Method for treating high concentration malodorous gas

Abstract

The application relates to the technical field of foul gas treatment, in particular to a high-concentration foul gas treatment method, which comprises the following steps: coating a slurry prepared by mixing bismuth halide oxide, aluminum-doped zinc oxide and a binder on the surface of a conductive substrate to obtain a working electrode after drying; performing constant-potential cathodic polarization treatment on the working electrode as a cathode in an electrolyte under the protection of an inert atmosphere; washing the treated working electrode, scraping the polarization product on the surface of the conductive substrate and drying to obtain a photocatalyst; and loading the photocatalyst into a photocatalytic reaction device, so that high-concentration foul gas passes through the photocatalytic reaction device and is treated under light irradiation. The treatment method can effectively degrade high-concentration hydrogen sulfide foul gas, and has good industrial practicability and popularization prospect.

Description

Technical Field

[0001] This invention relates to the field of odor gas treatment technology, specifically a method for treating high-concentration odor gases. Background Technology

[0002] Odor pollution is a common environmental problem in industrial production, wastewater treatment, and landfill processes. Hydrogen sulfide, in particular, is a colorless, highly toxic gas with a strong rotten egg odor; its olfactory threshold is extremely low, posing serious harm to the human nervous and respiratory systems. Industrial waste gases often contain high concentrations of hydrogen sulfide, such as natural gas purification tail gas, refinery acid gas, and paper mill black liquor treatment tail gas. Therefore, developing efficient technologies suitable for treating high concentrations of hydrogen sulfide gas is of significant practical importance.

[0003] Currently, the main methods for treating hydrogen sulfide gas include physical methods, chemical methods, biological methods, and photocatalytic oxidation methods.

[0004] Physical methods, such as activated carbon adsorption and solvent absorption, are simple to operate, but the adsorbent or absorbent needs to be regenerated or replaced regularly. Furthermore, their adsorption capacity is limited for high-concentration gases, leading to easy saturation and high operating costs. Chemical methods, such as the Claus process, alkaline absorption, and oxidation methods (e.g., hydrogen peroxide and sodium hypochlorite oxidation), offer high treatment efficiency, but typically require high temperatures, high pressures, or consume large amounts of chemical reagents, resulting in secondary pollution and significant equipment corrosion. Biological methods, such as biofilters and biotrickling filters, have low operating costs, but their treatment concentration range is limited, they have poor tolerance to high concentrations of hydrogen sulfide, and they have long start-up periods and require large floor space.

[0005] Photocatalytic oxidation utilizes reactive oxygen species generated by semiconductor photocatalysts under light conditions to hydrogen sulfide into harmless or low-toxic products such as elemental sulfur and sulfates. It is a green and sustainable technology for treating odorous gases, characterized by mild reaction conditions and the absence of additional chemical reagents. However, traditional photocatalysts suffer from limitations such as responsiveness only to ultraviolet light and high recombination rates of photogenerated carriers, resulting in low degradation efficiency for high concentrations of hydrogen sulfide under visible light. Summary of the Invention

[0006] Purpose of the invention: In view of the above-mentioned technical problems, the present invention proposes a method for treating high-concentration malodorous gases.

[0007] The technical solution adopted is as follows: A method for treating high-concentration malodorous gases includes: A slurry containing bismuth halide oxide, aluminum-doped zinc oxide and binder is coated onto the surface of a conductive substrate and dried to obtain the working electrode. Using the working electrode as the cathode, constant potential cathodic polarization treatment is carried out in an electrolyte at 15~35℃ under the protection of an inert atmosphere. The treated working electrode was washed, the polarization products on the surface of the conductive substrate were scraped off and dried to obtain the photocatalyst. The photocatalyst is loaded into the photocatalytic reaction device, and the high-concentration odorous gas is treated by passing through the photocatalytic reaction device under light conditions.

[0008] Furthermore, the bismuth halide is at least one of BiOX, Bi3O4X, Bi4O5X2, and Bi5O7X, where X is Br or I.

[0009] Furthermore, the bismuth-containing halide oxide is Bi4O5Br2.

[0010] Furthermore, the preparation method of the aluminum-doped zinc oxide is as follows: Zinc salt and aluminum salt are dissolved in deionized water to obtain a mixed solution; Under stirring conditions, a precipitant is added to the mixed solution to obtain a precipitate; The precipitate was separated, washed, and dried to obtain the precursor. The precursor is obtained by calcining it in air.

[0011] Furthermore, the molar ratio of zinc salt to aluminum salt is 1:0.01~0.03.

[0012] Furthermore, the calcination temperature is 600~800℃.

[0013] Further, the precipitant is at least one of sodium carbonate, sodium bicarbonate, sodium hydroxide, ammonia, or urea; preferably sodium carbonate, added in the form of an aqueous solution, the concentration of which is 0.5~2 mol / L, more preferably 1 mol / L.

[0014] Furthermore, the mass ratio of bismuth halide oxide to aluminum-doped zinc oxide is 7~9:1~3.

[0015] Furthermore, the adhesive is at least one of polyvinylidene fluoride, polytetrafluoroethylene, or sodium carboxymethyl cellulose.

[0016] Furthermore, the solvent added during the preparation of the slurry is N-methylpyrrolidone, anhydrous ethanol, or deionized water.

[0017] Furthermore, the conductive substrate is one of carbon paper, carbon cloth, nickel foam, titanium sheet, stainless steel mesh, or FTO conductive glass.

[0018] Furthermore, the electrolyte is an aqueous solution of sodium sulfate or a phosphate buffer solution with a pH value of 6.0 to 8.0.

[0019] Furthermore, using the working electrode as the cathode, a platinum sheet or graphite as the anode, and Ag / AgCl as the reference electrode, constant potential cathodic polarization treatment is performed in an electrolyte at 15~35℃ under an inert atmosphere; the potential of the constant potential cathodic polarization treatment is -0.6 to -1.2V (vs. Ag / AgCl), and the inert atmosphere is argon or nitrogen.

[0020] Furthermore, the constant potential cathode polarization treatment time is 20~60 min.

[0021] Furthermore, the high-concentration malodorous gas is hydrogen sulfide, with a concentration of 1000–3000 ppm.

[0022] This invention utilizes a composite of bismuth-containing halide oxide and aluminum-doped zinc oxide to form a working electrode, and employs a constant-potential cathode polarization method to introduce surface oxygen vacancies under mild conditions to prepare a photocatalyst for the photocatalytic degradation of high-concentration hydrogen sulfide gas. Compared with existing technologies, this invention offers the following advantages in principle: This invention utilizes the proton-coupled electron transfer reaction during constant-potential cathode polarization to inject electrons into the surface of bismuth halide oxides via an external circuit. Surface lattice oxygen accepts these electrons and combines with protons in water molecules, being removed as hydroxide ions to form oxygen vacancies. These surface oxygen vacancies are key active centers in the photocatalytic reaction; their enrichment significantly increases the adsorption sites for reactants and the sites for reactive oxygen species generation. Furthermore, by adjusting the cathode potential, polarization time, and electrolyte composition, the concentration of surface oxygen vacancies can be controlled, preventing excessive reduction and the formation of impurities such as metallic bismuth, thus achieving controllable preparation of oxygen vacancies.

[0023] Aluminum-doped zinc oxide (ANO) is a high-conductivity N-type semiconductor, uniformly dispersed among bismuth halide particles to form a continuous conductive network. During cathodic polarization, this network rapidly and uniformly transfers electrons to the bismuth halide surface, reducing electrode ohmic resistance and interfacial charge transfer resistance. This allows the applied cathode potential to effectively act on each bismuth halide grain, avoiding uneven polarization potential distribution and excessively low local current density caused by poor conductivity. Therefore, oxygen vacancies can be generated efficiently and uniformly on the bismuth halide surface. Simultaneously, the uniform electron distribution prevents excessive reduction caused by excessive local current density, ensuring the integrity of the material structure. Surface oxygen vacancies introduce defect energy levels into the band gap of bismuth halide, causing a redshift in the absorption edge and enhancing the utilization of visible light. Furthermore, as unsaturated coordination sites on the surface, oxygen vacancies can promote the migration of photogenerated holes to adsorbed hydrogen sulfide and the transfer of photogenerated electrons to generate reactive oxygen species such as superoxide radicals, thus facilitating the decomposition of hydrogen sulfide.

[0024] A tight heterojunction is formed between aluminum-doped zinc oxide and bismuth-containing oxide halide, with their band structures matched, generating a built-in electric field at the interface. Under light irradiation, the bismuth-containing oxide halide is excited to generate photogenerated electrons and holes. The photogenerated holes migrate to the valence band of the aluminum-doped zinc oxide, while the photogenerated electrons remain in the conduction band of the bismuth-containing oxide halide; this achieves spatial separation of photogenerated electrons and holes, inhibiting their recombination. This synergistic effect of the conductive network and oxygen vacancies significantly prolongs the lifetime of photogenerated carriers and improves the quantum efficiency of the photocatalytic reaction.

[0025] The constant potential cathode polarization treatment of this invention can be carried out at room temperature and pressure, with mild operation and controllable parameters, which is beneficial for the stable and reproducible preparation of high-performance photocatalysts on an industrial scale. It is suitable for continuous processing of high-concentration hydrogen sulfide gas and has good industrial applicability and prospects for promotion. Detailed Implementation

[0026] Unless otherwise specified in the examples, the conditions were performed under standard conditions or as recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products. Techniques not mentioned in this invention refer to existing technologies. Unless otherwise specified, the following examples and comparative examples are parallel experiments, using the same processing steps and parameters.

[0027] Example 1:

[0028] A method for treating high concentrations of malodorous gases: Weigh 5 mmol of bismuth nitrate pentahydrate and dissolve it in 20 mL of ethylene glycol; then add 5 mmol of potassium bromide and stir for 30 min until dissolved. Next, slowly add 8 mL of ultrapure water and 2 mL of ammonia water to the above solution, and stir the reaction at room temperature for 6 h. Collect the precipitate by vacuum filtration, wash it three times each with ultrapure water and anhydrous ethanol, dry it in a 60 °C oven for 12 h, and grind it to obtain Bi4O5Br2 powder.

[0029] Weigh 5.95 g of zinc nitrate hexahydrate (0.02 mol) and 0.15 g of aluminum nitrate nonahydrate (0.0004 mol, Al / Zn molar ratio 2%), dissolve them in 100 mL of deionized water, and stir until completely dissolved to obtain a mixed solution. While stirring, slowly add 1 mol / L sodium carbonate aqueous solution to the mixed solution to adjust the pH to 8.5, and continue stirring for 1 h to obtain a white precipitate. Centrifuge the precipitate, wash it three times each with deionized water and anhydrous ethanol, and dry it at 80 °C for 10 h to obtain the precursor powder. Place the precursor powder in a muffle furnace, heat it to 700 °C at a rate of 5 °C / min, calcine it in air for 2 h, and grind it after natural cooling to obtain aluminum-doped zinc oxide powder.

[0030] Bi4O5Br2 powder, aluminum-doped zinc oxide, and PVDF binder were mixed at a mass ratio of 8:2:0.5. An appropriate amount of N-methylpyrrolidone (NMP) was added as a solvent, and the mixture was ground for 30 minutes to form a uniform slurry. The slurry was then uniformly coated onto carbon paper, with a coating thickness of approximately 2 mg / cm². 2 The coated carbon paper was dried in an oven at 80℃ for 12 h to obtain the working electrode. This working electrode was used as the cathode, a platinum sheet as the anode, and an Ag / AgCl electrode as the reference electrode, forming a three-electrode system. The electrolyte was a 0.1 mol / L Na₂SO₄ aqueous solution with pH = 6.8. Under a nitrogen atmosphere, the electrolyte temperature was controlled at 25℃, a constant potential of -1.0V (vs. Ag / AgCl) was applied, and the treatment time was 40 min. The working electrode was removed, washed three times each with deionized water and anhydrous ethanol, and dried at 60℃ for 6 h under a nitrogen atmosphere. The dried working electrode was placed in a mortar, and the active material on the surface of the carbon paper was gently scraped off, collecting the scraped powder. This powder was then dried in a vacuum oven at 60℃ for 4 h to obtain the photocatalyst.

[0031] Photodegradation test: Weigh 0.2g of photocatalyst and pack it into a tubular fixed-bed reactor, with a catalyst bed height of approximately 2cm. The reactor ends are fixed with quartz wool. Using air with 50% humidity as the carrier gas, dilute the hydrogen sulfide standard gas to 2000ppm, and control the total gas flow rate at 50mL / min. First, purge the gas for 30 minutes under no-light conditions to allow the photocatalyst to reach adsorption equilibrium. Then, turn on the xenon lamp source (λ>420nm, light intensity 200mW / cm²). 2 The photocatalytic reaction begins, and the concentration of hydrogen sulfide in the outlet gas is measured at regular intervals using a hydrogen sulfide detector. The degradation rate is calculated using the following formula:

[0032] Where C0 is the inlet concentration, C t Let be the outlet concentration at time t under illumination.

[0033] Example 2:

[0034] The mixture is basically the same as in Example 1, except that Bi4O5Br2 powder, aluminum-doped zinc oxide and binder (PVDF) are mixed in a mass ratio of 9:1:0.5.

[0035] Example 3:

[0036] The mixture is basically the same as in Example 1, except that Bi4O5Br2 powder, aluminum-doped zinc oxide and binder (PVDF) are mixed in a mass ratio of 7:3:0.5.

[0037] Example 4:

[0038] It is basically the same as Example 1, except that the Al / Zn molar ratio is 1%.

[0039] Example 5:

[0040] It is basically the same as Example 1, except that the Al / Zn molar ratio is 3%.

[0041] Example 6:

[0042] It is basically the same as Example 1, except that the constant potential cathode polarization treatment time is 20 min.

[0043] Example 7:

[0044] It is basically the same as Example 1, except that the constant potential cathode polarization treatment time is 60 min.

[0045] Comparative Example 1: It is basically the same as Example 1, except that aluminum-doped zinc oxide is not added.

[0046] Comparative Example 2: It is basically the same as Example 1, except that zinc oxide is used instead of aluminum-doped zinc oxide.

[0047] The preparation method of zinc oxide is as follows: Weigh 5.95 g of zinc nitrate hexahydrate (0.02 mol) and dissolve it in 100 mL of deionized water. Stir until completely dissolved to obtain a mixed solution. While stirring, slowly add 1 mol / L sodium carbonate aqueous solution to the mixed solution to adjust the pH to 8.5. Continue stirring for 1 h to obtain a white precipitate. Centrifuge the precipitate, wash it three times each with deionized water and anhydrous ethanol, and dry it at 80 °C for 10 h to obtain the precursor powder. Place the precursor powder in a muffle furnace and calcine it at 700 °C at a rate of 5 °C / min for 2 h in air atmosphere. After natural cooling, grind it to obtain zinc oxide powder.

[0048] Comparative Example 3: The process is basically the same as in Example 1, except that constant potential cathode polarization treatment is not performed. Instead, Bi4O5Br2 powder, aluminum-doped zinc oxide and binder (PVDF) are directly mixed in a mass ratio of 8:2:0.5, and an appropriate amount of N-methylpyrrolidone (NMP) is added as a solvent. The mixture is ground for 30 minutes to form a uniform slurry, which is then dried in an oven at 80°C for 12 hours to obtain the photocatalyst.

[0049] Comparative Example 4: The process was basically the same as Comparative Example 3, except that the photocatalyst prepared in Comparative Example 3 was treated with a hydrogen / argon mixed gas (hydrogen gas fraction 5%) at 300°C for 2 hours.

[0050] Comparative Example 5: The reaction was basically the same as Comparative Example 3, except that 1 g of the photocatalyst prepared in Comparative Example 3 was dispersed in 100 mL of deionized water, sonicated for 10 min, and then placed in an ice-water bath and stirred for 15 min. 0.05 g of sodium borohydride was added in portions, and after the addition was complete, the reaction was continued in an ice bath with stirring for 30 min, then the ice-water bath was removed and the reaction was allowed to continue for 60 min. After the reaction was complete, the reaction solution was centrifuged. The precipitate was washed three times successively with deionized water and anhydrous ethanol, and finally dried in an 80℃ oven for 12 h to obtain the final product.

[0051] The photodegradation test results of the examples and comparative examples are shown in Table 1 below: Table 1 (%):

[0052] As shown in Table 1 above, the treatment method of the present invention can effectively degrade high-concentration hydrogen sulfide odorous gas. Example 1 showed the highest degradation rate at all time points, indicating that by using optimized composite ratio, aluminum doping amount, and cathode polarization conditions, an appropriate amount and uniformly distributed oxygen vacancies can be formed on the catalyst surface, and the conductive network of aluminum-doped zinc oxide can promote the migration of photogenerated electrons, thereby significantly improving the photocatalytic oxidation performance.

[0053] As can be seen from the comparison of Examples 1-7, when the mass ratio of Bi4O5Br2 to aluminum-doped zinc oxide deviates from the optimal value, the degradation rate decreases regardless of whether the proportion of conductive components decreases or increases. A moderate amount of aluminum doping is optimal; too low a doping level results in insufficient conductivity, while too high a level may generate impurities or carrier scattering, both of which are detrimental to performance improvement. Similarly, there is an optimal value for the cathode polarization time; too short a treatment time leads to insufficient oxygen vacancy concentration, while too long a time can easily cause over-reduction, thus weakening the photocatalytic activity.

[0054] As can be seen from the comparison between Example 1 and Comparative Example 1, the degradation rate is significantly reduced when no aluminum-doped zinc oxide is added, indicating that the addition of aluminum-doped zinc oxide significantly improves the electrode conductivity, promotes the transmission and separation of photogenerated electrons, and is an important component for improving photocatalytic efficiency.

[0055] A comparison of Example 1 and Comparative Example 2 shows that the degradation rate of zinc oxide replacing aluminum-doped zinc oxide is significantly lower than that of Example 1, but still higher than that of Comparative Example 1. This is because a heterogeneous interface can still be formed between zinc oxide and bismuth-containing halide oxides, which to some extent promotes photogenerated electron-hole separation, thus resulting in a higher degradation rate than Comparative Example 1 without aluminum-doped zinc oxide. However, undoped zinc oxide has a low carrier concentration and insufficient conductivity, making it difficult to form an efficient conductive path during cathode polarization. This limits the ability of electrons to transport to the surface of bismuth-containing halide oxides, leading to a lower efficiency in introducing oxygen vacancies onto the surface.

[0056] A comparison of Example 1 and Comparative Example 3 shows that the degradation rate was lowest without cathodic polarization treatment, indicating that the introduction of surface oxygen vacancies is the core factor in improving photocatalytic performance. Cathodic polarization can selectively remove lattice oxygen from the Bi4O5Br2 surface under mild conditions, forming abundant active sites and significantly improving the visible light photocatalytic oxidation ability of hydrogen sulfide.

[0057] As can be seen from the comparison between Example 1 and Comparative Example 4, although the high-temperature hydrogen reduction method can also introduce oxygen vacancies, the high-temperature treatment will destroy the layered structure of Bi4O5Br2, reduce the specific surface area, and may generate metallic bismuth impurities, which will offset the positive effect of oxygen vacancies, thus leading to a decrease in degradation rate.

[0058] As can be seen from the comparison between Example 1 and Comparative Example 5, although the sodium borohydride chemical reduction method can introduce oxygen vacancies at room temperature, it may have problems such as uneven reduction and damage to the surface structure, resulting in catalytic activity that is not as good as that of the electrochemical cathodic polarization method.

[0059] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for treating high-concentration malodorous gases, characterized in that, include: A slurry containing bismuth halide oxide, aluminum-doped zinc oxide and binder is coated onto the surface of a conductive substrate and dried to obtain the working electrode. Using the working electrode as the cathode, constant potential cathodic polarization treatment is carried out in an electrolyte at 15~35℃ under the protection of an inert atmosphere. The treated working electrode was washed, the polarization products on the surface of the conductive substrate were scraped off and dried to obtain the photocatalyst. The photocatalyst is loaded into the photocatalytic reaction device, and the high-concentration odorous gas is treated by passing through the photocatalytic reaction device under light conditions.

2. The method for treating high-concentration malodorous gases as described in claim 1, characterized in that, The bismuth halide oxide is at least one of BiOX, Bi3O4X, Bi4O5X2, and Bi5O7X, where X is Br or I.

3. The method for treating high-concentration malodorous gases as described in claim 2, characterized in that, The bismuth-containing halide oxide is .

4. The method for treating high-concentration malodorous gases as described in claim 1, characterized in that, The preparation method of the aluminum-doped zinc oxide is as follows: Zinc salt and aluminum salt are dissolved in deionized water to obtain a mixed solution; Under stirring conditions, a precipitant is added to the mixed solution to obtain a precipitate; The precipitate was separated, washed, and dried to obtain the precursor. The precursor is obtained by calcining it in air.

5. The method for treating high-concentration malodorous gases as described in claim 4, characterized in that, The molar ratio of zinc salt to aluminum salt is 1:0.01~0.

03.

6. The method for treating high-concentration malodorous gases as described in claim 4, characterized in that, The calcination temperature is 600~800℃.

7. The method for treating high-concentration malodorous gases as described in claim 1, characterized in that, The mass ratio of bismuth halide oxide to aluminum-doped zinc oxide is 7~9:1~3.

8. The method for treating high-concentration malodorous gases as described in claim 1, characterized in that, The electrolyte is an aqueous solution of sodium sulfate or a phosphate buffer solution with a pH value of 6.0 to 8.

0.

9. The method for treating high-concentration malodorous gases as described in claim 1, characterized in that, The constant potential cathode polarization treatment time is 20~60 min.

10. The method for treating high-concentration malodorous gases as described in claim 1, characterized in that, The high-concentration malodorous gas is hydrogen sulfide.

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