A composition of a molybdenum-containing catalyst and a preparation method and application thereof

Abstract

The present application relates to a kind of molybdenum-containing catalyst composition, by adjusting the composition structure and loading mode of catalyst, thereby improving the heat transfer performance and physical strength of catalyst, adding polyethylene glycol during the preparation of catalyst to modify, so that the structure of the prepared catalyst is more fastened, the life of catalyst is extended.The catalyst prepared by the method can be applied to the industrial device for preparing aldehyde by alcohol oxidation, such as preparing formaldehyde by methanol oxidation, etc.

Description

Technical Field

[0001] This invention relates to the field of catalyst preparation, specifically to a molybdenum-containing catalyst composition, its preparation method, and its application. Background Technology

[0002] Formaldehyde is an important basic organic chemical raw material, playing a crucial role in adjusting the future energy structure and developing the chemical industry. Since Germany first achieved industrial production of formaldehyde in 1888, the production methods for formaldehyde have evolved into several types depending on the raw materials used: non-catalytic oxidation using liquefied petroleum gas, dimethyl ether oxidation, methane oxidation, and methanol-air oxidation. As of 2010, over 90% of industrially produced formaldehyde was obtained using methanol as a raw material through methanol-air oxidation. Depending on the catalyst and process used, methanol-air oxidation is further divided into the silver process and the iron-molybdenum process.

[0003] Currently, there are many publicly disclosed patents for the production of formaldehyde using iron-molybdenum catalysts. For example, US3846341 describes a two-component iron-molybdenum gel catalyst. US4420421 describes using different raw materials, such as sodium molybdate, to achieve a methanol conversion rate of 93%–95% and a selectivity of 92%. CN108097259 describes using macromolecular heterocyclic compounds as raw materials to synthesize catalysts with different crystal sizes and morphologies, enabling the control of the spacing, ratio, and distribution of the binary active centers of iron and molybdenum. CN103933998A discloses a catalyst for the production of formaldehyde from methanol, with the active component including Mo. a Ni b Fe c Bi d Pr e Co f Ce g V h Cr i A j O k Wherein, A is one or more of lithium, sodium, potassium, and rubidium. CN109012682A discloses a modification method for a catalyst for the oxidation of methanol to formaldehyde, which relates to a method for preparing modified catalysts using a mechanochemical method.

[0004] Methanol oxidation is an exothermic reaction. To avoid catalyst sintering due to excessively high reaction temperature, which would affect catalyst life, most commercially available catalysts are packed with catalyst and ceramic rings in a layered mixing manner. However, the risk is that mechanical mixing can easily lead to poor mixing effect and temperature runaway. Summary of the Invention

[0005] The purpose of this invention is to provide a molybdenum-containing catalyst for the preparation of aldehydes by alcohol oxidation. Using the catalyst of this invention, the reaction temperature distribution is more uniform, the catalytic efficiency is high, the catalyst life is longer, and the aldehydes obtained have high selectivity.

[0006] The present invention adopts the following technical solution:

[0007] A composition containing a molybdenum catalyst comprises catalyst A, catalyst B, and catalyst C, with mass contents of 40-60%, 10-30%, and 20-50%, respectively.

[0008] Catalysts A, B, and C all comprise iron-containing compounds, molybdenum-containing compounds, silicon-containing compounds, and carbon-containing elements, wherein the molar ratio of Mo / Fe is 2.2-2.6. The content of each component in catalysts A, B, and C is as follows:

[0009] Catalyst A has a silica content of 0-10 wt% and a carbon content of 1-3 wt%.

[0010] Catalyst B has a silica content of 20-30 wt% and a carbon content of 1-3 wt%.

[0011] The catalyst contains 30-50 wt% silica and 1-3 wt% carbon.

[0012] In this invention, the preparation process of catalysts A, B, and C includes the following steps:

[0013] a) Add a certain amount of water and polyethylene glycol to the bottom of the reactor, and simultaneously add an aqueous solution containing molybdenum salt and an aqueous solution containing iron salt to the bottom of the reactor for co-precipitation. After co-precipitation, use ammonia water to control the pH value at 1.0 to 3.0, preferably 1.5 to 2.5.

[0014] In this process, the temperature of the reactor is controlled at 40–80°C for co-precipitation.

[0015] b) After co-precipitation, age the filter cake at 40℃~80℃ for 10-20h, then filter and wash to obtain the filter cake.

[0016] The filtration process can be carried out using other methods such as vacuum filtration and pressure filtration;

[0017] c) Dry the filter cake;

[0018] The drying process is a routine operation in this field. An oven can be used for drying, with a preferred drying temperature of 90-150℃ and a drying time of 10-20 hours.

[0019] d) The dried catalyst is calcined at 400℃~500℃ for 5-20h to obtain catalyst powder;

[0020] e) The catalyst powder is mixed with a certain amount of graphene and silica sol, extruded to obtain a shaped catalyst, and then calcined at 400-500℃ for 4-6 hours to obtain the finished catalyst.

[0021] Catalysts A, B, and C were obtained by controlling the amount of graphene and silica sol added.

[0022] In this invention, the molybdenum salt includes ammonium polymolybdate, preferably ammonium heptamolybdate; the iron salt includes ferric chloride, ferric nitrate, etc.

[0023] In this invention, polyethylene glycol is added during the preparation process. This organic compound can improve the binding force between active components and reduce the loss of active components during the reaction. The amount of polyethylene glycol added is 1-3 wt% of the catalyst powder mass.

[0024] In this invention, the catalyst is preferably hollow cylindrical, clover-shaped, cylindrical, or spherical, with hollow cylindrical being more preferred.

[0025] The present invention also relates to the application of the above-mentioned catalyst composition in the preparation of aldehydes by alcohol oxidation, wherein the catalyst loading order is as follows: catalyst A is in the bottom layer, catalyst B is in the middle layer, and catalyst C is in the top layer; the raw material is fed from the top of the reactor.

[0026] The catalyst prepared by this invention needs to be pretreated before use;

[0027] Preferably, the pretreatment includes the following steps: the catalyst is subjected to a volume hourly space velocity (VHSV) of 7000–12000 h⁻¹. -1 In an air or O2 / N2 mixed gas atmosphere, the temperature is increased to 200-400°C at a heating rate of 1-20°C / min and held for 1-180 min, preferably 30-150 min, and then heated with a volume hourly space velocity of 1000-3000 h⁻¹. -1 Purge with N2 for 1–180 min, preferably 30–150 min.

[0028] In this invention, the initial reaction temperature for the preparation of aldehydes by alcohol oxidation is 250-300℃; the reaction pressure is an absolute pressure of 0.05-0.3 MPa, preferably 0.06-0.2 MPa; and the gaseous feedstock volume hourly space velocity is 7000-12000 h⁻¹. -1 Preferred operating time: 8000-11000h -1 ;

[0029] The gaseous raw materials include methanol, dilution gas, and O2, wherein the molar ratio of methanol to dilution gas is 1:7 to 12, preferably 1:7.5 to 11; the molar ratio of methanol to O2 is 1:0.8 to 4, preferably 1:1 to 3.5; and the dilution gas is an inert gas, preferably N2.

[0030] The present invention has the following technical effects:

[0031] (1) By mixing inert filler (silica) and active components through in-situ synthesis, the problem of high bed temperature caused by uneven mixing of catalyst and ceramic ring in the prior art is avoided. At the same time, the active components of the catalyst are better dispersed, the intrinsic activity is improved, and the anti-sintering ability is stronger.

[0032] (2) The catalyst of the present invention improves the overall thermal conductivity of the catalyst by adding a material with high thermal conductivity (graphene), thereby making the bed temperature distribution more uniform and thus improving the stability of the catalyst.

[0033] (3) Polyethylene glycol was added during the catalyst preparation process to modify it, which strengthened the binding force between active components, reduced the loss of active components of the catalyst, and extended the life of the catalyst. Attached Figure Description

[0034] Figure 1 These are the catalyst layer temperature distribution curves for Comparative Example 7 and Example 1, where the horizontal axis represents the height of the catalyst from the bottom (in cm), and the vertical axis represents the temperature (in °C). Detailed Implementation

[0035] The method of the present invention will be described in detail below with reference to embodiments, but is not limited to the embodiments.

[0036] Unless otherwise specified, all reagents used below are of analytical grade.

[0037] Example 1

[0038] Preparation of catalyst A:

[0039] 1320g of ammonium heptamolybdate (chemical formula (NH4)6Mo7O) was added. 24 Solution A was obtained by dissolving 1360g of ferric nitrate nonahydrate (chemical formula Fe(NO3)3·9H2O) in 30kg of pure water. Solution B was obtained by dissolving 1360g of ferric nitrate nonahydrate (chemical formula Fe(NO3)3·9H2O) in 40kg of pure water. 500g of deionized water and 27g of polyethylene glycol were added to the bottom of the reactor, and the solution temperature in the reactor was maintained at 70℃. While stirring, solutions B and A were added to the reactor in parallel stream for co-precipitation. After precipitation, the pH of the system was adjusted to 2.0 with ammonia water, and the system was aged at 70℃ with stirring for 12h.

[0040] The slurry was filtered and washed to obtain a filter cake, which was dried at 120°C for 12 hours to obtain a block solid. After crushing, the catalyst powder was obtained and calcined at 450°C for 8 hours.

[0041] Take 500g of calcined powder, 15g of graphene, 100g of silica sol with a solid content of 40wt%, and a small amount of water, mix them evenly, and then extrude them using an extruder.

[0042] The shaped particles were calcined at 420℃ for 5 hours to obtain catalyst A, wherein the molybdenum-iron atomic ratio was 2.2, the silicon oxide content was about 7.2 wt%, and the carbon content was about 1.5 wt%.

[0043] The preparation process of catalyst B is the same as that of catalyst A, except that 500g of calcined powder, 15g of graphene, 500g of silica sol with a solid content of 40wt% and a certain amount of water are mixed evenly and extruded using an extruder; the shaped particles are then calcined at 420℃ for 5h to obtain catalyst B, which has a molybdenum-iron atomic ratio of 2.2, a silicon oxide content of approximately 27.9wt%, and a carbon content of approximately 1.5wt%.

[0044] The preparation process of catalyst C is the same as that of catalyst A, except that 500g of calcined powder, 20g of graphene, 800g of silica sol with a solid content of 50wt% and a certain amount of water are mixed evenly and extruded using an extruder; the shaped particles are then calcined at 420℃ for 5h to obtain catalyst C, which has a molybdenum-iron atomic ratio of 2.2, a silicon oxide content of approximately 43.4wt%, and a carbon content of approximately 1.5wt%.

[0045] Evaluation of oxidation experiment:

[0046] 100g of catalyst A, 30g of catalyst B, and 70g of catalyst C were loaded from bottom to top into a 160cm long reactor, with the reaction tube being a Ф21mm stainless steel tube. The catalyst pretreatment process was as follows: air was first introduced at a volume hourly space velocity (VHSV) of 10000h⁻¹. -1 The reaction tube temperature was increased from room temperature to 250°C at a rate of 5°C / min and held for 120 min, then purged with nitrogen for 180 min at a volume hourly space velocity (VHSV) of 10,000 h⁻¹. -1 .

[0047] After catalyst pretreatment, the mixture was subjected to a methanol:oxygen:nitrogen ratio of 1:1.3:10 (molar ratio) and a volume hourly space velocity of 10,000 h⁻¹. -1 (Standard conditions), the oxidation reaction is carried out at an initial reaction temperature of 250°C and at atmospheric pressure (feeding from the top of the reactor).

[0048] Example 2

[0049] The catalyst preparation process is the same as in Example 1, except for the evaluation experiment: 68g of catalyst A, 30g of catalyst B and 70g of catalyst C were loaded into a 160cm long reactor, wherein the reaction tube was a Ф21mm stainless steel reaction tube.

[0050] Example 3

[0051] The catalyst preparation process is the same as in Example 1, except for the evaluation experiment: 150g of catalyst A, 30g of catalyst B and 70g of catalyst C were loaded into a 160cm long reactor, wherein the reaction tube was a Ф21mm stainless steel reaction tube.

[0052] Example 4

[0053] The catalyst preparation process is the same as in Example 1. The difference is that during the catalyst A forming process, 500g of calcined powder, 15g of graphene and a certain amount of water are mixed evenly and extruded using an extruder. The formed particles are then calcined at 420℃ for 5h to obtain catalyst A, which has a molybdenum-iron atomic ratio of 2.2, a silicon oxide content of 0wt%, and a carbon content of approximately 1.8wt%.

[0054] The oxidation experiment evaluation process is the same as in Example 1.

[0055] Comparative Example 1

[0056] The catalyst preparation process is the same as in Example 1, except that during the catalyst A forming process, 500g of calcined powder, 15g of graphene, 200g of silica sol with a solid content of 40wt% and a certain amount of water are mixed evenly and extruded using an extruder; the formed particles are then calcined at 420℃ for 5h to obtain catalyst A, which has a molybdenum-iron atomic ratio of 2.2, a silicon oxide content of approximately 13.4wt%, and a carbon content of approximately 1.8wt%.

[0057] The oxidation experiment evaluation process is the same as in Example 1.

[0058] Comparative Example 2

[0059] The catalyst preparation process is the same as in Example 1, except that during the catalyst B forming process, 500g of calcined powder, 15g of graphene, 100g of silica sol with a solid content of 40wt% and a certain amount of water are mixed evenly and extruded using an extruder; the formed particles are then calcined at 420℃ for 5h to obtain catalyst B, which has a molybdenum-iron atomic ratio of 2.2, a silicon oxide content of approximately 7.2wt%, and a carbon content of approximately 2.0wt%.

[0060] The oxidation experiment evaluation process is the same as in Example 1.

[0061] Comparative Example 3

[0062] The catalyst preparation process is the same as in Example 1, except that during the catalyst B forming process, 500g of calcined powder, 15g of graphene, 700g of silica sol with a solid content of 40wt% and a certain amount of water are mixed evenly and extruded using an extruder; the formed particles are then calcined at 420℃ for 5h to obtain catalyst B, which has a molybdenum-iron atomic ratio of 2.2, a silicon oxide content of approximately 35.2wt%, and a carbon content of approximately 1.5wt%.

[0063] The oxidation experiment evaluation process is the same as in Example 1.

[0064] Comparative Example 4

[0065] The catalyst preparation process is the same as in Example 1, except that during the catalyst C forming process, 500g of calcined powder, 15g of graphene, 300g of silica sol with a solid content of 50wt% and a certain amount of water are mixed evenly and extruded using an extruder; the formed particles are then calcined at 420℃ for 5h to obtain catalyst C, which has a molybdenum-iron atomic ratio of 2.2, a silicon oxide content of approximately 22.5wt%, and a carbon content of approximately 1.2wt%.

[0066] The oxidation experiment evaluation process is the same as in Example 1.

[0067] Comparative Example 5

[0068] The catalyst preparation process is the same as in Example 1, except that during the catalyst C forming process, 500g of calcined powder, 15g of graphene, 1000g of silica sol with a solid content of 50wt% and a certain amount of water are mixed evenly and extruded using an extruder; the formed particles are then calcined at 420℃ for 5h to obtain catalyst C, with a molybdenum-iron atomic ratio of 2.2, a silicon oxide content of approximately 49.0wt%, and a carbon content of approximately 1.0wt%.

[0069] The oxidation experiment evaluation process is the same as in Example 1.

[0070] Comparative Example 6

[0071] The catalyst preparation process is the same as in Example 1, except that polyethylene glycol is not added during the preparation of catalysts A / B / C.

[0072] The oxidation experiment evaluation process is the same as in Example 1.

[0073] Comparative Example 7

[0074] Compared with Example 1, the difference lies in that catalyst C is a mixture of a commercial catalyst (mainly composed of iron and molybdenum, with a molybdenum / iron ratio of 2.2-2.6) and ceramic rings, with a mixing ratio of 56.6 wt% catalyst content and 43.4 wt% ceramic ring content; catalyst B is a mixture of a commercial catalyst and ceramic rings, with a mixing ratio of 72.1 wt% catalyst content and 27.9 wt% ceramic ring content; and catalyst A is a mixture of a commercial catalyst and ceramic rings, with a mixing ratio of 92.8 wt% catalyst content and 7.2 wt% ceramic ring content.

[0075] Comparative Example 8

[0076] Compared with Example 1, the difference is that only 200g of catalyst A was used in the oxidation experiment evaluation process, and catalysts B / C were not used.

[0077] Comparative Example 9

[0078] Compared with Example 1, the difference is that only 200g of catalyst B was used in the oxidation experiment evaluation process, and catalysts A / C were not used.

[0079] Comparative Example 10

[0080] Compared with Example 1, the difference is that only 200g of catalyst C was used in the oxidation experiment evaluation process, and catalysts A / B were not used.

[0081] The results of catalyst sampling and analysis after 1000 hours of operation are shown in the table below:

[0082] Methanol conversion rate % Formaldehyde selectivity % Hot spot temperature / ℃ Example 1 95.5 90.5 355 Example 2 95.3 90.6 351 Example 3 95.5 90.4 357 Example 4 95.1 90.6 350 Comparative Example 1 93.8 90.4 350 Comparative Example 2 95.8 88.2 361 Comparative Example 3 92.9 90.3 347 Comparative Example 4 95.9 87.9 371 Comparative Example 5 92.1 90.2 350 Comparative Example 6 93.1 88.6 347 Comparative Example 7 94.1 89.1 365 Comparative Example 8 96.2 71.2 398 Comparative Example 9 75.2 80.6 340 Comparative Example 10 68.2 89.2 322

[0083] The catalyst layer temperature distribution curves of Comparative Example 7 and Example 1 will be compared. Figure 1 As can be seen, after the catalyst of the present invention participates in the reaction, the temperature distribution is uniform and the evaluation results are more selective.

Claims

1. A composition containing a molybdenum catalyst, characterized in that, It contains catalyst A, catalyst B, and catalyst C, with mass contents of 40-60%, 10-30%, and 20-50%, respectively; the filling order is: catalyst A at the bottom, catalyst B in the middle layer, and catalyst C at the top, with the raw material fed from the top of the reactor; Catalyst A comprises an iron-containing compound, a molybdenum-containing compound, 0-10 wt% silicon dioxide, and carbon elements. Catalysts B and C both comprise an iron-containing compound, a molybdenum-containing compound, silicon dioxide, and carbon elements. The Mo / Fe molar ratio of catalysts A, B, and C is 2.2-2.

6. The content of each component in catalysts A, B, and C is as follows: Catalyst A contains 0-10 wt% silicon dioxide and 1-3 wt% carbon. Catalyst B contains 20-30 wt% silicon dioxide and 1-3 wt% carbon. The catalyst contains 30-50 wt% silica and 1-3 wt% carbon. The preparation methods of catalyst A, catalyst B, and catalyst C include the following steps: a) Add a certain amount of water and polyethylene glycol to the bottom of the reactor. Simultaneously add the aqueous solution containing molybdenum salt and the aqueous solution containing iron salt to the bottom of the reactor for co-precipitation. After co-precipitation, use ammonia water to control the pH value at 1.0-3.

0. b) After co-precipitation, the mixture is aged, then filtered and washed to obtain a filter cake; c) Dry the filter cake; d) The dried catalyst is calcined to obtain catalyst powder; e) The catalyst powder is mixed with a certain amount of graphene or a certain amount of graphene and silica sol, and then extruded to obtain a shaped catalyst, which is then calcined to obtain the finished catalyst.

2. The catalyst composition according to claim 1, wherein, In step a), the temperature is controlled at 40–80℃ for co-precipitation; The amount of polyethylene glycol added is 1-3 wt% of the catalyst powder.

3. The catalyst composition according to claim 1, wherein, In step a), the pH value is controlled between 1.5 and 2.

5.

4. The catalyst composition according to claim 1, wherein, Step b) Aging at 40℃~80℃ for 10-20h.

5. The catalyst composition according to claim 1, wherein, Step d) Calcination at 400℃~500℃ for 5-20h.

6. The composition of the catalyst according to claim 1, wherein, Step e) Calcination at 400-500℃ for 4-6 hours.

7. A method for preparing aldehydes by alcohol oxidation, using the composition of the catalyst described in claim 1.

8. The method according to claim 7, wherein, The initial reaction temperature for the oxidation of alcohols to aldehydes is 250-300℃; the reaction pressure is 0.05-0.3 MPa absolute; and the gaseous feedstock volume hourly space velocity is 7000-12000 h⁻¹. -1 .

9. The method according to claim 8, wherein, The gaseous raw materials include alcohol, dilution gas, and O2, wherein the dilution gas is an inert gas.

10. The method according to claim 9, wherein, The diluting gas is N2.

11. The method according to claim 9, wherein, The molar ratio of alcohol to diluent gas is 1:7 to 12, and the molar ratio of alcohol to O2 is 1:0.8 to 4.

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