JPH0424101B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a catalyst composition. More specifically, the present invention relates to a method for producing a catalyst composition suitable for producing maleic anhydride by oxidizing n-butane. A composite oxide containing vanadium and phosphorus as essential components is effective in a method for producing maleic anhydride by vapor phase oxidation of hydrocarbons having 4 carbon atoms, especially n-butane, n-butene, butadiene, etc. Are known. (US Pat. No. 3,293,268) It has also been reported that crystalline vanadyl phosphate ((VO ₂ )P ₂ O ₇ ) is effective as an active ingredient in this catalyst. [E. Bordles, P. Courtine, Journal of Catalysis (E. Bordles, P. Courtine, J. Catal.) 57, 236
(1979)] The crystalline phase of this compound can be identified by its characteristic X-ray diffraction pattern as shown in Table 1 below. Table-1 (VO) ₂ P ₂ O ₇ X-ray diffraction (Anticathode Cu-Kα) Main peak 2θ° (±0.2°) Intensification 14.2 20 15.7 20 18.5 20 23.0 100 28.4 90 30.0 50 33.7 40 36.8 40 lines According to the findings of the inventors, the crystal phase of this compound has considerably higher activity as a gas phase oxidation catalyst for n-butane and n-butenes than amorphous composite oxide catalysts based on conventional production methods. , especially for the oxidation of butane, the reaction proceeds even at temperatures as low as 100°C. Therefore, it is preferable in terms of the process to use catalytically active species having the X-ray diffraction peaks shown in Table 1 above. On the other hand, the reaction of producing maleic anhydride through gas phase oxidation from hydrocarbons having 4 carbon atoms is a strongly exothermic reaction including complete oxidation (i.e., production of carbon monoxide and carbon dioxide), which is a side reaction, and is energy efficient. It has been thought that the fluidized bed catalytic oxidation reaction is suitable because of the low explosive limit concentration of raw material hydrocarbons in air. Catalysts developed for this purpose have been prepared, for example, by spraying and drying a mixture containing vanadyl oxalate solution, phosphoric acid, silica sol, and appropriate activity-promoting components. (British Patent No. 1285075, etc.) Although the catalyst obtained in this way is effective for oxidizing butene, butadiene, etc., it is not sufficiently active for oxidizing butane, and usually requires a reaction temperature of 500°C or higher. do. There have also been some reports on fluidized bed catalysts for the oxidation of butane. for example,
JP-A-49-126587 discloses an example in which a pentavalent vanadium compound is brought into contact with a trivalent phosphorus compound to form a composite oxide, which is then ground into a fine powder and applied to a flow reaction. is listed. Although this method makes it possible to extract crystalline active ingredients and improve the activity, it is not sufficient in terms of catalyst strength and fluidity. Regarding the pulverized fluidized bed reaction using such fine powder of catalytically active components, Japanese Patent Application Laid-open No. 50-8788 and Japanese Patent Application Laid-open No. 56-878
-33038 etc. also pointed out the possibility, JP-A-56-
No. 65635 also points out the possibility of producing a fluidized bed catalyst by attaching a composite oxide to a carrier. As a result of extensive research aimed at developing a catalyst for gas phase oxidation of n-butane in a fluidized bed, the present inventors discovered that a special crystalline oxide containing vanadium and phosphorus as the first component, a second It was discovered that a catalyst with excellent strength and fluidity could be produced by preparing a slurry by mixing an aqueous solution containing vanadium and phosphorus as components and silica sol as a third component, spraying and drying the slurry, and completed the present invention. It is. The present invention will be explained in detail below. In the present invention, as a first component, a composite oxide containing substantially tetravalent vanadium and pentavalent phosphorus, which exhibits specific X-ray diffraction peaks, that is, the main X-ray diffraction peaks shown in Table 1, is used. use. This compound is known, usually by first preparing a precursor,
It can be manufactured by firing this. The following methods are known as methods for producing precursors. A solution containing tetravalent vanadium ions is prepared by reducing pentavalent panadium such as vanadium pentoxide in a non-oxidizing acidic solution such as a hydrochloric acid solution in combination with a reducing agent such as oxalic acid, A method in which the soluble vanadium-phosphorus complex produced after reacting with phosphoric acid is precipitated by adding water.
-95990), a pentavalent vanadium compound such as vanadium pentoxide and phosphoric acid are reacted in an aqueous medium in the presence of a reducing agent such as hydrazine hydrochloride or hydroxylamine hydrochloride, and concentrated or evaporated to dryness. Method for obtaining crystals by solidifying
45815), or a method in which vanadium pentoxide is reduced in an organic medium such as ethanol, isopropanol, or glycerol, reacted with phosphoric anhydride, and azeotropically dehydrated with a solvent such as benzene to precipitate crystals (U.S. Pat. 4283288) etc. are known. A precursor of the complex oxide, which is the first component, can be obtained by any of the above methods. This precursor exhibits the main X-ray diffraction peaks shown in Table 2 below. Table 2 Principal X-ray diffraction of the precursor of the first component (Anticathode Cu-
Kα) 2θ° (±0.2°) Strengthening 15.7 100 19.6 50 24.2 40 27.1 45 28.8 25 30.4 80 Although it is possible to use this precursor as the first component in the present invention, it is difficult to Invention is better. Note that the precursor can be represented by the composition formula (V ₂ O ₄ ) (P ₂ O ₅ ) (2H ₂ O). Therefore, the ratio of phosphorus to vanadium is P/V atomic ratio, which is logically 1.0, so vanadium compounds and phosphorus compounds have P/V atomic ratios of 1.0.
It is preferable to carry out the reaction within the range of 0.8 to 1.25 in terms of atomic ratio. When this precursor is calcined in the range of 400° to 600°C in the presence of butane or air containing butene or in an inert gas atmosphere such as argon or nitrogen, the main X-rays shown in Table 1 used in the present invention A first component having a diffraction peak is obtained. Further, the first component used in the present invention may be partially substituted with various metal ions having a small difference in ionic radius from vanadium ions. Such metal ions include iron, chromium, aluminum,
Ions such as titanium, cobalt, and magnesium are mentioned. When such a composite oxide partially substituted with metal ions is used as a catalyst, it can significantly improve the activity and stabilize the activity. The substitution ratio is 0.005 to 0.4 mole of metal per mole of vanadium element, more preferably 0.05
~0.2 mol. A method for introducing such other metal ions into a composite oxide is to introduce these metal ions into inorganic salts such as hydrochloride, sulfate, nitrate, carbonate, etc. during the production of the composite oxide precursor. An example is a method of adding it in the form of an organic salt such as an acid salt. The X-ray diffraction pattern of the substituted solid solution type composite oxide thus obtained is slightly shifted from the peaks shown in Table 1, but the 2θ° is within ±0.2°. It is best to pulverize the first component in advance before producing the slurry, e.g.
Pulverize to a particle size of 10μ or less, more preferably 5μ or less (measured by Coulter Counter method, etc.). For such treatment, machines well known to those skilled in the art, such as hammer mills, jet mills, colloid mills, sand grinders, etc., can be used, and either wet or dry methods may be employed. The aqueous solution containing vanadium and phosphorus as the second component in the present invention usually contains substantially tetravalent vanadium and pentavalent phosphorus, and it is preferable that at least a part of the vanadium be present as vanadium phosphate. This second component has an effect as a binder between the composite oxide of the first component and the silica sol as a carrier of the third component, and contributes to improving the fluidity and strength of the fluidized catalyst. Although the method for producing such an aqueous solution is not particularly limited, some examples are shown below. Generally, it is obtained by adding and dissolving a reducing agent and vanadium pentoxide in an aqueous solution containing phosphoric acid. The molar ratio of elemental phosphorus to elemental vanadium in the aqueous solution is preferably in the range of 0.5 to 10. Generally, aqueous solutions containing vanadium phosphate are unstable and it may be difficult to keep them stable for long periods of time, so oxalic acid can be present to stabilize the aqueous solution. The amount thereof is a molar ratio of oxalic acid to elemental vanadium of 1.2 or less, preferably in the range of 0.2 to 1. If the amount of oxalic acid is too large, it will have an unfavorable effect on the mechanical strength, bulk density and active surface of the catalyst. In other words, a range in which the molar ratio of oxalic acid to vanadium element is 1.2 or less can be said to be a range in which vanadyl oxalate is not formed. Specific examples of methods for producing aqueous solutions include the following methods. First, vanadium pentoxide is added to an aqueous solution containing phosphoric acid and oxalic acid so that the molar ratio of oxalic acid to vanadium element is 1.7 or less and preferably 0.7 or more to contain vanadyl phosphate and oxalic acid. This is a method of making an aqueous solution. Specifically, it is produced by dissolving oxalic acid in an acidic aqueous medium containing phosphoric acid, and adding vanadium pentoxide while maintaining the temperature at which reduction proceeds by slight heating. According to this method, after completion, 1.2 moles or less of oxalic acid will be present relative to elemental vanadium. Second, an acidic aqueous solution containing phosphoric acid is treated with a reducing agent other than oxalic acid, preferably an inorganic reducing agent such as hydrazine hydrate, hydrochloride or phosphate of hydrazine or hydroxylamine, or an organic reducing agent such as lactic acid. One or a mixture of two or more selected from these agents is added, and vanadium pentoxide is then added for reduction to obtain a homogeneous aqueous solution containing vanadyl phosphate. After this, oxalic acid is preferably added. The third method is to mix vanadium pentoxide, phosphoric acid and phosphorous acid in an aqueous medium and convert the mixture into tetravalent vanadium ions by the reducing action of the phosphorous acid. When the aqueous solution containing vanadyl phosphate obtained by this method is left to stand, a crystalline solid that gives a characteristic X-ray diffraction spectrum as shown in Table 3 below precipitates out.

[Table] Such precipitation of crystalline solids is not preferable from the purpose of the present invention, and when it is necessary to keep the aqueous solution stable for a long time, it is preferable to add oxalic acid. The aqueous solution containing vanadium and phosphorus described above may contain an organic solvent such as alcohol, ketone, or ether, if necessary. In the present invention, a catalyst composition is produced by mixing the above-described first and second components and silica sol as a third component to prepare a slurry, and spray drying the slurry. The silica sol is prepared in advance as a 10-50% by weight slurry, mixed with the first component and the second component, and stirred to form a uniform slurry. The ratio of the first component, second component and third component is dry weight %, first component: second component = 20:80
Selected within the range of ~80:20 second component: third component = 50:50 ~ 90:10 first component: third component = 50:50 ~ 90:10. Note that the dry weight of the second component can be calculated by assuming vanadium and phosphorus as V ₂ O ₄ and P ₂ O ₅ . If the amounts of the first component and the second component are too small relative to the third component, the catalyst strength will improve, but
A decrease in activity is observed. Also, the amount of the second component is
When the content of the first component is below the above range, the catalyst strength tends to decrease. The slurry thus obtained can be spray-dried to yield a catalyst composition with excellent fluidity and strength. The conditions for spray drying are usually to adjust the air volume and liquid supply amount appropriately to maintain the temperature of the gas in the drying area.
It is preferable to set the temperature 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 number of rotations of the disk 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 catalyst composition obtained as described above has a 400%
It is more preferable to use it after firing at a temperature in the range of ~600°C from the viewpoint of catalytic activity. At this time, it is preferable to carry out the firing in the presence of air containing butane or butenes, or in an inert gas atmosphere such as argon or nitrogen. The catalyst composition obtained as described above has excellent fluidity, strength, and activity, and contains hydrocarbons having 4 carbon atoms,
In particular, it is suitably used as a catalyst for producing maleic anhydride by oxidizing n-butane. The present invention will be explained below using examples. Example 1 (Synthesis of the first component) Put 40% of demineralized water into a 100-volume stirring tank lined with glass, and add phosphoric acid (85%, special reagent grade).
9.22Kg, hydrazine hydrochloride 1.30Kg - hydrazine hydrochloride
550g was added and dissolved. After the solution was heated to 75° C., 7.28 kg of vanadium pentoxide was added little by little while stirring, and after the entire amount was added, the solution was further boiled for 1 hour to complete the reduction. After concentrating this liquid to about 1/2 of the liquid volume using a rotary evaporator under reduced pressure,
The mixture was placed in six evaporation containers and evaporated to dryness at 170°C.
After confirming that a constant weight had been reached, the solid was crushed, boiled and washed with water, and filtered to completely remove residual hydrochloric acid. After washing with water, it was dried again at 170°C and finely ground in a hammer mill to obtain a precursor of the first component having an atomic ratio of P/V=1. A portion of this was fired at 500°C for 2 hours under a nitrogen stream, and then at the same temperature for 1 hour under a stream of air. As a result of X-ray diffraction measurement, the obtained first component is shown in Table 1.
It was confirmed that the peak shown in This was finely ground again using a hammer mill and used for slurry preparation. Example 2 (Synthesis of second component) Phosphoric acid (85%, special reagent grade) 1865 in 1000 ml of demineralized water
Dissolve g and 1500 g of oxalic acid and heat the solution to 80℃.
It was heated to Next, 1082 g of vanadium pentoxide was added little by little and dissolved. The P/V atomic ratio of the solution was 1.36, and it was a slightly viscous blue homogeneous solution. The liquid weight was made 4.75Kg by slight concentration, and the converted oxide concentration of [V ₂ O ₄ + P ₂ O ₅ ] was 45.0.
It was adjusted to % by weight. Example 3 (Production of fluidized catalyst by spray drying) The first component obtained in Example 1, the second component obtained in Example 2, and the third component silica sol slurry (SiO ₂ concentration 20% by weight) were mixed. , prepared a slurry for spray drying. The mixing amount is as follows. First component: 1.467Kg Second component: 1.087Kg Third component: 2.446Kg After mixing, the mixture was sufficiently uniformly mixed using a homogenizer for 40 minutes to obtain a slurry for spray drying. 15000rpm
It was sprayed from a high-speed rotating disk, dried, and dried with high-temperature drying air (inlet temperature 278°C). The amount of liquid supplied was 16/hour. The obtained catalyst was further heated to 500℃,
After calcination under a nitrogen stream for 2 hours, a part with a particle size of 25 to 88 μm was taken out using a sieve and subjected to an activity test and a strength test. The strength was determined by colliding catalyst particles against a SUB metal plate at high speed in a fluid state, measuring the crushing loss within 2 hours, and displaying the result as an index of mechanical strength. This value becomes smaller for stronger catalysts. Comparative Example In Example 3, instead of the first component, a precursor having an atomic ratio of P/V=1 obtained in Example 1 was used.
Except that 1.639Kg was used without firing.
A catalyst of a comparative example was obtained by spray drying in exactly the same manner, followed by similar firing and sieving operations. Reaction Example An activity test was carried out using an air mixture containing 4 mol % of n-butane, 20 ml of catalyst, and GHSV500 in a small fluidized bed reactor. The results are shown in Table-4. It is clear that the catalyst strength and activity are improved when the precursor is pre-calcined.

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Claims (1)

[Claims] 1. A crystalline composite oxide containing vanadium and phosphorus as a first component and exhibiting the following characteristic X-ray diffraction peaks, an aqueous solution containing vanadium and phosphorus as a second component, and A method for producing a catalyst composition, which comprises mixing silica sol as three components to prepare a slurry, and spray drying the slurry. 2θ° (±0.2°) (Anticathode Cu-Kα) 14.2 15.7 18.5 23.0 28.4 30.0 33.7 36.8 2 Claim 1, characterized in that the second component is an aqueous solution containing vanadyl phosphate the method of. 3 The mixing ratio of the first component, second component, and third component is dry weight %. First component: second component = 20:80 to 80:20 second component: third component = 50:50 to 90: 10. The method according to claim 1, wherein the ratio of first component to third component is in the range of 50:50 to 90:10. 4. The method according to claim 1, wherein the first component vanadium is substantially tetravalent. 5. The method according to claim 1 or 2, wherein the second component vanadium is substantially tetravalent.