Perfluorinated compound composite catalytic adsorbent, preparation method and application

Abstract

The invention relates to the field of gas adsorption, in particular to a perfluorinated compound composite catalytic adsorbent and a preparation method and application thereof.The perfluorinated compound composite catalytic adsorbent comprises a catalytic phase with the mass fraction being 10%-80% and an adsorption phase with the mass fraction being 20%-90%, and the preparation method comprises the following steps that S1, the catalytic phase and the adsorption phase are added into deionized water according to the proportion and stirred to be uniform, and mixed slurry is obtained; and S2, drying and molding the mixed slurry, and then carrying out heat treatment to obtain the composite catalytic adsorbent. The prepared composite catalyst can directly catalyze, decompose and fix fluorine in PFCs, and the defect that washing and wastewater treatment are still needed after decomposition of a conventional catalyst is overcome; the adsorbent after catalytic adsorption can be directly recycled as a fluorine source, so that resource waste is reduced; the catalytic adsorbent does not contain precious metal and is low in cost.

Description

Technical Field

[0001] The present invention relates to the field of gas adsorption, and particularly to a perfluorinated compound composite catalytic adsorbent, a preparation method and an application thereof. Background Art

[0002] Perfluorinated compounds (PFCs) are essential gases in the semiconductor manufacturing process and are also a type of greenhouse gas. In the semiconductor manufacturing process, PFCs can provide F as an etching reactant (etchant), and CFx can be used as a precursor for polymer films, which can be used to improve the etching profile and etching selectivity of the underlying film. Common PFCs include gases such as NF3, CF4, C2F4, C2F6, C3F6, C3F8, C4F6, C4F8, C5F8, CHF3, CH2F2, CH3F, etc. These perfluorinated compounds will generate waste gas emissions during production and use.

[0003] Due to the high stability of PFCs, these gases cannot be directly adsorbed by traditional adsorption materials (such as alkalis, activated carbon, etc.). Usually, catalysts such as alumina are required to decompose PFCs into HF first, and then absorbed and precipitated through a water washing tower and a complete set of wastewater treatment systems, which will generate a large amount of additional costs.

[0004] Chinese Patent with Publication No. CN111346601B discloses a ceramsite for adsorbing perfluorinated compounds in water and a preparation method thereof, which contains 40 - 80% of iron-containing solid waste, 5 - 20% of clay, 5 - 40% of straw, and 3 - 15% of pore-forming agent; the component composition of the iron-containing solid waste is as follows by mass fraction: SiO2: 40 - 55%; Fe2O3: 5 - 15%; TiO2: 1 - 10%; MgO: 10 - 15%; organic matter: 1 - 5%, others: 5 - 15%. These raw materials are calcined under high-temperature and oxygen-free conditions to obtain ceramsite; under the protection of a nitrogen atmosphere, the temperature is raised to 400 - 600°C at a programmed rate and pre-calcined for 20 - 40 min, and then the temperature is raised to 1000 - 1300°C and calcined for 20 - 40 min to obtain the adsorbent, but its adsorption efficiency is relatively low, and the removal efficiency of perfluorinated compounds is 80% - 95%.

[0005] Chinese Patent No. CN116020413B discloses an adsorbent material for removing perfluorinated compounds from water, its preparation method and application. Yttrium chloride hexahydrate is dissolved in water to obtain a precursor solution; the precursor solution is dropped onto an activated carbon material to obtain a precursor mixture; the precursor mixture is placed in a single-ended sealed quartz tube and calcined in a tube furnace, and at the same time, the air in the tube furnace is continuously pumped out by a vacuum pump to keep the system in a vacuum state to obtain a calcined sample; the calcined sample is washed and dried multiple times to obtain the adsorbent material for removing perfluorinated compounds from water. The adsorption capacity for typical perfluorinated compounds (perfluorooctanoic acid, PFOA) is 957.1 mg / g. However, the metal yttrium in the raw material yttrium chloride hexahydrate used in this adsorbent is relatively expensive, making it difficult to achieve large-scale production.

[0006] In summary, in view of the low adsorption efficiency of the existing adsorbent materials and the fact that the existing adsorbent materials are mostly used for the absorption of perfluorinated compounds in water and are not suitable for the absorption of gaseous (adsorbed under high-temperature conditions) perfluorinated compounds. Therefore, there is an urgent need to propose a perfluorinated compound composite catalytic adsorbent and its preparation method. Summary of the Invention

[0007] In view of the low adsorption efficiency of the existing adsorbent materials and the fact that the existing adsorbent materials are mostly used for the absorption of perfluorinated compounds in water and are not suitable for the absorption of gaseous perfluorinated compounds, the present application provides a perfluorinated compound composite catalytic adsorbent, its preparation method and application.

[0008] The technical solution of the present application: On the one hand, the present application provides a perfluorinated compound composite catalytic adsorbent, which includes a catalytic phase with a mass fraction of 10% - 80% and an adsorption phase with a mass fraction of 20% - 90%.

[0009] Preferably, the catalytic phase is any one or more of boehmite monohydrate, aluminum trihydrate or bayerite, and the adsorption phase is a metal oxide.

[0010] Preferably, the adsorption phase is any one or more of metal salts or hydroxides of Zn, Ca, Ba, Mg, Sr.

[0011] On the second hand, the present application provides a preparation method of a perfluorinated compound composite catalytic adsorbent, including the following steps:

[0012] Step S1. Add the catalytic phase and the adsorption phase to deionized water in proportion and stir evenly to obtain a mixed slurry;

[0013] Step S2. Dry and shape the mixed slurry, and then perform heat treatment to obtain the composite catalytic adsorbent.

[0014] Preferably, the mass ratio of the catalytic phase to the adsorption phase after mixing in step S1 to the mass of ionic water is 1:2 to 1:3.

[0015] Preferably, the drying temperature in step S2 is 150 - 350 °C, and the drying time is 10 - 15 h.

[0016] Preferably, the heat treatment temperature in step S2 is 500 - 700 °C, and the heat treatment time is 4 - 6 h.

[0017] In a third aspect, the present application provides an application of a perfluorinated compound composite catalytic adsorbent for catalytic adsorption of perfluorinated compounds, with an adsorption temperature of 500 - 800 °C.

[0018] Advantages of the present application:

[0019] (1) In the present application, the catalytic-adsorption synergy achieves "decomposition-fixation" in one step. The adsorption phase is an aluminum-based compound that may be converted into a highly active catalyst at high temperatures. The catalyst surface is rich in Lewis acid sites, which can break the C-F bond in perfluorinated compounds to generate free fluoride ions. The co-adsorption phase (metal oxide or hydroxide) can react with F - to form stable metal fluorides, achieving the fixation of fluorine and avoiding secondary pollution.

[0020] (2) Regarding the mechanism of the adsorption phase in the present application for fluorine source recovery, the generated metal fluorides are raw materials for the industrial fluorochemical industry and can be directly separated, purified, and utilized.

[0021] (3) Both the catalytic phase and the adsorption phase in the present application are inexpensive industrial raw materials without the need for precious metals or rare earth elements.

[0022] (4) The composite adsorbent in the present application remains stable at 500 - 800 °C and is suitable for the high-temperature environment of industrial waste gases (such as semiconductor etching and aluminum plant emissions). Detailed implementation manners

[0023] To further elaborate on the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following describes in detail the specific implementation manners, structures, features, and their effects of the present invention in combination with preferred embodiments.

[0024] The adsorption principle of the composite catalyst in the present application is as follows:

[0025] MeO + C x F y → MeF2 + CO2

[0026] PFCs undergo the above reaction in the composite catalytic adsorbent to fix fluorine elements in the form of metal fluorides.

[0027] Example 1

[0028] 1. Raw material preparation

[0029] (1) Catalytic phase: Boehmite monohydrate, purity ≥ 99%, particle size 1 - 5 μm.

[0030] (2) Adsorption phase: Ca(OH)2, purity ≥ 98%, particle size 5 - 10 μm.

[0031] (3) Deionized water.

[0032] 2. Preparation of mixed slurry

[0033] Step S1: Weigh 30 g of boehmite monohydrate and 70 g of Ca(OH)2, add 200 g of deionized water, and mix in a high-speed blender (500 rpm) for 30 min to form a homogeneous slurry.

[0034] Ensure the fluidity of the slurry through a solid-liquid ratio of 1:2, which is convenient for subsequent shaping and avoids increased drying energy consumption due to excessive moisture.

[0035] Step S2: Inject the mixed slurry into a mold to form spherical particles with a diameter of 5 mm. Dry at 250 °C for 12 h to remove moisture and obtain a dried green body. Place the dried green body in an adsorption column with a heating device, heat it to 650 °C at a rate of 5 °C / min, hold for 5 h, and then naturally cool to room temperature to obtain a composite catalytic adsorbent.

[0036] Low-temperature drying avoids premature decomposition of calcium hydroxide and maintains the activity of the adsorption phase. The spherical particles provide a large specific surface area, improving the subsequent catalytic adsorption efficiency. High-temperature treatment enables the material to form a stable porous structure, enhancing the anti-sintering ability and being suitable for high-temperature exhaust gas environments.

[0037] 3. Catalytic adsorption performance test

[0038] A mixed gas of CF4 and N2 (volume ratio 1:1), flow rate 100 mL / min. Fill the composite adsorbent into a fixed-bed reactor and conduct an adsorption test at 650 °C, with a removal rate of 99.5%.

[0039] Example 2

[0040] 1. Raw material preparation

[0041] (1) Catalytic phase: The mass ratio of boehmite monohydrate to bayerite is 1:1, purity ≥ 99%, particle size 1 - 5 μm.

[0042] (2) Adsorption phase: Ba(OH)2, purity ≥ 98%, particle size 5 - 10 μm.

[0043] (3) Deionized water.

[0044] 2. Preparation of Mixed Slurry

[0045] Step S1: Weigh 40 g of bayerite and 60 g of Ba(OH)₂, add 300 g of deionized water, and mix them in a high-speed blender (500 rpm) for 30 min to form a uniform slurry.

[0046] Ensure the fluidity of the slurry through a solid-liquid ratio of 1:3, which is convenient for subsequent forming, and at the same time avoid the increase in drying energy consumption caused by excessive moisture.

[0047] Step S2: Inject the mixed slurry into a mold to form spherical particles with a diameter of 5 mm. Dry at 150 °C for 13 h to remove moisture and obtain a dried green body. Place the dried green body in an adsorption column with a heating device, heat it to 580 °C at a rate of 5 °C / min, hold for 6 h, and then naturally cool to room temperature to obtain a composite catalytic adsorbent.

[0048] Low-temperature drying avoids premature decomposition of calcium hydroxide and maintains the activity of the adsorption phase. The spherical particles provide a large specific surface area, improving the subsequent catalytic adsorption efficiency. High-temperature treatment enables the material to form a stable porous structure, enhancing the anti-sintering ability and being suitable for high-temperature exhaust gas environments.

[0049] 3. Catalytic Adsorption Performance Test

[0050] A mixed gas of NF₃ and N₂ (volume ratio 1:1) with a flow rate of 100 mL / min. Fill the composite adsorbent into a fixed-bed reactor and conduct an adsorption test at 650 °C, with a removal rate of 99.3%.

[0051] Example 3

[0052] 1. Raw Material Preparation

[0053] (1) Catalytic phase: Aluminum trihydroxide, purity ≥ 99%, particle size 1 - 5 μm.

[0054] (2) Adsorption phase: The mass ratio of Mg(OH)₂ and Ca(OH)₂ is 1:1, purity ≥ 98%, particle size 5 - 10 μm.

[0055] (3) Deionized water.

[0056] 2. Preparation of Mixed Slurry

[0057] Step S1: Weigh 25 g of aluminum trihydroxide and 75 g of Mg(OH)₂, add 200 g of deionized water, and mix them in a high-speed blender (500 rpm) for 30 min to form a uniform slurry.

[0058] Ensure the fluidity of the slurry through a solid-liquid ratio of 1:2, which is convenient for subsequent forming, and at the same time avoid the increase in drying energy consumption caused by excessive moisture.

[0059] Step S2: Inject the mixed slurry into a mold to form spherical particles with a diameter of 5 mm. Dry at 200 °C for 10 h to remove moisture and obtain a dried green body. Place the dried green body in an adsorption column equipped with a heating device, heat it to 520 °C at a rate of 5 °C / min, hold for 4 h, and then naturally cool to room temperature to obtain a composite catalytic adsorbent.

[0060] Low-temperature drying avoids premature decomposition of calcium hydroxide and maintains the activity of the adsorption phase. The spherical particles provide a large specific surface area, improving the subsequent catalytic adsorption efficiency. High-temperature treatment enables the material to form a stable porous structure, enhancing the anti-sintering ability and making it suitable for high-temperature exhaust gas environments.

[0061] 3. Catalytic adsorption performance test

[0062] A mixed gas of C2F4 and N2 (volume ratio 1:1) with a flow rate of 100 mL / min. Fill the composite adsorbent into a fixed-bed reactor and conduct an adsorption test at 700 °C, with a removal rate of 99.2%.

[0063] Example 4

[0064] The difference between this example and Example 1 is that the adsorption phase is ZnCl2; after detection, the gas adsorption removal rate is 99.2%.

[0065] Example 5

[0066] The difference between this example and Example 1 is that the adsorption phase is SrCl2; after detection, the gas adsorption removal rate is 99.1%.

[0067] Example 6

[0068] The difference between this example and Example 1 is in Step S1: Weigh 10 g of boehmite and 90 g of Ca(OH)2, add 200 g of deionized water, and mix in a high-speed blender (500 rpm) for 30 min to form a homogeneous slurry. After detection, the gas adsorption removal rate is 99.4%.

[0069] Example 7

[0070] The difference between this example and Example 1 is in Step S1: Weigh 90 g of boehmite and 10 g of Ca(OH)2, add 200 g of deionized water, and mix in a high-speed blender (500 rpm) for 30 min to form a homogeneous slurry. After detection, the gas adsorption removal rate is 99.6%.

[0071] Example 8

[0072] The difference between this example and Example 1 lies in that the mixed gas of C2F6 and N2 (volume ratio 1:1) has a flow rate of 100 mL / min. The composite adsorbent is filled into a fixed-bed reactor, and an adsorption test is carried out at 700 °C, with a removal rate of 99.3%.

[0073] Example 9

[0074] The difference between this example and Example 1 lies in that the mixed gas of C3F6 and N2 (volume ratio 1:1) has a flow rate of 100 mL / min. The composite adsorbent is filled into a fixed-bed reactor, and an adsorption test is carried out at 700 °C, with a removal rate of 99.2%.

[0075] Example 10

[0076] The difference between this example and Example 1 lies in that the mixed gas of C3F8 and N2 (volume ratio 1:1) has a flow rate of 100 mL / min. The composite adsorbent is filled into a fixed-bed reactor, and an adsorption test is carried out at 700 °C, with a removal rate of 99.5%.

[0077] Example 11

[0078] The difference between this example and Example 1 lies in that the mixed gas of C4F6 and N2 (volume ratio 1:1) has a flow rate of 100 mL / min. The composite adsorbent is filled into a fixed-bed reactor, and an adsorption test is carried out at 700 °C, with a removal rate of 99.4%.

[0079] Example 12

[0080] The difference between this example and Example 1 lies in that the mixed gas of CH3F and N2 (volume ratio 1:1) has a flow rate of 100 mL / min. The composite adsorbent is filled into a fixed-bed reactor, and an adsorption test is carried out at 700 °C, with a removal rate of 99.5%.

[0081] Comparative Example 1

[0082] The difference between this comparative example and Example 1 lies in that the adsorbent in Technical Document CN111346601B is used. After detection, the adsorption rate is 75%.

[0083] By comparing the adsorption efficiencies of perfluorinated gases in Examples 1 to 12 and Comparative Example 1, it can be found that by using the preparation method of the present application, the adsorption efficiency can reach 99.5%. This is because in the present application, the catalytic-adsorption synergy achieves the "decomposition-fixation" in one step. The adsorption phase may be converted into a highly active catalyst at high temperature for the aluminum-based compound. The catalyst surface is rich in Lewis acid sites, which can break the C-F bond in the perfluorinated compound to generate free fluoride ions. The co-adsorption phase (metal oxide or hydroxide) can react with F - to form stable metal fluorides, realizing the fixation of fluorine and avoiding secondary pollution.

[0084] As described above, it is only the preferred embodiment of the present invention and does not impose any formal restrictions on the present invention. Although the present invention has been disclosed above in the preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to equivalent embodiments by using the above-disclosed technical content within the scope of the technical solution of the present invention. However, as long as it does not depart from the content of the technical solution of the present invention, any brief modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A perfluorinated compound composite catalytic adsorbent, characterized in that, It includes a catalytic phase with a mass fraction of 10% to 80% and an adsorption phase with a mass fraction of 20% to 90%.

2. The perfluorinated compound composite catalytic adsorbent according to claim 1, wherein The catalytic phase is any one or more of boehmite, aluminum trihydroxide or bayerite, and the adsorption phase is a metal oxide.

3. The perfluorinated compound composite catalytic adsorbent according to claim 1, wherein The adsorption phase is any one or more of metal salts or hydroxides of Zn, Ca, Ba, Mg, Sr.

4. The preparation method of a perfluorinated compound composite catalytic adsorbent according to any one of claims 1 to 3, characterized in that, It includes the following steps: Step S1. Add the catalytic phase and the adsorption phase into deionized water in proportion and stir evenly to obtain a mixed slurry; Step S2. Dry and form the mixed slurry, and then perform heat treatment to obtain a composite catalytic adsorbent.

5. The preparation method of a perfluorinated compound composite catalytic adsorbent according to claim 4, characterized in that, In step S1, the mass ratio of the catalytic phase and the adsorption phase after mixing to the mass of deionized water is 1:2 to 1:

3.

6. The preparation method of a perfluorinated compound composite catalytic adsorbent according to claim 4, characterized in that, The drying temperature in step S2 is 150 to 350 °C, and the drying time is 10 to 15 h.

7. The preparation method of a perfluorinated compound composite catalytic adsorbent according to claim 4, characterized in that, The heat treatment temperature in step S2 is 500 to 700 °C, and the heat treatment time is 4 to 6 h.

8. The application of a perfluorinated compound composite catalytic adsorbent according to any one of claims 1 to 3, characterized in that, It is used for catalytic adsorption of perfluorinated compounds, and the adsorption temperature is 500 to 800 °C.