A supported vanadium phosphorus oxygen catalyst

Abstract

The present invention provides a supported vanadium phosphorus oxygen catalyst, which is prepared by simultaneously adding hydroxyapatite to a solution of a vanadium phosphorus oxygen catalyst precursor prepared by a coprecipitation method, reacting to obtain a slurry, performing post-treatment to obtain a vanadium phosphorus oxygen catalyst precursor, and then performing molding first and then activation or activation first and then molding to obtain the catalyst. The above-mentioned catalyst uses hydroxyapatite as a carrier, which has the characteristics of large pore volume, large specific surface area and high strength, effectively improves the physical and chemical properties of the catalyst, improves the heat and mass transfer of the catalyst, and obtains a catalyst with high activity and selectivity; in addition, hydroxyapatite is mixed in the catalyst body phase, and the catalyst has excellent anti-phosphorus loss performance. In addition, the carrier itself has a high melting point and high temperature resistance, which can effectively reduce the amount of phosphorus supplementation reagent required for the catalyst during long-term operation, especially reduce the amount of phosphorus supplementation in the initial stage of start-up, shorten the catalyst start-up running-in period, and extend the catalyst operation cycle.

Description

Technical Field

[0001] The invention relates to the technical field of catalysts, and in particular to a supported vanadium phosphorus oxygen catalyst. Background Art

[0002] Maleic anhydride, also known as maleic anhydride, is the third largest organic anhydride after phthalic anhydride and acetic anhydride. Maleic anhydride has many structural characteristics and strong reactivity. It is an important organic chemical raw material and is widely used in the production of thermosetting resins, unsaturated polyester resins, pesticides and fine chemical products, such as an important intermediate for the synthesis of γ-butyrolactone, tetrahydrofuran and 1,4-butanediol. In the past, benzene was used as a raw material to produce maleic anhydride in industry, but due to the high cost of the benzene oxidation method and the use of raw material benzene, it has a great disadvantage in terms of environmental protection. People use butene instead of benzene as a raw material to produce maleic anhydride. However, since the 1970s, butene has gradually turned to cheap and easily available butane instead of benzene and butene as raw materials to produce maleic anhydride. In addition to the advantages of cheap raw materials, the n-butane oxidation process for producing maleic anhydride also has the advantages of less environmental pollution and low production cost of maleic anhydride, and the vanadium phosphorus oxygen catalyst is the most effective catalyst for the n-butane oxidation process for producing maleic anhydride.

[0003] At present, all vanadium phosphorus oxygen catalysts used in industrial applications are non-supported catalysts. Since vanadium phosphorus oxygen catalysts themselves have disadvantages such as small specific surface area, low strength, and poor heat transfer effect, and in order to improve the mechanical strength and wear resistance of the catalyst and extend its service life, people are exploring the use of supported vanadium phosphorus oxygen catalysts to improve these problems.

[0004] Patent CN10357310 uses an acid-treated TiO2-ZrO2 composite oxide carrier to prepare a supported vanadium phosphorus oxygen catalyst. The specific surface area and catalyst strength of the prepared supported catalyst are improved. At the same time, the acid treatment reduces the interaction between the carrier and the vanadium phosphorus oxygen catalyst, and improves the catalytic performance to a certain extent. The maximum yield of maleic anhydride can reach 60%.

[0005] Patent CN106140125 provides a method for preparing a supported n-butane oxidation to maleic anhydride VPO catalyst, using a monodispersed SiO2 microsphere carrier, and the prepared supported vanadium phosphorus oxygen catalyst has better heat transfer efficiency than the conventional non-supported VPO catalyst, and the catalyst shows good activity and selectivity at high space velocity and high butane concentration. Not only that, many scholars have also tried to use TiO2, MCM-41, SBA-15, ZrO2, Al2O3, AlPO4, SiC and other materials as carriers to make supported vanadium phosphorus oxygen catalysts, but compared with the bulk vanadium phosphorus oxygen catalyst, the reaction performance of the supported catalyst is reduced. The reason is that the selection and preparation process of the carrier of the supported catalyst are key factors affecting the performance of the catalyst. The interaction between a part of the carrier and the catalytic component will hinder the formation of the active component or cause changes in the composition of the active phase, thereby reducing the activity. In addition, most carriers need to be acid-modified during the preparation process, and the process flow is complicated. Summary of the invention

[0006] In view of the above shortcomings, the present invention provides a supported vanadium phosphorus oxygen catalyst, which uses hydroxyapatite as a carrier. Compared with the non-supported vanadium phosphorus oxygen catalyst, the pore volume, specific surface area and strength of the catalyst are increased. At the same time, the catalyst has stable performance and good anti-phosphorus loss performance. The preparation method of the catalyst is simple and easy to operate and control. The prepared catalyst has a high conversion rate of n-butane, high selectivity for maleic anhydride and stable activity in the catalytic reaction of n-butane oxidation to maleic anhydride.

[0007] The present invention adopts the following technical solutions to achieve the above technical objectives:

[0008] The technical purpose of the first aspect of the present invention is to provide a method for preparing a supported vanadium phosphorus oxygen catalyst, comprising the following steps: adding hydroxyapatite simultaneously to a solution of a vanadium phosphorus oxygen catalyst precursor prepared by a co-precipitation method, reacting to obtain a slurry, obtaining a vanadium phosphorus oxygen catalyst precursor through post-treatment, and then obtaining the supported vanadium phosphorus oxygen catalyst through first molding and then activation or first activation and then molding.

[0009] Further, the organic solvent used in the coprecipitation method to prepare the vanadium phosphorus oxygen catalyst precursor can be any solvent disclosed in the prior art. As a more specific technical solution, it is an alcohol solvent, more specifically, at least one selected from isobutyl alcohol, benzyl alcohol, ethylene glycol, 1,3-propylene glycol and 1,4-butanediol, preferably isobutyl alcohol. The coprecipitation reaction temperature is 90-115° C., and the reaction time is 4-18 hours, preferably 6-16 hours.

[0010] Furthermore, during the reaction, the mass ratio of hydroxyapatite to vanadium pentoxide is 0.1-3:10, preferably 0.3-2.5:10.

[0011] Furthermore, the specific surface area of ​​the hydroxyapatite is 40 to 70 m 2 / g, preferably 50~70m 2 / g; the number of particles with a particle size of 50~100nm accounts for more than 85%, preferably more than 86%, and more preferably more than 88%.

[0012] As one of the preferred technical solutions, the hydroxyapatite is prepared by a precipitation method with simple process, low reaction temperature and easy operation. As one of the more specific embodiments, the hydroxyapatite is prepared by the following steps: calcium salt and phosphate are dissolved in water at a molar ratio of Ca to P of 5:3, and the reaction is carried out at a temperature of 50-90°C and a pH of 9-13. The precipitate after the reaction is dried and calcined to obtain hydroxyapatite with good crystallization.

[0013] Furthermore, as one of the more specific embodiments, the supported vanadium phosphorus oxygen catalyst is prepared by the following method: vanadium pentoxide and hydroxyapatite are placed in an organic solvent, mixed thoroughly, phosphoric acid is added, the temperature is raised to 90-115°C, and the reaction is performed for 4-18 hours to obtain a reaction slurry, and a vanadium phosphorus oxygen catalyst precursor is obtained by filtering, washing, drying and calcining, and then the supported vanadium phosphorus oxygen catalyst is obtained by first forming and then activating or first activating and then forming.

[0014] Furthermore, the mixing ratio of the vanadium pentoxide and phosphoric acid is 0.75-1.40:1, preferably 0.95-1.2:1, based on the molar ratio of phosphorus to vanadium.

[0015] Furthermore, after the raw materials are mixed, the temperature is raised to the reaction temperature at a heating rate of 3 to 20° C. / h, preferably 6 to 15° C. / h, more preferably 8 to 12° C. / h.

[0016] Furthermore, the vanadium phosphorus oxygen catalyst precursor is dried at 70-140°C, preferably 80-110°C for 6-12 hours, and calcined at 170-260°C, preferably 190-240°C for 3-8 hours.

[0017] Furthermore, the molding method is a conventional molding method in the catalyst field such as tableting, extrusion or sphering. The prepared molded catalyst has a shape of strip, clover, four-leaf clover, Raschig ring, toothed ball, honeycomb or open-hole cylinder.

[0018] Furthermore, the activation is carried out in an atmosphere of one or more combinations of a mixture of air / inert gas, air / butane, air / water vapor and butane / inert gas. The activation temperature is 260-450° C., preferably 370-420° C., and the activation time is 3-30 hours, preferably 6-24 hours.

[0019] Furthermore, the preparation process of the vanadium phosphorus oxygen catalyst also includes the step of introducing an auxiliary agent. The auxiliary agent is selected from at least one of the elements Li, Na, K, Ca, Mg, Zn, Fe, Bi, Ni, Si, Mo, Co, Zr, Cu, Ti, La, Nb, B, Cr or Ce; the auxiliary agent is introduced into the catalyst in one of the following ways: (1) introduced into the reaction solution during the preparation of the vanadium phosphorus oxygen precursor; (2) introduced before or during the catalyst molding; (3) introduced by solution impregnation after the vanadium phosphorus oxygen catalyst is activated.

[0020] The second technical purpose of the present invention is to provide a vanadium phosphorus oxygen catalyst prepared by the above method. The catalyst is a supported catalyst with hydroxyapatite as a carrier, has a large pore volume and specific surface area, and has significantly increased strength, stable performance, and good anti-phosphorus loss performance.

[0021] The third aspect of the present invention is to provide a method for preparing maleic anhydride by oxidation of n-butane, which is catalyzed by the above-mentioned supported vanadium phosphorus oxygen catalyst and adopts a fixed bed, moving bed or fluidized bed reaction mode. The reaction conditions are: temperature of 375-445°C, pressure of normal pressure to 0.5MPa, and n-butane mixed gas space velocity of 800-2800h -1 , the concentration of n-butane is 1.0~1.8% (volume percentage).

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] (1) The supported vanadium phosphorus oxygen catalyst of the present invention selects hydroxyapatite as a carrier, which has the characteristics of large pore volume, large specific surface area and high strength, effectively improving the physical and chemical properties of the catalyst, enhancing the heat and mass transfer of the catalyst, and obtaining a catalyst with high activity and selectivity.

[0024] (2) The existing carrier in the prior art has the problem that the interaction between the carrier and the catalytic component will hinder the formation of the active component or cause the change of the active phase composition. However, the preparation method of the present invention has been verified that hydroxyapatite not only does not have the above problem, but also promotes the growth of seed crystals. Hydroxyapatite is a hydrogen phosphate. In the preparation process of the catalyst, it can promote the synthesis and growth of the precursor VOHPO4·0.5H2O as a seed crystal. The obtained precursor crystal structure is more regular and stable, the active center distribution of the obtained catalyst is uniform, and the activity, stability and maleic anhydride selectivity of the catalyst are higher.

[0025] (3) Hydroxyapatite is a hydrogen phosphate, which will increase the phosphorus content in the catalyst. Based on the preparation method, hydroxyapatite is mixed in the catalyst body phase, and its anti-phosphorus loss performance is excellent. In addition, the carrier itself has a high melting point and is resistant to high temperatures. It can effectively reduce the amount of phosphorus replenishment reagent required for the catalyst during long-term operation, especially reduce the amount of phosphorus replenishment in the initial stage of start-up, shorten the catalyst start-up run-in period, and extend the catalyst operation cycle.

[0026] (4) Most of the carriers in the existing technology, such as ZrO2 and Al2O3, need to be acid-modified, while hydroxyapatite does not need to be acid-modified and can be directly added during the preparation process, which shortens the preparation process of the supported catalyst. The entire preparation process is easy to control and is suitable for large-scale batch production, which is of great significance to industrialization.

[0027] Other features and advantages of the present invention will be described in detail in the following detailed description. DETAILED DESCRIPTION

[0028] The following non-limiting embodiments may enable a person skilled in the art to more fully understand the present invention, but are not intended to limit the present invention in any way.

[0029] In the following examples and comparative examples, the crystal phase was detected using a D / max-2500 X-ray diffractometer from RIGAKU, Japan, and the specific surface area was determined using an AUT0S0RB3B fully automatic specific surface area and pore size distribution instrument from Quantachrome, USA.

[0030] The hydroxyapatite used in the following examples was prepared by the following method:

[0031] Ca(NO3)3·4H2O and (NH4)2HPO4 were dissolved in deionized water to prepare aqueous solutions, and the pH of the two solutions was adjusted to 11 with ammonia water. Subsequently, the aqueous solutions of Ca(NO3)3·4H2O and (NH4)2HPO4 were reacted for 30 minutes at a molar ratio of Ca to P of 5:3, and the reaction temperature was controlled at 70°C and the pH was 11. The precipitate after the reaction was filtered, washed with distilled water, dried and calcined to obtain well-crystalline hydroxyapatite.

[0032] The basic properties of the prepared hydroxyapatite are as follows: specific surface area 57.2m 2 / g, and the number of particles with a particle size between 50-100nm accounts for 88%. In Examples 1-4, vanadium phosphorus oxygen catalyst precursor powder was prepared according to the method of the present invention:

[0033] Example 1

[0034] A four-necked flask with a stirring and reflux cooling device was used, 480 g of isobutanol and 25.0 g of vanadium pentoxide were added to the four-necked flask, the stirring speed was set to 600 r / min, the reaction temperature was gradually increased to 94°C at a heating rate of 10°C / h, 5.5 g of hydroxyapatite was added, mixed evenly, and then 40.0 g of concentrated phosphoric acid with a concentration of 95% was added, and the reflux reaction was continued for 10 hours to obtain a suspension of vanadium phosphorus oxygen catalyst precursor. After the temperature was reduced to 50°C, vacuum filtration was started, and the filter cake in the filtration process was washed three times with isobutanol. The filter cake was naturally air-dried at room temperature and then placed in an oven and dried at 120°C for 6 hours. Finally, the solid product was calcined at 250°C for 4 hours to obtain vanadium phosphorus oxygen catalyst precursor powder A1.

[0035] Example 2

[0036] A four-necked flask with a stirring and reflux cooling device was used, 260 g of isobutanol and 25.0 g of vanadium pentoxide were added to the four-necked flask, the stirring speed was set to 800 r / min, and then the reaction temperature was gradually increased to 97°C at a heating rate of 8°C / h, and then 3.0 g of hydroxyapatite and 0.1 g of auxiliary magnesium sulfate were added, followed by 38.0 g of concentrated phosphoric acid with a concentration of 100%, and the reflux reaction was continued for 12 hours to obtain a suspension of vanadium phosphorus oxygen catalyst precursor, and vacuum filtration was started after the temperature was reduced to 50°C. The filter cake in the filtration process was washed three times with isobutanol, and the filter cake was naturally air-dried at room temperature and placed in an oven, dried at 120°C for 8 hours, and finally the solid product was calcined at 250°C for 3 hours to obtain vanadium phosphorus oxygen catalyst precursor powder A2.

[0037] Example 3

[0038] A four-necked flask with a stirring and reflux cooling device was used, 300 g of isobutanol and 25.0 g of vanadium pentoxide were added to the four-necked flask, the stirring speed was set to 700 r / min, and then the reaction temperature was gradually increased to 101°C at a heating rate of 12°C / h, and then 2.0 g of hydroxyapatite and 0.15 g of an auxiliary potassium sulfate were added, and then 36.5 g of concentrated phosphoric acid with a concentration of 105% was added. The reflux reaction was continued for 18 hours to obtain a suspension of a vanadium phosphorus oxygen catalyst precursor. After the temperature was reduced to 50°C, vacuum filtration was started. The filter cake in the filtration process was washed three times with isobutanol, and the filter cake was naturally air-dried at room temperature and placed in an oven, dried at 120°C for 6 hours, and finally the solid product was calcined at 250°C for 3 hours to obtain a vanadium phosphorus oxygen catalyst precursor powder A3.

[0039] Example 4

[0040] A four-necked flask with a stirring and reflux cooling device was used, 390 g of isobutanol and 25.0 g of vanadium pentoxide were added to the four-necked flask, the stirring speed was set to 600 r / min, and then the reaction temperature was gradually increased to 105°C at a heating rate of 10°C / h, and then 1.0 g of hydroxyapatite and 0.18 g of auxiliary sodium sulfate were added, and then 33.0 g of concentrated phosphoric acid with a concentration of 115% was added. The reflux reaction was continued for 14 hours to obtain a suspension of vanadium phosphorus oxygen catalyst precursor. After the temperature was reduced to 50°C, vacuum filtration was started. The filter cake in the filtration process was washed three times with isobutanol, and the filter cake was naturally air-dried at room temperature and placed in an oven, dried at 120°C for 5 hours, and finally the solid product was calcined at 250°C for 6 hours to obtain vanadium phosphorus oxygen catalyst precursor powder A4.

[0041] Comparative Example 1

[0042] Except for not adding hydroxyapatite, other steps are the same as Example 1 to obtain vanadium phosphorus oxygen catalyst precursor B1.

[0043] Comparative Example 2

[0044] Except for adding a 200-400 nm titanium dioxide carrier treated with phosphoric acid solution instead of hydroxyapatite, the other steps are the same as Example 1 to obtain a vanadium phosphorus oxygen catalyst precursor B2. The acid treatment of titanium dioxide mainly involves immersing titanium dioxide in a phosphoric acid solution, stirring in an oil bath at 70°C, filtering, washing, and drying to obtain a carrier titanium dioxide.

[0045] Comparative Example 3

[0046] Except for adding 200-400 nm silicon dioxide microsphere carrier instead of hydroxyapatite, other steps are the same as Example 1 to obtain vanadium phosphorus oxygen catalyst precursor B3.

[0047] Performance measurement: The precursor powders prepared in the examples and comparative examples were extruded into cylindrical catalysts using a rotary tablet press and activated to obtain finished catalysts. The number of the finished catalysts was the same as that of the vanadium phosphorus oxide.

[0048] (1) Crystal phase determination: The finished catalysts A1-A4 in Examples 1-4 were subjected to crystal phase detection. The detection results showed that the main characteristic peaks of the catalysts were located at 2θ=22.9°, 28.3°, and 29.9°, and the corresponding crystal phase composition was vanadyl pyrophosphate, and the reproducibility of different batches was good.

[0049] (2) Specific surface area measurement: The specific surface area of ​​the finished vanadium phosphorus oxygen catalysts prepared in the above examples and comparative examples was measured. The results are shown in Table 1.

[0050] Table 1

[0051]

[0052] (3) Catalytic performance measurement: The precursors prepared in the examples and comparative examples were loaded into a small fixed bed reactor, and a butane / air mixture (butane volume concentration of 0.8%) was introduced. The activation temperature was raised to 250°C at a heating rate of 25°C / h, and then the temperature was raised to 405°C / h at a rate of 10°C / h and kept constant for 15 to 20 hours. The catalyst activation was completed to obtain a catalyst intermediate. Graphite powder with a mass fraction of 2% to 6% was added to the intermediate, and after mechanical mixing, it was extruded into strip catalysts using a rotary tablet press. The obtained catalyst was crushed and sieved to 5 to 10 mesh catalyst particles and placed in the reaction tube of a small reactor. The raw material was a 1.5v% n-butane / air mixture, and the volume space velocity was 1800h -1 , reaction temperature 385℃, reaction pressure 0.30MPa. After the device was stably operated for 2h, the reaction product was analyzed by gas chromatography. The initial activity evaluation results of the catalyst are shown in Table 2.

[0053] Table 2

[0054]

[0055] (4) Catalyst stability determination: After the finished catalysts prepared in the above examples and comparative examples were stably operated in the reaction device for 300 h, the catalyst performance was determined to determine the anti-phosphorus loss effect of the catalyst. The specific evaluation results are shown in Table 3.

[0056] Table 3

[0057]

[0058] As can be seen from Table 3, after running for 300 hours, the catalyst of the present invention has a smaller increase in butane molar conversion than the catalyst of the comparative example, while still having a higher maleic anhydride molar selectivity, that is, the maleic anhydride molar selectivity decreases less, indicating that the catalyst of the present invention has a good anti-phosphorus loss effect.

Claims

1. A method for preparing a supported vanadium phosphorus oxygen catalyst, comprising the following steps: Vanadium pentoxide and hydroxyapatite are placed in an organic solvent, fully mixed, phosphoric acid is added, the temperature is raised to 90-115°C, and the reaction is performed for 4-18 hours to obtain a reaction slurry, which is filtered, washed, dried and calcined to obtain a vanadium phosphorus oxygen catalyst precursor, and then the supported vanadium phosphorus oxygen catalyst is obtained by first forming and then activating or first activating and then forming; the mass ratio of hydroxyapatite to vanadium pentoxide is 0.1-3:10; the specific surface area of ​​the hydroxyapatite is 50-70m 2 / g, and the number of particles with a particle size of 50~100nm accounts for more than 85%.

2. The preparation method according to claim 1, characterized in that: The mass ratio of hydroxyapatite to vanadium pentoxide is 0.3~2.5:

10.

3. The preparation method according to claim 1, characterized in that: The hydroxyapatite particles with a particle size of 50-100 nm account for more than 86%.

4. The preparation method according to claim 3, characterized in that: The hydroxyapatite particles with a particle size of 50-100 nm account for more than 88%.

5. The preparation method according to claim 1, characterized in that: The hydroxyapatite is prepared by the following steps: dissolving calcium salt and phosphate in water at a molar ratio of Ca to P of 5:3, reacting at a temperature of 50-90° C. and a pH of 9-13, and drying and calcining the precipitate after the reaction to obtain the hydroxyapatite.

6. The preparation method according to claim 1, characterized in that: The organic solvent is selected from at least one of isobutyl alcohol, benzyl alcohol, ethylene glycol, 1,3-propylene glycol and 1,4-butanediol.

7. The preparation method according to claim 1, characterized in that: The mixing ratio of vanadium pentoxide and phosphoric acid is calculated based on a molar ratio of phosphorus to vanadium of 0.75-1.40:

1.

8. The preparation method according to claim 1, characterized in that: After the raw materials are mixed, the temperature is raised to the reaction temperature at a rate of 3-20°C / h.

9. The preparation method according to claim 8, characterized in that: After the raw materials are mixed, the temperature is raised to the reaction temperature at a rate of 6-15°C / h.

10. The preparation method according to claim 9, characterized in that: After the raw materials are mixed, the temperature is raised to the reaction temperature at a rate of 8-12°C / h.

11. The preparation method according to claim 1, characterized in that: The catalyst is further comprised of a step of introducing an auxiliary agent; the auxiliary agent is selected from at least one of the elements Li, Na, K, Ca, Mg, Zn, Fe, Bi, Ni, Si, Mo, Co, Zr, Cu, Ti, La, Nb, B, Cr or Ce; the auxiliary agent is introduced into the catalyst in one of the following ways: (1) introduced into the reaction solution during the preparation of the vanadium phosphorus oxide precursor; (2) introduced before or during the catalyst molding process; (3) After the vanadium phosphorus oxygen catalyst is activated, it is introduced by solution impregnation.

12. A vanadium phosphorus oxygen catalyst prepared by the method according to any one of claims 1 to 11.

13. A method for preparing maleic anhydride by oxidation of n-butane, the reaction being catalyzed by the vanadium phosphorus oxygen catalyst according to claim 12.

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