JPH0424104B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing an oxidation catalyst, and particularly to a method for producing a catalyst suitable for producing maleic anhydride by catalytic gas phase oxidation of n-butane. A composition containing vanadium, phosphorus and oxygen,
It is known that it is an effective catalyst for producing maleic anhydride by catalytic gas phase oxidation of butane, butene, butadiene, etc., and various proposals have been made regarding its production method. Vanadyl pyrophosphate ((VO) ₂ P ₂ O ₇ ), which is a crystalline compound exhibiting the characteristic X-ray diffraction spectrum shown in Table 1 below, is particularly effective for producing maleic anhydride from n-butane. (E.Bordes, P.Courtine, J.Catal.
57, 236 (1979)). Table 1 (VO) X-ray diffraction spectrum of ₂ P ₂ O ₇ (Anticathode: Cu-K
α) 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 On the other hand, production of maleic anhydride by catalytic vapor phase oxidation of n-butane Since this is accompanied by a large amount of heat generation, a fluidized bed reaction system is considered to be appropriate. The present invention provides a method for producing a catalyst that contains phosphorus and vanadium, provides a diffraction spectrum consistent with the X-ray diffraction spectrum of Table 1, and is suitable for use in a fluidized bed. According to the present invention, when an aqueous solution containing pentavalent phosphorus and tetravalent vanadium is heated to 110 to 250°C, a vanadium-phosphorus crystalline material exhibiting a characteristic X-ray diffraction spectrum shown in Table 2 below can be obtained. The first step is to obtain an aqueous slurry containing oxides, the second step is to spray dry this slurry to obtain a finely powdered solid, and this finely powdered solid is, if necessary, calcined, then treated with phosphoric acid and tetravalent A third step of mixing with a vanadyl phosphate solution containing vanadium and at least a part of which forms vanadyl phosphate and silica sol to form a homogeneous slurry, a fourth step of spray drying this slurry, and a fourth step. By sequentially performing each step of the fifth step of calcining the solid particles produced in step 1, a vanadium-phosphorous oxidation catalyst that exhibits a spectrum that matches the X-ray diffraction spectrum shown in Table 1 and is suitable for use in a fluidized bed. can be manufactured. Table 2 X-ray diffraction spectrum (Anticathode: Cu-Kα) 2θ (±0.2°) Intensity ratio 15.7° 100 19.6° 50 24.2° 40 27.0° 45 28.8° 25 30.4° 80 (Others: 18.5°, 21.8°, (A weak peak with an intensity ratio of about 10 to 20 is seen at 32.2°) To explain the present invention in detail, in the first step, the present invention contains tetravalent vanadium and pentavalent phosphorus, and is shown in Table 2. It is produced by hydrothermal synthesis of a crystalline composite oxide that gives the X-ray diffraction spectrum shown below. Phosphorus-vanadium-based crystalline composite oxides that give the X-ray diffraction spectra shown in Table 2 are known, and several manufacturing methods have been reported (Japanese Patent Application Laid-open Nos. 51-95990, 56-45815, US
(See No. P4283288). Unlike these known methods, the method of the present invention produces the above-mentioned crystalline composite oxide by hydrothermal synthesis. According to this method, the average particle diameter by Coulter counter method is 0.2~
Extremely fine crystals of 10μ are produced. Therefore, it is not always easy to separate by filtration, but spray drying produces a fine powder solid. Therefore, after solidifying in this manner, it is rather convenient to add other components to form a slurry again and spray dry it to obtain a catalyst. Hydrothermal synthesis involves reacting a pentavalent vanadium compound such as vanadium pentoxide in an acidic aqueous solution containing phosphoric acid and a non-halogen reducing agent such as hydrazine hydrate. This is then heated in a closed container at 110-250°C, preferably at 120-250°C.
This is done by holding the temperature at 180°C for about 0.5 to 200 hours. (See Japanese Patent Application No. 57-32110). The concentration of phosphoric acid in the acidic aqueous solution is 5-50% (by weight), preferably 5-35% (by weight). If the phosphoric acid concentration is too high, vanadium pentoxide may react with the phosphoric acid before being reduced, and the liquid viscosity will also become significantly high, making handling difficult. In addition, the amount of reducing agent used is the stoichiometric amount required to reduce pentavalent vanadium to tetravalent vanadium, and usually 95 to 120
Used in a range of %. As the reducing agent, non-halogen inorganic reducing agents such as hydrazine, hydroxylamine, or phosphates thereof are preferred. Organic reducing agents such as oxalic acid may also be used if desired, but are not industrially advantageous. Note that the reduction of vanadium should be carried out by adding vanadium pentoxide to an acidic aqueous solution prepared by dissolving phosphoric acid and a reducing agent in advance, and this makes it possible to produce crystals with good purity. can.
During hydrothermal synthesis, it is preferable to add a small amount of finely ground seed crystals to the aqueous solution. The crystalline composite oxide produced by this hydrothermal synthesis is approximately (V ₂ O ₄ )
It can be represented by the composition formula (P ₂ O ₅ )(2H ₂ O). Therefore, the ratio of phosphorus to vanadium is logically 1.0 in P/V atomic ratio, so vanadium compounds and phosphorus compounds have a P/V atomic ratio of 0.8 to 1.
It is preferable to carry out the reaction within a range of 1.25. Further, vanadium in this crystalline composite oxide may be partially substituted with various metal ions having a small difference in ionic radius from vanadium ions. Examples of such metal ions include ions of iron, chromium, aluminum, titanium, cobalt, magnesium, and the like. 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 such that the ratio of these metals in the crystalline composite oxide is 0.005 to 0.4 as metal per gram atom of vanadium, more preferably
It is selected in the range of 0.01 to 0.2 gram atom.
In order to introduce such other metal ions into the composite oxide, these metal ions can be added to the hydrothermal synthesis system using inorganic salts such as hydrochloride, sulfate, nitrate, carbonate, etc., or organic salts such as oxalate. One method is to add it in the form of The X-ray diffraction pattern of the substituted solid solution type composite oxide thus obtained is slightly shifted from the peaks shown in Table 2, but the 2θ° is within ±0.2°. The slurry obtained in the first step is solidified by spray drying in the second step. As mentioned above, since the crystalline composite oxide produced in the first step is extremely fine, it is not necessarily easy to separate the solid by filtration, but it is more convenient for spray drying. Spray drying can be carried out according to conventional methods. The inlet temperature of the drying gas is usually 200-350°C, and the outlet temperature is 100-350°C.
Although the fine powder solid obtained by spray drying can be used as is for the next slurry preparation, it is preferable to use it for the slurry preparation after baking. Firing is usually carried out in an inert gas atmosphere such as argon or nitrogen, but it can also be carried out in air. Firing usually takes place at 300-700℃, preferably
It is carried out at 450-600℃. This calcination may change the crystalline phase and result in a composite oxide having the X-ray diffraction pattern shown in Table 1, but this is preferable from the standpoint of catalytic performance. Therefore, usually the first
It is fired until it shows the X-ray diffraction pattern shown in the table. Note that when firing in air, care must be taken because excessive firing will further change the X-ray diffraction pattern shown in Table 1. Such excessive calcination does not provide the excellent performance catalyst intended by the present invention. In the present invention, the vanadyl phosphate solution used for slurry preparation in the third step contains tetravalent vanadium and pentavalent phosphorus, at least a part of which exists as vanadyl phosphate. This solution has an effect as a binder between the fine powder solid obtained in the second step or its calcined product and the silica sol as a carrier described later, and contributes to improving the fluidity and strength of the fluidized catalyst. Although the method for producing this 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 a pentavalent phosphorus compound, for example, phosphoric acid. The atomic ratio of phosphorus element to vanadium element in the aqueous solution is preferably in the range of 0.5 to 10. Generally, aqueous solutions containing vanadyl 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 is the molar ratio of oxalic acid to vanadium atoms.
It is 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 atoms 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 such that the molar ratio of oxalic acid to vanadium atoms is 1.7 or less, and preferably 0.7 or more, and vanadium pentoxide is added to the aqueous solution containing phosphoric acid and oxalic acid. and a method of preparing an aqueous solution containing oxalic acid. 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 the completion of reduction, for vanadium atoms,
There will be less than 1.2 moles of oxalic acid present. Second, a reducing agent other than oxalic acid, preferably hydrazine hydrate, is added to the acidic aqueous solution containing phosphoric acid.
hydrazine or hydroxylamine hydrochloride,
Add one or a mixture of two or more selected from inorganic reducing agents such as phosphates and organic reducing agents such as lactic acid, and then reduce by adding vanadium pentoxide to obtain a homogeneous aqueous solution containing vanadyl phosphate. obtain.
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. From the aqueous solution containing vanadyl phosphate obtained by this method, when 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 vanadyl phosphate solution containing vanadium and phosphorus may contain an organic solvent such as alcohol, ketone, or ether, if necessary. In the present invention, a slurry is prepared by mixing the fine powder solid obtained in the second step or the baked product thereof with the vanadyl phosphate solution and silica sol, and then spray-dried. Silica sol is Akajime 10-50
It is prepared as a concentration of % by weight, mixed with the fine powder solid and vanadyl phosphate solution, and stirred to form a homogeneous slurry. The ratio of fine powder solid, vanadyl phosphate solution and silica sol is 20:80 to 80: fine powder solid: vanadyl phosphate solution in dry weight%.
20, Vanadyl phosphate solution: Silica sol = 50:50~
90:10, fine powder solid: silica sol = 50:50-90:
Selected within a range of 10. The dry weight of the vanadyl phosphate solution _{is the
and P2O5} . If the amount of finely divided solid and vanadyl phosphate solution is too small relative to the silica sol, the catalyst strength will be improved but the activity will be decreased. Furthermore, if the amount of the vanadyl phosphate solution is less than the above range relative to the fine powder solid, the catalyst strength tends to decrease. When mixing fine powder solids, vanadyl phosphate solution, and silica sol, use a wet mixing device such as a ball mill, rod mill, stirring mill, sand grinder, ultra homo mixer, ultra tarax, or ultrasonic mill to make the slurry as homogeneous as possible. At the same time, it is preferable to make the fine powder solid as fine as possible. The slurry thus prepared is then spray dried into spherical solid particles. The conditions for spray drying are usually that the drying gas inlet temperature is between 200 and 350.
℃, and the outlet temperature should be between 100 and 350℃. In addition, by adjusting the liquid supply amount and disk rotation speed, the average particle diameter of solid particles obtained by spray drying was adjusted to 30.
It should be in the range of ~100 microns. A more preferred range of average particle size is 40 to 70 microns. The solid particles obtained as described above are further calcined to form an oxidation catalyst. Firing is usually 400-700
℃, preferably 450-600℃. As the firing atmosphere, air or air containing organic substances such as butane and butenes can be used. Firing may also be carried out in an inert gas atmosphere such as argon or nitrogen. By this firing, the crystalline oxide produced in the first step in the solid particles is changed into a composite oxide giving the X-ray diffraction pattern shown in Table 1. The oxidation catalyst obtained by the method of the present invention has excellent fluidity, strength and activity, and is suitable as a catalyst for producing maleic anhydride by oxidizing a hydrocarbon having 4 carbon atoms, particularly n-butane. EXAMPLES The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited to the following Examples unless it exceeds the gist thereof. Example 1 <Manufacture of crystalline oxide slurry> 38.0 kg of demineralized water and 85% phosphoric acid were placed in a pressure-resistant container with a jacket lined with 100% glass.
21.83Kg and 2.85Kg of 80% hydrazine hydrate solution were charged, and then vanadium pentoxide powder was added while stirring.
16.40Kg was added little by little, being careful not to foam. During this time, reduce the temperature rise due to heat generation and keep the liquid temperature between 60 and 80.
To maintain the temperature at °C, a low-temperature heating medium was circulated inside the jacket to remove heat. The addition of vanadium pentoxide was completed in about 4 hours, and a blue vanadyl phosphate solution was obtained. 1.0 kg of seed crystals were added to this, and then a heating medium at 160°C was circulated inside the jacket to heat it. The liquid temperature was raised to 140°C in 2 hours, and hydrothermal treatment was continued for 10 hours. During this time, the pressure was approximately 2.4KG. 90
After cooling to ℃, 10.3 kg of demineralized water was added to adjust the solid concentration in the slurry to about 35%, and the slurry was extracted. When this solid was subjected to X-ray diffraction measurement, it was found that it exhibited the main diffraction peaks shown in Table 2, confirming that it was a pure crystalline oxide. Furthermore, when the particle size distribution of the solids in the slurry was examined using the Coulter Counter method, it was found that the average particle size was 0.7μ. <Production of finely powdered solid> The above slurry was treated with Ultra Turrax for 30 minutes and spray-dried using a high-speed rotating disk type spray dryer to obtain a finely divided solid. The drying conditions were a gas inlet temperature of 360°C and an outlet temperature of 150-160°C. The particle size of the resulting fine powder is approximately 5-50μ
However, it has low strength and is suitable for use in the next step. Moreover, the P/V atomic ratio of this material is 1.05. <Manufacture of vanadyl phosphate solution) 6.929 kg of 85% phosphoric acid and 5.987 kg of oxalic acid (H ₂ C ₂ O ₄ .2H ₂ O) were added to 60 kg of demineralized water and dissolved while heating to 80° C. and stirring. Then vanadium pentoxide
Add 4.319Kg little by little, being careful not to foam.
After dissolving, it was allowed to cool. Add water to make the total amount 82.8Kg
And so. This solution has a P/V atomic ratio of 1.266 and contains 0.5 gmol of oxalic acid per gram atom of vanadium. Moreover, this solution was stable and did not cause solid precipitation even after being stored at room temperature for one month. <Preparation of slurry for spray drying, spray drying and calcination> Add 40 kg of vanadyl phosphate solution prepared above to 40 kg of vanadyl phosphate solution prepared above.
Add 6.20Kg of % silica sol solution while stirring,
Then, 3.865 kg of the fine powder solid obtained above was added.
This slurry was processed using a continuous wet pulverizer, sufficiently homogenized, and then sprayed using a spray dryer. The solids concentration of the slurry was 20%, the drying gas inlet temperature was 210°C, and the outlet temperature was 130°C. The average particle diameter of the obtained particles was 61μ, and both sphericity and strength were good. These spray-dried particles are heated to 500°C under nitrogen flow.
It was calcined for 2 hours and used as a catalyst. The X-ray diffraction spectrum of this catalyst has the diffraction peak groups shown in Table 1, indicating that a (VO) ₂ P ₂ O ₇ crystal phase is formed. Moreover, the intensity of this diffraction peak almost matched the intensity expected from the amount of fine powder solid used for catalyst preparation. Therefore, in the catalyst preparation process, it is thought that the crystalline phase produced by hydrothermal synthesis in the first step changed to the crystalline phase _{of V02P2O7} , and the vanadyl phosphate solution used as a binder _. It is considered that there is no change to the (VO) ₂ P ₂ O ₇ crystal phase. Example 2 The finely powdered solid obtained in Example 1 was divided into 2-capacity porcelain dishes and fired in a Matsukuru furnace. The inside of the furnace is sufficiently replaced with nitrogen before heating up, and while nitrogen is being circulated,
The temperature was maintained at 500°C for 2 hours, and then the temperature was lowered after gradually introducing air and maintaining the temperature at 500°C for another hour. The X-ray diffraction peak of the fine powder solid after firing is
It is the same as the X-ray diffraction peak shown in Table 1,
It was found that the crystal phase changed to (VO) ₂ P ₂ O ₇ . A catalyst was prepared by preparing a slurry, spray drying, and calcination in exactly the same manner as in Example 1, except that 3.47 kg of the finely powdered solid after calcination was used. The average particle diameter of the particles obtained by spray drying was 59μ, and both sphericity and strength were good. Further, the X-ray diffraction spectrum of the catalyst was almost the same as that of Example 1. Test example: 20 ml of catalyst (particle size 44~
116μ) and air containing 3% n-butane.
It was introduced into a reactor and reacted so as to give GHSV500. The product was absorbed into water, and the reaction results were determined by potentiometric titration of the aqueous solution and gas chromatographic analysis of the waste gas. The results are shown in Table 4.

【table】

Claims (1)

[Claims] 1. A vanadium-phosphorus crystalline oxide that exhibits the characteristic X-ray diffraction spectrum shown below when an aqueous solution containing pentavalent phosphorus and tetravalent vanadium is heated to 100 to 250°C. The first step is to obtain an aqueous slurry containing phosphoric acid and tetravalent vanadium. a third step of mixing with a vanadyl phosphate solution containing and at least a part of which forms vanadyl phosphate and silica sol to form a homogeneous slurry;
A method for producing a vanadium-phosphorus oxidation catalyst, comprising the steps of a fourth step of spray drying this slurry and a fifth step of calcining the solid particles produced in the fourth step. X-ray diffraction spectrum (Anticathode: Cu-Kα) 2θ (±0.2°) 15.7° 19.6° 24.2° 27.0° 28.8° 30.4° 2 The vanadyl phosphate solution in the third step contains less than 1.2 gmol per gram atom of vanadium The method according to claim 1, characterized in that it contains oxalic acid. 3. The method according to claim 1 or 2, wherein the P/V atomic ratio of the vanadyl phosphate solution in the third step is in the range of 0.5 to 10. 4 The P/V atomic ratio of the fired product obtained in the fifth step is
The method according to any one of claims 1 to 3, characterized in that it is in the range of 0.8 to 1.5. 5 The fine powder solid obtained in the second step was heated to 300 to 700
Claims 1 to 4, characterized in that the slurry is fired at ℃ and used for slurry preparation in the third step.
The method described in any of the paragraphs.