Catalyst for tail gas treatment of process for preparing formaldehyde through methanol oxidation by iron-molybdenum method, and preparation method and filling starting method thereof

Abstract

The invention discloses a catalyst for tail gas treatment of a process for preparing formaldehyde through methanol oxidation by an iron-molybdenum method, and a preparation method and a filling starting method thereof, and belongs to the technical field of catalysts, the catalyst is developed according to the characteristics of the tail gas of the process for preparing formaldehyde through methanol oxidation by the iron-molybdenum method, and catalyst carriers are two gamma-Al2O3 spherical carriers with different specifications, the active component is noble metal; in the preparation process, the dispersing agent is added, so that the active component precious metal platinum and palladium is highly dispersed in a nano-particle state, the utilization rate of the precious metal is increased, and the high-temperature coalescence phenomenon of the active component of the catalyst is improved by doping the auxiliary agent; compared with a market chemical industrial catalyst, the catalyst prepared by the invention has more excellent catalytic activity and high-temperature-resistant stability; the invention further provides a non-uniform mixing and filling starting method of the catalyst, the problem that the resistance drop of a spherical particle catalyst bed is large is more effectively solved, and the utilization rate of the catalyst and the tail gas treatment effect are further improved.

Description

Technical Field

[0001] The present invention relates to the technical field of catalysts, and particularly to a catalyst for treating the tail gas of the methanol oxidation to formaldehyde process by the iron-molybdenum method, a preparation method thereof, and a loading and starting method thereof. Background Art

[0002] At present, the industrialized and mature methanol oxidation to formaldehyde processes are divided into the "silver method process" and the "iron-molybdenum method process". Compared with the traditional silver method process, the iron-molybdenum method process for catalytic partial oxidation of methanol to formaldehyde has the advantages of lower reaction temperature, lower methanol unit consumption, the catalyst being insensitive to poisons and having a longer service life, and being able to produce high-concentration formaldehyde solution. Therefore, the silver method process has been gradually phased out by the iron-molybdenum method process in the market. At present, about 50 million tons of formaldehyde are produced annually by the iron-molybdenum method, and it is increasing year by year. However, in the process of producing formaldehyde using the iron-molybdenum method, after the reaction tail gas is recycled and absorbed, there are still a large amount of waste gases that cannot be absorbed, resulting in a large amount of toxic and harmful waste gases that need to be treated urgently.

[0003] According to research, for a 300,000-ton formaldehyde plant per year, the corresponding tail gas volume is about 30,000 - 40,000 m 3 / h, and the gas composition of the tail gas is: dimethyl ether 5500 - 6000 mg / m 3 , methanol 2500 - 3000 mg / m 3 , formaldehyde 2000 - 3000 mg / m 3 , water vapor 25000 - 30000 mg / m 3 , carbon monoxide 20000 - 25000 mg / m 3 , oxygen 70000 - 80000 mg / m 3 , and the rest is nitrogen. At present, the most effective method for treating such waste gases is catalytic combustion, which has the advantages of low energy consumption, high treatment efficiency, and no secondary pollution. The core of catalytic combustion lies in the design and optimization of the catalyst, and the performance of the catalyst determines the high and low of the waste gas treatment efficiency and the energy consumption.

[0004] At present, noble metal platinum-palladium catalysts are considered to be the most effective active components for catalytic combustion treatment of the above waste gases. Noble metal catalysts can be divided into two types according to the appearance morphology of the catalyst: honeycomb and granular. The honeycomb catalyst has a small pressure drop in the catalyst bed, but the treatment accuracy is relatively poor. The granular catalyst has a high treatment accuracy, but the catalyst is generally loaded in a loose manner, and the pressure drop of the catalyst bed is relatively large. A high front-end pressure is required when the gas passes through the bed. At present, most of the catalysts used industrially in the iron-molybdenum method process are imported foreign noble metal platinum-palladium granular catalysts. Domestic research reports on related catalysts are mostly on the research of single gas sources, and there are no related reports on catalysts for treating multi-pollution source atmospheres of the tail gas produced by such iron-molybdenum method processes.

[0005] Noble metal catalysts have good catalytic combustion performance, but the total reserves of noble metal resources are low, resulting in the continuous increase in the prices of noble metal Pt and Pd catalysts, making the cost of waste gas treatment catalysts too high. Controlling the cost of catalysts has also become an issue that cannot be ignored. To solve the cost problem, noble metal catalytic combustion catalysts usually load noble metals on carriers with a large specific surface area. However, when directly loading noble metals, noble metal particles are prone to coalescence during the impregnation roasting and long-term use at high temperatures of the catalyst, resulting in a decrease in the utilization rate of noble metals in the catalyst and a decline in activity.

[0006] Therefore, it is of great significance to study particulate catalysts with high dispersion and high stability of noble metals and suitable for treating multi-pollution source atmospheres of the tail gas in the iron-molybdenum process, and to study the packing method of particulate catalysts with low pressure drop. Summary of the Invention

[0007] One of the purposes of the present invention is to provide a catalyst for treating the tail gas of the iron-molybdenum process for methanol oxidation to formaldehyde to solve the above problems.

[0008] To achieve the above purpose, the technical solution adopted by the present invention is as follows: A catalyst for treating the tail gas of the iron-molybdenum process for methanol oxidation to formaldehyde, the catalyst uses two kinds of γ-Al2O3 spherical particles with diameters of 3-8 mm and 2-4 mm as carriers to load noble metals respectively. Among them, the noble metal loading amount of the γ-Al2O3 spherical particle catalyst with a diameter of 3-8 mm is 0.05-0.15 wt%, and the noble metal loading amount of the γ-Al2O3 spherical particle catalyst with a diameter of 2-4 mm is 0.16-0.5 wt%.

[0009] As a preferred technical solution, the specific surface area of the γ-Al2O3 spherical particles is between 100-300 m 2 / g; the noble metal is selected from at least one of Pt or Pd, and the noble metal precursor is selected as nitrate.

[0010] Another purpose of the present invention is to provide a preparation method of the above-mentioned catalyst for treating the tail gas of the iron-molybdenum process for methanol oxidation to formaldehyde. The technical solution adopted is that the method is: using the equal-volume impregnation method to impregnate the γ-Al2O3 spherical carrier particles in an aqueous solution containing noble metal salts, dispersants and additives. After impregnation, drying, roasting, and reduction are carried out to obtain the catalyst.

[0011] The present invention effectively improves the dispersion degree and high-temperature anti-coalescence performance of the noble metal active components of the two types of catalysts by adding dispersants and additives, and improves the removal effect of the catalyst on the tail gas of the iron-molybdenum process.

[0012] As a preferred technical solution, the dispersant is selected from at least one of ascorbic acid, citric acid, polyacrylic acid, and polyethylene glycol. The addition amount of the dispersant is determined according to the noble metal loading amount, and is preferably 1-6 times the mass of the supported noble metal.

[0013] As a preferred technical solution, the auxiliary agent is selected from at least one of sodium carbonate, sodium bicarbonate, cerium nitrate, zirconium nitrate, and lanthanum nitrate. The addition amount of the auxiliary agent is determined according to the noble metal loading amount, and is preferably 1-10 times the mass of the supported noble metal.

[0014] As a preferred technical solution, both the drying and calcination processes are carried out in an air atmosphere. The drying time is 2-5 h, the calcination temperature is programmed heating, the heating rate is 8-12 °C / min, and it is raised to 500-600 °C and maintained at a constant temperature for 3-5 h.

[0015] As a preferred technical solution, the reduction is carried out by one of hydrogen atmosphere, formaldehyde solution, and hydrazine hydrate (N2H4·H2O) solution reduction.

[0016] The third object of the present invention is to provide a method for loading and starting up the above catalyst. When the above catalyst is used for treating the tail gas of the iron-molybdenum method for methanol oxidation to formaldehyde, the catalyst with a diameter of 2-4 mm is loaded at the tail gas inlet, and the catalyst with a diameter of 3-8 mm is loaded at the tail gas outlet.

[0017] As a preferred technical solution, the loading amounts of the catalyst with a diameter of 2-4 mm and the catalyst with a diameter of 3-8 mm in terms of mass percentage are 25-35% and 65-75% respectively. Inert compact magnetic rings are loaded at both ends of the reactor. Before starting up, it is purged with a large amount of air. After the purging is completed, the tail gas is slowly introduced, and the temperature rise of the reaction bed layer is observed to prevent the occurrence of runaway temperature.

[0018] By means of the non-uniform state catalyst, the problem of too large pressure drop in the catalyst bed layer of spherical particle catalysts is effectively solved, and the utilization rate of the catalyst and the tail gas treatment effect are further improved.

[0019] Compared with the prior art, the advantages of the present invention are as follows:

[0020] (1) The catalyst noble metal is loaded on the large specific surface area γ-Al2O3 support by equal-volume impregnation, providing a stable physical structure performance for the catalyst;

[0021] (2) By adding a dispersant, the utilization rate of the noble metal, the active component of the catalyst, is increased, and the activity of the catalyst is improved. Under the condition of the same noble metal dosage, the catalyst has a better effect on purifying the waste gas of the formaldehyde process. The utilization rate of the noble metal is increased, and the noble metal dosage is significantly reduced;

[0022] (3) Improve the low-temperature activity and thermal stability of the catalyst by doping with additives, so that the catalyst still has high activity at a relatively low noble metal content, ensuring a high removal rate of the waste gas from the methanol oxidation to formaldehyde process by the iron-molybdenum method;

[0023] (4) Through the loading of non-uniform catalysts, load the catalysts with a high noble metal content and high low-temperature activity and a small particle diameter of 2-4 mm at the low-temperature part of the tail gas inlet. The waste gas ignites quickly at the inlet, and the heat released by the waste gas combustion is used to increase the temperature of the reaction bed layer, so that the catalysts with a large particle diameter of 3-8 mm and a low noble metal content loaded at the outlet have a relatively high bed layer temperature, and thus also have relatively high activity. The two types of catalysts cooperate with each other to produce the best treatment effect;

[0024] (5) Through the non-uniform loading of two types of catalysts with different particle sizes, effectively make up for the problem of too large pressure drop in the particle catalyst bed layer;

[0025] In short, the catalysts prepared by the above methods and the catalyst loading method can effectively synergize the advantages and disadvantages of the catalysts themselves, maximizing the use effect of the catalysts. The total amount of noble metals used in the catalyst is small, the utilization rate is high, the bed layer pressure is reduced, and at the same time, multi-component waste gases such as formaldehyde, methanol, dimethyl ether and carbon monoxide generated in the iron-molybdenum method formaldehyde production process can be efficiently removed.

[0026] The catalyst of the present invention has good activity, relatively low cost, excellent stability and is applicable to the preparation and loading driving method of noble metal platinum-palladium catalysts for treating the tail gas of the methanol oxidation to formaldehyde process by the iron-molybdenum method, solving the problems that the catalysts for treating the tail gas of the current methanol oxidation to formaldehyde process by the iron-molybdenum method rely on imports, have a high noble metal loading, a low actual utilization rate and a high cost. Specific Embodiments

[0027] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Those not specified in the embodiments are carried out according to conventional conditions or conditions recommended by the manufacturer. Those reagents or instruments not specified by the manufacturer can be obtained as conventional products through commercial purchase.

[0028] The carrier used in the following examples and comparative examples is γ-Al2O3, purchased from Taizhou Tianping Purification Materials Co., Ltd.

[0029] Now, the nouns mentioned in the present invention are described as follows:

[0030] g is the mass unit gram; ml is the volume unit milliliter; °C is the temperature unit degree Celsius; mol / L is the concentration unit mole per liter; vol% is the volume percentage concentration; wt% is the weight percentage; ml / min is the gas flow rate milliliter per minute.

[0031] Example 1

[0032] Preparation of a catalyst for treating the tail gas in the process of methanol oxidation to formaldehyde by the iron-molybdenum method includes the following steps:

[0033] (1) 6.724 g of a platinum nitrate solution with a concentration of 14.87 wt%, 2 g of anhydrous citric acid, and 8.0 g of sodium carbonate are made up to 550 ml with deionized water. 1000 g of γ-Al2O3 particles with a diameter of 3 - 8 mm are impregnated in an equal volume, and dried at 120°C for 2 h to obtain precursor a1;

[0034] (2) 13.448 g of a platinum nitrate solution with a concentration of 14.87 wt%, 4 g of anhydrous citric acid, and 12.0 g of sodium carbonate are made up to 550 ml with deionized water. 1000 g of γ-Al2O3 particles with a diameter of 2 - 4 mm are impregnated in an equal volume, and dried at 120°C for 2 h to obtain precursor a2;

[0035] (3) Precursor a1 and a2 are respectively placed in a muffle furnace, heated to 550°C at a heating rate of 10°C / min and calcined for 4 h, and cooled to room temperature to obtain precursors b1 and b2;

[0036] (4) Precursors b1 and b2 are respectively placed in a tube furnace at 200°C, and a mixed gas of 10 vol% H2 - 90 vol% N2 is introduced for reduction for 1 h to obtain the required catalysts c1 and c2;

[0037] The catalyst loading scheme is as follows: 60 ml of catalyst c2 is loaded at the tail gas inlet, 140 ml of catalyst c1 is loaded at the tail gas outlet, 100 ml of inert magnetic rings are loaded at the upper end of the catalyst bed, and 100 ml of inert magnetic rings are loaded at the lower end. The inert magnetic rings are in the shape of Raschig rings, with a diameter of 7 mm and a height of 1.5 cm. The catalyst evaluation results are shown in Table 1 below.

[0038] Example 2

[0039] Preparation of a catalyst for treating the tail gas in the process of methanol oxidation to formaldehyde by the iron-molybdenum method includes the following steps:

[0040] (1) 6.724 g of a platinum nitrate solution with a concentration of 14.87 wt%, 2.2 g of polyethylene glycol, and 5.6 g of sodium carbonate are made up to 550 ml with deionized water. 1000 g of γ-Al2O3 particles with a diameter of 3 - 8 mm are impregnated in an equal volume, and dried at 120°C for 2 h to obtain precursor a1;

[0041] (2) 13.71 g of a palladium nitrate solution with a concentration of 14.59 wt%, 1.8 g of polyacrylic acid, 8.4 g of cerium nitrate hexahydrate, and 3.2 g of zirconium nitrate are made up to 550 ml with deionized water. 1000 g of γ - Al2O3 particles with a diameter of 2 - 4 mm are impregnated in an equal volume, and dried at 120°C for 2 h to obtain precursor a2;

[0042] (3) Place precursors a1 and a2 in a muffle furnace respectively, raise the temperature to 550 °C at a heating rate of 10 °C / min and calcine for 4 h, then cool to room temperature to obtain precursors b1 and b2;

[0043] (4) Place precursors b1 and b2 in a tube furnace at 200 °C respectively, introduce a mixed gas of 10 vol% H2 - 90 vol% N2 to reduce for 1 h to prepare the required catalysts c1 and c2;

[0044] The catalyst loading scheme is as follows: 60 ml of catalyst c2 is loaded at the tail gas inlet, 140 ml of catalyst c1 is loaded at the tail gas outlet, 100 ml of inert magnetic rings are loaded at the upper end of the catalyst bed, and 100 ml of inert magnetic rings are loaded at the lower end. The catalyst evaluation results are shown in Table 1 below.

[0045] Example 3

[0046] Preparation of a catalyst for treating the tail gas in the process of methanol oxidation to formaldehyde by the iron-molybdenum method, comprising the following steps:

[0047] (1) Take 6.854 g of palladium nitrate solution with a concentration of 14.59 wt%, 1.4 g of ascorbic acid, 6.7 g of lanthanum nitrate hexahydrate, add deionized water to make up the volume to 550 ml, take 1000 g of γ-Al2O3 particles with a diameter of 3 - 8 mm for equal-volume impregnation, and dry at 120 °C for 2 h to obtain precursor a1;

[0048] (2) Take 13.448 g of platinum nitrate solution with a concentration of 14.87 wt%, 4 g of anhydrous citric acid, 6.8 g of cerium nitrate hexahydrate, 5.2 g of lanthanum nitrate hexahydrate, add deionized water to make up the volume to 550 ml, take 1000 g of γ-Al2O3 particles with a diameter of 2 - 4 mm for equal-volume impregnation, and dry at 120 °C for 2 h to obtain precursor a2;

[0049] (3) Place precursors a1 and a2 in a muffle furnace respectively, raise the temperature to 550 °C at a heating rate of 10 °C / min and calcine for 4 h, then cool to room temperature to obtain precursors b1 and b2;

[0050] (4) Place precursors b1 and b2 in an excessive mixed solution of 10 % N2H4·H2O - 90% H2O to reduce for 1 h to prepare the required catalysts c1 and c2;

[0051] The catalyst loading scheme is as follows: 60 ml of catalyst c2 is loaded at the tail gas inlet, 140 ml of catalyst c1 is loaded at the tail gas outlet, 100 ml of inert magnetic rings are loaded at the upper end of the catalyst bed, and 100 ml of inert magnetic rings are loaded at the lower end. The catalyst evaluation results are shown in Table 1 below.

[0052] Example 4

[0053] Preparation of a catalyst for treating the tail gas in the process of producing formaldehyde by the iron-molybdenum method for methanol oxidation, comprising the following steps:

[0054] (1) Add 6.854 g of palladium nitrate solution with a concentration of 14.59 wt%, 2.2 g of polyethylene glycol, and 9.7 g of sodium bicarbonate to deionized water and make up the volume to 550 ml. Take 1000 g of γ-Al2O3 particles with a diameter of 3-8 mm for isovolumetric impregnation, and dry at 120 °C for 2 h to obtain precursor a1;

[0055] (2) Add 6.724 g of platinum nitrate solution with a concentration of 14.87 wt%, 6.854 g of palladium nitrate solution with a concentration of 14.59 wt%, 4 g of anhydrous citric acid, and 12.0 g of sodium carbonate to deionized water and make up the volume to 550 ml. Take 1000 g of γ-Al2O3 particles with a diameter of 2-4 mm for isovolumetric impregnation, and dry at 120 °C for 2 h to obtain precursor a2;

[0056] (3) Place precursors a1 and a2 in a muffle furnace respectively, heat to 550 °C at a heating rate of 10 °C / min and calcine for 4 h, and cool to room temperature to obtain precursors b1 and b2;

[0057] (4) Place precursors b1 and b2 in a tubular furnace at 200 °C respectively, introduce a 10 vol% H2-90 vol% N2 mixed gas and reduce for 1 h to obtain the required catalysts c1 and c2;

[0058] The catalyst loading scheme is as follows: 60 ml of catalyst c2 is loaded at the tail gas inlet, 140 ml of catalyst c1 is loaded at the tail gas outlet, 100 ml of inert magnetic rings are loaded at the upper end of the catalyst bed, and 100 ml of inert magnetic rings are loaded at the lower end. The catalyst evaluation results are shown in Table 1 below.

[0059] Example 5

[0060] Preparation of a catalyst for treating the tail gas in the process of producing formaldehyde by the iron-molybdenum method for methanol oxidation, comprising the following steps:

[0061] (1) Add 6.724 g of platinum nitrate solution with a concentration of 14.87 wt%, 2 g of anhydrous citric acid, and 8.0 g of sodium carbonate to deionized water and make up the volume to 550 ml. Take 1000 g of γ-Al2O3 particles with a diameter of 3-8 mm for isovolumetric impregnation, and dry at 120 °C for 2 h to obtain precursor a1;

[0062] (2) Add 13.448 g of platinum nitrate solution with a concentration of 14.87 wt%, 4 g of anhydrous citric acid, and 12.0 g of sodium carbonate to deionized water and make up the volume to 550 ml. Take 1000 g of γ-Al2O3 particles with a diameter of 2-4 mm for isovolumetric impregnation, and dry at 120 °C for 2 h to obtain precursor a2;

[0063] (3) Place precursors a1 and a2 in a muffle furnace respectively, raise the temperature to 550 °C at a heating rate of 10 °C / min and calcine for 4 h, then cool to room temperature to obtain precursors b1 and b2;

[0064] (4) Place precursors b1 and b2 in an excessive 10 % N2H4·H2O - 90% H2O mixed solution respectively for reduction for 1 h, and dry at 120 °C to obtain the required catalysts c1 and c2;

[0065] The catalyst loading scheme is as follows: 60 ml of catalyst c2 is loaded at the tail gas inlet, 140 ml of catalyst c1 is loaded at the tail gas outlet, 100 ml of inert magnetic rings are loaded at the upper end of the catalyst bed, and 100 ml of inert magnetic rings are loaded at the lower end. The catalyst evaluation results are shown in Table 1 below.

[0066] Example 6

[0067] The preparation of a catalyst for treating the tail gas of the iron-molybdenum process for methanol oxidation to formaldehyde includes the following steps:

[0068] (1) Take 6.854 g of palladium nitrate solution with a concentration of 14.59 wt%, 2.8 g of ascorbic acid, and 12.6 g of cerium nitrate hexahydrate, add deionized water to make up the volume to 550 ml and shake well. Take 1000 g of γ-Al2O3 particles with a diameter of 3 - 8 mm for isovolumetric impregnation, and dry at 120 °C for 2 h to obtain precursor a1;

[0069] (2) Take 13.448 g of platinum nitrate solution with a concentration of 14.87 wt%, 4 g of anhydrous citric acid, and 12.0 g of sodium carbonate, add deionized water to make up the volume to 550 ml. Take 1000 g of γ-Al2O3 particles with a diameter of 2 - 4 mm for isovolumetric impregnation, and dry at 120 °C for 2 h to obtain precursor a2;

[0070] (3) Place precursors a1 and a2 in a muffle furnace respectively, raise the temperature to 550 °C at a heating rate of 10 °C / min and calcine for 4 h, then cool to room temperature to obtain precursors b1 and b2;

[0071] (4) Pass precursor b1 through a 10 vol% H2 - 90% vol N2 mixed gas for reduction for 1 h to obtain the required catalyst c1; place precursor b2 in an excessive 10 % N2H4·H2O - 90% H2O mixed solution for reduction for 1 h, and dry at 120 °C to obtain the required catalyst c2;

[0072] The catalyst loading scheme is as follows: 60 ml of catalyst c2 is loaded at the tail gas inlet, 140 ml of catalyst c1 is loaded at the tail gas outlet, 100 ml of inert magnetic rings are loaded at the upper end of the catalyst bed, and 100 ml of inert magnetic rings are loaded at the lower end. The catalyst evaluation results are shown in Table 1 below.

[0073] Comparative Example 1

[0074] This comparative example is based on Example 1. In steps (1) and (2), anhydrous citric acid is not added, and the remaining preparation method and loading method are the same as those in Example 1. The catalyst evaluation results are shown in Table 1 below.

[0075] Comparative Example 2

[0076] This comparative example is based on Example 1. In steps (1) and (2), sodium carbonate is not added, and the remaining preparation method and loading method are the same as those in Example 1. The catalyst evaluation results are shown in Table 1 below.

[0077] Comparative Example 3

[0078] This comparative example is based on Example 1. During loading, catalyst c1 is evenly loaded, and the rest is the same as in Example 1. The catalyst evaluation results are shown in Table 1 below.

[0079] Comparative Example 4

[0080] This comparative example is a commercially available industrial iron-molybdenum method methanol-to-formaldehyde tail gas treatment catalyst from Kline. The noble metal loading of 3-4 mm small particles is 0.3 wt%, and the noble metal loading of 4-6 mm large particles is 0.1 wt%. Compared with Example 1, the total noble metal consumption of the catalyst is slightly higher, and the loading method is the same as in Example 1.

[0081] Test Example

[0082] The catalyst activity evaluation was carried out on a fixed-bed reactor. The gas composition of the tail gas was as follows: dimethyl ether 6000 mg / m3, methanol 2700 mg / m3, formaldehyde 2500 mg / m3, water vapor 25000 - 30000 mg / m3, carbon monoxide 25000 mg / m3, oxygen 80000 mg / m3, and the rest was nitrogen. The amount of catalyst used was 200 ml, and the gas hourly space velocity was 9000 h -1 . The contents of dimethyl ether, methanol, carbon monoxide, and carbon dioxide were detected and analyzed by gas chromatography, and the formaldehyde content was analyzed by spectrophotometry. The detection results of the gas concentrations after catalytic combustion treatment are shown in Table 1.

[0083] Table 1 Detection Results of Gas Concentrations after Catalytic Combustion Treatment for Each Example and Comparative Example

[0084]

[0085] As can be seen from the data in Table 1, the performance of the catalyst prepared in the examples of the present invention for catalytic combustion of "iron-molybdenum method formaldehyde tail gas" is superior to that of the catalysts in the comparative examples.

[0086] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A catalyst for treating tail gas in a process of producing formaldehyde by oxidation of methanol using an iron-molybdenum method, characterized in that: The catalyst uses two types of γ-Al2O3 spherical particles with diameters of 3-8 mm and 2-4 mm as carriers to load precious metals, wherein: The precious metal loading of the γ-Al2O3 spherical particle catalyst with a diameter of 3-8mm is 0.05~0.15wt%, and the precious metal loading of the γ-Al2O3 spherical particle catalyst with a diameter of 2-4mm is 0.16~0.5wt%.

2. The catalyst for treating tail gas from methanol oxidation to formaldehyde process according to claim 1, characterized in that: The specific surface area of ​​the γ-Al2O3 spherical particles is between 100-300m 2 / g; the precious metal is selected from at least one of Pt and Pd.

3. The method for preparing the catalyst for treating tail gas of the process of producing formaldehyde by methanol oxidation using the iron-molybdenum method according to claim 1 or 2, characterized in that: The method comprises: using an equal volume impregnation method to immerse the gamma-Al2O3 spherical carrier particles in an aqueous solution containing a noble metal salt, a dispersant and an auxiliary agent, and after the impregnation is completed, drying, roasting and reducing are performed to obtain the catalyst.

4. The method according to claim 3, characterized in that The dispersant is selected from at least one of ascorbic acid, citric acid, polyacrylic acid and polyethylene glycol.

5. The method according to claim 3, characterized in that: The auxiliary agent is selected from at least one of sodium carbonate, sodium bicarbonate, cerium nitrate, zirconium nitrate and lanthanum nitrate.

6. The method according to claim 3, characterized in that The drying and calcining processes are both carried out in an air atmosphere, the drying time is 2 to 5 hours, the calcining temperature is programmed, the heating rate is 8 to 12°C / min, and the temperature is raised to 500 to 600°C and maintained at a constant temperature for 3 to 5 hours.

7. The method according to claim 3, characterized in that The reduction is carried out by using one of hydrogen atmosphere, formaldehyde solution and hydrated hydrazine solution.

8. The catalyst loading and starting method according to claim 1 or 2, characterized in that: The catalyst with a diameter of 2-4 mm is loaded at the exhaust gas inlet, and the catalyst with a diameter of 3-8 mm is loaded at the exhaust gas outlet.

9. The method according to claim 8, characterized in that The loading mass percentages of the catalyst with a diameter of 2-4 mm and the catalyst with a diameter of 3-8 mm are 25-35% and 65-75%, respectively.

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