Natural gas catalytic combustion catalyst and preparation method thereof

Abstract

The invention relates to the technical field of natural gas catalytic combustion catalysts, in particular to a natural gas catalytic combustion catalyst and a preparation method thereof.The catalyst comprises a catalyst prepared through sol-gel and a catalyst prepared through a hydrothermal method; substrates are arranged in the catalyst prepared by the sol-gel method and the catalyst prepared by the hydrothermal method, and a first catalytic material is arranged in the catalyst prepared by the sol-gel method; the preparation method comprises a sol-gel preparation method and a hydrothermal preparation method. The catalyst can be prepared through two technical means, the catalytic effect of the catalyst is ensured, the conversion temperature needed by natural gas during combustion is effectively reduced, natural gas can be better completely oxidized in a low-temperature environment, material selection and preparation can be conducted according to actual conditions, and the catalytic effect is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of natural gas catalytic combustion catalysts, and in particular to a natural gas catalytic combustion catalyst and a preparation method thereof. Background Art

[0002] Natural gas (CH4) is less polluting than oil, coal and other fuels, and emits less pollutants such as CO2, SO2 and NOx during combustion. Catalytic combustion is an effective way to further control and eliminate NOx. Compared with ordinary combustion methods, catalytic combustion has higher combustion efficiency and energy utilization.

[0003] Compared with traditional flame combustion, catalytic combustion has the following advantages: 1. Low ignition temperature (10% conversion temperature), low energy consumption, stable combustion, and even after reaching the ignition temperature, the oxidation reaction can be completed without external heat transfer; 2. High purification efficiency. The emission level of pollutants (NOX and incomplete combustion products, etc.) is low, and the general organic waste gas conversion rate is above 98%. The generation of NOX gas can be greatly reduced at the ignition temperature. The CC-20 methane catalytic combustion catalyst developed by the Catalysis Pilot Laboratory of the Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences has a methane volume fraction of less than 5×10-6 in the exhaust gas after the reaction; 3. It adapts to a wide range of oxygen concentrations, has no secondary pollution, and has mild combustion, low operating costs, and convenient operation and management; 4. Low noise.

[0004] The biggest difficulty in catalytic combustion technology is to choose a suitable catalyst. Catalytic combustion catalysts mainly include supported noble metals, perovskite-type and hexaaluminate-type catalysts.

[0005] Supported precious metal catalysts have good complete oxidation activity and stability. Pt and Pd are common precious metals. Precious metals are easy to volatilize, sinter and poison at high temperatures, and their high prices limit their application in high-temperature combustion of methane. They are usually used in the low-temperature ignition stage of the burner. ABO3 perovskite composite oxides and hexaaluminate catalysts are generally called non-metallic catalysts. When perovskite catalysts are used at high temperatures, they also have the phenomenon of high-temperature sintering to reduce the specific surface area, which has an adverse effect on activity. Supported precious metal catalysts and perovskite catalysts are more suitable for the low-temperature stage of methane combustion, while non-precious metal catalysts are suitable for high-temperature catalytic combustion of methane.

[0006] The invention discloses a catalytic combustion catalyst with the publication number of CN101537351B, which is composed of a catalytic component and a carrier. The catalytic component is alkaline earth metal, rare earth metal, subgroup metal and zirconium oxide. Based on 100 parts of zirconium oxide, the alkaline earth metal is 2-40 parts, the rare earth metal is 6-30 parts, the subgroup metal is 1-30 parts, the rare earth metal is selected from lanthanum and cerium, the weight ratio of lanthanum to cerium is (3-20):1, the subgroup element is selected from one of titanium, iron, cobalt, nickel, zinc, manganese and copper, and the carrier is activated carbon, which is 60-98% by weight of the catalyst. Compared with the prior art, the catalyst has the characteristics of relatively low cost, low temperature for 100% conversion of natural gas and low CO and NOx emissions after combustion.

[0007] The above technical solution cannot fully reduce the natural gas conversion temperature and cannot achieve complete oxidation of natural gas in a low temperature environment, so it needs to be improved. Summary of the invention

[0008] The purpose of the present invention is to solve the shortcomings of the prior art and to propose a natural gas catalytic combustion catalyst and a preparation method.

[0009] In order to achieve the above object, the present invention adopts the following technical solutions:

[0010] Catalysts for catalytic combustion of natural gas, including catalysts prepared by sol-gel method and catalysts prepared by hydrothermal method;

[0011] The catalyst prepared by the sol-gel method and the catalyst prepared by the hydrothermal method are both provided with a substrate, the catalyst prepared by the sol-gel method is provided with a first catalytic material, and the catalyst prepared by the hydrothermal method is provided with a second catalytic material;

[0012] The substrate is made of any one of alumina and aluminosilicate;

[0013] The first catalyst material and the second catalyst material both contain substance A and urea.

[0014] The first catalytic material in the catalyst prepared by the sol-gel method is deionized water and CeO2 powder;

[0015] The second catalytic material in the catalyst prepared by the hydrothermal method adopts methanol solution and ethanol aqueous solution. Compared with the prior art, the present application can prepare the catalyst by two technical means and ensure the catalytic effect of the catalyst, so as to effectively reduce the conversion temperature required for natural gas during combustion, so as to better completely oxidize natural gas in a low temperature environment, and can select and prepare materials according to actual conditions to ensure the catalytic effect.

[0016] Preferably, the substance A is a mixture of Co / Zr / Mn salts.

[0017] Furthermore, basic reaction materials are provided for the catalyst to realize the preparation of the catalyst.

[0018] The present invention also proposes a sol-gel preparation method for a natural gas catalytic combustion catalyst, which is applicable to the above-mentioned natural gas catalytic combustion catalyst and comprises the following steps:

[0019] S1. Material dissolution: Solution A and urea (1:1 molar ratio) were dissolved in 30 ml of deionized water respectively;

[0020] S2, stirring and mixing: mixing the separately prepared dilute urea aqueous solution and saturated solution A. Stirring the product at 30° C. for 2 h;

[0021] S3. Stirring and drying: CeO2 powder is then added, and the homogenous solution is dried at about 80°C under strong stirring to completely evaporate the water.

[0022] S4. Powder calcination: The obtained powder was calcined at 400° C. for 4 hours, and a sample was collected.

[0023] Furthermore, the manufacturing steps are simple and convenient, which is convenient for technicians in this field to prepare efficiently. At the same time, the operating steps and conditions are clear, which ensures the effect and quality of the later preparation.

[0024] The present invention also proposes a hydrothermal preparation method for a natural gas catalytic combustion catalyst, which is applicable to the above-mentioned natural gas catalytic combustion catalyst and comprises the following steps:

[0025] S1. Dissolution and stirring: Weigh substance A and 30 mmol of urea and dissolve them in 70 ml of methanol solution. Stir the obtained mixed solution magnetically at a rate of 700 rpm for 30 min.

[0026] S2, heating and cooling: the obtained pink transparent solution is transferred to a 100 ml inner tank equipped with a stainless steel hydrothermal reactor shell, placed in a constant temperature electric heating box, adjusted to 180°C, and maintained for 12 hours. After it is naturally cooled to room temperature;

[0027] S3, centrifugal collection: the precipitate in the kettle is washed 3-5 times with a 50% ethanol aqueous solution at 10000 rpm; finally, the precipitate is collected by centrifugation;

[0028] S4, drying and crushing: the collected products are placed in an oven and dried at 80°C overnight; the dried block samples are ground into fine powder using a mortar;

[0029] S5. Preparation by staged heating: transfer all the pink powder to a porcelain boat of suitable size and place it in a tubular furnace. Set the heating rate to rise from room temperature to 200°C at 1°C min-1, then rise from 200°C to 300°C at 5°C min-1, and maintain for 2h. The final sample is recorded as Co3O4 nanocloud.

[0030] Furthermore, the manufacturing steps are simple and convenient, which is convenient for technicians in this field to prepare efficiently. At the same time, the operating steps and conditions are clear, which ensures the effect and quality of the later preparation.

[0031] Preferably, the equipment used in S1-S4 includes a muffle furnace, a constant temperature stirrer, an oven, a beaker, a measuring cylinder, and a balance.

[0032] Furthermore, the production of high quality catalysts is achieved using conventional components.

[0033] Preferably, the equipment used in S1-S5 includes a tubular furnace, a centrifuge, a muffle furnace, a constant temperature stirrer, an oven, a beaker, a measuring cylinder, and a balance.

[0034] Furthermore, the production of high quality catalysts is achieved using conventional components.

[0035] The beneficial effects of the present invention are:

[0036] 1. The catalyst is prepared by two technical means and the catalytic effect of the catalyst is ensured to effectively reduce the conversion temperature required for natural gas combustion, so as to better enable the natural gas to be completely oxidized in a low-temperature environment, and the material selection and preparation can be carried out according to the actual situation to ensure the catalytic effect;

[0037] 2. The manufacturing steps of the two schemes are simple and convenient, which is convenient for technicians in this field to prepare efficiently. At the same time, the operating steps and conditions are clear to ensure the effect and quality of the later preparation. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a diagram showing the steps for preparing the sol-gel of the natural gas catalytic combustion catalyst proposed by the present invention;

[0039] Figure 2 This is a diagram of the hydrothermal preparation steps of the natural gas catalytic combustion catalyst proposed by the present invention. DETAILED DESCRIPTION

[0040] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0041] Reference Figure 1-2, natural gas catalytic combustion catalysts, including catalysts prepared by sol-gel method and catalysts prepared by hydrothermal method;

[0042] The catalyst prepared by sol-gel and the catalyst prepared by hydrothermal method are both provided with a substrate, the catalyst prepared by sol-gel is provided with a first catalytic material, and the catalyst prepared by hydrothermal method is provided with a second catalytic material;

[0043] The substrate is made of either alumina or aluminosilicate;

[0044] The first catalyst material and the second catalyst material both contain substance A and urea.

[0045] The first catalytic material in the catalyst prepared by sol-gel is deionized water and CeO2 powder;

[0046] The second catalytic material in the catalyst prepared by the hydrothermal method is a methanol solution or an ethanol aqueous solution.

[0047] In the present invention, substance A is a mixture of Co / Zr / Mn salts.

[0048] The present invention also proposes a sol-gel preparation method for a natural gas catalytic combustion catalyst, which is applicable to the above-mentioned natural gas catalytic combustion catalyst and comprises the following steps:

[0049] S1. Material dissolution: Solution A and urea (1:1 molar ratio) were dissolved in 30 ml of deionized water respectively;

[0050] S2, stirring and mixing: mixing the separately prepared dilute urea aqueous solution and saturated solution A. Stirring the product at 30° C. for 2 h;

[0051] S3. Stirring and drying: CeO2 powder is then added, and the homogenous solution is dried at about 80°C under strong stirring to completely evaporate the water.

[0052] S4. Powder calcination: The obtained powder was calcined at 400° C. for 4 hours, and a sample was collected.

[0053] In the present invention, the equipment used in S1-S4 includes a muffle furnace, a constant temperature stirrer, an oven, a beaker, a measuring cylinder, and a balance.

[0054] The present invention also proposes a hydrothermal preparation method for a natural gas catalytic combustion catalyst, which is applicable to the above-mentioned natural gas catalytic combustion catalyst and comprises the following steps:

[0055] S1. Dissolution and stirring: Weigh substance A and 30 mmol of urea and dissolve them in 70 ml of methanol solution. Stir the obtained mixed solution magnetically at a rate of 700 rpm for 30 min.

[0056] S2, heating and cooling: the obtained pink transparent solution is transferred to a 100 ml inner tank equipped with a stainless steel hydrothermal reactor shell, placed in a constant temperature electric heating box, adjusted to 180°C, and maintained for 12 hours. After it is naturally cooled to room temperature;

[0057] S3, centrifugal collection: the precipitate in the kettle is washed 3-5 times with a 50% ethanol aqueous solution at 10000 rpm; finally, the precipitate is collected by centrifugation;

[0058] S4, drying and crushing: the collected products are placed in an oven and dried at 80°C overnight; the dried block samples are ground into fine powder using a mortar;

[0059] S5. Preparation by staged heating: transfer all the pink powder to a porcelain boat of suitable size and place it in a tubular furnace. Set the heating rate to rise from room temperature to 200°C at 1°C min-1, then rise from 200°C to 300°C at 5°C min-1, and maintain for 2h. The final sample is recorded as Co3O4 nanocloud.

[0060] In the present invention, the equipment used in S1-S5 includes a tubular furnace, a centrifuge, a muffle furnace, a constant temperature stirrer, an oven, a beaker, a measuring cylinder, and a balance. Selecting corresponding equipment according to the operating steps can fully improve the preparation effect and quality, thereby improving the operating efficiency.

[0061] In the present invention, during actual production and preparation, ZIF-67 material can also be used. ZIF-67 is a metal organic framework material, and its basic structure is composed of iron, imidazole and benzoic acid, in which iron is the central ion, connecting different imidazoles and benzoic acids to form a three-dimensional network structure. This structure has highly ordered pores and a high specific surface area, and can be used in gas adsorption, separation, catalysis and other fields. The unique structure of ZIF-67 determines that it has good stability and controllability, and its properties and functions can be changed by chemical modification;

[0062] The preparation attempts of ZIF-67 and other simple nanoparticles will decide whether to use ZIF-67 in the future based on the yield. The preparation of simple nanoparticles will be carried out according to the above experimental steps. Based on the experimental results, the above experimental steps will be selected and improved to continue to improve the catalytic effect.

[0063] Principle of natural gas catalytic combustion catalyst:

[0064] The main component of natural gas is methane, which also contains other alkanes. Taking methane as an example, the combustion of methane is a highly exothermic reaction. During the oxidation of methane, the following reactions occur: (1), (2), (3), and (4). According to the reaction equation, the catalytic combustion of methane is a highly exothermic reaction, which means that the oxidation of methane has a great advantage in thermodynamics. However, due to the four symmetrical CH bonds of methane and the extremely high bond energy of each chemical bond (439KJ / mol), CH4 molecules are not easy to activate, and a higher temperature is required to oxidize methane. In order to achieve complete oxidation of methane under low temperature conditions, it is generally believed that there are four mechanisms: the (LH) mechanism and the (RE) mechanism dominated by adsorbed oxygen; the (MKV) mechanism dominated by lattice oxygen; and the (TT) mechanism dominated by both.

[0065] CH4(g)+2O2(g)=CO2(g)+2HO△H(298K))=-891KJ / mol#(1)

[0066] CH4(g)+2CO2(g)=2CO(g)+2H2(g)△H(298K)=-261KJ / mol#(2)

[0067] 2CH4(g)+O2(g)=2CO(g)+4H2(g)△H(298K)=-36KJJ / mol#(3)

[0068] H2O(g)+CO(g)=CO(g)+H2(g)△H(298K)-49.1KJ / mol#(4)

[0069] The following is a detailed introduction:

[0070] The LH mechanism believes that the activation energy of molecular oxygen adsorption on the catalyst surface is significantly lower than that of CH4 molecules, and molecular oxygen is preferentially adsorbed on the catalyst surface to form adsorbed oxygen. At the same time, adsorbed oxygen is easier to combine with CH4 molecules than molecular oxygen, causing the hydrogen molecules in them to separate, destroying the stable structure of CH4, and generating active methyl radicals, thereby promoting CH4 oxidation. The LH mechanism is mainly used for precious metals and their supported oxide systems.

[0071] The RE mechanism believes that the CH4 molecule first combines with the lattice oxygen in the catalyst, causing the C-H bond in the CH4 molecule to break and form free radicals, which are then oxidized. At the same time, the CH4 molecule consumes lattice oxygen during the combination with the catalyst, generating weakly electrically charged oxygen vacancies, which adsorb molecular oxygen to supplement the loss of lattice oxygen in the catalyst.

[0072] The MVK mechanism can be divided into the following three steps:

[0073] In the first step, gaseous CH4 molecules are adsorbed on the active sites of the catalyst to form adsorbed CH4.

[0074] In the second step, the adsorbed CH4 molecules are destroyed by the surface lattice oxygen to form Finally, it is oxidized to adsorbed CO2 and H2O, and oxygen vacancies are formed. This step can be described as catalyst reduction.

[0075] In the third step, the adsorbed CO2 and H2O desorb from the surface to form gaseous CO2 and H2O. At the same time, the internal lattice oxygen migrates to the surface, and the oxygen vacancies are refilled with surface adsorbed oxygen. This step can be described as catalyst reoxidation.

[0076] For precious metal catalysts, the strength of their catalytic ability mainly comes from d-orbital electrons. The more d-orbital electrons there are, the larger the atomic radius is, and the stronger the catalytic effect of the electrons is. The catalytic performance is Pt>Ir>Os>Pd>Rh>Ru. However, in practical applications, Pd and Pt have demonstrated excellent low-temperature catalytic activity and have received widespread attention.

[0077] For non-precious metal catalysts, they follow the RE or MVK mechanism, that is, oxidizing CH4 through lattice oxygen. Therefore, the number of lattice oxygen and the specific surface area of ​​the catalyst determine the performance of the non-precious metal catalyst, that is, catalytic combustion is not catalytic methane, but catalytic oxygen, which reduces the combustion conditions of methane. Since Co3O4 has the best performance, we choose Co as the basic preparation raw material. And by doping other elements, increase its oxygen vacancies and achieve better catalytic effects.

[0078] Introduction to Co-based catalysts:

[0079] Co3O4 is a common form of Co-based catalysts, and its catalytic activity mainly depends on the following aspects: morphology and structure, temperature, and the number of oxygen vacancies.

[0080] Morphology and structure: The nanostructure of Co3O4 has a great influence on the catalytic activity. According to previous experimental results, the (111) crystal plane has better catalytic activity. 2+ , with more oxygen vacancies, thus enhancing the catalytic performance.

[0081] Temperature: Above 550°C, serious sintering problems will occur, which significantly reduces its catalytic performance. The stability of Co ions can be enhanced by loading.

[0082] The number of oxygen vacancies: The number of oxygen vacancies determines the catalytic activity of the catalyst. Doping with other elements can increase the number of oxygen vacancies without increasing the difficulty of synthesis. Therefore, the synthesis method of Co-based catalysts uses the doping method to enhance their performance.

[0083] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A natural gas catalytic combustion catalyst, characterized in that: Including catalysts prepared by sol-gel method and catalysts prepared by hydrothermal method; The catalyst prepared by the sol-gel method and the catalyst prepared by the hydrothermal method are both provided with a substrate, the catalyst prepared by the sol-gel method is provided with a first catalytic material, and the catalyst prepared by the hydrothermal method is provided with a second catalytic material; The substrate is made of any one of alumina and aluminosilicate; The first catalyst material and the second catalyst material both contain substance A and urea. The first catalytic material in the catalyst prepared by the sol-gel method is deionized water and CeO2 powder; The second catalytic material in the catalyst prepared by the hydrothermal method is a methanol solution or an ethanol aqueous solution.

2. The natural gas catalytic combustion catalyst according to claim 1, characterized in that: The substance A is a mixture of Co / Zr / Mn salts.

3. A sol-gel preparation method for a natural gas catalytic combustion catalyst, characterized in that: The natural gas catalytic combustion catalyst applicable to any one of claims 1 to 2 comprises the following steps: S1. Material dissolution: Solution A and urea (1:1 molar ratio) were dissolved in 30 ml of deionized water respectively; S2, stirring and mixing: mixing the separately prepared dilute urea aqueous solution and saturated solution A. Stirring the product at 30° C. for 2 h; S3. Stirring and drying: CeO2 powder is then added, and the homogenous solution is dried at about 80°C under strong stirring to completely evaporate the water. S4. Powder calcination: The obtained powder was calcined at 400° C. for 4 hours, and a sample was collected.

4. A hydrothermal method for preparing a natural gas catalytic combustion catalyst, characterized in that: The natural gas catalytic combustion catalyst applicable to any one of claims 1 to 2 comprises the following steps: S1. Dissolution and stirring: Weigh substance A and 30 mmol of urea and dissolve them in 70 ml of methanol solution. Stir the obtained mixed solution magnetically at a rate of 700 rpm for 30 min. S2, heating and cooling: the obtained pink transparent solution is transferred to a 100 ml inner tank equipped with a stainless steel hydrothermal reactor shell, placed in a constant temperature electric heating box, adjusted to 180°C, and maintained for 12 hours. After it is naturally cooled to room temperature; S3, centrifugal collection: the precipitate in the kettle is washed 3-5 times with a 50% ethanol aqueous solution at 10000 rpm; finally, the precipitate is centrifuged and collected; S4, drying and crushing: the collected products are placed in an oven and dried at 80°C overnight; the dried block samples are ground into fine powder using a mortar; S5. Preparation by staged heating: transfer all the pink powder to a porcelain boat of suitable size and place it in a tubular furnace. Set the heating rate to rise from room temperature to 200°C at 1°C min-1, then rise from 200°C to 300°C at 5°C min-1, and maintain for 2h. The final sample is recorded as Co3O4 nanocloud.

5. The method for preparing a natural gas catalytic combustion catalyst according to claim 3, characterized in that: The equipment used in S1-S4 includes a muffle furnace, a constant temperature stirrer, an oven, a beaker, a measuring cylinder, and a balance.

6. The method for preparing a natural gas catalytic combustion catalyst according to claim 4, characterized in that: The equipment used in S1-S5 includes a tubular furnace, a centrifuge, a muffle furnace, a constant temperature stirrer, an oven, a beaker, a measuring cylinder, and a balance.

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