JP2018016566A - Method for producing butadiene - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing butadiene in which the contents of acetaldehyde and methacrolein are reduced in such a manner that the consumption of a quick chilling agent is suppressed.SOLUTION: Provided is a method for producing butadiene comprising: a reaction step where an n-butene-containing raw material gas and an oxygen-containing gas are contacted with a catalyst in a reactor to produce a butadiene-containing reaction product gas; and a rapid cooling step where the reaction product gas is cleaned in a rapid cooling tower with a rapid cooling agent, and, as the rapid cooling agent, amide water solution containing amide, water and an acid solvent is used.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing butadiene.

  As a method for industrially producing 1,3-butadiene (hereinafter also simply referred to as “butadiene”), BBP (mainly a mixture of hydrocarbons having 3 to 5 carbon atoms) obtained by naphtha cracking is extracted into a solvent. , Butane, butene, acetylenes, high boiling components and low boiling components are selectively removed.

As a method for producing butadiene, in addition to naphtha cracking, a method for producing butadiene from butene by a catalytic oxidative dehydrogenation reaction is also known. In this method, oxygen-containing compounds such as organic acids, aldehydes, ketones, and furans are generated in addition to the target butadiene. Among these by-products, a compound having a large boiling point difference between butadiene and a by-product and having no azeotropic point can be removed by distillation. However, acetaldehyde, which is one of by-products, has not only a small difference in boiling point from butadiene, but also has an azeotropic point, so that only an azeotropic composition can be removed by distillation. Further, since methacrolein is highly reactive with butadiene, it reacts with butadiene in the heating section of the distillation tower and loses butadiene.
In Patent Document 1, a raw material gas containing a monoolefin having 4 or more carbon atoms and a molecular oxygen-containing gas are supplied to a reactor, and a corresponding conjugated diene is produced by an oxidative dehydrogenation reaction in the presence of a catalyst. In the method for producing a conjugated diene having a reaction step for obtaining a gas, a production method in which the acetylene hydrocarbon concentration of the product gas is 0.016% by volume or less is described. In this method, a method of cooling the generated gas using cooling water is described.
Patent Document 2 includes a step of quenching a reaction gas containing butadiene produced by bringing n-butene into contact with a catalyst in a fluidized bed reactor, using a quenching tower having two or more sections, and the quenching tower Describes a method for producing butadiene in which the circulating fluid of at least one selected from Group IA, Group IIA and ammonia.
In Patent Document 3, a step of supplying a hydrocarbon containing a monoolefin having 4 or more carbon atoms and oxygen to generate a reaction product gas containing a conjugated diolefin, and feeding the reaction product gas into a quenching tower, And a step of washing with a quenching agent, and a method for producing a conjugated diolefin is described using an organic amine aqueous solution as the quenching agent.

JP 2010-90082 A JP 2012-67048 A International Publication No. 2012/157495 Pamphlet

Patent Document 1 describes a method of washing a reaction product gas with cooling water in a cooling step. However, the cooling water has a low ability to remove aldehydes and carboxylic acids by-produced by the reaction, and there is a possibility that by-products scattered in the subsequent process block the pipe.
Patent Document 2 describes a method in which at least one selected from Group IA, Group IIA and ammonia is used as the circulating liquid in the quenching tower. However, the circulating liquid can remove carboxylic acids, but has a low ability to remove aldehydes, and aldehydes scattered in the subsequent process react with butadiene to lower the production efficiency of butadiene. In particular, methacrolein easily reacts with butadiene and is preferably removed by a quenching tower.
Patent Document 3 describes a method using an organic amine aqueous solution as a coolant. As shown in Comparative Examples described later, the monoethanolamine aqueous solution used in Examples of Patent Document 3 has a high ability to remove acetaldehyde and methacrolein. However, monoethanolamine aqueous solution is highly consumed because it reacts with other aldehydes, ketones, and carboxylic acids.

  This invention is made | formed in view of the said problem, and it aims at providing the method which can manufacture butadiene with little content of acetaldehyde and methacrolein, suppressing consumption of a quenching agent.

  The present inventors removed butadiene having a low content of acetaldehyde and methacrolein by removing acetaldehyde and methacrolein with a quenching agent that can be selectively removed, and removing other by-products by distillation. Invented a method of manufacturing by suppressing the consumption of quenching agent. As a result of repeated studies, the present inventors have found that the above object can be achieved by using an aqueous amide solution containing amide, water and an acidic solvent as a quenching agent, and completed the present invention. That is, the present invention is as follows.

[1]
A reaction step in which a raw material gas containing n-butene and an oxygen-containing gas are brought into contact with a catalyst in a reactor to produce a reaction product gas containing butadiene, and the reaction product gas is washed with a quenching agent in a quenching tower. A method for producing butadiene, which comprises using an aqueous amide solution containing an amide, water and an acidic solvent as the quenching agent.
[2]
The method for producing butadiene according to [1], wherein the pH of the aqueous amide solution is controlled to 0.1 to 6.0.
[3]
The method for producing butadiene according to [1] or [2], wherein the amide is at least one selected from the group consisting of urea, formamide, acetamide, ethylamide, and acrylamide.

  According to the present invention, the consumption of the quenching agent can be suppressed by selectively removing acetaldehyde and methacrolein as by-products, and high-purity butadiene can be obtained.

FIG. 1 is a diagram showing an example of a quenching tower used in the method for producing butadiene of the present embodiment. FIG. 2 is a diagram illustrating an example of a quenching tower used in the method for producing butadiene of the present embodiment. FIG. 3 is a diagram showing an example of a quenching tower used in the method for producing butadiene of the present embodiment. FIG. 4 is a diagram showing an example of a quenching tower used in the method for producing butadiene of the present embodiment. FIG. 5 is a diagram schematically showing an example of a butadiene production apparatus of the present embodiment. FIG. 6 is a diagram schematically showing another example of the apparatus for producing butadiene of the present embodiment.

  Hereinafter, a mode for carrying out the present invention (hereinafter referred to as “the present embodiment”) will be described in detail. In addition, this invention is not limited to the following embodiment, It can implement by changing variously within the range of the summary.

[1] Method for Producing Butadiene The method for producing butadiene of this embodiment is a reaction in which a raw material gas containing n-butene and an oxygen-containing gas are brought into contact with a catalyst in a reactor to produce a reaction product gas containing butadiene. And a quenching step of washing the reaction product gas with a quenching agent in a quenching tower, and using an amide aqueous solution containing amide, water, and an acidic solvent as the quenching agent.

(1) Source gas and oxygen-containing gas In the present embodiment, the source gas refers to a gas containing n-butene, which is a monoolefin having 4 carbon atoms. In the raw material gas used in the present embodiment, the concentration of n-butene is preferably 40% by weight or more, more preferably 50% by weight or more, and further preferably 60% by weight or more. Specific n-butene corresponds to 1-butene and 2-butene. The ratio of 1-butene to 2-butene in n-butene is not particularly limited, and 1-butene can be arbitrarily used in the range of 0 to 100% by weight, and 2-butene can be arbitrarily used in the range of 100 to 0% by weight. . Further, 2-butene includes a trans isomer and a cis isomer, and these ratios can be arbitrarily used within the range of 100 to 0% by weight of the trans isomer and 0 to 100% by weight of the cis isomer, respectively.
This source gas may contain i-butene, and i-butene is preferably 10% by weight or less, more preferably 6% by weight or less, and further preferably 3% by weight or less with respect to n-butene. In addition to n-butane and i-butane, this raw material gas may contain a hydrocarbon having 3 or less carbon atoms and a hydrocarbon having 5 or more carbon atoms.
This raw material gas is, for example, catalytic conversion of C4 fraction by-produced by fluid catalytic cracking (FCC) of residual components obtained by extracting butadiene from C4 fraction by-produced by naphtha pyrolysis or by heavy oil fraction, ethylene or ethanol. From the C4 fraction produced as a by-product in the reaction, i-butene is converted into t-butyl alcohol (hereinafter also referred to as “TBA”), methyl-tert-butyl ether (hereinafter also referred to as “MTBE”), ethyl-tert-butyl ether (hereinafter referred to as “ETBE”). It can also be obtained by separation by a method of forming a compound having 8 carbon atoms by a dimerization reaction.

The raw material gas does not necessarily have to be highly pure, and any mixture or industrial grade can be used. For example, a component obtained by extracting butadiene from a C4 fraction by-produced by naphtha pyrolysis (hereinafter also referred to as “BBS”), a residual component obtained by further separating isobutene from BBS (hereinafter also referred to as “BBSS”), and a flow of a heavy oil fraction C4 fraction produced as a by-product in catalytic cracking (hereinafter also referred to as “FCC”), and the remaining component from which isobutene was further separated, C4 component obtained by dehydrogenation reaction or oxidative dehydrogenation reaction of n-butane, and ethylene dimerization N-butene obtained in this manner, the C4 component obtained by the catalytic conversion reaction of ethylene or ethanol, and the residual component from which isobutene is further separated can be used.
Isobutene can be separated by reacting with TBA and alcohol by hydration reaction, skeletal isomerization to MTBE, ETBE, n-butene, selective adsorption, dimerization, and the like. Ethylene can be obtained by naphtha pyrolysis, ethane pyrolysis, or ethanol dehydration reaction, and industrial ethanol and biomass ethanol can be used as ethanol. Biomass ethanol is ethanol obtained from plant resources. Specifically, it is not particularly limited. For example, ethanol obtained from fermentation of sugarcane, corn, etc., waste wood, thinned wood, rice straw, agricultural products, and other woody resources. Ethanol obtained is mentioned.

From the viewpoint of butadiene productivity, the n-butene concentration in the raw material gas is preferably 2% by volume or more with respect to the total of 100% by volume of the raw material gas and the oxygen-containing gas, and from the viewpoint of suppressing the load on the catalyst. 30 volume% or less is preferable. More preferably, it is 3 to 25% by volume. When the n-butene concentration in the raw material gas is high, accumulation of reaction products and coke deposition increase, and the catalyst life tends to be shortened due to catalyst deterioration.
The oxygen-containing gas refers to a gas containing oxygen. Normally, air is used, but a gas whose oxygen concentration is increased by mixing oxygen with air or a gas whose oxygen concentration is decreased by mixing air with an inert gas such as helium or nitrogen is used. You can also.

  The raw material gas containing n-butene and the oxygen-containing gas may contain paraffin, water, steam, hydrogen, nitrogen, carbon dioxide, carbon monoxide and the like in addition to the components described above. Examples of paraffin are not particularly limited, and examples thereof include methane, ethane, propane, butane, pentane, hexane, heptane, octane, and nonane. Moreover, after separating the target product butadiene from the reaction product gas, at least a part of the unreacted butene can be recycled to the fluidized bed reactor.

(2) Reactor For the production of butadiene by the catalytic oxidative dehydrogenation reaction of n-butene, for example, a fluidized bed reactor, a fixed bed reactor, or a moving bed reactor can be employed. A fluidized bed reactor is preferred because the catalyst can be easily extracted and added.

  The fluidized bed reactor has a reactor, a gas disperser provided therein, an insert for maintaining a good flow state and a cyclone as its main components, and a catalyst previously accommodated in the reactor. Is a reactor having a structure in which the gas is brought into contact with the raw material gas while being caused to flow by an air flow. A fluidized bed reactor described in a fluidized bed handbook (published by Baifukan Co., Ltd., 1999) can be used, but a bubble fluidized bed reactor is particularly suitable. The generated heat of reaction can be removed using a cooling pipe inserted in the reactor.

(3) Reaction step A raw material gas containing n-butene and an oxygen-containing gas are supplied to the reactor. The molar ratio of n-butene to oxygen is preferably 0.4 to 2.5, more preferably 0.6 to 2.1, in terms of n-butene / oxygen. If the molar ratio of n-butene to oxygen is 2.5 or less, the decomposition reaction of the produced conjugated diolefin tends to be suppressed, and if it is 0.4 or more, the reactivity of n-butene tends to improve. It is in.

  The method for introducing the raw material gas containing n-butene and the oxygen-containing gas into the reactor is not limited. The raw material gas containing n-butene and the oxygen-containing gas may be mixed and introduced into the reactor filled with the catalyst, or may be introduced independently. Further, the gas to be subjected to the reaction can be heated to a predetermined reaction temperature after being introduced into the reactor, but in order to continuously react efficiently, it is usually preferable to preheat and introduce it into the reactor. .

  The reaction temperature is preferably 300 to 420 ° C. When the reaction temperature is set to 300 ° C. or higher, conversion of n-butene occurs easily, and when the reaction temperature is set to 420 ° C. or lower, combustion decomposition of butadiene produced tends to be kept low. A more preferable reaction temperature is 300 to 400 ° C, particularly preferably 310 to 390 ° C. Since the oxidative dehydrogenation reaction from n-butene to butadiene is an exothermic reaction, the heat is usually removed so as to obtain a suitable reaction temperature. The reaction temperature can be adjusted to the above range by removing the reaction heat from the cooling pipe or by supplying heat from the heating device.

  The reaction pressure is preferably from atmospheric pressure to 0.8 MPaG. The contact time between the gas supplied to the reactor and the catalyst is 0.5 to 20 (sec · g / cc), preferably 0.6 to 10 (sec · g / cc). The contact time is defined by the following formula.

(Wherein, W is the catalyst charge (g), F is the total flow rate of the source gas and the oxygen-containing gas (NL / hour, NTP conversion value (0 ° C., converted to 1 atm)), T is the reaction temperature ( C), P represents the reaction pressure (MPaG).

  Butadiene is produced by contacting the catalyst, the raw material gas supplied to the reactor, and the oxygen-containing gas in the reactor. Since the yield and / or selectivity of the product depends on the raw material, the catalyst, the reaction temperature, etc., these conditions may be set as appropriate so that the yield and / or selectivity is a desirable value.

(4) Quenching step The method for producing butadiene of the present embodiment includes a step of feeding the reaction product gas into a quenching tower and washing it with a quenching agent (hereinafter also referred to as “quenching step”).

  In the quenching step, an amide aqueous solution (hereinafter also referred to as “amide aqueous solution”) containing amide, water and an acidic solvent is used as the quenching agent. It is preferable to further use an aromatic organic solvent in combination as the second quenching agent. When an aromatic organic solvent is used in combination as the second quenching agent, higher purity butadiene can be obtained.

  In the quenching step, for example, the reaction product gas is fed into the quenching tower from the bottom and rises in the quenching tower. For example, since an aqueous amide solution that is a quenching agent is sprayed in the quenching tower, the reaction product gas is washed in contact with the aqueous amide solution and flows out from the top of the tower. Further, when an aromatic organic solvent (hereinafter also referred to as “aromatic solvent”), which is the second quenching agent, is sprayed, the reaction product gas is also brought into contact with the aromatic solvent and washed.

  In the production of butadiene by catalytic oxidative dehydrogenation, in addition to the main reaction for producing butadiene from n-butene, for example, because it is an oxidation reaction, side reactions for producing oxygenated compounds such as carboxylic acids, aldehydes, and ketones, A secondary reaction in which the produced butadiene and by-products become reaction raw materials proceeds. By-products that have a large difference in boiling point from the target product, butadiene, and do not azeotrope, are preferably removed by distillation. However, since acetaldehyde has a small boiling point difference from butadiene and has an azeotropic point, it can be removed only by azeotropic composition by distillation. The product butadiene is used as a raw material for synthetic rubber and resin by polymerization reaction, but the presence of acetaldehyde inhibits the polymerization reaction, so in the case of butadiene production by catalytic oxidative dehydrogenation, the concentration of acetaldehyde in the exit gas of the quenching tower Is preferably 0.10% by weight or less, and more preferably 0.05% by weight or less. In addition, methacrolein has a large boiling point difference from butadiene and can be removed by distillation. However, when heated, it reacts with butadiene to produce 4-methyl-4-formyl-1-cyclohexene and loses butadiene. It is preferable to do. Accordingly, the concentration of methacrolein in the quenching tower outlet gas is preferably 0.30% by weight or less, and more preferably 0.25% by weight or less. Amides have the characteristic of reacting selectively with aldehydes. For example, when acetic acid, methacrylic acid, acetaldehyde, methacrolein, and acetone are contained in the reaction product gas, the acid component dissolves in the amide aqueous solution, and methacrolein and acetaldehyde react with the amide and are removed from the reaction product gas. . Acetone flows out to the subsequent step, but has low reactivity with butadiene and can be removed by a purification step in the subsequent step. By selectively removing highly reactive methacrolein and acetaldehyde that cannot be removed by distillation, and removing by-products that can be removed by distillation, the consumption of amide as a quenching agent is suppressed. Can do.

  On the other hand, high-boiling by-products such as benzoic acid, phthalic acid, phenol, benzophenone, and 9-fluorenone are sublimable and may block the piping at the exit of the quenching tower. In order to remove these by-products, in addition to quenching with an aqueous amide solution, it is also one of preferred embodiments to select a quenching agent that is more excellent in compatibility with by-products from the viewpoint of dissolution and removal. . That is, by using an aromatic organic solvent in addition to the amide aqueous solution as a quenching agent for the reaction product gas, a by-product having a high boiling point such as benzoic acid, phthalic acid, phenol, benzophenone, 9-fluorenone and the like. The effect of removing is obtained. The type and amount of the by-product varies depending on the reaction conditions such as the catalyst, temperature, and pressure as well as the raw materials, and the optimum quenching agent is selected according to the composition of the by-product. Therefore, selecting a quenching agent from the viewpoint of compatibility with the component to be removed is extremely useful for industrial production of butadiene.

  The quenching tower is preferably a multistage quenching tower having two or more compartments, and more preferably a multistage quenching tower having three or more compartments from the viewpoint of efficiently bringing a quenching agent into contact with the reaction product gas. In the quenching tower, the quenching agent extracted in each section is sprayed as a circulating liquid above the extraction position, and after cooling the reaction product gas and removing by-products, it becomes the extracted liquid in each section. . On the other hand, the gas containing butadiene flowing out from the top of the quenching tower is sent to the next step. Of the extracted quenching agent, the aqueous amide solution is preferably cooled and then returned to the quenching tower and sprayed again. Of the extracted quenching agent, the aromatic solvent is preferably adjusted to a liquid temperature of room temperature to 70 ° C. according to the boiling point, solubility, and sublimation property of the aromatic by-product. It is preferable to spray again. Moreover, in order to reduce the load of the degassing operation of the inert gas in the purification process described later, the outlet gas temperature of the quenching tower is preferably controlled to an appropriate temperature. For this control, it is effective that the quenching agent is cooled to an appropriate temperature before re-spraying the aqueous amide solution and supplied to the upper stage of the quenching tower. At this time, the temperature of the quenching agent is controlled to 80 ° C. or lower, preferably 0 to 70 ° C., and the outlet gas temperature of the quenching tower is controlled to 70 ° C. or lower, preferably 5 to 60 ° C. The quenching tower can be independently provided, for example, the first quenching tower is cleaning the reaction product gas with an aromatic solvent, and the second quenching tower is cleaning the reaction product gas with an amide aqueous solution.

  The supply amount of the quenching agent may be appropriately set according to the type and temperature of the quenching agent, the type and amount of by-products to be removed, the size and number of stages of the quenching tower, and the like. In the aspect of reusing the extracted quenching agent, a necessary supply amount may be obtained by adding a new quenching agent by an amount that the quenching agent to be reused is insufficient with respect to the necessary amount.

  When different quenching agents are used in each stage in a multistage quenching tower, depending on the combination of quenching agents, the extracted liquid becomes a mixture of the aqueous phase and the oil phase. Prior to this, it is preferable that the extracted liquid is oil-water separated with a decanter. For example, when an aqueous amide solution and an aromatic organic solvent are used in combination as a quenching agent, the effluent is supplied to a decanter and separated into oil and water, and then the aqueous amide solution and aromatic organic solvent are resprayed on each stage Is a preferred embodiment.

A spray nozzle can be used for spraying the quenching agent, and the spray amount, the number of spray nozzles, and the arrangement may be appropriately determined in consideration of the contact between the quenching agent and the reaction product gas and the amount of reaction product gas fed. . It is also one of preferred embodiments that an empty tower, a tray, and a packing are provided in each section in the quenching tower.
The aqueous amide solution before washing supplied to the quenching tower is at room temperature, and the pH during circulation is preferably controlled to 0.1 to 6.0, preferably 0.5 to 4. By making the aqueous amide solution acidic at pH 6.0 or lower, the carbonyl group of the aldehyde is activated and the reaction rate with the amide increases. Since the surface of the quenching tower is corroded when the amide aqueous solution is lower than pH 0.1, the aqueous amide solution is controlled to have a pH of 0.1 or more. When circulating the washed amide aqueous solution as a quenching agent, always monitor the pH of the amide aqueous solution with a pH meter, and if the pH of the amide aqueous solution approaches the upper or lower limit of the above range, add it to the amide aqueous solution. It is preferable to control the pH of the amide aqueous solution by the amount of the acidic solvent to be produced. The acidic solvent used for controlling the pH is not particularly limited, but acetic acid, nitric acid, and sulfuric acid are preferable. In addition, the reaction product gas supplied from the reactor to the quenching tower may contain organic acids such as acetic acid, benzoic acid, acrylic acid, and methacrylic acid. May contain solvents. Therefore, even if the initial aqueous amide solution does not contain an acidic solvent, an acidic solvent may be contained if the quenching agent is recycled. The aqueous amide solution may be supplied to the quenching tower adjusted in advance to a predetermined concentration, or may be mixed and supplied before supplying the amide, water, and acidic solvent to the quenching tower. As the quenching agent used for circulation in the quenching tower and washing of the reaction product gas, in addition to the aqueous amide solution and the aromatic solvent, water may be used independently for each section of the quenching tower. The waste amide aqueous solution and the waste aromatic solvent containing by-products discharged as the partition liquid of the quenching tower can be incinerated. Since the waste amide aqueous solution does not contain an alkali metal that corrodes the refractory brick of the incinerator, there is no risk of damaging the refractory brick.

Examples of the amide contained in the aqueous amide solution include, but are not limited to, a compound containing a —CONH ₂ group, and examples include amides such as urea, formamide, acetamide, ethylamide, and acrylamide. These amides may be used alone or in combination of two or more. A preferred amide is urea. It is presumed that acetaldehyde and methacrolein are effectively removed because the amino group of amide reacts with the carbonyl group of acetaldehyde and methacrolein to produce an imine derivative. Moreover, since the reactivity of an amide is gentle compared with an organic amine, it is estimated that the aldehyde with higher reactivity than a ketone is selectively removed.

  When an aqueous amide solution is used as a quenching agent, the amide concentration in the aqueous amide solution is preferably 1 to 30% by weight, and more preferably 3 to 20% by weight from the viewpoint of the removal efficiency of aldehydes and the like. When the amide concentration is 1% by weight or more, the reaction rate with the aldehyde can be sufficiently increased, and when the amide concentration is 30% by weight or less, the aldehyde selectivity can be increased.

  Although it does not specifically limit as an example of an aromatic solvent, For example, o-xylene, m-xylene, p-xylene, mixed xylene, toluene, ethylbenzene, diethylbenzene, 1,2,3,4,5,6,7,8 -Decahydronaphthalene, cumene, branched and straight chain alkylbenzene, pseudocumene and the like. Preferred aromatic solvents are o-xylene, m-xylene, p-xylene, mixed xylene and toluene, and particularly preferred aromatic solvents are o-xylene, m-xylene and toluene. These aromatic solvents may be used alone or in combination of two or more. Benzoic acid, which is an organic acid, has low water solubility, so it is likely to flow out of the quenching tower accompanying the reaction product gas, and even if it is quenched with an amide aqueous solution, The present inventors have experimentally confirmed that it is no longer detected by combining the washing with the aromatic solvent. The reason for this is that benzoic acid, which is the same aromatic compound as the aromatic solvent, has high compatibility with the aromatic solvent due to the strong π-π electron interaction between the aromatic rings, and is effective from the reaction product gas. It is thought that it was dissolved and removed. Aromatic compounds such as phthalic acid, phenol, benzophenone, and 9-fluorenone are also removed from the reaction product gas by washing with an aromatic solvent. Therefore, a removal mechanism similar to benzoic acid can be considered.

  The amount of aromatic by-products such as benzoic acid, phthalic acid, phenol, benzophenone, and 9-fluorenone varies depending on the concentration and composition of n-butene in the hydrocarbon raw material, and reaction conditions, and further conditions for quenching tower operation Therefore, it is difficult to specify the concentration of benzoic acid, phthalic acid, phenol, benzophenone, 9-fluorenone, etc. in the extracted liquid from each section of the quenching tower. However, according to the study by the present inventors, if the concentration in the aromatic solvent extracted from each compartment of benzoic acid, which is the main component of the aromatic reaction byproduct flowing out from the quenching tower, is 500 ppm by weight or more. It may be judged that aromatic by-products such as benzoic acid, phthalic acid, phenol, benzophenone and 9-fluorenone are sufficiently removed from the reaction product gas.

  In general, the quenching tower is connected to the reactor without pressure adjustment, and is almost equal to the pressure of the reactor. Therefore, in order to optimize the pressure in the reactor, the pressure in the quenching tower is preferably 0.01 to 0.4 MPaG, more preferably 0.02 to 0.3 MPaG, and still more preferably 0.03 to 0.2 MPaG. .

  In the butadiene production method of the present embodiment, it is preferable that the quenching tower has a plurality of upper and lower sections. Hereinafter, the case where the quenching tower has a plurality of upper and lower sections will be specifically described with reference to the drawings.

  FIG. 1 shows an example of a quenching tower 2 used in the method for producing butadiene of this embodiment. The quenching tower 2 is an example having two sections. Chimneys 21 are fitted in the middle stage, and sections are formed above and below the chimney 21, respectively. A packed bed 22 is provided on the chimney 21. An aqueous amide solution is sprayed as a quenching agent from a spraying device 23B installed under the chimney 21 and a spraying device 23A installed on the packed bed 22, respectively.

  The chimney 21 is open at the center. The opening is provided with a weir protruding upward. As shown in FIG. 1, the sprayed quenching agent accumulates in a tray installed integrally on the chimney 21 (hereinafter, the quenching agent accumulated in the quenching tower is not shown) and flows out to the circulation path. To do. The sprayed quenching agent also collects at the bottom of the tower and flows out to the circulation path. The quenching agent that has flowed out is supplied to the spraying devices 23A and 23B via the pumps 24A and 24B, and is circulated. The packed bed 22 contains a packing material. In the said packed bed 22, both are made to contact efficiently, inhibiting the passage of a quenching agent and gas. The kind of filler is not particularly limited, and known fillers such as Raschig rings, cascade rings, and pole rings can be used. The method of filling is not particularly limited, and may be regular or irregular.

  The reaction product gas flowing out from the reactor is introduced into the quenching tower 2 from the bottom of the tower, and rises in the tower while in contact with the quenching agent. Then, as shown in FIG. 1, some gas passes through the gap between the chimneys 21, passes through the packed bed 22, and flows out from the top of the tower (hereinafter, the gas flow in the quenching tower is not shown).

  The quenching tower 2 shown in FIG. 2 is the same as the example shown in FIG. 1 except that a decanter is provided in the quenching agent circulation path and two types of quenching agents are used, and only the differences will be described below. . An aqueous amide solution is sprayed from the spraying device 23A, and an aromatic solvent is sprayed from the spraying device 23B. The tray installed integrally on the chimney 21 and the quenching agent accumulated in the tower bottom flow into the decanters 25A and 25B through the circulation paths. In the quenching tower 2 shown in FIG. 2, two types of quenching agents are used. The quenching agent flowing into the circulation path contains an aqueous phase and an oil phase. The aqueous phase and the oil phase of the quenching agent are separated by the decanters 25A and 25B. The decanter outlet is set so that an aqueous amide solution is supplied to the spraying device 23A and an oily aromatic solvent is supplied to the spraying device 23B. The oil phase separated by the decanter 25A and the aqueous phase separated by the 25B may be discarded or recycled. In the case of recycling, the oil phase separated at 25A can be supplied to the pump of 24B, and the water phase separated at 25B can be supplied to the pump of 24A. Alternatively, only the oil phase may be recycled and the aqueous phase discarded.

  The quenching tower 2 shown in FIG. 3 is provided with two chimneys and two packed beds, spray devices 23A and 23B are provided on the respective packed beds 22A and 22B, and spray devices 23C are provided below the chimney 21B. Except for the quenching tower having three sections, it is the same as the example shown in FIG. After the amide aqueous solution supplied from each spraying device comes into contact with the gas in the tower, it is recovered by the tray installed integrally on the chimney 21A, the tray installed integrally on 21B, and the tower bottom. Then, they are returned to the spraying devices 23A, 23B, and 23C through the circulation paths, respectively.

  The quenching tower 2 shown in FIG. 4 is the same as the apparatus shown in FIG. 3 except that a decanter is provided in each circulation path and two types of quenching agents are used. The amide aqueous solution is supplied from the spraying devices 23A and 23B, and the aromatic solvent is supplied from the spraying device 23C. The quenching agent supplied from each spraying device is collected in the tray installed integrally on the chimney 21A, the tray installed integrally on 21B, and the tower bottom, and then provided in each circulation path. The decanters 25A, 25B and 25C are separated into an oil phase and an aqueous phase. The decanter outlet is set so that the amide aqueous solution is supplied to the spraying devices 23A and 23B, and the aromatic solvent is supplied to the spraying device 23C.

When the quenching tower has a plurality of upper and lower compartments and an amide aqueous solution and an aromatic solvent are used together as a quenching agent, an aromatic solvent is used as the quenching agent in the lowermost compartment of the plurality of compartments, and the bottom As the quenching agent in the compartment above the compartment, it is preferable to use an amide aqueous solution. When the aromatic solvent is used as a quenching agent, the by-product is removed by dissolution in the aromatic solvent. For this reason, the used aromatic solvent can be reused by distillation or the like. As a result, the overall manufacturing cost is advantageously reduced. On the other hand, when the aqueous amide solution is used as a quenching agent, the by-product is reacted with the amide to remove it. Therefore, unlike the case of the aromatic solvent, it is difficult to separate the aqueous amide solution from the by-product and reuse the aqueous amide solution. When the quenching tower has a plurality of upper and lower compartments, the amount of by-products is usually the highest when the reaction product gas is introduced into the bottom of the quenching tower, and is removed and reduced every time the compartment is passed upward. . Therefore, when an aqueous amide solution and an aromatic solvent are used in combination as a quenching agent, it is necessary to select a reusable aromatic solvent as the quenching agent in the lowest compartment that comes into contact with the reaction product gas first. From the viewpoint of From the above, the quenching tower has a plurality of upper and lower sections, and in the case of a general quenching tower configuration in which a reaction product gas is introduced from the tower bottom side of the quenching tower, an aromatic solvent is used as a quenching agent at the bottom stage. It is a preferable aspect in terms of cost to use and remove a relatively large by-product by dissolving it, and then to remove the remaining by-product by reacting with an aqueous amide solution. In the quenching tower 2 shown in FIG. 4, the aromatic solvent can be sprayed from either of the spraying devices 23A and 23B by changing the inlets of the decanters 25A and 25B.
1 to 4, the supply pipes and discharge pipes for the quenching agent such as the amide aqueous solution and the cooling means installed in front of the spraying device are omitted, but these means are provided as necessary. It's okay.

(5) Purification step The reaction product gas flowing out from the quenching tower is obtained by known techniques such as Japanese Patent Publication No. 45-17407, Japanese Patent Publication No. 60-126235 and Japanese Patent Publication No. 3-48891, Synthetic Rubber Handbook (92 -100 pages, 1969), PETROTECH, Vol. 2, No. 4 (59-65 pages, 1978) and the like. For example, after introducing the gas flowing out from the top of the quenching tower into the butadiene extraction distillation tower described in the above-mentioned synthetic rubber handbook and separating butadiene and butane / butenes, high-boiling components such as 2-butene are removed in the butadiene purification tower. It can be removed and product butadiene can be recovered. At this time, the product butadiene is preferably purified to a purity of 99.0% or more.

[2] Catalyst Hereinafter, the catalyst used in the present embodiment will be described.

  The catalyst used in the present embodiment is not particularly limited as long as it is a catalyst in which an oxide containing a metal is supported on a carrier. Examples of such a metal include molybdenum (Mo), bismuth (Bi), iron (Fe), Nickel (Ni), potassium (K), rubidium (Rb), magnesium (Mg), cesium (Ce), cobalt (Co), tungsten (W) and the like are preferable, and among them, Mo, Bi and Fe are more preferable. The composition of the metal is adjusted so as to form a desired oxide, and it is considered that oxidative dehydrogenation of butadiene from n-butene is performed by lattice oxygen in the oxide.

  The carrier can be effectively used in the range of 30 to 70% by weight, preferably 40 to 60% by weight, based on the total of the carrier and the oxide. The carrier is preferably silica, alumina, titania or zirconia, and a more preferred carrier is silica. Silica is an inert carrier compared to other carriers, and has a good binding action with the catalyst without reducing the activity and selectivity of the catalyst with respect to the target product. In addition, by supporting the oxide on the support, physical properties suitable for a fluidized bed reaction such as particle shape / size / distribution, fluidity, and mechanical strength can be imparted.

[3] Butadiene production apparatus The butadiene production apparatus of this embodiment preferably includes a reactor in which a catalyst containing a metal oxide and a carrier is accommodated, and a quenching tower connected to the reactor.
The said manufacturing apparatus can be used suitably for the manufacturing method of the butadiene mentioned above. Specifically, for example, a hydrocarbon containing n-butene and oxygen are supplied to a reactor in the production apparatus, and a reaction product gas containing produced butadiene flows into the quenching tower, and the inside of the quenching tower The reaction product gas is washed with a quenching agent. As the quenching agent, it is preferable to use an aqueous amide solution and further use an aromatic organic solvent in combination.

  Hereinafter, with reference to FIG. 5 and FIG. 6, the suitable aspect of the butadiene manufacturing apparatus of this embodiment is demonstrated in detail.

  FIG. 5 is a diagram schematically showing an example of a butadiene production apparatus of the present embodiment. The reaction product gas flowing out from the reactor is sent to the quenching tower from the bottom, and is washed in contact with the amide aqueous solution, or the amide aqueous solution and the aromatic solvent in the quenching tower. The washed reaction product gas flows out from the top of the tower and is introduced into the bottom of the absorption tower. The reaction product gas introduced into the bottom of the absorption tower is absorbed in a solvent (for example, xylene, mixed xylene or toluene) in the absorption tower, and flows out from the bottom as a butadiene-containing solution. On the other hand, off-gas flows out from the top of the absorption tower. The butadiene-containing solution flowing out from the bottom of the absorption tower is introduced into the upper part of the stabilizer. When an inert gas (inert gas) is contained in the raw material component, the stabilizer separates the inert gas from the butadiene-containing solution. The butadiene-containing solution from which the inert gas has been separated flows out from the bottom of the stabilizer and is introduced into the flash column. After the solvent is separated from the butadiene-containing solution in the flash tower, a solution containing butadiene and water flows out from the top of the tower and is supplied to the cooler. The crude butadiene from which water has been separated by the cooler is supplied to the middle stage of the first extractive distillation column. In the first extractive distillation column, a solvent (for example, dimethylformamide) is sprayed from the top of the column, and a solution of crude butadiene is generated and flows out from the bottom of the column. The solution of the crude butadiene that has flowed out is introduced into the stripping tower, and for example, butane is separated from the top of the tower. In the stripping tower, the solvent of the crude butadiene solution is separated, and the crude butadiene discharged from the top of the tower is introduced into the second extractive distillation tower. In the second extractive distillation column, as in the first extractive distillation column, the solvent is sprayed from the top of the column to produce a crude butadiene solution. The second extractive distillation column is operated at a temperature at which a component containing butadiene flows out from the top of the column and a solvent in which impurities such as acetylene are dissolved is separated from the bottom of the column. Thereby, crude butadiene flows out from the top of the second extractive distillation column. When the low boiling point compound (for example, methylacetylene) and the high boiling point compound (for example, 2-butene) are separated from the crude butadiene flowing out from the second extractive distillation column in the first and second distillation columns, can get.

  FIG. 6 is a diagram schematically showing another example of the apparatus for producing butadiene of the present embodiment. The reactor, quenching tower, and tower after the first extractive distillation tower in the apparatus shown in FIG. 6 are the same as in the example shown in FIG. 5, and only the differences will be described next. The reaction product gas washed in the quenching tower is introduced into a dehydration tower filled with a dehydrating agent such as molecular sieve, flows out from the tower bottom, and is supplied to the solvent absorption tower. The reaction product gas comes into contact with the solvent sprayed in the solvent absorption tower to produce a butadiene-containing solution. The produced butadiene-containing solution flows out from the tower bottom and is introduced into the degassing tower and the solvent separation tower. When the inert gas (inert gas) is contained in the raw material component, the inert gas is separated from the butadiene-containing solution in the deaeration tower. And a solvent is isolate | separated from a butadiene containing solution with a solvent separation tower, and a crude butadiene is obtained.

  In the examples shown in FIGS. 5 and 6, the description of the compressor, drain pot, heat exchanger, etc. is omitted, but these are necessary for the operation or efficiency of the apparatus, and for the purpose of effective use of heat. And can be added as appropriate. For example, referring to the devices described in JP-A-60-193931, JP-A-2003-128595, and JP-A-2010-90082 is not limited to adding a compressor, a drain pot, a heat exchanger, and the like. It is effective in. These prior documents can also be referred to in terms of the operating temperature, pressure, type of solvent, etc. of the distillation column.

  EXAMPLES The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the examples described below.

(Response results)
In the examples and comparative examples, the n-butene conversion, 1,3-butadiene selectivity, and yield used to express the reaction results were defined by the following equations.

(Reactor)
As a fluidized bed reaction type reactor, a SUS304 fluidized bed reactor having a tube diameter of 3 inches and a height of 950 mm was used. The oxygen-containing gas was supplied from the bottom of the reactor, and the source gas containing n-butene was supplied from a nozzle located 150 mm above the bottom of the reactor.

(Raw material gas containing n-butene)
BBSS or n-butene was used as a raw material gas containing n-butene. BBSS has a C4 component composition molar ratio of 1-butene: 2-trans-butene: 2-cis-butene: isobutene: n-butane: isobutane: butadiene = 41.30: 17.70: 13.50: 5. 60: 16.10: 4.70: 1.10. n-butene has a C4 component composition molar ratio of 1-butene: 2-trans-butene: 2-cis-butene: isobutene: n-butane: isobutane: butadiene = 98.00: 0.05: 0.05: It was 0.85: 0.99: 0.03: 0.03.
(Oxygen-containing gas)
Air was diluted with nitrogen as the oxygen-containing gas.

  The reaction was carried out at a concentration of n-butene of 2 to 30% by weight. n-butene / oxygen was set to 0.4 to 2.5. The total flow rate of the source gas containing n-butene and the oxygen-containing gas was supplied to the reactor at 920 NL / hour (NTP conversion).

(Reaction conditions)
The reaction was performed under the conditions of reaction temperature T = 340 to 390 ° C., reaction pressure P = 0.05 MPaG, and catalyst packed weight W = 1580 to 1980 g.

(Contact time)
The contact time was defined by the following formula.
(Wherein, W is the catalyst charge (g), F is the raw material mixed gas flow rate (NL / hour, NTP conversion), T is the reaction temperature (° C.), and P is the reaction pressure (MPaG))

(Analysis of reaction product gas)
The analysis of the reaction product gas was performed by gas chromatography (GC-2010 (manufactured by Shimadzu Corporation)) directly connected to a fluidized bed reactor, analysis column: HP-ALS (manufactured by Agilent J & W), carrier gas: helium, column temperature: gas injection Then, hold at 100 ° C. for 8 minutes, then heat up to 195 ° C. at 10 ° C./minute, then hold at 195 ° C. for 40 minutes, TCD (thermal conductivity detector) / FID (hydrogen flame ion detector) (Setting temperature: 250 ° C.).

(Quenching tower)
As the quenching tower, a quenching tower made of SUS304 having a can part (tower bottom) having a tube diameter of 200 mm and a height of 300 mm and a tower part (quenching part) having a tube diameter of 100 mm and a height of 1000 mm at the upper part thereof was used. The quenching section was divided into three stages, and the liquid extracted from the upper stage, the middle stage, and the lower stage was sprayed on the stages extracted at 100, 100, and 100 L / hour, respectively.

(Analysis of quenching tower bottom liquid)
The analysis of the quenching tower bottom liquid was performed in the following two ways.
(1) Gas chromatography (GC-2010 (manufactured by Shimadzu Corporation), analytical column: CPVolamine (manufactured by VARIAN), carrier gas: helium, column temperature: held at 40 ° C. for 10 minutes, and then increased to 300 ° C. at 10 ° C./min. Temperature / holding, FID (hydrogen flame ion detector) set temperature: 250 ° C.).
(2) Gas chromatograph mass spectrometer (GCMS-QP2010Plus (manufactured by Shimadzu Corporation); GC analytical column: DB-WAX (manufactured by Agilent J & W), carrier gas: helium, column temperature: held at 60 ° C. for 11 minutes after gas injection. After that, the temperature is raised to 135 ° C. at 7.5 ° C./min, and then to 250 ° C. at 11.5 ° C./min, and held for 20 minutes; ionization mode: electron ionization (EI) MS ion source temperature: 200 ° C. MS sample chamber temperature: 250 ° C.).

(Unit of quenching agent)
The unit of quenching agent was defined by the following formula.

Example 1
An oxide (a) the composition of the catalyst metal element is represented by _{Mo 12 Bi 0.6 0Fe 1.8 Ni 5.0} K 0.09 Rb 0.05 Mg 2.0 Ce 0.75, was used catalyst supported on 50% by weight of the silica.

(B) Production reaction of butadiene 1980 g of (a) catalyst was placed in a fluidized bed reactor made of SUS304 having a tube diameter of 3 inches and a height of 950 mm. BBSS flow rate = 75 NL / hour, air = 228 NL / hour, nitrogen = 617 NL / hour (total flow rate F = 920 NL / hour), supplied to the reactor, reaction temperature T = 360 ° C., reaction pressure P = 0.05 MPaG Reaction was performed by contacting with the catalyst (a) under the conditions to obtain a reaction product gas. At this time, the contact time with the catalyst was 5.0 (g · sec / cc).

  The analysis of the reaction product gas was performed as described above by gas chromatography directly connected to the reactor and quenching tower. As for the reaction results 24 hours after the start of the reaction, the n-butene conversion rate was 95.9%, the butadiene selectivity was 82.8%, and the butadiene yield was 79.4%.

(C) Rapid cooling step The reaction product gas obtained in the step (b) above is SUS304 having a quenching section (tube diameter 100 mm, height 1000 mm) at the top of the quench tower (bottom (tube diameter 200 mm, height 300 mm)). ). 10 wt% aqueous urea solution adjusted to pH 1.8 with nitric acid was sprayed from the upper, middle and lower stages of the quenching tower as quenching agents at 100 L / hr, respectively, and exhaust gas was obtained from the top of the quenching tower. . At this time, the temperature of the exhaust gas from the top of the quenching tower was 50 ° C., the concentration of acetaldehyde in the exhaust gas after 24 hours was 0.05% by weight, and the concentration of methacrolein was 0.16% by weight. It was. The basic unit of urea was 0.054 kg-urea / kg-butadiene.

(D) Purification of butadiene Using the apparatus shown in FIG. 6, the exhaust gas after quenching was subjected to a dehydration step, a recovery step, a deaeration step, a butadiene separation step, and a crude butadiene purification step. More specifically, a purification device is assembled in the same manner as the downstream portion of the quench tower in FIG. 1 of JP 2010-90082 A, and the exhaust gas from the top of the quenching tower is separated from condensed water, pressurized by a compressor, After recooling and water separation, it was introduced into a dehydration tower packed with molecular sieves. The dehydrated gas was introduced into the recovery tower and brought into countercurrent contact with dimethylformamide set at a liquid temperature of 30 to 40 ° C. The obtained butadiene solution was introduced into an extractive distillation column and purified to obtain butadiene having a purity of 99.5%.

(Example 2)
Production of butadiene and quenching of the reaction product gas in the same manner as in Example 1 except that a 1 wt% aqueous urea solution having a pH adjusted to 0.1 was used as the reaction product gas quenching agent in the step (c). Purification of butadiene was performed. The concentration of acetaldehyde in the exhaust gas from the top of the quenching tower after 24 hours was 0.07% by weight, and the concentration of methacrolein was 0.17% by weight. The basic unit of urea was 0.049 kg-urea / kg-butadiene. The obtained butadiene solution was introduced into an extractive distillation column and purified to obtain butadiene having a purity of 99.4%.

(Example 3)
Production of butadiene and quenching of the reaction product gas in the same manner as in Example 1 except that a 30 wt% urea aqueous solution whose pH was adjusted to 4.0 was used as the reaction product gas quenching agent in the step (c). Purification of butadiene was performed. The concentration of acetaldehyde in the exhaust gas from the top of the quenching tower after 24 hours was 0.10% by weight, and the concentration of methacrolein was 0.28% by weight. The basic unit of urea was 0.039 kg-urea / kg-butadiene. The resulting butadiene solution was introduced into an extractive distillation column and purified to obtain butadiene having a purity of 99.0%.

Example 4
Production of butadiene in the same manner as in Example 1 except that BBSS flow rate in the step (b) = 152 NL / hour, air = 551 NL / hour, nitrogen = 199 NL / hour (total flow rate F = 920 NL / hour), The reaction product gas was quenched and butadiene was purified. The concentration of acetaldehyde in the exhaust gas from the top of the quenching tower after 24 hours was 0.07% by weight, and the concentration of methacrolein was 0.18% by weight. The basic unit of urea was 0.057 kg-urea / kg-butadiene. The obtained butadiene solution was introduced into an extractive distillation column and purified to obtain butadiene having a purity of 99.3%.

(Example 5)
In the step (b), the amount of catalyst is 1580 g, the raw material gas is n-butene (flow rate = 75 NL / hour), the air flow rate is 295 NL / hour, the nitrogen flow rate is 550 NL / hour (total flow rate F = 920 NL). Except that, the production of butadiene, the quenching of the reaction product gas, and the purification of butadiene were carried out in the same manner as in Example 1. In the step (b), the contact time with the catalyst was 4.0 (g · sec / cc). n-butene has a C4 component composition molar ratio of 1-butene: 2-trans-butene: 2-cis-butene: isobutene: n-butane: isobutane: butadiene = 98.00: 0.05: 0.05: It was 0.85: 0.99: 0.03: 0.03.

  The analysis of the reaction product gas was performed as described above by gas chromatography directly connected to the reactor and quenching tower. As for the reaction results 24 hours after the start of the reaction, the conversion of n-butene was 98.2%, the selectivity of butadiene was 88.6%, and the butadiene yield was 87.0%.

  In the step (c), the temperature of the exhaust gas from the top of the quenching tower is 50 ° C., the concentration of acetaldehyde in the exhaust gas after 24 hours is 0.02% by weight, and the concentration of methacrolein is 0.2%. It was 04% by weight. The basic unit of urea was 0.038 kg-urea / kg-butadiene. The obtained butadiene solution was introduced into an extractive distillation column and purified to obtain butadiene having a purity of 99.5%.

(Example 6)
In the same manner as in Example 1, except that a 10 wt% aqueous urea solution whose pH was adjusted to 2.5 with acetic acid was used as a quenching agent for the reaction product gas in the step (c), production of butadiene and reaction product gas Quenching and butadiene purification were performed. The concentration of acetaldehyde in the exhaust gas from the top of the quenching tower after 24 hours was 0.08% by weight, and the concentration of methacrolein was 0.22% by weight. The basic unit of urea was 0.041 kg-urea / kg-butadiene. The obtained butadiene solution was introduced into an extractive distillation column and purified to obtain butadiene having a purity of 99.4%.

(Example 7)
As a quenching agent for the reaction product gas in the step (c), a 10 wt% urea aqueous solution adjusted to pH 1.8 with sulfuric acid is sprayed at 100 L / hour from the upper stage of the quenching tower, and the middle and upper stages of the quenching tower are sprayed. Except that toluene was sprayed at 100 L / hour, butadiene production, reaction product gas quenching, and butadiene purification were performed in the same manner as in Example 1. The concentration of acetaldehyde in the exhaust gas from the top of the quenching tower after 24 hours was 0.05% by weight, and the concentration of methacrolein was 0.18% by weight. The basic unit of urea was 0.053 kg-urea / kg-butadiene. The obtained butadiene solution was introduced into an extractive distillation column and purified to obtain butadiene having a purity of 99.5%.

(Example 8)
Production of butadiene and quenching of the reaction product gas in the same manner as in Example 1 except that a 10% by weight aqueous solution of acetamide having a pH adjusted to 1.8 was used as the reaction product gas quenching agent in the step (c). Purification of butadiene was performed. The concentration of acetaldehyde in the exhaust gas from the top of the quenching tower after 24 hours was 0.08% by weight, and the concentration of methacrolein was 0.20% by weight. The basic unit of urea was 0.050 kg-urea / kg-butadiene. The obtained butadiene solution was introduced into an extractive distillation column and purified to obtain butadiene having a purity of 99.4%.

(Comparative Example 1)
Production of butadiene, quenching of the reaction product gas, and purification of butadiene were carried out in the same manner as in Example 1 except that water was used as the quenching agent for the reaction product gas in the step (c). The concentration of acetaldehyde in the exhaust gas from the top of the quenching tower after 24 hours was 0.15% by weight, and the concentration of methacrolein was 0.36% by weight. The resulting butadiene solution was introduced into an extractive distillation column and purified to obtain butadiene having a purity of 98.6%.

(Comparative Example 2)
Production of butadiene, quenching of the reaction product gas, purification of butadiene, as in Example 1, except that a 25% by weight aqueous solution of caustic soda having a pH of 12.6 was used as a quenching agent for the reaction product gas in the quenching step of (c) above. Went. The concentration of acetaldehyde in the exhaust gas from the top of the quenching tower after 24 hours was 0.13% by weight, and the concentration of methacrolein was 0.35% by weight. The basic unit of caustic soda was 0.024 kg-caustic soda / kg-butadiene. The obtained butadiene solution was introduced into an extractive distillation column and purified to obtain butadiene having a purity of 98.7%.

(Comparative Example 3)
Production of butadiene, quenching of the reaction product gas, purification of butadiene, as in Example 1, except that 25 wt% monoethanolamine having a pH of 8.7 was used as the reaction product gas quenching agent in the step (c). Went. The concentration of acetaldehyde in the exhaust gas after 24 hours was 0.04% by weight, and the concentration of methacrolein was 0.05% by weight. The basic unit of monoethanolamine was 0.086 kg-monoethanolamine / kg-butadiene. Thus, it was found that when the monoethanolamine aqueous solution is used as a quenching agent for the reaction product gas, it also reacts with aldehydes other than acetaldehyde, ketones, and carboxylic acids, so that the amount of consumption increases. The obtained butadiene solution was introduced into an extractive distillation column and purified to obtain butadiene having a purity of 99.5%.

(Comparative Example 4)
In the same manner as in Example 1, except that a 30 wt% aqueous urea solution mixed with water and urea was used as the reaction product gas quenching agent in the step (c), butadiene production, reaction product gas quenching, Purification was performed. The concentration of acetaldehyde in the exhaust gas after 24 hours was 0.12% by weight, and the concentration of methacrolein was 0.31% by weight. The basic unit of urea was 0.014 kg-urea / kg-butadiene. The resulting butadiene solution was introduced into an extractive distillation column and purified to obtain butadiene having a purity of 98.5%.

  For example, conjugated diolefins corresponding to these monoolefins are produced by catalytic oxidative dehydrogenation reaction using hydrocarbons containing monoolefins having 4 or more carbon atoms and molecular oxygen using a catalyst containing a metal oxide and a support. In this regard, in the production method of the present invention, it is possible to produce a conjugated diolefin that can be suitably used as a raw material for synthetic rubber, resin, etc., by sufficiently reducing impurities that inhibit the polymerization of the conjugated diolefin in the rapid cooling step. it can.

1: reactor, 2: quenching tower, 3: absorption tower, 4: stabilizer, 5: flash tower, 6: cooler, 7: extractive distillation tower, 8: stripping tower, 9: extractive distillation tower, 10: distillation tower 11: distillation column, 12: butadiene, 13: dehydration column, 14: solvent absorption column, 15: degassing column, 16: solvent separation column, 21: chimney, 21A: chimney, 21B: chimney, 21C: chimney, 22 : Packed bed, 22A: packed bed, 22B: packed bed, 22C: packed bed, 23A: spraying device, 23B: spraying device, 23C: spraying device, 23D: spraying device, 24A: pump, 24B: pump, 24C: pump 24D: pump, 25A: decanter, 25B: decanter, 25C: decanter, 25D: decanter, 31: reaction product gas, 32: reaction product gas after quenching (washing), 33: gas flow, 41: quenching agent

Claims (3)

  A reaction step in which a raw material gas containing n-butene and an oxygen-containing gas are brought into contact with a catalyst in a reactor to produce a reaction product gas containing butadiene, and the reaction product gas is washed with a quenching agent in a quenching tower. A method for producing butadiene, which comprises using an aqueous amide solution containing an amide, water and an acidic solvent as the quenching agent.   The method for producing butadiene according to claim 1, wherein the pH of the aqueous amide solution is controlled to 0.1 to 6.0.   The method for producing butadiene according to claim 1 or 2, wherein the amide is at least one selected from the group consisting of urea, formamide, acetamide, ethylamide, and acrylamide.