JPH0455966B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing vanadium-phosphorous oxide particles. More specifically, the present invention relates to a method for producing vanadium-phosphorous oxide particles suitable as a catalyst for producing maleic anhydride by gas-phase oxidation of butane. Many catalysts and processes have already been proposed for producing maleic anhydride by gas-phase oxidation of straight-chain aliphatic hydrocarbons having 4 carbon atoms. In particular, regarding methods using butenes, butane, etc. as raw materials, crystalline vanadium-phosphorus oxides have recently been proposed, and crystallographic studies are also underway (E. E.Bordes, P.Courtine,
J. Catal., ) 57 , 236-52 (1979)). Crystalline vanadium-phosphorous oxides have high activity and are particularly effective in oxidizing butane. However, even if composite oxides have the same crystal type, problems may arise in crystal purity due to the manufacturing method, or various impurities may melt during activation, resulting in a decrease in specific surface area and pore volume. In many cases, it is unsuitable for use as a catalyst, as small particles are produced. Various methods for producing vanadium-phosphorus oxides are already known (Japanese Patent Application Laid-Open No. 51-95990, JP-A No. 53-146992,
Japanese Patent Publication No. 53-2631, US Pat. Problems in industrial implementation or catalytic activity as a fluidized catalyst,
The strength was not sufficient. The present inventors have arrived at the present invention as a result of studies aimed at improving the various problems mentioned above. That is, the first invention of the present application is a first step in which phosphoric acid, an inorganic reducing agent, and vanadium pentoxide are reacted in an aqueous medium, and then subjected to hydrothermal treatment to obtain a slurry containing a crystalline vanadium-phosphorus oxide. A second step of separating the vanadium-phosphorus oxide from the slurry obtained in the first step. The aqueous solution obtained in the second step after the vanadium-phosphorus oxide separation is diluted or concentrated as necessary. Third step of adding and dissolving acid, reducing agent, and vanadium pentoxide. Mixing the crystalline vanadium-phosphorous oxide obtained in the second step, or its calcined product, and silica sol into the aqueous solution obtained in the third step. Fourth step of obtaining slurry Spray drying the slurry obtained in the fourth step,
The gist of the invention is a method for producing vanadium-phosphorous oxide particles, which comprises a fifth step of firing, and the second invention comprises reacting phosphoric acid, an inorganic reducing agent, and vanadium pentoxide in an aqueous medium, A first step in which hydrothermal treatment is then performed to obtain a slurry containing crystalline vanadium-phosphorous oxide.The slurry obtained in the first step is diluted or concentrated as necessary, and phosphoric acid, reducing agent and pentaacid Second step of adding and dissolving water vanadium Third step of adding silica sol to the slurry obtained in the second step Spray drying the slurry obtained in the third step,
The gist of the present invention is a method for producing vanadium-phosphorous oxide particles, which includes a fourth step of firing. The present invention will be explained in detail below. In the first and second inventions of the present application, in an aqueous medium,
The first step is to react phosphoric acid, an inorganic reducing agent, and vanadium pentoxide, and then perform a hydrothermal treatment to obtain a slurry containing a crystalline vanadium-phosphorus oxide. The inorganic reducing agent used in the present invention is preferably hydrazine (usually commercially available as an aqueous solution of hydrazine hydrate) or its phosphate, and hydroxylamine or its phosphate, but is not particularly limited. However, other inorganic acid salts,
For example, salts leave halogen ions behind and are disadvantageous in terms of reactor material, so they are not preferred industrially. In addition, as an inorganic reducing agent, trivalent phosphorus compounds such as phosphorous acid have a slow reduction rate, and in order to make a homogeneous solution, it is necessary to boil and reflux the slurry containing vanadium pentoxide for a long time. The drawback is that the reducing agent is expensive and energy consumption is also large. Organic reducing agents such as oxalic acid and alcohol are also generally known as reducing agents. However, according to the results of studies conducted by the present inventors, hydrothermal synthesis in the presence of an excessive amount of organic compound is disadvantageous in terms of economy and crystal formation. For example, if 0.5 mol or more of oxalic acid is present per gram atom of vanadium, the crystal formation reaction will not proceed unless the hydrothermal synthesis conditions are made harsher. Water is generally used as the aqueous medium. Alcohol, carboxylic acid, ethers, if desired
A hydrophilic organic solvent such as ketones may be used in combination, but since the rate of reduction of vanadium is reduced, the amount used should be 50% by weight or less in the aqueous medium. The amount of phosphoric acid used is determined by the molar ratio of phosphorus atoms to vanadium atoms (hereinafter referred to as P/V) in the vanadium-phosphorus oxide particles that are the target product.
It is preferable to add in a range of 0.8 to 1.5. The phosphoric acid concentration in the aqueous medium is between 5 and 50% by weight, preferably between 5 and 35% by weight. If the concentration of phosphoric acid in the aqueous medium is too high, vanadium pentoxide may react with the phosphoric acid before it is reduced, and the viscosity of the solution increases significantly, making handling difficult. Moreover, if this concentration is too low, the reaction vessel may become too large, which may cause problems. The amount of the inorganic reducing agent used is the stoichiometric amount required to reduce pentavalent vanadium to tetravalent vanadium, and is usually used in a range of 95 to 120% of the stoichiometric amount. In the present invention, a method is preferred in which vanadium pentoxide is added and dissolved in an acidic aqueous medium in which phosphoric acid and an inorganic reducing agent are dissolved in advance. Generally, a method is known in which vanadium pentoxide is reduced in advance and then phosphoric acid is added for reaction. However, this method produces low-valent vanadium oxide, which has low reactivity with phosphoric acid, and also produces a homogeneous solution. As a result, a catalyst with sufficient catalytic activity may not be obtained. When vanadium pentoxide is added to an aqueous medium containing an inorganic reducing agent such as hydrazine or hydroxylamine and phosphoric acid, reduction proceeds with foaming, and a blue homogeneous solution containing tetravalent vanadium ions is eventually formed. . At this time, it generates heat by itself, but it may also be heated slightly from the outside. Alternatively, after the foaming has subsided, the solution may be boiled to complete the reaction. The time required to make a homogeneous solution is
Although it depends on the reaction amount, it is usually 5 minutes to 5 hours. If this solution is allowed to stand for a long time, undesirable precipitation may occur, so it must be immediately subjected to the next hydrothermal treatment. Note that a component for promoting the activity of the butane oxidation reaction may be added at a stage before the hydrothermal reaction is performed. Examples of the activity-promoting component include compounds such as iron, chromium, aluminum, titanium, cobalt, and magnesium. These compounds are not particularly limited as long as they are soluble in the solution obtained in the present invention, but preferably inorganic acid salts such as chlorides, sulfates, nitrates, and carbonates, and organic acids such as acetic acid and oxalic acid. Salt is an example. In the case of titanium, the use of peroxides is also possible. The timing of addition is not particularly limited as long as it is at a stage before hydrothermal treatment. The amount added should be adjusted to a range of 0.01 to 0.4 mol of metal per mol of vanadium element, and more preferably 0.02 to 0.2 mol. The above-mentioned metal components may be one kind or a mixture of two kinds if desired. In the present invention, the solution obtained by the above method is heated at 110°C to 250°C, preferably at 120°C in a substantially sealed container to prevent water evaporation.
Hydrothermal treatment is carried out at a temperature ranging from ℃ to 180℃. The hydrothermal treatment
It is preferable to carry out for about 0.5 to 200 hours. Hydrothermal treatment in this manner produces a pale blue slurry containing fine crystals. This crystal is vanadium-
It is a phosphorus-based oxide, and its main component is usually a compound having a main X-ray diffraction pattern (anticathode; Cu-Kα) as shown in Table 1 below. Table 1 2θ゜ (±0.2゜) Intensity ratio 15.7 100 19.6 50 24.2 40 27.1 45 28.8 25 30.4 80 This compound is a crystalline vanadium-phosphorus oxide described in the aforementioned Japanese Patent Application Laid-Open No. 51-95990. is the same as After completing this first step, the oxide is separated from the obtained slurry, or the oxide is not separated and the process proceeds to the second step. Below, the case of the first invention in which the slurry is separated will be described. From the slurry obtained in the first step, the crystalline oxide is separated by suitable means, the obtained aqueous solution is appropriately diluted or concentrated, and phosphoric acid, a reducing agent and vanadium pentoxide are added. Generally, it is obtained by adding and dissolving a reducing agent and vanadium pentoxide in an aqueous solution containing phosphoric acid. The reducing agent used here is not particularly limited, and includes inorganic reducing agents such as hydrazine hydrate, hydrochloride and phosphate of hydrazine or hydroxylamine, and organic reducing agents such as lactic acid and oxalic acid. The molar ratio of phosphorus atoms to vanadium atoms in an aqueous solution is
It is preferably in the range of 0.5 to 10. In addition, at this time,
It should be selected so that the P/V of the finally obtained granules is 0.8 to 1.5. The amount of reducing agent used is sufficient to reduce vanadium pentoxide. In an aqueous solution, vanadium and phosphorus are thought to exist as vanadyl phosphate, but vanadyl phosphate solutions are unstable, so if this aqueous solution needs to remain stable for a long time, Preferably, oxalic acid is present in the.
The amount is the molar ratio of oxalic acid to vanadium atoms, and is 1.2 or less, preferably in the range of 0.2 to 1.
Too much oxalic acid will have an unfavorable effect on the mechanical strength, bulk density, and active surface of the catalyst. Further, when oxalic acid is used as a reducing agent, this objective can be achieved by using an excess of oxalic acid so that the above amount of oxalic acid remains after completion of the reduction. The resulting aqueous solution has two major implications. For one thing, this aqueous solution has the effect of acting as a binder between the vanadium-phosphorous oxide and the catalyst carrier, and improves the strength of the catalyst. For one thing, it solves the problem of waste produced in the catalyst manufacturing process (first step), making it possible to rationalize the catalyst manufacturing process. Next, the vanadium-phosphorus oxide separated in the second step or its calcined product and silica sol as a catalyst carrier are mixed into this aqueous solution containing vanadium and phosphorus. The vanadium-phosphorous oxide separated in the second step may be one that is separately produced and stored in the first step. A fired product of vanadium-phosphorous oxide and an oxide fired at a temperature of 400 to 600°C.
It is preferable to carry out the reaction in the presence of air which may contain butenes or in an atmosphere of an inert gas such as argon or nitrogen. When an oxide exhibiting the X-ray diffraction peaks shown in Table 1 is fired, it changes into a crystal exhibiting the main X-ray diffraction peak (anticathode; Cu-Kα) as shown in Table 2. Table 2 2θ° (±0.2°) Intensity ratio 14.2 20 15.7 20 18.5 20 23.0 100 28.4 90 30.0 50 33.7 40 36.8 40 It is preferable to use this calcined product in terms of the strength and activity of the catalyst. It is preferable to use the silica sol directly as a 10 to 50% by weight solution, or to adjust the concentration in advance if necessary. The mixing ratio of the vanadium-phosphorus oxide, the aqueous solution containing vanadium and phosphorus, and the silica sol is preferably within the following range. However, the proportions are shown in dry weight %, and in the case of an aqueous solution containing vanadium and phosphorus, vanadium and phosphorus are converted into V ₂ O ₄
Calculated as the total amount of and P ₂ O ₅ . Vanadium-phosphorus oxide: aqueous solution = 20:80-80:20, aqueous solution: silica sol = 50:50-90:10, vanadium-phosphorus oxide: silica sol = 50:50-90:10
selected from the range. In the fifth step, the slurry thus obtained is spray-dried and calcined to obtain phosphorus-vanadium-based oxide particles useful as a catalyst with excellent fluidity, strength, and activity. The spray drying conditions are usually adjusted appropriately by adjusting the air volume and liquid supply volume.
The gas temperature in the drying area is preferably set in the range of 120 to 350°C, and the inlet temperature of the drying gas at this time is usually 200 to 350°C. Further, the amount of liquid supplied and the disk rotation speed are adjusted so that the average diameter of the catalyst particles after spray drying is about 30 to 100 microns, more preferably 40 to 70 microns. The granules obtained in the above manner have a particle size of 400 to 600
Fired in the °C range. At this time, it is preferable to carry out the firing in the presence of air that may contain butane or butenes, or in an inert gas atmosphere such as argon or nitrogen. As above, the first invention of the present application has been explained in detail, but the second invention can be carried out in exactly the same ratio and type of the compounds used, and in the end, it is substantially the same as the first invention. The same granules are obtained. The difference from the first invention is the second step of the second invention, in which the vanadium-phosphorus oxide is not separated, and phosphoric acid,
Add reducing agent and vanadium pentoxide. However, if necessary, a part of the vanadium-phosphorous oxide may be extracted or added. The quantitative ratio of phosphoric acid, reducing agent and vanadium pentoxide to be added is determined in the same manner as in the first invention with respect to the aqueous solution excluding the vanadium-phosphorus oxide in the slurry. Even if phosphoric acid, a reducing agent, and vanadium pentoxide are added in the presence of a vanadium-phosphorus oxide, the already formed vanadium-phosphorus oxide does not change. As detailed above, according to the present invention, carbon number 4
A vanadium-phosphorous oxide granule is obtained which is suitable as a fluidized catalyst for the oxidation of hydrocarbons, especially n-butane. The present invention will be explained below with reference to Examples. Example 1 (First step of the first and second inventions) In a jacketed container with a capacity of 100 and glass lined, water 24.6 and 85% phosphoric acid 14.156
1.73 kg of 85% hydrazine hydrate solution was added and stirred. Then vanadium pentoxide 10.635Kg
was added while being careful not to generate bubbles, and a uniform blue solution was obtained. After that, the temperature of the heating medium was increased, and after confirming that bubble generation had stopped, the container was sealed and the temperature was increased until the liquid temperature reached 120°C. The time required to raise the temperature was about 1 hour.
Heating was further continued at this temperature for 12 hours to complete the hydrothermal synthesis. When a small amount of the slurry was passed through and the pale blue precipitate was subjected to X-ray diffraction measurement, it was found that the X-ray spectrum shown in Table 1 was obtained. The composition formula of a solid is a summary of elemental analysis (V ₂ O ₄ ) (P ₂ O ₅ )
(2H ₂ O), and this compositional formula corresponds to a concentration of 40% by weight. Example 2 (Second and third steps of the first invention) The aqueous slurry obtained in Example 1 was filtered through a centrifugal filter to obtain about 27 kg of liquid and 23.1 kg of wet cake. The cake was dried in a hot air dryer at 170°C to constant weight. The liquid had a pale blue color, and the elution of tetravalent vanadyl ions was clear. Add 9.25 kg of 85% phosphoric acid and 8.9 kg of oxalic acid to this liquid,
The mixture was heated and dissolved, and then 6.46 kg of vanadium pentoxide was added little by little and dissolved. Example 3 (Fourth step of the first invention) 5.0 kg of the dry cake obtained in Example 2 and 13.7 kg of the solution were mixed with 5.0 kg of the 40% silica sol slurry, and thoroughly stirred for 40 minutes using a homogenizer.
The slurry exhibited high viscosity and at least some gelation progressed. The total concentration of oxide (V ₂ O ₄ +P ₂ O ₅ ) and crystalline oxide in the solution portion of the slurry was about 40% by weight. The ratio of the crystalline oxide to the solution portion of the oxide and silica sol in this slurry was 45/35/20. Example 4 (Fifth step of the first invention) The slurry obtained in the fourth step of Example 3 was spray-dried using a spray dryer. The slurry is
It is sprayed from a rotating disk at 15,000 rpm and dried by contact with heated air. The temperature of the drying air is 270℃ at the inlet, and the gas temperature at the outlet of the spray dryer is
It was 138℃. The obtained catalyst (P/V = 1.088) was activated by fluidized calcining at 500°C for 2 hours under a nitrogen stream, and then
It was classified and used for the reaction. Reaction Example 1 After activation of the catalyst, particles having a particle size of 25 to 88μ were classified using a sieve. The average particle size was 56μ. This 50 ml was charged into a small fluidized bed reactor. A mixed gas of n-butane and air at various concentrations was introduced into the reactor and reacted at GHSV500. The product was collected in water and quantified by potentiometric titration and gas chromatography of the waste gas. The reaction results are shown in Table-3.

[Table] Example 6 (Second invention) 622.55 g of 85% phosphoric acid, 73.6 g of 85% hydrazine hydrate aqueous solution and 2550 g of demineralized water were mixed in 10 beakers, and then 454.75 g of vanadium pentoxide was added.
Stirred. The temperature of the liquid rose to approximately 60°C as it bubbled, but once the bubbling had almost stopped, it was heated to a boiling point to complete the reduction. After boiling this liquid and concentrating the liquid weight to 2500g, transfer it to a 2.5 capacity autoclave.
The mixture was heated to 130°C in a closed container and subjected to hydrothermal treatment for 5 hours. The resulting viscous slurry is cooled and
Transferred again to 10 beakers with a small amount of water.
Next, 85% phosphoric acid 384.46g, oxalic acid 382.80g, water
600 ml and 276.16 g of vanadium pentoxide were added, and the temperature was slowly raised while stirring. The reduction proceeded with foaming, and the entire mixture turned into a blue slurry, which was then further boiled to complete the reduction. The entire slurry was concentrated to 3200 g. The total weight of the oxide (V ₂ O ₄ + P ₂ O ₅ ) in the solution portion and the weight of the crystalline oxide in the slurry thus obtained was 40%, and the crystalline oxidation portion and the solution component The weight ratio in terms of oxide is approximately 58:42. When a small amount of the slurry was passed through and subjected to X-ray diffraction measurement, the spectrum completely matched the spectrum shown in Table 1. This was the same spectrum as the crystals in the slurry obtained by hydrothermal treatment, and it was found that no change in the crystal structure occurred during the secondary dissolution process of vanadium pentoxide. Next, 1800 g of 30% concentration silica sol was added and thoroughly mixed using a homogenizer to prepare a viscous slurry for spray drying. After drying under the same conditions as in Example 4, the resulting catalyst was activated by firing at 350°C for 1 hour under air flow, then at 500°C under nitrogen flow for 2 hours, and then classified.
used in the reaction. The SiO ₂ content in the catalyst in terms of oxide is 30%. Example 7 A slurry containing a crystalline oxide was obtained in exactly the same manner as in Example 1, and then filtered through a centrifuge and a cake was dried. The mixture was ground into small pieces and fired in a firing tube under nitrogen atmosphere for 2 hours. The X-ray diffraction peak of this product matched those shown in Table-2. The resulting nodules approx.
18.0Kg was finely ground using a hammer mill. Next, 1180 g of 85% phosphoric acid and 800 g of oxalic acid were added to 3500 g of the liquid and dissolved by heating, and 576.6 g of vanadium pentoxide was added little by little and dissolved. Add 1785g of 40% silica sol solution to this, and finely ground oxide solid
1000 g was added and sufficiently stirred and mixed using a homogenizer to obtain a slurry for spray drying. After drying under the same conditions as in Example 4, the resulting catalyst was activated by firing in the same manner as in Example 7, and then classified and used in the reaction. _SiO2 content in the catalyst in terms of oxide is 25%
It is. Reaction Example 2 The catalysts of Examples 6 and 7 were classified in the same manner as in Reaction Example 1, and an activity test was conducted under the same conditions. The results are shown in Table 4.

【table】

Claims (1)

[Claims] 1. A first step in which phosphoric acid, an inorganic reducing agent, and vanadium pentoxide are reacted in an aqueous medium, followed by hydrothermal treatment to obtain a slurry containing a crystalline vanadium-phosphorus oxide. A second step of separating the vanadium-phosphorus oxide from the slurry obtained in the first step. The aqueous solution obtained in the second step after separation of the vanadium-phosphorus oxide is diluted or concentrated as necessary. A third step of adding and dissolving phosphoric acid, a reducing agent, and vanadium pentoxide.The crystalline vanadium-phosphorous oxide obtained in the second step, or its calcined product, and silica sol are added to the aqueous solution obtained in the third step. Fourth step of mixing to obtain slurry Spray drying the slurry obtained in the fourth step,
A method for producing vanadium-phosphorous oxide particles, comprising a fifth step of firing. 2. The method according to claim 1, wherein the molar ratio of phosphorus atoms to vanadium atoms in the vanadium-phosphorous oxide particles obtained in the fifth step is 0.8 to 1.5. 3. The method according to claim 1, wherein the molar ratio of phosphorus atoms to vanadium atoms in the aqueous solution obtained in the third step is 0.5 to 10. 4. A first step in which phosphoric acid, an inorganic reducing agent, and vanadium pentoxide are reacted in an aqueous medium, followed by hydrothermal treatment to obtain a slurry containing a crystalline vanadium-phosphorus oxide. A second step in which the slurry obtained in the first step is diluted or concentrated as necessary, and phosphoric acid, a reducing agent, and vanadium pentoxide are added and dissolved. A third step of adding silica sol to the slurry obtained in the second step. Spray drying the slurry obtained in the third step,
A method for producing vanadium-phosphorous oxide particles, comprising a fourth step of firing. 5. The method according to claim 4, wherein the molar ratio of phosphorus atoms to vanadium atoms in the vanadium-phosphorous oxide particles obtained in the fourth step is 0.8 to 15. 6 The molar ratio of phosphorus atoms to vanadium atoms in the solution portion in the slurry obtained in the second step is
5. The method according to claim 4, characterized in that it is between 0.5 and 10.