JP5780038B2 - Method for producing conjugated diene - Google Patents

Description

  The present invention relates to a method for producing a conjugated diene, and more particularly to a method for producing a conjugated diene such as butadiene by a catalytic oxidative dehydrogenation reaction of a monoolefin having 4 or more carbon atoms such as n-butene.

A method for producing a conjugated diene such as butadiene by subjecting a monoolefin such as n-butene to an oxidative dehydrogenation reaction in the presence of a catalyst is conventionally known.
This reaction proceeds, for example, according to the following reaction formula, and water is by-produced.
C ₄ H ₈ + 1 / 2O ₂ → C ₄ H ₆ + H ₂ O
The production of butadiene by the catalytic oxidative dehydrogenation reaction of n-butene is industrially made from a C ₄ fraction (C ₄ hydrocarbon mixture, hereinafter sometimes referred to as “BB”) by-produced by naphtha cracking. In the butadiene extraction and separation process, a mixture containing 1-butene, 2-butene, butane and the like obtained by separating butadiene in an extractive distillation column (hereinafter, this mixture may be referred to as “BBSS”). ) Has been proposed for producing butadiene from butene contained therein.

  As a specific method, a step of obtaining a product gas containing a conjugated diene produced by an oxidative dehydrogenation reaction between a source gas containing a monoolefin having 4 or more carbon atoms and oxygen gas, and cooling the product gas, cooling A method of dehydrating the generated product gas and a step of recovering the conjugated diene by bringing the dehydrated product gas into contact with a solvent (Japanese Patent Laid-Open No. 2010-90083), or an acetylene hydrocarbon concentration of 0.016 vol. For example, there is a method (Japanese Patent Laid-Open No. 2010-90082) for reducing the load of extractive distillation for separation of acetylenes by obtaining a product gas suppressed to less than or equal to%.

JP 2010-90083 A JP 2010-90082 A

  Although the above Patent Documents 1 and 2 do not describe any problem of coking in which a carbon substance is deposited on the catalyst, according to the study by the present inventors, by the oxidative dehydrogenation reaction in the presence of the catalyst, When producing butadiene from butene, branched monoolefins such as isobutene and linear n-butene contained in the raw material gas (for example, BB or BBSS) and the high-boiling carbon components are added as a secondary component in the oxidative dehydrogenation reaction. As a result, coking on the catalyst progresses, the catalytic activity decreases, and with the progress of coking, the differential pressure of the reactor increases, and it has been found that there is a problem that hinders long-term operation. When coking progresses on the catalyst, the operation is stopped and high boiling point carbon components must be removed by decoking or the like. This shutdown operation and decoking cause a decrease in productivity in butadiene production.

  The present invention has been made in view of the above problems, and in a method for producing a conjugated diene such as butadiene by a catalytic oxidative dehydrogenation reaction of a monoolefin such as n-butene, a carbon content such as coke is produced during the reaction. An object of the present invention is to provide an industrially advantageous method for producing butadiene that prevents accumulation on a catalyst, moderates the progress of coking, and allows stable operation.

  As a result of intensive studies to solve the above problems, the present inventors have supplied a mixed gas obtained by mixing a raw material gas containing a monoolefin having 4 or more carbon atoms and a molecular oxygen-containing gas to the reactor, In the method for producing a conjugated diene in which a gas containing a corresponding conjugated diene produced by an oxidative dehydrogenation reaction is obtained, the catalyst in the reactor is cracked for some reason, and further pulverized, and these are generated in the reactor. Based on the idea that local agglomeration tends to cause a reaction that produces a high-boiling carbon component, the amount of cracked or crushed catalyst (weight ratio) relative to the total amount of catalyst present in the reactor is specified. By carrying out the reaction within the range, the coking speed that hinders stable operation of the plant can be reduced, the operation can be performed more safely, and butadiene can be produced stably at a higher yield. It was heading.

The present invention has been achieved based on such findings, and the gist of the present invention is the following [1] to [6].
[1] A mixed gas obtained by mixing a raw material gas containing a monoolefin having 4 or more carbon atoms and a molecular oxygen-containing gas is supplied to a reactor having a catalyst, and a corresponding conjugated diene is generated by an oxidative dehydrogenation reaction. In the method for producing a conjugated diene that obtains a product gas containing the conjugated diene, the crushing rate of the catalyst in the reactor represented by the following formula (1) is 0.0 wt% or more and 40.0 wt% or less. A process for producing a conjugated diene characterized by

Crushing rate (% by weight) = {(weight of crushed catalyst in reactor) / (total catalyst weight in reactor)} × 100 (1)
(In the formula, the crushing catalyst is selected by a sieve having an opening of 4.5 to 4.9 mm.)
[2] The method for producing a conjugated diene as described in [1], wherein the reactor further includes a solid having no reactivity with the catalyst.
[3] The production of the conjugated diene according to [1] or [2], wherein the ratio (volume ratio) of the flow rate of the mixed gas to the total catalyst amount in the reactor is 500 to 5000 h ^−1. Method.

[4] The method for producing a conjugated diene according to any one of [1] to [3], wherein the catalyst contains at least molybdenum and bismuth.
[5] The method for producing a conjugated diene according to any one of [1] to [4], wherein the catalyst is a composite oxide catalyst represented by the following general formula (2).
Mo _a Bi _b Co _c Ni _{d F e} X _f Y _g Z _h Si _i O _j (2)
Wherein X is at least one element selected from the group consisting of magnesium (Mg), calcium (Ca), zinc (Zn), cerium (Ce) and samarium (Sm), and Y is sodium (Na) , Potassium (K), rubidium (Rb), cesium (Cs) and at least one element selected from the group consisting of thallium (Tl), Z is boron (B), phosphorus (P), arsenic (As) And at least one element selected from the group consisting of tungsten (W), and a to j represent atomic ratios of the respective elements, and when a = 12, b = 0.1 to 7, c = 0 to 10, d = 0 to 10 (provided c + d = 1 to 10), e = 0.05 to 3, f = 0 to 2, g = 0.04 to 2, h = 0 to 3, i = 0 to 0 48, and j satisfies the oxidation state of other elements Numerical value is.)
[6] Gas containing 1-butene, cis-2-butene, trans-2-butene or a mixture thereof obtained by dimerization of ethylene as the raw material gas, dehydrogenation or oxidative dehydrogenation of n-butane Any one of [1] to [5], which is a gas containing a large amount of hydrocarbons having 4 carbon atoms, which is obtained when fluidized catalytic cracking of a butene fraction or a heavy oil fraction produced by A method for producing a conjugated diene according to Item.

  According to the present invention, the stable operation of the plant can be continuously performed by maintaining the shape of the catalyst in the reactor.

It is a systematic diagram 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.
In the present invention, a raw material gas containing a monoolefin having 4 or more carbon atoms and a molecular oxygen-containing gas are supplied to a reactor having a catalyst layer, and a corresponding conjugated diene is produced by an oxidative dehydrogenation reaction.

<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). In addition, as the raw material gas containing a monoolefin having 4 or more carbon atoms, it is not necessary to use the isolated monoolefin having 4 or more carbon atoms, and it can be used in the form of any mixture as required. . For example, in order to obtain butadiene, high-purity n-butene (1-butene and / or 2-butene) can be used as a raw material gas, but the C ₄ fraction by-produced by the above-described naphtha decomposition ( Dehydrogenation or oxidation of fractions (BBSS) and n-butane mainly composed of n-butene (1-butene and / or 2-butene) obtained by separating butadiene and i-butene (isobutene) from BB) A butene fraction produced by the dehydrogenation 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 heavy oil fractions obtained by distilling crude oil at oil refineries and the like are decomposed in a fluidized bed using a powdered solid catalyst and converted to low boiling point hydrocarbons. ) Gas containing a large number of hydrocarbons having 4 carbon atoms obtained from (hereinafter sometimes abbreviated as FCC-C4) as raw material gas, 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 70.00 to 99.99 vol%.

<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 preferably a composite oxide catalyst containing at least molybdenum, bismuth and cobalt. Among these, a composite oxide catalyst represented by the following general formula (2) is more preferable.

_{Mo a Bi b Co c Ni d} Fe e X f Y g Z h Si i O j (2)
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 = 0.1-1, c = 0-10, d = 0-10 (where c + d = 1-10), e = 0.05-3, f = 0-2, g = 0.04-2, h = 0-3, i = 0-48, 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 if necessary, silica, or obtained by drying this It is preferable to produce by a method comprising a pre-process for producing a catalyst precursor by heat-treating a dried product, and a post-process for integrating the catalyst precursor, molybdenum compound and bismuth compound together with an aqueous solvent, drying and firing. . 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 (a ₁ ) of the total atomic ratio (a) of molybdenum, The molybdenum used in the step is preferably molybdenum corresponding to the remaining atomic ratio (a ₂ ) obtained by subtracting a ₁ from the total atomic ratio (a) of molybdenum. The a ₁ is preferably a value satisfying 0.5 <a ₁ / (c + d + e) <3, and the a ₂ is preferably a value satisfying 0 <a 2 / 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 one of molybdenum (corresponding to a ₁ in the total atomic ratio a), iron, nickel or cobalt as a catalyst component. . In addition, this aqueous solution, water slurry, or cake may contain the silica as needed.
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 in which a mixture of an iron compound and a nickel compound and / or a cobalt compound is added to an aqueous solution of a molybdenum compound while heating. In addition, it is preferable to perform addition and mixing of silica in this previous step as required.

The aqueous solution or aqueous dispersion of the raw material compound 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 (%) = [(W ₀ −W ₁ ) / W ₀ ] × 100
W ₀ : Weight (g) of the catalyst precursor after drying at 150 ° C. for 3 hours to remove adhering moisture
W ₁ : Weight (g) after further heat-treating the catalyst precursor excluding adhering moisture at 500 ° C. for 2 hours
In the step after the, the integration of the pre-catalyst precursor and the molybdenum compound obtained in step (remaining a ₂ corresponds to minus a ₁ equivalent of the total atomic ratio a) and bismuth compounds, carried out 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. Specific examples of components other than oxygen that can be contained in the molecular oxygen-containing gas of the present invention include nitrogen, argon, neon, helium, CO, CO ₂ , and water. In the case of nitrogen, the amount of these components other than oxygen 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. In addition, as a ratio of the raw material gas in the mixed gas of this invention, it is 4.2 vol% or more normally, Preferably it is 7.6 vol% or more, More preferably, it is 8.0 vol% or more. As this 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 vol% or less,
Preferably, it is 17.0 vol% or less, More preferably, it is 15.0 vol% or less. The smaller this value is, the less the causative substance of coking on the catalyst in the raw material gas is.

<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 0.8 to 4.5, more preferably 1.0 to 4.0 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.

The typical composition of the mixed gas is shown below.
[Mixed gas composition]
-N-butene: 50 to 100 vol% with respect to the total of C ₄ fractions
-C ₄ fraction total: 5-15 vol%
・ O ₂ : ₄₀ to 120 vol / vol% with respect to the total of C ₄ fractions
· _N 2: _{C 4} fraction summed for 500~1000vol / vol%
・ 90 to 900 vol / vol% with respect to the total of H ₂ O: C ₄ fractions
When the raw material gas supplied to the reactor is mixed with the molecular oxygen-containing gas, it becomes a mixture of oxygen and combustible gas, so that each gas (raw material gas, air, and necessary) is not included in the explosion range. The composition control at the inlet of the reactor is performed while monitoring the flow rate with a flow meter installed in a pipe that supplies nitrogen gas and water (steam) according to the conditions. For example, n-butene (1-butene and / or When butadiene is produced from 2-butene), it is adjusted to the range of the mixed gas composition described later. The explosion range here is a range having a composition in which a mixed gas of oxygen and combustible gas is ignited in the presence of some ignition source. It is known that if the concentration of combustible gas is lower than a certain value, it will not ignite even if an ignition source is present, and this concentration is called the lower explosion limit. It is also known that if the concentration of combustible gas is higher than a certain value, it will not ignite even if an ignition source is present, and this concentration is called the upper limit of explosion. Each value depends on the oxygen concentration. In general, the lower the oxygen concentration, the closer the values are, and the two match when the oxygen concentration reaches a certain value. The oxygen concentration at this time is called a critical oxygen concentration. If the oxygen concentration is lower than this, the mixed gas will not be ignited regardless of the concentration of the combustible gas.

  When starting the reaction of the present invention, the amount of molecular oxygen-containing gas, nitrogen and water vapor supplied to the reactor is first adjusted so that the oxygen concentration at the inlet of the reactor is below the critical oxygen concentration, and then combustible. Supply of combustible gas (mainly raw material gas), and then supply of flammable gas (mainly raw material gas) and molecular oxygen-containing gas such as air so that the concentration of combustible gas becomes higher than the upper limit of explosion It is good to increase. When the supply amount of the combustible gas (mainly source gas) and the molecular oxygen-containing gas is increased, the supply amount of the mixed gas may be made constant by decreasing the supply amount of nitrogen and / or water vapor. By doing so, the residence time of the mixed gas in the piping and the reactor can be kept constant, and the pressure fluctuation can be suppressed.

  In addition, even if it is outside the explosion range, it may ignite if kept for a certain period of time under a certain temperature and pressure condition. This holding time is called ignition delay time. When designing around the reactor, it is necessary to design so that the residence time of the raw material piping and the product gas piping is less than the ignition delay time. Although the ignition delay time depends on temperature, pressure, and composition, it cannot be generally stated. However, the residence time of the mixed gas pipe is 1000 seconds or less, the residence time of the product gas pipe is 10 seconds or less, or the product gas is 350 seconds within 10 seconds. It is desirable to cool to below.

  The lower limit of the ratio of the raw material gas in the mixed gas of the present invention is usually 4.2 vol% or more, preferably 7.6 vol% or more, more preferably 9.3 vol% 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 usually 20.0 vol% or less, preferably 17.0 vol% or less, and more preferably 15.0 vol% or less. As this upper limit value becomes smaller, the causative substance of coking on the catalyst in the raw material gas also decreases, so that the catalyst coking is less likely to occur.

<Reactor>
The reactor used for the oxidative dehydrogenation reaction of the present invention is not particularly limited, and specific examples include a tubular reactor, a tank reactor, or a fluidized bed reactor, preferably a fixed bed reactor, More preferred are fixed bed multitubular reactors and plate reactors, and most preferred is a fixed bed multitubular reactor. These reactors are generally used industrially and are not particularly limited.

  When the reactor is a fixed bed reactor, the 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. The catalyst layer may include a layer containing a catalyst and a layer containing only a catalyst, but the catalyst layer includes a layer containing a catalyst and a solid that is not reactive with the catalyst. Therefore, it is preferable to have a solid material having no reactivity in the catalyst layer. 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 ratio represented by the following formula (3) is preferably 10% by volume or more, more preferably 15 volumes. % Or more, more preferably 20% by 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 vol% or less, preferably 90 vol% or less, and more preferably 80 vol% or less. The smaller the upper limit value, the smaller the reactor can be made, and the construction cost and operation cost can be suppressed.

Dilution rate (volume%) = [(volume of solid material not reactive with catalyst) / (volume of catalyst + volume of solid material not reactive with catalyst)] × 100 (3)
As described above, the catalyst layer provided in the reactor may be a single layer or two or more layers, but preferably has 2 to 5 layers. As the number of catalyst layers increases, the catalyst filling operation tends to become complicated, and as the number of catalyst layers decreases, it tends to be easier. When two or more catalyst layers are provided in the reactor, the dilution rate of each catalyst layer can be appropriately determined depending on the reaction conditions and reaction temperature, but it is preferable to provide catalyst layers having different dilution rates.

  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.

  Moreover, in this invention, you may have a layer formed only in a solid substance without reactivity other than said catalyst layer in a fixed bed reactor. In general, it is preferable to provide a layer formed of only a non-reactive solid substance in both or one of the closest position to the raw material gas inlet of the reactor and the closest position to the product gas outlet. The size of these layers can be appropriately determined according to the size of the catalyst layer, the size of the reactor, and the reaction conditions.

In the present invention, the solid catalyst in the catalyst layer needs to have a crushing rate (wt%) represented by the following formula (1) of 0.0 wt% or more and 40.0 wt% or less.
Crushing rate (% by weight) = {(weight of crushed catalyst in reactor) / (total catalyst weight in reactor)} × 100 (1)
In the above formula, the crushed catalyst refers to an initial shape in which the catalyst used in the reactor is manufactured, or a shape that is not equivalent to the shape when the reactor is filled. Specifically, the catalyst is generated when the catalyst is cracked or pulverized in the reactor. Usually, the size of the crushed catalyst is small compared to the size when the catalyst is produced or when the catalyst is charged into the reactor. The crushing catalyst can be identified by opening the reactor after stopping the oxidative dehydrogenation reaction, extracting the contents in the reactor, and then selecting them visually or by sieving. When the contents in the reactor are extracted from the reactor, it is preferable to extract the contents so that the contents are not destroyed. When the contents extracted from the reactor are sieved, the sieve opening varies depending on the size of the solid catalyst to be used, but cracked by using a sieve with an aperture of 4.5 mm to 4.9 mm. It is possible to separate and recover the catalyst and the pulverized catalyst. In addition, when there exists a non-reactive solid substance in a reactor, before specifying a crushing catalyst, it is preferable to remove beforehand.

The weight of the crushed catalyst thus identified can be measured to obtain the weight of the crushed catalyst in the reactor. The total catalyst weight in the reactor may be measured in advance before the reactor is filled with the catalyst used for the reaction.
When the reactor is a fixed-bed multitubular reactor, that is, when the reactor is filled with the same type of catalyst and the same weight as the catalyst, and there are a plurality of reaction tubes having the same length and diameter, For all reaction tubes, the crushed catalyst may be identified and the weight of the crushed catalyst may be measured. However, at least one reaction tube is selected from the plurality of reaction tubes, and the crushed catalyst is identified and its You may measure a weight and you may obtain | require a crushing rate by making the average value of the weight of the crushing catalyst obtained in those reaction tubes into the weight of the crushing catalyst in a reactor. At this time, the total catalyst weight in the reactor is the total weight of the catalyst in the reaction tube selected above.

  In the present invention, the solid catalyst in the catalyst layer needs to have a crush rate (wt%) represented by the above formula (1) of 0.0 wt% or more and 40.0 wt% or less. 0.0 wt% or more and 30.0 wt% or less. More preferably, they are 5.0 weight% or more and 25.0 weight% or less. The smaller this value is, the more time is required for filling the catalyst, and the strength of the catalyst during production tends to be increased.

<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 adjusted to 250 to 450 ° C, preferably 280 to 400 ° C. 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). The reaction temperature here means the temperature of the heat medium.

  Moreover, the reactor internal temperature in this invention is although it does not specifically limit, Usually, 250-450 degreeC, Preferably, it is 280-400 degreeC, More preferably, it is 320-395 degreeC. 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 the lower limit is usually 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. As this value decreases, the explosion range tends to narrow.

  The residence time of the reactor in the present invention is not particularly limited, but the lower limit is preferably 0.72 seconds or more, more preferably 0.90 seconds or more. There is a merit that the higher the value, the higher the conversion rate of monoolefin in the raw material gas. On the other hand, the upper limit is preferably 2.80 seconds or less, and more preferably 2.10 seconds or less. The smaller this value, the smaller the reactor.

In the present invention, the ratio of the flow rate of the mixed gas to the amount of catalyst in the reactor (hereinafter sometimes abbreviated as SV) is not particularly limited, but is preferably 500 to 5000 h ⁻¹ , more preferably. Is 1300-4500 h ⁻¹ , particularly preferably 1700-4000 h ⁻¹ . 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 vol%, Preferably, it is 102-107 vol%, More preferably, it is 103-105 vol%. 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 usually 1 to 15 vol%, preferably 5 to 13 vol%, More preferably, it is 9-11 vol%. 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 usually 0 to 7 vol%, preferably 0 to 4 vol%, more preferably 0 to 2 vol%. 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 vol% in the reaction gas.

<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 the cooling process which cools the product gas containing a conjugated diene. The cooling step is not particularly limited as long as the product gas extracted from the reactor outlet can be cooled. Preferably, a cooling solvent and the product gas are directly contacted and cooled. Although it does not specifically limit as a cooling solvent, Preferably it is water and alkaline aqueous solution, Most preferably, it is water.

Further, the cooling temperature of the product gas varies depending on the temperature of the product gas extracted from the outlet of the reactor, the kind of the cooling solvent, and the like, but is usually 5 to 100 ° C, preferably 10 to 50 ° C, and more preferably 15 to 15 ° C. Cool to 40 ° 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.
In addition, when cooling using a cooling tower, if the product gas contains a large amount of high-boiling by-products, solid precipitates caused by polymerization of high-boiling by-products or high-boiling by-products in the process. Accumulation of water is 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.

Therefore, as much as possible, it is preferable to remove the high boiling point by-product in the product gas withdrawn from the reactor outlet with a filter or the like in advance so as not to bring it into the cooling step.
(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. Usually, 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. It is -35 vol%, Preferably it is 10-30 vol% (When this passes the cooling process which uses water, a water concentration is reduced to 100 volppm-2.0 vol%). Moreover, as a dew point, it is 0-100 degreeC, Preferably, it is 10-80 degreeC.

A means for removing moisture from the product 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 usually 10 to 10,000 volppm, preferably 20 to 1000 volppm, and the dew point is -60 to 80 ° C, preferably -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. Although it will not specifically limit if it is a process after reaction about a solvent absorption process, It is preferable to provide after the above-mentioned dehydration process.

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 0.25-1.0 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, although the temperature in the absorption tower 10 is not specifically limited, Usually, 0-50 degreeC, Preferably, it is 10-40 degreeC, More preferably, it is 20-30 degreeC. The higher this temperature is, the more advantageous is that oxygen, nitrogen, etc. are less likely to be absorbed by the solvent, and the lower, there is an advantage that the absorption efficiency of hydrocarbons such as conjugated dienes is improved.
The organic solvent for use in the solvent absorption process of the present invention, but are not limited to, aromatic hydrocarbons, saturated hydrocarbons and C ₆ -C ₈ of C ₆ -C _10, an amide compound 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, C _{6 to} C ₈ 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 1-100 weight times normally with respect to the flow volume of the target product supplied to a collection | recovery process, Preferably, it is 2-50 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 200 ° C, preferably 80 to 180 ° C, more preferably 100 to 160 ° 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. 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, Air (molecular oxygen-containing gas) and water (steam) were introduced, and the mixed gas was heated to about 150 to 400 ° C. with a preheater (not shown), and then the catalyst was filled from the pipe 100. Feed to multi-tube reactor 1 (oxidation dehydrogenation reactor). The reaction product gas from the reactor 1 is supplied to the quench tower 2 through the pipe 105 and cooled to about 20 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 room temperature 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 gas after water separation 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 10 to 30 ° 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, the 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.

Hereinafter, the present invention will be described more specifically with reference to examples.
[Production Example 1: 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 resulting catalyst precursor particulate solid (ignition loss: 1.4 wt%) was ground and dispersed in a solution of ammonia water 10ml was added ammonium paramolybdate 40.1g of pure water 150 ml. 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 the slurry was added.

Next, 58.1 g of bismuth carbonate in which 0.45% of Na was dissolved 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 tablets with a diameter of 5 mm and a height of 4 mm using 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
The atomic ratio of _{a 1} and _{a 2} of molybdenum during catalyst preparation was 6.9 and 5.1 respectively.

[Example 1]
Inert ball (1) is placed in a stainless steel reaction tube with an inner diameter of 23.0 mm and a height of 500 mm.
The size per particle: about 0.065 mm ³ ) was filled in 27 ml (packed layer length: 201 mm), and 8.6 ml of the composite oxide catalyst produced in Production Example 1 was placed on the packed bed of inert balls. And an inert ball (size per grain: about 0.065 mm ³ ) 2.9 ml were mixed and filled to form a first catalyst layer (hereinafter referred to as “catalyst layer 1”). The packed bed length of the catalyst layer 1 was 32 mm, and the catalyst dilution rate was 25%. Next, on the catalyst layer 1, 2.9 ml of the composite oxide catalyst produced in Production Example 1 and inert balls (size per grain: about 0.0
65 mm ³ ) and mixed with 8.6 ml to form a second catalyst layer (hereinafter referred to as “catalyst layer 2”).
”). The packed layer length of the catalyst layer 2 was 31 mm, and the catalyst dilution rate was 75%. The total amount of catalyst charged into the reactor was 11.5 ml (total weight of packed catalyst: 7.51 g).

An insertion tube having an outer diameter of 2.0 mm was installed in these reaction tubes, and a thermocouple was installed in the insertion tube to measure the temperature in the reactor. An electric furnace was used as the heat medium.
Then, nitrogen is supplied to the preheater at 1.8 L / hr in advance, air is 11.8 L / hr, and water vapor is 5.5 L / hr, and then a raw material gas having the composition shown in Table 1 is supplied to 2.8 L. / Hr, mixed in a preheater and heated to 350 ° C. as a mixed gas (reactor introduction gas composition = nitrogen: 8.1 vol%, air: 53.9 vol%, water vapor: 25.0 vol%, raw material Gas: 13.0 vol%). Table 1 shows the composition (mol%) of typical components contained in the source gas. At this time, the total gas flow rate was 21.9 ml / h with respect to the catalyst amount of 11.5 ml, and the SV calculated by the above formula (3) was 1900 h ⁻¹ .

The mixed gas was supplied to the above reactor, and an oxidative dehydrogenation reaction was performed. The average temperature in the reactor was 367 ° C., and the pressure was 2 kPa in terms of gauge pressure. When the product gas obtained from the reactor outlet was analyzed by gas chromatography (model number GC4000 manufactured by GL Sciences), the n-butene conversion rate (1-butene, cis-2-butene, trans-2-butene in total) Conversion ratio) was 87.7 mol%, and the butadiene selectivity was 90.7 mol%. After carrying out the oxidative dehydrogenation reaction for 200 hours, the entire amount of the catalyst was taken out from the reaction tube, and the crushing catalyst was visually identified. % By weight. Thereafter, the amount of carbon adhering to all the extracted catalysts was measured (measuring device: carbon sulfur analyzer, model number CS600, manufactured by LECO), and it was 3.5 wt%. The results are shown in Table-1.

[Comparative Example 1]
In Example 1, 9.8 ml of the composite oxide catalyst produced in advance in Production Example 1 was pulverized so that the particle size would be half or less (catalyst weight: 6.57 g), and inert balls (per one grain) The catalyst layer 1 is a mixture packed with 3.2 ml of about 0.065 mm ³ ), and 3.2 ml of the composite oxide catalyst produced in advance in Production Example 1 on the catalyst layer 1. Were all pulverized so that the particle size was less than half (catalyst weight: 2.14 g) and mixed with 7.7 ml of inert balls (size per one granule: about 0.065 mm ³ ). As a catalyst layer 2 (total weight of packed catalyst: 8.71 g), the supply amounts of nitrogen and water vapor were changed to 3.9 L / hr and 6.2 L / hr, respectively, and the total gas flow rate was 24.7 L. Oxidative dehydrogenation in the same way except that / hr was changed Reaction was performed.

When the product gas obtained from the reactor outlet was analyzed by gas chromatography (model number GC4000 manufactured by GL Sciences), the n-butene conversion rate (1-butene, cis-2-butene, trans-2-butene in total) Conversion ratio) was 90.4 mol%, and the butadiene selectivity was 85.8 mol%. After carrying out the oxidative dehydrogenation reaction for 200 hours, the entire amount of the catalyst was taken out from the reaction tube. The crushing rate was 100% by weight. The amount of carbon adhering to the catalyst was measured (measuring device: carbon sulfur analyzer manufactured by LECO, model number CS600). The measured carbon concentration of the pulverized catalyst was 10.8 wt%. The results are shown in Table-1.

[Example 2]
In Comparative Example 1, 2.6 ml of the composite oxide catalyst produced in Production Example 1 in advance was pulverized so that the particle size thereof was half or less (catalyst weight: 1.74 g). A mixture of 7.2 ml (catalyst weight: 4.82 g) of the composite oxide catalyst produced in advance in Production Example 1 and 3.3 ml of inert balls (size per grain: about 0.065 mm ³ ) is mixed and filled. The catalyst layer 1 was used as a catalyst layer 1. On the catalyst layer 1, 3.3 ml (catalyst weight: 2.21 g) of the composite oxide catalyst produced in advance in Production Example 1 and inert balls (size per grain: About 0.065 mm ³ ) oxidative dehydrogenation was performed in the same manner as in Comparative Example 1 except that the catalyst layer 2 was mixed and filled with 9.8 ml as catalyst layer 2 (total weight of the filled catalyst: 8.77 g). Reaction was performed.

When the product gas obtained from the reactor outlet was analyzed by gas chromatography (model number GC4000 manufactured by GL Sciences), the n-butene conversion rate (1-butene, cis-2-butene, trans-2-butene in total) Conversion ratio) was 87.4 mol%, and the butadiene selectivity was 84.6 mol%. After conducting the oxidative dehydrogenation reaction for 200 hours, the entire catalyst was taken out from the reaction tube. The crushing rate was 20% by weight. The amount of carbon adhering to the catalyst was measured (measuring device: carbon sulfur analyzer manufactured by LECO, model number CS600). The measured carbon concentration of the pulverized catalyst was 3.9 wt%. The results are shown in Table-1.

[Comparative Example 2]
In Example 2, 6.5 ml of the composite oxide catalyst produced in advance in Production Example 1 was pulverized so that the particle size would be half or less (catalyst weight: 4.36 g). The mixed oxide catalyst 3.3 ml (catalyst weight: 2.21 g) produced in Production Example 1 in advance and 3.3 ml of inert balls (size per one grain: about 0.065 mm ³ ) are mixed and filled. The catalyst layer 1 was used as a catalyst layer 1. On the catalyst layer 1, 3.3 ml (catalyst weight: 2.21 g) of the composite oxide catalyst produced in advance in Production Example 1 and inert balls (size per grain: About 0.065 mm ³ ) oxidative dehydrogenation was carried out in the same manner as in Example 2 except that catalyst layer 2 was prepared by mixing with 9.8 ml (total weight of packed catalyst: 8.78 g). Reaction was performed.

When the product gas obtained from the reactor outlet was analyzed by gas chromatography (model number GC4000 manufactured by GL Sciences), the n-butene conversion rate (1-butene, cis-2-butene, trans-2-butene in total) Conversion ratio) was 88.6 mol%, and the butadiene selectivity was 84.4 mol%. After conducting the oxidative dehydrogenation reaction for 200 hours, the entire catalyst was taken out from the reaction tube. The crushing rate was 50% by weight. The amount of carbon adhering to the catalyst was measured (measuring device: carbon sulfur analyzer manufactured by LECO, model number CS600). The measured carbon concentration of the pulverized catalyst was 12.8 wt%. The results are shown in Table-1.

  When Examples 1 and 2 are compared with Comparative Examples 1 and 2, since the extracted catalyst carbon composition of Examples 1 and 2 is smaller than the extracted catalyst carbon composition of Comparative Examples 1 and 2, the crushing rate is 0.0% by weight. If it is 40.0 weight% or less above, when manufacturing butadiene from n-butene, it turns out that carbon components, such as coke, adhere to the catalyst in a reactor.

DESCRIPTION OF SYMBOLS 1 Reactor 2 Quench tower 3, 6, 13 Cooler 4, 7, 14 Drain pot 8A, 8B Dehydrator 9 Heater 10 Solvent absorption tower 11 Deaeration tower 12 Solvent separation tower 101-121 Piping

Claims (6)

A mixed gas obtained by mixing a raw material gas containing a monoolefin having 4 or more carbon atoms and a molecular oxygen-containing gas is supplied to a reactor having a catalyst, and a corresponding conjugated diene is generated by an oxidative dehydrogenation reaction. In the method for producing a conjugated diene for obtaining a product gas containing diene, the crushing rate of the catalyst in the reactor represented by the following formula (1) is 0.0 wt% or more and 40.0 wt% or less. A method for producing a conjugated diene.
Crushing rate (% by weight) = {(weight of crushed catalyst in reactor) / (total catalyst weight in reactor)} × 100 (1)
(In the formula, the crushing catalyst is selected by a sieve having an opening of 4.5 to 4.9 mm.)   The method for producing a conjugated diene according to claim 1, wherein the reactor further includes a solid that is not reactive with the catalyst. The method for producing a conjugated diene according to claim 1 or 2, wherein a ratio (volume ratio) of a flow rate of the mixed gas to a total catalyst amount in the reactor is 500 to 5000 h- ¹ .   The method for producing a conjugated diene according to any one of claims 1 to 3, wherein the catalyst contains at least molybdenum and bismuth. The said catalyst is a complex oxide catalyst represented by following General formula (2), The manufacturing method of the conjugated diene of any one of Claims 1-4 characterized by the above-mentioned.
Mo _a Bi _b Co _c Ni _{d F e} X _f Y _g Z _h Si _i O _j (2)
Wherein X is at least one element selected from the group consisting of magnesium (Mg), calcium (Ca), zinc (Zn), cerium (Ce) and samarium (Sm), and Y is sodium (Na) , Potassium (K), rubidium (Rb), cesium (Cs) and at least one element selected from the group consisting of thallium (Tl), Z is boron (B), phosphorus (P), arsenic (As) And at least one element selected from the group consisting of tungsten (W), and a to j represent atomic ratios of the respective elements, and when a = 12, b = 0.1 to 7, c = 0 to 10, d = 0 to 10 (provided c + d = 1 to 10), e = 0.05 to 3, f = 0 to 2, g = 0.04 to 2, h = 0 to 3, i = 0 to 0 48, and j satisfies the oxidation state of other elements Numerical value is.) The raw material gas is produced by dehydrogenation or oxidative dehydrogenation of gas containing 1-butene, cis-2-butene, trans-2-butene or a mixture thereof obtained by dimerization of ethylene, or a mixture thereof. The conjugate according to any one of claims 1 to 5, which is a gas containing a large amount of hydrocarbons having 4 carbon atoms obtained when fluidly cracking a butene fraction or a heavy oil fraction. Diene production method.

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