A catalyst for low-temperature catalytic combustion of dichloromethane and its preparation method and application

Abstract

The present invention relates to a catalyst for the low-temperature catalytic combustion of dichloromethane, its preparation method, and application. The catalyst comprises a carrier zirconium dioxide and supported tungsten and chromium, wherein the tungsten and chromium are both present in the form of oxides, with the mass fractions of tungsten and chromium being 1-30wt% and 1-12wt%, respectively. Compared with the prior art, the catalyst of the present invention can effectively inhibit the chlorination reaction and has the advantages of high efficiency and stability.

Description

Technical Field

[0001] The present invention relates to a preparation method and application of a catalyst for catalytic combustion of dichloromethane, and in particular to a preparation method and application of a zirconium dioxide catalyst loaded with chromium and tungsten. Background Art

[0002] Chlorinated volatile organic compounds (CVOCs) pose serious risks to the environment and human health due to their high toxicity, high chemical stability, and low biodegradability. For example, dichloromethane, a common chlorinated alkane, can be used as a raw material, intermediate, or medium for synthetic resins, pharmaceuticals, and pesticides, and as a cleaner for electronic components, printed circuit boards, and metals. Furthermore, as a good solvent, dichloromethane is widely used in industries such as film production, organic synthesis, and paints and coatings. Therefore, given its industrial production and application, source control methods are currently difficult to implement, making it crucial to limit and treat emitted CVOCs.

[0003] Among a series of comprehensive treatment methods for CVOCs, catalytic combustion is a more mature industrial treatment method. Compared with traditional direct thermal combustion methods, it requires lower temperatures and produces fewer secondary pollutants. At the same time, its treatment efficiency for low-concentration CVOCs is higher than that of absorption and adsorption methods, so it is widely used. In the catalytic combustion process of CVOCs, the main problem faced by catalysts is chlorine poisoning and deactivation. For example, precious metal catalysts may form oxychlorine compounds or increase chlorination activity to produce polychlorinated by-products, and the presence of precious metals increases the cost of the catalyst, resulting in limited application of precious metal catalysts. Relatively speaking, transition metal catalysts usually have good redox ability and acidity, and are superior to precious metal catalysts in resistance to chlorine poisoning, so they are more concerned. But in general, no matter what kind of catalyst, a series of modifications are required to achieve high activity, high stability, and high selectivity to adapt to industrial applications.

[0004] Patent CN201710174182.8 discloses a catalyst for low-temperature catalytic combustion of chlorinated hydrocarbon compounds, which consists of a carrier nano-cerium oxide and a loaded tungsten, wherein the tungsten exists in the form of tungsten oxide, and the loading amount of the tungsten element is 1 to 20% by weight. Compared with nano-cerium oxide without tungsten loading, the catalyst has significantly improved catalytic activity, has excellent catalytic activity for chlorinated aliphatic hydrocarbons and chlorinated aromatic hydrocarbons, and has strong resistance to chlorine poisoning and long life. However, this technology does not consider the effect of water on the performance of the catalyst, and the waste gas treated in the actual industrial process often contains a large amount of water; in addition, the dispersion ability of tungsten on cerium oxide is poor, and under the condition of low surface tungsten atomic density (greater than 4.5W atom / nm 2, that is, 4.5 tungsten atoms per square nanometer, which corresponds to a loading of 8wt% in the above patent) will form crystalline tungsten trioxide (WO3). Therefore, when the catalyst reacts under high temperature conditions, the tungsten on the surface easily agglomerates to form WO3, resulting in a decrease in activity. Summary of the Invention

[0005] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and provide a catalyst for the low-temperature catalytic combustion of dichloromethane that is efficient, stable and can effectively inhibit chlorination reaction, as well as its preparation method and application.

[0006] The object of the present invention can be achieved by the following technical solution: a catalyst for low-temperature catalytic combustion of dichloromethane, consisting of a carrier zirconium dioxide and loaded tungsten and chromium, wherein the tungsten and chromium are both in the form of oxides, and the mass fractions of the tungsten element and the chromium element are 1-30wt% and 1-12wt%, respectively.

[0007] As a further improvement, the optimal mass fraction of the loaded chromium element is 4-8%, and the optimal mass fraction of the loaded tungsten element is 8-15%.

[0008] The present invention also provides a method for preparing a catalyst for low-temperature catalytic combustion of dichloromethane, comprising the following steps:

[0009] A. Preparation of the precursor of the zirconium dioxide support by precipitation-hydrothermal method;

[0010] B. According to the chromium loading, the corresponding volume of the aqueous solution of the chromium precursor is impregnated onto the precursor of the zirconium dioxide support prepared in step A, stirred evenly, allowed to stand for 4 to 8 hours, and then dried at 110 to 120° C., and then calcined at 450 to 650° C. for 2 to 4 hours (preferably, the calcination temperature is 450° C. and the calcination time is 4 hours) to obtain an intermediate catalyst;

[0011] C. According to the tungsten loading amount, the corresponding volume of the aqueous solution of the tungsten precursor is impregnated onto the intermediate catalyst prepared in step B, stirred evenly, allowed to stand for 4 to 8 hours, and then dried at 110 to 120°C, and then calcined at 450 to 650°C for 2 to 4 hours (preferably, the calcination temperature is 450°C and the calcination time is 4 hours) to obtain the catalyst.

[0012] Furthermore, the precipitation-hydrothermal method described in step A is specifically as follows: dissolving a soluble zirconium salt in water, adjusting the pH value to 9-10 (preferably by slowly adding ammonia water), stirring for 1-3 hours, standing and aging for 2-4 hours, then filtering and washing the precipitate, and re-dispersing the obtained filter cake in water, and then transferring it to an autoclave with a polytetrafluoroethylene liner, and hydrothermally treating it at 160-200 ° C for 6-8 hours (preferably the hydrothermal treatment temperature is 180 ° C for 6 hours), cooling to room temperature, filtering and washing the precipitate, and drying it at 110-120 ° C to obtain a precursor of the zirconium dioxide carrier.

[0013] Furthermore, the chromium precursor in step B is a soluble chromium salt, including chromium nitrate, chromium chloride, etc., preferably chromium nitrate, and the concentration of chromium element in the chromium precursor aqueous solution is 30-40 g / L.

[0014] Furthermore, the tungsten precursor in step C is a soluble tungsten salt, preferably ammonium metatungstate, and the concentration of tungsten element in the aqueous solution of the tungsten precursor is 80-100 g / L.

[0015] The present invention also provides an application of the catalyst, wherein the catalyst is applied to the low-temperature catalytic combustion of dichloromethane.

[0016] Furthermore, the reaction temperature of the catalyst catalyzing dichloromethane is 100-400°C.

[0017] Furthermore, the water vapor content in the reaction atmosphere of the catalyst is 0 to 50,000 ppm, preferably 5,000 to 25,000 ppm.

[0018] Furthermore, the catalyst catalyzes the reaction of dichloromethane at a pressure of 0.1-0.5 MPa, a dichloromethane concentration of 100-5000 ppm, an oxygen concentration of 0-10 vol%, and a space velocity of 10000-100000 / hour.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The catalyst carrier of this invention utilizes ZrO2, a material with excellent physical and chemical stability. ZrO2 exhibits high temperature resistance, corrosion resistance, wear resistance, and high hardness, and has been widely used in structural ceramics, fuel cells, sensors, thermal insulation materials, and other fields. Tungsten and chromium are selected as the active components for the catalyst. Tungsten improves the catalyst's acidity and water resistance, enhances hydrogen chloride selectivity, and inhibits the production of polychlorinated byproducts and oxychlorides. The interaction between tungsten and zirconium dioxide further increases the dispersion of surface tungsten atoms and the carrier's resistance to sintering. Chromium rapidly oxidizes and decomposes reaction intermediates, thereby reducing carbon deposits and carbon monoxide formation, and protecting tungsten from chlorine poisoning.

[0021] The catalyst preparation method of the present invention adopts a precipitation-hydrothermal method and an impregnation method, has a simple process, and uses inexpensive zirconium nitrate, chromium nitrate and ammonium metatungstate as raw materials, which is low in cost.

[0022] In actual experimental testing, the catalyst catalyzes the oxidation of dichloromethane at low temperatures, with carbon dioxide and hydrogen chloride as the primary products, with no other polychlorinated byproducts. It exhibits strong resistance to chlorine and water, a long lifespan, and high thermal stability. Furthermore, in the presence of water (regardless of the presence of oxygen), it achieves efficient conversion of dichloromethane and high selectivity for carbon dioxide and hydrogen chloride, making it suitable for industrial waste gas treatment under complex conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the test result of water resistance of the catalyst. DETAILED DESCRIPTION

[0024] The present invention is described in detail below with reference to specific embodiments.

[0025] Examples 1 to 5

[0026] A catalyst for low-temperature catalytic combustion of dichloromethane is prepared by the following method:

[0027] (1) Preparation of carrier

[0028] Dissolve 20g of anhydrous zirconium nitrate in 200mL of deionized water and stir vigorously for half an hour. Then slowly add ammonia water to adjust the pH to 9-10. After standing at room temperature for 2 hours, filter and wash the precipitate until the filtrate is neutral. The filter cake is then redispersed in 60mL of deionized water and transferred to an autoclave with a polytetrafluoroethylene lining. Hydrothermally treat at 180°C for 6 hours. After cooling to room temperature, filter and wash the precipitate, dry it at 110°C for 12 hours, and then calcine it in a muffle furnace at 450°C for 4 hours to obtain a zirconium dioxide supported catalyst, labeled as ZrO2.

[0029] (2) Preparation of tungsten and chromium catalysts supported on zirconium dioxide

[0030] Chromium nitrate was dissolved in water to prepare an aqueous solution with a chromium content of 40 g / L. The aqueous chromium nitrate solution shown in Table 1 was impregnated onto 2 g of a zirconium dioxide carrier, stirred evenly, allowed to stand at room temperature for 6 hours, dried in an oven at 110°C for 12 hours, and then calcined in a muffle furnace at 450°C for 4 hours to obtain an intermediate catalyst. Ammonium metatungstate was prepared into an aqueous solution with a tungsten content of 100 g / L. The aqueous ammonium metatungstate solution shown in Table 1 was impregnated onto the corresponding intermediate catalyst, stirred evenly, allowed to stand at room temperature for 6 hours, dried in an oven at 110°C for 12 hours, and then calcined in a muffle furnace at 450°C for 4 hours to obtain a final catalyst.

[0031] The tungsten and chromium loading mass fractions in Example 1 are 2% and 4% respectively, marked as 2W / 4Cr / ZrO2; the tungsten and chromium loading mass fractions in Example 2 are 4% and 4% respectively, marked as 4W / 4Cr / ZrO2; the tungsten and chromium loading mass fractions in Example 3 are 8% and 4% respectively, marked as 8W / 4Cr / ZrO2; the tungsten and chromium loading mass fractions in Example 4 are 15% and 4% respectively, marked as 15W / 4Cr / ZrO2; the tungsten and chromium loading mass fractions in Example 5 are 30% and 4% respectively, marked as 30W / 4Cr / ZrO2.

[0032] Comparative Example 1

[0033] Preparation of zirconium dioxide support

[0034] Dissolve 20g of anhydrous zirconium nitrate in 200mL of deionized water and stir vigorously for half an hour. Then slowly add ammonia water to adjust the pH to 9-10. After standing at room temperature for 2 hours, filter and wash the precipitate until the filtrate is neutral. The filter cake is then redispersed in 60mL of deionized water and transferred to an autoclave with a polytetrafluoroethylene lining. Hydrothermally treat at 180°C for 6 hours. After cooling to room temperature, filter and wash the precipitate, dry it at 110°C for 12 hours, and then calcine it in a muffle furnace at 450°C for 4 hours to obtain a zirconium dioxide supported catalyst, labeled as ZrO2.

[0035] Comparative Example 2 Preparation of Cerium Tungsten Catalyst

[0036] The catalyst prepared from the best example in CN201710174182.8 was used as comparative example 2, marked as 8W / CeO2.

[0037] Table 1 Tungsten and chromium loadings and dichloromethane catalytic combustion test results for Examples 1 to 5 and Comparative Examples 1 and 2

[0038]

[0039] Example 6: Catalytic combustion experiments with different catalyst loadings

[0040] Low-temperature catalytic combustion experiments of dichloromethane were carried out using the catalysts of Examples 1 to 5 and Comparative Examples 1 and 2. All experiments were carried out in a fixed-bed microreactor with a catalyst dosage of 200 mg. A K-type thermocouple was used to automatically control the temperature, and a microinjection pump was used to inject dichloromethane into the vaporization chamber, and then mixed with dry air and high-purity nitrogen and introduced into the reactor for catalytic combustion. A mass flow meter was used to control the total gas flow rate to 100 mL / min, the concentration of dichloromethane to 1000 ppm, the oxygen concentration to 10 vol%, and the rest to nitrogen. The amount of waste gas processed per gram of catalyst per hour was 30 L, and the reaction pressure was normal pressure. The relationship between the conversion rate of dichloromethane and the reaction temperature is shown in Table 1. T in the table is 50％ 、T 90％ The reaction temperatures are required for the conversion rates to reach 50% and 90%, respectively. Product analysis shows that the main reaction products are carbon dioxide, hydrogen chloride and a small amount of chlorine or methyl chloride.

[0041] The catalytic activity of Examples 1 to 5 was significantly improved compared to that of Comparative Examples 1 and 2. The specific activity order is: 15W / 4Cr / ZrO2 > 30W / 4Cr / ZrO2 > 8W / 4Cr / ZrO2 > 4W / 4Cr / ZrO2 > 8W / CeO2 > 2W / 4Cr / ZrO2 > ZrO2. From the perspective of surface tungsten atomic density, the tungsten dispersion on the surface of ZrO2 is higher than that of CeO2 under the same loading conditions, which can effectively avoid the tungsten in the reaction process.

[0042] Example 7 Catalytic combustion experiment of dichloromethane on catalysts calcined at different temperatures

[0043] According to the method of Example 6, the calcination temperature of the catalyst was changed to 750° C., and then the catalytic combustion experiments of dichloromethane were carried out respectively. The other reaction conditions remained unchanged. The experimental results are shown in Table 2.

[0044] Table 2 Results of dichloromethane catalytic combustion experiments on catalysts calcined at different temperatures

[0045]

[0046] As shown in Table 2, after calcination at 750°C, the activity of the W and Cr dual-component loaded catalyst decreases relatively little, and it has better thermal stability.

[0047] Example 8 Catalytic combustion experiment of dichloromethane under water conditions

[0048] According to the method of Example 6, 50,000 ppm of water vapor was added to the reaction atmosphere, and catalytic combustion experiments were carried out on different catalysts. The other reaction conditions remained unchanged. The experimental results are shown in Table 3.

[0049] Table 3 Results of catalytic combustion experiments of dichloromethane on different catalysts under water conditions

[0050]

[0051]

[0052] As shown in Table 3, under the condition of high water content in the carrier gas (50,000 ppm, volume fraction of 5%), the W and Cr dual-component loaded catalyst exhibits good water resistance and small activity loss, which is significantly better than Comparative Example 2 and has good industrial application prospects.

[0053] Example 9 Water resistance test of catalyst

[0054] According to the method of Example 6, water resistance test was carried out on Comparative Example 2 and Example 4, the reaction temperature was controlled to 300 ° C, the other reaction conditions remained unchanged, the water content in the carrier gas was changed and the change in dichloromethane conversion was observed. The test results were as follows: Figure 1 shown.

[0055] Depend on Figure 1 As can be seen, when the water content in the carrier gas was first increased and then decreased to the original levels (50,000 ppm and 15,000 ppm), Comparative Example 2 was unable to recover its initial activity, indicating that the inhibitory effect of water on the catalyst is irreversible. In contrast, Example 4 maintained essentially stable activity before and after the change in water content, demonstrating better water resistance.

[0056] Example 10 Catalytic combustion stability test of the catalyst

[0057] According to the method of Example 6, combustion experiments were carried out on different catalysts, with the reaction temperatures controlled at 250 and 300° C., respectively, while the other reaction conditions remained unchanged. The catalytic combustion stability test results of the catalysts are shown in Table 4.

[0058] Table 4 Catalytic combustion stability test results of catalysts

[0059]

[0060]

[0061] As shown in Table 4, compared to Comparative Examples 1 and 2, each Example exhibited superior resistance to chlorine poisoning and stability at various temperatures. Specifically, at a reaction temperature of 250°C, the dichloromethane conversion rate in Example 4 remained above 90% over a 20-hour period. Product analysis indicated that the primary products in each Example were carbon dioxide, hydrogen chloride, and chlorine, with no secondary polluting polychlorinated products formed.

[0062] The above describes the basic principles, main features, and advantages of the present invention. Those skilled in the art will appreciate that the present invention is not limited to the foregoing embodiments. The foregoing embodiments and descriptions merely illustrate the principles of the present invention. Various changes and modifications are possible without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. Application of a catalyst for low-temperature catalytic combustion of dichloromethane, characterized in that: The catalyst is applied to the low-temperature catalytic combustion of dichloromethane. The catalyst is composed of a carrier zirconium dioxide and supported tungsten and chromium, wherein the tungsten and chromium are both present in the form of oxides, and the mass fractions of the tungsten element and the chromium element are 1-30wt% and 1-12wt%, respectively. The reaction temperature of the catalyst for catalyzing dichloromethane is 100-400°C. The catalyst is prepared by the following method: A. Preparation of the zirconium dioxide support precursor by precipitation-hydrothermal method; B. Based on the chromium loading, impregnate the zirconium dioxide support precursor prepared in step A with a corresponding volume of the aqueous solution of the chromium precursor. Stir evenly, let it stand for 4-8 hours, then dry it at 110-120°C. Calcinate it at 450-650°C for 2-4 hours to obtain the intermediate catalyst. C. Based on the desired tungsten loading, impregnate the intermediate catalyst prepared in step B with a corresponding volume of the aqueous solution of the tungsten precursor. Stir evenly, let it stand for 4-8 hours, then dry it at 110-120°C. Calcinate it at 450-650°C for 2-4 hours to obtain the catalyst.

2. The use of a catalyst for low-temperature catalytic combustion of dichloromethane according to claim 1, characterized in that: The precipitation-hydrothermal method described in step A is specifically as follows: dissolving a soluble zirconium salt in water, adjusting the pH value to 9-10, stirring for 1-3 hours, standing and aging for 2-4 hours, then filtering and washing the precipitate, and re-dispersing the obtained filter cake in water, followed by hydrothermal treatment at 160-200 ° C for 6-8 hours, cooling to room temperature, filtering and washing the precipitate, and drying at 110-120 ° C to obtain a precursor of the zirconium dioxide support.

3. The use of a catalyst for low-temperature catalytic combustion of dichloromethane according to claim 2, characterized in that: Ammonia was used to adjust the pH value.

4. The use of a catalyst for low-temperature catalytic combustion of dichloromethane according to claim 1, characterized in that: The chromium precursor described in step B is a soluble chromium salt, and the concentration of chromium element in the chromium precursor aqueous solution is 30-40 g / L.

5. The use of a catalyst for low-temperature catalytic combustion of dichloromethane according to claim 1, characterized in that: The tungsten precursor in step C is a soluble tungsten salt, and the concentration of tungsten element in the tungsten precursor aqueous solution is 80-100 g / L.

6. Use of a catalyst for low-temperature catalytic combustion of dichloromethane according to claim 1, characterized in that: The reaction temperature of the catalyst catalyzing dichloromethane is 100-400°C.

7. Use of a catalyst for low-temperature catalytic combustion of dichloromethane according to claim 1, characterized in that: The water vapor content in the reaction atmosphere of the catalyst is 0-50000 ppm.

8. Use of a catalyst for low-temperature catalytic combustion of dichloromethane according to claim 1, characterized in that: The catalyst catalyzes the reaction of dichloromethane at a pressure of 0.1-0.5 MPa, a dichloromethane concentration of 100-5000 ppm, an oxygen concentration of 0-10 vol%, and a space velocity of 10000-100000 / hour.

Images