High-water-resistance catalyst for spraying exhaust gas VOCs (Volatile Organic Compounds) and preparation method thereof

Abstract

The invention discloses a high-water-resistance catalyst for spraying exhaust gas VOCs (volatile organic compounds). The catalyst comprises the following active components: CeO2 and Cr2O3, the carrier of the catalyst comprises the following raw materials in percentage by weight: 15 to 35 percent of SiO2, 18 to 32 percent of Al2O3, 8 to 15 percent of MgO, 5 to 8 percent of Fe2O3, 5 to 10 percent of CaO, 2 to 5 percent of Na2O, 2 to 5 percent of K2O, 8 to 12 percent of CO2 and the balance of H2O. The invention further provides a preparation method of the high-water-resistance catalyst for spraying the VOCs in the waste gas. The preparation method comprises the steps of carrier preparation, carrier pretreatment, active component coating and catalyst preparation. According to the present invention, the active components are subjected to the impregnation method, such that the water resistance of the active components is improved, the selective adsorption performance of the catalyst on the VOCs component is enhanced through the nano-scale micropores so as to improve the catalytic conversion efficiency of the VOCs, the chromium and the transition metal cerium are adopted as the active components, the raw materials are easily available, the preparation cost of the catalyst is reduced, and the good application prospect is provided.

Description

Technical Field

[0001] The invention relates to the technical field of spraying waste gas treatment, and in particular to a highly water-resistant catalyst for spraying waste gas VOCs and a preparation method thereof. Background Art

[0002] Industrial spraying operations produce a large number of VOCs containing complex components such as alkanes, alkenes, aromatic hydrocarbons, and halogenated hydrocarbons. These VOCs are easily decomposed in the environment, causing air pollution, such as ozone (O3) generation and PM2.5 pollution. Some VOCs are highly toxic and have special odors, which can easily cause serious harm to human skin, blood, respiratory system, and nervous system.

[0003] In the existing technology, the high cost of precious metal catalysts limits their widespread application, while transition metal catalysts are gradually becoming an alternative due to their abundant resources, low cost and good water resistance. However, how to further improve the water resistance and catalytic stability of the catalyst, as well as reduce the cost, is still a technical challenge facing the treatment of VOCs in industrial coatings. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a highly water-resistant catalyst for spraying exhaust gas VOCs and a preparation method thereof.

[0005] In order to have a basic understanding of some aspects of the disclosed embodiments, a brief summary is given below. This summary is not intended to be a general review, nor is it intended to identify key / important components or to delineate the scope of protection of these embodiments. Its only purpose is to present some concepts in a simple form as a preface to the detailed description that follows.

[0006] The present invention adopts the following technical solution:

[0007] The present invention provides a highly water-resistant catalyst for spraying waste gas VOCs, wherein the spraying waste gas is a waste gas containing at least alkanes, olefins, acetone, isopropanol, benzene series, ethyl acetate, dichloromethane and dichloroethane;

[0008] The active components of the catalyst are: CeO2 and Cr2O3; wherein the molar ratio of CeO2 to Cr2O3 is 4:1-2:1.

[0009] Furthermore, the catalyst carrier is honeycomb ceramic.

[0010] Furthermore, by weight percentage: the raw material of the catalyst carrier contains 15-35% SiO2, 18-32% Al2O3, 8-15% MgO, 5-8% Fe2O3, 5-10% CaO, 2-5% Na2O, 2-5% K2O, 8-12% CO2, and the balance is H2O.

[0011] Furthermore, the catalyst carrier is a honeycomb ceramic having a chemical composition of 32.5% SiO2, 25.6% Al2O3, 12.1% MgO, 8.5% Fe2O3, 6.4% CaO, 4.2% Na2O, 3.3% K2O, 6.6% CO2 and a loss on ignition of 0.8% obtained by firing.

[0012] Furthermore, the weight ratio of the active component of the catalyst to the carrier is 0.2:100-2:100.

[0013] The present invention also provides a method for preparing a highly water-resistant catalyst for spraying exhaust gas VOCs, comprising the following steps:

[0014] Preparation of vector:

[0015] After pressing, a honeycomb ceramic blank with an outer size of 100 mm×100 mm×50 mm, a pore size of 1.5 mm×1.5 mm, and a wall thickness of 0.5 mm is obtained, and the honeycomb ceramic blank is dried in an oven at 60° C. for 12 hours, and then fired at 950-1350° C. for 8-24 hours before forming;

[0016] Carrier pretreatment:

[0017] The sintered carrier is immersed in a HNO3 solution with a pH of 4-6 for acid etching for 6-10 hours, filtered out and neutralized with a NaOH solution with a pH of 8-9 for 0.5-4 hours, and rinsed with deionized water for 3-5 times and then dried;

[0018] Active component coating and catalyst preparation:

[0019] Take Ce(NO3)3·6H2O and Cr(NO3)3·9H2O respectively, and mix them in a molar ratio of CeO2 to Cr2O3 of 4:1-2:1;

[0020] Add deionized water and stir with a stirrer for 0.5 h until Ce(NO3)3·6H2O and Cr(NO3)3·9H2O are fully dissolved;

[0021] Weigh the carrier and place it completely in the mixed solution, then immerse the stirred mixed solution at room temperature for 6 hours;

[0022] The impregnated catalyst samples were taken out and washed alternately with anhydrous ethanol and deionized water for 3 times each;

[0023] The washed catalyst sample was placed in an oven at 90 °C and dried for 12 h;

[0024] The dried catalyst sample was placed in a muffle furnace at 500 °C for secondary calcination for 3 h, with a heating rate of 2 °C min -1 ;

[0025] The catalyst sample calcined in the muffle furnace was allowed to cool naturally to room temperature, and the theoretical loading amount of each active component was calculated by weighing the change in mass after impregnation, so that the weight ratio of the active component to the carrier was 0.2:100-2:100, and the finished catalyst was obtained.

[0026] Furthermore, the catalyst prepared by the preparation method is used for catalytic oxidation treatment of VOCs-containing waste gas generated by industrial coating.

[0027] The beneficial effects brought by the present invention are:

[0028] 1. The highly water-resistant catalyst proposed in this application has low preparation cost, strong water resistance, high catalytic stability, can adapt to the oxidation reaction catalyst of complex industrial waste gas, and is suitable for efficient treatment of industrial coating VOCs waste gas;

[0029] 2. The active components are impregnated to improve their water resistance. At the same time, the nanoscale micropores enhance the catalyst's selective adsorption of VOCs components, thereby improving the catalytic conversion efficiency of VOCs. Chromium and transition metal cerium are used as active components, and the raw materials are easily available, which reduces the preparation cost of the catalyst and has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0031] Figure 1 The test results of the catalyst of the present invention compared with the blank sample;

[0032] Figure 2 This is a scanning electron microscope ×10000 result image of the catalyst coating of Example 1;

[0033] Figure 3 This is the XRD result of the catalyst in Example 1. DETAILED DESCRIPTION

[0034] The embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. It should be clear that the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] There are many types of industrial coatings, the most common of which are furniture, cars, ships, aerospace, general equipment and special equipment surface spraying and maintenance. The volatile organic compounds (VOCs) produced by industrial spraying are of many types and complex composition, including alkanes, olefins, aromatic hydrocarbons, halogenated hydrocarbons and other compounds.

[0036] There are many technologies for VOCs treatment in industrial coatings, among which catalytic oxidation is widely used in pollution control in the industrial coating industry due to its advantages of high removal efficiency, low energy consumption, and no secondary pollutants. Catalysts are the core of this technology, among which the most common are precious metal catalysts. The high prices of precious metal catalysts such as platinum and ruthenium and the scarcity of raw materials limit their large-scale application. Currently, transition metal catalysts are the most studied. Transition metal catalysts have the characteristics of abundant resources, low catalyst cost, strong water resistance and anti-poisoning performance, and have become the main alternative to precious metal catalyst materials.

[0037] In order to improve the water resistance of industrial coating waste gas VOCs catalyst, the present invention provides a high water resistance catalyst for spraying waste gas VOCs, the spraying waste gas is a waste gas containing at least alkanes, olefins, acetone, isopropanol, benzene series, ethyl acetate, dichloromethane and dichloroethane. In particular, it refers to the spraying waste gas VOCs generated by industrial coating, which has the characteristics of complex composition and high water vapor content. Generally speaking, the moisture content can reach more than 3.6%wt.

[0038] The catalyst includes a carrier and an active component. The carrier is a basic component of the supported catalyst, which provides a physical support structure for carrying the active component of the catalyst. The active component is the key component in the catalyst that directly participates in the catalytic reaction and accelerates the chemical reaction rate. It is the core of the catalyst to play a catalytic role. Through interaction with the reactants, it changes the reaction path or reduces the activation energy of the reaction, and it itself is not consumed or is rarely consumed in the reaction.

[0039] The active components of the catalyst are: CeO2 and Cr2O3; wherein the molar ratio of CeO2 to Cr2O3 is 4:1-2:1.

[0040] The carrier of the catalyst is honeycomb ceramics. According to weight percentage: the raw materials of the carrier of the catalyst contain 15-35% SiO2, 18-32% Al2O3, 8-15% MgO, 5-8% Fe2O3, 5-10% CaO, 2-5% Na2O, 2-5% K2O, 8-12% CO2, and the balance is H2O.

[0041] Specifically, the catalyst carrier is a honeycomb ceramic having a chemical composition of 32.5% SiO2, 25.6% Al2O3, 12.1% MgO, 8.5% Fe2O3, 6.4% CaO, 4.2% Na2O, 3.3% K2O, 6.6% CO2 and a loss on ignition of 0.8% obtained by firing.

[0042] The weight ratio of the active component of the catalyst to the carrier is 0.2:100-2:100.

[0043] The highly water-resistant catalyst proposed in the present application uses honeycomb ceramics as carriers. The raw materials of the carriers mainly contain SiO2, Al2O3, MgO, Fe2O3, CaO, Na2O, K2O, CO2 and H2O, and the weight percentages of the components are 15-35%, 18-32%, 8-15%, 5-8%, 5-10%, 2-5%, 2-5%, 8-12% and 1-2% respectively. After the raw materials of the carriers are prepared according to the above proportions, they are pressed and formed into honeycomb ceramic blanks with an outer size of 100mm×100mm×50mm, a pore size of 1.5mm×1.5mm and a wall thickness of 0.5mm, and are formed by one-time firing at 950-1350°C. The catalyst carriers fired once are acid-etched, neutralized with alkali, washed with deionized water 3-5 times, and dried.

[0044] The highly water-resistant catalyst proposed in this application selects CeO2 and Cr2O3 as active components, the molar ratio of CeO2 and Cr2O3 is 4:1-2:1, and the weight ratio of the active component to the carrier is 0.2:100-2:100. The active component is evenly coated on the surface of the carrier and the inner surface of the honeycomb pores by impregnation to form a nanoparticle coating to improve the hydrophobicity of the catalyst. The porous surface increases the probability of the catalyst contacting VOCs, thereby improving the efficiency of the oxidation reaction.

[0045] The highly water-resistant catalyst proposed in the present application has low preparation cost, strong water resistance, high catalytic stability, can adapt to the oxidation reaction catalyst of complex industrial waste gas, and is suitable for efficient treatment of industrial coating VOCs waste gas. In an optional embodiment, the industrial coating VOCs waste gas is a waste gas containing at least alkanes, olefins, acetone, isopropanol, benzene series, ethyl acetate, dichloromethane and dichloroethane.

[0046] The present invention also provides a method for preparing a highly water-resistant catalyst for spraying exhaust gas VOCs, comprising the following steps: preparing a carrier, pretreating the carrier, coating an active component and preparing a catalyst.

[0047] Preparation of vector:

[0048] Clay, porcelain stone, feldspar, quartz, etc. are configured into a carrier raw material according to the composition of 15-35% SiO2, 18-32% Al2O3, 8-15% MgO, 5-8% Fe2O3, 5-10% CaO, 2-5% Na2O, 2-5% K2O, 8-12% CO2, and the balance H2O, and the carrier raw material is ground to more than 200 meshes;

[0049] After pressing, a honeycomb ceramic blank with an outer size of 100mm×100mm×50mm, a pore size of 1.5mm×1.5mm, and a wall thickness of 0.5mm is obtained. The honeycomb ceramic blank is dried in an oven at 60°C for 12h, and then fired at 950-1350°C for 8-24h to form.

[0050] Carrier pretreatment:

[0051] The sintered carrier is immersed in a HNO3 solution with a pH value of 4-6 for acid etching for 6-10 hours, filtered out and then neutralized with a NaOH solution with a pH value of 8-9 for 0.5-4 hours, and then rinsed with deionized water for 3-5 times and dried.

[0052] Active component coating and catalyst preparation:

[0053] Use an electronic balance to weigh a certain amount of Ce(NO3)3·6H2O and Cr(NO3)3·9H2O respectively, and mix them in a molar ratio of CeO2 to Cr2O3 of 4:1-2:1;

[0054] Add deionized water and stir with a stirrer for 0.5 h until Ce(NO3)3·6H2O and Cr(NO3)3·9H2O are fully dissolved;

[0055] Weigh the carrier and place it completely in the mixed solution, then immerse the stirred mixed solution at room temperature for 6 hours;

[0056] The impregnated catalyst samples were taken out and washed alternately with anhydrous ethanol and deionized water for 3 times each;

[0057] The washed catalyst sample was placed in an oven at 90 °C and dried for 12 h;

[0058] The dried catalyst sample was placed in a muffle furnace at 500 °C for secondary calcination for 3 h, with a heating rate of 2 °C min -1 ;

[0059] The catalyst sample calcined in the muffle furnace was allowed to cool naturally to room temperature, and the theoretical loading amount of each active component was calculated by weighing the change in mass after impregnation, so that the weight ratio of active component to carrier was 0.2:100-2:100, and the finished catalyst was obtained. The active component was introduced on the carrier surface and the inner surface of the honeycomb of the catalyst by the impregnation method to form a nano coating, which enhanced the water resistance of the catalyst.

[0060] The catalyst prepared by the preparation method of a highly water-resistant catalyst for spraying VOCs in exhaust gas disclosed in the present invention, or the catalyst disclosed above can be used for catalytic oxidation treatment of VOCs-containing exhaust gas generated by industrial coating, such as exhaust gas generated by automobile painting; in particular, the main components of the exhaust gas include at least toluene, xylene, trimethylbenzene, ethyl chloride and vinyl chloride, with a total hydrocarbon concentration of 155.82 ppm, a benzene concentration of 5.43 ppm, a toluene concentration of 4.24 ppm, a xylene concentration of 5.58 ppm, and a moisture content of 3.6% wt in the exhaust gas.

[0061] Embodiment 1:

[0062] like Figure 1-3 As shown, in order to investigate the catalytic oxidation effect of the catalyst prepared by the present invention, the catalytic conversion effect of dichloromethane (DCM) was analyzed by experiment using the catalyst coated with active components, and a blank sample experiment was performed using a catalyst carrier without active component coating.

[0063] The experiment used a catalyst carrier prepared by the present invention, the chemical composition of the carrier was 32.5% SiO2, 25.6% Al2O3, 12.1% MgO, 8.5% Fe2O3, 6.4% CaO, 4.2% Na2O, 3.3% K2O, 6.6% CO2, and a honeycomb ceramic with a loss on ignition of 0.8%. The weight ratio of the active component of the catalyst to the carrier was 0.68:100.

[0064] The catalyst performance test was conducted in a tubular heating furnace with a length of 500 mm and a quartz tube with an inner diameter of 12 mm. An appropriate amount of sample was cut along the honeycomb hole direction of the catalyst and blank sample and placed in the quartz tube, which was fixed with quartz wool. The designed air velocity of the catalyst and blank sample was 20,000 h -1 The reaction temperatures of the tube furnace were set at 150°C, 200°C, 250°C, 300°C, 350°C and 400°C. The simulated gas DCM concentration was 500 ppm, and the rest was air. Water was injected into the simulated gas to keep the water content of the gas at 4% (wt). The gas composition after the reaction was tested using a gas chromatograph equipped with an FID detector and an HP series capillary column.

[0065] Figure 1These are the test results of catalyst samples and blank samples. The results show that the catalyst loaded with active components has a significant effect on DCM removal, and the conversion rate of DCM can reach 90.4% at 300°C.

[0066] Embodiment 2:

[0067] The catalyst prepared by the present invention is used for industrial application. The waste gas to be catalytically oxidized is from automobile painting. The designed waste gas volume is 1000m 3 / h. The GC+FID detector was used to analyze the concentrations of total hydrocarbons and benzene series before and after the waste gas treatment. The main components of the waste gas were toluene, xylene, trimethylbenzene, ethyl chloride, vinyl chloride and other components. The total hydrocarbon concentration was 155.82ppm, the benzene concentration was 5.43ppm, the toluene concentration was 4.24ppm, the xylene concentration was 5.58ppm, and the moisture content of the waste gas was 3.6% (wt).

[0068] The catalyst described in Example 1 was used for catalytic oxidation, and the designed air velocity was 20000h -1 The catalytic reaction temperature was set at 290°C.

[0069] After catalytic oxidation reaction, the total hydrocarbon concentration in the exhaust gas is 13.68ppm, benzene concentration is 1.34ppm, toluene is 0.59ppm, and xylene is 0.51ppm. The total hydrocarbon removal rate is 91.2%, the benzene conversion rate is 75.3%, and the benzene series conversion rate is 88.8%.

[0070] In summary, the highly water-resistant catalyst for spraying exhaust gas VOCs prepared according to this scheme has easily available raw materials for the catalyst carrier, high strength, long life and low cost. The active component is impregnated to improve the water resistance of the active component, while the nano-scale micropores enhance the selective adsorption performance of the catalyst for VOCs components, thereby improving the catalytic conversion efficiency of VOCs. Chromium and transition metal cerium are used as active components, the raw materials are easily available, the preparation cost of the catalyst is reduced, and it has good application prospects.

[0071] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A highly water-resistant catalyst for spraying exhaust gas VOCs, characterized in that: The active components of the catalyst are CeO2 and Cr2O3, wherein the molar ratio of CeO2 to Cr2O3 is 4:1-2:

1.

2. A highly water-resistant catalyst for spraying exhaust gas VOCs according to claim 1, characterized in that: The catalyst carrier is honeycomb ceramic.

3. A highly water-resistant catalyst for spraying exhaust gas VOCs according to claim 2, characterized in that: By weight percentage: the raw materials of the catalyst carrier contain 15-35% SiO2, 18-32% Al2O3, 8-15% MgO, 5-8% Fe2O3, 5-10% CaO, 2-5% Na2O, 2-5% K2O, 8-12% CO2, and the balance is H2O.

4. A highly water-resistant catalyst for spraying exhaust gas VOCs according to claim 3, characterized in that: The catalyst carrier is a honeycomb ceramic having a chemical composition of 32.5% SiO2, 25.6% Al2O3, 12.1% MgO, 8.5% Fe2O3, 6.4% CaO, 4.2% Na2O, 3.3% K2O, 6.6% CO2 and a loss on ignition of 0.8% obtained by firing.

5. A highly water-resistant catalyst for spraying exhaust gas VOCs according to claim 4, characterized in that: The weight ratio of the active component of the catalyst to the carrier is 0.2:100-2:

100.

6. A method for preparing a highly water-resistant catalyst for spraying exhaust gas VOCs, characterized in that: The steps include: Preparation of vector: After pressing, a honeycomb ceramic blank with an outer size of 100 mm×100 mm×50 mm, a pore size of 1.5 mm×1.5 mm, and a wall thickness of 0.5 mm is obtained, and the honeycomb ceramic blank is dried in an oven at 60° C. for 12 hours, and then fired at 950-1350° C. for 8-24 hours before forming; Carrier pretreatment: The sintered carrier is immersed in a HNO3 solution with a pH of 4-6 for acid etching for 6-10 hours, filtered out and neutralized with a NaOH solution with a pH of 8-9 for 0.5-4 hours, and rinsed with deionized water for 3-5 times and then dried; Active component coating and catalyst preparation: Take Ce(NO3)3·6H2O and Cr(NO3)3·9H2O respectively, and mix them in a molar ratio of CeO2 to Cr2O3 of 4:1-2:1; Add deionized water and stir with a stirrer for 0.5 h until Ce(NO3)3·6H2O and Cr(NO3)3·9H2O are fully dissolved; Weigh the carrier and place it completely in the mixed solution, then immerse the stirred mixed solution at room temperature for 6 hours; The impregnated catalyst samples were taken out and washed alternately with anhydrous ethanol and deionized water for 3 times each; The washed catalyst sample was placed in an oven at 90 °C and dried for 12 h; The dried catalyst sample was placed in a muffle furnace at 500 °C for secondary calcination for 3 h, with a heating rate of 2 °C min -1 ; The catalyst sample calcined in the muffle furnace was allowed to cool naturally to room temperature, and the theoretical loading amount of each active component was calculated by weighing the change in mass after impregnation, so that the weight ratio of the active component to the carrier was 0.2:100-2:100, and the finished catalyst was obtained.

7. The method for preparing a highly water-resistant catalyst for spraying exhaust gas VOCs according to claim 6, characterized in that: The catalyst prepared by the preparation method is used for catalytic oxidation treatment of VOCs-containing waste gas generated by industrial coating.

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