Preparation method of vanadium phosphorus oxide catalyst for preparing maleic anhydride through n-butane oxidation

Abstract

The invention discloses a preparation method of a vanadium phosphorus oxide catalyst for preparing maleic anhydride through n-butane oxidation. Comprising the following steps: (1) adding vanadium pentoxide and a template agent A into an isobutanol and benzyl alcohol solution for reaction; (2) cooling, adding strong phosphoric acid and a template agent B, and heating for reaction to obtain a precursor of the vanadium phosphorus oxide catalyst; and (3) activating the precursor to obtain the vanadium phosphorus oxide catalyst with hierarchical pores. The nano vanadium phosphorus oxide catalyst with a hierarchical pore structure is formed by adopting a double-template method, so that the diffusion limitation of a traditional vanadium phosphorus oxide catalyst during reaction is overcome, the specific surface area and the surface acidity of the catalyst are increased, and the catalytic activity and the stability of maleic anhydride prepared by oxidizing n-butane are improved.

Description

Technical Field

[0001] The invention relates to a catalyst, in particular to a method for preparing a vanadium phosphorus oxygen catalyst for preparing maleic anhydride by oxidation of n-butane. Background Art

[0002] Maleic anhydride (maleic anhydride) is an unsaturated five-membered cyclic anhydride. There is a conjugated maleyl group (one ethylene bond connecting two carbonyl groups) in the molecular structure, so it has high activity and can undergo a variety of chemical reactions such as addition, self-polymerization, amidation, oxidation-reduction, etc. It is one of the three major anhydrides (phthalic anhydride and acetic anhydride). Maleic anhydride, as an important chemical intermediate, can be used to produce 1,4-butanediol, tetrahydrofuran, fumaric acid, polyester resin, alkyd resin, etc. At present, in the process of preparing maleic anhydride by oxidation of n-butane, the commonly used catalyst is vanadium phosphorus oxide (VPO) catalyst, but there are problems such as low catalyst activity, poor stability, low maleic anhydride yield, harsh reaction conditions, and high energy consumption. Therefore, in order to improve the activity of VPO catalyst and the yield of target product, scholars at home and abroad have done a lot of research work.

[0003] The VPO catalyst used in industry is a bulk catalyst, the main component of which is vanadyl pyrophosphate ((VO)2P2O7). There are three commonly used methods for preparing VPO catalysts: aqueous phase method (VPA), organic phase method (VPO), and two-step method (VPD). The early synthesis used the aqueous phase method, which can generate an α-(VO)2P2O7 phase with a nearly ideal structure, a stable structure, and less deep oxides during the reaction, but the catalyst has a low specific surface area (<10m 2 / g), but has the defects of low reaction rate and poor activity. At present, the organic phase method is mainly used in industry, but there are still problems of impure crystal phase and low crystallinity. The two-step method mainly reduces VOPO4·2H2O in alcohol solvent to obtain the precursor VOPO4·0.5H2O. Compared with VPA and VPO, it has lower crystallinity and cumbersome synthesis process, so it has not been widely promoted.

[0004] Patent 100563826C discloses a method for preparing an unsupported vanadium phosphorus oxygen catalyst, wherein vanadium pentoxide is reduced in a benzyl alcohol or isobutyl alcohol-benzyl alcohol mixed solution, and then polyethylene glycol (PEG-6000) and phosphoric acid (85%) are added and the mixture is refluxed to obtain a vanadium phosphorus oxygen catalyst. The catalyst has a low specific surface area, poor catalyst activity, and is easily deactivated.

[0005] Patent CN113117708A discloses a method for preparing a vanadium phosphorus oxygen catalyst, which adopts a two-step method. In the first step, vanadium pentoxide is co-precipitated with isobutyl alcohol / or benzyl alcohol and concentrated phosphoric acid, and then filtered, dried and roasted to obtain nano vanadium phosphorus oxide. Then, the product of the first step is used as a seed crystal to repeat the synthesis process to obtain vanadium phosphorus oxide with a stepped pore structure. The catalyst synthesis process is complicated, the organic matter consumption is large, the catalyst preparation cost is increased, and the two drying and calcination processes also have a potential risk of environmental pollution.

[0006] Therefore, developing a highly active and stable catalyst for the oxidation of n-butane to maleic anhydride is an urgent problem to be solved. Summary of the invention

[0007] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a method for preparing a catalyst for the oxidation of n-butane to maleic anhydride. The method adopts a dual template method to regulate the morphology and pore structure of the vanadium phosphorus oxygen catalyst, improve the mass transfer and heat transfer process of the catalyst in the reaction, and ultimately improve the catalyst activity and stability.

[0008] In order to achieve the above object, the technical solution of the present invention is:

[0009] A method for preparing a vanadium phosphorus oxygen catalyst for oxidation of n-butane to maleic anhydride comprises the following steps:

[0010] (1) mixing vanadium pentoxide, isobutyl alcohol, benzyl alcohol and template A, heating and stirring to react, and obtaining a colloid containing tetravalent vanadium oxide;

[0011] (2) After cooling the solution, concentrated phosphoric acid and template B are added, and the temperature is raised again to react to obtain a solution containing a vanadium phosphorus oxygen catalyst precursor;

[0012] (3) washing, drying and forming the solution containing the precursor to obtain VOHPO4·0.5H2O, a precursor of the vanadium phosphorus oxygen catalyst;

[0013] (4) The formed precursor is activated in an air atmosphere containing n-butane to obtain a vanadium phosphorus oxygen catalyst, the main active component of which is vanadyl pyrophosphate ((VO)2P2O7).

[0014] Wherein, the template agent A in step (1) is one of polyvinyl alcohol, polyethylene glycol, polyvinyl pyrrolidone, and polypropylene glycol; the template agent B is one of polystyrene, dimethylformamide, hexadecyltrimethylammonium bromide, tetrapropylammonium hydroxide, polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer, polymethacrylic acid-maleic acid co-maleic acid PMMA, and polyoxyethylene fatty alcohol ether.

[0015] The present invention regulates the morphology and pore structure of the catalyst by adding a dual template agent during the synthesis process. The sequential addition of the dual template agents can form a nano material with a multi-level pore structure. The template agent also has a structure-guiding effect, increases the active crystal surface of the catalyst, and improves the selectivity of the catalyst.

[0016] The molar ratio of concentrated phosphoric acid to vanadium in vanadium pentoxide described in the present invention is 0.8-1.4, the volume ratio of the mass of vanadium pentoxide to solution is 8-12:1, the mass ratio of the template agent to vanadium pentoxide is 0.05-1.2:1, the mass ratio of the template agent A to vanadium pentoxide is 0.05-1.2:1, and the mass ratio of the template agent B to vanadium pentoxide is 0.6-1.1:1.

[0017] The volume ratio of isobutanol to benzyl alcohol described in the present invention is 4-6:1.

[0018] The heating temperature in the present invention is 90-155° C., the stirring rate is 100-350 rpm, and the reaction time is 1-6 hours.

[0019] In step (2) of the present invention, the temperature is lowered to 60-90° C., the concentration of concentrated phosphoric acid is 85%-105%, the temperature is raised again to 100-155° C., and the reaction time is 3-17 hours.

[0020] The washing in step (3) of the present invention is performed by washing with one or both of anhydrous ethanol and ultrapure water for 1 to 6 times, and the drying temperature is 80 to 150° C.;

[0021] In the air containing n-butane in step (4) of the present invention, the volume concentration of n-butane is 1-1.5%, the volume concentration of water vapor is 0-12%, the activation temperature is 400-480° C., and the activation time is 1-16 hours.

[0022] The molding method described in the present invention is: the precursor powder and graphite are mixed and pressed into a spherical shape, a cylindrical shape, a hollow cylindrical shape, and a clover shape; the mass ratio of the graphite to the precursor powder is 0.005-0.1.

[0023] The present invention has found that an auxiliary agent can be introduced in the preparation process of the vanadium phosphorus oxygen catalyst, and the auxiliary agent is selected from one or more of the elements Mg, Ca, Al, Bi, Fe, Co, Ni, Cu, Zn, Mn, Mo, Ce, Zr, and La. The auxiliary agent can be introduced by (1) adding it to the reaction solution simultaneously with vanadium pentoxide during the synthesis of the precursor vanadium phosphorus oxygen precursor; or (2) introducing it by impregnation after the vanadium phosphorus oxygen catalyst is activated.

[0024] Compared with the prior art, the present invention has the following beneficial effects: the catalyst prepared by the present invention has a mesoporous-macroporous multi-level pore structure, a rich pore structure, and a large specific surface area. The structure-guiding effect of the template agent forms more active crystal faces, thereby improving the selectivity of maleic anhydride. The multi-level pore structure improves mass transfer and heat transfer during the oxidation of n-butane, reduces the hot spot problem caused by oxidation heat release, and ultimately improves the activity and stability of the catalyst. DETAILED DESCRIPTION

[0025] The present invention is illustrated by the following examples, but is not limited to the following examples. Without departing from the scope of the preceding and following descriptions, various modifications are included within the technical scope of the present invention.

[0026] Embodiment 1:

[0027] A reactor with a stirring and reflux device is used, 160 mL of isobutyl alcohol and 40 mL of benzyl alcohol are mixed, 20 g of vanadium pentoxide and 1 g of polyvinyl pyrrolidone are added to the above solution, stirring is started, the speed is set to 200 r / min, the temperature is raised to 135 ° C, the heating reaction is continued for 3 hours, and the temperature is finally lowered. When the temperature drops to 70-80 ° C, 14.78 mL of 85% concentrated phosphoric acid and 0.5 g of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer are quickly added and the temperature is raised to 135 ° C again, and the reaction is completed after 16 hours. After the reaction product is cooled to room temperature, it is washed and dried. It is washed with anhydrous ethanol and ultrapure water three times each, and the filter cake is dried at 120 ° C in a blast drying oven for 6 hours to obtain a vanadium phosphorus oxygen catalyst precursor. After adding 0.2 g of graphite to the precursor, it is pressed into tablets at 10 MPa, crushed, and 20-40 mesh particles are taken and activated in a fixed bed reactor. Specific surface area 61m 2 / g, mesopore diameter is 36nm, and macropore diameter is 245nm.

[0028] Embodiment 2:

[0029] Use a reactor with a stirring and reflux device, take 150mL of isobutyl alcohol and 30mL of benzyl alcohol, add 20g of vanadium pentoxide and 1.2g of polyvinyl alcohol to the above solution, start stirring, set the speed to 200r / min, heat to 135℃, heat the reaction for 3h and then stop cooling. When the temperature drops to 70-80℃, quickly add 14.78mL of 85% concentrated phosphoric acid and 0.6g of hexadecyltrimethylammonium bromide, heat to 125℃ again, and end the reaction after 6h. After the reaction product cools to room temperature, wash and dry. Wash three times with anhydrous ethanol, and dry the filter cake at 120℃ in a forced air drying oven for 6h to obtain a vanadium phosphorus oxygen catalyst precursor. After adding 0.1g of graphite to the precursor, press it into tablets at 10MPa, crush it into particles of 20-40 mesh, and activate it in a fixed bed reactor. Specific surface area 58m 2 / g, mesopore diameter is 35nm, and macropore diameter is 158nm.

[0030] Embodiment 3:

[0031] Use a reactor with a stirring and reflux device, take 170mL of isobutanol and 30mL of benzyl alcohol, mix them, add 20g of vanadium pentoxide and 0.8g of polypropylene glycol to the above solution, start stirring, set the speed to 200r / min, heat to 135℃, heat the reaction for 3h and then end the cooling. When the temperature drops to 70-80℃, quickly add 16.25mL of 85% concentrated phosphoric acid and 0.6g of polymethacrylic acid-maleic acid co-maleic acid, heat to 135℃ again, and end the reaction after 6h. After the reaction product cools to room temperature, wash and dry. Wash with anhydrous ethanol and ultrapure water three times each, and dry the filter cake at 150℃ in a blast drying oven for 6h to obtain a vanadium phosphorus oxygen catalyst precursor. After adding 0.4g of graphite to the precursor, press it into tablets at 10MPa, crush it into particles of 20-40 mesh, and activate it in a fixed bed reactor. Specific surface area 48m 2 / g, mesopore diameter is 34nm, and macropore diameter is 260nm.

[0032] Embodiment 4:

[0033] Use a reactor with a stirring and reflux device, take 150mL of isobutanol and 50mL of benzyl alcohol, mix them, add 20g of vanadium pentoxide and 2g of polyethylene glycol to the above solution, start stirring, set the speed to 200r / min, heat to 135℃, heat the reaction for 3h and then end the cooling. When the temperature drops to 70-80℃, quickly add 85% concentrated phosphoric acid 13.52mLh and 0.5g of tetrapropylammonium hydroxide, heat to 135℃ again, and end the reaction after 6h. After the reaction product cools to room temperature, wash and dry. Wash three times with anhydrous ethanol, and dry the filter cake at 120℃ in a forced air drying oven for 6h to obtain a vanadium phosphorus oxygen catalyst precursor. After adding 0.25g of graphite to the precursor, press it into tablets at 10MPa, crush it into particles of 20-40 mesh, and activate it in a fixed bed reactor. Specific surface area 63m 2 / g, mesopore diameter is 38nm, and macropore diameter is 98nm.

[0034] Embodiment 5:

[0035] Use a reactor with a stirring and reflux device, take 160mL of isobutanol and 40mL of benzyl alcohol, mix them, add 20g of vanadium pentoxide, 1g of polyethylene glycol, and 0.03g of FeCl2 to the above solution, start stirring, set the speed to 200r / min, heat to 135℃, heat the reaction for 3h and then stop cooling. When the temperature drops to 70-80℃, quickly add 16.25mL of 85% concentrated phosphoric acid and 0.5g of hexadecyltrimethylammonium bromide, heat to 135℃ again, and end the reaction after 6h. After the reaction product cools to room temperature, wash and dry it. Wash it three times with anhydrous ethanol, and dry the filter cake at 120℃ in a forced air drying oven for 6h to obtain a vanadium phosphorus oxygen catalyst precursor. After adding 0.3g of graphite to the precursor, press it into tablets at 10MPa, crush it into particles of 20-40 mesh, and activate it in a fixed bed reactor. Specific surface area 62m 2 / g, mesopore diameter is 42nm, and macropore diameter is 160nm.

[0036] Embodiment 6:

[0037] A reactor with a stirring and reflux device is used to mix 180 mL of isobutyl alcohol and 30 mL of benzyl alcohol, and 20 g of vanadium pentoxide and 1.5 g of polypropylene glycol are added to the above solution, stirring is turned on, the speed is set to 200 r / min, the temperature is raised to 135 ° C, and the heating reaction is completed after 3 hours of cooling. When the temperature drops to 70-80 ° C, 14.78 mL of 85% concentrated phosphoric acid and 0.5 g of tetrapropylammonium hydroxide are quickly added, and the temperature is raised to 135 ° C again. The reaction ends after 6 hours. The reaction product is washed and dried after cooling to room temperature. It is washed with anhydrous ethanol and ultrapure water three times each, and the filter cake is dried at 120 ° C in a blast drying oven for 6 hours to obtain a vanadium phosphorus oxygen catalyst precursor. After adding 0.1 g of graphite to the precursor, it is pressed at 10 MPa, crushed into 20-40 mesh particles, and 0.05 g of ammonium phosphomolybdate is loaded by impregnation method, then dried and calcined, and activated in a fixed bed reactor. Specific surface area: 51m 2 / g, mesopore diameter is 45nm, and macropore diameter is 138nm.

[0038] Comparative Example 1:

[0039] Use a reactor with a stirring and reflux device, take 160mL of isobutanol and 40mL of benzyl alcohol, mix them, add 20g of vanadium pentoxide to the above solution, start stirring, set the speed to 200r / min, heat to 135℃, heat the reaction for 3h and then end the cooling. When the temperature drops to 70-80℃, quickly add 14.78mL of 85% concentrated phosphoric acid, heat to 135℃ again, and end the reaction after 6h. After the reaction product cools to room temperature, filter, wash and dry. The filtration process is washed three times with anhydrous ethanol, and the filter cake is dried at 120℃ in a forced air drying oven for 6h to obtain a vanadium phosphorus oxygen catalyst precursor. After adding 0.2g of graphite to the precursor, it is pressed into tablets at 10MPa, crushed into particles of 20-40 mesh, and activated in a fixed bed reactor. Specific surface area 19m 2 / g, mesopore diameter 29nm.

[0040] 3 mL of the catalyst from the above examples was loaded into a tubular micro fixed bed reactor and heated to 450°C at 10°C / min for 3 hours before activity testing. Activation conditions: 1.5% n-butane / air mixed gas composition, reaction space velocity of 2000 h -1 The experimental conditions were: reaction temperature was 380°C, the inlet gas of the fixed bed reactor consisted of a 1.35% n-butane / air mixture, and the reaction space velocity was 2000 h -1 The reaction results are shown in Table 1.

[0041] Table 1 Performance evaluation results of n-butane oxidation to maleic anhydride in various examples and comparative examples

[0042] Conversion rate Selectivity Yield Comparative Example 1 79.2％ 70.1％ 55.5％ Example 1 93.1％ 75.3％ 70.1％ Example 2 88.1％ 76.4％ 67.3％ Example 3 90.9％ 74.4％ 67.6％ Example 4 86.3％ 75.3％ 65.0％ Example 5 91.8％ 76.2％ 70.0％ Example 5 97.8％ 74.2％ 72.6％ Example 6 99.4％ 79.6％ 79.1％

Claims

1. A method for preparing a vanadium-phosphorus-oxygen catalyst for oxidation of n-butane to maleic anhydride, characterized in that: The steps include: (1) mixing vanadium pentoxide, isobutyl alcohol, benzyl alcohol and template A, heating and stirring to react, and obtaining an oxide colloid containing tetravalent vanadium; (2) After cooling the reaction mixture, concentrated phosphoric acid and template B are added, and the temperature is raised again to react to obtain a solution containing a vanadium phosphorus oxygen catalyst precursor; (3) washing, drying and molding the solution containing the vanadium phosphorus oxygen catalyst precursor to obtain the vanadium phosphorus oxygen catalyst precursor VOHPO4·0.5H2O; (4) activating the formed precursor in an air atmosphere containing n-butane to obtain a vanadium phosphorus oxygen catalyst; Wherein, the template agent A in step (1) is one of polyvinyl alcohol, polyethylene glycol, polyvinyl pyrrolidone, and polypropylene glycol; the template agent B is one of polystyrene, dimethylformamide, hexadecyltrimethylammonium bromide, tetrapropylammonium hydroxide, polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer, polymethacrylic acid-maleic acid co-maleic acid, and polyoxyethylene fatty alcohol ether.

2. The preparation method according to claim 1, characterized in that The molar ratio of the concentrated phosphoric acid to vanadium in vanadium pentoxide is 0.8-1.4:1, the mass ratio of the template A to vanadium pentoxide is 0.05-1.2:1, and the mass ratio of the template B to vanadium pentoxide is 0.6-1.1:

1.

3. The preparation method according to claim 1, characterized in that The volume ratio of isobutanol to benzyl alcohol in step (1) is 4-6:

1.

4. The preparation method according to claim 1, characterized in that The heating temperature in step (1) is 90-155° C., the stirring rate is 100-350 rpm, and the reaction time is 1-6 h.

5. The preparation method according to claim 1, characterized in that The cooling in step (2) refers to cooling to 60-90° C., the concentration of the concentrated phosphoric acid is 85-105%, the temperature of the next heating is 100-155° C., the stirring rate is 100-350 rpm, and the reaction time is 3-17 h.

6. The preparation method according to claim 1, characterized in that The washing in step (3) is carried out using one or both of anhydrous ethanol and ultrapure water, and the washing is performed 1 to 6 times. The drying temperature is 80 to 150°C.

7. The preparation method according to claim 1, characterized in that In the air containing n-butane described in step (4), the volume concentration of n-butane is 1-1.5%, the volume concentration of water vapor is 0-12%, the activation temperature is 400-480° C., and the activation time is 1-16 hours.

8. The molding method according to claim 1, characterized in that The molding method described in step (3) is: mixing the precursor and graphite to press into a spherical shape, a cylindrical shape, a hollow cylindrical shape, or a clover leaf shape; the mass ratio of the graphite to the precursor is 0.005 to 0.05:

1.

9. The preparation method according to claim 1, characterized in that In the preparation process of the vanadium phosphorus oxygen catalyst, an auxiliary agent is also introduced, and the auxiliary agent is selected from one or more of the elements Mg, Ca, Al, Bi, Fe, Co, Ni, Cu, Zn, Mn, Mo, Ce, Zr, and La.

10. The preparation method according to claim 9, characterized in that The methods for introducing the additive include: (1) adding it to the reaction solution simultaneously with vanadium pentoxide during the synthesis of the precursor vanadium phosphorus oxide precursor; or (2) introducing it by impregnation after the vanadium phosphorus oxide catalyst is activated.