Silver-based denitration catalyst suitable for denitration of tail gas of natural gas fuel engine and preparation method of silver-based denitration catalyst

Abstract

The invention discloses a silver-based denitration catalyst suitable for denitration of tail gas of a natural gas fuel engine and a preparation method of the silver-based denitration catalyst. The method comprises the following steps: 1) treating alumina powder by using an ethidene diamine wet impregnation method, and then drying to obtain a solid A; (2) mixing the solid A with a glucose solution to form slurry A, then putting the slurry A into an ice-water bath, continuously stirring, and dropwise adding a silver precursor solution in the stirring process to obtain slurry B; 3) filtering the slurry B to obtain a solid B, washing for multiple times, and drying; and 4) calcining the solid B dried in the step 3) in the air at 300-600 DEG C for 3-6 hours to obtain the silver-based denitration catalyst. The catalyst prepared by the method has high Ag nanoparticle dispersity, and can achieve more than 80% of NOx purification efficiency and more than 90% of CH4 oxidation conversion rate in tail gas treatment of a natural gas fuel engine. The method is simple in preparation and low in cost, and has basic conditions for large-scale commercial application.

Description

Technical Field

[0001] The present invention relates to the fields of atmospheric environmental governance, catalyst technology, environmentally friendly ships, and the like, and relates to a catalyst that can be used for the selective catalytic reduction removal of nitrogen oxides (NOx) and a preparation method thereof, and can be used in the field of exhaust purification of low-speed, medium-speed, and high-speed marine diesel engines, and specifically relates to a silver-based denitration catalyst that is suitable for denitration of exhaust gas from natural gas fueled engines and a preparation method thereof. Technical Background

[0002] Nitrogen oxides (NO x ) is one of the important components of air pollutants, which has a direct harm to the health of humans and animals. With the implementation of IMO Tier III regulations and the gradual expansion of emission control areas (ECA), it is increasingly urgent to research and develop processes suitable for ship engine exhaust purification. Selective catalytic reduction (SCR) is currently widely recognized as an effective method for removing NO x One of the methods, in recent years, it has played a key role in thermal power generation, automobile, shipbuilding and other industries. This process is to select a suitable reducing agent (ammonia and hydrocarbon, etc.) under the action of a catalyst to selectively catalyze the reaction with nitrogen oxides (NOx) at a certain temperature to generate non-toxic and harmless nitrogen and water. The catalyst plays a very important role in this process. Currently, the main catalyst used is the vanadium tungsten titanium (VW / TiO2) system catalyst, which has the characteristics of high catalyst activity, high stability, and good sulfur resistance. However, this catalyst also has its disadvantages. First, the activity is not high in the low temperature range (below 300°C), and there are many limiting factors in the application of mobile source (such as ships) exhaust gas treatment; secondly, because the vanadium element is biologically toxic, it will cause harm to the environment and the health of operators during long-term continuous use. Based on these reasons, in recent years, many scientific research institutions and enterprises have been committed to researching and developing SCR catalysts with better performance and wider application range to replace the current vanadium-based catalysts.

[0003] CN112604696A discloses a method for preparing a denitrification catalyst for purifying ship diesel engine exhaust. First, a hydrothermal synthesis method is used to prepare an Al2O3 carrier with a regular nano-microsphere morphology; then the active component Ag is loaded on the freshly prepared Al2O3 carrier by a wet impregnation method. However, the steps for preparing the Al2O3 carrier by this method are complicated, and the obtained xAg / Al2O3-S denitrification agent can only achieve good NO at above 400°C. x conversion rate, it is impossible to achieve a high NOx purification rate at 300°C.

[0004] In addition, for natural gas fueled engines, in addition to NOx, there is often escaped methane (CH4) in their exhaust. Methane is a greenhouse gas, and its emission will also pollute the atmospheric environment. Therefore, the development of a catalyst suitable for denitrification of natural gas fueled engine exhaust requires not only high efficiency NO x The removal capacity also requires the ability to reduce the conversion rate of CH4 to reduce greenhouse gas emissions.

[0005] In summary, although there are some SCR catalyst preparation methods and technologies, there are still problems such as complex preparation, insufficient low-temperature activity and inability to simultaneously reduce CH4 conversion rate. Therefore, it is necessary to research and develop a catalyst that is simple to prepare, has high low-temperature activity, good environmental performance and can simultaneously reduce NO x The new SCR catalyst for reducing CH4 emissions is of great significance for improving the exhaust purification efficiency of natural gas fueled engines and reducing atmospheric pollutant emissions. Summary of the invention

[0006] The purpose of the present invention is to provide a new silver-based denitration catalyst suitable for denitration of exhaust gas from natural gas fueled engines and a preparation method thereof, so as to solve the problems of complex preparation, insufficient low-temperature activity, and inability to simultaneously reduce the conversion rate of escaped methane (CH4) existing in the current SCR catalyst. The present invention fully combines the exhaust emission characteristics of marine natural gas fueled engines. Compared with the existing catalysts, the denitration catalyst has higher activity, simpler preparation method, and can simultaneously achieve high purification of escaped CH4.

[0007] In order to achieve the above object, the technical solution of the present invention is as follows:

[0008] The present invention provides a method for preparing a silver-based denitration catalyst suitable for denitration of tail gas from a natural gas fuel engine, comprising the following steps:

[0009] 1) treating alumina powder by wet impregnation with ethylenediamine, and then drying to obtain solid A;

[0010] 2) mixing solid A with a glucose solution to form slurry A, then placing slurry A in an ice water bath and stirring continuously, while dropping a silver precursor solution during stirring to obtain slurry B;

[0011] 3) filtering the slurry B to obtain solid B, washing it several times and then drying it;

[0012] 4) The solid B dried in step 3) is calcined in air at a temperature of 300-600° C. for 3-6 hours to obtain a silver-based denitration catalyst.

[0013] The method uses silver salt solution as a precursor and Al2O3 powder as a catalyst carrier. The Al2O3 powder is treated with ethylenediamine solution to improve the surface properties and structure of the alumina powder, which can effectively enhance the interaction between the Ag component and the alumina carrier. The glucose solution acts as a liquid phase reducing agent in the preparation of the catalyst.

[0014] Furthermore, the amount of the silver precursor solution used must control the mass fraction of silver in the silver-based denitration catalyst to be within the range of 2%-5%.

[0015] Furthermore, the alumina powder used is one or more of α-Al2O3 and γ-Al2O3.

[0016] Furthermore, the drying in step 1) is vacuum drying at a temperature in the range of 50-100°C.

[0017] Furthermore, in step 1), the aluminum oxide powder is wet-impregnated with ethylenediamine for no less than 3 hours.

[0018] Furthermore, the temperature of the ice water bath is controlled within the range of 0-5°C.

[0019] Furthermore, the silver precursor solution is one or more of a silver chloride solution, a silver nitrate solution, and a silver sulfate solution.

[0020] Furthermore, in step 3), the drying temperature is in the range of 60-100° C., and the drying time is controlled in the range of 8-24 hours.

[0021] The present invention also provides a silver-based denitration catalyst suitable for denitration of tail gas from a natural gas fuel engine, prepared according to the aforementioned method, wherein the mass fraction of silver in the silver-based denitration catalyst is in the range of 2%-5%.

[0022] Technical effects of the present invention:

[0023] (1) The Ag-based catalyst prepared by the present invention can achieve the simultaneous removal of methane and nitrogen oxides from the exhaust gas of natural gas fuel engines, which has significant advantages over the traditional vanadium-based catalyst that can only achieve denitrification;

[0024] (2) The Ag-based catalyst prepared by the present invention has a low Ag loading and a high Ag nanoparticle dispersion;

[0025] (3) The Ag-based catalyst prepared by the present invention can achieve a NOx purification rate of more than 80% at 300°C, while the escape CH4 purification rate reaches more than 90%;

[0026] (4) The Ag-based catalyst prepared by the present invention is safe and harmless, and has a significant advantage over the biological toxicity of vanadium-based catalysts;

[0027] (5) The Ag-based catalyst prepared by the present invention is simple to operate, low in cost, and easy to use commercially. DETAILED DESCRIPTION

[0028] The present invention is further described below with reference to the embodiments, but the contents of the present invention are not limited thereto.

[0029] Example 1

[0030] Silver nitrate solution is used as a precursor and γ-Al2O3 is used as a catalyst carrier. The γ-Al2O3 carrier is first wet-impregnated with an ethylenediamine solution for 4 hours, and then vacuum-dried at 60°C; the dried carrier is mixed with a glucose solution to form a slurry A, which is placed in an ice-water bath and the temperature is controlled at about 5°C; the silver nitrate precursor solution is continuously dripped into the slurry A and continuously stirred to obtain a slurry B; the obtained slurry B is filtered and the solid is repeatedly washed with distilled water; the obtained solid is dried at 80°C for 12 hours; the dried solid is calcined at 500°C in air for 4 hours to obtain a silver-based denitration catalyst, which is loaded with 2wt.% Ag. Slurry A contains 2g of carrier, 4g of glucose and 20ml of deionized water. The preparation method of the silver nitrate precursor solution includes: weighing the silver nitrate solid according to the 2wt.% Ag mass of 2g of carrier, and then dissolving it with 10ml of deionized water.

[0031] The catalytic activity test of the catalyst was carried out in a fixed reactor system consisting of a quartz reactor tube. The catalyst was fixed between quartz wool plugs and a K-type thermocouple was placed in the center of the catalyst bed. Each gas in the feed system was individually controlled by a mass flow controller. The feed gas stream consisted of 500 ppm NO; 4000 ppm methane; 6% O2 and Ar balance gas were added to the reactor and gradually heated from 250°C to 300°C at 1°C intervals, staying at each temperature for 40 minutes to obtain stable conditions. The total gas flow rate was 200 ml min -1 / 0.4g catalyst, sieved to obtain a particle size of 40-60 mesh. The inlet and outlet NOx concentrations were measured by the chemiluminescent NO / NO2 / NOx analyzer of Thermo Fisher Scientific. The oxidation of CH4 was measured online using the gas chromatography method of Zhejiang Fuli Analytical Instrument Co., Ltd. using a suitable filling column. After testing, the prepared catalyst can achieve a NOx purification rate of 83% and a CH4 purification rate of more than 92% at 283°C, which meets the use requirements.

[0032] Example 2

[0033] Silver chloride solution is used as a precursor and α-Al2O3 is used as a catalyst carrier. The α-Al2O3 carrier is first wet-impregnated with an ethylenediamine solution for 4 hours, and then vacuum-dried at 60°C; the dried carrier is mixed with a glucose solution to form a slurry A, which is placed in an ice-water bath and the temperature is controlled at about 5°C; the silver chloride precursor solution is continuously lowered in the slurry A, and the temperature is continuously stirred to obtain a slurry B; the obtained slurry B is filtered and the solid is repeatedly washed, and the washing water is distilled water; the obtained solid is dried at 80°C for 12 hours; the dried solid is calcined at 500°C in air for 4 hours to obtain a silver-based denitration catalyst, which is loaded with 2wt.% Ag. Slurry A contains 2g of carrier, 4g of glucose and 20ml of deionized water. The preparation method of the silver chloride precursor solution includes: weighing the silver chloride solid according to the 2wt.% Ag mass of 2g of carrier, and then dissolving it with 10ml of deionized water.

[0034] The catalytic activity test process of the catalyst is exactly the same as that of Example 1. According to the test, the prepared catalyst can achieve a NOx purification rate of more than 81% and a CH4 purification rate of more than 90% at 289°C, which meets the use requirements.

[0035] Example 3

[0036] Silver chloride solution is used as a precursor and γ-Al2O3 is used as a catalyst carrier. The γ-Al2O3 carrier is first wet-impregnated with an ethylenediamine solution for 5 hours, and then vacuum-dried at 50°C; the dried sample is mixed with a glucose solution to form a slurry A, which is placed in an ice-water bath and the temperature is controlled at about 5°C; the silver chloride precursor solution is continuously dripped into the slurry A and continuously stirred to obtain a slurry B; the obtained slurry B is filtered and the solid is repeatedly washed with distilled water; the obtained solid is dried at 100°C for 8 hours; the dried solid is calcined at 600°C in air for 3 hours to obtain a silver-based denitration catalyst, which is loaded with 5wt.% Ag. Slurry A contains 2g of carrier, 4g of glucose and 20ml of deionized water. The preparation method of the silver chloride precursor solution includes: weighing the silver chloride solid according to the 5wt.% Ag mass of 2g of carrier, and then dissolving it with 10ml of deionized water.

[0037] The catalytic activity test process of the catalyst is exactly the same as that of Example 1. According to the test, the prepared catalyst can achieve a NOx purification rate of more than 83% and a CH4 purification rate of more than 90% at 287°C, which meets the use requirements.

[0038] Example 4

[0039] Silver sulfate solution is used as a precursor and γ-Al2O3 is used as a catalyst carrier. The γ-Al2O3 carrier is first wet-impregnated with an ethylenediamine solution for 3 hours, and then vacuum-dried at 100°C; the dried sample is mixed with a glucose solution to form a slurry A, which is placed in an ice-water bath and the temperature is controlled at about 0°C; the silver sulfate precursor solution is continuously dripped into the slurry A and continuously stirred to obtain a slurry B; the obtained slurry B is filtered and the solid is repeatedly washed with distilled water; the obtained solid is dried at 60°C for 24 hours; the dried solid is calcined at 300°C in air for 6 hours to obtain a silver-based denitration catalyst, which is loaded with 2wt.% Ag. Slurry A contains 2g of carrier, 4g of glucose and 20ml of deionized water. The preparation method of the silver sulfate precursor solution includes: weighing the silver sulfate solid according to the 2wt.% Ag mass of 2g of carrier, and then dissolving it with 10ml of deionized water.

[0040] The catalytic activity test process of the catalyst is exactly the same as that of Example 1. According to the test, the prepared catalyst can achieve a NOx purification rate of more than 80% and a CH4 purification rate of more than 90% at 295°C, which meets the use requirements.

[0041] Comparative Example

[0042] The catalyst prepared in Example 3 of CN112604696A was used for comparison. The catalyst evaluation method was the same as that in Example 1 of the present invention. After testing, the sample 4wt.% Ag / Al2O3-S prepared in Example 3 of CN112604696A had a NOx purification rate of 62% and a CH4 purification rate of 75% at 300°C.

Claims

1. A method for preparing a silver-based denitration catalyst suitable for denitration of exhaust gas from a natural gas fuel engine, characterized in that: The following steps are involved: 1) treating alumina powder by wet impregnation with ethylenediamine, and then drying to obtain solid A; 2) mixing solid A with a glucose solution to form slurry A, then placing slurry A in an ice water bath and stirring continuously, while dropping a silver precursor solution during stirring to obtain slurry B; 3) filtering the slurry B to obtain solid B, washing it several times and then drying it; 4) The solid B dried in step 3) is calcined in air at a temperature of 300-600° C. for 3-6 hours to obtain a silver-based denitration catalyst.

2. The method according to claim 1, characterized in that The amount of silver precursor solution used must be controlled so that the mass fraction of silver in the silver-based denitration catalyst is within the range of 2%-5%.

3. The method according to claim 1, characterized in that: The alumina powder used is one or more of α-Al2O3 and γ-Al2O3.

4. The method according to claim 1, characterized in that The drying in step 1) is vacuum drying at a temperature in the range of 50-100°C.

5. The method according to claim 1, characterized in that In step 1), the aluminum oxide powder is wet-impregnated with ethylenediamine for no less than 3 hours.

6. The method according to claim 1, characterized in that The temperature of the ice water bath is controlled within the range of 0-5°C.

7. The method according to claim 1, characterized in that The silver precursor solution is one or more of a silver chloride solution, a silver nitrate solution, and a silver sulfate solution.

8. The method according to claim 1, characterized in that The drying temperature in step 3) is in the range of 60-100° C., and the drying time is controlled in the range of 8-24 hours.

9. A silver-based denitration catalyst suitable for denitration of exhaust gas from a natural gas fuel engine prepared according to the method of any one of claims 1 to 8, characterized in that: The mass fraction of silver in the silver-based denitration catalyst is in the range of 2%-5%.