JP2001206871A - Method for oxidizing alkane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for reacting an alkane with molecular oxygen in the presence of an oxide catalyst containing molybdenum, vanadium, niobium and tellurium and carried on a carrier, by which the operation can stably be continued in high selectivity, while inhibiting the deterioration of the catalyst with the passage of time. SOLUTION: This method for oxidizing the alkane, comprising reacting the 3 to 6C alkane with molecular oxygen in the presence of an oxide catalyst containing molybdenum, vanadium, niobium and tellurium and carried on a carrier in a fluidized bed reactor, characterized in that the supply of a gas containing the alkane and the supply of a gas containing the oxygen are carried out using nozzles, respectively, which are disposed so that the gas flow from the nozzle for supplying the gas containing the alkane is collided with the gas flow from the nozzle for supplying the gas containing the oxygen, and in that the concentration of the oxygen in the gas at the exit of the reactor is controlled to >=0.1 vol.%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for reacting an alkane with molecular oxygen in a fluidized bed reactor using an oxide catalyst supported on a carrier.

[0002]

2. Description of the Related Art It is well known that an alkene such as propylene or isobutene is reacted with ammonia and oxygen in a molecular state in the presence of an oxide catalyst to produce a corresponding unsaturated nitrile. Specifically, production of acrylonitrile or methacrylonitrile using propylene or isobutene as a raw material is performed. On the other hand, as compared with alkenes, alkane, which is cheaper and readily available, is used as a raw material, and is reacted with ammonia and oxygen in a molecular state using an oxide catalyst supported on a carrier to obtain unsaturated nitriles, unsaturated carboxylic acids. Attention has been focused on methods for producing useful compounds such as, for example, and many catalysts used for these reactions have been proposed.

[0003] Japanese Patent No. 2608768, Japanese Unexamined Patent Publication No.
No. 208136, Japanese Patent Application No. 9-282304,
Japanese Patent Application No. 9-355496 discloses an oxide catalyst containing molybdenum, vanadium, niobium, and tellurium as a catalyst for producing acrylonitrile by gas phase catalytic oxidation in the presence of ammonia of propane. The preparation of these catalysts is also disclosed in JP-A-6-2853072, JP-A-11-475908 and the like.

It has been found that these catalysts deteriorate the catalyst, that is, reduce the selectivity of unsaturated carboxylic acid and unsaturated nitrile by continuously performing a gas phase catalytic reaction using an alkane as a raw material. In the gazette, it is only disclosed about the initial catalyst performance, it is important in industrial implementation, to suppress the deterioration of the catalyst,
There is no disclosure of a method for maintaining stable operation. On the other hand, Japanese Patent Application Laid-Open No. H11-263745 discloses a method of suppressing deterioration of a catalyst over time of an oxide catalyst containing molybdenum, vanadium, niobium, and tellurium by using at least a part of an oxide catalyst in a reactor. It discloses that it is brought into contact with a specific gas. However, this method requires an extra step such as switching of a reaction gas or an extra internal structure of a reactor such as a partition wall, and a simpler method has been required.

[0005]

DISCLOSURE OF THE INVENTION The present invention relates to a method for reacting an alkane with molecular oxygen using an oxide catalyst containing molybdenum, vanadium, niobium, and tellurium supported on a carrier. It is an object of the present invention to provide a method capable of suppressing deterioration and maintaining stable operation.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies in order to solve the above-mentioned problems, and as a result, have developed a fluidized catalyst using an oxide catalyst supported on a carrier and containing molybdenum, vanadium, niobium and tellurium. In a bed reactor, 3 carbon atoms
In reacting the alkane with oxygen in a molecular state, the gas containing the alkane and the gas containing oxygen are supplied from the nozzle for supplying the gas containing alkane through the nozzle for supplying the gas containing oxygen. By using the respective nozzles arranged so as to collide with the gas flow at the same time, and controlling the oxygen concentration in the gas at the outlet of the reactor so as to be 1.0% by volume or more, thereby performing the reaction with time. The present inventors have found that it is possible to suppress the deterioration of and to continue the operation stably, and have completed the present invention.

That is, the present invention provides a reaction between an alkane having 3 to 6 carbon atoms and oxygen in a molecular state in a fluidized bed reactor using an oxide catalyst supported on a carrier and containing molybdenum, vanadium, niobium and tellurium. In making the supply of the gas containing alkane and the gas containing oxygen, the gas flow from the nozzle for supplying the gas containing alkane is arranged such that the gas flow from the nozzle for supplying the gas containing oxygen collides with the gas flow from the nozzle for supplying the gas containing oxygen. The present invention relates to a method for alkane oxidation reaction, wherein the reaction is carried out using a nozzle and controlled so that the oxygen concentration in the gas at the outlet of the reactor becomes 1.0% by volume or more. Preferably, the reaction is carried out in the presence of ammonia in addition to an alkane having 3 to 6 carbon atoms and molecular oxygen.

The gas containing the alkane is supplied by using a nozzle provided so that the gas flow from the nozzle for supplying the gas containing alkane collides with the gas flow from the nozzle for supplying the gas containing oxygen. . Thereby, the deterioration of the catalyst can be suppressed, and the operation can be stably continued. On the other hand, when a gas flow from a nozzle for supplying a gas containing an alkane is used so as not to collide with a gas flow from a nozzle for supplying a gas containing oxygen, the catalyst is deteriorated. Therefore, stable operation cannot be continued.

The installation of the nozzles for causing the gas flow to collide can be performed by installing the nozzles so that both nozzles face each other. Further, the present invention can also be implemented by setting the lines extending in the gas blowing direction from the respective nozzles in a positional relationship such that the lines intersect with each other. The gas flow from a plurality of nozzles may collide with the gas flow from one nozzle. That is, a gas flow from two or more nozzles for supplying a gas containing oxygen may collide with a gas flow from one nozzle for supplying a gas containing alkane, or a gas containing oxygen may be supplied. The gas flow from two or more nozzles that supply the gas containing the alkane may collide with the gas flow from one nozzle.

[0010] Preferably, the method is carried out by making a nozzle for supplying a gas containing oxygen face one nozzle for supplying a gas containing alkane. There is no particular limitation on the spatial positional relationship between the nozzle for supplying the gas containing alkane and the nozzle for supplying the gas containing oxygen, and the nozzle for supplying the gas containing alkane is above the nozzle for supplying the gas containing oxygen. May be on the lower side or vice versa. Further, they may be opposed in the horizontal direction.

The distance between the nozzle for supplying the alkane and the nozzle for supplying oxygen is not particularly limited, but is preferably in the range of 2 to 100 cm, more preferably 5 to 70 cm.
The range of m is most preferably in the range of 10 to 50 cm. The number and arrangement of the nozzles are determined in consideration of the gas distribution in the reactor. For example, when a nozzle for supplying an alkane and a nozzle for supplying oxygen are arranged so as to face each other at a ratio of 1: 1, the number of each nozzle is preferably 1 to the sectional area (m ² ) of the reactor. 100 pieces / m ^2, more preferably 5 to 50 / m ^2, and most preferably from to place at 10 to 30 / m ^2. Preferably, they are arranged symmetrically and evenly.

The gas blowing speed is preferably 10 to
It is 200 m / sec, most preferably 20 to 100 m / sec. The inner diameter of the nozzle is not particularly limited, and can be determined in consideration of the supplied gas amount, the blowing speed, and the number of nozzles. Further, the reaction is performed while controlling the residual oxygen concentration in the gas at the outlet of the reactor to be 1.0% by volume or more, preferably 2.0% by volume or more, more preferably 3.0% by volume or more. This suppresses catalyst deterioration,
Operation can be continued stably. If the oxygen concentration in the reactor outlet gas is less than 1% by volume, stable operation cannot be continued due to deterioration of the catalyst.

The control of the oxygen concentration in the outlet gas can be carried out by appropriately adjusting the supply amount of the alkane-containing gas or the alkane concentration in the gas. Further, it can also be carried out by changing the supply amount of the gas containing oxygen or the oxygen concentration in the gas. Further, it can be carried out by adjusting the amount of the catalyst, the reaction temperature, the reaction pressure and the like. By simultaneously satisfying these two requirements, deterioration of the catalyst can be suppressed, and the operation can be stably continued.

The alkane having 3 to 6 carbon atoms used in this reaction includes propane, n-butane, isobutane, cyclohexane, etc., but propane and isobutane are preferred, and propane is most preferred. For example, acrylonitrile and acrylic acid can be produced from propane, and methacrylonitrile and methacrylic acid can be produced from isobutane. In addition, since the alkene contained in the alkane can also perform a gas phase contact reaction with the catalyst of the present invention,
Even if alkene contains propylene, isobutene, or the like as the alkene, there is no particular problem.

The gas containing an alkane is a gas that mainly supplies an alkane to a reactor. Ammonia may be contained, or oxygen may be contained within a range that does not form detonation. The gas containing oxygen is a gas that mainly supplies oxygen to the reactor. Alkanes, ammonia, carbon monoxide, and the like can be contained within a range that does not form explosive gas. As the oxygen source, it is usually preferable to use air, but it is also possible to use a gas having an increased oxygen concentration by mixing oxygen and air, or separating and removing nitrogen and the like from air. In addition, the raw material gas can be diluted with an inert gas such as helium, argon, nitrogen, carbon dioxide, or water vapor and supplied to the reaction. The molar ratio of oxygen is 0.5 to 6 times, preferably 1 to 4 times the amount of the alkane.

When ammonia is allowed to coexist, the ammonia used does not necessarily have to be of high purity, but may be of industrial grade. The molar ratio of ammonia supplied to the reaction is 0 to 4 times the alkane,
Preferably it is 0 to 2 times, more preferably 0 to 1.5 times. The method of supplying ammonia is not particularly limited,
It may be carried out by a method such as supplying after mixing with alkane, supplying after mixing with oxygen, or supplying alone.
Preferably, it is supplied after being mixed with an alkane, or is supplied alone, and more preferably, is supplied after being mixed with an alkane.

The reaction is carried out using a fluidized bed reactor.
The gas phase catalytic oxidation reaction of alkanes using the catalyst of the present invention is 3
It is carried out in a temperature range of from 00 to 500C, preferably from 320 to 480C. The reaction is performed at a reaction pressure of 50 to 400 kPa, preferably 80 to 250 kPa. The contact time between the raw material gas and the catalyst is 0.1 to 20 (sec · g / c).
c), preferably 0.5 to 10 (sec · g / cc).

The method of the present invention can be applied to various reaction types. For example, the method of separating and collecting and recycling unreacted alkanes, the method of recycling without separation,
A method in which the reaction is performed in a single flow without recycling, a method in which the reaction is performed in a multi-stage reactor, and a method in which these are appropriately combined are exemplified. The catalyst of the present invention comprises an oxide catalyst represented by the general formula (1) and containing molybdenum, vanadium, niobium and tellurium. _{Mo 1 V a Nb b Te c} A d O x ····· (1) ( where in Ueshiki, A is, B, Al, Ga, W , Cr, T
a, Ti, Zr, Hf, Mn, Re, Fe, Ru, C
o, Rh, Ni, Pd, Pt, Ag, Zn, In, P,
At least one element selected from Bi, Ge, Sn, Sb, Pb, rare earth elements and alkaline earth metals.
a, b, c, d, and x represent the atomic ratios of vanadium, niobium, tellurium, A, and oxygen to one atom of molybdenum, respectively, and 0.01 ≦ a ≦ 1.0, 0.01 ≦ b ≦ 1.
0, 0.01 ≦ c ≦ 1.0. D is the sum of the atomic ratios of all the elements added as A.
≦ d ≦ 0.3. x is a value determined by the oxidation state of each element. )

The oxide catalyst of the present invention is used by being supported on a carrier. By supporting the oxide catalyst on a carrier, abrasion resistance can be imparted to the oxide catalyst. Examples of the carrier include silica, alumina, silica-alumina, magnesia, titania, zirconia, and niobium oxide. These can be used alone or in combination. A preferred carrier is silica. The support can be used in an amount of 10 to 70% by weight, preferably 20 to 60% by weight, more preferably 25 to 55% by weight, based on the total amount of the oxide catalyst and the support.

The oxide catalyst of the present invention can be prepared by a known method, for example, as described in JP-A-5-208136 and JP-A-6-285.
It can be prepared by the methods described in Japanese Patent Application No. 3072, Japanese Patent Application No. 9-282304, Japanese Patent Application No. 9-355496, Japanese Patent Application Laid-Open No. 11-47598, and the like.
As a representative element source of each element used in the present invention, ammonium paramolybdate [(N
_{H 4) 6 Mo 7 O 24} · 4H 2 O ], ammonium metavanadate as the vanadium source (NH ₄ VO _3), niobate niobium source [Nb ₂ 0 ₅ · nH ₂ O], telluric acid as a tellurium source (H ₆ TeO ₆ ), but is not particularly limited as long as the target element is contained.

For example, molybdenum sources include molybdenum trioxide (MoO ₃ ), molybdenum pentachloride (MoCl ₅ ),
Phosphomolybdic acid [H ₃ PMo ₁₂ O _40], such as silicomolybdic acid [H ₄ SiMo ₁₂ O _40] is, as the vanadium source vanadium pentoxide (V ₂ O _5), vanadium chloride (VC
l _4, VCl _3), and the like. Further, molybdenum vanadic acid, which is a mixed coordination type of molybdenum and vanadium, or the like can also be used. Niobium sources include niobium pentoxide (Nb ₂ O ₅ ) and niobium pentachloride (NbCl ₅ ).
Examples of tellurium sources include tellurium dioxide (TeO ₂ ) and ammonium tellurate [(NH ₄ ) ₂ TeO ₄ ).

In addition, as the element sources of the elements other than the above,
Oxides, ammonium salts, nitrates, hydrochlorides, sulfates, organic acid salts and the like can be mentioned. The carrier source of the carrier used in the present invention is not particularly limited, and oxides, hydroxides, inorganic salts, organic acid salts and the like containing the target element can be used.
In addition, a sol or a gel may be used.
The raw material slurry is prepared by adding a raw material liquid of a carrier source to a liquid obtained by dissolving elemental sources such as molybdenum, vanadium, and tellurium in water or a nitric acid aqueous solution, and further adding a liquid obtained by dissolving a niobium source. be able to. The order of adding the raw materials including the carrier can be changed.

The obtained raw material slurry can be dried by spray drying, evaporation to dryness, vacuum drying, freeze drying, or the like. In particular, it is preferable to use a spray drying method to obtain spherical particles for use in a fluidized bed reaction. The resulting dried product is substantially free of oxygen in the presence of 450
The firing is carried out at a temperature in the range of ８００800 ° C., preferably 500-700 ° C., and more preferably 550-680 ° C. for 1-20 hours. If necessary, in air at 100-450 ° C,
Pre-firing may be performed. Firing and pre-firing can be performed in a rotary furnace, a tunnel furnace, a muffle furnace, a fluidized firing furnace, or the like.

[0024]

Next, the present invention will be described in detail with reference to examples and reference examples. The alkane conversion and the selectivity of unsaturated nitrile used to represent the reaction results are defined by the following formula. Alkane conversion (%) = (moles of alkane reacted)
{(Moles of supplied alkane) × 100 Unsaturated nitrile selectivity (%) = (moles of unsaturated nitrile generated) ÷ (moles of reacted alkane) × 100

(Catalyst Preparation Example) An oxide catalyst represented by Mo ₁ V _0.32 Nb _0.12 Te _0.22 O _x supported on 34.0% by weight of silica was prepared as follows. 219k of water
g, 51.6 kg of ammonium heptamolybdate,
Ammonium metavanadate 11.0 kg, telluric acid 1
4.8 kg were sequentially added and dissolved by heating to 60 ° C., followed by cooling to 30 ° C. to obtain a mixed aqueous solution. To this mixture, 74.0 kg of a mixed aqueous solution of niobic acid and oxalic acid having a niobium concentration of 0.47 (mol-Nb / kg) and an oxalic acid concentration of 1.22 (mol-oxalic acid / kg) and 30% by weight of silica were added. 113 kg of the contained silica sol was sequentially added and mixed to obtain a catalyst raw material slurry. This slurry was spray-dried at 200 ° C. to obtain a powder. This powder was fired in a rotary furnace at 600 ° C. for 2 hours in a nitrogen atmosphere. The oxygen concentration in nitrogen was 3 ppm or less.

[0026]

Example 1 600 kg of catalyst prepared by the method of Preparation Example
Was packed in a SUS fluidized bed reactor having an inner diameter of 600 mm. A nozzle for supplying a gas containing an alkane was installed vertically downward at a position 30 cm above the bottom of the catalyst filling section of the reactor. The installation positions were the center of the reactor and the vertices of a square of 340 mm on a side centered on the center of the reactor (a total of five places). A nozzle for supplying a gas containing oxygen was installed vertically upward on the bottom surface of the catalyst packed portion of the reactor. The installation positions were set at positions (5 places) vertically overlapping the nozzles for supplying the gas containing the alkane.

The temperature of the catalyst layer was maintained at 430 ° C., and propane (24.0 Nm ³ / H) and ammonia (24.0 Nm ³ / H) were supplied from the upper nozzle, and air (310 Nm ³ / H) was supplied from the lower nozzle.
m ³ / H were supplied. Reactor outlet pressure is 50 kPa
(Gauge pressure). 24 hours after the start of the steady-state reaction, the conversion was 80.3%, the acrylonitrile selectivity was 58.3%, and the oxygen concentration at the outlet was 1.1%. The operation could be continued stably, the conversion after 700 hours from the start of the steady-state reaction was 80.5%, the selectivity for acrylonitrile was 58.2%, and the oxygen concentration at the outlet was 1.0%.

[0028]

Comparative Example 1 The same reactor as in Example 1 was used except that the central nozzle among the nozzles for supplying oxygen was sealed.
The reaction was carried out under the same conditions as in Example 1. Steady-state reaction start 2
After 4 hours, the conversion was 79.8%, the acrylonitrile selectivity was 58.2%, and the oxygen concentration at the outlet was 1.1%.
As the operation was continued, the acrylonitrile selectivity gradually decreased, and the conversion after 180 hours from the start of the steady-state reaction was 80.4%, and the acrylonitrile selectivity was 56.3.
% And the oxygen concentration at the outlet was 1.0%. It was judged that further continuation of the operation was difficult, and the operation was stopped.

[0029]

Comparative Example 2 Catalyst 600 k Prepared by the Method of Catalyst Preparation Example
g was charged to the same reactor as in Example 1. The temperature of the catalyst layer was maintained at 430 ° C., and propane 24.7 was injected from the upper nozzle.
The Nm ³ / H and ammonia 24.7Nm ³ / H, air was supplied 309 nm ³ / H from the lower side of the nozzle. The reactor was operated at an outlet pressure of 50 kPa (gauge pressure). The conversion rate after 24 hours from the start of the steady-state reaction was 79.
The acrylonitrile selectivity was 58.5%, and the outlet oxygen concentration was 0.5%. As the operation was continued, the acrylonitrile selectivity gradually decreased. The conversion after 156 hours from the start of the steady-state reaction was 79.8%, the acrylonitrile selectivity was 56.8%, and the oxygen concentration at the outlet was 0.4%.
%Met. It was judged that further continuation of the operation was difficult, and the operation was stopped.

[0030]

Example 2 The same reactor as in Example 1 was charged with 330 kg of the catalyst prepared in the Preparation Example. The temperature of the catalyst layer is 430 ° C
To keep the 39.7Nm ³ / H and ammonia 25.8Nm ³ / H from the upper nozzle, air was supplied 297 nm ³ / H from the lower side of the nozzle. Reactor outlet pressure is 50
The operation was performed while controlling to kPa (gauge pressure). 24 hours after the start of the steady-state reaction, the conversion was 52.3%, the acrylonitrile selectivity was 65.8%, and the oxygen concentration at the outlet was 3.0%.
Met. The operation can be continued stably, the conversion after 700 hours from the start of the steady-state reaction is 50.6%, the acrylonitrile selectivity is 65.5%, and the oxygen concentration at the outlet is 3.1.
%Met.

[0031]

According to the method of the present invention, when an alkane is reacted with molecular oxygen in a fluidized bed reactor using an oxide catalyst supported on a carrier, catalyst deterioration is suppressed and stable operation is achieved. Can be continued.

Continued on front page F-term (reference) 4G069 AA03 BA01A BA02A BA02B BA03A BA04A BA05A BA06A BB04A BB06A BB06B BC08A BC16A BC17A BC18A BC21A BC22A BC23A BC25A BC26A BC32A BC35A BC38A BC50A BCBC BCA BCBC BC BC BC71A BC72A BC75A BD03A BD07A BD10A BD10B CB07 CB14 CB53 CB54 DA08 EA02Y FC08 4H006 AA02 AC46 AC54 BA12 BA14 BA15 BA30 BC13 BD81 BE14 BE30 QN24 4H039 CA65 CA70 CC30 CL50

Claims (2)

[Claims] 1. A fluidized bed reactor using an oxide catalyst supported on a carrier and containing molybdenum, vanadium, niobium, and tellurium represented by the general formula (1), having 3 to 3 carbon atoms.
When reacting the alkane 6 with molecular oxygen,
The supply of the gas containing alkane and the gas containing oxygen includes the respective nozzles arranged so that the gas flow from the nozzle for supplying the gas containing alkane collides with the gas flow from the nozzle for supplying the gas containing oxygen. A method of alkane oxidation reaction, characterized in that the reaction is carried out using a gas and the reaction is controlled such that the oxygen concentration in the gas at the outlet of the reactor becomes 1.0% by volume or more. _{Mo 1 V a Nb b Te c} A d O x ····· (1) ( where in Ueshiki, A is, B, Al, Ga, W , Cr, T
a, Ti, Zr, Hf, Mn, Re, Fe, Ru, C
o, Rh, Ni, Pd, Pt, Ag, Zn, In, P,
At least one element selected from Bi, Ge, Sn, Sb, Pb, rare earth elements and alkaline earth metals.
a, b, c, d, and x represent the atomic ratio of vanadium, niobium, tellurium, A, and oxygen to one atom of molybdenum, respectively, and 0.01 ≦ a ≦ 1.0, 0.01 ≦ b ≦ 1.
0, 0.01 ≦ c ≦ 1.0. D is the sum of the atomic ratios of all the elements added as A.
≦ d ≦ 0.3. x is a value determined by the oxidation state of each element. ) 2. The method according to claim 1, wherein the reaction is carried out in the presence of ammonia in addition to an alkane having 3 to 6 carbon atoms and oxygen in a molecular state.