JP2012111751A - Method for producing conjugated diene - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a conjugated diene such as butadiene by a catalytic oxidative dehydrogenation reaction of a monoolefin such as n-butene, by which the generation and accumulation of high boiling point by-products can be prevented, and a stable operation can be continued to industrially advantageously produce the conjugated diene.SOLUTION: The method for producing the conjugated diene, comprising supplying a raw material gas containing a ≥4C monoolefin and a molecular oxygen-containing gas into a reactor, performing an oxidative dehydrogenation reaction in the presence of a catalyst to obtain a corresponding conjugated diene-containing produced gas, and then bringing the produced gas into contact with an organic solvent to obtain a solution containing the conjugated diene, is characterized in that the concentration of a 1 to 4C organic carboxylic acid in the solution is ≤0.45 wt.%.

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”). In general, the butadiene produced is brought into contact with an organic solvent by reacting a reaction product gas containing butadiene with the organic solvent, and the butadiene is absorbed in the organic solvent. To separate and recover butadiene.

  As a specific method, for example, in order to remove a by-product carbonyl compound from a reaction mixture gas containing 1,3-butadiene produced by an oxidative dehydrogenation reaction of a monoolefin such as n-butene, A method in which a carbonyl compound is absorbed in an absorbing solvent by bringing it into contact with an absorbing solvent comprising an organic acid aqueous solution (Japanese Patent Laid-Open No. 60-184029), or a non-condensable gas from a product gas having a high concentration of non-condensable gas. In order to recover butadiene substantially free of gas and moisture, there is a method of contacting with a hydrocarbon absorbing solvent having a boiling range of 110 to 180 ° C. (Japanese Patent Laid-Open No. 60-193931).

JP 60-184029 A JP-A-60-193931

  In Patent Documents 1 and 2, the conjugated diene is absorbed in an organic solvent to obtain a solution containing the conjugated diene, and then the solution is distilled to separate the solvent and recover the purified conjugated diene. Although it is not described that a polymer is generated in a solution to be distilled, according to the study by the present inventors, an organic solvent in which a conjugated diene is absorbed by contact with an organic solvent and a reaction product gas is absorbed. In the process of continuously distilling water, a problem has been found that high-boiling compounds accumulate in the distillation column.

  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, the product gas obtained after the reaction is cooled, Provided is an industrially advantageous method for producing a conjugated diene capable of reducing the disappearance of the conjugated diene in a process of collecting and purifying the conjugated diene contained in the cooling gas with an organic solvent and continuing stable operation. For the purpose.

As a result of intensive studies to solve the above-mentioned problems, the inventors of the present invention are produced by polymerization of conventional conjugated dienes from a component of a polymer produced by polymerizing conjugated dienes and a component of a high boiling point compound. Based on the idea that high-boiling compounds are generated in a reaction route different from the polymer formation route, components other than the conjugated diene contained in the solution after contacting the product gas with an organic solvent were analyzed. It was found that unsaturated aldehydes and cyclohexenyls exist in the solution, and the unsaturated aldehydes react with conjugated dienes to form high-boiling compounds such as cyclohexenyls. And in this solution, unsaturated aldehydes and cyclohexenyls are generated due to organic carboxylic acids having 1 to 4 carbon atoms, so by setting this concentration to a specific concentration, conjugated dienes and unsaturated The present inventors have found that the reaction with aldehydes and cyclohexenyls can be suppressed and high boiling point compounds can be reduced.

The present invention has been achieved on the basis of such findings, and the gist thereof is as follows [1] to [8].
[1] A raw material gas containing a monoolefin having 4 or more carbon atoms and a molecular oxygen-containing gas are supplied to a reactor, and a corresponding conjugated diene produced by performing an oxidative dehydrogenation reaction in the presence of a catalyst is included. After obtaining the product gas, the product gas is brought into contact with an organic solvent to obtain a solution containing the conjugated diene. The concentration of the organic carboxylic acid having 1 to 4 carbon atoms in the solution is 0.45 wt% or less. A method for producing a conjugated diene.
[2] The method for producing a conjugated diene according to [1], wherein the organic solvent is a hydrocarbon solvent.
[3] The method for producing a conjugated diene according to [1] or [2], wherein the amount of water in the organic solvent is 0.01 to 10 wt%.
[4] In any one of [1] to [3], the concentration of the linear monoolefin having 4 or more carbon atoms in the raw material gas is 50.00 to 99.99 mol%. The manufacturing method of conjugated diene of description.
[5] The method for producing a conjugated diene according to any one of [1] to [4], further comprising a step of cooling the product gas.
[6] The method for producing a conjugated diene according to [5], wherein the product gas is cooled by contacting with a cooling solvent.
[7] The method for producing a conjugated diene according to [6], wherein the cooling solvent is water or an aqueous alkali solution.
[8] The method for producing a conjugated diene according to any one of [1] to [7], wherein the catalyst is a composite oxide catalyst represented by the following general formula (1).

Mo _a Bi _b Co _c Ni _{d F e} X _f Y _g Z _h Si _i O _j (1)
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.)

  According to the present invention, in the step of distilling and separating the obtained conjugated diene, the production of high-boiling by-products can be suppressed and clogging can be prevented, and the disappearance of butadiene can be reduced.

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, and a corresponding conjugated diene is produced by an oxidative dehydrogenation reaction in the presence of a catalyst.

  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% by volume or less, preferably 20% by volume or less, more preferably 10% by volume or less, and particularly preferably 1% by volume 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 preferably 50.00 to 99.99 vol%, and more preferably 70.00 to 99.90 vol%. is there. If this amount is small, the concentration of 1-butene or 2-butene as the main raw material will decrease and the reaction will slow down, or the yield of butadiene as the target product will tend to decrease. Energy for removing impurities from monoolefins having 4 or more carbon atoms is required.

  Next, the catalyst suitably used in the present invention will be described. The catalyst used in the present invention is an oxidative dehydrogenation catalyst, 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 = 0.1-1, 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 a drying obtained by drying this It is preferable to produce the catalyst precursor by a heat treatment, and a method including a post-process comprising a catalyst precursor, a molybdenum compound and a bismuth compound integrated with an aqueous solvent, followed by 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 <a1 / (c + d + e) <3, and the a ₂ 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 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. If necessary, addition and mixing of silica are preferably performed in this previous step.

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.

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.

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. May be. 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 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 vol% or less, preferably 17.0 vol% or less, and more preferably 15.0 vol% 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.

  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
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.

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.

  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.

  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. Since the sequential oxidation reaction from linear monoolefins having 4 or more carbon atoms in the raw material gas progresses as the temperature in the reactor is increased, the number of carbon atoms in the solution containing conjugated dienes described later is 1 to 4 The concentration of the organic carboxylic acid tends to increase, while the concentration tends to decrease as the reactor temperature decreases. 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 MPa or more, 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 0.80 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 7.20 seconds or less, and more preferably 2.77 seconds or less. The smaller this value, the smaller the reactor.

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-bun), specifically, 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.

  In this invention, it is preferable to further have the process (henceforth abbreviated as a cooling process) which cools the product gas containing the conjugated diene obtained from a reactor. Any cooling process may be used as long as the product gas obtained from the reactor outlet can be cooled. Preferably, a cooling solvent and a product gas are directly contacted in a cooling tower and cooled. The cooling solvent is preferably water or an alkaline aqueous solution. By using these cooling solvents, an organic carboxylic acid having 1 to 4 carbon atoms may be extracted into the cooling solvent, and thus an organic carboxylic acid having 1 to 4 carbon atoms in a solution containing a conjugated diene described later. The concentration of can be lowered. Moreover, you may cool with coolers, such as a heat exchanger, before and after cooling with a cooling tower.

  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. When cooling using a cooling tower, the pressure in the cooling tower is not particularly limited, but is usually 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.

Moreover, in this invention, you may have the process (henceforth abbreviated as 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 when the solvent is used in the subsequent process.
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. 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, but usually 4 to 35 vol. %, Preferably 10 to 30 vol% of water. Moreover, the water concentration in the product gas after passing the cooling process which uses water as a cooling solvent by the process which has a cooling process is 100 volppm-2.0 vol% normally. 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 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. .

In the present invention, the step of bringing the product gas into contact with an organic solvent, absorbing hydrocarbons such as olefin and conjugated diene in the organic solvent, and obtaining a solution containing the conjugated diene (hereinafter sometimes abbreviated as a solvent absorption step). I need. The solvent absorption step may be provided anywhere as long as it is a subsequent step of the reactor, but is preferably provided after the cooling step or the dehydration step described above.
As a specific method for absorbing the generated gas in the organic solvent in the solvent absorption step, there is a method using an absorption tower. 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. Among these, a spray tower, a bubble bell tower, and a perforated plate tower are preferable.

  When an absorption tower is used, the organic 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. Compounds and the like are absorbed in organic solvents. 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 an absorption tower is used, 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. 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, 0-50 degreeC, Preferably, it is 10-40 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 organic solvent used in the solvent absorption step of the present invention is preferably a hydrocarbon solvent, more preferably a hydrocarbon solvent having 6 or more carbon atoms, and still more preferably aliphatic saturation having 6 to 10 carbon atoms. It is a solvent comprising a hydrocarbon or an aromatic hydrocarbon having 6 to 8 carbon atoms, or a solvent comprising an amide compound. Specifically, for example, dimethylformamide (DMF), toluene, xylene, N-methyl-2-pyrrolidone (NMP) and the like can be used. Among these, toluene is particularly preferably used because it is difficult to dissolve the inorganic gas.

In the present invention, an organic carboxylic acid having 1 to 4 carbon atoms is present in a solution containing a conjugated diene, and the organic carboxylic acid having 1 to 4 carbon atoms is a raw material mainly containing a monoolefin having 4 or more carbon atoms. It is generated when the gas undergoes an oxidative dehydrogenation reaction, and is entrained in the product gas together with the target product, conjugated diene, and flows out of the reactor. The organic carboxylic acid of the present invention includes those generated by the sequential oxidation reaction of branched monoolefins in the raw material gas and those generated by the sequential oxidation reaction of linear monoolefins. When the monoolefin of several 4 or more is butene, specific examples of the organic carboxylic acid generated by the sequential oxidation reaction of isobutene include formic acid, acetic acid, acrylic acid, methacrylic acid,
Examples of the organic carboxylic acid generated by the sequential oxidation reaction of n-butene include maleic acid, phthalic acid, propionic acid, butyric acid, isobutyric acid, oxalic acid, and crotonic acid. Among these, one or more selected from the group consisting of formic acid, acetic acid and maleic acid is preferable.

  These organic carboxylic acids having 1 to 4 carbon atoms supply a raw material gas containing a monoolefin having 4 or more carbon atoms and a molecular oxygen-containing gas to the reactor, and perform an oxidative dehydrogenation reaction in the presence of a catalyst. The by-product derived from the straight-chain monoolefin in the raw material gas is introduced into the solvent absorption process or is included in advance in the organic solvent used in the solvent absorption process. As, there are many organic carboxylic acids having 1 to 4 carbon atoms resulting from by-products derived from linear monoolefins in the raw material gas.

  In the present invention, the concentration of the organic carboxylic acid having 1 to 4 carbon atoms in the solution containing conjugated diene is 0.45 wt% or less, preferably 1.0 wt ppm or more and 0.40 wt% or less, more preferably 1 .2 wtppm or more and 1000 wtppm or less, more preferably 1.3 wtppm or more and 100 wtppm or less. As the concentration value increases, the conjugated diene tends to become a high-boiling compound, and as the concentration value decreases, the amount of the organic solvent used tends to increase.

  In the present invention, an unsaturated aldehyde may be present in the solution before the separation of the conjugated diene, and the conjugated diene and the unsaturated aldehyde form a high-boiling component of the cyclohexenyl skeleton, resulting in a yield of the conjugated diene. It tends to decrease. Examples of the unsaturated aldehyde include acrolein, methacrolein, crotonaldehyde, acetaldehyde, benzaldehyde, 2-butenone, and methylbenzaldehyde.

  The amount of the organic solvent used in the solvent absorption step is not particularly limited, but is usually 1 to 100 times by weight, preferably 2 to 50 times the flow rate of the conjugated diene in the product gas supplied from the reactor. Weight times. As the amount of the organic solvent used increases, it tends to be uneconomical, and as the amount used decreases, the absorption efficiency of the conjugated diene tends to decrease. The water concentration in the organic solvent in the solvent absorption step is usually 0.01 to 10 wt%, preferably 0.05 to 5 wt%. When the moisture concentration is high, there is a possibility of causing corrosion of the device, and the smaller the moisture concentration, the more energy is required for purifying the organic solvent or removing moisture from the generated gas.

The solution containing the conjugated diene obtained in the solvent absorption step mainly contains the conjugated diene that is the target product. The concentration of the conjugated diene in the solution is usually 1 to 20% by weight. , Preferably 3 to 10% by weight. The higher the concentration of the conjugated diene in this solution, the more the amount of conjugated diene lost due to polymerization or volatilization tends to increase, and the lower the concentration, the greater the amount of organic solvent circulating in the same production volume. The energy cost required tends to increase.
Further, since a slight amount of nitrogen and oxygen is also absorbed in the resulting solution containing the conjugated diene, it may have a deaeration step of gasifying and removing nitrogen and oxygen dissolved in the solution.

  It is preferable to include a step of supplying the obtained solution containing a conjugated diene to a separator and separating it into an organic solvent and a conjugated diene by distillation (hereinafter sometimes abbreviated as a separation step). By this step, a conjugated diene having a relatively high purity can be obtained. In addition, the thing which exists in the separator of a separation process as a solution, and the state in which the process for isolate | separating conjugated diene was made | formed is also contained in the solution containing the conjugated diene in this invention.

As the separator, distillation separation is usually carried out using a distillation column having a reboiler at the bottom of the column and a condenser at the top of the column. Is extracted. After the separated organic solvent is recovered, it is preferably recycled to the above-described solvent absorption step and used again as an organic solvent for contacting with the product gas. As the organic solvent circulates and reuses, in addition to the organic carboxylic acid having 1 to 4 carbon atoms, other impurities may accumulate in the organic solvent. Circulating while removing these impurities together with organic carboxylic acids having 1 to 4 carbon atoms from organic solvents by known purification methods such as distillation, decantation, sedimentation, contact treatment with adsorbents, ion exchange resins, etc. Is 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.

  A conjugated diene having a relatively high purity can be obtained in the separation step of the conjugated diene, and this may have a purification step in which the conjugated diene is further purified by distillation purification or the like. 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. Note that the product gas obtained from the reactor 1 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”.

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>
According to the process flow shown in FIG. 1, 1,3-butadiene was continuously produced. The reaction tube in the reactor 1 provided with 113 reaction tubes having an inner diameter of 27 mm and a length of 3500 mm was combined with 367 ml of the composite oxide catalyst produced in Production Example 1 and an inert ball (Tip) per reaction tube.
ton Corp. 367 ml).

  Air, nitrogen and water vapor are respectively supplied at the following flow rates, and BBSS having the composition shown in Table 1 is supplied as the raw material gas at the following flow rates, mixed with air, nitrogen and water vapor in the pipe, and then a preheater (Fig. (Not shown) was heated to 214 ° C. and then supplied to the reactor 1 to carry out an oxidative dehydrogenation reaction. In addition, the temperature inside the reaction tube was adjusted to 332 to 380 ° C. by flowing a heat medium at 331 ° C. on the barrel side in the reactor 1.

・ BBSS: 13.2 vol / hr
・ Air: 62.4 vol / hr
・ Nitrogen: 29.9 vol / hr
Water vapor: 35.3 vol / hr
The product gas containing butadiene extracted from the outlet of the reactor 1 was brought into contact with water in the quench tower 2 and cooled to 20 and then further cooled to 8 ° C. in the cooler 3.

Here, the condensed water in the product gas was recovered in the drain pot 4. The product gas cooled to 8 ° C. was pressurized to 0.3 MPa by the compressor 5 and further cooled to about 17 ° C. by the cooler 6 to condense the water and recovered in the drain pot 7.
The product gas compressed by the compressor 5 was supplied to a dehydration tower 8A or 8B packed with molecular sieve 3A (manufactured by Union Showa Co., Ltd.) and dehydrated.

  The product gas dehydrated in the dehydration tower 8A or 8B is supplied to the solvent absorption tower 10 and toluene, which is the absorption solvent, is supplied to the upper part of the solvent absorption tower 10 at 600 kg / h, at a pressure of 0.2 MpaG and a temperature of 16 ° C. Under the conditions, a countercurrent contact was made to absorb hydrocarbons such as butadiene in the product gas, and a solution containing butadiene was obtained from the bottom of the solvent absorption tower 10. The water concentration of the solution containing butadiene was 0.3 wt%. Then, oxygen and nitrogen in the solution are separated by the deaeration tower 11, and further, toluene is separated from the solution at the tower bottom temperature of 120 ° C. and the pressure of 0.1 MpaG by the solvent separation tower 12 to recover 1,3-butadiene. did. At the same time, the bottoms were sampled from the bottom of the deaeration tower 11.

The sampled degassed liquid from the deaeration tower 11 is put into a stainless steel autoclave having a capacity of 400 mL, nitrogen gas is introduced, the pressure of the container is raised to 0.1 MPaG, and the liquid temperature inside the autoclave is raised to 140 ° C. for 2 hours. Heated. When the solution sampled in advance before heating was analyzed by gas chromatography (manufactured by Shimadzu, model number GC-14B FID (column: BPX-5 and AL ₂ O ₃ / Na ₂ SO ₄ )), the concentration of formic acid in the solution was 1 wtppm. The concentration of maleic acid was 0.4 wtppm. Simultaneously, this solution was analyzed by gel permeation chromatography (detector Toso RI-8020 and Shimadzu SPD-6A UV, column: TSK-GEL G-500HHR and G-1000HHR). The concentration of high boiling point compounds (hereinafter referred to as “GPC-HB”) when the peak component at 1000 to 1500 positions (retention time in polypropylene glycol diol type) was quantified using benzyl N-butyl phthalate (molecular weight 312.36) as a sample. (Abbreviated as “concentration”) was 0.0181 wt%.

After heating for 2 hours, the autoclave was cooled to room temperature and analyzed by gas chromatography and gel permeation chromatography as before heating. The concentration of formic acid in the solution was 1 wtppm and the concentration of maleic acid was 0.4 wtppm. The GPC-HB concentration was 0.0215 wt%. The GPC-HB concentration increased by 0.0034 wt% before and after heating.

[Comparative Example 1]
Example 1 except that formic acid was added to a solution having a GPC-HB concentration of 0.0158 wt% in the sampled solution before heating so that the formic acid concentration was 0.5 wt%.
It carried out like. The concentration of formic acid in the solution after heating was 0.5 wt%, the concentration of maleic acid was 0.4 wtppm, and the concentration of GPC-HB was 0.0212 wt%. The GPC-HB concentration increased by 0.0054 wt% before and after heating.

When Example 1 and Comparative Example 1 are compared, if the concentration of formic acid in the solution containing 1,3-butadiene is 0.45 wt% or less, it is higher than 120 ° C., which is the column bottom temperature of the solvent separation column 12. It can be seen that even when heated at a temperature, the amount of GPC-HB, which is a high-boiling component, can be suppressed.
From this result, in the process of continuously producing butadiene, it is recovered by setting the concentration of the organic carboxylic acid having 1 to 4 carbon atoms in the solution containing butadiene in the solvent separation column 12 to 0.45 wt or less. It is expected that butadiene loss can be suppressed and blockage due to accumulation of high-boiling components in the tower can be prevented.

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 101-126 Piping

Claims (8)

  A raw material gas containing a monoolefin having 4 or more carbon atoms and a molecular oxygen-containing gas are supplied to a reactor, and a product gas containing a corresponding conjugated diene produced by performing an oxidative dehydrogenation reaction in the presence of a catalyst. After the obtained gas is brought into contact with an organic solvent to obtain a solution containing the conjugated diene, the concentration of the organic carboxylic acid having 1 to 4 carbon atoms in the solution is 0.45 wt% or less. A method for producing a conjugated diene.   The method for producing a conjugated diene according to claim 1, wherein the organic solvent is a hydrocarbon solvent.   The method for producing a conjugated diene according to claim 1 or 2, wherein the amount of water in the organic solvent is 0.01 to 10 wt%.   The conjugated diene according to any one of claims 1 to 3, wherein the concentration of the linear monoolefin having 4 or more carbon atoms in the raw material gas is 50.00 to 99.99 mol%. Production method.   The method for producing a conjugated diene according to any one of claims 1 to 4, further comprising a step of cooling the product gas.   The method for producing a conjugated diene according to claim 5, wherein the product gas is cooled by contacting with a cooling solvent.   The method for producing a conjugated diene according to claim 6, wherein the cooling solvent is water or an aqueous alkali solution. The method for producing a conjugated diene according to any one of claims 1 to 7, wherein the catalyst is a complex oxide catalyst represented by the following general formula (1).
Mo _a Bi _b Co _c Ni _{d F e} X _f Y _g Z _h Si _i O _j (1)
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.)

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