Preparation method and application of supported formaldehyde catalyst

Abstract

The invention discloses a preparation method and application of a supported formaldehyde catalyst, and belongs to the technical field of formaldehyde preparation. The preparation method comprises the following steps: respectively dissolving ferric salt and molybdenum salt in water, and heating to obtain a ferric salt solution and a molybdenum salt solution; dropwise adding a molybdenum salt solution into the ferric salt solution, and carrying out aging treatment; filtering, washing and drying to obtain catalyst powder; preparing slurry containing water, a dispersing agent and catalyst powder, and dipping the carrier in the slurry; and drying and roasting to obtain the supported formaldehyde catalyst. A fixed bed reactor is filled with the supported formaldehyde catalyst according to the corresponding loading capacity, reaction heat release is uniform, the conversion rate is high, and high product selectivity is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of formaldehyde preparation, and particularly relates to a preparation method and application of a supported formaldehyde catalyst. Background Art

[0002] Formaldehyde, as an important basic chemical raw material, is widely used in fields such as resin synthesis, plastic processing, pharmaceutical preparation, and textile industry. Currently, formaldehyde is mainly produced industrially through the methanol oxidative dehydrogenation process, and the performance of the catalyst directly determines the reaction efficiency and economy.

[0003] Iron molybdenum oxide (Mo-Fe-O) catalyst is the mainstream catalyst for the current methanol oxidation to formaldehyde process. The reaction temperature (300 - 450 °C) is significantly lower than that of silver catalyst, and the formaldehyde selectivity can reach over 90%. Currently, the preparation methods of iron molybdenum oxide catalyst include: 1) Coprecipitation method: Dissolve soluble iron salt and molybdate in water according to a certain ratio, add a precipitant under stirring, adjust the pH to neutral or alkaline to form a coprecipitate. After the precipitate is filtered, washed, and dried, it is calcined at high temperature for activation. 2) Impregnation method: Immerse a porous support in a mixed solution containing iron and molybdenum, remove the excess liquid, and then dry and calcine to load the active components on the surface of the support. 3) Sol-gel method: Hydrolyze the precursors of iron and molybdenum (such as metal alkoxides) in a solvent to form a sol, and obtain a nano-scale catalyst through gelation, drying, and calcination. 4) Mechanical mixing method: Mix and grind solid powders such as iron oxide and ammonium molybdate in proportion, and then press or granulate and calcine to form a composite oxide. 5) Hydrothermal / solvothermal method: React an iron source and a molybdenum source in high-temperature and high-pressure water or organic solvents to directly crystallize the catalyst precursor, and obtain the catalyst after washing, drying, and calcination. However, the existing preparation technologies still have key problems such as high cost, low conversion rate, and low selectivity.

[0004] Therefore, there is an urgent need to develop a new catalyst preparation method to further improve the conversion rate and selectivity of the methanol to formaldehyde reaction by improving the forming process. Summary of the Invention

[0005] To solve the problems of the existing technology, the present invention provides a preparation method of a supported formaldehyde catalyst, which has high conversion rate and selectivity in the methanol oxidation to formaldehyde reaction.

[0006] To achieve the above object, the technical solutions adopted by the present invention include: The present invention provides a preparation method of a supported formaldehyde catalyst, and the preparation method includes the following steps: (1) Dissolve an iron salt in water and heat to obtain an iron salt solution; (2) Dissolve a molybdenum salt in water and heat to obtain a molybdenum salt solution; (3) Add a molybdate solution dropwise to an iron salt solution and carry out an aging treatment; (4) Filter, wash, and dry to obtain a catalyst powder; (5) Prepare a slurry containing water, a dispersant, and the catalyst powder, and immerse the carrier therein; (6) Dry and calcine to obtain the supported formaldehyde catalyst.

[0007] Optionally, in step (1), the heating temperature is 55 - 60 °C.

[0008] Optionally, the iron salt is selected from at least one of iron nitrate, iron chloride, polyferric chloride, and iron sulfate.

[0009] Optionally, in step (2), the heating temperature is 60 - 75 °C.

[0010] Optionally, the molybdate is selected from at least one of ammonium molybdate, sodium molybdate, potassium molybdate, and ammonium heptamolybdate.

[0011] Optionally, in step (3), the dropping rate is 5 - 15 mL / min, and can be selected from 6 mL / min, 8 mL / min, 9 mL / min, 10 mL / min, 12 mL / min, 14 mL / min, and any value between any two of them.

[0012] Optionally, in step (3), the molar ratio of iron to molybdenum atoms after dropping is 0.5 - 1.5.

[0013] Optionally, the temperature of the aging treatment is 80 - 95 °C, and the time is 6 - 10 h.

[0014] Optionally, in step (4), the drying temperature is 120 - 140 °C, and the time is 8 - 12 h.

[0015] Optionally, in step (5), the mass ratio of water to the catalyst powder is 6 - 1, and the mass ratio of the catalyst powder to the dispersant is 10 - 1.

[0016] Optionally, the dispersant is selected from at least one of cellulose, polyethylene glycol, polyacrylamide, and polyethylene oxide.

[0017] Optionally, the carrier is selected from ceramic Raschig rings.

[0018] Optionally, the impregnation temperature is 20 - 50 °C, and the time is 1 - 2 h.

[0019] The impregnation temperature can be selected from 25 °C, 30 °C, 35 °C, 40 °C, 45 °C, and any value between any two of them.

[0020] Optionally, the catalyst powder accounts for 5 wt% - 60 wt% of the total mass of the catalyst powder and the carrier.

[0021] Optionally, in step (6), the drying temperature is 40 - 120 °C and the time is 8 - 12 h.

[0022] Optionally, the calcination temperature is 300 - 320 °C and the time is 4 - 6 h.

[0023] The present invention also provides a supported formaldehyde catalyst prepared by the above preparation method. The supported formaldehyde catalyst includes a carrier and an active component supported on the surface of the carrier. In the active component, the proportion of Fe2O3 is 25 wt% - 40 wt%, and the proportion of MoO3 is 75 wt% - 60 wt%; the loading amount of the active component is 5 wt% - 60 wt%.

[0024] The present invention also provides an application of the above supported formaldehyde catalyst in the reaction of methanol to formaldehyde.

[0025] Optionally, the reaction uses a fixed-bed reactor, and supported formaldehyde catalysts with different loading amounts are loaded according to the bed layers. From the top to the bottom of the fixed-bed reactor, between different bed layers, the loading amount of the supported formaldehyde catalyst increases layer by layer. Or, from the top to the bottom of the fixed-bed reactor, between different bed layers, the loading amount of the supported formaldehyde catalyst first increases and then decreases.

[0026] Optionally, between different bed layers, the loading amount increases or decreases by an amplitude of 5 wt% - 50 wt%.

[0027] The beneficial effects of the present invention include: In the traditional method, there is a phenomenon of local heat release in the catalyst, and the heat release amount is not easy to control, which leads to a low selectivity of the product, or there is a phenomenon of incomplete local reaction, resulting in a low conversion rate of the reaction. The present invention optimizes the forming preparation method of the supported formaldehyde catalyst, and obtains a catalyst with an active component supported on a Raschig ring through impregnation, and the active component is evenly distributed. During the use of the fixed-bed reactor, the catalyst is loaded in a manner that the loading amount increases layer by layer or first increases and then decreases, and the reaction has a higher conversion rate and selectivity. Description of the Drawings

[0028] Figure 1 In the figure, (1) is a schematic diagram of the catalyst loading method of Comparative Example 1; (2) is a schematic diagram of the catalyst loading method of Example 3; (3) is a schematic diagram of the catalyst loading method of Example 5. Detailed Embodiments

[0029] The present invention will be further described in detail below in conjunction with embodiments. The following embodiments can enable those of ordinary skill in the art to more comprehensively understand the present invention, but do not limit the present invention in any way. Example 1

[0030] Add 314 mL of deionized water into a 1 L precipitation kettle, add 300 g of ferric nitrate nonahydrate, stir at 25 Hz, and heat up to 55 °C; add 240 mL of deionized water into a 1 L batching kettle, add 200 g of ammonium heptamolybdate, heat to 60 °C, stir for 10 min, take a sample to observe that the batching kettle is clear, turn off the stirring, and obtain an ammonium heptamolybdate solution; turn on the heating system of the precipitation kettle, when the temperature of the precipitation kettle reaches 60 °C, turn on the batching dropping, and drop the ammonium heptamolybdate solution into the precipitation kettle at a rate of 5 mL / min. The slurry in the precipitation kettle is aged at 85 °C for 6 hours. After the aging is completed, the temperature is lowered. After the kettle temperature is lowered below 30 °C, filtration and washing are carried out, and it is dried at 130 °C for 12 hours and then tested for dry basis and reserved to obtain catalyst powder. Example 2

[0031] Take 30 g of deionized water, add 1 g of polyethylene oxide for dissolution, take 5 g of the catalyst powder described in Example 1, add them together into an impregnation kettle for slurry ball milling, and then put 95 g of Raschig ring ceramic carriers (with an outer diameter of φ6 mm and an inner diameter of φ4 mm) into the impregnation kettle for equal amount stirring impregnation. The impregnation time is 2 hours and the impregnation temperature is 25 °C. Then, drying is carried out in an oven according to the programmed heating method. The initial temperature is 40 °C, and it is heated to 120 °C at a rate of 3 °C / min, kept at 120 °C for 10 hours, and then calcined at 300 °C for 4 hours to obtain a supported catalyst with an effective load content of 5%.

[0032] Take 40 g of deionized water, add 2 g of polyethylene oxide for dissolution, take 10 g of the catalyst powder described in Example 1, add them together into an impregnation kettle for slurry ball milling, and then put 90 g of Raschig ring ceramic carriers (with an outer diameter of φ6 mm and an inner diameter of φ4 mm) into the impregnation kettle for equal amount stirring impregnation. The impregnation time is 2 hours and the impregnation temperature is 25 °C. Then, drying is carried out in an oven according to the programmed heating method. The initial temperature is 40 °C, and it is heated to 120 °C at a rate of 3 °C / min, kept at 120 °C for 10 hours, and then calcined at 300 °C for 4 hours to obtain a supported catalyst with an effective load content of 10%.

[0033] Take 90 g of deionized water, add 12 g of polyethylene oxide and dissolve it. Take 50 g of the catalyst powder described in Example 1, add them together into an impregnation kettle for slurry ball milling. Then put 50 g of Raschig ring ceramic carriers (with an outer diameter of φ6 mm and an inner diameter of φ4 mm) into the impregnation kettle for equal amount stirring impregnation. The impregnation time is 2 hours and the impregnation temperature is 25 °C. Then use an oven to dry it in a programmed heating mode. The initial temperature is 40 °C, heat up to 120 °C at a rate of 3 °C / min, keep the temperature at 120 °C for 10 hours, and then calcine at 300 °C for 4 hours to obtain a supported catalyst with a supported content of 50%.

[0034] Prepare supported catalysts with supported contents of 5%, 10%, 20%, 25%, 30%, 35%, 40%, 45%, and 50% respectively according to this method for standby. Example 3

[0035] Carry out a fixed-bed evaluation on the above supported catalysts. Evaluation method: The reaction raw material is methanol, the reaction gases are air and nitrogen, the methanol concentration is 0.143 g / L, the reaction space velocity is 1.4 h -1 , the reaction pressure is slightly positive pressure, the reaction temperature is 300 °C, the diameter of the fixed-bed reactor is 24 mm, the height of the fixed-bed reactor is 40 cm, and the reaction raw material enters from the upper part of the fixed-bed reactor.

[0036] Load the supported catalysts with different loadings according to the bed layer. The loading method is as Figure 1 (2) shown. After running for 2 hours, take samples for analysis and evaluate to obtain relevant reaction data, as shown in Table 1. Example 4

[0037] Load the bed layer in the order of loadings of 10%, 20%, 30%, 45%, 50%, 25%, and 10%. Then evaluate according to the evaluation method described in Example 3. After running for 2 hours, take samples for analysis and evaluate to obtain relevant reaction data, as shown in Table 1. Example 5

[0038] Load the supported catalysts with different loadings incrementally according to the bed layer. The loading method is as Figure 1 (3) shown. Then evaluate according to the evaluation method described in Example 3. After running for 2 hours, take samples for analysis and evaluate to obtain relevant reaction data, as shown in Table 1. Comparative Example 1

[0039] Load the supported catalysts with loadings of 5%, 20%, 35%, and 50% separately. The loading method is as Figure 1As shown in (1) (only the supported catalyst with a single loading amount is filled in the reactor), and then the evaluation is carried out according to the evaluation method described in Example 3. After running for 2 hours, samples are taken for analysis, and relevant reaction data are obtained through evaluation, as shown in Table 1. Comparative Example 2

[0040] The supported catalysts with loadings of 50%, 40%, 30%, 20%, 10%, and 5% are filled in a decreasing manner according to the bed layer, and then the evaluation is carried out according to the evaluation method described in Example 3. After running for 2 hours, samples are taken for analysis, and relevant reaction data are obtained through evaluation, as shown in Table 1. Comparative Example 3

[0041] The catalyst powder described in Example 1 is directly extruded into Raschig rings with an outer diameter of φ6 mm and an inner diameter of φ4 mm. The obtained Raschig rings are filled in a fixed-bed reactor, and then the evaluation is carried out according to the evaluation method described in Example 3. After running for 2 hours, samples are taken for analysis, and relevant reaction data are obtained through evaluation, as shown in Table 1.

[0042]

[0043] Although specific aspects of the present invention have been explained and described, it is obvious to those skilled in the art that many other changes and modifications can be made without departing from the spirit and scope of the present invention. Therefore, the appended claims are intended to cover all such changes and modifications that fall within the scope of the present invention.

Claims

1. A preparation method of a supported formaldehyde catalyst, characterized in that, The preparation method includes the following steps: (1) Dissolve the iron salt in water and heat to obtain an iron salt solution; (2) Dissolve the molybdenum salt in water and heat to obtain a molybdenum salt solution; (3) Dropwise add the molybdenum salt solution to the iron salt solution and perform an aging treatment; (4) Filter, wash, and dry to obtain the catalyst powder; (5) Prepare a slurry containing water, a dispersant, and the catalyst powder, and immerse the carrier therein; (6) Dry and calcine to obtain the supported formaldehyde catalyst.

2. The preparation method according to claim 1, characterized in that, In step (1), the heating temperature is 55 - 60 °C; and / or, the iron salt is selected from at least one of iron nitrate, iron chloride, polyferric chloride, and iron sulfate; and / or, in step (2), the heating temperature is 60 - 75 °C; and / or, the molybdenum salt is selected from at least one of ammonium molybdate, sodium molybdate, potassium molybdate, and ammonium heptamolybdate.

3. The preparation method according to claim 1 or 2, characterized in that, In step (3), the dropping rate is 5 - 15 mL / min, and the molar ratio of iron to molybdenum atoms after dropping is 0.5 - 1.5; and / or, the temperature of the aging treatment is 80 - 95 °C, and the time is 6 - 10 h.

4. The preparation method according to any one of claims 1 to 3, characterized in that, In step (4), the drying temperature is 120 - 140 °C, and the time is 8 - 12 h.

5. The preparation method according to any one of claims 1 to 4, characterized in that, In step (5), the mass ratio of water to the catalyst powder is 6 - 1, and the mass ratio of the catalyst powder to the dispersant is 10 - 1; and / or, the dispersant is selected from at least one of cellulose, polyethylene glycol, polyacrylamide, and polyethylene oxide; and / or, the carrier is selected from ceramic Raschig rings; and / or, the temperature of the immersion is 20 - 50 °C, and the time is 1 - 2 h; and / or, the catalyst powder accounts for 5 wt% - 60 wt% of the total mass of the catalyst powder and the carrier.

6. The preparation method according to any one of claims 1 to 5, characterized in that, In step (6), the drying temperature is 40 - 120 °C, and the time is 8 - 12 h; and / or, the calcination temperature is 300 - 320 °C, and the time is 4 - 6 h.

7. A supported formaldehyde catalyst prepared by the preparation method according to any one of claims 1 to 6, characterized in that, The supported formaldehyde catalyst includes a carrier and an active component supported on the surface of the carrier. In the active component, the proportion of Fe2O3 is 25 wt% - 40 wt%, and the proportion of MoO3 is 75 wt% - 60 wt%; The loading amount of the active component is 5 wt% - 60 wt%.

8. Application of the supported formaldehyde catalyst according to claim 7 in the reaction of methanol to formaldehyde.

9. The application according to claim 8, characterized in that, The reaction uses a fixed-bed reactor, and the supported formaldehyde catalysts with different loading amounts are loaded according to the bed layers, From the top to the bottom of the fixed-bed reactor, between different bed layers, the loading amount of the supported formaldehyde catalyst increases layer by layer; Or, from the top to the bottom of the fixed-bed reactor, between different bed layers, the loading amount of the supported formaldehyde catalyst first increases and then decreases.

10. The application according to claim 8 or 9, characterized in that, Between different bed layers, the loading amount increases or decreases in an amplitude of 5 wt% - 50 wt%.

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