CN116510744A

CN116510744A - Preparation of nickel-manganese modified fly ash ozone oxidation catalyst by hot alkali method

Info

Publication number: CN116510744A
Application number: CN202310463332.2A
Authority: CN
Inventors: 陈瑶姬; 胡达清; 廖达琛; 顾雅洁; 奚爽; 孙科; 常星岚; 陈瑞富; 孙鹏飞; 董晓平
Original assignee: Zhejiang Sci Tech University ZSTU; Zhejiang Tiandi Environmental Protection Technology Co Ltd
Current assignee: Zhejiang Sci Tech University ZSTU; Zhejiang Tiandi Environmental Protection Technology Co Ltd
Priority date: 2023-04-26
Filing date: 2023-04-26
Publication date: 2023-08-01

Abstract

The invention discloses a method for preparing nickel-manganese modified fly ash ozone oxidation catalyst by a hot alkali method, wherein the acid-treated fly ash reacts with nickel hydroxide and potassium permanganate in alkaline solution at a temperature lower than 100 ℃, and the nickel-manganese modified fly ash ozone oxidation catalyst is obtained by taking solid after the reaction, washing the solid to be neutral and drying the solid at a temperature lower than 100 ℃. The invention also discloses the nickel-manganese modified fly ash ozone oxidation catalyst prepared by the method and application thereof in catalytic ozone oxidation treatment of sewage. The invention uses one-step normal pressure heat alkali treatment process to replace the traditional preparation process of the fly ash metal oxide supported catalyst, shortens the flow of the fly ash modification process, reduces the operation and energy consumption, and reduces the synthesis cost. The invention breaks through the bottleneck of single reaction mechanism of the traditional metal oxide supported fly ash catalyst, realizes the ozone catalytic oxidation mechanism of coexistence of non-free radicals and free radicals, and achieves the purpose of efficiently degrading organic matters in water.

Description

Preparation of nickel-manganese modified fly ash ozone oxidation catalyst by hot alkali method

Technical Field

The invention relates to the technical field of recycling of fly ash and purification of organic pollutants in water, in particular to a method for preparing a nickel-manganese modified fly ash ozone oxidation catalyst by a hot alkaline method, a catalyst and application thereof.

Background

The ozone oxidation catalyst is a necessary matching material in the application of ozone wastewater treatment, and needs to be replaced once in 2-3 years, and has vigorous requirements. Along with the gradual expansion of the application of ozone in the field of wastewater treatment, particularly in the field of removing organic pollutants in water body by ozone oxidation, the use amount and the running cost of ozone can be effectively reduced by adding a proper catalyst, so that the development industry of the relevant ozone oxidation catalyst enters a new development period. In view of the high cost of metal oxides, it is currently widely used in industry to load a lower content of metal active phase on the surface of some catalytic carriers, so as to obtain an ozone catalyst with certain properties. The application of alumina as a carrier is most widely used, and the alumina accounts for more than 70% of industrial supported catalysts. The current selling price of the ozone catalyst product is 8000-15000 yuan/ton, wherein the consumption of active raw material components is low and the process cost is low, but the consumption of alumina serving as a carrier is large and the unit price is high (4000-6000 yuan/ton), which is a key factor influencing the cost of the supported catalyst.

The fly ash is used as a solid waste product of high-temperature combustion and is mainly applied to the fields of building materials and the like with low added value for many years. However, in theory, fly ash has unique chemical composition, stable physical and chemical properties and remarkable cost advantages, is a low-cost carrier for replacing alumina, and has great potential in industrial application. By carrying out proper surface activation and metal active phase loading on the fly ash, the corresponding fly ash-based catalyst product can be obtained, and the high additional utilization value and space of the fly ash are improved. The chemical composition of the fly ash is similar to that of clay and mainly comprises SiO ₂ (40wt％～60wt％)、Al ₂ O ₃ (15wt％～35wt％)、Fe ₂ O ₃ (2-15 wt%), caO (1-10 wt%), mgO (1-10 wt%) and unburned carbon as well as other elements and trace elements. Therefore, the fly ash is used as an ozone oxidation catalyst carrier, and firstly the impurities, especially some alkali metal elements, need to be treated as clean as possible, and unstable oxides can be formed in the ozone oxidation process, so that the overall catalytic activity is affected. The common pretreatment method is mainly to dissolve out metal impurities on the surface of the fly ash by acidification. Secondly, the fly ash is used as an ozone catalyst and mainly plays a role of a carrier, active ingredients such as metal oxides and the like are loaded on the surface of the (modified) fly ash, and the catalytic performance of the system is improved by expanding a gas/liquid/solid interface. Therefore, the fly ash is required to have a larger specific surface area and a more ideal pore structure at least after modification. The common method is to corrode the amorphous structure of the glass body on the surface of the fly ash through alkali modification, promote the dissolution of soluble silicate, increase the surface roughness of the fly ash and widen the pore channel structure. At present, research has pointed out that fly ash treated by acid and alkali does have ideal specific surface area, and ozone oxidation catalyst with certain performance can be obtained by impregnating and calcining metal salt ions on the surface. If the metal with better catalytic ozone activity such as manganese oxide is selected, the metal salt is used for soaking and calcining (usually not less than 500 ℃) is carried out in a higher temperature range, so that the corresponding oxide-supported coal ash ozone catalyst is obtained. Therefore, the process of synthesizing the ozone oxidation catalyst by using the fly ash needs to provide additional calcination temperature and a large amount of energy consumption, and the process and the cost of industrial production are increased.

According to the reaction mechanism, the organic matters in the water body are difficult to thoroughly degrade by single ozone oxidation, and even if ozone with higher concentration is utilized, the organic matters in the macromolecular water body can only be degraded into secondary micromolecular intermediates, and the organic matters are difficult to further mineralize into CO ₂ And H ₂ O. The common catalyst generally promotes the reaction of the ozone and the active sites on the surface of the catalyst by improving the utilization rate of the ozone to generate oxidation free radicals or active oxygen, so that the oxidation and decomposition of organic matters are accelerated by releasing the oxygen into a water body, the consumption of the ozone is further reduced, and the process cost is optimized. The reaction mechanism of ozone catalytic oxidation in the water environment is mainly divided into a free radical mechanism and a non-free radical mechanism, and the general metal oxide tends to show only one single reaction mechanism. For example, the free radical reaction mechanism mainly comprises oxidation free radicals including hydroxyl free radicals and superoxide free radicals, and the oxidation species have high catalytic oxidation capability on most macromolecular organic matters such as aromatic hydrocarbon, phenols and the like, and can oxidize the matters into intermediate products such as small molecular acids and the like, but are difficult to deeply mineralize. The oxidation species under the non-free radical mechanism, including singlet oxygen, atomic oxygen, metal complex and the like, have weaker oxidation capability to macromolecules and aromatic pollutants due to relatively lower oxidation-reduction potential, but have a reaction rate constant to small molecular acids which is several orders of magnitude higher than that of the free radical mechanism, thereby being more beneficial to deeply mineralizing the small molecular acids and the like formed by target pollutants. It is conceivable that the coal ash ozone catalyst prepared by using common metal oxide load has complex synthesis procedures and higher preparation cost; the actual processing efficiency also creates a bottleneck due to the singleness of the reaction mechanism.

Disclosure of Invention

Aiming at the technical problems and the defects in the field, the invention provides a method for preparing a nickel-manganese modified fly ash ozone oxidation catalyst by a hot alkaline method. The invention uses the fly ash treated by acid as the main raw material, simplifies the following multi-step processes of alkali treatment, metal salt impregnation, calcination and the like into a one-step normal pressure heat alkali treatment process, reduces synthesis steps and reduces cost. The catalyst of the invention is a fly ash ozone oxidation catalyst containing nickel oxyhydroxide and manganese dioxide on the surface. In the heat treatment process of the alkaline solution environment, the surface silicon oxide is dissolved out and reconstructed, the specific surface area is increased, the pore channel structure is remolded, and the adsorption performance of the catalyst on the organic matters in the water body is improved. Nickel hydroxide and potassium permanganate react in an alkaline environment to generate nickel oxyhydroxide and manganese dioxide and are anchored in a remolded pore canal structure in the silicate leaching process, so that a reaction point with high-efficiency ozone catalytic performance is formed. The reaction point can show the concurrent oxidation mechanism of free radicals and non-free radicals in the process of degrading organic matters in the water body by ozone catalysis. The hydroxyl radical oxidation pathway is that hydroxyl radical is released into the solution to accelerate the organic matters in the water body; the manganese dioxide and the ozone react to form singlet oxygen and atomic oxygen, the singlet oxygen and the atomic oxygen participate in a non-radical oxidation way of the organic matters, and a concurrent reaction mechanism of the singlet oxygen and the atomic oxygen can play a good role in carrying out deep oxidation on most of the organic matters in the water body, and the macromolecular organic matters are decomposed into micromolecular acids and the like through a free radical oxidation mechanism, and then the deep mineralization is realized through a non-radical oxidation mechanism.

The specific technical scheme is as follows:

the method for preparing the nickel-manganese modified fly ash ozone oxidation catalyst by a hot alkali method comprises the steps of reacting the fly ash subjected to acid treatment with nickel hydroxide and potassium permanganate in an alkaline solution at a temperature lower than 100 ℃, taking solids after the reaction to wash to be neutral, and drying at a temperature lower than 100 ℃ to obtain the nickel-manganese modified fly ash ozone oxidation catalyst.

In the method, the molar ratio of potassium permanganate to nickel hydroxide is not less than 3:1, so that sufficient or even excessive oxidant potassium permanganate is ensured to oxidize nickel hydroxide, nickel hydroxide can be completely oxidized from divalent nickel to trivalent nickel to synthesize nickel oxyhydroxide, and the excessive potassium permanganate can be removed by washing.

The nickel oxyhydroxide produced by the reaction according to the method is easy to decompose at the temperature of more than 100 ℃, so the reaction temperature and the drying temperature of the method are both lower than 100 ℃. In addition, the method does not need to carry out treatment processes such as roasting after drying.

The fly ash treated by the acid can be prepared by the following steps: and (3) mixing the washed fly ash with hydrochloric acid, heating and stirring, washing the solid with water, and drying to obtain the acid-treated fly ash. In a preferred embodiment, the HCl concentration in the hydrochloric acid is between 0.5 and 1.5mol/L.

In one embodiment, the alkaline solution is a potassium hydroxide solution, and no other impurity ions are introduced. In a preferred embodiment, the KOH concentration in the potassium hydroxide solution is in the range of 0.5 to 2mol/L.

In a preferred embodiment, the temperature of the reaction is 50-90 ℃.

In a preferred example, the mass ratio of the fly ash in the nickel-manganese modified fly ash ozone oxidation catalyst is 85% -98%, and the balance is metal active phase nickel oxyhydroxide and manganese dioxide.

In a preferred embodiment, the drying temperature is 80-90 ℃.

The invention also provides the nickel-manganese modified fly ash ozone oxidation catalyst prepared by the method.

The invention also provides application of the nickel-manganese modified fly ash ozone oxidation catalyst in catalyzing ozone oxidation treatment of sewage, wherein the pH value of the sewage is alkaline. The alkaline sewage environment is favorable for the stable existence and long-term effect of the nickel oxyhydroxide in the catalyst.

Compared with the prior art, the invention has the beneficial effects that:

1. the ozone oxidation catalyst is prepared by utilizing the solid waste of the fly ash, so that the purposes of resource utilization and environmental pollutant treatment are achieved, and the high additional utilization value and space of the fly ash are improved.

2. The one-step normal pressure heat alkali treatment process is utilized to replace the traditional preparation process of the fly ash metal oxide supported catalyst, so that the flow of the fly ash modification process is shortened, the operation and energy consumption are reduced, and the synthesis cost is reduced.

3. Breaks through the bottleneck of single reaction mechanism of the traditional metal oxide supported fly ash catalyst, realizes the ozone catalytic oxidation mechanism of coexistence of non-free radicals and free radicals, and achieves the purpose of efficiently degrading organic matters in water.

Drawings

FIG. 1 is a graph showing ultraviolet absorption spectra of methylene blue concentrations corresponding to different sampling times for the catalysts of example 3 (left panel of FIG. 1), example 4 (middle panel of FIG. 1), and example 5 (right panel of FIG. 1).

FIG. 2 is a graph showing the characterization results of Electron Paramagnetic Resonance (EPR) test of the catalyst of example 5 under the reaction conditions of the application examples (except that the catalyst is free of methylene blue), wherein hydroxyl radicals (left graph of FIG. 2), superoxide radicals (middle graph of FIG. 2) and singlet oxygen (right graph of FIG. 2) are generated on the surface of the catalyst in the process of qualitative catalytic ozonation.

FIG. 3 is a graph showing the degradation rate of p-benzoquinone (p-BQ) and L-Histidine (L-Histidine) before and after adding Tertiary Butanol (TBA), p-benzoquinone (p-BQ) as a capturing agent corresponding to hydroxyl radical, superoxide radical and singlet oxygen in the process of degrading methylene blue by using the catalyst of example 5.

Detailed Description

The invention will be further elucidated with reference to the drawings and to specific embodiments. It is to be understood that these examples are illustrative of the present invention and are not intended to limit the scope of the present invention.

The methods of operation, under which specific conditions are not noted in the examples below, are generally in accordance with conventional conditions, or in accordance with the conditions recommended by the manufacturer.

Unless otherwise indicated, the solid-to-liquid ratios refer to mass ratios.

Comparative example 1

1) Washing the fly ash with clear water, drying at 120 ℃ for 12 hours, and grinding to obtain the water-washed fly ash with uniform texture;

2) Mixing the water-washed fly ash with 0.5mol/L HCl solution at a solid-to-liquid ratio of 1:10, stirring at 85 ℃ for 2 hours, filtering, washing the obtained solid product with water, and drying at 120 ℃ for 12 hours to obtain the acidified fly ash.

Comparative example 2

The difference from comparative example 1 was only that the HCl solution concentration was 1.5mol/L, and the rest was the same.

Example 1

The process was further carried out on the basis of comparative example 2:

3) Preparing 500mL of 0.5mol/L potassium hydroxide solution, adding 50g of acidified fly ash, 5g of nickel hydroxide and 2.8g of potassium permanganate powder while stirring, reacting for 15 hours at the constant temperature of 50 ℃, taking solid, washing the solid with deionized water for several times until the pH value is neutral, drying for 24 hours at the temperature of 80 ℃ in vacuum, and sorting the obtained sample by using a 100-mesh sieve to obtain the nickel-manganese modified fly ash ozonation catalyst.

Example 2

The difference from example 1 was only that the concentration of the potassium hydroxide solution was 1mol/L, and the rest was the same.

Example 3

The difference from example 1 was only that the concentration of the potassium hydroxide solution was 2mol/L, and the rest was the same.

Example 4

The only difference from example 3 is the reaction at a constant temperature of 70℃and the remainder is the same.

Example 5

The only difference from example 3 is the reaction at a constant temperature of 90℃and the remainder the same.

Example 6

The difference from example 5 was only that the nickel hydroxide was added in an amount of 2.5g, and the potassium permanganate powder was added in an amount of 1.4g, all of which were the same.

Example 7

The difference from example 5 was only that the amount of nickel hydroxide added was 1.25g, and the amount of potassium permanganate powder added was 0.7g, all the other things being equal.

Example 8

The only difference from example 5 is that the vacuum drying temperature is 90℃and the remainder is the same.

Comparative example 3

The process was further carried out on the basis of example 5:

4) Roasting the obtained nickel-manganese modified fly ash ozonation catalyst for 5 hours in an air atmosphere at 500 ℃ to obtain the nickel-manganese oxide modified fly ash catalyst.

Application example

2g of the coal ash ozone oxidation catalyst of each example and the coal ash ozone oxidation catalyst of the comparative example are respectively added into a glass container with a volume of 1L, the pH=10 is controlled, and under the condition that the reaction temperature is 25 ℃, 1L of methylene blue aqueous solution with a concentration of 500mg/L is put in, so that the coal ash ozone oxidation catalyst and the methylene blue in the container reach adsorption equilibrium, the stable concentration of the methylene blue is about 420mg/L, then ozone gas is introduced according to a concentration of 10mg/min for catalytic reaction, sampling is carried out every 5min along with the reaction, and the degradation efficiency of the methylene blue is recorded by an ultraviolet spectrophotometry. Table 1 shows the removal of methylene blue from the water.

TABLE 1

Comparative examples 1 and 2 are differences in hydrochloric acid concentration, and mainly aim at removing impurities on the surface of the fly ash and alkali metals such as magnesium and calcium, and the difference between the impurities is not large.

Example 1-example 3 are mainly potassium hydroxide lye concentration differences, and 2mol/L potassium hydroxide lye is found to be more suitable for the strength of the surface pore-forming degree of the fly ash in the one-step normal pressure heat alkali treatment process.

Example 3-example 5 mainly refers to the difference of stirring temperature, optimizes the temperature aiming at the dissolution efficiency of the surface silicon oxide of the fly ash in the alkali liquor and the pore channel structure, and simultaneously gives consideration to the optimal temperature of the reaction of nickel hydroxide and potassium permanganate, and the methylene blue removal effect is shown in figure 1, and is found to be optimal at 90 ℃.

In examples 5 to 7, the main changes were the addition amount of the metal materials, and the fly ash was found to be the best in 90wt% (example 5), the next 95wt% (example 6), and the worst in 97wt% (example 7) for the proportions of 90wt% (example 5), 95wt% (example 6), and 97wt% (example 7) in the products, respectively.

Examples 5 and 8 mainly examined the drying temperature in the final step, and examined the influence of the drying temperature and time on the formation of the active sites on the needle surface, and as a result, it was found that the influence of the drying temperature increased from 80℃to 90℃was not great.

Comparative example 3 the surface of the catalyst obtained by impregnation roasting was mainly a composite oxide of nickel oxide and manganese oxide. The high-temperature roasting can lead the surface of the catalyst to have more oxygen vacancies and surface active oxygen, so that the catalyst tends to oxidize by utilizing molecular oxygen to form atomic oxygen or singlet oxygen on the defects or vacancies in the oxidation reaction process of the organic matters, thus more non-free radical oxidation paths are mainly used, and the manganese-nickel composite oxide further promotes lattice distortion and strengthens the effect of the lattice defects. From the observation of the performance test of comparative example 3, it is known that the degradation rate of methylene blue in the initial stage of the reaction is lower, mainly because the methylene blue macromolecular organic matter is cracked into small molecular organic matter in the initial stage of the reaction, and the process is more sensitive to the free radical reaction mechanism; with the extension of the reaction time, the pollutants in the solution are gradually changed into small molecular organic matters, which is favorable for a non-free radical oxidation mechanism, thereby improving the reaction rate.

FIG. 2 is a graph showing the characterization of the catalyst of example 5 by Electron Paramagnetic Resonance (EPR) under the reaction conditions of the application examples (except for the absence of methylene blue), wherein the catalyst was qualitatively found to generate hydroxyl radicals (left graph of FIG. 2), superoxide radicals (middle graph of FIG. 2) and singlet oxygen (right graph of FIG. 2) on the surface during catalytic ozonation.

FIG. 3 shows the change of the degradation rate of Tertiary Butanol (TBA), p-benzoquinone (p-BQ) and L-Histidine (L-Histidine) corresponding to the capture agents of hydroxyl free radical, superoxide free radical and singlet oxygen in the process of degrading methylene blue by the catalyst of example 5, and the three capture agents can be found to have obvious negative effects on the degradation effect of methylene blue respectively, thus further proving the existence of hydroxyl free radical, superoxide free radical and singlet oxygen, and illustrating that the catalyst of the invention follows the ozone catalytic oxidation mechanism of coexistence of non-free radicals and free radicals.

Further, it will be understood that various changes and modifications may be made by those skilled in the art after reading the foregoing description of the invention, and such equivalents are intended to fall within the scope of the claims appended hereto.

Claims

1. A method for preparing nickel-manganese modified fly ash ozone oxidation catalyst by hot alkali method is characterized in that the acid-treated fly ash reacts with nickel hydroxide and potassium permanganate in alkaline solution at a temperature lower than 100 ℃, and the nickel-manganese modified fly ash ozone oxidation catalyst is obtained by taking solid after the reaction, washing to neutrality and drying at a temperature lower than 100 ℃.

2. The method of claim 1, wherein the molar ratio of potassium permanganate to nickel hydroxide is not less than 3:1.

3. The method of claim 1, wherein the acid-treated fly ash is prepared by: and (3) mixing the washed fly ash with hydrochloric acid, heating and stirring, washing the solid with water, and drying to obtain the acid-treated fly ash.

4. A process according to claim 3, characterized in that the concentration of HCl in the hydrochloric acid is 0.5-1.5mol/L.

5. The method according to claim 1, wherein the alkaline solution is a potassium hydroxide solution having a concentration of KOH of 0.5 to 2mol/L.

6. The method of claim 1, wherein the temperature of the reaction is 50-90 ℃.

7. The method according to claim 1, wherein the nickel-manganese modified fly ash ozone oxidation catalyst comprises 85-98% of fly ash by mass and the balance of metal active phase nickel oxyhydroxide and manganese dioxide.

8. The method of claim 1, wherein the drying temperature is 80-90 ℃.

9. The nickel-manganese modified fly ash ozonation catalyst prepared by the method of any one of claims 1-8.

10. The use of the nickel manganese modified fly ash ozonation catalyst according to claim 9 for catalytic ozonation of wastewater, wherein the pH of the wastewater is alkaline.