JP2010280653A - Method for producing conjugated diene - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce butadiene in a stable manner with higher yield in a method for producing a conjugated diene such as butadiene by a catalytic oxidative dehydrogenation reaction of a monoolefin such as n-butene. Provide a way to do it.
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. At the start-up of the reaction, the supply amount per unit time of the raw material gas to the reactor should be 80% or more of the allowable maximum supply amount within less than 100 hours from the start of the supply of the raw material gas to the reactor. A method for producing a conjugated diene.
[Selection] Figure 1

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.

  Conventionally, as a typical method for producing butadiene by the catalytic oxidative dehydrogenation reaction of n-butene, butadiene is produced by vapor-phase catalytic oxidative dehydrogenation of butene, and the product gas containing butadiene is cooled to generate the butadiene. After removing high-boiling by-products, a method of compressing the product gas through a step of removing aldehydes in the product gas and recovering butadiene from the compressed product gas is known (for example, Patent Documents). 1).

  Further, the composite oxide catalyst described later used in the present invention is described in Patent Document 3, and it is described that this composite oxide catalyst is used as a catalyst for producing butadiene by oxidative dehydrogenation of butene. There is no description of a typical method for producing butadiene, and further, there is no description of a method for starting up a reaction in producing butadiene from butene by using a multi-tubular reactor using the catalyst.

  On the other hand, in Patent Document 2, in a method for producing acrylic acid and acrolein by performing a gas phase catalytic oxidation reaction with an oxygen-containing gas using propylene as a raw material using a multitubular reactor, a reaction start-up is disclosed. When the operation was performed with the propylene supply amount being 100% of the maximum supply amount in 15 hours from the start, the catalyst was deactivated when the reactor was opened and the reaction tube was inspected one month after the start of operation. In order to suppress the deactivation of the catalyst and produce acrylic acid and acrolein in a high yield, the amount of the raw material supplied to the reactor per unit time at the start-up of the reaction is After reaching 30% or more of the allowable maximum supply amount per unit time, the method of maintaining the supply amount per unit time of raw materials at 30% or more and less than 80% of the allowable maximum supply amount for at least 20 hours or more It is draft.

JP 60-115532 A JP 2005-336085 A JP 2003-220335 A

In patent documents 1 and 3, in producing butadiene by the oxidative dehydrogenation reaction of butene,
There is no information on how to start up the reaction. For example, as described in Patent Document 2, when producing butadiene by an oxidative dehydrogenation reaction of butene, the supply amount of the raw material per unit time to the reactor is started by supplying the raw material to the reactor. It is conceivable to use a method in which the amount supplied in stages is increased with respect to the elapsed time from the start, but according to this method, the supply amount per unit time of the raw material to the reactor is the maximum allowable supply (The maximum amount of raw material gas that can be supplied to the reactor per unit time, which correlates with the production capacity of the reactor and is determined by the design stage of the reactor) is 80% or more of the differential pressure of the reactor. As a result, there was a problem that the operation could not be continued. For this reason, it is necessary to frequently stop the operation and start the reaction again, which increases the operating cost.

  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 operation can be continued more safely and is high. An object is to provide a method capable of stably producing butadiene in a yield.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have produced butadiene by the oxidative dehydrogenation reaction of butene. At the start-up of the reaction, the start of the supply of the raw material gas to the reactor is less than 48 hours. In the meantime, the supply amount per unit time of the raw material gas to the reactor is 80% or more of the allowable maximum supply amount to the reactor in the steady operation, so that the operation can be performed more safely and the yield is higher. And found that butadiene can be produced stably.

The present invention has been achieved on the basis of such findings, and the following [1] to [5] are summarized.
[1] In supplying a raw material gas containing a monoolefin having 4 or more carbon atoms and a molecular oxygen-containing gas to a reactor and producing a corresponding conjugated diene by an oxidative dehydrogenation reaction in the presence of a catalyst, At the start-up of the reaction, the supply amount per unit time of the raw material gas to the reactor is set to 80% or more of the allowable maximum supply amount within less than 100 hours from the start of the supply of the raw material gas to the reactor. A process for producing a conjugated diene.
[2] The method for producing a conjugated diene according to claim 1, wherein the catalyst is a composite oxide catalyst containing at least molybdenum, bismuth, and cobalt.
[3] The method for producing a conjugated diene according to [1] or [2], 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 = 0.5 to 7, 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 = 5 48, and j satisfies the oxidation state of other elements Numerical value is.)
[4] A method in which the composite oxide catalyst is manufactured through a process of integrating and heating a source compound of each component element constituting the composite oxide catalyst in an aqueous system, the molybdenum compound, an iron compound, A pre-process for producing a catalyst precursor by heating a raw material compound aqueous solution containing at least one selected from the group consisting of a nickel compound and a cobalt compound and silica, or a dried product obtained by drying the aqueous solution, and the catalyst precursor; The method for producing a conjugated diene according to [3], wherein the method is produced by a method comprising a step of integrating a body, a molybdenum compound and a bismuth compound together with an aqueous solvent, followed by drying and firing.
[5] Gas containing 1-butene, cis-2-butene, trans-2-butene or a mixture thereof obtained by dimerization of ethylene as the raw material gas, dehydrogenation or oxidative dehydrogenation of n-butane [1] to [4], characterized in that the gas contains a butene fraction produced by the above, or a gas containing a large amount of hydrocarbons having 4 carbon atoms obtained by fluid catalytic cracking of a heavy oil fraction. The manufacturing method of the conjugated diene in any one.

  According to the present invention, when producing a conjugated diene by a catalytic oxidative dehydrogenation reaction of a monoolefin, the conjugated diene can be produced stably and continuously without reducing the yield.

It is a systematic diagram which shows embodiment of the manufacturing method of the conjugated diene of this invention. It is a schematic sectional drawing which shows one embodiment of the multitubular heat exchanger type | mold reactor used for the oxidative dehydrogenation reaction of this invention. The graph which shows transition with respect to the elapsed time of the supply amount of BBSS with respect to the allowable maximum supply amount in Example 1, and reactor differential pressure | voltage. The graph which shows transition with respect to the elapsed time of the supply amount of BBSS with respect to the permissible maximum supply amount in the comparative example 1, and a reactor differential pressure | voltage.

Hereinafter, embodiments of the method for producing a conjugated diene of the present invention will be described in detail. However, the description described below is an example (representative example) of an embodiment of the present invention, and the present invention is limited to these contents. Not.
The method for producing a conjugated diene according to the present invention is performed by supplying a raw material gas containing a monoolefin having 4 or more carbon atoms and a molecular oxygen-containing gas to a reactor and performing an oxidative dehydrogenation reaction in the presence of a catalyst. In the production of the conjugated diene, during the start-up of the reaction, the supply amount per unit time of the raw material gas to the reactor is reduced to 80% of the maximum allowable supply amount during the start of the supply of the raw material gas to the reactor for less than 100 hours. % Or more.

  In the present invention, the “allowable maximum supply amount” is conventionally known to be the maximum amount that may be supplied to the reactor per unit time of the raw material gas, and the production capacity of the reactor Correlates and is determined at the reactor design stage. This value is determined in various ways depending on the chemical process, and is determined based on various conditions. Generally, when designing a chemical process, the target product obtained by the reaction to be carried out in the reactor first. A target value for the production volume of the reactor (sometimes referred to as the “reactor nominal capacity”) and depending on the reaction rate determined by the catalyst used in the reaction, the reactor residence time, reaction temperature, reaction pressure Supply of raw materials when the reaction is stably carried out in the reactor in the steady state and the nominal capacity of the reactor is satisfied from the composition of the raw materials used, the size of the reactor, etc. The quantity is called the “allowable maximum supply”. The “allowable maximum supply amount” in the present invention is determined by a similar procedure.

In the present invention, as described above, at the start-up of the reaction, from the start of supply of the raw material gas to the reactor, it is less than 100 hours, preferably less than 48 hours, more preferably less than 36 hours, Particularly preferably less than 24 hours, most preferably less than 20 hours, and most preferably less than 12 hours, the supply amount of the raw material gas to the reactor per unit time is 80% or more of the maximum allowable supply amount. To do. The shorter the time for which the supply amount per unit time of the raw material gas to the reactor is 80% or more of the maximum allowable supply amount, the more the catalyst coking and pulverization that lead to the pressure increase of the reactor tend to be suppressed. Although the cause of catalyst coking and pulverization is not clear, it is considered that the start-up operation is performed so as to avoid the explosion range of the inlet composition of the reactor as described later. That is, it is considered that coke is generated by performing the reaction in a state where the oxygen concentration in the reaction gas is low, and the catalyst is deteriorated. In order to avoid this, it is desirable to operate so as to pass through an operation region where the oxygen concentration is low in a short time.

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 reaction. 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-butanediene 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) by-produced in the above-described naphtha decomposition. 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. ) From 4 carbon atoms
A gas containing a large amount of hydrocarbons (hereinafter sometimes abbreviated as FCC-C4) is used as a raw material gas, or a gas obtained by removing impurities such as phosphorus and arsenic from FCC-C4 is used as a raw material gas. There is no problem. 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 ratio of 1-butene, cis-2-butene, and trans-2-butene in the composition of monoolefin such as n-butene is not limited and can take any value.

  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 this amount is too large, the concentration of 1-butene or 2-butene as the main raw material will decrease, and the reaction will be slow, or undesirable by-products will tend to increase.

In FIG. 1, 1 is a reactor, 2 is a quench tower, 3, 6 and 13 are coolers (heat exchangers), 4, 7 and 14 are drain pots, 8A and 8B are dehydration towers, and 9 is a heater (heat (Exchanger), 10 is a solvent absorption tower, 11 is a degassing tower, 12 is a solvent separation tower, and 100 to 126 are pipes.
The reactor used for the oxidative dehydrogenation reaction of the present invention is not particularly limited, but a multitubular reactor is preferably used. The multitubular reactor is generally used industrially and is not particularly limited.

FIG. 2 shows a schematic cross-sectional view of a multitubular heat exchange reactor used in the oxidative dehydrogenation reaction of the present invention. Reaction tubes 21a and 21b are fixed and arranged on tube plates 24a and 24b in a reactor shell 22 of a multitubular reactor. A raw material supply port which is an inlet of a raw material gas for reaction and a product outlet which is an outlet of a product are 23a or 23b. If the flow of the process gas and the heat medium is countercurrent, the flow direction of the process gas may be any. In FIG. 2, the flow direction of the heat medium in the reactor shell is indicated by an arrow as an upward flow. Therefore, 23a is a raw material supply port. In this case, the heat medium is supplied from the heat medium supply port 26a and is extracted from the heat medium outlet 26b. It is desirable to install a baffle plate inside the reactor shell for the purpose of allowing the heat medium to flow uniformly. The kind of baffle plate is not specifically limited, A well-known thing can be used. For example, as shown in FIG. 2, baffle plates 25a and 25b may be installed alternately, and the heat medium may meander and flow through the shell. Alternatively, a plurality of perforated baffle plates 25a having openings near the center of the reactor shell and perforated baffle plates 25b arranged so as to have openings between the outer periphery of the reactor shell are alternately arranged. You may do it.

Although the temperature control of the heat medium depends on the performance of the catalyst used, the temperature difference of the heat medium between the heat medium supply line 26a and the heat medium extraction line 26b is 1 to 10 ° C, preferably 2 to 6 ° C. Done.
The number of baffles installed in the reactor shell is not particularly limited. In addition, a thermometer is inserted into the reaction tube in a part of the reaction tube disposed in the reactor, and a single thermometer measures temperatures of 5 to 20 points in the tube axis direction.

  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) are introduced, and these mixed gases are heated to about 150 to 250 ° C. with a preheater (not shown), and then the catalyst 100 is filled with the catalyst through the pipe 100. Feed to dehydrogenation reactor 1. The raw material, nitrogen gas, air, and water (steam) may be supplied directly to the oxidative dehydrogenation reactor 1 through separate pipes, but may be supplied to the oxidative dehydrogenation reactor 1 in a uniformly mixed state. preferable. This is because it is possible to prevent a situation in which a non-uniform mixed gas partially forms explosive gas in the reactor or a raw material having a different composition is supplied to each tube in the multi-tube reactor.

The molecular oxygen-containing gas 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. From the viewpoint of cost necessary for industrially preparing a molecular oxygen-containing gas, the molecular oxygen is 50% by volume or less, preferably 30% by volume or less, more preferably 25% by volume or less. preferable. 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.

  Further, when supplying the raw material gas to the reactor 1, nitrogen gas and water (water vapor) may be supplied. Nitrogen gas adjusts the concentration of flammable gas such as butene and oxygen so that the reaction gas does not form explosive gas, so water (steam) has the same concentration of flammable gas and oxygen as nitrogen gas. It is preferable to supply it to the reactor 1 as a raw material gas together with butene and molecular oxygen-containing gas for the reason of adjusting and suppressing the coking of the catalyst.

In the present invention, the supply sequence of the raw material gas, nitrogen gas, molecular oxygen-containing gas, and water (water vapor) at the start-up of the reaction is not particularly limited, but preferably before the raw material gas is introduced into the raw material supply port 3a. In addition, it is preferable to introduce nitrogen gas, molecular oxygen-containing gas, and water (water vapor) into the raw material supply port 3a in advance. In this case, the source gas is supplied to the source supply port 3a.
Before introduction into the heat medium, the heat medium is supplied from the heat medium supply port 6a, the heat medium is extracted from the heat medium outlet 6b, and the temperature outside the reaction tube (reactor shell side) is raised in advance to a predetermined temperature. More preferably, the raw material gas is supplied to the raw material supply port 3a. The temperature at this time is preferably around the reaction temperature, but is not particularly limited. Before supplying the heat medium to the reactor, the reactor may be heated in advance by supplying nitrogen gas, molecular oxygen-containing gas, and water (water vapor) heated by the preheater to the raw material supply port 3a. .

  In the present invention, at the start-up of the reaction, the supply amount per unit time of the raw material gas to the reactor is set to 80% of the allowable maximum supply amount within less than 100 hours from the start of the supply of the raw material gas to the reactor. In the meantime, the supply amount of nitrogen gas, molecular oxygen-containing gas, water (water vapor), etc. supplied to the reactor together with the raw material gas during that period is as follows. The composition of the gas and the mixed gas of water (water vapor) is adjusted so as not to enter the explosion range.

  When the raw material gas supplied to the reactor 1 is mixed with the molecular oxygen-containing gas, it becomes a mixture of oxygen and a combustible gas, so that each gas (butene, air, and Control the composition at the inlet of the reactor while monitoring the flow rate with a flow meter installed in a pipe that supplies nitrogen gas and water (water vapor) as necessary, for example, adjusting to the range of the raw material gas composition described later Is done. 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 such as air, nitrogen, and water vapor supplied to the reactor first is adjusted so that the oxygen concentration at the reactor inlet is below the critical oxygen concentration. After that, the supply of combustible gas is started, and then the supply amount of the combustible gas and the molecular oxygen-containing gas such as air is increased so that the combustible gas concentration becomes higher than the upper limit of explosion. When the supply amount of the combustible 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 gas in the pipe 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, but the residence time of the mixed raw material 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 within 10 seconds. It is desirable to cool to below.

Below, the typical composition of source gas is shown.
<Raw 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
The reactor 1 is filled with an after-mentioned oxidative dehydrogenation reaction catalyst, and n-butene reacts with oxygen on the catalyst to produce butadiene and water. This oxidative dehydrogenation reaction is an exothermic reaction, and the temperature rises due to the reaction, but the reaction temperature is preferably adjusted to a range of 280 to 400 ° C. The temperature of the catalyst layer is controlled to be constant using nitrite or the like.

  The pressure in the reactor 1 is not particularly limited, but the lower limit is usually 0 MPaG or more, preferably 0.002 MPaG or more, more preferably 0.02 MPaG or more, and particularly preferably 0.05 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 reaction tower 1 is not particularly limited, but the lower limit is usually 0.36 seconds or longer, preferably 0.72 seconds or longer, more preferably 1.2 seconds or longer. There is a merit that the higher the value, the higher the conversion rate. On the other hand, the upper limit is 7.2 seconds or less, preferably 3.6 seconds or less, and more preferably 1.8 seconds. The smaller this value, the smaller the reactor.

  The concentration of the conjugated diene corresponding to the monoolefin in the raw material gas contained in the product gas depends on the concentration of the monoolefin contained in the raw material gas, but is usually 1 to 15 vol%, preferably 5 to 13 vol%, More preferably, it is 9-11 mol%. The higher the conjugated diene concentration, the lower the recovery cost, and the lower the conjugated diene, there is the advantage that side reactions such as polymerization are less likely to 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%. When the inlet composition of the reactor 1 is above the upper explosion limit, the composition at the outlet of the reactor 1 is also usually higher than the upper explosion limit, and there is no risk of explosion. However, in the present invention, there is a possibility that the concentration of hydrocarbons in the gas decreases and enters the explosion range in the step of bringing the product gas into contact with the absorbing solvent and absorbing hydrocarbons such as olefins and conjugated dienes in the solvent. To avoid this, it is conceivable that the product gas is diluted with an inert gas such as nitrogen and then contacted with the absorbing solvent. However, the reaction is performed so that the composition at the outlet of the reactor 1 or the outlet of the quench tower 2 is below the critical oxygen concentration. It is easier to adjust the inlet conditions and reaction conditions of the vessel 1. For example, an oxygen concentration meter may be installed at the exit of the quench tower 2 and the flow rate of air supplied to the reactor 1 may be adjusted or the reaction temperature may be adjusted so that this becomes 8% or less.

The flow rate difference between the inlet and the outlet of the reactor 1 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 normal inlet flow rate is 100. It is -110 volume%, Preferably, it is 102-107 volume%, More preferably, it is 103-105 volume%. The outlet flow rate increases because the number of molecules increases stoichiometrically in the reaction in which butene is oxidatively dehydrogenated to produce butadiene and water, and in the reaction in which CO and CO ₂ are produced as a side 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.

  Moreover, in this invention, you may have a cooling process which cools the product gas discharged | emitted from a reactor. The cooling process is not particularly limited as long as the process can cool the product gas. Specifically, for example, as shown in FIG. 1, it can be cooled by a quench tower. That is, the reaction product gas from the reactor 1 is then fed from the pipe 105 to the quench tower 2 and cooled to about 20 to 99 ° C. Cooling water is introduced into the quench tower 2 from the pipe 106, and water that has cooled the generated gas by countercurrent contact with the generated gas is discharged from the pipe 107. The cooling waste water is cooled by a heat exchanger (not shown) and is circulated again in the quench tower 2.

  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. The dehydration step is not particularly limited as long as it is a step 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 cooling step. Specifically, for example, as shown in FIG. 1, the product gas cooled in the quench tower 2 flows out from the top of the tower, and this cooling gas then passes through the cooler 3 from the pipe 108 to room temperature (about 10 to 30 ° C.). ). The condensed water generated by cooling is separated into the drain pot 4 through the pipe 109. The water-separated gas is further pressurized to about 0.1 to 0.5 MPa by the compressor 5 through the pipe 110, and 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 usually a wet gas having a water content of about 0.5 to 2 vol% and a dew point of about 0 to 20 ° C. This gas is introduced into the dehydration towers 8A and 8B and dehydrated. Is done.

In FIG. 1, the dehydration towers 8A and 8B are filled with a desiccant (moisture adsorbent) such as a molecular sieve, whereby 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 and dehydrated, and the dehydrated gas is 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 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 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.
In the dehydration tower, high-boiling components contained in the reaction gas other than water are adsorbed and removed.

In addition, although the dehydration process by the dehydration towers 8A and 8B is not necessarily required, by performing such a dehydration process, the apparatus corrosion and the decomposition | disassembly of a solvent by the water | moisture content in the butadiene collection | recovery process by solvent absorption mentioned below are prevented below. Can be preferred.
Usually, in the dehydration treatment using a desiccant such as molecular sieve, the water content in the dehydrated gas supplied to the solvent absorption tower 10 is usually 10 to 10000 volppm, preferably 20 to 1000 volppm, and the dew point is − 60-80 degreeC, Preferably, it is -50-20 degreeC.

  In this invention, you may have a collection | recovery process which makes a solvent absorb the product gas discharged | emitted from a reactor, and collect | recovers. 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 dehydration step. Specifically, for example, in FIG. 1, 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 is supplied to the solvent absorption tower 10. The butadiene, unreacted n-butene and butane in the gas are absorbed by the solvent by being fed and in countercurrent contact with the solvent from the pipe 115. The component (residual gas) that has not been absorbed by the solvent is discharged from the top of the solvent absorption tower through the pipe 117 and is discarded by combustion.

Although the pressure in the solvent absorption tower 10 is not specifically limited, Usually, it is 0.1-2.0 MPaG, Preferably, it is 0.2-1.5 MPaG, More preferably, it is 0.25-1.0 MPaG. The greater the pressure, the better the absorption efficiency, and the smaller the pressure, the lower the construction and operation costs.
Although the temperature in the solvent absorption tower 10 is not specifically limited, Usually, 0-50 degreeC, Preferably, it is 10-40 degreeC, More preferably, it is 20-30 degreeC. The higher this temperature is, the more advantageous it is that oxygen, nitrogen and the like are less likely to be absorbed by the solvent, and the smaller, there is an advantage that the absorption efficiency of hydrocarbons such as butadiene is improved.

The solvent absorption liquid is extracted from the bottom of the solvent absorption tower and sent to the deaeration tower 11 through the pipe 116.
As the absorption solvent used for the recovery of butadiene in the solvent absorption tower 10, C _{6 to} C ₁₀ saturated hydrocarbons, C _{6 to} C ₈ aromatic hydrocarbons, amide compounds, and the like are used. For example, dimethylformamide (DMF), toluene, N-methyl-2-pyrrolidone (NMP), etc. can be used. The amount of solvent used is not particularly limited, but it is uneconomical if it is too much, and the recovery efficiency of butadiene is lowered if it is too small. Therefore, it is preferable to supply the solvent in such an amount that the butadiene concentration in the obtained solvent absorbing solution is about 1 to 20% by weight, preferably about 3 to 10% by weight.

  Depending on the type of solvent, butanes and butadiene have different solubility in solvents, so if you select the type of solvent, the ratio of C4 gas to the solvent, the temperature of the solvent, and the pressure, at least part of the butanes will absorb butadiene. Purge can be performed from the top of the solvent absorption tower. When BBSS is used as the raw material of the present invention and the crude butadiene obtained in the present invention is returned to the butadiene extraction process, it is necessary to provide a process for removing butane since butane accumulates in the raw material BBSS. If butane is separated by a solvent absorption tower, it is economically advantageous because it is not necessary to provide new equipment.

  In the present invention, since a slight amount of nitrogen and oxygen is also absorbed in the solvent absorption liquid of butadiene obtained in the recovery process, there is a deaeration process in which nitrogen and oxygen dissolved in the solvent absorption liquid are gasified and removed. You may do it. 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. Specifically, for example, in FIG. 1, by supplying the solvent absorption liquid of butadiene obtained in the solvent absorption tower 10 to the deaeration tower 11 and heating it to about 50 to 150 ° C., nitrogen dissolved in the liquid or Oxygen can be removed by gasification. At this time, since butene, butadiene, and a part of the solvent are also gasified, they are liquefied by a capacitor provided at the top of the degassing tower 11 and recovered in the absorbing liquid. Butene and butadiene which have not been condensed are withdrawn 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 butadiene. On the other hand, the degassed treatment liquid is fed to the solvent separation tower 12 through the pipe 119.

  Butadiene can be obtained through a separation step in which butadiene is separated from the solvent absorption liquid of butadiene thus obtained. The separation step is not particularly limited as long as it is a step capable of separating butadiene from a solvent-absorbing solution of butadiene, but butadiene can usually be separated by distillation separation. Specifically, for example, in FIG. 1, in the solvent separation tower 12, butadiene is distilled and separated by a reboiler and a condenser, and a butadiene fraction is extracted from the top of the tower via a pipe 120. The separated solvent is extracted from the bottom of the tower through a pipe 121 and circulated and used as an absorbing solvent for the solvent absorbing tower 10.

Impurities may accumulate during recycling of the solvent, and a part of the solvent may be extracted and removed by a known purification method such as distillation, decantation, sedimentation, or contact treatment with an adsorbent or ion exchange resin. desirable. The purified solvent can be used again as a butadiene absorption solvent.
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 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 distilled butadiene 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. .

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 becomes difficult to distill butadiene from the top pressure. 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 butadiene and the solvent, it is preferable that the theoretical column 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.

[catalyst]
Hereinafter, the oxidative dehydrogenation catalyst suitably used in the present invention will be described.
The catalyst used in the present invention is preferably a composite oxide catalyst containing at least molybdenum, bismuth and cobalt, and more preferably 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 = 0-10, d = 0-10 (where c + d = 1-10), e = 0.05-3, f = 0-2, g = 0.04-2, h = 0-3, i = 5 In the range of 48, j is a number that satisfies the oxidation state of other elements In 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 a high catalytic activity and a high yield, and a reaction product gas having a low acetylene content can be obtained.

Hereinafter, a method for producing a composite oxide catalyst suitable for the present invention will be described.
In the method for producing the composite oxidation / BR 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 subsequent 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 1 <a ₁ / (c + d + e) <3. Furthermore, it is preferable that a ₂ is a value satisfying 0 <a ₂ / b <8.

Source compounds of the above component elements include oxides, nitrates, carbonates, ammonium salts, hydroxides, carboxylates, ammonium carboxylates, ammonium halides, 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 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 a later step, 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.

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 obtained granular solid of the catalyst precursor (loss on ignition: 1.4% by weight) was pulverized, and 40.1 g of ammonium paramolybdate was dispersed in a solution prepared by adding 10 ml of ammonia water to 150 ml of pure water. Next, 0.85 g of borax and 0.36 g of potassium nitrate were dissolved in 40 ml of pure water under heating at 25 ° C., and 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: Production of 1,3-butadiene]
1,3-butadiene was produced by the method shown in FIG. Moreover, as the reactor, the same reactor as that shown in FIG. 2 was used. In the present invention, gas chromatography (GC-2014 manufactured by Shimadzu Corporation) was used for gas analysis.
A multi-tube reactor (reactor shell (inner diameter: 500 mm), length from a raw material supply port to a product discharge port: 5332 mm) having 113 reaction tubes with an inner diameter of 27 mm and a length of 3500 mm per reaction tube, 1162 ml of the composite oxide catalyst produced in Production Example 1 and 407 ml of inert balls (manufactured by Tipton Corp.) were charged. Of these reaction tubes, three reaction tubes were provided with thermometers, and the temperature in the reactor was measured. The thermometer used was able to measure the temperature distribution of the catalyst layer from the inlet to the outlet of the reaction tube with a multi-point thermocouple (manufactured by Okazaki Manufacturing Co., Ltd.). Dibenzyltoluene was used as the heat medium, and the temperature was measured with a thermocouple (manufactured by Yamazato Sangyo Co., Ltd.) installed at the heat medium supply port 26a. As shown in FIG. 2, baffle plates 25a and 25b are alternately installed so that the heat medium meanders and flows in the shell. The maximum allowable feed rate for this reactor was 16.5 Nm ³ / h.

The reactor was preliminarily supplied with a mixed gas of air (molecular oxygen: 21%) and nitrogen (purity 99.99% or more), and then heated to flow through a heating medium. Water vapor was supplied when the temperature of the heat medium supply port 26a reached about 300 ° C. The amount of gas supplied at this time is the same as the elapsed time of 0 hours in Table 1.
Then, after the temperature in the reactor reached 302 ° C., supply of BBSS discharged from the butadiene extraction and separation process from the C ₄ fraction by-produced by naphtha decomposition was started. The composition of the supplied BBSS is shown in Table 2.

At the flow rates shown in Table 1, air, nitrogen and water vapor are supplied from respective supply lines, mixed before being supplied to the reactor, and heated to 214 ° C. with a preheater using water vapor at a pressure of 30 KG as a heating source. After heating, it was supplied to the raw material supply port of the reactor 1.
The elapsed time in Table 1 is the time from the start of the supply of BBSS. The supply amount of BBSS reached 80% (12.6 Nm ³ / h) of the maximum allowable supply amount after 6.25 hours. Thereafter, the reaction was continued while the supply amount of BBSS was 80% of the allowable maximum supply amount. Around the reaction tube in the reaction tower 1,
The temperature inside the reaction tube was adjusted by flowing a heat medium having a temperature shown in Table 2. The differential pressure between the inlet and outlet of the reactor at this time increased as the BBSS flow rate increased as shown in Table 2, but did not increase after the BBSS flow rate was kept constant. FIG. 3 is a graph showing the transition of the supply amount (%) of BBSS and the reactor differential pressure against the allowable maximum supply amount with respect to the elapsed time.

The product gas from the reactor 1 was brought into contact with water in the quench tower 2 and cooled to 75 ° C., and further cooled to room temperature in the cooler 3. This gas was sampled from a sampling port installed behind the cooler 3 and analyzed by the above gas chromatography. As a result, the reaction results after 171 hours were a butene conversion rate of 91.9% and a butadiene selectivity of 86.4%.
[Comparative Example 1]
The same procedure as in Example 1 was performed except that the flow rates of BBSS, air, nitrogen, and water vapor were changed as shown in Table 3. The supply amount of BBSS reached 80.6% of the maximum allowable supply amount after 121.5 hours. Since the differential pressure in the reactor continued to rise after the BBSS flow rate became constant, the reaction was stopped after 174.5 hours. The reaction results after 174 hours were a butene conversion rate of 92.8% and a butadiene selectivity of 84.9%.

  From Example 1 and Comparative Example 1, at the time of reaction start-up, BBSS, which is a raw material gas, is set to 80% or more of the maximum allowable supply amount in a short time from the start of raw material supply, thereby suppressing an increase in the differential pressure of the reactor And can continue stably even during steady operation. Moreover, even when the allowable maximum supply amount is set to 80% or more in a short time from the start of raw material supply and when the relatively maximum time is set to 80% or more of the allowable maximum supply amount, the reaction results in the steady operation are obtained. Is the same, it can be seen that the activity of the catalyst is not affected.

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 21a, 21b Reaction tube 22 Reactor shell 23a Raw material supply port 23b Product discharge port 24a, 24b Tube plate 25a, 25b Perforated baffle plate 26a Heat medium supply port 26b Heat medium outlet

Claims (5)

  Start-up of the reaction in supplying the raw material gas containing monoolefin having 4 or more carbon atoms and molecular oxygen-containing gas to the reactor and producing the corresponding conjugated diene by oxidative dehydrogenation reaction in the presence of catalyst In this case, the conjugate is characterized in that the supply amount per unit time of the raw material gas to the reactor is 80% or more of the allowable maximum supply amount within less than 100 hours from the start of the supply of the raw material gas to the reactor. Diene production method.   The method for producing a conjugated diene according to claim 1, wherein the catalyst is a composite oxide catalyst containing at least molybdenum, bismuth, and cobalt. The said catalyst is a complex oxide catalyst represented by following General formula (1), The manufacturing method of the conjugated diene of Claim 1 or 2 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 = 0-10, d = 0-10 (where c + d = 1-10), e = 0.05-3, f = 0-2, g = 0.04-2, h = 0-3, i = 5 48, and j satisfies the oxidation state of other elements Numerical value is.)   The composite oxide catalyst is a method of manufacturing through a step of heating a source compound of each component element constituting the composite oxide catalyst integrated in an aqueous system, comprising a molybdenum compound, an iron compound, a nickel compound, and 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 cobalt compounds and silica, or a dried product obtained by drying the same, and the catalyst precursor, molybdenum The method for producing a conjugated diene according to claim 3, wherein the compound and the bismuth compound are produced together with an aqueous solvent, and the method comprises a post-process comprising drying and firing.   The raw material gas is produced by dehydrogenation or oxidative dehydrogenation of gas containing 1-butene, cis-2-butene, trans-2-butene or a mixture thereof obtained by dimerization of ethylene, or a mixture thereof. 5. A gas containing a butene fraction or a gas containing a large amount of hydrocarbons having 4 carbon atoms obtained when fluid heavy oil fraction is subjected to fluid catalytic cracking. A process for producing conjugated dienes.

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