JP2015157243A - Oxide catalyst and method for producing the same, and method for producing unsaturated nitrile using the oxide catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oxide catalyst which provides a high yield of unsaturated nitrile in an ammoxidation reaction of an olefin, and can maintain good activity even when it is exposed to repeated reduction load.SOLUTION: Provided is an oxide catalyst used for a gas-phase contact ammoxidation reaction of an olefin, containing molybdenum, bismuth, iron, and nickel, in which the nickel is unevenly distributed in an outer portion of a particle of the oxide catalyst.

Description

  The present invention relates to an oxide catalyst, a method for producing the same, and a method for producing an unsaturated nitrile using the oxide catalyst.

  A method for obtaining acrylonitrile by vapor-phase catalytic oxidation of propylene with molecular oxygen in the presence of ammonia is widely known as an “ammoxidation process” and is currently widely practiced on an industrial scale.

  In order to carry out the ammoxidation process more efficiently on an industrial scale, various studies have been made on the catalyst used in this process, and a catalyst comprising a composite oxide such as Mo—Bi—Fe, Fe—Sb, etc. It has been known. For example, Patent Documents 1 and 2 disclose catalysts in which other components are added in addition to molybdenum, bismuth and iron.

Japanese Patent No. 3214984 Japanese Patent No. 5188005

  However, when the present inventors prepared the catalysts described in Patent Documents 1 and 2, these catalysts were able to greatly improve the initial yield of the reaction, but with regard to the resistance to the reduction load during long-time operation. It has not yet been fully satisfactory, and it has been found that further improvements are necessary.

  The present invention has been made in view of the above circumstances, and provides an oxide catalyst capable of providing a high unsaturated nitrile yield in an olefin ammoxidation reaction and maintaining good activity even when subjected to repeated reduction loads. It is an object of the present invention to provide a method and a method for producing an unsaturated nitrile using the oxide catalyst.

  The inventors have made various studies in order to achieve the above object, and that even if the prepared metal composition is the same oxide catalyst, the metal distribution in the catalyst is not always uniform. I found it. This is considered to be due to the presence of a plurality of metal oxides in a complexed state in the catalyst and the movement of the metal element in the process of catalyst preparation including calcination. And when the present inventors examined the distribution state of the metal oxide particle which exists in a catalyst particle, when the metal element which comprises a catalyst distributes to a specific state, a high unsaturated nitrile yield is obtained. At the same time, it has been found that good activity can be maintained even under repeated reduction loads, and the present invention has been completed.

That is, the present invention is as follows.
[1] Oxide catalyst used for gas phase catalytic ammoxidation reaction of olefin or gas phase catalytic oxidation reaction of monoolefin, comprising molybdenum, bismuth, iron and nickel, and particles of the oxide catalyst An oxide catalyst in which nickel is unevenly distributed at the outer edge of the catalyst.
[2] A characteristic X-ray generated when an electron beam is irradiated to nickel existing at the center of the particle, when the average intensity of the characteristic X-ray generated when the nickel existing at the outer edge is irradiated with an electron beam The oxide catalyst according to [1], which is 1.2 times or more of the average strength.
[3] A method for producing an oxide catalyst according to [1] or [2],
Mixing molybdenum, bismuth, iron, nickel, silica having an average primary particle diameter of 5 nm or more and less than 20 nm, and silica having an average primary particle diameter of 20 nm or more and less than 125 nm, a precursor slurry A step of preparing
The precursor slurry is spray-dried to obtain dry particles, and the dry particles are heated from room temperature to a temperature set in a range of 200 ° C. to 350 ° C. over 1 hour, and the dry particles are temporarily Calcination to obtain pre-fired particles;
The calcined particles are heated for 1 hour or more from the temperature set in the step of obtaining the calcined particles to a temperature set within a range of 500 ° C. to 750 ° C., and the calcined particles are calcined. Obtaining an oxide catalyst. A method for producing an oxide catalyst.
[4] A method for producing an unsaturated nitrile, wherein the oxide catalyst according to [1] or [2] is used to react an olefin with molecular oxygen and ammonia to produce an unsaturated nitrile.

  ADVANTAGE OF THE INVENTION According to this invention, while giving a high unsaturated nitrile yield in the ammoxidation reaction of an olefin, the oxide catalyst which can maintain favorable activity even if it receives repeated reduction load, its manufacturing method, and its oxide catalyst A method for producing an unsaturated nitrile using can be provided.

It is a schematic diagram for demonstrating uneven distribution of nickel in the oxide catalyst of this embodiment.

  Hereinafter, a mode for carrying out the present invention (hereinafter simply referred to as “the present embodiment”) will be described with reference to the drawings as necessary. However, the present invention is limited to the following embodiment. However, various modifications can be made without departing from the scope of the invention. The positional relationship such as up, down, left, and right is based on the positional relationship shown in the drawings unless otherwise specified. Further, the dimensional ratios in the drawings are not limited to the illustrated ratios.

[1] Oxide Catalyst The oxide catalyst of the present embodiment is an oxide catalyst used for a gas phase catalytic ammoxidation reaction of olefin, which contains molybdenum, bismuth, iron, and nickel, Nickel is unevenly distributed at the outer edge.

(1) Composition The oxide catalyst in this embodiment contains molybdenum, bismuth, iron, and nickel as essential components. In general, in a Mo—Bi—Fe-based catalyst, each metal element is assumed to have the following functions. That is, molybdenum plays a role as an adsorption site for olefins such as propylene and an activation site for ammonia to generate NH species. Bismuth acts as an activation site for olefins such as propylene and monoolefins such as n-butene, and draws α-position hydrogen to produce π-allyl species. Iron contributes to the exchange of oxygen from the gas phase to the active site by Fe ³⁺ / Fe ²⁺ redox. Moreover, nickel is believed to stabilize the Fe ²⁺ by causing solid solution of Fe ²⁺ in NiMoO ₄ structure. The function of each metal element in these catalysts is described in, for example, Grasselli, R .; K. , “Handbook of Heterogeneous Catalysis 5”, Wiley VCH, 1997, p2302.

  The content ratio of each metal element of molybdenum, bismuth, iron and nickel in the oxide catalyst is not particularly limited, and may be the same as the conventional one. For example, from the viewpoint of making the crystal phase composition ratio appropriate for the expression of the catalytic function, the atomic ratio of bismuth is 0.1 to 1, iron is 0.1 to 3, and nickel is 2 to 10 with respect to 12 atoms of molybdenum. Preferably there is.

In addition to molybdenum, bismuth, iron and nickel, the metal component optionally contained in the oxide catalyst is (a) at least one metal selected from the group consisting of cerium, chromium and manganese An element, (b) at least one metal element selected from the group consisting of cobalt and magnesium, and (c) at least one metal element selected from the group consisting of potassium, rubidium, and cesium. Of these, the metal element (a) is presumed to have a redox function in the oxide catalyst as well as iron, and increase the high-temperature stability of the crystal phase of the main catalyst. In addition, the metal element (b) is presumed to stabilize Fe ²⁺ in the M ^II MoO ₄ structure. It is presumed that the metal element (c) covers the acid sites on the catalyst surface and suppresses side reactions. These functions are considered to further improve the catalyst performance.

  From the viewpoint of further effectively and surely exerting the function of each metal element to further improve the catalyst performance, in the oxide catalyst, the metal element of (a) is 0 to 3 atoms with respect to 12 atoms of molybdenum. The metal element (b) is preferably contained in 4 to 12 atoms, and the metal element (c) is preferably contained in 0.01 to 2 atoms.

(2) Distribution of nickel In the oxide catalyst of the present embodiment, nickel is present at a high concentration in the outer edge portion of the catalyst particles, that is, unevenly distributed. Here, in the present specification, the “uneven distribution” of nickel indicates that the presence ratio of nickel in a certain region of catalyst particles is higher than that in other regions. The distribution of various elements contained in the oxide catalyst can be confirmed from the wavelength and intensity of characteristic X-rays generated from each region of the oxide catalyst sample irradiated with an electron beam. More specifically, for example, the distribution of various elements can be confirmed by an analytical technique such as EDX (energy dispersive X-ray spectroscopy) or EPMA (electron beam microanalysis).

  In addition, the “outer edge” of the particle refers to a region from the outer periphery of the particle cross section to a portion inside 20% of the particle diameter, and the “center” of the particle described later refers to a region inside the outer edge. . “Particle diameter” refers to the distance between two points where an arbitrary straight line passing through the center of gravity of the particle cross section intersects the outer periphery of the particle cross section. The outer periphery and particle diameter of the particle cross section of the oxide catalyst can be discriminated from the electron microscope image.

  Regarding the uneven distribution of nickel in the oxide catalyst, the average intensity of characteristic X-rays generated when an electron beam is irradiated onto nickel existing at the outer edge of the catalyst particle is irradiated with an electron beam at the center of the catalyst particle. It can be said that nickel is more unevenly distributed when the average intensity of characteristic X-rays generated is 1.05 times or more. The average intensity of the characteristic X-ray generated when the nickel existing in the outer edge portion of the catalyst particle is irradiated with an electron beam is equal to the characteristic X-ray generated when the nickel existing in the central portion of the catalyst particle is irradiated with the electron beam. The average strength is more preferably 1.20 times or more. Thus, nickel is unevenly distributed, so that the effects of the present invention can be more effectively and reliably exhibited.

Next, as an example, a case where the nickel distribution in the oxide catalyst is measured using EPMA will be described. The analysis conditions by EPMA are as follows.
Equipment: Product name “JXA-8500F” manufactured by JEOL Ltd.
Measurement conditions: Acceleration voltage ... 15.0 kV, irradiation current ... 50 nA, magnification ... * 1000, beam diameter ... 20 [mu] m

  As a pretreatment, the particle sample of the oxide catalyst is immersed in an epoxy resin before curing (manufactured by Gatan Co., Ltd., main resin Resin-G2 and curing agent Hardener-G2 (both are trade names)) and is heated to 130 ° C. The particle sample is embedded in the epoxy resin by heating to cure the epoxy resin. Next, the obtained embedded material is roughly polished with water-resistant sandpaper (# 2000) to expose the cross section of the particle sample. Next, the coarsely polished material is set in an ion milling apparatus, and precision cross-section processing is performed on the cross-section of the oxide catalyst particle sample with an Ar ion beam for 6 hours. The measurement sample thus obtained is placed on a predetermined sample stage, and the nickel distribution is measured by EPMA.

The conditions for ion milling are as follows.
Equipment: Product name “E-3500” manufactured by Hitachi High-Technologies Corporation
Measurement conditions: acceleration voltage ... 6 kV, discharge voltage ... 4 kV, stage control ... 1, milling time ... 6 hours, introduced gas ... Ar

  When calculating the average intensity of the characteristic X-ray of nickel, the surface analysis of the cross section is performed as follows. First, among the oxide catalyst particles, particles having a particle diameter in a predetermined range are selected by a filter. Next, a measurement sample is prepared as described above for the selected catalyst. Next, surface analysis of the cross section of the measurement sample is performed on particles whose cross section is exposed.

  More specifically, for example, a surface analysis of the cross section of particles having a particle size in the range of 40 to 70 μm by measurement of particle size distribution described later is performed. Such particles can be regarded as being exposed to the center of the particles or the vicinity thereof. Even for an oxide catalyst whose average particle size does not fall within this range, the particles having a particle size of 40 to 70 μm are contained, and the particles having the particle size are selected by a filter or the like. When the average intensity of the characteristic X-ray of nickel is measured and the distribution of nickel is analyzed, if nickel is unevenly distributed at the outer edge of the particle, it can be said that a preferable uneven state is satisfied. According to the recognition of the present inventors, in the case of an oxide catalyst used in a fluidized bed reaction, catalyst particles having a particle size of 40 to 70 μm exhibit particularly efficient catalytic action, so at least in the oxide catalyst having this particle size. If nickel is unevenly distributed, the effects of the present invention can be achieved.

Here, the average particle size of the catalyst particles is determined by measuring the particle size distribution according to JIS R 1629-1997 “Method for measuring particle size distribution of fine ceramic raw material by laser diffraction / scattering method”, and averaging on a volume basis. It is what I have sought. More specifically, a part of the dry powder is baked in air at 400 ° C. for 1 hour, and the obtained particles are subjected to a laser diffraction scattering method particle size distribution measuring device (manufactured by BECKMAN COULTER, model number: LS230). Measured. Here, the reason why the average particle size is measured after “calcining in air at 400 ° C. for 1 hour” is to prevent the dry powder from being dissolved in water. That is, “calcination in air at 400 ° C. for 1 hour” is exclusively for measurement, and is not related to the later-described firing step. It may be considered that the particle diameter does not substantially change before and after the firing.
More specifically, the average particle diameter may be measured as follows according to the manual attached to the laser diffraction scattering particle size distribution measuring apparatus. First, the background is measured with RunSpeed60. On the other hand, 0.2 g of particles to be measured are weighed into an appropriately sized screw tube, and 10 mL of water is added thereto. The screw tube is then capped (sealed) and shaken well to disperse the particles in water. An ultrasonic wave of 300 W is applied by the apparatus and the screw tube is shaken sufficiently again. Thereafter, while continuing to apply ultrasonic waves, the particles dispersed in water are injected into the apparatus main body using a dropper so as to have an appropriate concentration (concentration 10, PIDS60). When the concentration display is stabilized, the application of ultrasonic waves is stopped, and after standing for 10 seconds, measurement is started (measurement time 90 seconds). The median diameter value of the obtained measurement result is defined as the average particle diameter.

  Specifically, the cross-sectional surface analysis irradiates the cross section of the catalyst particle with an electron beam and obtains a reflected electron image based on characteristic X-rays generated therefrom. Based on the reflected electron image, line analysis data passing through the center (center of gravity) of the particle cross section is extracted and used. Here, the “average intensity” refers to the average value of the intensity excluding the background, and the average value of the characteristic X-ray intensity in one line analysis data of one particle is arbitrarily selected 2 Further averaged over the particle diameter of the book, the averaged value means the value averaged over 10 particles. The interval of data capture is preferably 1 μm or less. The background is determined based on the intensity at a location where the presence of the catalyst is confirmed from the reflected electron image of the catalyst particle cross section.

(3) Support When the production of unsaturated nitrile is carried out industrially, it is desirable that the catalyst has sufficient strength. From such a viewpoint, the oxide catalyst of the present embodiment comprises a support and its It is preferable to include a composite oxide containing molybdenum, bismuth, iron, and nickel supported on a carrier. Examples of the carrier are not particularly limited, and examples thereof include silica, alumina, titania, silica / alumina, and silica / titania. Of these, silica is preferred from the viewpoint of increasing the yield of unsaturated nitrile. An oxide catalyst including silica as a support has a more excellent fluidity in a fluidized bed ammoxidation reaction. From the viewpoint of wear resistance, the silica content is preferably 40% by mass or more based on the total amount of the composite metal oxide and silica. Moreover, it is preferable that a silica content is 60 mass% or less from a viewpoint of obtaining sufficient catalyst activity and a better selectivity.

  Silica as the carrier includes silica (a) having an average primary particle diameter of 20 nm or more and less than 125 nm, more preferably 20 nm or more and less than 50 nm, and silica having an average particle diameter of primary particles of 5 nm or more and less than 20 nm (b ). By using such a silica raw material, it is possible to suppress a decrease in catalyst strength and to suppress an increase in the production of by-products when used in the production of an unsaturated nitrile. The average particle size of the primary particles is measured in the same manner as the flat particle size of the catalyst particles.

  The raw material of silica (a) and silica (b) is preferably silica sol from the viewpoint of more effectively and reliably achieving the effects of the present invention. From the same viewpoint, the content of silica (a) in the total amount of silica is 20% by mass or more and 80% by mass or less, and the content of silica (b) is 80% by mass or less and 20% by mass or more. preferable. Silica (a) and silica (b) are used individually by 1 type or in combination of 2 or more types, respectively.

  The particle shape of the oxide catalyst in the present embodiment is preferably spherical from the viewpoint of making fluidity in the reactor favorable.

  FIG. 1 is a schematic diagram for explaining the uneven distribution of nickel in the oxide catalyst of the present embodiment. In FIG. 1, one line analysis data in a cross section of one catalyst particle is shown. In the line analysis data, the characteristic X-ray intensity of nickel existing at the outer edge and the center of the particle and the average value thereof. Is shown. In FIG. 1, the average value of the characteristic X-ray intensity of nickel existing at the outer edge of the particle is larger than the average value of the characteristic X-ray intensity of nickel existing at the center of the particle.

[2] Method for Producing Oxide Catalyst The method for producing an oxide catalyst according to this embodiment is a method for producing the above oxide catalyst, and includes (i) a precursor containing molybdenum, bismuth, iron, and nickel. A step of preparing a slurry, (ii) a step of spray drying the precursor slurry to obtain dry particles, and (iii) a step of firing the dry particles.

[Step (i)]
Step (i) is a step of preparing a catalyst precursor slurry containing the above-mentioned metal element, and when the oxide catalyst includes a support, the components serving as the support source may be mixed in this step. Good. In the step (i), for example, after preparing a solution containing a component that becomes a supply source of molybdenum, this solution is mixed with other metal elements and, if necessary, a component that becomes a supply source of a carrier, and a precursor A slurry is obtained. Hereinafter, the method for preparing the precursor slurry will be described by taking the case where the oxide catalyst includes a silica carrier as an example, but the method for manufacturing the oxide catalyst of the present embodiment is not limited thereto.

  The supply source (raw material) of each metal element contained in the precursor slurry is preferably a salt that is soluble in water or nitric acid. Sources of molybdenum, bismuth, iron and nickel metal elements, and other metal elements added to the oxide catalyst as needed, include ammonium salts, nitrates, hydrochloric acid soluble in water or nitric acid. Examples include salts, sulfates, organic acid salts and inorganic acids. In particular, an ammonium salt is preferable as a supply source of molybdenum, and a nitrate is preferable as a supply source of bismuth, iron, nickel, and other metal elements. In addition to being easy to handle, nitrates are also preferred in that they do not cause residual chlorine that occurs when hydrochloride is used or residual sulfur that occurs when sulfate is used. Specific examples of the supply source of each metal element include ammonium paramolybdate, bismuth nitrate, ferric nitrate, and nickel nitrate. Further, as a supply source of silica as a carrier, silica sol is preferable from the viewpoint of more effectively and reliably achieving the effects of the present invention. Furthermore, from the same viewpoint, the preferable concentration of silica in the silica sol is 10 to 50% by mass. The concentration of the aqueous solution to be added can be appropriately adjusted so that the concentration is suitable for spray drying of the precursor slurry described later.

  The precursor slurry may contain a coordinating organic compound. Here, the “coordinating organic compound” refers to an organic compound having a lone electron pair and coordinated to a metal. The coordination style may be single or multi-seat. Specific examples of the coordinating organic compound include tartaric acid, malic acid, citric acid and ethylenediamine.

  Although the upper limit of content of a coordination organic compound is not specifically limited, It is preferable to make it contain so that it may become 15 mass% or less with respect to the mass of the oxide catalyst finally obtained industrially. By setting the content of the coordinating organic compound to 15% by mass or less, it is possible to suppress the generation of heat and cracking of the catalyst particles due to the decomposition and diffusion of organic substances in the catalyst production stage.

  The coordinating organic compound may be dissolved in an acid or water and added to the precursor slurry, or may be added as a complex compound with iron.

  In the preparation of the precursor slurry, the order of mixing the sources is not particularly limited. For example, while stirring the silica sol, an aqueous solution containing a component that is a source of molybdenum is added thereto, and then a source of a metal element other than molybdenum, such as a compound of a metal component (preferably a nitrate), is added. A solution dissolved in an aqueous solvent (preferably an aqueous nitric acid solution) is added, and finally an aqueous solution containing a coordinating organic compound is added. Prior to mixing with silica sol, (a) a metal element supply source other than iron and a coordinating organic compound may be mixed first, and then an iron supply source may be mixed therewith, (b) An iron supply source and a coordinating organic compound may be mixed first, and another metal element supply source may be mixed therewith. (C) A metal element supply source in order to an aqueous solution of the coordinating organic compound May be added. In any of these cases (a) to (c), the content of the coordinating organic compound is preferably as described above. The metal element supply source other than molybdenum may be added to the silica sol without being mixed in advance after being dissolved in an aqueous solvent, or the aqueous solution of the metal element supply source other than molybdenum and the coordinating organic compound. The aqueous solution may be mixed before adding to the silica sol.

[Step (ii)]
Step (ii) in the method for producing an oxide catalyst of the present embodiment is a step of spray drying the precursor slurry. In this step, dry particles which are spherical fine particles suitable for fluidized bed reaction can be obtained by spray drying the precursor slurry. The spray drying apparatus may be a general one such as a rotary disk type or a nozzle type, and spray drying is performed so as to obtain an oxide catalyst having a particle size suitable as a fluidized bed catalyst by adjusting operating conditions. . The particle size suitable as a fluidized bed catalyst is 25 to 180 μm in average particle size. As an example of spray drying to obtain catalyst particles having a suitable particle size, a centrifugal atomizing apparatus (for example, manufactured by Okawara Kako Co., Ltd.) equipped with a dish-shaped rotor installed in the center of the upper part of the dryer. Spray drying performed using an OC-16 type spray dryer) while maintaining the inlet air temperature of the dryer at 240 ° C and the outlet temperature at 140 ° C.

[Step (iii)]
Step (iii) in the method for producing an oxide catalyst of the present embodiment is a step of firing the dried particles obtained by spray drying. This step preferably has the following firing steps from the viewpoint of more easily obtaining the oxide catalyst of the present embodiment, and in particular, when at least one of the metal element supply sources contains nitrate ions. It is preferable to have each of the following firing steps.

[A] Temporary calcination In the preliminary calcination step, the temperature of the dried particles is preferably raised from room temperature to a temperature set in the range of 200 ° C to 350 ° C, preferably in the range of 280 ° C to 350 ° C, more preferably the above. Pre-baking is carried out by holding at the set temperature (hereinafter, the temperature held in the pre-baking is referred to as “pre-baking temperature”) to obtain pre-baked particles. The set temperature and pre-baking temperature are more preferably 280 ° C to 350 ° C, and even more preferably 300 ° C to 330 ° C. The temperature raising time is preferably 1 hour or longer, more preferably 1 to 10 hours, and further preferably 2 to 5 hours. At this time, the rate of temperature rise need not be constant. The pre-baking is intended to gradually burn components contained in the supply source of each metal element remaining in the dry particles, for example, ammonium nitrate or nitric acid derived from metal nitrate. The holding time in the above holding is preferably 1 hour or more, more preferably 2 to 10 hours, and further preferably 2 to 5 hours. By setting the set temperature and pre-baking temperature within the above range, or setting the temperature raising time and holding time within the above range, the movement of the metal element within the particles becomes a desired level. The nickel element is easily distributed in a desired region. That is, it is preferable to set the set temperature and the upper limit of the preliminary firing temperature, and the lower limit of the temperature raising time and the holding time in the preliminary firing so as not to impair the freedom of movement of the metal element.

[B] Main calcination In the main calcination step, the calcined particles obtained in the preliminary calcination are preferably heated to a temperature set within a range of 500 ° C. to 750 ° C. to obtain an oxide catalyst. The heating temperature (main baking temperature) in the main baking is higher than the temporary baking temperature, more preferably 550 ° C to 700 ° C, and further preferably 580 ° C to 650 ° C. The purpose of the main firing is to grow the crystal of the particles while maintaining the distribution of the nickel element in the temporarily fired particles obtained by the preliminary firing. From this viewpoint, the holding time at the heating temperature in the main baking is preferably 2 to 12 hours, more preferably 2 to 10 hours, and further preferably 2 to 6 hours. It is preferable to adjust the holding time from the viewpoint of preventing the specific surface area of the catalyst from decreasing and the activity from decreasing. Further, from the same viewpoint, when the main baking temperature is higher than the temporary baking temperature in the temporary baking, it is preferable to increase the temperature from the temporary baking temperature to the main baking temperature over 1 hour, and more preferably 1 to 10 The temperature is increased over a period of time, more preferably 1 to 5 hours, particularly preferably 1 to 3 hours.

  By passing through the above process, in the obtained oxide catalyst, nickel is unevenly distributed in the outer edge part of particle | grains, and the above-mentioned oxide catalyst of this embodiment can be obtained.

[3] Method for Producing Unsaturated Nitrile The method for producing an unsaturated nitrile of the present embodiment uses the above oxide catalyst to react olefins such as propylene and isobutene with ammonia and molecular oxygen (that is, gas phase catalytic ammonia). Oxidation reaction) to produce unsaturated nitriles such as acrylonitrile and methacrylonitrile.

  Olefins such as propylene and ammonia, which are raw materials for the ammoxidation reaction, do not necessarily have high purity, and industrial grade ones can also be used. Usually, air is used as the oxygen source of molecular oxygen. The volume ratio of ammonia and air to olefins such as propylene is preferably 1: 0.9 to 1.7: 7 to 11, more preferably 1: 1.0 to 1.5: 8, as olefin: ammonia: air. Is in the range of -10.

  Moreover, reaction temperature becomes like this. Preferably it is 400-460 degreeC, More preferably, it is the range of 410-440 degreeC. The reaction pressure is preferably in the range of normal pressure to 3 atmospheres. The contact time between the raw material mixed gas containing olefin, ammonia and molecular oxygen and the catalyst is preferably 1 to 8 seconds, more preferably 2 to 6 seconds.

  According to the present embodiment, a high unsaturated nitrile yield is provided in the ammoxidation reaction of olefins such as propylene, and the stability of the reaction is good even during a long operation, and particularly good even when subjected to repeated reduction loads. It is possible to provide an oxide catalyst capable of maintaining a high activity. Moreover, the oxide catalyst of this embodiment may be suitably used also for manufacture of the unsaturated aldehyde or conjugated diolefin by the oxidation reaction of a monoolefin.

  Hereinafter, the present embodiment will be described more specifically by way of examples. However, the present embodiment is not limited to the following examples unless it exceeds the gist thereof. In addition, Table 1 shows compositions and production conditions of the oxide catalysts of Examples and Comparative Examples.

(Distribution analysis of nickel in the cross section of catalyst particles)
The nickel distribution in the cross section of the catalyst particles was analyzed according to the measurement by EPMA using the product name “JXA-8500F” manufactured by JEOL Ltd. described in “(2) Nickel distribution”. Regarding the average intensity of the characteristic X-rays derived from the obtained nickel, the ratio of the outer edge part to the center part of the catalyst particles is shown in Table 1 as (the intensity of the outer edge part / the strength of the center part).

(Ammoxidation reaction of propylene)
50 mL of the oxide catalyst obtained in Example 1 was accommodated in a Pyrex (registered trademark) glass fluidized bed reaction tube having an inner diameter of 25 mm in which 12 pieces of 10-mesh wire mesh were incorporated at intervals of 1 cm. In the reaction tube, the reaction temperature was 430 ° C., the reaction pressure was normal pressure, and a mixed gas of 9% by volume of propylene (the volume ratio of propylene: ammonia: oxygen: helium was 1: 1.2: 1.85: 7.06). ) At a flow rate of 3.64 mL (converted to NTP) per second and contacted with the oxide catalyst to proceed the ammoxidation reaction of propylene. The results of this reaction were evaluated by propylene conversion, acrylonitrile selectivity, and acrylonitrile yield defined by the following formula. The results are shown in Table 2.

  The oxide catalysts obtained in Examples 2 to 7 and the oxide catalysts obtained in Comparative Examples 1 to 5 were also used for the ammoxidation reaction of propylene in the same manner as the oxide catalyst obtained in Example 1. It was. However, after fixing the volume of propylene in the raw material mixed gas to 9% by volume and the volume ratio of ammonia to propylene at 1: 1.2, the volume ratio of oxygen to propylene was appropriately selected from the range of 1.8 to 1.9. Moreover, the contact time defined by the following formula was appropriately changed according to the reaction activity of each oxide catalyst. The results of propylene conversion, acrylonitrile selectivity, and acrylonitrile yield are shown in Table 2.

ここで、Ｖは触媒量（ｍＬ）、Ｆは原料混合ガスの流量（ｍＬ−ＮＴＰ／秒）、Ｔは反応温度（℃）を示す。

Here, V represents the catalyst amount (mL), F represents the flow rate of the raw material mixed gas (mL-NTP / sec), and T represents the reaction temperature (° C.).

(Reduction resistance test of catalyst)
The oxide catalyst was weighed in a SUS reaction tube having an inner diameter of 10 mm, the reaction temperature was 440 ° C., the reaction pressure was normal pressure, and a propylene: ammonia: oxygen: helium: water volume of 5.4% by volume of propylene. A ratio of 3.24: 3.89: 6.12: 40.75: 6.00) was passed through the reaction tube at a flow rate of 60.0 cc (converted to NTP) per minute. Under this reaction condition, the oxygen supply was intermittently interrupted 60 times every 5 minutes and replaced with helium, and the reaction was continued. Propylene conversion rate before the oxygen was shut off for the first time (in the table, expressed as “propylene conversion rate before test”). The ratio of “Propylene conversion after test” is calculated. The results are shown in Table 2. The higher this value, the higher the reduction resistance of the catalyst.

[Example 1]
An oxide catalyst in which an oxide having a composition represented by Mo _12.0 Bi _0.45 Ce _0.90 Co _3.0 Fe _1.7 K _0.09 Ni _2.0 Mg _2.0 Rb _0.04 is supported on 50% by mass of silica based on the total amount of the catalyst is as follows. It was prepared as follows.
43.1 g of bismuth nitrate [Bi (NO ₃ ) ₃ .5H ₂ O] and 76.2 g of cerium nitrate [Ce (NO ₃ ) ₃ .6H ₂ O] in 395.1 g of a 16.6% by mass nitric acid aqueous solution 133.9 g of iron nitrate [Fe (NO ₃ ) ₃ .9H ₂ O], 114.6 g of nickel nitrate [Ni (NO ₃ ) ₂ .6H ₂ O], 171.8 g of cobalt nitrate [Co (NO _{3 2} · 6H ₂ O], 101.4 g of magnesium nitrate [Mg (NO ₃ ) ₂ · 6H ₂ O], 1.77 g of potassium nitrate [KNO ₃ ] and 1.15 g of rubidium nitrate [RbNO ₃ ] average particle diameter of primary particles of SiO ₂ 12nm liquid in a mixture of aqueous silica sol 833.3g average particle diameter of aqueous silica sol 833.3g primary particles containing SiO ₂ of 41 nm 30 wt% containing 30 wt% Added. A solution in which 413.8 g of ammonium paramolybdate [(NH ₄ ) ₆ Mo ₇ O ₂₄ · 4H ₂ O] was dissolved in 738.7 g of water was added and mixed and stirred to obtain a precursor slurry. . Subsequently, the obtained precursor slurry was spray-dried using a centrifugal atomizer equipped with a dish-shaped rotor installed in the center of the upper part of the dryer. The precursor slurry was spray-dried while maintaining the dryer inlet air temperature at 240 ° C and the outlet temperature at 140 ° C. The dry particles thus obtained were transferred to a kiln and fired in an air atmosphere. Specifically, first, the temperature was raised from room temperature to 320 ° C. over 2 hours, held at 320 ° C. for 2 hours and pre-baked to obtain pre-fired particles. Subsequently, the temperature was raised to 580 ° C. over 3 hours, and the calcined particles were finally calcined at 580 ° C. for 2 hours to obtain an oxide catalyst.

[Example 2]
An oxide catalyst in which an oxide having a composition represented by Mo _12.0 Bi _0.50 Ce _1.01 Fe _1.01 Ni _5.61 Mg _2.24 Rb _0.11 was supported on 40% by mass of silica based on the total amount of the catalyst was prepared as follows. . To a mixture of aqueous silica sol 666.7g average particle diameter of aqueous silica sol 666.7g primary particles containing SiO ₂ of 41 nm 30 wt% mean particle diameter of primary particles comprising SiO ₂ of 12 nm 30 wt%, water in advance A solution in which 490.6 g of ammonium paramolybdate [(NH ₄ ) ₆ Mo ₇ O ₂₄ · 4H ₂ O] was mixed and dissolved in 875.8 g was added with stirring. 396.8 g of aqueous nitric acid solution with 56.8 g of bismuth nitrate [Bi (NO ₃ ) ₃ .5H ₂ O], 101.4 g of cerium nitrate [Ce (NO ₃ ) ₃ .6H ₂ O], 94.3 g of iron nitrate [Fe (NO ₃ ) ₃ · 9H ₂ O], 381.2 g of nickel nitrate [Ni (NO ₃ ) ₂ · 6H ₂ O], 134.7 g of magnesium nitrate [Mg (NO ₃ ) ₂ · 6H ₂ O] And 3.73 g of nitric acid Rubidium [RbNO _3] added to and mixed stirring to a solution prepared by dissolving, to obtain a precursor slurry. The obtained precursor slurry was spray-dried using a centrifugal atomizer equipped with a dish-shaped rotor installed in the center of the upper part of the dryer. The precursor slurry was spray-dried while maintaining the dryer inlet air temperature at 240 ° C and the outlet temperature at 140 ° C. The dry particles thus obtained were transferred to a kiln and fired in an air atmosphere. Specifically, first, the temperature was raised from room temperature to 320 ° C. over 2 hours, held at 320 ° C. for 3 hours and pre-baked to obtain pre-fired particles. Subsequently, the temperature was raised to 580 ° C. over 3 hours, and the calcined particles were finally calcined at 580 ° C. for 2 hours to obtain an oxide catalyst.

[Example 3]
Further, an aqueous solution in which 50.0 g of tartaric acid was dissolved in 150 g of water was added to the precursor slurry obtained in Example 2 and mixed by stirring. This was used as the precursor slurry, and the firing temperature in the main firing. An oxide catalyst was prepared in the same manner as in Example 2 except that the temperature was changed from 580 ° C. to 620 ° C.

[Example 4]
Dry particles were obtained in the same manner as in Example 1. The obtained dried particles were transferred to a kiln, heated from room temperature to 210 ° C. in an air atmosphere over 2 hours, held at 210 ° C. for 2 hours and calcined to obtain temporarily calcined particles. Subsequently, the temperature was raised to 580 ° C. over 3 hours, and the calcined particles were finally calcined at 580 ° C. for 2 hours to obtain an oxide catalyst.

[Example 5]
Dry particles were obtained in the same manner as in Example 1. The obtained dry particles were transferred to a kiln, heated in an air atmosphere from room temperature to 340 ° C. over 2 hours, held at 340 ° C. for 2 hours and pre-fired to obtain pre-fired particles. Subsequently, the temperature was raised to 580 ° C. over 3 hours, and the calcined particles were finally calcined at 580 ° C. for 2 hours to obtain an oxide catalyst.

[Example 6]
Dry particles were obtained in the same manner as in Example 1. The obtained dried particles were transferred to a kiln, heated from room temperature to 320 ° C. over 4 hours in an air atmosphere, held at 320 ° C. for 2 hours, and temporarily fired to obtain temporarily fired particles. Subsequently, the temperature was raised to 580 ° C. over 2 hours, and the calcined particles were calcined at 580 ° C. for 2 hours to obtain an oxide catalyst.

[Example 7]
Dry particles were obtained in the same manner as in Example 1. The obtained dried particles were transferred to a kiln, heated from room temperature to 320 ° C. over 2 hours in an air atmosphere, and held at 320 ° C. for 2 hours to be pre-fired to obtain pre-fired particles. Subsequently, the temperature was raised to 580 ° C. over 5 hours, and the calcined particles were calcined at 580 ° C. for 2 hours to obtain an oxide catalyst.

[Comparative Example 1]
Dry particles were obtained in the same manner as in Example 1. The obtained dried particles were transferred to a kiln maintained at 350 ° C., calcined at 350 ° C. for 1 hour in an air atmosphere, heated to 580 ° C. over 1 hour, and the calcined particles were heated at 580 ° C. for 2 hours. Calcination gave an oxide catalyst.

[Comparative Example 2]
The silica sol as a silica raw material was changed to only 1333.3 g of an aqueous silica sol containing 30% by mass of SiO ₂ having an average primary particle diameter of 12 nm, and the firing temperature in the main firing was changed from 580 ° C. to 610 ° C. Except that, an oxide catalyst was prepared in the same manner as in Example 1.

[Comparative Example 3]
Dry particles were obtained in the same manner as in Example 1. The obtained dried particles were transferred to a kiln, heated from room temperature to 400 ° C. in an air atmosphere over 2 hours, held at 400 ° C. for 2 hours and calcined to obtain temporarily calcined particles. Subsequently, the temperature was raised to 580 ° C. over 2 hours, and the calcined particles were calcined at 580 ° C. for 2 hours to obtain an oxide catalyst.

[Comparative Example 4]
Dry particles were obtained in the same manner as in Example 1. The obtained dried particles were transferred to a kiln, heated from room temperature to 300 ° C. in an air atmosphere over 2 hours, held at 300 ° C. for 1 hour and temporarily fired to obtain temporarily fired particles. Subsequently, the temperature was raised to 580 ° C. over 0.5 hours, and the calcined particles were calcined at 580 ° C. for 2 hours to obtain an oxide catalyst.

[Comparative Example 5]
Dry particles were obtained in the same manner as in Example 1. The obtained dried particles were transferred to a kiln, heated from room temperature to 190 ° C. over 2 hours in an air atmosphere, held at 190 ° C. for 2 hours, and calcined to obtain temporarily calcined particles. Subsequently, the calcined particles were heated to 580 ° C. in an air atmosphere over 2 hours, and the calcined particles were finally calcined at 580 ° C. for 2 hours to obtain an oxide catalyst.

  From the results shown in Tables 1 and 2, the oxide catalyst in the present embodiment gives an unsaturated nitrile in a high yield in the gas-phase catalytic ammoxidation reaction of olefin, and also stabilizes the reaction even in a long time operation. It was found that the activity was good, and particularly good activity could be maintained even under repeated reduction loads.

  The present invention is used when an unsaturated nitrile is produced by reacting an olefin with molecular oxygen and ammonia, or when an unsaturated aldehyde or a conjugated diolefin is produced by reacting an olefin with molecular oxygen. As an oxide catalyst to be used, it has industrial applicability.

Claims (4)

  An oxide catalyst used in a gas phase catalytic ammoxidation reaction of an olefin or a gas phase catalytic oxidation reaction of a monoolefin, comprising molybdenum, bismuth, iron, and nickel, and an outer edge of the oxide catalyst particles An oxide catalyst in which nickel is unevenly distributed.   The average intensity of characteristic X-rays generated when an electron beam is applied to nickel existing at the outer edge is the average intensity of characteristic X-rays generated when an electron beam is applied to nickel existing at the center of the particle The oxide catalyst of Claim 1 which is 1.2 times or more with respect to. A method for producing an oxide catalyst according to claim 1 or 2,
Mixing molybdenum, bismuth, iron, nickel, silica having an average primary particle diameter of 5 nm or more and less than 20 nm, and silica having an average primary particle diameter of 20 nm or more and less than 125 nm, a precursor slurry A step of preparing
The precursor slurry is spray-dried to obtain dry particles, and the dry particles are heated from room temperature to a temperature set in a range of 200 ° C. to 350 ° C. over 1 hour, and the dry particles are temporarily Calcination to obtain pre-fired particles;
The calcined particles are heated for 1 hour or more from the temperature set in the step of obtaining the calcined particles to a temperature set within a range of 500 ° C. to 750 ° C., and the calcined particles are calcined. Obtaining an oxide catalyst. A method for producing an oxide catalyst.   A method for producing an unsaturated nitrile, wherein an unsaturated nitrile is produced by reacting an olefin with molecular oxygen and ammonia using the oxide catalyst according to claim 1.

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