JP2011148764A - Method for producing conjugated diene - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an industrially profitable method for producing a conjugated diene such as butadiene by the catalytic oxidative dehydrogenation reaction of a monoolefin such as n-butene, by which the production of high boiling point by-products and the accumulation of solid deposits can be inhibited, and the operation can stably be continued. <P>SOLUTION: The method for producing a conjugated diene, comprising mixing a raw material gas containing a ≥4C monoolefin with a molecular oxygen-containing gas to obtain a mixture gas, and then subjecting the mixture gas to an oxidative dehydrogenation reaction in the presence of a catalyst in a reactor to obtain a production gas containing the corresponding conjugated diene, is characterized in that the ratio of the flow rate of the mixture gas to the amount of the catalyst in the reactor is 1,500 to 5,000 h<SP>-1</SP>, and the conversion of a ≥4C monoolefin is ≤87%. <P>COPYRIGHT: (C)2011,JPO&INPIT

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.

Specifically, butene is vapor-phase contact oxidatively dehydrogenated to produce butadiene, the product gas containing butadiene is cooled to remove high-boiling by-products from the product gas, and then aldehydes in the product gas. There are some which have a step of compressing the product gas through a step of removing butadiene and recovering butadiene from the compressed product gas (for example, Patent Document 1 or Patent Document 2).
On the other hand, Patent Document 3 describes a composite oxide catalyst containing at least one of molybdenum, iron, nickel or cobalt and silica as a catalyst for producing butadiene by the oxidative dehydrogenation reaction of butene. The manufacturing method of is not described.

JP 60-115532 A JP 60-126235 A JP 2003-220335 A

  When the butadiene is produced from butene by the catalysts and production methods of Patent Documents 1 to 3 above, impurities contained in the raw material gas (for example, BB, BBSS) are contained in the product gas obtained by the oxidative dehydrogenation reaction. When the product gas containing the high-boiling by-product is cooled in the subsequent cooling step, it becomes a high-boiling by-product in the oxidative dehydrogenation reaction. There was a problem that solids were deposited in the cooling process and solids were accumulated in the cooling process as the operation continued, resulting in clogging in the cooling process and the inability to continue the operation.

  This invention was made in view of the said subject, Comprising: In the method of manufacturing conjugated dienes, such as a butadiene, by the catalytic oxidative dehydrogenation reaction of monoolefins, such as n-butene, it is contained in the product gas obtained after reaction An object of the present invention is to provide an industrially advantageous method for producing butadiene that can reduce the amount of solids caused by high-boiling by-products and prevent accumulation in the cooling process and can stably continue operation. To do.

As a result of intensive studies to solve the above problems, the present inventors have supplied a raw material gas containing a monoolefin having 4 or more carbon atoms and a reaction raw material gas containing a molecular oxygen-containing gas to the reactor, and the presence of the catalyst. The ratio of the flow rate of the mixed gas to the amount of catalyst in the reactor is 1500 to 5000 h ⁻¹ , and the conversion rate of monoolefin having 4 or more carbon atoms is 84% or less. In addition, by obtaining a gas containing the corresponding conjugated diene, it is possible to reduce the amount of solid clogging that hinders stable operation of the plant, and it is possible to operate more safely and to produce butadiene stably at a higher yield. Found that can be done.

The present invention has been achieved on the basis of such findings, and the gist thereof is as follows [1] to [7].
[1] A raw material gas containing a monoolefin having 4 or more carbon atoms and a molecular oxygen-containing gas are mixed to obtain a mixed gas, and the mixed gas is supplied to a reactor, and an oxidative dehydrogenation reaction is performed in the presence of a catalyst. In order to obtain a product gas containing the corresponding conjugated diene produced by performing the above, the ratio of the flow rate of the mixed gas to the amount of catalyst in the reactor is 1500 to 5000 h ⁻¹ , and the number of carbon atoms is 4 or more. A process for producing a conjugated diene, wherein the conversion rate of monoolefin is 87% or less.

[2] The method for producing a conjugated diene according to [1], wherein water vapor supplied to the reactor is in a ratio of 0.5 to 5.0 with respect to a supply amount of the raw material gas.
[3] The method for producing a conjugated diene according to [1] or [2], wherein the concentration of the olefin having 3 or less carbon atoms in the raw material gas is 0.010 to 0.500 vol%.
[4] The concentration of a linear monoolefin having 4 or more carbon atoms in the raw material gas is 70.00 to 99.99 vol%, [1] to [3] A process for producing conjugated dienes.

[5] The method for producing a conjugated diene according to any one of [1] to [4], wherein the product gas and water are contacted and cooled.
[6] The method for producing a conjugated diene according to any one of [1] to [5], wherein the catalyst is a composite oxide catalyst containing at least molybdenum, bismuth, and cobalt.

[7] The method for producing a conjugated diene according to [6], wherein the composite oxide 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 = 0.5 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.)

  ADVANTAGE OF THE INVENTION According to this invention, the production amount of the high boiling point by-product which precipitates in the cooling process after a reaction process can be reduced, and the stable operation of a plant becomes possible continuously.

It is a systematic diagram of the process 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.
Among the methods for producing conjugated dienes of the present invention, as a representative example, the present invention will be described in detail with reference to FIG. 1 showing a system diagram of a production process in the case of producing butadiene from n-butene. The invention is not limited to the production of butadiene from n-butene (1-butene, 2-butene), but contact of monoolefins having 4 or more carbon atoms, preferably 4 to 6 carbon atoms, such as pentene, methylbutene and dimethylbutene. It is effectively applied to the production of the corresponding conjugated diene by oxidative dehydrogenation. These monoolefins do not necessarily need to be used in an isolated form, and can be used in the form of any mixture as required. For example, when 1,3-butadiene is to be obtained, high-purity 1-butene or 2-butene can be used as a raw material, but butadiene from the C ₄ fraction (BB) produced as a by-product in the naphtha decomposition described above. And a fraction (BBSS) mainly comprising n-butene (1-butene and 2-butene) obtained by separating i-butene and a butene fraction produced by dehydrogenation or oxidative dehydrogenation of n-butane 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. 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.

  Further, the source 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 branched monoolefins such as isobutene; saturated hydrocarbons such as propane, n-butane, i-butane, and pentane; olefins such as propylene and pentene; 1,2-butadiene. And 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. If the amount is too large, the concentration of 1-butene or 2-butene, which are the main raw materials, decreases and the reaction becomes slow, or the yield of 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 70.00 to 99.99 mol%, more preferably 70.00 to 99.0 mol%. More preferably, it is 70.00-90.0 mol%.
In the present invention, the concentration of the olefin having 3 or less carbon atoms in the raw material gas is preferably from 0.010 to 0.500 vol%. In the case where the conjugated diene is butadiene and butadiene is produced from n-butene, examples of the olefin having 3 or less carbon atoms include ethylene and propylene, with propylene being particularly preferred. This concentration is usually from 0.010 to 0.500 vol%, preferably from 0.012 to 0.450 vol%, more preferably from 0.015 to 0.400 vol%. When deviating from this range, polymerization components such as acrolein tend to increase.

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, and specifically preferably air. It is. From the viewpoint of cost required for industrially preparing a molecular oxygen-containing gas, the molecular oxygen is usually 50% by volume or less, preferably 30% by volume or less, 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 to obtain a mixed gas, and the mixed gas is supplied to the reactor. , And water (steam) 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.

  Further, the method of supplying the source gas, the molecular oxygen-containing gas, the nitrogen gas, and water (water vapor) is not particularly limited, and may be supplied by separate pipes, but the formation of the blast is surely avoided. Therefore, before obtaining the mixed gas, nitrogen gas is supplied to the raw material gas in advance, or nitrogen gas is supplied to the molecular oxygen-containing gas, and then the raw material gas and the molecular oxygen-containing gas are supplied. It is preferable to mix to obtain a mixed gas.

  In the present invention, it is preferable to introduce water vapor into the reactor 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, water vapor is introduced at a ratio of 0.5 to 5.0 with respect to the supply amount of the raw material gas, preferably 0.8 to 4.5, and more preferably 1.0 to 4.0. It is.

  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 typical composition of the mixed gas is shown below.
<Combination gas composition>
n- butene: _{C 4} fraction 50～100Vol% of the total
C ₄ fractions total: 5-15 vol%
O _{2: C 4} fraction summed for 40~120vol / vol%
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
In addition, as a ratio of the raw material gas in the mixed gas of the present invention, it is usually 4.2 vol% or more, preferably 7.6 vol% or more, and more preferably 9.3 vol% or more. 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. As this ratio increases, the construction cost and the cost required for operation tend to decrease, and as the ratio decreases, solids tend not to be generated.

  The reactor used in 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, and more. Preferred are fixed bed multitubular reactors and plate reactors, and most preferred are fixed bed multitubular reactors. These reactors are generally used industrially and are not particularly limited.

  The reactor of the present invention is packed with an oxidative dehydrogenation reaction catalyst described later, and the catalyst is a fixed bed used for producing a corresponding conjugated diene from a monoolefin having 4 or more carbon atoms and oxygen. It is preferable that the reactor is used by being charged, and it is more preferable that n-butene is used by being charged in a fixed bed reactor used to react with oxygen to produce butadiene and water.

  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 temperature of the catalyst layer in the reactor during the oxidative dehydrogenation reaction in the present invention is not particularly limited, but is usually 250 to 450 ° C, preferably 280 to 400 ° C, more preferably 320 to 395 ° C. . In addition, there exists a tendency for catalyst activity to fall rapidly, so that this temperature becomes large, and it exists in the tendency for the yield of the conjugated diene which is a target product to fall, so that it becomes small. The temperature of the catalyst layer 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.

  The pressure in the reactor of the present invention is not particularly limited, but is usually 0 MPaG or more, preferably 0.001 MPa or more, and more preferably 0.01 MPaG or more. There is an advantage that a larger amount of the reaction gas can be supplied to the reactor as the pressure value increases. On the other hand, it is usually 0.5 MPaG or less, preferably 0.3 MPaG or less, and more preferably 0.1 MPaG. The smaller the pressure value, the narrower the explosion range.

  The residence time of the reactor in the present invention is not particularly limited, but is usually 0.72 seconds or longer, preferably 0.80 seconds or longer, more preferably 0.90 seconds or longer. 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, it is usually 2.40 seconds or less, preferably 2.00 seconds or less, and more preferably 1.90 seconds. The smaller this value, the smaller the reactor.

In the present invention, the flow rate ratio of the mixed gas to the catalyst amount in the reactor is 1500～5000H ^-1, preferably a 1800～4500H ^-1, more preferably at 1894～4000H ^-1 is there. As this value increases, solid precipitation tends to be suppressed, and as the value decreases, solid tends to precipitate more easily.
The 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.

  The present invention is characterized in that the conversion rate of a linear monoolefin having 4 or more carbon atoms in the raw material gas is 87% or less. This conversion rate is the amount of linear monoolefin having 4 or more carbon atoms in the raw material gas consumed by the oxidative dehydrogenation reaction with respect to the supply amount of linear monoolefin having 4 or more carbon atoms in the raw material gas. It is a ratio, and when producing butadiene from n-butene, it is the conversion of n-butene. When the conversion rate exceeds 87%, the yield of the conjugated diene that is the target product tends to decrease. Moreover, Preferably it is 86.5% or less, More preferably, it is 86.0% or less. As this value is smaller, solids tend not to precipitate. Furthermore, the lower limit of the conversion of n-butene is usually 60%, and preferably 70% from the viewpoint of productivity. More preferably, it is 80%.

  In the present invention, when the conversion rate of a linear monoolefin having 4 or more carbon atoms is 87% or less, generation of solids due to high-boiling by-products can be suppressed. A method for controlling the conversion rate of the straight chain monoolefin having 4 or more carbon atoms is not particularly limited, but the conversion rate can be controlled by changing the reaction temperature and the mixed gas composition. When the conversion rate is increased, the reaction temperature is raised, while when the conversion rate is lowered, the reaction temperature can be lowered to a certain value.

In the present invention, the ratio of the flow rate of the mixed gas to the amount of catalyst in the reactor is 1500 to 5000 h ⁻¹ , and the conversion rate of the linear monoolefin having 4 or more carbon atoms is 87% or less. Thus, it is possible to reduce the amount of solid matter resulting from high-boiling by-products contained in the product gas obtained after the reaction. Although this reason is not necessarily clear, the following reason is guessed.

  That is, under the conditions of the oxidative dehydrogenation reaction of impurities contained in the raw material gas, a sequential reaction between impurities and impurities and products proceeds to generate high boiling point by-products. Since there is a correlation between the conversion rate of the monoolefin having 4 or more carbon atoms in the raw material gas and the ratio of the flow rate of the mixed gas to the amount of the catalyst in the reactor, this range is included in controlling the sequential reaction. Thus, by setting these in the numerical range of the present invention, it is possible to suppress the sequential reaction produced by the high-boiling by-product and to obtain the conjugated diene as the target product with high selectivity. Become.

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 producing butadiene from n- butenes (1-butene and / or 2-butene), the outlet flow increases has CO and CO ₂ in the reaction or side reactions butene is oxidative dehydrogenation to produce butadiene and water This is because the number of molecules increases stoichiometrically in the reaction to be generated. 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.

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

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

For this reason, it is preferable to avoid introducing high-boiling by-products in the product gas into the cooling process as much as possible.
Moreover, in this invention, you may have a dehydration process which removes the water | moisture content contained in the product gas discharged | emitted from a reactor. Providing a dehydration step is preferable because it can prevent equipment corrosion due to moisture in each step in the subsequent process and accumulation of impurities in the solvent used in the solvent absorption step and solvent separation step described later.

  The dehydration process of the present invention is not particularly limited as long as it is a process capable of removing moisture contained in the product gas. The dehydration step may be performed anywhere as long as it is a subsequent step of the reactor, but it is preferable to perform the dehydration step after the above-described cooling step. Normally, the amount of water contained in the product gas discharged from the reactor varies depending on the type of raw material gas, the amount of molecular oxygen-containing gas, and water vapor mixed with the raw material gas. It is contained in the gas at a rate of 4 to 35 vol%, preferably 10 to 30 vol%. Further, when water is used as a cooling solvent in the preceding cooling step, the amount of water contained in the product gas is 100 volppm to 2.0 vol%, and the dew point is 0 to 100 ° C, preferably 10 to 80 ° C.

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 this invention, you may have the collection | recovery process which collect | recovers the product gas discharged | emitted from the reactor exit. From the viewpoint of reducing the energy cost required for the separation, it is preferable to recover the product gas by absorbing it in a solvent. The recovery process is not particularly limited as long as it can be recovered by absorbing the product gas in a solvent. The recovery step may be performed anywhere as long as it is a subsequent step of the reactor, but it is preferable to perform the recovery step after the above-described cooling step and dehydration step.

As a specific method of absorbing the product gas in the solvent in the recovery 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 recovery 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, Preferably, it is 0.25 to 1.0 MPaG. The larger the pressure, the better the absorption efficiency, and the smaller the pressure, the less energy required for boosting the gas when the gas is introduced into the absorption tower, and the further the reduced oxygen amount in the liquid.

Moreover, the temperature in an absorption tower is although it does not specifically limit, Usually, 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, and the like are less likely to be absorbed by the solvent, and the smaller is the advantage that the absorption efficiency of hydrocarbons such as conjugated dienes is improved.
The absorption solvent for use in the recovery 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 in which the product gas obtained in the recovery process is absorbed (hereinafter sometimes referred to as “solvent absorption liquid”) mainly contains the conjugated diene that is the target product, and the solvent absorption of the conjugated diene. The concentration in the liquid is usually 1 to 20% by weight, preferably 3 to 10% by weight. The higher the concentration of the conjugated diene in the solvent absorbent, the more the amount of conjugated diene lost due to polymerization or volatilization tends to increase. The energy cost required tends to increase.

In the present invention, since the solvent absorption liquid obtained in the recovery process also absorbs a small amount of nitrogen and oxygen, the solvent absorption liquid has a degassing step for gasifying and removing nitrogen and oxygen dissolved in the solvent absorption liquid. May be. 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.
The crude conjugated diene can be obtained through a separation step in which the crude conjugated diene is separated from the solvent absorption liquid of the conjugated diene thus obtained. 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. Although the pressure at the time of distillation of the distillation column used in a desirable separation step can be arbitrarily set, it is usually preferable that the column top pressure is 0.05 to 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 crude conjugated diene is obtained in the step of separating the conjugated diene. The crude conjugated diene can be 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%.

[Oxidation dehydrogenation catalyst]
Hereinafter, the oxidative dehydrogenation catalyst suitably used in the present invention will be described. The catalyst for the oxidative dehydrogenation reaction used in the present invention is not particularly limited as long as it is a catalyst capable of producing a corresponding conjugated diene using a monoolefin having 4 or more carbon atoms and oxygen as raw materials, but at least molybdenum and bismuth. And a complex oxide catalyst containing cobalt.

Of these, a composite oxide catalyst represented by the following general formula (1) is more preferable.
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 = 0.5 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.)
In addition, this composite oxide catalyst is a method of manufacturing through a step of heating the source compounds of the component elements constituting the composite oxide catalyst by integrating them in an aqueous system, and the molybdenum oxide, iron compound, nickel A pre-process for producing a catalyst precursor by heat-treating a raw material compound aqueous solution containing at least one selected from the group consisting of a compound and a cobalt compound and silica, or a dried product obtained by drying the same, and the catalyst precursor The molybdenum compound and the bismuth compound are preferably produced by a method having a post-process of integrating and drying and calcining with an aqueous solvent, and if it is a composite oxide catalyst produced by such a method, A conjugated diene such as butadiene can be produced with high catalytic activity and high yield, and a reaction product gas having a low aldehyde content can be obtained.

Next, a method for producing a composite oxide catalyst suitable for the present invention will be described.
In this method for producing a composite oxide catalyst, the molybdenum used in the preceding step is molybdenum corresponding to a partial atomic ratio (a ₁ ) of the total atomic ratio (a) of molybdenum, The molybdenum used 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 1 <a ₁ / (c + d + e) <3. Furthermore, it is preferable that a ₂ is a value satisfying 0 <a ₂ / b <8.

The above-mentioned component element source compounds include oxides, nitrates, carbonates, ammonium salts, hydroxides, carboxylates, carboxylic acid ammonium salts, halogenated / BR> tower cJ um salts, hydrogen acids of the component elements , Acetylacetonate, alkoxide and the like, and specific examples thereof include the following.
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 above 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 raw material compound aqueous solution used in the previous step is an aqueous solution, water slurry or cake containing at least molybdenum (corresponding to a ₁ in the total atomic ratio a), iron, nickel or cobalt, and silica as a catalyst component.
The raw material compound aqueous solution 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 of mixing the above-mentioned source compounds in a lump, (b) a method of mixing the above-mentioned source compounds in a lump and aging, and (c) a method of mixing each of the above-mentioned source compounds. Supply of each component element is a method of stepwise mixing, (d) a method of repeatedly mixing and aging the above-mentioned source compounds stepwise, and a method of combining (b) to (d). 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 above integration, for example, a solution obtained by mixing an acidic salt selected from catalyst components, and a solution obtained by mixing a basic salt selected from catalyst components, Specific examples include a method of adding a mixture of an iron compound and a nickel compound and / or a cobalt compound to an aqueous solution of a molybdenum compound while heating, and mixing silica.

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

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

The aging time is preferably 2 to 12 hours, and preferably 3 to 8 hours. If the aging time is less than 2 hours, the activity and selectivity of the catalyst may not be sufficiently developed. On the other hand, the aging effect does not increase even if it exceeds 12 hours, which is disadvantageous for industrial implementation.
Any method can be adopted as the stirring method, and examples thereof include a method using a stirrer having a stirring blade and a method using external circulation using a pump.

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

  The raw material salt aqueous solution or granules or cakes obtained by drying the aqueous 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. Note that the loss on ignition is a value given by the following equation as described above.
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 heat-treating the catalyst precursor excluding adhering moisture at 500 ° C. for 2 hours
In the step after the, the integration of the above procatalyst 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 composite oxide catalyst thus obtained is usually packed in a reaction tower together with an inert ball for adjusting the reaction activity to form a fixed bed.
As the inert ball, a ceramic spherical body such as alumina or zirconia is used. The inert ball is usually the same size as the composite oxide catalyst, and its particle size is about 2 to 10 mm.

[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 a process relating to the manufacturing method 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.

A vaporizer (n-butene as a raw material or a mixture containing n-butene such as BBSS described above is
Gasified by not shown) and introduced from the pipe 101, and nitrogen gas, air (molecular oxygen-containing gas), and water (water vapor) are introduced from the pipes 102, 103, and 104, respectively, and a mixed gas thereof. Is heated to about 150 to 400 ° C. by a preheater (not shown), and then supplied from a pipe 100 to a multitubular reactor 1 (oxidation dehydrogenation reactor) filled with a catalyst. 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, 123b, and moisture is desorbed by heating the desiccant. . The nitrogen gas containing the desorbed water is cooled to room temperature by the cooler 13 through the pipes 124 a, 124 b, and 124, and the condensed water is separated from the pipe 125 into the drain pot 14 and then discharged from the pipe 126.

When the desiccant in the dehydration tower 8A reaches saturation, the gas flow path is switched, the compressed gas is dehydrated in the dehydration tower 8B, and the desiccant in the dehydration tower 8A is regenerated.
The regeneration time of the desiccant in the dehydration tower in the dehydration step is not particularly limited, but is usually 6 to 48 hours, preferably 12 to 36 hours, and more preferably 18 to 30 hours.
The dehydrated gas from the dehydration towers 8A and 8B is cooled to about 10 to 30 ° C. by a cooler (not shown) as necessary, and then sent to the solvent absorption tower 10 to be sent from the pipe 115 to the solvent (absorption) Solvent). Thereby, the conjugated diene and the unreacted raw material gas in the dehydrated gas are absorbed by the absorption solvent. The component (off gas) that has not been absorbed by the absorption solvent is discharged from the top of the solvent absorption tower 10 via the pipe 117 and is combusted and discarded. At this time, if a solvent having a relatively low boiling point such as toluene is used as the absorbing solvent, an amount of the solvent that cannot be ignored economically may be volatilized through the pipe 117. In such a case, a step of recovering a solvent having a low boiling point using a solvent having a higher boiling point may be provided at the end of the pipe 117. In this solvent absorption tower 10, the solvent absorption liquid in which butadiene and unreacted source gas are absorbed by the absorption solvent is extracted from the bottom of the solvent absorption tower 10 and fed to the deaeration tower 11 through the pipe 116. Since a certain amount of nitrogen and oxygen are also absorbed in the solvent absorption liquid of butadiene obtained in the solvent absorption tower 10, the solvent absorption liquid is then supplied to the deaeration tower 11 and heated. Gasify and remove dissolved nitrogen and oxygen. At this time, some of the butadiene, the raw material gas, and the solvent may be gasified. Therefore, this is liquefied by a capacitor (not shown) provided at the top of the degassing tower 11 to be solvent. Collect in absorbent. Uncondensed raw material gas, butadiene, and the like are extracted from the pipe 118 as a mixed gas of nitrogen and oxygen, and are circulated to the inlet side of the compressor 5 and processed again in order to increase the recovery rate of the conjugated diene. On the other hand, the degassed treatment liquid from which the solvent absorption liquid has been degassed is sent to the solvent separation tower 12 through the pipe 119.

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

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
From the atomic ratio, the composite oxide catalyst obtained in Production Example 1 has a to j in the above formula (1), a = 12, b = 5, c = 2.5, d = 2, respectively. 0.5, e = 0.4, f = 0, g = 0.35 (Y is sodium), g = 0.08 (Y is potassium), h = 0.2, i = 24.

The atomic ratio of _{a 1} and _{a 2} of molybdenum during catalyst preparation was 6.9 and 5.1 respectively.
[Example 1]
A stainless steel reaction tube having an inner diameter of 23.0 mm and a length of 500 mm was mixed with 20.0 ml of the composite oxide catalyst produced in Production Example 1 and 20.0 ml of inert balls (Chipton) and filled.

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 in advance at 8.1 L / hr, air at 16.9 L / hr, and water vapor at 9.5 L / hr, and then BBSS which is a raw material gas having the composition shown in Table 1 is supplied. 3.5 L / hr was supplied, mixed in a preheater and heated to 335 ° C. as a mixed gas (reactor introduced mixed gas composition = nitrogen: 21.3 vol%, air: 44.5 vol%, water vapor: 25.%). 0 vol%, raw material gas: 9.2 vol%). Table 1 shows typical component compositions (vol%) contained in BBSS which is a raw material gas. The linear monoolefin was 1-butene, cis-2-butene and trans-2-butene, and the total of these concentrations (concentration of the linear monoolefin) was 74.7 vol%. Propylene was contained as an olefin having 3 or less carbon atoms, and its concentration was 0.145 vol%. At this time, the mixed gas flow rate was 38.0 L / hr, and the ratio of the catalyst amount in the reactor to the mixed gas flow rate was 1900 h ⁻¹ . The water vapor / BBSS ratio was 2.7.

The oxidative dehydrogenation reaction was carried out by supplying the above reactor. The catalyst layer temperature in the reactor was an average of 353 ° C., and the pressure was 2 kPa as a gauge pressure. The product gas from the outlet of the reactor was cooled in a cooling pipe provided with a filter, then contacted with water, further cooled, and analyzed by gas chromatography (model number GC-8A, GC-9A manufactured by Shimadzu Corporation).
The n-butene conversion rate (the conversion rate of 1-butene, cis-2-butene and trans-2-butene in total) was 83.0%, and the butadiene selectivity was 97.7%. The reaction was stopped after 8 hours, and the amount of solid by-products trapped on the filter in the cooling tube was 147.2 mg, and the amount of solid by-products produced per hour was 18.4 mg / hr. The amount of butadiene produced was 4776 mg / hr, and the amount of solids produced relative to the amount of butadiene produced was 0.39 wt%. The results are shown in Table 1.

[Example 2]
In Example 1, nitrogen was supplied to the preheater at 12.8 L / hr, air was 26.6 L / hr, and water vapor was 15.0 L / hr, and then the raw material gas used in Example 1 was used. 5.6 L / hr of BBSS having the same composition as BBSS was supplied, mixed in the preheater and heated to 356 ° C as a mixed gas, and the catalyst layer temperature in the reactor was changed to 378 ° C. Elementary reaction was performed (reactor introduction gas composition = nitrogen: 21.3 vol%, air: 44.5 vol%, water vapor: 25.0 vol%, source gas: 9.2 vol%). The mixed gas flow rate at this time was 60.0 L / hr, and the ratio of the catalyst amount in the reactor to the mixed gas flow rate was 3000 h ⁻¹ . The water vapor / BBSS ratio was 2.6.

In addition, n-butene conversion rate (conversion rate in total of 1-butene, cis-2-butene, and trans-2-butene), butadiene selectivity, and solid by-product trapped in the filter in the cooling pipe at this time Table 1 shows the amount of solid by-products produced per hour, the amount of butadiene produced, and the amount of solids produced relative to the amount of butadiene produced.
[Example 3]
In Example 1, nitrogen was supplied to the preheater at 12.9 L / hr, air at 16.2 L / hr, and water vapor at 14.3 L / hr, and then used as a source gas in Example 1. BBSS having the same composition as BBSS is supplied at 3.6 L / hr, mixed in a preheater and heated to 348 ° C. as a mixed gas, and the catalyst layer temperature in the reactor is changed to 360 ° C. Elementary reaction was performed (reactor introduction gas composition = nitrogen: 27.4 vol%, air: 34.5 vol%, water vapor: 30.4 vol%, source gas: 7.6 vol%). At this time, the flow rate of the mixed gas was 47.0 L / hr, and the ratio of the catalyst amount in the reactor to the flow rate of the mixed gas was 2350 h ⁻¹ . The water vapor / BBSS ratio was 4.0.

In addition, n-butene conversion rate at this time (conversion rate in total of 1-butene, cis-2-butene, trans-2-butene), butadiene selectivity, solid by-product trapped in the filter in the cooling pipe, Table 1 shows the amount of solid by-products produced per hour, the amount of butadiene produced, and the amount of solids produced relative to the amount of butadiene produced.
[Example 4]
In Example 1, it implemented on the same conditions except having changed the pressure of the reactor as shown in Table 1. In addition, n-butene conversion rate at this time (conversion rate in total of 1-butene, cis-2-butene, trans-2-butene), butadiene selectivity, solid by-product trapped in the filter in the cooling pipe, Table 1 shows the amount of solid by-products produced per hour, the amount of butadiene produced, and the amount of solids produced relative to the amount of butadiene produced.

[Comparative Example 1]
In Example 1, nitrogen was supplied to the preheater at 11.9 L / hr, air at 16.2 L / hr, and water vapor at 5.7 L / hr, and then used as a source gas in Example 1. BBSS having the same composition as BBSS is supplied at 3.5 L / hr, mixed in a preheater and heated to 335 ° C as a mixed gas, and the catalyst layer temperature in the reactor is changed to 356 ° C. Elementary reaction was carried out (reactor introduction gas composition = nitrogen: 31.3 vol%, air: 44.5 v)
ol%, water vapor: 15.0 vol%, raw material gas: 9.2 vol%). At this time, the total gas flow rate was 37.3 L / hr with respect to the catalyst amount of 20.0 ml, and the ratio of the catalyst amount in the reactor to the flow rate of the mixed gas was 1865 h ⁻¹ . The ratio of water vapor / BBSS was 1.6.

In addition, n-butene conversion rate at this time (conversion rate in total of 1-butene, cis-2-butene, trans-2-butene), butadiene selectivity, solid by-product trapped in the filter in the cooling pipe, Table 1 shows the amount of solid by-products produced per hour, the amount of butadiene produced, and the amount of solids produced relative to the amount of butadiene produced.
[Comparative Example 2]
Nitrogen was supplied to the preheater at 7.2 L / hr, air was 9.0 L / hr, and water vapor was 8.0 L / hr, and then the same composition as that of the BBSS used in Example 1 was used as a raw material gas. BBSS was supplied at 2.0 L / hr, mixed in a preheater and heated to 330 ° C. as a mixed gas, and the reaction was carried out in the same manner as in Example 1 except that the temperature of the catalyst layer in the reactor was changed to 338 ° C. (Reactor introduction gas composition = nitrogen: 27.5 vol%, air: 33.4 vol%, water vapor: 30.5 vol%, raw material gas: 7.6 vol%). At this time, the total gas flow rate was 26.2 L / hr with respect to the catalyst amount of 20.0 ml, and the ratio of the catalyst amount in the reactor to the flow rate of the mixed gas was 1310 h ⁻¹ . The water vapor / BBSS ratio was 4.0.

In addition, n-butene conversion rate at this time (conversion rate in total of 1-butene, cis-2-butene, trans-2-butene), butadiene selectivity, solid by-product trapped in the filter in the cooling pipe, Table 1 shows the amount of solid by-products produced per hour, the amount of butadiene produced, and the amount of solids produced relative to the amount of butadiene produced.
[Comparative Example 3]
In Example 1, it implemented on the same conditions except having changed the pressure of the reactor as shown in Table 1. In addition, n-butene conversion rate at this time (conversion rate in total of 1-butene, cis-2-butene, trans-2-butene), butadiene selectivity, solid by-product trapped in the filter in the cooling pipe, Table 1 shows the amount of solid by-products produced per hour, the amount of butadiene produced, and the amount of solids produced relative to the amount of butadiene produced.

  When Examples 1-3 are compared with Comparative Examples 1-2, the amount of by-product solids produced relative to the amount of butadiene produced in Examples 1-3 is a by-product solid produced relative to the amount of butadiene produced in Comparative Examples 1-2. It can be seen from Examples 1 to 3 that the generation of by-product solids contained in the cooling water can be suppressed while maintaining a high selectivity of butadiene. Further, when Examples 1 and 4 are compared with Comparative Example 3, the amount of by-product solids produced relative to the amount of butadiene produced in Examples 1 and 4 in which the pressure in the reactor is low is smaller than that produced in Comparative Example 3. In Examples 1 and 4 where the pressure in the reactor is low because the amount of raw solids is less, the generation of by-product solids contained in the cooling water can be suppressed while maintaining a high selectivity of butadiene. I understand that.

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

Claims (7)

Mixing a raw material gas containing a monoolefin having 4 or more carbon atoms and a molecular oxygen-containing gas to obtain a mixed gas, supplying the mixed gas to a reactor, and performing an oxidative dehydrogenation reaction in the presence of a catalyst In the production of the product gas containing the corresponding conjugated diene produced by the above, the ratio of the flow rate of the mixed gas to the amount of catalyst in the reactor is 1500 to 5000 h ⁻¹ and the monoolefin having 4 or more carbon atoms is used. A method for producing a conjugated diene, wherein the conversion is 87% or less.   The method for producing a conjugated diene according to claim 1, wherein the water vapor supplied to the reactor is in a ratio of 0.5 to 5.0 with respect to the supply amount of the raw material gas.   The method for producing a conjugated diene according to claim 1 or 2, wherein the concentration of the olefin having 3 or less carbon atoms in the raw material gas is 0.010 to 0.500 vol%.   The method for producing a 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 70.00 to 99.99 vol%. .   The method for producing a conjugated diene according to any one of claims 1 to 4, wherein the product gas and water are contacted and cooled.   The said catalyst is a complex oxide catalyst containing at least molybdenum, bismuth, and cobalt, The manufacturing method of the conjugated diene in any one of Claims 1-5 characterized by the above-mentioned. The said complex oxide catalyst is a complex oxide catalyst represented by following General formula (1), The manufacturing method of the conjugated diene of Claim 6 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 (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 = 0.5 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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