JP2011006381A - Method for producing conjugated diene - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a conjugated diene such as butadiene by catalytic oxidative dehydrogenation of a monoolefin such as n-butene, wherein butadiene is prevented from polymerizing so that the operation can more safely be carried out and butadiene is stably produced at a higher yield.SOLUTION: The method for producing a conjugated diene including supplying a mixed gas obtained by mixing a raw material gas comprising a 4C or greater monoolefin with a gas comprising molecular oxygen to a reactor, subjecting the mixed gas to oxidative dehydrogenation in the presence of a catalyst to obtain a product gas comprising a conjugated diene, bringing the product gas into contact with an absorbent solvent to obtain a solvent absorption liquid, subsequently degassing the solvent absorption liquid, and subsequently isolating/recovering the conjugated diene from the solvent absorption liquid by distillation, is characterized in that the absorbent solvent contains a polymerization inhibitor in an amount of from 1 to 3,000 ppm by weight and the concentration of a peroxide present in the solvent absorption liquid is kept not higher than 100 ppm by weight by heating the solvent absorption liquid.

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.

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

As an industrial production method of butadiene by this catalytic oxidative dehydrogenation reaction, from a C ₄ fraction (mixture of hydrocarbons having 4 carbon atoms; hereinafter sometimes referred to as “BB”) produced as a by-product in naphtha decomposition. In the process for extracting and separating butadiene, a mixture containing 1-butene, 2-butene 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 in the BBSS.

As a typical process showing the process of extracting and separating butadiene from the C ₄ fraction, the process shown in FIG. 2 can be given as an example. First, the C ₄ fraction is introduced into the first extractive distillation column 32 via the evaporation column 31, and butadiene and the like are extracted with an extractant (dimethylformamide (DMF) or the like), and other C ₄ components (hereinafter referred to as “ May be referred to as “BBS”). Next, the i-butene is removed from the BBS in the i-butene separation column 33, and BBSS is discharged out of the system.

  The butadiene extract from the first extractive distillation column 32 is then separated in the pre-dispersion tower 34 and the first diffusion tower 35 from the extractant DMF and the like, and then introduced into the second extractive distillation tower 37 via the compressor 36. , And re-extracted with an extractant (DMF, etc.). The acetylenes separated in the second extractive distillation tower 37 are recovered as fuel through a butadiene recovery tower 38 and a second diffusion tower 39.

  The crude BD from the second extractive distillation column 37 is further purified by the first distillation column 40 and the second distillation column 41 to recover high-purity 1,3-butadiene. In FIG. 2, reference numerals 200 to 219 denote piping.

As a typical method for producing butadiene by the catalytic oxidative dehydrogenation reaction of n-butene, Patent Document 1 proposes a method for producing butadiene as shown below.
(1) a reaction step of producing butadiene by vapor-phase catalytic oxidative dehydrogenation of n-butene,
(2) a cooling step of cooling the product gas obtained from the reaction step and removing a trace amount of high-boiling by-products contained in the product gas;
(3) an aldehyde removal step for removing a small amount of aldehydes contained in the cooled product gas;
(4) a compression step for compressing the derived product gas;
(5) A C ₄ recovery step of recovering C ₄ components including butadiene and other C ₄ hydrocarbons from the compressed product gas.

  Moreover, the catalyst described in patent document 2 can be mention | raise | lifted as an example of the complex oxide catalyst used by the catalytic oxidation dehydrogenation reaction of n-butene. Patent Document 2 describes that this composite oxide catalyst is used as a catalyst for producing butadiene by oxidative dehydrogenation of butene.

JP 60-115532 A JP 2003-220335 A

  By the way, it is known that butadiene is easily polymerized in a liquid phase to form a polymer. The resulting butadiene polymer is called popcorn polymer. When polymerization proceeds in the equipment / piping, the equipment / piping is damaged or the polymer is taken out from the equipment into the atmosphere. There have been many reports of fires. For this reason, it is important to prevent polymerization of butadiene in a method in which butene is oxidatively dehydrogenated to produce butadiene and butadiene is recovered from the produced gas using a solvent.

  However, Patent Documents 1 and 2 do not describe the polymerization of butadiene when butadiene is produced by oxidative dehydrogenation of butene and then hydrocarbons containing butadiene are recovered from the product gas using a solvent. .

  By the way, it is known that the polymerization of butadiene is a precursor of butadiene peroxide, and it is easily generated when butadiene is heated in the presence of oxygen. For this reason, it is conceivable to prevent oxidation of butadiene when dissolved in a solvent by removing oxygen from the solvent in which butadiene is dissolved.

  As a simple method for removing oxygen from the solvent, there is a method of heating the solvent. As described above, there is a possibility that peroxide of butadiene is generated by heating the solvent, and the solvent is often circulated. Since the peroxide generated by heating remains in the solvent, the peroxide accumulates and may cause explosive polymerization of butadiene.

  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 polymerization of the conjugated diene is prevented. An object of the present invention is to provide a method which can be safely operated and can stably produce a conjugated diene at a high yield.

As a result of intensive studies to solve the above-mentioned problems, the present inventors supply a mixed gas obtained by mixing a raw material gas containing a monoolefin having 4 or more carbon atoms and a molecular oxygen-containing gas to the reactor. In the presence of a catalyst, a product gas containing a conjugated diene produced by an oxidative dehydrogenation reaction is obtained, and the product gas is brought into contact with an absorbing solvent to obtain a solvent absorbing solution, and then the solvent absorbing solution is degassed. Then, in the method for producing a conjugated diene in which the conjugated diene is separated and recovered from the solvent absorption liquid by distillation separation, the absorption solvent contains 1 to 3000 wtppm of a polymerization inhibitor, and the solvent absorption liquid is heated. By doing so, the said subject was able to be solved by making the peroxide density | concentration in this solvent absorption liquid into 100 wtppm or less.
Furthermore, it is good also considering the temperature at the time of deaerating a solvent absorption liquid as 50 to 120 degreeC. Furthermore, the temperature at which the solvent absorbing liquid is heated may be 100 ° C. or higher and 200 ° C. or lower.

  By using an absorbing solvent containing a predetermined amount of a polymerization inhibitor, it is possible to suppress the generation of peroxide concentration in the absorbing solvent, and it is possible to suppress the generation of conjugated diene polymer.

  Then, the peroxide of the conjugated diene that has been generated so far can be decomposed and dissolved in the absorption solvent to which the above-described polymerization inhibitor is added, so that generation of peroxide of the conjugated diene is suppressed. It is possible to decompose the conjugated diene polymer and suppress the production of the conjugated diene polymer.

It is a process figure which shows embodiment of the manufacturing method of the conjugated diene of this invention. It is a process diagram showing an extraction separation process butadiene from C ₄ fraction.

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

  In the method for producing a conjugated diene according to the present invention, a mixed gas obtained by mixing a raw material gas containing a monoolefin having 4 or more carbon atoms and a molecular oxygen-containing gas is supplied to a reactor, and in the presence of a catalyst. The product gas containing the conjugated diene produced by the oxidative dehydrogenation reaction is obtained, the product gas is brought into contact with the absorption solvent to obtain the solvent absorption liquid, the solvent absorption liquid is degassed, and then distilled and separated. , A method for separating and recovering the conjugated diene from the solvent absorbing solution.

  The process of the manufacturing method of the said conjugated diene is demonstrated using FIG. This process includes a source gas oxidative dehydrogenation step (step (A)), a quench step (step (B)), a dehydration step (step (C)), a solvent absorption step (step (D)), a degassing step ( It consists of each process of a process (E)) and a solvent separation process (process (F)).

<Process (A) (oxidative dehydrogenation process)>
First, the process (A) which is an oxidative dehydrogenation process is demonstrated.
The raw material gas is introduced from the pipe 101, and air as a molecular oxygen-containing gas and, if necessary, inert gas (inert gas) and water (water vapor) are introduced from the pipes 102, 103, and 104. After the mixed gas is heated to about 150 to 250 ° C. by a preheater (not shown), it is supplied from a pipe 100 to a multitubular reactor (oxidation dehydrogenation reactor) 1 filled with a catalyst. The raw material gas, nitrogen gas, air, and water (water vapor) may be supplied directly to the reactor 1 through separate pipes, but are preferably supplied to the reactor 1 in a uniformly mixed state. This is because it is possible to prevent a situation in which a non-uniform mixed gas partially forms a squeal in the reactor 1 or a raw material having a different composition is supplied to each tube in the reactor 1. is there.

[Molecular oxygen-containing gas]
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. is there. From the viewpoint of the cost necessary for industrially preparing the molecular oxygen-containing gas, the molecular oxygen is 50% by volume or less, preferably 30% by volume or less, more preferably 21% 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.

[Inert gas, water (water vapor)]
Since the inert gas (inert gas) adjusts the concentration of flammable gas such as butene and oxygen so that the mixed gas does not form squeal in the reactor 1, water (steam) is For the reason of adjusting the concentrations of the combustible gas and oxygen as well as the nitrogen gas and for suppressing the coking of the catalyst, these are supplied together with butene and molecular oxygen-containing gas to the reactor 1 as a raw material gas. Is preferred. Examples of the inert gas include nitrogen, argon, carbon dioxide and the like. Among these, nitrogen is preferable from the economical viewpoint.

[Raw material gas]
The source gas refers to a gaseous product obtained by gasifying a conjugated diene source with a vaporizer (not shown in FIG. 1). For example, when trying to obtain 1,3-butadiene (BD), high-purity 1-butene or 2-butene can be used as a raw material, but the C ₄ fraction by-produced by the above-described naphtha decomposition is used. A fraction (BBSS) composed of n-butene (1-butene and 2-butene) obtained by separating butadiene and i-butene from (BB) as a main component and a monoolefin having 4 carbon atoms including isobutene and the like. And a butene fraction produced by n-butane dehydrogenation or oxidative dehydrogenation reaction can also be used. Further, a gas containing high-purity 1-butene, cis-2-butene, trans-2-butene or a mixture thereof obtained by dimerization of ethylene may be used as a raw material gas. As the ethylene, ethylene obtained by a method such as ethane dehydrogenation, ethanol dehydration, or naphtha decomposition can be used. Furthermore, fluid catalytic cracking (Fluid Catalytic Cracking) in which heavy oil fractions obtained by distilling crude oil at oil refineries and the like are decomposed in a fluidized bed using a powdered solid catalyst and converted to low boiling point hydrocarbons. ) Gas containing a large number of hydrocarbons having 4 carbon atoms obtained from (hereinafter sometimes abbreviated as FCC-C4) as raw material gas, or removing impurities such as phosphorus and arsenic from FCC-C4 It is possible to use the raw material as a raw material gas.

  Furthermore, when trying to obtain a conjugated diene other than 1,3-butadiene (BD), the main component is a monoolefin having 5 or more carbon atoms, preferably 5 to 6 carbon atoms, such as pentene, methylbutene, and dimethylbutene. Can be used.

  Therefore, a conjugated diene having 4 or more carbon atoms, preferably 4 to 6 carbon atoms, is obtained by using a monoolefin having 4 or more carbon atoms, preferably 4 to 6 carbon atoms, as a main component of the raw material gas. Can do. 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.

  In the present specification, the main component is a component containing 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. Say. 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; Examples thereof include dienes such as butadiene; acetylenes such as methylacetylene, vinylacetylene, and ethylacetylene. Further, 1,3-butadiene, which is the target of the reaction, may be included. The amount of these impurities 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 with respect to the total amount of the raw material gas. 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 by-products tend to increase.

[Mixed gas composition]
The composition of the mixed gas of the raw material gas to, _{O 2} is 40~120vol / vol%, _{N 2} is 500~1000vol / vol%, _{H 2} O is preferably 90~900vol / vol%, _{O 2} is 100~115vol / vol%, _{N 2} is 600~800vol / vol%, _{H 2} O is more preferably 100~200vol / vol%. If the ratio of O _{2 to} the source gas deviates from this range, even if the reaction temperature is adjusted, it tends to be difficult to adjust the outlet O ₂ concentration. In addition, as the ratio of N ₂ or H ₂ O increases, the raw material gas becomes thinner and the efficiency tends to deteriorate. On the other hand, as the ratio decreases, the reaction gas enters an explosive composition or heat removal becomes difficult. Tend.

[Explosion range of mixed gas]
Since the mixed gas is a mixture of oxygen and flammable gas, supply each gas (flammable gas, air, and inert gas and water (water vapor) if necessary) so as not to enter the explosion range. The composition of the inlet of the reactor 1 is controlled while monitoring the flow rate with a flow meter installed in the piping to be adjusted to the above mixed gas composition.

  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 oxygen concentration at the inlet of the reactor is reduced below the critical oxygen concentration by adjusting the amount of air, inert gas, and water vapor containing the molecular oxygen-containing gas supplied to the reactor first. After that, start supplying flammable gas, and then increase the supply of flammable gas and molecular oxygen-containing gas such as air so that the concentration of flammable gas is higher than the upper limit of explosion. good.

  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 the inert gas such as water vapor or nitrogen. If it does in this way, the gas residence time in piping and a reactor can be kept constant, and the fluctuation of pressure can be controlled.

  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.

[Conditions for oxidative dehydrogenation]
The reactor 1 is filled with an oxidative dehydrogenation reaction catalyst, which will be described later, on which the raw material gas reacts with oxygen to produce conjugated diene 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 reactor 1 is preferably cooled as appropriate, for example, by removing heat with a heat medium (dibenzyltoluene, nitrite, etc.), and the temperature of the catalyst layer is preferably controlled to be constant.

  The pressure in the reactor 1 is not particularly limited, but 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 or less. As this value decreases, the explosion range tends to narrow.

  The residence time of the reactor 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 or less. The smaller this value, the smaller the reactor.

[Components in the product gas]
The concentration of the conjugated diene corresponding to the monoolefin in the raw material gas contained in the product gas produced by the above reaction depends on the concentration of the monoolefin contained in the raw material gas, but usually 1 to 15 vol%, preferably 5-13 vol%, more preferably 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%.

[Explosion range of generated gas]
By the way, when the composition of the inlet of the reactor 1 is higher than the upper limit of explosion, the composition of the outlet of the reactor 1 is usually higher than the upper limit of explosion, and there is no fear of explosion. However, in the present invention, a solvent absorption step (step (step (C)) in which the produced gas (which becomes a compressed gas or a dehydrated gas in step (C)) is brought into contact with an absorption solvent to absorb hydrocarbons such as olefin and conjugated diene. D)), the concentration of hydrocarbons in the gas is lowered in this step, and there is a possibility of entering the explosion range. In order 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, but the composition at the outlet of the reactor 1 or the outlet of the quench tower 2 is less than the critical oxygen concentration. It is easier to adjust the reactor 1 inlet conditions and reaction conditions. For example, an oxygen concentration meter is installed at the outlet of the quench tower 2 and the air flow rate supplied to the reactor 1 is adjusted so that the oxygen concentration meter is 8% or less, or the reaction temperature is adjusted.

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 to 110% by volume, preferably 102 to 107% by volume, more preferably 103 to 105% by volume. The reason why the outlet flow rate is increased is that the number of molecules increases stoichiometrically in the reaction in which olefin in the raw material gas is oxidatively dehydrogenated to produce conjugated diene and water, and in the reaction in which CO or CO ₂ is produced by 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.

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

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

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

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

Next, a method for producing a composite oxide catalyst suitable for the present invention will be described.
First, in this method for producing a composite oxide catalyst, the molybdenum used in the previous step is molybdenum corresponding to a partial atomic ratio (a ₁ ) of the total atomic ratio (a) of molybdenum, The molybdenum used in the step is preferably molybdenum corresponding to the remaining atomic ratio (a ₂ ) obtained by subtracting a ₁ from the total atomic ratio (a) of molybdenum. The a ₁ is preferably a value satisfying 1 <a ₁ / (c + d + e) <3, and the a ₂ is preferably a value satisfying 0 <a ₂ / b <8.

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

Examples of Mo supply source compounds include ammonium paramolybdate, molybdenum trioxide, molybdic acid, ammonium phosphomolybdate, and phosphomolybdic acid.
Examples of Fe source compounds include ferric nitrate, ferric sulfate, ferric chloride, and ferric acetate.
Examples of the Co source compound include cobalt nitrate, cobalt sulfate, cobalt chloride, cobalt carbonate, and cobalt acetate.
Examples of the Ni source compound include nickel nitrate, nickel sulfate, nickel chloride, nickel carbonate, nickel acetate and the like.
Examples of Si source compounds include silica, granular silica, colloidal silica, and fumed silica.

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

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

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

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

Examples of the source compound for B include borax, ammonium borate, and boric acid.
Examples of P source compounds include ammonium phosphomolybdate, ammonium phosphate, phosphoric acid, phosphorus pentoxide, and the like.
Examples of the source compound for As include dialsenooctammonium molybdate, ammonium dialseno18 tungstate, and the like.
Examples of W source compounds include ammonium paratungstate, tungsten trioxide, tungstic acid, and phosphotungstic acid.

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

The aqueous solution or aqueous dispersion of the raw material compound used in the previous step is an aqueous solution, water slurry or water containing at least one of molybdenum (corresponding to a ₁ in the total atomic ratio a), iron, nickel or cobalt and silica as a catalyst component. It is a cake.

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

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

  The aqueous solution or aqueous dispersion of the raw material compound containing silica thus obtained is heated to 60 to 90 ° C. and aged.

  The aging means that the catalyst precursor slurry is stirred at a predetermined temperature for a predetermined time. This aging increases the viscosity of the slurry, reduces the sedimentation of the solid components in the slurry, and is particularly effective in suppressing the heterogeneity of components in the subsequent drying process. The catalytic activity such as the raw material conversion rate and selectivity of the product catalyst becomes better.

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

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

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

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

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

The ignition loss of the catalyst precursor obtained after the heat treatment is preferably 0.5 to 5% by weight, more preferably 1 to 3% by weight. By setting the ignition loss within this range, a catalyst having a high raw material conversion rate and high selectivity can be obtained. The loss on ignition is a value given by the following equation.
Burning loss (%) = [(W ₀ −W ₁ ) / W ₀ ] × 100
W ₀ : Weight (g) of the catalyst precursor after drying at 150 ° C. for 3 hours to remove adhering moisture
W ₁ : Weight (g) after further heat-treating the catalyst precursor excluding adhering moisture at 500 ° C. for 2 hours

In the step after the, the integration of the pre-catalyst precursor and the molybdenum compound obtained in step (remaining a ₂ corresponds to minus a ₁ equivalent of the total atomic ratio a) and bismuth compounds, carried out in an aqueous solvent . At this time, it is preferable to add ammonia water. The addition of the X, Y, and Z components is also preferably performed in the subsequent step. Further, the bismuth source compound of the present invention is bismuth which is hardly soluble or insoluble in water. This compound is preferably used in the form of a powder. These compounds as the catalyst production raw material may be particles larger than the powder, but are preferably smaller particles in view of the heating step in which thermal diffusion should be performed. Therefore, if these compounds as raw materials are not such particles, they should be pulverized before the heating step.

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

The 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 (B) (quenching process)>
Next, the process (B) which is a quench process is demonstrated.
In FIG. 1, the reaction product gas from the reactor 1 is supplied to the quench tower 2 through a 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 temperature of the cooling water depends on the cooling temperature of the reaction product gas, but is usually 10 to 90 ° C, preferably 20 to 70 ° C, and more preferably 30 to 60 ° C.

<Process (C) (Dehydration process)>
Next, step (C) which is a dehydration step will be described.
The product gas cooled in the quench tower 2 flows out from the top of the tower, and then is cooled to room temperature (about 10 to 30 ° C.) via the cooler 3 from the pipe 108. The condensed water generated by cooling is separated into the drain pot 4 through the pipe 109. The 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 water separation is usually a wet gas with a water content of about 0.5 to 2 vol% and a dew point of about 0 to 20 ° C., and this gas is introduced into the dehydration towers 8A and 8B as necessary. And dehydrated.

  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, 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.
In addition, in the dehydration towers 8A and 8B, high-boiling components contained in the compressed 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 by the water | moisture content and decomposition | disassembly of a solvent in a subsequent solvent absorption process can be prevented, and it is preferable. In the case where the dehydration towers 8A and 8B are not provided, water may accumulate in the absorption solvent, so it is desirable to separate the absorption solvent and water by a known method such as distillation or decantation. The separation method may be appropriately selected according to the nature of the solvent.

  Usually, the moisture content in the gas is usually 10 to 10000 volppm, preferably 20 to 1000 volppm by dehydration treatment using a desiccant such as molecular sieve, and the dew point is −60 to 80 ° C., preferably -50 to 20 ° C.

<Process (D) (solvent absorption process)>
Next, the process (D) which is a solvent absorption process is demonstrated.
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. When 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 volatilize 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, for example, decane, may be provided at the end of the pipe 117.

  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. There is an advantage that the higher the pressure, the better the absorption efficiency.

  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 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.

  In this solvent absorption tower 10, the solvent absorption liquid in which the conjugated diene or unreacted raw material gas is 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. .

As the absorption solvent used for recovering the conjugated diene in the solvent absorption tower 10, a C _{6 to} C ₁₀ saturated hydrocarbon, a C _{6 to} C ₈ aromatic hydrocarbon, an amide compound, or the like is used. For example, dimethylformamide (DMF), toluene, N-methyl-2-pyrrolidone (NMP), etc. can be used. Although there is no restriction | limiting in particular in the usage-amount of an absorption solvent, when there are too many, it is uneconomical, and when there are too few, the collection | recovery efficiency of a conjugated diene will fall. Therefore, it is preferable to supply the solvent in such an amount that the conjugated diene concentration in the obtained solvent absorbing solution is about 1 to 20% by weight, preferably about 3 to 10% by weight.

  When the conjugated diene is butadiene, depending on the type of absorbing solvent, butanes and butadiene differ in solubility in the absorbing solvent, so the type of absorbing solvent, the ratio of C4 gas to the absorbing solvent, the temperature and pressure of the absorbing solvent are selected. This makes it possible to purge at least a part of butanes from the top of the solvent absorption tower while absorbing butadiene. 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 in the solvent absorption tower, there is no need to provide new equipment, which is economically advantageous.

  This absorption solvent contains a polymerization inhibitor. Examples of this polymerization inhibitor include hydroquinone, di-n-butylamine, phenyl-β-naphthylamine, phenyl-α-naphthylamine, diethylhydroxylamine, sodium nitrite, sodium hydrogen nitrite, pt-butylcatechol and the like. 2 or more types may be combined.

  The amount of the polymerization inhibitor is preferably 1 wtppm or more, and preferably 10 wtppm or more in the absorbing solvent. On the other hand, the upper limit is preferably 3000 wtppm, and preferably 1000 wtppm. If it is less than 1 wtppm, there is a tendency that the oxygen concentration in the absorbing solvent cannot be sufficiently reduced. As a result, it becomes difficult to make the peroxide concentration in the absorbing solvent below a predetermined concentration. It may be difficult to suppress the generation. On the other hand, although it may be more than 3000 wtppm, it is difficult to exert the effect of adding a polymerization inhibitor, and about 3000 wtppm is sufficient.

  Since these polymerization inhibitors react with oxygen and are consumed or lost in the solvent purification process, it is desirable to periodically analyze and replenish them.

<Process (E) (Deaeration process)>
Next, the process (E) which is a deaeration process is demonstrated.
Since the solvent absorption liquid of the conjugated diene obtained in the solvent absorption tower 10 also absorbs some amounts of nitrogen and oxygen, this solvent absorption liquid is then supplied to the deaeration tower 11 to degas the solvent absorption liquid. When heating, that is, the temperature at the bottom of the column is about 50 to 120 ° C., preferably 80 to 100 ° C., nitrogen and oxygen dissolved in the liquid are gasified and removed. If the temperature is too low, oxygen cannot be sufficiently removed, and if the temperature is too high, the oxide of the conjugated diene tends to increase.

  At this time, since butene, butadiene, and a part of the solvent are also gasified, they are liquefied by a condenser 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.

  Moreover, the temperature at the time of heating the bottoms from the degassing tower 11, that is, the degassed solvent absorption liquid, is 100 ° C. or higher and 200 ° C. or lower and heated to a temperature higher than the bottom of the degas tower Then, it is provided to the solvent separation tower 12. This heating may be performed by the reboiler of the solvent separation column 12. By setting the bottoms from the degassing tower 11 to this temperature condition, the characteristic of decomposing butadiene peroxide can be exhibited. The temperature condition is preferably 100 ° C. or higher, and preferably 120 ° C. or higher. Moreover, 180 degrees C or less is good and 160 degrees C or less is more preferable.

  The absorption solvent used in the step (D) contains a predetermined amount of a specific polymerization inhibitor, and in this step (E), the bottom temperature of the deaeration tower 11 is set within a predetermined range, and the deaeration tower 11 is heated at a predetermined temperature to the degassed solvent absorption liquid, so that the peroxide concentration in the absorption solvent can be 100 wtppm or less. Since the peroxide concentration in the absorbing solvent can be set to a predetermined concentration or less, it is possible to suppress an increase in the peroxide concentration when the absorbing solvent is circulated through the step (F) described later, Induction of polymerization of the conjugated diene can be suppressed.

  In the distillation condenser of the deaeration tower 11, since the polymerization inhibitor in the absorption solvent is separated by distillation, it is desirable to supply a solvent containing the polymerization inhibitor. In particular, since the polymerization easily proceeds when the conjugated diene is liquefied, it is preferable to spray a solvent containing a polymerization inhibitor on the condensation surface.

<Step (F) (Solvent Separation Step)>
[Solvent separation]
Subsequently, the process (F) which is a solvent separation process is demonstrated.
In the solvent separation tower 12, the conjugated diene is distilled and separated from the solvent absorption liquid by the reboiler and the condenser, and the conjugated diene fraction is extracted from the top of the tower via the pipe 120. The separated solvent absorption liquid mainly composed of the separated absorption solvent is extracted from the tower bottom via the pipe 121 and circulated and used as the absorption solvent of the solvent absorption tower 10.

  In the distillation condenser (not shown) of the solvent separation column 12, since the polymerization inhibitor is distilled and separated, it is desirable to add the polymerization inhibitor. However, when the absorption solvent to which the polymerization inhibitor is added is sprayed, the product conjugate Diene is mixed with absorbing solvent. Therefore, it is desirable to supply a conjugated diene to which a polymerization inhibitor is added.

  The residual solvent absorption liquid may accumulate impurities during cyclic use, and a part of the residual solvent absorption liquid is extracted by a known purification method such as distillation, decantation, sedimentation, contact treatment with an adsorbent, ion exchange resin, or the like. It is desirable to remove impurities. Of the residual solvent absorbing solution, the purified absorbing solvent can be returned to the process and used. The lost absorbing solvent is preferably supplemented with a fresh absorbing solvent or a stored absorbing solvent.

  Although the pressure at the time of distillation of the solvent separation 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 great 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 solvent separation 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.

  In the present invention, the effluent of the degassing tower 11 is heated at a temperature of 100 ° C. or higher and higher than the bottom of the degassing tower 11 to decompose the conjugated diene peroxide. It is convenient to heat the effluent with a reboiler. If the heating temperature is too low, decomposition of the peroxide tends not to proceed.

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

[Purification of crude conjugated diene]
In the conjugated diene separation step, a crude conjugated diene is obtained. When the crude conjugated diene is a crude butadiene, a crude butadiene having a butadiene purity of about 40 to 98 vol%, preferably about 60 to 95 vol% is usually obtained.

  In the present invention, in particular, BBSS containing n-butene discharged from the butadiene extraction and separation process from the C4 fraction obtained by naphtha decomposition shown in FIG. 2 is used as a raw material gas for the catalytic oxidative dehydrogenation reaction. 2 or when the butadiene extraction / separation process is provided in the vicinity of the butadiene production process by the catalytic oxidative dehydrogenation reaction, the crude butadiene obtained in the separation step is extracted and separated by the extraction / separation process shown in FIG. The first extractive distillation column 32 is preferably supplied to the inlet side and purified together with the C4 fraction obtained by naphtha decomposition. When pure 1-butene or 2-butene is used as a raw material for the catalytic oxidative dehydrogenation and all the butene is converted into butadiene, it is supplied to the inlet side of the first distillation column 40 and supplied from the second extractive distillation column 37. Along with the crude butadiene, the light distillation component may be removed by the first distillation column 40 and then the heavy distillation component may be removed by the second distillation column 41 for purification.

[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 added to the slurry.
Next, 58.1 g of bismuth subcarbonate in which Na was dissolved in 0.45% was added and mixed with stirring. After the slurry was heated and 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
In addition, the atomic ratios a1 and a2 of molybdenum during preparation were 6.9 and 5.1, respectively.

[Example 1] (Production of 1,3-butadiene)
1,3-butadiene was produced using the process shown in FIG. In addition, the gas chromatography (Shimadzu Corporation make: GC-2014) was used for the analysis of the gas in an Example.
The reaction tube in the reactor 1 provided with 113 reaction tubes having an inner diameter of 27 mm and a length of 3500 mm, and 1162 ml of the composite oxide catalyst produced in Production Example 1 and an inert ball (manufactured by Tipton Corp.) per reaction tube. 407 ml was charged.
Of these reaction tubes, three reaction tubes were provided with thermometers, and the temperature in the reactor was measured. The thermometer used was a multipoint thermocouple (manufactured by Okazaki Manufacturing Co., Ltd.), and the temperature distribution of the catalyst layer was measured from the inlet to the outlet of the reaction tube.
In addition, a mixed gas of air (molecular oxygen: 21%) and nitrogen (purity: 99.99% or more) was supplied to the reactor in advance, and the temperature was raised by flowing a heating medium (dibenzyltoluene). After the reactor temperature reaches 302 ° C., BBSS discharged from the butadiene extraction and separation process by-produced by naphtha decomposition, air, nitrogen, and water vapor are flowed at the following flow rates (reactor reaction). Per tube) and mixed as a raw material gas, heated to 217 ° C. with a preheater, and then supplied to the reactor 1. A 319 ° C. heating medium (dibenzyltoluene) was allowed to flow around the reaction tube in the reactor 1 to adjust the temperature inside the reaction tube to 341 to 352 ° C.

BBSS: 13.2 capacity part / hr
・ Air: 77.3 parts by volume / hr
・ Nitrogen: 28.5 parts by volume / hr
Water vapor: 22.4 parts by volume / hr

The composition of the BBSS is as follows.
Propane: 0.035 mol%
・ Cyclopropane: 0.057 mol%
Propylene: 0.109 mol%
Isobutane: 4.784 mol%
-N-butane: 16.903 mol%
・ Trans-2-butene: 16.903 mol%
-1-butene: 43.487 mol%
Isobutene: 2.264 mol%
・ 2,2-Dimethylpropane: 0.197 mol%
Cis-2-butene: 12.950 mol%
・ Isopentane: 0.044 mol%
・ N-Pentane: 0.002 mol%
・ 1,2-Butadiene: 0.686 mol%
・ 1,3-Butadiene: 1.075 mol%
・ Methylacetylene: 0.017 mol%
・ 3-Methyl-1-butene: 0.057 mol%
・ 2-Pentene: 0.001 mol%
Vinyl acetylene: 0.006 mol%
・ Ethylacetylene: 0.282 mol%

The product gas from the reactor 1 was brought into contact with water in the quench tower 2 and cooled to 86 ° C., and further cooled to room temperature in the cooler 3.
When the sample was sampled from the sampling port installed at the outlet of the cooler 3 and analyzed by the gas chromatography described above, the composition of the product gas obtained was as follows. The water condensed here was collected in the drain pot 4. This gas was pressurized to 3 MPa by the compressor 5 and further cooled to about 17 ° C. by the cooler 6 to condense the water and recovered in the drain pot 7.
Propane: 0.004 mol%
・ Cyclopropane: 0.005 mol%
Propylene: 0.001 mol%
・ Isobutane: 0.487 mol%
-N-butane: 1.948 mol%
・ Trans-2-butene: 0.340 mol%
-1-butene: 0.002 mol%
・ Isobutene: 0.000 mol%
・ 2,2-Dimethylpropane: 0.021 mol%
・ Cis-2-butene: 0.129 mol%
・ Isopentane: 0.005 mol%
・ N-Pentane: 0.000 mol%
・ 1,2-Butadiene: 0.000 mol%
・ 1,3-Butadiene: 7.109 mol%
・ Methylacetylene: 0.000 mol%
-3-methyl-1-butene: 0.000 mol%
・ 2-Pentene: 0.000 mol%
Vinyl acetylene: 0.000 mol%
・ Ethylacetylene: 0.000 mol%
・ Fran: 0.112 mol%
・ O ₂ : 5.776 mol%
・ N ₂ : 80.21 mol%
・ CO ₂ : 1.832 mol%
・ CO: 0.596 mol%

  The compressed gas was supplied to a dehydration tower 8A or 8B packed with molecular sieve 3A (manufactured by Union Showa Co., Ltd.).

The dehydration gas was supplied to the vicinity of the bottom of the solvent absorption tower 10 at a pressure of 0.2 MpaG and a temperature of 16 ° C. From the top of the tower, 600 kg / h of toluene containing 580 ppm of pt-butylcatechol (TBC) was supplied, and both were counter-contacted to absorb hydrocarbons such as butadiene.
Subsequently, oxygen and nitrogen were separated in the deaeration tower 11, and further, 1,3-butadiene was separated and recovered from toluene in the solvent separation tower 12. The bottom temperature of the solvent separation tower was 135 ° C.
As a result of sampling the bottoms of the deaeration tower and the solvent separation tower and analyzing the peroxide, the results were as follows.
・ Peroxide concentration in the degassed tower bottoms ... 4ppm
-Peroxide concentration in the solvent separation tower bottom liquid ... Not detected (less than 2 ppm)

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 31 Evaporation tower 32 First extraction distillation tower 33 i-butene separation tower 34 Pre-emission tower 35 First emission tower 36 Compressor 37 Second extraction distillation tower 38 Butadiene recovery tower 39 Second stripping tower 40 First distillation tower 42 Second distillation tower 100-126 Piping

Claims (8)

  A mixed gas obtained by mixing a raw material gas containing a monoolefin having 4 or more carbon atoms and a molecular oxygen-containing gas is supplied to a reactor, and a conjugated diene produced by an oxidative dehydrogenation reaction in the presence of a catalyst. After the product gas is contacted with an absorbing solvent to obtain a solvent absorbing liquid, the solvent absorbing liquid is degassed, and then the conjugated diene is separated from the solvent absorbing liquid by distillation separation. In the method for producing a conjugated diene to be recovered, 1 to 3000 wtppm of a polymerization inhibitor is contained in the absorbing solvent, and the solvent absorbing solution is heated to reduce the peroxide concentration in the solvent absorbing solution to 100 wtppm or less. 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. The said catalyst is a complex oxide catalyst represented by following General formula (1), The manufacturing method of the conjugated diene of Claim 2 characterized by the above-mentioned.
_{Mo a Bi b Co c Ni d} Fe 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 catalyst produced through a process of integrating and heating the source compound of each component element constituting the composite oxide catalyst in an aqueous system,
An aqueous solution or aqueous dispersion of a raw material compound containing at least one selected from the group consisting of a molybdenum compound, an iron compound, a nickel compound and a cobalt compound and silica, or a dried product obtained by drying the catalyst, is heat treated. It is manufactured by a method having a pre-process for manufacturing a precursor and a post-process for integrating the catalyst precursor, a molybdenum compound and a bismuth compound together with an aqueous solvent, drying and firing. 3. A method for producing a conjugated diene according to 3.   The polymerization inhibitor is one selected from hydroquinone, di-n-butylamine, phenyl-β-naphthylamine, phenyl-α-naphthylamine, diethylhydroxylamine, sodium nitrite, sodium hydrogen nitrite, and pt-butylcatechol. The method for producing a conjugated diene according to any one of claims 1 to 4, wherein the method is a plurality of agents.   The method for producing a conjugated diene according to any one of claims 1 to 5, wherein a temperature at which the solvent absorbing liquid is degassed is 50 ° C or higher and 120 ° C or lower.   The method for producing a conjugated diene according to any one of claims 1 to 6, wherein a temperature at which the degassed solvent absorbing liquid is heated is 100 ° C or higher and 200 ° C or lower.   The raw material gas is produced by dehydrogenation or oxidative dehydrogenation of gas containing 1-butene, cis-2-butene, trans-2-butene or a mixture thereof obtained by dimerization of ethylene, or a mixture thereof. The gas containing a butene fraction, or a gas containing a large amount of hydrocarbons having 4 carbon atoms obtained when fluid oil cracking a heavy oil fraction, according to any one of claims 1 to 7, The manufacturing method of conjugated diene of description.

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