JPH11343262A - Production of acrylic acid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing acrylic acid in high yield and high energy efficiency from acrolein by vapor phase catalytic oxidation. SOLUTION: This method for producing acrylic acid comprises catalytically oxidizing acrolein with molecular oxygen at 200350 deg.C in the presence of a catalyst comprising a metal oxide having a metal element ratio represented by the formula: MoVi Sbj Ak [A is Nb or Ta; (i) and (j) are each 0.01-1.5 and (j/i) is 0.3 to 1 and (k) is 0.001-3.0] and produced by a step (1) for reacting V<+5> with Sb<+3> at >=170 deg.C in the presence of Mo<+6> in an aqueous medium and blowing molecular oxygen or a gas containing the oxygen into the reaction solution during the reaction or after finishing the reaction and a step (2) for adding a compound containing the above component A as a constitutional element to reaction product obtained in the step (1), uniformly mixing these components and baking the resultant mixture.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing acrylic acid by gas phase catalytic oxidation of acrolein, and more particularly, to a method for producing acrylic acid in high yield by using a specific catalyst. It is about.

[0002]

2. Description of the Related Art As a catalyst used in a reaction for producing acrylic acid by contacting acrolein with oxygen in a high-temperature gas phase, a molybdenum-vanadium catalyst is generally known. In JP-A-8-206504,
Mo-VW-Cu-XYZ (x is antimony or tin, Y is magnesium, calcium, strontium or barium, Z is titanium, zirconium or A cerium-based composite oxide has been proposed. Specifically, according to a catalyst such as Mo ₁₂ V _6.1 W ₁ Cu _2.3 Sb _1.2 ,
The acrylic acid yield of about 93 to 94% is maintained even after 0 hours.

On the other hand, JP-A-8-299797 proposes a catalyst comprising the same metal as disclosed in JP-A-8-206504. The feature of the catalyst described in the publication is that the peak intensity at 2θ of 22.2 ± 0.3 ° in X-ray diffraction is maximum, and the catalyst has high activity and high mechanical strength even at a low temperature. It has the property of. For example, with a catalyst such as Mo ₁₂ V ₃ W _1.2 Cu _1.2 Sb _0.5 , a high acrylic acid yield reaching 97% at a reaction temperature of about 250 ° C. has been obtained. In addition, 6-9658
In the publication, Sb-Mo-V-Ni-XY (X is Si or Al,
Y is Cu or W) based catalysts, which are said to be applicable to both ammoxidation and gas phase catalytic reactions for producing acrylic acid from acrolein.

[0004] However, conventionally known catalysts used in the gas phase catalytic reaction for producing acrylic acid from acrolein require a long contact between acrolein and oxygen gas due to the low reaction temperature, or There is a problem that the catalyst life is short, and improvement has been desired. The present inventors have previously studied a method for producing acrylic acid in a single step by a gas phase contact reaction between propane and oxygen gas, and by using a composite metal oxide obtained by a specific production method as a catalyst. Have found that acrylic acid can be obtained in high yield, and have filed a patent application for the catalyst. The present invention has been further studied, and the above metal oxide is effective as a catalyst also in a gas phase catalytic reaction for producing acrylic acid from acrolein,
Further, it has been found that the use of this allows the gas-phase contact reaction to be carried out under conditions of high energy efficiency and that the life of the catalyst is long.

[0005]

SUMMARY OF THE INVENTION The present invention provides a catalyst produced by the following steps (1) and (2), wherein the proportion of the metal element is a metal oxide represented by the following composition formula (I): A process for producing acrylic acid, comprising subjecting acrolein and molecular oxygen to catalytic oxidation at a temperature of 200 to 350 ° C in the presence. MoViSbjAk (I) (where A is Nb or Ta. I and j are
Each is 0.01 to 1.5 and j / i = 0.3 to 1, and k is 0.001 to 3.0. Step (1): V ⁺⁵ and Sb ⁺³ are reacted at a temperature of 70 ° C. or more in an aqueous medium in the presence of Mo ⁺⁶ , and during or after the reaction, molecular oxygen is added to the reaction solution. Or a step of blowing the gas containing oxygen. Step (2): The reaction product obtained in the step (1) is
A compound containing A as a constituent element is added and uniformly mixed,
Hereinafter, the present invention will be described in more detail.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, there is provided a catalyst which is produced through the steps (1) and (2) and has a metal element ratio of a metal oxide represented by the composition formula (I). In the presence, acrolein and molecular oxygen (hereinafter referred to as oxygen gas) are subjected to a gas phase contact reaction at a temperature of 200 to 350 ° C, preferably 220 to 320 ° C. In the gas phase contact reaction of the present invention, it is preferable to coexist a gas other than acrolein and oxygen gas, and as a preferable gas, it is known to suppress the combustion of an inert gas as a diluent gas and generated acrylic acid. Steam and the like. A preferred ratio of each component introduced into the reaction system is acrolein; 1 to 15%, molecular oxygen;
5%, steam; 0-40% and inert gas; 20-8
0%, more preferably acrolein;
2%, oxygen gas; 2 to 20%, steam; 3 to 30% and inert gas; 50 to 70%. Acrolein, oxygen gas, and the like may be separately supplied to the reactor and mixed in the reactor, or the gases may be mixed in advance and introduced into the reactor as a mixed gas. In the present invention, the gas as a whole has a space velocity of 500 to 500.
It is preferable to 20,000 h ^-1 preferably fed to the reaction system in 1,000~10,000h ^-1.

Next, a method for producing the catalyst used in the present invention will be described. In the step (1) employed for the production of the catalyst, Sb ⁺³ , V ⁺⁵ and Mo ⁺⁶
The oxidation-reduction reaction takes place in an aqueous medium at a temperature of 70 ° C. or higher. When this reaction is represented by a chemical formula, the main reaction is represented by the following formula (A). V ⁺⁵ + Sb ⁺³ → V ⁺³ + Sb ⁺⁵ (a) In the three reaction systems, when Mo ⁺⁶ does not exist, it is known that the next reaction occurs in parallel with the above reaction. (Studies in Surface Science and Catalysis
Vol. 82, p. 281 (1994)]. V ⁺³ + V ⁺⁵ → 2V ⁺⁴ (b) On the other hand, in the present invention in which Mo ⁺⁶ coexists, V ⁺³ generated in the reaction (a) is quickly converted to V ⁺ by the Mo ⁺⁶ .
As a result of oxidation to ⁺⁴ , the reaction (b) is suppressed, and most of the V ⁺⁵ used is involved in the reaction (a).

As the V ⁺⁵ compound containing V ⁺⁵ as a constituent element used in the above-mentioned redox reaction, ammonium monvanadate or vanadium pentoxide is preferable. As the Sb ⁺³ compound containing Sb ⁺³ as a constituent element, Preferably, antimony trioxide or antimony acetate is used, and examples of the Mo ⁺⁶ compound having Mo ⁺⁶ as a constituent element include ammonium molybdate, molybdenum oxide, molybdic acid, and the like. Ammonium molybdate.

The Mo ⁺⁶ compound, V ⁺⁵ in the oxidation-reduction reaction
The use ratio of the compound and the Sb ⁺³ compound is such that the atomic ratio of Mo, V and Sb constituting the target catalyst is represented by the following composition formula. V ⁺⁵ compound and S
The use ratio of the b ⁺³ compound is Sb ⁺³ : V ⁺⁵ = (0.
3-1): 1. If the ratio of Sb ⁺³ is less than 0.3, the selectivity for acrylic acid is low, while if it exceeds 1, the conversion of acrolein is low. When i and j in the following composition formula are less than 0.01 or more than 1.5, the conversion of acrolein and the selectivity for acrylic acid in the acrylic acid production reaction are inferior. MoViSbj (where i and j are 0.01 to 1.5)
It is. ) More preferred i and j are from 0.1 to 1.

The preferred amount of the metal compound in the aqueous medium is 3 to 30 parts by weight in total of three metal compounds per 100 parts by weight of water. If the total amount of the three metal compounds exceeds 30 parts by weight, a part of the V compound or the Mo compound becomes insoluble, and the oxidation-reduction reaction tends to be incomplete. The above reaction does not proceed unless heated at 70 ° C. or higher, and the preferred reaction temperature is around the boiling point of the aqueous medium. The reaction time is preferably about 5 to 15 hours.

The degree of progress of the reaction is determined by the pentavalent S in the reaction solution.
b is quantitatively analyzed, and can be determined by comparing the amount thereof with the amount of trivalent Sb initially charged. That is, to the obtained reaction solution, a 1N oxalic acid aqueous solution 10 times or more the amount of the solution was added, and Sb
After sedimentation and separation of only Sb, pentavalent Sb can be quantitatively analyzed by titrating the precipitate with hydroiodic acid. The valences of Mo and V in the reaction solution can be determined by measurement of an electron spin resonance spectrum or the like.

In the step (1) of the present invention, as described above, oxygen gas or a gas containing the oxygen gas (generally referred to as an oxygen-containing gas) is blown into the redox reaction solution. The oxygen-containing gas may be blown into the oxidation-reduction reaction solution either during the progress of the oxidation-reduction reaction or after the completion of the reaction. It is preferable to stir the reaction solution during the blowing of the oxygen-containing gas. The preferred oxygen gas concentration in the oxygen-containing gas is
0.5 vol% or more, more preferably 1 to 20
vol%, particularly preferably 2 to 15 vol% (hereinafter abbreviated as%). When the oxygen gas concentration in the oxygen-containing gas is less than 0.5%, the activity of the finally obtained catalyst may be low.

The preferred blowing rate (flow rate) depends on the amount of the oxidation-reduction reaction solution.
If it is about 500 ml, 3-12 liter / Hr is preferable. The blowing time of the oxygen-containing gas into the reaction solution is as follows:
4 hours or more are preferred. A more preferred blowing time is 5 to 10 hours. When the blowing time of the oxygen-containing gas is less than 4 hours, the activity of the obtained catalyst may be low. By blowing oxygen-containing gas into the reaction solution,
It is unclear how molecular oxygen reacts with other compounds in the reaction solution system. However, in the present invention, Mo ⁺⁶ oxidizing V ⁺³ to V ⁺⁴ is temporarily reduced to Mo ^+5, and a part of the Mo ⁺⁶ is again converted to Mo ^+6. Confirmed from ⁺⁵ analysis. From the above chemical changes, it is inferred that molecular oxygen oxidizes Mo ⁺⁵ .

In the step (2) of the present invention, an Nb compound or a Ta compound is added to a dispersion containing Mo, V and Sb as a reaction product of the above-mentioned reaction or an evaporated dry product thereof, and uniformly mixed. . Examples of the Nb compound or Ta compound include niobium oxide, niobic acid, tantalum oxide, and tantalic acid. The Nb compound or Ta compound may be used in a form in which these are dispersed in water, but more preferably in the form of an aqueous solution of oxalate using oxalic acid or the like. The amount of the Nb compound or Ta compound used is
The amount is such that Nb or Ta is 0.001 to 3.0 when Mo is 1 in the atomic ratio of metal in the obtained catalyst. Nb or T when Mo in catalyst is 1
If the ratio of a is less than 0.001, the catalyst will be degraded, while if it exceeds 3.0, the catalyst will have low activity and the conversion of acrolein will be poor.

The mixture of the metal compounds obtained by the above-mentioned operation is converted into the metal oxide to be used as the catalyst of the present invention by subjecting the mixture to drying, if necessary, by evaporating to dryness or spray drying, followed by calcination treatment. You. Such firing is preferably performed in two stages. That is,
First, in the presence of oxygen gas, for example, in air, 250 to 3
It is preferable to perform heating at 50 ° C. for 4 to 10 hours, and then perform firing at 500 to 660 ° C. for 1 to 3 hours in an inert gas. Confirmation of the content of the metal element in the metal oxide obtained by the calcination can be performed by X-ray fluorescence analysis.

The metal oxide obtained by the above method is characterized in that it has a large peak at the following four diffraction angles 2θ in powder X-ray diffraction (X-ray source; Cu-Kα ray). 2θ Relative intensity 22.1 10 to 120 22.3 60 to 80 28.2 100 36.2 20 to 50

The catalyst for producing acrylic acid obtained by the above method is preferably pulverized to an appropriate particle size to increase the surface area. As the pulverization method, either a dry pulverization method or a wet pulverization method may be used. Examples of the crusher include a mortar and a ball mill. The preferred particle size of the catalyst is 20 μm or less, more preferably 5 μm.
μm or less. The present catalyst can be used in a state of no carrier, but can also be used in a state of being supported on a carrier such as silica, alumina, silica-alumina and silicon carbide having an appropriate particle size. Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.

[0018]

Example 1 (Production of catalyst) 6.15 g of ammonium metavanadate was added to 130 ml of distilled water in a 300 ml glass flask, and dissolved by heating under stirring.
6.35 g of antimony trioxide and 30.5 g of ammonium molybdate were added. While rotating the stirrer at a rate of 360 revolutions / minute of the mixed liquid composed of the above components, an air / nitrogen mixed gas having an oxygen gas concentration of 15% was added to the liquid.
Blowing was performed at a flow rate of 00 ml / min, the temperature was raised to 92 ° C., and the reaction was performed for 5 hours. The resulting blue colloidal dispersion was cooled to room temperature, and a room temperature aqueous solution in which 13.15 g of oxalic acid and 3.25 g of niobic acid were dissolved in 90 ml of distilled water was added. After vigorously stirring the obtained mixture for 30 minutes, a spherical (diameter: 3 mm) carrier 200 made of alumina was used.
ml was added and evaporated to dryness with stirring.

The alumina carrier supporting the above metal compound by the above operation was calcined in air at 300 ° C. for 5 hours. Then, further in a nitrogen gas stream at 600 ° C.
For 2 hours to obtain the target metal oxide on the alumina carrier. The atomic ratio of the obtained metal oxide is Mo / V / Sb / Nb = 1.0 / 0.3 / 0.25
/0.10. The results of X-ray diffraction measurement of this metal oxide showed that 2θ was 22.1, 22.3,
There are relatively large peaks at angles of 28.2 and 36.2, and their peak intensity ratio is 87/64 /
It was 100/27.

(Acrylic acid production test) 30 ml of the above catalyst was filled into a quartz reaction tube of 18 mmφ. 27 reaction tubes
The mixture was heated to 0 ° C., and a mixed gas composed of 4.5% of acrolein, 7.1% of oxygen gas, 63.4% of nitrogen gas, and 25% of steam was added thereto at a rate of SV = 4000 / hr (contact time 0.9%). Per second) to synthesize acrylic acid. Acrolein conversion is 99.2%, acrylic acid yield is 98.6%, and selectivity to acrylic acid is 9
It was 9.3%. The conversion, the selectivity, and the yield were calculated by the following formulas (all calculated by the number of moles). Acrolein conversion (%) = (supplied acrolein-unreacted acrolein) / supplied acrolein-Acrylic acid selectivity (%) = formed acrylic acid / (supplied acrolein-unreacted acrolein)-Acrylic acid yield (%) = acrolein Conversion x Acrylic acid selectivity

[0021]

Example 2 In the step (1) for producing a catalyst, except that a mixed gas of air and nitrogen gas having an oxygen gas concentration of 4% was blown into an aqueous dispersion of a metal compound at a flow rate of 100 ml / min. Was carried out under the same conditions as in Example 1 except that the reaction temperature was set to 300 ° C., except that a catalyst produced in the same manner as in Example 1 was used. As a result, the conversion of acrolein was 99.0%,
The acrylic acid yield was 91.1%, and the selectivity to acrylic acid was 92%.

[0022]

EXAMPLE 3 In the step (1) for producing a catalyst, except that a mixed gas of air and nitrogen gas having an oxygen gas concentration of 20% was blown into an aqueous dispersion of a metal compound at a flow rate of 100 ml / min. Was carried out under the same conditions as in Example 1 except that the reaction temperature was set to 280 ° C. using the catalysts produced in the same manner as in Example 1. As a result, the conversion of acrolein was 99.3.
%, Acrylic acid yield was 96.5%, and selectivity to acrylic acid was 97.2%.

[0023]

Comparative Example 1 In the same manner as in Example 1, except that in the step (1) for producing the catalyst, each component mixture was maintained at 92 ° C. for 12 hours without blowing the oxygen-containing gas into the aqueous dispersion. To produce a catalyst. Hereinafter, when the reaction temperature is 3
The production of acrylic acid was carried out under the same conditions as in Example 1 except that the temperature was changed to 10 ° C. As a result, the conversion of acrolein was 99.6%, the yield of acrylic acid was 75.7%, and the conversion to acrylic acid was also carried out. The selectivity was 76.2%.

[0024]

According to the present invention, acrylic acid can be synthesized from acrolein in high yield, the space velocity of the supplied gas can be increased, and the proportion of water vapor used in combination can be reduced. When energy efficiency is high.

Claims (1)

[Claims] 1. An acrolein and a molecular compound which are produced by the following steps (1) and (2) and whose metal element ratio is a metal oxide represented by the following composition formula (I): A method for producing acrylic acid, wherein oxygen is contact-oxidized at a temperature of 200 to 350 ° C. MoViSbjAk (I) (where A is Nb or Ta. I and j are
Each is 0.01 to 1.5 and j / i = 0.3 to 1, and k is 0.001 to 3.0. Step (1): V ⁺⁵ and Sb ⁺³ are reacted at a temperature of 70 ° C. or more in an aqueous medium in the presence of Mo ⁺⁶ , and during or after the reaction, molecular oxygen is added to the reaction solution. Or a step of blowing the gas containing oxygen. Step (2): The reaction product obtained in the step (1) is
A compound containing A as a constituent element is added and uniformly mixed,
Firing the resulting mixture