TECHNICAL FIELD

The present invention relates to a catalytic oxidation method for performing gas-phase catalytic oxidation with molecular oxygen in a tubular reactor, more specifically, in a fixed-bed multitubular reactor, by using a -composite oxide catalyst containing molybdenum, in which the catalyst is prevented from deterioration due to sublimation of molybdenum.

BACKGROUND ART

In a selective reaction such as gas-phase catalytic oxidation reaction for producing acrolein or methacrolein from propylene, isobutene or tertiary butanol, gas-phase catalytic ammoxidation reaction for producing acrylonitrile or methacrylonitrile from propylene or isobutene, and gas-phase catalytic oxidative dehydrogenation reaction for producing butadiene from butene, a molybdenum bismuth-based composite oxide catalyst is well-known to be a useful catalyst and is industrially widely used in practice.

Examples of the method for producing a conjugated diene such as butadiene by an oxidative dehydrogenation reaction of butenes include a gas-phase catalytic oxidative dehydrogenation reaction according to the following reaction formula:
C4H8+½O2→C4H6+H2O

As for the production of butadiene by gas-phase catalytic oxidative dehydrogenation reaction of n-butene, a method of producing butadiene from butene contained in a mixture containing 1-butene as well as 2-butene, butane, etc. (hereinafter, this mixture is sometimes referred to as “BBSS”), which is obtained by separating butadiene in an extractive distillation column in an extraction separation process of butadiene from a C4 fraction (a mixture of hydrocarbons having 4 carbon atoms; hereinafter sometimes referred to as “BB”) produced as a byproduct in naphtha cracking, is performed in industry.

As the catalyst used for this production of butadiene by gas-phase catalytic oxidative dehydrogenation reaction of butene, a composite oxide catalyst containing molybdenum (Mo) and bismuth (Bi) as main components is known to be an effective catalyst. For example, Patent Literature 1 describes a production method for a composite oxide catalyst containing, as essential components, at least one of molybdenum, iron, nickel and cobalt, and silica, which is a composite oxide catalyst for producing butadiene by gas-phase catalytic oxidative dehydrogenation of n-butene with molecular oxygen. In addition, Patent Literature 2 describes a composite oxide catalyst containing, as essential components, molybdenum (Mo), bismuth (Bi) and iron (Fe) and containing, as other essential components, one or more elements selected from nickel (Ni) and cobalt (Co), one or more elements selected from the group consisting of potassium (K), rubidium (Rb) and cesium (Cs), and silica, in which the content of the silica component in the catalyst is from 3 to 10 mass %.

However, the catalyst containing molybdenum has a problem that when the reaction is continued for a long period of time, molybdenum as an essential component sublimates and the catalyst deteriorates over time, leading to a reduction in the reaction activity and selectivity. Regarding a method for obtaining a catalyst having a reduced deterioration rate and a long life, although some proposals have been made, they are incomplete, and sooner or later, the catalyst must be replaced. Accordingly, some methods for regenerating and utilizing a catalyst of which performance is deteriorated have been proposed.

Patent Literature 3 describes a technique where molybdenum is moved (supplied) from an inside of a catalyst to a surface of the catalyst by a method of applying a heat treatment at a temperature of 380 to 540° C. in an atmosphere substantially composed of air and the activity is thereby recovered. In addition, Patent Literature 4 describes a technique for enhancing the butadiene yield by combining two kinds of molybdenum-bismuth catalysts differing in an activity.

BACKGROUND ART LITERATURE

Patent Literature

Patent Literature 1: JP-A-2003-220335

Patent Literature 2: JP-A-2011-178719

Patent Literature 3: JP-A-S61-33234

Patent Literature 4: KR-A-2013-0046458

SUMMARY OF INVENTION

Technical Problem

Meanwhile, it is well known for a long time that one of causes of catalyst deterioration is sublimation of molybdenum, and as the method for regenerating the deteriorated catalyst, a method for replenishing molybdenum in some way is necessary. In the case of a fixed bed, molybdenum needs to be replenished from the upper part of a catalyst layer.

The regeneration method by a heat treatment described in Patent Literature 3 is explained as owing its success to an effect of reoxidizing a metal ion in its reduced state or an effect of restoring the catalyst surface composition having changed due to sublimation of a component such as molybdenum, by the diffusion from a solid interior. However, the regeneration effect by these effects is insufficient, and a portion having a large degree of deterioration, such as gas inlet portion, cannot be completely regenerated, or it is difficult to repeat the regeneration a number of times.

In addition, Patent Literature 4 is silent on the replenishment of molybdenum.

The present invention has been made in consideration of these problems. That is, an object of the present invention is to suppress performance deterioration of a composite oxide-based catalyst containing molybdenum, bismuth, iron, etc. at the time of carrying out gas-phase catalytic partial oxidation with molecular oxygen by using a fixed-bed multitubular reactor.

Means for Solving Problem

The present invention relates to a catalytic oxidation method for performing gas-phase catalytic oxidation with molecular oxygen in a fixed-bed multitubular reactor by using a composite oxide catalyst containing molybdenum, in which a molybdenum compound filling the upper part of a catalyst layer is reacted with water to make a volatile molybdenum compound and thereby prevent the catalyst from deterioration due to sublimation of molybdenum from active components of the catalyst; a production method for an oxidative dehydrogenation reaction product such as conjugated diene; and a production method for an oxidation reaction product such as acrolein and/or acrylic acid.

[1] A catalytic oxidation method of performing a catalytic oxidation reaction by using a tubular reactor in the presence of a molybdenum composite oxide catalyst, wherein:

a molybdenum compound layer containing a molybdenum compound and a composite oxide catalyst layer containing a molybdenum composite oxide catalyst are arranged in this order from a reaction raw material supply port side of the tubular reactor, and

under a flow of a mixed gas at 440° C. composed of a composition containing 75 vol % of air and 25 vol % of water vapor, a molybdenum sublimation amount (μg/NL) of the molybdenum compound is larger than a molybdenum sublimation amount (μg/NL) of the molybdenum composite oxide catalyst.

[2] The catalytic oxidation method according to [1], wherein a temperature of the molybdenum compound layer in the catalytic oxidation reaction is equal to or lower than a reaction temperature.

[3] The catalytic oxidation method according to [1] or [2], wherein a difference between the molybdenum sublimation amount of the molybdenum compound and the molybdenum sublimation amount of the molybdenum composite oxide catalyst is from 0.2 to 6 μg/NL.

[4] The catalytic oxidation method according to any one of [1] to [3], wherein 20 mass % or more of the molybdenum compound is molybdenum oxide. [5] A method for producing, from an organic compound, an oxidative dehydrogenation reaction product corresponding to the organic compound by an oxidative dehydrogenation reaction in the presence of a molybdenum composite oxide catalyst by using a tubular reactor, wherein:

a molybdenum compound layer containing a molybdenum compound and a composite oxide catalyst layer containing a molybdenum composite oxide catalyst are arranged in this order from a reaction raw material supply port side of the tubular reactor, and

under a flow of a mixed gas at 440° C. composed of a composition containing 75 vol % of air and 25 vol % of water vapor, a molybdenum sublimation amount (μg/NL) of the molybdenum compound is larger than a molybdenum sublimation amount (μg/NL) of the molybdenum composite oxide catalyst.

[6] The method for producing an oxidative dehydrogenation reaction product according to [5], wherein the organic compound is monoolefins having from 4 to 6 carbon atoms and the oxidative dehydrogenation reaction product is a conjugated diene.

[7] A method for producing, from an organic compound, an oxidation reaction product corresponding to the organic compound by an oxidation reaction in the presence of a molybdenum composite oxide catalyst by using a tubular reactor, wherein:

a molybdenum compound layer containing a molybdenum compound and a composite oxide catalyst layer containing a molybdenum composite oxide catalyst are arranged in this order from a reaction raw material supply port side of the tubular reactor, and

under a flow of a mixed gas at 440° C. composed of a composition containing 75 vol % of air and 25 vol % of water vapor, a molybdenum sublimation amount (μg/NL) of the molybdenum compound is larger than a molybdenum sublimation amount (μg/NL) of the molybdenum composite oxide catalyst.

[8] The method for producing an oxidation reaction product according to [7], wherein the organic compound is propylene and the oxidation reaction product is at least either one of acrolein and acrylic acid.

[9] A catalytic oxidation method including performing a catalytic oxidation reaction in a tubular reactor in the presence of a composite oxide catalyst containing molybdenum, wherein:

the composite oxide catalyst is divided into two or more catalyst layers,

a molybdenum concentration in a catalyst in a catalyst layer closest to a reaction raw material supply port of the tubular reactor is higher than a molybdenum concentration of other catalyst layers, and

a temperature during the catalytic oxidation reaction of the catalyst layer closest to a reaction raw material supply port is lower than a temperature during the catalytic oxidation reaction of other catalyst layers.

[10] The catalytic oxidation method according to [9], wherein the temperature of the catalyst layer closest to the reaction raw material supply port is lower than a preset temperature of a heating medium.

[11] The catalytic oxidation method according to [9] or [10], wherein the molybdenum concentration in the catalyst in the catalyst layer closest to the reaction raw material supply port is 1.2 times or more and 3 times or less of a molybdenum concentration in a catalyst in a catalyst layer having a catalyst with a highest molybdenum concentration out of other catalyst layers.

[12] A method for gas-phase catalytic oxidation of olefins, including performing a gas-phase catalytic oxidation of olefins by using the catalytic oxidation method according to any one of [9] to [11], wherein:

the molybdenum amount in the catalyst in the catalyst layer closest to the reaction raw material support port is 5 mass % or more relative to a total amount of molybdenum amounts in the all other catalyst layers.

[13] The method for gas-phase catalytic oxidation of olefins according to [12], wherein 20 mass % or more of the catalyst in the catalyst layer closest to the reaction raw material supply port is molybdenum oxide.

[14] A method for producing a conjugated diene by performing an oxidative dehydrogenation reaction of butenes in the presence of a composite oxide catalyst containing molybdenum by use of a tubular reactor, wherein:

the composite oxide catalyst is divided into two or more catalyst layers,

a molybdenum concentration in a catalyst in a catalyst layer closest to a reaction raw material supply port of the tubular reactor is higher than a molybdenum concentration of other catalyst layers, and

a temperature during the catalytic oxidation reaction of the catalyst layer closest to the reaction raw material supply port is lower than a temperature during the catalytic oxidation reaction of other catalyst layers.

Effects of Invention

According to the present invention, a catalytic oxidation reaction can be performed with suppressing a molybdenum sublimation loss in a catalyst during the reaction and reducing a decrease in activity of the catalyst.

