WO2015087668A1

WO2015087668A1 - Method for producing 1,3-butadiene

Info

Publication number: WO2015087668A1
Application number: PCT/JP2014/080558
Authority: WO
Inventors: 裕子岡田; 裕一郎佐々木; 悠深見
Original assignee: Jsr株式会社
Priority date: 2013-12-12
Filing date: 2014-11-18
Publication date: 2015-06-18
Also published as: JPWO2015087668A1

Abstract

The purpose of the present invention is to provide a method for producing butadiene, which does not undergo the precipitation of a by-product and therefore does not cause the clogging of a cooling column or a pipe due to the precipitation of the by-product, and which can be operated steadily and continuously. The present invention is a method for producing 1,3-butadiene, which comprises a step of carrying out an oxidative dehydrogenation reaction of a raw material gas containing n-butene with a gas containing molecular oxygen in the presence of a metal oxide catalyst to produce a product gas containing 1,3-butadiene and a step of cooling the product gas, wherein the gas is brought into contact with a cooling solvent comprising an organic solvent and an aqueous alkali metal compound solution in the cooling step.

Description

Method for producing 1,3-butadiene

The present invention relates to a method for producing 1,3-butadiene.

Conventionally, as a method for producing 1,3-butadiene (hereinafter also referred to as “butadiene”), other than butadiene from a fraction having 4 carbon atoms (hereinafter also referred to as “C4 fraction”) obtained by cracking naphtha. The method of isolate | separating these components by distillation is employ | adopted. Butadiene is increasing in demand as a raw material for synthetic rubber, etc., but the supply of C4 fraction has decreased due to factors such as the shift of ethylene production from naphtha cracking to ethane pyrolysis. Therefore, there is a demand for production of butadiene that does not use a C4 fraction as a raw material.

In view of the above requirements, a method for separating butadiene from a product gas obtained by oxidative dehydrogenation of n-butene has attracted attention as a method for producing butadiene. Since the oxidative dehydrogenation reaction is a gas phase reaction at a high temperature, it is usually necessary to introduce the product gas obtained into a cooling tower or the like and contact it with water or cool it by contacting with water. However, the resulting product gas contains by-products such as water-soluble by-products other than butadiene and poorly water-soluble high-boiling by-products, and these by-products are precipitated by cooling. Since the cooling tower and the piping are closed, there is a disadvantage that continuous operation becomes difficult.

Therefore, for example, (1) a method for removing by-products using oil that dissolves by-products such as paraffin oil, naphthenic oil, and aromatic oil (see Japanese Patent Publication No. 49-6283), (2) cooling tower The method of making it possible to separate the by-product with water by setting the temperature of the product gas introduced to the temperature of 170 ° C. or higher and the temperature of the inner wall surface of the cooling tower to 140 ° C. or higher 60-315531), (3) A method for avoiding the precipitation of by-products in the product gas by setting the obtained product gas to 300 ° C. to 221 ° C. before cooling in the cooling tower No. 2011-1341) is proposed.

However, in the method (1), since the oil component corresponding to the vapor pressure is contained in the product gas after cooling, a step of separately collecting this oil component is required. In the method (2), a method for maintaining the temperature of the product gas and the inner wall surface of the cooling tower at a specific temperature has been proposed. At the specific temperature, precipitation of high-boiling by-products occurs, and the cooling tower There is a risk of blockage of pipes and pipes. Further, in the method (3), since two or more parallel lines corresponding to the by-products to be deposited are installed, there is a disadvantage that line blockage management, line switching work, cleaning work, etc. occur. is there.

In addition, in international publication 2012/157495, it is proposed to use what contains organic amine aqueous solution and an aromatic organic solvent as a cooling agent. However, the invention of the above-mentioned document uses an aqueous solution of an organic amine, which is a bifunctional compound, as a cooling solvent, thereby removing the organic amine by causing an acid-base reaction or an aldol condensation with a by-product. It is a feature. Furthermore, as described in paragraph 0039, the above document intentionally excludes the use of an alkaline aqueous solution such as an aqueous solution of caustic soda that causes a simple neutralization reaction as a coolant, and within the intended scope of the present invention. Absent.

Japanese Patent Publication No.49-6283 JP-A-60-115531 JP 2011-1341 A International Publication No. 2012/157495

The present invention has been made on the basis of the circumstances as described above, and the object thereof is to suppress precipitation of by-products and blockage of cooling towers and piping, and stable and continuous operation can be achieved. It is to provide a method for producing butadiene.

The invention made to solve the above problems is
A step of obtaining a product gas containing 1,3-butadiene by an oxidative dehydrogenation reaction of a source gas containing n-butene and a molecular oxygen-containing gas in the presence of a metal oxide catalyst, and a step of cooling the product gas And in the cooling step, a cooling solvent containing an organic solvent and an aqueous alkali metal compound solution is brought into contact with a gas.

According to the method for producing butadiene, by using a cooling solvent containing an organic solvent in addition to the aqueous alkali metal compound solution in the cooling step, a water-insoluble high-boiling point together with a water-soluble byproduct that is soluble in the aqueous alkali metal compound solution. By-products can be dissolved in the cooling solvent. Thereby, it can suppress that a by-product precipitates when manufacturing a butadiene and obstruct | occludes a cooling tower and piping, and can operate stably continuously.

According to the method for producing butadiene of the present invention, when producing butadiene from a product gas obtained by oxidative dehydrogenation of n-butene, it is possible to suppress the clogging of cooling towers and piping due to precipitation of by-products. , Stable and continuous operation.

It is a flowchart which shows the manufacturing method of the butadiene which concerns on embodiment of this invention.

A method for producing butadiene according to an embodiment of the present invention will be described with reference to FIG. The method for producing butadiene according to the present embodiment includes a reaction process, a cooling process, a rough separation process, a separation process, and a desorption process. Hereinafter, each process is explained in full detail.

<Reaction process>
In this step, 1,3-butadiene is produced by an oxidative dehydrogenation reaction between a source gas containing n-butene (hereinafter also referred to as “source gas”) and a molecular oxygen-containing gas in the presence of a metal oxide catalyst. Get gas. First, after heating the source gas, air as molecular oxygen-containing gas, and optionally inert gas (inert gas) and water (water vapor) to about 200 ° C. to 350 ° C. with a preheater (not shown) These are supplied from a pipe 100 to a reactor 1 filled with a metal oxide catalyst as shown in FIG. The raw material gas, inert gas, air, and water (steam) may be supplied directly to the reactor 1 from separate pipes, but are preferably supplied to the reactor 1 in a uniformly mixed state in advance. This is because, for example, it is possible to prevent a situation in which a non-uniform mixed gas partially forms explosive gas in the reactor 1.

(Molecular oxygen-containing gas)
The molecular oxygen-containing gas is usually a gas containing 10% by volume or more of molecular oxygen, preferably contains 15% by volume or more of molecular oxygen, and more preferably contains 20% by volume or more of molecular oxygen. As the molecular oxygen-containing gas, air is preferable. Further, the molecular oxygen-containing gas may contain any impurity such as nitrogen, argon, neon, helium, CO, CO ₂ , and water as long as the effects of the present invention are not impaired. In the case of nitrogen, the amount of this impurity is usually 90% by volume or less, preferably 85% by volume or less, and more preferably 80% by volume or less. The amount of components other than nitrogen is usually 10% by volume or less, preferably 1% by volume or less. If the amount of this impurity is too large, it tends to be difficult to supply oxygen necessary for the reaction.

(Inert gas)
The inert gas (inert gas) is preferably supplied to the reactor 1 together with the raw material gas containing n-butene and the molecular oxygen-containing gas. By adding this inert gas, the concentration of the combustible gas such as butene and oxygen can be adjusted so that the mixed gas does not form squeal in the reactor 1. As the inert gas nitrogen, argon, CO ₂ and the like. Among these, nitrogen is preferable from an economical point of view.

(Water (steam))
The reactor 1 is preferably supplied with water (steam). Water (steam) can adjust the concentration of the raw material gas and oxygen in the same manner as the inert gas, and can reduce the coking of the metal oxide catalyst.

(Raw material gas)
The raw material gas refers to a gaseous material obtained by gasifying a raw material of 1,3-butadiene with a vaporizer (not shown in FIG. 1). The raw material is n-butene, which is a monoolefin having 4 carbon atoms. As n-butene, for example, a fraction mainly composed of n-butene (1-butene and 2-butene) obtained by separating butadiene and i-butene from a C ₄ fraction by-produced by naphtha decomposition (raffinate 2) And a butene fraction produced by dehydrogenation or oxidative dehydrogenation of n-butane can be used. 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 gas, or from which impurities such as phosphorus are removed from FCC-C4 Can also be used as a raw material gas. The concentration of n-butene in the source gas is usually 40% by volume or more, preferably 60% by volume or more, more preferably 75% by volume or more, and particularly preferably 99% by volume or more.

Further, the source gas may contain an arbitrary impurity as long as the effects of the present invention are not impaired. Specific examples of the impurities include branched monoolefins such as i-butene; saturated hydrocarbons such as propane, n-butane and i-butane. The source gas may contain 1,3-butadiene, which is a target of reaction, as an impurity. The amount of these impurities is usually 60% by volume or less, preferably 40% by volume or less, more preferably 25% by volume or less, and particularly preferably 1% by volume or less based on the total amount of the raw material gas. If the amount is too large, the concentration of 1-butene or 2-butene, which are the main raw materials, decreases, and the reaction tends to be slow, or by-products tend to increase.

(Composition of mixed gas)
The lower limit of the concentration of n-butene in the mixed gas is preferably 2% by volume, more preferably 3% by volume, and even more preferably 5% by volume from the viewpoint of butadiene productivity. On the other hand, the upper limit of the concentration of n-butene in the mixed gas is preferably 30% by volume, more preferably 25% by volume, and still more preferably 20% by volume from the viewpoint of suppressing the load on the metal oxide catalyst. As a composition of the mixed gas, the lower limit of the ratio of O _{2 to} 100 parts by volume of the source gas is preferably 50 parts by volume, and more preferably 70 parts by volume. The upper limit of the O ₂ ratio is preferably 150 parts by volume, and more preferably 110 parts by volume. The lower limit of the ratio of _{N 2} for the raw material gas 100 parts by volume, preferably 200 parts by volume, more preferably 300 parts by volume. The upper limit of the N ₂ ratio is preferably 2,000 parts by volume, and more preferably 1,500 parts by volume. The lower limit of the ratio of _{H 2} O for the raw material gas 100 parts by volume, preferably 0 parts by volume, more preferably 100 parts by volume. The upper limit of the H ₂ O ratio is preferably 900 parts by volume, and more preferably 300 parts by volume. If the ratio of O _{2 to} the raw material gas deviates from this range, even if the reaction temperature is adjusted, it tends to be difficult to adjust the O ₂ concentration at the reactor 1 outlet. In addition, as the ratio of N ₂ and H ₂ O increases, the raw material gas becomes thinner and the efficiency tends to deteriorate. On the other hand, as the ratio decreases, the mixed gas enters the explosion composition and heat removal becomes difficult. Tend.

(Explosion range of mixed gas)
Since the above mixed gas is a mixture of oxygen and combustible source gas, each gas (source gas, air, and inert gas and water (water vapor) if necessary) so as not to enter the explosion range. The composition of the inlet of the reactor 1 is controlled while monitoring the flow rate with a flow meter (not shown) installed in a pipe for supplying the gas to adjust the mixed gas composition described above.

In addition, the explosion range here is a range having a composition in which the mixed gas is ignited in the presence of some ignition source. It is known that if the concentration of the source gas is lower than a certain value, it will not ignite even if an ignition source is present, and this concentration is called the lower explosion limit. In addition, it is known that if the concentration of the raw material gas is higher than a certain value, it does not ignite even if an ignition source is present, and this concentration is called the upper limit of explosion. Each value depends on the oxygen concentration. In general, the lower the oxygen concentration, the closer the values are, and the two match when the oxygen concentration reaches a certain value. The oxygen concentration at this time is called a critical oxygen concentration. If the oxygen concentration is lower than this, the mixed gas does not ignite regardless of the concentration of the raw material gas.

When the oxidative dehydrogenation reaction in this step is started, the amount of molecular oxygen-containing gas, inert gas and water vapor supplied to the reactor 1 is first adjusted so that the oxygen concentration at the inlet of the reactor 1 is the critical oxygen concentration. The supply of the source gas is started after the following, and then the supply amount of the molecular oxygen-containing gas such as the source gas and air is increased so that the source gas concentration is higher than the upper limit of explosion. .

When the supply amount of the source gas and the molecular oxygen-containing gas is increased, the supply amount of the mixed gas may be made constant by decreasing the supply amount of water vapor. If it does in this way, the gas residence time in piping or the reactor 1 is kept constant, and the fluctuation | variation of a pressure can be suppressed.

[Conditions for oxidative dehydrogenation]
The reactor 1 is filled with a metal oxide catalyst, which will be described later. Under this catalyst, the raw material gas reacts with oxygen to produce a gas containing 1,3-butadiene.

In this oxidative dehydrogenation reaction, unsaturated carbonyl compounds having 3 to 4 carbon atoms such as acrolein, acrylic acid, methacrolein, methacrylic acid, maleic acid, fumaric acid and maleic anhydride can be generated in the product gas. When the concentration of the unsaturated carbonyl compound is high, the unsaturated carbonyl compound dissolves and accumulates in the cooling solvent circulated in the cooling step described later, the absorption solvent circulated in the rough separation step, and the extraction solvent circulated in the extractive distillation step. It becomes easy to induce the generation of by-products.

As a condition for setting the unsaturated carbonyl compound concentration within a certain range, there is a method of adjusting the reaction temperature during the oxidative dehydrogenation reaction. This oxidative dehydrogenation reaction is an exothermic reaction, and the temperature rises due to the reaction. The lower limit of the reaction temperature is usually 300 ° C, preferably 320 ° C. On the other hand, the upper limit of the reaction temperature is usually 400 ° C., and preferably 380 ° C. By setting the reaction temperature within the above range, coking of the catalyst can be suppressed, and the concentration of the unsaturated carbonyl compound having 3 to 4 carbon atoms can be set within a certain range. If the reaction temperature is less than 300 ° C., the conversion of n-butene may decrease. On the other hand, when the reaction temperature is higher than 400 ° C., the concentration of the unsaturated carbonyl compound having 3 to 4 carbon atoms is increased, which tends to cause accumulation of by-products in the absorption solvent or extraction solvent and coking of the catalyst.

In addition, it is preferable that the reactor 1 is appropriately cooled by, for example, removing heat with a heat medium (dibenzyltoluene, nitrite, or the like) and the temperature of the catalyst layer is controlled to be constant.

The lower limit of the pressure in the reactor 1 is not particularly limited, but is usually 0 MPaG, preferably 0.02 MPaG, and more preferably 0.05 MPaG. On the other hand, the upper limit is usually 0.5 MPaG, preferably 0.3 MPaG, and more preferably 0.1 MPaG.

The lower limit of the gas hourly space velocity in the oxidative dehydrogenation reaction (GHSV), preferably 500hr ^{^-1,} 800hr ^-1 are more preferred. On the other hand, the upper limit of GHSV, preferably 5,000hr ^{^-1,} 3,000hr ^-1 are more preferred. By setting such a gas hourly space velocity, an efficient reaction can be promoted. The gas hourly space velocity (GHSV) is obtained by the following equation.
GHSV [hr ⁻¹ ] = gas flow rate [Nm ³ / hr] ÷ catalyst layer volume [m ³ ]
In the above formula, “catalyst layer volume” refers to the entire volume (apparent volume) including voids.

[Concentration of each component in the product gas]
The lower limit of the N ₂ concentration in the product gas generated by the oxidative dehydrogenation reaction is preferably 35% by volume, and more preferably 45% by volume. The upper limit of the N ₂ concentration is preferably 90% by volume, and more preferably 80% by volume. The lower limit of the H ₂ O concentration, preferably 5% by volume, more preferably 8% by volume. The upper limit of the H ₂ O concentration is preferably 60% by volume, and more preferably 40% by volume. The lower limit of the butadiene concentration is preferably 3% by volume, and more preferably 5% by volume. The upper limit of the butadiene concentration is preferably 20% by volume, more preferably 15% by volume. By setting the concentration of each component in the product gas within the above range, the efficiency of the butadiene purification process can be improved, and side reactions of butadiene occurring in the purification process can be suppressed, thereby accumulating by-products. Can be suppressed.

(Metal oxide catalyst)
Next, the metal oxide catalyst used in this step will be described. The catalyst is not particularly limited as long as it functions as an oxidative dehydrogenation catalyst for a raw material gas, and a known catalyst can be used. For example, molybdenum (Mo), bismuth (Bi), and iron (Fe) are used. The thing containing the metal oxide which has at least is mentioned. As said metal oxide, the composite metal oxide represented by following formula (1) is preferable.

Mo (a) Bi (b) Fe (c) X (d) Y (e) Z (f) O (g) (1)

In formula (1), X represents at least one element selected from Ni and Co. Y represents at least one element selected from the group consisting of Li, Na, K, Rb, Cs, and Tl. Z represents at least one element selected from the group consisting of Mg, Ca, Ce, Zn, Cr, Sb, As, B, P, and W. a, b, c, d, e, f, g represent the atomic ratio of each element. When a = 12, b = 0.1 to 8, c = 0.1 to 20, d = 0 to 20, e = 0 to 4, f = 0 to 2, and g is the number of oxygen atoms necessary to satisfy the valence of each component.

The metal oxide catalyst is highly active and highly selective in the method of producing butadiene by oxidative dehydrogenation using molecular oxygen, and further has excellent life stability.

The method for preparing the catalyst is not particularly limited, and a known method such as an evaporation / drying method using a raw material of each element, a spray drying method, 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, An alkoxide etc. are mentioned. The catalyst may be used by supporting it on an inert carrier, and examples of the carrier species include silica, alumina, silicon carbide and the like.

<Cooling process>
In this step, the product gas from the reactor 1 is cooled. This cooling process includes, for example, a rapid cooling process by the cooling tower 2 and a heat exchange process by the heat exchanger 3.

(Cooling tower 2)
The product gas from the reactor 1 is sent to the cooling tower 2 through the pipe 101. From the upper part, a cooling solvent is introduced from the pipe 102, and this cooling solvent is brought into contact with the supplied product gas. Examples of the cooling tower 2 include a packed tower, a plate tower, a spray tower, a wet wall tower, and a bubble tower, and a packed tower and a plate tower are preferable. Examples of the packing material used in the packed tower include irregular packing materials such as Raschig rings, Berle saddles and cascade mini rings, and regular packing materials such as flexi packs and mela packs. The cooling method in the cooling tower 2 is preferably a rapid cooling method in which the cooling solvent and the product gas are brought into countercurrent contact in a packed tower using an irregular packing material. The product gas is cooled to about 30 ° C. or higher and 99 ° C. or lower by this countercurrent contact. As the cooling solvent, a mixed system of an organic solvent and an alkali metal compound aqueous solution is used. By using such a cooling solvent, water-insoluble by-products such as acrylic acid, methacrylic acid, maleic acid, fumaric acid, and maleic anhydride generated in the above-mentioned oxidative dehydrogenation reaction and poorly water-soluble such as fluorenone and anthraquinone High-boiling by-products can also be removed by dissolving in a cooling solvent. Further, by using an alkali metal aqueous solution, an acid such as acrylic acid is neutralized to suppress corrosion of the apparatus. In addition, the said cooling solvent may contain other solvents other than an organic solvent and alkali metal compound aqueous solution. The cooled solvent is discharged from the pipe 103. Although the temperature of the cooling solvent to be introduced depends on the cooling temperature of the reaction product gas, the lower limit thereof is preferably 10 ° C., more preferably 20 ° C. On the other hand, as an upper limit of the temperature of a cooling medium, 90 degreeC is preferable, 70 degreeC is more preferable, and 40 degreeC is further more preferable.

Although the pressure in the cooling tower 2 is not particularly limited, the lower limit thereof is preferably 0 MPaG, more preferably 0.1 MPaG, and further preferably 0.2 MPaG. On the other hand, the upper limit of the pressure in the cooling tower 2 is preferably 1.5 MPaG, more preferably 1.0 MPaG, and even more preferably 0.5 MPaG. By setting the pressure in the cooling tower 2 within the specific range, it is possible to more effectively remove by-products with the cooling solvent. As a minimum of the temperature in the cooling tower 2, 0 degreeC is preferable and 20 degreeC is more preferable. On the other hand, as an upper limit of the temperature in the

cooling tower

2, 100 degreeC is preferable and 80 degreeC is more preferable.

The organic solvent in the cooling step is preferably an aromatic compound, an amide compound, a sulfur compound, a nitrile compound, a ketone compound, an alcohol, or a combination thereof. By using a cooling solvent containing the specific organic solvent, it is possible to more effectively remove poorly water-soluble high-boiling by-products, and to further reduce process instability due to accumulation of these by-products. . In addition, these organic solvents may be used individually by 1 type, and may use 2 or more types together.

Examples of the aromatic compound include toluene, xylene, benzene and the like.

Examples of the amide compound include dimethylformamide and N-methyl-2-pyrrolidone (NMP).

Examples of the sulfur compound include dimethyl sulfoxide (DMSO) and sulfolane.

Examples of the nitrile compound include acetonitrile and butyronitrile.

Examples of the ketone compound include cyclohexanone and acetophenone.

Examples of the alcohols include methyl alcohol, ethyl alcohol, allyl alcohol, crotyl alcohol, and cyclopentanol.

Of these, the organic solvent in the cooling step is preferably an aromatic compound, and more preferably toluene.

The aqueous alkali metal compound solution in the cooling solvent is preferably an aqueous alkali metal hydroxide solution, such as an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution, or an aqueous lithium hydroxide solution. Among these, a sodium hydroxide aqueous solution and a potassium hydroxide aqueous solution are more preferable, and a sodium hydroxide aqueous solution is more preferable. Moreover, as a minimum of the alkali hydroxide density | concentration of alkali metal compound aqueous solution, 1 mass% is preferable, 2 mass% is more preferable, and 3 mass% is further more preferable. On the other hand, the upper limit of the alkali hydroxide concentration of the aqueous alkali metal compound solution is preferably 50% by mass, more preferably 40% by mass, and still more preferably 30% by mass. In addition, these alkali metal compound aqueous solutions may be used individually by 1 type, and may use 2 or more types together. Ammonia and amines can be used for the purpose of neutralization and carbon dioxide absorption, but ammonia is a toxic gas and is dangerous to use, and amines are weaker than alkali metals and are used for neutralization. Since the amount of use increases and the unit price is high, the butadiene production cost increases.

When the organic solvent in the cooling step is an aromatic compound, the lower limit of the content of the aqueous alkali metal compound solution in the cooling solvent is preferably 10% by mass, more preferably 20% by mass, and even more preferably 30% by mass. On the other hand, the upper limit of the content of the alkali metal compound aqueous solution in the cooling solvent is preferably 80% by mass, more preferably 75% by mass, and even more preferably 70% by mass. Thus, by setting the content of the alkali metal compound aqueous solution in the cooling solvent in the case where the organic solvent is an aromatic compound within the above specific range, the water-soluble by-product and the slightly water-soluble high-boiling by-product are cooled with the cooling solvent. Can be dissolved and removed more effectively.

When the organic solvent in the cooling step is an amide compound, a sulfur compound, a nitrile compound, a ketone compound, an alcohol, or a combination thereof, the lower limit of the content of the aqueous alkali metal compound solution in the cooling solvent is 5% by mass. 10 mass% is preferable and 15 mass% is more preferable. As an upper limit of content of the alkali metal compound aqueous solution in the said cooling solvent, 80 mass% is preferable, 70 mass% is more preferable, and 60 mass% is further more preferable. Thus, by making the content of the alkali metal compound aqueous solution in the cooling solvent in the case where the organic solvent is other than the aromatic compound within the specified range, the by-product is effectively dissolved and removed by the cooling solvent. Can do.

<Separation process>
The cooling solvent is circulated to the cooling tower 2 through the pipe 122 and used. A part of the cooling solvent used for circulation is extracted from the pipe 103 and separated into an organic solvent and an aqueous alkali metal compound solution in the decanter 10. The separated alkali metal compound aqueous solution containing an organic acid such as maleic acid or acrylic acid is discharged from the pipe 120. On the other hand, the separated organic solvent is sent to the regenerator 11 through the pipe 121. By-products such as poorly water-soluble high-boiling by-products are accumulated in the separated organic solvent, the by-products are removed in the regenerator 11. The organic solvent after removing the by-products is reused to the cooling tower 2 through the pipe 102. By circulating the cooling solvent in this way, the drainage load from the pipe 120 can be reduced. In the present invention, this separation step may not be provided.

The concentration of each component in the product gas at the outlet of the cooling tower 2 is preferably 30% by volume and more preferably 40% by volume as the lower limit of N ₂ . The upper limit of the N _2, is preferably 80 vol%, more preferably 70% by volume. The lower limit of H ₂ O, preferably 5% by volume, more preferably 10% by volume. The upper limit of the H ₂ O, preferably 60 vol%, more preferably 45% by volume. The lower limit of butadiene is preferably 3% by volume, and more preferably 5% by volume. The upper limit of butadiene is preferably 20% by volume, and more preferably 15% by volume.

(Heat exchanger)
The product gas cooled in the cooling tower 2 flows out from the top of the cooling tower 2 and is cooled to about room temperature (10 ° C. or more and 30 ° C. or less) through the heat exchanger 3 from the pipe 104 to obtain a cooled product gas.

As the concentration of each component of the cooling product gas in the heat exchanger 3 outlet, the lower limit of the N _2, is preferably 60 vol%, more preferably 70% by volume. The upper limit of the N _2, is preferably 94 vol%, more preferably 85% by volume. The lower limit of H ₂ O, 1% by volume is preferred. The upper limit of the H ₂ O, preferably 20 vol%, more preferably 10% by volume. The lower limit of butadiene is preferably 3% by volume, and more preferably 4% by volume. The upper limit of butadiene is preferably 20% by volume, and more preferably 15% by volume. By setting the concentration of each component of the cooled product gas within the above range, the concentration of butadiene in the cooled product gas can be controlled within the above range, and thereby the absorption efficiency into the absorbing solvent can be increased in the next step.

<Rough separation process (absorption process)>
In this step, the cooled product gas is roughly separated into molecular oxygen and inert gases and other gases by selective absorption into an absorbing solvent. Here, “other gas” refers to a gas containing at least butadiene and unreacted n-butene absorbed in the absorbing solvent. The rough separation step can be omitted.

The cooling product gas is pressurized by the compressor 4 and further cooled by the heat exchanger 5 as necessary. The cooled product gas is sent from the pipe 107 to the absorption tower 6. From the upper part of the absorption tower 6, the absorption solvent whose temperature is adjusted through the heat exchanger 123 is introduced from the pipe 108, and the absorption solvent and the cooled product gas are brought into countercurrent contact. As a result, other gases (gas containing butadiene and unreacted n-butene) in the cooled product gas are absorbed by the absorption solvent, and molecular oxygen and inert gases are roughly separated from other gases. .

Although the pressure in the absorption tower 6 is not particularly limited, the lower limit of the pressure is preferably 0.1 MPaG, more preferably 0.2 MPaG. As an upper limit of pressure, 1.5 MPaG is preferable and 1.0 MPaG is more preferable. The larger the pressure, the higher the absorption efficiency, and the smaller the pressure, the more energy required for boosting when introducing gas into the absorption tower 6 can be reduced.

Further, the temperature in the absorption tower 6 is not particularly limited, but the lower limit of the temperature is preferably 0 ° C, more preferably 10 ° C. As an upper limit of temperature, 60 degreeC is preferable and 50 degreeC is more preferable. The higher this temperature is, the more advantageous it is that oxygen, nitrogen, etc. are less likely to be absorbed by the solvent, and the lower, there is an advantage that the absorption efficiency of hydrocarbons such as butadiene is improved.

(Absorbing solvent)
Examples of the absorbing solvent used in this step include those containing as a main component the same organic solvent as exemplified as the organic solvent in the cooling step. The main component is preferably the same as the organic solvent used in the cooling step, more preferably toluene or acetonitrile, and even more preferably toluene. Here, the “main component” means that the organic solvent content in the absorbing solvent at the time of supply is 50% by mass or more. As a minimum of content of the above-mentioned organic solvent in the above-mentioned absorption solvent, 55 mass% is preferred and 60 mass% is more preferred. The upper limit of the content of the organic solvent in the absorbing solvent is preferably 100% by mass.

When the absorption solvent contains toluene as a main component, the content of toluene in the absorption solvent is preferably 80% by mass or more, more preferably 90% by mass or more, and further preferably 100% by mass.

When the absorption solvent contains acetonitrile as a main component, the absorption solvent preferably further contains at least one selected from the group consisting of water and alcohol. When the absorption solvent further contains water, the selectivity of the absorption solvent can be increased. However, if the water content becomes too high, hydrocarbons cannot be completely dissolved in acetonitrile in the absorption solvent and the two-phase. Will be separated. Therefore, when the absorption solvent further contains alcohol in addition to water, the solubility of hydrocarbons (other gases) in acetonitrile does not decrease even if the water content is increased, The water content can be increased.

Examples of the alcohol include those having 8 or less carbon atoms from the viewpoint of the affinity between hydrocarbons and water. Of these, alcohols having a carbon number of 5 or less whose boiling point is close to those of acetonitrile are preferable, and methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, sec-butyl alcohol, tert-butyl alcohol More preferable are aliphatic saturated alcohols such as n-pentyl alcohol, aliphatic unsaturated alcohols such as allyl alcohol and crotyl alcohol, and alicyclic alcohols such as cyclopentanol, and ethyl alcohol is particularly preferable.

When the absorption solvent contains acetonitrile as a main component, the lower limit of the water content in the absorption solvent is preferably 5% by mass, and more preferably 10% by mass. The upper limit of the water content in the absorbing solvent is preferably 35% by mass and more preferably 25% by mass. By setting the water content within the above range, the selectivity of the absorbing solvent can be effectively increased.

When the absorption solvent contains acetonitrile as a main component, the lower limit of the alcohol content in the absorption solvent is preferably 5% by mass. As an upper limit of content of the alcohol in the said absorption solvent, 30 mass% is preferable and 15 mass% is more preferable. By setting the alcohol content within the above range, the solubility of hydrocarbons (other gases) in acetonitrile does not decrease even when the water content is increased, and the water content in the absorbing solvent is increased. be able to.

When the absorption solvent contains acetonitrile as a main component, the absorption solvent may contain other solvents other than acetonitrile, alcohol and water.

The amount of the absorbing solvent used in the rough separation step is not particularly limited, but the lower limit of the amount of the absorbing solvent used with respect to the total flow rate of butadiene and unreacted n-butene in the product gas supplied from the reactor 1 is as follows. 1 mass times is preferable and 5 mass times is more preferable. On the other hand, as an upper limit of the usage-amount of an absorption solvent, 100 mass times is preferable and 50 mass times is more preferable. By making the usage-amount of an absorption solvent into the said range, absorption efficiency, such as a butadiene, can be improved. When the amount of the absorbing solvent used is too large, it tends to be uneconomical, and when it is too small, the absorption efficiency of butadiene or the like tends to be lowered.

The lower limit of the temperature of the absorbing solvent is preferably 0 ° C. The upper limit of the temperature of the absorbing solvent is preferably 60 ° C, more preferably 40 ° C. By setting the temperature of the absorption solvent in the above range, the absorption efficiency of hydrocarbons such as butadiene can be further improved. Therefore, it is preferable to adjust the temperature with an apparatus such as the heat exchanger 123.

Components that have not been absorbed by the absorbing solvent (molecular oxygen and inert gases) are discharged from the top of the absorption tower 6 and sent to the cleaning tower 7 through the pipe 110. The molecular oxygen and inert gases are washed with oil (when the absorbing solvent contains toluene as a main component) or water (when the absorbing solvent contains acetonitrile as a main component) supplied from the pipe 118 of the cleaning tower 7. Thus, the absorbing solvent mixed (entrained) with the molecular oxygen and the inert gas is removed, and the removed absorbing solvent is recovered from the pipe 117. The cleaned molecular oxygen and inert gas may be sent to the reaction process from the pipe 119 and recycled.

<Demelting process>
In this step, the solvent is separated from the absorbing solvent containing butadiene to obtain a gas stream containing butadiene. Specifically, an absorption solvent containing butadiene obtained from the bottom of the absorption tower 6 is supplied to the demelting tower 8 through the pipe 109. In the demelting tower 8, distillation separation is performed, and a gas stream containing butadiene is obtained from the top of the tower via a pipe 113. The separated solvent is extracted from the bottom of the column and circulated and used as the absorption solvent of the absorption tower 6 through the pipe 111. After a part of the solvent is supplied to the solvent regeneration tower 9 through the pipe 112 and impurities in the solvent are separated. It is recycled to the absorption tower 6 through the pipe 116. The separated impurities are discharged through

pipes

114 and 115 connected to the upper and lower sides of the solvent regeneration tower 9.

The pressure in the demelting tower 8 is not particularly limited, but the lower limit is preferably 0.03 MPaG, more preferably 0.2 MPaG. As an upper limit of the pressure in the demelting tower 8, 1.0 MPaG is preferable and 0.6 MPaG is more preferable.

The lower limit of the bottom temperature of the demelting tower 8 is preferably 80 ° C., more preferably 100 ° C. On the other hand, the upper limit of the bottom temperature of the demelting tower 8 is preferably 200 ° C and more preferably 180 ° C.

The pressure in the solvent regeneration tower 9 is not particularly limited, but the lower limit is preferably 0 MPaG. The upper limit of the pressure in the solvent regeneration tower 9 is preferably 0.8 MPaG, and more preferably 0.5 MPaG.

Specific examples of the method for producing butadiene will be described below, but the present invention is not limited to the following examples. The gas composition analysis described in the following examples was performed using gas chromatography under the conditions shown in Table 1 below. H ₂ O was calculated by adding the amount of water obtained by the ice-cold trap at the time of gas sampling.

[Example 1]
Example 1 is a method for producing butadiene according to an embodiment of the present invention. Hereinafter, Example 1 will be described with reference to FIG.

<Reaction process>
(A) Catalyst Mo ₁₂ Bi ₅ Fe _0.5 Ni ₂ Co ₃ K _0.1 Cs _0.1 Sb _0.2 in a ratio of 20% of the total volume of catalyst to spherical silica The catalyst supported on was used.

Reactor 1 of FIG. 1 (inner diameter 21.2 mm, outer diameter 25.4 mm) filled with the catalyst (a) with a catalyst length of 4,000 mm is supplied with a raw material gas / air / water vapor / nitrogen containing n-butene. A mixed gas mixed at a volume ratio of 0.0 / 4.3 / 1.2 / 3.4 was supplied at a gas hourly space velocity (GHSV) of 1,000 hr ⁻¹ and reacted at 320 ° C. to 330 ° C. A product gas containing 1,3-butadiene was obtained.

<Cooling process>
The product gas extracted from the reactor 1 was introduced into the cooling tower 2 having an outer diameter of ¼ inch, a height of 1,600 mm, and a material SUS316L filled with Raschig rings of φ5 × 5 mm inside. In the cooling tower 2, the introduced introduced gas was brought into contact with a cooling solvent containing toluene and a 5 mass% aqueous sodium hydroxide solution at a ratio of 1: 1 under the condition of a pressure of 0.01 MPaG and cooled to 67 ° C. Then, it cooled to room temperature (30 degreeC) with the heat exchanger 3. FIG. The ratio of each gas component in the product gas at the outlet of the cooling tower 2 is such that 1,3-butadiene / unreacted n-butene / N ₂ / H ₂ O / O ₂ / COx is 8.5 / 1.0 / 66 / The volume ratio was 19 / 4.1 / 1.4. After 10 days, the operation was stopped, and the filter installed after the cooling tower 2 was confirmed. The cooling solvent was circulated and used, and a part thereof was extracted and introduced into the decanter 10 to separate toluene and aqueous sodium hydroxide solution. The separated toluene contains by-products such as fluorenone and anthraquinone. After introducing the by-products into the regenerator 11 and removing the by-products, the toluene was reused. The separated sodium hydroxide aqueous solution contained organic acids such as maleic acid and acrylic acid.

<Rough separation process (absorption process)>
The cooled product gas obtained in the cooling step was pressurized to 0.4 MPaG by the compressor 4 and cooled to 50 ° C. by the heat exchanger 5. The cooled gas is supplied from the bottom of the absorption tower 6 in which a regular packing is arranged inside with a material SUS304 with an outer diameter of 11/2 inches, a height of 1,000 mm, and 10 parts of toluene (absorbing solvent) from the top of the tower. Supplied at ° C. The amount of toluene supplied was 16 times by mass with respect to 1,3-butadiene and unreacted n-butene to be absorbed in toluene.

The gas extracted from the top of the column without being absorbed by toluene contained 91% by volume of N ₂ , 5% by volume of O ₂ , and 4% by volume of impurities such as COx. The gas obtained from the top of the tower was sent to the washing tower 7 and a small amount of solvent contained in the gas was removed with oil, and then part of the solvent was sent to the reaction process and recycled.

<Demelting process>
The solvent containing 1,3-butadiene obtained from the bottom of the absorption tower 6 is supplied to a demelting tower 8 having an outer diameter of 11/2 inches, a height of 1,000 mm, and a material SS400 with a packing inside. A gas stream substantially free of solvent was obtained from the top of the column. The gas obtained from the top of the desorption tower 8 contained 75% by volume of 1,3-butadiene, 8% by volume of n-butene, and 17% by volume of impurities such as COx and solvent. .

The solvent substantially free of 1,3-butadiene extracted from the bottom of the desulfurization tower 8 is cooled by a heat exchanger and then supplied to the absorption tower 6 for recycling. A part of the solvent is regenerated. It was supplied to the tower 9 and was recycled to the absorption tower 6 after the impurities were separated.

[Example 2]
In Example 1, butadiene was produced in the same manner except that a 25% by mass aqueous sodium hydroxide solution was used as the cooling solvent in the cooling tower 2. There was no change in the substances and concentrations contained in the partially extracted toluene and sodium hydroxide. When the filter installed after the cooling tower 2 was confirmed, there was no adhesion | attachment visually. The lower the amount of sodium hydroxide used, the lower the butadiene production cost.

[Comparative Example 1]
In Example 1, butadiene was produced in the same manner except that a 5% by mass aqueous sodium hydroxide solution was used as the cooling solvent for the cooling tower 2. When the filter installed after the cooling tower 2 was confirmed, deposits were visually observed.

According to the butadiene production method of the present invention, when producing butadiene from a product gas obtained by oxidative dehydrogenation of n-butene, it is possible to suppress the precipitation of by-products and blockage of cooling towers and piping. , Stable and continuous operation.

1 Reactor 2 Cooling Tower 3 Heat Exchanger 4 Compressor 5 Heat Exchanger 6 Absorption Tower 7 Washing Tower 8 Demelting Tower 9 Solvent Regeneration Tower 10 Decanter 11 Regenerator 100 to 122 Piping 123 Heat Exchanger

Claims

A step of obtaining a product gas containing 1,3-butadiene by an oxidative dehydrogenation reaction between a source gas containing n-butene and a molecular oxygen-containing gas in the presence of a metal oxide catalyst, and a step of cooling the product gas. Have
A method for producing 1,3-butadiene, wherein a cooling solvent containing an organic solvent and an aqueous alkali metal compound solution is brought into contact with a gas in the cooling step.
The method for producing 1,3-butadiene according to claim 1, wherein the organic solvent in the cooling step is an aromatic compound, an amide compound, a sulfur compound, a nitrile compound, a ketone compound, an alcohol, or a combination thereof.
The organic solvent in the cooling step is an aromatic compound,
The method for producing 1,3-butadiene according to claim 2, wherein the content of the aqueous alkali metal compound solution in the cooling solvent is 10% by mass or more and 80% by mass or less.
The organic solvent in the cooling step is an amide compound, a sulfur compound, a nitrile compound, an alcohol or a combination thereof,
The method for producing 1,3-butadiene according to claim 2, wherein the content of the aqueous alkali metal compound solution in the cooling solvent is 5% by mass or more and 80% by mass or less.
The method for producing 1,3-butadiene according to any one of claims 1 to 4, wherein the cooling solvent is circulated and used in the cooling step.
The method for producing 1,3-butadiene according to claim 5, further comprising a step of extracting a part of the cooling solvent to be circulated and separating it into an organic solvent and an aqueous alkali metal compound solution.
The method for producing 1,3-butadiene according to claim 6, further comprising a step of separating the by-product accumulated in the organic solvent obtained in the separation step.
The method for producing 1,3-butadiene according to any one of claims 1 to 7, wherein the cooling step is performed under a pressure of 0 MPaG to 0.5 MPaG.