Method for preparing denitration catalyst through dry coating, denitration catalyst and application

Abstract

The invention relates to the technical field of denitration catalysts, and provides a method for preparing a denitration catalyst through dry coating, the denitration catalyst and application, the denitration catalyst prepared by adopting the method does not need to introduce water and does not need to be roasted at high temperature, and the denitration catalyst with more excellent catalytic activity can be obtained. The method comprises the following steps: S1, fully mixing catalyst powder and polytetrafluoroethylene according to a mass ratio of 1: (0.001-0.15) at 60-100 DEG C to obtain a precursor; s2, preparing the precursor into a precursor sheet at the temperature of 160-250 DEG C; s3, the precursor sheet is hot-pressed on the surface of a base body, the denitration catalyst is obtained, and the base body is a formed carrier or a formed finished product catalyst.

Description

Technical Field

[0001] The present invention relates to the technical field of denitration catalysts, and in particular to a method for preparing a denitration catalyst by dry coating, the denitration catalyst and applications. Background Art

[0002] As productivity grows, energy demand increases. Energy use often generates nitrogen oxides (NOx). These include those released from fossil fuels, those generated by the reaction of nitrogen and oxygen in high-temperature environments, and those generated by the reaction of nitrogen and oxygen in the air during electrical discharges. These NOx contribute to acid rain and photochemical smog, posing a threat to human health.

[0003] Currently, the most established denitrification method involves the catalytic reduction of nitrogen oxides using ammonia or urea. The most commonly used denitrification catalyst is a vanadium-based catalyst, consisting of V2O5 as the active component, WO3 as the additive, and a TiO2 carrier. These catalysts are widely used in the power industry and for automobile exhaust treatment. The operating temperature of vanadium-based catalysts is 300-400°C, which is consistent with the flue gas temperature of conventional coal-fired boilers before entering the economizer (a shell-and-tube heat exchanger used for flue gas heat recovery).

[0004] For natural gas boilers, since the natural gas has been desulfurized before entering the boiler, the sulfur content in the boiler flue gas is low, and the exhaust does not need to consider SO X By reducing the dew point, the flue gas temperature can be reduced to very low temperatures, typically around 120-180°C. Currently, the most effective way to reduce flue gas temperature is to increase the content of active components and promoters. Therefore, increasing the content of active components and promoters through coating has become a hot topic in the field of denitrification catalysts. Existing technologies mainly use wet coating technology to increase the content of active components and promoters. However, wet coating technology also brings problems such as pollution, energy waste, and / or insignificant improvement in catalyst activity. Summary of the Invention

[0005] In response to the problems of pollution and energy waste in the prior art of preparing denitration catalysts by wet coating, the present invention provides a method for preparing a denitration catalyst by dry coating, a denitration catalyst and its application. The method of the present invention is used to prepare the denitration catalyst without the need to introduce water or perform high-temperature calcination, and can obtain a denitration catalyst with better catalytic activity. At the same time, it can effectively overcome the disadvantages of wet coating technology such as pollution and energy waste.

[0006] To achieve its purpose, the present invention provides the following technical solutions:

[0007] In one aspect, the present invention provides a method for preparing a denitration catalyst by dry coating, the method comprising the following steps:

[0008] S1. Fully mix the catalyst powder and polytetrafluoroethylene at a mass ratio of 1:0.001-0.15 at 60-100° C. to obtain a precursor;

[0009] S2, preparing the precursor into a precursor sheet at a temperature of 160-250° C.;

[0010] S3. Hot-pressing the precursor sheet onto the surface of a substrate to obtain the denitration catalyst, wherein the substrate is a formed carrier or a formed finished catalyst.

[0011] Preferably, in step S1, the mass ratio of the catalyst powder to polytetrafluoroethylene is 1:0.01-0.1.

[0012] Preferably, in step S1, the catalyst powder includes an active component and a promoter;

[0013] The active component is selected from one or more of manganese oxide and vanadium oxide;

[0014] The promoter is selected from one or more of cobalt oxide, tungsten oxide and titanium dioxide.

[0015] In some embodiments, the manganese oxide is selected from one or more of manganese monoxide, manganese dioxide, manganese trioxide, manganese tetraoxide and manganese pentoxide;

[0016] And / or, the vanadium oxide is selected from one or more of vanadium monoxide, vanadium trioxide, vanadium dioxide, and vanadium pentoxide;

[0017] And / or, the cobalt oxide is selected from one or two of cobalt trioxide, cobalt dioxide, and cobalt monoxide;

[0018] And / or, the tungsten oxide is selected from tungsten trioxide.

[0019] In some embodiments, the mass ratio of the active component to the co-catalyst is 0.03-30.

[0020] In some embodiments, in step S3, the substrate is plate-shaped or honeycomb-shaped;

[0021] and / or, the finished catalyst is a titanium-based catalyst or a carbon-based catalyst;

[0022] And / or, the carrier is one or more of titanium dioxide and cordierite.

[0023] Preferably, in step S3, the hot pressing temperature is 160-250° C., and the hot pressing pressure is ≥0.02 MPa.

[0024] Preferably, in step S1, the mixing time is 5 min-10 h.

[0025] Another aspect of the present invention provides a denitration catalyst prepared by the method described above.

[0026] In another aspect, the present invention provides use of the above-mentioned denitration catalyst in the catalytic reduction of nitrogen oxides, wherein the catalytic reduction of the nitrogen oxides is carried out using ammonia or urea as a reducing agent.

[0027] The technical solution provided by the present invention has at least the following beneficial effects:

[0028] 1. The present invention loads the catalytically active components on the substrate through dry coating. The entire coating process does not introduce any aqueous solution and does not require a high-temperature roasting process. It can overcome the disadvantages of traditional coating processes such as pollution and high energy consumption. Moreover, the denitration catalyst prepared by the method of the present invention has significantly better catalytic activity than the denitration catalyst prepared by the wet coating process.

[0029] 2. The method of the present invention has a simple component formula for dry coating, a simple preparation process, and does not have the problem of being unable to form when a large amount of catalytically active components are loaded in the traditional wet coating process. DETAILED DESCRIPTION

[0030] In order to facilitate the understanding of the present invention, the present invention will be further described below in conjunction with examples. It should be understood that the following examples are only for a better understanding of the present invention and do not mean that the present invention is limited to the following examples.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention pertains. The term "and / or" as may be used herein includes any and all combinations of one or more of the associated listed items.

[0032] In one aspect, the present invention provides a method for preparing a denitration catalyst by dry coating, the method comprising the following steps:

[0033] S1. The catalyst powder and polytetrafluoroethylene (PTFE) are fully mixed in a mass ratio of 1:0.001-0.15 (e.g., 1:0.001, 1:0.005, 1:0.01, 1:0.05, 1:0.1, 1:0.15) at 60-100° C. (e.g., 60° C., 70° C., 80° C., 90° C., 100° C., preferably 70-100° C.) to obtain a precursor;

[0034] S2, preparing the precursor into a precursor sheet at a temperature of 160-250° C. (e.g., 160° C., 180° C., 200° C., 220° C., 240° C., 250° C.);

[0035] S3. Hot-pressing the precursor sheet onto the surface of a substrate to obtain the denitration catalyst, wherein the substrate is a formed carrier or a formed finished catalyst.

[0036] The present invention uses polytetrafluoroethylene as a binder, first fully mixes the catalyst powder and polytetrafluoroethylene at 60-100°C, then heats up to 160-250°C to form a thin sheet, and then hot-presses and bonds it to the substrate. This method can use a very small amount of binder to allow the active components of the catalyst to be well loaded on the substrate through a dry method, and the entire coating process does not introduce any aqueous solution, does not require a high-temperature roasting process, and does not involve a secondary sintering process. On the one hand, it can overcome the disadvantages of traditional coating processes such as pollution and high energy consumption, and on the other hand, it avoids the adverse effects of wet coating involving aqueous solutions and high-temperature roasting processes on the catalytic activity of the catalyst. The method of the present invention has a simple formula of components required for dry coating, a simple preparation process, and does not have the problem of being unable to form when loading a large amount of catalytically active components in traditional wet coating processes. The denitrification catalyst prepared by the method of the present invention has significantly better catalytic activity than the denitrification catalyst prepared by the wet coating process.

[0037] In the preparation method of the present invention, the catalyst powder and polytetrafluoroethylene must first be fully mixed at 60-100°C, and then heated to 160-250°C to prepare thin sheets. The inventors have found that if the mixing operation at 60-100°C in step S1 is omitted, or the temperature of the mixing operation is too low or too high, it will be difficult to subsequently obtain thin sheets that can be well attached to the surface of the substrate by hot pressing. The present invention controls the mixing temperature at 60-100°C in step S1 and the thin sheet preparation temperature at 160-250°C in step S2, and controls the catalyst powder and polytetrafluoroethylene in a mass ratio of 1:0.001-0.15. Through the mutual combination of the above-mentioned temperatures and mixing ratios, the catalyst components can be well attached to the substrate with a simple coating formula and operation, and a denitrification catalyst with improved catalytic activity can be obtained.

[0038] In the method of the present invention, the mass ratio of catalyst powder to polytetrafluoroethylene is 1:0.001-0.15. This method allows the catalyst powder to adhere well to the substrate surface via a dry process using only a small amount of polytetrafluoroethylene, resulting in a denitration catalyst with excellent catalytic activity. Too little polytetrafluoroethylene will prevent molding, while too much will reduce catalytic efficiency. More preferably, in step S1, the mass ratio of catalyst powder to polytetrafluoroethylene is 1:0.01-0.1 (e.g., 1:0.01, 1:0.03, 1:0.05, 1:0.07, 1:0.1). Using this preferred mass ratio not only facilitates molding but also achieves better catalytic efficiency compared to using lower or higher amounts of polytetrafluoroethylene.

[0039] In the present invention, the catalyst powder in the denitration catalyst can be composed of catalysts currently available in the art that exhibit denitration catalytic activity. Preferably, in step S1, the catalyst powder comprises an active component and a co-catalyst; the active component is selected from one or more of manganese oxide and vanadium oxide; and the co-catalyst is selected from one or more of cobalt oxide, tungsten oxide, and titanium dioxide.

[0040] In some embodiments, the manganese oxide is selected from one or more of manganese monoxide, manganese dioxide, manganese trioxide, manganese tetraoxide and manganese pentoxide;

[0041] In some embodiments, the vanadium oxide is selected from one or more of vanadium monoxide, vanadium trioxide, vanadium dioxide, and vanadium pentoxide;

[0042] In some embodiments, the cobalt oxide is selected from one or two of cobalt trioxide, cobalt dioxide, and cobalt monoxide;

[0043] In some embodiments, the tungsten oxide is selected from tungsten trioxide.

[0044] The ratio of the active component to the co-catalyst in the catalyst powder can be a corresponding ratio suitable for denitration in the art, and there is no particular limitation. In some embodiments, the mass ratio of the active component to the co-catalyst is 0.03-30, for example, 0.03, 0.1, 0.5, 1, 5, 10, 15, or 30.

[0045] In the present invention, in step S3, the substrate is a plate-type or honeycomb-type substrate, that is, a carrier that has been formed into a plate-type or honeycomb-type, or a plate-type or honeycomb-type finished catalyst is used as the substrate; preferably, the finished catalyst is a titanium-based catalyst or a carbon-based catalyst, which can be a commercially available product, or prepared according to a process well known in the art, such as a carbon-based denitrification catalyst or a titanium-based denitrification catalyst; preferably, the carrier is one or more of titanium dioxide and cordierite. For existing finished catalysts, the method of the present invention can be used to further hot-press the catalyst powder on the basis of the finished catalyst according to the actual requirements of the catalytic performance to obtain the desired catalytic activity. The method of the present invention can flexibly adjust the catalytic performance of the existing finished catalyst according to demand; the method of the present invention can also flexibly adjust the loading amount of the catalytically active component by adjusting the thickness of the precursor sheet to obtain a product with the required catalytic activity, and there is no problem of the traditional roasting method that cannot be formed when the loading amount of the catalytically active component is large.

[0046] Preferably, in step S3, the hot pressing temperature is 160-250°C (e.g., 160°C, 180°C, 200°C, 220°C, 250°C, preferably 160-220°C), and the hot pressing pressure is ≥ 0.02 MPa. The specific pressure required for hot pressing is based on the ability to smoothly adhere the sheet to the substrate surface.

[0047] In some examples, in step S1, the mixing time is 5 min-10 h, for example, 5 min, 10 min, 20 min, 30 min, 60 min, 2 h, 5 h, 10 h; preferably, in step S1, the mixing time is 30 min-2 h. In step S1, the mixing can be performed, for example, by grinding, kneading, or the like.

[0048] Another aspect of the present invention provides a denitration catalyst prepared by the method described above.

[0049] On the other hand, the present invention provides the use of the above-mentioned denitration catalyst in the catalytic reduction of nitrogen oxides, and the catalytic reduction of the nitrogen oxides is carried out using ammonia or urea as a reducing agent. Furthermore, the denitration catalyst of the present invention is particularly suitable for use in the treatment of low-temperature flue gas. The low-temperature flue gas in this application generally refers to flue gas of 120-180°C, such as the flue gas of a gas boiler. Of course, in addition to gas boilers, the flue gas of other types of boilers can also be used if the temperature is within this range. The catalyst provided by the present invention has been measured to be able to perform good flue gas treatment at an operating temperature of 120-180°C. The denitration catalyst can be specifically loaded in a fixed bed / fluidized bed / slurry bed reactor.

[0050] The present invention is further described below by way of examples, but it should not be understood that the present invention is limited thereto.

[0051] Where specific experimental steps or conditions are not specified in the examples, the corresponding conventional experimental steps or conditions in the art can be used. Reagents or instruments used without specifying the manufacturer are all commercially available conventional products.

[0052] Example 1:

[0053] First, 1g of Mn2O5 and 1g of CoO2 were mixed uniformly, followed by the addition of 0.2g of PTFE. The mixture was then heated to 80°C and ground at 80°C for 15 minutes. The mixture was then heated to 200°C and pressed into a 1mm thick precursor sheet using a double-roll mill. While still hot, the precursor sheet was hot-pressed onto the surface of a honeycomb titanium dioxide support at 195°C and 0.1 MPa. The mixture was held at this temperature for 3 minutes and then cooled to room temperature to yield the denitration catalyst of Example 1.

[0054] Comparative Example 1

[0055] This comparative example uses the same honeycomb titanium dioxide carrier as in Example 1 to prepare a denitration catalyst. The steps for preparing the denitration catalyst in this comparative example are as follows:

[0056] First, a manganese salt (specifically manganese sulfate) and a cobalt salt (specifically cobalt sulfate) were uniformly mixed to obtain a mixture. The amount of manganese salt used was determined to yield 1g of Mn2O5 by calcination, and the amount of cobalt salt used was determined to yield 1g of CoO2 by calcination. 0.04g of PEO (polyethylene oxide), 0.02g of CMC (carboxymethyl cellulose), and 0.6ml of water were then added to the mixture. The mixture was heated to 80°C and uniformly mixed at 80°C. The resulting mixture was then applied to the surface of a honeycomb titanium dioxide support and calcined at 600°C for 6 hours to obtain the denitration catalyst of Comparative Example 1.

[0057] Example 2:

[0058] First, 500g of V2O5 and 1000g of WO3 were mixed evenly, followed by the addition of 60g of PTFE. The mixture was then heated to 90°C and kneaded at 90°C for 100 minutes using a small mixer. The mixture was then heated to 200°C and pressed into a 0.5mm thick precursor sheet using a double-roll mill. While still hot, the precursor sheet was hot-pressed onto the surface of a finished titanium-based catalyst at 160°C and 1 MPa. The mixture was held at this temperature for 5 minutes and then cooled to room temperature to yield the denitration catalyst of Example 2. The finished titanium-based catalyst used in this example was prepared according to Comparative Example 1.

[0059] Example 3

[0060] First, 500g of V2O5 and 1000g of WO3 were mixed evenly, followed by the addition of 60g of PTFE. The mixture was then heated to 60°C and kneaded at 60°C for 600 minutes using a small mixer. The mixture was then heated to 200°C and pressed into a 0.5mm thick precursor sheet using a double-roll mill. While still hot, the precursor sheet was hot-pressed onto the surface of a finished titanium-based catalyst at 250°C and 1 MPa. The mixture was held at this temperature for 15 minutes and then cooled to room temperature to yield the denitration catalyst of Example 3. The finished titanium-based catalyst used in this example was prepared according to Comparative Example 1.

[0061] Example 4

[0062] First, 500g of V2O5 and 1000g of WO3 were mixed evenly, followed by the addition of 225g of PTFE. The mixture was then heated to 90°C and kneaded at 90°C for 100 minutes using a small mixer. The mixture was then heated to 200°C and pressed into a 0.5mm thick precursor sheet using a double-roll mill. While still hot, the precursor sheet was hot-pressed onto the surface of a finished titanium-based catalyst at 160°C and 1 MPa. The mixture was held at this temperature for 5 minutes and then cooled to room temperature to yield the denitration catalyst of Example 4. The finished titanium-based catalyst used in this example was prepared according to Comparative Example 1.

[0063] Testing method for the denitration performance of the denitration catalysts prepared in each embodiment and comparative example:

[0064] The pollutant control reaction atmosphere is used as the treatment object, that is, the SCR reaction atmosphere exists in the reaction atmosphere, and the components of the reaction atmosphere contain 500ppm of NO. To ensure the progress of the SCR reaction, NH3 is sprayed into the reaction atmosphere (the amount of NH3 sprayed is the same as the NO content in the reaction atmosphere), and O2 is introduced (the amount of O2 introduced accounts for 5% of the total volume flow of the reaction atmosphere), and N2 is used as the balance gas; the total gas flow rate of the reaction atmosphere is 1Nm 3 .h -1 .

[0065] The catalyst sample was placed in a tubular reactor and reacted in the aforementioned atmosphere within the range of 100-200°C (starting at 100°C and ramping up to 200°C). During the reaction, starting at the starting temperature, each temperature interval was measured as a test point (e.g., 120°C, 140°C, 160°C, and 180°C). The temperature was maintained at each test point for 1 hour. After the reaction reached a steady state, the gas composition at the reactor inlet and outlet was measured using a Fourier transform infrared gas analyzer (GASMET, Finland, Model DX-4000). The NOx conversion rate was calculated using the following formula, as shown in the table below.

[0066]

[0067] Wherein, M0 is the NOx concentration at the reactor inlet; M1 is the NOx concentration at the reactor outlet;

[0068] The test results are shown in Table 1:

[0069] Table 1. Denitration catalyst reaction conversion rates prepared in various examples and comparative examples

[0070]

[0071] As shown in Table 1, the catalytic activity of the denitration catalyst prepared in the present embodiment is significantly improved compared to the catalyst prepared using the wet coating technique. While the catalytically active component content of Comparative Example 1 is comparable to that of Example 1, the catalytic activity of the denitration catalyst prepared in Example 1 is significantly superior to that of Comparative Example 1. Example 2 significantly improves the catalytic activity of the denitration catalyst in Comparative Example 1 by further employing the present invention's method to load the catalytically active component on Comparative Example 1.

[0072] It will be readily understood that the above embodiments are merely examples for clarity of description and are not intended to limit the present invention to these examples. Those skilled in the art will readily appreciate that other variations or modifications based on the above description are possible. It is not necessary and impossible to provide an exhaustive list of all possible implementations. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for preparing a denitration catalyst by dry coating, characterized in that: The method comprises the following steps: S1. Fully mix the catalyst powder and polytetrafluoroethylene at a mass ratio of 1:0.001-0.15 at 60-100° C. to obtain a precursor; S2, preparing the precursor into a precursor sheet at a temperature of 160-250° C.; S3. Hot-pressing the precursor sheet onto the surface of a substrate to obtain the denitration catalyst, wherein the substrate is a formed carrier or a formed finished catalyst.

2. The method according to claim 1, characterized in that In step S1, the mass ratio of the catalyst powder to polytetrafluoroethylene is 1:0.01-0.

1.

3. The method according to claim 1 or 2, characterized in that In step S1, the catalyst powder includes an active component and a promoter; The active component is selected from one or more of manganese oxide and vanadium oxide; The promoter is selected from one or more of cobalt oxide, tungsten oxide and titanium dioxide.

4. The method according to claim 3, characterized in that The manganese oxide is selected from one or more of manganese monoxide, manganese dioxide, manganese trioxide, manganese tetraoxide and manganese pentoxide; And / or, the vanadium oxide is selected from one or more of vanadium monoxide, vanadium trioxide, vanadium dioxide, and vanadium pentoxide; And / or, the cobalt oxide is selected from one or two of cobalt trioxide, cobalt dioxide, and cobalt monoxide; And / or, the tungsten oxide is selected from tungsten trioxide.

5. The method according to claim 3, characterized in that The mass ratio of the active component to the co-catalyst is 0.03-30.

6. The method according to claim 1 or 2, characterized in that In step S3, the substrate is a plate type or a honeycomb type; and / or, the finished catalyst is a titanium-based catalyst or a carbon-based catalyst; And / or, the carrier is one or more of titanium dioxide and cordierite.

7. The method according to claim 1 or 2, characterized in that In step S3, the hot pressing temperature is 160-250° C., and the hot pressing pressure is ≥0.02 MPa.

8. The method according to claim 1 or 2, characterized in that In step S1, the mixing time is 5 min-10 h.

9. A denitration catalyst prepared by the method according to any one of claims 1 to 8.

10. Use of the denitration catalyst according to claim 9 in catalytic reduction of nitrogen oxides, wherein ammonia or urea is used as a reducing agent to carry out catalytic reduction of the nitrogen oxides.

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