharge voltage and power supply duty cycle, and the gas parameters include intake air flow rate and intake air concentration.

Specifically, the discharge voltage is measured by recording with an oscilloscope, and the method comprises the following specific operation steps:

s41: the connecting equipment, considering safety, anti-interference and convenient operation, the reactor 5 is placed on the left side of the high-voltage power supply 6 host, no other electrical appliances and instruments are placed near the reactor 5, the voltage regulator 7 is placed on the high-voltage power supply 6, the other control and detection instruments are placed on the right side of the high-voltage power supply 6 host, and the schematic diagram of the discharge voltage and current detection circuit is shown in the attached figure 2.

S42, turning on the oscilloscope, turning on the power switch, and calibrating the oscilloscope;

s43: the oscilloscope starts to detect and record data, presses a 'measure' key, rotates a 'level' button to stabilize the waveform without flickering, adjusts the attenuation multiple of each channel to ensure that the waveform just fully covers the display range of the oscilloscope, and then stores the data in a U disk designated file;

s44: plotting and calculating the voltage and current, and opening the file stored before on a computer; an example of a curve U, I-t, U, I-t, is shown in FIG. 3 using Origin software.

The value of the Y coordinate of the voltage output signal is 1000:1 of the voltage divided by the capacitor, which is one thousandth of the actual discharge voltage, and the value of the Y coordinate of the current output signal is the voltage value obtained by sampling the current by the sampling resistor of 50 omega, i.e. I (A) multiplied by 50 (omega), so that the value of the output current is the value of the acquired ordinate divided by 50.

Further, VOC before and after treatment_SZhejiang fuli concentration analyzerModel 9790 gas chromatograph manufactured by Limited company for measuring VOC by adopting area external standard method_SConcentration calibration, the concrete operation steps are as follows:

preparing an ethanol solution of styrene, uniformly mixing 50ml of absolute ethanol and 1ml of styrene, and then sequentially injecting 0.1 mu l, 0.2 mu l, 0.3 mu l, 0.4 mu l, 0.5 mu l, 0.6 mu l, 0.7 mu l, 0.8 mu l, 0.9 mu l and 1.0 mu l into a gas chromatograph to obtain chromatographic peak areas with different concentrations, and finally obtaining a standard curve of the styrene by fitting, wherein the illustration is shown in figure 4.

Further, the degradation rate is determined by the formula

The energy efficiency is determined by the formula

In the formula, eta is the degradation rate of volatile organic pollutants; c₀Is the initial concentration (mg/m) of volatile organic contaminants³)；C₁Is the concentration (mg/m) of the volatile organic pollutants after reaction³) (ii) a Energy efficiency (g/kwh) for volatile organic pollutants; m is the molecular weight (g/mol) of the volatile organic pollutants; v is the velocity of the gas (L/min); p is discharge power (W).

Further, the discharge power is measured by a voltage-charge lissajous diagram method, which is based on the principle that a measuring capacitor C is connected in series on the ground side of the discharge reactor, the voltage at the discharge poles is V, and if the discharge delivers a charge of Q, the current flowing through the circuit is:

the discharge power is therefore:

wherein T is a discharge period(s); f is the discharge frequency (Hz).

The Lissajous figure detection circuit is connected with a schematic diagram shown in the attached figure 5, an oscilloscope power supply is turned on, a knob is adjusted to enable a waveform to just fully cover an oscilloscope screen, a Display key is pressed down, a Display mode is adjusted to Display a closed curve, namely a Lissajous figure, as shown in the attached figure 6, the ordinate of an I-t curve is set as an X-axis coordinate, the ordinate of a V-t curve is set as a Y-axis coordinate, and the Sa-Lissajous figure is made by Origin software, as shown in the attached figure 7. It can be found that the area enclosed by the closed curve is exactly in a direct proportion to the energy consumed by the discharge in one period, and then the discharge power is: p ═ fA.

Further, the concentration of ozone in the degradation product is mainly detected by a portable ozone detector. The analysis of the product was mainly carried out by analyzing the kinds of gaseous and solid by-products of the reaction using Trace-DSQ single quadrupole gas chromatography-mass spectrometer (GC-MS) of Thermo Fisher, USA, respectively. According to the difference of the peak-appearing time of the total ion flow, the chromatogram is retrieved from the NIST spectrum library for qualitative analysis, and the corresponding degradation reaction mechanism is further discussed according to the product. The detection conditions are as follows: the mass spectrum detector is 100eV, the injection port temperature is 300 ℃, the carrier gas is high-purity helium, and the detection fragment range is 50-450 amu.

5. Different electrical parameters and gas parameters are changed, and the influence of other single factors on the degradation of volatile organic pollutants by the low-temperature plasma is researched.

Specifically, under the conditions that the power frequency is 200Hz, the styrene inlet concentration is 37-90mg/m3, the gas flow is 0.48m3/h, and the pulse duty ratio is 50%, the influence of the discharge voltage on the degradation performance of the styrene is researched, and the result is shown in Table 1 and the attached figure 8;

TABLE 1 influence of discharge Voltage on the degradation Rate of styrene and energy efficiency

As can be seen from table 1 and fig. 8, the degradation rate of styrene is greater as the discharge voltage is increased under otherwise the same conditions. When the discharge voltage is 22.8kV, the degradation rate of styrene is 12.69%, and when the discharge voltage is 37.2kV, the degradation rate of styrene is 88.48%, which is improved by 75.79%, because the energy density is increased due to the increase of the discharge voltage, the more energetic electrons and active groups are generated in the reactor, the more the styrene is easy to collide with the energetic electrons for reaction, and the degradation rate of styrene is improved accordingly. However, the higher the voltage, the better, and it can be seen in fig. 8 that when the voltage is increased to 38.8kV, the styrene degradation rate is also reduced, which may be caused by the phenomenon that dielectric breakdown occurs due to the high local field strength, so that plasma cannot be generated. Meanwhile, the energy efficiency is increased and then reduced along with the increase of the discharge voltage, when the voltage is 35.6kV, the energy efficiency is the largest, the energy loss is the smallest, and the discharge voltage of 35.6kV is selected as the optimal voltage in consideration of the economical efficiency of industrial application.

Further, the inlet concentration of styrene is 23-38mg/m under the condition that the power frequency is 200Hz³Gas flow of 0.48m³The results of studying the effect of the power supply duty ratio on the degradation performance of styrene under the condition of a discharge voltage of 35.6kV are shown in Table 2 and FIG. 9;

TABLE 2 Effect of duty cycle on styrene degradation Rate and energy efficiency

As can be seen from table 2 and fig. 9, the degradation rate of styrene increases with the increase of the power supply duty ratio, when the power supply duty ratio is 0.05, the degradation rate is 78.61%, and when the power supply duty ratio is 0.5, the degradation rate of styrene is 96.62%, which is increased by 18.01%, because when the power supply duty ratio is larger and larger, the discharge time is longer and longer, and the generated active particles are more and more, so the degradation rate of styrene increases. It can also be seen from fig. 9 that the power supply duty cycle is not the main factor affecting the degradation performance of styrene. However, the higher the power supply duty ratio, the better, the energy consumption problem exists, it can be seen that the energy efficiency curve is parabolic, and when the power supply duty ratio is 30%, the energy efficiency of styrene is the highest, the energy consumption is the smallest, namely, an optimal power supply duty ratio of 30% exists, which has a certain meaning for reducing the energy consumption of the plasma in the application of treating the waste gas.

Further, the influence of the discharge voltage on the degradation performance of styrene was investigated under the conditions of a power frequency of 200Hz, a discharge voltage of 35.6kV, a gas flow rate of 0.48m3/h, and a pulse duty ratio of 30%, and the results are shown in Table 3 and FIG. 10.

TABLE 3 influence of concentration on the degradation rate of styrene and energy efficiency

As can be seen from Table 3 and FIG. 10, the degradation rate of styrene decreases with increasing gas concentration, when the inlet concentration is 51.7668mg/m³When the concentration is 1006.5341mg/m, the degradation rate of the styrene is 86.48 percent³When the degradation rate is 7.73%, the degradation rate is reduced by 78.75%, and the influence of the gas concentration on the degradation rate of the styrene is still great. Under the condition of certain discharge conditions, the number of active particles generated by the reactor is certain, so that the probability of collision of a single styrene molecule with the active particles is lower along with the increase of the initial concentration, and the degradation rate of the styrene is reduced. However, it can be found that the energy efficiency is increased along with the increase of the concentration, and the concentration of the actual waste gas is higher, so the conclusion is favorable for guiding the treatment of the actual waste gas.

Further, the inlet concentration of styrene is 16-88mg/m under the condition that the power frequency is 200Hz³The results of examining the influence of the gas flow rate on the degradation performance of styrene under the conditions of a discharge voltage of 35.6kV and a power supply duty ratio of 30% are shown in table 4 and fig. 11.

TABLE 4 influence of the flow on the degradation rate of styrene and energy efficiency

As is apparent from Table 4 and FIG. 11, under other conditions, the degradation rate of styrene tends to decrease with the increase of the gas flow rate, and when the gas flow rate is 0.24m³/h、0.32m³/h、0.48m³/h、0.64m³/h、 0.8m³The degradation rates of styrene are 0.7992, 0.6953, 0.342, 0.2608 and 0.2265 respectively. This is because as the gas flow rate increases, the shorter the gas residence time under the reactor, the less the probability of styrene molecules colliding with high-energy electrons, and thus the degradation rate of styrene decreases. However, it can be seen from FIG. 11 that the energy efficiency of styrene increases with increasing flow rate. The actual gas flow of the waste gas is relatively large, so the conclusion also has certain significance on the treatment of the actual waste gas.

Further, a GC-MS coupling technology is adopted to analyze gaseous product species of the dielectric barrier discharge plasma degraded styrene, a gas sample injection needle is adopted to carry gas sample injection, and gas sampling bags are adopted for gas storage. As shown in the attached FIG. 12, it can be seen that the main gaseous products of the coaxial dual-dielectric barrier discharge plasma degradation of single styrene are benzene, toluene, aromatic aldehyde, aromatic acid, phenyl ethylene oxide and other aromatic compounds. Also, a yellow oily substance was observed to appear on the wall of the plasma reactor after several hours of discharge.

At present, the research on the reaction mechanism of low-temperature plasma for purifying organic waste gas is rare, but the process of low-temperature plasma for purifying VOCs is generally considered to be divided into three aspects: the high-energy electrons directly collide with VOCs molecules, huge high-energy electron energy is generated at the moment of discharge, and once the energy required by molecular chemical bond breakage is exceeded, chemical bonds of some gas pollutant molecules can be directly opened; the high-energy electrons react with background gas to generate a large amount of active particles; the active particles then undergo a series of reactions with previously formed fragment groups or atoms, thereby eventually mineralizing the VOCs molecules into CO2, CO and H2O. The following three aspects are respectively used for researching and explaining the reaction mechanism of the coaxial double-dielectric barrier discharge plasma for degrading the single styrene.

a high-energy electrons directly collide with styrene molecules

C₆H₅-CH＝CH₂+e→C₆H₅-CH-CH₂·

C₆H₅-CH＝CH₂+e→C₆H₅-CH＝CH·+H·

C₆H₅-CH＝CH₂+e→C₆H₅·+·CH＝CH₂

C₆H₅-CH＝CH₂+e→C₆H₄·-CH＝CH₂+H·

C₆H₅-CH＝CH₂+e→CH₂-CH-C(CH)＝CH-CH＝CH-CH·

b high energy electrons reacting with background gas

O₂+e→O+O

O·+H·→OH·

O₂+H·→HO₂·

c reactive particles reacting with the formed fragment groups or atoms

The OH, H and oxygen atoms continue to react with groups such as phenyl and vinyl generated by the direct collision of high-energy electrons and styrene molecules, and finally the groups are oxidized into CO and CO₂And H₂And O. The product analysis also found that the degradation products were benzaldehyde, phenol, etc., which were the result of the reaction of these radical fragments with oxygen. Benzene and toluene are found in the gaseous product, which further illustrates the crucial role of h.radicals in the degradation reaction. Nitrogen-containing substances such as p-nitrophenol and the like are also found in the solid product, and although the bond energy of nitrogen is large, a small amount of nitrogen is broken by high-energy electrons, so that some nitrogen-containing compounds are generated.

In summary, under the laboratory conditions, the coaxial dual-medium barrier discharge plasma reactor is used to study the influence of reactant concentration, flow, power duty ratio, discharge voltage on the degradation rate and energy efficiency of styrene, with low-concentration styrene in the air as the target study object, and the conclusion is as follows:

(1) the degradation rate of styrene can be obviously improved by the increase of the discharge voltage, when the discharge voltage is 22.8kV, the degradation rate of styrene is 12.69%, and when the discharge voltage is 37.2kV, the degradation rate of styrene reaches 88.48%, which is sufficiently improved by 75.79%. The energy efficiency is increased and then reduced, and when the voltage is 35.6kV, the energy efficiency is the maximum, and the higher degradation rate can be kept.

(2) The degradation rate of styrene can be increased to a certain extent by increasing the duty ratio, the maximum degradation rate of 96.62% is reached when the duty ratio is 0.5, the energy efficiency curve is increased and then reduced, and the maximum degradation rate is reached when the duty ratio is 30%, namely the energy consumption is minimum.

(3) The degradation rate curve of styrene shows a downward trend with increasing flow rate, while the energy efficiency curve shows an upward trend with the opposite, at a flow rate of 0.8m³At/h, the energy efficiency reaches a maximum.

(4) The increase of the concentration can obviously reduce the degradation rate of the styrene, and when the inlet concentration is 51.7668mg/m³When the concentration is 1006.5341mg/m, the degradation rate of the styrene is 86.48 percent³When the concentration of the styrene is higher and higher, the degradation rate is 7.73 percent, the degradation rate is reduced by 78.75 percent, and the energy efficiency is increased along with the concentration of the styrene, and the concentration is 1006.5341mg/m³To a maximum.

Example two:

the research method for degrading the volatile organic pollutant m-xylene by the low-temperature plasma has the same specific steps, and the adopted measuring system and measuring method as the embodiment.

Under the condition that the power frequency is 200Hz, the inlet concentration of the m-xylene is 30-67mg/m³Gas flow of 0.48m³The results of studying the effect of discharge voltage on the degradation performance of meta-xylene under the condition of 50% duty ratio of power supply are shown in table 5 and fig. 13.

TABLE 5 Effect of discharge Voltage on meta-xylene degradation Rate and energy efficiency

As can be seen from Table 5 and FIG. 13, the degradation rate of m-xylene increased with an increase in discharge voltage. When the discharge voltage is 19.6kV, the degradation rate of the m-xylene is 16.44%, and when the discharge voltage is 40kV, the degradation rate of the m-xylene is 51.08%, which is improved by 34.64%, because the increase of the discharge voltage leads to the increase of the energy density, so that the more high-energy electrons and active groups are generated in the reactor, the more the m-xylene molecules are easy to collide with the high-energy electrons for reaction, and the degradation rate of the m-xylene is improved. However, it can also be seen from FIGS. 8 and 13 that the degradation rate of meta-xylene is lower than that of styrene, and is only 51.08% at the highest, indicating that meta-xylene is more difficult to degrade than styrene. Meanwhile, the energy efficiency is increased firstly and then reduced along with the increase of the discharge voltage, when the voltage is 37.5kV, the energy efficiency is maximum, the energy loss is minimum, and the voltage is very close to the optimal voltage for styrene degradation, so that the optimal voltage of different types of VOCs is not greatly different, and the method has great guiding significance for the subsequent treatment of mixed gas.

Further, the inlet concentration of the m-xylene is 49-83mg/m under the condition that the power frequency is 200Hz³Gas flow of 0.48m³The effect of the power duty ratio on the degradation performance of meta-xylene under the discharge voltage of 37.5kV was investigated, and the results are shown in Table 6 and FIG. 14.

TABLE 6 influence of duty cycle on meta-xylene degradation rate and energy efficiency

As is apparent from table 6 and fig. 14, as the duty ratio of the power supply is larger and larger, the meta-xylene curve tends to be upward, and when the duty ratio of the power supply is 50%, the degradation rate of the meta-xylene reaches a maximum of 66.84%, because the duty ratio of the pulse power supply is a ratio of the pulse time to the total pulse period, and the larger the duty ratio of the pulse power supply is, the longer the pulse time is, the more active particles are generated, and the degradation rate of the meta-xylene increases. It can also be seen from fig. 14 that the energy efficiency curve rises first and then falls, reaching a maximum at a power duty cycle of 40%, unlike styrene, which has an optimum power duty cycle of 30% and is 10% smaller than m-xylene, which is likely to be smaller since styrene is more easily degraded than m-xylene, producing more active particles at the same voltage, and therefore requiring a shorter pulse time.

Further, the effect of the gas concentration on the degradation performance of meta-xylene was investigated under the conditions of a power frequency of 200Hz, a discharge voltage of 37.5kV, a gas flow rate of 0.48m3/h, and a pulse duty of 30%, and the results are shown in Table 7 and FIG. 15:

TABLE 7 Effect of concentration on meta-xylene degradation Rate and energy efficiency

As can be seen from Table 7 and FIG. 15, the degradation rate of meta-xylene decreased with increasing concentration, when the gas concentration was 30mg/m³When the gas concentration is 1059mg/m, the degradation rate of m-xylene is 64.56%³When the degradation rate is 38.56%, the degradation rate is reduced by 26%, and compared with styrene, the degradation rate of the m-xylene is found to have a more gradual trend, which indicates that the styrene is more sensitive to the condition of the inlet concentration. Under the condition of certain discharge conditions, the number of active particles generated by the reactor is certain, so that as the gas concentration is increased, single m-xylene molecules are more difficult to collide with the active particles, and the degradation rate of the m-xylene is reduced. However, the energy efficiency is increased along with the increase of the concentration as the same as that of styrene, and the conclusion has guiding significance for treating mixed waste gas in industry and also shows good development prospect of purifying industrial waste gas by low-temperature plasma.

Further, the method comprisesUnder the condition that the power frequency is 200Hz, the inlet concentration of the m-xylene is 17-75mg/m³The results of studying the effect of gas flow rate on meta-xylene degradation performance under the conditions of discharge voltage of 37.5kV and pulse duty ratio of 30% are shown in table 8 and fig. 16:

TABLE 8 influence of flow on meta-xylene degradation Rate and energy efficiency

As is apparent from Table 8 and FIG. 16, under other conditions, the degradation rate of meta-xylene tended to decrease as the gas flow rate increased, and when the gas flow rate was 0.24mg/m³、0.32mg/m³、0.48mg/m³、 0.64mg/m³、0.8mg/m³The degradation rates of styrene were 0.4881, 0.4491, 0.3177, 0.1335, and 0.064, respectively. This is because the shorter the gas stays under the reactor as the gas flow rate increases, the smaller the probability of the m-xylene molecules colliding with the energetic electrons, and the degradation rate of m-xylene decreases. However, it can be seen from fig. 15 that the energy efficiency of meta-xylene increases with the increase of the flow rate, which is consistent with the rule of styrene flow rate and energy efficiency, and the flow rate of the general practical industrial waste gas is relatively large, so that the conclusion is of certain significance for the treatment of the practical industrial waste gas.

Furthermore, the gas product type of the dielectric barrier discharge plasma degraded metaxylene is analyzed by adopting a GC-MS coupling technology, a gas sample injection needle is adopted for sample injection with gas, and a gas sampling bag is adopted for gas storage. The analysis is shown in FIG. 17. As can be seen from the figure, the main gaseous products of the coaxial dual-dielectric barrier discharge plasma for degrading the mono-m-xylene are found to be ketones such as hexenone and nonanone, aldehydes such as 3-methylbutyraldehyde and pentanal, alcohols such as pentanol and octenol, acids such as n-hexanoic acid and the like through GC-MS analysis, and the existence of a small amount of amines and amides is also found, which indicates that in the process of degrading the m-xylene through the coaxial dual-dielectric barrier discharge plasma, although the bond energy of nitrogen is very large, a small amount of nitrogen is broken by high-energy electrons, so that some nitrogen-containing compounds are generated. As a result of the examination, a siloxane copolymer or the like was also found, and actually, a solid phase flowed out of the column at an elevated temperature. Also, a yellow oily substance was observed to appear on the wall of the plasma reactor after several hours of discharge.

Furthermore, the research and the explanation are respectively carried out on the reaction mechanism of the coaxial double-dielectric barrier discharge plasma for degrading the single metaxylene from three aspects of direct collision of high-energy electrons and styrene molecules, action of the high-energy electrons and background gas and reaction of active particles and formed fragment groups or atoms.

a high-energy electrons directly collide with styrene molecules

The collision of high-energy electrons with meta-xylene molecules can cause the following three reactions: the C-H bond on the methyl group is broken; the C-C bond between the methyl group and the benzene ring is broken; replacing H on the benzene ring.

b high energy electrons reacting with background gas

O₂+e→O+O

O·+H·→OH·

O₂+H·→HO₂·

c reactive particles reacting with the formed fragment groups or atoms

The reaction between active particles and fragment groups generated by collision of high-energy electrons with background gas mainly has two aspects, one is that C-C bonds on benzene rings of m-xylene are broken, the benzene rings are opened, some intermediate products such as alkanes, acids, ketones and the like are generated under the action of free radicals, and finally the intermediate products are oxidized into CO2, CO and H2O under the action of active particles, and the other is that C-H bonds on methyl groups in m-xylene and C-H bonds on the benzene rings are broken to generate some benzene ring derivatives under the action of the active particles, for example: the organic matters with benzene rings such as m-tolualdehyde, m-methylbenzyl alcohol, 3, 5-xylenol and the like are detected in the analysis of the front solid products because the organic matters with the benzene rings generally have larger molecular weights and are difficult to volatilize, so that the organic matters are easier to accumulate on the inner wall of the reactor.

In summary, under laboratory conditions, a coaxial dual-dielectric barrier discharge plasma reactor is used to study the effects of reactant concentration, gas flow, power duty ratio and discharge voltage on the degradation rate and energy efficiency of m-xylene, and it is found that the degradation rate curve and the energy curve have the same trend as styrene in example one, but the overall degradation rate and energy efficiency of m-xylene are lower than that of styrene, the degradation rate of m-xylene is only 66.84% at most, and the maximum degradation rate of styrene is as high as 96.62%, which indicates that m-xylene is more difficult to degrade and has higher energy consumption than styrene. It was also found that the magnitude of the increase and decrease in meta-xylene degradation rate was also small compared to styrene, indicating that styrene is more sensitive to these several influencing factors and is more demanding on laboratory conditions.

Example three:

the research method for degrading the mixed gas of the volatile organic pollutant styrene and the m-xylene by the low-temperature plasma comprises the specific steps, and the adopted measuring system and measuring method are the same as those of the first embodiment and the second embodiment.

The inlet concentration of styrene is 42-74mg/m under the condition that the power frequency is 200Hz³The inlet concentration of the m-xylene is 32-83mg/m³Gas flow of 0.48m³And h, under the condition that the duty ratio of the power supply is 50%, researching the influence of the discharge voltage on the degradation performance of the mixed gas of styrene and m-xylene, and comparing the effect with the treatment effect of single styrene and single m-xylene. The results are shown in Table 9 and FIG. 18;

TABLE 9 Effect of discharge Voltage on degradation rates of Mixed gas and Single-type gas

As can be seen from table 9 and fig. 18, similarly, the degradation rate of the mixed gas of styrene and m-xylene increases with an increase in discharge voltage, and the degradation rate curve is approximately the same as the single gas curve. But also can find that the degradation rate of the mixed gas is reduced compared with that of the single gas, the degradation rate curve of the single gas is wholly lower than that of the mixed gas, the interval between the degradation rate curve of the single styrene and the styrene curve in the mixed gas is obviously much smaller than that of m-xylene, and compared with the single gas, the maximum degradation rate of the styrene reaches about 85 percent, but the maximum degradation rate of the m-xylene is reduced to 34.21% from 51.08% of a single component, namely the influence of the m-xylene on mixed gas is larger, the styrene is less affected, and the specific reason is not particularly clear, which may be because the meta-xylene and styrene compete with each other in the active particles, the competitive action of styrene is stronger, and the styrene is more easily decomposed by active particles, so that the degradation of m-xylene is inhibited; it is also possible that when the mixed gas of meta-xylene and styrene is degraded, a secondary product is generated to inhibit the degradation of meta-xylene, so that the degradation rate is reduced.

On the other hand, the energy efficiencies of styrene and m-xylene in the case of a single kind of gas and in the case of a mixed gas are shown in Table 10, and the total energy efficiency of the mixed gas reached 9.32g/kWh at a discharge voltage of 20kV, and increased to 12.14g/kWh at a discharge voltage of 25 kV. From table 10, it can be found that the energy efficiency of the mixed gas is higher than that of the single gas, which indicates that the mixed gas can utilize energy more fully, because the initial concentration of the pollutants in the mixed gas is increased, the competition of the pollutants for energy is promoted, the pollutant molecules are easier to collide with the active particles, so that the total energy efficiency is increased, and the comprehensive degradation performance of the pollutants is optimized. The types of industrial waste gas are often complex, so the research result is beneficial to the application of the low-temperature plasma degraded waste gas in industry.

TABLE 10 energy efficiency comparison of single and mixed VOCs

Further, the gas flow rate is 0.48m at a power frequency of 200Hz³And h, under the condition that the pulse duty ratio is 50 percent and the discharge voltage is 30kV, the influence of the gas concentration on the degradation performance of the mixed gas of styrene and m-xylene is researched and compared with the treatment effect of single styrene and single m-xylene. The results are shown in Table 11 and FIG. 19:

TABLE 11 Effect of concentration on the degradation rates of Mixed and Single gas species

As can be seen from Table 11 and FIG. 19, the gas concentration and the degradation rate were approximately the same in both the single gas-feed condition and the mixed gas feed condition, the degradation rate decreased with the increase in the gas concentration, and it was also found that the overall degradation rate was significantly higher than that of the mixed gas in the single gas-feed condition. The concentration is from 20mg/m³Increasing to 1500mg/m³The single gas styrene degradation rate is reduced from 88.53% to 32.91%. And the degradation rate of the styrene in the mixed gas is reduced from 86.48% to 24.52%. The single gas meta-xylene degradation rate is reduced from 64.56% to 38.56%, and the meta-xylene degradation rate is reduced from 53.85% to 24.12% under the condition of mixed gas. It can also be seen from FIG. 19 that the degradation rate curve for styrene alone is significantly less separated from the styrene curve in the mixed gas than for meta-xylene, indicating that styrene is less affected by meta-xylene and is more easily degraded than meta-xylene in the mixed gas. It has also been found that styrene is more sensitive to concentration than meta-xylene, and that the percentage of degradation of styrene decreases from the lowest concentration to the highest concentration in either single or mixed conditions as compared to meta-xylene.

Further, the concentration of styrene is 17-89mg/m under the condition that the power frequency is 200Hz³The concentration of the m-xylene is 16-41mg/m³When the discharge voltage is 30kV under the condition that the power supply duty ratio is 50%, the influence of the gas flow rate on the degradation performance of the styrene-m-xylene mixed gas is studied and compared with the treatment effect of a single styrene and a single m-xylene, and the results are shown in table 12 and fig. 20:

TABLE 12 Effect of flow on degradation rates of Mixed and Single gas species

As can be seen from Table 12 and FIG. 20, the degradation rate curves of styrene and meta-xylene in the single gas and mixed gas conditions were approximately the same, the degradation rate was decreased with the increase of the flow rate, and the overall degradation rate was found to be significantly higher than that of the mixed gas in the single gas condition. The flow rate is increased from 0.24m3/h to 0.8m3/h, and the single gas styrene degradation rate is reduced from 59.92% to 22.65%. And the degradation rate of the styrene in the mixed gas is reduced from 56.73 percent to 19.7 percent. The single gas meta-xylene degradation rate is reduced from 48.81% to 6.4%, and the meta-xylene degradation rate under the mixed gas condition is reduced from 35.21% to 3.4%. It can also be seen from FIG. 18 that the degradation rate curve for styrene alone is significantly less spaced from the mixed gas styrene curve than for meta-xylene, indicating that styrene is less affected by meta-xylene in the mixed gas and is more easily degraded than meta-xylene.

Further, a GC-MS combined technology is adopted to analyze a solid product generated when the coaxial double-dielectric barrier discharge plasma degrades the mixed gas of the styrene and the m-xylene, a coking product is dissolved in absolute ethyl alcohol, liquid sampling is adopted, and the detection result is shown in an attached figure 21.

As can be seen from the attached FIG. 21, the solid products of the coaxial dual-dielectric barrier discharge reactor degrading the mixed gas of styrene and m-xylene are mainly benzene ring derivatives, such as: benzoic acid, phenol, m-methylbenzaldehyde, m-methylbenzoic acid, m-methylbenzyl alcohol, p-nitrotoluene, p-nitrophenol, nitrobenzyl alcohol, hydroxyacetophenone, 2-methylphenyl benzoate, and the like, and also nitrogen-containing substances and carboxyl-containing substances such as amines in small amounts.

In summary, under the laboratory conditions, the mixed gas of styrene and m-xylene with low concentration in the air is used as the research object, and the coaxial dual-dielectric barrier discharge plasma reactor is used to research the influence of the concentration, flow and discharge voltage of the reactant on the degradation rate of the mixed gas of styrene and m-xylene, and compared with the degradation rate under the single gas condition, the conclusion is as follows:

(1) the degradation rate curve trend of the mixed gas of styrene and m-xylene is approximately the same as that of the mixed gas under the condition of single gas, but the degradation rates of the styrene and the m-xylene under the mixed gas are lower than that under the condition of single gas. The overall degradation rate of the mixed gas intermediate xylene is larger than that of styrene, and compared with a single gas, the maximum degradation rate of the styrene in the mixed gas reaches about 85%, but the maximum degradation rate of the mixed gas intermediate xylene is reduced to only 34.21% from 51.08% of the single component, which shows that the mixed gas intermediate xylene is more influenced than the styrene and is more difficult to degrade than the styrene.

(2) The overall energy efficiency of the mixed gas is higher than that of the single gas, and the total energy efficiency of the mixed gas is increased to 12.14g/kWh at the discharge voltage of 25 kV. Under the condition of single gas, the energy efficiencies of the styrene and the m-xylene are respectively only 9.63g/kWh and 5.32 g/kWh. The mixed gas can more fully utilize energy.

Example four:

the research of the first to third embodiments is still only in a laboratory stage, the industrial waste gas is often complex in type, large in gas amount and large in concentration, and the research is more practical in order to be closer to the practical situation. Therefore, the present application further performs an expansion experiment on the basis of the first to third embodiments to study the degradation efficiency of the low-temperature plasma on the volatile organic pollutants, and performs a preliminary expansion experiment on the reactor by taking m-xylene as an example, and 45 dielectric barrier reactions are performedThe reactors are connected in parallel, the reactor is enlarged, and the discharge current, the gas flow, the degradation rate of the gas concentration to the m-xylene and the product O are researched₃The effect of concentration. The specific research method comprises the following steps:

1. assembling each part of the low-temperature plasma degradation system of the expanded experiment, and checking the air tightness of the low-temperature plasma degradation system;

specifically, the low-temperature plasma degradation system is shown in fig. 22 and comprises a pulse high-voltage power supply system, a plasma reactor 9 and a fan 10;

the pulse high-voltage power supply system comprises a pulse high-voltage power supply 81 and a power supply console 82, wherein the power supply console 82 controls the pulse high-voltage power supply 81 to output high-voltage current; the power supply control console 82 is provided with a power switch 821 for controlling the start and stop of the pulse high-voltage power supply 81, a voltage detection interface 822 and a current detection interface 823 for connecting an oscilloscope to detect a voltage value and a current value, a frequency converter 824 for adjusting frequency and a host 825 of the control console, and the main technical parameters of the power supply control console 82 are as follows:

a power supply: 220V single-phase AC

Rated output power 4000VA

The peak voltage of the output pulse is 15kV-40kV and is continuously adjustable

Pulse polarity positive polarity

Pulse width of 500ns or less

Rising edge of pulse is less than or equal to 20ns

The pulse repetition frequency is continuously adjustable from 0Hz to 100Hz

Leakage current of the instrument per se is less than 1 muA

The using environment temperature is-20-40 DEG C

Relative humidity not more than 80%.

The plasma reactor 9 is formed by connecting 45 dielectric barrier reactors in parallel, one end of the plasma reactor 9 is provided with an air inlet 91, the other end of the plasma reactor is provided with an air outlet 92, one end of the air inlet 91 is also provided with an air inlet sampling valve 93 for sampling the gas in the air inlet 91, and one end of the air outlet 92 is provided with an air outlet sampling valve 94 for sampling the gas in the air outlet 92; the plasma reactor 9 is also provided with a high-voltage input end 95 below, the high-voltage input end 95 is connected with the pulse high-voltage power supply 81, and the fan 10 is connected with the air inlet 91 and used for supplying air to the plasma reactor 9.

The model number of the fan 10 is 4-72, and the air volume is 780-1460m³The wind pressure is 52-36mmH₂O。

2. Zero setting, namely confirming that the indication of the frequency instrument is zero;

3. starting, turning on a main power supply and a fan switch;

4. changing the electrical parameters and gas parameters of the reactor, and sampling and analyzing the gas at the inlet and the outlet of the reactor when the gas concentration is relatively stable;

5. repeating the steps, changing the electrical parameters or the gas parameters, and researching the influence of other single factors.

6. And (4) shutting down, and pulling down a main power supply and a fan switch after the work is finished.

The specific operation procedures of step 4 and step 5 are the same as those of the first to third embodiments,

under the condition that the power frequency is 200Hz, the inlet concentration of the m-xylene is 30-90mg/m³Flow rate of 20m³The results of examining the effect of discharge current on the degradation rate of m-xylene and the concentration of ozone produced under the conditions of/h are shown in FIG. 23.

As can be seen from FIG. 23, as the results of the study of example two show, the degradation rate of m-xylene increases with increasing current, the degradation rate of m-xylene is 10.12% at 1.8A and 33.51% at 6A, which increases by 23.39%, and the overall degradation rate is slightly lower than that of example two, although the difference between the degradation rate and the overall degradation rate is not very large, which is probably related to the uneven distribution of the flow pattern and energy density of the gas in the reactor in each reactor, so the overall degradation rate is slightly lower than that of the laboratory study of example two. But the highest degradation rate reaches about 30 percent, so that the low-temperature plasma has a great development prospect in future large-scale industrial application.

Can also be seen in FIG. 23The ozone concentration in the product is continuously increased along with the continuous increase of the current, because the generated high-energy electrons are continuously increased along with the continuous increase of the current, namely the continuous increase of the electric field intensity, so that the collision probability of oxygen molecules and the high-energy electrons is greatly increased, the oxygen plasma concentration is increased, and the ozone concentration is increased. When the current is 6A, the ozone concentration reaches 390mg/m³Far exceeding the safe concentration standard.

To further study the mechanism of ozone formation, the gas flow was 20m at a power frequency of 10Hz when the background gas was air only, i.e., when the initial concentration of m-xylene was zero³The ozone yield was investigated at/h and was compared with an initial concentration of 50mg/m of meta-xylene³The ozone yield was compared and the comparison results are shown in Table 13 and FIG. 24.

TABLE 13 variation of ozone concentration with and without meta-xylene

As can be seen from Table 13 and FIG. 24, the ozone concentration was higher than 50mg/m in the air-only background gas condition regardless of whether the current was 1.8A or 2.4A³Ozone concentration at initial concentration conditions. The ozone concentration at the initial concentration of 0 m-xylene was 186mg/m at a current of 1.8A³Initial concentration of meta-xylene was 50mg/m³The ozone concentration is 93mg/m³Reduced by 93mg/m³. At a current of 2.4A, the ozone concentration was reduced by 138mg/m³. This may be at an initial concentration of 50mg/m of m-xylene³In time, ozone generated by air discharge is used to oxidize the meta-xylene molecules in contact therewith, resulting in a substantial reduction in ozone concentration.

Further, under the power frequency of 200Hz, the inlet concentration of the m-xylene is 30-90mg/m³The effect of gas flow rate on meta-xylene degradation rate and product ozone concentration was investigated under the condition of 6A current, and the results are shown in FIG. 25.

As can be seen from FIG. 25, the degradation rate curve of meta-xylene decreased with increasing gas flow rate, which was 20m at a gas flow rate³At the time of the reaction, the degradation rate of m-xylene was 30.2%, and the gas flow rate was 56m³At the time of the reaction solution/h, the degradation rate of the m-xylene is 3.4 percent and is reduced by 26.8 percent. Meanwhile, the ozone concentration is gradually reduced along with the increase of the gas flow, and the gas flow is 20m³At the time of the reaction, the ozone concentration is 461mg/m³At a gas flow rate of 56m³At the time of the reaction, the ozone concentration is 77mg/m³The ozone concentration is reduced by 384mg/m³. The reason why the concentration of ozone is reduced is that as the gas flow rate increases, the retention time of the m-xylene molecules in the reactor is also shortened, the m-xylene molecules are more difficult to collide with the energetic electrons and the active particles, the concentration of the oxygen plasma is greatly reduced, and the concentration of ozone is also greatly reduced. It was also found that the ozone concentration is more sensitive to wind speed variables than to current, and that an increase in gas flow rate leads to a sharp drop in ozone concentration.

Further, the gas flow rate is 20m at a power frequency of 200Hz³The results of studying the influence of gas concentration on the degradation rate of m-xylene and the concentration of ozone in the product under the condition of current of 6A are shown in FIG. 26;

as can be seen from FIG. 26, the degradation rate of meta-xylene becomes smaller and smaller with increasing gas concentration, at a concentration of 30mg/m³The degradation rate of m-xylene is 43.2% at a concentration of 1000mg/m³In time, the degradation rate of m-xylene is 10.2%, and the degradation rate of m-xylene is reduced by 33%. This rule is the same as the study result of example two.

It can also be seen from FIG. 26 that the concentration of ozone becomes smaller and smaller with the increase of the concentration, and the concentration is 30mg/m³When the ozone concentration is 368mg/m³At a concentration of 1000mg/m³When the ozone concentration is 44mg/m³The ozone concentration is reduced by 324mg/m³. This is because the higher the concentration of m-xylene, the lower the number of energetic electrons per m-xylene molecule, the lower the probability of collision between oxygen molecules and energetic electrons, and the lower the oxygen concentrationThe plasma concentration is reduced and thus the ozone concentration is also greatly reduced.

In summary, the method takes the low-concentration m-xylene in the air as a research object, carries out preliminary amplification experiment on the reactors to make the reactor more approximate to the actual situation of the atmospheric waste gas, connects a plurality of dielectric barrier reactors in parallel, amplifies the reactors, mainly studies the discharge current, the gas flow, the gas concentration p-m-xylene degradation rate and the product O₃The effect of concentration. The specific conclusions are as follows:

(1) the current increase can obviously improve the degradation rate of the m-xylene, the degradation rate of the m-xylene is 10.12 percent when the current is 1.8A, the degradation rate is 33.51 percent when the current is 6A, the degradation rate is increased by 23.39 percent, the ozone concentration is higher and higher along with the increase of the current, and the ozone concentration reaches 390mg/m when the current is 6A³Far exceeding the safe concentration standard.

(2) Along with the increase of the gas flow, the degradation rate curve of the m-xylene and the ozone concentration curve both show a descending trend, and the gas flow is 20m³At the time of the reaction, the degradation rate of m-xylene was 30.2%, and the gas flow rate was 56m³At the time of the reaction solution/h, the degradation rate of the m-xylene is 3.4 percent and is reduced by 26.8 percent. The gas flow has great influence on the concentration of the product ozone, and the gas flow is 20m³At the time of the reaction, the ozone concentration is 461mg/m³At a gas flow rate of 56m³At the time of the reaction, the ozone concentration is 77mg/m³The ozone concentration is reduced by 384mg/m³。

(3) With the increase of the concentration of the m-xylene, the degradation rate curve of the m-xylene and the concentration of the ozone both show a descending trend, and the concentration has a larger influence on the concentration of the ozone in the m-xylene product, and the concentration is 30mg/m³When the ozone concentration is 368mg/m³At a concentration of 1000mg/m³When the ozone concentration is 44mg/m³The ozone concentration is reduced by 324mg/m³。

(4) In an expanded experiment of the m-xylene, the difference between the overall degradation rate of the m-xylene and the degradation rate at a laboratory stage is not large, the difference is slightly lower than that at the laboratory stage, the maximum degradation rate reaches about 30%, and the development prospect of further industrial application of the low-temperature plasma degraded VOCs is shown.

(5) The ozone concentration of the product is higher than the initial concentration of meta-xylene of 50mg/m when the background gas is air only³The concentration of ozone in time indicates that a part of the ozone generated by air discharge is used for oxidizing m-xylene molecules in contact with the ozone.

The foregoing shows and describes the general principles, essential features, and advantages of the invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to illustrate the principle of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the present invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.

Claims

1. The method for researching the degradation efficiency of the low-temperature plasma on the volatile organic pollutants is characterized by comprising the following steps,

s1: assembling each part of the laboratory low-temperature plasma degradation system;

2. The method for researching the degradation efficiency of volatile organic pollutants by using low-temperature plasma according to claim 1, is characterized in that: the volatile organic pollutant is styrene or m-xylene or mixed gas of styrene and m-xylene.

3. The method for researching the degradation efficiency of volatile organic pollutants by using low-temperature plasma according to claim 1, is characterized in that: the electrical parameters described in steps S4 and S5 include discharge voltage, discharge current, and power supply duty ratio, and the gas parameters include intake air flow rate and intake air concentration.

4. The method for researching the degradation efficiency of volatile organic pollutants by using low-temperature plasma according to claim 1, is characterized in that: the determination formula of the degradation rate of the low-temperature plasma on the volatile organic pollutants in the step S4 is as follows

The energy efficiency is determined by the formula

In the formula, eta is the degradation rate of volatile organic pollutants; c₀Is the initial concentration of the volatile organic contaminant; c₁Is the concentration of the volatile organic pollutants after reaction; energy efficiency as volatile organic pollutants; m is the molecular weight of the volatile organic pollutants; v is the velocity of the gas; p is the discharge power.

5. The method for researching the degradation efficiency of volatile organic pollutants by using low-temperature plasma according to claim 1, is characterized in that: the determination of the degradation products in step S4 includes the determination of gaseous products and solid products.

6. The method for researching the degradation efficiency of volatile organic pollutants by using low-temperature plasma according to claim 1, is characterized in that: the laboratory low-temperature plasma degradation system in the step S1 comprises a gas distribution system, a reactor (5), a power supply system and an analysis test system; the gas distribution system for preparing gas is connected with an inlet of the reactor (5), the power supply system provides a power supply for the reactor (5), the analysis and test system comprises an electrical parameter test system and a gas parameter test system, the electrical parameter test system is electrically connected with the power supply system, and the gas parameter test system tests parameters of gas at an inlet and an outlet of the reactor (5).

7. The method for researching the degradation efficiency of the volatile organic pollutants by the low-temperature plasma according to claim 6, wherein the air distribution system comprises a dry air compression bottle (1), a glass rotameter (2), a volatile organic pollutant generation bottle (3) and a mixing bottle (4); the air in the dry air compression bottle (1) and the volatile organic pollutants in the volatile organic pollutants generating bottle (3) are mixed and diluted in the mixing bottle (4) and then are introduced into the reactor (5), and the glass rotameter (2) is connected to the dry air compression bottle (1) and the volatile organic pollutants generating bottle (3) and is used for controlling the flow of the mixed air and the organic pollutants.

8. The method for researching the degradation efficiency of volatile organic pollutants by using low-temperature plasma according to claim 1, is characterized in that: the low-temperature plasma degradation system for the expanded experiment in the step S6 comprises a pulse high-voltage power supply system, a reactor (9), a fan (10) and an analysis test system; a fan (10) for preparing gas is communicated with an inlet of the reactor (9), and the pulse high-voltage power supply system is electrically connected with the reactor (9); the analysis test system comprises an electrical parameter test system and a gas parameter test system, the electrical parameter test system is electrically connected with the pulse high-voltage power supply system, and the gas parameter test system tests parameters of gas at an inlet and an outlet of the reactor (9).

9. The method for researching the degradation efficiency of volatile organic pollutants by using low-temperature plasma according to claim 8, is characterized in that: the reactor (9) comprises more than one low-temperature plasma reactor, and a plurality of low-temperature plasma reactors are connected in parallel.