JP2005074377A - Method for producing metal oxide catalyst - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a catalyst which is used in the production reaction of acrylic acid by the air oxidation of propane or in the production reaction of acrylonitrile by the ammoxidation of propane. <P>SOLUTION: In a method for producing a metal oxide, a metal B compound (1), ammonia water (2) containing ammonia in at least 0.4 mole ratio to the metal B, and nitric acid or ammonium nitrate (3) containing nitrate ions in at least 2.0 mole ratio to the metal B are added into an aqueous solution or dispersion obtained by heating a molybdenum compound, a vanadium compound, and a metal A compound in an aqueous medium, and the obtained aqueous liquid, after being dried, is burned. The composition of the metal oxide is shown by the formula: MoViAjBkOy (whrein A is Te or Sb; and B is at least one element selected from Nb, Ta, W, Ti, Zr, rare earth elements, and alkali metal elements). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing a metal oxide catalyst used for producing acrylic acid by vapor phase catalytic oxidation of propane and acrylonitrile by ammoxidation of propane.

  In general, acrylic acid is produced by a two-stage oxidation reaction in which propylene and oxygen are brought into contact with each other in the presence of a catalyst to produce acrolein, and then the obtained acrolein is brought into contact with oxygen. However, in recent years, a method for producing acrylic acid in one step using propane as a starting material has been studied, and many proposals have been made regarding the catalyst used at that time. Typical examples include metal oxide catalysts such as [Mo, Te, V, Nb] (Patent Document 1) and [Mo, Sb, V, Nb] (Patent Documents 2 and 3).

  More recently, several patents have been filed for inventions related to the improvement of the metal oxide catalyst. For example, in Patent Document 4, a niobium compound is mixed with a reaction aqueous solution obtained by reacting a molybdenum compound, a vanadium compound and an antimony compound in an aqueous medium at 70 ° C. or higher, and the resulting mixture is evaporated to dryness. A method for producing a catalyst that is calcined at a high temperature is disclosed.

  Patent Document 5 proposes an invention in which nitric acid or ammonium nitrate is added to a reaction aqueous solution obtained by reacting a molybdenum compound, a vanadium compound, and an antimony compound in the invention described in Patent Document 4, in addition to the niobium compound. ing. According to the invention proposed in Patent Document 5, it is described that the wear resistance of the obtained catalyst is improved and a catalyst suitable for a fluidized bed reaction can be produced.

JP-A-7-010801 (Claims) JP-A-9-312063 (Claims) Japanese Patent Laid-Open No. 10-036311 (Claims) JP-A-10-137585 (Claims) JP 2000-254496 A (Claims and [0004])

  However, in the catalysts described in Patent Documents 1 to 5, the yield of acrylic acid in the one-stage oxidation reaction of propane has not reached a satisfactory level. The problem to be solved by the present invention is to provide a catalyst capable of producing acrylic acid with higher yield.

  The present inventors have found that in the process of forming a catalyst active phase in the production of a catalyst, aggregation of catalyst particles (primary particles) including the active phase occurs, and the overall catalyst activity is reduced due to such aggregation. As a result of investigating a method for suppressing aggregation between particles, it has been found that it is effective to add a substance having a foaming action during the production of the catalyst, and the present invention has been completed.

That is, the present invention provides an aqueous solution or dispersion obtained by heating Mo compound, V compound and metal A compound in an aqueous medium.
(1) Metal B compound,
(2) Addition of ammonia water containing ammonia in a molar ratio of 0.4 or more with respect to metal B, and (3) nitric acid or ammonium nitrate containing nitrate ions in a molar ratio of 2.0 or more with respect to metal B The resulting aqueous liquid is dried and then calcined at a temperature of 250 to 380 ° C. in the presence of air, and the resulting catalyst precursor is calcined at a higher temperature. It is a manufacturing method of the metal oxide represented.
Composition formula; MoVi Aj Bk Oy
(In the formula, A is Te or Sb, and B is at least one element selected from Nb, Ta, W, Ti, Zr, a rare earth element and an alkali metal element. 01 to 1.5, and j / i = 0.3 to 1.0, k is 0.001 to 3.0, and y is a number determined by the oxidation state of other elements. .)
Furthermore, the present invention is a method for producing acrylic acid or acrylonitrile, characterized in that propane is oxidized or ammoxidized by a gas phase catalytic reaction in the presence of the metal oxide catalyst.

Hereinafter, the present invention will be described in more detail.
First, the Mo compound, the V compound, and the metal A compound are heated in an aqueous medium. Heating conditions are 40 degreeC or more, Preferably it is 1 to 10 hours at 40-100 degreeC, More preferably, it is 2 to 5 hours. It is preferable to stir the aqueous dispersion during heating.
The metal A is Te or Sb, and examples of the Te compound include metal tellurium, tellurium dioxide, orthotelluric acid, metatelluric acid, and ammonium tellurate. The metal tellurium is preferably finely pulverized in advance, or fine particles of 5.0 μm or less obtained by reducing tellurium dioxide and telluric acid in an aqueous medium with a reducing agent. As the Sb compound, metal antimony and antimony trioxide are preferably used.

  Examples of the Mo compound include ammonium molybdate, molybdenum oxide, and molybdic acid. Among these compounds, ammonium molybdate is preferable because it is water-soluble. As the V compound, ammonium metavanadate, vanadium pentoxide and the like are preferable.

  The preferable timing of charging the Mo compound and the V compound is before the heating of the aqueous medium, but a part thereof may be added to the heated aqueous medium before the heating. Such split charging may improve the performance of the catalyst. The reason is not clear, but it is presumed that more active phases are formed by suppressing the excessive reaction under heating. The ratio of Mo compound and V compound added to the aqueous medium after heating is 10 to 95%, preferably 50 to 90%, based on the whole.

  The addition amount of the Mo compound, metal A compound and V compound is such that the atomic ratio (i and j) of V and metal A to Mo is 0.01 to 1.5, respectively, and the atomic ratio of metal A to V (j / I) is an amount such that 0.3 to 1.0. If the mixing ratio of Mo, V, and metal A is out of the above range, a metal oxide catalyst having the desired performance cannot be obtained.

A compound containing ammonia water and metal B (hereinafter referred to as metal B compound) is added to the reaction solution obtained by the above operation. The addition temperature is not particularly limited, and may usually be room temperature. The metal B is at least one element selected from Nb, Ta, W, Ti, Zr, a rare earth element, and an alkali metal element.
The amount of ammonia water added is such that ammonia with respect to metal B has a molar ratio of 0.4 or more, preferably 0.8 to 3.0. If the molar ratio of ammonia to metal B is less than 0.4, no effect can be obtained. On the other hand, even if it exceeds 3.0, the effect is not increased, and waste gas treatment costs.
By adding ammonia water and metal B compound, a fine precipitate is formed in the reaction solution.
Examples of the metal B compound that can be used in the present invention include oxides, nitrates, carboxylates, oxoacid salts, and oxalates. The insoluble metal B compound may be used after being dispersed in water. In this case, it can be dissolved in water by using oxalic acid or the like in combination.

  The addition amount of the metal B compound is an amount in which the metal B is 0.001 to 3.0 when Mo is 1 in the atomic ratio of the metal in the obtained metal oxide catalyst. In the same catalyst, when the ratio of metal B when Mo is 1 is less than 0.001, deterioration of the obtained catalyst is likely to occur. On the other hand, if it exceeds 3.0, the activity of the resulting catalyst is lowered, and the conversion rate of propane is poor.

  Nitric acid or ammonium nitrate is added to a fine precipitate dispersion obtained by adding aqueous ammonia and metal B compound. The amount of nitric acid or ammonium nitrate added is such that nitrate ions are in a molar ratio to metal B of 2.0 to 6.0, preferably 2.2 to 4.0. If the amount of nitrate ion added is less than 2.0, the effect is small. On the other hand, if it exceeds 6.0, the effect is not increased, and problems such as generation of waste gas and danger of explosion due to ammonium nitrate occur.

The resulting slurry is evaporated to dryness and the resulting paste is further dried to dryness in a dryer. The obtained dried product is fired in the presence of oxygen at a temperature of 250 to 380 ° C., preferably 280 to 360 ° C. for 0.5 to 10 hours, preferably 1 to 3 hours (hereinafter referred to as a pre-baking step).
By observing with a scanning electron microscope or measuring the pore volume of the solid material obtained through the preliminary calcination step, that is, the catalyst precursor, it is found that the solid material is extremely porous. On the other hand, when ammonia water and nitric acid or ammonium nitrate are not added, the precursor that has been pre-baked does not become porous. From such a fact, it is presumed that the aqueous ammonia, nitric acid or ammonium nitrate in the present invention acts as a foaming agent during firing.

The precursor is calcined in the absence of oxygen at a temperature of 480 to 640 ° C, preferably 570 to 620 ° C for 0.5 to 6 hours, preferably 1 to 3 hours (hereinafter referred to as main firing).
By the main calcination, a specific crystal having catalytic activity is formed in the metal oxide. In the present invention, a porous solid is obtained by preliminary calcination, and in this case, aggregation of primary particles including an active phase in the solid is suppressed, and as a result, crystals having catalytic activity occupy the catalyst surface. The rate increases. Thereby, it is presumed that the catalyst obtained in the present invention has high catalytic activity.

A metal oxide catalyst represented by the following composition formula can be obtained by the two-stage firing.
Composition formula: MoViAjBkOy (wherein A, B, i, j, k and y are as described above) The measurement of the metal content in the metal oxide catalyst can be carried out by fluorescent X-ray analysis or the like. it can.
The metal oxide catalyst obtained by the above method can be used as it is. However, it is preferable to use by increasing the surface area of the catalyst by crushing to an appropriate particle size. As a pulverization method, any of a dry pulverization method and a wet pulverization method can be employed.
Specific examples of the pulverizer include a mortar and a ball mill. In the case of wet grinding, examples of the solvent used as a grinding aid include water and alcohols.
When the catalyst is used after being pulverized, the particle size is preferably 5 μm or less, more preferably 1.0 μm or less.
In addition, the metal oxide catalyst can be used without a carrier, but can also be used by being supported on a known carrier such as silica, alumina, silica alumina, silicon carbide or the like having an appropriate particle size. The carrying amount is not particularly limited and conforms to the conventional carrying amount.

Next, the gas phase catalytic oxidation reaction of propane using the metal oxide catalyst produced by the above method will be described.
Acrylic acid is produced by introducing propane and molecular oxygen (hereinafter referred to as oxygen gas), which are acrylic acid production raw materials, into a reactor filled with the metal oxide catalyst and maintained at a high temperature.
Propane and oxygen gas may be separately introduced into the reactor, and both may be mixed in the reactor, or may be introduced into the reactor in a state where both are mixed in advance. In order to control the reaction, it is preferable to use nitrogen, steam, carbon dioxide gas, or the like as the diluent gas.
When propane and air are used as raw materials, the use ratio of air to propane is preferably 30 times or less in volume ratio, and more preferably 0.2 to 20 times.
A preferable reaction temperature is 300 to 460 ° C, and 350 to 420 ° C is more preferable. As the space velocity (hereinafter referred to as SV) of the source gas, 1000 to 8000 hr ⁻¹ is appropriate. When the space velocity is less than 1000 hr ^{−1, the} space time yield of the target compound, acrylic acid, is low, and when it exceeds 8000 hr ⁻¹ , the reaction rate decreases.

Unreacted propane contained in the reaction gas discharged from the reactor outlet and propylene as an intermediate product can be used as fuel, but they are separated from other components in the reaction gas and returned to the reactor. Can also be reused.
The metal oxide catalyst produced according to the present invention can also be applied to propane ammoxidation, and acrylonitrile can be synthesized in a high yield. The ammoxidation conditions are substantially in accordance with the above-mentioned vapor phase catalytic oxidation conditions for propane.

  According to the production method of the present invention, a metal oxide catalyst capable of producing acrylic acid in high yield from propane can be easily obtained. Further, the metal oxide catalyst has an excellent performance that does not impair the selectivity of acrylic acid production even under low water vapor reaction conditions with low wastewater treatment and purification costs. The metal oxide catalyst can also be used for ammoxidation of propane.

Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples.
In each example, a catalyst containing Te is obtained so that a catalyst containing metal is obtained in the ratio Mo / V / Te / Nb = 1.0 / 0.25 / 0.13 / 0.16. In the catalyst containing, each raw material was mix | blended so that the catalyst containing a metal might be obtained in the ratio of Mo / V / Sb / Nb = 1.0 / 0.30 / 0.23 / 0.10.

1.0 g (0.8 to 1.0 ml) of the catalyst produced in each example was packed in a 10 mmφ quartz reaction tube. The reaction temperature (temperature measured by a thermocouple fixed at the center of the catalyst layer) was controlled to 380 ° C. for the catalyst containing Te and 400 ° C. for the catalyst containing Sb. By supplying a mixed gas of 6.4% by volume of propane, 9.6% by volume of oxygen gas, 36.1% by volume of nitrogen gas, and 47.7% by volume of water vapor to the reaction tube at a space velocity of 2560 / hr ⁻¹ , Acrylic acid was produced.

The composition of each product component in the reaction product was analyzed. Using the results of the composition analysis, the propane conversion and acrylic acid selectivity shown in the following formulas were calculated (both on a molar basis), and the performance of the catalyst used was evaluated based on these values. Propane conversion (%) = 100 × (feed propane-unreacted propane) / feed propane acrylic acid selectivity (%) = 100 × produced acrylic acid / (feed propane-unreacted propane)
Acrylic acid yield (%) = propane conversion × acrylic acid selectivity / 100

To a 500 ml glass flask, add 3.64 g of tellurium dioxide and 60 ml of distilled water and add 2.8 g of hydrazine monohydrate (80 wt% as hydrazine) while stirring at a rate of 300 rpm at 80 ° C. Maintain for 12 hours under these conditions. Over time, the first white powder went gray and finally became a black suspension dispersion.
The obtained dispersion is separated into a black solid and a transparent colorless filtrate by filter paper. Next, the solid on the filter paper was washed with 200 ml of distilled water. After the washing liquid passes through the filter paper, the solid matter remaining on the filter paper is collected in a sample bottle while washing with distilled water to obtain an aqueous dispersion of tellurium. Divide the dispersion into two equal parts with a balance while stirring.
Half of the sample was dried at 50 ° C. for 2 hours, and then subjected to X-ray diffraction analysis and electron microscope observation. As a result of X-ray diffraction analysis, the obtained black powder was diffracted at 2θ at angles of 22.98, 27.52, 38.24, 40.42, 43.32, 45.88, 49.62 °. A line was shown and assigned no phase of tellurium dioxide and pure metal tellurium.
The other half of the tellurium dispersion was used for the following catalyst preparation.

To a 500 ml glass flask, 2.66 g of ammonium metavanadate, 3.0 g of ammonium molybdate, and 50 ml of distilled water were added and dissolved with stirring at the boiling point of water.
The above-mentioned half metal tellurium dispersion is added to the resulting solution and heat-treated for 1 hour. 12.45 g of ammonium molybdate is dissolved in the obtained reaction solution, and 1.0 g of 30% ammonia water is further added dropwise, and the reaction solution becomes 60 ° C. after several minutes while stirring. Meanwhile, 5.89 g of oxalic acid and 2.32 g of niobic acid were dissolved in 160 ml of distilled water to prepare an aqueous solution at room temperature, and this aqueous solution was added to the reaction solution. The obtained mixed solution was vigorously stirred for 10 minutes, and then 2.5 g of ammonium nitrate was mixed with this mixed solution. Thereafter, the mixture was concentrated by heating, and further dried with a 120 ° C. dryer.

The obtained dried product was fired in air at 320 ° C. for 1.5 hours. The obtained catalyst precursor was pulverized, the obtained particles were sieved to 16 to 30 mesh, and the pore volume was measured by the following method.
About 0.2 g of the precursor is weighed and placed on a 30 mesh screen. Drop toluene on the precursor with a dropper and wait about 1 minute until it penetrates into the pores. Next, excess toluene is dropped, the precursor particles into which toluene has been sucked are spread on a filter paper, vibrated, sucked off the toluene adhering to the surface, and weighed again. Table 1 shows the pore volume values converted from the amount of toluene adsorbed in this way.

Next, the precursor particles that have been pre-fired are filled into a 12 mm diameter stainless steel fired tube, both ends are tightened with screws, and then fired at 590 ° C. for 1.5 hours to obtain a metal oxide catalyst. It was. The result of X-ray fluorescence composition analysis of the atomic ratio of the components of the catalyst was Mo / V / Te / Nb = 1.0 / 0.25 / 0.13 / 0.16 (molar ratio).
For the catalyst, the BET specific surface area was measured with a HORIBA SA6201 continuous flow type surface area meter, and the results are shown in Table 1.
The obtained catalyst was tableted and further pulverized to 16 to 30 mesh and used for the production reaction of acrylic acid. The results of the production reaction of acrylic acid are also shown in Table 1. In Table 1, AA is acrylic acid, and P is propane.

  A catalyst was prepared in the same manner as in Example 1, except that the amount of 30% aqueous ammonia added dropwise to the reaction solution was 1.4 g, and the amount of ammonium nitrate added to the mixed solution was 2.5 g. Using this catalyst, acrylic acid was produced under the same conditions as in Example 1. The results are shown in Table 1.

  A catalyst was prepared in the same manner as in Example 1, except that the amount of 30% aqueous ammonia added dropwise to the reaction solution was 1.4 g, and the amount of ammonium nitrate added to the mixed solution was 3.0 g. Using this catalyst, acrylic acid was produced under the same conditions as in Example 1. The results are shown in Table 1.

  A catalyst was prepared in the same manner as in Example 1, except that the amount of 30% aqueous ammonia added dropwise to the reaction solution was 1.4 g, and the amount of ammonium nitrate added to the mixed solution was 3.5 g. Using this catalyst, acrylic acid was produced under the same conditions as in Example 1. The results are shown in Table 1.

Comparative Example 1
A catalyst was prepared in the same manner as in Example 1 except that ammonia water was not added dropwise to the reaction solution and the amount of ammonium nitrate added to the mixture solution was 2.5 g. Using this catalyst, acrylic acid was produced under the same conditions as in Example 1. The results are shown in Table 1.

Comparative Example 2
A catalyst was prepared in the same manner as in Example 1, except that the amount of 30% aqueous ammonia added dropwise to the reaction solution was 1.0 g, and the amount of ammonium nitrate added to the mixed solution was 2.0 g. Using this catalyst, acrylic acid was produced under the same conditions as in Example 1. The results are shown in Table 1.

  In Table 1, the pore volume is a value measured for a catalyst precursor obtained by calcining at 320 ° C. for 1.5 hours in the presence of oxygen, and the specific surface area is 1 at 590 ° C. in the absence of oxygen. .BET specific surface area value measured for a catalyst obtained by calcination for 5 hours. In addition, this point is the same also in Table 2 mentioned later.

To a 500 ml glass flask, 6.15 g of ammonium metavanadate, 4.70 g of antimony trioxide and 90 ml of distilled water were added and refluxed at the boiling point of water for 2 hours with stirring. Thereafter, 10.0 g of a 7.7 wt% hydrogen peroxide solution was added (the slurry turned yellow), and then the heating was stopped. The temperature of the reaction solution was naturally lowered, and when the temperature reached 95 ° C., a solution prepared by dissolving 30.9 g of ammonium molybdate in 40 g of distilled water was added dropwise over 8 minutes. The yellow reaction liquid gradually turned orange by the dropwise addition of ammonium molybdate. Subsequently, 10.0 g of 3% aqueous ammonia was dropped into the reaction solution over 2 minutes, and the temperature of the reaction solution was naturally lowered to 55 ° C. while stirring.
Meanwhile, 11.03 g of oxalic acid and 2.83 g of niobic acid were dissolved in 87 ml of distilled water to prepare an aqueous solution at room temperature, and this aqueous solution was added to the reaction solution (changed to yellow). The obtained mixed solution was vigorously stirred for 10 minutes, and then 6.25 g of ammonium nitrate was mixed with this mixed solution. Subsequently, 0.98 g of metal antimony powder was added, and the mixture was heated and concentrated (changed to dark blue), and further dried with a 120 ° C. dryer.

The obtained dried product was baked in air at 320 ° C. for 1.5 hours. Then, it filled in the stainless steel baking pipe | tube with an internal diameter of 12 mm, both ends were screwed, and the metal oxide catalyst was obtained by baking at 590 degreeC for 1.5 hours. Table 2 shows the pore volume of the catalyst precursor after the preliminary calcination and the BET specific surface area of the catalyst after the final calcination.
The atomic ratio of the components of the catalyst was Mo / V / Sb / Nb = 1.0 / 0.30 / 0.23 / 0.10 (molar ratio) as a result of fluorescent X-ray composition analysis.
The obtained catalyst was tableted and further pulverized to 16 to 30 mesh and used for the production reaction of acrylic acid. Acrylic acid was produced under the same conditions as in Example 1 except that the reaction temperature was set to 400 ° C. using this catalyst. The results are shown in Table 2.

Comparative Example 3
A catalyst was prepared in the same manner as in Example 5 except that ammonia water was not added dropwise to the reaction solution and the amount of ammonium nitrate added to the mixture solution was 5.0 g. Using this catalyst, acrylic acid was produced under the same conditions as in Example 5. The results are shown in Table 2.

  According to the metal oxide catalyst obtained by the present invention, acrylic acid can be produced in high yield using propane and air as raw materials, and acrylonitrile can be produced in high yield using propane and ammonia as raw materials. Can do.

4 is an electron micrograph at a magnification of 10,000 times of a precursor obtained after preliminary calcination (at 320 ° C. for 1 hour) in the catalyst production of Example 4. FIG. 4 is an electron micrograph at a magnification of 30,000 times of a metal oxide catalyst obtained after main calcination (1.5 hours at 590 ° C.) in the catalyst production of Example 4. FIG. 4 is an electron micrograph at a magnification of 10,000 times of a precursor obtained after preliminary calcination (at 320 ° C. for 1 hour) in the catalyst production of Comparative Example 1. FIG. 4 is an electron micrograph at a magnification of 30,000 times of a metal oxide catalyst obtained after the main calcination (1.5 hours at 590 ° C.) in the catalyst production of Comparative Example 1.

Claims (3)

In an aqueous solution or dispersion obtained by heating Mo compound, V compound and metal A compound in an aqueous medium,
(1) Metal B compound,
(2) ammonia water containing ammonia in a molar ratio of 0.4 or more with respect to metal B, and

(3) After adding nitric acid or ammonium nitrate containing nitrate ions with a molar ratio of 2.0 or more to metal B, and drying the resulting aqueous liquid, at a temperature of 250 to 380 ° C. in the presence of air. A method for producing a metal oxide represented by the following composition formula, characterized by calcining and calcining the resulting catalyst precursor at a higher temperature.
Composition formula; MoVi Aj Bk Oy
(In the formula, A is Te or Sb, and B is at least one element selected from Nb, Ta, W, Ti, Zr, a rare earth element and an alkali metal element. 01 to 1.5, and j / i = 0.3 to 1.0, k is 0.001 to 3.0, and y is a number determined by the oxidation state of other elements. .)   The method for producing a metal oxide catalyst according to claim 1, wherein the volume of pores present in the catalyst precursor is 0.20 ml / g or more. The method for producing a metal oxide catalyst according to claim 1 or 2, wherein the catalyst precursor is calcined at a temperature of 480 to 640 ° C in the absence of oxygen.