Catalyst for treating cvocs catalytic combustion, and preparation method and application thereof

Abstract

The application discloses a catalyst for treating catalytic combustion of CVOCs and a preparation method and application thereof. The preparation method comprises the following steps: (1) impregnating cerium nitrate and trimethyl phosphate on a carrier, drying, and calcining at 600-800 DEG C to form a modified carrier containing a cerium phosphate crystal phase; and (2) impregnating active metal ruthenium on the modified carrier, drying, and calcining to obtain the catalyst for treating catalytic combustion of CVOCs. The catalyst can be used for catalytic combustion degradation of dichloromethane, chlorobenzene, chloroethylene, dichloroethane, dichloroethylene, oxygen-containing chloropropane and other CVOCs. For catalytic combustion degradation of CVOCs, the catalyst can exhibit high activity, high chlorine resistance, low selectivity of polychlorinated by-products and high thermal stability, and has certain industrial application prospect.

Description

Technical Field

[0001] This invention relates to the field of industrial waste gas treatment technology, specifically to a highly active, chlorine-poison-resistant, and high-temperature stable chlorine-containing VOCs catalytic combustion catalyst, its preparation method, and its application. Background Technology

[0002] Chlorine-containing volatile organic compounds (CVOCs) have excellent solubility and inertness, and are widely used in pharmaceuticals, chemical industries, resin industries, petroleum industries, coatings, electronics, and other industries. However, due to the high electronegativity of chlorine (Cl) in CVOCs, they are difficult to degrade in nature, exhibiting high toxicity and easy accumulation in living organisms. When released into the atmosphere, they cause serious harm to the ecological environment and human health.

[0003] Given that CVOCs are not entirely replaceable in production, their emission during the production process is unavoidable. Eliminating CVOCs through back-end treatment is the only feasible method.

[0004] Among numerous CVOCs treatment technologies, catalytic combustion stands out for its advantages, including low operating temperature, high efficiency, wide applicability, and lack of secondary pollution, making it the most widely used and efficient treatment technology. Developing highly active, chlorine-poison-resistant, and highly stable catalysts is crucial for the industrial application of this technology.

[0005] Chinese patent CN110302773B discloses a catalyst for the catalytic combustion of chlorine-containing volatile organic compounds, its preparation method, and its application. This catalyst involves loading cerium oxide onto titanium dioxide-modified fly ash-based zeolite. The preparation method is low-cost, simple, highly resistant to chlorine poisoning, and can efficiently and stably remove chlorine-containing VOCs.

[0006] Chinese patent CN110624549B discloses a catalyst for treating CVOC by catalytic combustion and its preparation method. The catalyst is obtained by using acidic salts of transition metals as raw materials and by precipitation and high-temperature activation with hydrogen. It has the characteristics of simple preparation process, low cost, easy control of preparation conditions and synthesis.

[0007] The catalysts mentioned in the above patent literature exhibit certain activity and stability for chlorine-containing VOCs. However, practical industrial applications place higher demands on the catalysts' low-temperature activity, resistance to chlorine poisoning, product selectivity, and high-temperature stability. Therefore, there is a need to develop catalysts with higher activity, higher stability, higher product selectivity, and higher thermal stability for the catalytic degradation of chlorine-containing VOCs. Summary of the Invention

[0008] To address the aforementioned technical problems and shortcomings in the field, this invention provides a catalyst for treating the catalytic combustion of CVOCs, its preparation method, and its application.

[0009] The catalyst of this invention employs an impregnation method to load cerium nitrate and trimethyl phosphate onto a support, followed by medium-high temperature calcination to form the desired cerium phosphate crystalline phase. Then, ruthenium, a noble metal, is loaded onto the modified support through impregnation (e.g., equal-volume impregnation). The cerium phosphate formed according to this method exhibits strong chemical stability and will not be chlorinated during the reaction, thus improving the catalyst's resistance to chlorine poisoning. Simultaneously, its strong acidity inhibits the adsorption of inorganic chlorine on the catalyst surface during the reaction, thereby preventing chlorine poisoning. Furthermore, the loading of ruthenium onto the cerium phosphate formed by this method creates a strong metal-support interaction, preventing particle aggregation of the noble metal under high-temperature conditions and resulting in high thermal stability of the catalyst.

[0010] The catalyst involved in this invention exhibits high activity, high selectivity, high chlorine resistance and high temperature stability for common chlorine-containing VOCs such as dichloromethane, chlorobenzene, vinyl chloride, dichloroethane, dichloroethylene, and oxychloropropane, and has certain industrial application prospects.

[0011] The specific technical solution is as follows:

[0012] [1] A method for preparing a catalyst for treating the catalytic combustion of CVOCs, comprising the steps of:

[0013] (1) Cerium nitrate and trimethyl phosphate are impregnated onto a support, dried, and calcined at 600-800℃ (e.g., 650℃) to form a modified support containing cerium phosphate crystal phase;

[0014] (2) The active metal ruthenium is impregnated and loaded onto the modified support, and then dried and calcined to obtain the catalyst for treating CVOCs catalytic combustion.

[0015] The preparation method of this invention employs a two-step impregnation and loading approach. First, cerium nitrate and trimethyl phosphate are impregnated and calcined at 600–800°C to form a modified support containing the desired cerium phosphate crystalline phase. Then, active metal ruthenium is impregnated and loaded onto the modified support and calcined to obtain the catalyst product. This two-step impregnation and loading method allows for high dispersion of cerium phosphate, and the desired cerium phosphate crystalline phase structure can be obtained by controlling the calcination temperature. Furthermore, it maximizes the loading of active metal ruthenium onto the cerium phosphate crystalline phase already uniformly distributed on the support surface, enhancing the interaction between the active metal ruthenium and the cerium phosphate crystalline phase. Compared to a direct one-step simultaneous impregnation and loading of cerium phosphate and ruthenium, this method offers numerous advantages and advancements.

[0016] In step (1), the support can be placed in a deionized aqueous solution of cerium nitrate and trimethyl phosphate, and then stirred, dried and calcined to form a modified support containing cerium phosphate crystal phase.

[0017] In step (1), the molar ratio of Ce in cerium nitrate to P in trimethyl phosphate is preferably 1:0.25-1, and more preferably 1:0.5-1. This makes it easier to form the cerium phosphate phase required by the present invention, and the slight excess of cerium ensures that P exists in the cerium phosphate phase required by the present invention. If P exists in other forms, it will inhibit the catalyst activity. In addition, the cerium oxide formed by the excess cerium can also provide some catalytic activity, but since cerium oxide is unstable at high temperatures, cerium should not be in excessive amounts.

[0018] In step (1), the support may include at least one of alumina (e.g., γ-Al₂O₃), silicon dioxide, cerium-zirconium solid solution, and magnesium aluminum spinel. Further, based on the total molar percentage of cerium and zirconium in the cerium-zirconium solid solution being 100%, the molar fraction of zirconium in the cerium-zirconium solid solution may be 25%–35%, preferably 30%, and the molar fraction of cerium may be 65%–75%, preferably 70%.

[0019] In step (1), the mass ratio of Ce in cerium nitrate to the support is preferably 5-20:100, and more preferably 5-10:100, which is beneficial for improving catalyst activity and maintaining a high specific surface area of ​​the catalyst. Excessive Ce loading will reduce the specific surface area of ​​the catalyst, leading to a decrease in catalyst activity.

[0020] In a preferred embodiment, the mass ratio of Ce in cerium nitrate to the support is 10:100, and the molar ratio of Ce in cerium nitrate to P in trimethyl phosphate is 1:0.5. Under these conditions, the catalyst obtained exhibits the best performance in treating the catalytic combustion of CVOCs.

[0021] In step (1), the roasting time can be 3.5 to 4.5 hours, for example, 4 hours.

[0022] In step (2), the active metal ruthenium can be impregnated onto the modified support using an equal-volume impregnation method.

[0023] In step (2), at least one of ruthenium chloride and ruthenium nitrate can be used as the impregnation precursor.

[0024] In step (2), the mass ratio of the impregnated active metal ruthenium to the modified carrier can be 0.5 to 5:100, for example 1:100, 1.5:100, etc.

[0025] In step (2), the roasting temperature can be 440-460°C, for example 450°C.

[0026] In step (2), the roasting time is 3.5 to 4.5 hours, for example, 4 hours.

[0027] In step (2), the heating rate of the roasting can be 1 to 10 °C / min, for example, 5 °C / min.

[0028] [2] A catalyst for treating CVOCs catalytic combustion prepared according to the preparation method described in [1].

[0029] [3] Application of the catalyst described in [2] in the catalytic combustion of CVOCs.

[0030] [4] A method for treating CVOCs by catalytic combustion using the catalyst described in [2].

[0031] Compared with the prior art, the beneficial effects of this invention are as follows:

[0032] The catalyst of this invention can be used for the catalytic combustion degradation of CVOCs such as dichloromethane, chlorobenzene, vinyl chloride, dichloroethane, dichloroethylene, and oxychloropropane. For the catalytic combustion degradation of CVOCs, the catalyst of this invention exhibits high activity, high chlorine resistance, low selectivity for polychlorinated byproducts, and thermal stability, and has certain industrial application prospects. Detailed Implementation

[0033] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Operating methods not specifically specified in the following embodiments are generally performed under conventional conditions or as recommended by the manufacturer. Unless otherwise specified, the materials used in the following examples are commercially available or obtained according to existing technology. In the following examples, the cerium-zirconium solid solution used is a commercially available product, wherein the molar percentage of zirconium oxide is 30% and the molar percentage of cerium oxide is 70%.

[0034] Example 1:

[0035] 1) Weigh 1.55g of cerium nitrate hexahydrate and 0.5g of trimethyl phosphate and dissolve them in a beaker containing 50g of deionized water. After stirring for 30min, add 10g of γ-Al₂O₃ to the solution and continue stirring for 1h. Then place the beaker in an 85℃ water bath and heat while stirring for 3h. Next, dry it in an oven at 120℃ for 6h. Finally, calcine it in a muffle furnace at 650℃ for 4h to obtain the modified support. The room temperature rate of the muffle furnace was 5℃ / min.

[0036] 2) Weigh 0.5 g of a 10 wt% ruthenium nitrate solution and dissolve it in 2 g of deionized water. Weigh 5 g of the modified support and add the solution dropwise to the surface of the modified support while stirring until the solution is completely added. After standing for 6 hours, dry at 120℃ for 6 hours. Finally, calcine at 450℃ for 4 hours to obtain the catalyst.

[0037] Example 2:

[0038] The only difference from Example 1 is that 10g of magnesium aluminum spinel is used instead of 10g of γ-Al2O3, and all other aspects are the same, resulting in a catalyst.

[0039] Example 3:

[0040] The only difference from Example 1 is that 10g of cerium-zirconium solid solution was used instead of 10g of γ-Al2O3; all other aspects are the same, and a catalyst was obtained.

[0041] Example 4:

[0042] The only difference from Example 3 was that the amount of cerium nitrate hexahydrate was changed to 3.10 g, and all other aspects were the same, resulting in a catalyst.

[0043] Example 5:

[0044] The only difference from Example 4 was that the amount of trimethyl phosphate was changed to 1.0 g, and all other aspects were the same, resulting in a catalyst.

[0045] Example 6:

[0046] The only difference from Example 5 was that the amount of ruthenium nitrate solution was changed to 0.75g, and all other aspects were the same, resulting in a catalyst.

[0047] Comparative Example 1:

[0048] 0.5 g of a 10 wt% ruthenium nitrate solution was dissolved in 2 g of deionized water. 5 g of γ-Al₂O₃ support was weighed, and the solution was added dropwise to the surface of the support while stirring continuously until the solution was completely added. After standing for 6 hours, the solution was dried at 120 °C for 6 hours. Finally, it was calcined at 450 °C for 4 hours to obtain the catalyst.

[0049] Comparative Example 2:

[0050] The only difference from Comparative Example 1 was that the support was changed to 5g of cerium-zirconium solid solution; all other aspects were the same, and a catalyst was obtained.

[0051] Comparative Example 3:

[0052] The only difference from Example 3 is that the calcination temperature in 1) was changed from 650°C to 400°C, and all other conditions were the same, resulting in a catalyst.

[0053] Powder catalyst activity evaluation:

[0054] The catalysts described in Examples 1-6 and Comparative Examples 1-3 were evaluated for their activity in the catalytic combustion of dichloromethane in a fixed-bed reactor. 200 mg of 40-60 mesh powdered catalyst (CAT) was weighed into the fixed-bed reactor, and air was introduced at a flow rate of 44.4 mL / min and dichloromethane at a flow rate of 22.2 mL / min with a concentration of 3000 mg / m³. 3 The mixture of gases. The concentration of dichloromethane in the reactor is 1000 mg / m³. 3 The total mass hourly space velocity (MHSV) was 20000 mL / (h·g cat). The concentration of dichloromethane was determined by gas chromatography. The concentration of dichloromethane in the reactor tail gas was measured under different temperature conditions using a programmed temperature rise method. The conversion rate of dichloromethane was calculated, and the temperature at which the dichloromethane conversion rate reached 90% was recorded as T. 90 Simultaneously test T 90 .

[0055] The evaluation results of the catalyst are shown in Table 1.

[0056] Table 1

[0057] catalyst <![CDATA[T 90 (℃)]]> Example 1 270.6 Example 2 272.4 Example 3 268.6 Example 4 265.1 Example 5 268.3 Example 6 260.2 Comparative Example 1 362.5 Comparative Example 2 332.6 Comparative Example 3 322.6

[0058] Selectivity of polychlorinated byproducts:

[0059] Following the activity evaluation experimental conditions described above, the selectivity of the catalysts involved in Examples 1-6 and Comparative Examples 1-3 to polychlorinated byproducts was tested at 300°C. The selectivity results are shown in Table 2 below.

[0060] Table 2

[0061] catalyst Selectivity of polychlorinated byproducts (%) Example 1 ≤0.1 Example 2 ≤0.1 Example 3 ≤0.1 Example 4 ≤0.1 Example 5 ≤0.1 Example 6 ≤0.1 Comparative Example 1 6.0 Comparative Example 2 5.4 Comparative Example 3 3.6

[0062] Catalyst thermal stability test:

[0063] The powder catalysts involved in Examples 1-6 and Comparative Examples 1-3 were aged in a muffle furnace at 700°C for 10 hours, and then removed. The catalytic activity of the catalysts for dichloromethane was evaluated under the same activity evaluation conditions as described above. The catalyst activity after high-temperature treatment is shown in Table 3.

[0064] Table 3

[0065] catalyst <![CDATA[T 90 (℃)]]> Example 1 273.6 Example 2 275.4 Example 3 272.6 Example 4 268.1 Example 5 273.3 Example 6 266.2 Comparative Example 1 410.5 Comparative Example 2 376.5 Comparative Example 3 362.5

[0066] Catalyst stability test:

[0067] Weigh 200 mg of the 40-60 mesh powdered catalyst from Example 1 into a fixed-bed reactor. Introduce air at a flow rate of 44.4 mL / min and dichloromethane at a flow rate of 22.2 mL / min, with a concentration of 3000 mg / m³. 3 The mixture of gases. The concentration of dichloromethane in the reactor is 1000 mg / m³. 3 The total mass hourly space velocity (MHSV) was 20,000 ml / (h·g cat). The reaction was carried out continuously at 280 °C for 100 h. The catalyst activity at different reaction times was recorded, and the corresponding results are shown in Table 4.

[0068] Table 4

[0069] Reaction time (h) Dichloromethane conversion rate (%) 20 95.3 40 95.2 60 95.2 80 95.1 100 95.2 120 95.1 140 95.0 160 95.2 180 95.1 200 95.1

[0070] As can be seen from Tables 1 and 2, the catalysts in the embodiments of the present invention exhibit higher activity compared to the comparative examples. Furthermore, the catalysts of the present invention are significantly superior to the comparative examples in suppressing more toxic polychlorinated byproducts due to the formation of the desired cerium phosphate crystal phase.

[0071] As can be seen from Table 3, the catalyst involved in this invention showed no significant decrease in activity after aging at 700℃, while the comparative example showed a significant decrease in activity.

[0072] The data in Table 4 show that the catalyst exhibits high stability during a continuous reaction at 280℃ for 200 hours.

[0073] Furthermore, it should be understood that after reading the above description of the present invention, those skilled in the art can make various alterations or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims.

Claims

1. The application of a catalyst for treating CVOCs catalytic combustion in the treatment of CVOCs catalytic combustion, characterized in that, The method for preparing the catalyst includes the following steps: (1) Cerium nitrate and trimethyl phosphate are impregnated onto a support, dried, and calcined at 600~800℃ to form a modified support containing cerium phosphate crystal phase; the support is a cerium-zirconium solid solution; based on the total molar amount of cerium and zirconium in the cerium-zirconium solid solution being 100%, the molar fraction of zirconium in the cerium-zirconium solid solution is 25%~35%, and the molar fraction of cerium is 65%~75%; the mass ratio of Ce in cerium nitrate to the support is 5:100; (2) The active metal ruthenium is impregnated and loaded onto the modified support, and then dried and calcined to obtain the catalyst for treating CVOCs catalytic combustion.

2. The application according to claim 1, characterized in that, In step (1), the molar ratio of Ce in cerium nitrate to P in trimethyl phosphate is 1:0.25~1; In step (1), the calcination holding time is 3.5 to 4.5 hours, and the calcination heating rate is 1 to 10 °C / min.

3. The application according to claim 1, characterized in that, In step (2), active metal ruthenium is impregnated onto the modified support using an equal-volume impregnation method, wherein at least one of ruthenium chloride and ruthenium nitrate is used as the impregnation precursor.

4. The application according to claim 1, characterized in that, In step (2), the mass ratio of the impregnated active metal ruthenium to the modified carrier is 0.5~5:

100.

5. The application according to claim 1, characterized in that, In step (2), the roasting temperature is 440~460℃ and the roasting time is 3.5~4.5 hours.