Method for regenerating iron-molybdenum catalyst through acid treatment, catalyst and application

Abstract

The invention relates to a method for regenerating an iron-molybdenum catalyst through acid treatment and application of the catalyst. An iron-molybdenum catalyst is mainly applied to production of formaldehyde through methanol oxidation, and generally needs to be replaced after being used for about one year. The activity of the inactivated catalyst can be recovered by adopting a regeneration method, so that the service life of the catalyst is prolonged. The regeneration process of the iron-molybdenum catalyst disclosed by the invention comprises the following steps: firstly, preparing an acid solution with a certain concentration, putting the inactivated iron-molybdenum catalyst into the acid solution for full reaction, and filtering, washing, drying and roasting to obtain the regenerated catalyst. The method is characterized in that the regenerated iron-molybdenum catalyst is used for evaluating the reaction for preparing formaldehyde through methanol oxidation in a fixed bed reactor, the conversion rate is up to 99%, the formaldehyde selectivity is 92% or above, the regeneration process is simple and easy for large-scale industrialization, the performance of the catalyst is effectively ensured, and the economic benefit can be remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of catalyst regeneration technology, specifically relating to a method for regenerating iron-molybdenum catalysts by acid treatment and the application of the regenerated iron-molybdenum catalysts. Background Technology

[0002] Formaldehyde is an important organic chemical raw material and intermediate, widely used in pharmaceuticals, pesticides, synthetic resins, textiles, and papermaking. Currently, formaldehyde is the most important downstream product of methanol globally. Statistics show that approximately one-third of the world's methanol is used to produce formaldehyde, and my country is the largest producer and consumer of formaldehyde. Therefore, optimizing the formaldehyde-to-methanol production process is essential. Industrially, the production of formaldehyde from methanol is divided into two processes based on the type of catalyst and reaction conditions: the "silver process" and the "iron-molybdenum process." Compared to the silver process, the iron-molybdenum catalyst has a wider range of applications, lower reaction temperature requirements, higher selectivity, higher formaldehyde concentration, longer catalyst life, simpler preparation, and higher efficiency.

[0003] Iron-molybdenum catalysts are mainly used in the production of formaldehyde from methanol oxidation and generally need to be replaced after about one year of use. The main reason for the deactivation of iron-molybdenum catalysts is that their active component, molybdenum oxide, is gradually lost during the reaction. Simultaneously, the iron oxide formed by the oxidation of ferric molybdate causes structural changes and sintering of the catalyst, and the generated Fe2O3 results in very low selectivity for the methanol oxidation to formaldehyde. Common methods for regenerating metal catalysts include high-temperature reduction with reducing gas or high-temperature oxidation with oxidizing gas. Patent CN108187671B discloses a regeneration method for an alumina-supported platinum-tin dehydrogenation catalyst, in which the deactivated catalyst is contacted with a regeneration gas for carbonization and chlorination, and the treated catalyst is then contacted with a reducing gas for reduction, thus achieving catalyst regeneration. Patent CN107754815B discloses a regeneration method for a Cu / Fe3O4 water-gas shift catalyst. After the Cu / Fe3O4 catalyst undergoes water-gas reactivity evaluation, it is switched to an oxidizing atmosphere, maintained for a certain period, and then reactivated through reduction, which significantly restores the low-temperature shift reaction activity of the catalyst, i.e., catalyst regeneration. The aforementioned patents describe some methods for regenerating metal catalysts, but these are not applicable to the regeneration of iron-molybdenum catalysts. Furthermore, these methods only alter the deposits on the catalyst surface and cannot address the issues of metal oxidation and imbalance within the catalyst. Therefore, research is needed on regeneration methods for iron-molybdenum catalysts in the methanol oxidation to formaldehyde reaction, which is of great significance for achieving continuous industrial production. Summary of the Invention

[0004] The purpose of this invention is to provide a method for regenerating iron-molybdenum catalysts through acid treatment. This method uses acid to treat deactivated iron-molybdenum catalysts, causing the oxides sintered on the catalyst surface to react and restoring the molar ratio of molybdenum to iron atoms in the catalyst, thus significantly improving catalyst activity.

[0005] The acid treatment disclosed in this invention enables the regeneration of the iron-molybdenum catalyst through the following process.

[0006] The iron-molybdenum catalyst used for the deactivation of formaldehyde through methanol oxidation is placed in an acid solution and stirred for reaction. The acid is one or more of hydrochloric acid, nitric acid, sulfuric acid, perchloric acid, formic acid, acetic acid, oxalic acid, and sulfonic acid. The concentration of the acid solution is 0.05–2.0 mol / L, preferably 0.1–1.5 mol / L, and more preferably 0.15–1 mol / L. The acid solution mainly reacts with the iron in the catalyst, dissolving it into the liquid. Filtration is used to separate the solid and liquid phases. By adjusting the acid concentration and reaction time, the degree of reaction between the acid and iron is changed, thereby controlling the iron content in the catalyst in the solid after solid-liquid separation. The molar ratio of molybdenum atoms to iron atoms in the catalyst is controlled to be 2:1–5:1, preferably 2:1–4:1. The reaction temperature between the deactivated iron-molybdenum catalyst and the acid solution is 10℃–100℃ (preferably 20℃–80℃, more preferably 25℃–70℃), and the reaction time is 3–15 h (preferably 5–13 h, more preferably 7–12 h). After the reaction, the mixture is filtered to separate the solid and liquid phases. The solid is dried at a temperature of 40℃ to 140℃ (preferably 50℃ to 120℃, more preferably 70℃ to 110℃); the calcination temperature is 250℃ to 650℃ (preferably 300℃ to 600℃, more preferably 350℃ to 500℃) for 3 to 15 hours (preferably 5 to 13 hours, more preferably 7 to 11 hours). Finally, a regenerated iron-molybdenum catalyst is obtained.

[0007] The regenerated iron-molybdenum catalyst was granulated into 40-60 mesh particles and packed into a fixed-bed reactor. Under atmospheric pressure, a mixture of N2 and O2 with an oxygen concentration of 6%–15% was introduced, the reaction temperature was 200–350℃, and anhydrous methanol was fed into the system at a rate of 0.01–0.03 mL / min, with a volume hourly space velocity (VHSV) of 7000–11000 h⁻¹. -1 .

[0008] The acid-treated iron-molybdenum catalyst regeneration method disclosed in this invention has the following characteristics: (1) The deactivation of the iron-molybdenum catalyst is due to the oxidation of some iron in the catalyst to Fe2O3, which causes a decrease in formaldehyde selectivity. Acid treatment can react with Fe2O3 to dissolve it and improve formaldehyde selectivity. (2) Molybdenum sublimation loss is the main reason for the deactivation of the iron-molybdenum catalyst. Acid can react with the iron in the deactivated iron-molybdenum catalyst, increasing the molybdenum-iron atomic ratio and restoring the catalyst performance.

[0009] The present invention has the following advantages: (1) The regeneration process of the iron-molybdenum catalyst is simple, the reaction conditions are relatively mild, and the energy consumption is low. (2) The regenerated iron-molybdenum catalyst has a very good recovery of activity in the methanol oxidation to formaldehyde process, and can basically be restored to the level of the fresh catalyst.

[0010] Iron-molybdenum catalysts are mainly used in the production of formaldehyde from methanol oxidation and generally need to be replaced after about one year of use. Deactivated catalysts can be regenerated to restore their activity and extend their service life. The iron-molybdenum catalyst regenerated in this invention was evaluated in a fixed-bed reactor for the methanol oxidation to formaldehyde reaction, achieving a conversion rate as high as 99% and a formaldehyde selectivity of over 92%. This regeneration process is simple, easily scalable for large-scale industrial application, effectively ensures catalyst performance, and significantly improves economic benefits. 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 acid treatment. 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 the deactivated iron-molybdenum catalyst: The fresh iron-molybdenum catalyst was a commercially available industrial catalyst, a composite oxide of iron and molybdenum with a molar ratio of molybdenum to iron of 2:1 to 4:1 (3:1 in this case). The fresh iron-molybdenum catalyst was reacted in a fixed-bed reactor, and after 6 to 12 months (9 months in this case) of methanol oxidation to formaldehyde reaction, the catalyst performance deteriorated and became deactivated. The deactivated catalyst had a molar ratio of molybdenum to iron between 1.0 and 2.0 (1.5 in this case), a methanol conversion rate of 55% to 65% (62% in this case), and a formaldehyde selectivity of 88% to 95% (91% in this case).

[0014] Example 1

[0015] Prepare 100 mL of 0.25 mol / L hydrochloric acid solution. Add 10 g of deactivated iron-molybdenum catalyst (molybdenum-iron atomic molar ratio 1.5) to the hydrochloric acid solution and stir at 25 °C for 10 h. The hydrochloric acid solution reacts with the iron in the catalyst, and some of it dissolves in the acid solution. The reaction solution is filtered to separate the solid and liquid phases. The filter cake is dried at 100 °C and calcined in a muffle furnace at 400 °C for 10 h to obtain a regenerated iron-molybdenum catalyst with a molybdenum-iron atomic molar ratio of 2.9. The regenerated catalyst is directly extruded and granulated into 40-60 mesh particles. A catalyst loading volume of 0.9 mL is placed in a fixed-bed reactor to a loading height of 15 cm. Under atmospheric pressure, a mixture of N2 and O2 with an oxygen volume concentration of 10% (0.15 L / min) is introduced. Anhydrous methanol is fed into the system at a rate of 0.02 mL / min. The reaction temperature is 250 °C, and the volume hourly space velocity (VHSV) is 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 90%.

[0016] Example 2

[0017] 2.40 g of anhydrous oxalic acid was weighed and prepared into a 0.25 mol / L acid solution. 10 g of deactivated iron-molybdenum catalyst (molybdenum-iron atomic molar ratio 1.5) was added to the oxalic acid solution, and the mixture was stirred at 25 °C for 10 h. The oxalic acid solution reacted with the iron in the catalyst, dissolving it in the acid solution. The reaction solution was filtered to separate the solid and liquid phases. The filter cake was dried at 100 °C and partially calcined in a muffle furnace at 400 °C for 10 h to obtain a regenerated iron-molybdenum catalyst with a molybdenum-iron atomic molar ratio of 2.9. The regenerated catalyst was directly extruded and granulated into 40-60 mesh particles. A catalyst loading volume of 0.9 mL was placed in a fixed-bed reactor to a height of 15 cm. Under atmospheric pressure, a mixture of N2 and O2 with an oxygen volume concentration of 10% (0.15 L / min) was introduced, and anhydrous methanol was fed into the system at a rate of 0.02 mL / min. The reaction temperature was 250 °C, and 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] 2.50 g of 98% concentrated sulfuric acid was weighed and prepared into a 0.25 mol / L acid solution. 10 g of deactivated iron-molybdenum catalyst (molybdenum-iron atomic molar ratio 1.5) was added to the sulfuric acid solution, and the mixture was stirred at 25°C for 10 h. The sulfuric acid solution reacted with the iron in the catalyst, and some of the iron dissolved in the acid solution. The reaction solution was filtered to separate the solid and liquid phases. The filter cake was dried at 100°C and calcined in a muffle furnace at 400°C for 10 h to obtain a regenerated iron-molybdenum catalyst with a molybdenum-iron atomic molar ratio of 2.9. The regenerated catalyst was directly extruded and granulated into 40-60 mesh particles. A catalyst loading volume of 0.9 mL was placed in a fixed-bed reactor to a height of 15 cm. Under atmospheric pressure, a mixture of N2 and O2 with an oxygen volume concentration of 10% was introduced at 0.15 L / min. Anhydrous methanol was fed into the system at a rate of 0.02 mL / min. The reaction temperature was 250°C, and 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 93% and a formaldehyde selectivity of 89%.

[0020] Example 4

[0021] 3.20 g of concentrated nitric acid was weighed and prepared into a 0.25 mol / L acid solution. 10 g of deactivated iron-molybdenum catalyst (molybdenum-iron atomic molar ratio 1.5) was added to the nitric acid solution, and the mixture was stirred at 25 °C for 10 h. The nitric acid solution reacted with the iron in the catalyst, and some of the iron dissolved in the acid solution. The reaction solution was filtered to separate the solid and liquid phases. The filter cake was dried at 100 °C and calcined in a muffle furnace at 400 °C for 10 h to obtain a regenerated iron-molybdenum catalyst with a molybdenum-iron atomic molar ratio of 2.9. The regenerated catalyst was directly extruded and granulated into 40-60 mesh particles. A catalyst loading volume of 0.9 mL was placed in a fixed-bed reactor to a height of 15 cm. Under atmospheric pressure, a mixture of N2 and O2 with an oxygen volume concentration of 10% (0.15 L / min) was introduced, and anhydrous methanol was fed into the system at a rate of 0.02 mL / min. The reaction temperature was 250 °C, and 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 87%.

[0022] Example 5

[0023] Weigh 5.00 g of perchloric acid and prepare a 0.25 mol / L acid solution. Add 10 g of deactivated iron-molybdenum catalyst (molybdenum-iron atomic molar ratio 1.5) to the perchloric acid solution and stir at 25 °C for 10 h. The perchloric acid solution reacts with the iron in the catalyst, and some of it dissolves in the acid solution. The reaction solution is filtered to separate the solid and liquid phases. The filter cake is dried at 100 °C and calcined in a muffle furnace at 400 °C for 10 h to obtain a regenerated iron-molybdenum catalyst with a molybdenum-iron atomic molar ratio of 2.9. The regenerated catalyst is directly extruded and granulated into 40-60 mesh particles. The catalyst is loaded into a fixed-bed reactor with a loading volume of 0.9 mL and a loading height of 15 cm. Under atmospheric pressure, a mixture of N2 and O2 with an oxygen volume concentration of 10% (0.15 L / min) is introduced, and anhydrous methanol is fed into the system at a rate of 0.02 mL / min. The reaction temperature is 250 °C and the volume hourly space velocity (VHSV) is 9000 h⁻¹. -1 Analysis and calculations of the gaseous and liquid phase products showed that the methanol conversion rate was 87% and the formaldehyde selectivity was 90%.

[0024] Example 6

[0025] Weigh 2.5g of formic acid and prepare a 0.25mol / L acid solution. Add 10g of deactivated iron-molybdenum catalyst (molybdenum-iron atomic molar ratio 1.5) to the perchloric acid solution and stir at 25℃ for 10h. The perchloric acid solution reacts with the iron in the catalyst, and some of it dissolves in the acid solution. The reaction solution is filtered to separate the solid and liquid phases. The filter cake is dried at 100℃ and calcined in a muffle furnace at 400℃ for 10h to obtain a regenerated iron-molybdenum catalyst with a molybdenum-iron atomic molar ratio of 2.9. The regenerated catalyst is directly extruded and granulated into 40-60 mesh particles. The catalyst is loaded into a fixed-bed reactor with a loading volume of 0.9mL and a loading height of 15cm. Under atmospheric pressure, a mixture of N2 and O2 with an oxygen volume concentration of 10% (0.15L / min) is introduced, and anhydrous methanol is fed into the system at a rate of 0.02mL / min. The reaction temperature is 250℃ and the volume hourly space velocity (VHSV) is 9000h⁻¹. -1 Analysis and calculations of the gaseous and liquid phase products showed that the methanol conversion rate was 85% and the formaldehyde selectivity was 88%.

[0026] Example 7

[0027] 4.90 g of methanesulfonic acid was weighed and prepared into a 0.25 mol / L acid solution. 10 g of deactivated iron-molybdenum catalyst (molybdenum-iron atomic molar ratio 1.5) was added to the methanesulfonic acid solution, and the mixture was stirred at 25 °C for 10 h. The methanesulfonic acid solution reacted with the iron in the catalyst, and some of the iron dissolved in the acid solution. The reaction solution was filtered to separate the solid and liquid phases. The filter cake was dried at 100 °C and calcined in a muffle furnace at 400 °C for 10 h to obtain a regenerated iron-molybdenum catalyst with a molybdenum-iron atomic molar ratio of 2.9. The regenerated catalyst was directly extruded and granulated into 40-60 mesh particles. A catalyst loading volume of 0.9 mL was placed in a fixed-bed reactor to a height of 15 cm. Under atmospheric pressure, a mixture of N2 and O2 with an oxygen volume concentration of 10% was introduced at 0.15 L / min. Anhydrous methanol was fed into the system at a rate of 0.02 mL / min. The reaction temperature was 250 °C, and the volume hourly space velocity (HSV) 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%.

[0028] Example 8

[0029] Weigh 1.50 g of glacial acetic acid and prepare a 0.25 mol / L acid solution. Add 10 g of deactivated iron-molybdenum catalyst (molybdenum-iron atomic molar ratio 1.5) to the acetic acid solution and stir at 25 °C for 10 h. The acetic acid solution reacts with the iron in the catalyst, and some of it dissolves in the acid solution. The reaction solution is filtered to separate the solid and liquid phases. The filter cake is dried at 100 °C and calcined in a muffle furnace at 400 °C for 10 h to obtain a regenerated iron-molybdenum catalyst with a molybdenum-iron atomic molar ratio of 2.9. The regenerated catalyst is directly extruded and granulated into 40-60 mesh particles. The catalyst is loaded into a fixed-bed reactor with a loading volume of 0.9 mL and a loading height of 15 cm. Under atmospheric pressure, a mixture of N2 and O2 with an oxygen volume concentration of 10% (0.15 L / min) is introduced, and anhydrous methanol is fed into the system at a rate of 0.02 mL / min. The reaction temperature is 250 °C and the volume hourly space velocity (VHSV) is 9000 h⁻¹. -1 Analysis and calculations of the gaseous and liquid phase products showed a methanol conversion rate of 95% and a formaldehyde selectivity of 91%.

[0030] Example 9

[0031] 0.90 g of anhydrous oxalic acid was weighed and prepared into a 0.10 mol / L acid solution. 10 g of deactivated iron-molybdenum catalyst (molybdenum-iron atomic molar ratio 1.5) was added to the oxalic acid solution, and the mixture was stirred at 25 °C for 10 h. The oxalic acid solution reacted with the iron in the catalyst, and some of the iron dissolved in the acid solution. The reaction solution was filtered to separate the solid and liquid phases. The filter cake was dried at 100 °C and calcined in a muffle furnace at 400 °C for 10 h to obtain a regenerated iron-molybdenum catalyst with a molybdenum-iron atomic molar ratio of 2.1. The regenerated catalyst was directly extruded and granulated into 40-60 mesh particles. A catalyst loading volume of 0.9 mL was placed in a fixed-bed reactor to a height of 15 cm. Under atmospheric pressure, a mixture of N2 and O2 with an oxygen volume concentration of 10% (0.15 L / min) was introduced, and anhydrous methanol was fed into the system at a rate of 0.02 mL / min. The reaction temperature was 250 °C, and 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 78% and a formaldehyde selectivity of 81%.

[0032] Example 10

[0033] 4.80 g of anhydrous oxalic acid was weighed and prepared into a 0.5 mol / L acid solution. 10 g of deactivated iron-molybdenum catalyst (molybdenum-iron atomic molar ratio 1.5) was added to the oxalic acid solution, and the mixture was stirred at 25 °C for 10 h. The oxalic acid solution reacted with the iron in the catalyst, and some of the iron dissolved in the acid solution. The reaction solution was filtered to separate the solid and liquid phases. The filter cake was dried at 100 °C and calcined in a muffle furnace at 400 °C for 10 h to obtain a regenerated iron-molybdenum catalyst with a molybdenum-iron atomic molar ratio of 3.8. The regenerated catalyst was directly extruded and granulated into 40-60 mesh particles. A catalyst loading volume of 0.9 mL was placed in a fixed-bed reactor to a height of 15 cm. Under atmospheric pressure, a mixture of N2 and O2 with an oxygen volume concentration of 10% (0.15 L / min) was introduced, and anhydrous methanol was fed into the system at a rate of 0.02 mL / min. The reaction temperature was 250 °C, and 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 87% and the formaldehyde selectivity was 78%.

[0034] Example 11

[0035] 2.40 g of anhydrous oxalic acid was weighed and prepared into a 0.25 mol / L acid solution. 10 g of deactivated iron-molybdenum catalyst (molybdenum-iron atomic molar ratio 1.5) was added to the oxalic acid solution, and the mixture was stirred at 25 °C for 10 h. The oxalic acid solution reacted with the iron in the catalyst, and some of the iron dissolved in the acid solution. The reaction solution was filtered to separate the solid and liquid phases. The filter cake was dried at 100 °C and calcined in a muffle furnace at 300 °C for 10 h to obtain a regenerated iron-molybdenum catalyst with a molybdenum-iron atomic molar ratio of 2.9. The regenerated catalyst was directly extruded and granulated into 40-60 mesh particles. A catalyst loading volume of 0.9 mL was placed in a fixed-bed reactor to a height of 15 cm. Under atmospheric pressure, a mixture of N2 and O2 with an oxygen volume concentration of 10% (0.15 L / min) was introduced, and anhydrous methanol was fed into the system at a rate of 0.02 mL / min. The reaction temperature was 250 °C, and 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 68% and the formaldehyde selectivity was 87%.

[0036] Example 12

[0037] 2.40 g of anhydrous oxalic acid was weighed and prepared into a 0.25 mol / L acid solution. 10 g of deactivated iron-molybdenum catalyst (molybdenum-iron atomic molar ratio 1.5) was added to the oxalic acid solution, and the mixture was stirred at 25 °C for 10 h. The oxalic acid solution reacted with the iron in the catalyst, and some of the iron dissolved in the acid solution. The reaction solution was filtered to separate the solid and liquid phases. The filter cake was dried at 100 °C and calcined in a muffle furnace at 600 °C for 10 h to obtain a regenerated iron-molybdenum catalyst with a molybdenum-iron atomic molar ratio of 2.9. The regenerated catalyst was directly extruded and granulated into 40-60 mesh particles. A catalyst loading volume of 0.9 mL was placed in a fixed-bed reactor to a height of 15 cm. Under atmospheric pressure, a mixture of N2 and O2 with an oxygen volume concentration of 10% (0.15 L / min) was introduced, and anhydrous methanol was fed into the system at a rate of 0.02 mL / min. The reaction temperature was 250 °C, and 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 83%.

[0038] Example 13

[0039] 2.40 g of anhydrous oxalic acid was weighed and prepared into a 0.25 mol / L acid solution. 10 g of deactivated iron-molybdenum catalyst (molybdenum-iron atomic molar ratio 1.5) was added to the oxalic acid solution, and the mixture was stirred at 25 °C for 10 h. The oxalic acid solution reacted with the iron in the catalyst, and some of the iron dissolved in the acid solution. The reaction solution was filtered to separate the solid and liquid phases. The filter cake was dried at 100 °C and calcined in a muffle furnace at 400 °C for 10 h to obtain a regenerated iron-molybdenum catalyst with a molybdenum-iron atomic molar ratio of 2.9. The regenerated catalyst was directly extruded and granulated into 40-60 mesh particles. A catalyst loading volume of 0.9 mL was placed in a fixed-bed reactor to a height of 15 cm. Under atmospheric pressure, a mixture of N2 and O2 with an oxygen volume concentration of 10% (0.15 L / min) was introduced, and anhydrous methanol was fed into the system at a rate of 0.02 mL / min. The reaction temperature was 220 °C, and 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 84% and a formaldehyde selectivity of 91%.

[0040] Example 14

[0041] 2.40 g of anhydrous oxalic acid was weighed and prepared into a 0.25 mol / L acid solution. 10 g of deactivated iron-molybdenum catalyst (molybdenum-iron atomic molar ratio 1.5) was added to the oxalic acid solution, and the mixture was stirred at 25 °C for 10 h. The oxalic acid solution reacted with the iron in the catalyst, and some of the iron dissolved in the acid solution. The reaction solution was filtered to separate the solid and liquid phases. The filter cake was dried at 100 °C and calcined in a muffle furnace at 400 °C for 10 h to obtain a regenerated iron-molybdenum catalyst with a molybdenum-iron atomic molar ratio of 2.9. The regenerated catalyst was directly extruded and granulated into 40-60 mesh particles. A catalyst loading volume of 0.9 mL was placed in a fixed-bed reactor to a height of 15 cm. Under atmospheric pressure, a mixture of N2 and O2 with an oxygen volume concentration of 10% (0.15 L / min) was introduced, and anhydrous methanol was fed into the system at a rate of 0.02 mL / min. The reaction temperature was 280 °C, and 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 82%.

[0042] Example 15

[0043] 2.40 g of anhydrous oxalic acid was weighed and prepared into a 0.25 mol / L acid solution. 10 g of deactivated iron-molybdenum catalyst (molybdenum-iron atomic molar ratio 1.5) was added to the oxalic acid solution, and the mixture was stirred at 25 °C for 10 h. The oxalic acid solution reacted with the iron in the catalyst, and some of the iron dissolved in the acid solution. The reaction solution was filtered to separate the solid and liquid phases. The filter cake was dried at 100 °C and calcined in a muffle furnace at 400 °C for 10 h to obtain a regenerated iron-molybdenum catalyst with a molybdenum-iron atomic molar ratio of 2.9. The regenerated catalyst was directly extruded and granulated into 40-60 mesh particles. A catalyst loading volume of 0.9 mL was placed in a fixed-bed reactor to a height of 15 cm. Under atmospheric pressure, a mixture of N2 and O2 with an oxygen volume concentration of 10% (0.12 L / min) was introduced, and anhydrous methanol was fed into the system at a rate of 0.015 mL / min. The reaction temperature was 250 °C, and 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 84%.

[0044] Example 16

[0045] 2.40 g of anhydrous oxalic acid was weighed and prepared into a 0.25 mol / L acid solution. 10 g of deactivated iron-molybdenum catalyst (molybdenum-iron atomic molar ratio 1.5) was added to the oxalic acid solution, and the mixture was stirred at 25 °C for 10 h. The oxalic acid solution reacted with the iron in the catalyst, and some of the iron dissolved in the acid solution. The reaction solution was filtered to separate the solid and liquid phases. The filter cake was dried at 100 °C and calcined in a muffle furnace at 400 °C for 10 h to obtain a regenerated iron-molybdenum catalyst with a molybdenum-iron atomic molar ratio of 2.9. The regenerated catalyst was directly extruded and granulated into 40-60 mesh particles. A catalyst loading volume of 0.9 mL was placed in a fixed-bed reactor to a height of 15 cm. Under atmospheric pressure, a mixture of N2 and O2 with an oxygen volume concentration of 10% (0.18 L / min) was introduced, and anhydrous methanol was fed into the system at a rate of 0.025 mL / min. The reaction temperature was 250 °C, and the volume hourly space velocity (VHSV) was 11000 h⁻¹. -1 Analysis of the gaseous and liquid phase products showed a methanol conversion rate of 82% and a formaldehyde selectivity of 83%.

[0046] Comparative Example 1

[0047] 28.8 g of anhydrous oxalic acid was weighed and prepared into a 3 mol / L acid solution. 10 g of deactivated iron-molybdenum catalyst (molybdenum-iron atomic molar ratio 1.5) was added to the oxalic acid solution, and the mixture was stirred at 25 °C for 10 h. The oxalic acid solution reacted with the iron in the catalyst, and some of the iron dissolved in the acid solution. The reaction solution was filtered to separate the solid and liquid phases. The filter cake was dried at 100 °C and calcined in a muffle furnace at 400 °C for 10 h to obtain a regenerated iron-molybdenum catalyst with a molybdenum-iron atomic molar ratio of 4.0. The regenerated catalyst was directly extruded and granulated into 40-60 mesh particles. A catalyst loading volume of 0.9 mL was placed in a fixed-bed reactor to a height of 15 cm. Under atmospheric pressure, a mixture of N2 and O2 with an oxygen volume concentration of 10% (0.12 L / min) was introduced, and anhydrous methanol was fed into the system at a rate of 0.015 mL / min. The reaction temperature was 250 °C, and the volume hourly space velocity (VHSV) was 7000 h⁻¹. -1 Analysis and calculations of the gaseous and liquid phase products showed that the methanol conversion rate was 91% and the formaldehyde selectivity was 44%.

[0048] Comparative Example 2

[0049] Weigh 0.2 g of anhydrous oxalic acid and prepare a 0.02 mol / L acid solution. Add 10 g of deactivated iron-molybdenum catalyst (molybdenum-iron atomic molar ratio 1.5) to the oxalic acid solution and stir at 25 °C for 10 h. The oxalic acid solution reacts with the iron in the catalyst, and some of it dissolves in the acid solution. Filter the reaction solution to separate the solid and liquid phases. Dry the filter cake at 100 °C and calcine it in a muffle furnace at 400 °C for 10 h to obtain a regenerated iron-molybdenum catalyst with a molybdenum-iron atomic molar ratio of 1.7. The regenerated catalyst is directly extruded and granulated into 40-60 mesh particles. The catalyst is loaded into a fixed-bed reactor with a loading volume of 0.9 mL and a loading height of 15 cm. Under atmospheric pressure, a mixture of N2 and O2 with an oxygen volume concentration of 10% (0.12 L / min) is introduced. Anhydrous methanol is fed into the system at a rate of 0.015 mL / min. The reaction temperature is 250 °C and the volume hourly space velocity (VHSV) is 7000 h⁻¹. -1 Analysis of the gaseous and liquid phase products showed a methanol conversion rate of 35% and a formaldehyde selectivity of 41%.

[0050] Comparative Example 3

[0051] 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 to a height of 15cm. Under atmospheric pressure, a mixture of N2 and O2 with an oxygen volume concentration of 10% (0.12L / min) was introduced, 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%.

[0052] 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 by acid treatment, characterized in that: The deactivated iron-molybdenum catalyst used for the oxidation of methanol to formaldehyde was placed in an acid solution and stirred to react. After the reaction, the mixture was filtered to separate the solid and liquid. The solid was washed, dried, and calcined to obtain the regenerated catalyst.

2. The method according to claim 1, characterized in that: The acid used to treat the iron-molybdenum catalyst is one or more of the following: hydrochloric acid, nitric acid, sulfuric acid, perchloric acid, formic acid, acetic acid, oxalic acid, and sulfonic acid. The concentration of the acid solution is 0.05–2.0 mol / L, preferably 0.1–1.5 mol / L, and more preferably 0.15–1 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: The reaction temperature between the deactivated iron-molybdenum catalyst and the acid solution is 10℃~100℃ (preferably 20℃~80℃, more preferably 25℃~70℃), and the reaction time is 3~15h (preferably 5~13h, more preferably 7~12h).

4. The method according to claim 1, characterized in that: After solid-liquid separation, the solid is dried at a temperature of 40℃ to 140℃ (preferably 50℃ to 120℃, more preferably 70℃ to 110℃); the calcination temperature is 250℃ to 650℃ (preferably 300℃ to 600℃, more preferably 350℃ to 500℃), and the time is 3 to 15 hours (preferably 5 to 13 hours, more preferably 7 to 11 hours).

5. The method according to claim 1, characterized in that: The acid solution reacts with the deactivated iron-molybdenum catalyst. The acid solution mainly reacts with the iron in the catalyst and dissolves into the liquid. The solid and liquid are separated by filtration. The degree of reaction between the acid and the iron is changed by adjusting the acid concentration and the reaction time, thereby controlling the iron content in the catalyst in the solid after solid-liquid separation. The molar ratio of molybdenum atoms to iron atoms in the regenerated catalyst is controlled to be 2:1 to 5:1, preferably 2:1 to 4:

1.

6. The application of the regenerated iron-molybdenum catalyst of claim 5 in the catalytic oxidation of methanol to formaldehyde.

7. The application according to claim 6, characterized in that: In the methanol oxidation to formaldehyde reaction, the regenerated iron-molybdenum catalyst is granulated into 40-60 mesh particles; under atmospheric pressure, a mixture of N2 and O2 is introduced, with an oxygen volume concentration of 6%–15% in the mixture; the reaction temperature is 200℃–350℃; and anhydrous methanol is fed into the system at a rate of 0.01–0.03 mL / min, with a volume hourly space velocity of 7000–11000 h⁻¹. -1 .

8. The application according to claim 1 or 7, characterized in that: The preferred reaction temperature for methanol to formaldehyde production is 220℃~270℃, the preferred catalyst loading volume is 0.7~1.0mL, and the preferred volume hourly space velocity (VHSV) is 8000~10000h. -1 .