JP5842689B2 - Method for producing conjugated diene - Google Patents

Description

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

A method for producing a conjugated diene such as butadiene by subjecting a monoolefin such as n-butene to an oxidative dehydrogenation reaction in the presence of a catalyst is conventionally known.
This reaction proceeds, for example, according to the following reaction formula, and water is by-produced.
C ₄ H ₈ + 1 / 2O ₂ → C ₄ H ₆ + H ₂ O
As a typical catalyst for producing butadiene by oxidative dehydrogenation of n-butene, there is a metal oxide catalyst containing molybdenum. For example, Patent Document 1 includes at least one of molybdenum, iron, nickel, or cobalt and silica. A mixed metal oxide catalyst is described.

  The metal oxide catalyst containing molybdenum is also used when an unsaturated nitrile such as acrylonitrile is obtained by reacting propylene with ammonia and oxygen by an ammoxidation method. In Non-Patent Document 1, water and a molybdenum compound are used. It has been shown that it reacts to produce volatile molybdenum hydrate, and the volatilized molybdenum may be deposited in a cooling pipe or the like in the reactor to corrode the material. For this reason, Patent Document 2 describes that the adhesion of the molybdenum compound can be suppressed by configuring the reaction apparatus with a material having a standard electrode potential of an oxidation reaction in an aqueous solution system of −0.2 V or more and 2.8 V or less. Yes.

JP 2003-220335 A JP 2006-247452 A

J. et al. Buiten, J .; Catalysis, 10, 188-199 (1968)

  Although the above-mentioned Patent Document 1 does not describe a specific method for producing butadiene, the oxidative dehydrogenation reaction for producing butadiene from butene is an exothermic reaction, and thus a heat exchange reaction in which the reaction is performed while removing heat with a refrigerant or the like. When butadiene is produced from butene as a raw material in the presence of a molybdenum-containing metal oxide catalyst using a reactor (fixed bed reactor, fluidized bed reactor, etc.), carbon content adheres to the reactor and the catalyst (hereinafter referred to as (Sometimes called "coking"). In particular, when coking occurs on the cooling surface in the reactor, the heat removal effect decreases and the reaction cannot be controlled. Therefore, when coking occurs, the reaction is stopped and the reactor is opened and adhered to the reactor each time. In order to remove carbon, it had to be washed, and butadiene could not be produced stably for a long period of time. Moreover, if coking progresses remarkably in the reactor, the reactor may be blocked, the differential pressure before and after the reactor will increase, and the reaction may not be controlled.

  This invention is made | formed in view of the said subject, Comprising: In the method of manufacturing conjugated dienes, such as a butadiene, by the catalytic oxidative dehydrogenation reaction of monoolefins, such as n-butene, it can industrially operate stably. The object is to provide an advantageous process for the production of butadiene.

As a result of intensive studies to solve the above problems, the inventors of the present invention have made it possible that water produced as a by-product in the production of butadiene by the oxidative dehydrogenation reaction of butene comes into contact with the molybdenum-containing metal oxide catalyst, thereby Part of the molybdenum becomes volatile molybdenum hydroxide, which is released from the catalyst and adheres to the cooling surface in the reactor, and precipitates as molybdenum oxide on the cooling surface, The mechanism by which coking occurs starting from the deposited part was estimated.
Based on this estimation, it has been found that reducing the concentration of molybdenum oxide (molybdenum amount) on the cooling transmission surface to a specific amount or less can suppress coking, and the present invention has been completed.

The gist of the present invention is the following [1] to [4].
[1] A raw material gas containing a monoolefin having 4 or more carbon atoms and a molecular oxygen-containing gas are supplied to a heat exchange reactor having a molybdenum-containing metal oxide catalyst, and the reaction heat is removed using a refrigerant. The conjugated diene is produced by performing an oxidative dehydrogenation reaction while maintaining the amount of molybdenum adhering to the cooling surface in the reactor at 1.7 mg / m ² or less. Production method.
[2] The method for producing a conjugated diene as described in [1], wherein the molybdenum-containing metal oxide catalyst is a composite metal oxide catalyst further containing bismuth and cobalt.
[3] A fraction whose main component is n-butene (1-butene and 2-butene) obtained by separating butadiene and i-butene from a C4 fraction (BB) by-produced by naphtha decomposition. (BBSS), a gas containing 1-butene, cis-2-butene, trans-2-butene or a mixture thereof obtained by dimerization of ethylene, butene fraction produced by dehydrogenation or oxidative dehydrogenation of n-butane Or at least one gas selected from the group consisting of gases containing a large amount of hydrocarbons having 4 carbon atoms, obtained by fluid catalytic cracking of a heavy oil fraction [1] or The method for producing a conjugated diene according to [2].
[4] The method for producing a conjugated diene according to any one of [1] to [3], wherein an average roughness Ra of the surface of the cooling transmission surface is 3 μm or less.

  According to the present invention, coking of the cooling transfer surface in the reactor can be suppressed, and the heat removal effect of the reaction heat can be reduced, and the reactor can be prevented from being blocked by coking. And it can be expected to continue the oxidative dehydrogenation reaction for stably producing butadiene for a long period of time.

It is the schematic of the apparatus used in Reference Example 1 of this invention. It is the schematic of the multitubular reactor (heat exchanger type reactor) used for the oxidative dehydrogenation reaction used in the Example of this invention. FIG. 2 (a) is a plan view of the multitubular reactor, and FIG. 2 (b) is a schematic cross-sectional view of the multitubular reactor. It is a figure which occupies the state of coking of the molybdenum containing metal oxide catalyst of the present invention and a cooling transmission surface typically.

Hereinafter, embodiments of the method for producing a conjugated diene of the present invention will be described in detail. However, the description described below is an example (representative example) of an embodiment of the present invention, and the present invention is limited to these contents. Not.
In the present specification, “mass%” and “wt%”, and “part by mass” and “part by weight” have the same meaning.

In the method for producing conjugated dienes of the present invention, the present invention will be described in detail by taking as an example the case of producing butadiene from typical n-butene. The present invention is not limited to n-butene (1-butene, 2 The production of corresponding conjugated dienes by catalytic oxidative dehydrogenation of monoolefins having 4 or more carbon atoms, preferably 4 to 6 carbon atoms, such as pentene, methylbutene, dimethylbutene, etc. Effectively applied to.

These monoolefins do not necessarily need to be used in an isolated form, and can be used in the form of any mixture as required. For example, when 1,3-butadiene is to be produced from n-butene (1-butene, 2-butene), high-purity 1-butene or 2-butene can be used as a raw material. byproduct _{C 4} fraction obtained by separating butadiene and i- butene from (BB) n- butenes (1-butene and 2-butene) fraction as a main component (BBSS) of and n- butane dehydration A butene fraction produced by elemental or oxidative dehydrogenation can also be used. 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, 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.

  Further, the source gas may contain an arbitrary impurity as long as the effects of the present invention are not impaired. Specific examples of impurities that may be included include branched monoolefins such as isobutene; saturated hydrocarbons such as propane, n-butane, i-butane, and pentane; olefins such as propylene and pentene; 1,2-butadiene. And acetylenes such as methyl acetylene, vinyl acetylene, and ethyl acetylene. The amount of this impurity is usually 40% by volume or less, preferably 20% by volume or less, more preferably 10% by volume or less, and particularly preferably 1% by volume or less. If the amount is too large, the concentration of 1-butene or 2-butene, which are the main raw materials, decreases, and the reaction becomes slow, or the yield of the target product tends to decrease.

  The type of the reactor used in the oxidative dehydrogenation reaction of the present invention is not particularly limited. However, since the oxidative dehydrogenation reaction is a reaction with a large calorific value, it is usually a heat exchange type reactor suitable for removing heat of reaction. Are preferably used. Specific examples include a tube-type, tank-type or plate-type fixed bed reactor or fluidized bed reactor, preferably a fixed bed reactor, more preferably a fixed bed multitubular reactor or a plate type reaction. And most preferably a fixed bed multitubular reactor. These reactors are generally used industrially and are not particularly limited.

  A mixture containing n-butene as a raw material or n-butene such as the above-mentioned BBSS is usually gasified in advance with a vaporizer or the like before being introduced into the reactor, and then nitrogen gas, air (molecular oxygen-containing gas), And water (steam) with a molybdenum-containing metal oxide catalyst. The raw material gas, nitrogen gas, air and water (steam) may be directly supplied to the reactor through separate pipes, but are preferably supplied to the reactor at the same time in a uniformly mixed state. This is because a non-uniform mixed gas can partially form a squeal in the reactor, and in the case of a multi-tube reactor, it is possible to prevent raw materials having different compositions from being supplied to each tube. .

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 required for industrially preparing a molecular oxygen-containing gas, the molecular oxygen is usually 50% by volume or less, preferably 30% by volume or less, more preferably 25% by volume or less. .

Moreover, the molecular oxygen-containing gas may contain an arbitrary impurity as long as the effects of the present invention are not impaired. Specific examples of impurities that may be included include nitrogen, argon, neon, helium, CO, CO ₂ , and water. In the case of nitrogen, the amount of this impurity is usually 90% by volume or less, preferably 85% by volume or less, more preferably 80% by volume or less. In the case of components other than nitrogen, it is usually 10% by volume or less, preferably 1% by volume or less. When this amount is too large, it tends to be difficult to supply oxygen necessary for the reaction.

  In supplying the raw material gas to the reactor, nitrogen gas and water (water vapor) may be supplied together with the raw material gas. However, the nitrogen gas may be made of butene or the like so that the reactive gas does not form explosive gas. For the purpose of adjusting the concentration of flammable gas and oxygen, water (water vapor), like nitrogen gas, for adjusting the concentration of flammable gas and oxygen and for suppressing the coking of the catalyst, molecular oxygen It is preferable to supply to a reactor with containing gas and source gas.

  When the raw material gas supplied to the reactor is mixed with the molecular oxygen-containing gas, it becomes a mixture of oxygen and combustible gas, so that each gas (butene, air, and as necessary) will not enter the explosion range. Accordingly, while controlling the flow rate with a flow meter installed in a pipe supplying nitrogen gas and water (water vapor), the composition control at the reactor inlet is performed, for example, adjusted to the range of the raw material gas composition described later. . The explosion range here is a range having a composition in which a mixed gas of oxygen and combustible gas is ignited in the presence of some ignition source. It is known that if the concentration of combustible gas is lower than a certain value, it will not ignite even if an ignition source is present, and this concentration is called the lower explosion limit. It is also known that if the concentration of combustible gas is higher than a certain value, it will not ignite even if an ignition source is present, and this concentration is called the upper limit of explosion. Each value depends on the oxygen concentration. In general, the lower the oxygen concentration, the closer the values are, and the two match when the oxygen concentration reaches a certain value. The oxygen concentration at this time is called a critical oxygen concentration. If the oxygen concentration is lower than this, the mixed gas will not be ignited regardless of the concentration of the combustible gas.

  When starting the reaction of the present invention, the amount of molecular oxygen-containing gas 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, supply of combustible gas (mainly raw material gas) is started, and then combustible gas (mainly raw material gas) and molecular oxygen-containing gas such as air so that the concentration of combustible gas becomes higher than the upper limit of explosion. It is better to increase the supply amount. When the supply amount of the combustible gas (mainly source gas) and the molecular oxygen-containing gas is increased, the supply amount of the mixed gas may be made constant by decreasing the supply amount of nitrogen and / or water vapor. By doing so, the residence time of the 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%
30 to 900 vol / vol% with respect to the total of H ₂ O: C ₄ fractions
A molybdenum-containing metal oxide catalyst, which will be described later, is present in the reactor, 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 catalyst and the reaction gas in the reactor are removed by a refrigerant (for example, dibenzyltoluene, nitrate, nitrite, etc.) through the cooling surface in contact. It is preferable to control the temperature in the reactor to be constant by removing heat.

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

  Although the residence time of a reactor is not specifically limited, Preferably it is 0.72 second or more, More preferably, it is 0.80 second or more. There is a merit that as the value of the residence time increases, the conversion rate of the monoolefin in the raw material gas increases. On the other hand, the residence time of the reactor is preferably 5 seconds or less, more preferably 4 seconds or less. The smaller the residence time value, the smaller the reactor.

  The conjugated diene produced by the oxidative dehydrogenation reaction in the reactor is contained in the product gas flowing out from the reactor outlet, but the conjugated diene corresponding to the monoolefin in the feed gas contained in the product gas. The concentration depends on the concentration of the monoolefin contained in the raw material gas, but is usually 1 to 15 vol%, preferably 2 to 13 vol%, more preferably 3 to 11 vol%. The larger the conjugated diene concentration, the lower the recovery cost, and the smaller the conjugated diene, there is an advantage that side reactions such as polymerization are less likely to occur when compression is performed in the subsequent stage after the reactor outlet. In addition, unreacted monoolefin may also be contained in the product gas, and the concentration thereof is usually 0 to 7 vol%, preferably 0 to 4 vol%, more preferably 0 to 2 vol%.

In the present invention, the by-product contained in the product gas is not particularly limited, and examples thereof include aldehydes. These amounts are not particularly limited, but are usually 0.20 to 1.00% by weight, preferably 0.21 to 0.50% by weight in the product gas.
In addition, high-boiling by-products may be present in the by-products contained in the product gas, and these high-boiling by-products are specifically phthalic acids and polycyclic aromatics. Specific examples include phthalic acid, benzoic acid, anthraquinone and the like. These amounts are not particularly limited, but are usually 0.01 to 0.15% by weight, preferably 0.01 to 0.03% by weight in the product gas.

The catalyst used in the present invention is a metal oxide catalyst containing molybdenum, and is not particularly limited as long as it is a metal oxide catalyst containing molybdenum. However, in addition to molybdenum, a composite metal oxide catalyst further containing bismuth and cobalt is more suitable. preferable. These catalysts themselves are known catalysts, and can be produced by, for example, the method disclosed in Patent Document 1 or the like.
The shape of the catalyst is not particularly limited, but can be appropriately changed according to the type of the reactor. For example, in the case of a fluidized bed reactor, it may be used in the form of powder or fine particles. In the case of a fixed bed reactor, the catalyst of the fixed bed reactor may be formed into an arbitrary shape by a method such as extrusion molding, tableting molding or support molding. In addition, an inert ball may be present in the reactor together with the catalyst in order to adjust the reaction activity. The inert ball is not particularly limited as long as it is composed of a catalyst, a raw material gas, a molecular oxygen-containing gas and an inert substance. For example, silica, alumina, zirconia, ceramic spheres, and the like are used. The size of the inert ball is usually the same size as the catalyst, and its diameter is about 2 to 10 mm when used in a fixed bed reactor, and about 10 to 300 μm when used in a fluidized bed reactor.

In the present invention, the amount of molybdenum adhering to the cooling transmission surface in the reactor is maintained at 20 mg / m ² or less (here, the amount of molybdenum is the amount of molybdenum adhering to the cooling transmission surface per unit area of the cooling transmission surface). That is.) The molybdenum content is preferably 15 mg / m ² , more preferably 10 mg / m ² , and particularly preferably 5 mg / m ² .

  The “cooling transmission surface in the reactor” includes a transmission surface that can remove heat generated in the reactor by exchanging heat between the catalyst, the reaction gas, and the refrigerant through the surface in the reactor. It is a waste. For example, when the heat exchange reactor is a tube-type, tank-type, or plate-type fixed bed reactor, specifically, the surface is in contact with a packed catalyst or reaction gas. In the case of a fluidized bed reactor, it is a surface that comes into contact with a catalyst of a pipe through which a cooling medium installed in the reactor flows, or a surface that comes into contact with a reaction gas of a reaction gas cooler installed outside the reactor. .

  As in the present invention, when a gas-phase oxidative dehydrogenation reaction is performed using a metal oxide catalyst containing molybdenum and monoolefin and oxygen, conjugated diene and water are produced. It volatilizes as a hydrate and precipitates as molybdenum oxide on the cooling surface for removing heat generated by the reaction. In the atmosphere in which conjugated diene exists, the precipitated molybdenum oxide acts as a catalyst for polymerizing conjugated dienes so that the high molecular weight carbonaceous material covers molybdenum oxide as shown in FIG. It is thought that caulking occurs.

  According to the mechanism as described above, once coking occurs on the cooling transfer surface in the reactor, coke adheres to the surface of the heat transfer tube in contact with the catalyst. The amount is reduced. Furthermore, in the fixed bed type reactor, the flow of the raw material becomes difficult due to the clogging of the catalyst layer, and the reaction must be stopped, the catalyst removed, and the reaction tube washed. In a fluidized bed type reactor, it becomes difficult to control the reaction temperature due to deterioration of the fluidity of the catalyst due to coke.

As a method of maintaining the amount of molybdenum adhering to the cooling transmission surface at 20 mg / m ² or less, the molybdenum component of the molybdenum-containing metal oxide catalyst is suppressed from volatilizing, or the volatilized molybdenum is oxidized on the cooling transmission surface by molybdenum oxidation. It is sufficient to suppress the precipitation as an object, and the means can be implemented using the above-described means for controlling the roughness of the cooling surface, the temperature difference between the reaction temperature and the refrigerant temperature, steam, and the like.

  Examples of means for suppressing volatilization of metal molybdenum in the catalyst include, for example, lowering the reaction temperature or lowering the concentration of water vapor in the reactor when supplying water vapor together with the raw material gas to the reactor. Is mentioned. These may be performed alone or in combination. When suppressing the volatilization of molybdenum by lowering the reaction temperature, the higher the vapor pressure of the molybdenum, the higher the vapor pressure, so the lower the temperature, the more preferable because the volatilization of the molybdenum is suppressed, but the lower the reaction temperature. As a result, the reaction rate decreases, and the reactor for performing the oxidative dehydrogenation reaction may become large.

As a means for suppressing the precipitation of molybdenum oxide, for example, the temperature difference between the reaction temperature and the cooling medium is reduced to reduce the difference between the molybdenum concentration in the reactor and the vapor pressure on the cooling transmission surface, There is a method of reducing the roughness of the surface of the transmission surface. These methods may be used alone or in combination.
A method for reducing the difference between the reaction temperature and the cooling medium is not particularly limited. For example, in a fixed bed reactor, 5 to 220 ° C, preferably 15 to 150 ° C, more preferably 20 to 100 ° C is suitably used. If this temperature difference is too small, a large heat transfer area is required for heat removal. Conversely, if it is too large, problems in the reactor structure (mechanical strength) and reaction temperature tend to be difficult to control. .

In addition, when a fluidized bed reactor is used, as represented by the method of immersing the heat transfer tube in the catalyst layer, the heat transfer tube in which the catalyst is flowed using the raw material gas and the heat transfer medium is circulated. The reaction heat is generally removed by bringing the outer surface of the catalyst into contact with the catalyst.
Generally, in a fluidized bed reactor, steam is generated and heat is removed by the latent heat of vaporization. Since the temperature of the steam is determined by the pressure of the cooling medium, the pressure is generally 1-10. Operated at 0 MPaG. When the temperature is high (pressure is high), there is a problem that the construction cost for satisfying the pressure resistance of the device is high, and when the temperature is low (pressure is low), the temperature of the generated steam is low and the industry is low. This is economically undesirable because the use is lost and the steam is wasted. Therefore, the pressure is usually 1.0 to 10.0 MPaG, preferably 1.5 to 5.0 MPaG. The temperature of hot water is preferably 180 to 310 ° C, more preferably 200 to 265 ° C. Accordingly, the difference from the reaction temperature is preferably 15 to 220 ° C, more preferably 30 to 200 ° C.

When the surface roughness of the cooling transmission surface is increased, molybdenum oxide is more likely to precipitate and adhere, so that coking increases. Smaller roughness tends to suppress the precipitation of molybdenum. A method for reducing the surface roughness is not particularly limited, but generally, a method such as mechanical polishing with an abrasive such as a buff, electrolytic polishing, or plating is preferably used. In the mechanical polishing method, a smaller surface roughness can be obtained by reducing the size of the abrasive used. When electrolytic polishing is performed, a smooth surface such as a mirror surface is achieved, and Ra can be suitably reduced. As a method for performing plating, electrolytic plating, electroless plating, or the like is preferably used, and plating containing nickel as a main component is preferably used in view of corrosion of the reactor and cost. Electrolytic polishing and plating are more preferred because they can smooth the polishing marks of mechanical polishing. The surface roughness is 10 μm or less, preferably 5 μm or less, more preferably 3 μm or less in terms of average roughness Ra.
[Example]
Hereinafter, the present invention will be described more specifically with reference to examples.

[Reference Example 1]
Observation of Coking with Molybdenum Trioxide (MoO ₃ ) Using the apparatus shown in FIG. 1, a caulking experiment of molybdenum trioxide was performed. A glass reaction tube having an inner diameter of 6 mm was filled with 1 gram of molybdenum trioxide (manufactured by Wako Pure Chemical Industries, Ltd.). 1,3-butadiene, oxygen, nitrogen and water vapor were mixed from the raw material gas supply port at a rate of 2.0 NL / h.

  The glass reaction tube was heated to 360 ° C. with an electric heater, and the mixed gas was allowed to flow through the reaction tube for 48 hours while part of the waste gas flowing out from the outlet of the reaction tube was discharged from the discharge port. After 48 hours, when the supply of the mixed gas was stopped and the molybdenum trioxide was taken out from the reaction tube, the color changed to black and it was firmly fixed. Further, when the temperature was increased under air flow with a thermobalance TGA / DSC type 1 manufactured by METTLER and the weight loss between 200 and 500 ° C. was examined, there was a weight loss of 13.6% by weight.

From this result, it can be seen that MoO ₃ generates a carbonaceous compound (coke) by contact with water and a gas in which butadiene exists, and vigorously cokes.

[Reference Example 2]
Production of Composite Metal 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 Butadiene by Butene Oxidative Dehydrogenation Butadiene was produced by butene oxidative dehydrogenation using a multi-tube fixed bed reactor shown in FIG.
Prior to the oxidative dehydrogenation reaction of butene, 5 tubes were randomly extracted in advance from 113 tubes (length: 3,500 mm, inner diameter: 27 mm, material: SUS304) in the reactor of FIG. The inner surfaces of these five reaction tubes were polished with 180 # buff (JIS H 0400). The surface roughness of the inner surface of the reaction tube was measured using a surface roughness measuring device (Mitutoyo Co., Ltd., model: SJ-301), and the average of the five surface roughnesses (surface roughness Ra) was 1. It was 3 μm.

  The bottom of each of the five polished reaction tubes was mixed and filled with 78 ml of the catalyst obtained in Reference Example 2 and 22 ml of inert balls. Furthermore, 73 ml of catalyst and 275 ml of inert balls were mixed and filled in the upper part. The molybdenum concentration in the catalyst particles used for the reaction was 24.2% by weight, the silica concentration in the catalyst particles was 14.2% by weight, and the catalyst filling amount packed in the catalyst layer height of 20 cm was 63 g. there were.

In addition, 108 unreacted reaction tubes other than the five were similarly filled with catalyst and inert balls.
Note that the differential pressure in the reaction tube was measured as follows. That is, 15 NL / min of nitrogen was passed from above each reaction tube, the pressure at the inlet of the reaction tube was measured, and the difference from the atmospheric pressure was taken as the reaction tube differential pressure before starting the reaction. The results of differential pressure measurement are shown in Table-4.

Then, BBSS, air, nitrogen and water vapor having a composition shown in Table 2 discharged from a butadiene extraction and separation process from a C4 fraction by-produced by naphtha decomposition as a raw material gas are respectively 15.7 Nm ³ / h, 81 supplied at a flow rate of .7Nm ³ /h,62.5Nm ³ / h and 17.7 nm ³ / h, after heating to 214 ° C. in preheater was supplied from the raw material gas inlet to the multi-tubular reactor. A refrigerant having a temperature of 360 ° C. was flowed to the barrel side of the reactor to adjust the maximum temperature inside the reaction tube to 395 to 400 ° C.

The reaction was stopped after 2000 hours of continuous operation while extracting the product gas containing butadiene having the composition shown in Table 3 obtained from the product gas outlet. After stopping the reaction, the differential pressure in the reaction tube was measured as before the reaction. The results are shown in Table-4.
Further, the wall deposit between 200 mm was scraped upward from the lower end of the catalyst layer of five polished reaction tubes, and the amount of the adhering molybdenum compound was measured. Further, the adhered substances on the wall of the five polished reaction tubes were analyzed with a fluorescent X-ray analyzer (manufactured by Philips Inc., model: PW2405 type fluorescent X).
Line spectrometer). Further, the concentrations of molybdenum and bismuth were obtained from a calibration curve prepared in advance using a substance having a known concentration. The results are shown in Table-4.

The precipitated molybdenum concentration is calculated by the following formula.
Precipitated molybdenum amount = Molybdenum amount in the deposit-Molybdenum amount in the deposited catalyst
= Molybdenum content in deposit-Bismuth content in deposit x (Molybdenum / bismuth weight ratio in catalyst)
In addition, the molybdenum amount (mg) in the deposit is calculated by the following formula.

Molybdenum content in deposit (mg) = (weight of deposit) x (molybdenum concentration determined by fluorescent X-ray analysis)
The amount of bismuth (mg) in the deposit is calculated by the following formula as in the molybdenum analysis.
Amount of bismuth in deposit (mg) = (weight of deposit) x (bismuth concentration determined by fluorescent X-ray analysis)
Further, the molybdenum / bismuth weight ratio in the catalyst was 1.10.

The amount of molybdenum (mg / m ² ) adhering in the reaction tube is calculated by the amount of precipitated molybdenum / 0.017 because the surface area of the wall of 200 mm is 3.14 × 0.027 × 0.2 = 0.17 m ^2. Is done.

[Example 2]
In Example 1, the inner surfaces of the five reaction tubes were polished with 400 # buff (JIS H 0400) and 5
All were carried out in the same manner except that the average value of the surface roughness of the book (surface roughness Ra) was 1.1 μm. The results are shown in Table-4.
[Example 3]
In Example 1, the inner surfaces of the five reaction tubes were polished with 600 # buff (JIS H 0400) and 5
All were carried out in the same manner except that the average value (surface roughness Ra) of the surface roughness of the book was 0.39 μm. The results are shown in Table-4.

[Comparative Example 1]
In Example 1, the same process was carried out except that the inner surface of the five reaction tubes was not polished and the average value of the five surface roughnesses (surface roughness Ra) was 3.2 μm. The results are shown in Table-4.

From the results of Examples 1 to 3 and Comparative Example 1, by maintaining the amount of molybdenum adhering to the cooling transmission surface in the reactor to 20 mg / m ² or less, the differential pressure of the reaction tube is reduced, and the reaction tube by coking is used. The effect that can avoid the blockage is expected.

DESCRIPTION OF SYMBOLS 1 Glass reaction tube 2 Raw material gas supply port 3 Temperature indicator 4 Temperature indicator protective tube 5 Electric heater 6 Molybdenum trioxide 7 Outlet 10 Multitubular reactor 11 Reaction tube 12 Reactor body side 13 Raw material gas inlet 14 Generation | occurrence | production Gas outlet 15 Refrigerant inlet 16 Refrigerant outlet 17 Inert layer 18 Catalyst layer lower layer 19 Catalyst layer upper layer 20 Cooling surface in reactor 21 Molybdenum-containing metal oxide catalyst

Claims (4)

Oxidation dehydration while supplying a raw gas containing monoolefin having 4 or more carbon atoms and a molecular oxygen-containing gas to a heat exchange reactor having a molybdenum-containing metal oxide catalyst and removing reaction heat using a refrigerant A method for producing a corresponding conjugated diene by performing an elementary reaction, wherein the amount of molybdenum adhering to a cooling surface in the reactor is maintained at 1.7 mg / m ² or less.   The method for producing a conjugated diene according to claim 1, wherein the molybdenum-containing metal oxide catalyst is a composite metal oxide catalyst further containing bismuth and cobalt. The raw material gas is a fraction (BBSS) containing n-butene (1-butene and 2-butene) as a main component obtained by separating butadiene and i-butene from a C4 fraction (BB) by-produced by naphtha decomposition. ), A gas containing 1-butene, cis-2-butene, trans-2butene or a mixture thereof obtained by dimerization of ethylene, butene fraction produced by dehydrogenation or oxidative dehydrogenation of n-butane, And at least one kind of gas selected from the group consisting of gases containing a large amount of hydrocarbons having 4 carbon atoms, obtained when fluid heavy oil fraction is subjected to fluid catalytic cracking. The manufacturing method of conjugated diene of description.   The method for producing a conjugated diene according to any one of claims 1 to 3, wherein the average roughness Ra of the surface of the cooling transmission surface is 3 µm or less.

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