CN114887481A - Catalytic degradation method of VOCs - Google Patents
Catalytic degradation method of VOCs Download PDFInfo
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Abstract
The invention discloses a catalytic degradation method of VOCs (volatile organic compounds). A manganese-based hydrotalcite catalyst is placed on a sand core at the downstream position of a plasma discharge tube of a dielectric barrier discharge low-temperature plasma reactor, VOCs to be degraded are mixed with oxygen and then pass through the reactor, and are degraded by the medium barrier discharge low-temperature plasma and the manganese-based hydrotalcite in a synergetic catalytic manner. The method adopts dielectric barrier discharge low-temperature plasma and Mn-based hydrotalcite to synergistically catalyze and degrade VOCs; the energy efficiency is improved by 20 to 30 percent. The Mn-based hydrotalcite catalyst has good stability, and in addition, because the dielectric barrier discharge is relatively close to the catalyst, a large amount of active substances generated by the discharge react with VOCs adsorbed on the surface of a downstream catalyst and unreacted intermediate products, the aim of regenerating the catalyst can be fulfilled while the VOCs are purified, and therefore, the catalyst can be recycled.
Description
Technical Field
The invention relates to the technical field of air pollution control, in particular to a catalytic degradation method of VOCs.
Background
The low-temperature plasma can generate O, OH and O 3 The catalyst has equal strong oxidizing particles and no great selectivity, and is widely used for degrading VOCs in waste gas. However, when VOCs are degraded by plasma, intermediate products and byproducts are generated, so that exhaust gas degraded by single plasma cannot reach the standard and is discharged. In addition, when the traditional plasma degrades the organic waste gas, certain aerosol particles still exist in the product due to incomplete degradation, and the particles coke on the inner wall of the reaction tube to influence the discharge stability.
Hydrotalcite-like layered materials, also known as hydrotalcite-type anionic clays, are important anionic layered materials. Typical hydrotalcite structure is Zn 6 Al 2 (OH) 16 CO 3 •4H 2 O, because of its unique structure and performance, has wide application in the field of photocatalytic degradation.
Hydrotalcite-like compounds (LDHs) are ion plate layered compounds composed of positive charge-carrying laminates and interlayer anions, and have a chemical composition general formula of [ M 2+ 1-x M 3+ x (OH) 2 ] x+ (A n- ) x/n •mH 2 O, wherein M 2+ And M 3+ Divalent metal cations and trivalent metal cations on the laminate, respectively, a represents an anion intercalated between the layers, and m represents the number of water molecules contained between the layers.
Layered Double Hydroxides (LDHs) are of various types, and the composition of metal ions on a main body laminate, the charge of the main body laminate, the type and the quantity of intercalation anions can be changed. The double-layer structure of the LDHs is beneficial to improving the specific surface area, provides more attachment sites for active substances and shows better catalytic performance than that of a catalyst prepared by a conventional synthesis method.
For example, chinese patent document CN 110653004a (application No. 201910839179.2) discloses a catalyst for trapping and catalyzing degradation of VOCs, and a preparation method and application thereof, wherein the catalyst is a hydrotalcite-like-molecular sieve composite catalyst, and the general formula is mg (M) (al) O — N, wherein M is one or more selected from Cr, Mn, Fe, Co, Cu, Zn, Ce, In, Cd, Zr, Mo, or Sn; n is a molecular sieve, and the metal oxide and the spinel are both used as active components. The modified catalyst provided by the invention is used for treating benzene-containing VOCs at normal temperature in cooperation with ozone.
Disclosure of Invention
The invention aims to solve the technical problem of providing a method for degrading VOCs (volatile organic compounds) by utilizing the concerted catalysis of Dielectric Barrier Discharge (DBD) low-temperature plasma and Mn-based hydrotalcite.
The technical scheme for realizing the aim of the invention is a catalytic degradation method of VOCs, wherein a manganese-based hydrotalcite catalyst is placed on a sand core at the downstream position of a plasma discharge tube of a dielectric barrier discharge low-temperature plasma reactor, VOCs to be degraded and oxygen are mixed and then pass through the reactor, and the VOCs is degraded by the medium barrier discharge low-temperature plasma and the manganese-based hydrotalcite in a synergetic catalytic manner.
The dielectric barrier discharge low-temperature plasma reactor comprises a high-voltage electrode, a low-voltage electrode, an insulating medium and a sand core, wherein the high-voltage electrode is a solid metal rod or metal powder, the low-voltage electrode is a copper foil or an aluminum foil, and the insulating medium is a quartz tube; the quartz tube and the high-voltage electrode are coaxially arranged, and the low-voltage electrode is arranged outside the quartz tube; the sand core is arranged at the position 10-15 mm downstream of the plasma discharge tube, and the manganese-based hydrotalcite catalyst is placed on the sand core.
Optionally, the manganese-based hydrotalcite catalyst is a hydrotalcite-like catalyst doped with Ni, Co, Mn, or a hydrotalcite-like catalyst doped with Co, Mn.
Furthermore, when the manganese-based hydrotalcite-like catalyst is a Ni, Co and Mn doped hydrotalcite-like catalyst, the manganese-based hydrotalcite-like catalyst is NiCoMn-LDHs or NiCo 2 Mn-LDHs or NiCoMn 2 –LDHs。
The preparation method of the manganese-based hydrotalcite-like catalyst comprises the following steps: dissolving nickel salt, cobalt salt, manganese salt and urea in deionized water to obtain a mixed salt solution; stirring the mixed salt solution, transferring the obtained clear solution into a hydrothermal reaction kettle, and placing the hydrothermal reaction kettle in an oven at the temperature of 130-150 ℃ for 18-24 hours; cooling the reacted materials to room temperature, filtering, and collecting precipitates; washing and drying the precipitate to obtain the manganese-based hydrotalcite-like catalyst containing nickel, cobalt and manganese. The molar ratio of urea to total metals was 3.3: 1.
optionally, the manganese-based hydrotalcite-like catalyst is MnCo-LDHs.
The preparation method of the MnCo-LDHs manganese-based hydrotalcite-like catalyst comprises the following steps: dissolving cobalt salt, manganese salt and urea in deionized water to obtain a mixed salt solution; stirring the mixed salt solution, transferring the obtained clear solution into a hydrothermal reaction kettle, and placing the hydrothermal reaction kettle in an oven at the temperature of 130-150 ℃ for 18-24 hours; cooling the reacted materials to room temperature, filtering, and collecting precipitates; washing and drying the precipitate to obtain the manganese-based hydrotalcite-like catalyst containing nickel, cobalt and manganese.
In the mixed gas of VOCs and oxygen, the volume fraction of oxygen is 2-20%.
Furthermore, the mixed gas of the VOCs and the oxygen also contains water vapor, and the volume fraction of the water vapor is 2-30%. The invention has the positive effects that:
(1) the method adopts Dielectric Barrier Discharge (DBD) low-temperature plasma and Mn-based hydrotalcite to synergistically catalyze and degrade VOCs; the energy efficiency is improved by 20 to 30 percent.
The Mn-based hydrotalcite catalyst has good stability, and in addition, because the DBD is relatively close to the catalyst, a large amount of active substances generated by DBD discharge react with VOCs adsorbed on the surface of a downstream catalyst and unreacted intermediate products, the aim of catalyst regeneration can be achieved while the VOCs are purified, and therefore the catalyst can be recycled.
(2) Compared with the traditional manganese oxide catalyst, the Mn-based hydrotalcite catalyst has Mn ions with a mixed valence state of a porous structure, mild surface acidity and alkalinity and excellent exchange property, and has more oxygen vacancies than the conventional MnOx; ozone generated by plasma discharge can be converted into active oxygen species on oxygen vacancies on the surface of the Mn-based hydrotalcite catalyst, so that deep oxidation of VOCs and intermediate products is promoted, coking is reduced, the concentration of byproducts is remarkably reduced, and CO is promoted 2 Selectivity and degree of mineralization; at the same time, etcPlasma generated O 3 The catalyst has enough residence time on the surface of the catalyst to decompose and generate active oxygen, and is suitable for catalytic purification of industrial VOCs under high gas flow rate and atmospheric gas flow.
(3) For the Mn-based hydrotalcite structure, after Co and Ni are added, the specific surface area of the catalyst can be improved, more Mn active sites with catalytic activity can be exposed, and further the valence state and the dispersion state of Mn elements are regulated and controlled, so that the catalytic capability of the Mn-based hydrotalcite structure on VOCs is greatly improved.
Compared with Mn-LDHs, the addition of Co and Ni increases the interlayer spacing of the hydrotalcite and reduces the forbidden bandwidth Eg. The smaller the Eg, the easier the electron is excited, and the more the transition from the valence band to the conduction band generates photogenerated holes and photogenerated electrons, so that the better the photocatalytic activity is.
Drawings
FIG. 1 is a schematic diagram of a dielectric barrier discharge plasma catalytic reactor.
FIG. 2 is an XRD diffractogram of NiCoMn, CoMn-like hydrotalcites prepared in examples.
Fig. 3 is an SEM image of NiCoMn-based hydrotalcite of example 1.
FIG. 4 is a graph showing the spectrum analysis of NiCoMn-based hydrotalcite of example 1.
FIG. 5 shows examples of NiCoMn-LDHs, NiCo 2 Mn-LDHs and NiCoMn 2 XRD diffractogram of LDHs.
FIG. 6 is a graph showing the toluene conversion in test example 1.
FIG. 7 is a graph showing the by-product concentration in test example 1.
FIG. 8 shows CO at different energy densities during the catalytic degradation of low-temperature plasma and NiCoMn-LDHs 2 And (4) a selectivity graph.
Detailed Description
(example 1)
In the embodiment, VOCs are catalytically degraded by using a Dielectric Barrier Discharge (DBD) low-temperature plasma and NiCoMn-LDHs in a synergistic manner.
The reactor used in this example is a plasma catalytic reactor, the structure of which is shown in fig. 1, and is an integrated post-catalytic reactor.
The plasma catalytic reactor is a coaxial double-medium barrier discharge reactor and comprises a high-voltage electrode, a low-voltage electrode, an insulating medium and a sand core.
In this embodiment, the high voltage electrode is a solid metal rod or metal powder with an outer diameter of 9 mm, the low voltage electrode is a copper foil or aluminum foil with a length of 10 cm, and the insulating medium is a quartz tube with a wall thickness of 1.5-2 mm, and is coaxially disposed with the inner electrode (high voltage electrode). The low voltage electrode is arranged outside the quartz tube. The sand core is arranged at the position 10-15 mm downstream of the plasma discharge tube, and the NiCoMn-LDHs catalyst is placed on the sand core.
Under the condition that the wall thickness of the insulating medium quartz tube is not changed, the size of a discharge gap can be changed by changing the inner diameter and the outer diameter of the quartz tube, and the discharge length can be changed by changing the length of an outer electrode (a low-voltage electrode).
In this embodiment, the plasma power supply is a low-temperature plasma experimental power supply, the input voltage is 220V and 50 Hz alternating current, the contact voltage regulator is matched, the output voltage regulation range is 0-30 kV, the output frequency regulation range is about 5-25 kHz, and the plasma power supply generally works at the central frequency (about 9.7 kHz) of the maximum output power. In plasma experiments, the input power and energy density of the plasma reactor were adjusted by varying the input voltage, keeping the discharge frequency constant at the center frequency.
The preparation method of NiCoMn-LDHs comprises the following steps:
dissolving weighed solid nickel sulfate (0.0067 mol), cobalt sulfate (0.0067 mol), manganese sulfate (0.0067 mol) and urea (0.066 mol) in deionized water to obtain a mixed salt solution. During the synthesis, the molar ratio of urea to total metals is ensured to be 3.3: 1.
the mixed salt solution was stirred vigorously for 30 minutes under a magnetic stirrer, and then the clear solution was transferred to a hydrothermal reaction kettle and placed in an oven at 150 ℃ for 18 hours.
Cooling the reacted materials to room temperature (10-35 ℃), filtering, and collecting precipitates; the precipitate is washed 5 times by deionized water and dried for 5h at 105 ℃ to obtain NiCoMn-LDHs which is ground for standby.
The XRD diffraction pattern of NiCoMn-LDHs prepared by the embodiment is shown in figure 2, and the matching degree of the XRD pattern and hydrotalcite-like structure PDF #40-0215 in a PDF card library is high. The NiCoMn-LDHs prepared in this example have a typical layered structure of hydrotalcite, show diffraction peaks of a typical rhombohedral structure of hydrotalcite, and four characteristic diffraction peaks appearing at 2 θ of 11.5 °, 23.1 °, 34.2 °, and 38.7 ° respectively correspond to crystal planes (003), (006), (012), and (015), which reflects the layered structure of LDHs.
An SEM image of NiCoMn-LDHs prepared in the embodiment is shown in FIG. 3, and as can be seen from FIG. 3, the NiCoMn-LDHs catalyst prepared in the embodiment has a typical lamellar structure and very conforms to the apparent morphological characteristics of hydrotalcite-like compound.
The spectrum analysis of NiCoMn-LDHs prepared in this example is shown in FIG. 4.
The method for degrading VOCs by adopting the medium barrier discharge (DBD) low-temperature plasma and NiCoMn-LDHs to carry out concerted catalysis comprises the following steps:
firstly, filling 0.5g of NiCoMn-LDHs (NiCoMn hydrotalcite-like compounds) catalyst on a sand core at the lower part of a plasma catalytic reactor at normal temperature and normal pressure to form a two-section plasma catalytic reactor.
Adjusting the input power of plasma discharge, wherein the input energy density of the plasma discharge corresponding to the set power is 210J/L; VOCs to be degraded (toluene in this example, with an initial concentration of 1000 mg/m) are introduced into the gas inlet of the reactor 3 Gas flow lL/min, O 2 The volume fraction is 2-20%), performing the concerted catalytic degradation on the VOCs, and allowing the gas subjected to the catalytic degradation to flow out from the gas outlet end of the reactor to finish the process of concerted catalytic degradation of the VOCs by the plasma and NiCoMn-LDHs.
In the co-catalytic degradation process, the higher the gas flow, the higher the catalyst loading.
(example 2)
In the embodiment, VOCs are catalytically degraded by using a Dielectric Barrier Discharge (DBD) low-temperature plasma and MnCo-LDHs in a synergistic manner.
The preparation method of MnCo-LDHs comprises the following steps:
dissolving weighed cobalt sulfate (0.01 mol), manganese sulfate solid (0.01 mol) and urea (0.066) in deionized water to obtain a mixed salt solution. During the synthesis, the molar ratio of urea to total metals was 3.3: 1.
the mixed salt solution was stirred vigorously for 15 minutes under a magnetic stirrer, and then the clear solution was transferred to a hydrothermal kettle and placed in an oven at 150 ℃ for 18 hours.
Cooling the reacted materials to room temperature, filtering, and collecting precipitates; washing the precipitate with deionized water for 5 times, drying at 105 ℃ for 5h to obtain MnCo-LDHs, and grinding for later use.
The XRD diffraction pattern of MnCo-LDHs prepared by the embodiment is shown in figure 2, and the matching degree of the XRD pattern and the hydrotalcite-like structure PDF #40-0215 in the PDF card library is high.
The procedure of degrading VOCs by using the medium barrier discharge (DBD) low-temperature plasma and MnCo-LDHs in cooperation with catalysis was the same as in example 1, except that 0.5g of MnCo-LDHs catalyst was loaded on a sand core at the lower part of the plasma catalytic reactor.
(example 3)
In this embodiment, a method for degrading VOCs by using a Dielectric Barrier Discharge (DBD) low-temperature plasma and NiCoMn-LDHs in a concerted catalytic manner is used, and the rest is the same as in example 1, except that the preparation method of the NiCoMn-LDHs is as follows:
dissolving weighed solid nickel sulfate (0.01 mol), cobalt sulfate (0.01 mol), manganese sulfate (0.01 mol) and urea (0.099 mol) in deionized water to obtain a mixed salt solution. During the synthesis, the molar ratio of urea to total metals is ensured to be 3.3: 1.
the mixed salt solution was stirred vigorously for 15 minutes under a magnetic stirrer, and then the clear solution was transferred to a hydrothermal reaction kettle and placed in an oven at 130 ℃ for 24 hours.
Cooling the reacted materials to room temperature, filtering, and collecting precipitates; washing the precipitate with deionized water for 3 times, and vacuum drying at 80 deg.C for 5h to obtain NiCoMn-LDHs containing Ni, Co and Mn, and grinding for use.
(example 4)
In this embodiment, a Dielectric Barrier Discharge (DBD) low temperature plasma and NiCo are used 2 Reactor for degrading VOCs (volatile organic compounds) through Mn-LDHs (manganese-layered double hydroxides) concerted catalysisThe same catalytic degradation method as in example 1, wherein NiCo 2 The preparation method of Mn-LDHs comprises the following steps:
dissolving weighed nickel sulfate (0.0075 mol), cobalt sulfate (0.015 mol), manganese sulfate solid (0.0075 mol) and urea (0.099 mol) in deionized water to obtain a mixed salt solution. During the synthesis, the molar ratio of urea to total metals was 3.3: 1.
the mixed solution was stirred vigorously for 15 minutes under a magnetic stirrer, and then the clear solution was transferred to a hydrothermal kettle and placed in an oven at 130 ℃ for 24 hours.
Cooling the reacted materials to room temperature, filtering, and collecting precipitates; washing the precipitate with deionized water for 3 times, and vacuum drying at 80 deg.C for 5 hr to obtain NiCo containing Ni, Co and Mn 2 And (3) grinding the Mn-LDHs for later use, and filling the Mn-LDHs on a sand core at the lower part of the plasma catalytic reactor when in use.
(example 5)
In this embodiment, a Dielectric Barrier Discharge (DBD) low temperature plasma and NiCoMn are used 2 -LDHs synergistically catalytically degrading VOCs using the same reactor and catalytic degradation method as in example 1, wherein NiCoMn 2 The preparation method of the LDHs comprises the following steps:
dissolving weighed nickel sulfate (0.0075 mol), cobalt sulfate (0.0075 mol), manganese sulfate solid (0.015 mol) and urea (0.099 mol) in deionized water to obtain a mixed salt solution. During the synthesis, the molar ratio of urea to total metals was 3.3: 1.
the mixed solution was stirred vigorously for 15 minutes under a magnetic stirrer, and then the clear solution was transferred to a hydrothermal kettle and placed in an oven at 130 ℃ for 24 hours.
Cooling the reacted materials to room temperature, filtering, and collecting precipitates; washing the precipitate with deionized water for 3 times, and vacuum drying at 80 deg.C for 5 hr to obtain NiCoMn containing Ni, Co and Mn 2 And (4) grinding the LDHs for standby, and filling the LDHs on a sand core at the lower part of the plasma catalytic reactor when in use.
NiCoMn-LDHs prepared in example 3, NiCo prepared in example 4 2 Mn-LDHs, NiCoMn prepared in example 5 2 -LDHThe XRD diffraction pattern of s is shown in figure 5, and accords with JCPDS 40-0215 standard cards; four characteristic diffraction peaks appearing at 2 theta of 11.5 DEG, 23.1 DEG, 34.2 DEG and 38.7 DEG respectively correspond to (003), (006), (012) and (015) crystal planes, and reflect the layered structure of LDHs. In addition, MnCO appears at 24.33 DEG and 31.43 DEG 3 May be due to CO contained in air during the catalyst synthesis 2 And (4) causing.
(test example 1)
In the test example, the degradation rates of VOCs (volatile organic compounds) degraded by the aid of low-temperature Dielectric Barrier Discharge (DBD) plasma and NiCoMn-LDHs in a synergetic catalytic mode, VOCs degraded by the aid of low-temperature Dielectric Barrier Discharge (DBD) plasma and MnCo-LDHs in a synergetic catalytic mode and VOCs degraded by the aid of low-temperature Dielectric Barrier Discharge (DBD) plasma are compared, and the test process is as follows:
the VOCs gas was configured as follows: after the nitrogen from the compressed steel cylinder is controlled to have a certain flow by a Mass Flow Controller (MFC), the nitrogen is used as carrier gas or balance gas to pass through a polytetrafluoroethylene tube with the outer diameter of 3 mm, then the nitrogen enters a stainless steel tank (the stainless steel tank adopts low-temperature water tank temperature control or water bath temperature control), VOCs steam is carried out, the nitrogen and the oxygen which are controlled by the mass flow controller are fully mixed in a mixer, VOCs gas with stable concentration is formed and enters a DBD discharge reactor, and a plasma catalysis VOCs degradation experiment is carried out.
Under normal temperature and normal pressure, 0.5g of manganese-based hydrotalcite-like catalyst is filled on a sand core at the lower part of the plasma catalytic reactor to form a two-section plasma catalytic reactor. The initial concentration of the introduced toluene is 1000 mg/m 3 Gas to be degraded, gas flow lL/min, O 2 The concentration is 6%, the input power of the plasma discharge is adjusted, the corresponding input energy density of the plasma discharge is respectively 105, 156, 210, 258 and 295J/L, and the toluene degradation experiment is started.
The toluene concentration was measured by gas chromatography with FID detector using HP-5ms capillary column (30 m.times.250 μm.times.0.25 μm) to calculate the toluene degradation rate, and the NO and NO in the effluent gas were measured by smoke analyzer (MGA 6 type smoke analyzer, MRU, Germany) 2 CO and CO 2 Concentration of (2)The concentration of ozone generated by the discharge was measured by an ozone analyzer (model 106-M, 2B, USA). The test results are shown in fig. 6, 7 and 8.
As shown in FIG. 6, the experimental result shows that compared with the DBD and NiCoMn-LDH catalyzed toluene degradation, the toluene degradation rate is improved by 20.1% when the input energy density is 210J/L; compared with the single DBD, when the energy density is 210J/L, the toluene degradation rate is improved by 14.2%, and the catalytic effect of NiCoMn-LDHs is better than that of CoMn-LDHs.
In addition, when the plasma is post-catalyzed, the catalyst can effectively utilize O 3 By-products NO and O 3 And is greatly lowered as shown in fig. 7.
FIG. 8 records CO at different energy densities 2 Selectivity, CO 2 Selectivity is proportional to energy density.
(test example 2)
The test example investigates the influence of different factors on the cooperative catalytic degradation of toluene by the plasma and NiCoMn-LDHs, and the test process is as follows:
at normal temperature and normal pressure, 0.5g of NiCoMn hydrotalcite-like catalyst is filled on a sand core at the lower part of the plasma catalytic reactor to form a two-section plasma catalytic reactor.
The VOCs gas is configured as follows: after the nitrogen from the compressed steel cylinder is controlled to have a certain flow by a Mass Flow Controller (MFC), the nitrogen is used as carrier gas or balance gas to pass through a polytetrafluoroethylene tube with the outer diameter of 3 mm, then the nitrogen enters a stainless steel tank (the stainless steel tank adopts low-temperature water tank temperature control or water bath temperature control), VOCs steam is carried out, the nitrogen and the oxygen which are controlled by the mass flow controller are fully mixed in a mixer, VOCs gas with stable concentration is formed and enters a DBD discharge reactor, and a plasma catalysis VOCs degradation experiment is carried out.
The degradation effect of VOCs and the influence on byproducts are inspected by changing factors such as humidity, oxygen content and the like. During the specific operation, another path of nitrogen with a certain flow is added and is introduced into a gas washing bottle filled with deionized water in a water bath, and then the nitrogen and VOCs are mixed in a mixer and enter a plasma reactor. Determination of VOCs relative by hygrometerHumidity, the humidity was adjusted during the experiment by changing the temperature of the water bath. By controlling O 2 The oxygen content is controlled, typically in a volume fraction of 2% to 20%.
The initial concentration of the introduced toluene is 1500 mg/m 3 Gas to be degraded, O 2 The concentration is 4%, the gas flow rates are changed to be 0.2L/min, 0.5L/min, 1L/min, 2L/min and 5L/min respectively, the input power of plasma discharge is adjusted, the corresponding input energy density of the plasma discharge is 105, 156, 210, 258 and 295J/L respectively, and a toluene degradation experiment is carried out.
Measuring toluene concentration with gas chromatography with FID detector, wherein the chromatography column is HP-5ms capillary column (30 m × 250 μm × 0.25 μm), calculating toluene degradation rate, and measuring NO and NO in the effluent gas with smoke analyzer 2 The concentration of carbon oxides (carbon monoxide and carbon dioxide) in the product was determined by using an ozone analyzer to determine the concentration of ozone generated by the discharge and a gas chromatograph equipped with a methane reformer and a TDX-01 type packed column having a length of 1m as a chromatographic column.
The results are as follows:
1. effect of gas flow rate on toluene degradation.
The experimental result shows that the flow rate of the gas flow has great influence on the catalytic conversion of the toluene, and the smaller the flow rate of the gas flow is, the longer the toluene stays in the reactor, and the higher the toluene conversion rate is. At 0.5L/min, at 210J/L, the toluene conversion rate is as high as 95.2%, when the flow rate is increased to 5L/min, the degradation rate is reduced to 42.1%, and the concentration of generated ozone is reduced by about 30%.
2. Influence of gas humidity on toluene degradation.
When the relative humidity of air is increased from 0% to 40%, the toluene degradation rate is increased with the increase of humidity, but when the humidity is continuously increased from 40% to 70%, the toluene degradation rate is decreased.
Meanwhile, the humidity has a certain inhibiting effect on the byproduct ozone, because the water molecules are electronegative molecules, the water molecules can capture high-energy electrons generated by discharge, the average energy of the electrons can be reduced, and the quantity of active particles generated by discharge is reduced. Further, O generated during the discharge chemically reacts with water molecules, so that the concentration of O is lowered and the formation of ozone is slowed down.
The volume fraction of water vapor in the mixed gas of VOCs and oxygen is recommended to be 2-30%.
3. The effect of oxygen content on toluene degradation effect and by-products.
The higher the oxygen content, the by-product O 3 The more amount is formed.
Claims (10)
1. A method for catalyzing and degrading VOCs is characterized by comprising the following steps: manganese-based hydrotalcite catalysts are placed on sand cores at the downstream position of a plasma discharge tube of the dielectric barrier discharge low-temperature plasma reactor, VOCs to be degraded are mixed with oxygen and then pass through the reactor, and the mixture is degraded by the dielectric barrier discharge low-temperature plasma and the manganese-based hydrotalcite in a synergetic catalytic mode.
2. The method of claim 1 for the catalytic degradation of VOCs, wherein: the dielectric barrier discharge low-temperature plasma reactor comprises a high-voltage electrode, a low-voltage electrode, an insulating medium and a sand core, wherein the high-voltage electrode is a solid metal rod or metal powder, the low-voltage electrode is a copper foil or an aluminum foil, and the insulating medium is a quartz tube; the quartz tube and the high-voltage electrode are coaxially arranged, and the low-voltage electrode is arranged outside the quartz tube; the sand core is arranged at the position 10-15 mm downstream of the plasma discharge tube, and the manganese-based hydrotalcite catalyst is placed on the sand core.
3. The method of claim 1 for the catalytic degradation of VOCs, wherein: the manganese-based hydrotalcite-like catalyst is a hydrotalcite-like catalyst doped with Ni, Co and Mn, or a hydrotalcite-like catalyst doped with Co and Mn.
4. A method of catalytically degrading VOCs according to claim 3, wherein: when the manganese-based hydrotalcite catalyst is a Ni, Co and Mn doped hydrotalcite-like catalyst, the manganese-based hydrotalcite-like catalyst is NiCoMn-LDHs or NiCo 2 Mn-LDHs or NiCoMn 2 –LDHs。
5. The method for the catalytic degradation of VOCs according to claim 4, wherein said manganese-based hydrotalcite-like catalyst is prepared by the following steps: dissolving nickel salt, cobalt salt, manganese salt and urea in deionized water to obtain a mixed salt solution; stirring the mixed salt solution, transferring the obtained clear solution into a hydrothermal reaction kettle, and placing the hydrothermal reaction kettle in an oven at the temperature of between 130 and 150 ℃ for 18 to 24 hours; cooling the reacted materials to room temperature, filtering, and collecting precipitates; washing and drying the precipitate to obtain the manganese-based hydrotalcite-like catalyst containing nickel, cobalt and manganese.
6. The method of claim 5 for the catalytic degradation of VOCs wherein: the molar ratio of urea to total metals was 3.3: 1.
7. a method of catalytically degrading VOCs according to claim 3, wherein: the manganese-based hydrotalcite catalyst is MnCo-LDHs.
8. The method for the catalytic degradation of VOCs according to claim 7, wherein said manganese-based hydrotalcite-like catalyst is prepared by the following steps: dissolving cobalt salt, manganese salt and urea in deionized water to obtain a mixed salt solution; stirring the mixed salt solution, transferring the obtained clear solution into a hydrothermal reaction kettle, and placing the hydrothermal reaction kettle in an oven at the temperature of 130-150 ℃ for 18-24 hours; cooling the reacted materials to room temperature, filtering, and collecting precipitates; washing and drying the precipitate to obtain the manganese-based hydrotalcite-like catalyst containing nickel, cobalt and manganese.
9. The method of claim 1 for the catalytic degradation of VOCs comprising: the oxygen content in the mixed gas of VOCs and oxygen is 2-20%.
10. The method of claim 1 for the catalytic degradation of VOCs, wherein: the mixed gas of VOCs and oxygen also contains water vapor, and the volume fraction of the water vapor is 2-30%.
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