JP2014177408A - Method of producing conjugated diene - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of producing a conjugated diene by using a molybdenum-containing metal oxide catalyst which suppresses calking of the catalyst in adjusting the production quantity, especially reducing the production quantity, to retain the catalyst activity.SOLUTION: A method of producing a conjugated diene comprises mixing a raw material gas containing a 4C or higher monoolefin with a molecular oxygen-containing gas, supplying the mixed gas to a reactor, supplying to a fixed-bed reactor provided with a molybdenum-containing metal oxide catalyst and carrying out an oxidation dehydrogenation reaction to produce the corresponding conjugated diene. The concentration of the raw material gas in the mixed gas is modified when the ratio of the obtained conjugated diene to the mixed gas is modified during a normal operation.

Description

  The present invention relates to a method for producing a conjugated diene, and more particularly to a method for producing a conjugated diene for adjusting the production amount of the obtained conjugated diene during steady operation.

As a method for producing a conjugated diene such as butadiene (hereinafter sometimes referred to as “BD”) by oxidative dehydrogenation reaction of a monoolefin such as n-butene in the presence of a catalyst, contact according to the following reaction formula: Examples thereof include oxidative dehydrogenation. In this reaction, water is by-produced.
C ₄ H ₈ + 1 / 2O ₂ → C ₄ H ₆ + H ₂ O
A metal oxide catalyst containing molybdenum is known as a catalyst used in the industrial production method of butadiene by this catalytic oxidative dehydrogenation (Patent Document 1).

  By the way, as for the manufacturing apparatus which manufactures the conjugated diene from the said monoolefin, the output is set according to the plan at the time of plant construction, and the apparatus is designed. However, it may be necessary to adjust the production amount from a set value for convenience of supply and demand.

  There is no literature on the production adjustment technology when producing conjugated dienes from monoolefins, but in the production process of acrylic acid and the production of petroleum products such as naphtha, light oil and kerosene from light hydrocarbon gas. Techniques for adjusting the production amount by adjusting the supply amount of the raw material up and down are known (Patent Documents 2 and 3).

JP 2011-006395 A JP 2005-170909 A JP 2009-242158 A

  By the way, in the case of producing a conjugated diene from a monoolefin, a metal oxide catalyst containing molybdenum is often used as a catalyst. In this case, when the supply amount of the raw material is adjusted as in Patent Documents 2 and 3, especially when the supply amount is reduced, the flow rate in the reactor is reduced and coking is performed, and the catalyst activity may be reduced.

  As another method of adjusting the supply amount, a method of adjusting the reaction temperature while maintaining the supply amount of the raw material can be considered. However, it was confirmed that when the reaction temperature was adjusted, particularly when the reaction temperature was lowered, coking was performed in the same manner as described above, and the catalytic activity was lowered.

  Therefore, the present invention provides a method for producing a conjugated diene using a metal oxide catalyst containing molybdenum, and suppresses the catalyst from being coked when adjusting the production amount, particularly when reducing the production amount. The purpose is to retain activity.

As a result of intensive studies to solve the above problems, the present inventors mixed a raw material gas containing a monoolefin having 4 or more carbon atoms and a molecular oxygen-containing gas, and supplied the mixed gas to the reactor. A method for producing a corresponding conjugated diene by supplying a fixed bed reactor having a molybdenum-containing metal oxide catalyst and performing an oxidative dehydrogenation reaction, wherein the ratio of the conjugated diene obtained to the mixed gas is When changing from the ratio in the steady operation, it was found that if the concentration of the raw material gas in the mixed gas is changed, coking can be avoided and stable operation can be continued. That is, the gist of the present invention resides in the following [1] to [4].
[1] A raw material gas containing a monoolefin having 4 or more carbon atoms and a molecular oxygen-containing gas are mixed, and this mixed gas is supplied to a reactor and supplied to a fixed bed reactor having a molybdenum-containing metal oxide catalyst. And a method for producing a corresponding conjugated diene by performing an oxidative dehydrogenation reaction. When the ratio of the conjugated diene to the mixed gas is changed from the ratio in steady operation, The method for producing a conjugated diene, wherein the concentration of the source gas is changed.
[2] The conjugate according to [1], wherein the supply amount of the mixed gas to the fixed bed reactor is maintained before and after changing the ratio of the conjugated diene obtained with respect to the mixed gas. Diene production method.
[3] The production of the conjugated diene according to [1] or [2], wherein the ratio of the conjugated diene obtained relative to the mixed gas is changed by changing the temperature of the fixed bed reactor. Method.
[4] When the ratio of the conjugated diene obtained with respect to the mixed gas is changed from the ratio in the steady operation, the amount of change in the raw material gas conversion rate by changing the concentration of the raw material gas in the mixed gas is The method for producing a conjugated diene according to any one of [1] to [3], which is −20 mol% to +20 mol% with respect to the raw material gas conversion rate during the steady operation.

  According to the present invention, in producing a conjugated diene by oxidative dehydrogenation of a monoolefin having 4 or more carbon atoms, the ratio of the conjugated diene obtained with respect to the mixed gas is changed from the ratio in steady operation, particularly reduced. In this case, by changing the concentration of the raw material gas in the mixed gas, coking to the catalyst is suppressed and the catalytic activity can be maintained.

The process figure which shows embodiment of the manufacturing method of the conjugated diene of this invention.

  Hereinafter, embodiments of the method for producing a conjugated diene of the present invention will be described in detail. However, the description described below is an example (representative example) of an embodiment of the present invention, and the present invention is limited to these contents. Not.

  The present invention supplies a raw material gas containing a monoolefin having 4 or more carbon atoms and a molecular oxygen-containing gas to a fixed bed reactor having a predetermined oxidative dehydrogenation reaction catalyst, and a corresponding conjugated diene by oxidative dehydrogenation reaction. It is invention about the method of manufacturing.

<Raw material gas containing monoolefin with 4 or more carbon atoms>
The raw material gas of the present invention contains a monoolefin having 4 or more carbon atoms. Examples of the monoolefin having 4 or more carbon atoms include butene (n-butene such as 1-butene and / or 2-butene, isobutene), and pentene. And monoolefins having 4 or more carbon atoms, preferably 4 to 6 carbon atoms, such as methylbutene and dimethylbutene, which can be effectively applied to the production of the corresponding conjugated dienes by catalytic oxidative dehydrogenation. Among these, it is most suitably used for the production of butadiene from n-butene (n-butene such as 1-butene and / or 2-butene).

  Moreover, it is not necessary to use the isolated monoolefin having 4 or more carbon atoms as a raw material gas containing a monoolefin having 4 or more carbon atoms, and it can be used in the form of an arbitrary mixture as necessary. . For example, when obtaining butadiene, high-purity n-butene (1-butene and / or 2-butene) can be used as a raw material gas, but the C4 fraction (BB) produced as a by-product in the above-described naphtha decomposition is used. Dehydrogenation or oxidative dehydration of n-butene (1-Butene and / or 2-butene) -based fraction (BBSS) and n-butane obtained by separating butadiene and i-butene (isobutene) from A butene fraction produced by an elementary reaction can also be used. Further, a gas containing high-purity 1-butene, cis-2-butene, trans-2-butene or a mixture thereof obtained by dimerization of ethylene may be used as a raw material gas. As the ethylene, ethylene obtained by a method such as ethane dehydrogenation, ethanol dehydration, or naphtha decomposition can be used. Furthermore, fluid catalytic cracking (Fluid Catalytic Cracking), in which a heavy oil fraction obtained by distilling crude oil in an oil refinery plant or the like is decomposed using a powdered solid catalyst in a fluidized bed state and converted to low boiling point hydrocarbon ) Gas containing a large number of hydrocarbons having 4 carbon atoms obtained from (hereinafter sometimes abbreviated as FCC-C4) as it is, or removing impurities such as phosphorus and arsenic from FCC-C4 It is possible to use the raw material as a raw material gas. Note that the main component referred to here is usually 40% by volume or more, preferably 60% by volume or more, more preferably 75% by volume or more, and particularly preferably 99% by volume or more with respect to the raw material gas.

  In addition, the source gas of the present invention may contain an arbitrary impurity as long as the effects of the present invention are not impaired. When producing butadiene from n-butene (1-butene and 2-butene), as impurities that may be contained, specifically, branched monoolefins such as isobutene; propane, n-butane, i-butane, Saturated hydrocarbons such as pentane; olefins such as propylene and pentene; dienes such as 1,2-butadiene; acetylenes such as methyl acetylene, vinyl acetylene and ethyl acetylene. The amount of this impurity is usually 40% or less, preferably 20% or less, more preferably 10% or less, and particularly preferably 1% or less. When the amount is too large, the concentration of 1-butene or 2-butene as the main raw material is lowered to slow the reaction, or the yield of butadiene as the target product tends to decrease. In the present invention, the concentration of the linear monoolefin having 4 or more carbon atoms in the raw material gas is not particularly limited, but is usually 50.0 to 99.99% by volume in normal operation, preferably It is 55.0-99.9 volume%, More preferably, it is 60.0-99.9 volume%.

<Oxidation dehydrogenation catalyst>
Next, the oxidative dehydrogenation catalyst suitably used in the present invention will be described. The oxidative dehydrogenation catalyst used in the present invention is a metal oxide catalyst containing molybdenum, and is preferably a composite oxide catalyst containing at least molybdenum, bismuth and cobalt. Among these, a composite oxide catalyst represented by the following general formula (1) is more preferable.

_{Mo a Bi b Co c Ni d} Fe e X f Y g Z h Si i O j (1)
In the formula, X is at least one element selected from the group consisting of magnesium (Mg), calcium (Ca), zinc (Zn), cerium (Ce), and samarium (Sm). Y is at least one element selected from the group consisting of sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and thallium (Tl). Z is at least one element selected from the group consisting of boron (B), phosphorus (P), arsenic (As), and tungsten (W).
Further, a to j represent atomic ratios of the respective elements. When a = 12, b = 0.5 to 7, c = 0 to 10, d = 0 to 10 (provided that c + d = 1 to 10), e = 0.05 to 3, f = 0 to 2, g = 0.04 to 2, h = 0 to 3, i = 5 to 48, and j is a numerical value that satisfies the oxidation state of other elements It is.

  Further, this composite oxide catalyst is preferably manufactured through a process in which the source compounds of the component elements constituting the composite oxide catalyst are integrated and heated in an aqueous system. For example, all of the source compounds of the component elements may be integrated and heated in the aqueous system.

  Among them, an aqueous solution or an aqueous dispersion of a raw material compound containing at least one selected from the group consisting of a molybdenum compound, an iron compound, a nickel compound, and a cobalt compound and silica, or a dried product obtained by drying this is heat-treated. Thus, it is preferable to produce the catalyst precursor by a method having a pre-process and a post-process in which the catalyst precursor, the molybdenum compound and the bismuth compound are integrated with an aqueous solvent, dried and fired. When this method is used, the obtained composite oxide catalyst exhibits high catalytic activity, so that a conjugated diene such as butadiene can be produced in a high yield, and a reaction product gas having a low aldehyde content is obtained. be able to. The aqueous solvent refers to water, an organic solvent having compatibility with water such as methanol and ethanol, or a mixture thereof.

Next, a method for producing a composite oxide catalyst suitable for the present invention will be described.
First, in this method for producing a composite oxide catalyst, the molybdenum used in the previous step is molybdenum corresponding to a partial atomic ratio (a1) of the total atomic ratio (a) of molybdenum, Is preferably molybdenum corresponding to the remaining atomic ratio (a2) obtained by subtracting a1 from the total atomic ratio (a) of molybdenum. The a1 is preferably a value satisfying 1 <a1 / (c + d + e) <3, and the a2 is preferably a value satisfying 0 <a2 / b <8.

  Source compounds of the component elements include oxides, nitrates, carbonates, ammonium salts, hydroxides, carboxylates, ammonium carboxylates, ammonium halide salts, hydrogen acids, acetylacetonates, alkoxides of the component elements. The following are mentioned as the specific example.

Examples of Mo supply source compounds include ammonium paramolybdate, molybdenum trioxide, molybdic acid, ammonium phosphomolybdate, and phosphomolybdic acid.
Examples of Fe source compounds include ferric nitrate, ferric sulfate, ferric chloride, and ferric acetate.

Examples of the Co source compound include cobalt nitrate, cobalt sulfate, cobalt chloride, cobalt carbonate, and cobalt acetate.
Examples of the Ni source compound include nickel nitrate, nickel sulfate, nickel chloride, nickel carbonate, nickel acetate and the like.

Examples of Si source compounds include silica, granular silica, colloidal silica, and fumed silica.
Examples of Bi source compounds include bismuth chloride, bismuth nitrate, bismuth oxide, and bismuth subcarbonate. In addition, Bi component in which X component (one or more of Mg, Ca, Zn, Ce, and Sm) and Y component (one or more of Na, K, Rb, Cs, and Tl) are dissolved. It can also be supplied as a complex carbonate compound of the X component and the Y component.

  For example, when Na is used as the Y component, a complex carbonate compound of Bi and Na can be obtained by dropping an aqueous solution of a water-soluble bismuth compound such as bismuth nitrate into an aqueous solution of sodium carbonate or sodium bicarbonate. The precipitate can be produced by washing with water and drying.

In addition, the complex carbonate compound of Bi and the X component is prepared by mixing an aqueous solution of a water-soluble compound such as bismuth nitrate and nitrate of the X component with an aqueous solution of ammonium carbonate or ammonium bicarbonate, etc. It can be produced by washing with water and drying.
When sodium carbonate or sodium bicarbonate is used instead of the ammonium carbonate or ammonium bicarbonate, a complex carbonate compound with Bi, Na and X components can be produced.

Examples of source compounds of other component elements include the following.
Examples of the source compound for K include potassium nitrate, potassium sulfate, potassium chloride, potassium carbonate, and potassium acetate.
Examples of Rb source compounds include rubidium nitrate, rubidium sulfate, rubidium chloride, rubidium carbonate, and rubidium acetate.

Examples of the Cs supply source compound include cesium nitrate, cesium sulfate, cesium chloride, cesium carbonate, and cesium acetate.
Examples of Tl source compounds include thallium nitrate, thallium chloride, thallium carbonate, and thallium acetate.

Examples of the source compound for B include borax, ammonium borate, and boric acid.
Examples of P source compounds include ammonium phosphomolybdate, ammonium phosphate, phosphoric acid, phosphorus pentoxide, and the like.

Examples of the source compound for As include dialsenooctammonium molybdate, ammonium dialseno18 tungstate, and the like.
Examples of W source compounds include ammonium paratungstate, tungsten trioxide, tungstic acid, and phosphotungstic acid.

Examples of the Mg source compound include magnesium nitrate, magnesium sulfate, magnesium chloride, magnesium carbonate, and magnesium acetate.
Examples of the source compound for Ca include calcium nitrate, calcium sulfate, calcium chloride, calcium carbonate, and calcium acetate.

Examples of the Zn source compound include zinc nitrate, zinc sulfate, zinc chloride, zinc carbonate, and zinc acetate.
Examples of the Ce source compound include cerium nitrate, cerium sulfate, cerium chloride, cerium carbonate, and cerium acetate.
Examples of Sm source compounds include samarium nitrate, samarium sulfate, samarium chloride, samarium carbonate, and samarium acetate.

  The aqueous solution or aqueous dispersion of the raw material compound used in the previous step is an aqueous solution, water slurry or cake containing at least molybdenum (corresponding to a1 in the total atomic ratio a), iron, nickel or cobalt, and silica as a catalyst component. It is.

  The aqueous solution or dispersion of the raw material compound is prepared by integrating the source compound in an aqueous system. Here, the integration of each component element source compound in an aqueous system means that the aqueous solution or aqueous dispersion of each component element source compound is mixed or / and aged in stages. Say. (B) a method in which the source compounds are mixed together, (b) a method in which the source compounds are mixed together and aged, and (c) each of the source compounds. (D) supplying each component element in any one of the following methods: (d) stepwise mixing and maturation of each of the above source compounds, and (b) to (d) are combined. It is included in the concept of integration of the source compound in an aqueous system. Here, aging refers to the processing of industrial raw materials or semi-finished products under specific conditions such as constant temperature for a certain period of time to obtain the required physical and chemical properties, increase or advance the prescribed reaction, etc. The fixed time is usually in the range of 10 minutes to 24 hours, and the fixed temperature is usually in the range of room temperature to the boiling point of the aqueous solution or aqueous dispersion.

  As a specific method of the integration, for example, a solution obtained by mixing an acidic salt selected from catalyst components, and a solution obtained by mixing a basic salt selected from catalyst components, Specific examples include a method of adding a mixture of an iron compound and a nickel compound and / or a cobalt compound to an aqueous solution of a molybdenum compound while heating, and mixing silica.

The aqueous solution or aqueous dispersion of the raw material compound containing silica thus obtained is heated to 60 to 90 ° C. and aged.
The aging means that the catalyst precursor slurry is stirred at a predetermined temperature for a predetermined time. This aging increases the viscosity of the slurry, reduces the sedimentation of the solid components in the slurry, and is particularly effective in suppressing the heterogeneity of components in the subsequent drying process. The catalytic activity such as the raw material conversion rate and selectivity of the product catalyst becomes better.

  60-90 degreeC is preferable and the temperature in the said ripening has more preferable 70-85 degreeC. When the aging temperature is less than 60 ° C., the aging effect is not sufficient, and good activity may not be obtained. On the other hand, when it exceeds 90 ° C., the water is often evaporated during the aging time, which is disadvantageous for industrial implementation. Further, if the temperature exceeds 100 ° C., a pressure vessel is required for the dissolution tank, and handling becomes complicated, which is extremely disadvantageous in terms of economy and operability.

  The aging time is preferably 2 to 12 hours, and preferably 3 to 8 hours. If the aging time is less than 2 hours, the activity and selectivity of the catalyst may not be sufficiently developed. On the other hand, the aging effect does not increase even if it exceeds 12 hours, which is disadvantageous for industrial implementation.

  Any method can be adopted as the stirring method, and examples thereof include a method using a stirrer having a stirring blade and a method using external circulation using a pump.

  The aged slurry is subjected to heat treatment as it is or after drying. There is no particular limitation on the drying method in the case of drying and the state of the dried product to be obtained. For example, a powdery dried product may be obtained using a normal spray dryer, slurry dryer, drum dryer, etc. Alternatively, a block-like or flake-like dried product may be obtained using a normal box-type dryer or a tunnel-type firing furnace.

  The raw salt water solution or granules or cakes obtained by drying the raw salt solution are heat-treated in air at a temperature of 200 to 400 ° C., preferably 250 to 350 ° C. for a short time. There are no particular limitations on the type and method of the furnace at that time, and for example, it may be heated with a dry matter fixed using a normal box-type furnace, tunnel-type furnace, etc., or a rotary kiln. It is possible to heat the dried product while flowing it.

The ignition loss of the catalyst precursor obtained after the heat treatment is preferably 0.5 to 5% by weight, more preferably 1 to 3% by weight. By setting the ignition loss within this range, a catalyst having a high raw material conversion rate and high selectivity can be obtained. The loss on ignition is a value given by the following equation.
Burning loss (%) = [(W0−W1) / W0] × 100
W0: Weight (g) of catalyst precursor dried at 150 ° C. for 3 hours to remove adhering moisture
W1: Weight (g) after heat-treating the catalyst precursor excluding adhering moisture at 500 ° C. for 2 hours

  In the subsequent step, the catalyst precursor obtained in the previous step, the molybdenum compound (corresponding to the remaining a2 obtained by subtracting the equivalent of a1 from the total atomic ratio a), and the bismuth compound are integrated in an aqueous solvent. At this time, it is preferable to add ammonia water. The addition of the X, Y, and Z components is also preferably performed in the subsequent step. Further, the bismuth source compound of the present invention is bismuth which is hardly soluble or insoluble in water. This compound is preferably used in the form of a powder. These compounds as the catalyst production raw material may be particles larger than the powder, but are preferably smaller particles in view of the heating step in which thermal diffusion should be performed. Therefore, if these compounds as raw materials are not such particles, they should be pulverized before the heating step.

Next, the obtained slurry is sufficiently stirred and then dried. The dried product thus obtained is shaped into an arbitrary shape by a method such as extrusion molding, tableting molding or support molding.
Next, this is preferably subjected to a final heat treatment for about 1 to 16 hours under a temperature condition of 450 to 650 ° C. As described above, a composite oxide catalyst having a high activity and a desired oxidation product in a high yield can be obtained.

<Molecular oxygen-containing gas>
The molecular oxygen-containing gas of the present invention is usually a gas containing 10% by volume or more of molecular oxygen, preferably 15% by volume or more, more preferably 20% by volume or more. Air. From the viewpoint of increasing the cost necessary for industrially preparing the molecular oxygen-containing gas, the upper limit of the molecular oxygen content is usually 50% by volume or less, preferably 30% by volume. Hereinafter, it is more preferably 25% by volume or less. Moreover, the molecular oxygen-containing gas may contain an arbitrary impurity as long as the effects of the present invention are not impaired.

Specific examples of impurities that may be included include nitrogen, argon, neon, helium, CO, CO ₂ , and water. In the case of nitrogen, the amount of this impurity is usually 90% by volume or less, preferably 85% by volume or less, more preferably 80% by volume or less. In the case of components other than nitrogen, it is usually 10% by volume or less, preferably 1% by volume or less. When this amount is too large, it tends to be difficult to supply oxygen necessary for the reaction.

<Gas supply>
In the present invention, when supplying the raw material gas to the reactor, the raw material gas and the molecular oxygen-containing gas are mixed, and the mixed gas (hereinafter sometimes referred to as “mixed gas”) is supplied to the reactor. There is a need. The ratio of the raw material gas in the mixed gas of the present invention is usually 4.2% by volume or more, preferably 7.6% by volume or more, and more preferably 8.0% by volume in a steady operation state. % Or more. As this lower limit value increases, the size of the reactor can be reduced, and the cost for construction and operation tends to decrease. On the other hand, the upper limit is 20.0% by volume or less, preferably 17.0% by volume or less, and more preferably 15.0% by volume or less. The smaller the upper limit value is, the less the causative substance of coking on the catalyst in the raw material gas is reduced.

<Nitrogen gas, water (water vapor)>
In addition to the mixed gas, nitrogen gas and water (water vapor) may be supplied to the reactor. Nitrogen gas adjusts the concentration of combustible gas and oxygen in the same way as nitrogen gas, because the concentration of combustible gas and oxygen is adjusted so that the mixed gas does not form squeal. For reasons and to suppress coking of the catalyst, it is preferable that water (water vapor) and nitrogen gas are further mixed with the mixed gas and supplied to the reactor.

  When water vapor is supplied to the reactor, it is preferably introduced at a ratio of 0.5 to 5.0 with respect to the supply amount of the raw material gas. As this ratio increases, the amount of wastewater tends to increase, and as the ratio decreases, the yield of the target product butadiene tends to decrease. Therefore, the water vapor is preferably 0.7 to 4.5 with respect to the supply amount of the raw material gas.

  When nitrogen gas is supplied to the reactor, it is preferably introduced at a ratio (volume ratio) of 0.5 to 8.0 with respect to the supply amount of the raw material gas. As this ratio increases, the load of the process of compressing the product gas in the subsequent process tends to increase, and as the ratio decreases, the amount of steam used to supply the reactor tends to increase. Therefore, the nitrogen gas is preferably supplied at a ratio (volume ratio) of 1.0 to 6.0, more preferably 2.0 to 5.0 with respect to the supply amount of the raw material gas.

  The method of supplying the mixed gas of the source gas and the molecular oxygen-containing gas, the nitrogen gas supplied as necessary, and water (water vapor) is not particularly limited, and may be supplied through separate pipes. In order to avoid the formation of the gas reliably, before obtaining the mixed gas, nitrogen gas is supplied to the source gas or the molecular oxygen-containing gas in advance, and in this state, the source gas and the molecular oxygen-containing gas are mixed. It is preferable to mix to obtain a mixed gas and supply the mixed gas.

  Since the gas mixture supplied to the reactor is a mixture of oxygen and combustible gas, each gas (raw gas, air, and if necessary, nitrogen gas and water (water vapor)) should not enter the explosion range. The composition of the mixed gas at the inlet of the reactor can be controlled while monitoring the flow rate with a flow meter installed in the pipe supplying the mixed gas (when a C4 fraction is used).

<Fixed bed reactor>
The fixed bed reactor used in the oxidative dehydrogenation reaction of the present invention is not particularly limited, but preferably includes a fixed bed multitubular reactor and a plate reactor, and more preferably a fixed bed multitubular reactor. It is.

In addition, this reactor has a catalyst layer having the above-described oxidative dehydrogenation reaction catalyst. The catalyst layer may be composed of a layer composed only of the catalyst, or may be composed only of a layer containing a catalyst and a solid that is not reactive with the catalyst, or a solid that is not reactive with the catalyst and the catalyst. It may be composed of a plurality of layers including a substance and a layer composed only of a catalyst. When the catalyst layer includes a layer containing a catalyst and a solid that is not reactive with the catalyst, a rapid temperature increase of the catalyst layer due to heat generation during the reaction can be suppressed. In the case of having a plurality of layers, the plurality of layers are formed in layers from the inlet of the reactor toward the direction of the product gas outlet of the reactor. When the catalyst layer includes a layer containing a catalyst and a solid that is not reactive with the catalyst, the catalyst dilution rate represented by the following formula is preferably 10% by volume or more, more preferably 20% by volume or more, More preferably, it is 30 volume% or more. As this lower limit value increases, the occurrence of hot spots in the catalyst layer can be suppressed, and the effect of suppressing the accumulation of carbon content on the catalyst becomes higher. The upper limit of the dilution rate of the catalyst layer is not particularly limited, but is usually 99% by volume or less, preferably 90% by volume or less, and more preferably 80% by volume or less. The smaller the upper limit value, the smaller the reactor can be made, and the construction cost and operation cost can be reduced. As described above, the catalyst layer provided in the reactor may be a single layer or two or more layers.
Dilution rate (volume%) = [(volume of solids not reactive with catalyst) / (volume of catalyst + volume of solids not reactive with catalyst)] × 100

  The non-reactive solid used in the present invention is stable under conjugated diene formation reaction conditions, and is a material that is not reactive with raw materials such as monoolefins having 4 or more carbon atoms, and products such as conjugated diene. If it is a thing, it will not specifically limit, Generally, it may also be called an inert ball | bowl. Specific examples include ceramic materials such as alumina and zirconia. Moreover, the shape is not specifically limited, Any of spherical shape, a column shape, a ring shape, and an indefinite shape may be sufficient. Moreover, the magnitude | size should just be a magnitude | size equivalent to the catalyst used by this invention. The particle size is usually about 2 to 10 mm.

  The packing length of the catalyst layer is the activity of the catalyst to be packed (when diluted with a non-reactive solid, the activity as a diluted catalyst), the size of the reactor, the reaction raw material gas temperature, the reaction temperature, If reaction conditions are decided, it can obtain | require by mass balance and a heat balance calculation.

<Reaction conditions>
The oxidative dehydrogenation reaction of the present invention is an exothermic reaction, and the temperature rises due to the reaction. In the present invention, the reaction temperature is usually 250 to 450 ° C., preferably 280 to 400 ° C. in normal operation. Adjusted. As the temperature increases, the catalytic activity tends to decrease rapidly, and as the temperature decreases, the yield of the conjugated diene that is the target product tends to decrease. The reaction temperature can be controlled using a heat medium (for example, dibenzyltoluene or nitrite). In addition, the reaction temperature here is the temperature of a heat medium.

  In the present invention, the temperature in the reactor is not particularly limited, but is usually 250 to 450 ° C, preferably 280 to 400 ° C, more preferably 320 to 395 ° C in normal operation. When the temperature of the catalyst layer exceeds 450 ° C., the catalytic activity tends to decrease rapidly as the reaction is continued. On the other hand, when the temperature of the catalyst layer is lower than 250 ° C., the conjugate which is the target product. The yield of diene tends to decrease. The temperature in the reactor is determined by the reaction conditions, but can be controlled by the dilution rate of the catalyst layer, the flow rate of the mixed gas, and the like. In addition, the temperature in a reactor here is the temperature of the product gas in the exit of a reactor, or the temperature of the catalyst layer in the case of the reactor which has a catalyst layer.

  The pressure in the reactor of the present invention is not particularly limited, but in normal operation, the lower limit is 0 MPaG or more, preferably 0.001 MPaG or more, and more preferably 0.01 MPaG or more. As this value increases, there is an advantage that a large amount of reaction gas can be supplied to the reactor. On the other hand, the upper limit is 0.5 MPaG or less, preferably 0.3 MPaG or less, and more preferably 0.1 MPaG or less. As this value decreases, the explosion range tends to narrow.

In the present invention, the flow rate ratio of the mixed gas to the catalyst amount in the reactor is 1000～10000H ^-1, preferably a 1500～7000H ^-1, more preferably at 2000～5000H ^-1 is there. As this value increases, solid precipitation tends to be suppressed, and as the value decreases, solid tends to precipitate more easily.

The flow rate difference between the inlet and outlet of the reactor depends on the flow rate of the raw material gas at the reactor inlet and the flow rate of the product gas at the reactor outlet, but the ratio of the outlet flow rate to the inlet flow rate is usually 100. It is -110 volume%, Preferably, it is 102-107 volume%, More preferably, it is 103-105 volume%. When butadiene is produced from n-butene (1-butene and 2-butene), the outlet flow rate increases because butene is oxidized and dehydrogenated to produce butadiene and water, and CO and CO ₂ are produced. This is because the number of molecules increases stoichiometrically in the reaction. A small increase in the outlet flow rate is not preferable because the reaction does not proceed, and an excessive increase in the outlet flow rate is not preferable because CO and CO ₂ increase due to side reactions.

  Thus, the conjugated diene corresponding to the monoolefin is produced by the oxidative dehydrogenation reaction of the monoolefin in the raw material gas, and the produced gas containing the conjugated diene is obtained. The concentration of the conjugated diene corresponding to the monoolefin in the raw material gas contained in the product gas depends on the concentration of the monoolefin contained in the raw material gas, but is 1 to 15% by volume, preferably in a steady operation state. Is 2 to 13% by volume, more preferably 3 to 11% by volume. The higher the conjugated diene concentration, the lower the recovery cost, and the lower the conjugated diene, the lower the advantage that side reactions such as polymerization hardly occur when compressed in the next step. In addition, unreacted monoolefin may also be contained in the product gas, and the concentration thereof is 0 to 7% by volume, preferably 0 to 4% by volume, more preferably 0 in normal operation. ~ 2% by volume. In the present invention, the high-boiling by-product contained in the product gas is one having a boiling point of 200 to 500 ° C. under normal pressure, although it varies depending on the type of impurities contained in the raw material gas used. When producing butadiene from n-butene (1-butene and 2-butene), specific examples include phthalic acid, anthraquinone, fluorenone and the like. These amounts are not particularly limited, but are usually 0.05 to 0.10% by volume in the reaction gas.

<Adjustment of production volume>
In the production of the conjugated diene, the production amount may be changed from a constant condition of stable operation. The operation is performed by changing the ratio of the conjugated diene obtained with respect to the mixed gas during the operation under the constant condition. This change, particularly a method of reducing the proportion of the conjugated diene obtained, can be carried out by changing the temperature of the fixed bed reactor, in particular by lowering this temperature.

  At the same time, the concentration of the raw material gas in the mixed gas is changed, particularly reduced. By doing so, the catalyst can be prevented from coking.

  By the way, before and after changing the amount of the obtained conjugated diene, particularly before and after reducing the amount of the obtained conjugated diene, the supply amount of the mixed gas to the fixed bed reactor can be reduced. And can be maintained. However, the catalyst will coke unless the concentration of the raw material gas is reduced when the supply amount is changed, particularly when it is reduced.

  In the present invention, when the ratio of the conjugated diene obtained with respect to the mixed gas is changed from the ratio in the steady operation, the change in the raw material gas conversion rate by changing the concentration of the raw material gas in the mixed gas The amount is preferably −20 mol% or more and +20 mol% or less, and preferably −18 mol% or more and +18 mol% or less with respect to the raw material gas conversion rate in the steady operation. When the conversion rate change amount is −20 mol% or less, the production amount is significantly reduced, and when it is +20 mol% or more, there is a problem that the by-product is increased and the BD selectivity is lowered.

<Post process>
The method for producing a conjugated diene of the present invention further includes a cooling step, a dehydration step, a solvent absorption step, a separation step, a purification step and the like in order to separate the conjugated diene from the product gas containing the conjugated diene. Also good. Note that the product gas obtained from the reactor becomes compressed gas and dehydrated gas in the dehydration step. However, these gases have the same content ratio other than water, and since most of the contained water is liquid, the component ratio of the gas portion of each gas may be considered to be the same. For this reason, hereinafter, the generated gas, the compressed gas, and the dehydrated gas may be simply referred to as “generated gas”.

(Cooling process)
In this invention, you may have a cooling process which cools the product gas containing the conjugated diene obtained from a reactor. The cooling step is not particularly limited as long as the product gas obtained from the outlet of the reactor can be cooled, but a method of cooling by directly contacting the cooling solvent and the product gas is preferably used. Although it does not specifically limit as a cooling solvent, Preferably it is water and alkaline aqueous solution, Most preferably, it is water.

  The cooling temperature of the product gas varies depending on the product gas temperature obtained from the reactor outlet, the kind of the cooling solvent, etc., but is usually 5 to 100 ° C., preferably 10 to 50 ° C., more preferably 15 to 40. Cool to ° C. The higher the temperature to be cooled, the lower the construction cost and the cost required for operation. The lower the temperature, the lower the load on the process of compressing the product gas. Although the pressure in a cooling tower is not specifically limited, Usually, it is 0.03 MPaG. If the product gas contains a large amount of high-boiling by-products, polymerization between the high-boiling by-products and deposition of solid precipitates due to the high-boiling by-products in the process are likely to occur. Moreover, since the cooling solvent used in the cooling tower is often circulated, clogging with solid precipitates may occur when the production of the conjugated diene is continued continuously. For this reason, it is preferable to avoid introducing high-boiling by-products in the product gas into the cooling process as much as possible.

(Dehydration process)
Moreover, in this invention, you may have a dehydration process which removes the water | moisture content contained in the product gas discharged | emitted from a reactor. Providing a dehydration step is preferable because it can prevent equipment corrosion due to moisture in each step in the subsequent process and accumulation of impurities in the solvent used in the solvent absorption step and solvent separation step described later.

  The dehydration process of the present invention is not particularly limited as long as it is a process capable of removing moisture contained in the product gas. The dehydration step may be performed anywhere as long as it is a subsequent step of the reactor, but it is preferable to perform the dehydration step after the above-described cooling step. Normally, the amount of water contained in the product gas discharged from the reactor varies depending on the type of raw material gas, the amount of molecular oxygen-containing gas, and water vapor mixed with the raw material gas. In this case, the water content is 4 to 35% by volume, preferably 10 to 30% by volume. (When this passes the cooling process using water, the water concentration is reduced to 100 volume ppm to 2.0 volume%). Moreover, as a dew point, it is 0-100 degreeC, Preferably, it is 10-80 degreeC.

  A means for dehydrating water from the generated gas is not particularly limited, and a desiccant (moisture adsorbent) such as calcium oxide, calcium chloride, or molecular sieve can be used. Of these, desiccants (moisture adsorbents) such as molecular sieves are preferably used from the viewpoint of ease of regeneration and ease of handling.

  When a desiccant such as molecular sieve is used in the dehydration step, high-boiling by-products contained in the product gas other than water are adsorbed and removed. The high-boiling by-products removed here are anthraquinone, fluorenone, phthalic acid, and the like.

  The water content in the product gas obtained through the dehydration step is 10 to 10,000 ppm by volume, preferably 20 to 1,000 ppm by volume in the state of steady operation, and the dew point is -60 to 80 ° C, preferably Is −50 to 20 ° C. As the water content in the product gas increases, the contamination of the reboiler of the solvent absorption tower and the solvent separation tower tends to increase. On the other hand, when the content decreases, the utility cost used in the dehydration process tends to increase. .

(Solvent absorption process)
In the present invention, it is preferable to have a solvent absorption step in which the product gas is brought into contact with an absorption solvent to absorb a hydrocarbon such as olefin or conjugated diene in the absorption solvent to obtain a solvent containing the conjugated diene. As a preferable reason, it is preferable to recover the conjugated diene by absorbing the product gas in a solvent from the viewpoint of reducing the energy cost required for the separation of the conjugated diene. The solvent absorption step may be performed anywhere as long as it is a subsequent step of the reactor, but is preferably provided after the above-described dehydration step.

  As a specific method for absorbing the product gas in the solvent absorption step, for example, a method using an absorption tower is preferable. As the type of the absorption tower, a packed tower, a wet wall tower, a spray tower, a cyclone scrubber, a bubble tower, a bubble stirring tank, a plate tower (bubble bell tower, perforated plate tower), a foam separation tower, and the like can be used. A spray tower, a bubble bell tower, and a perforated plate tower are preferable.

  In the case of using an absorption tower, the absorption solvent and the product gas are usually brought into countercurrent contact so that the conjugated diene in the product gas and the unreacted monoolefin having 4 or more carbon atoms and the hydrocarbon having 3 or less carbon atoms are used. The compound is absorbed into the solvent. Examples of the hydrocarbon compound having 3 or less carbon atoms include methane, acetylene, ethylene, ethane, methylacetylene, propylene, propane, and allene.

  In the solvent absorption step, when the product gas is recovered using an absorption tower, the pressure in the absorption tower is not particularly limited, but is usually 0.1 to 2.0 MPaG, preferably 0.2 to 1.5 MPaG, More preferably, it is 0.2-1.0 MPaG. The larger the pressure, the better the absorption efficiency, and the smaller the pressure, the less energy required for boosting the gas when the gas is introduced into the absorption tower, and the further the reduced oxygen amount in the liquid.

  Moreover, the temperature in an absorption tower is although it does not specifically limit, Usually, -10-50 degreeC, Preferably, it is -5-40 degreeC, More preferably, it is 0-30 degreeC. The higher this temperature is, the more advantageous is that oxygen, nitrogen, and the like are less likely to be absorbed by the solvent, and the smaller is the advantage that the absorption efficiency of hydrocarbons such as conjugated dienes is improved.

  The absorption solvent used in the solvent absorption step of the present invention is not particularly limited, and C6-C10 saturated hydrocarbons, C6-C8 aromatic hydrocarbons, amide compounds, and the like are used. Specifically, for example, dimethylformamide (DMF), toluene, xylene, N-methyl-2-pyrrolidone (NMP) and the like can be used. Among these, C6-C8 aromatic hydrocarbons are preferable because toluene is difficult to dissolve inorganic gas, and toluene is particularly preferable.

  Although there is no restriction | limiting in particular in the usage-amount of an absorption solvent, It is 0.1-10 weight times normally with respect to the flow volume of the target product supplied to a collection | recovery process, Preferably, it is 1-10 weight times. As the amount of the absorbing solvent used increases, it tends to be uneconomical, and as the amount used decreases, the recovery efficiency of the conjugated diene tends to decrease.

  The solvent containing a conjugated diene obtained in the solvent absorption step mainly contains a conjugated diene that is a target product, and the concentration of the conjugated diene in the solvent absorption liquid is usually 1 to 20% by weight. Yes, preferably 3 to 10% by weight. The higher the concentration of the conjugated diene in this solvent, the more conjugated diene is lost due to polymerization or volatilization. The lower the concentration, the more the solvent needs to be circulated in the same production amount. Energy costs tend to increase.

  Further, since a slight amount of nitrogen and oxygen is also absorbed in the solvent containing the conjugated diene obtained, a deaeration step of gasifying and removing nitrogen and oxygen dissolved in the solvent may be provided. The degassing step is not particularly limited as long as it is a step capable of gasifying and removing nitrogen and oxygen dissolved in the solvent absorption liquid.

(Separation process)
A separation step of separating the crude conjugated diene from the solvent containing the conjugated diene thus obtained may be included, and the crude conjugated diene can be obtained by this step. The separation step is not particularly limited as long as the crude conjugated diene can be separated from the solvent absorption liquid of the conjugated diene, but the crude conjugated diene can be usually separated by distillation separation. Specifically, for example, a conjugated diene is distilled and separated by a reboiler and a condenser, and a conjugated diene fraction is extracted from the vicinity of the top of the column. The separated absorption solvent is extracted from the bottom of the column, and when it has a recovery step that uses the solvent in the previous step, it is recycled as an absorption solvent in the recovery step. Impurities may accumulate during recycling of the solvent, and a part of the solvent may be extracted and removed by a known purification method such as distillation, decantation, sedimentation, or contact treatment with an adsorbent or ion exchange resin. desirable.

  Although the pressure at the time of distillation of the distillation column used at a separation process can be set arbitrarily, it is usually preferred that the column top pressure is 0.05-2.0 MPaG. More preferably, the tower top pressure is 0.1 to 1.0 MPaG, and particularly preferably 0.15 to 0.8 MPaG. If the pressure at the top of the column is too low, a large amount of cost is required to condense the conjugated diene distilled off at a low temperature, and if it is too high, the temperature at the bottom of the distillation column increases, resulting in an increase in steam costs. End up.

  The tower bottom temperature is usually 50 to 230 ° C, preferably 80 to 200 ° C, more preferably 100 to 200 ° C. If the column bottom temperature is too low, it will be difficult to distill the conjugated diene from the column top. If the temperature is too high, the solvent will be distilled off from the top of the column. The reflux ratio may be 1 to 10, and preferably 2 to 4.

  As the distillation column, either a packed column or a plate column can be used, but multistage distillation is preferred. In order to separate the conjugated diene and the solvent, it is preferable that the theoretical column of the distillation column is 5 or more, particularly 10 to 20 plates. A distillation column having more than 50 stages is not preferable for economics of construction of the distillation column, operational difficulty, and safety management. If the number of stages is too small, separation becomes difficult.

(Purification process)
Although the crude conjugated diene is obtained in the conjugated diene separation step, the crude conjugated diene may be further purified by distillation purification or the like to obtain a purified high-purity conjugated diene. Although the pressure at the time of distillation of the distillation column used here can be set arbitrarily, it is usually preferred that the column top pressure is 0.05 to 0.4 MPaG. More preferably, the tower top pressure is 0.1 to 0.3 MPaG, and particularly preferably in the range of 0.15 to 0.2 MPaG. If the pressure at the top of the column is too low, a large amount of cost is required to condense the conjugated diene distilled off at a low temperature, and if it is too high, the temperature at the bottom of the distillation column increases, resulting in an increase in steam costs. End up.

  The tower bottom temperature is usually 30 ° C to 100 ° C, preferably 40 ° C to 80 ° C, more preferably 50 ° C to 60 ° C. If the column bottom temperature is too low, it will be difficult to distill the conjugated diene from the column top. If the temperature is too high, the amount of condensation at the top of the tower increases and costs increase. The reflux ratio may be 1 to 10, and preferably 2 to 4.

  As the distillation column, either a packed column or a plate column can be used, but multistage distillation is preferred. In order to separate impurities such as conjugated diene and furan, it is preferable that the number of theoretical stages of the distillation column is 5 or more, particularly 10 to 20 stages. A distillation column having more than 50 stages is not preferable for economics of construction of the distillation column, operational difficulty, and safety management. If the number of stages is too small, separation becomes difficult. The purified conjugated diene thus obtained is a conjugated diene having a purity of 99.0 to 99.9%.

[Process embodiment]
Below, with reference to drawings, embodiment of the process regarding the manufacturing method of the conjugated diene of this invention is described, giving the example which manufactures butadiene.

FIG. 1 shows one embodiment of the process of the present invention.
In FIG. 1, 1 is a reactor, 2 is a quench tower, 3, 6 and 13 are coolers (heat exchangers), 4, 7 and 14 are drain pots, 8A and 8B are dehydration towers, and 9 is a heater (heat (Exchanger), 10 is a solvent absorption tower, 11 is a degassing tower, 12 is a solvent separation tower, and 100 to 126 are pipes.
FIG. 1 shows a case where butene is used as BBSS and butadiene is used as the resulting conjugated diene.

  The raw material n-butene or a mixture containing n-butene such as BBSS is gasified by a vaporizer (not shown) and introduced from the pipe 101, and from the pipes 102, 103, and 104, nitrogen gas, After introducing air (molecular oxygen-containing gas) and water (water vapor), and heating the mixed gas to about 150 to 400 ° C. with a preheater (not shown), the catalyst was filled from the pipe 100. A multi-tubular reactor 1 (oxidation dehydrogenation reactor) is supplied. The reaction product gas from the reactor 1 is fed to the quench tower 2 through the pipe 105 and cooled to about 5 to 99 ° C.

  Cooling water is introduced into the quench tower 2 through the pipe 106 and is in countercurrent contact with the product gas. And the water which cooled the product gas by this countercurrent contact is discharged | emitted from the piping 107. FIG. The cooling waste water is cooled by a heat exchanger (not shown) and is circulated again in the quench tower 2.

  The product gas cooled in the quench tower 2 is distilled from the top of the tower, and then cooled to about 5 to 50 ° C. via the cooler 3 from the pipe 108. The condensed water generated by cooling is separated into the drain pot 4 through the pipe 109. The water-separated gas is further pressurized to about 0.1 to 0.5 MPa by the compressor 5 through the pipe 110, and the pressurized gas is cooled again to about 5 to 50 ° C. by the cooler 6 through the pipe 111. Condensed water generated by cooling is separated from the pipe 112 into the drain pot 7. The compressed gas after the water separation is introduced into the dehydration towers 8A and 8B filled with a desiccant such as molecular sieve and dehydrated. In the dehydration towers 8A and 8B, dehydration of the compressed gas and regeneration by heating and drying of the desiccant are performed alternately. That is, the compressed gas is first introduced into the dehydration tower 8A through the pipes 113 and 113a, dehydrated, and supplied to the solvent absorption tower 10 through the pipes 114a and 114.

  During this time, nitrogen gas heated to about 150 to 250 ° C. is introduced into the dehydration tower 8B through the pipe 122, the heater 9, and the pipes 123, 123a, and 123b, and moisture is desorbed by heating the desiccant. . The nitrogen gas containing the desorbed water is cooled to room temperature by the cooler 13 through the pipes 124 a, 124 b, and 124, and the condensed water is separated from the pipe 125 into the drain pot 14 and then discharged from the pipe 126.

  When the desiccant in the dehydration tower 8A reaches saturation, the gas flow path is switched, the compressed gas is dehydrated in the dehydration tower 8B, and the desiccant in the dehydration tower 8A is regenerated.

  The regeneration time of the desiccant in the dehydration tower in the dehydration step is not particularly limited, but is usually 6 to 48 hours, preferably 12 to 36 hours, and more preferably 18 to 30 hours.

  The dehydrated gas from the dehydration towers 8A and 8B is cooled to about 10 to 30 ° C. by a cooler (not shown) as necessary, and then sent to the solvent absorption tower 10 to be sent from the pipe 115 to the solvent (absorption) Solvent). Thereby, the conjugated diene and the unreacted raw material gas in the dehydrated gas are absorbed by the absorption solvent. The component (off gas) that has not been absorbed by the absorption solvent is discharged from the top of the solvent absorption tower 10 via the pipe 117 and is combusted and discarded. At this time, if a solvent having a relatively low boiling point such as toluene is used as the absorbing solvent, an amount of the solvent that cannot be ignored economically may be volatilized through the pipe 117. In such a case, a step of recovering a solvent having a low boiling point using a solvent having a higher boiling point may be provided at the end of the pipe 117. In this solvent absorption tower 10, the solvent absorption liquid in which butadiene and unreacted source gas are absorbed by the absorption solvent is extracted from the bottom of the solvent absorption tower 10 and fed to the deaeration tower 11 through the pipe 116. Since a certain amount of nitrogen and oxygen are also absorbed in the solvent absorption liquid of butadiene obtained in the solvent absorption tower 10, the solvent absorption liquid is then supplied to the deaeration tower 11 and heated. Gasify and remove dissolved nitrogen and oxygen.

  At this time, some of the butadiene, the raw material gas, and the solvent may be gasified. Therefore, this is liquefied by a capacitor (not shown) provided at the top of the degassing tower 11 to be solvent. Collect in absorbent. Uncondensed raw material gas, butadiene, and the like are extracted from the pipe 118 as a mixed gas of nitrogen and oxygen, and are circulated to the inlet side of the compressor 5 and processed again in order to increase the recovery rate of the conjugated diene. On the other hand, the degassed treatment liquid from which the solvent absorption liquid has been degassed is sent to the solvent separation tower 12 through the pipe 119.

  In the solvent separation column 12, conjugated diene is distilled and separated by a reboiler and a condenser, and a crude butadiene fraction is extracted from the top of the column via a pipe 120. The separated absorption solvent is extracted from the bottom of the tower through a pipe 121 and is circulated and used as the absorption solvent of the solvent absorption tower 10.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention more concretely, this invention is not limited to a following example at all.

[Production Example] (Preparation of composite oxide catalyst)
54 g of ammonium paramolybdate was dissolved in 250 ml of pure water by heating to 70 ° C. Next, 7.18 g of ferric nitrate, 31.8 g of cobalt nitrate, and 31.8 g of nickel nitrate were dissolved in 60 ml of pure water by heating to 70 ° C. These solutions were gradually mixed with thorough stirring.

  Next, 64 g of silica was added and stirred thoroughly. This slurry was heated to 75 ° C. and aged for 5 hours. Thereafter, the slurry was dried by heating and then subjected to heat treatment at 300 ° C. for 1 hour in an air atmosphere.

  The obtained granular solid of the catalyst precursor (loss on ignition: 1.4% by weight) was pulverized, and 40.1 g of ammonium paramolybdate was dispersed in a solution prepared by adding 10 ml of ammonia water to 150 ml of pure water. Next, 0.85 g of borax and 0.36 g of potassium nitrate were dissolved in 40 ml of pure water under heating at 25 ° C. and added to the slurry.

Next, 58.1 g of bismuth subcarbonate in which Na was dissolved in 0.45% was added and mixed with stirring. After the slurry was heat-dried at 130 ° C. for 12 hours, the obtained granular solid was formed into a tablet having a diameter of 5 mm and a height of 4 mm with a small molding machine, and then baked at 500 ° C. for 4 hours. The catalyst was obtained. The catalyst calculated from the charged raw materials was a complex oxide having the following atomic ratio.
Mo: Bi: Co: Ni: Fe: Na: B: K: Si = 12: 5: 2.5: 2.5: 0.4: 0.35: 0.2: 0.08: 24
In addition, the atomic ratios a1 and a2 of molybdenum at the time of preparation were 6.9 and 5.1, respectively.

[Example 1]
As the fixed bed reactor, a Pyrex reaction tube having an inner diameter of 6 mm and a length of 175 mm at the upper part and a lower part of 4 mm and a length of 125 mm was used, and 0.41 g of the catalyst prepared in the production example was charged into the inner diameter part of 6 mm. An insertion tube with an outer diameter of 1.6 mm was installed in this reaction tube, and a thermocouple was installed in the insertion tube to measure the temperature in the reactor. An electric heater was used as a heating source. Then, an oxidative dehydrogenation reaction was performed on the reactor under the following reaction conditions (hereinafter sometimes abbreviated as “condition 1”).
Condition 1: Nitrogen was supplied to the reactor at 1.222 L / hr, oxygen was 0.286 L / hr, water vapor was 0.200 L / hr, and a raw material gas having the composition shown in Table 1 was supplied at 0.292 L / hr. The catalyst layer outlet temperature was raised to 380 ° C. (reactor introduction gas composition = nitrogen: 61.1 vol%, oxygen: 14.3 vol%, water vapor: 10.0 vol%, source gas: 14.6 vol%). At this time, the total gas flow rate was 2.00 L / h and SV was 4878 / h with respect to the catalyst amount of 0.41 mL.
The product gas from the reactor outlet was cooled and analyzed by gas chromatography. The n-butene conversion rate (the total conversion rate of 1-butene, cis-2-butene and trans-2-butene) was 80.6 mol%, and the butadiene selectivity was 81.7 mol%. The amount of coke deposited on the catalyst layer after the reaction continued for 200 hours was 18.7 wt%, and coke was deposited.
Next, under the above condition 1, the reactor is supplied with nitrogen at 1.209 L / hr, oxygen at 0.245 L / hr, water vapor at 0.200 L / hr, and a raw material gas having the composition shown in Table 1 at 0.244 L / hr. The reaction was carried out under the same conditions except for supplying hr (reactor introduction gas composition = nitrogen: 64.5 vol%, oxygen: 13.3 vol%, steam: 10.0 vol%, source gas: 12.2 vol%).
The product gas from the reactor outlet was cooled and analyzed by gas chromatography. The n-butene conversion rate (the total conversion rate of 1-butene, cis-2-butene and trans-2-butene) was 84.2 mol%, and the butadiene selectivity was 85.8 mol%. The amount of coke deposited on the catalyst layer after the reaction continued for 200 hours was 0.267 wt%, and stable operation was possible.
From the above results, if the concentration of the raw material gas in the mixed gas introduced into the reactor is low, coke adhesion to the catalyst can be prevented by reducing the raw material gas concentration when reducing the production amount of conjugated diene under the same reaction conditions. It was suggested that it can be done.

[Example 2]
In condition 1 of Example 1, SV is 4878 / h, nitrogen is 1.209 L / hr, oxygen is 0.245 L / hr, water vapor is 0.200 L / hr, and the raw material gas having the composition shown in Table 1 is 0. 244 L / hr was supplied, the catalyst layer outlet temperature was raised to 380 ° C. with a heater, and oxidative dehydrogenation reaction was carried out to produce butadiene (reactor introduced mixed gas composition = nitrogen: 64.5 vol%, oxygen: 13 3 vol%, water vapor: 10.0 vol%, raw material gas: 12.2 vol%). (Hereinafter, this reaction condition may be abbreviated as “condition 2”.)
The product gas from the reactor outlet was cooled and analyzed by gas chromatography. The n-butene conversion rate (the total conversion rate of 1-butene, cis-2-butene and trans-2-butene) was 84.2 mol%, and the butadiene selectivity was 85.8 mol%. The amount of coke deposited on the catalyst layer after the reaction continued for 200 hours was 0.267 wt%, and stable operation was possible.
Next, from the reaction conditions of the above-mentioned condition 2, SV is 4761 / h, the raw material gas concentration in the reactor introduction mixed gas is decreased, and the gas composition is nitrogen: 70.0 vol%, oxygen: 9.7 vol%, water vapor When reacted at 10.0 vol%, raw material gas: 10.3 vol%, and a temperature of 375 ° C, the n-butene conversion was 73.8 mol% and the butadiene selectivity was 87.5 mol%. Even after the reaction continued for 200 hours under these conditions, catalyst coking was not observed and stable operation was possible.

[Example 3]
After carrying out the reaction under the same reaction conditions (condition 2) as in the first half of Example 2, the SV was 3333 / h, the raw material gas concentration in the reactor-introduced mixed gas was lowered, and the composition was nitrogen: 69.6 vol. %, Oxygen: 10.1 vol%, water vapor: 10.0 vol%, raw material gas: 10.3 vol%, and the reaction was carried out by changing the reaction conditions at a temperature of 360 ° C. The n-butene conversion was 91.4 mol% The butadiene selectivity was 84.7 mol%. Even after the reaction was continued for 200 hours under the changed reaction conditions, catalyst coking was not observed and stable operation was possible.

[Example 4]
After carrying out the reaction under the same reaction conditions (condition 2) as in the first half of Example 2, the SV was 2105 / h, the raw material gas in the mixed gas introduced into the reactor was lowered, and the gas composition was nitrogen: 70.4 vol% , Oxygen: 9.6 vol%, water vapor: 10.0 vol%, raw material gas: 10.0 vol%, the reaction temperature was changed to 350 ° C and the reaction conditions were changed, and the n-butene conversion was 68.8 mol%, butadiene The selectivity was 90.2 mol%. Even after the reaction was continued for 200 hours under the changed reaction conditions, catalyst coking was not observed and stable operation was possible.
From the above, it has been clarified that production adjustment is possible by avoiding coking by lowering the raw material gas concentration in the mixed gas introduced into the reactor. Further, from Examples 2 to 4, it was found that even if the reaction temperature was lowered, coking was avoided and production adjustment was possible by reducing the raw material concentration.

[Comparative Example 1]
After performing the reaction under the same reaction conditions (condition 2) as in the first half of Example 2, the reaction was performed at SV of 1900 / h and at a temperature of 350 ° C. without changing the concentration of the raw material gas in the mixed gas introduced into the reactor. As a result, the n-butene conversion rate was 87.7 mol%, and the butadiene selectivity was 90.7 mol%. After the reaction was continued for 200 hours, adhesion of coke to the catalyst layer was observed, and the catalyst had to be replaced.
As described above, when only the SV is reduced without reducing the concentration of the raw material gas in the mixed gas introduced into the reactor, catalyst coking proceeds, and production adjustment is impossible.

DESCRIPTION OF SYMBOLS 1 Reactor 2 Quench tower 3, 6, 13 Cooler 4, 7, 14 Drain pot 5 Compressor 8A, 8B Dehydration tower 9 Heater (heat exchanger)
DESCRIPTION OF SYMBOLS 10 Solvent absorption tower 11 Deaeration tower 12 Solvent separation tower 100-126 Piping

Claims (4)

A raw material gas containing a monoolefin having 4 or more carbon atoms and a molecular oxygen-containing gas are mixed, and this mixed gas is supplied to a reactor, and then supplied to a fixed bed reactor having a molybdenum-containing metal oxide catalyst. It is a method for producing a corresponding conjugated diene by performing a dehydrogenation reaction,
A method for producing a conjugated diene, wherein the concentration of the raw material gas in the mixed gas is changed when the ratio of the conjugated diene obtained with respect to the mixed gas is changed from the ratio in the steady operation.   The conjugated diene production according to claim 1, wherein the supply amount of the mixed gas to the fixed bed reactor is maintained before and after changing the ratio of the conjugated diene obtained with respect to the mixed gas. Method.   The method for producing a conjugated diene according to claim 1 or 2, wherein the ratio of the conjugated diene obtained with respect to the mixed gas is changed by changing the temperature of the fixed bed reactor.   When the ratio of the conjugated diene obtained with respect to the mixed gas is changed from the ratio in the steady operation, the amount of change in the raw material gas conversion rate by changing the concentration of the raw material gas in the mixed gas is the steady state. The method for producing a conjugated diene according to any one of claims 1 to 3, which is -20 mol% to +20 mol% with respect to the raw material gas conversion rate during operation.

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