Preparation method of low pressure drop butane selective oxidation vanadium phosphorus oxygen catalyst

Abstract

This invention discloses a method for preparing and applying a low-pressure-drop butane selective oxidation vanadium-phosphorus oxide catalyst. Its key feature lies in utilizing the hydrogen-bonded network structure of a eutectic solvent to form hydrogen bonds with the vanadium-phosphorus oxide precursor. A molded vanadium-phosphorus oxide catalyst precursor with eutectic solvent in its pore walls is obtained through die pressing. High-temperature calcination removes the eutectic solvent from the pore walls, thereby constructing gas transport channels, reducing reaction bed pressure, and simultaneously exposing more active sites, thus achieving a simultaneous increase in catalytic efficiency. Compared with existing technologies, this invention allows for controllable adjustment of pore size by adjusting the type of eutectic solvent, thereby controlling the pressure drop. The proposed method is simple, environmentally friendly, and can be scaled up, showing broad application prospects.

Description

Technical Field

[0001] This invention relates to the field of vanadium phosphorus oxide (VPO) catalyst preparation, and more particularly to the preparation and application of a low-pressure-drop vanadium phosphorus oxide catalyst. Background Technology

[0002] In recent years, with the increasing demand for biodegradable plastics, the preparation of maleic anhydride, its main monomer, has attracted widespread attention. Among these processes, the n-butane selective oxidation fixed-bed process has become the mainstream preparation method for maleic anhydride due to its advantages such as being environmentally friendly, having high atom utilization, and being relatively low-cost. Vanadium-phosphorus-oxygen catalyst is currently the only catalyst for this reaction to have achieved industrial application. In actual industrial operation, the catalyst powder is pressed into hollow cylindrical structures using molds, with a wall thickness of approximately 1.5 mm and an inner diameter of 3.0 mm. Within the actual fixed-bed reaction, the reaction pressure drop is relatively large, and the reactant gases are affected by mass transfer resistance within the catalyst bed, resulting in a reaction that only occurs on the catalyst surface, while the internal active components cannot fully exert their effects.

[0003] Optimizing the structure, process, composition, and molding technology of shaped catalysts can effectively reduce catalyst bed pressure drop, increase reaction space velocity, and reduce mass transfer barriers, thereby enhancing catalytic activity. Catalyst bed pressure drop is related to factors such as the shape of the shaped catalyst, the microscopic pore structure of the annular walls, bed height, and the gas flow rate of the reactants. By optimizing the molding process of powdered catalysts and controlling the microstructure of the shaped catalyst, it is possible to construct reactant gas mass transfer channels within the catalyst annular walls, increasing exposed active sites, thereby reducing bed pressure drop and improving catalytic performance.

[0004] Eutectic solvents are a novel type of functional solvent composed of hydrogen bond donors and acceptors, possessing a large number of hydrogen bond networks and active sites within their molecules. Therefore, through rational structural design, they can form hydrogen bond structures with various molecules, thus acting as highly efficient binders. Furthermore, during subsequent activation, eutectic solvents can undergo partial or complete decomposition, enabling the construction of micropores. Therefore, by using eutectic solvents as functional molding aids, the mechanical strength of the catalyst can be ensured while simultaneously achieving the construction of microchannels in the pore walls. Summary of the Invention

[0005] To address the aforementioned problems, the present invention aims to provide a method for preparing and applying low-pressure-drop VPO catalysts using a eutectic solvent molding aid. The method involves mechanically mixing a VPO catalyst precursor with a specific mass of a eutectic solvent, then molding the mixed precursor powder into cylindrical catalysts using a tablet press. The resulting cylindrical catalyst is then activated under a specific atmosphere, thereby achieving the preparation of a low-pressure-drop VPO catalyst with a rich microporous structure, and enabling the selective oxidation of n-butane to maleic anhydride.

[0006] To achieve the objectives of this invention, the invention is implemented through the following technical solutions:

[0007] A method for preparing a low-pressure-drop butane selective vanadium-phosphorus oxide catalyst is characterized by using a eutectic solvent as a forming aid, utilizing its hydrogen bonding effect to bind precursor powder, followed by high-temperature decomposition to achieve microporous channel construction, thereby obtaining the low-pressure-drop butane selective vanadium-phosphorus oxide catalyst. The specific preparation steps are as follows:

[0008] (1) Place 10g of vanadium pentoxide in a container, add 80mL of isobutanol and 20mL of benzyl alcohol mixed solvent, stir and heat to 135℃ for 3 hours, then cool to 80℃, add 7.3mL of 85% phosphoric acid, heat to 135℃ and continue to react for 16 hours, wash and dry the product to obtain the precursor, whose main component is vanadium pyrophosphate hemihydrate.

[0009] (2) The above precursor powder and eutectic solvent are stirred and mixed in a certain mass ratio to obtain a mixture, wherein the eutectic solvent is a eutectic solvent formed by quaternary ammonium salt, polyhydroxycarboxylic acid, alcohol and amino acid.

[0010] (3) The mixture obtained in step (2) is pressed into tablets using a fully automatic high-speed rotating tablet press. The mold used is a hollow ring.

[0011] (4) The catalyst was calcined in an oxygen-containing atmosphere to obtain a low-pressure-drop vanadium-phosphorus-oxygen catalyst with rich micropores. The pressure drop was tested in a micro fixed-bed reactor.

[0012] The present invention also provides the application of the low-pressure-drop vanadium-phosphorus-oxygen catalyst obtained by the above method in the selective oxidation of n-butane to maleic anhydride.

[0013] Compared with the prior art, the present invention has the following significant technical effects and advantages.

[0014] (1) The eutectic solvent used in this invention is simple to synthesize and is more economical and environmentally friendly than traditional molding aids.

[0015] (2) Compared with traditional molding aids, eutectic solvents have a large number of hydrogen bond network structures, which can connect precursor molecules in the form of hydrogen bonds, making the powder more tightly connected and improving the mechanical strength of the molding catalyst.

[0016] (3) During the later activation process, the functional eutectic solvent will decompose from the ring wall, generating a raw material gas transport channel, exposing the internal active sites, and reducing the bed pressure drop of the catalyst. Attached Figure Description

[0017] Figure 1This is a high-resolution three-dimensional X-ray microscope cross-sectional image of the low-pressure-drop VPO catalyst obtained in Example 5 of the present invention.

[0018] Figure 2 These are high-resolution three-dimensional X-ray micrographs of the pore structure of the low-pressure-drop VPO catalyst obtained in Example 5 of the present invention.

[0019] Figure 3 This is a high-resolution three-dimensional X-ray microscope cross-sectional image of the VPO catalyst obtained in the comparative example of this invention.

[0020] Figure 4 These are high-resolution three-dimensional X-ray micrographs of the pore structure of the VPO catalyst obtained in the comparative example of this invention. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0022] This invention provides a method for preparing a low-pressure-drop butane selective vanadium-phosphorus oxide catalyst, which includes the following steps:

[0023] (1) Place 10g of vanadium pentoxide in a container, add 80mL of isobutanol and 20mL of benzyl alcohol mixed solvent, stir and heat to 135℃ for 3 hours, then cool to 80℃, add 7.3mL of 85% phosphoric acid, heat to 135℃ and continue to react for 16 hours, wash and dry the product to obtain the precursor, whose main component is vanadium pyrophosphate hemihydrate.

[0024] (2) The above precursor powder and eutectic solvent are stirred and mixed in a certain mass ratio to obtain a mixture, wherein the eutectic solvent is a eutectic solvent formed by quaternary ammonium salt, polyhydroxycarboxylic acid, alcohol and amino acid.

[0025] (3) The mixture obtained in step (2) is pressed into tablets using a fully automatic high-speed rotating tablet press. The mold used is a hollow ring.

[0026] (4) The catalyst was calcined in an oxygen-containing atmosphere to obtain a low-pressure-drop vanadium-phosphorus-oxygen catalyst with rich micropores. The pressure drop was tested in a micro fixed-bed reactor.

[0027] In this invention, the eutectic solvent hydrogen bond acceptor is a quaternary ammonium salt, and the hydrogen bond donor is a polysaccharide or polyol containing multiple hydroxyl groups. The resulting eutectic solvent possesses a rich hydrogen bond network structure, which can chemically bind the catalyst precursor powder. Furthermore, the long alkyl chains of its cations can undergo self-assembly during the binding process, acting as a soft template. During subsequent high-temperature activation, the introduced eutectic solvent decomposes, forming a microporous structure for gas transport within the molded catalyst, resulting in a low-pressure-drop vanadium-phosphorus oxygen catalyst with highly active sites.

[0028] In this invention, the method of forming a eutectic solvent from quaternary ammonium salts with polyhydroxycarboxylic acids, alcohols, and amino acids is prior art. Those skilled in the art can refer to the methods disclosed in the prior art for preparation, for example, according to the following method:

[0029] Hydrogen bond donors (such as glucose) and hydrogen bond acceptors (such as betaine) in the eutectic solvent are added to a flask at a molar ratio of 1:(1-3), heated to 80°C, and magnetically stirred for 1-5 hours until a homogeneous mixture is formed.

[0030] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The technical objectives and beneficial effects of the present invention can be better achieved and realized through the following preferred solutions.

[0031] Preferably, the quaternary ammonium salt in step (2) includes choline chloride, betaine, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrabutylammonium hydroxide, and alkylammonium bromide (C8-C10). 12 The polyhydroxy alcohols and amino acids include any one or a combination of at least two of oxalic acid, ethylene glycol, glycerol, glucose, alanine, glutamic acid, tryptophan, and serine. The polyhydroxy alcohols and amino acids are not limited to those listed above; other polyhydroxy alcohols and amino acids commonly used in the art that can react with quaternary ammonium salts to form eutectic solvents can also be used in this invention, preferably glucose.

[0032] Preferably, the mass ratio of the vanadium-phosphorus-oxygen catalyst precursor powder to the eutectic solvent in step (2) is 10:(0.5-10), for example: 10:0.5, 10:1, 10:3, 10:5, 10:7, 10:10, etc. If the mass ratio is lower than 10:0.5, the amount of eutectic solvent is too small to act as a binder and soft template; if the mass ratio is higher than 10:10, the amount of eutectic solvent is too large, which will lead to too many internal pores in the catalyst after decomposition, reducing the mechanical strength of the catalyst. More preferably, the mass ratio of the vanadium-phosphorus-oxygen catalyst precursor powder to the eutectic solvent is 10:4.

[0033] Preferably, the roasting temperature in step (4) is 400℃~500℃, such as 400℃, 420℃, 460℃, 550℃, etc. More preferably, the roasting temperature is 420℃.

[0034] Preferably, the roasting time in step (4) is 10 to 16 hours, such as 10 hours, 12 hours, 14 hours, 14.5 hours, 15 hours, 15.5 hours, 16 hours, etc. More preferably, the roasting time is 12 hours.

[0035] Preferably, the mixture of air and butane in step (4) has a volume ratio of butane to air of (0-2%):1, for example, 0% (pure air), 1.3%, 1.5%, 1.8%, 2%, etc. More preferably, the oxygen-containing atmosphere is a mixture of butane and air of 1.35%.

[0036] As a further preferred embodiment of the method described in this invention, the method includes the following steps:

[0037] (1) Place 10g of vanadium pentoxide in a container, add 80mL of isobutanol and 20mL of benzyl alcohol mixed solvent, stir and heat to 135℃ for 3 hours, then cool to 80℃, add 7.3mL of 85% phosphoric acid, heat to 135℃ and continue to react for 16 hours, wash and dry the product to obtain the precursor, whose main component is vanadium pyrophosphate hemihydrate.

[0038] (2) The above precursor powder and eutectic solvent are stirred and mixed at a mass ratio of 10:(0.5~10) to obtain a mixture, wherein the eutectic solvent is a eutectic solvent formed by quaternary ammonium salt, polyhydroxycarboxylic acid, alcohol and amino acid.

[0039] (3) The mixture obtained in step (2) is pressed into tablets using a fully automatic high-speed rotating tablet press. The mold used is a hollow ring.

[0040] (4) The vanadium-phosphorus-oxygen catalyst with rich micropores was calcined at 400℃~500℃ for 10~16h in an oxygen-containing atmosphere to obtain the pressure drop of the vanadium-phosphorus-oxygen catalyst with low pressure drop. The pressure drop was obtained by the pressure difference between the upper and lower ends of the 6-meter fixed bed reactor.

[0041] The present invention also includes the application of the above-mentioned low-pressure-drop vanadium-phosphorus-oxygen catalyst in the selective oxidation of n-butane to maleic anhydride.

[0042] Preferably, the reaction conditions for the selective oxidation of n-butane to prepare maleic anhydride are: a hot spot temperature of 420°C and a space velocity of 2000 h⁻¹ for the n-butane-air mixture. -1 The concentration of n-butane is 1.8% v%.

[0043] The following specific examples illustrate the preparation method of low-pressure-drop vanadium-phosphorus-oxygen catalysts. The compounds in the following examples can be prepared directly using existing methods.

[0044] Example 1

[0045] (1) Place 10g of vanadium pentoxide in a container, add 80mL of isobutanol and 20mL of benzyl alcohol mixed solvent, stir and heat to 135℃ for 3 hours, then cool to 80℃, add 7.3mL of 85% phosphoric acid, heat to 135℃ and continue to react for 16 hours, wash and dry the product to obtain the precursor, whose main component is vanadium pyrophosphate hemihydrate.

[0046] (2) The above precursor powder and choline chloride-glucose eutectic solvent are mixed at a mass ratio of 10:0.5 to obtain a mixture.

[0047] (3) The mixture obtained in step (2) is pressed into tablets using a fully automatic high-speed rotating tablet press. The mold used is a hollow ring.

[0048] (4) The vanadium-phosphorus-oxygen catalyst was obtained by calcining at 400°C for 10 hours in air atmosphere. Its pressure drop was obtained by the pressure difference between the upper and lower ends of the 6-meter fixed bed reactor.

[0049] Testing: The pressure drop of the catalyst in the 6-meter fixed-bed reactor was measured to be 16 kPa. At the hot spot temperature of 420℃, the space velocity of the n-butane-air mixture was 2000 h⁻¹. -1 Under reaction conditions with a n-butane concentration of 1.8 v%, the n-butane conversion rate was 90.7%, the maleic anhydride selectivity was 55.3%, and the maleic anhydride yield was 84.8%.

[0050] Example 2

[0051] (1) Same as Example 1.

[0052] (2) Compared with Example 1, the mass ratio of precursor powder to choline chloride-glucose eutectic solvent was adjusted to 10:4.

[0053] (3) Same as Example 1.

[0054] (4) Compared with Example 1, the calcination atmosphere was adjusted to a mixture of 1.3% n-butane and air, the calcination time was adjusted to 12h, and the calcination temperature was adjusted to 420℃.

[0055] Testing: The pressure drop of the catalyst in the 6-meter fixed-bed reactor was measured to be 9 kPa. At the hot spot temperature of 420℃, the space velocity of the n-butane-air mixture was 2000 h⁻¹. -1Under reaction conditions with a n-butane concentration of 1.8 v%, the n-butane conversion rate was 98.7%, the maleic anhydride selectivity was 60.3%, and the maleic anhydride yield was 100.6%.

[0056] Example 3

[0057] (1) Same as Example 1.

[0058] (2) Compared with Example 1, the mass ratio of precursor powder to choline chloride-glucose eutectic solvent was adjusted to 1:1.

[0059] (3) Same as Example 1.

[0060] (4) Same as Example 1.

[0061] Testing: The pressure drop of the catalyst in the 6-meter fixed-bed reactor was measured to be 5 kPa. At the hot spot temperature of 420℃, the space velocity of the n-butane-air mixture was 2000 h⁻¹. -1 Under reaction conditions with a n-butane concentration of 1.8 v%, the n-butane conversion rate was 96.7%, the maleic anhydride selectivity was 54.8%, and the maleic anhydride yield was 89.6%.

[0062] Example 4

[0063] (1) Same as Example 1.

[0064] (2) Compared with Example 1, the eutectic solvent was adjusted to betaine-ethylene glycol; the mass ratio of precursor powder to betaine-ethylene glycol eutectic solvent was adjusted to 10:4.

[0065] (3) Same as Example 1.

[0066] (4) Compared with Example 1, the calcination atmosphere was adjusted to a mixture of 1.3% n-butane and air, and the calcination time was adjusted to 12h.

[0067] Testing: The pressure drop of the catalyst in the 6-meter fixed-bed reactor was measured to be 13 kPa. At the hot spot temperature of 420℃, the space velocity of the n-butane-air mixture was 2000 h⁻¹. -1 Under reaction conditions with a n-butane concentration of 1.8 v%, the n-butane conversion rate was 92.8%, the maleic anhydride selectivity was 55.6%, and the maleic anhydride yield was 87.2%.

[0068] Example 5

[0069] (1) Same as Example 1.

[0070] (2) Compared with Example 1, the eutectic solvent was adjusted to betaine-ethylene glycol; the mass ratio of precursor powder to betaine-ethylene glycol eutectic solvent was adjusted to 10:4.

[0071] (3) Same as Example 1.

[0072] (4) Compared with Example 1, the calcination atmosphere was adjusted to a mixture of 1.3% n-butane and air, the calcination time was adjusted to 16h, and the calcination temperature was adjusted to 500℃.

[0073] Testing: The pressure drop of the catalyst in the 6-meter fixed-bed reactor was measured to be 11 kPa. At the hot spot temperature of 420℃, the space velocity of the n-butane-air mixture was 2000 h⁻¹. -1 Under reaction conditions with a n-butane concentration of 1.8 v%, the n-butane conversion rate was 89.6%, the maleic anhydride selectivity was 51.2%, and the maleic anhydride yield was 77.5%.

[0074] Example 6

[0075] (1) Same as Example 1.

[0076] (2) Compared with Example 1, the eutectic solvent was adjusted to tetrabutylammonium hydroxide-glutamic acid; the mass ratio of precursor powder to tetrabutylammonium hydroxide-glutamic acid eutectic solvent was adjusted to 1:1.

[0077] (3) Same as Example 1.

[0078] (4) Compared with Example 1, the calcination atmosphere was adjusted to a mixture of 1.3% n-butane and air, the calcination time was adjusted to 16h, and the calcination temperature was adjusted to 500℃.

[0079] Testing: The pressure drop of the catalyst in the 6-meter fixed-bed reactor was measured to be 19 kPa. At the hot spot temperature of 420℃, the space velocity of the n-butane-air mixture was 2000 h⁻¹. -1 Under reaction conditions with a n-butane concentration of 1.8 v%, the n-butane conversion rate was 87.6%, the maleic anhydride selectivity was 56.2%, and the maleic anhydride yield was 83.2%.

[0080] Comparative Example

[0081] (1) Same as Example 1.

[0082] (2) Compared with Example 1, no eutectic solvent was added.

[0083] (3) Same as Example 1.

[0084] (4) Same as Example 1.

[0085] Testing: The pressure drop of the catalyst in the 6-meter fixed-bed reactor was measured to be 21 kPa. At the hot spot temperature of 420℃, the space velocity of the n-butane-air mixture was 2000 h⁻¹. -1Under reaction conditions with a n-butane concentration of 1.8 v%, the n-butane conversion rate was 80.3%, the maleic anhydride selectivity was 50.1%, and the maleic anhydride yield was 67.9%.

[0086] Comparing Example 2 with the comparative example reveals that, with the same catalytic material and the same catalyst loading method, the strategy proposed in this invention significantly reduces the bed pressure drop. This demonstrates that the eutectic solvent used as a forming aid can create a microporous structure for gas transport within the catalyst wall, reducing mass transfer barriers and decreasing the bed pressure drop from 21 kPa to 9 kPa. Simultaneously, due to the construction of the reaction microchannels, more active sites are exposed. Therefore, under the same reaction conditions, the mass yield of maleic anhydride in Example 5 is 100.6%, while in the comparative example it is only 67.9%. Figure 1 and Figure 3 , Figure 2 and Figure 4 It can also be seen that the vanadium-phosphorus-oxygen catalyst ring wall obtained by the method proposed in this invention has a rich through-pore structure. These pores can provide transport channels for butane in the reactor, so that it can fully contact the active sites while reducing the bed pressure drop.

[0087] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a low-pressure-drop butane selective vanadium-phosphorus oxygen oxidation catalyst, characterized in that, The method includes the following steps: (1) Place 10g of vanadium pentoxide in a container, add 80mL of isobutanol and 20mL of benzyl alcohol mixed solvent, stir and heat to 135℃ for 3 hours, then cool to 80℃, add 7.3mL of 85% phosphoric acid, heat to 135℃ and continue to react for 16 hours, wash and dry the product to obtain the precursor, whose main component is vanadium pyrophosphate hemihydrate. (2) The above precursor powder and eutectic solvent are stirred and mixed at a certain mass ratio to obtain a mixture. (3) The mixture obtained in step (2) is pressed into tablets using a fully automatic high-speed rotating tablet press. The mold used is a hollow ring. (4) The catalyst was calcined in an oxygen-containing atmosphere to obtain a low-pressure-drop vanadium-phosphorus-oxygen catalyst with rich micropores. The pressure drop was tested in a micro fixed-bed reactor.

2. The catalyst according to claim 1, characterized in that: The eutectic solvent is a eutectic solvent formed by quaternary ammonium salts, polyhydroxycarboxylic acids, alcohols, and amino acids.

3. The eutectic solvent according to claim 2, characterized in that: Quaternary ammonium salts include choline chloride, betaine, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrabutylammonium hydroxide, and alkylammonium bromide (C8-C9). 12 The polyhydroxy alcohol and amino acid include any one or at least two of the following: oxalic acid, ethylene glycol, glycerol, glucose, alanine, glutamic acid, tryptophan, and serine.

4. The catalyst according to claim 1, characterized in that: The mass ratio of the vanadium phosphorus oxygen catalyst precursor powder to the eutectic solvent is 10:(0.5-10).

5. The catalyst according to claim 1, characterized in that: The roasting temperature is 400℃~500℃.

6. The catalyst according to claim 1, characterized in that: The roasting time is 10 to 16 hours.

7. The catalyst according to claim 1, characterized in that: The mixture of air and butane gas has a volume ratio of butane to air of (0-2%):1.

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