CN101269333A - Process for producing unsaturated aldehydes and/or unsaturated carboxylic acids - Google Patents

Abstract

Unsaturated aldehyde and/or unsaturated carboxylic acid are produced with excellent transform rate and satisfactory yield rate by catalysis gas phase oxidization of at least one compound selected from the group consisting of propylene, isobutylene and tert-butyl alcohol. Two or more sorts of catalysts composed by special mixed oxides whose types of ingredients forming metals and proportion of content are different, are filled into a reaction pipe, thereby enhancing catalysis activity from an inlet of feeding gas to an outlet of feeding gas, then the feeding gas is fed into the reaction pipe, and wherein the catalysts are obtained by the following steps of: drying water solution or water suspension comprising all kinds of catalyst ingredients, afterwards, calcining the water solution or water suspension in an ambience with the gas comprising molecular oxygen, then performing heat treatment in presence of deoxidized substances.

Description

Process for producing unsaturated aldehydes and/or unsaturated carboxylic acids

field of invention

The present invention relates to a method for producing unsaturated aldehyde unsaturated carboxylic acid, comprising feeding feed gas and molecular oxygen containing at least one compound selected from propylene, isobutene and tert-butanol into a reaction tube, The at least one compound is catalytically oxidized in the gas phase to give unsaturated aldehydes and/or unsaturated carboxylic acids.

Description of related fields

As an example of a method for producing unsaturated aldehydes and/or unsaturated carboxylic acids, a method is proposed comprising feeding a feed gas containing at least one compound selected from propylene, isobutylene and tert-butanol and molecular oxygen Feed into a reaction tube to catalytically oxidize at least one compound in a gas phase, wherein after preparing a plurality of catalysts having different catalytic activities by changing the kinds and amounts of metal components constituting the catalyst, these catalysts are filled in the reaction tube tube, whereby the catalyst activity increases from the feed gas inlet to the feed gas outlet, and the feed gas is fed into the reaction tube (see US Patent No. 5,276,178 and JP-A-2000-351744).

However, such conventional methods are not necessarily satisfactory in terms of conversion of propylene, isobutene or tert-butanol or in yield of unsaturated aldehydes and/or unsaturated carboxylic acids.

Summary of the invention

The object of the present invention is to provide a process by which unsaturated aldehydes and/or unsaturated aldehydes and/or or unsaturated carboxylic acids.

The inventors of the present invention have found through their intensive investigations that the above-mentioned object can be achieved by filling a plurality of different kinds of catalysts composed of specific mixed oxides differing in the kinds and/or content ratios of components constituting metals into the reaction tube, whereby the catalytic activity increases from the feed gas inlet to the feed gas outlet, and then the feed gas is fed into the reaction tube, and wherein the catalyst is obtained by drying an aqueous solution containing each catalyst component or aqueous suspension, then calcined in an atmosphere of gas containing molecular oxygen, followed by heat treatment in the presence of reducing species. Therefore, the present invention has been accomplished based on the above-mentioned findings.

The present invention therefore provides a process for the production of unsaturated aldehydes and/or unsaturated carboxylic acids comprising the steps of:

feeding feed gas and molecular oxygen containing at least one compound selected from propylene, isobutene and tert-butanol into the reaction tube, and

gas phase catalytic oxidation of said at least one compound to produce the corresponding said unsaturated aldehyde and/or unsaturated carboxylic acid, wherein

(1) at least two catalysts with different catalytic activities are filled in the reaction tube, thereby increasing the catalytic activity from the feed gas inlet to the feed gas outlet of the reaction tube,

(2) The catalysts each independently include a mixed oxide represented by the following formula (I):

Mo _a Bi _b Fe _c A _d B _e C _f D _g O _x (I)

in

Mo, Bi and Fe represent molybdenum, bismuth and iron, respectively,

A means nickel and/or cobalt,

B represents at least one element selected from manganese, zinc, calcium, magnesium, tin and lead,

C represents at least one element selected from phosphorus, boron, arsenic, tellurium, tungsten, antimony, silicon, aluminum, titanium, zirconium and cerium,

D represents at least one element selected from potassium, rubidium, cesium and thallium,

O stands for oxygen,

a, b, c, d, e, f and g satisfy the following relationship: when a is equal to 12, 0<b≤10, 0<c≤10, 1≤d≤10, 0≤e≤10, 0≤f ≤10 and 0<g≤2, and x is a value determined according to the oxidation state of other elements,

(3) the catalysts are different from each other in the kind and/or content ratio of metal elements constituting the catalyst, and

(4) The catalysts are each independently obtained by drying an aqueous solution or aqueous suspension containing the catalyst components, followed by calcining in an atmosphere of a gas containing molecular oxygen, followed by heat treatment in the presence of a reducing substance.

According to the present invention, by catalytic gas-phase oxidation of at least one compound selected from propene, isobutene and tert-butanol, its corresponding unsaturated aldehyde and/or unsaturated carboxylic acid can be produced in satisfactory yield with good conversion .

Detailed description of the invention

In the present invention, the feed gas containing at least one compound selected from propylene, isobutene and tert-butanol and molecular oxygen are fed to a variety of catalysts with different catalytic activities, thus from the feed gas inlet to the feed A reaction tube with increased catalytic activity at the gas outlet. The more kinds of catalysts, the more effective in terms of reaction results and temperature control in the reaction tubes, however, the preparation or filling of the catalysts is also more complicated. In consideration of these factors, it is preferable to use two catalysts.

The catalysts used in the present invention are each independently a mixed oxide represented by the following formula (I):

Mo _a Bi _b Fe _c A _d B _e C _f D _g O _x (I)

in

Mo, Bi and Fe represent molybdenum, bismuth and iron, respectively,

A means nickel and/or cobalt,

B represents at least one element selected from manganese, zinc, calcium, magnesium, tin and lead,

C represents at least one element selected from phosphorus, boron, arsenic, tellurium, tungsten, antimony, silicon, aluminum, titanium, zirconium and cerium,

D represents at least one element selected from potassium, rubidium, cesium and thallium,

O stands for oxygen,

When a is equal to 12, a, b, c, d, e, f and g satisfy the following relations: 0<b≤10, 0<c≤10, 1≤d≤10, 0≤e≤10, 0≤f ≤10 and 0<g≤2, and x is a value determined according to the oxidation states of other elements.

The catalysts differ in the types and/or content ratios of metal elements constituting the catalysts. "The catalyst is different in the kind of metal element constituting the catalyst" means that at least one element of A, B, C, or D of one catalyst is different from the corresponding element of another catalyst. In addition, "the catalysts are different in the content ratio of the metal elements constituting the catalyst" means that in one case, when a is set to 12 in one catalyst, the values of b, c, d, e, f, and g Compared with the values of b, c, d, e, f and g in another catalyst when a is set to 12, the values of b, c, d, e, f and g in one catalyst At least one is different from the corresponding value in another catalyst.

The catalyst preferably comprises a mixed oxide represented by the following formula (II):

Mo _a Bi _b Fe _c Co _d Sb _f Cs _g O _x (II):

Where Mo, Bi, Fe, Co, Sb and Cs represent molybdenum, bismuth, iron, cobalt, antimony and cesium, respectively,

When a is equal to 12, a, b, c, d, e, f and g satisfy the following relations: 0<b≤10, 0<c≤10, 1≤d≤10, 0≤e≤10, 0≤f ≤10 and 0<g≤2, and x is a value determined according to the oxidation states of other elements.

In this case, the types and/or content ratios of the metal elements constituting the catalysts differ from one catalyst to another.

In a preferred embodiment of the catalyst and its packing state in the reaction tube, two catalysts are packed in the reaction tube, and one catalyst comprising a mixed oxide of formula (II) in which f is not 0 is packed into the feed In the reaction tube on the side of the gas inlet, another catalyst comprising the mixed oxide of formula (II) where f is 0 is filled into the reaction tube on the side of the feed gas outlet, and filled into the reaction tube on the side of the feed inlet. The content ratios of molybdenum, bismuth, iron and cobalt of the catalyst in the reaction tube were respectively the same as those of the catalyst filled in the reaction tube on the feed gas outlet side.

Now, the method of preparing the catalyst used according to the present invention will be described below. The catalysts with different catalytic activities used in the present invention are prepared independently of each other. As raw materials for this catalyst, compounds of various elements constituting the catalyst, such as oxides, nitrates, sulfates, carbonates, hydroxides, carbonates and their ammonium salts, and their halides are used in a certain proportion by This can satisfy the optimum content ratio of elements. For example, molybdenum trioxide, molybdic acid, ammonium paramolybdate and the like can be used as the molybdenum compound. Bismuth oxide, bismuth nitrate, bismuth sulfate, and the like can be used as the bismuth compound. Iron (III) nitrate, iron (III) sulfate, iron (III) chloride and the like can be used as the iron compound. Cobalt nitrate, cobalt sulfate, cobalt chloride and the like can be used as the cobalt compound. Antimony trioxide, antimony(III) chloride and the like can be used as the antimony compound. Cesium nitrate, cesium carbonate, cesium hydroxide and the like can be used as the cesium compound.

In the present invention, an aqueous solution or an aqueous suspension can be prepared by mixing catalyst raw materials in water, and then drying the solution or suspension. Then, the dried mixture is calcined in an atmosphere containing molecular oxygen. Certain catalyst feedstocks, such as antimony compounds, may be added after drying. Each step can be performed according to a conventional method (see, for example, JP-A-59-46132, JP-A-60-163830 and JP-A-2000-288396). For example, drying can be performed using a kneader, box drier, tumble air drier, spray drier, rinse drier, and the like. The concentration of molecular oxygen in the molecular oxygen-containing gas is usually 1 to 30% by volume, and preferably 10 to 25% by volume. Ambient air or pure oxygen is typically used as the source of molecular oxygen. This gas source is typically used as the molecular oxygen-containing gas after dilution with nitrogen, carbon dioxide, water, helium, argon, etc., if necessary. The calcination temperature is usually 300-600°C, preferably 400-550°C. The calcination time is usually 5 minutes to 40 hours, preferably 1 to 20 hours.

The calcined product resulting from the calcination is heat-treated in the presence of reducing substances. This treatment in the presence of reducing substances is generally referred to hereinafter as reduction treatment for short.

Examples of reducing substances include, for example, hydrogen, ammonia, carbon monoxide, hydrocarbons, alcohols, aldehydes, and amines. Optionally, two or more of these reducing materials may be used. Hydrocarbons, alcohols, aldehydes and amines preferably each have from 1 to about 6 carbon atoms. Examples of such hydrocarbons include saturated aliphatic hydrocarbons such as methane, ethane, propane, n-butane and isobutane, unsaturated aliphatic hydrocarbons such as ethylene, propylene, α-butene, β-butene and isobutene, and aromatic Hydrocarbons such as benzene. Examples of such alcohols include saturated aliphatic alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol and tert-butanol, unsaturated aliphatic alcohols such as allyl alcohol, butene alcohols and methallyl alcohols, and aromatic alcohols such as phenol. Examples of such aldehydes include saturated aliphatic aldehydes such as formaldehyde, acetaldehyde, propionaldehyde, n-butyraldehyde and isobutyraldehyde, and unsaturated aliphatic aldehydes such as acrolein, crolein and methacrolein. Examples of such amines include saturated aliphatic amines such as methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine and triethylamine, unsaturated aliphatic amines such as allylamine and diallylamine, and aromatic amines such as aniline.

The reduction treatment is generally performed by subjecting the calcined product to heat treatment in an atmosphere of a gas containing a reducing substance. The concentration of the reducing substance in the gas is usually 0.1 to 50% by volume, and preferably 1 to 30% by volume. The reducing species can be diluted with nitrogen, carbon dioxide, water, helium, argon, etc. to achieve this concentration. Molecular oxygen is tolerated unless it interferes with the effectiveness of the reducing treatment. However, molecular oxygen may not be allowed to exist.

The temperature for the reduction treatment is usually 200-600°C, and preferably 250-550°C. The time for the reduction treatment is usually 5 minutes to 20 hours, and preferably 30 minutes to 10 hours. It is preferable to place the calcined product in a tubular or box-shaped container and keep the container ventilated with a gas containing reducing substances for reduction treatment. At this time, the gas discharged from the container can be recycled and reused if necessary.

Reductive treatments generally cause mass loss. This may be due to the loss of lattice oxygen atoms from the catalyst. The mass loss is preferably 0.05 to 6 mass%, and preferably 0.1 to 5 mass%. If the mass loss exceeds 6% by mass due to excessive reduction, the mass loss can be compensated by recalcination in an atmosphere containing molecular oxygen.

Mass loss can be calculated using the following equation:

Mass loss (%)=100×[(weight of calcined product before reduction treatment)-(weight of calcined product after reduction treatment)]/(weight of calcined product before reduction treatment)

Depending on the kind of reducing substance used, heat treatment conditions, and the like, in the reducing treatment, the reducing substance itself, decomposition products obtained from the reducing substance, and the like may remain in the catalyst after the reducing treatment. In this case, the mass loss can be calculated by measuring the weight of the residue in the catalyst and then calculating the weight after reduction treatment by subtracting the weight of the residue from the weight of the catalyst containing the residue. The residue of the curved form is charcoal, and thus the weight of the residue can be determined, for example, by total carbon (TC) analysis.

The catalyst is typically molded into the desired shape and then used in the process of the invention. In molding, the catalyst can be molded into the form of rings, pellets, balls, etc. by tableting, extrusion molding, and the like. The shapes of the catalysts used in the present invention may be the same or different. Molding may be performed in an atmosphere containing molecular oxygen before and after calcination, or after reduction treatment. In molding, in order to improve the mechanical strength of the catalyst, a substance substantially inert to a given oxidation reaction such as inorganic fibers may be added as described in JP-A-9-52053.

Therefore, catalysts with different activities were prepared. The catalytic activity of each catalyst can be evaluated by phase catalytic oxidation of at least one raw material compound selected from propylene, isobutene, and tert-butanol using molecular oxygen in the presence of the catalyst and measuring the conversion rate of the compound. Gas-phase catalytic oxidation is performed by filling such a catalyst in a reaction tube so that the catalytic activity, that is, the conversion ratio from the feed gas inlet to the feed gas outlet is increased, and supplying feed gas containing raw material compounds and molecular oxygen. In industrial production, it is preferable to use a fixed-bed multi-tubular reactor containing the above-mentioned reaction tubes.

Air is usually used as the source of molecular oxygen. The feed gas may contain nitrogen, carbon dioxide, carbon monoxide, water vapor, etc. in addition to the starting compounds and molecular oxygen.

By the gas-phase catalytic oxidation described above, acrolein and/or acrylic acid can be produced from propylene in a satisfactorily high yield. Alternatively, methacrolein and/or methacrylic acid can be produced in satisfactory yields from isobutene or tert-butanol.

The reaction temperature is usually 250-400°C. The reaction pressure may be reduced pressure, however, it is usually normal pressure to 500 kPa. The amount of molecular oxygen is usually 1 to 3 moles per mole of the raw material compound. The space velocity SV of the feed gas at STP (Standard Temperature and Pressure) is typically 500-5000 ⁻¹ .

Example

Examples of the present invention are shown below, which, however, do not limit the present invention in any way. In these examples, unless otherwise stated, the unit "ml/min" indicates the flow rate of the gas at STP. In these examples, conversion (%) and yield are defined as follows:

Conversion rate (%)=[(feeding isobutene molar weight)-(unreacted isobutene molar weight)]/(feeding isobutene molar weight)

Total yield (%)=100*(total molar weight of methacrolein and methacrylic acid)/(feeding isobutylene molar weight)

Reference Example 1

Preparation of catalyst a (catalyst without reduction treatment)

4414 grams of ammonium molybdate [(NH ₄ ) ₆ Mo ₇ O ₂₄ ·4H ₂ O] was dissolved in 5000 grams of warm water to form Liquid A. 2020 g of iron(III) nitrate [Fe(NO ₃ ) ₃ 9H ₂ O], 4366 g of cobalt nitrate [Co(NO ₃ ) ₂ 6H ₂ O] and 195 g of cesium nitrate [CsNO ₃ ] were dissolved in 2000 g Warm water and then further dissolved 970 grams of bismuth nitrate [Bi(NO ₃ ) ₃ .5H ₂ O] to form Liquid B. Liquid B was added to Liquid A while stirring to form a suspension. The suspension is then dried using a flash dryer to obtain a dry product. 6 parts by mass of alumina-silica fiber (RFC400-SL produced by Saint-GobainTM) was added to 100 parts of dry material. The resulting mixture was molded into a ring shape having an outer diameter of 6.3 mm, an inner diameter of 2.5 mm, and a length of 6 mm, and then calcined at 525° C. for 6 hours under air flow to obtain a catalyst a. For every 12 atoms of molybdenum, the catalyst contained 0.96 atoms of bismuth, 2.4 atoms of iron, 7.2 atoms of cobalt and 0.48 atoms of cesium.

Example 1

Preparation of catalyst A (reduction treated catalyst)

Catalyst A was prepared by filling catalyst a into a glass tube, and then flowing a mixed gas of hydrogen/nitrogen (5/95 volume) through the glass tube to perform reduction treatment at 350° C. for 8 hours. Similar to catalyst a, this catalyst contained 0.96 bismuth atoms, 2.4 iron atoms, 7.2 cobalt atoms and 0.48 cesium atoms per 12 molybdenum atoms, and the mass loss by reduction treatment was 0.90 mass%.

Reference Example 2

Preparation of catalyst b (catalyst without reduction treatment)

Catalyst b was prepared using the same method as in Comparative Example 1, except that 2.54 parts by mass of antimony trioxide (Sb ₂ O ₃ ) was added to 100 parts by mass of dry material in Comparative Example 1 and the calcination temperature was changed to 546°C. For every 12 atoms of molybdenum, the catalyst contained 0.96 atoms of bismuth, 0.48 atoms of antimony, 2.4 atoms of iron, 7.2 atoms of cobalt and 0.48 atoms of cesium.

Example 2

Preparation of catalyst B (reduction treated catalyst)

Catalyst B was prepared by filling catalyst b into a glass tube, and then flowing a mixed gas of hydrogen/nitrogen (5/95 volume) through the glass tube to perform reduction treatment at 350° C. for 8 hours. Similar to catalyst b, for every 12 atoms of molybdenum, this catalyst contains 0.96 atoms of bismuth, 0.48 atoms of antimony, 2.4 atoms of iron, 7.2 atoms of cobalt, and 0.48 atoms of cesium, and the mass loss from the reduction treatment is 1.28 mass %.

Reference Example 3

Preparation of catalyst c (catalyst without reduction treatment)

Catalyst c was prepared in the same manner as in Comparative Example 1 except that the amount of cesium nitrate was changed to 273 grams. For every 12 atoms of molybdenum, the catalyst contained 0.96 atoms of bismuth, 2.4 atoms of iron, 7.2 atoms of cobalt and 0.67 atoms of cesium.

Example 3

Catalyst C preparation (reduction treated catalyst)

Catalyst C was prepared by filling catalyst c into a glass tube, and then flowing a mixed gas of hydrogen/nitrogen (5/95 volume) through the glass tube to perform reduction treatment at 350° C. for 8 hours. Similar to catalyst c, this catalyst contained 0.96 bismuth atoms, 2.4 iron atoms, 7.2 cobalt atoms, and 0.67 cesium atoms per 12 molybdenum atoms, and had a mass loss of 0.77% by mass in the reduction treatment.

Reference Example 4

Preparation of catalyst d (catalyst without reduction treatment)

6 parts by mass of alumina-silica fiber (RFC400-SL produced by Saint-Gobain™) and 2.54 parts by mass of antimony trioxide (Sb ₂ O ₃ ) were added to 100 parts of dry material obtained in Comparative Example 3. The resulting mixture was molded into a ring shape having an outer diameter of 6.3 mm, an inner diameter of 2.5 mm, and a length of 6 mm, and then calcined at 490° C. for 6 hours under air flow to obtain a catalyst d. For every 12 atoms of molybdenum, the catalyst contained 0.96 atoms of bismuth, 0.29 atoms of antimony, 2.4 atoms of iron, 7.2 atoms of cobalt and 0.67 atoms of cesium.

Example 4

Catalyst D preparation (reduction treated catalyst)

Catalyst D was prepared by filling catalyst D into a glass tube, and then flowing a mixed gas of hydrogen/nitrogen (5/95 volume) through the glass tube to perform reduction treatment at 350° C. for 8 hours. Similar to catalyst b, for every 12 atoms of molybdenum, this catalyst contains 0.96 atoms of bismuth, 0.29 atoms of antimony, 2.4 atoms of iron, 7.2 atoms of cobalt, and 0.67 atoms of cesium, and the mass loss from the reduction treatment is 1.17 mass %.

Comparative Example 1

Oxidation Using Catalyst A (Catalyst A Monolayer)

14.30 ml of catalyst A was diluted with 30 g of corundum and filled in a glass reactor with an inner diameter of 18 mm (SHINANO-RUNDUM GC F16 manufactured by Shinano Electric Refining Co., Ltd.). The oxidation reaction was performed at a reaction temperature of 330°C by feeding a mixed gas of isobutylene/oxygen/nitrogen/water vapor (1.0/2.2/6.2/2.0 mol) to the reaction tube at a flow rate of 157.5 ml/min. The conversion of isobutene and the total yield of methacrolein and methacrylic acid are shown in Table 1.

Comparative Example 2

Oxidation Using Catalyst A (Catalyst A Monolayer)

The oxidation reaction was carried out in the same manner as in Comparative Example 1 except that the reaction temperature was changed to 340°C. The conversion of isobutene and the total yield of methacrolein and methacrylic acid are shown in Table 1.

Comparative Example 3

Oxidation Using Catalyst A (Catalyst A Monolayer)

The oxidation reaction was carried out in the same manner as in Comparative Example 1 except that the reaction temperature was changed to 350°C. The conversion of isobutene and the total yield of methacrolein and methacrylic acid are shown in Table 1.

Comparative Example 4

Oxidation using Catalyst B (Catalyst B monolayer)

The oxidation reaction was carried out in the same manner as in Comparative Example 1 except that catalyst A was changed to catalyst B. The conversion of isobutene and the total yield of methacrolein and methacrylic acid are shown in Table 1.

Comparative Example 5

Oxidation Using Catalyst C (Catalyst C Monolayer)

The oxidation reaction was carried out in the same manner as in Comparative Example 1 except that catalyst A was changed to catalyst C and the reaction temperature was changed to 340°C. The conversion of isobutene and the total yield of methacrolein and methacrylic acid are shown in Table 1.

Comparative Example 6

Oxidation Using Catalyst D (Catalyst D Monolayer)

The oxidation reaction was carried out in the same manner as in Comparative Example 1 except that catalyst A was changed to catalyst D and the reaction temperature was changed to 350°C. The conversion of isobutene and the total yield of methacrolein and methacrylic acid are shown in Table 1.

Example 5

Oxidation Using Catalysts B and A (Catalyst B/Catalyst A Double Layer)

7.15 ml of catalyst B was diluted with 15 g of corundum and filled in a glass reactor with an inner diameter of 18 mm near the feed gas inlet side (SHINANO-RUNDUM GC F16 produced by Shinano Electric Refining Co., Ltd.), and 7.15 ml of Catalyst B was diluted with 15 grams of corundum and then filled on the side near the feed gas outlet (SHINANO-RUNDUM GC F16 produced by Shinano Electric Refining Co., Ltd.). The oxidation reaction was performed at a reaction temperature of 330°C by feeding a mixed gas of isobutylene/oxygen/nitrogen/water vapor (1.0/2.2/6.2/2.0 mol) to the reaction tube at a flow rate of 157.5 ml/min. The conversion of isobutene and the total yield of methacrolein and methacrylic acid are shown in Table 1.

Example 6

Oxidation Using Catalysts C and A (Catalyst C/Catalyst A Double Layer)

The oxidation reaction was carried out in the same manner as in Example 5 except that catalyst B was changed to catalyst C and the reaction temperature was changed to 340°C. The conversion of isobutene and the total yield of methacrolein and methacrylic acid are shown in Table 1.

Example 7

Oxidation Using Catalysts D and A (Catalyst D/Catalyst A Double Layer)

The oxidation reaction was carried out in the same manner as in Example 5 except that catalyst B was changed to catalyst D and the reaction temperature was changed to 350°C. The conversion of isobutene and the total yield of methacrolein and methacrylic acid are shown in Table 1.

Comparative Example 7

Oxidation using catalysts b and a (catalyst b/catalyst a double layer)

The oxidation reaction was carried out in the same manner as in Example 5, except that catalyst B and catalyst A were changed to catalyst b and catalyst a, respectively. The conversion of isobutene and the total yield of methacrolein and methacrylic acid are shown in Table 1.

Comparative Example 8

Oxidation using catalysts c and a (catalyst c/catalyst a double layer)

The oxidation reaction was carried out in the same manner as in Example 5, except that catalyst B and catalyst A were changed to catalyst c and catalyst a, respectively, and the reaction temperature was changed to 340°C. The conversion of isobutene and the overall yield of methacrolein and methacrylic acid are shown in Table 1.

Comparative Example 9

Oxidation using catalysts d and a (catalyst d/catalyst a bilayer)

The oxidation reaction was carried out in the same manner as in Example 5, except that catalyst B and catalyst A were changed to catalyst d and catalyst a, respectively, and the reaction temperature was changed to 350°C. The conversion of isobutene and the total yield of methacrolein and methacrylic acid are shown in Table 1.

Table 1

Claims (8)

1. A method for producing unsaturated aldehydes and/or unsaturated carboxylic acids, comprising the steps of: feeding feed gas and molecular oxygen containing at least one compound selected from propylene, isobutene and tert-butanol into the reaction tube, and Catalytic oxidation of said at least one compound in the gas phase to produce the corresponding said unsaturated aldehyde and/or unsaturated carboxylic acid, wherein (1) at least two catalysts with different catalytic activities are filled in the reaction tube, thereby increasing the catalytic activity from the feed gas inlet to the feed gas outlet of the reaction tube, (2) The catalysts each independently include a mixed oxide represented by the following formula (I): Mo _a Bi _b Fe _c A _d B _e C _f D _g O _x (I) in Mo, Bi and Fe represent molybdenum, bismuth and iron, respectively, A means nickel and/or cobalt, B represents at least one element selected from manganese, zinc, calcium, magnesium, tin and lead, C represents at least one element selected from phosphorus, boron, arsenic, tellurium, tungsten, antimony, silicon, aluminum, titanium, zirconium and cerium, D represents at least one element selected from potassium, rubidium, cesium and thallium, O stands for oxygen, a, b, c, d, e, f and g satisfy the following relationship: when a is equal to 12, 0<b≤10, 0<c≤10, 1≤d≤10, 0≤e≤10, 0≤f ≤10 and 0<g≤2, and x is a value determined according to the oxidation state of other elements, (3) the catalysts differ from each other in the kind and/or content of metal elements constituting the catalyst, and (4) The catalysts are each independently obtained by drying an aqueous solution or aqueous suspension containing the catalyst components, followed by calcining in an atmosphere of a gas containing molecular oxygen, followed by heat treatment in the presence of a reducing substance. 2. The method according to claim 1, wherein the catalysts each independently comprise a mixed oxide represented by the following formula (II): Mo _a Bi _b Fe _c Co _d Sb _f Cs _g O _x (II): Where Mo, Bi, Fe, Co, Sb and Cs represent molybdenum, bismuth, iron, cobalt, antimony and cesium, respectively, When a is equal to 12, a, b, c, d, e, f and g satisfy the following relations: 0<b≤10, 0<c≤10, 1≤d≤10, 0≤e≤10, 0≤f ≤10 and 0<g≤2, and x is a value determined according to the oxidation states of other elements. 3. The method according to claim 1 or 2, wherein the number of kinds of catalysts filled into the reaction tube is two. 4. The method according to claim 3, wherein a catalyst comprising a mixed oxide of formula (II) wherein f is not 0 is packed into the reaction tube on the feed gas inlet side, and a catalyst comprising a mixed oxide wherein f is 0 Another catalyst of the mixed oxide of formula (II) is filled in the reaction tube on the side of the feed gas outlet, and the molybdenum, bismuth, iron and cobalt of the catalyst in the reaction tube on the side of the feed gas inlet are filled The content ratios were the same as those of the catalyst filled into the reaction tube on the feed gas outlet side, respectively. 5. The method according to any one of claims 1-4, wherein the calcination is carried out at 300-600°C. 6. The method according to any one of claims 1-5, wherein the heat treatment is carried out at 200-600°C. 7. The method according to any one of claims 1-6, wherein the catalyst mass loss due to heat treatment is 0.05-6 mass%. 8. The method according to any one of claims 1-7, wherein the reducing substance is at least one compound selected from the group consisting of hydrogen, ammonia, carbon monoxide, hydrocarbons with 1-6 carbon atoms, hydrocarbons with 1-6 Alcohols with 6 carbon atoms, aldehydes with 1-6 carbon atoms and amines with 1-6 carbon atoms.