A method for preparing a choline-based low co-solvent-enhanced vanadium phosphorus oxygen catalyst

Abstract

The present invention discloses a method for preparing a vanadium phosphorus oxygen catalyst strengthened by a choline low co-solvent. The method comprises the following steps: (1) mixing vanadium pentoxide, isobutyl alcohol, benzyl alcohol and a low co-solvent, heating and stirring to react; (2) cooling the solution, adding concentrated phosphoric acid, heating again to react, and obtaining a solution containing a vanadium phosphorus oxygen catalyst precursor; (3) filtering, washing, drying and molding the solution containing the precursor to obtain a vanadium phosphorus oxygen catalyst precursor. (4) After molding the precursor, activating it in an air atmosphere containing n-butane to obtain a vanadium phosphorus oxygen catalyst vanadium pyrophosphate. The choline low co-solvent is made of choline chloride, an organic acid and a metal oxide. The vanadium phosphorus oxygen catalyst synthesized by the present invention has higher catalytic activity in the reaction of n-butane oxidation to maleic anhydride.

Description

Technical Field

[0001] The invention relates to a catalyst, in particular to a preparation method of a choline low co-solvent-reinforced vanadium phosphorus oxygen catalyst and application thereof. Background Art

[0002] Maleic anhydride, also known as maleic anhydride, is an important chemical intermediate that can be used to produce 1,4-butanediol, tetrahydrofuran, fumaric acid, polyester resin, alkyd resin, etc. At present, the main production processes include benzene oxidation, C4 fraction oxidation, and n-butane oxidation. Due to the influence of factors such as the rising benzene price and environmental factors, n-butane oxidation has dominated in recent years. Vanadium phosphorus oxide (VPO) catalyst is the most effective catalyst for n-butane oxidation, and its preparation method and reaction mechanism have attracted the attention of many scholars.

[0003] It is generally believed that VPO catalyst is derived from the precursor hemihydrated vanadium hydrogen phosphate through topological transformation, and vanadium pyrophosphate is the main active phase of VPO catalyst. The hemihydrated vanadium hydrogen phosphate synthesized in isobutanol solution by the traditional organic phase method has a sheet structure and finally accumulates into a rose or rosette shape. The activated catalyst has a low specific surface area, few active sites, and poor activity. The crystal structure and grain size of the precursor have an important influence on the activity of the catalyst. In order to improve the activity and selectivity of vanadium phosphorus oxygen catalysts, domestic and foreign scholars have done a lot of research work.

[0004] At present, the strengthening methods of vanadium phosphorus oxygen catalysts mainly improve the performance of catalysts by adding metal additives, organic additives, heteropoly acids and ionic liquids, etc., to change the surface valence state, redox characteristics, acidity and alkalinity, surface P / V, etc. of the catalysts. Patent CN1282631A introduces metal nitrates Zr, Mo and Zn, and patent CN118045616A introduces non-metallic components S, Se and B. These methods cannot achieve precise control of the catalyst structure, and the loss of additive elements will occur during the use of the catalyst, resulting in a decrease in catalytic activity and secondary pollution problems.

[0005] Patent CN108722455A obtains a vanadium phosphorus oxygen catalyst with dual pores by introducing two ionic liquids during the synthesis process. However, ionic liquids are difficult to synthesize, the raw material price is high, and there are problems such as chemical toxicity and environmental pollution, which are not suitable for promotion and application. Patent CN115722239B strengthens the vanadium phosphorus oxygen catalyst by introducing a metal-based alcohol low co-solvent during the synthesis process. The metal anions and metal cations formed by the asymmetric splitting of the metal-based alcohol low co-solvent have low hydrogen bonding effects. During the synthesis of the vanadium phosphorus oxygen catalyst, the regulating effect on the catalyst is limited, and the alkaline earth metal used causes the catalyst surface acidity to decrease, the n-butane conversion rate to decrease, and the catalyst activity to decrease.

[0006] Therefore, there is an urgent need for a method to strengthen the vanadium phosphorus oxygen catalyst, improve the stability of the catalyst, and ensure the activity and selectivity of n-butane oxidation to maleic anhydride. 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 vanadium phosphorus oxygen catalyst strengthened by a choline-based low co-solvent. The method uses a low co-solvent of choline chloride, an organic acid and a metal oxide, and through the coordinated regulation of the crystal face induction and electronic effect of the vanadium phosphorus oxygen catalyst, ultimately improves the activity and stability of the catalyst in the reaction.

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

[0009] A method for preparing a choline-based low co-solvent-enhanced vanadium phosphorus oxygen catalyst comprises the following steps:

[0010] (1) mixing vanadium pentoxide, isobutyl alcohol, benzyl alcohol and a choline-based low co-solvent, heating and stirring to react, to obtain a solution containing tetravalent vanadium oxide colloid,

[0011] (3) After cooling the solution, concentrated phosphoric acid is added and the temperature is raised again to react to obtain a solution containing a vanadium phosphorus oxygen catalyst precursor.

[0012] (4) filtering, washing, drying and molding the solution containing the precursor to obtain a precursor of the vanadium phosphorus oxygen catalyst (VOHPO4·0.5H2O),

[0013] (5) After the precursor is formed, it is activated in an air atmosphere containing n-butane to obtain a vanadium phosphorus oxygen catalyst, the main active component of which is vanadium pyrophosphate ((VO)2P2O7).

[0014] Wherein, the choline low co-solvent in step (1) is synthesized by choline chloride, an organic acid and a metal oxide. The organic acid is one of lactic acid, oxalic acid, malonic acid, succinic acid, citric acid, capric acid and lauric acid, and the metal oxide is one of copper oxide, cuprous oxide, chromium oxide, manganese oxide, iron oxide, cobalt oxide, nickel oxide and zinc oxide.

[0015] The present invention adds a choline-based low co-solvent during the precursor synthesis process, wherein (1) the halogen anion Cl- formed by choline chloride and the organic acid ligand forms a strong hydrogen bond with the COOH of the organic acid ligand, and through the interaction with the vanadium phosphorus oxide catalyst precursor, the catalyst synthesis process is regulated, the formation of the precursor active crystal surface is induced, and the surface valence and redox properties of the catalyst are regulated. (2) The polar functional group of choline chloride forms a hydrogen bond with the hydroxyl group or oxygen atom on the surface of the metal oxide, which is helpful for the dispersion and dissolution of the metal oxide. The metal is used as a structural auxiliary agent or an electronic auxiliary agent to improve the performance of the vanadium phosphorus oxide catalyst, and different from the traditional loading method, the choline-based low co-solvent in the present invention has a strong solubilizing property, which improves the dispersion and solubility of the metal, and the metal element will be doped into the lattice of the vanadium phosphorus oxide, and will not be lost during the reaction process; (3) choline chloride has a certain hydrophobicity, and by changing the structure at the molecular level in the synthesis of the vanadium phosphorus oxide precursor, the van der Waals force between the vanadium oxides is weakened, thereby promoting the dispersion of the metal oxide, and forming a vanadium phosphorus oxide catalyst with a nanostructure.

[0016] The low co-solvent is prepared by mixing choline chloride, an organic acid and a metal oxide, and stirring and heating at 60-150° C. until all of the mixture is dissolved, wherein the molar ratio of the choline chloride, the organic acid and the metal oxide is 1:(0.8-3):(0.05-0.2).

[0017] The molar ratio of phosphorus to vanadium in step (1) is 0.8-1.4:1; the volume ratio of the mass of vanadium pentoxide to the solution is 8-12:1; and the mass ratio of the low co-solvent to vanadium pentoxide is 0.05-1.2:1.

[0018] The volume ratio of isobutanol to benzyl alcohol in the step (1) is 4 to 6:1.

[0019] In the step (1), the heating temperature is 90-155° C., the stirring rate is 100-350 rpm, and the reaction time is 1-6 hours.

[0020] In the step (2), 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., the stirring rate is 100-350 rpm, and the reaction time is 3-17 h.

[0021] The washing in step (3) is performed 1 to 3 times using one or both of anhydrous ethanol and ultrapure water, and the drying temperature is 80 to 150°C.

[0022] In the air containing n-butane in step (4), the volume concentration of n-butane is 1-1.5%, the volume concentration of water vapor is 1-12%, the activation temperature is 400-480° C., and the activation time is 1-16 hours.

[0023] The molding method comprises: mixing the precursor powder and graphite to press into a spherical shape, a cylindrical shape, a hollow cylindrical shape, or a clover leaf shape; and the mass ratio of the graphite to the precursor powder is 0.005 to 0.05:1.

[0024] Compared with the prior art, the present invention has the following beneficial effects: the synthesis process of the present invention is simple, and the vanadium phosphorus oxygen catalyst is synthesized by adding a choline-based low co-solvent containing a metal. The choline-based low co-solvent acts as a structure-directing agent to regulate the synthesis process of the catalyst, induces the formation of active crystal faces of the precursor, exposes more active crystal faces, and has a higher specific surface area; as an electron promoter, it regulates the surface valence state and redox properties of the catalyst. At the same time, the addition of the choline-based low co-solvent improves the crystallinity of the catalyst, changes the defect sites on the catalytic surface, and the conversion rate of n-butane and the selectivity of maleic anhydride in the n-butane oxidation reaction to prepare maleic anhydride are simultaneously improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The invention relates to a precursor (A) of a choline-based low co-solvent-enhanced vanadium phosphorus oxygen catalyst and a catalyst (B) after activation. DETAILED DESCRIPTION

[0026] 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.

[0027] Embodiment 1:

[0028] (1) Synthesis of low co-solvent: Use a round-bottom flask to add 5 g of choline chloride and 4.7 g of malonic acid in sequence, stir at 60° C. until the mixture becomes a colorless transparent liquid, then add 1.4 g of copper oxide until it is completely dissolved to form a low co-solvent.

[0029] (2) Using a reactor equipped with a stirring and reflux device, 20 g of vanadium pentoxide, 160 mL of isobutanol and 40 mL of benzyl alcohol were mixed, and then 0.7 g of the above-synthesized low co-solvent was added, stirring was started, the speed was set to 200 r / min, the temperature was raised to 135°C, and the reaction was heated for 3 hours before cooling down. When the temperature dropped to 70-80°C, 14.78 mL of 85% concentrated phosphoric acid was quickly added, and the temperature was raised to 135°C again. The reaction was terminated after 16 hours. After the reaction product cooled to room temperature, it was washed and dried. The product was washed with anhydrous ethanol and ultrapure water three times each, and the filter cake was dried at 120°C in a forced air drying oven for 6 hours to obtain a vanadium phosphorus oxygen catalyst precursor. After adding 0.2 g of graphite to the precursor, it was pressed into tablets at 10 MPa, crushed, and particles of 20-40 mesh were taken and activated in a fixed bed reactor. The precursor of the choline low co-solvent-enhanced vanadium phosphorus oxygen catalyst and the activated catalyst thereof are as follows Figure 1 shown.

[0030] Embodiment 2:

[0031] (1) Synthesis of low co-solvent: Use a round-bottom flask to add 5.0 g of choline chloride and 4.0 g of oxalic acid in sequence, stir at 80° C. until the mixture becomes a colorless transparent liquid, then add 1.3 g of iron oxide until it is completely dissolved to form a low co-solvent.

[0032] (2) Same as step 2 in Example 1.

[0033] Embodiment 3:

[0034] (1) Synthesis of low co-solvent: Use a round-bottom flask to add 5.0 g of choline chloride and 8.6 g of citric acid in sequence, stir at 80° C. until the mixture becomes a colorless transparent liquid, and then add 1.8 g of cuprous oxide until it is completely dissolved to form a low co-solvent.

[0035] (2) Same as step 2 in Example 1.

[0036] Embodiment 4:

[0037] (1) Synthesis of low co-solvent: Use a round-bottom flask to add 5.0 g of choline chloride and 6.7 g of tartaric acid in sequence, stir at 80° C. until the mixture becomes a colorless transparent liquid, and then add 1.6 g of nickel oxide until it is completely dissolved to form a low co-solvent.

[0038] (2) Same as step 2 in Example 1.

[0039] Embodiment 5:

[0040] (1) Synthesis of low co-solvent: Using a round-bottom flask, add 5.0 g of choline chloride and 2.7 g of acetic acid in sequence, stir at 80° C. until the mixture becomes a colorless transparent liquid, and then add 1.1 g of cobalt oxide until it is completely dissolved to form a low co-solvent.

[0041] (2) Same as step 2 in Example 1.

[0042] Embodiment 6:

[0043] (1) Synthesis of low co-solvent: Use a round-bottom flask to add 5.0 g of choline chloride and 4.0 g of oxalic acid in sequence, stir at 80° C. until the mixture becomes a colorless transparent liquid, and then add 1.3 g of zinc oxide until it is completely dissolved to form a low co-solvent.

[0044] (2) Same as step 2 in Example 1.

[0045] Comparative Example 1:

[0046] No low co-solvent was added and the synthesis method was the same as step (2) of Example 1.

[0047] Comparative Example 2:

[0048] (1) Synthesis of low co-solvent: Use a round-bottom flask to add 5.0 g of choline chloride and 4.0 g of oxalic acid in sequence and stir at 80° C. until a colorless transparent liquid is formed to form a low co-solvent.

[0049] (2) Same as step 2 in Example 1.

[0050] 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 390°C, the inlet gas of the fixed bed reactor consisted of a 1.5% n-butane / air mixture, and the reaction space velocity was 2000 h -1 The reaction results are shown in Table 1.

[0051] Table 1 Performance evaluation results of n-butane oxidation to maleic anhydride in various examples and comparative examples

[0052] Conversion rate Selectivity Yield Example 1 94.2％ 74.1％ 69.8％ Example 2 95.8％ 75.2％ 72.0％ Example 3 93.2％ 78.3％ 73.0％ Example 4 91.4％ 72.3％ 66.1％ Example 5 97.6％ 79.2％ 77.3％ Example 6 89.4％ 71.6％ 64.0％ Comparative Example 1 70.2％ 55.1％ 38.7％ Comparative Example 2 68.5％ 53.5％ 36.6％

Claims

1. A method for preparing a choline-based low co-solvent-enhanced vanadium phosphorus oxygen catalyst, characterized in that: The steps include: (1) mixing vanadium pentoxide, isobutyl alcohol, benzyl alcohol and a choline-based low co-solvent, heating and stirring to react, and obtaining a solution containing tetravalent vanadium oxide colloid; (2) After cooling the solution, adding concentrated phosphoric acid, and heating again to react, to obtain a solution containing a vanadium phosphorus oxygen catalyst precursor; (3) filtering, washing, drying and molding the solution containing the precursor to obtain a precursor of the vanadium phosphorus oxygen catalyst; (4) After the precursor is formed, it is activated in an air atmosphere containing n-butane to obtain a vanadium phosphorus oxygen catalyst; Wherein, the choline low co-solvent in step (1) is made of choline chloride, organic acid and metal oxide.

2. The preparation method according to claim 1, characterized in that: The choline low co-solvent is prepared by mixing choline chloride, an organic acid and a metal oxide, and stirring and heating at 60 to 150° C. until all of the mixture is dissolved, wherein the molar ratio of the choline chloride, the organic acid and the metal oxide is 1:0.8 to 3:0.05 to 0.

2.

3. The preparation method according to claim 2, characterized in that: The organic acid is one of lactic acid, oxalic acid, malonic acid, succinic acid, citric acid, capric acid and lauric acid; the metal oxide is one of copper oxide, cuprous oxide, chromium oxide, manganese oxide, iron oxide, cobalt oxide, nickel oxide and zinc oxide.

4. The preparation method according to claim 1, characterized in that The molar ratio of the concentrated phosphoric acid to the vanadium in vanadium pentoxide in step (1) is 0.8-1.4:1; and the mass ratio of the choline low co-solvent to vanadium pentoxide is 0.05-1.2:

1.

5. 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.

6. 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.

7. The preparation method according to claim 1, characterized in that In step (2), 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., the stirring rate is 100-350 rpm, and the reaction time is 3-17 h.

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

9. 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 1-12%, the activation temperature is 400-480° C., and the activation time is 1-16 hours.

10. The preparation method according to claim 1, characterized in that The molding method in step (4) is: mixing the precursor and graphite to press into a spherical shape, a cylindrical shape, a hollow cylindrical shape, or a clover leaf shape, wherein the mass ratio of the graphite to the precursor is 0.005 to 0.05:1.

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