JP5942391B2 - Reaction tube, multitubular reactor and method for producing unsaturated compound using the same - Google Patents

Description

  The present invention relates to a reaction tube, a multitubular reactor, and a method for producing an unsaturated compound using the same.

  The production or production of unsaturated compounds by oxidative dehydrogenation of raw material gases, such as the production of methacrylic acid from isobutylene and the production of butadiene from n-butene, has been studied or commercialized. In the production of unsaturated compounds by this oxidative dehydrogenation reaction, a multitubular reactor equipped with a plurality of reaction tubes is generally used from the viewpoint of productivity and the like.

  In the production of the unsaturated compound, not only the oxidative dehydrogenation reaction as a main reaction but also a combustion reaction as a side reaction occurs. This combustion reaction occurs slowly even under normal conditions, but if a rapid combustion reaction occurs, there is a possibility that a fire will occur and lead to an explosion. At this time, if a multi-tube reactor is used as the reactor, an explosion in one reaction tube tends to spread to the entire reactor, and therefore the influence of the explosion is very large. Therefore, in order to prevent the occurrence of the explosion itself, in general, a large amount of inert gas such as nitrogen is circulated in the reaction tube together with the raw material gas and the oxygen gas, and the reaction is performed as a gas composition outside the explosion range. However, in this case, since a large amount of the inert gas is used, there are inconveniences such as an increase in cost due to the use of the inert gas and a decrease in productivity due to a relatively small supply amount of the raw material gas.

  Under such circumstances, as a technique for performing the above-described oxidative dehydrogenation reaction while avoiding an explosion, the concentration of the combustible gas in the gas supplied to the reactor is set to the upper explosion limit or more, and the oxygen concentration in the product gas There has been proposed a method for producing a conjugated diene in which is 2.5 vol% or more and 8.0 vol% or less (see JP 2011-6395 A). However, since the above production method adjusts the oxygen concentration in the product gas, it has a practical disadvantage that it is necessary to control the reaction conditions such as the composition of the supplied gas. Therefore, there is a demand for means for improving cost and productivity while suppressing the effects of explosions.

JP 2011-6395 A

  The present invention has been made based on the above-described circumstances, and can minimize the influence of a fire or explosion, and can achieve cost reduction and high productivity. It is an object of the present invention to provide a reaction tube that can be produced, a multi-tube reactor equipped with the same, and a method for producing an unsaturated compound using the multi-tube reactor.

The invention made to solve the above problems is
A reaction tube filled with a catalyst and used for producing an unsaturated compound by oxidative dehydrogenation of a raw material gas,
It comprises a plurality of flame extinguishing elements inserted at least at both ends.

  According to the reaction tube, since the flame extinguishing elements are inserted at both ends, even if a fire or explosion occurs in one reaction tube, the flame does not propagate outside the reaction tube. ing. Therefore, when the reaction tube is used in a multi-tube reactor, even when a fire or explosion occurs, the influence can be suppressed to one tube. In addition, according to the reaction tube, since the influence of fire and explosion can be minimized as described above, the reaction can be performed even with a composition within the explosion limit. Therefore, according to the reaction tube, the amount of inert gas used can be reduced, and as a result, the cost can be reduced and the apparatus can be downsized. Further, according to the reaction tube, productivity can be increased because the concentration of the raw material gas can be relatively increased by reducing the amount of the inert gas used.

  It is preferable that the reaction tube includes three or more flame extinguishing elements, and the catalyst filling region is separated into two or more regions by the flame extinguishing elements. In this way, by separating the catalyst filling area into a plurality of areas by the flame extinguishing element, the area where the flame spreads in the event of a fire or explosion can be further narrowed to one area in the tube, resulting in a fire or explosion. The influence of the case can be further suppressed.

  The flame extinguishing element is preferably a crimp ribbon type element. Thus, by using the crimp ribbon type element, it is possible to enhance the flame extinguishing function such as effectively extinguishing even when the flame propagation speed is high such as so-called detonation.

  The multitubular reactor of the present invention includes a plurality of the reaction tubes. Since the multitubular reactor includes a plurality of the reaction tubes, even if a fire or explosion occurs in one reaction tube, the influence can be minimized. In addition, according to the multitubular reactor, the amount of inert gas used can be reduced, so that cost reduction, downsizing of the apparatus, high productivity, and the like can be achieved.

  The production method of an unsaturated compound of the present invention is a production method in which a mixed gas containing a raw material gas and a molecular oxygen-containing gas is supplied to the multitubular reactor, and an oxidative dehydrogenation reaction of the raw material gas is performed. Since the production method uses the multi-tubular reactor, it is possible to minimize the effects of fires and explosions, and to reduce the amount of inert gas used. In addition, high productivity can be achieved.

  The source gas preferably contains n-butene. Thus, butadiene can be efficiently produced as an unsaturated compound by using n-butene.

  The content of molecular nitrogen with respect to 1 mol of molecular oxygen in the mixed gas is preferably 5 mol or less. Thus, by reducing the content of molecular nitrogen, which is an inert gas, the cost can be reduced and the flow rate of the raw material gas can be relatively increased. Reduction and downsizing of the apparatus can be achieved.

  As described above, according to the reaction tube of the present invention and the multitubular reactor equipped with the same, even when a fire or explosion occurs, the influence can be minimized, and the cost and cost can be reduced. Productivity can be increased. Therefore, according to the production method of the present invention, an unsaturated compound can be produced at low cost and high productivity.

It is a typical sectional view showing the reaction tube concerning one embodiment of the present invention. FIG. 2 is a schematic perspective view showing a crimp ribbon type element provided in the reaction tube of FIG. 1. FIG. 2 is a schematic cross-sectional view showing a multitubular reactor using the reaction tube of FIG. 1.

  Hereinafter, embodiments of a reaction tube, a multi-tube reactor, and an unsaturated compound production method using the same according to the present invention will be described in detail with reference to the drawings as appropriate.

[Reaction tube]
The reaction tube 1 in FIG. 1 mainly includes a tube body 2, a catalyst 3, and four flame extinguishing elements 4.

  The tube body 2 has a tubular shape. The tube body 2 is not particularly limited, and a known one that is usually used for a reaction tube can be used.

  The material of the tube body 2 is not particularly limited, but is usually a metal. By using the metal pipe main body 2, the thermal conductivity of the pipe main body 2 is increased, and the reactivity can be increased. As said metal, stainless steel and carbon steel are preferable from points, such as thermal conductivity and heat resistance.

  The size of the tube body 2 is not particularly limited, and can be appropriately set according to the reaction conditions such as the raw material gas, the type of unsaturated compound to be obtained, the reaction temperature, and the pressure. The length of the tube body 2 can be, for example, 1,000 mm or more and 6,000 mm or less. The outer diameter of the tube body 2 can be, for example, 10 mm or more and 100 mm or less. The inner diameter of the tube body 2 can be, for example, 5 mm or more and 50 mm or less.

  The catalyst 3 is filled in the tube body 2.

  The filled region of the catalyst 3 is separated by a plurality of flame extinguishing elements 4. Specifically, the filling region is divided into three regions by the extinguishing elements (extinguishing elements 4b and 4c) other than the pair of extinguishing elements 4a and 4d inserted into both ends of the tube main body 2. In this way, by separating the filling region of the catalyst 3 in the reaction tube 1 (tube body 2) into a plurality of regions by the flame extinguishing element, it is possible to keep the range where the flame spreads only in that region even when an explosion occurs. it can. Therefore, since the range where a flame spreads can be narrowed, the influence at the time of an explosion can be suppressed.

  The catalyst 3 is usually a solid catalyst. The catalyst 3 may be a supported catalyst supported on a carrier or a non-supported catalyst. In the case of a supported catalyst, for example, α-alumina or silica can be used as the carrier.

  The catalyst 3 may be a fixed bed or a fluidized bed, but is preferably a fixed bed. By using a fixed bed, reaction controllability and the like can be improved.

  Although it does not specifically limit as a shape of the catalyst 3, Usually, it is a particulate form. The shape of the particle is not particularly limited, and examples thereof include an indefinite shape, a spherical shape, and a cylindrical shape.

The size of the catalyst 3 is not particularly limited, but the average particle size is preferably 0.1 mm or more and 20 mm or less, and more preferably 1 mm or more and 10 mm or less. Here, the average particle size refers to a particle size (D ₅₀ ) of 50% integrated distribution from the small particle size side in the particle size distribution. By setting the average particle diameter of the catalyst within the above range, the reaction efficiency can be increased.

  Although it does not specifically limit as a filling factor of the catalyst 3, 50 volume% or more is preferable, 70 volume% or more is more preferable, 80 volume% or more and 96 volume% or less are further more preferable. By setting it as such a filling rate, high reactivity can be exhibited, suppressing a pressure loss. This filling rate refers to the volume ratio of the catalyst in the space between the flame extinguishing elements inside the tube body 2.

  The type of the catalyst 3 is not particularly limited as long as it functions as a catalyst for the oxidative dehydrogenation reaction of the raw material gas, and a known one can be used.

The catalyst 3 is preferably a molybdenum-bismuth multi-component metal oxide catalyst, more preferably a catalyst represented by the following formula (1).
_{Mo a Bi b Fe c Co d} Ni e Sb f X g Y h Z i Si j O k ··· (1)

  In the above formula (1), X is selected from the group consisting of magnesium (Mg), calcium (Ca), zinc (Zn), cerium (Ce), samarium (Sm), indium (In) and chromium (Cr). At least one element. Y is at least one element selected from the group consisting of sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), lithium (Li), and thallium (Tl). Z is at least one element selected from the group consisting of boron (B), phosphorus (P), arsenic (As), and tungsten (W). a to k represent atomic ratios of the respective elements. When a = 12, b = 0 to 8, c = 0 to 20, d = 0 to 16, e = 0 to 12, f = 0 to 0. 6, g = 0 to 8, h = 0 to 20, i = 0 to 6, j = 0 to 48. k is a numerical value that satisfies the oxidation state of other elements.

  The method for preparing the catalyst is not particularly limited, and a known method such as an evaporation to dryness method using a raw material of each element or an oxide mixing method can be employed. The raw material of each of the above elements is not particularly limited. For example, oxides, nitrates, carbonates, ammonium salts, hydroxides, carboxylates, carboxylate ammonium salts, ammonium halide salts, hydrogen acids, component elements, Examples include acetylacetonate and alkoxide.

  All the flame extinguishing elements 4 (extinguishing elements 4 a to 4 d) are inserted into the pipe body 2. The flame extinguishing elements 4a and 4d are fitted into both end portions of the reaction tube 1 (tube body 2). That is, in the pipe body 2, the catalyst 3 is disposed between a pair of flame extinguishing elements (extinguishing elements 4a and 4d) located at the outermost position. Further, the flame extinguishing elements (flaming extinguishing elements 4b and 4c) other than the pair of flame extinguishing elements are inserted so as to separate the catalyst 3 into three regions as described above. These four flame extinguishing elements 4 may be provided at equal intervals, or may be provided at different intervals.

  According to the reaction tube 1, since the filling region of the catalyst 3 is separated into three regions by the four extinguishing elements in this way, the range in which the flame spreads during the explosion can be further narrowed to one region in the tube. Therefore, it is possible to further suppress the influence when an explosion occurs.

  Furthermore, according to the reaction tube, since the filling region (reacting space) of the catalyst 3 is separated into a plurality of regions, the source gas has a space where the reaction proceeds and a space where the reaction does not proceed (extinguishing element). Will pass repeatedly. By performing such a reaction, productivity and the like can be increased by suppressing the occurrence of hot spots and facilitating temperature control in the reaction.

  The flame extinguishing element 4 is not particularly limited, and a wire netting element, a crimp ribbon type (corrugated sheet) element, or the like can be used. Among these, a crimp ribbon type element can be preferably used. By using a crimp ribbon element, the flame extinguishing function can be enhanced. In addition, the crimp ribbon type element is excellent in strength against mechanical and thermal shocks, so that it is possible to further reduce the influence on other regions when an explosion occurs.

  A crimp ribbon type element suitably used as the flame extinguishing element 4 will be described below with reference to FIG. The crimp ribbon type element 11 of FIG. 2 includes a central axis 12, a flat ribbon 13, and a corrugated ribbon 14 (a ribbon with a crimp). The flat ribbon 13 and the wave ribbon 14 are overlapped and wound around the central axis 12 in a spiral shape. By winding both ribbons (flat ribbon 13 and corrugated ribbon 14) in this way, a cellular structure having a large number of pores 15 having a substantially triangular cross section is obtained. An annular wall plate 16 is fitted on the outermost periphery of both ribbons in the wound state. Both ribbons are fixed by the wall plate 16.

  The material of the crimp ribbon element 11 is usually made of metal such as stainless steel or ceramics. Among these, metal is preferable and stainless steel is more preferable in terms of durability, flame resistance, and the like.

  The size of the pore 15 is not particularly limited, but the equivalent diameter is preferably less than the maximum safe clearance of the unsaturated compound to be produced. Here, the equivalent diameter is calculated by (cross-sectional area × 4 / sum of peripheral length). The maximum safety gap is a value inherent to the combustible gas. For example, the maximum safety gap of butadiene is 0.79 mm. Therefore, in the case of producing butadiene by the oxidative dehydrogenation reaction of butene, the equivalent diameter of the pore 15 is preferably less than 0.79 mm. By setting the pores 15 to such a size, the flame extinguishing function can be effectively exhibited. The lower limit of the equivalent diameter of the pore 15 is not particularly limited, but is preferably 0.01 mm or more from the viewpoint of suppressing a decrease in pressure loss.

  The length of the flame extinguishing element 4 (crimp ribbon type element 11) (the length in the axial direction of the tube body 2) is not particularly limited, but is preferably 10 mm or more and 60 mm or less, for example. By setting the length of the flame extinguishing element 4 within the above range, it is possible to achieve both a sufficient flame extinguishing function and a suppression of pressure loss.

  A plurality of crimp ribbon elements 11 may be used as one flame extinguishing element 4. Thus, the flame extinguishing function can be enhanced by using a plurality of crimp ribbon elements 11.

[Multi-tube reactor]
The multitubular reactor 21 of FIG. 3 mainly includes a reactor shell 22 and a plurality of reaction tubes 1 provided in parallel in the reactor shell 22. The reaction tube 1 is the same as the reaction tube 1 of FIG. The number of reaction tubes 1 is not particularly limited, and can be, for example, 100 or more and 10,000 or less. The plurality of reaction tubes 1 are fixed by a pair of upper and lower tube plates 23a and 23b.

  The reactor shell 22 has a raw material supply port 24 formed in the upper portion and a product discharge port 25 formed in the lower portion. Furthermore, the reactor shell 22 has a heat medium supply port 26 formed at the lower side surface and a heat medium discharge port 27 formed at the upper side surface. Thus, in the multitubular reactor 21, the raw material (mixed gas including the raw material gas) and the product (the gas including the unsaturated compound obtained) pass through the reaction tubes 1 from the upper side toward the lower side. The heat medium flows from the lower side toward the upper side.

  The heat medium is not particularly limited, and salts such as nitrite and nitrate, organic solvents such as dibenzyltoluene, and the like can be used.

  The reactor shell 22 has a plurality of baffle plates 28 provided perpendicularly to the plurality of reaction tubes 1 inside. The baffle plate 28 allows the heat medium to flow uniformly in the reactor shell 22. The kind of baffle plate 28 is not specifically limited, A well-known thing can be used.

  Since the multitubular reactor 21 includes a plurality of the reaction tubes 1, even if an explosion occurs in one reaction tube, the influence can be minimized. Further, according to the multi-tubular reactor 21, the amount of inert gas used can be reduced, so that cost reduction and high productivity can be achieved.

[Method for producing unsaturated compound]
The production method of an unsaturated compound of the present invention is a production method in which a mixed gas containing a raw material gas and a molecular oxygen-containing gas is supplied to the multitubular reactor, and an oxidative dehydrogenation reaction of the raw material gas is performed. Since the production method uses the multi-tubular reactor, even if an explosion occurs, the impact can be minimized, and the amount of inert gas used can be reduced. Productivity can be increased.

  The unsaturated compound as the raw material and the target product in the production method is not particularly limited as long as it corresponds to the production method for obtaining the unsaturated compound by oxidative dehydrogenation reaction of the raw material gas. The production method includes, for example, a production method for obtaining styrene by oxidative dehydrogenation of ethylbenzene, a production method for obtaining olefins and the like by oxidative dehydrogenation of paraffin, a production method for obtaining conjugated dienes and the like by oxidative dehydrogenation of olefins, and other alcohols. It can be applied to a production method for obtaining an aldehyde, a ketone or the like by oxidative dehydrogenation.

  Among these, the said manufacturing method can be used suitably for the manufacturing method which obtains conjugated diene by the oxidative dehydrogenation of an olefin. Examples of the olefin include butene, pentene, methylbutene, and dimethylbutene.

  Further, in the production method, the raw material gas preferably contains an olefin having 4 or more carbon atoms, more preferably contains an olefin having 4 to 6 carbon atoms, and more preferably n-butene. As the n-butene, one or more of 1-butene and 2-butene (cis-2-butene and trans-2-butene) can be used. Among these, it is particularly preferable that 1-butene is included as n-butene.

  Hereinafter, the embodiment of the production method will be described in detail by taking, as an example, the case where butadiene is obtained by the oxidative dehydrogenation reaction of n-butene, that is, the raw material gas contains n-butene.

  The content of n-butene contained in the source gas is not particularly limited, but is preferably 80% by volume or more, and more preferably 95% by volume or more from the viewpoint of productivity. Further, the ratio of 1-butene, cis-2-butene, and trans-2-butene in n-butene is not limited, and can take any value. However, in order to obtain high purity butadiene, the concentration of 1-butene relative to n-butene is preferably 30 mol% or more, more preferably 90 mol% or more, and even more preferably 98 mol% or more.

The n- butene, obtained for example from C ₄ fraction by-produced in naphtha cracking to separate butadiene and i- butene n- butene (1-butene and 2-butene) fraction as a main component (raffinate 2 Or a butene fraction produced by dehydrogenation or oxidative dehydrogenation of n-butane. A gas containing high-purity 1-butene, cis-2-butene, trans-2-butene or a mixture thereof obtained by dimerization of ethylene can also be used. Furthermore, fluid catalytic cracking (Fluid Catalytic), which decomposes heavy oil fraction obtained when crude oil is distilled in an oil refinery plant, etc., using a powdered solid catalyst in a fluidized bed state and converts it into low boiling point hydrocarbons. Gas containing a large amount of hydrocarbons having 4 carbon atoms obtained from Cracking (hereinafter sometimes abbreviated as FCC-C4) as raw material gas, or from which impurities such as phosphorus are removed from FCC-C4 Can also be used as a raw material gas.

  The source gas containing n-butene may contain any impurity other than n-butene 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 these impurities is usually 20% by volume or less, preferably 10% by volume or less, more preferably 1% by volume or less, and still more preferably 0.1% by volume or less. If the amount of this impurity is too large, the concentration of 1-butene or 2-butene, which are the main raw materials, decreases and the reaction becomes slow, and undesirable by-products tend to increase.

  In the manufacturing method, n-butene or a mixture containing n-butene serving as a raw material gas is gasified with a vaporizer, and the raw material gas is mixed with a molecular oxygen-containing gas to obtain a mixed gas. This mixed gas is preferably heated to about 150 to 250 ° C. by a preheater and supplied to the multitubular reactor.

  The molecular oxygen-containing gas refers to a gas containing 10% by volume or more of molecular oxygen gas. As content of this molecular oxygen, 15 volume% or more is preferable and 20 volume% or more is more preferable. The upper limit of the molecular oxygen content is preferably 50% by volume, more preferably 30% by volume, and even more preferably 25% by volume. By setting the upper limit to the above value, the cost necessary for industrially preparing the molecular oxygen-containing gas can be suppressed. The molecular oxygen-containing gas is preferably air.

Further, 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, and CO ₂ . 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. If this amount is too large, it tends to be difficult to supply molecular oxygen necessary for the reaction.

  As content of molecular oxygen gas with respect to 1 volume part of source gas in the said mixed gas, 0.5 volume part or more and 10 volume parts or less are preferable, and 1 volume part or more and 8 volume parts or less are more preferable. By setting it as such content ratio, an oxidative dehydrogenation reaction etc. can be performed efficiently.

  In addition to the raw material gas and the molecular oxygen-containing gas, water (water vapor) may be further added to the mixed gas. By adding water to the mixed gas, the concentration of the raw material gas and molecular oxygen can be adjusted, and the coking of the catalyst can be suppressed.

  As content of the water vapor | steam with respect to 1 volume part of source gas in the said mixed gas, 0.3 volume part or more and 5 volume part or less are preferable, and 0.6 volume part or more and 2 volume part or less are more preferable. By setting it as such content ratio, an oxidative dehydrogenation reaction etc. can be performed efficiently.

  The molecular nitrogen content relative to 1 mol (volume part) of molecular oxygen in the mixed gas is preferably 5 mol (volume part) or less, preferably 3 mol (volume part) or more and 4.5 mol (volume part) or less. It is more preferable that it is 3.5 (volume part) mol or more and 4 (volume part) mol or less. Usually, in such an oxidative dehydrogenation reaction, nitrogen gas as an inert gas is generally added to the mixed gas in order to make the composition out of the explosion range as described above. However, in the manufacturing method, since the influence at the time of fire or explosion is reduced as described above, the content of nitrogen gas as an inert gas can be reduced as in the above range. That is, even if an inert gas is not added separately, a mixed gas in which only a raw material gas, air as a molecular oxygen-containing gas, and water (water vapor) as necessary can be used. Therefore, according to the production method, since the content of molecular nitrogen, which is an inert gas, is reduced in this way, the cost can be reduced and the flow rate of the source gas can be relatively increased. , Productivity can be improved. In addition, since the amount of inert gas used is reduced, the amount of off-gas generated is reduced, and devices such as reactors, quench towers, compressors, and solvent absorption towers can be downsized. Further, since the amount of inert gas having a high original unit price is small in off-gas, there is no need to reuse it, and productivity can be increased from this point. Furthermore, the reactivity can be improved by reducing the inert gas, and the amount of catalyst used can be reduced.

  In addition, according to the said manufacturing method, since the influence at the time of a fire or an explosion is reduced as mentioned above, it can react with various mixed gas compositions irrespective of the explosion limit inside and outside.

  The raw material gas, air, and water (steam) used as necessary may be supplied to the multitubular reactor from separate pipes, but it is preferable to supply them in a uniformly mixed state. By doing in this way, it can suppress that the heterogeneous mixed gas forms a blast partially in a reactor, or supplies the raw material of a different composition for every reaction tube.

  The reaction temperature (temperature in the reaction tube) in the oxidative dehydrogenation reaction is not particularly limited, but is preferably 300 ° C or higher and 420 ° C or lower, more preferably 320 ° C or higher and 400 ° C or lower, and further preferably 340 ° C or higher and 380 ° C or lower. . By setting it as such temperature, an efficient reaction can be advanced.

  The pressure in the oxidative dehydrogenation reaction (pressure in the reaction tube) is not particularly limited, but is preferably from atmospheric pressure to 0.5 MPa, more preferably from atmospheric pressure to 0.1 MPa. By setting it as such a range, the possibility of a fire and an explosion can be reduced, maintaining the supply amount of mixed gas.

The gas hourly space velocity in the oxidative dehydrogenation reaction (GHSV), preferably 300 hr ^-1 or more 8,000Hr ^-1 or less, 1,000 hr ^-1 or more 3,000Hr ^-1 or less is more preferable. By setting such a gas hourly space velocity, an efficient reaction can be promoted.

  In this way, by performing the oxidative dehydrogenation reaction of the raw material gas using the multitubular reactor, a product gas containing an unsaturated compound (butadiene or the like) is discharged from the product discharge port. Hereinafter, each process performed as needed after the oxidative dehydrogenation reaction will be described. As said process, a cooling process, a dehydration process, a collection process, a deaeration process, and a separation process can be performed in this order.

  In the cooling step, the product gas discharged from the multitubular reactor is cooled. The cooling process is not particularly limited as long as the process can cool the product gas. Specifically, for example, it can be cooled by a quench tower.

  In the dehydration step, moisture contained in the product gas is removed after the cooling step. Specifically, for example, the product gas containing moisture cooled in the quench tower is dehydrated in a dehydration tower or the like.

In the recovery step, after the dehydration step, the product gas is absorbed by the solvent and recovered. Specifically, for example, the product gas from the dehydration tower is fed to the solvent absorption tower, and the product gas is brought into countercurrent contact with the solvent. By doing so, butadiene in the gas, unreacted n-butene and the like are absorbed by the solvent. Components (residual gas) that have not been absorbed by the solvent are discharged from the top of the solvent absorption tower and discarded by combustion. The solvent absorption liquid is extracted from the bottom of the solvent absorption tower and fed to the deaeration tower. As the absorption solvent used for recovery of butadiene in this solvent absorption tower, C _{6 to} C ₁₀ saturated hydrocarbons, C _{6 to} C ₈ aromatic hydrocarbons, amide compounds, and the like are used. For example, dimethylformamide (DMF), toluene, N-methyl-2-pyrrolidone (NMP), etc. can be used.

  In the degassing step, nitrogen and oxygen dissolved in the solvent absorption liquid of butadiene obtained in the recovery step are removed by gasification. The degassing method is not particularly limited as long as it is a method capable of gasifying and removing nitrogen and oxygen dissolved in the solvent absorption liquid. Specifically, for example, by supplying the solvent absorption liquid of butadiene obtained in the solvent absorption tower to the deaeration tower and heating to about 50 to 150 ° C., nitrogen and oxygen dissolved in the liquid are gasified and removed. can do.

  In the separation step, butadiene is separated from the solvent absorption liquid of butadiene. The separation method is not particularly limited as long as it is a method capable of separating butadiene from a solvent absorption solution of butadiene, but is usually performed by distillation separation. Specifically, for example, butadiene is separated by distillation in a solvent separation tower (purification tower), and a butadiene fraction is extracted from the top of the tower. The separated solvent is extracted from the bottom of the column and recycled as an absorption solvent for the solvent absorption column (purification column).

  The reaction tube, the multi-tube reactor and the method for producing an unsaturated compound of the present invention are not limited to the above embodiment. For example, the reaction tube may not have three or more flame extinguishing elements, but may have a pair of flame extinguishing elements that are inserted into both end portions. Thus, by having a pair of flame-extinguishing elements at both ends, the influence of the explosion can be suppressed only to the tube.

  Moreover, you may use the element which consists of a structure filled with the fine catalyst powder as a flame-extinguishing element. In such a structure, when the gap between the catalyst powders is less than the maximum safety gap, it functions as a flame extinguishing element. In this flame extinguishing element, since the reaction proceeds when the raw material gas passes through the flame extinguishing element portion, the reaction efficiency can be increased.

  Furthermore, in a multi-tube reactor, the heat medium for the reaction tube can be divided into a plurality of regions, and the heat medium can be controlled at different temperatures. For example, the heat medium is divided into three regions, and the temperature gradually increases from the raw material inflow side in the reaction tube to low temperature (for example, about 200 ° C.), medium temperature (for example, 200 to 300 ° C.), and high temperature (for example, 300 to 350 ° C.). It can also be set as follows. By doing in this way, generation | occurrence | production of a side reaction can be suppressed and reaction efficiency can be improved. In this case, a flame extinguishing element can also be arranged at a position corresponding to the boundary of each region. By disposing the flame extinguishing element in this way, temperature control in the reaction becomes easy and reaction controllability can be improved.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples.

  In addition, 1-butene conversion rate, butadiene selectivity, and butadiene yield in the following evaluations are calculated by the following formulas, respectively.

[Example 1]
A reaction tube of Example 1 was prepared using the following tube body, catalyst, and flame-extinguishing element. That is, the reaction tube having the shape shown in FIG. 1 (four flame extinguishing elements) was obtained by alternately filling the flame extinguishing elements and the catalyst inside the tube main body. The packed region of the catalyst was separated into three regions, and the axial length of each region was set to 200 mm. In addition, let each separated filling area | region be the area | region a, the area | region b, and the area | region c in order from the source gas supply side (upstream side). A thermocouple was installed in each area for temperature measurement. In addition, a spark plug was installed in the area a in order to evaluate the influence of the explosion.
Tube body: Carbon steel pipe for boiler and heat exchanger
(STB340, outer diameter 25.4mm, length 1800mm)
Catalyst: Average particle size 3mm
Composition Mo12-Bi1-Fe8-Co5-Ni1-Sb0.2-K0.3
Carrier α-alumina Flame extinguishing element: Crimp ribbon type element with axial length of 30 mm

[Comparative Example 1]
A reaction tube of Comparative Example 1 was obtained in the same manner as in Example 1 except that no flame-extinguishing element was inserted.

[Evaluation 1]
The effect of ignition was evaluated by using each reaction tube and igniting while producing an unsaturated compound (butadiene) under the following reaction conditions.
(Reaction conditions)
・ Reaction temperature 350 ℃
・ Reaction pressure 0.05 MPa
・ Heat medium Molten salt ・ GHSV 1,600 hr ⁻¹
-Mixed gas composition Raw material gas: Molecular oxygen-containing gas: Water vapor = 3: 93: 4
1-butene was used as the source gas, and air was used as the molecular oxygen-containing gas.
At this time, molecular oxygen gas is 6.5 times (volume ratio) with respect to the source gas, and water vapor is 1.3 times (volume ratio) with respect to the source gas.

(Evaluation method)
Evaluation was performed according to the following procedure.
1. The heat medium was circulated so that the temperature of each region of the catalyst was 350 ° C.
2. Gases (air and water vapor) other than the raw material gas were circulated in the reaction tube at the following flow rates.
Air: 10 mol / hr
Water vapor: 0.44 mol / hr
3. Subsequently, source gas (1-butene) was circulated at 0.33 mol / hr.
4). The spark plug was used to ignite the inside of the tube by generating an electric spark.
5. The temperature rise after ignition was measured and the outlet gas was analyzed.
6). The reaction was stopped and the appearance of the catalyst was observed.

  In Example 1, the temperature of the area | region a rose after ignition. The temperature increase in the regions b and c was 40% smaller than that in Comparative Example 1. The amount of by-products (COx) in the outlet gas was 90% less than that in Comparative Example 1. The amount of butadiene in the outlet gas was 65% higher than that in Comparative Example 1. As for the catalyst after the reaction, soot in the regions b and c was somewhat attached.

[Evaluation 2]
Using the reaction tube of Example 1, an unsaturated compound (butadiene) was produced under the following reaction conditions and the mixed gas composition shown in Table 2.
(Reaction conditions)
・ Reaction temperature 350 ℃
・ Reaction pressure 0.05 MPa
・ GHSV 1,600 hr ^-1
Table 1 shows the 1-butene conversion, butadiene selectivity, and butadiene yield in each mixed gas composition.

As shown from the above evaluation 1, when the reaction tube of the example was used, the ignited flame was confined in the region a because the temperature rise in the regions b and c and the amount of soot attached to the catalyst were small. Is shown. On the other hand, in the reaction tube of Comparative Example 1 that does not have a flame extinguishing element, it can be seen that the flame spreads throughout the reaction tube due to ignition, and the influence of ignition (explosion) increases. Moreover, as shown from the evaluation 2, it can be seen that when N ₂ gas is not added to the mixed gas, all of 1-butene conversion, butadiene selectivity, and butadiene yield are increased.

  As described above, according to the present invention, it can be suitably used for the production of unsaturated compounds such as the production of butadiene by the dehydrogenation reaction of butene.

DESCRIPTION OF SYMBOLS 1 Reaction tube 2 Tube body 3 Catalyst 4, 4a, 4b, 4c, 4d Flame extinguishing element 11 Crimp ribbon element 12 Center axis 13 Flat ribbon 14 Wave ribbon 15 Pore 16 Wall plate 21 Multi-tubular reactor 22 Reactor shell 23a 23b Tube plate 24 Raw material supply port 25 Product discharge port 26 Heat medium supply port 27 Heat medium discharge port 28 Baffle plate

Claims (6)

A reaction tube filled with a catalyst and used for producing an unsaturated compound by oxidative dehydrogenation of a raw material gas,
It includes a plurality of flame extinguishing elements that are inserted into at least both end portions,
The anti-inflammatory element is a crimped ribbon type element to have a pore,
A reaction tube, wherein an equivalent diameter of the pores calculated by a cross-sectional area × 4 / (sum of peripheral lengths) is 0.01 mm or more and less than a maximum safe clearance of the unsaturated compound to be manufactured.   The reaction tube according to claim 1, further comprising three or more flame extinguishing elements, wherein the catalyst filling region is separated into two or more regions by the flame extinguishing elements. A multitubular reactor comprising the plurality of reaction tubes according to claim 1 or 2 . A method for producing an unsaturated compound, wherein a mixed gas containing a raw material gas and a molecular oxygen-containing gas is supplied to the multitubular reactor according to claim 3 and an oxidative dehydrogenation reaction of the raw material gas is performed. The method for producing an unsaturated compound according to claim 4 , wherein the source gas contains n-butene. Method for producing an unsaturated compound according to claim 4 or claim 5 content of molecular nitrogen to molecular oxygen to 1 mole of the mixed gas is 5 moles or less.

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