A method for recovering molybdenum from a waste methanol oxidation to formaldehyde iron-molybdenum catalyst
Through steps such as calcination, grinding, and ammonia reaction, molybdenum is efficiently recovered from the iron-molybdenum catalyst for the oxidation of waste methanol to formaldehyde, solving the problem of low recovery rate and achieving efficient recovery while maintaining catalyst performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SOUTHWEST RES & DESIGN INST OF CHEM IND
- Filing Date
- 2023-12-14
- Publication Date
- 2026-05-12
AI Technical Summary
Existing technologies for recovering molybdenum from waste iron-molybdenum-formaldehyde catalysts have low recovery rates, resulting in economic losses and waste of molybdenum resources.
Molybdenum was recovered from waste methanol oxidation to formaldehyde iron-molybdenum catalyst by means of calcination, grinding, reaction of ammonia and hydrogen peroxide, and crystallization of ammonium molybdate. The recovery rate of molybdenum was improved by controlling temperature, pH value and stirring speed, and the recovered molybdenum was used to prepare catalysts.
The total molybdenum recovery rate reached as high as 98%. The recovered molybdenum can be used to prepare catalysts, which is economical and environmentally friendly, and the performance of the catalysts is comparable to that of catalysts prepared from fresh raw materials.
Smart Images
Figure CN117758070B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of organic chemical catalysts, specifically a method for recovering molybdenum from a waste methanol oxidation to formaldehyde iron-molybdenum catalyst. Background Technology
[0002] Formaldehyde is an important basic organic chemical raw material and one of the most important derivatives of methanol. It is mainly used in the production of thermosetting resins, pentaerythritol, polyoxymethylene, 1,4-butanediol (BDO), pyridine, ethylene glycol, trihydroxymethane, and other chemical products. Domestically and internationally, the main formaldehyde production technologies used are the iron-molybdenum process and the silver process. Due to factors such as safety, environmental protection, unit consumption, energy consumption, and formaldehyde quality, the silver process is gradually being replaced by the iron-molybdenum process. Furthermore, with the increasing demand for high-concentration formaldehyde in downstream processes such as BDO, the number of iron-molybdenum formaldehyde plants is rapidly increasing.
[0003] With the increase in iron-molybdenum formaldehyde production facilities, a large amount of waste iron-molybdenum formaldehyde catalyst is generated. Metallic molybdenum is the main component of iron-molybdenum catalysts, accounting for more than 50% of the catalyst mass, and its price is high, especially since 2023 when the average price of molybdenum products has increased significantly year-on-year, with increases generally exceeding 50%. Therefore, from both economic and environmental perspectives, it is necessary to recover molybdenum from waste iron-molybdenum formaldehyde catalysts.
[0004] Currently, the main method for recovering molybdenum from waste iron-molybdenum-formaldehyde catalysts is ammonia leaching. While the process is simple and easy to operate, the molybdenum recovery rate is low. The molybdenum content in the ammonia leaching residue can typically reach over 10%, and this residue, as hazardous waste, not only causes economic losses but also wastes molybdenum resources. Summary of the Invention
[0005] The purpose of this invention is to address the problem of low molybdenum recovery rates in current waste iron-molybdenum formaldehyde catalysts by providing a method for recovering molybdenum from waste methanol oxidation to formaldehyde iron-molybdenum catalysts. This method is safe, environmentally friendly, simple to operate, and achieves high molybdenum recovery rates. Furthermore, the iron-molybdenum catalyst prepared using the recovered molybdenum exhibits the same performance as the catalyst prepared using fresh raw materials.
[0006] To achieve the above-mentioned objectives, the specific technical solution of this invention is as follows:
[0007] A method for recovering molybdenum from a waste methanol oxidation catalyst for formaldehyde production includes the following steps:
[0008] 1) The waste methanol oxidation to formaldehyde iron-molybdenum catalyst is sieved to remove the ceramic rings mixed in the waste catalyst. Then the waste catalyst is calcined at 450℃~550℃ for 2~5 hours, cooled, ground and sieved.
[0009] 2) The waste catalyst ground in step 1) is reacted with ammonia water, and a small amount of hydrogen peroxide is added at the same time. The temperature is raised to 70℃~100℃, and the reaction is carried out for 4 hours to 8 hours. Then the temperature is lowered and filtered to obtain ammonium molybdate solution and ammonia leaching residue.
[0010] 3) Heat the ammonium molybdate solution to concentrate and remove ammonia, controlling the concentration temperature at 70℃~100℃ and the solution pH at 6.5~5.5. When the ammonium molybdate solution is concentrated to the specified density, control the stirring speed and cool down to obtain ammonium molybdate crystals I.
[0011] 4) React the ammonia leaching residue from step 2) with sodium hydroxide solution, heat to 70℃~90℃, react for 2 hours~6 hours, cool down, filter to obtain reaction filtrate and filter residue, wash the filter residue with process water, filter, and mix the washed filtrate with the reaction filtrate to obtain sodium molybdate solution.
[0012] 5) Add nitric acid solution to the sodium molybdate solution obtained in step 4) to adjust the pH to 1, heat to 70℃~90℃, react for 0.5 hours~2 hours, filter to obtain molybdate precipitate and filtrate, wash the molybdate precipitate and dissolve it with ammonia to obtain ammonium molybdate solution.
[0013] 6) Heat the ammonium molybdate solution from step 5) to concentrate and evaporate ammonia, controlling the concentration temperature at 70℃~100℃ and the solution pH at 6.5~5.5. When the ammonium molybdate solution is concentrated to the specified density, control the stirring speed and cool down to obtain ammonium molybdate crystals II.
[0014] 7) Dissolve the filter residue from step 4) in nitric acid and then filter it to prepare a ferric nitrate solution of a certain concentration.
[0015] 8) Mix the ammonium molybdate crystals from step 3) with the ammonium molybdate crystals II obtained in step 6), then prepare a solution, co-precipitate it with the ferric nitrate solution from step 7) at a certain temperature, add additives, age, dry, shape, and calcine at high temperature to produce a methanol oxidation to formaldehyde catalyst.
[0016] In a preferred embodiment of this application, in step 1), calcination is performed to remove organic coke impurities adsorbed on the spent catalyst. Grinding and sieving the spent catalyst is to control its particle size. A larger particle size will result in insufficient reaction and affect molybdenum recovery, while a smaller particle size will increase the cost of ball milling. After calcination and grinding, the particle size of the spent catalyst is controlled to be below 0.77 mm; more preferably, it is 0.19 mm to 0.38 mm.
[0017] In a preferred embodiment of this application, the concentration of ammonia in step 2) is 5 wt% to 25 wt%; the mass ratio of ammonia to waste catalyst is 5:1 to 20:1; the concentration of hydrogen peroxide is 30 wt%, and the amount added is 1 wt% to 0.05 wt% of the mass of the waste catalyst.
[0018] Because the spent catalyst contains small amounts of molybdenum dioxide and ferrous molybdate, this portion of molybdenum dioxide does not react with ammonia, while the ferrous molybdate reacts with ammonia to form an iron-ammonia complex that enters the solution.
[0019] FeMoO4+2NH4OH=(NH4)2MoO4+Fe(OH)2
[0020] Fe(OH)2+4NH4OH=[Fe(NH3)4](OH)2+4H2O.
[0021] Therefore, a small amount of hydrogen peroxide needs to be added to oxidize molybdenum dioxide to molybdenum trioxide and ferrous molybdate to ferric molybdate.
[0022] 2FeMoO4+H2O2+4NH4OH=2Fe(OH)3+2(NH4)2MoO4
[0023] MoO2+H2O2+2NH4OH=(NH4)2MoO4+2H2O.
[0024] In a preferred embodiment of this application, in step 3), the ammonium molybdate solution needs to be concentrated to a specified density before cooling and crystallization. A higher solution density will cause other ammonium molybdate to precipitate during crystallization, while a lower solution density will result in a lower crystallization rate and increased energy consumption. The ammonium molybdate solution is concentrated to a density of 1.35 g / cm³. 3 ~1.52g / cm 3 The stirring speed is 120 r / min to 200 r / min; the final crystallization temperature of ammonium molybdate is 15℃ to 25℃.
[0025] In a preferred embodiment of this application, in step 4), the concentration of sodium hydroxide solution is 5wt% to 10wt%, and the mass ratio of sodium hydroxide solution to waste catalyst (ground waste catalyst) is 9:20 to 3:5.
[0026] In a preferred embodiment of this application, in step 4), the mass ratio of process water to filter residue is 1:1, and the washing and filtering are performed twice.
[0027] In a preferred embodiment of this application, in step 5), the nitric acid is a dilute nitric acid with a concentration of 10wt% to 20wt%; the ammonia concentration is 5wt% to 10wt%; the density of the ammonium molybdate solution affects the subsequent concentration and ammonia stripping process. A lower density of the ammonium molybdate solution will increase the energy consumption of the concentration and ammonia stripping process, while a higher density will cause the ammonia to not evaporate in time, resulting in the precipitation of other forms of ammonium molybdate during solution crystallization; the density of the ammonium molybdate solution is 1.15 g / cm³. 3 ~1.21g / cm 3 .
[0028] In a preferred embodiment of this application, in step 6), the ammonium molybdate solution is concentrated to a density of 1.35 g / cm³. 3 ~1.52g / cm 3 The stirring speed is 120 r / min to 200 r / min. The final crystallization temperature is 15℃ to 25℃.
[0029] In a preferred embodiment of this application, the nitric acid in step 7) is a dilute nitric acid with a concentration of 10wt% to 20wt%; the ferric nitrate solution is filtered to remove trace amounts of insoluble substances such as graphite from the solution, and the filtered ferric nitrate solution is prepared into a solution of a specified concentration as required; the concentration of ferric nitrate is 0.1mol / L to 0.8mol / L.
[0030] As a preferred embodiment of this application, the above method or combination of method steps is used to recover molybdenum from the iron-molybdenum catalyst used in the oxidation of waste methanol to formaldehyde, and the total molybdenum recovery rate is greater than 98%.
[0031] Compared with existing technologies, the beneficial effects of the present invention are as follows:
[0032] (i) The recovery method provided by the present invention firstly uses ammonia water to react with the waste catalyst. By adding hydrogen peroxide to oxidize the molybdenum dioxide and ferrous ions in the waste catalyst, the recovery rate of molybdenum is improved while the iron content in the ammonium molybdate solution is reduced. Then, sodium hydroxide solution is used to further recover molybdenum from the ammonia leaching residue. The molybdenum recovery rate is high, and the total molybdenum recovery rate is greater than 98%.
[0033] (ii) The recovery method provided by the present invention recovers molybdenum in the form of ammonium molybdate crystals, which can be used to prepare catalysts or sold as products, and has a wide range of applications.
[0034] (III) The recycling method provided by this invention uses the recovered molybdenum to prepare catalysts or sell it as a product, and uses the recovered ferric nitrate to prepare catalysts. The waste catalyst is almost completely utilized and no new solid waste is generated. The operation is simple and the process is safe and environmentally friendly.
[0035] (iv) The recovery method provided by the present invention uses a methanol oxidation to formaldehyde catalyst prepared by recovering ammonium molybdate and ferric nitrate solution. The catalyst strength and performance evaluation results are comparable to those of the catalyst prepared from fresh raw materials. Attached Figure Description
[0036] Figure 1 The image shows the XRD characterization of the molybdic acid crystals prepared in Examples 1-5.
[0037] Figure 2 This is a SEM characterization image of the iron-molybdenum methanol oxidation to formaldehyde catalyst prepared from recycled raw materials.
[0038] Figure 3 This is a SEM characterization image of the iron-molybdenum methanol-to-formaldehyde catalyst prepared from fresh raw materials. Detailed Implementation
[0039] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. However, this should not be construed as limiting the scope of the invention to the following embodiments. Various substitutions and modifications made based on ordinary technical knowledge and common practice in the art without departing from the above-described technical concept of this invention should be included within the scope of this invention.
[0040] The features and performance of the present invention will be further described in detail below with reference to embodiments.
[0041] In the following examples, the preparation of the methanol oxidation to formaldehyde catalyst is a prior art technique, which can be referred to as "Research on Iron-Molybdenum Catalysts for Methanol Oxidation to Formaldehyde" by Li Suyan or "Research on Iron-Molybdenum Catalysts for Methanol Oxidation to Formaldehyde" by Zhu Xiaoxue et al.
[0042] Example 1:
[0043] This embodiment provides a method for recovering molybdenum from a waste methanol oxidation catalyst for formaldehyde production, specifically including the following steps:
[0044] The spent methanol-to-formaldehyde iron-molybdenum catalyst was sieved to remove impurities such as ceramic rings. The catalyst was then calcined at 450℃ for 5 hours, cooled, ground, and sieved again to remove particles smaller than 0.38 mm. 1000 g of the ground catalyst was weighed and reacted with 5000 g of 25 wt% ammonia solution, along with 8 g of hydrogen peroxide. The mixture was heated to 80℃ and reacted for 4 hours. After cooling, the mixture was filtered to obtain an ammonium molybdate solution and ammonia leaching residue. The ammonium molybdate solution was concentrated at 70℃ to remove ammonia, resulting in a pH of 6.50. The solution was concentrated to a density of 1.35 g / cm³. 3 Then, the stirring speed was controlled at 200 r / min, the temperature was lowered to 15℃, and the mixture was filtered to obtain ammonium molybdate crystals I. The ammonia leaching residue was reacted with 500 g of a 10 wt% sodium hydroxide solution, the temperature was raised to 70℃, and after reacting for 4 hours, the mixture was cooled and filtered to obtain the reaction filtrate and filter residue. The filter residue was washed twice with an equal mass of process water and then filtered. The obtained filter residue was dissolved in 15 wt% nitric acid and then filtered to obtain a ferric nitrate solution. The washed filtrate was mixed with the reaction filtrate to obtain a sodium molybdate solution. 10 wt% nitric acid was added to the sodium molybdate solution to adjust the pH to 1, the temperature was raised to 75℃, and after reacting for 1.5 hours, the mixture was filtered to obtain molybdate precipitate and filtrate. The molybdate precipitate was dissolved in 5 wt% ammonia water to obtain a solution with a density of 1.15 g / cm³. 3An ammonium molybdate solution was prepared. The ammonium molybdate solution was heated to 70℃ and concentrated to remove ammonia. The solution pH was 6.50. The solution was then concentrated to a density of 1.35 g / cm³. 3 Then, the stirring speed was controlled at 200 r / min, the temperature was lowered to 15℃, and the mixture was filtered to obtain ammonium molybdate crystals II. The molybdenum content was analyzed by atomic absorption spectrophotometry, and the total molybdenum recovery rate was 98.74%.
[0045] The recovered ferric nitrate solution was prepared into a ferric nitrate solution of a certain concentration, and then co-precipitated with a solution prepared by ammonium molybdate crystals (ammonium molybdate crystal I and ammonium molybdate crystal II) at a certain temperature. Additives were added, the mixture was aged, dried, shaped, and calcined at high temperature to produce a methanol oxidation to formaldehyde catalyst.
[0046] Example 2
[0047] This embodiment provides a method for recovering molybdenum from a waste methanol oxidation catalyst for formaldehyde production, specifically including the following steps:
[0048] The spent methanol-to-formaldehyde iron-molybdenum catalyst was sieved to remove impurities such as ceramic rings. The catalyst was then calcined at 500℃ for 3 hours, cooled, ground, and sieved again to remove particles smaller than 0.19 mm. 1000 g of the ground catalyst was weighed and reacted with 5000 g of 20 wt% ammonia solution, along with 10 g of hydrogen peroxide. The mixture was heated to 70℃ and reacted for 4 hours. After cooling, the mixture was filtered to obtain an ammonium molybdate solution and ammonia leaching residue. The ammonium molybdate solution was concentrated at 70℃ to remove ammonia, resulting in a pH of 6.00. The solution was concentrated to a density of 1.38 g / cm³. 3 Then, the stirring speed was controlled at 150 r / min, the temperature was lowered to 20℃, and the mixture was filtered to obtain ammonium molybdate crystals I. The ammonia leaching residue was reacted with 450 g of a 10 wt% sodium hydroxide solution, the temperature was raised to 75℃, and after reacting for 2 hours, the mixture was cooled and filtered to obtain the reaction filtrate and filter residue. The filter residue was washed twice with an equal mass of process water and then filtered. The obtained filter residue was dissolved in 20 wt% nitric acid and then filtered to obtain a ferric nitrate solution. The washed filtrate was mixed with the reaction filtrate to obtain a sodium molybdate solution. 15 wt% nitric acid was added to the sodium molybdate solution to adjust the pH to 1, the temperature was raised to 70℃, and after reacting for 2 hours, the mixture was filtered to obtain molybdate precipitate and filtrate. The molybdate precipitate was dissolved in 5 wt% ammonia water to obtain a solution with a density of 1.15 g / cm³. 3 An ammonium molybdate solution was prepared. The ammonium molybdate solution was heated to 70℃ and concentrated to remove ammonia. The solution pH was 6.00. The solution was then concentrated to a density of 1.38 g / cm³. 3 Then, the stirring speed was controlled at 150 r / min, the temperature was lowered to 20℃, and the mixture was filtered to obtain ammonium molybdate crystals II. The molybdenum content was analyzed by atomic absorption spectrophotometry, and the total molybdenum recovery rate was 98.45%.
[0049] The recovered ferric nitrate solution was prepared into a ferric nitrate solution of a certain concentration, and then co-precipitated with a solution prepared by ammonium molybdate crystals (ammonium molybdate crystal I and ammonium molybdate crystal II) at a certain temperature. Additives were added, the mixture was aged, dried, shaped, and calcined at high temperature to produce a methanol oxidation to formaldehyde catalyst.
[0050] Example 3
[0051] This embodiment provides a method for recovering molybdenum from a waste methanol oxidation catalyst for formaldehyde production, specifically including the following steps:
[0052] The spent methanol-to-formaldehyde iron-molybdenum catalyst was sieved to remove impurities such as ceramic rings. The catalyst was then calcined at 500℃ for 3 hours, cooled, ground, and sieved again to remove particles smaller than 0.52 mm. 1000 g of the ground catalyst was weighed and reacted with 20000 g of 5 wt% ammonia solution, along with 10 g of hydrogen peroxide. The mixture was heated to 90℃ and reacted for 6 hours. After cooling, the mixture was filtered to obtain an ammonium molybdate solution and ammonia leaching residue. The ammonium molybdate solution was heated to 100℃ and concentrated to remove ammonia. The solution pH was 5.50. The solution was concentrated to a density of 1.52 g / cm³. 3 Then, the stirring speed was controlled at 120 r / min, the temperature was lowered to 25℃, and the mixture was filtered to obtain ammonium molybdate crystals I. The ammonia leaching residue was reacted with 600 g of a 5 wt% sodium hydroxide solution, heated to 80℃, and reacted for 6 hours. After cooling, the mixture was filtered to obtain the reaction filtrate and filter residue. The filter residue was washed twice with an equal mass of process water and then filtered again. The resulting filter residue was dissolved in 15 wt% nitric acid and filtered to obtain a ferric nitrate solution. The washed filtrate was mixed with the reaction filtrate to obtain a sodium molybdate solution. 20 wt% nitric acid was added to the sodium molybdate solution to adjust the pH to 1, the temperature was raised to 90℃, and the mixture was reacted for 0.5 hours. After filtration, molybdate precipitate and filtrate were obtained. The molybdate precipitate was dissolved in 10 wt% ammonia water to obtain a solution with a density of 1.21 g / cm³. 3 An ammonium molybdate solution was prepared. The ammonium molybdate solution was heated to 100℃ to concentrate and evaporate the ammonia. The solution pH was 5.50. The solution was then concentrated to a density of 1.52 g / cm³. 3 Then, the stirring speed was controlled at 120 r / min, the temperature was lowered to 25℃, and the mixture was filtered to obtain ammonium molybdate crystals II. The molybdenum content was analyzed by atomic absorption spectrophotometry, and the total molybdenum recovery rate was 99.02%.
[0053] The recovered ferric nitrate solution was prepared into a ferric nitrate solution of a certain concentration, and then co-precipitated with a solution prepared by ammonium molybdate crystals (ammonium molybdate crystal I and ammonium molybdate crystal II) at a certain temperature. Additives were added, the mixture was aged, dried, shaped, and calcined at high temperature to produce a methanol oxidation to formaldehyde catalyst.
[0054] Example 4
[0055] This embodiment provides a method for recovering molybdenum from a waste methanol oxidation catalyst for formaldehyde production, specifically including the following steps:
[0056] The spent methanol-to-formaldehyde iron-molybdenum catalyst was sieved to remove impurities such as ceramic rings. The catalyst was then calcined at 450℃ for 4 hours, cooled, ground, and sieved again to remove particles smaller than 0.38 mm. 1000 g of the ground catalyst was weighed and reacted with 10000 g of 10 wt% ammonia solution, along with 8 g of hydrogen peroxide. The mixture was heated to 80℃ and reacted for 5 hours. After cooling and filtration, ammonium molybdate solution and ammonia leaching residue were obtained. The ammonium molybdate solution was heated to 90℃ and concentrated to remove ammonia. The solution pH was 6.00. The solution was concentrated to a density of 1.38 g / cm³. 3 Then, the stirring speed was controlled at 150 r / min, the temperature was lowered to 20℃, and the mixture was filtered to obtain ammonium molybdate crystals I. The ammonia leaching residue was reacted with 550 g of 8 wt% sodium hydroxide solution, the temperature was raised to 70℃, and after reacting for 3 hours, the mixture was cooled and filtered to obtain the reaction filtrate and filter residue. The filter residue was washed twice with an equal mass of process water and then filtered. The obtained filter residue was dissolved in 10 wt% nitric acid and then filtered to obtain ferric nitrate solution. The washed filtrate was mixed with the reaction filtrate to obtain sodium molybdate solution. 20 wt% nitric acid was added to the sodium molybdate solution to adjust the pH to 1, the temperature was raised to 85℃, and after reacting for 1 hour, the mixture was filtered to obtain molybdate precipitate and filtrate. The molybdate precipitate was dissolved in 10 wt% ammonia water to obtain a solution with a density of 1.20 g / cm³. 3 An ammonium molybdate solution was prepared. The ammonium molybdate solution was heated to 90℃ and concentrated to remove ammonia. The solution pH was 6.00. The solution was then concentrated to a density of 1.38 g / cm³. 3 Then, the stirring speed was controlled at 150 r / min, the temperature was lowered to 20℃, and the mixture was filtered to obtain ammonium molybdate crystals II. The molybdenum content was analyzed by atomic absorption spectrophotometry, and the total molybdenum recovery rate was 99.34%.
[0057] The recovered ferric nitrate solution was prepared into a ferric nitrate solution of a certain concentration, and then co-precipitated with a solution prepared by ammonium molybdate crystals (ammonium molybdate crystal I and ammonium molybdate crystal II) at a certain temperature. Additives were added, the mixture was aged, dried, shaped, and calcined at high temperature to produce a methanol oxidation to formaldehyde catalyst.
[0058] Example 5
[0059] This embodiment provides a method for recovering molybdenum from a waste methanol oxidation catalyst for formaldehyde production, specifically including the following steps:
[0060] The spent methanol-to-formaldehyde iron-molybdenum catalyst was sieved to remove impurities such as ceramic rings. The catalyst was then calcined at 550℃ for 3 hours, cooled, ground, and sieved again to remove particles smaller than 0.77 mm. 1000 g of the ground catalyst was weighed and reacted with 8000 g of 15 wt% ammonia solution, along with 10 g of hydrogen peroxide. The mixture was heated to 100℃ and reacted for 8 hours. After cooling and filtration, ammonium molybdate solution and ammonia leaching residue were obtained. The ammonium molybdate solution was heated to 90℃ and concentrated to remove ammonia. The solution pH was 5.80. The solution was concentrated to a density of 1.40 g / cm³. 3 Then, the stirring speed was controlled at 150 r / min, the temperature was lowered to 20℃, and the mixture was filtered to obtain ammonium molybdate crystals I. The ammonia leaching residue was reacted with 600 g of a 5 wt% sodium hydroxide solution, heated to 90℃, and reacted for 4 hours. After cooling, the mixture was filtered to obtain the reaction filtrate and filter residue. The filter residue was washed twice with an equal mass of process water and then filtered again. The resulting filter residue was dissolved in 15 wt% nitric acid and filtered to obtain a ferric nitrate solution. The washed filtrate was mixed with the reaction filtrate to obtain a sodium molybdate solution. 15 wt% nitric acid was added to the sodium molybdate solution to adjust the pH to 1, the temperature was raised to 90℃, and the mixture was reacted for 0.5 hours. After filtration, molybdate precipitate and filtrate were obtained. The molybdate precipitate was dissolved in 8 wt% ammonia water to obtain a solution with a density of 1.18 g / cm³. 3 An ammonium molybdate solution was prepared. The ammonium molybdate solution was heated to 90℃ and concentrated to remove ammonia. The solution pH was 5.80. The solution was then concentrated to a density of 1.40 g / cm³. 3 Then, the stirring speed was controlled at 150 r / min, the temperature was lowered to 20℃, and the mixture was filtered to obtain ammonium molybdate crystals II. The molybdenum content was analyzed by atomic absorption spectrophotometry, and the total molybdenum recovery rate was 98.75%.
[0061] The recovered ferric nitrate solution was prepared into a ferric nitrate solution of a certain concentration, and then co-precipitated with a solution prepared by ammonium molybdate crystals (ammonium molybdate crystal I and ammonium molybdate crystal II) at a certain temperature. Additives were added, the mixture was aged, dried, shaped, and calcined at high temperature to produce a methanol oxidation to formaldehyde catalyst.
[0062] Experimental Example
[0063] The performance of the iron-molybdenum catalyst samples for methanol oxidation to formaldehyde prepared in Examples 1-5 was tested. The test results are shown in Table 1.
[0064] Catalyst evaluation conditions:
[0065] The catalyst loading is 12 ml (6 ml catalyst + 6 ml high-temperature resistant ceramic rings), the methanol volume percentage in the feed gas is 10%, the oxygen volume percentage in the carrier gas is 10%, and the gas space velocity is 10000 h⁻¹. -1The feed gas inlet temperature was 230℃, and the reaction pressure was 0.1 MPa. The product composition was analyzed online using an Agilent 7890 gas chromatograph.
[0066] Table 1 Performance evaluation of iron-molybdenum catalyst samples for methanol oxidation to formaldehyde
[0067]
[0068]
[0069] Note: The control sample is catalyst F3 in CN 115845865 A.
[0070] As can be seen from the table above, the methanol oxidation to formaldehyde iron-molybdenum catalyst sample prepared by this method is comparable to the catalyst prepared from fresh raw materials in terms of catalyst strength and performance evaluation results.
[0071] The embodiments described above merely illustrate specific implementation methods of this application, and while the descriptions are detailed and specific, they should not be construed as limiting the scope of protection of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the technical solution of this application, and these modifications and improvements all fall within the scope of protection of this application.
[0072] This background section is provided to generally present the context of the invention. The work of the currently named inventors, the work to the extent described in this background section, and aspects of this section that did not constitute prior art at the time of application are neither expressly nor impliedly acknowledged as prior art to the invention.
Claims
1. A method for recovering molybdenum from a waste methanol oxidation catalyst for formaldehyde production, characterized in that, Includes the following steps: 1) The waste methanol oxidation to formaldehyde iron-molybdenum catalyst is sieved to remove the ceramic rings mixed in the waste catalyst. Then the waste catalyst is calcined at 450℃~550℃ for 2~5 hours, cooled, ground and sieved. 2) The waste catalyst ground in step 1) is reacted with ammonia water, and a small amount of hydrogen peroxide is added at the same time. The temperature is raised to 70℃~100℃, and the reaction is carried out for 4 hours to 8 hours. Then the temperature is lowered and filtered to obtain ammonium molybdate solution and ammonia leaching residue. 3) Heat the ammonium molybdate solution to concentrate and remove ammonia, controlling the concentration temperature at 70℃~100℃ and the solution pH at 5.5~6.
5. When the ammonium molybdate solution is concentrated to the specified density, control the stirring speed and cool down to obtain ammonium molybdate crystals I. 4) React the ammonia leaching residue from step 2) with sodium hydroxide solution, heat to 70℃~90℃, react for 2 hours~6 hours, cool down, filter to obtain reaction filtrate and filter residue, wash the filter residue with process water, filter, and mix the washed filtrate with the reaction filtrate to obtain sodium molybdate solution. 5) Add nitric acid solution to the sodium molybdate solution obtained in step 4) to adjust the pH to 1, heat to 70℃~90℃, react for 0.5 hours~2 hours, filter to obtain molybdate precipitate and filtrate, wash the molybdate precipitate and dissolve it with ammonia to obtain ammonium molybdate solution. 6) Heat the ammonium molybdate solution from step 5) to concentrate and evaporate ammonia, controlling the concentration temperature at 70℃~100℃ and the solution pH at 5.5~6.
5. When the ammonium molybdate solution is concentrated to the specified density, control the stirring speed and cool down to obtain ammonium molybdate crystals II. 7) Dissolve the filter residue from step 4) in nitric acid and then filter it to prepare a ferric nitrate solution of a certain concentration. 8) Mix the ammonium molybdate crystals I obtained in step 3) with the ammonium molybdate crystals II obtained in step 6), then prepare a solution, co-precipitate it with the ferric nitrate solution in step 7) at a certain temperature, add the additives, age it, dry it, shape it, and calcine it at high temperature to prepare a methanol oxidation to formaldehyde catalyst. In step 2), the concentration of ammonia is 5 wt% to 25 wt%; the mass ratio of ammonia to waste catalyst is 5:1 to 20:1; the concentration of hydrogen peroxide is 30 wt%, and the amount added is 0.05 wt% to 1 wt% of the mass of waste catalyst. In step 3), the ammonium molybdate solution is concentrated to a density of 1.35 g / cm³. 3 ~1.52g / cm 3 The stirring speed is 120 r / min to 200 r / min; the final crystallization temperature of ammonium molybdate is 15℃ to 25℃. In step 6), the ammonium molybdate solution is concentrated to a density of 1.35 g / cm³. 3 ~1.52g / cm 3 The stirring speed is 120 r / min to 200 r / min; the crystallization endpoint temperature is 15℃ to 25℃.
2. The method for recovering molybdenum from the iron-molybdenum catalyst for the oxidation of waste methanol to formaldehyde according to claim 1, characterized in that, In step 1), the waste catalyst is roasted and ground to a particle size controlled below 0.77 mm.
3. The method for recovering molybdenum from a waste methanol oxidation catalyst for formaldehyde production according to claim 1, characterized in that, In step 4), the concentration of sodium hydroxide solution is 5wt% to 10wt%, and the mass ratio of sodium hydroxide solution to waste catalyst is 9:20 to 3:
5.
4. The method for recovering molybdenum from a waste methanol oxidation catalyst for formaldehyde production according to claim 1, characterized in that, In step 4), the mass ratio of process water to filter residue is 1:1; the washing and filtration are performed twice.
5. The method for recovering molybdenum from a waste methanol oxidation catalyst for formaldehyde production according to claim 1, characterized in that, In step 5), the nitric acid is a dilute nitric acid with a concentration of 10wt% to 20wt%; the ammonia solution has a concentration of 5wt% to 10wt%; and the ammonium molybdate solution has a density of 1.15 g / cm³. 3 ~1.21g / cm 3 .
6. The method for recovering molybdenum from a waste methanol oxidation catalyst for formaldehyde production according to claim 1, characterized in that, The nitric acid mentioned in step 7) is a dilute nitric acid with a concentration of 10wt% to 20wt%; the ferric nitrate concentration is 0.1mol / L to 0.8mol / L.
7. The method for recovering molybdenum from a waste methanol oxidation to formaldehyde iron-molybdenum catalyst according to any one of claims 1-6, characterized in that, Using this method, the overall molybdenum recovery rate is greater than 98%.