A method for activating a vanadyl phosphate catalyst for the oxidation of butane to maleic anhydride

Abstract

This invention discloses a method for activating a vanadium oxyphosphate catalyst for the oxidation of butane to maleic anhydride and its application. The key feature is the use of different plasma-coupled heat treatment methods to activate existing vanadium oxyphosphate catalyst precursors through high-temperature calcination, resulting in a vanadium oxyphosphate catalyst with abundant defect sites. This achieves high adsorption and activation effects for butane, while simultaneously exposing more active sites, leading to a significant improvement in catalytic efficiency. Compared with existing technologies, this invention allows for the control of the catalyst surface microstructure by adjusting the type of plasma, avoiding the need for complex mixed gas preparation processes. The proposed method is simple, environmentally friendly, and can be widely applied, possessing broad application prospects.

Description

Technical Field

[0001] This invention relates to the field of vanadium oxyphosphide (VPO) catalysts and the preparation of maleic anhydride, specifically to a method for activating vanadium oxyphosphide catalysts and their applications. Background Technology

[0002] Maleic anhydride is the world's third-largest organic acid anhydride. As an important chemical intermediate, it has wide applications and a broad market in biodegradable plastics, high-end pesticides, food, and pharmaceuticals. The selective oxidation of n-butane to produce maleic anhydride is currently the mainstream process due to its economic efficiency, environmental friendliness, and high atom utilization. Vanadium phosphorus oxide (VPO) catalyst is currently the only industrially available catalyst for this reaction.

[0003] VPO catalysts typically use vanadium pentoxide as the vanadium source, phosphoric acid as the phosphorus source, and a mixed organic alcohol as the solvent and reducing agent. Under prolonged thermal reflux conditions, a precursor for the vanadium-phosphorus-oxygen catalyst is obtained, the main component of which is hemihydrated vanadium pyrophosphate. This precursor is then activated by high-temperature calcination under specific atmosphere and temperature to obtain the final active phase with catalytic properties. Different activation conditions often yield vanadium-phosphorus-oxygen catalysts with different crystal forms, valence states, and microstructures. Since the selective oxidation of butane is a structure-sensitive reaction, its performance is significantly affected by the catalyst's microstructure. Therefore, increasing research focuses on controlling the activation conditions to regulate the structure of the vanadium-phosphorus-oxygen catalyst, thereby obtaining optimal catalytic performance.

[0004] CN118477666A discloses a method for external activation of vanadium-phosphorus-oxygen catalysts. The method uses a mixed gas atmosphere of water vapor and nitrogen and calcines the catalyst in a self-made cylindrical external activation furnace at a temperature of 400℃~450℃ for 3~8h. This method is suitable for large-scale catalyst activation processes, and the obtained catalyst has relatively stable butane conversion and maleic anhydride selectivity.

[0005] CN1068053A discloses a multi-step vanadium-phosphorus-oxygen catalyst activation method, which involves gradually performing high-temperature activation in a mixed gas atmosphere of air, water vapor, and inert atmosphere to obtain active components with excellent performance.

[0006] The aforementioned and existing methods all activate the precursor by controlling the calcination atmosphere and calcination process, thereby controlling the valence state and crystal phase of the active catalyst and thus affecting its catalytic performance. However, existing activation methods cannot effectively control the active sites of the catalyst, such as defect sites and adsorption sites, and involve complex atmosphere adjustments, making the operation quite complicated. Therefore, finding an activation method that can effectively control catalyst sites and ensure catalyst selectivity and conversion rate has become an important goal pursued by current activation methods. Summary of the Invention

[0007] To address the shortcomings of existing activation technologies, this invention provides a method for activating vanadium-phosphorus-oxygen catalysts and its applications.

[0008] The inventors of this invention previously discovered that plasma, as a novel external field enhancement strategy, can controllably construct specific defects on the catalyst surface by adjusting parameters such as plasma type, power, temperature, and time. This allows for the control of active sites, crystal structure, and valence ratio, thereby improving the catalytic performance of the catalyst.

[0009] Therefore, the present invention provides a plasma activation method for vanadium phosphorus oxygen catalyst and its application, the specific preparation of which includes the following steps:

[0010] (1) Spread a certain mass of vanadium phosphorus oxygen precursor powder in a quartz ceramic boat, place it in a tube furnace connected with a plasma excitation device, and evacuate the entire system for 10 minutes to ensure that the system is in a vacuum state.

[0011] (2) Ensure the system is in a vacuum state, introduce a specific gas at a certain flow rate to excite the plasma, and after the flow rate stabilizes, turn on the plasma excitation device and set the plasma excitation power.

[0012] (3) Under the condition that plasma is continuously generated and introduced into the tube furnace, a programmed heating program is set so that the precursor powder is calcined and activated under plasma irradiation at a certain temperature and time, and finally vanadium phosphorus oxygen active catalyst is obtained.

[0013] According to an embodiment of the present invention, the precursor of the vanadium phosphorus oxygen catalyst can be a precursor obtained by conventional methods in the art when preparing the vanadium phosphorus oxygen catalyst. Specifically, the crystal phase structure of the precursor of the vanadium phosphorus oxygen catalyst is hemihydrated pyrophosphate oxyacid, VOHPO4·0.5H2O.

[0014] The present invention also provides the application of the plasma-activated vanadium phosphorus oxygen catalyst obtained by the above method in the selective oxidation of n-butane to maleic anhydride.

[0015] Compared with the prior art, the present invention has the following significant technical effects and advantages:

[0016] (1) The plasma activation method used in this invention can construct different types of defect sites on the vanadium-phosphorus-oxygen catalyst body by controlling the type of plasma, thereby achieving efficient adsorption and activation of the reaction gas.

[0017] (2) Compared with the traditional multi-atmosphere gradient activation method, the plasma activation method provided by the present invention does not require a complex atmosphere conditioning process and the process is simple;

[0018] (3) Using this method, in the later activation process, plasma can break the hydrogen bond structure between the vanadium phosphorus oxygen catalyst layers, expose more active sites, and improve the catalyst performance. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0020] This invention provides a plasma activation method for vanadium-phosphorus-oxygen catalysts and its application, the specific preparation of which includes the following steps:

[0021] (1) Spread a certain mass of vanadium phosphorus oxygen precursor powder in a quartz ceramic boat, place it in a tube furnace connected with a plasma excitation device, and evacuate the entire system for 10 minutes to ensure that the system is in a vacuum state.

[0022] (2) Ensure the system is in a vacuum state, introduce a specific gas at a certain flow rate to excite the plasma, and after the flow rate stabilizes, turn on the plasma excitation device and set the plasma excitation power.

[0023] (3) Under the condition that plasma is continuously generated and introduced into the tube furnace, a programmable heating program is set so that the precursor powder is calcined and activated under plasma irradiation to finally obtain vanadium phosphorus oxygen active catalyst.

[0024] 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.

[0025] Preferably, the mass of the vanadium-phosphorus-oxygen precursor powder in step (1) is 0.5g to 5g, for example, 0.5g, 1.0g, 1.5g, 2.0g, 2.5g, 3.0g, or 5.0g. More preferably, the mass of the vanadium-phosphorus-oxygen precursor powder is 3.0g. When the mass is less than 0.5g, the final catalyst mass is too small, making subsequent performance testing difficult. When the mass is greater than 5.0g, the plasma cannot cover all the precursor powder, resulting in poor uniformity of the final catalyst.

[0026] Preferably, the gas introduced in step (2) is a combination of at least one or more of the following mixed gases: nitrogen, oxygen, argon, helium, water vapor, and butane; for example, nitrogen, oxygen, helium, nitrogen-oxygen, or nitrogen-butane. More preferably, the gas is a combination of nitrogen and butane.

[0027] Preferably, the flow rate of the gas in step (2) is 10 to 200 mL / min, for example: 10 mL / min, 30 mL / min, 50 mL / min, 100 mL / min, 130 mL / min, 170 mL / min, 200 mL / min. More preferably, the flow rate of the gas is 150 mL / min.

[0028] Preferably, the plasma excitation power in step (2) is 50W to 200W, for example: 50W, 70W, 90W, 100W, 150W, 200W. More preferably, the plasma excitation power is 150W.

[0029] Preferably, the heating rate in step (2) is 2 to 15 °C / min, for example: 2 °C / min, 5 °C / min, 7 °C / min, 10 °C / min, 12 °C / min, 15 °C / min. More preferably, the heating rate is 5 °C / min.

[0030] Preferably, the roasting temperature in step (2) is 400-480°C, for example: 400°C, 420°C, 460°C, 470°C, 480°C. More preferably, the roasting temperature is 420°C.

[0031] Preferably, the roasting time in step (2) 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.

[0032] As a further preferred embodiment of the method described in this invention, the method includes the following steps:

[0033] (1) Spread 0.5g to 5g of vanadium phosphorus oxygen precursor powder in a quartz ceramic boat, place it in a tube furnace connected with a plasma excitation device, and evacuate the entire system for 10 minutes to ensure that the system is in a vacuum state.

[0034] (2) Ensure the system is in a vacuum state, and introduce at least one or more mixed gases of nitrogen, oxygen, argon, helium, water vapor and butane at a flow rate of 10 to 200 mL / min to excite the plasma. After the flow rate stabilizes, turn on the plasma excitation device and set the plasma excitation power to 50 W to 200 W.

[0035] (3) Under the condition that plasma is continuously generated and introduced into the tube furnace, the temperature is increased to 400-480°C at a heating rate of 2-15°C / min, so that the precursor powder is calcined and activated under plasma irradiation for 10-16 hours, and finally the vanadium phosphorus oxygen active catalyst is obtained.

[0036] 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.

[0037] 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%.

[0038] 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.

[0039] Example 1

[0040] (1) Spread 0.5g of vanadium-phosphorus-oxygen precursor powder in a quartz ceramic boat, place it in a tube furnace connected with a plasma excitation device, and evacuate the entire system for 10 minutes to ensure that the system is in a vacuum state.

[0041] (2) Ensure the system is in a vacuum state, and introduce nitrogen gas at a flow rate of 10 mL / min to excite the plasma. After the flow rate stabilizes, turn on the plasma excitation device and set the plasma excitation power to 50 W.

[0042] (3) Under the condition that plasma is continuously generated and introduced into the tube furnace, the temperature is increased to 400°C at a heating rate of 2°C / min, so that the precursor powder is calcined and activated for 10h under plasma irradiation, and finally the vanadium phosphorus oxygen active catalyst is obtained.

[0043] Detection: At the reaction hotspot 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 92.2%, the maleic anhydride selectivity was 54.3%, and the maleic anhydride yield was 84.6%.

[0044] Example 2

[0045] (1) Spread 2g of vanadium phosphorus oxygen precursor powder in a quartz ceramic boat, place it in a tube furnace connected with a plasma excitation device, and evacuate the entire system for 10 minutes to ensure that the system is in a vacuum state.

[0046] (2) Ensure the system is in a vacuum state, and introduce nitrogen gas at a flow rate of 50 mL / min to excite the plasma. After the flow rate stabilizes, turn on the plasma excitation device and set the plasma excitation power to 100 W.

[0047] (3) Under the condition that plasma is continuously generated and introduced into the tube furnace, the temperature is increased to 420°C at a heating rate of 5°C / min, so that the precursor powder is calcined and activated for 12 hours under plasma irradiation, and finally the vanadium phosphorus oxygen active catalyst is obtained.

[0048] Detection: At the reaction hotspot 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 93.6%, the maleic anhydride selectivity was 55.7%, and the maleic anhydride yield was 88.1%.

[0049] Example 3

[0050] (1) Spread 3g of vanadium phosphorus oxygen precursor powder in a quartz ceramic boat, place it in a tube furnace connected with a plasma excitation device, and evacuate the entire system for 10 minutes to ensure that the system is in a vacuum state.

[0051] (2) Ensure the system is in a vacuum state, and introduce a combination of nitrogen and butane gas at a flow rate of 150 mL / min to excite the plasma. After the flow rate stabilizes, turn on the plasma excitation device and set the plasma excitation power to 150 W.

[0052] (3) Under the condition that plasma is continuously generated and introduced into the tube furnace, the temperature is increased to 420°C at a heating rate of 5°C / min, so that the precursor powder is calcined and activated for 12 hours under plasma irradiation, and finally the vanadium phosphorus oxygen active catalyst is obtained.

[0053] Detection: At the reaction hotspot 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 95.7%, the maleic anhydride selectivity was 65.3%, and the maleic anhydride yield was 105.6%.

[0054] Example 4

[0055] (1) Spread 5g of vanadium phosphorus oxygen precursor powder in a quartz ceramic boat, place it in a tube furnace connected with a plasma excitation device, and evacuate the entire system for 10 minutes to ensure that the system is in a vacuum state.

[0056] (2) Ensure the system is in a vacuum state, introduce oxygen at a flow rate of 200 mL / min to excite the plasma, and after the flow rate stabilizes, turn on the plasma excitation device and set the plasma excitation power to 200 W.

[0057] (3) Under the condition that plasma is continuously generated and introduced into the tube furnace, the temperature is increased to 450°C at a heating rate of 10°C / min, so that the precursor powder is calcined and activated for 16 hours under plasma irradiation, and finally the vanadium phosphorus oxygen active catalyst is obtained.

[0058] Detection: At the reaction hotspot 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 96.3%, the maleic anhydride selectivity was 59.2%, and the maleic anhydride yield was 96.3%.

[0059] Example 5

[0060] (1) Spread 5g of vanadium phosphorus oxygen precursor powder in a quartz ceramic boat, place it in a tube furnace connected with a plasma excitation device, and evacuate the entire system for 10 minutes to ensure that the system is in a vacuum state.

[0061] (2) Ensure the system is in a vacuum state, and introduce argon gas at a flow rate of 200 mL / min to excite the plasma. After the flow rate stabilizes, turn on the plasma excitation device and set the plasma excitation power to 200 W.

[0062] (3) Under the condition that plasma is continuously generated and introduced into the tube furnace, the temperature is increased to 480°C at a heating rate of 15°C / min, so that the precursor powder is calcined and activated for 16 hours under plasma irradiation, and finally the vanadium phosphorus oxygen active catalyst is obtained.

[0063] Detection: At the reaction hotspot 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 90.8%, the maleic anhydride selectivity was 62.7%, and the maleic anhydride yield was 96.2%.

[0064] Example 6

[0065] (1) Spread 3g of vanadium phosphorus oxygen precursor powder in a quartz ceramic boat, place it in a tube furnace connected with a plasma excitation device, and evacuate the entire system for 10 minutes to ensure that the system is in a vacuum state.

[0066] (2) Ensure the system is in a vacuum state, and introduce nitrogen gas at a flow rate of 150 mL / min to excite the plasma. After the flow rate stabilizes, turn on the plasma excitation device and set the plasma excitation power to 200 W.

[0067] (3) Under the condition that plasma is continuously generated and introduced into the tube furnace, the temperature is increased to 420°C at a heating rate of 10°C / min, so that the precursor powder is calcined and activated for 16 hours under plasma irradiation, and finally the vanadium phosphorus oxygen active catalyst is obtained.

[0068] Detection: At the reaction hotspot 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 95.7%, the maleic anhydride selectivity was 60.2%, and the maleic anhydride yield was 97.3%.

[0069] Comparative Example

[0070] (1) Spread 3g of vanadium phosphorus oxygen precursor powder in a quartz ceramic boat, place it in a tube furnace, and evacuate the entire system for 10 minutes to ensure that the system is in a vacuum state.

[0071] (2) Ensure the system is in a vacuum state, and introduce a combination of nitrogen and butane gas at a flow rate of 150 mL / min without turning on the plasma excitation device.

[0072] (3) The temperature was increased to 420℃ at a heating rate of 5℃ / min and calcined for 12h to finally obtain the vanadium phosphorus oxygen active catalyst.

[0073] Detection: At the reaction hotspot 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 85.3%, the maleic anhydride selectivity was 59.7%, and the maleic anhydride yield was 86.1%.

[0074] Comparing Example 3 with the Comparative Example, it can be found that, with the same catalytic material and activation calcination procedure, under the condition of plasma application, due to the formation of defective active sites on the catalyst surface, the mass yield of maleic anhydride in Example 3 was 105.6%, while in the Comparative Example it was only 86.1%.

[0075] 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 plasma activation method for vanadium-phosphorus-oxygen catalysts and its application, characterized in that, The method includes the following steps: (1) Spread a certain mass of vanadium phosphorus oxygen precursor powder in a quartz ceramic boat, place it in a tube furnace connected with a plasma excitation device, and evacuate the entire system for 10 minutes to ensure that the system is in a vacuum state. (2) Ensure the system is in a vacuum state, introduce a specific gas at a certain flow rate to excite the plasma, and after the flow rate stabilizes, turn on the plasma excitation device and set the plasma excitation power. (3) Under the condition that plasma is continuously generated and introduced into the tube furnace, a programmable heating program is set so that the precursor powder is calcined and activated under plasma irradiation to finally obtain vanadium phosphorus oxygen active catalyst.

2. The catalyst precursor according to claim 1, characterized in that: The mass of the vanadium phosphorus oxygen precursor powder is 0.5g to 5g.

3. The gas according to claim 1, characterized in that: The introduced gas is a combination of at least one or more of the following: nitrogen, oxygen, argon, helium, water vapor, and butane.

4. The gas flow rate according to claim 1, characterized in that: The flow rate of the gas is 10–200 mL / min.

5. The excitation power according to claim 1, characterized in that: The plasma excitation power is 50W to 200W.

6. The heating rate according to claim 1, characterized in that: The heating rate is 2–15 °C / min.

7. The calcination temperature according to claim 1, characterized in that: The roasting temperature is 400–480°C.

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