A highly water-resistant catalyst for VOCs in spray exhaust gas and its preparation method

Abstract

The present invention discloses a highly water-resistant catalyst for spraying VOCs in exhaust gas. The active components of the catalyst are CeO2 and Cr2O3. The raw materials of the catalyst carrier contain, by weight percentage, 15-35% SiO2, 18-32% Al2O3, 8-15% MgO, 5-8% Fe2O3, 5-10% CaO, 2-5% Na2O, 2-5% K2O, 8-12% CO2, with the balance being H2O. The present invention also provides a method for preparing the highly water-resistant catalyst for spraying VOCs in exhaust gas, comprising preparing the carrier, pretreating the carrier, coating the active components, and preparing the catalyst. The active components are impregnated to improve their water resistance. The nanoscale micropores enhance the catalyst's selective adsorption of VOC components, thereby improving the catalytic conversion efficiency of VOCs. Chromium and the transition metal cerium are used as the active components, and the raw materials are readily available, reducing the catalyst preparation cost. The catalyst has good application prospects.

Description

Technical Field

[0001] The present 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 generate large amounts of VOCs, including complex components such as alkanes, alkenes, aromatic hydrocarbons, and halogenated hydrocarbons. These VOCs easily decompose in the environment, contributing to air pollution such as ozone (O3) formation and PM2.5 pollution. Some VOCs are highly toxic and have a distinctive odor, which can cause serious damage to the human skin, blood, respiratory system, and nervous system.

[0003] Existing technologies limit the widespread application of precious metal catalysts due to their high cost. Transition metal catalysts, however, are becoming an increasingly popular alternative due to their abundant resources, low cost, and excellent water resistance. However, further improving the water resistance and catalytic stability of these catalysts, while also reducing their cost, remains a technical challenge in 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] To provide a basic understanding of some aspects of the disclosed embodiments, the following is a brief summary. This summary is not intended to be a comprehensive review, identify key or essential elements, or delineate the scope of these embodiments. Its sole purpose is to present some concepts in a simplified form as a prelude to the detailed description that follows.

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

[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, isopropyl alcohol, 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. 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 being formed.

[0016] Carrier pretreatment:

[0017] Immerse the sintered support in a HNO3 solution with a pH of 4-6 for acid etching for 6-10 hours, remove it by filtration, and neutralize it with a NaOH solution with a pH of 8-9 for 0.5-4 hours, rinse it with deionized water 3-5 times, and then dry it;

[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] Deionized water was added and stirred with a stirrer for 0.5 h until Ce(NO3)3·6H2O and Cr(NO3)3·9H2O were 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 firing 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. 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 to obtain the finished catalyst.

[0026] Furthermore, the catalyst prepared by this 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, and can be adapted to the oxidation reaction catalyst of complex industrial waste gas, and is suitable for the efficient treatment of VOCs waste gas from industrial coatings;

[0029] 2. The active components are impregnated to improve their water resistance. At the same time, the nano-scale 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 following briefly introduces the drawings required for use in the embodiments or the description of the prior art. 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 any 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 microscopy image of the catalyst coating of Example 1 at ×10000;

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

[0034] The following describes embodiments of the present invention in detail with reference to the accompanying drawings. It should be understood that the embodiments described are only some of the embodiments of the present invention, and not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are intended to fall within the scope of protection of the present invention.

[0035] Industrial coatings are used in a wide variety of applications, most commonly spraying and repairing furniture, cars, ships, aerospace, general-purpose equipment, and specialized equipment. The volatile organic compounds (VOCs) produced by industrial spraying are diverse and complex, including alkanes, alkenes, aromatic hydrocarbons, halogenated hydrocarbons, and other compounds.

[0036] There are various technologies for VOC removal in industrial coatings. Catalytic oxidation is widely used in the industry due to its high removal efficiency, low energy consumption, and lack of secondary pollutants. The catalyst is the core of this technology, with precious metal catalysts being the most common. However, the high price and scarcity of raw materials for precious metal catalysts such as platinum and ruthenium limit their large-scale application. Currently, transition metal catalysts are the most widely studied. Due to their abundant resources, low catalyst cost, and strong resistance to water and poisoning, transition metal catalysts have become the primary alternative to precious metal catalysts.

[0037] To improve the water resistance of VOC catalysts used in industrial painting waste gas, the present invention provides a highly water-resistant catalyst for spraying VOCs. This spraying waste gas, specifically VOCs generated by industrial painting, contains at least alkanes, alkenes, acetone, isopropyl alcohol, benzene series, ethyl acetate, methylene chloride, and ethylene dichloride. This refers specifically to VOCs generated by industrial painting, which have complex compositions and high moisture content, typically exceeding 3.6% by weight.

[0038] The catalyst consists of a support and an active component. The support is a fundamental component of a supported catalyst, providing a physical support structure for the active component. 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's catalytic function, interacting with the reactants to alter the reaction path or reduce the activation energy of the reaction, while consuming little or no energy in the reaction itself.

[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 catalyst carrier is a honeycomb ceramic. The raw materials of the catalyst carrier contain, by weight percentage, 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.

[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 this application utilizes a honeycomb ceramic carrier. The carrier's raw materials primarily contain SiO2, Al2O3, MgO, Fe2O3, CaO, Na2O, K2O, CO2, and H2O, with weight percentages of 15-35%, 18-32%, 8-15%, 5-8%, 5-10%, 2-5%, 2-5%, 8-12%, and 1-2%, respectively. The carrier raw materials are prepared according to the above proportions and then pressed into a honeycomb ceramic blank with dimensions of 100 mm x 100 mm x 50 mm, a pore size of 1.5 mm x 1.5 mm, and a wall thickness of 0.5 mm. The blank is then fired in a single step at 950-1350°C. The fired catalyst carrier is then acid-etched, neutralized with alkali, rinsed 3-5 times with deionized water, and dried.

[0044] The highly water-resistant catalyst proposed in this application uses CeO2 and Cr2O3 as active components, with a molar ratio of CeO2 to Cr2O3 of 4:1-2:1, and a weight ratio of active components to support of 0.2:100-2:100. Through impregnation, the active components are evenly coated on the support surface and the inner surface of the honeycomb pores, forming a nanoparticle coating that enhances the catalyst's hydrophobicity. The porous surface increases the catalyst's contact with VOCs, thereby improving the oxidation reaction efficiency.

[0045] The highly water-resistant catalyst proposed in this application has low preparation cost, strong water resistance, and high catalytic stability. It can adapt to the oxidation reaction catalyst of complex industrial waste gas and is suitable for the 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, alkenes, acetone, isopropyl alcohol, 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 the active component, and preparing the catalyst.

[0047] Preparation of vector:

[0048] Clay, porcelain stone, feldspar, quartz, etc. are prepared into a carrier raw material according to a 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 a size of more than 200 mesh;

[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 12 hours, and then fired at 950-1350°C for 8-24 hours before being formed.

[0050] Carrier pretreatment:

[0051] 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, rinsed with deionized water for 3-5 times and then dried.

[0052] Active component coating and catalyst preparation:

[0053] A certain amount of Ce(NO3)3·6H2O and Cr(NO3)3·9H2O were weighed using an electronic balance, and mixed at a molar ratio of CeO2 to Cr2O3 of 4:1-2:1;

[0054] Deionized water was added and stirred with a stirrer for 0.5 h until Ce(NO3)3·6H2O and Cr(NO3)3·9H2O were 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 firing for 3 h, with a heating rate of 2 °C min -1 ;

[0059] After calcining the catalyst sample in the muffle furnace, it was allowed to cool naturally to room temperature. The theoretical loading of each active component was calculated by weighing the change in mass after impregnation, achieving a weight ratio of active component to carrier of 0.2:100-2:100 to obtain the finished catalyst. The active components were introduced into the catalyst carrier surface and the inner surface of the honeycomb through impregnation, forming a nano-coating that enhanced the catalyst's water resistance.

[0060] The catalyst prepared by the preparation method of a highly water-resistant catalyst for spraying exhaust VOCs 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.

[0061] Example 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 components coated.

[0063] The experiment used a catalyst carrier prepared according to the present invention. The carrier had 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, and 6.6% CO2, and a honeycomb ceramic with a loss on ignition of 0.8%. The weight ratio of the catalyst active component to the carrier was 0.68:100.

[0064] The catalyst performance test was conducted using a 500mm long tubular heating furnace and a quartz tube with an inner diameter of 12mm. An appropriate amount of sample was cut along the honeycomb hole direction of the catalyst and blank sample and placed in the quartz tube. Quartz wool was used for fixing. The design air velocity of the catalyst and blank sample was 20,000h -1 The reaction temperatures in the tubular furnace were set at 150°C, 200°C, 250°C, 300°C, 350°C, and 400°C. The simulated gas contained 500 ppm DCM, with the remainder being air. Water was injected into the simulated gas to maintain a water content of 4% (wt). Post-reaction gas composition was analyzed 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 DCM conversion rate can reach 90.4% at 300°C.

[0066] Example 2:

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

[0068] The catalyst described in Example 1 was used for catalytic oxidation, with a design space velocity of 20,000 h -1 The catalytic reaction temperature was set at 290°C.

[0069] After catalytic oxidation, the exhaust gas contained 13.68 ppm of total hydrocarbons, 1.34 ppm of benzene, 0.59 ppm of toluene, and 0.51 ppm of xylene. The total hydrocarbon removal rate reached 91.2%, the benzene conversion rate reached 75.3%, and the benzene series conversion rate reached 88.8%.

[0070] In summary, the highly water-resistant catalyst for spraying VOCs in exhaust gas, prepared according to this scheme, features readily available raw materials, high strength, long life, and low cost. The active components are impregnated, enhancing their water resistance. The nanoscale micropores enhance the catalyst's selective adsorption of VOCs, thereby improving the catalytic conversion efficiency of VOCs. The use of chromium and the transition metal cerium as active components, coupled with readily available raw materials, reduces catalyst preparation costs and demonstrates promising application prospects.

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

Claims

1. Application of a highly water-resistant catalyst for catalytic oxidation treatment of VOCs in spray exhaust gas, characterized in that: The spraying waste gas is a spraying waste gas VOCs generated by industrial coating, containing at least toluene, xylene, trimethylbenzene, ethyl chloride, and vinyl chloride, with a total hydrocarbon concentration of 155.82ppm, a benzene concentration of 5.43ppm, a toluene concentration of 4.24ppm, and a xylene concentration of 5.58ppm. The moisture content of the waste gas is 3.6%wt; The active components of the catalyst are: CeO2 and Cr2O3; wherein the molar ratio of CeO2 to Cr2O3 is 4:1-2:1; The catalyst carrier is a honeycomb ceramic. The raw materials of the catalyst carrier contain, by weight percentage, 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. 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, and 6.6% CO2 obtained by firing, and a loss on ignition of 0.8%. The weight ratio of the active component of the catalyst to the carrier is 0.2:100-2:100.

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