Space decoupling type engine tail gas treatment method and device

Abstract

The invention provides an engine tail gas treatment method. The engine tail gas treatment method comprises the steps that ammonia gas is introduced into an ammonia gas decomposition module through an ammonia gas generation module; under the action of an ammonia decomposition catalyst loaded in the ammonia decomposition module, the ammonia is subjected to an ammonia decomposition reaction in the ammonia decomposition module to obtain hydrogen and nitrogen; hydrogen obtained through decomposition of the ammonia gas decomposition module and carbon dioxide tail gas generated by an engine are mixed in a methanation module, and mixed gas is obtained; under the action of a methanation catalyst loaded in the methanation module, the mixed gas is subjected to a methanation reaction in the methanation module, and methane and water are obtained; and the pressurizing module is used for pressurizing methane from the methanation module and introducing the methane into the engine for supplying energy to the engine. Gas exhausted by the whole engine is converted from carbon dioxide into ammonia decomposition byproduct nitrogen and methanation byproduct water, emission of harmful gas is reduced, and cyclic utilization of energy is achieved.

Description

Technical Field

[0001] The present invention relates to the field of engine exhaust treatment, and in particular to a spatially decoupled engine exhaust treatment method and device. Background Art

[0002] As the world's demand for reducing carbon emissions and achieving sustainable energy production grows, developing vehicles that use clean fuels is the key to reducing carbon emissions from traditional fuel vehicles. As a zero-carbon fuel, ammonia has a high hydrogen content and is easy to store and transport, making it a hot topic in clean energy applications.

[0003] In addition, the use of NH3 as engine fuel is also a trend, but due to the difficulty of NH3 combustion, N2O and NO x The emissions are high, so using NH3 to power engines is not practical until mature technology is available.

[0004] Therefore, a method for treating and utilizing tail gas based on an existing engine is needed. Summary of the invention

[0005] In view of this, in order to at least partially solve at least one of the above-mentioned technical problems, the present invention provides an engine exhaust treatment method and device.

[0006] According to an embodiment of one aspect of the present invention, there is provided a method for treating engine exhaust gas, comprising:

[0007] Ammonia is introduced into the ammonia decomposition module through the ammonia generation module;

[0008] Under the action of the ammonia decomposition catalyst loaded in the ammonia decomposition module, ammonia undergoes an ammonia decomposition reaction in the ammonia decomposition module to obtain hydrogen and nitrogen;

[0009] The hydrogen obtained by decomposition of the ammonia decomposition module and the carbon dioxide tail gas generated by the engine are mixed in the methanation module to obtain a mixed gas;

[0010] Under the action of the methanation catalyst loaded in the methanation module, the mixed gas undergoes a methanation reaction in the methanation module to obtain methane and water;

[0011] The methane from the methanation module is pressurized and introduced into the engine to power the engine.

[0012] According to another embodiment of the present invention, there is provided an engine exhaust treatment device, comprising:

[0013] An ammonia generation module, used for generating ammonia;

[0014] An ammonia decomposition module loaded with an ammonia decomposition catalyst is arranged at the exhaust gas outlet of the engine and is used to decompose the ammonia generated by the ammonia generation module under the action of the ammonia decomposition catalyst to obtain hydrogen and nitrogen;

[0015] A methanation module loaded with a methanation catalyst is arranged at the exhaust gas outlet of the engine, and is used to methanate the hydrogen obtained by the ammonia decomposition module and the carbon dioxide exhaust gas produced by the engine under the action of the methanation catalyst to obtain methane and water;

[0016] The energy supply module is used to pass the methane obtained by the methanation module into the engine to supply energy to the engine.

[0017] According to an embodiment of the present invention, a large amount of carbon dioxide gas in the exhaust gas of the engine is utilized, and the hydrogen and carbon dioxide generated by the decomposition of ammonia are used for methanation reaction under corresponding catalyst conditions. Through the step-by-step application of the two-stage reaction temperature and the gradual cooling of the exhaust gas from the engine, methane gas that can be used for engine power supply is generated, and the reaction conversion rate is significantly improved, thereby increasing the utilization of the methane energy supply system on the basis of the original energy supply system of the engine. At the same time, ammonia, as a carbon-free hydrogen carrier, has a high volume and mass energy density, and the storage and transportation technology is relatively mature. Hydrogen is obtained by decomposing ammonia, and there is no need to store and transport hydrogen, which increases safety. The gas exhausted by the entire engine is converted from carbon dioxide to nitrogen, a by-product of ammonia decomposition, and water, a by-product of methanation, reducing nitrogen oxides (NO x ) and other harmful gas emissions, realizes the recycling of energy, improves energy efficiency, and realizes the operation of "ammonia-powered" engines with low or even carbon-free emissions. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The above and other objects, features and advantages of the present invention will become more apparent through the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:

[0019] Figure 1 Schematic diagram of the engine exhaust treatment method according to an embodiment of the present invention; (a) is a chemical reaction path diagram; (b) is a schematic diagram of the assembly of the engine and the exhaust pipe; (c) is a schematic diagram of the engine exhaust treatment device;

[0020] Figure 2 The figures are performance characterization diagrams of ruthenium-based nanocluster magnesium aluminate catalysts; (a) is a spherical aberration-corrected scanning transmission electron micrograph of the Ru / MgAl2O4 catalyst prepared in Example 1; (b) is an X-ray absorption spectrum of the Ru / MgAl2O4 catalyst prepared in Example 1;

[0021] Figure 3The catalytic performance test results of the ruthenium-based nanocluster magnesium aluminate catalyst of the embodiment of the present invention are shown in FIG. (a) is the result of hydrogen temperature-programmed reduction; (b) is the result of carbon dioxide temperature-programmed desorption experiment;

[0022] Figure 4 The catalytic performance test results of ruthenium-based nanocluster magnesium aluminate catalyst are shown in Figure 2; (a) shows the change of ammonia conversion rate with temperature; (b) shows the change of carbon dioxide conversion rate and methane selectivity with temperature; (c) shows the change of carbon dioxide conversion rate and chemical equilibrium with temperature. DETAILED DESCRIPTION

[0023] Below, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the present invention. In the following detailed description, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of embodiments of the present invention. However, it is apparent that one or more embodiments may also be implemented without these specific details. In addition, in the following description, descriptions of known structures and technologies are omitted to avoid unnecessary confusion of concepts of the present invention.

[0024] The terms used herein are only for describing specific embodiments and are not intended to limit the present invention. The term "comprising" used herein indicates the existence of features, steps, operations, but does not exclude the existence or addition of one or more other features.

[0025] In the case of using expressions such as "at least one of A, B, and C, etc.", it should generally be interpreted in accordance with the meaning of the expression generally understood by those skilled in the art (for example, "a system having at least one of A, B, and C" should include but is not limited to a system having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, C, etc.). In the case of using expressions such as "at least one of A, B, or C, etc.", it should generally be interpreted in accordance with the meaning of the expression generally understood by those skilled in the art (for example, "a system having at least one of A, B, or C" should include but is not limited to a system having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, C, etc.).

[0026] In the process of realizing the concept of the present invention, it was found that the use of hydrogen obtained by ammonia decomposition to hydrogenate the carbon dioxide emitted by traditional engines can effectively reduce greenhouse gas emissions. The hydrogenated methane can be used as an intermediate fuel for the engine, which can effectively improve the energy efficiency and combustion characteristics of traditional fuel vehicle systems and reduce pollution emissions. Therefore, an ammonia engine system based on the combination of ammonia decomposition hydrogen production and methanation (ammonia decomposition, 2NH3 → 3H2 + N2, ΔG 298K= 87.2 kJ / mol; carbon dioxide methanation, CO2 + 4H2→CH4 + 2H2O, ΔG 298K = -130.8 kJ / mol), which is expected to achieve carbon neutrality, provide an efficient energy conversion method, and further promote the development of ammonia engines.

[0027] Specifically, according to an embodiment of one aspect of the present invention, a method for treating engine exhaust gas is provided, comprising the following steps S1 to S5:

[0028] Figure 1 Schematic diagram of the engine exhaust treatment method and device according to an embodiment of the present invention; (a) is a chemical reaction pathway diagram; (b) is a schematic diagram of the engine and exhaust pipe assembly; (c) is a schematic diagram of the engine exhaust treatment device.

[0029] Step S1: introducing ammonia into the ammonia decomposition module through the ammonia generation module.

[0030] Step S2: Under the action of the ammonia decomposition catalyst loaded in the ammonia decomposition module, the ammonia undergoes an ammonia decomposition reaction in the ammonia decomposition module to obtain hydrogen and nitrogen.

[0031] Step S3: The hydrogen obtained by decomposition of the ammonia decomposition module and the carbon dioxide tail gas generated by the engine are mixed in the methanation module to obtain a mixed gas.

[0032] Step S4: Under the action of the methanation catalyst loaded in the methanation module, the mixed gas undergoes a methanation reaction in the methanation module to obtain methane and water.

[0033] Step S5: pressurizing the methane from the methanation module and passing it into the engine to power the engine.

[0034] According to the embodiment of the present invention, in step S1, ammonia is very easy to compress and liquefy, and storage and transportation are safe and convenient. The volume energy density of liquid ammonia is much greater than that of liquid hydrogen. The hydrogen storage density of the same volume of liquid ammonia is 60% higher than that of liquid hydrogen. In addition, the storage and transportation cost of liquid ammonia is lower, the explosion limit range of ammonia is narrower, the boiling point is higher, the possibility of fire and explosion is lower, and ammonia has a pungent smell, so leakage is easy to be found, which is safer and more reliable.

[0035] According to an embodiment of the present invention, in step S2, the ammonia decomposition catalyst includes a catalyst that can decompose ammonia into nitrogen and hydrogen, and the ammonia decomposition catalyst can significantly reduce the activation energy of the ammonia decomposition reaction and increase the reaction rate. The ammonia decomposition reaction is an endothermic entropy-increasing reaction. Conventional processes usually require a higher temperature to achieve complete decomposition of ammonia. It is generally believed that a high conversion rate of ammonia decomposition reaction should be achieved above 800°C, and the temperature of the engine exhaust gas usually does not exceed 800°C. Therefore, the addition of the catalyst can enable the ammonia to achieve a decomposition reaction at the engine exhaust temperature, while improving the conversion rate of ammonia.

[0036] According to an embodiment of the present invention, in step S3, a large amount of carbon dioxide gas will be generated during the combustion process due to the presence of carbon elements, which is also one of the main components of engine exhaust. By mixing hydrogen and carbon dioxide exhaust, these two gases can be used more efficiently. Hydrogen can be used as a reducing agent, and carbon dioxide can be used as a carbon source to participate in the methanation reaction together to generate methane and water.

[0037] According to an embodiment of the present invention, in step S4, the methanation reaction is a highly exothermic process. The better the activity of the catalyst, the faster the methanation reaction rate. By using a methanation catalyst, a higher carbon dioxide conversion rate and a higher methane yield can be achieved, while reducing the occurrence of side reactions, thereby generating methane with higher purity.

[0038] According to an embodiment of the present invention, in step S5, in the methanation module, the generated methane gas usually needs to be pressurized by a boosting device such as a boosting pump, a compressor, etc. to increase its pressure and density so that it is suitable for the combustion requirements of the engine.

[0039] According to an embodiment of the present invention, a large amount of carbon dioxide gas in the exhaust gas of the engine is utilized, and the hydrogen and carbon dioxide generated by the decomposition of ammonia are used for methanation reaction under corresponding catalyst conditions. Through the step-by-step application of the two-stage reaction temperature and the gradual cooling of the exhaust gas from the engine, methane gas that can be used for engine power supply is generated, and the reaction conversion rate is significantly improved, thereby increasing the utilization of the methane energy supply system on the basis of the original energy supply system of the engine. At the same time, ammonia, as a carbon-free hydrogen carrier, has a high volume and mass energy density, and the storage and transportation technology is relatively mature. Hydrogen is obtained by decomposing ammonia, and there is no need to store and transport hydrogen, which increases safety. The gas exhausted by the entire engine is converted from carbon dioxide to nitrogen, a by-product of ammonia decomposition, and water, a by-product of methanation, reducing nitrogen oxides (NO x ) and other harmful gas emissions, realizes the recycling of energy, improves energy efficiency, and realizes the operation of "ammonia-powered" engines with low or even carbon-free emissions.

[0040] According to an embodiment of the present invention, the engine is an internal combustion engine powered by fuel oil and / or methane as raw materials.

[0041] According to an embodiment of the present invention, Figure 1 As shown in (b), the generated methane returns to the engine from the tailpipe through the pipeline for combustion and energy supply. For example, in a four-cylinder internal combustion engine, the other three cylinders are powered by burning fuel, and one cylinder is powered by burning methane, forming a hybrid engine. At the same time, ammonia is considered to be a potential renewable resource, so it can not only save fuel usage and resources, but also reduce pollutants and carbon emissions, making it more environmentally friendly. Methane engines can also be modified to increase resource utilization efficiency while reducing carbon emissions.

[0042] In some specific embodiments of the present invention, the modification of the engine exhaust treatment can be to add methane-powered cylinders to the original engine.

[0043] In some specific embodiments of the present invention, methane gas can be used for energy supply, and a new power system can be added to realize energy supply by a dual power system.

[0044] In some specific embodiments of the present invention, methane can be mixed with fuel and then burned to provide energy.

[0045] According to an embodiment of the present invention, the concentrations of ammonia, hydrogen and carbon dioxide tail gas are monitored respectively by concentration sensors;

[0046] According to the concentration monitoring results of ammonia, hydrogen and carbon dioxide tail gas, the flow rates of ammonia and carbon dioxide tail gas are respectively controlled by flow controllers to adjust the degree of methanation reaction.

[0047] According to an embodiment of the present invention, Figure 1 (c) It can be seen that the concentrations of ammonia, hydrogen and carbon dioxide can be monitored by concentration sensors. The monitored values ​​of each concentration can be further calculated. According to the chemical equilibrium and kinetics of the methanation reaction, the current concentration data can be evaluated to determine whether the flow of ammonia and carbon dioxide tail gas needs to be adjusted to optimize the reaction. The flow controller can accurately adjust the gas flow rate to achieve fine control of the reaction conditions to maintain the optimal degree of methanation reaction and reduce the waste of reactants and the generation of by-products.

[0048] According to an embodiment of the present invention, the ammonia decomposition catalyst includes at least one of a ruthenium-based nanocluster catalyst and a nickel-based nanocluster catalyst;

[0049] The methanation catalyst comprises at least one of a nickel-based or a ruthenium-based catalyst;

[0050] The loading amounts of the ammonia decomposition catalyst and the methanation catalyst are 1-5 kg ​​and 40-200 meshes respectively.

[0051] According to the embodiments of the present invention, the ruthenium-based catalyst is one of the most effective catalysts in the ammonia decomposition reaction, and can achieve complete conversion of ammonia at a relatively low temperature. The nickel-based catalyst is one of the catalysts that exhibit the most outstanding activity among non-precious metal catalysts, is low in cost, and has high catalytic activity, and can be used on a large scale.

[0052] Furthermore, the active sites of the catalyst play a decisive role in the reaction path of carbon dioxide methanation and also have a significant effect on the activation of carbon dioxide. Nickel is one of the most active metals in carbon dioxide methanation catalysts. Nickel-based catalysts not only have high methanation activity, but are also widely distributed in nature and therefore have low costs. Ruthenium, as one of the precious metal catalysts, exhibits significant low-temperature activity in carbon dioxide methanation reactions. According to the engine exhaust gas flow rate of 0.1-1.0 m3 / s, it can be determined that the catalyst loading of the ammonia decomposition module and the methanation module is 1~5 kg, and the particle size is 40~200 mesh.

[0053] According to an embodiment of the present invention, the loading amounts of the ammonia decomposition catalyst and the methanation catalyst are 1 kg, 2 kg, 3 kg, 4 kg, and 5 kg, respectively, but are not limited to the listed values, and other values ​​not listed within the numerical range are also applicable. The particle sizes of the ammonia decomposition catalyst and the methanation catalyst are 40 mesh, 60 mesh, 100 mesh, 120 mesh, 150 mesh, 180 mesh, 200 mesh, and 220 mesh, respectively.

[0054] In some specific embodiments of the present invention, ruthenium-based and nickel-based catalysts can also be used together as methanation catalysts. The combination of nickel and ruthenium is intended to transfer the high activity characteristics of ruthenium to the Ni-based catalyst without the need for a high ruthenium loading. At the same time, ruthenium can provide additional methanation sites and overflow hydrogen into nearby nickel sites, thereby improving the catalytic activity.

[0055] According to an embodiment of the present invention, the ammonia decomposition catalyst is a ruthenium-based nanocluster magnesium aluminate catalyst; and the methanation catalyst is a nickel-based aluminum oxide.

[0056] According to an embodiment of the present invention, a method for preparing a ruthenium-based nanocluster catalyst for ammonia decomposition comprises: preparing magnesium-aluminum hydrotalcite by a coprecipitation method; drying and screening the magnesium-aluminum hydrotalcite, and then performing a first calcination at 800-1200° C. to obtain a magnesium-aluminum composite oxide support, wherein the magnesium-aluminum composite oxide support comprises magnesium oxide and spinel-structured magnesium aluminate; using an equal volume impregnation method, impregnating the magnesium-aluminum composite oxide support into a ruthenium salt solution, drying, and then performing a second calcination at 300-600° C. to obtain a ruthenium-based nanocluster catalyst.

[0057] The ruthenium-based nanocluster catalyst prepared by the above method has a single-atom nanocatalytic structure, and the atomically dispersed metal ruthenium provides a larger metal surface area for the catalytic reaction to occur; at the same time, it is obtained by high-temperature calcination of the magnesium-aluminum hydrotalcite precursor, has high thermal stability, and has a strong "anchoring" effect on precious metals, especially ruthenium; in addition, the magnesium-aluminum hydrotalcite is synthesized by a simple co-precipitation method, and the specific morphology of the magnesium-aluminum hydrotalcite creates a higher specific surface area and total pore volume for the carrier to accommodate more active sites.

[0058] According to an embodiment of the present invention, the activity of the nickel-based catalyst can be further improved by modifying the metal oxide carrier, and different oxide carriers will affect the methanation yield. The nickel-based alumina catalyst has high catalytic activity and good anti-carbon deposition performance, and its performance can be optimized by different methods and doping modification, so it can be used as a catalyst for the methanation reaction of carbon dioxide.

[0059] According to an embodiment of the present invention, the temperature of the ammonia decomposition reaction is 400-600° C.; the temperature of the methanation reaction is 250-400° C.; and the pressure of the methane entering the engine for energy supply after supercharging is 0.5-1.5 bar.

[0060] According to an embodiment of the present invention, the temperature of ammonia decomposition can be 400°C, 450°C, 500°C, 550°C, 600°C, but is not limited to the listed values, and other values ​​not listed in the numerical range are also applicable. The temperature of the methanation reaction can be 250°C, 300°C, 350°C, 400°C, but is not limited to the listed values, and other values ​​not listed in the numerical range are also applicable.

[0061] According to the embodiment of the present invention, the reaction temperature of ammonia decomposing into hydrogen and nitrogen is usually between 800℃ and 850℃, but the temperature of the exhaust gas discharged from the engine to the exhaust manifold is about 800~900℃, which will be reduced to 600~700℃ after passing through the front three-way catalytic converter, and only 400℃ at idle speed. Therefore, it is necessary to select a suitable catalyst to reduce the reaction temperature to the range of 400~600℃ while allowing sufficient reaction.

[0062] According to an embodiment of the present invention, an ammonia decomposition reaction module is arranged at the end near the engine in the exhaust pipe, while a methanation reaction module is arranged at the end far from the engine. The distance between the ammonia decomposition module and the engine is smaller than the distance between the methanation reaction module and the engine. As the engine exhaust gas decreases in temperature as the distance from the engine along the exhaust pipe into the atmosphere increases, a natural temperature difference can be formed, which meets the respective temperature ranges of the ammonia decomposition reaction and the methanation reaction.

[0063] According to an embodiment of the present invention, the pressure of methane entering the engine for energy supply after supercharging may be 0.5 bar, 0.7 bar, 0.9 bar, 1.1 bar, 1.2 bar, or 1.5 bar, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0064] According to another embodiment of the present invention, there is provided an engine exhaust treatment device, such as Figure 1 (b) and Figure 1 (c) as shown, including:

[0065] An ammonia generation module, used for generating ammonia;

[0066] An ammonia decomposition module loaded with an ammonia decomposition catalyst is arranged at the exhaust gas outlet of the engine and is used to decompose the ammonia generated by the ammonia generation module under the action of the ammonia decomposition catalyst to obtain hydrogen and nitrogen;

[0067] A methanation module loaded with a methanation catalyst is arranged at the exhaust gas outlet of the engine, and is used to methanate the hydrogen obtained by the ammonia decomposition module and the carbon dioxide exhaust gas produced by the engine under the action of the methanation catalyst to obtain methane and water;

[0068] The energy supply module is used to pass the methane obtained by the methanation module into the engine to supply energy to the engine.

[0069] According to an embodiment of the present invention, the ammonia generation module can be achieved by loading an ammonia cracker in a system where a vehicle or other engine is located, or storing and outputting ammonia through an ammonia storage tank. It can also use solid ammonia technology (SSCR) to use inorganic salt powder as an ammonia storage material and release ammonia from the ammonia storage material by heating.

[0070] According to an embodiment of the present invention, the engine exhaust treatment device can be used to modify the existing engine. The two reaction modules respectively select catalysts that are more conducive to the reaction, so as to achieve higher efficiency in the recycling of exhaust gas. Not only can the substance and temperature of the exhaust gas be utilized, but also carbon emissions can be reduced to protect the environment, while improving energy utilization efficiency. There is no need to change the structure of the engine on a large scale, and it can be applied to various types of internal combustion engines in current vehicles to save the original fuel usage of the internal combustion engine.

[0071] According to an embodiment of the present invention, Figure 1As shown in (b), both the ammonia decomposition module and the methanation module can be realized by a reactor such as a membrane or a fixed bed coated on the engine exhaust pipe. The ammonia decomposition module uses the heat in the exhaust pipe to carry out the ammonia decomposition reaction without exchanging substances with the exhaust gas. The hydrogen obtained by the decomposition is connected to the exhaust pipe through an external pipeline and is used for the subsequent methanation module to carry out the methanation reaction. Furthermore, the methanation module is connected to the exhaust pipe, and uses the carbon dioxide in the exhaust pipe and the newly added hydrogen from the external pipeline to carry out the methanation reaction to obtain methane gas.

[0072] Specifically, the ammonia decomposition module and the methanation module can be constructed by installing a shell, a cushion layer, a carrier and a catalyst on the basis of the original tail gas pipe. A temperature sensor can also be configured to monitor the reaction temperature.

[0073] In some specific implementations of the present invention, a turbocharger is provided in the energy supply module to pressurize the methane produced by the methanation module and then pump it into the engine through a pipeline for combustion and energy supply.

[0074] In some specific embodiments of the present invention, a separation device is provided in the energy supply module to purify the methane gas entering the engine, for example, nitrogen and water are separated by membrane separation technology to obtain methane with higher purity for energy supply.

[0075] According to an embodiment of the present invention, the engine exhaust treatment device may further include:

[0076] An ammonia sensor is arranged between the ammonia generation module and the ammonia decomposition module to monitor the concentration of ammonia;

[0077] A hydrogen sensor is provided between the ammonia decomposition module and the methanation module to monitor the concentration of hydrogen;

[0078] Carbon dioxide sensor, used to monitor the concentration of carbon dioxide exhaust produced by the engine;

[0079] An ammonia flow controller, used to control the flow of ammonia entering the ammonia decomposition module according to the monitoring results of the ammonia sensor and the hydrogen sensor;

[0080] The carbon dioxide flow controller is used to control the flow of the engine carbon dioxide exhaust gas entering the methanation module through the monitoring results of the hydrogen sensor and the carbon dioxide sensor.

[0081] According to an embodiment of the present invention, an ammonia sensor can monitor the concentration of ammonia participating in the ammonia decomposition reaction, and a hydrogen sensor can monitor the concentration of hydrogen generated after the decomposition of ammonia. Through the monitoring values ​​of ammonia and hydrogen concentrations, the corresponding ammonia flow rate can be further configured according to the chemical reaction balance, so that the ammonia decomposition reaction can be more complete, the conversion rate can be improved, the generation of by-products can be reduced, and the waste of ammonia can be reduced.

[0082] According to an embodiment of the present invention, the carbon dioxide sensor can monitor the concentration of carbon dioxide in the exhaust gas, configure the concentration of the input carbon dioxide according to the concentrations of carbon dioxide and hydrogen and the chemical reaction equilibrium of the carbon dioxide methanation reaction, and adjust the stoichiometric ratio of carbon dioxide and hydrogen, so that the carbon dioxide methanation reaction can be fully carried out, thereby improving the conversion rate and reducing the generation of by-products, thereby achieving a carbon dioxide conversion rate of nearly 100%, so that methane can be used to supply energy to the engine.

[0083] According to an embodiment of the present invention, the engine exhaust treatment device may further include: an ammonia capture module, disposed between the ammonia decomposition module and the methanation module, for capturing ammonia that has not been completely reacted in the ammonia decomposition module.

[0084] According to an embodiment of the present invention, the ammonia trap may be dilute sulfuric acid or other solid ammonia absorbing materials. The ammonia trap may also be connected to an ammonia generating module to release the captured ammonia for use in the ammonia decomposition reaction; or the ammonia trap may be replaced regularly to reuse the ammonia collected in the ammonia trap in other ways. Ammonia has a pungent odor, and by collecting it in the trap, it can be prevented from being discharged into the atmosphere through the tail pipe to pollute the environment.

[0085] The scheme of the present invention will be further explained below based on specific embodiments.

[0086] Example 1 Preparation of Ruthenium-based Nanocluster Magnesium Aluminate Catalyst

[0087] Preparation of 5%Ru / MgAl2O4 catalyst

[0088] Step S1: weigh 19.2305 g of Mg(NO3)2·6H2O and 11.2540 g of Al(NO3)3·9H2O, add 100 mL of deionized water to fully dissolve to obtain a salt solution, then mix with 3 mol / L of sodium hydroxide and 2 mol / L of sodium carbonate as a precipitant, and co-titrate the salt solution to a pH of 10 to obtain a precipitate solution;

[0089] Step S2: After stirring the precipitate solution at 100° C. and aging for 24 h, the aged precipitate is fully dried in a forced air drying oven at 120° C. to obtain a carrier precursor magnesium-aluminum hydrotalcite;

[0090] Step S3: crushing and screening the carrier precursor magnesium-aluminum hydrotalcite, and then placing it in a muffle furnace at 1000°C for calcination for 2 h, i.e., the first calcination, to obtain a MgAl2O4 carrier;

[0091] Step S4: The calcined MgAl2O4 carrier is taken out and loaded with 5% metal Ru by an equal volume impregnation method, and then placed in a muffle furnace for calcination at 500°C for 2 h, i.e., the second calcination, to obtain a 5% Ru / MgAl2O4 nanocluster catalyst.

[0092] Figure 2 : It is a performance characterization diagram of the ruthenium-based nanocluster magnesium aluminate catalyst; (a) is a spherical aberration-corrected scanning transmission electron micrograph of the Ru / MgAl2O4 catalyst prepared in Example 1; (b) is an X-ray absorption spectrum of the Ru / MgAl2O4 catalyst prepared in Example 1.

[0093] according to Figure 2 It can be seen that spherical aberration-corrected transmission electron microscopy shows the formation of ruthenium clusters with a size of about 1.2 nm, and X-ray absorption spectroscopy data proves that ruthenium mainly exists in metallic form.

[0094] Example 2 Catalytic Performance Test of Ruthenium-based Nanocluster Magnesium Aluminate Catalyst

[0095] Test conditions:

[0096] The gas composition before the ammonia decomposition reactor is: 8 mL / min CO2 + 42 mL / min N2, the NH3 controller flow rate is 21 mL / min, and the temperature is 400 o C. The catalyst is Ru / MgAl2O4 prepared in Example 1; the temperature of the carbon dioxide reactor is 350 o C, the pressure is 3 Mpa, and the catalyst is a commercially available Ni / Al2O3 catalyst.

[0097] Catalyst preparation: 0.1 g of Ru / MgAl2O4 and commercially available Ni / Al2O3 catalysts were granulated into 40-60 mesh and reduced in situ with 50 mL / min H2 for 2 h; the catalysts were then diluted with 0.6 g of quartz sand and placed in the ammonia decomposition reactor and the carbon dioxide reactor.

[0098] Product testing:

[0099] The gas at the end of the carbon dioxide methanation reactor is introduced into an online gas chromatograph equipped with a thermal conductivity detector and a hydrogen flame ionization detector for detection. Before the product flows into the gas chromatograph, the generated water is removed using a trap filled with anhydrous calcium sulfate. The calculation formulas for CO2 conversion, ammonia conversion, and methane selectivity are as follows:

[0100] X(CO2)=(CO2,in-CO2,out) / CO2,in×100%

[0101] X(NH3)=(NH3,in-NH3,out) / NH3,in×100%

[0102] S(CH4)= CH4,out / (CO2,in-CO2,out),in×100%

[0103] Among them, X(CO2), X(NH3) and S(CH4) represent CO2 conversion rate, NH3 conversion rate and CH4 selectivity respectively; CO2,in, CO2,out, NH3,in, NH3,out and CH4,out are CO2 input molar amount, CO2 output molar amount, NH3 input molar amount, NH3 output molar amount and CH4 output molar amount respectively.

[0104] Test results: NH3 conversion rate is 45.9%, CO2 conversion rate is 97.0%, and CH4 selectivity is 100%.

[0105] Figure 3 The catalytic performance test results of the ruthenium-based nanocluster magnesium aluminate catalyst of the embodiment of the present invention are shown in FIG. (a) is the result of hydrogen temperature-programmed reduction; (b) is the result of carbon dioxide temperature-programmed desorption experiment.

[0106] according to Figure 3 It can be seen that the hydrogen temperature-programmed reduction results indicate the uniform metal-support effect of the catalyst, and the carbon dioxide temperature-programmed desorption experimental results demonstrate the concentrated basic site distribution of the catalyst.

[0107] Example 3 Catalytic Performance Test of Ruthenium-based Nanocluster Magnesium Aluminate Catalyst

[0108] The same test method and detection calculation method as in Example 2 were used, except that the temperature of the ammonia decomposition reactor was 550°C.

[0109] Test results: NH3 conversion rate is 100%, CO2 conversion rate is 97.0%, and CH4 selectivity is 100%.

[0110] Example 4 Catalytic Performance Test of Ruthenium-based Nanocluster Magnesium Aluminate Catalyst

[0111] The same test method and detection calculation method as in Example 2 were used, except that the temperature of the ammonia decomposition reactor was 400°C.

[0112] Test results: NH3 conversion rate is 83.1%, CO2 conversion rate is 19.9%, and CH4 selectivity is 100%.

[0113] Example 5 Catalytic Performance Test of Ruthenium-based Nanocluster Magnesium Aluminate Catalyst

[0114] The same test method and detection calculation method as in Example 2 were used, except that the temperature of the ammonia decomposition reactor was 550°C and the temperature of the carbon dioxide reactor was 500°C.

[0115] Test results: NH3 conversion rate is 100%, CO2 conversion rate is 72.2%, and CH4 selectivity is 100%.

[0116] Figure 4 The catalytic performance test results of ruthenium-based nanocluster magnesium aluminate catalyst are shown in Figure 2; (a) shows the change of ammonia conversion rate with temperature; (b) shows the change of carbon dioxide conversion rate and methane selectivity with temperature; (c) shows the change of carbon dioxide conversion rate and chemical equilibrium with temperature.

[0117] according to Figure 4 It can be seen that under the action of ruthenium-based nanocluster magnesium aluminate catalyst, the conversion rate of ammonia can reach a relatively high level above 450°C, and can be close to 100% ammonia conversion rate above 500°C; the conversion rate of carbon dioxide methanation reaction can reach a relatively high level above 300°C, and can be close to 100% carbon dioxide conversion rate above 350°C.

[0118] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for treating engine exhaust, comprising: Ammonia is introduced into the ammonia decomposition module through the ammonia generation module; Under the action of the ammonia decomposition catalyst loaded in the ammonia decomposition module, the ammonia undergoes an ammonia decomposition reaction in the ammonia decomposition module to obtain hydrogen and nitrogen; The hydrogen obtained by decomposition of the ammonia decomposition module and the carbon dioxide tail gas generated by the engine are mixed in the methanation module to obtain a mixed gas; Under the action of the methanation catalyst loaded in the methanation module, the mixed gas undergoes a methanation reaction in the methanation module to obtain methane and water; The methane from the methanation module is pressurized and introduced into the engine to power the engine.

2. The method according to claim 1, wherein: The engine is an internal combustion engine powered by fuel oil and / or methane as raw materials.

3. The method according to claim 1, wherein: Also includes: The concentrations of the ammonia, the hydrogen and the carbon dioxide tail gas are respectively monitored by concentration sensors; According to the monitoring results of the concentrations of the ammonia, hydrogen and carbon dioxide tail gas, the flow rates of the ammonia and carbon dioxide tail gas are respectively controlled by flow controllers to adjust the degree of the methanation reaction.

4. The method according to claim 1, wherein: The ammonia decomposition catalyst includes at least one of a ruthenium-based nanocluster catalyst and a nickel-based nanocluster catalyst; The methanation catalyst comprises at least one of a nickel-based or a ruthenium-based catalyst; The loading amounts of the ammonia decomposition catalyst and the methanation catalyst are 1-5 kg ​​respectively, and the particle sizes are 40-200 meshes.

5. The method according to claim 1 or 4, wherein: The ammonia decomposition catalyst is a ruthenium-based nanocluster magnesium aluminate catalyst; The methanation catalyst is nickel-based alumina.

6. The method according to claim 1 or 5, wherein: The temperature of the ammonia decomposition reaction is 400-600°C; The temperature of the methanation reaction is 250-400°C; The pressure of the supercharged methane entering the engine to supply energy is 0.5~1.5 bar.

7. A device for treating engine exhaust, comprising: An ammonia generation module, used for generating ammonia; An ammonia decomposition module loaded with an ammonia decomposition catalyst is arranged at the exhaust gas outlet of the engine and is used to decompose the ammonia generated by the ammonia generation module under the action of the ammonia decomposition catalyst to obtain hydrogen and nitrogen; A methanation module loaded with a methanation catalyst is arranged at the exhaust gas outlet of the engine, and is used to carry out a methanation reaction on the hydrogen obtained by the ammonia decomposition module and the carbon dioxide exhaust gas produced by the engine under the action of the methanation catalyst to obtain methane and water; The energy supply module is used to pass the methane obtained by the methanation module into the engine to supply energy to the engine.

8. The device according to claim 7, wherein: Also includes: an ammonia sensor, disposed between the ammonia generation module and the ammonia decomposition module, for monitoring the concentration of the ammonia; A hydrogen sensor, disposed between the ammonia decomposition module and the methanation module, for monitoring the concentration of the hydrogen; Carbon dioxide sensor, used to monitor the concentration of carbon dioxide exhaust produced by the engine; an ammonia flow controller, used to control the flow of the ammonia gas entering the ammonia decomposition module according to the monitoring results of the ammonia gas sensor and the hydrogen gas sensor; A carbon dioxide flow controller is used to control the flow of the engine carbon dioxide exhaust gas entering the methanation module through the monitoring results of the hydrogen sensor and the carbon dioxide sensor.

9. The device according to claim 7, wherein: Also includes: The ammonia capture module is arranged between the ammonia decomposition module and the methanation module, and is used to capture the ammonia that has not been completely reacted in the ammonia decomposition module.

10. The device according to claim 7, wherein: The ammonia decomposition module and the methanation module are respectively at least one of a membrane or fixed bed reactor coated on the engine tailpipe.

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