JP5780124B2 - Method for producing conjugated diene - Google Patents

Description

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

A method for producing a conjugated diene such as butadiene by subjecting a monoolefin such as n-butene to an oxidative dehydrogenation reaction in the presence of a catalyst is conventionally known.
This reaction proceeds, for example, according to the following reaction formula, and water is by-produced.
C ₄ H ₈ + 1 / 2O ₂ → C ₄ H ₆ + H ₂ O

  The production of butadiene by catalytic oxidative dehydrogenation of n-butene is industrially produced from C4 fraction (C4 hydrocarbon mixture, hereinafter sometimes referred to as “BB”) produced as a by-product in naphtha cracking. In a mixture containing 1-butene, 2-butene, butane, and the like (hereinafter, this mixture may be referred to as “BBSS”) obtained by separating butadiene in an extractive distillation column in the extractive separation process. Has been proposed for producing butadiene from butene contained in.

  It is also known that aldehydes are produced as a by-product when butadiene is produced from raw material butene by oxidative dehydrogenation as in the above reaction formula. Since these by-products are easily polymerized into a polymer, a post-treatment step after the reactor (a step of bringing a product gas containing butadiene obtained from the reactor outlet into contact with an absorbing solvent to obtain a solution containing a conjugated diene, In the process of separating the butadiene purified by distillation of the solution containing the conjugated diene, there is a possibility of causing operational troubles due to polymer blockage, and thus a method for removing these aldehydes has been studied. Specifically, a method of treating the product gas containing butadiene obtained from the reactor outlet with an absorbing solvent containing a halogen compound (Patent Document 1), a method of treating with an alkaline absorbing solvent (Patent Document 2), and There exists the method (patent document 3) etc. which process using an acidic solvent.

US Pat. No. 3,327,001 Japanese Patent Publication No. 45-17646 JP 60-184029 A

The above method of Patent Documents 1 to 3, the reactor but from the product gas containing butadiene obtained from the outlet and removing the pre-aldehydes before separating butadiene, this product gas N ₂ and O ₂ Since aldehydes are diluted by the amount of these non-condensable gases, the aldehydes to be removed are extremely low in concentration. From the viewpoint of separation efficiency and processing equipment size, it has not been a sufficiently advantageous method in a process for producing butadiene on an industrial scale. Further, when an absorption solvent containing a halogen compound is used, there is a problem that corrosion of the device material is likely to occur, and an expensive special metal is required as a component material of the device to withstand long-term use. Further, it has been found that when an alkaline solvent is used, the condensation reaction of aldehydes progresses, and solid suspended matters are generated, which hinders stable operation.

  The present invention solves the above-mentioned conventional problems, and provides a conjugated diene obtained by subjecting a raw material gas containing a monoolefin having 4 or more carbon atoms and a molecular oxygen-containing gas to an oxidative dehydrogenation reaction in the presence of a catalyst. It is an object of the present invention to provide a method for producing a conjugated diene in which aldehydes by-produced by the reaction are efficiently removed from the contained gas by an industrially advantageous treatment method to recover the conjugated diene in a high yield.

The present inventors have produced a target product from a product gas containing a conjugated diene obtained by subjecting a source gas containing a monoolefin having 4 or more carbon atoms and a molecular oxygen-containing gas to an oxidative dehydrogenation reaction in the presence of a catalyst. As a result of earnest study on an economically advantageous purification method that can efficiently remove aldehydes while suppressing loss of conjugated diene, the conjugated diene obtained at the reactor outlet as in the conventional method Rather than removing aldehyde before separating butadiene from the product gas, the purified conjugated diene is obtained by distilling a solution containing the conjugated diene obtained by absorbing the product gas in an organic solvent to obtain a purified conjugated diene. It has been found that the aldehydes in the purified conjugated diene can be efficiently removed by treating the aldehyde contained in the solution with a solvent that satisfies specific conditions.
That is, the gist of the present invention resides in the following [1] to [4].

[1] A product gas containing a conjugated diene obtained by subjecting a source gas containing a monoolefin having 4 or more carbon atoms and a molecular oxygen-containing gas to an oxidative dehydrogenation reaction in the presence of a catalyst is converted from the product gas to an aldehyde. A product gas absorption step of obtaining a solution B containing the conjugated diene by absorbing the organic solvent A without separating the organic solvent A, and distilling the solution B containing the conjugated diene Conjugated diene D containing aldehyde , organic solvent A and high-boiling fraction, conjugated diene separation step, conjugated diene D containing aldehyde, and infinite dilution activity coefficient γ ^∞ of aldehyde at 25 ° C Comprising a aldehyde separation step in which a solvent is absorbed with a solvent C of 6.0 or less and the aldehyde in the conjugated diene D is removed by solvent absorption. Law.

[2] The method for producing a conjugated diene according to [1], further comprising a conjugated diene recovery step of recovering the conjugated diene dissolved in the solvent C brought into contact with the conjugated diene D containing the aldehyde. .

[3] The method for producing a conjugated diene according to [2], wherein the conjugated diene recovery step is performed by extraction or distillation.

[4] Gas containing 1-butene, cis-2-butene, trans-2-butene or a mixture thereof obtained by dimerization of ethylene as the raw material gas, n-butane dehydrogenation or oxidative dehydrogenation reaction Any one of [1] to [3], which is a gas containing a large amount of hydrocarbons having 4 carbon atoms, which is obtained when fluidizing and cracking a butene fraction or a heavy oil fraction produced by The manufacturing method of conjugated diene of description.

  According to the present invention, a raw material gas containing a monoolefin having 4 or more carbon atoms and a molecular oxygen-containing gas are reacted from a product gas containing a conjugated diene obtained by an oxidative dehydrogenation reaction in the presence of a catalyst. An industrially and economically advantageous conjugated diene that can efficiently recover aldehydes by-products while efficiently recovering the conjugated diene while suppressing loss of the conjugated diene that is the target product. A manufacturing method is provided.

  That is, the present invention is not a method of removing aldehyde before separating butadiene from a product gas containing a conjugated diene obtained at the reactor outlet as in the conventional method, but the product gas is absorbed in an organic solvent, A solution containing the conjugated diene from which the condensable gas is separated is obtained, and this is distilled to obtain a purified conjugated diene (aldehyde-containing conjugated diene gas D described later). The aldehyde contained in the purified conjugated diene is removed, and the removal target Since the aldehyde is removed in a state of being concentrated to some extent, the separation and removal efficiency of the aldehyde can be enhanced. In the separation of the aldehyde from the purified conjugated diene, the aldehyde can be separated and removed efficiently by separating the aldehyde by solvent absorption using a specific solvent.

It is a systematic diagram which shows an example of embodiment of the manufacturing method of the conjugated diene of this invention. It is a systematic diagram which shows an example of embodiment of the conjugated diene recovery process by extraction in this invention. It is a systematic diagram which shows an example of embodiment of the conjugated diene recovery process by distillation in this invention.

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

In the examples described later, the present invention will be described in detail by taking, as an example, a case where butadiene is produced from typical n-butene among the methods for producing conjugated dienes to be treated according to the present invention. The present invention is not limited to the production of butadiene from n-butene (1-butene, 2-butene), but is a monoolefin having 4 or more carbon atoms, preferably 4 to 6 carbon atoms, such as pentene, methylbutene and dimethylbutene. It is effectively applied to the production of the corresponding conjugated diene by catalytic oxidative dehydrogenation of These monoolefins do not necessarily need to be used in an isolated form, and can be used in the form of any mixture as required. For example, when 1,3-butadiene is to be produced from n-butene (1-butene, 2-butene), high-purity 1-butene or 2-butene can be used as a raw material. _{C 4} fraction obtained by separating butadiene and i- butene from (BB) n- butenes (1-butene and 2-butene) fraction as a main component which in-product (BBSS) and n- butane A butene fraction produced by dehydrogenation or oxidative dehydrogenation can also be used. Further, a gas containing high-purity 1-butene, cis-2-butene, trans-2-butene or a mixture thereof obtained by dimerization of ethylene may be used as a raw material gas. As the ethylene, ethylene obtained by a method such as ethane dehydrogenation, ethanol dehydration, or naphtha decomposition can be used. Furthermore, fluid catalytic cracking (Fluid Catalytic Cracking) in which the heavy oil fraction obtained when distilling crude oil at an oil refining plant, etc. is decomposed using a powdered solid catalyst in a fluidized bed state and converted into low-boiling hydrocarbons. The gas containing a large number of hydrocarbons having 4 carbon atoms obtained from (hereinafter sometimes abbreviated as FCC-C4) can be used as a raw material gas, and from this FCC-C4, phosphorus, arsenic, etc. A material from which these impurities are removed may be used as a raw material gas.
The “main component” as used herein refers to a component that occupies usually 40 vol% or more, preferably 50 vol% or more, more preferably 60 vol% or more, and particularly preferably 70 vol% or more with respect to the raw material gas.

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

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

  In the present invention, the by-product contained in the product gas is not particularly limited, but mainly includes aldehydes to be removed in the present invention. These amounts are usually 0.20 to 1.00 wt%, preferably 0.21 to 0.30 wt% in the product gas. Representative examples of aldehydes include formaldehyde, acetaldehyde, acrolein and methacrolein.

In the method for producing a conjugated diene of the present invention, a conjugated diene obtained by subjecting a raw material gas containing a monoolefin having 4 or more carbon atoms and a molecular oxygen-containing gas to an oxidative dehydrogenation reaction in the presence of a catalyst in a reactor. The produced gas absorption step is performed by absorbing the produced gas in the organic solvent A to obtain the solution B containing the conjugated diene, and the conjugated diene D containing the aldehyde is separated by distilling the solution B containing the conjugated diene. A conjugated diene separation step, a conjugated diene D containing the aldehyde, and a solvent C having an infinite dilution activity coefficient γ ^∞ of 6.0 or less at 25 ° C. The aldehyde is removed through an aldehyde separation step for removing the aldehyde therein, and the conjugated diene is recovered.
The present invention may further include a cooling step for cooling the product gas from the reactor before the product gas absorption step, and a conjugate containing an aldehyde in the aldehyde separation step after the aldehyde separation step. A conjugated diene recovery step for recovering the conjugated diene dissolved in the solvent C brought into contact with the diene D may be provided.

FIG. 1 is a system diagram showing an example of an embodiment of a method for producing a conjugated diene of the present invention. A raw material gas containing a monoolefin having 4 or more carbon atoms is introduced into a reactor 1 in the presence of a catalyst. A product gas containing a conjugated diene is obtained by oxidative dehydrogenation. After this product gas is cooled in the cooling tower 2 (cooling step), it is absorbed by the organic solvent A in the absorption tower 3 to obtain a solution B containing a conjugated diene (product gas absorption step). The solution B containing the conjugated diene from the absorption tower 3 is deaerated in the degassing tower 4 and then distilled in the distillation tower 5 to distill and separate the conjugated diene D containing aldehyde and the organic solvent A. (Conjugated diene separation step). The organic solvent A separated here can be purified by the purification means 6 and recycled to the absorption tower 3. On the other hand, the conjugated diene gas D containing the aldehyde obtained in the distillation column 5 is in contact with the solvent C having an infinite dilution activity coefficient γ ^∞ of 6.0 or less at 25 ° C. in the absorption column 7. The aldehyde in the conjugated diene gas D is removed by solvent absorption (aldehyde separation step). The conjugated diene from which the aldehyde has been removed is collected as a product after further purification treatment such as dehydration treatment as necessary. In addition, since the solvent C after contacting the aldehyde-containing conjugated diene gas D in the absorption tower 7 contains the conjugated diene together with the aldehyde, the solvent C is fed to the conjugated diene recovery tower 8 to recover the conjugated diene by extraction or distillation ( Conjugated diene recovery step), the recovered conjugated diene is appropriately made into a product together with the conjugated diene from the absorption tower 7 according to the recovery form, or is circulated to the preceding step. Moreover, in this case, you may have the process (solvent reproduction | regeneration process) which reproduces | regenerates the solvent C containing the aldehyde after conjugated diene is removed from the solvent C in this way.
Hereinafter, each step will be described.

<Cooling process>
The cooling step is not particularly limited as long as it is a step that can cool the product gas of about 200 to 400 ° C. obtained from the outlet of the reactor 1, but a normal cooling operation includes a spray tower, a packed tower, a plate tower, and the like. Used.
Preferably, the cooling medium and the product gas are directly contacted in the cooling tower 2 and cooled. Although it does not specifically limit as a cooling medium, Preferably it is water and alkaline aqueous solution, Most preferably, it is water. Moreover, you may cool with coolers, such as a heat exchanger, before and after cooling with such a cooling tower 2. FIG. In addition, before and after this cooling, the product gas may be pressurized by a compressor to supply the product gas to the absorption tower 3, and a process of cooling → compression → cooling may be performed.

  The gas temperature after cooling is set to a temperature at which the product gas from the reactor 1 can be efficiently operated in the next step. Specifically, the cooling temperature of the product gas varies depending on the product gas temperature obtained from the outlet of the reactor, the kind of the cooling medium, and the like, but is usually 5 to 100 ° C, preferably 10 to 60 ° C, and more preferably 15 to 50. Set to ° C. For example, assuming that industrial water is used as the cooling medium, the final temperature after cooling can be set to 30 to 50 ° C. (when the temperature difference ΔT with respect to industrial water is set to 10 ° C.).

The higher the cooling temperature, the lower the cost for construction and operation of the cooling tower, and the lower the temperature, the lower the load for the next compression process.
When the product gas is cooled by the cooling tower, the pressure in the cooling tower is not particularly limited, but is usually 0.01 to 0.05 MPaG, for example, 0.03 MPaG.

  If the product gas contains a large amount of high-boiling by-products, polymerization between the high-boiling by-products and deposition of solid precipitates due to the high-boiling by-products in the process are likely to occur. Moreover, since the cooling medium used in the cooling tower is often circulated, clogging with solid precipitates may occur when the production of the conjugated diene is continued. For this reason, it is preferable to avoid introducing high-boiling by-products in the product gas into the cooling process as much as possible. For this purpose, it is preferable not to increase the raw material conversion rate in the reactor 1 or to set the temperature in the reactor appropriately.

<Production gas absorption process>
The produced gas that has undergone the cooling process as described above is fed to the produced gas absorption process.
In the product gas absorption step, the product gas is brought into contact with the organic solvent A in the absorption tower 3 so that the conjugated diene and unreacted raw materials in the product gas are absorbed by the organic solvent A, and the conjugated diene is contained. Solution B is obtained. That is, conjugated dienes, unreacted raw materials, aldehydes and other trace impurities contained in the product gas are absorbed by the organic solvent A, while inorganic gases such as nitrogen and oxygen are discharged from the top of the absorption tower 3. These inorganic gases are recycled to the reactor 1 after appropriate treatment.

  The organic solvent A used for absorbing the conjugated diene, the unreacted raw material and the like preferably has a high solubility in the conjugated diene and a high boiling point from the viewpoint of reduction of solvent loss and absorption efficiency of the conjugated diene. As the organic solvent A, a saturated hydrocarbon having 6 to 10 carbon atoms, an aromatic hydrocarbon having 6 to 8 carbon atoms, an amide compound, or the like is used. Specifically, for example, dimethylformamide (DMF), toluene, xylene, N-methyl-2-pyrrolidone (NMP) and the like can be used. These may use only 1 type and may mix and use 2 or more types. Among these, an aromatic hydrocarbon having 6 to 8 carbon atoms is preferable because it is difficult to dissolve the inorganic gas, and toluene is particularly preferable.

The amount of the organic solvent A used for the absorption of the product gas is not particularly limited, but in order to improve the absorption efficiency without increasing the size of the absorption tower 3, the liquid gas is a ratio of the absorption liquid amount and the generation gas amount. The ratio is generally 0.5 to 10 L-liquid / Nm ³ -gas.

<Conjugated diene separation step>
The solution B containing the conjugated diene obtained by absorption with the organic solvent A is obtained by removing a small amount of accompanying non-condensable gas (mainly nitrogen, oxygen, etc.) with a degassing tower 4 and then a distillation tower (conjugated diene separation tower). ) 5 to separate into conjugated diene and unreacted raw material and organic solvent A. This separation / separation operation is preferably carried out by distillation because the conjugated diene can be recovered with high purity.

  From the top of the distillation column 5 for separating the conjugated diene, a conjugated diene gas D containing a conjugated diene as a main component and further containing an aldehyde is obtained. The gas D may contain butene or furan. The gas D generally contains 30 to 90 wt% of conjugated diene, and is contained in an amount of 50 to 99 wt%, preferably 70 to 99 wt% as a total amount of the conjugated diene and the raw material olefins. Further, aldehydes as impurities are contained in an amount of 0.01 to 20 wt%, preferably 5 wt% or less.

  On the other hand, the column bottom liquid obtained from the column bottom of the distillation column 5 contains an organic solvent A and a high-boiling component other than the conjugated diene in the aldehyde-containing conjugated diene gas, and other than the organic solvent A by purification means such as distillation. The low-boiling components (mainly aldehydes) and high-boiling components (for example, aldehyde-derived high-boiling components) are removed and purified, and then recycled to the product gas absorption tower 3.

<Aldehyde separation process>
The conjugated diene gas D containing the aldehyde separated in the distillation column 5 is supplied to the aldehyde absorption tower 7 to remove the aldehydes contained therein, thereby obtaining a gas containing the conjugated diene as a main component and containing no aldehydes. .

  In the present invention, the aldehydes are removed from the aldehyde-containing conjugated diene gas D by solvent absorption. That is, distillation conditions can be applied under conditions where the difference in boiling point between the conjugated diene to be separated and the aldehyde is sufficiently large and does not have an azeotropic point. For example, low-boiling aldehydes such as acetaldehyde and formaldehyde In the separation of butadiene and butadiene, distillation is not suitable because the boiling point difference is extremely small and the azeotropic point is present. Therefore, solvent absorption is employed in the present invention.

A preferable solvent as an absorbing liquid when performing an absorption operation is a solvent (solvent C) satisfying an infinite dilution activity coefficient γ∞ ≦ 6.0 with respect to the absorbing solvent (solvent) of aldehyde (solute), more preferably γ∞. ≦ 6.0 and an infinite dilution activity coefficient γ∞ (hereinafter referred to as “γ∞ _B ”) of the conjugated diene to the solvent, and an infinite dilution activity coefficient γ∞ (hereinafter referred to as “γ” of the aldehyde to the solvent). ∞ _a "and referred. the ratio at which the separation factor S _{of) (= γ∞ B / γ∞ a} ) is a solvent having 1.5 or more.

In the present invention, the infinite dilution activity coefficient γ∞ means the activity coefficient of the solute component when the concentration of the solute component in the solvent component at 25 ° C. is extremely low. In general, the activity coefficient can be understood as an index indicating the affinity between the solvent component and the solute component. The larger the value, the lower the affinity between the solvent component and the solute component, and the lower the affinity. It is known that the smaller the coefficient value, the greater the affinity.
For example, taking an aldehyde and a solvent as an example, the smaller the γ∞ _A is, the higher the ability to absorb the aldehyde, and the larger the separation factor S described above, the more selective the aldehyde over the conjugated diene. Means to absorb. In order to calculate the infinite dilution activity coefficient γ∞, an activity coefficient model such as an NRTL model or a UNIFAC model is generally used. As a typical example, UNIFAC-Dortmund (DDBST company DDSP ver 10) Etc.

As the absorbing solvent C, those having γ∞ _A ≦ 6.0 and S ≧ 1.5 are particularly preferable. Examples of such a solvent C, as long as it satisfies the above conditions, H 2 _O, methanol, ethanol, propanol, acetone, 1,4-dioxane and the like, is particularly preferred H _{2 O.} The solvent C may be a mixed solvent of two or more solvents.

  The operating conditions (operating temperature, operating pressure, gas-liquid ratio) of the absorption tower 7 are designed according to a general absorption tower design method in consideration of a desired aldehyde removal rate and loss rate of conjugated dienes. For example, by increasing the operating pressure of the absorption tower, the solubility of aldehydes in the absorbing solvent can be increased, so that a desired aldehyde removal rate can be achieved with a smaller amount of absorbing solvent. On the other hand, since the solubility of conjugated dienes increases, the loss of conjugated dienes also increases. Generally, the operating pressure is set in the range of normal pressure to 1 MPa, and in particular, the operating pressure of the distillation column (conjugated diene separation column) 5 in the previous step and the temperature of the absorbing solvent C (preferably a temperature difference ΔT with industrial water) And about 30 to 45 ° C. when the temperature is 10 ° C.), the amount of the absorbing solvent necessary for the desired aldehyde removal rate is comprehensively determined.

The supply amount of the solvent C used for aldehyde absorption varies depending on the operating conditions of the absorption tower 7, but in general, in order to sufficiently increase the absorption efficiency without increasing the size of the absorption tower 7, the absorption tower 7 It is preferable that the supply amount of the solvent C used for absorption of the aldehyde is about 0.5 to 10 L / hr per 1 Nm ³ / hr of the aldehyde-containing conjugated diene gas D introduced into 7.

<Conjugated diene recovery process>
In the aldehyde separation step, when the solvent C that has contacted the aldehyde-containing conjugated diene gas D in the absorption tower 7 and absorbed and removed the aldehyde in the gas D contains conjugated diene, the conjugated diene in the solvent C becomes a loss and is conjugated. Reduces diene recovery. When the loss of conjugated dienes in the aldehyde separation step cannot be ignored, the solvent C from the aldehyde separation step is subjected to a conjugated diene recovery step.

Although there is no restriction | limiting in particular as a collection method of the conjugated diene from the solvent C, Extraction operation and distillation operation are mentioned. In the most preferred embodiment of the present invention, the aldehyde-absorbing solvent C is H ₂ O, and in that case, an extraction operation using an organic solvent is suitable for recovering the conjugated dienes.

  Hereinafter, this conjugated diene recovery step will be described with reference to FIGS. FIG. 2 is a system diagram showing a conjugated diene recovery step by an extraction operation, and FIG. 3 is a system diagram showing a conjugated diene recovery step by a distillation operation.

When recovering the conjugated dienes dissolved in the solvent C by the extraction operation, as shown in FIG. 2, the solvent C flowing out from the absorption tower 7 is fed to the extraction tank 10, and the solvent C (H ₂ O) and It is brought into contact with a solvent having low mutual solubility (that is, forming a two-liquid phase) (hereinafter sometimes referred to as “extraction solvent E”), and the conjugated diene in the solvent C is converted into the extraction solvent E with a high recovery rate. Dissolve. The recovery rate of conjugated dienes at this time is usually 50 to 100%, preferably 70 to 100%, more preferably 80 to 100%. The extraction operation may be performed in a complete mixing tank or an extraction tower, and the contact method may be either a countercurrent method or a cocurrent method. These contact methods and apparatus sizes can be selected according to the time required for liquid-liquid separation and the amount of processing liquid.

There is no restriction | limiting in particular in the temperature at the time of extracting, Usually, 0-50 degreeC, Preferably it is 30-45 degreeC.
Moreover, it is preferable to operate at a normal pressure.

The solvent used in the extraction operation is not particularly limited as long as it is a solvent that forms a two-liquid phase with the solvent C used in aldehyde absorption, but in the product gas absorption process, the solvent used to absorb the product gas in the oxidative dehydrogenation reaction. That is, it is preferable to use the same solvent as the organic solvent A as the extraction solvent E from the viewpoint of reducing the process cost. In that case, since the extraction solvent E containing the conjugated diene obtained from the extraction tank 10 can be recycled to the absorption tower 3 in the product gas absorption step, loss of the conjugated diene can be suppressed.
When a solvent other than the organic solvent A is used as the extraction solvent E, it is preferably reused as the extraction solvent E after a separation operation (regeneration treatment) between the conjugated diene and the extraction solvent E.

  On the other hand, the conjugated diene is removed by extraction, and the solvent C containing only aldehydes can be reused after being regenerated or subjected to waste liquid treatment. In the case of reusing the solvent C without performing the regeneration treatment, if the aldehyde concentration in the solvent C is increased, the aldehyde recovery rate in the absorption operation is lowered, and therefore, a treatment such as partial discharge from the system is performed. preferable.

  The use amount of the extraction solvent E is not particularly limited as long as it is an amount capable of efficiently extracting and recovering the conjugated diene in the solvent C from the absorption tower 7, but the extraction tank 10 is enlarged. In order to obtain high extraction efficiency without doing this, it is preferable to use about 0.5 to 2.0 times (mass basis) as a guide for the solvent C introduced into the extraction tank 10.

  In the case of recovering the conjugated diene dissolved in the absorption solvent C by distillation operation, as shown in FIG. 3, the absorption solvent C flowing out from the absorption tower 7 is supplied to the distillation tower 11, and the conjugated diene and the solvent C are respectively supplied to the tower. Collect from the top and bottom. Although there are no restrictions on the operating conditions (theoretical plate number, operating pressure, operating temperature, reflux ratio, gas-liquid ratio in the tower) when performing this distillation operation, the aldehyde absorbed in the solvent C in the aldehyde separation step of the previous step It is necessary to select operating conditions so as not to be mixed into the recovered conjugated diene. The operation pressure of the distillation column is determined in consideration of the utility cost required for the cooling operation at the top of the column and the heating operation at the bottom of the column, the pressure resistance of the material used, etc., and preferably the column top temperature is 30 to 50 ° C. Select the operating pressure so that

  The solvent C obtained by recovering and removing the conjugated diene and containing the aldehyde obtained from the bottom of the column after the distillation operation can be reused after being regenerated or subjected to waste liquid treatment. In the case of reusing the solvent C without performing the regeneration treatment, if the aldehyde concentration in the solvent C is increased, the aldehyde recovery rate in the absorption operation is lowered, and therefore, a treatment such as partial discharge from the system is performed. preferable.

<Solvent regeneration process>
As a method for removing aldehyde from the solvent C containing aldehyde obtained by recovering the conjugated diene from the solvent C in the above conjugated diene recovery step, the aldehyde is diffused in the diffusion tower 12 as shown in FIG. The method of removing is mentioned. As a means for diffusing this aldehyde, distillation operation can be mentioned. Although there are no restrictions on the operating conditions for aldehyde emission in the distillation tower, it is usually set so that 80 to 100%, preferably 90 to 100%, of aldehydes can be removed. A part of the solvent C from which aldehyde has been removed by diffusion is discharged out of the system as needed and used for waste liquid treatment, and the remainder is recycled to the absorption tower 7 which is an aldehyde separation step.

  Hereinafter, the present invention will be described more specifically with reference to examples.

In the following, abbreviations indicate the following.
1BTE: 1-butene t2BTE: trans-2-butene c2BTE: cis-2-butene isoBTE: isobutene n-BTA: n-butane isoBTA: isobutane isoBTY: isobutylene TOL: toluene 1,3-BD: 1,3-butadiene

  In Examples 1 and 2 and Comparative Example 1 below, the aldehyde-containing butadiene supplied to the aldehyde absorption tower is aldehyde-containing butadiene obtained by the process shown in Production Example 1 below.

[Production Example 1]
Source gas (composition, 1BTE: 43.0 vol%, t2BTE: 18.2 vol%, c2BTE: 13.3 vol%, isoBTE: 2.5 vol%, nBTA: 15.2 vol%, isoBTA: 4.7 vol%), N ₂ , air and steam, respectively ^{5209Nm 3 / hr, 19,133Nm 3 /} hr, and mixed with 28,883Nm ³ /hr,5913.6Nm 3 / hr, and fed to the oxidative dehydrogenation reactor (heating medium temperature 360 ° C. A maximum temperature in the reactor of 400 ° C., a reactor outlet pressure of 140 kPa), a product gas containing butadiene, butene and an inorganic gas is obtained. The mass flow rate of the product gas is 75810.4 kg / hr, and its mass fraction is mainly N ₂ : 70.9%, O ₂ : 5.3%, t2BTE: 1.6%, c2BTE: 0.9% Butadiene: 8.8%. Aldehydes as reaction by-products are methacrolein: 0.6%, acrolein: 0.2%, acetaldehyde: 0.2%, 2-butenone: 746 ppm. On the other hand, the molar flow rate was 2640 kmol / hr, and the molar fraction was mainly N ₂ : 72.7%, O ₂ : 4.8%, t2BTE: 0.8%, c2BTE: 0.5%, butadiene: 4. 7%. Aldehydes as reaction by-products are methacrolein: 0.2%, acrolein: 0.1%, acetaldehyde: 0.2%, 2-butenone: 300 ppm.

The reaction product gas is cooled to 45 ° C., and then the pressure is increased to 830 kPa by a compressor. Cool the compressed gas to 25 ° C. The cooled product gas is absorbed by the solvent with toluene in an absorption tower (top pressure 800 kPa).
As a result, an inorganic gas mainly composed of N ₂ can be obtained from the top of the absorption tower, and a solution containing toluene, butadiene, and butenes can be obtained from the bottom of the tower. The toluene flow rate used for absorption is 109 ton / hr, the column top gas flow rate is 59,655 kg / hr, and the column bottom liquid amount is 118.6 ton / hr. Further, the composition (mass fraction) of the column top gas is N ₂ : 90.1%, O ₂ : 6.8%, CO ₂ : 1%, toluene: 1.7% (in the molar fraction, N ₂ : 92 2%, O ₂ : 6.1%, CO ₂ : 0.7%, toluene: 0.5%). On the other hand, the composition (mass fraction) of the tower bottom liquid is mainly toluene: 88.8%, butadiene: 5.8%, t2BTE: 1.1%, c2BTE: 0.6%, methacrolein: 0.5 %, Acrolein: 0.2%, acetaldehyde: 0.1% (in terms of mole fraction, toluene: 83.5%, butadiene: 9.4%, t2BTE: 1.6%, c2BTE: 1.0%, methacrolein : 0.6%, acrolein: 0.2%, acetaldehyde: 0.3%).

  A toluene solution containing butadiene obtained by solvent absorption with toluene is degassed by a degassing tower (top pressure 200 kPa), and then distilled and separated into butadiene and toluene in a distillation tower (top pressure 500 kPa). The mass flow rate of the aldehyde-containing butadiene mainly composed of butadiene and butene thus obtained is 9341.1 kg / hr (molar flow rate 174.9 kmol / hr), and its composition (mass fraction) is mainly 73.1% butadiene, Butenes 22.2%, acetaldehyde 3.0%, formaldehyde 1.2% (in terms of mole fraction, butadiene 72.1%, butenes 21.2%, acetaldehyde 3.6%, formaldehyde 2.1%) .

[Example 1]
Indicating the aldehyde absorption simulation results using H _{2 O} as the aldehyde absorbent solvent C.
The infinite dilution activity coefficient γ∞ _A (calculated using 25 ° C., UNIF-DMD) of acetaldehyde with respect to H ₂ O is 5.0. Further, the infinite dilution activity coefficient γ∞ _B of butadiene with respect to water is 43.06, and the separation coefficient S is 8.6.

In addition, the simulation shown below is performed using the process simulation software "ASPENPLUS (V7.2)" of ASPENTECH, and a physical property model uses UNIFAC-DMD. The column bottom recovery rate in the table is calculated by the following formula. Here, the raw material gas is an aldehyde-containing butadiene gas supplied to the aldehyde absorption tower.
Column bottom recovery rate = (each component amount contained in the column bottom liquid / each component amount contained in the raw material gas) × 100

The aldehyde-containing butadiene obtained by the process of Production Example 1 is supplied to the lowermost stage of the aldehyde absorption tower 7 shown in FIG. 2 (however, extraction operation is not performed in this example).
The aldehyde absorption tower 7 has 15 theoretical stages, the top pressure is set to 470 kPa, and the differential pressure for each stage is set to 1.4 kPa. The temperature of the aldehyde-containing butadiene supplied to the absorption tower 7 was set to 53.9 ° C., and the temperature of H ₂ O as the absorption solvent C was set to 25 ° C. (assuming cooling with cold water). The mass flow rate of aldehyde-containing butadiene is 9246 kg / hr (molar flow rate is 171.6 kmol / hr), and its composition (mass fraction) is mainly butadiene: 73.8%, butenes: 22.5%, aldehydes: 3.0% (in terms of molar fraction, butadiene: 73.5%, butenes: 21.6%, aldehydes: 3.7%). The aldehyde removal rate and butadiene loss rate in the absorption tower 7 when H ₂ O was supplied at 7800 kg / hr from the top of the tower were calculated by simulation.
As a result, the removal rate of aldehydes is 91.9%, and the loss rate of butadiene is about 12.5% (both are based on mass).

[Comparative Example 1]
An aldehyde absorption simulation result in the same process as in Example 1 except that cyclohexane was used instead of H ₂ O as the aldehyde absorbing solvent C is shown.
The infinite dilution activity coefficient γ∞ _A (calculated using UNIF-DMD) of acetaldehyde for cyclohexane is 6.6, the infinite dilution activity coefficient γ∞ _B of butadiene for cyclohexane is 1.2, and the separation factor S is 0.18.

In addition, the simulation shown below is performed using the process simulation software "ASPENPLUS (V7.2)" of ASPENTTECH similarly to Example 1, and the physical property model similarly uses UNIFAC-DMD. The column bottom recovery rate in the table is also calculated in the same manner as in Example 1.
As a result, the acetaldehyde removal rate in the aldehyde absorption tower is 42.5%, and the butadiene loss rate is 52.3% (both are based on mass).

  The results of Example 1 and Comparative Example 1 are summarized in Table 1.

[Example 2]
Using H ₂ O as the aldehyde absorbing solvent C, the aldehyde-containing butadiene obtained by the process of Production Example 1 is fed to the aldehyde absorbing tower 7 shown in FIG. 2 to remove the aldehyde, and the solvent C used for absorbing the aldehyde. A simulation of removing and recovering butanediene from the extraction tank 10 is performed.

In addition, the simulation shown below was performed using the process simulation software "ASPENPLUS (V7.2)" of ASPENTTECH, and the physical property model used NRTL-HOC. The tower top recovery rate in the table is calculated by the following formula. Here, the raw material gas is an aldehyde-containing butadiene gas supplied to the aldehyde absorption tower 7.
Tower top recovery rate = (each component amount contained in the tower top gas / each component amount contained in the raw material gas) × 100

  The mass flow rate of aldehyde-containing butadiene is 9257 kg / hr, and its composition (mass fraction) is mainly butadiene: 72.5%, butenes: 22.7%, acetaldehyde: 3.0%, formaldehyde: 1.2% It is. The molar flow rate is 173.5 kmol / hr, and its composition (molar fraction) is mainly butadiene: 71.5%, butenes: 21.6%, acetaldehyde: 3.7%, formaldehyde: 2.1% is there.

The aldehyde absorption tower has 15 theoretical plates, the top pressure is set to 470 kPa, and the differential pressure for each stage is set to 1.4 kPa. From the top of the column, H ₂ O is supplied at a rate of 21220 kg / hr (molar flow rate 1178 kmol / hr) as the aldehyde absorbing solvent C. The temperature of the aldehyde-containing butadiene supplied to the absorption tower 7 is set to 47.7 ° C., and the temperature of H ₂ O as the absorption solvent C is set to 50 ° C. (assuming cooling with industrial water). When aldehyde absorption is performed, the column top gas amount is 8761 kg / hr (molar flow rate 163.4 kmol / hr), and the column bottom liquid amount is 211716.1 kg / hr (molar flow rate 1188.0 kmol / hr). The tower top recovery rates of acetaldehyde and formaldehyde are both 0.0% (both are based on mass) (therefore, the removal ratio of each component in the absorption tower 7 is 100%). The butadiene tower top recovery rate is 97.9% of the butadiene in the raw material gas.

  The tower bottom liquid containing a small amount of butadiene, butenes and removed aldehydes from the bottom of the aldehyde absorption tower 7 is supplied to a mixer-settler type extraction tank 10. To recover butadiene and butenes dissolved in a small amount in the bottom liquid, toluene is supplied to the extraction tank 10 at 14000 kg / hr (molar flow rate 152.2 kmol / hr) and mixed with the bottom liquid discharged from the aldehyde absorption tower 7. To do. The operating conditions of the extraction tank 10 are a temperature of 45 ° C. and a pressure of 101.3 kPa. The mixed liquid is supplied to a liquid-liquid separator and separated into an oil layer and an aqueous layer.

  As a result, it is possible to obtain 14252.2 kg / hr (molar flow rate 158.4 kmol / hr) of an oil layer containing butadiene and butenes, and 21463.9 kg / hr (molar flow rate 1181.7 kmol / hr) of an aqueous layer containing aldehydes. it can. The oil layer containing butadiene and butenes is circulated and used as the organic solvent A of the absorption tower (absorption tower 3 in FIG. 1) for separating butadiene, which is a pre-process of the aldehyde absorption tower. On the other hand, an aqueous layer containing a large amount of aldehydes is sent to a wastewater treatment facility as wastewater. The amount of butadiene in the aqueous layer containing a large amount of aldehyde treated as waste water is 3.5 kg / hr (molar flow rate 0.06 kmol / hr), and the loss rate is 0.1% (that is, butadiene recovery in this process). The rate is 99.9%).

  From the above results, according to the present invention, a raw material gas containing a monoolefin having 4 or more carbon atoms such as n-butene and a molecular oxygen-containing gas are obtained by an oxidative dehydrogenation reaction in the presence of a catalyst. From the product gas containing conjugated dienes such as butadiene, aldehydes produced as a by-product in the reaction are efficiently removed while suppressing loss of the conjugated diene, which is the target product, and the conjugated dienes are recovered in a high yield. I can see that

DESCRIPTION OF SYMBOLS 1 Reactor 2 Cooling tower 3 Absorption tower 4 Deaeration tower 5 Distillation tower 6 Purification means 7 Absorption tower 8 Conjugated diene recovery tower 10 Extraction tank 11 Distillation tower 12 Stripping tower

Claims (5)

An aldehyde is removed from a product gas containing a conjugated diene obtained by subjecting a raw material gas containing a monoolefin having 4 or more carbon atoms and a molecular oxygen-containing gas to an oxidative dehydrogenation reaction in the presence of a catalyst. A product gas absorption step for obtaining a solution B containing the conjugated diene in which the non-aggregating gas is separated by absorbing the organic solvent A without performing an operation ;
A conjugated diene separation step of separating the conjugated diene D containing aldehyde from the organic solvent A and high-boiling components by distilling the solution B containing the conjugated diene;
Aldehyde that removes aldehyde in conjugated diene D by solvent absorption by contacting conjugated diene D containing aldehyde with solvent C having an infinite dilution activity coefficient γ ^∞ of 6.0 or less at 25 ° C. A method for producing a conjugated diene, comprising: a separation step.   The method for producing a conjugated diene according to claim 1, further comprising a conjugated diene recovery step of recovering the conjugated diene dissolved in the solvent C brought into contact with the conjugated diene D containing the aldehyde.   The method for producing a conjugated diene according to claim 2, wherein the conjugated diene recovery step is performed by extraction or distillation.   The raw material gas is produced by dehydrogenation or oxidative dehydrogenation of gas containing 1-butene, cis-2-butene, trans-2-butene or a mixture thereof obtained by dimerization of ethylene, or a mixture thereof. The conjugate according to any one of claims 1 to 3, which is a gas containing a large amount of hydrocarbons having 4 carbon atoms, which is obtained when fluidly cracking a butene fraction or a heavy oil fraction. Diene production method. Furthermore, it has a deaeration process for removing the non-aggregating gas accompanying the solution B containing the conjugated diene, and the solution B containing the conjugated diene after the deaeration process is fed to the conjugated diene separation process. The method for producing a conjugated diene according to any one of claims 1 to 4, wherein:

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