Regeneration method of iron-molybdenum catalyst for preparing formaldehyde through methanol oxidation and application of catalyst

Abstract

The invention relates to a method for regenerating an iron-molybdenum catalyst through alkali treatment and application. The iron-molybdenum catalyst is mainly applied to the process of preparing formaldehyde through methanol oxidation, and the average service life of the catalyst is 6-12 months. A specific regeneration process of the inactivated iron-molybdenum catalyst comprises the following steps: firstly, treating the inactivated iron-molybdenum catalyst by using an alkali solution to obtain a molybdenum-containing solution molybdenum source, and then synthesizing the solution molybdenum source and a soluble iron salt solution again to obtain the regenerated catalyst. The method is characterized in that the iron-molybdenum catalyst inactivated by alkali treatment is regenerated and then re-evaluated, the methanol oxidation reaction for preparing formaldehyde is carried out on a fixed bed reactor, the methanol conversion rate can reach 99% at most, and the formaldehyde selectivity reaches up to 92%. According to the regeneration method, high reaction activity and selectivity of the iron-molybdenum catalyst are recovered, and the regeneration method has remarkable economic benefits.

Description

Technical Field

[0001] This invention relates to the technical field of catalyst recovery and regeneration, specifically to a method for regenerating an iron-molybdenum catalyst for the oxidation of methanol to formaldehyde and the application of the catalyst. Background Technology

[0002] Formaldehyde is a colorless gas with a pungent odor. It is readily soluble in water and also in organic solvents such as ethanol and ether. Formaldehyde is chemically reactive and can react with many compounds to form various derivatives. It is widely used in industrial production as a raw material for manufacturing synthetic resins, paints, plastics, and artificial fibers. It is also a crucial raw material for adhesives (urea-formaldehyde resin, melamine resin, and phenolic resin) used in the manufacture of engineered wood products. Currently, urea-formaldehyde resin (UF) is the primary adhesive used in the production of engineered wood products worldwide. Urea-formaldehyde resin is made from formaldehyde and urea through addition and condensation reactions under specific conditions. The wide industrial applications of these derivatives make formaldehyde an important industrial raw material.

[0003] In the production of formaldehyde, methods include non-catalytic oxidation using liquefied petroleum gas (LPG), methanol-air oxidation, and methane oxidation. Considering the economic viability of raw materials, methanol-air oxidation is currently the most common method for formaldehyde production. Methanol-air oxidation is further divided into silver-catalyzed oxidation and iron-molybdenum oxide-catalyzed oxidation. Compared to silver catalysis, the iron-molybdenum method has a lower reaction temperature, resulting in fewer side reactions, higher selectivity, lower formaldehyde consumption per unit volume, less formaldehyde decomposition, higher formaldehyde concentration, higher catalyst efficiency, and longer lifespan. New production capacity primarily utilizes the iron-molybdenum method, which employs iron-molybdenum catalysts.

[0004] Currently, the average lifespan of industrial iron-molybdenum catalysts is 6–12 months. Deactivation is caused by molybdenum sublimation loss, phase decomposition, catalyst pulverization, and high-temperature sintering during the reaction process. Early regeneration methods for metal oxide catalysts involved high-temperature reduction with reducing gases or high-temperature oxidation with oxidizing gases. However, these methods only altered the deposits on the catalyst surface and did not address the issue of catalyst particle sintering. Patent CN118341493A discloses a regeneration method for Ni-based catalysts, which involves in-situ regeneration of deactivated catalysts in a fixed-bed reactor, followed by sequential hydrogen regeneration treatment at low and high temperatures to remove impurities from the catalyst surface and improve its activity. Patent CN116966937A discloses a regeneration method for platinum-based catalysts, which involves adding the platinum-based catalyst to a mixed solution of hydrochloric acid and hydrogen peroxide. This converts the platinum sintered on the catalyst into chloroplatinic acid, which is stably supported on a platinum-based catalyst support, exhibiting excellent target reaction selectivity and reactant conversion in the catalytic dehydrogenation of propane to propylene. Patent CN109225260A discloses a method for regenerating sulfur-poisoned Ce-based SCR denitration catalysts. The sulfur-poisoned Ce-based SCR denitration catalyst is ball-milled, sieved, and the powder is transferred to an atmosphere furnace and calcined under air. The resulting regenerated catalyst shows a significant recovery of activity. While the above processes all involve regeneration methods for nickel, platinum, and cerium catalysts, they are not applicable to the regeneration of iron-molybdenum catalysts and cannot solve problems such as molybdenum sublimation and high-temperature sintering. Therefore, finding an efficient method for regenerating iron-molybdenum catalysts is of significant practical importance. Summary of the Invention

[0005] The present invention aims to provide a method for regenerating an iron-molybdenum catalyst for the methanol-to-formaldehyde oxidation process. This method involves treating the deactivated iron-molybdenum catalyst with an alkaline solution to recover the molybdenum source, which is then used to resynthesize the iron-molybdenum catalyst. This method offers high recovery efficiency and economic benefits. The regenerated catalyst exhibits high activity, selectivity, and stability, along with a long reaction lifetime.

[0006] The alkaline treatment involved in this invention regenerates the iron-molybdenum catalyst through the following process.

[0007] The regenerated catalyst can be synthesized by the following method: First, prepare an alkaline solution of 0.5–8 mol / L, add the deactivated iron-molybdenum catalyst to the alkaline solution, stir and react at 20℃–80℃ for 1–6 h, then filter to separate the solid and liquid to obtain a molybdenum source solution; prepare a fresh iron source, with the molar ratio of molybdenum atoms to iron atoms controlled at 2–4, and synthesize the iron-molybdenum catalyst by one or more of the following methods: co-precipitation, solid-phase ball milling, impregnation, and sol-gel method to obtain the regenerated iron-molybdenum catalyst.

[0008] The regenerated iron-molybdenum catalyst was evaluated in a fixed-bed reactor. The catalyst was directly extruded and granulated into 40-60 mesh particles, which were then loaded into the fixed-bed reactor. Under atmospheric pressure, a mixture of N2 and O2 was simultaneously introduced, with an O2 volume concentration of 5%–15%, and the reaction temperature was 200–350 °C. Anhydrous methanol was fed into the system at a rate of 0.01–0.03 mL / min to initiate the reaction, with a volume hourly space velocity (VHSV) of 7000–11000 h⁻¹. -1 .

[0009] Iron-molybdenum catalysts are mainly used in the methanol oxidation to formaldehyde process, with an average catalyst life of 6–12 months. This method is characterized by: regenerating the deactivated iron-molybdenum catalyst using alkali treatment, then re-evaluating it, and conducting the methanol oxidation to formaldehyde reaction in a fixed-bed reactor. The methanol conversion rate can reach up to 99%, and the formaldehyde selectivity is as high as 92%. This regeneration method restores the high reactivity and selectivity of the iron-molybdenum catalyst, resulting in significant economic benefits.

[0010] The advantages of this method are: (1) Alkali treatment of deactivated iron-molybdenum catalyst can efficiently recover rare metal molybdenum for resynthesis of iron-molybdenum catalyst, and the molybdenum-iron atomic ratio of the regenerated catalyst can be controlled. (2) This method can effectively solve the problems of high-temperature sintering on the surface of deactivated catalyst and component loss. (3) The conversion rate, formaldehyde selectivity and formaldehyde yield of the regenerated catalyst are comparable to the catalytic performance of the new iron-molybdenum catalyst, which significantly improves the economic benefits of the formaldehyde production plant. Detailed Implementation

[0011] To provide a more detailed description of the present invention, several specific implementation examples are given below, but the present invention is not limited to these embodiments.

[0012] The deactivated iron-molybdenum catalyst was regenerated by treating it with alkali solution. The regenerated catalyst was then used in a fixed-bed reactor to oxidize methanol to formaldehyde. The resulting gas-liquid phase reaction products were analyzed and calculated separately.

[0013] The following examples illustrate the process of obtaining deactivated iron-molybdenum catalysts: The fresh iron-molybdenum catalyst was a commercially available industrial catalyst, a composite oxide of iron and molybdenum with a molybdenum-iron molar ratio of 2–4:1 (3:1 in this case). The fresh iron-molybdenum catalyst was reacted in a fixed-bed reactor, and after 6–12 months (9 months in this case) of methanol oxidation to formaldehyde reaction, the catalyst performance degraded and became deactivated. The deactivated catalyst had a molybdenum-iron atomic molar ratio between 1.0 and 2.0 (1.5 in this case), a methanol conversion rate of 55%–65% (62% in this case), and a formaldehyde selectivity of 88%–95% (91% in this case).

[0014] Example 1

[0015] Weigh 12.00 g of NaOH and prepare a 3 mol / L NaOH solution. Add 10 g of deactivated iron-molybdenum catalyst (molybdenum-iron atomic molar ratio 1.5) to the solution. Stir the reaction at 30 °C for 2.5 h. Filter to separate the solid and liquid phases. Use the liquid as the molybdenum source for synthesizing the iron-molybdenum catalyst and synthesize the catalyst using a co-precipitation method. Weigh 8.48 g of ferric nitrate nonahydrate and prepare a 0.25 mol / L aqueous solution of the iron source. Add ferric nitrate solution dropwise to the molybdenum source. Stir at room temperature for 1 h, let stand for 1 h, filter to separate the solid and liquid phases, wash and dry the solid, and calcine in a muffle furnace at 400 °C for 10 h to obtain the regenerated catalyst with an iron-molybdenum atomic molar ratio of 2.5. Directly extrude and granulate the catalyst into 40-60 mesh particles. 0.9 mL of catalyst is loaded into a fixed-bed reactor, filling a 15 cm bed. Under atmospheric pressure, a mixture of N2 and O2 (O2 volume content 10%) was simultaneously introduced at a rate of 0.15 L / min. The reaction temperature was 250 °C, and anhydrous methanol was fed into the system at a rate of 0.02 mL / min to initiate the reaction. The volume hourly space velocity (VHSV) was 9000 h⁻¹. -1 Analysis and calculations of the gaseous and liquid phase products showed a methanol conversion rate of 91% and a formaldehyde selectivity of 88%.

[0016] Example 2

[0017] Prepare a 5 mol / L ammonia solution by mixing 20 mL of 25 wt% ammonia water with ultrapure water. Add 10 g of deactivated iron-molybdenum catalyst (molybdenum-iron atomic molar ratio 1.5) to the solution. Stir at 30 °C for 2.5 h, then filter to separate the solid and liquid phases. Use the liquid as the molybdenum source for synthesizing the iron-molybdenum catalyst via co-precipitation. Weigh 8.48 g of ferric nitrate nonahydrate and prepare a 0.25 mol / L iron source solution. Add ferric nitrate solution dropwise to the molybdenum source. Stir at room temperature for 1 h, allow to stand until room temperature, filter, wash, and dry. Calcinate in a muffle furnace at 400 °C for 10 h to obtain the regenerated catalyst with an iron-molybdenum atomic molar ratio of 2.5. Directly extrude and granulate the catalyst into 40-60 mesh particles. 0.9 mL of catalyst is loaded into a fixed-bed reactor, filling a 15 cm bed. Under atmospheric pressure, a mixture of N2 and O2 (O2 volume content 10%) was simultaneously introduced at a rate of 0.15 L / min. The reaction temperature was 250 °C, and anhydrous methanol was fed into the system at a rate of 0.02 mL / min to initiate the reaction. The volume hourly space velocity (VHSV) was 9000 h⁻¹. -1 Analysis and calculations of the gaseous and liquid phase products showed a methanol conversion rate of 99% and a formaldehyde selectivity of 92%.

[0018] Example 3

[0019] 14.41 g of ammonium carbonate was weighed and prepared into a 3 mol / L ammonium carbonate solution. 10 g of deactivated iron-molybdenum catalyst (molybdenum-iron atomic molar ratio 1.5) was added to the solution. The mixture was stirred at 30 °C for 2.5 h. The solid and liquid phases were separated by filtration. The liquid was used as the molybdenum source for the synthesis of the iron-molybdenum catalyst, and the catalyst was synthesized using a co-precipitation method. 8.48 g of ferric nitrate nonahydrate was weighed and prepared into a 0.25 mol / L iron source solution. Ferric nitrate solution was added dropwise to the molybdenum source. After stirring at room temperature for 1 h, the mixture was allowed to stand until room temperature, then filtered, washed, and dried. The resulting product was calcined in a muffle furnace at 400 °C for 10 h to obtain a regenerated catalyst with an iron-molybdenum atomic molar ratio of 2.5. The catalyst was directly extruded and granulated into 40-60 mesh particles. 0.9 mL of the catalyst was loaded into a fixed-bed reactor, filling a 15 cm bed. Under atmospheric pressure, a mixture of N2 and O2 (O2 volume content 10%) was simultaneously introduced at a rate of 0.15 L / min. The reaction temperature was 250 °C, and anhydrous methanol was fed into the system at a rate of 0.02 mL / min to initiate the reaction. The volume hourly space velocity (VHSV) was 9000 h⁻¹. -1 Analysis and calculations of the gaseous and liquid phase products showed that the methanol conversion rate was 86% and the formaldehyde selectivity was 89%.

[0020] Example 4

[0021] 23.72 g of ammonium carbonate was weighed and prepared into a 3 mol / L ammonium bicarbonate solution. 10 g of deactivated iron-molybdenum catalyst (molybdenum-iron atomic molar ratio 1.5) was added to the solution. The mixture was stirred at 30 °C for 2.5 h. The solid and liquid phases were separated by filtration. The liquid was used as the molybdenum source for the synthesis of the iron-molybdenum catalyst, and the catalyst was synthesized using a co-precipitation method. 8.48 g of ferric nitrate nonahydrate was weighed and prepared into a 0.25 mol / L iron source solution. Ferric nitrate solution was added dropwise to the molybdenum source. After stirring at room temperature for 1 h, the mixture was allowed to stand until room temperature, then filtered, washed, and dried. The resulting product was calcined in a muffle furnace at 400 °C for 10 h to obtain a regenerated catalyst with an iron-molybdenum atomic molar ratio of 2.5. The catalyst was directly extruded and granulated into 40-60 mesh particles. 0.9 mL of the catalyst was loaded into a fixed-bed reactor, filling a 15 cm bed. Under atmospheric pressure, a mixture of N2 and O2 (O2 volume content 10%) was simultaneously introduced at a rate of 0.15 L / min. The reaction temperature was 250 °C, and anhydrous methanol was fed into the system at a rate of 0.02 mL / min to initiate the reaction. The volume hourly space velocity (VHSV) was 9000 h⁻¹. -1 Analysis and calculations of the gaseous and liquid phase products showed that the methanol conversion rate was 83% and the formaldehyde selectivity was 88%.

[0022] Example 5

[0023] 16.80 g of potassium hydroxide was weighed and prepared into a 3 mol / L potassium hydroxide solution. 10 g of deactivated iron-molybdenum catalyst (molybdenum-iron atomic molar ratio 1.5) was added to the solution. The mixture was stirred at 30 °C for 2.5 h. The solid and liquid were separated by filtration. The liquid was used as the molybdenum source for the synthesis of the iron-molybdenum catalyst, and the catalyst was synthesized using a co-precipitation method. 8.48 g of ferric nitrate nonahydrate was weighed and prepared into a 0.25 mol / L iron source solution. Ferric nitrate solution was added dropwise to the molybdenum source. After stirring at room temperature for 1 h, the mixture was allowed to stand until room temperature, then filtered, washed, and dried. The resulting product was calcined in a muffle furnace at 400 °C for 10 h to obtain a regenerated catalyst with an iron-molybdenum atomic molar ratio of 2.5. The catalyst was directly extruded and granulated into 40-60 mesh particles. 0.9 mL of the catalyst was loaded into a fixed-bed reactor, filling a 15 cm bed. Under atmospheric pressure, a mixture of N2 and O2 (O2 volume content 10%) was simultaneously introduced at a rate of 0.15 L / min. The reaction temperature was 250 °C, and anhydrous methanol was fed into the system at a rate of 0.02 mL / min to initiate the reaction. The volume hourly space velocity (VHSV) was 9000 h⁻¹. -1 Analysis and calculations of the gaseous and liquid phase products showed that the methanol conversion rate was 86% and the formaldehyde selectivity was 84%.

[0024] Example 6

[0025] A 5 mol / L ammonia solution was prepared by mixing 20 mL of 25 wt% ammonia water with ultrapure water. 10 g of deactivated iron-molybdenum catalyst (molybdenum-iron atomic molar ratio 1.5) was added, and the mixture was stirred at 30 °C for 2.5 h. The mixture was then filtered to separate the solid and liquid phases. The liquid was used as the molybdenum source for synthesizing the iron-molybdenum catalyst, and the catalyst was synthesized using an impregnation method. The molybdenum source solution was evaporated at high temperature, dried, and calcined at 500 °C to obtain molybdenum oxide. 8.48 g of ferric nitrate nonahydrate was weighed and used to prepare an iron source solution. The ferric nitrate solution was repeatedly and completely impregnated onto the molybdenum oxide support. After drying in an oven, the solution was calcined in a muffle furnace at 400 °C for 10 h to obtain a regenerated catalyst with a molybdenum-iron atomic molar ratio of 2.5. The catalyst was directly extruded and granulated into 40-60 mesh particles. 0.9 mL of the catalyst was loaded into a fixed-bed reactor, filling a 15 cm bed. Under atmospheric pressure, a mixture of N2 and O2 (O2 volume content 10%) was simultaneously introduced at a rate of 0.15 L / min. The reaction temperature was 250 °C, and anhydrous methanol was fed into the system at a rate of 0.02 mL / min to initiate the reaction. The volume hourly space velocity (VHSV) was 9000 h⁻¹. -1 Analysis and calculations of the gaseous and liquid phase products showed a methanol conversion rate of 93% and a formaldehyde selectivity of 78%.

[0026] Example 7

[0027] A 5 mol / L ammonia solution was prepared by mixing 20 mL of 25 wt% ammonia water with ultrapure water. 10 g of deactivated iron-molybdenum catalyst (molybdenum-iron atomic molar ratio 1.5) was added, and the mixture was stirred at 30 °C for 2.5 h. The mixture was then filtered to separate the solid and liquid phases. The liquid was used as the molybdenum source for synthesizing the iron-molybdenum catalyst. The solution was evaporated at high temperature, dried, and calcined at 500 °C to obtain molybdenum oxide. The catalyst was then synthesized using a solid-phase ball milling method. 1.60 g of Fe₂O₃ was weighed and mixed with molybdenum oxide in a ball mill. The mixture was ball-milled at 500 r / min for 2 h. The sample was then calcined at 400 °C for 10 h to obtain a regenerated catalyst with an iron-molybdenum atomic molar ratio of 2.5. The catalyst was directly extruded and granulated into 40-60 mesh particles. 0.9 mL of the catalyst was loaded into a fixed-bed reactor, filling a 15 cm bed. Under atmospheric pressure, a mixture of N2 and O2 (O2 volume content 10%) was simultaneously introduced at a rate of 0.15 L / min. The reaction temperature was 250 °C, and anhydrous methanol was fed into the system at a rate of 0.02 mL / min to initiate the reaction. The volume hourly space velocity (VHSV) was 9000 h⁻¹. -1 Analysis and calculations of the gaseous and liquid phase products showed a methanol conversion rate of 90% and a formaldehyde selectivity of 91%.

[0028] Example 8

[0029] Prepare a 5 mol / L ammonia solution by mixing 20 mL of 25 wt% ammonia water with ultrapure water. Add 10 g of deactivated iron-molybdenum catalyst (molybdenum-iron atomic molar ratio 1.5) to the solution. Stir the reaction at 30 °C for 2.5 h. Filter to separate the solid and liquid phases. Use the liquid as the molybdenum source for synthesizing the iron-molybdenum catalyst using the sol-gel method. Weigh 8.48 g of ferric nitrate nonahydrate and prepare a 0.25 mol / L iron source solution. Add ferric nitrate solution dropwise to the molybdenum source solution and mix. Add citric acid solution (citric acid and total metal ion concentrations are both 0.25 mol / L). After stirring evenly, evaporate the solution in a 70 °C water bath to obtain a transparent sol. Dry the sol at 100 °C for 12 h to obtain a dry gel. Calcinate the gel in a muffle furnace at 400 °C for 10 h to obtain a regenerated catalyst with an iron-molybdenum atomic molar ratio of 2.5. Directly extrude and granulate the catalyst into 40-60 mesh particles. 0.9 mL of the catalyst is loaded into a fixed-bed reactor, filling a 15 cm bed. Under atmospheric pressure, a mixture of N2 and O2 (O2 volume content 10%) was simultaneously introduced at a rate of 0.15 L / min. The reaction temperature was 250 °C, and anhydrous methanol was fed into the system at a rate of 0.02 mL / min to initiate the reaction. The volume hourly space velocity (VHSV) was 9000 h⁻¹. -1 Analysis and calculations of the gaseous and liquid phase products showed a methanol conversion rate of 92% and a formaldehyde selectivity of 88%.

[0030] Example 9

[0031] Prepare a 5 mol / L ammonia solution by mixing 20 mL of 25 wt% ammonia water with ultrapure water. Add 10 g of deactivated iron-molybdenum catalyst (molybdenum-iron atomic molar ratio 1.5) to the solution. Stir the reaction at 30 °C for 2.5 h. Filter to separate the solid and liquid phases. Use the liquid as the molybdenum source for synthesizing the iron-molybdenum catalyst via co-precipitation. Weigh 5.41 g of FeCl3·6H2O and prepare a 0.25 mol / L iron source solution. Add ferric chloride solution dropwise to the molybdenum source. Stir at room temperature for 1 h, allow to stand until room temperature, filter, wash, and dry. Calcine in a muffle furnace at 400 °C for 10 h to obtain the regenerated catalyst with an iron-molybdenum atomic molar ratio of 2.5. Directly extrude and granulate the catalyst into 40-60 mesh particles. 0.9 mL of catalyst is loaded into a fixed-bed reactor, filling a 15 cm bed. Under atmospheric pressure, a mixture of N2 and O2 (O2 volume content 10%) was simultaneously introduced at a rate of 0.15 L / min. The reaction temperature was 250 °C, and anhydrous methanol was fed into the system at a rate of 0.02 mL / min to initiate the reaction. The volume hourly space velocity (VHSV) was 9000 h⁻¹. -1 Analysis and calculations of the gaseous and liquid phase products showed a methanol conversion rate of 93% and a formaldehyde selectivity of 85%.

[0032] Example 10

[0033] Prepare a 5 mol / L ammonia solution by mixing 20 mL of 25 wt% ammonia water with ultrapure water. Add 10 g of deactivated iron-molybdenum catalyst (molybdenum-iron atomic molar ratio 1.5) to the solution. Stir at 30 °C for 2.5 h, then filter to separate the solid and liquid phases. Use the liquid as the molybdenum source for synthesizing the iron-molybdenum catalyst via co-precipitation. Weigh 4.00 g of Fe2(SO4)3·xH2O and prepare a 0.13 mol / L iron source solution. Add ferric sulfate solution dropwise to the molybdenum source. After stirring at room temperature for 1 h, allow to stand until room temperature, filter, wash, and dry. Calcine in a muffle furnace at 400 °C for 10 h to obtain the regenerated catalyst with an iron-molybdenum atomic molar ratio of 2.5. Directly extrude and granulate the catalyst into 40-60 mesh particles. 0.9 mL of catalyst is loaded into a fixed-bed reactor, filling a 15 cm bed. Under atmospheric pressure, a mixture of N2 and O2 (O2 volume content 10%) was simultaneously introduced at a rate of 0.15 L / min. The reaction temperature was 250 °C, and anhydrous methanol was fed into the system at a rate of 0.02 mL / min to initiate the reaction. The volume hourly space velocity (VHSV) was 9000 h⁻¹. -1 Analysis and calculations of the gaseous and liquid phase products showed a methanol conversion rate of 94% and a formaldehyde selectivity of 89%.

[0034] Example 11

[0035] Prepare a 5 mol / L ammonia solution by mixing 20 mL of 25 wt% ammonia water with ultrapure water. Add 10 g of deactivated iron-molybdenum catalyst (molybdenum-iron atomic molar ratio 1.5) to the solution. Stir the reaction at 30 °C for 2.5 h. Filter to separate the solid and liquid phases. Use the liquid as the molybdenum source for synthesizing the iron-molybdenum catalyst via co-precipitation. Weigh 10.60 g of ferric nitrate nonahydrate and prepare a 0.25 mol / L iron source solution. Add ferric nitrate solution dropwise to the molybdenum source. Stir at room temperature for 1 h, allow to stand until room temperature, filter, wash, and dry. Calcinate in a muffle furnace at 400 °C for 10 h to obtain the regenerated catalyst with an iron-molybdenum atomic molar ratio of 2. Directly extrude and granulate the catalyst into 40-60 mesh particles. 0.9 mL of catalyst is loaded into a fixed-bed reactor, filling a 15 cm bed. Under atmospheric pressure, a mixture of N2 and O2 (O2 volume content 10%) was simultaneously introduced at a rate of 0.15 L / min. The reaction temperature was 250 °C, and anhydrous methanol was fed into the system at a rate of 0.02 mL / min to initiate the reaction. The volume hourly space velocity (VHSV) was 9000 h⁻¹. -1 Analysis of the gaseous and liquid phase products showed a methanol conversion rate of 79% and a formaldehyde selectivity of 81%.

[0036] Example 12

[0037] Prepare a 5 mol / L ammonia solution by mixing 20 mL of 25 wt% ammonia water with ultrapure water. Add 10 g of deactivated iron-molybdenum catalyst (molybdenum-iron atomic molar ratio 1.5) to the solution. Stir the reaction at 30 °C for 2.5 h. Filter to separate the solid and liquid phases. Use the liquid as the molybdenum source for synthesizing the iron-molybdenum catalyst via co-precipitation. Weigh 7.07 g of ferric nitrate nonahydrate and prepare a 0.25 mol / L iron source solution. Add ferric nitrate solution dropwise to the molybdenum source. Stir at room temperature for 1 h, allow to stand until room temperature, filter, wash, and dry. Calcinate in a muffle furnace at 400 °C for 10 h to obtain the regenerated catalyst with an iron-molybdenum atomic molar ratio of 3. Directly extrude and granulate the catalyst into 40-60 mesh particles. 0.9 mL of catalyst is loaded into a fixed-bed reactor, filling a 15 cm bed. Under atmospheric pressure, a mixture of N2 and O2 (O2 volume content 10%) was simultaneously introduced at a rate of 0.15 L / min. The reaction temperature was 250 °C, and anhydrous methanol was fed into the system at a rate of 0.02 mL / min to initiate the reaction. The volume hourly space velocity (VHSV) was 9000 h⁻¹. -1 Analysis of the gaseous and liquid phase products showed a methanol conversion rate of 96% and a formaldehyde selectivity of 90%.

[0038] Example 13

[0039] Prepare a 5 mol / L ammonia solution by mixing 20 mL of 25 wt% ammonia water with ultrapure water. Add 10 g of deactivated iron-molybdenum catalyst (molybdenum-iron atomic molar ratio 1.5) to the solution. Stir at 30 °C for 2.5 h, then filter to separate the solid and liquid phases. Use the liquid as the molybdenum source for synthesizing the iron-molybdenum catalyst via co-precipitation. Weigh 8.48 g of ferric nitrate nonahydrate and prepare a 0.25 mol / L iron source solution. Add ferric nitrate solution dropwise to the molybdenum source. Stir at room temperature for 1 h, allow to stand until room temperature, filter, wash, and dry. Calcinate in a muffle furnace at 400 °C for 10 h to obtain the regenerated catalyst with an iron-molybdenum atomic molar ratio of 2.5. Directly extrude and granulate the catalyst into 40-60 mesh particles. 0.9 mL of catalyst is loaded into a fixed-bed reactor, filling a 15 cm bed. Under atmospheric pressure, a mixture of N2 and O2 (O2 volume content 10%) was simultaneously introduced at a rate of 0.15 L / min. The reaction temperature was 250 °C, and anhydrous methanol was fed into the system at a rate of 0.02 mL / min to initiate the reaction. The volume hourly space velocity (VHSV) was 9000 h⁻¹. -1 Analysis and calculations of the gaseous and liquid phase products showed that the methanol conversion rate was 81% and the formaldehyde selectivity was 83%.

[0040] Example 14

[0041] Prepare a 5 mol / L ammonia solution by mixing 20 mL of 25 wt% ammonia water with ultrapure water. Add 10 g of deactivated iron-molybdenum catalyst (molybdenum-iron atomic molar ratio 1.5) to the solution. Stir at 30 °C for 2.5 h, then filter to separate the solid and liquid phases. Use the liquid as the molybdenum source for synthesizing the iron-molybdenum catalyst via co-precipitation. Weigh 8.48 g of ferric nitrate nonahydrate and prepare a 0.25 mol / L iron source solution. Add ferric nitrate solution dropwise to the molybdenum source. Stir at room temperature for 1 h, allow to stand until room temperature, filter, wash, and dry. Calcinate in a muffle furnace at 400 °C for 10 h to obtain the regenerated catalyst with an iron-molybdenum atomic molar ratio of 2.5. Directly extrude and granulate the catalyst into 40-60 mesh particles. 0.9 mL of catalyst is loaded into a fixed-bed reactor, filling a 15 cm bed. Under atmospheric pressure, a mixture of N2 and O2 (O2 volume content 10%) was simultaneously introduced at a rate of 0.15 L / min. The reaction temperature was 250 °C, and anhydrous methanol was fed into the system at a rate of 0.02 mL / min to initiate the reaction. The volume hourly space velocity (VHSV) was 9000 h⁻¹. -1 Analysis and calculations of the gaseous and liquid phase products showed that the methanol conversion rate was 90% and the formaldehyde selectivity was 77%.

[0042] Example 15

[0043] Prepare a 5 mol / L ammonia solution by mixing 20 mL of 25 wt% ammonia water with ultrapure water. Add 10 g of deactivated iron-molybdenum catalyst (molybdenum-iron atomic molar ratio 1.5) to the solution. Stir at 30 °C for 2.5 h, then filter to separate the solid and liquid phases. Use the liquid as the molybdenum source for synthesizing the iron-molybdenum catalyst via co-precipitation. Weigh 8.48 g of ferric nitrate nonahydrate and prepare a 0.25 mol / L iron source solution. Add ferric nitrate solution dropwise to the molybdenum source. Stir at room temperature for 1 h, allow to stand until room temperature, filter, wash, and dry. Calcinate in a muffle furnace at 400 °C for 10 h to obtain the regenerated catalyst with an iron-molybdenum atomic molar ratio of 2.5. Directly extrude and granulate the catalyst into 40-60 mesh particles. 0.9 mL of catalyst is loaded into a fixed-bed reactor, filling a 15 cm bed. Under atmospheric pressure, a mixture of N2 and O2 (O2 volume content 10%) was simultaneously introduced at a rate of 0.15 L / min. The reaction temperature was 220 °C, and anhydrous methanol was fed into the system at a rate of 0.02 mL / min to initiate the reaction. The volume hourly space velocity (VHSV) was 9000 h⁻¹. -1 Analysis and calculations of the gaseous and liquid phase products showed that the methanol conversion rate was 84% ​​and the formaldehyde selectivity was 97%.

[0044] Example 16

[0045] Prepare a 5 mol / L ammonia solution by mixing 20 mL of 25 wt% ammonia water with ultrapure water. Add 10 g of deactivated iron-molybdenum catalyst (molybdenum-iron atomic molar ratio 1.5) to the solution. Stir at 30 °C for 2.5 h, then filter to separate the solid and liquid phases. Use the liquid as the molybdenum source for synthesizing the iron-molybdenum catalyst via co-precipitation. Weigh 8.48 g of ferric nitrate nonahydrate and prepare a 0.25 mol / L iron source solution. Add ferric nitrate solution dropwise to the molybdenum source. Stir at room temperature for 1 h, allow to stand until room temperature, filter, wash, and dry. Calcinate in a muffle furnace at 400 °C for 10 h to obtain the regenerated catalyst with an iron-molybdenum atomic molar ratio of 2.5. Directly extrude and granulate the catalyst into 40-60 mesh particles. 0.9 mL of catalyst is loaded into a fixed-bed reactor, filling a 15 cm bed. Under atmospheric pressure, a mixture of N2 and O2 (O2 volume content 10%) was simultaneously introduced at a rate of 0.15 L / min. The reaction temperature was 280 °C, and anhydrous methanol was fed into the system at a rate of 0.02 mL / min to initiate the reaction. The volume hourly space velocity (VHSV) was 9000 h⁻¹. -1 Analysis and calculations of the gaseous and liquid phase products showed a methanol conversion rate of 99% and a formaldehyde selectivity of 85%.

[0046] Example 17

[0047] Prepare a 5 mol / L ammonia solution by mixing 20 mL of 25 wt% ammonia water with ultrapure water. Add 10 g of deactivated iron-molybdenum catalyst (molybdenum-iron atomic molar ratio 1.5) to the solution. Stir at 30 °C for 2.5 h, then filter to separate the solid and liquid phases. Use the liquid as the molybdenum source for synthesizing the iron-molybdenum catalyst via co-precipitation. Weigh 8.48 g of ferric nitrate nonahydrate and prepare a 0.25 mol / L iron source solution. Add ferric nitrate solution dropwise to the molybdenum source. Stir at room temperature for 1 h, allow to stand until room temperature, filter, wash, and dry. Calcinate in a muffle furnace at 400 °C for 10 h to obtain the regenerated catalyst with an iron-molybdenum atomic molar ratio of 2.5. Directly extrude and granulate the catalyst into 40-60 mesh particles. 0.9 mL of catalyst is loaded into a fixed-bed reactor, filling a 15 cm bed. Under atmospheric pressure, a mixture of N2 and O2 (O2 volume content 10%) was simultaneously introduced at a rate of 0.12 L / min. The reaction temperature was 250 °C, and anhydrous methanol was fed into the system at a rate of 0.015 mL / min to initiate the reaction. The volume hourly space velocity (VHSV) was 7000 h⁻¹. -1 Analysis and calculations of the gaseous and liquid phase products showed a methanol conversion rate of 99% and a formaldehyde selectivity of 90%.

[0048] Example 18

[0049] Prepare a 5 mol / L ammonia solution by mixing 20 mL of 25 wt% ammonia water with ultrapure water. Add 10 g of deactivated iron-molybdenum catalyst (molybdenum-iron atomic molar ratio 1.5) to the solution. Stir at 30 °C for 2.5 h, then filter to separate the solid and liquid phases. Use the liquid as the molybdenum source for synthesizing the iron-molybdenum catalyst via co-precipitation. Weigh 8.48 g of ferric nitrate nonahydrate and prepare a 0.25 mol / L iron source solution. Add ferric nitrate solution dropwise to the molybdenum source. Stir at room temperature for 1 h, allow to stand until room temperature, filter, wash, and dry. Calcinate in a muffle furnace at 400 °C for 10 h to obtain the regenerated catalyst with an iron-molybdenum atomic molar ratio of 2.5. Directly extrude and granulate the catalyst into 40-60 mesh particles. 0.9 mL of catalyst is loaded into a fixed-bed reactor, filling a 15 cm bed. Under atmospheric pressure, a mixture of N2 and O2 (O2 volume content 10%) was simultaneously introduced at a rate of 0.19 L / min, the reaction temperature was 250 °C, and anhydrous methanol was fed into the system at a rate of 0.025 mL / min to initiate the reaction, with a volume hourly space velocity (VHSV) of 11000 h⁻¹. -1 Analysis and calculations of the gaseous and liquid phase products showed that the methanol conversion rate was 88% and the formaldehyde selectivity was 86%.

[0050] Comparative Example 1

[0051] Prepare a 5 mol / L ammonia solution by mixing 20 mL of 25 wt% ammonia water with ultrapure water. Add 10 g of deactivated iron-molybdenum catalyst (molybdenum-iron atomic molar ratio 1.5) to the solution. Stir the reaction at 30 °C for 2.5 h. Filter to separate the solid and liquid phases. Use the liquid as the molybdenum source for synthesizing the iron-molybdenum catalyst via co-precipitation. Weigh 3.53 g of ferric nitrate nonahydrate and prepare a 0.25 mol / L iron source solution. Add ferric nitrate solution dropwise to the molybdenum source. Stir at room temperature for 1 h, allow to stand until room temperature, filter, wash, and dry. Calcinate in a muffle furnace at 400 °C for 10 h to obtain the regenerated catalyst with an iron-molybdenum atomic molar ratio of 6. Directly extrude and granulate the catalyst into 40-60 mesh particles. 0.9 mL of catalyst is loaded into a fixed-bed reactor, filling a 15 cm bed. Under atmospheric pressure, a mixture of N2 and O2 (O2 volume content 10%) was simultaneously introduced at a rate of 0.15 L / min. The reaction temperature was 250 °C, and anhydrous methanol was fed into the system at a rate of 0.02 mL / min to initiate the reaction. The volume hourly space velocity (VHSV) was 9000 h⁻¹. -1 Analysis of the gaseous and liquid phase products showed a methanol conversion rate of 54% and a formaldehyde selectivity of 63%.

[0052] Comparative Example 2

[0053] Prepare a 5 mol / L ammonia solution by mixing 20 mL of 25 wt% ammonia water with ultrapure water. Add 10 g of deactivated iron-molybdenum catalyst (molybdenum-iron atomic molar ratio 1.5) to the solution. Stir the reaction at 30 °C for 2.5 h. Filter to separate the solid and liquid phases. Use the liquid as the molybdenum source for synthesizing the iron-molybdenum catalyst via co-precipitation. Weigh 21.20 g of ferric nitrate nonahydrate and prepare a 0.25 mol / L iron source solution. Add ferric nitrate solution dropwise to the molybdenum source. Stir at room temperature for 1 h, allow to stand until room temperature, filter, wash, and dry. Calcinate in a muffle furnace at 400 °C for 10 h to obtain the regenerated catalyst with an iron-molybdenum atomic molar ratio of 1. Directly extrude and granulate the catalyst into 40-60 mesh particles. 0.9 mL of catalyst is loaded into a fixed-bed reactor, filling a 15 cm bed. Under atmospheric pressure, a mixture of N2 and O2 (O2 volume content 10%) was simultaneously introduced at a rate of 0.15 L / min. The reaction temperature was 250 °C, and anhydrous methanol was fed into the system at a rate of 0.02 mL / min to initiate the reaction. The volume hourly space velocity (VHSV) was 9000 h⁻¹. -1 Analysis of the gaseous and liquid phase products showed a methanol conversion rate of 68% and a formaldehyde selectivity of 43%.

[0054] Comparative Example 3

[0055] 10g of deactivated iron-molybdenum catalyst (molybdenum-iron atomic molar ratio 1.5) was weighed and calcined in a muffle furnace at 400℃ for 2 hours. Simultaneously, a nitrogen-air mixture (nitrogen:air = 1:1, volume ratio) was introduced during calcination to obtain the regenerated catalyst. The catalyst was granulated into 40-60 mesh particles, and 0.9mL of catalyst was loaded into a fixed-bed reactor, filling a 15cm bed. Under atmospheric pressure, a mixture of N2 and O2 (O2 volume content 10%) was simultaneously introduced at a rate of 0.15L / min. The reaction temperature was 250℃, and anhydrous methanol was fed into the system at a rate of 0.02mL / min to initiate the reaction, with a volume hourly space velocity (VHSV) of 9000h⁻¹. -1 Analysis and calculations of the gaseous and liquid phase products showed that the methanol conversion rate was 54% and the formaldehyde selectivity was 46%.

[0056] The above descriptions are merely a few embodiments of this application and do not constitute any limitation on this application. Any changes or modifications made to the technical content disclosed above without departing from the scope of the technical solution of this application are equivalent to equivalent implementation cases and all fall within the scope of the technical solution.

Claims

1. A method for regenerating an iron-molybdenum catalyst used in the oxidation of methanol to formaldehyde, characterized in that: 1) Treat the deactivated iron-molybdenum catalyst after catalytic oxidation of methanol to formaldehyde with alkaline solution. After the reaction, filter to separate the solid and liquid. The liquid is the molybdenum source for synthesizing the iron-molybdenum catalyst. 2) Then, by combining it with a fresh active metal iron source, an iron-molybdenum regeneration catalyst can be obtained.

2. The method according to claim 1, characterized in that: The alkaline solution is one or more of ammonia, ammonium carbonate, ammonium bicarbonate, sodium hydroxide, and potassium hydroxide; its concentration is 0.5–8 mol / L, preferably 1–7 mol / L, and more preferably 1–6 mol / L. The iron-molybdenum catalyst is an iron-molybdenum composite oxide with a molar ratio of 2 to 4:

1.

3. The method according to claim 1 or 2, characterized in that: In step 1), a 0.5-8 mol / L alkaline solution is first prepared, and the deactivated iron-molybdenum catalyst is added to the alkaline solution. The reaction is stirred at 20℃-80℃ (preferably 20℃-70℃, more preferably 25℃-60℃) for 1-6 hours (preferably 1-5 hours, more preferably 1-3 hours). After that, the solid and liquid are separated by filtration to obtain a molybdenum source solution. The mass ratio of alkaline solution to deactivated iron-molybdenum catalyst is 2 to 15, preferably 4 to 13, and more preferably 5 to 12.

4. The method according to claim 1, characterized in that: In step 2), a fresh active metal iron source is prepared, and the recovered molybdenum source solution is combined with the active metal iron source to synthesize an iron-molybdenum regeneration catalyst. The molar ratio of molybdenum atoms to iron atoms in the iron-molybdenum regeneration catalyst is controlled at 2 to 5, preferably 2 to 4.

5. The method according to claim 1, characterized in that: The method for synthesizing the iron-molybdenum regenerated catalyst employs one or more of the following methods: co-precipitation, solid-phase ball milling, impregnation, and sol-gel method.

6. The method according to claim 1, 4, or 5, characterized in that: The active metallic iron is one or more of the following: ferric nitrate, ferric oxide, ferric chloride, ferric sulfate, ferric tribromide, ferric perchlorate, and ferric dihydrogen phosphate.

7. The application of the regenerated iron-molybdenum catalyst according to claim 1 or 5 in the catalytic oxidation of methanol to formaldehyde, characterized in that: The regenerated iron-molybdenum catalyst was directly extruded and granulated into 40-60 mesh particles, which were then loaded into a fixed-bed reactor. Under atmospheric pressure, a mixture of N2 and O2 was simultaneously introduced, with an O2 volume concentration of 5%–15%, and the reaction temperature was 200–350℃. Methanol was fed into the system at a rate of 0.01–0.03 mL / min to initiate the reaction, with a volume hourly space velocity (VHSV) of 6000–12000 h⁻¹. -1 .

8. The application according to claim 7, characterized in that: The preferred reaction temperature for methanol-to-formaldehyde production is 230℃~280℃, and the preferred reaction volume hourly space velocity is 7000~11000h. -1 .