CN114797449A - Based on theta-Al 2 O 3 Catalyst for high-efficiency catalytic decomposition of CF in electrolytic aluminum flue gas 4 And HF by-product resource recovery method - Google Patents
Based on theta-Al 2 O 3 Catalyst for high-efficiency catalytic decomposition of CF in electrolytic aluminum flue gas 4 And HF by-product resource recovery method Download PDFInfo
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- 238000000034 method Methods 0.000 title claims abstract description 52
- 239000003054 catalyst Substances 0.000 title claims abstract description 50
- 229910052782 aluminium Inorganic materials 0.000 title claims abstract description 43
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 title claims abstract description 43
- 229910018072 Al 2 O 3 Inorganic materials 0.000 title claims abstract description 41
- 238000003421 catalytic decomposition reaction Methods 0.000 title claims abstract description 33
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 title claims abstract description 31
- 239000003546 flue gas Substances 0.000 title claims abstract description 31
- 239000006227 byproduct Substances 0.000 title claims abstract description 26
- 238000011084 recovery Methods 0.000 title claims abstract description 12
- 239000007789 gas Substances 0.000 claims abstract description 38
- 239000002135 nanosheet Substances 0.000 claims abstract description 35
- 238000004064 recycling Methods 0.000 claims abstract description 24
- 229910004261 CaF 2 Inorganic materials 0.000 claims abstract description 19
- 238000000354 decomposition reaction Methods 0.000 claims abstract description 15
- 239000011737 fluorine Substances 0.000 claims abstract description 13
- 229910052731 fluorine Inorganic materials 0.000 claims abstract description 13
- 239000007788 liquid Substances 0.000 claims abstract description 13
- 239000002699 waste material Substances 0.000 claims abstract description 12
- YCKRFDGAMUMZLT-UHFFFAOYSA-N Fluorine atom Chemical compound [F] YCKRFDGAMUMZLT-UHFFFAOYSA-N 0.000 claims abstract description 11
- 238000009388 chemical precipitation Methods 0.000 claims abstract description 10
- 239000000463 material Substances 0.000 claims abstract description 9
- 230000035484 reaction time Effects 0.000 claims abstract description 7
- 238000001027 hydrothermal synthesis Methods 0.000 claims abstract description 6
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 42
- 239000000243 solution Substances 0.000 claims description 39
- 238000006243 chemical reaction Methods 0.000 claims description 34
- 239000008367 deionised water Substances 0.000 claims description 25
- 229910021641 deionized water Inorganic materials 0.000 claims description 25
- 238000003756 stirring Methods 0.000 claims description 21
- 239000011734 sodium Substances 0.000 claims description 18
- 238000001035 drying Methods 0.000 claims description 16
- 239000002244 precipitate Substances 0.000 claims description 16
- 238000010438 heat treatment Methods 0.000 claims description 14
- KFZMGEQAYNKOFK-UHFFFAOYSA-N Isopropanol Chemical compound CC(C)O KFZMGEQAYNKOFK-UHFFFAOYSA-N 0.000 claims description 12
- 230000008569 process Effects 0.000 claims description 11
- 239000002243 precursor Substances 0.000 claims description 9
- 239000000843 powder Substances 0.000 claims description 8
- 238000009834 vaporization Methods 0.000 claims description 8
- 230000008016 vaporization Effects 0.000 claims description 8
- 238000001816 cooling Methods 0.000 claims description 7
- 238000012360 testing method Methods 0.000 claims description 7
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 claims description 6
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 6
- SMZOGRDCAXLAAR-UHFFFAOYSA-N aluminium isopropoxide Chemical compound [Al+3].CC(C)[O-].CC(C)[O-].CC(C)[O-] SMZOGRDCAXLAAR-UHFFFAOYSA-N 0.000 claims description 6
- 235000011114 ammonium hydroxide Nutrition 0.000 claims description 6
- 238000002156 mixing Methods 0.000 claims description 6
- 239000000741 silica gel Substances 0.000 claims description 6
- 229910002027 silica gel Inorganic materials 0.000 claims description 6
- 238000003837 high-temperature calcination Methods 0.000 claims description 5
- PMZURENOXWZQFD-UHFFFAOYSA-L Sodium Sulfate Chemical compound [Na+].[Na+].[O-]S([O-])(=O)=O PMZURENOXWZQFD-UHFFFAOYSA-L 0.000 claims description 4
- DIZPMCHEQGEION-UHFFFAOYSA-H aluminium sulfate (anhydrous) Chemical compound [Al+3].[Al+3].[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O DIZPMCHEQGEION-UHFFFAOYSA-H 0.000 claims description 4
- 238000001354 calcination Methods 0.000 claims description 4
- -1 fluoride ions Chemical class 0.000 claims description 4
- 150000002500 ions Chemical class 0.000 claims description 4
- 239000011259 mixed solution Substances 0.000 claims description 4
- 238000000643 oven drying Methods 0.000 claims description 4
- 229910052938 sodium sulfate Inorganic materials 0.000 claims description 4
- 235000011152 sodium sulphate Nutrition 0.000 claims description 4
- 238000005406 washing Methods 0.000 claims description 4
- 238000010521 absorption reaction Methods 0.000 claims description 3
- 239000002274 desiccant Substances 0.000 claims description 3
- 239000000956 alloy Substances 0.000 claims description 2
- 229910045601 alloy Inorganic materials 0.000 claims description 2
- 239000012295 chemical reaction liquid Substances 0.000 claims description 2
- 238000011049 filling Methods 0.000 claims description 2
- 238000004321 preservation Methods 0.000 claims description 2
- 229910001415 sodium ion Inorganic materials 0.000 claims description 2
- 238000010998 test method Methods 0.000 claims description 2
- 230000003197 catalytic effect Effects 0.000 abstract description 10
- 239000002994 raw material Substances 0.000 abstract description 5
- 238000002360 preparation method Methods 0.000 abstract description 4
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 12
- 229910002092 carbon dioxide Inorganic materials 0.000 description 6
- 239000001569 carbon dioxide Substances 0.000 description 6
- 230000007062 hydrolysis Effects 0.000 description 6
- 238000006460 hydrolysis reaction Methods 0.000 description 6
- 230000000694 effects Effects 0.000 description 4
- KRHYYFGTRYWZRS-UHFFFAOYSA-M Fluoride anion Chemical compound [F-] KRHYYFGTRYWZRS-UHFFFAOYSA-M 0.000 description 3
- 230000000630 rising effect Effects 0.000 description 3
- 238000002441 X-ray diffraction Methods 0.000 description 2
- TXEYQDLBPFQVAA-UHFFFAOYSA-N tetrafluoromethane Chemical compound FC(F)(F)F TXEYQDLBPFQVAA-UHFFFAOYSA-N 0.000 description 2
- 239000002841 Lewis acid Substances 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
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- 150000001875 compounds Chemical class 0.000 description 1
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- 238000013461 design Methods 0.000 description 1
- 230000004907 flux Effects 0.000 description 1
- 230000003301 hydrolyzing effect Effects 0.000 description 1
- 150000007517 lewis acids Chemical class 0.000 description 1
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- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 239000002064 nanoplatelet Substances 0.000 description 1
- 230000001590 oxidative effect Effects 0.000 description 1
- 238000011056 performance test Methods 0.000 description 1
- 238000004626 scanning electron microscopy Methods 0.000 description 1
- 230000009466 transformation Effects 0.000 description 1
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- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/34—Chemical or biological purification of waste gases
- B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
- B01D53/86—Catalytic processes
- B01D53/8659—Removing halogens or halogen compounds
- B01D53/8662—Organic halogen compounds
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- B01J21/00—Catalysts comprising the elements, oxides, or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium, or hafnium
- B01J21/02—Boron or aluminium; Oxides or hydroxides thereof
- B01J21/04—Alumina
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- B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
- B01J37/08—Heat treatment
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- C01—INORGANIC CHEMISTRY
- C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
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Abstract
The invention belongs to the field of resources and environment, and particularly relates to a material based on theta-Al 2 O 3 Catalyst for high-efficiency catalytic decomposition of CF in electrolytic aluminum flue gas 4 And a method for recycling HF byproducts. Firstly preparing theta-Al by a hydrothermal method 2 O 3 Nanosheets, achieving theta-Al on a fixed bed 2 O 3 Efficient decomposition of CF by nanosheet catalyst 4 Is collectedThe obtained HF waste liquid is subjected to chemical precipitation to obtain Na 3 AlF 6 And CaF 2 . The invention is based on highly efficient catalytic CF 4 Of theta-Al 2 O 3 The catalyst has excellent catalytic performance and stability. In the preparation process, the reaction time is short, the method is simple and feasible, and Na obtained by recycling HF waste liquid 3 AlF 6 And CaF 2 The fluorine circulation of fluorine-containing gas in the electrolytic aluminum flue gas is realized for the raw material in the electrolytic aluminum industry. Catalytic decomposition of CF 4 The efficiency can reach 100 percent, the single service life can reach 350h, Na 3 AlF 6 The recovery rate can reach 92.2 percent, and the CaF 2 The recovery rate can reach 7.6 percent, and the whole F ‑ The recovery rate can reach 99.9%.
Description
Technical Field
The invention belongs to the field of resources and environment, and particularly relates to a material based on theta-Al 2 O 3 Catalyst for high-efficiency catalytic decomposition of CF in electrolytic aluminum flue gas 4 And a method for recycling HF byproducts.
Background
The yield of electrolytic aluminum in China is steadily increased year by year, the yield of electrolytic aluminum in China is as high as 3850 ten thousand tons in 2021 years, and 2Kg CF (carbon fluoride) is generated for every ton of electrolytic aluminum due to the anode effect in the production process of electrolytic aluminum 4 Based on the electrolytic aluminum yield in China in 2021 year, 3850 ten thousand tons of aluminum can generate at least 7.6 thousand tons of CF 4 The Global Warming Potential (GWP) of the compound is carbon dioxide (CO) 2 ) 7390 times of (1), its emission equivalent is 4.9 hundred million tons of CO 2 And CO in electrolytic aluminum industry 2 Is only 0.38 million tons and CF 4 Is very stable and takes 50,000 years to decompose naturally in the atmosphere. Therefore, CF for treating industrial emission of electrolytic aluminum 4 Gas is of particular importance.
On the other hand, the C-F bond is very strong and the bond energy is 543kJ mol -1 Destroy CF 4 The structure of the molecule requires more severe conditions. Because of simple operation, large treatment flux and high treatment temperatureThe CF is treated by the catalytic hydrolysis method which is the most effective and suitable means at present 4 Molecular, theta-Al 2 O 3 The nanosheet catalyst has large specific surface area and abundant Lewis acid sites, and is used for catalyzing and hydrolyzing CF 4 The ideal catalyst of (1). The end product obtained by decomposing CF4 by catalytic hydrolysis method is CO 2 And HF, absorbing the HF by a water bottle, collecting the obtained HF waste liquid, and obtaining Na by a chemical precipitation method 3 AlF 6 And CaF 2 Can be used as raw materials in the electrolytic aluminum industry. At present, no theta-Al based alloy exists 2 O 3 Catalyst for high-efficiency catalytic decomposition of CF in electrolytic aluminum flue gas 4 And related patent reports of HF byproduct recycling.
Disclosure of Invention
The invention aims to provide a catalyst based on theta-Al 2 O 3 Catalyst for high-efficiency catalytic decomposition of CF in electrolytic aluminum flue gas 4 And HF byproduct recycling method based on efficient catalytic CF 4 Of theta-Al 2 O 3 The catalyst has excellent catalytic performance and stability. In the preparation process, the reaction time is short, the method is simple and feasible, and Na obtained by recycling HF waste liquid 3 AlF 6 And CaF 2 The fluorine circulation of fluorine-containing gas in the electrolytic aluminum flue gas is realized for the raw material in the electrolytic aluminum industry.
In order to achieve the purpose, the invention adopts the following technical scheme:
based on theta-Al 2 O 3 Catalyst for high-efficiency catalytic decomposition of CF in electrolytic aluminum flue gas 4 And HF byproduct recycling method, namely preparing theta-Al by a hydrothermal method 2 O 3 Nanosheets, achieving theta-Al on a fixed bed 2 O 3 Efficient decomposition of CF by nanosheet catalyst 4 Collecting the obtained HF waste liquid, and obtaining Na by a chemical precipitation method 3 AlF 6 And CaF 2 。
The base is based on theta-Al 2 O 3 Catalyst for high-efficiency catalytic decomposition of CF in electrolytic aluminum flue gas 4 And HF byproduct recycling method, and theta-Al preparation method 2 O 3 The specific steps of the nano sheet are as follows:
(1) adding aluminum isopropoxide into the isopropanol solution, and fully stirring to obtain a mixed reaction solution;
(2) adding deionized water into the obtained mixed reaction liquid, fully stirring, transferring to a reaction kettle, reacting at 100-120 ℃ for 0.5-2 h, cooling, washing, centrifuging and drying to obtain white precursor powder;
(3) transferring the obtained white precursor powder into a crucible, calcining at high temperature, and cooling to obtain theta-Al 2 O 3 Nanosheets, i.e. the highly efficient catalytic decomposition of CF 4 Of theta-Al 2 O 3 A nanosheet catalyst material.
The base is based on theta-Al 2 O 3 Catalyst for high-efficiency catalytic decomposition of CF in electrolytic aluminum flue gas 4 And HF by-product resource method, in step (1), the addition amount of aluminium isopropoxide is 10.000g, the addition amount of isopropanol is 100ml, the stirring rotational speed is 500 revolutions per minute, the stirring time is 12 h; in the step (2), the adding amount of deionized water is 10ml, the stirring time is 10min, the capacity of the reaction kettle is 150ml, the reaction temperature is 110 ℃, and the reaction time is 1 h.
The base is based on theta-Al 2 O 3 Catalyst for high-efficiency catalytic decomposition of CF in electrolytic aluminum flue gas 4 And a HF byproduct recycling method, wherein in the step (3), the high-temperature calcination temperature is 850-950 ℃, the reaction time is 3-5 h, and in the temperature rise process: the temperature rising rate from the room temperature to 600 ℃ is 4-6 ℃/min, and the temperature rising rate from 600 ℃ to 850-950 ℃ is 0.5-2 ℃/min.
The base is based on theta-Al 2 O 3 Catalyst for high-efficiency catalytic decomposition of CF in electrolytic aluminum flue gas 4 And HF by-product resource recovery method, theta-Al on fixed bed 2 O 3 Efficient decomposition of CF by nanosheet catalyst 4 The test method comprises the following specific processes:
(1) mixing theta-Al 2 O 3 The nano-sheet catalyst is filled into a reaction bin of the fixed bed, and CF is pre-introduced from an air supply system 4 Mixing with Ar gas;
(2) heating a reaction bin of the fixed bed to a test temperature, heating a vaporization chamber, and introducing water vapor into the reaction bin;
(3) the tail gas obtained in the above process firstly passes through a deionized water bottle and then is dried through a drying tube, and the dried gas enters a gas chromatograph to detect the components and the content of the gas.
The base is based on theta-Al 2 O 3 Catalyst for high-efficiency catalytic decomposition of CF in electrolytic aluminum flue gas 4 And a HF byproduct recycling method, wherein in the step (1), the fixed bed consists of an air supply system, a vaporization chamber, a reaction bin, a deionized water bottle, a drying tube and a gas chromatograph.
The base is based on theta-Al 2 O 3 Catalyst for high-efficiency catalytic decomposition of CF in electrolytic aluminum flue gas 4 And HF byproduct recycling method, in step (1), theta-Al 2 O 3 The filling amount of the nanosheet catalyst is 1.000g, and the inner diameter of the reaction bin is 19 mm; in volume percent, CF 4 The mixed gas with Ar gas comprises the following components: 0.5% CF 4 99.5 percent of Ar gas, and the flow rate of the mixed gas is 33.3 ml/min; in the step (2), the temperature of the reaction bin is 650-750 ℃, and the heating rate is 10 ℃/min; the heating temperature of the vaporization chamber is 200 ℃, and the water inlet rate is 0.007 ml/min; in the step (3), the volume of the deionized water bottle is 500ml, and the amount of the added deionized water is 300 ml; the drying tube is in a cylindrical shape, the added drying agent is allochroic silica gel, and the adding amount of the allochroic silica gel is 500 g.
The base is based on theta-Al 2 O 3 Catalyst for high-efficiency catalytic decomposition of CF in electrolytic aluminum flue gas 4 And HF by-product recycling method, CF 4 The volume ratio to water vapor was 1: 50.
The base is based on theta-Al 2 O 3 Catalyst for high-efficiency catalytic decomposition of CF in electrolytic aluminum flue gas 4 And HF by-product resource recovering method, chemical precipitation method to obtain Na 3 AlF 6 And CaF 2 The recovery method comprises the following specific processes:
(1) towards absorption CF 4 Adding ammonia water into HF deionized water solution generated after decomposition, adjusting pH value of the solution to 8, adding sodium sulfate and aluminum sulfate, and fully stirringThen keeping the temperature of the mixed solution in a water bath, centrifugally separating precipitate and clear liquid, drying the precipitate to obtain Na 3 AlF 6 ；
(2) Adding CaCl into the above clear solution 2 Adjusting the pH value of the solution to 10, fully stirring, centrifuging to separate precipitate and clear solution, and drying the precipitate to obtain CaF 2 。
The base is based on theta-Al 2 O 3 Catalyst for high-efficiency catalytic decomposition of CF in electrolytic aluminum flue gas 4 And a method for recycling HF byproducts, wherein in the step (1), the fluorine content of an HF deionized water solution is 23g/L, the mass concentration of ammonia water is 25-28%, the molar ratio of Na ions/Al ions/F ions is 4:1:6, and the heat preservation temperature of a water bath kettle is 80 ℃; in step (2), CaCl 2 The addition amount is 2.4 times of the molar amount of the fluoride ions in the clear solution.
The design idea of the invention is as follows: based on catalytic hydrolysis method, theta-Al is realized on a fixed bed 2 O 3 Efficient decomposition of CF in electrolytic aluminum flue gas on catalyst 4 ，CF 4 Will decompose into CO 2 And HF gas, wherein the HF gas is absorbed by a water bottle to obtain HF waste liquid, fluorine ions in the HF waste liquid are precipitated by a simple chemical precipitation method, and the obtained Na is recovered 3 AlF 6 And CaF 2 Is a raw material in the electrolytic aluminum industry so as to realize the fluorine circulation of fluorine-containing gas in the electrolytic aluminum flue gas.
The invention has the remarkable advantages and beneficial effects that:
the method adopts hydrothermal and high-temperature calcination treatment to obtain the theta-Al 2 O 3 The nano-sheet catalyst has the advantages of cheap and easily-obtained raw materials, short reaction time, low cost, simplicity, feasibility, good reproducibility and excellent performance. theta-Al 2 O 3 Catalytic decomposition of CF by nanosheet catalyst 4 The efficiency can reach 100 percent, the single service life can reach 350h, Na 3 AlF 6 The recovery rate can reach 92.2 percent, and the CaF 2 The recovery rate can reach 7.6 percent, and the fluorine ions (F) are integrated - ) The recovery rate can reach 99.9%.
Drawings
FIG. 1 is a view showing a formula of theta-Al 2 O 3 X-ray diffraction of nanosheetsFigure (a). In the figure, the abscissa 2 θ represents the diffraction angle (degree) and the ordinate Intensity represents the Intensity (a.u.).
FIG. 2 is a view showing a formula of theta-Al 2 O 3 Scanning electron microscopy of the nanoplatelets.
FIG. 3 is a view showing a formula of theta-Al 2 O 3 Catalytic hydrolysis of nanosheets CF 4 Performance graph of (2). Wherein the abscissa Time represents Time (hours) and the ordinate CF 4 conversion stands for CF 4 Decomposition rate (%) of (b).
FIG. 4 shows Na obtained by recycling HF waste liquid 3 AlF 6 (a) And CaF 2 (b) X-ray diffraction pattern of (a). In the figure, the abscissa 2 θ represents the diffraction angle (degree) and the ordinate Intensity represents the Intensity (a.u.).
Detailed Description
In the specific implementation process, the theta-Al is prepared by a hydrothermal method 2 O 3 Nanosheets, achieving theta-Al on a fixed bed 2 O 3 Efficient decomposition of CF by nanosheet catalyst 4 Collecting the obtained HF waste liquid, and obtaining Na by a chemical precipitation method 3 AlF 6 And CaF 2 . The main functions and effects of the hydrothermal reaction are: under the conditions of high temperature and high pressure, the reaction is carried out under the condition of approaching homogeneous phase, and the nano sheet material with good dispersity, high purity and controllable morphology is obtained. The main functions and effects of the high-temperature calcination treatment are as follows: and further oxidizing the precursor obtained by the hydrothermal reaction to obtain the oxide nanosheet material. The main functions and effects of the chemical precipitation method are as follows: fluoride ion (F) in deionized water to be absorbed with HF - ) Settled to Na 3 AlF 6 And CaF 2 And the fluorine circulation of the fluorine-containing gas in the electrolytic aluminum flue gas is realized.
The present invention is further illustrated by the following examples, but the scope of the present invention is not limited to the following examples.
EXAMPLE 1 efficient catalytic decomposition of CF 4 θ-Al 2 O 3 Preparation of nanosheet catalyst
(1) Adding aluminum isopropoxide into an isopropanol solution, and fully stirring to obtain a mixed reaction solution;
(2) adding deionized water into the obtained mixed reaction solution, fully stirring, transferring to a reaction kettle for reaction, cooling, washing, centrifuging and drying to obtain white precursor powder;
(3) transferring the obtained white precursor powder into a crucible, calcining at high temperature, and cooling to obtain theta-Al 2 O 3 Nanosheets, i.e. the highly efficient catalytic decomposition of CF 4 Of theta-Al 2 O 3 A nanosheet catalyst material.
In the embodiment, 10.000g of aluminum isopropoxide is added into 100ml of isopropanol solution, the stirring speed is 500 r/min, and the mixture is fully stirred for 12 hours to obtain a mixed reaction solution; adding 10ml of deionized water into the mixed reaction solution, fully stirring for 10min, transferring to a reaction kettle with the specification of 150ml, reacting for 1h at 110 ℃, cooling, washing, centrifuging and drying to obtain white precursor powder; transferring the obtained white precursor powder into a crucible, and then calcining at high temperature for 4 hours at 900 ℃ to obtain theta-Al 2 O 3 Nanosheets, i.e. the highly efficient catalytic decomposition of CF 4 Of theta-Al 2 O 3 A nanosheet catalyst material.
In the temperature rising process of high-temperature calcination: the heating rate from room temperature to 600 ℃ is 5 ℃/min, the heating rate from 600 ℃ to 900 ℃ is 1 ℃/min, and the functions are as follows: controlling Al 2 O 3 Crystal phase transformation rate to obtain pure theta phase Al 2 O 3 。
As can be seen from FIGS. 1 and 2, the material obtained in this example was confirmed to be θ -Al 2 O 3 The nano-sheet has the following specification and size: theta-Al 2 O 3 The diameter of the nano-sheet is 50nm, and the thickness is 20 nm.
Example 2CF 4 Catalytic hydrolysis Performance test
(1) Mixing theta-Al 2 O 3 1.000g of the nanosheet catalyst is filled into a reaction bin of a fixed bed, the inner diameter of the reaction bin is 19mm, and CF is pre-introduced from an air supply system 4 Mixing with Ar gas;
(2) heating a reaction bin of the fixed bed to a test temperature, heating a vaporization chamber, and introducing water vapor into the reaction bin;
(3) the tail gas obtained in the above process firstly passes through a deionized water bottle and then is dried through a drying tube, and the dried gas enters a gas chromatograph to detect the components and the content of the gas. The volume of the deionized water bottle is 500ml, and the added deionized water amount is 300 ml; the drying tube is cylindrical, the added drying agent is allochroic silica gel, and the addition amount of the allochroic silica gel is 500 g.
In this example, the theta-Al obtained in example 1 was used 2 O 3 Nanosheet CF 4 And (3) testing the catalytic hydrolysis performance under the following test conditions: the reaction temperature is 750 ℃, and the heating rate is 10 ℃/min; CF (compact flash) 4 In a mixed gas with Ar gas, CF 4 The volume concentration of the mixed gas is 0.5 percent, the rest is Ar gas, and the flow rate of the mixed gas is 33.3 ml/min; the heating temperature of the vaporization chamber is 200 ℃, the water inlet rate is 0.007ml/min, and the water vapor inlet amount is CF 4 /H 2 The volume ratio of O (gas) is 1: 50. The test results are shown in FIG. 3, first 100h, CF 4 The decomposition rate of (2) was maintained at 100%, and when the test time exceeded 100 hours, the decomposition efficiency began to slowly decrease, and to 350 hours, the decomposition efficiency was about 50%.
Example 3 recovery of fluoride ion (F) from HF waste stream by chemical precipitation - )
(1) Towards absorption CF 4 Adding ammonia water into HF deionized water solution generated after decomposition, adjusting pH value of the solution to 8, adding sodium sulfate and aluminum sulfate, stirring fully, keeping the temperature of the mixed solution in a water bath kettle, centrifugally separating precipitate and clear liquid, and drying the precipitate to obtain Na 3 AlF 6 ；
(2) Adding CaCl into the above clear solution 2 Adjusting pH of the solution to 10, stirring, centrifuging to separate precipitate and clear solution, oven drying the precipitate to obtain CaF 2 。
In this example, CF was absorbed in example 2 4 Adding ammonia water with the mass concentration of 26% into HF deionized water solution (the fluorine content of the HF deionized water solution is 23g/L) generated after decomposition, adjusting the pH value of the solution to 8, and adding sodium sulfate and aluminum sulfate to enable Na in the solution to be in an Na state + /Al 3+ /F - In a molar ratio of 4:1:6, fully stirring, and placing the mixed solution in a water bath kettle at 80 DEG CMaintaining the temperature, centrifuging to separate precipitate and clear solution, oven drying the precipitate to obtain Na 3 AlF 6 (ii) a Adding CaCl into the above clear solution 2 ，CaCl 2 Adding 2.4 times of molar amount of fluoride ion in the clear solution, adjusting pH of the solution to 10, stirring, centrifuging to separate precipitate and clear solution, and oven drying the precipitate to obtain CaF 2 。
As is clear from FIGS. 4(a) and (b), F in the HF waste liquid - With Na 3 AlF 6 And CaF 2 Is recycled.
The above description is only a preferred embodiment of the present invention, and all equivalent changes and modifications made in accordance with the claims of the present invention should be covered by the present invention.
Claims (10)
1. Based on theta-Al 2 O 3 Catalyst for high-efficiency catalytic decomposition of CF in electrolytic aluminum flue gas 4 And a method for recycling HF byproducts, which is characterized in that theta-Al is prepared by a hydrothermal method 2 O 3 Nanosheets, achieving theta-Al on a fixed bed 2 O 3 Efficient decomposition of CF by nanosheet catalyst 4 Collecting the obtained HF waste liquid, and obtaining Na by a chemical precipitation method 3 AlF 6 And CaF 2 。
2. theta-Al based on as claimed in claim 1 2 O 3 Catalyst for high-efficiency catalytic decomposition of CF in electrolytic aluminum flue gas 4 And a method for recycling HF by-products, characterized in that theta-Al is prepared 2 O 3 The specific steps of the nano sheet are as follows:
(1) adding aluminum isopropoxide into an isopropanol solution, and fully stirring to obtain a mixed reaction solution;
(2) adding deionized water into the obtained mixed reaction liquid, fully stirring, transferring to a reaction kettle, reacting at 100-120 ℃ for 0.5-2 h, cooling, washing, centrifuging and drying to obtain white precursor powder;
(3) transferring the obtained white precursor powder into a crucible, calcining at high temperature, and cooling to obtain theta-Al 2 O 3 Nanosheets, i.e. the highly efficient catalytic decomposition of CF 4 Of theta-Al 2 O 3 A nanosheet catalyst material.
3. theta-Al based alloy according to claim 2 2 O 3 Catalyst for high-efficiency catalytic decomposition of CF in electrolytic aluminum flue gas 4 And a HF byproduct recycling method, which is characterized in that in the step (1), the addition amount of aluminum isopropoxide is 10.000g, the addition amount of isopropanol is 100ml, the stirring speed is 500 r/min, and the stirring time is 12 h; in the step (2), the adding amount of deionized water is 10ml, the stirring time is 10min, the capacity of the reaction kettle is 150ml, the reaction temperature is 110 ℃, and the reaction time is 1 h.
4. theta-Al based on as claimed in claim 2 2 O 3 Catalyst for high-efficiency catalytic decomposition of CF in electrolytic aluminum flue gas 4 And a HF byproduct recycling method, which is characterized in that in the step (3), the high-temperature calcination temperature is 850-950 ℃, the reaction time is 3-5 h, and in the temperature rise process: the temperature rise rate from room temperature to 600 ℃ is 4-6 ℃/min, and the temperature rise rate from 600 ℃ to 850-950 ℃ is 0.5-2 ℃/min.
5. theta-Al based on as claimed in claim 1 2 O 3 Catalyst for high-efficiency catalytic decomposition of CF in electrolytic aluminum flue gas 4 And a method for recycling HF by-products, characterized in that theta-Al is present on a fixed bed 2 O 3 Efficient decomposition of CF by nanosheet catalyst 4 The test method comprises the following specific processes:
(1) mixing theta-Al 2 O 3 The nano-sheet catalyst is filled into a reaction bin of the fixed bed, and CF is pre-introduced from an air supply system 4 Mixing with Ar gas;
(2) heating a reaction bin of the fixed bed to a test temperature, heating a vaporization chamber, and introducing water vapor into the reaction bin;
(3) the tail gas obtained in the above process firstly passes through a deionized water bottle and then is dried through a drying tube, and the dried gas enters a gas chromatograph to detect the components and the content of the gas.
6. theta-Al based on claim 5 2 O 3 Catalyst for high-efficiency catalytic decomposition of CF in electrolytic aluminum flue gas 4 And the HF byproduct recycling method is characterized in that in the step (1), the fixed bed consists of an air supply system, a vaporization chamber, a reaction bin, a deionized water bottle, a drying tube and a gas chromatograph.
7. theta-Al based on claim 5 2 O 3 Catalyst for high-efficiency catalytic decomposition of CF in electrolytic aluminum flue gas 4 And a HF byproduct recycling method, characterized in that, in the step (1), theta-Al is added 2 O 3 The filling amount of the nanosheet catalyst is 1.000g, and the inner diameter of the reaction bin is 19 mm; in volume percent, CF 4 The mixed gas with Ar gas comprises the following components: 0.5% CF 4 99.5 percent of Ar gas, and the flow rate of the mixed gas is 33.3 ml/min; in the step (2), the temperature of the reaction bin is 650-750 ℃, and the heating rate is 10 ℃/min; the heating temperature of the vaporization chamber is 200 ℃, and the water inlet rate is 0.007 ml/min; in the step (3), the volume of the deionized water bottle is 500ml, and the amount of the added deionized water is 300 ml; the drying tube is in a cylindrical shape, the added drying agent is allochroic silica gel, and the adding amount of the allochroic silica gel is 500 g.
8. theta-Al based on claim 7 2 O 3 Catalyst for efficient catalytic decomposition of CF in electrolytic aluminum flue gas 4 And HF byproduct recycling method, characterized in that CF 4 The volume ratio to water vapor was 1: 50.
9. theta-Al based on as claimed in claim 1, 2 or 5 2 O 3 Catalyst for high-efficiency catalytic decomposition of CF in electrolytic aluminum flue gas 4 And a method for recycling HF byproducts, which is characterized in that Na is obtained by a chemical precipitation method 3 AlF 6 And CaF 2 The recovery method comprises the following specific processes:
(1) towards absorption CF 4 Adding ammonia water into HF deionized water solution generated after decomposition, and adjusting the pH value of the solution to pAdding sodium sulfate and aluminum sulfate, stirring, maintaining the temperature of the mixed solution in a water bath, centrifuging to separate precipitate and clear solution, and oven drying the precipitate to obtain Na 3 AlF 6 ；
(2) Adding CaCl into the above clear solution 2 Adjusting the pH value of the solution to 10, fully stirring, centrifuging to separate precipitate and clear solution, and drying the precipitate to obtain CaF 2 。
10. theta-Al based on claim 9 2 O 3 Catalyst for high-efficiency catalytic decomposition of CF in electrolytic aluminum flue gas 4 And a method for recycling HF byproducts, which is characterized in that in the step (1), the fluorine content of the HF deionized water solution is 23g/L, the mass concentration of ammonia water is 25-28%, the molar ratio of Na ions/Al ions/F ions is 4:1:6, and the heat preservation temperature of a water bath kettle is 80 ℃; in step (2), CaCl 2 The addition amount is 2.4 times of the molar amount of the fluoride ions in the clear solution.
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