Doped photocatalytic reduction catalyst, preparation method and application thereof

Abstract

The application discloses a doped photocatalytic reduction catalyst and a preparation method and application thereof, relates to the technical field of catalyst materials, and specifically discloses a doped photocatalytic reduction catalyst, which comprises the following raw materials in percentage by mass: tetrabutyl titanate 10-20%; a nickel source 4-8%; a cadmium source 1-2%; an ethanol aqueous solvent 40-60%; concentrated hydrochloric acid 1-10%; and diatomite 10-30%. The tetrabutyl titanate, the nickel source and the cadmium source account for 5-30% of the total amount of the raw materials, the amount ratio of the tetrabutyl titanate, the nickel source and the cadmium source is 1:0.1-0.3:0.02-0.06, and the amount ratio of ethanol and water in the ethanol aqueous solvent is 1-5:1. The obtained reduction catalyst can be used in a process for generating chloroacetic acid by adopting a dichloroacetic acid dechlorination method, so that the process can be carried out under normal pressure, the catalytic reaction condition is mild, the conversion rate of dichloroacetic acid is high, and the process is suitable for popularization and application to industrialization and large-scale production.

Description

Technical Field

[0001] This invention relates to the field of catalyst materials technology, specifically to a doped photocatalytic reduction catalyst, its preparation method, and its application. Background Technology

[0002] Photocatalytic reduction is a reaction process that uses photothermal energy to provide kinetic energy and release electrons. Therefore, it involves the absorption of visible, near-infrared, or ultraviolet light, enabling photoelectrocatalytic reactions. The reaction being catalyzed and reduced is also called a photoelectrocatalytic reduction reaction. In photocatalytic reduction technology, the charge, energy band structure, and additives of materials can be adjusted using photocatalysts to obtain highly efficient, stable, and catalytically active materials.

[0003] Therefore, photocatalysis technology is widely used in chemical reactions, such as modifying aggregate surfaces, preparing polymer buffer layers, sensing, and other novel structures and materials. Photocatalytic materials can not only deposit capacitor-controlled catalysis, but also achieve catalytic reactions in a short time without requiring any external energy, thus exhibiting significant environmental friendliness and economic efficiency.

[0004] Furthermore, photocatalytic reduction possesses a series of unique advantages, such as energy saving, environmental friendliness, high efficiency, ease of operation, and low cost. Even under adverse conditions such as high toxicity, high temperature, and high pressure, photocatalytic reduction can still achieve highly efficient catalysis under effective conditions. In addition, photocatalytic reduction can generate thermal and electrical energy at different temperatures, and the temperature conditions under extreme biological and chemical conditions are unmatched by traditional catalytic reactions, giving it greater application prospects.

[0005] The inventors of this company considered applying photocatalysis technology to the synthesis process of chloroacetic acid to improve its yield and combine the advantages of photocatalysis technology.

[0006] Chloroacetic acid is an important fine chemical product and organic chemical intermediate, widely used as an active compound. In the pesticide industry, chloroacetic acid can be used to synthesize more than 20 commonly used insecticides, herbicides, and plant growth regulators; in the pharmaceutical industry, chloroacetic acid and its esters are mainly used to produce vitamins, hormones, and other drugs; in the dye industry, chloroacetic acid is mainly used to synthesize reactive dyes; in addition, chloroacetic acid is also an important organic synthesis intermediate, used to prepare fine chemicals such as malonic acid, malononitrile, and malonate esters. my country's chloroacetic acid production accounts for more than 50% of the world's total output, making it a major producer of chloroacetic acid products. While its production capacity has grown rapidly over the years, the development of its production technology has been relatively slow. Compared with foreign continuous chlorination and continuous hydrogenation processes, the domestic chloroacetic acid production process, whether using sulfur catalysis or acetic anhydride catalysis, inevitably produces a large amount of mother liquor. The composition of the mother liquor varies depending on the degree of chlorination, crystallization temperature, and water content, and generally consists of chloroacetic acid, dichloroacetic acid, acetic acid, and chlorination intermediates.

[0007] Currently, the industry is gradually beginning to treat the mother liquor produced in chloroacetic acid production in order to obtain a higher yield of chloroacetic acid, as well as to improve the conversion rate of raw materials, reduce the discharge of waste liquid, lower reaction conditions, and reduce production costs. Summary of the Invention

[0008] The purpose of this invention is to provide a doped photocatalytic reduction catalyst, its preparation method, and its application. The obtained reduction catalyst can be used in the process of producing chloroacetic acid by dechlorination of dichloroacetic acid, so that the process can be carried out under normal pressure conditions, the catalytic reaction conditions are mild, the conversion rate of dichloroacetic acid is high, and it is suitable for industrialization and large-scale production.

[0009] This invention is achieved through the following technical solution: A doped photocatalytic reduction catalyst, comprising, by mass percentage, the following raw materials: Tetrabutyl titanate 10~20%; Nickel source 4~8%; Cadmium source 1-2%; Ethanol as a water solvent: 40-60%; Concentrated hydrochloric acid 1~10%; Diatomaceous earth 10-30%; Among them, tetrabutyl titanate, nickel source and cadmium source account for 5-30% of the total raw materials, the ratio of tetrabutyl titanate, nickel source and cadmium source is 1:0.1-0.3:0.02-0.06, and the ratio of ethanol to water in ethanol aqueous solvent is 1-5:1.

[0010] Furthermore, the nickel source includes, but is not limited to, nickel oxide, nickel nitrate, and nickel carbonate.

[0011] Furthermore, the cadmium source includes, but is not limited to, cadmium oxide, cadmium nitrate, and cadmium chloride.

[0012] A method for preparing a doped photocatalytic reduction catalyst as described above includes the following steps: A. Take each raw material according to the aforementioned formula ratio and set aside; B. Take tetrabutyl titanate, nickel source and cadmium source, and dissolve them in ethanol aqueous solvent. Use concentrated hydrochloric acid as catalyst, add diatomaceous earth, and mix and stir at 70~90℃ for 6~12h. C. Evaporate the solvent from the reacted material under reduced pressure and dry it at 100~120℃ for 2~6h to obtain a dry solid; D. The dry solid was calcined at 1000~1500℃ for 2h to obtain a photocatalytic reduction catalyst.

[0013] Furthermore, in step C, the pressure conditions for evaporating the solvent under reduced pressure are -90 to -70 kPa.

[0014] The application of any of the aforementioned doped photocatalytic reduction catalysts in the chloroacetic acid synthesis process.

[0015] Furthermore, the application includes the following steps: I. Take acetic acid and chlorine as raw materials, and under the catalysis of acetic anhydride, control the reaction temperature at 90~105℃ to obtain a chlorinated liquid containing acetic acid; II. The chlorination solution from step I is subjected to multi-stage cooling and crystallization to obtain solid chloroacetic acid and mother liquor; Ⅲ. Take the mother liquor from step Ⅱ, add 0.1~2% of the total mass of the material to doped photocatalytic reduction catalyst, heat to 70~90℃, and irradiate with visible light or ultraviolet light for 6~24h to obtain secondary chlorination liquid; IV. The secondary chlorination solution is cooled and crystallized through multiple stages to obtain solid chloroacetic acid and secondary mother liquor. The secondary mother liquor is sent to step II for further recycling.

[0016] Furthermore, in step I, the molar ratio of acetic acid to chlorine is 1:1.0~1.2, and the amount of acetic anhydride added is 0.5~5% of the total material mass.

[0017] Furthermore, in steps II and IV, the multi-stage cooling crystallization operation method involves sequentially cooling the mother liquor with cooling water at 60℃, 50℃, 40℃, 30℃, and 20℃, and holding each temperature range for 2 hours to allow crystals to precipitate.

[0018] Furthermore, in step III, light with a wavelength of 260~700nm is selected for illumination.

[0019] Compared with the prior art, the present invention has the following advantages and beneficial effects: I. In this invention, by using the raw materials and corresponding proportions of this scheme, a doped photocatalytic reduction catalyst, also known as a photocatalyst, can be obtained, which is particularly suitable for the process of synthesizing chloroacetic acid by acetic anhydride catalysis. Furthermore, the aforementioned raw materials are widely available, readily accessible, and renewable.

[0020] II. This invention proposes a method for preparing a doped photocatalytic reduction catalyst. Based on the raw material ratio of this method, a supported doped photocatalytic reduction catalyst with stable quality and uniform structure can be obtained. Furthermore, this supported doped photocatalytic reduction catalyst has a large specific surface area, which is beneficial for increasing the contact between substances during application; and the dopant is uniformly dispersed, providing favorable conditions for photocatalysis and photoelectric conversion.

[0021] Third, in this invention, after applying the doped photocatalytic reduction catalyst obtained in this scheme to the process of synthesizing chloroacetic acid by acetic anhydride catalysis, the conversion rate of chloroacetic acid in the dechlorination step of dichloroacetic acid can be significantly improved, reaching as high as 70% or more. Furthermore, the method disclosed in this scheme allows for catalytic reaction under normal pressure, with mild reaction conditions and relatively low equipment requirements, facilitating its application to industrial and large-scale production.

[0022] Fourth, in this invention, when the doped photocatalytic reduction catalyst of this scheme is applied to the process of chloroacetic acid, it can be irradiated with light of wavelength 260~700nm, that is, visible light and / or ultraviolet light can be selected for irradiation. The range of light selection is wider, the application field of this doped photocatalytic reduction catalyst is wider, and the requirements for reaction conditions are lower.

[0023] V. This invention proposes a chloroacetic acid synthesis process using a doped photocatalytic reduction catalyst. This process employs selective catalytic hydrogenation dechlorination of the chlorinated liquid after chlorination to prepare high-purity chloroacetic acid. This process has the advantages of high product quality and low raw material consumption. Simultaneously, the resulting secondary mother liquor is returned to the preceding step II for recycling, significantly reducing the external discharge of mother liquor. Furthermore, this process can be carried out continuously, featuring convenient operation and a short cycle time.

[0024] VI. The novel doped photocatalytic reduction catalyst proposed in this invention provides a new approach for optimizing the process of preparing chloroacetic acid by catalytic chlorination of acetic anhydride.

[0025] VII. In the process of synthesizing chloroacetic acid in this invention, in steps II and IV, the mother liquor is cooled in stages with cooling water at 60°C, 50°C, 40°C, 30°C and 20°C, and each temperature range is held for 2 hours to allow crystallization. This allows for the precipitation of more qualified products in one go, reduces the amount of mother liquor post-processing equipment used, and improves the efficiency of mother liquor post-processing. Attached Figure Description

[0026] Figure 1 This is a BET analysis result diagram of the doped photocatalytic reduction catalyst obtained in Group 2 of Example 1.

[0027] Figure 2 This is a BET analysis result diagram of the doped photocatalytic reduction catalyst obtained in Group 6 of Example 1.

[0028] Figure 3 This is a BET analysis result diagram of the doped photocatalytic reduction catalyst obtained in Group 7 of Example 1. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to embodiments, but the implementation of the present invention is not limited thereto.

[0030] Example 1 In this embodiment, the raw materials were taken according to the proportions (by mass percentage) of each group in Table 1 below, and the doped photocatalytic reduction catalyst was prepared according to the preparation method described below.

[0031] Table 1 The preparation method of doped photocatalytic reduction catalyst includes the following steps: A. Take each raw material according to the formula ratio of each group in Table 1 above. The amount of tetrabutyl titanate added in each group for a single experiment is 100g.

[0032] B. First, add ethanol-water solvent to a 2000mL four-necked flask. Then, take tetrabutyl titanate, nickel source, and cadmium source according to the proportions of each group of raw materials. In this example, nickel nitrate and cadmium nitrate are used as examples of nickel and cadmium sources, respectively. Under stirring conditions, fully dissolve the solid raw materials such as tetrabutyl titanate, nickel nitrate, and cadmium nitrate in the ethanol-water solvent. Use concentrated hydrochloric acid as a catalyst, add diatomaceous earth, and heat to 70°C and keep at that temperature for 12 hours.

[0033] In this step, after multiple experiments, it has been verified that the holding temperature should be controlled within the range of 70~90℃, and the temperature should be maintained for 6~12 hours while stirring. If the holding temperature is too low (<70℃), the loading of titanium and its metal dopants is likely to decrease; if the holding time is too short, the loading of titanium and its metal dopants is also likely to decrease; if the holding temperature is too high (>90℃) or the holding time is too long, the specific surface area of ​​the product is likely to be low, thus reducing the quality of the catalyst product.

[0034] C. The solvent in the reacted material is evaporated under reduced pressure, with the pressure controlled at -70 kPa, and then dried at 100°C for 6 hours to obtain a dry solid.

[0035] In this step, after multiple experiments, it has been verified that the pressure should be controlled at -90~-70kPa and the drying temperature should be controlled at 100~120℃ for 2~6 hours.

[0036] D. The dried solid is sent to a muffle furnace and calcined at 1000℃ for 2 hours. After passivation treatment, a photocatalytic reduction catalyst is obtained.

[0037] In this step, the calcination temperature should be controlled within the range of 1000~1500℃.

[0038] Example 2 The photocatalytic reduction catalysts obtained from groups 1 to 8 above, as well as the product obtained from Comparative Example 1, were then tested to examine parameters such as titanium dioxide loading, nickel loading, cadmium loading, specific surface area (BET), and dichloroacetic acid conversion rate. The results are shown in Table 2. Figures 1-3 These are the BET analysis reports for the photocatalytic reduction catalysts obtained in groups 2, 6, and 7, respectively.

[0039] The testing methods involved are as follows: The detection methods for titanium dioxide are based on standard GB19591; the detection methods for nickel content are based on standard SH / T0346-92; the detection methods for cadmium are based on standard GB / T4372.4; and the detection methods for chloroacetic acid and dichloroacetic acid content are based on standard HG T 3271.

[0040] Table 2 Table 2 shows that the doped photocatalytic reduction catalysts obtained in groups 1, 4, and 7 have relatively higher BET values ​​and higher titanium loading, which also means that the catalysts have a larger contact area in the catalytic process, resulting in better photocatalytic effect and higher conversion rate. (See attached table.) Figures 1-3 It can also be seen that the photocatalytic reduction catalyst in group 7 has a higher BET and a better catalytic effect.

[0041] Example 3 In this embodiment, the doped photocatalytic reduction catalysts or products obtained by each implementation group in Example 1 are used in the chloroacetic acid synthesis process.

[0042] A dichloroacetic acid reduction process includes the following steps, with parameters adjusted according to the process conditions in Table 3: I. In this step, the chlorination mother liquor obtained from the chlorination of acetic acid by our company is used. Take 1000g of raw material glacial acetic acid into a 2000mL four-necked flask, add 3% acetic anhydride as catalyst, pass chlorine gas, and under the catalytic action of acetic anhydride, control the reaction temperature at 97℃ and react for 2h to obtain a chlorinated liquid containing acetic acid. The tail gas is used to recover hydrochloric acid.

[0043] Generally, the process conditions in this step are as follows: add 0.5-5% acetic anhydride as catalyst, pass chlorine gas, and under the catalytic action of acetic anhydride, the reaction temperature should be controlled at 90-105℃ for 1-3 hours to obtain a chlorinated liquid containing acetic acid, and recover hydrochloric acid from the tail gas.

[0044] II. The chlorination solution from step I was subjected to a stepped cooling process using cooling water at 60℃, 50℃, 40℃, 30℃, and 20℃, with each temperature range maintained for 2 hours to crystallize, resulting in qualified solid chloroacetic acid (content reaching 98%) and mother liquor. The dichloroacetic acid content in the mother liquor was approximately 40%. In this step, the holding time for each temperature segment should be controlled to be 1 to 6 hours. In this embodiment, considering both time cost and reaction efficiency, the holding time for each temperature segment is controlled to be 2 hours to allow crystallization.

[0045] III. Transfer the mother liquor from step II into a photocatalytic reactor, circulate hydrogen gas, and add 0.1-2% of the total material weight of doped photocatalytic reduction catalyst (hereinafter referred to as photocatalyst). Raise the temperature to 75°C (in this step, the temperature should be controlled at 70-90°C; considering reaction efficiency and production cost, this embodiment uses a more optimal holding temperature of 75°C for investigation). Irradiate with UV light while stirring. The byproduct hydrogen chloride is absorbed by water to obtain byproduct hydrochloric acid. After 12 hours of irradiation, the process is stopped, and the dichloroacetic acid content in mother liquor A is detected to have decreased to 10-20%. In this step, the illumination time should be set between 6 and 24 hours according to production needs. In this embodiment, considering both product yield and economic benefits, the illumination time is set to 12 hours.

[0046] In this step, light with a wavelength of 260-600 nm was used for heat preservation irradiation. Considering that using ultraviolet light alone would increase the oxidation reaction, and using visible light alone would result in low electron activity, this embodiment does not consider using ultraviolet or visible light alone for catalysis. The catalysis in each group of examples was carried out under the irradiation conditions shown in Table 3.

[0047] IV. The secondary chlorination solution is cooled in stages using cooling water at 60℃, 50℃, 40℃, 30℃, and 20℃, with each temperature range maintained for 1-6 hours to crystallize, yielding solid chloroacetic acid (content 98%) and secondary mother liquor. The secondary mother liquor contains approximately 20% dichloroacetic acid. The secondary mother liquor is then sent to step II for further recycling.

[0048] The yield of solid chloroacetic acid and the conversion rate of dichloroacetic acid in steps I and III of the reaction process were investigated, and the results are shown in Table 4.

[0049] Table 3 Table 4 As shown in Tables 3 and 4, the conversion rates of dichloroacetic acid obtained from groups 14 and 15 are relatively high. Comparing the same catalyst amounts of 0.5% (groups 10, 13, and 16), 1% (groups 11, 14, and 17), and 1.5% (groups 12, 15, and 18), the photocatalyst synthesized in group 7 exhibits significantly superior catalytic performance. Overall, the catalyst synthesized in group 7 has the best conversion rate. Considering the unit catalytic efficiency and overall cost, the preferred dosage is 1% from group 14. Comparing ultraviolet and visible light wavelengths: 200–500 nm (groups 10, 15, and 17), 260–600 nm (groups 12, 14, and 16), and 300–700 nm (groups 11, 13, and 18), the catalytic reduction efficiency is highest when the UV wavelength is controlled between 260–600 nm.

[0050] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications or equivalent changes made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A doped photocatalytic reduction catalyst, characterized in that, By weight percentage, it includes the following raw materials: Tetrabutyl titanate 10~20%; Nickel source 4~8%; Cadmium source 1~2%; Ethanol as a water solvent: 40-60%; Concentrated hydrochloric acid 1~10%; Diatomaceous earth 10-30%; Among them, tetrabutyl titanate, nickel source and cadmium source account for 5-30% of the total raw materials, the ratio of tetrabutyl titanate, nickel source and cadmium source is 1:0.1-0.3:0.02-0.06, and the ratio of ethanol to water in ethanol aqueous solvent is 1-5:

1.

2. The doped photocatalytic reduction catalyst according to claim 1, characterized in that: The nickel source includes nickel oxide, nickel nitrate, and nickel carbonate.

3. The doped photocatalytic reduction catalyst according to claim 1, characterized in that: The cadmium sources include cadmium oxide, cadmium nitrate, and cadmium chloride.

4. A method for preparing the doped photocatalytic reduction catalyst as described in claim 1, characterized in that, Includes the following steps: A. Take each raw material according to the formula ratio described in claim 1 for later use; B. Take tetrabutyl titanate, nickel source and cadmium source, and dissolve them in ethanol aqueous solvent. Use concentrated hydrochloric acid as catalyst, add diatomaceous earth, and mix and stir at 70~90℃ for 6~12h. C. Evaporate the solvent from the reacted material under reduced pressure and dry it at 100~120℃ for 2~6h to obtain a dry solid; D. The dry solid was calcined at 1000~1500℃ for 2h to obtain a photocatalytic reduction catalyst.

5. The method for preparing a doped photocatalytic reduction catalyst according to claim 4, characterized in that: In step C, the pressure conditions for evaporating the solvent under reduced pressure are -90 to -70 kPa.

6. The application of the doped photocatalytic reduction catalyst as described in any one of claims 1 to 5 in the chloroacetic acid synthesis process.

7. The application according to claim 6, characterized in that, Includes the following steps: I. Take acetic acid and chlorine as raw materials, and under the catalysis of acetic anhydride, control the reaction temperature at 90~105℃ to obtain a chlorinated liquid containing acetic acid; II. The chlorination solution from step I is subjected to multi-stage cooling and crystallization to obtain solid chloroacetic acid and mother liquor; Ⅲ. Take the mother liquor from step Ⅱ, add 0.1~2% of the total mass of the material to doped photocatalytic reduction catalyst, heat to 70~90℃, and irradiate with visible light or ultraviolet light for 6~24h to obtain secondary chlorination liquid; IV. The secondary chlorination solution is cooled and crystallized through multiple stages to obtain solid chloroacetic acid and secondary mother liquor. The secondary mother liquor is sent to step II for further recycling.

8. The application according to claim 7, characterized in that: In step I, the molar ratio of acetic acid to chlorine is 1:1.0~1.2, and the amount of acetic anhydride added is 0.5~5% of the total material mass.

9. The application according to claim 7, characterized in that: In steps II and IV, the multi-stage cooling crystallization operation method is to sequentially cool the mother liquor with cooling water at 60℃, 50℃, 40℃, 30℃, and 20℃, and keep each temperature range for 2 hours to allow crystals to precipitate.

10. The application according to claim 7, characterized in that: In step III, light with a wavelength of 260~700nm is selected for illumination.

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