JP3523455B2 - Fixed bed reactor and method for producing unsaturated carboxylic acid - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a fixed-bed reactor packed with a catalyst containing at least molybdenum and vanadium, which is used in the synthesis of unsaturated carboxylic acid by vapor-phase catalytic oxidation of unsaturated aldehyde. . The present invention also relates to a method for producing unsaturated carboxylic acid using such a fixed bed reactor.

[0002]

2. Description of the Related Art Generally, in order to fill a fixed bed reactor with a catalyst formed body such as a formed catalyst or a supported catalyst used in the synthesis of an unsaturated carboxylic acid by vapor phase catalytic oxidation of an unsaturated aldehyde. The method of dropping and dropping from the upper part of the reactor is adopted. During the reaction, when the raw material gas is passed through the reactor, a pressure loss occurs due to the filled catalyst compact itself, and at the same time, the pressure loss is further increased due to the powdered or collapsed catalyst due to physical impact at the time of dropping. There is a problem that In the reaction for synthesizing unsaturated carboxylic acid by gas-phase catalytic oxidation of unsaturated aldehyde using molecular oxygen, the target unsaturated compound can be obtained by performing the reaction under lower pressure in order to suppress the successive oxidation. The carboxylic acid can be obtained in high yield. However, when this reaction is carried out under the conditions of an industrial scale, pressure loss occurs due to the reasons described above, and the degree of pressure loss increases, so that it is difficult to carry out the reaction under low pressure.

As an attempt to suppress the pressure loss in the reactor, JP-B-62-36739 and JP-B-6.
There is a report in Japanese Patent Publication No. 2-36740 that the pressure loss can be suppressed by the shape of the catalyst molded body. However,
Actually, it is not enough to devise the shape of the catalyst,
At present, there is a demand for a method for reducing pressure loss. Further, Japanese Patent Laid-Open No. 4-119901 discloses that a reforming catalyst and a filling auxiliary material are mixed in reforming a hydrocarbon fuel, and a stainless steel Raschig ring is used as a filling auxiliary material in Examples. Some examples are given. However, in this case, the bulk volume of the auxiliary filling material is about 0.1 times that of the reforming catalyst, and even if an attempt is made to drop a uniform mixture of the two from the upper part of the reactor to fill it into a uniform mixed state, it is not uniform. There was a problem that it became a mixed state. In an exothermic reaction such as an oxidation reaction, the filling auxiliary material also serves as a diluent that prevents the generation of hot spots, and if there is an insufficiently diluted portion, hot spots may occur.

[0004]

The object of the present invention is to fix an unsaturated carboxylic acid which can be produced by vapor-phase catalytic oxidation of unsaturated aldhydrides with a small pressure loss and suppressed generation of hot spots. It is to provide a bed reactor and a method for producing an unsaturated carboxylic acid in good yield.

[0005]

The present invention relates to a catalyst molded body containing at least molybdenum and vanadium, which is used in the gas phase catalytic oxidation of an unsaturated aldehyde with molecular oxygen to synthesize an unsaturated carboxylic acid. , The bulk volume is 0.3 to 3.5 times that of the catalyst molded body, and the packing density is 0.
It is a reactor for a fixed bed, which is filled together with a metal Raschig ring of 5 to 1.5 kg / l. Further, the present invention is a method for producing an unsaturated carboxylic acid, which comprises subjecting an unsaturated aldehyde to gas phase catalytic oxidation using molecular oxygen using such a fixed bed reactor.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is a fixed bed reactor in which a catalyst molded body and a metallic Raschig ring having a specific bulk volume and a specific packing density are packed together. Metal Raschig rings used in the present invention have 0.3 to 3.5 times the bulk volume of the catalytic moldings, and 0.5 to 1.5
It is necessary to have a packing density of kg / l. The bulk volume, good Mashiku is 0.5 to 3 times the shaped catalyst bodies. Packing density is favored properly, a 0.6~1.3kg / l.

Here, the bulk volume is an apparent volume including voids. For example, if the shape of the catalyst or filling auxiliary material is a ring or a Raschig ring, the bulk volume of these is equivalent to the volume of a cylinder surrounded by the outer side surface.

The filling density is the filling amount of the filling auxiliary material per unit volume, and the filling auxiliary material is dropped into a reaction tube made of stainless steel having an inner diameter of 26 mm to fill the filling auxiliary material. It is obtained by dividing the weight by the volume occupied by the fill aid.

As described above, by setting the bulk volume of the metal Raschig ring to a specific range that is not extremely different from that of the catalyst molded body, even if a mixture of the catalyst molded body and the metal Raschig ring is uniformly mixed in advance. The effect of preventing hot spots during the reaction can be obtained without causing a non-uniform mixed state. Furthermore, by setting the bulk volume within the above specific range, it is possible to prevent the catalyst molded body from entering the voids of the metallic Raschig ring, and to obtain the effect of suppressing the pressure loss in the reactor.

Further, by setting the packing density of the metal Raschig ring in a specific range, when the mixture of the metal Raschig ring and the catalyst molded body is packed, the pressure in the reactor caused by the pulverization or the collapse of the catalyst molded body is caused. Loss can be suppressed. In particular, the effect of suppressing the pressure loss is great in the case of a fixed bed reactor in which a ring-shaped catalyst or the like, which has a relatively low physical strength and is liable to be pulverized or decomposed when packed in the reactor.

The amount of metallic Raschig rings filled with the catalyst is preferably 1 to 300 parts by weight, and more preferably 10 to 150 parts by weight, based on 100 parts by weight of the total amount of the catalyst charged in the reactor. . The outer diameter of the metal Raschig ring is preferably 2.5 to 13.0 mm, particularly preferably 3.0 to 8.0 mm. The length of the metal Raschig ring is preferably 2.5 to 13.0 mm, particularly preferably 3.0 to 8.0 mm.

As the metal Raschig ring, a normal Raschig ring, that is, a cylindrical Raschig ring having a through hole can be used. Further, as the metal Raschig ring, as shown in FIG. 1, a metal Raschig ring having a through hole 2 and an opening 4 on a side surface can be used, and the metal Raschig ring having such a shape also has a pressure loss reducing effect. Have. The opening 4 can be formed by cutting a part of the side surface of the metal Raschig ring and bending the cut portion inward to form the bent portion 3.

Further, the material of the metallic Raschig ring may be any material as long as it does not inhibit the reaction of unsaturated aldehyde in the gas phase catalytic oxidation using molecular oxygen, and examples thereof include carbon steel, stainless steel and titanium. However, stainless steel is preferable in terms of industrial mechanical strength, ease of handling, price, and the like.

Examples of the unsaturated carboxylic acid production by vapor phase catalytic oxidation of unsaturated aldehydes in the present invention include acrylic acid production by vapor phase catalytic oxidation of acrolein and methacrylic acid production by vapor phase catalytic oxidation of methacrolein. To be

As the catalyst for producing acrylic acid by vapor-phase catalytic oxidation of acrolein, one having a composition represented by the following general formula (1) is preferable.

[0016] _{Mo a V b A c X d} Y e O f ··· (1) ( wherein wherein Mo, V and O are respectively molybdenum, vanadium and oxygen, A is copper, iron, cobalt, chromium , At least one element selected from the group consisting of aluminum and strontium, X is germanium,
At least one element selected from the group consisting of boron, arsenic, selenium, silver, silicon, sodium, tellurium, lithium, antimony, phosphorus, potassium and barium is shown, and Y is magnesium, titanium, manganese, zinc, zirconium, At least one element selected from the group consisting of niobium, tungsten, tantalum, calcium, tin and bismuth is shown. a, b, c, d, e and f represent the atomic ratio of each element, and when a = 12, b = 0.5 to 1
0, c = 0 to 6, d = 0 to 6, e = 0 to 10, and f
Is the number of oxygen atoms required to satisfy the valences of the above components. )

Further, as a catalyst for producing methacrylic acid by vapor-phase catalytic oxidation of methacrolein, those having a composition represented by the following general formula (2) are preferable.

P _a Mo _b V _c Cu _d X _e Y _f Z _g O _h (2) (wherein P, Mo, V, Cu and O are phosphorus, molybdenum, vanadium, copper and oxygen, respectively) X is at least one element selected from the group consisting of arsenic, antimony, bismuth, germanium, zirconium, tellurium, silver, selenium, silicon, tungsten and boron, and Y is iron, zinc, chromium, magnesium. , At least one element selected from the group consisting of tantalum, manganese, cobalt, barium, gallium, cerium and lanthanum, and Z is at least one element selected from the group consisting of potassium, rubidium, cesium and thallium. A, b, c, d, e, f, g, and h represent the atomic ratio of each element, and when b = 12, a = 0.5 to 3, c
= 0.01 to 3, d = 0 to 2, e = 0 to 3, f = 0
3, g = 0.01 to 3, and h is the number of oxygen atoms required to satisfy the valence of each component. )

The method for preparing the catalyst used in the present invention does not need to be limited to a special method, and as long as there is no significant uneven distribution of the components, the well-known evaporation-drying method, precipitation method, Various methods such as an oxide mixing method can be used. As a raw material of the catalyst component, a combination of oxides of each element, nitrates, carbonates, ammonium salts, hydroxides and the like can be used.

The catalyst used in the present invention is a molded catalyst such as a molded catalyst or a supported catalyst. The method for shaping the molding catalyst and the shape thereof are not particularly limited, and using a usual tableting molding machine, an extrusion molding machine, a rolling granulator, and the like,
It is possible to use those shaped into an arbitrary shape such as a spherical shape, a columnar shape, a ring shape (cylindrical shape), or a star shape.

When a supported catalyst is used, the type and shape of the carrier is not particularly limited, and a carrier such as silica, alumina, silica-alumina, magnesia, titania is used, and its shape is spherical. , Cylindrical, ring-shaped (cylindrical), plate-shaped and the like.

When shaping the catalyst molded body, conventionally known additives such as organic compounds such as polyvinyl alcohol and carboxymethyl cellulose, inorganic compounds such as graphite and diatomaceous earth, glass fibers, ceramic fibers, carbon fibers and the like. There is no problem even if the above inorganic fiber is added.

In the fixed bed reactor used in the present invention, a catalyst molding containing at least molybdenum and vanadium in order to synthesize unsaturated carboxylic acid by gas phase catalytic oxidation of unsaturated aldehyde using molecular oxygen. And a metal Raschig ring having a bulk volume of 0.3 to 3.5 times that of the catalyst molded body and a packing density of 0.5 to 1.5 kg / l. Such a metal Raschig ring rarely powders or disintegrates the catalyst at the time of filling, and provides an appropriate void in the filled catalyst layer to prevent the pressure loss from increasing. It also has the effect of suppressing the generation of hot spots during the reaction. For this purpose, it is preferable that the catalyst at the inlet of the reaction gas be in a state of being diluted by metallic Raschig rings. However, the mixed state of the catalyst molded body and the metallic Raschig ring in the fixed bed reactor may be uniform throughout the catalyst layer, or the mixed state may be different in the multiple layers divided from the reaction gas inlet portion to the outlet portion of the catalyst layer. Alternatively, the mixed state may change continuously.

As an example of the method of filling the catalyst and the metallic Raschig ring in order to obtain such a fixed reactor, the catalyst molded body and the metallic Raschig ring are preliminarily and uniformly mixed to form a mixture. A method of dropping from the upper part of the reactor into the reactor and filling the reactor can be mentioned.

The unsaturated carboxylic acid can be produced by passing a gas containing at least an unsaturated aldehyde and oxygen through the fixed bed reactor and subjecting the unsaturated aldehyde to gas phase catalytic oxidation with molecular oxygen.

When the unsaturated carboxylic acid is produced by using the fixed bed reactor of the present invention, the concentration of unsaturated aldehyde in the raw material gas can be varied over a wide range, but the concentration is 1
-20% is suitable, and 3-10% is particularly preferable. Further, the raw material unsaturated aldehyde may contain a small amount of impurities such as water and lower saturated aldehyde, and these impurities do not substantially affect the reaction.

It is economical to use air as the oxygen source, but air enriched with pure oxygen can be used if necessary.
The oxygen concentration in the raw material gas is defined by the molar ratio to the unsaturated aldehyde, and this value is 0.3 to 4, particularly 0.4 to 2.
5 is preferable. The raw material gas may be diluted by adding an inert gas such as nitrogen, steam or carbon dioxide gas. The reaction pressure is preferably atmospheric pressure to several atmospheres. The reaction temperature can be selected in the range of 230 to 450 ° C, but particularly preferably 250 to 400 ° C.

[0028]

EXAMPLES The present invention will be specifically described below with reference to examples. Parts in the following examples and comparative examples are parts by weight. Further, the pressure loss rate in the reactor is defined by the following equation (3).

Pressure loss rate (%) = 100−B / A × 100 (3) where A is the gas pressure at the reactor inlet (kgf / cm ² · G),
B is the gas pressure (kgf / cm ² · G) at the reactor outlet.

Example 1 100 parts of ammonium paramolybdate and 16.6 parts of ammonium metavanadate were dissolved in 1000 parts of pure water. A solution prepared by dissolving 22.9 parts of ferric nitrate in 200 parts of pure water was added thereto, and subsequently, a solution prepared by dissolving 1.3 parts of barium nitrate in 200 parts of pure water was added. Next, the general formula Na ₂
A solution of 3.9 parts of water glass represented by O · 2.2SiO ₂ · 2.2H ₂ O dissolved in 30 parts of pure water was added.
52.4 parts of 20% silica sol was added. This mixed solution was evaporated to dryness with heating and stirring, and the obtained solid was heated to 130 ° C.
It was dried for 16 hours and crushed.

An outer diameter of 5 m was obtained from the dried powder by a tablet molding machine.
m, the inner diameter was 2 mm, and the average length was 4 mm. This was heat-treated at 380 ° C. for 5 hours under a mixed gas flow of oxygen 1% and nitrogen 99% (volume%) to obtain a catalyst molded body. The composition of elements other than oxygen of the obtained catalyst molded body (the same applies hereinafter) was as follows. Mo ₁₂ V ₃ Fe _1.2 Si _4.5 Na _0.7 Ba _0.1

1500 g of the above catalyst molded body and 5 mm outer diameter,
The difference between the outer diameter and the inner diameter is 0.4 mm, the length is 5 mm, and the packing density is 1.
Raschig ring (catalyst molding) made of 1 kg / l SUS304
The volume-to-volume ratio of 1.25) 600 g is evenly mixed
And mix the mixture with stainless steel with an inner diameter of 26 mm and a length of 5 m.
Fixed-bed reaction by dropping into a reaction tube for filling
I got a vessel. In this reactor, acrolein 5%, oxygen 10
%, Steam 30% and nitrogen 55% (volume%)
Gas 1500 Nl / hr, outlet pressure 1.0 kgf / c
m ²・ Pass it so that it becomes G, and let it react at 240 ℃
It was As a result, the production rate of acrylic acid was 3.12 mol /
It was hr. The pressure loss rate at this time is 26.2%.
Met. The volume of Raschig rings in this example is
π x (5/2)²× 5 mm³And the bulk volume of the catalyst compact is π
X (5/2)²× 4 mm³Is.

COMPARATIVE EXAMPLE 1 In Example 1, spherical ceramic balls having a packing density of 1.22 kg / l and a diameter of 7 mm were used in place of the Raschig rings made of SUS304 (the bulk volume ratio to the catalyst molded body was 2.2.
Catalyst preparation, packing and reaction were performed in the same manner as in Example 1 except that 9) was used. As a result, the production rate of acrylic acid was 3.07 mol / hr. The pressure loss rate at this time was 42.0%.

Comparative Example 2 In Example 1, as a filling auxiliary material, the outer diameter was 10 mm, the difference between the outer diameter and the inner diameter was 0.4 mm, the length was 10 mm, and the filling density was 0.
Example 1 except that 6 kg / l SUS304 Raschig rings (bulk-volume ratio to catalyst compact 10) were used.
Catalyst preparation, packing and reaction were carried out in the same manner as in. As a result, the production rate of acrylic acid was 3.05 mol / hr, but hot spots were observed and the dilution effect was small. The pressure loss rate at this time was 38.3%.

Example 2 In accordance with Example 1, a mixed solution containing the following catalyst components was prepared. Mo ₁₂ V _3.5 Fe _0.7 Co _0.5 Sr _0.4 Ag _0.05 Si _4.5 N
a _0.7 This mixed solution was evaporated to dryness with heating and stirring, and the obtained solid was dried at 130 ° C. for 16 hours and pulverized. 20 parts of pure water and 10 parts of an inorganic fiber having an average length of 200 μm were mixed with 100 parts of this dried powder, and the mixture was shaped into a ring shape having an outer diameter of 8 mm, an inner diameter of 4 mm and an average length of 5 mm by an extruder. This was heat-treated at 380 ° C. for 5 hours under a mixed gas flow of oxygen 1% and nitrogen 99% (volume%) to obtain a catalyst molded body.

The present catalyst molded body 1500 g and outer diameter 8 mm, difference between outer and inner diameter 0.4 mm, length 8 mm, packing density 1.1
600 g of a Raschig ring made of SUS304 (bulk volume ratio to the catalyst molded body: 1.6) of kg / l was uniformly mixed and filled and reacted under the same conditions as in Example 1. As a result, the production rate of acrylic acid was 3.08 mol / hr. The pressure loss rate at this time was 23.6%.

Comparative Example 3 In Example 2, instead of the Raschig ring made of SUS304, the outer diameter was 6 mm, the difference between the outer diameter and the inner diameter was 2.0 mm, and the length was 6
A catalyst was prepared, filled and reacted in the same manner as in Example 2 except that a Raschig ring made of porcelain having a mm and a packing density of 1.26 kg / l (bulk volume ratio to the catalyst molded body was 0.675) was used. As a result, the production rate of acrylic acid was 3.01.
It was mol / hr. The pressure loss rate at this time is 3
It was 8.5%.

Example 3 100 parts of molybdenum trioxide, 3.2 parts of vanadium pentoxide
Parts, 0.4 parts boric acid, 4.7 parts and 8 parts antimony pentoxide
10.0 parts of 5% by weight phosphoric acid are mixed with 800 parts of pure water.
After heating and stirring this under reflux for 3 hours, copper (II) oxide was added.
0.5 part, cobalt oxide 0.9 part and manganese nitrate 0.
8 parts was added, and the mixture was further heated and stirred under reflux for 2 hours. The slurry is cooled to 50 ° C. and cesium bicarbonate 11.2
A solution of 30 parts of pure water in 30 parts of pure water was added and stirred for 15 minutes, and then a solution of 10 parts of ammonium nitrate in 30 parts of pure water was added. This was evaporated to dryness with heating and stirring, and the obtained solid was dried at 130 ° C. for 16 hours and then pulverized. To 100 parts of this dry powder, 3 parts of polyvinyl alcohol having a degree of polymerization of 500 and 15 parts of pure water were mixed and kneaded, and an extruder was used to form an outer diameter of 6 mm, an inner diameter of 3 mm, and an average length of 5
It was formed into a ring shape of mm. 380 this under air circulation
Heat treatment was carried out at 5 ° C for 5 hours to obtain a catalyst molded body. The composition of the elements of the obtained catalyst molded body was as follows. P _1.5 Mo ₁₂ V _0.6 Cu _0.1 Sb _0.5 B _0.1 Mn _0.05 Co _0.2
Cs ₁

1500 g of the above-mentioned catalyst molded body and an outer diameter of 6 m
m, difference between outer diameter and inner diameter 0.4 mm, length 6 mm, packing density
Raschig ring (catalyst made of 1.0 kg / l SUS304)
Uniformly mix 600g of bulk volume ratio 1.2)
In a stainless steel reaction tube with an inner diameter of 26 mm and a length of 5 m.
A fixed bed reactor was obtained by dropping and filling. This
In the reactor of methacrolein 5%, oxygen 10%, steam 3
150% of raw material mixed gas of 0% and 55% (volume%) of nitrogen
0Nl / hr, outlet pressure 1.0kgf / cm ²・ Become G
And was allowed to react at 280 ° C. as a result,
The production rate of methacrylic acid was 2.58 mol / hr.
It was The pressure loss rate at this time was 25.3%.

Comparative Example 4 In Example 3, spherical ceramic balls having a packing density of 1.22 kg / l and a diameter of 7 mm were used in place of the Raschig rings made of SUS304 (the bulk volume ratio to the catalyst molded body was 1.2).
Catalyst preparation as in Example 3 except that 7) was used,
The filling and reaction were carried out. As a result, the production rate of methacrylic acid was 2.50 mol / hr. The pressure loss rate at this time was 42.3%.

Comparative Example 5 In Example 3, as a filling auxiliary material, the outer diameter was 5 mm, the difference between the outer diameter and the inner diameter was 0.8 mm, the length was 5 mm, and the packing density was 2.0 k.
Catalyst preparation, packing, and reaction were performed in the same manner as in Example 3 except that Raschig rings made of SUS304 (bulk volume ratio to catalyst formed body: 0.69) of g / l were used. As a result, the production rate of methacrylic acid was 2.48 mol / hr. The pressure loss rate at this time was 51.2%.

Example 4 100 parts of ammonium paramolybdate, 3.3 parts of ammonium metavanadate and 4.8 parts of potassium nitrate were dissolved in 400 parts of pure water. While stirring this, a solution prepared by dissolving 8.2 parts of 85 wt% phosphoric acid in 10 parts of pure water was added,
Further, a solution prepared by dissolving 2.3 parts of copper nitrate in 10 parts of pure water was added. Next, after adding a solution of 2.8 parts of zinc nitrate dissolved in 10 parts of pure water, the temperature was raised to 95 ° C. 60% by weight to this
A solution prepared by dissolving 2.2 parts of arsenic acid in 10 parts of pure water was added, and subsequently 1.0 part of germanium dioxide was added. This mixture was evaporated to dryness with heating and stirring, and the resulting solid was added to 130
It was dried at ℃ for 16 hours and crushed. This dry powder was shaped into a ring having an outer diameter of 5 mm, an inner diameter of 2 mm and an average length of 5 mm by a tablet molding machine. 5 at 380 ℃ under air circulation
Heat treatment was carried out for a time to obtain a catalyst molded body. The elemental composition of the obtained catalyst compact was as follows. P _1.5 Mo ₁₂ V _0.6 Cu _0.2 As _0.2 Ge _0.2 Zn _0.2 K ₁

1500 g of the above-mentioned catalyst molded body and an outer diameter of 5 mm,
The difference between the outer diameter and the inner diameter is 0.4 mm, the length is 5 mm, and the packing density is 1.
600 g of 1 kg / l carbon steel Raschig rings (volume ratio to catalyst compact of 1) were uniformly mixed and filled and reacted under the same conditions as in Example 3. As a result, the production rate of methacrylic acid was 2.45 mol / hr. The pressure loss rate at this time was 21.8%.

Comparative Example 6 In Example 4, a spherical silica-alumina porous body having a packing density of 0.97 kg / l and a diameter of 6 mm was used instead of the Raschig ring made of carbon steel (the bulk volume ratio to the catalyst molded body was 1.1.
Catalyst preparation as in Example 3 except that 5) was used,
The filling and reaction were carried out. As a result, the production rate of methacrylic acid was 2.39 mol / hr. The pressure loss at this time was 35.5%.

Comparative Example 7 In Example 4, charging and reaction were carried out under the same conditions as in Example 4, except that Raschig rings made of carbon steel were not mixed. As a result, hot spots were generated and the reaction could not be performed stably.

[0046]

EFFECTS OF THE INVENTION The use of the fixed bed reactor of the present invention makes it possible to reduce pressure loss and suppress the generation of hot spots, and when this reactor is used to carry out the gas phase catalytic oxidation reaction of unsaturated aldehydes. Thus, unsaturated carboxylic acid can be produced in good yield.

[Brief description of drawings]

FIG. 1 is a perspective view showing an example of a Raschig ring.

[Explanation of symbols] 1 ... Raschig ring, 2 ... through hole, 3 ...
・ Aperture

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI B01J 35/02 B01J 35/02 C07C 47/22 C07C 47/22 (72) Inventor Oh Kita No. 20 Miyukicho, Otake City, Hiroshima Prefecture No. 1 Mitsubishi Rayon Co., Ltd. Central Research Laboratory (56) References JP 62-106043 (JP, A) JP 1-165543 (JP, A) JP 7-224002 (JP, A) ( 58) Fields investigated (Int.Cl. ⁷ , DB name) B01J 19/00-19/32

Claims (2)

(57) [Claims] 1. A catalyst molded body containing at least molybdenum and vanadium, which is used when synthesizing an unsaturated carboxylic acid by vapor-phase catalytic oxidation of an unsaturated aldehyde using molecular oxygen, and a bulk molded catalyst body. A fixed bed reactor, which is 0.3 to 3.5 times the packing density and is packed together with a metal Raschig ring having a packing density of 0.5 to 1.5 kg / l. 2. A catalyst containing at least molybdenum and vanadium and having a bulk volume of 0.3 to 3.5 with respect to the catalyst molded body.
A double bed and a fixed bed reactor which is packed together with a metal Raschig ring having a packing density of 0.5 to 1.5 kg / l and an unsaturated aldehyde in a gas phase using molecular oxygen. A method for producing an unsaturated carboxylic acid, which comprises catalytic oxidation.