CN114733345B - Method for degrading VOCs (volatile organic compounds) by catalyzing ozone oxidation through alpha-crystal manganese dioxide - Google Patents

Method for degrading VOCs (volatile organic compounds) by catalyzing ozone oxidation through alpha-crystal manganese dioxide Download PDF

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CN114733345B
CN114733345B CN202210516744.3A CN202210516744A CN114733345B CN 114733345 B CN114733345 B CN 114733345B CN 202210516744 A CN202210516744 A CN 202210516744A CN 114733345 B CN114733345 B CN 114733345B
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vocs
manganese dioxide
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ozone
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CN114733345A (en
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贺泓
陆宇琴
邓华
单文坡
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Institute of Urban Environment of CAS
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Abstract

The invention provides a method for degrading VOCs (volatile organic compounds) by catalyzing ozone oxidation by manganese dioxide in an alpha crystal form, which comprises the following steps: and (3) allowing the mixed gas of the VOCs and ozone to pass through a reaction device filled with alpha-crystal manganese dioxide to perform catalytic ozonation reaction to degrade the VOCs. In the method, the alpha crystal form manganese dioxide is obtained by roasting at 550-700 ℃ to convert delta crystal form, and shows excellent VOCs ozone catalytic activity and CO 2 Selectivity, high conversion rate of VOCs and no by-product generation after reaction; the method is simple to operate and suitable for large-scale popularization and application.

Description

Method for degrading VOCs (volatile organic compounds) by catalyzing ozone oxidation through alpha-crystal manganese dioxide
Technical Field
The invention relates to the technical field of VOC waste gas treatment, in particular to a method for degrading VOCs (volatile organic compounds) by catalyzing ozone oxidation through alpha-crystal manganese dioxide.
Background
The discharge amount of Volatile Organic Compounds (VOCs) in the atmosphere is increasing year by year, which not only seriously threatens the ecological environment, but also poses a great threat to human health. The combustion method can directly convert VOCs into harmless small molecules such as COx and H 2 O, but requires a large amount of energy to maintain. Catalytic oxidation technology reduces the reaction temperature of the incinerator from 1000 ℃ to below 600 ℃, but still requires temperatures above 200 ℃ for effective treatment. Ozone, as a strong oxidant, is commonly used for removing organic matters in wastewater and disinfecting microorganisms. Ozone significantly reduces the apparent activation energy of oxidation of VOCs more than oxygen, but ozone alone eliminates indoor contaminating VOCs with very low removal efficiency and produces certain byproducts such as aldehydes and organic acids.
CN111617633A discloses a preparation method of VOCs (volatile organic compounds) degraded by a multi-shell photocatalyst and activated carbon in a composite manner, which comprises the following steps: s1 preparation of three-layer hollow SiO 2 Nanospheres, S2 with SiO 2 Adding a titanium source into a template and then carrying out hydrothermal reaction to prepare the multi-shell photocatalyst TiO 2 S3 in Multi-Shell TiO 2 A certain proportion of noble metal is loaded on the surface, S4 is the TiO loaded with noble metal 2 And evenly mixing with activated carbon in a proper proportion to obtain the composite material. The composite material prepared by the method can provide a larger specific surface area, multiple reflection of light can be realized by the inner cavity of the composite material, so that more photoproduction voids are generated, and the composite material is combined with the rich pore diameter structure of the activated carbon, so that adsorption and degradation of VOCs can be carried out simultaneously, and the composite material is a novel efficient and energy-saving material for degrading VOCs. However, the activated carbon is saturated in adsorption after being used for a period of time and needs to be replaced frequently.
CN110368790A discloses an air purification method, system and application for catalytic oxidative degradation of VOCs. The air purification method comprises the following steps: enabling the air containing the VOCs to enter an ozone generating device through an air inducing device to generate free oxygen radicals and ozone, and simultaneously degrading partial organic matters in the air containing the VOCs into micromolecular compounds; the air treated by the ozone generating device enters a catalytic oxidation reaction device and contacts with a catalyst in the presence of free oxygen radicals and ozone, so that VOCs molecules are degraded through catalytic oxidation to obtain primary purified air; and then, enabling the primarily purified air to enter a filtering and sterilizing device to obtain secondarily purified air, wherein the filtering and sterilizing device comprises a photocatalytic filtering component and activated carbon fibers, and the photocatalytic filtering component is loaded with active nano particles with sterilizing performance, so that VOCs can be efficiently and completely digested deeply at the temperature of-10-40 ℃, and the purpose of deeply degrading and purifying the air is fulfilled. However, the active nanoparticles in the method are nano silver and/or nano titanium dioxide, which results in higher cost for degrading VOCs.
CN104607172A discloses a preparation method of a cerium-doped plasma catalyst, which comprises the following specific steps: grinding after pretreatment of the catalytic material; ultrasonic stirring in industrial silica sol solution for 0.5-2 hr, wherein the nano TiO is 2 And the ferroelectric material is 50-10% by mass: 50% -90%; adding a cerium-containing compound into the solution, and ultrasonically stirring for 0.5-2 h; gamma-Al is mixed 2 O 3 Cleaning, drying, putting into the solution, stirring and performing ultrasonic treatment for 0.5-2 h, drying at 105 ℃, putting into a muffle furnace, calcining for 0.5-2h at 200-300 ℃, and calcining for 2-4 h at 400-600 ℃. However, when the applied voltage of the catalyst is 17kV, the degradation rates of the empty tube, the single titanium dioxide catalyst and the cerium-doped catalyst on toluene are respectively 25.4%, 62.3% and 70.3%, and the catalytic degradation rate is lower.
Therefore, the development of a method for catalyzing the ozone oxidation of VOCs, which has the advantages of low treatment cost, no byproduct generation and high catalytic degradation rate, is of great significance.
Disclosure of Invention
In view of the problems in the prior art, the invention provides a method for catalyzing ozone to oxidize and degrade VOCs by using alpha crystal form manganese dioxide, which has low cost, is roasted at the high temperature of 550-700 ℃, takes the alpha crystal form manganese dioxide obtained by delta crystal form conversion as a catalyst to catalyze ozone to oxidize and degrade the VOCs, has high conversion rate of the VOCs and high ozone decomposition rate, does not generate byproducts, and is suitable for large-scale popularization and application.
In order to achieve the purpose, the invention adopts the following technical scheme:
the invention provides a method for degrading VOCs (volatile organic compounds) by catalyzing ozone oxidation by manganese dioxide in an alpha crystal form, which comprises the following steps:
the VOCs mixed gas and ozone pass through a reaction device filled with alpha-crystal manganese dioxide to carry out catalytic ozonation reaction to degrade VOCs;
the preparation method of the alpha-crystal manganese dioxide comprises the following steps:
after the soluble divalent manganese salt and the potassium permanganate are dissolved in the ionized water according to the molar ratio of (0.5-1) to (3-6), the hydrothermal reaction is carried out for 8-24 h at the temperature of 180-280 ℃; and after the reaction is finished, sequentially collecting, washing and filtering the product, drying the product in an oven at 80 ℃, and roasting the dried sample at 550-700 ℃ for 3-5 h to obtain the alpha-crystal manganese dioxide.
The method for degrading VOCs by catalyzing ozone oxidation through the alpha-crystal manganese dioxide adopts alpha-crystal manganese dioxide obtained by converting delta crystal as a catalyst and acts with ozone after being roasted at the high temperature of 550-700 ℃, so that the high-efficiency decomposition of VOCs can be realized at the low temperature even at the room temperature of 20 ℃, products are carbon dioxide and carbon monoxide, and no secondary pollution is caused. Compared with alpha-crystal manganese dioxide or delta-crystal manganese dioxide, beta-crystal manganese dioxide and gamma-crystal manganese dioxide prepared by roasting at a lower temperature, the alpha-crystal manganese dioxide obtained by roasting at the high temperature has a nanowire structure, can generate more active oxygen species (including singlet oxygen, superoxide radical and hydroxyl radical), and is high in catalytic activity.
The method for catalyzing the ozone to oxidize and degrade the VOCs by the manganese dioxide with the alpha crystal form has simple operation and low requirement on reaction equipment, achieves the aim of efficiently decomposing the VOCs by controlling the conditions such as the ratio of the VOCs to the ozone in a system, the reaction temperature, the airspeed and the like, and is suitable for large-scale popularization and application in VOCs waste gas treatment.
Preferably, the mixed gas of the VOCs includes organic substances.
Preferably, the organic matter comprises any one or a combination of at least two of toluene, acetone, ethyl acetate, o-xylene or benzene, wherein typical but non-limiting combinations include a combination of toluene and acetone, a combination of ethyl acetate and benzene, a combination of toluene and ethyl acetate, a combination of acetone and o-xylene, a combination of toluene, acetone and ethyl acetate or a combination of o-xylene, toluene and acetone.
Preferably, the mixed gas of VOCs further comprises an inert gas, and the inert gas mainly serves as a balance gas of the mixed gas of VOCs.
Preferably, the inert gas comprises any one or a combination of at least two of nitrogen, helium or argon, with typical but non-limiting combinations including a combination of nitrogen and helium, argon and nitrogen, helium, argon and nitrogen or argon, nitrogen and helium.
Preferably, the volume ratio of the organic matters to the ozone in the mixed gas of the VOCs is (1-5) to (6-16), and can be, for example, 1.
The volume ratio of the organic matters to the ozone in the VOCs mixed gas is preferably (1-5) to (6-16), so that the organic matters can be efficiently decomposed and converted under the combined action of the ozone and the alpha-crystal manganese dioxide. When the ozone amount in the mixed gas of VOCs is less, the generation of side products of carboxylate, such as benzoate and the like, can be caused, and the side products are accumulated on the surface of the alpha-crystal manganese dioxide of the catalyst, so that the catalyst is inactivated; when the amount of ozone in the mixed gas of VOCs is large, the ozone is self-decomposed, and the ozone utilization rate is low.
Preferably, the reaction space velocity of the mixed gas of the VOCs is 60 to 480L/h/g, and can be 60L/h/g, 100L/h/g, 200L/h/g, 250L/h/g, 300L/h/g, 350L/h/g, 400L/h/g or 480L/h/g, for example.
Preferably, the reaction apparatus is a fixed bed reactor.
Preferably, the temperature of the catalytic ozonation reaction is 20 to 60 ℃, and may be, for example, 20 ℃, 30 ℃,40 ℃, 50 ℃ or 60 ℃.
The temperature of the catalytic ozonation reaction is preferably 20-60 ℃, and the self-decomposition of ozone can be caused by overhigh temperature, so that the catalytic activity of the alpha-crystal manganese dioxide is reduced; when the temperature is too low, the activity of free radical substances generated by ozone is not high, VOCs cannot be completely oxidized, and intermediate byproducts are also generated and adsorbed on the surface of the alpha-crystal manganese dioxide catalyst, so that the activity of the catalyst is influenced, and the decomposition and conversion of the VOCs are further influenced.
Preferably, the soluble divalent manganese salt comprises any one of manganese sulfate tetrahydrate, manganese chloride or manganese nitrate or a combination of at least two thereof, with typical but non-limiting combinations including combinations of manganese sulfate tetrahydrate and manganese chloride, manganese nitrate and manganese sulfate tetrahydrate, manganese chloride and manganese nitrate or combinations of three of manganese sulfate tetrahydrate, manganese chloride and manganese nitrate.
The recitation of numerical ranges herein includes not only the above-recited values, but also any values between any of the above-recited numerical ranges not recited, and for brevity and clarity, is not intended to be exhaustive of the specific values encompassed within the range.
As a preferable technical scheme of the invention, the method comprises the following steps:
the mixed gas of VOCs and ozone pass through a fixed bed reactor filled with alpha-crystal manganese dioxide, and the VOCs are degraded through catalytic ozonation reaction at the temperature of 20-60 ℃; the volume ratio of organic matters to ozone in the VOCs mixed gas is (1-5) to (6-16); the reaction space velocity of the VOCs mixed gas is 60-480L/h/g;
the preparation method of the alpha-crystal manganese dioxide comprises the following steps:
after dissolving soluble divalent manganese salt and potassium permanganate in ionic water according to the molar ratio of (0.5-1) to (3-6), carrying out hydrothermal reaction at 180-280 ℃ for 8-24 h; and after the reaction is finished, sequentially collecting, washing and filtering the product, drying the product in an oven at 80 ℃, and roasting the dried sample at 550-700 ℃ for 3-5 h to obtain the alpha-crystal manganese dioxide.
Compared with the prior art, the invention has at least the following beneficial effects:
the method for catalyzing ozone to oxidize and degrade VOCs by using the alpha-crystal manganese dioxide provided by the invention adopts roasting at the high temperature of 550-700 ℃, the alpha-crystal manganese dioxide obtained by delta-crystal conversion efficiently degrades VOCs at room temperature, when the ozone decomposition rate is 100% and the selectivity of carbon oxides is 100%, the conversion rate of toluene can reach over 74% under better conditions, and the harmless treatment of VOCs waste gas is realized without secondary pollution.
Drawings
FIG. 1 is a graph of toluene conversion as a function of time for example 1 and comparative examples 1 to 4.
FIG. 2 is a graph showing the time-course change of the ozone decomposition rate in example 1 and comparative examples 1 to 4.
FIG. 3 is a graph showing the change in carbon monoxide yield with time in example 1 and comparative examples 1 to 4.
Fig. 4 is a graph showing the change in carbon dioxide yield with time in example 1 and comparative examples 1 to 4.
FIG. 5 is a scanning electron micrograph of manganese dioxide in the alpha crystalline form of example 1.
Fig. 6 is a scanning electron micrograph of manganese dioxide of α crystal form in comparative example 1.
Fig. 7 is a scanning electron micrograph of manganese dioxide in gamma crystalline form in comparative example 2.
Fig. 8 is a scanning electron micrograph of manganese dioxide in the beta crystalline form of comparative example 3.
Fig. 9 is a scanning electron micrograph of manganese dioxide in the delta crystal form in comparative example 4.
Fig. 10 is an XRD pattern of manganese dioxide in example 1 and comparative examples 1 to 4.
Fig. 11 is a graph of the radical content of manganese dioxide in example 1, comparative example 1 and comparative example 4.
Detailed Description
The technical scheme of the invention is further explained by the specific implementation mode in combination with the attached drawings.
The present invention is described in further detail below. The following examples are merely illustrative of the present invention and do not represent or limit the scope of the claims, which are defined by the claims.
The toluene and nitrogen gases in the following examples and comparative examples are cylinder gases supplied by successful gas Co., ltd, of Fujian Nanan city, and the ozone gas is produced by a UV-M2 type ultraviolet ozone generator manufactured by science and technology Co., ltd, manufactured by Beijing Tonglin.
Example 1
The embodiment provides a method for catalyzing ozone to oxidize and degrade VOCs by using manganese dioxide in an alpha crystal form, which comprises the following steps:
the mixed gas of VOCs and ozone pass through a fixed bed reactor filled with alpha-crystal manganese dioxide, and the VOCs are degraded through catalytic ozonation reaction at the temperature of 30 ℃; the volume ratio of toluene to ozone in the VOCs mixed gas is 1; introducing nitrogen into the mixed gas of the VOCs to serve as balance gas, and controlling the flow of the mixed gas of the VOCs to be 200mL/min; the using amount of the catalyst in the catalytic ozonation reaction is 0.1g, and the reaction space velocity of the VOCs mixed gas is 120L/h/g;
the preparation method of the alpha-crystal manganese dioxide comprises the following steps:
the molar ratio of the tetrahydrate manganese sulfate to the potassium permanganate is 1:5.84, dissolving in deionized water, and carrying out hydrothermal reaction at 240 ℃ for 24 hours; and after the reaction is finished, sequentially collecting, washing and filtering the product, drying the product in an oven at 80 ℃, and roasting the dried sample at 700 ℃ for 3 hours to obtain the alpha-crystal manganese dioxide.
Example 2
The embodiment provides a method for catalyzing ozone to oxidize and degrade VOCs by using manganese dioxide in an alpha crystal form, which comprises the following steps:
the mixed gas of VOCs and ozone pass through a fixed bed reactor filled with alpha-crystal manganese dioxide, and the VOCs are degraded through catalytic ozonation reaction at the temperature of 30 ℃; the volume ratio of toluene to ozone in the mixed gas of VOCs is 1; introducing nitrogen into the mixed gas of the VOCs to serve as balance gas, and controlling the flow of the mixed gas of the VOCs to be 200mL/min; the using amount of the catalyst in the catalytic ozonation reaction is 0.1g, and the reaction space velocity of the VOCs mixed gas is 120L/h/g;
the preparation method of the alpha-crystal manganese dioxide comprises the following steps:
the molar ratio of manganese chloride to potassium permanganate is 1:5.84, mixing, and then carrying out hydrothermal reaction at 220 ℃ for 24 hours; and after the reaction is finished, sequentially collecting, washing and filtering the product, drying the product in an oven at 80 ℃, and roasting the dried sample at 600 ℃ for 3 hours to obtain the alpha-crystal manganese dioxide.
Example 3
The embodiment provides a method for catalyzing ozone to oxidize and degrade VOCs by using manganese dioxide in an alpha crystal form, which comprises the following steps:
the mixed gas of VOCs and ozone pass through a fixed bed reactor filled with alpha-crystal manganese dioxide, and the VOCs are degraded through catalytic ozonation reaction at the temperature of 40 ℃; the volume ratio of toluene to ozone in the VOCs mixed gas is 1; introducing nitrogen into the mixed gas of the VOCs to serve as balance gas, and controlling the flow of the mixed gas of the VOCs to be 100mL/min; the using amount of the catalyst in the catalytic ozonation reaction is 0.05g, and the reaction space velocity of the VOCs mixed gas is 240L/h/g;
the preparation method of the alpha-crystal manganese dioxide comprises the following steps:
manganese nitrate, potassium permanganate and deionized water according to a molar ratio of 1:5.84, and after mixing, carrying out hydrothermal reaction at the temperature of 260 ℃ for 24 hours; and after the reaction is finished, sequentially collecting, washing and filtering the product, drying the product in an oven at 80 ℃, and roasting the dried sample at 550 ℃ for 3 hours to obtain the alpha-crystal manganese dioxide.
Example 4
This example provides a method for catalytic ozonation degradation of VOCs by manganese dioxide in an α crystal form, which is the same as in example 1 except that the volume ratio of toluene to ozone in the mixed gas of VOCs "1.
Example 5
The embodiment provides a method for catalytic ozonation degradation of VOCs by manganese dioxide in an alpha crystal form, which is the same as that in example 1 except that the volume ratio of toluene to ozone in mixed gas of the VOCs, namely' 1
Example 6
This example provides a method for degrading VOCs by catalytic ozonation with manganese dioxide in an α crystal form, which is the same as example 1 except that "0.1g" of the catalyst used in the catalytic ozonation reaction is replaced by "0.01g", and accordingly, the reaction idle speed of the mixed gas of VOCs is 1200L/h/g.
Example 7
This example provides a method for degrading VOCs by catalytic ozonation with manganese dioxide in an α crystal form, which is the same as in example 1, except that the usage amount of the catalyst in the catalytic ozonation reaction is changed to "0.1g", and accordingly, the reaction idle speed of the mixed gas of VOCs is changed to 60L/h/g.
Example 8
This example provides a method for catalytic ozonation degradation of VOCs by manganese dioxide in an alpha crystal form, which is the same as in example 1 except that the temperature for catalytic ozonation reaction is changed to "10" instead of "30".
Example 9
This example provides a method for catalytic ozonation degradation of VOCs using manganese dioxide in the alpha crystal form, which is the same as in example 1 except that the temperature for catalytic ozonation reaction, namely "30" is replaced with "85".
Comparative example 1
This comparative example provides a method for catalytic ozonation degradation of VOCs with manganese dioxide, which is the same as in example 1, except that "manganese dioxide of α crystal form" was replaced with manganese dioxide of α crystal form obtained by the following preparation method.
The preparation method of the manganese dioxide of the alpha crystal form in the comparative example comprises the following steps:
the mass ratio of the manganese sulfate tetrahydrate to the potassium permanganate to the deionized water is 0.656. After the reaction was complete, the product was collected, washed, filtered, placed in an 80 ℃ oven to dry overnight, after which the dried sample was calcined at 300 ℃ for 3h.
Comparative example 2
The comparative example provides a method for degrading VOCs by catalyzing ozone oxidation with manganese dioxide, which is the same as that in example 1 except that 'manganese dioxide with alpha crystal form' is replaced by 'manganese dioxide with gamma crystal form'.
The preparation method of gamma-crystal manganese dioxide in the comparative example comprises the following steps:
after stirring for 30min to form a uniform 80mL solution, manganese sulfate tetrahydrate, ammonium persulfate and deionized water in a mass ratio of 4.219 to 5.719. After the reaction was complete, the product was collected, washed, filtered, placed in an 80 ℃ oven to dry overnight, after which the dried sample was calcined at 300 ℃ for 3h.
Comparative example 3
The comparative example provides a method for degrading VOCs by catalyzing ozone oxidation with manganese dioxide, which is the same as that in example 1 except that 'manganese dioxide with alpha crystal form' is replaced by 'manganese dioxide with beta crystal form'.
The preparation method of the manganese dioxide of beta crystal form in the comparative example comprises the following steps:
manganese sulfate tetrahydrate, ammonium persulfate and deionized water in a mass ratio of 2.113.85. After the reaction was complete, the product was collected, washed, filtered, placed in an 80 ℃ oven to dry overnight, after which the dried sample was calcined at 300 ℃ for 3h.
Comparative example 4
The comparative example provides a method for degrading VOCs by catalyzing ozone oxidation through manganese dioxide, which is the same as that in example 1 except that the roasting temperature of 600 ℃ in the preparation method of alpha-crystal manganese dioxide is replaced by 300 ℃.
In the comparative example, the roasting temperature is only 300 ℃, and manganese dioxide with delta crystal form is finally obtained.
The toluene substance was measured by a gas chromatography (agilent 7890B) method, and the toluene conversion of the above examples and comparative examples was calculated by the formula of conversion = (initial concentration-concentration after reaction)/initial concentration × 100%, wherein the toluene conversion in example 1 and comparative examples 1 to 4 is shown in fig. 1 as a graph with time.
It can be seen from fig. 1 that comparative examples 1, 2, and 3 have a gradual decrease in the deactivated toluene conversion of the catalyst due to the accumulation of intermediate by-products. The toluene conversion rate of example 1 is far better than that of comparative examples 1, 2 and 3, and 360min is stabilized at 85%.
The ozone concentration was measured by an ozone analyzer (Tonglin 3S-J5000) method, and the ozonolysis rates of the above examples and comparative examples were calculated by the formula of conversion = (initial concentration-concentration after reaction)/initial concentration X100%, wherein the ozonolysis rates in example 1 and comparative examples 1 to 4 are shown in FIG. 2 as a graph with time.
As can be seen from FIG. 2, the degradation performance of example 1 to ozone is still 100% after 360min, and the rest four comparative examples are all caused by the generation of intermediate by-products, and the accumulation on the surface of the catalyst causes the deactivation of the catalyst.
The carbon monoxide concentration was measured by the infrared spectroscopy (semefet IS 50) method, and the carbon monoxide yields of the above examples and comparative examples were calculated by the formula of yield = carbon monoxide concentration/(initial concentration of toluene × 7) × 100%, where the carbon monoxide yields in example 1 and comparative examples 1 to 4 are shown in fig. 3 as a graph with time.
It can be seen from fig. 3 that the carbon monoxide yield and the ozonolysis rate are linearly related.
The carbon dioxide concentration was measured by the infrared spectroscopy (semefei IS 50) method, and the carbon dioxide yields of the above examples and comparative examples were calculated by the formula of yield = carbon dioxide concentration/(initial concentration of toluene × 7) × 100%, wherein the carbon dioxide yields in example 1 and comparative examples 1 to 4 are plotted as a time course as shown in fig. 4.
From fig. 4 it can be seen that toluene is mainly converted to carbon dioxide, and that the carbon dioxide yield and the ozonolysis rate are linearly related.
A scanning electron microscope image of α -crystalline manganese dioxide in example 1 is shown in fig. 5, a scanning electron microscope image of α -crystalline manganese dioxide in comparative example 1 is shown in fig. 6, a scanning electron microscope image of γ -crystalline manganese dioxide in comparative example 2 is shown in fig. 7, a scanning electron microscope image of β -crystalline manganese dioxide in comparative example 3 is shown in fig. 8, and a scanning electron microscope image of δ -crystalline manganese dioxide in comparative example 4 is shown in fig. 9.
As can be seen from fig. 5, manganese dioxide of α crystal form in example 1 has a nanowire-like structure, and as can be seen from fig. 6, α -MnO in comparative example 1 2 The nanoneedle structure has sharp ends, and as can be seen from FIG. 7, the gamma-MnO in comparative example 2 2 The thicker nanorods, as can be seen from FIG. 8, in comparative example 3 are beta-MnO 2 Is a nanorod of a square prism shape having a large cross section, and as can be seen from FIG. 9, in comparative example 4, delta-MnO 2 The basic structure is a staggered nano sheet, and a bud shape is formed.
The XRD patterns of manganese dioxide in example 1 and comparative examples 1 to 4 are shown in fig. 10, and it can be seen from fig. 10 that manganese dioxide in example 1 is in the α crystal form, manganese dioxide in comparative example 2 is in the γ crystal form, manganese dioxide in comparative example 3 is in the β crystal form, and manganese dioxide in comparative example 4 is in the δ crystal form.
The manganese dioxide of example 1, comparative example 1 and comparative example 4 was subjected to a radical test and the radical content profile is shown in fig. 11. As can be seen from fig. 11, the manganese dioxide of example 1 was able to generate more active oxygen species (including singlet oxygen, superoxide radicals, hydroxyl radicals) followed by comparative example 4, comparative example 1, consistent with the activity data.
The toluene conversion, ozonolysis and carbon oxide selectivity results in the above examples and comparative examples are shown in table 1. Wherein, carbon oxide selectivity = (carbon dioxide concentration + carbon monoxide concentration)/(initial toluene concentration × 7 × toluene conversion) × 100% was calculated from the equation.
TABLE 1
Figure BDA0003639973770000121
Figure BDA0003639973770000131
As can be seen from table 1:
(1) It can be seen from the comprehensive examples 1 to 9 that the method for degrading VOCs by catalyzing ozone oxidation with alpha-crystal manganese dioxide provided by the invention realizes efficient degradation of VOCs at room temperature, when the ozone decomposition rate is 100% and the selectivity of oxycarbide is 100%, the conversion rate of toluene can reach more than 74% under better conditions, and the harmless treatment of VOCs waste gas is realized without secondary pollution;
(2) Combining example 1 with examples 4-5, it can be seen that the volume ratio of toluene and ozone in the mixed gas of VOCs described in example 1 is 1; in example 5, because the amount of ozone is large, the ozone utilization rate is low, although ozone can still be effectively decomposed, the ozone decomposition rate is 100%, the toluene conversion rate is also improved to 97%, but the carbon oxide selectivity is greatly reduced to only 87%; therefore, the volume ratio of the organic matters to the ozone in the VOCs mixed gas is limited within a specific range, so that the generation of byproducts can be avoided, the ozone can be effectively utilized, the efficient decomposition and conversion of the VOCs are realized, and no secondary pollution is generated;
(3) It can be seen from the combination of example 1 and examples 6-7 that the amount of the catalyst used in the catalytic ozonation reaction in example 1 is 0.1g, and accordingly the reaction space velocity of the VOCs mixed gas is 120L/h/g, compared to the amounts of the catalyst used in the catalytic ozonation reaction in examples 6-7, which are 0.01g and 0.2g, respectively, and accordingly the reaction space velocities of the VOCs mixed gas are 1200L/h/g and 60L/h/g, respectively, the amount of the catalyst used in example 6 is too small to catalyze ozone to perform oxidative degradation of VOCs well, the toluene conversion is 72%, the ozone decomposition rate is only 52%, and the carbon oxide selectivity is only 66%; the use of the catalyst in example 7 is high and does not improve the toluene conversion rate and the carbon oxide selectivity, and the excessive use of the catalyst increases the cost of degrading VOCs; therefore, the reaction space velocity of the mixed gas of the VOCs is limited within a specific range, so that the high-efficiency decomposition and conversion of the VOCs can be realized, the cost can be saved, and the large-scale popularization and application can be realized;
(4) By combining example 1 with examples 8 to 9, it can be seen that the temperature of the catalytic ozonation reaction in example 1 is 20 ℃, compared with the temperatures of 10 ℃ and 85 ℃ in examples 8 to 9, respectively, in example 8, because the temperature of the catalytic ozonation reaction is too low, the activity of free radical substances generated by ozone is not high, the VOCs cannot be completely oxidized, and intermediate byproducts are also generated to be adsorbed on the surface of the alpha-crystal manganese dioxide of the catalyst, so that the activity of the catalyst is affected, the decomposition and conversion of the VOCs are affected, the toluene conversion rate is only 69%, the ozone decomposition rate is only 19%, and the carbon oxide selectivity is only 37%; in example 9, the temperature of the catalytic oxidation reaction is too high, although the selectivity of the carbon oxide is 98% and the decomposition rate of the ozone is still 100%, the self-decomposition of the ozone is caused, the utilization rate of the ozone is reduced, and the conversion rate of the toluene is only 40%; therefore, the temperature for catalyzing the ozone oxidation reaction is limited within a specific range, so that the self-decomposition of ozone can be avoided, and the high-efficiency decomposition and conversion of VOCs can be realized;
(5) It can be seen from the combination of example 1 and comparative examples 1 to 4 that, compared with the manganese dioxide of α crystal form obtained by using different raw material ratios and different hydrothermal reaction conditions, drying conditions and baking conditions in comparative example 1, the manganese dioxide of α crystal form in comparative example 2, the manganese dioxide of γ crystal form in comparative example 3, the manganese dioxide of β crystal form in comparative example 3 and the manganese dioxide of δ crystal form in comparative example 4, the manganese dioxide of α crystal form in example 1 has a nanowire-like structure, has a larger specific surface area and high catalytic activity, while the manganese dioxide of α -MnO in comparative example 1 is 2 Nanoneedle structure with sharp ends, gamma-MnO in comparative example 2 2 Thicker nanorods, beta-MnO in comparative example 3 2 Is a square prism shaped nano-rod with larger cross section, delta-MnO in comparative example 4 2 The basic structure is a staggered nano sheet, a bud shape is formed, and as the structures of manganese dioxide in comparative examples 1-4 are different from those in example 1, the catalytic activity is lower, and the toluene conversion rate, the ozone decomposition rate and the carbon oxide selectivity are much lower than those in example 1; therefore, the invention adopts the manganese dioxide of alpha crystal form obtained by roasting at high temperature as the catalyst to act together with ozone, realizes the high-efficiency decomposition and conversion of VOCs, and the decomposition products are carbon dioxide and carbon monoxide without secondary pollution.
In conclusion, the method for degrading VOCs by catalyzing ozone oxidation through the alpha-crystal manganese dioxide realizes efficient decomposition of VOCs and generates no by-product after reaction; the method is simple to operate and suitable for large-scale popularization and application.
The applicant declares that the above description is only a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and it should be understood by those skilled in the art that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are within the scope and disclosure of the present invention.

Claims (11)

1. The method for catalyzing ozone to oxidize and degrade VOCs by using manganese dioxide in alpha crystal form is characterized by comprising the following steps:
the VOCs mixed gas and ozone pass through a reaction device filled with alpha-crystal manganese dioxide to carry out catalytic ozonation reaction to degrade VOCs;
the preparation method of the alpha-crystal manganese dioxide comprises the following steps:
dissolving soluble divalent manganese salt and potassium permanganate in ionized water according to the molar ratio of (0.5 to 1) to (3 to 6), and carrying out hydrothermal reaction at the temperature of 180 to 280 ℃ for 8 to 24h; and after the reaction is finished, sequentially collecting, washing and filtering the product, drying the product in an oven at 80 ℃, and roasting the dried sample at 550-700 ℃ for 3-5h to obtain the alpha-crystalline manganese dioxide.
2. The method of claim 1, wherein the mixture of VOCs includes organic compounds.
3. The method of claim 2, wherein the organic material comprises any one of toluene, acetone, ethyl acetate, o-xylene, or benzene, or a combination of at least two thereof.
4. The method of claim 1, wherein the mixture of VOCs further comprises an inert gas.
5. The method of claim 4, wherein the inert gas comprises any one of nitrogen, helium, or argon, or a combination of at least two thereof.
6. The method as claimed in claim 2, wherein the volume ratio of the organic substances to the ozone in the VOCs mixed gas is (1 to 5) to (6 to 16).
7. The method as claimed in claim 1, wherein the reaction space velocity of the mixed gas of VOCs is 60 to 480L/h/g.
8. The method of claim 1, wherein the reaction apparatus is a fixed bed reactor.
9. The process as claimed in claim 1, wherein the temperature of the catalytic ozonation reaction is from 20 to 60 ℃.
10. The method of claim 1, wherein the soluble divalent manganese salt comprises any one of manganese sulfate tetrahydrate, manganese chloride, or manganese nitrate, or a combination of at least two thereof.
11. The method according to any one of claims 1 to 10, comprising the steps of:
the mixed gas of VOCs and ozone pass through a fixed bed reactor filled with alpha-crystal manganese dioxide, and the VOCs are degraded through catalytic ozone oxidation reaction at the temperature of 20-60 ℃; the volume ratio of the organic matters to the ozone in the VOCs mixed gas is (1-5) to (6-16); the reaction space velocity of the VOCs mixed gas is 60 to 480L/h/g;
the preparation method of the alpha-crystal manganese dioxide comprises the following steps:
dissolving soluble divalent manganese salt and potassium permanganate in ionic water according to the molar ratio of (0.5 to 1) to (3 to 6), and carrying out hydrothermal reaction at the temperature of 180 to 280 ℃ for 8 to 24h; and after the reaction is finished, sequentially collecting, washing and filtering the product, drying the product in an oven at 80 ℃, and roasting the dried sample at 550-700 ℃ for 3-5h to obtain the alpha-crystalline manganese dioxide.
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