JPH0424102B2 - - 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 an oxidation catalyst suitable for producing maleic anhydride from 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. (U.S. Patent No. 3293268) 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. Journal of Catalysis (E.
Bordes, P. Courtine, J. Catal.) 57, 236 (1979)]
This compound can be identified by its crystalline phase exhibiting an 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 crystalline phase of this compound has significantly higher activity as a gas phase oxidation catalyst for n-butane and n-butenes than amorphous composite oxide catalysts based on conventional production. , 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 include, for example, catalysts prepared 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 thus obtained 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. There have also been some reports on fluidized bed catalysts for the oxidation of butane. For example, JP-A-49-
No. 126587 discloses that a pentavalent vanadium compound is brought into contact with a trivalent phosphorus compound to form a composite oxide,
An example is described in which the powder was then ground into a fine powder and then applied to a fluid reaction. 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. The pulverized fluidized bed reaction using such fine powder of catalytically active components is described in 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 intensive studies 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, 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, and then spraying and drying the slurry. Filed (Patent Applications 1986-52645 and 57-74920)
reference). The crystalline oxide used as the first component in these applications exhibits an X-ray diffraction pattern similar to that shown in Table 1 above, and is therefore essentially (VO) ₂ P ₂ O ₇ It is thought to be vanadyl pyrophosphate, which has the chemical formula: On the other hand, the aforementioned E.
According to Bordes et al., when vanadyl pyrophosphate represented by (VO) ₂ P ₂ O ₇ is heated to high temperature in an oxygen-containing atmosphere, vanadium is oxidized from tetravalent to pentavalent according to the following formula, and the following table - It is said that the compound transforms into a crystalline vanadyl phosphate compound that exhibits a characteristic X-ray diffraction pattern of 2. (VO ₂ ) ₂ P ₂ +1/20 ₂ 2β-VOPO _4Table -2 X-ray diffraction peak (Anticathode Cu-Kα) 2θ Peak intensity 17.1 Strong 19.3 Strong 26.2 Strongest 28.1 Medium 29.1 Strongest 30.0 Medium 34.0 Medium 40.8 Medium 41.6 Medium The present inventors investigated the relationship between the degree of oxidation of vanadium to pentavalent in the vanadyl pyrophosphate, crystal structure, and performance as a catalyst for maleic anhydride, and found that the ratio of pentavalent vanadium was 35%. Until this point, the aforementioned crystal structure of vanadyl pyrophosphate is maintained, but as the oxidation progresses further, a broad peak appears at 2θ = 21.4° (anticathode Cu-Kα), and the crystal structure is destroyed and transition occurs. It was also found that the catalytic performance was even better than vanadyl pyrophosphate itself until the proportion of pentavalent vanadium reached 35%. The present invention was completed based on this knowledge, and its gist is that it contains phosphorus and tetravalent and pentavalent vanadium, and that pentavalent vanadium accounts for 35% or less of the total vanadium, and that The characteristic X of
A first component made of a crystalline composite oxide showing a line diffraction peak, a second component made of an aqueous solution containing vanadium and phosphorus, and a third component made of silica sol are mixed to form a slurry, and this is spray-dried. A method for producing an oxidation catalyst is provided. To explain the present invention in detail, in the present invention, a crystalline vanadium-phosphorus oxide exhibiting the X-ray diffraction peaks shown in Table 1 is used as the first component.
A compound that gives such a diffraction spectrum is vanadyl pyrophosphate, represented by (VO) ₂ P ₂ O ₇ . This product is usually produced by producing a precursor compound and then firing it. As a precursor, for example, VOPO ₄ 2H ₂ O,
(NH ₄ ) ₂ [(VO) ₂ C ₂ O ₄ (H ₂ PO ₄ ) ₂ ]・5H ₂ O is known (E.Bordes.P.Courtine, mentioned above). Crystalline vanadium-phosphorous oxides with characteristic X-ray diffraction spectra are also useful as precursors. Table 3 X-ray diffraction peak (Anticathode Cu-Kα) 2θ° (±0.2°) Intensification 15.7 100 19.6 50 24.2 40 27.1 45 28.8 25 30.4 80 This precursor compound is known, and its manufacturing method is as follows. There is a method like this. A solution containing tetravalent vanadium ions is prepared by reducing pentavalent panadium such as vanadium pentoxide with a reducing agent such as oxalic acid in a non-oxidizing acidic solution such as a hydrochloric acid solution. After reacting with
Method of precipitation by adding water (Japanese Patent Application Laid-open No. 51-95990
), 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. A method for obtaining crystals (Japanese Patent Application Laid-Open No. 56-45815), or by reducing vanadium pentoxide in an organic medium such as ethanol, isopropanol, or glycerol, reacting it with phosphoric anhydride, and azeotropically dehydrating it with a solvent such as benzene. A method of precipitating crystals (US Pat. No. 4,283,288) is known. In addition, the present inventors have developed a method for producing a precursor having the above-mentioned characteristic X-ray diffraction spectrum by a hydrothermal synthesis method in which an aqueous solution containing tetravalent vanadium ions and phosphoric acid is heated to a temperature of 110 to 250°C. (See Japanese Patent Application No. 57-32110). The precursor obtained by these methods is (V ₂ O ₄ )
It can be represented by the composition formula (P ₂ O ₅ )(2H ₅ O). Therefore, the ratio of phosphorus to vanadium is theoretically 1.0 in P/V atomic ratio, so in any case of production, the vanadium compound and the phosphorus compound should have a P/V atomic ratio within the range of 0.8 to 1.25. It is preferable to react. 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. 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 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°. When this precursor is fired in an inert gas atmosphere such as argon or nitrogen, a compound having the main X-ray diffraction peaks shown in Table 1 is obtained. Since vanadium in this compound is substantially in a tetravalent state, the first component of the present invention can be obtained by calcining this in air to make a part of the vanadium in a pentavalent state. The ratio of pentavalent vanadium in the first component is correlated with the performance of the final catalyst.
In general, best results are obtained when the proportion of pentavalent vanadium is between 15 and 25%, and performance decreases as the proportion increases or decreases above this range. When the proportion of pentavalent vanadium exceeds 35%, the crystalline phase of (VO) ₂ P ₂ O ₇ begins to break down.
Such excessively oxidized calcined products sometimes have the disadvantage of forming gummy solids during catalyst production, and only catalysts with poor performance can be obtained. Therefore, firing in air must be carried out within a range in which the proportion of pentavalent vanadium remains at 35% or less. A preferred proportion of pentavalent vanadium in the first component is 5-35%. In addition, instead of firing in two stages with inert gas and air, the aforementioned precursor is fired in air diluted with inert gas, and has the X-ray diffraction peak shown in Table 1, and a predetermined result. The first component may also contain a proportion of pentavalent vanadium. When the precursor is fired in normal air to form the first component, care must be taken in terms of temperature control, etc. so that oxidation of vanadium does not proceed excessively. The firing of the precursor can be carried out in any type of furnace, but typically a Matsufuru furnace, a rotary kiln, a fluidized bed firing furnace, etc. are used. The firing temperature is suitably 430 to 700°C, which is the dehydration temperature of the precursor, and preferably 450 to 600°C. In addition, from the point of view of the strength of the final catalyst, the first component is preferably fine particles with an average particle size of 10 μ or less, particularly 5 μ or less, as determined by the Coulter Counter method. It is preferred to grind in stages or after calcination. According to the hydrothermal synthesis method described above, fine precursors can be produced, so when a slurry containing fine precursors obtained by hydrothermal synthesis is spray-dried, fine precursors of the above-mentioned size can be produced. can be obtained directly. When pulverizing, a known wet or dry pulverizer such as a hammer mill, jet mill, colloid mill, or sand grinder can be used. When performing wet pulverization, it may be performed after mixing with either or all of the second component and the third component to form a slurry. 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 produced by adding and dissolving a reducing agent and vanadium pentoxide in an aqueous solution containing 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, an aqueous solution containing vanadium phosphate is unstable and it may be difficult to keep it stable for a long time, so oxalic acid can be present to stabilize the aqueous solution. The amount thereof is a molar ratio of oxalic acid to vanadium element 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, a method of adding vanadium pentoxide to an aqueous solution containing phosphoric acid and oxalic acid such that the molar ratio of oxalic acid to vanadium element is 1.7 or less, and preferably 0.7 or more to obtain an aqueous solution containing vanadyl phosphate and oxalic acid. It is. 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 of the reduction, 1.2 moles or less of oxalic acid will exist based on the vanadium element. Second, a reducing agent other than oxalic acid is added to the acidic aqueous solution containing phosphoric acid, preferably an inorganic reducing agent such as hydrazine hydrate, hydrazine or hydroxylamine hydrochloride, phosphate, or an organic reducing agent such as lactic acid. adding one or a mixture of two or more,
Vanadium pentoxide is then added for reduction to obtain a homogeneous vanadium phosphate-containing aqueous solution. After this,
Preferably oxalic acid is 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 4 below precipitates.

[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 mentioned above may contain alcohol, ketone,
An organic solvent such as ether may be used in combination. 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 to 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 also 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 gas temperature in the drying area.
It is best to set it 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 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. The firing is preferably carried out in air, air containing butane or butenes, or 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. Preparation of the first component Preparation of the precursor In a 100 liter capacity glass-lined pressure vessel with jacket, add 38.0 kg of demineralized water, 85%
12.83 kg of phosphoric acid and 2.85 kg of 80% hydrazine hydrate solution were charged and stirred to form a homogeneous solution. 16.40 kg of vanadium pentoxide was added little by little and dissolved while being careful not to foam. During this time, increase the liquid temperature to 60-80℃.
A low-temperature heating medium was passed through the jacket to maintain the temperature below. After dissolution was completed and foaming stopped, 1.0 kg of precursor seed crystals were added and preheated to 160°C. A high-temperature heating medium was passed through the jacket to heat it in a closed state. The temperature was raised to 140°C in 1.5 hours. Subsequently, heating and stirring were continued for 10 hours. During this time, the internal pressure of the container is approximately
It was constant at 2.4Kg/cm ² G. After cooling to 90℃,
10.3 kg of demineralized water was added and the contents were taken out and allowed to cool. A small amount of this slurry was passed through and the X-ray diffraction spectrum of the pale blue solid obtained was measured.
It was found that it completely matched that of the first component precursor shown in No. 3. The slurry was made sufficiently homogeneous using a stirring device, and then spray-dried using a spray dryer with a high-speed rotating disk to obtain a finely powdered precursor solid. Drying conditions are gas inlet temperature
The temperature was 330-370°C and the outlet temperature was 160°C. The P/V atomic ratio of this powder was 1.05. Firing of Precursor (Part 1) The precursor obtained above was calcined in a small rotary kiln at 520° C. for a residence time of 15 minutes under nitrogen gas flow. The X-ray diffraction spectrum of this product is shown in Table 1.
It was exactly the same as the one. Also, the ratio of pentavalent vanadium to the total vanadium in this product is 0.
It was %. Calcination of the precursor (Part 2) The precursor obtained above was calcined in a small rotary kiln under nitrogen gas flow at 520°C for a residence time of 15 minutes, and then further in the same rotary kiln under air flow at 580°C for a residence time of 15 minutes. Baked in 15 minutes.
The X-ray diffraction spectrum of this product was exactly the same as that in Table 1, and the ratio of pentavalent vanadium to the total vanadium was 21.7%. Firing of Precursor (Part 3) The precursor obtained above was calcined in a small rotary kiln at 500° C. for a residence time of 15 minutes under the flow of air diluted with nitrogen (oxygen concentration 2%). The X-ray diffraction spectrum of this product is exactly the same as that in Table 1, and the ratio of pentavalent vanadium is 16.3.
It was %. Firing of Precursor (Part 4) The precursor obtained above was placed in 2-volume porcelain baking dishes in an amount of 1 kg each, and then dispersed and stacked in a Matsufuru furnace with an internal volume of 500 ml. After the inside of the furnace was sufficiently purged with nitrogen gas, it was heated and fired at 550°C for 2 hours.
Next, air was gradually introduced into the furnace, and the mixture was heated at 550° C. for 1 hour, and then allowed to cool. The X-ray diffraction spectrum of this product was exactly the same as shown in Table 1, and the proportion of pentavalent vanadium was 23.4%. Calcination of the precursor (Part 5) Same as above (Part 4) except that the firing temperature was 600℃
was repeated. The X-ray diffraction spectrum of the fired product almost matched Table 1, but a broad and weak peak appeared at 2θ=21.4°. However, β- shown in Table-2
No peak of VOPO ₄ was detected. The proportion of pentavalent vanadium in this product was 35.2%. Preparation of the second component 6.929 kg of 85% phosphoric acid and 4.789 kg of oxalic acid (H ₂ C ₂ O ₄ .2H ₂ O) were added to 50 kg of demineralized water, and the mixture was heated to 80° C. and dissolved with stirring. To this, 4.319 kg of vanadium pentoxide was added little by little, being careful not to foam, and dissolved. After this was left to cool, water was added to make the total amount 67.1 kg, which was used as the second component. Example To 20.0 kg of the second component obtained above, 3.82 kg of a 40% concentration silica sol solution and 2.14 kg of the fired precursor obtained above were added to form a slurry. This was sufficiently homogenized using a continuous wet pulverizer, and then spray-dried using a spray dryer equipped with a high-speed rotating disk. The drying conditions were an inlet gas temperature of 200-210°C and an outlet gas temperature of 120-130°C. The average particle size of the obtained powder was between 58 and 62μ. This was fired in a fluidized firing furnace at 350°C for 1 hour under air flow, and then activated by firing at 500°C for 2 hours under nitrogen gas flow. This was sieved and a portion with a particle size of 44 to 116 μm was collected and used as a catalyst. Test Example The catalyst obtained above was placed in a heat-resistant glass fluidized bed reactor, and air containing 3% (by volume) n-butane was introduced into the reactor at GHSV500 to produce maleic anhydride. The product was collected by absorption in water. The reaction results were calculated from potentiometric titration of the absorption liquid and gas chromatograph analysis of the waste gas. The results are shown in Table-5.

【table】

Claims (1)

[Claims] 1. Contains phosphorus and tetravalent and pentavalent vanadium,
A first component consisting of a crystalline composite oxide in which pentavalent vanadium accounts for 35% or less of the total vanadium and exhibiting the following characteristic X-ray diffraction peaks, and a second component consisting of an aqueous solution containing vanadium and phosphorus. ,
and a third component consisting of silica sol are mixed to form a slurry, and the slurry is spray-dried. X-ray diffraction peak (Anticathode Cu-Kα) 2θ (±0.2°) 14.2° 15.7 18.5 23.0 28.4 30.0 33.7 36.8 2 The first component shows the following characteristic X-ray diffraction peak, and contains pentavalent vanadium. It must be prepared by firing a substantially non-containing crystalline composite oxide in an oxygen-containing atmosphere, or firing it in an oxygen-free atmosphere and then firing it in an oxygen-containing atmosphere. A method according to claim 1, characterized in that: X-ray diffraction peak 2θ (±0.2°) 15.7 19.6 24.2 27.1 28.8 30.4 3 The method according to claim 1 or 2, wherein the second component is an aqueous solution containing vanadyl phosphate. . 4. The method according to any one of claims 1 to 3, wherein the second component vanadium is substantially tetravalent.