Core-shell type difunctional sewage catalytic oxidation catalyst and preparation method thereof

Abstract

The invention relates to a core-shell type difunctional sewage catalytic oxidation catalyst and a preparation method thereof. (a) mixing activated carbon or a molecular sieve or a mixture thereof with a binder to obtain an inner core; (b) mixing the inner core with modified aluminum oxide and water, forming spheres through a granulator, and drying and roasting to obtain the core-shell structure catalyst, (c) impregnating the core-shell structure catalyst with a phosphoric acid solution, drying and roasting to obtain modified aluminum oxide; (d) carrying out excessive impregnation on the modified aluminum oxide by adopting a soluble precursor aqueous solution loaded with a metal oxide, and carrying out liquid-solid separation, drying and roasting to obtain a loaded catalyst; and (e) carrying out excessive impregnation on the supported catalyst by adopting a soluble precursor aqueous solution of a transition metal oxide, and carrying out liquid-solid separation, drying and roasting to obtain the negative core-shell type bifunctional sewage catalytic oxidation catalyst. The sewage COD removal efficiency is effectively improved, and the catalyst loaded metal dosage and the production cost are reduced.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, specifically relating to a core-shell bifunctional wastewater catalytic oxidation catalyst and its preparation method. Background Technology

[0002] Common ozone catalytic oxidation catalysts are prepared by supporting metals or metal oxides on a series of porous catalyst materials such as zeolites, amorphous alumina, silica gel, and molecular sieves, and then preparing them into particles or spheres of 3-10 mm. They have the characteristics of large specific surface area, long catalyst lifetime, and easy separation and recovery.

[0003] Patent CN 111229225A discloses an iron composite catalyst for ozone catalytic oxidation and its preparation method. The catalyst preparation is divided into two processes: support preparation and catalyst preparation. First, iron oxide and active alumina are mixed evenly, a binder solution is added, the mixture is pressed into blocks, dried and calcined to obtain a catalyst composite support. Then, the prepared catalyst is soaked in an iron salt solution, dried and calcined to obtain the catalyst.

[0004] The patent with publication number CN115025768B discloses a spherical alumina-based hydrophobic ozone catalytic oxidation catalyst and its preparation method and application. The preparation method includes the following steps: (1) mixing a silane reagent containing carbon-fluorine bonds with an organic solvent to obtain a modified solution; (2) completely or partially immersing the pretreated alumina-based ozone catalytic oxidation catalyst pellets in the modified solution prepared in step (1); (3) heating and drying the alumina-based ozone catalytic oxidation catalyst pellets after step (2) to obtain the spherical alumina-based hydrophobic ozone catalytic oxidation catalyst.

[0005] However, the wastewater catalytic oxidation catalysts prepared in the above-mentioned technologies are typically reacted under normal temperature and pressure conditions. The wastewater residence time in the empty tower of the reactor is approximately 1–3 hours, and the porosity of the reactor after catalyst loading is generally 15–25%. The actual contact time between the wastewater and the catalyst in the reactor is no more than 45 minutes. Because the catalytic oxidation catalyst uses porous catalyst materials as supports and has a large particle size, within the process parameter range, the actual contact between the wastewater and the catalyst exists only in the surface layer of the catalyst. This results in a small effective catalytic reaction area, low mass transfer efficiency, low utilization rate of the inner layer of the catalyst, easy loss of supported metals, and increased use of supported metals, leading to increased costs, low COD removal efficiency of wastewater, and easy deactivation of the catalyst. Summary of the Invention

[0006] In order to overcome the shortcomings of the existing technology, the present invention aims to provide a core-shell bifunctional wastewater catalytic oxidation catalyst and its preparation method. When used in the wastewater catalytic oxidation process, the catalyst effectively improves the COD removal efficiency of wastewater through catalytic oxidation + adsorption. Furthermore, by utilizing the surface catalytic principle of catalytic oxidation, the amount of metal loaded on the catalyst and the production cost are significantly reduced, thereby improving the overall economic benefits of the technology.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A core-shell bifunctional wastewater catalytic oxidation catalyst, comprising a core and an outer shell;

[0009] The core is made of activated carbon, molecular sieve, or a mixture of activated carbon and molecular sieve, and a binder is used to bind the core together; it has adsorption function.

[0010] The shell is modified alumina and its supported metal oxide, and the shell covers the core; the shell has a catalytic oxidation reaction function;

[0011] The catalyst is a sphere with a radius of 2 to 5 mm, wherein the core radius is 1.0 to 4.8 mm, the shell thickness is 0.2 to 1.0 mm, and 0 to 0.1 mm of transition metal oxides are present on the outer surface of the shell;

[0012] The binder content accounts for 2 to 10% of the core mass;

[0013] The modified alumina is phosphorus-modified alumina, with phosphorus modification using P2O5, and the P2O5 content accounting for 3.0 to 7.0 wt% of the modified alumina mass. The loaded metal oxide is one or more of manganese oxide, iron oxide, copper oxide, cerium oxide, and nickel oxide, and the loaded metal oxide content accounts for 3 to 15 wt% of the shell mass, with the remainder being modified alumina.

[0014] Furthermore, the specific surface area of ​​the activated carbon is 600–3000 m². 2 / g, iodine adsorption value ≥900mg / g.

[0015] Furthermore, the molecular sieve is one or a mixture of several of ZSM-5, USY, SAPO-34, SBA-15, and MCM-41;

[0016] Furthermore, the binder is one of coal tar pitch, polyvinyl alcohol, starch, boehmite, and dextrin;

[0017] Furthermore, when the supported metal oxide is iron oxide or cerium oxide, the molar ratio of Fe:Ce is 8 to 15:1;

[0018] Furthermore, the iron oxide is a rod-shaped FeOOH with a grain size of 100–1000 nm.

[0019] Furthermore, when the supported metal oxide is copper oxide or cerium oxide, the molar ratio of Cu:Ce is 3 to 10:1.

[0020] Furthermore, the transition metal oxide is one of manganese oxide and nickel oxide, and the content of the transition metal oxide accounts for 0.02 to 0.5 wt% of the shell mass, based on the shell mass.

[0021] A method for preparing a core-shell bifunctional wastewater catalytic oxidation catalyst includes the following steps:

[0022] (a) Activated carbon or molecular sieve or a mixture thereof are mixed with a binder and granulated to obtain a core with a radius of 1.2 to 4.8 mm;

[0023] (b) The core described in step (a) is mixed with modified alumina and water, and granulated to form spheres. After drying and calcination, a core-shell structured catalyst is obtained.

[0024] (c) The core-shell structure catalyst described in step (b) was impregnated with phosphoric acid solution for 1 to 8 hours, and then dried and calcined to obtain modified alumina;

[0025] (d) The modified alumina described in step (c) was subjected to over-impregnation for 3 to 6 hours using an aqueous solution of a soluble precursor of supported metal oxide. After liquid-solid separation, drying, and calcination, a supported catalyst was obtained.

[0026] (e) The supported catalyst described in step (d) is subjected to over-impregnation for 10 to 30 minutes using an aqueous solution of a soluble precursor of a transition metal oxide. After liquid-solid separation, drying, and calcination, a core-shell bifunctional wastewater catalytic oxidation catalyst is obtained.

[0027] Furthermore, the drying conditions for steps (b), (c), (d), and (e) are 60–125°C, drying time is 6–12 h, calcination temperature is 450–600°C, and calcination time is 4–8 h.

[0028] In step (a), the binder content accounts for 2 to 10% of the core mass;

[0029] In step (b), the volume ratio of the core to modified alumina and water is (0-1):(0.1-1):(0.015-0.3); and the core volume is not 0.

[0030] In step (c), the concentration range of the phosphoric acid solution is 0.3-2 mol / L;

[0031] In step (d), the concentration of the loaded metal oxide is 0.2-4 mol / L;

[0032] The ratio of transition metal oxide precursors is 0.2-2 mol / L.

[0033] Furthermore, the drying and calcination of the kernel containing activated carbon are carried out under an inert gas atmosphere;

[0034] Furthermore, the phosphoric acid mentioned in step (c) is one or a mixture of two of H3PO4, NH4PO3, NH4H2PO4, and (NH4)3PO4;

[0035] The soluble precursors of the loaded metal oxides and transition metal oxides mentioned in step (d) are one or a mixture of several of the following: nitrites, nitrates, chlorides, sulfates, and sulfites.

[0036] Furthermore, in step (d), when the loaded metal oxide is iron oxide and the precursor is soluble ferrous sulfate or ferrous nitrate, the impregnation temperature is 45–75°C, oxygen is introduced, and the pH is maintained between 6.5 and 8.0.

[0037] Furthermore, the catalyst is applied to the ozone catalytic oxidation reaction for COD removal in municipal and chemical wastewater, especially in the deep treatment section of organic matter at the front end of the wastewater treatment plant's external discharge.

[0038] The beneficial effects of this invention are:

[0039] This invention fully utilizes the process characteristics, organic matter degradation properties, and catalyst surface catalytic principles of existing wastewater catalytic oxidation processes to construct a bifunctional catalytic oxidation catalyst with shell catalytic oxidation and inner layer adsorption. First, by controlling the thickness of the shell catalytic oxide layer and combining catalyst design with the catalytic oxidation process, the catalytic reaction zone of the catalyst shell is maximized, thereby significantly reducing the overall metal loading of the catalyst and effectively lowering costs. Then, the core, with its adsorption function, adsorbs recalcitrant organic matter after the catalytic reaction, enhancing the degradation depth of wastewater organic matter. Second, based on the principle that the concentration of dissolved ozone and wastewater organic matter decreases gradually from the catalyst surface to the inner layer, and the reaction characteristic of gradually increasing wastewater degradation difficulty, a highly active transition metal oxide coating is added to the catalyst shell to construct a highly active reactive zone, improving the overall degradation capacity of wastewater organic matter. Third, by modifying the shell alumina with phosphorus (P), the alumina possesses more -OH groups, which not only facilitates the generation of superoxide radicals but also effectively reduces the loss rate of the loaded metal oxide, extending the catalyst lifespan. Finally, using small-grained, highly dispersed FeOOH as the active center enhances the activity of the iron-based catalytic oxidation catalyst, further reducing catalyst costs and the degradation capacity of wastewater organic matter. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the catalyst of the present invention. Detailed Implementation

[0042] The present invention will now be described in further detail with reference to the accompanying drawings.

[0043] In each example and comparative example, the oxidation state composition of the prepared catalyst samples was determined by X-ray fluorescence method.

[0044] like Figure 1 As shown, a core-shell bifunctional wastewater catalytic oxidation catalyst includes a core and an outer shell.

[0045] The core is made of activated carbon, molecular sieve, or a mixture of activated carbon and molecular sieve, and a binder is used to bind the core together; it has adsorption function.

[0046] The shell is modified alumina and its supported metal oxide, and the shell covers the core; the shell has a catalytic oxidation reaction function;

[0047] The catalyst is a sphere with a radius of 2 to 5 mm, wherein the core radius is 1.0 to 4.8 mm, the shell thickness is 0.2 to 1.0 mm, and the outer surface of the shell contains 0 to 0.1 mm of transition metal oxides.

[0048] Example 1:

[0049] 50g of activated carbon was mixed with 3.5g of coal tar pitch binder and granulated to obtain a core with a radius of 3.6mm. The core was mixed with 16g of activated alumina and 4.8g of water, and granulated into spheres. After drying at 65℃ for 8h and calcining at 450℃ for 4h, a core-shell structure catalyst with a radius of 4mm and a shell thickness of 0.4mm was obtained. The core-shell structure catalyst was impregnated with 1.0mol / L H3PO4 solution for 6h, dried at 85℃ for 12h and calcined at 550℃ for 4h to obtain modified alumina with a P2O5 content of 4.2wt% of the shell mass. 2.5mol / L (NO3) -Modified alumina was over-impregnated with a mixed solution of copper nitrate and cerium nitrate for 4 hours. After liquid-solid separation, drying at 85℃ for 4 hours, and calcination at 550℃ for 4 hours, a supported catalyst was obtained with a Cu:Ce molar ratio of 8. The supported catalyst was then over-impregnated with a 0.3 mol / L manganese nitrate solution for 25 minutes. After liquid-solid separation, drying at 85℃ for 4 hours, and calcination at 550℃ for 4 hours, a core-shell bifunctional wastewater catalytic oxidation catalyst was obtained. The contents of copper oxide, cerium oxide, and manganese oxide accounted for 7.2 wt% of the shell mass, and the manganese oxide content accounted for 0.32 wt% of the shell mass. The specific surface area of ​​the activated carbon was 1800 m². 2 / g, iodine adsorption value ≥960mg / g; drying and calcination were both carried out under N2 conditions.

[0050] Example 2:

[0051] The difference from Example 1 is that 35g of activated carbon was mixed with 15g of ZSM-5 molecular sieve and 4.2g of alumina binder; the core radius was 3.2mm and the shell thickness was 0.8mm; the supported catalyst was over-impregnated with a 0.4mol / L nickel nitrate solution (NiO precursor) for 15min, followed by liquid-solid separation, drying at 105℃ for 6h, and calcination at 600℃ for 4h to obtain a core-shell bifunctional wastewater catalytic oxidation catalyst. The P2O5 content accounted for 5.7wt% of the shell mass, the copper oxide, cerium oxide, and nickel oxide content accounted for 6.7wt% of the shell mass, the nickel oxide content accounted for 0.45wt% of the shell mass, and the Cu:Ce molar ratio was 10; drying and calcination were both carried out under N2 conditions.

[0052] Example 3:

[0053] 50g of activated carbon was mixed with 2.5g of pseudoboehmite binder, and granulated to obtain a core with a radius of 2.8mm. The core was mixed with 45g of activated alumina and 13.8g of water, and granulated to form spheres. After drying at 85℃ for 6h and calcining, a core-shell structure catalyst with a radius of 3.5mm and a shell thickness of 0.7mm was obtained. The core-shell structure catalyst was impregnated with 0.6mol / L NH4H2PO4 solution for 8h, dried at 90℃ for 8h and calcined at 550℃ for 6h to obtain modified alumina with a P2O5 content of 4.5wt% of the shell mass. 3.7mol / L (SO4) 2- +NO3 -Modified alumina was subjected to excess impregnation with ferric sulfate and cerium nitrate solution for 5 hours, followed by liquid-solid separation, drying at 85℃ for 6 hours, and calcination at 550℃ for 4 hours to obtain a supported catalyst. The modified catalyst was then subjected to excess impregnation with 0.2 mol / L manganese nitrate solution for 10 minutes, followed by liquid-solid separation, drying at 85℃ for 6 hours, and calcination at 600℃ for 4 hours to obtain a core-shell bifunctional wastewater catalytic oxidation catalyst. The supported metal oxides were manganese oxide, iron oxide, and cerium oxide, accounting for 14.2 wt% of the shell mass, with manganese oxide accounting for 0.32 wt% of the shell mass. The Fe:Ce molar ratio was 8–15:1. The activated carbon had a specific surface area of ​​1500 m². 2 / g, iodine adsorption value ≥918mg / g; drying and calcination were both completed under N2 conditions.

[0054] Example 4:

[0055] The difference from Example 3 is that 2.3 mol / L (SO4) was used. 2- +NO3 - The modified alumina was subjected to an over-impregnation of ferrous sulfate and cerium nitrate solution for 6 hours at an impregnation temperature of 65°C, with oxygen introduced and pH maintained at 6.8. The resulting iron oxide was FeOOH with a rod-like structure and a grain size of 650 nm.

[0056] Comparative Example 1: A CuO-CeO2 catalytic oxidation catalyst supported on commercially available alumina ceramic balls, wherein CuO accounts for 4.5 wt% of the total mass of the alumina ceramic balls and CeO2 accounts for 2.0 wt% of the total mass of the ceramic balls.

[0057] Comparative Example 2: Fe2O3-CeO2 catalytic oxidation catalyst supported on commercially available alumina ceramic balls, wherein Fe2O3 accounts for 12.9 wt% of the total mass of the alumina ceramic balls and CeO2 accounts for 1.75 wt% of the total mass of the ceramic balls.

[0058] Using wastewater from both a coal chemical industrial park and a fine chemical industrial park as raw materials, the performance of the catalysts was evaluated under the same catalyst loading and operating conditions. The evaluation results of the catalysts in Examples 1-4 and Comparative Examples 1 and 2 are shown in Table 1.

[0059]

[0060] As can be seen from Table 1, under the same process conditions, the COD removal rate of the catalyst of this invention is significantly higher for both high-COD wastewater from coal chemical industrial parks and fine chemical industrial parks.

[0061] The present invention has been described in detail with reference to the above embodiments. Those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific embodiments of the present invention without departing from the spirit and scope of the present invention, and such modifications or equivalent substitutions should be covered within the scope of the claims.

Claims

1. A core-shell bifunctional wastewater catalytic oxidation catalyst, characterized in that, Including the kernel and its outer casing; The core is made of activated carbon, molecular sieve, or a mixture of activated carbon and molecular sieve, and the core is bonded together by a binder. The shell is modified alumina and its supported metal oxide, and the shell covers the core. The catalyst is a sphere with a radius of 2 to 5 mm, wherein the core radius is 1.0 to 4.8 mm, the shell thickness is 0.2 to 1.0 mm, and the outer surface of the shell contains 0 to 0.1 mm of transition metal oxides.

2. The core-shell bifunctional wastewater catalytic oxidation catalyst according to claim 1, characterized in that, The binder content accounts for 2 to 10% of the core mass; The modified alumina is phosphorus-modified alumina, with phosphorus modification selected from P2O5, and the P2O5 content accounting for 3.0 to 7.0 wt% of the shell mass. The loaded metal oxide is one or more of manganese oxide, iron oxide, copper oxide, cerium oxide, and nickel oxide, and the content of the loaded metal oxide accounts for 3 to 15 wt% of the shell mass, with the remainder being modified alumina.

3. The core-shell bifunctional wastewater catalytic oxidation catalyst according to claim 1, characterized in that, The specific surface area of ​​the activated carbon is 600-3000 m². 2 / g, iodine adsorption value ≥900mg / g; The molecular sieve is one or a mixture of several of ZSM-5, USY, SAPO-34, SBA-15, and MCM-41.

4. The core-shell bifunctional wastewater catalytic oxidation catalyst according to claim 3, characterized in that, The binder is one of coal tar pitch, polyvinyl alcohol, starch, boehmite, and xanthodextrin. When the supported metal oxide is iron oxide or cerium oxide, the molar ratio of Fe:Ce is 8 to 15:

1. The iron oxide is FeOOH with a rod-like structure and a grain size of 100-1000 nm; When the loaded metal oxide is copper oxide or cerium oxide, the molar ratio of Cu:Ce is 3 to 10:

1.

5. The core-shell bifunctional wastewater catalytic oxidation catalyst according to claim 4, characterized in that, The transition metal oxide is one of manganese oxide and nickel oxide, and the content of the transition metal oxide accounts for 0.02 to 0.5 wt% of the shell mass, based on the shell mass.

6. A method for preparing a core-shell bifunctional wastewater catalytic oxidation catalyst according to any one of claims 1-5, characterized in that, Includes the following steps: (a) Activated carbon or molecular sieve or a mixture thereof are mixed with a binder and granulated to obtain a core with a radius of 1.2 to 4.8 mm; (b) The core described in step (a) is mixed with modified alumina and water, and granulated to form spheres. After drying and calcination, a core-shell structured catalyst is obtained. (c) The core-shell structure catalyst described in step (b) was impregnated with phosphoric acid solution for 1 to 8 hours, and then dried and calcined to obtain modified alumina; (d) The modified alumina described in step (c) was subjected to over-impregnation for 3 to 6 hours using an aqueous solution of a soluble precursor of supported metal oxide. After liquid-solid separation, drying, and calcination, a supported catalyst was obtained. (e) The supported catalyst described in step (d) is subjected to over-impregnation for 10 to 30 minutes using an aqueous solution of a soluble precursor of a transition metal oxide. After liquid-solid separation, drying, and calcination, a core-shell bifunctional wastewater catalytic oxidation catalyst is obtained.

7. The method for preparing a core-shell bifunctional wastewater catalytic oxidation catalyst according to claim 6, characterized in that, The drying conditions for steps (b), (c), (d), and (e) are 60–125°C, drying time is 6–12 h, calcination temperature is 450–600°C, and calcination time is 4–8 h. In step (a), the binder content accounts for 2 to 10% of the core mass; In step (b), the volume ratio of the core to modified alumina and water is (0-1):(0.1-1):(0.015-0.3); and the core volume is not 0. In step (c), the concentration range of the phosphoric acid solution is 0.3-2 mol / L; In step (d), the concentration of the loaded metal oxide is 0.2-4 mol / L; The ratio of precursors for transition metal oxides is 0.2-2 mol / L.

8. The method for preparing a core-shell bifunctional wastewater catalytic oxidation catalyst according to claim 7, characterized in that, When the kernel contains activated carbon, both drying and calcination are carried out under an inert gas atmosphere. The phosphoric acid mentioned in step (c) is one or a mixture of two of H3PO4, NH4PO3, NH4H2PO4, and (NH4)3PO4; The soluble precursors of the loaded metal oxides and transition metal oxides mentioned in step (d) are one or a mixture of several of the following: nitrites, nitrates, chlorides, sulfates, and sulfites.

9. The method for preparing a core-shell bifunctional wastewater catalytic oxidation catalyst according to claim 8, characterized in that, In step (d), when the loaded metal oxide is iron oxide and the precursor is soluble ferrous sulfate or ferrous nitrate, the impregnation temperature is 45–75°C, oxygen is introduced, and the pH is maintained between 6.5 and 8.

0.

10. The application of the catalyst according to any one of claims 1-5, characterized in that, The catalyst is used in the ozone catalytic oxidation reaction to remove COD from municipal and chemical wastewater, especially in the deep treatment section of organic matter at the front end of the wastewater treatment plant's external discharge.

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