JPH0899915A - Method for recovering 2,6-dimethylnaphthalene - Google Patents

Abstract

PURPOSE: To provide an industrial and advantageous method for recovering 2,6-dimethylnaphthalene (2,6-DMN), capable of efficiently recovering high-purity 2,6-DMN and recycling a raw material. CONSTITUTION: A hydrocarbon mixture containing 2,6-DMN is brought into contact with m-nitrobenzoic acid (m-NBA) in the presence of an aromatic hydrocarbon to form a complex consisting essentially of m-NBA and 2,6-DMN and the complex is precipitated and made into a slurry state (first process). Then the slurry is separated into the complex and a liquid (second process) and the separated complex is wholly or partially returned to the first process (third process) The residual complex is brought into contact with a two-phase based liquid comprising a lower hydrocarbon and an aqueous solution of a lower aliphatic alcohol and decomposed and the two phases are separated (forth process). m-NBA is recovered from the aqueous solution of the alcohol containing m-NBA and returned to the first process (fifth process). The hydrocarbon is partially recovered from the phase of the hydrocarbon, crystal of 2,6-DMN is precipitated and made into a slurry state (sixth process) to separate and recover 2,6-DMN from the slurry.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for isolating and recovering 2,6-DMN from a mixture containing 2,6-dimethylnaphthalene (hereinafter abbreviated as "2,6-DMN").

[0002]

2. Description of the Related Art Dimethylnaphthalene (DMN) is used as a surfactant raw material and a heating medium, and there are 10 isomers. Among these, 2,6-DMN is contained in light cracked gas oil (LCO), reformed oil, coal tar, and the like, together with other isomers. The following methods are already known as methods for isolating and recovering 2,6-DMN from these.

That is, the 2,6-DMN is the other DMN.
Since the symmetry is better than that of the isomer, it is easy to form a complex. Therefore, a complex of 2,6-DMN alone is formed in a hydrocarbon mixture containing 2,6-DMN together with other DMN isomers. There is a method of isolating and recovering 2,6-DMN by separating it from a hydrocarbon mixture. For complex formation, for example, m-nitrobenzoic acid (hereinafter referred to as “m-NB
A) (abbreviated as "A") (Japanese Patent Publication No. 47-29893, etc.) is known.

Further, as a method for decomposing the complex formed by the above method and recovering 2,6-DMN, 1) using lower saturated hydrocarbon and water, 2,6-DMN is added to the hydrocarbon, Two-phase decomposition method in which m-NBA is dissolved in water (Japanese Patent Publication No. 47-30174, JP-A-6-
116177, etc.), 2) by dissolving the complex using a lower aliphatic alcohol, and then cooling
Method for precipitating 6-DMN (Japanese Patent Publication No. 47-44728)
And the like) have been proposed.

[0005]

However, in the above method, the required amount of m-NBA is higher than the solubility of the hydrocarbon mixture in the complex formation step, and therefore m-N which does not dissolve is dissolved.
BA comes into contact with the hydrocarbon mixture containing 2,6-DMN in the solid state, and the utilization efficiency of m-NBA is low,
As a result, there is a drawback that the capture rate of 2,6-DMN is lowered. In the complex decomposition step,
The method of Japanese Patent Publication No. 47-30174 of 1) requires a large amount of water because the solubility of m-NBA in water is small, and as a result, it is difficult to reuse the captured m-NBA. According to the method of Japanese Laid-Open Patent Publication No. 116177, although a small amount of water is required, a large amount of heat is required, and m-NBA
May dissolve in the oil phase in a small amount, so that a multi-stage repeated operation may be required. In the method 2), m-NB
In order to separate A and 2,6-DMN, it is necessary to repeat the operation of dissolution and cooling, which not only requires a large amount of solvent, but also reduces the yield of 2,6-DMN. was there.

Therefore, an object of the present invention is to provide a method for efficiently recovering highly pure 2,6-DMN which does not have the above-mentioned drawbacks and which can effectively use the raw materials.

[0007]

DISCLOSURE OF THE INVENTION In view of such circumstances, the inventors of the present invention have conducted diligent research and as a result, as a result, a hydrocarbon mixture containing 2,6-DMN was treated with m-NB in the presence of an aromatic hydrocarbon.
By contacting with A, a complex mainly composed of m-NBA and 2,6-DMN is formed, this is precipitated and separated, and the separated complex is added to the above-mentioned new mixture to form a complex again. For example, the purity of 2,6-DMN in the complex can be improved, and by using the lower aliphatic alcohol aqueous solution in the complex decomposition step, m-NBA
However, it shows high solubility in a phase composed of a lower aliphatic alcohol aqueous solution, and has good separability from a lower hydrocarbon phase, and the reaction proceeds efficiently at a much lower temperature than before,
Since m-NBA can be easily reused, and the purity of 2,6-DMN is improved in the state of a complex, a step for improving the purity such as recrystallization after decomposition is unnecessary. Therefore, the present invention has been completed and the present invention has been completed.

That is, the present invention includes the following steps (1) to
(7) (1) A hydrocarbon mixture containing 2,6-dimethylnaphthalene is contacted with m-nitrobenzoic acid in the presence of an aromatic hydrocarbon, so that m-nitrobenzoic acid and 2,6-dimethylnaphthalene are mixed with each other. In the complex forming step of forming a main complex and precipitating the complex into a slurry state, the complex separated in the subsequent step (2) and further separated from the complex in the subsequent steps (4) and (5) M-nitrobenzoic acid to be mixed into the system of the above complex formation step to repeatedly form a complex and precipitate the complex to form a slurry state,
(2) A step of separating the slurry obtained in the step (1) into a complex and a liquid, and (3) returning all or part of the complex separated in the step (2) to the step (1). The step of transferring the residue to the step (4), and the complex transferred in the steps (4) and (3) are decomposed by contacting with a two-phase liquid composed of a lower hydrocarbon and a lower aliphatic alcohol aqueous solution. Then, a step of separating the two phases, (5) recovering all or part of the lower aliphatic alcohol aqueous solution from the lower aliphatic alcohol aqueous solution containing m-nitrobenzoic acid obtained in the step (4), m -Step of returning nitrobenzoic acid to the step (1), (6) Part of the lower hydrocarbon is recovered from the lower hydrocarbon phase obtained in the step (4), and 2,6-dimethylnaphthalene is obtained. A step of precipitating crystals mainly composed of to form a slurry state, (7 From the slurry obtained in the step (6), a crystal composed mainly of 2,6-dimethylnaphthalene, comprising the step, which is separated into a phase of lower hydrocarbons 2,
A method for recovering 6-dimethylnaphthalene is provided. Furthermore, the present invention provides the above step as step (8),
The present invention provides a method for recovering 2,6-DMN by adding a step of isomerizing the liquid phase obtained in the step (2) to 2,6-DMN.

In the present invention, the raw material hydrocarbon mixture used in the complex formation step (1) is not particularly limited as long as it is a hydrocarbon mixture containing 2,6-DMN, and examples thereof include quinoline and indole. A hydrocarbon mixture containing a nitrogen compound, a sulfur-containing compound such as thiophene or thionaphthene is not particularly problematic, and a hydrocarbon mixture having a low concentration of DMNs can also be used. Specific examples of the raw material hydrocarbon mixture include LCO, oils such as reformed oil obtained in each process of the petroleum refining industry, coal tar, and the like. In particular, these raw materials are used in the boiling range of DMNs. It is more preferable to pre-distill to a fraction of about 260 to 270 ° C., and it goes without saying that a mixture of DMNs itself can be used.

The aromatic hydrocarbon used as the solvent is preferably a monocyclic one, such as benzene, toluene and xylene. The addition amount of these is preferably about 0.2 or more in terms of weight ratio to the raw materials, and in view of economic efficiency, it is particularly about 0.2 to 5.
It is preferably used in the range of 0, more preferably about 0.5 to 3.0.

M-NB which forms a complex with 2,6-DMN
When the compounding amount of A is too small, the capturing rate of 2,6-DMN is lowered, and even when it is too large, the compounding effect of m-NBA is saturated and an improving effect of the capturing rate of 2,6-DMN is observed. Therefore, the weight ratio to 2,6-DMN in the raw hydrocarbon mixture is preferably about 0.8 to 7.5, and more preferably about 1.0 to 6.5. Further, from the step (5) described later, a small amount of the lower aliphatic alcohol aqueous solution may be mixed when m-NBA is reused in the step (1). There is no hindrance.

Regarding the complex circulated in the step (3), if the compounding amount is too small, 2,
If the effect of improving the purity of 6-DMN becomes small, and conversely if it is too large, the amount of the raw material hydrocarbon mixture used decreases, and 2,6-
Since the amount of DMN recovered is reduced, the weight ratio to the raw hydrocarbon mixture is about 0.1 to 3.0, particularly about 1.0 to 2.
It is preferably 0.

The above hydrocarbon mixture, the complex returned from the step (3) described later, the aromatic hydrocarbon and m-NBA.
The addition order of is not particularly limited. However, it is possible to previously mix the complex and m-NBA with an aromatic hydrocarbon, and add a slurry state to the raw material hydrocarbon mixture,
It is more preferable for promptly proceeding the complex formation reaction.
In order to make the complex formation reaction more efficient, the reaction temperature is set to 40 to 140 ° C., preferably 50 to 100 ° C., in which the aromatic hydrocarbon has a suitable solubility of m-NBA, and about 10 minutes to 1 minute. After sufficiently stirring for about an hour, the mixture may be left standing to cool or forcedly cooled while stirring to room temperature to precipitate the complex. Regarding cooling, jacket cooling in the reaction tank, external cooling by a heat exchanger, and the like are conceivable, but adiabatic cooling in the reaction tank to remove water and aromatic hydrocarbons is particularly preferable.

Although the complex formed is a complex of m-NBA and 2,6-DMN, 2,6-
Even when a hydrocarbon mixture containing other DMN isomers is used together with DMN, it is mainly a complex of 2,6-DMN and m-NBA, and other DMN in this raw material is used.
It is difficult to form a complex with isomers. Therefore, according to the present invention, when a hydrocarbon mixture containing 2,6-DMN and other isomers is used as a raw material, it is possible to separate and collect DMN containing 2,6-DMN with high purity. it can.

In the step (2) of the present invention, the above (1)
After the step of is completed, the complex is separated by a general solid-liquid separation method such as filtration or centrifugation. At this time, it goes without saying that the complex does not completely migrate to the solid side, but a small amount thereof migrates to the liquid layer side. All or a part of the complex separated in the step (2) is transferred to the step (1) in the step (3), and the rest is transferred to the step (4).

The step (4) is a step of contacting the complex with a two-phase liquid composed of a lower hydrocarbon and a lower aliphatic alcohol aqueous solution to decompose the complex. In this step, as the lower aliphatic alcohol of the lower aliphatic alcohol aqueous solution, an aliphatic saturated monohydric alcohol having about 1 to 4 carbon atoms such as methanol, ethanol, propanol and butanol, and water may be ion-exchanged water or pure water. Preferably used, lower hydrocarbons include petroleum ether, pentane,
Hexane, heptane, octane, nonane, ligroin,
5 to 1 carbon atoms such as cyclohexane and cyclopentane
Lower hydrocarbons of about 0 can be preferably used.

In the method of the present invention, the concentration of the lower aliphatic alcohol in the lower aliphatic alcohol aqueous solution is 60 to 95% by weight (hereinafter abbreviated as "%"), preferably 75 to 85%. If the concentration of the lower aliphatic alcohol is less than 60%, m-NBA cannot be dissolved, so separation may be hindered unless the amount of the lower aliphatic alcohol aqueous solution phase is increased. Also,
When it is more than 95%, the separation from the lower hydrocarbon phase becomes poor and the transfer of 2,6-DMN to the lower aliphatic alcohol aqueous solution side increases.

The amount of the lower aliphatic alcohol aqueous solution defined as described above is such that m-NBA and 2,6-D are used.
A weight ratio of 0.5 to 10 times, preferably 2 to 4 times, is suitable for the total amount of the complex with MN. If the amount of the lower aliphatic alcohol aqueous solution is less than the above range, m-NB
If A cannot dissolve, and too much,
Not only is the transfer of 2,6-DMN to the lower aliphatic alcohol aqueous solution phase side increased, but the amount of the complex to be separated decreases, which is economically undesirable.

The amount of the lower hydrocarbon used may be at least twice the weight of the total amount of the complex of m-NBA and 2,6-DMN. If it is less than that, 2,6-DMN
Becomes impossible or extremely difficult to transfer to the lower hydrocarbon phase, so that decomposition does not occur. Further, since the amount of m-NBA is transferred to the lower hydrocarbon phase even if the amount is too large, the upper limit is set to 10 times, and preferably 3 to 8 times.

A two-phase liquid containing the above aqueous solution of lower aliphatic alcohol and lower hydrocarbon, m-NBA and 2,6
The order of contacting each of these components when contacting the complex with -DMN is not particularly limited.

In the step (4), the decomposition temperature of the complex is 10
It is suitable to set the temperature to ˜55 ° C., preferably 20 to 40 ° C. If the temperature is lower than this range, not only the reaction rate of decomposition slows down, but also the complex cannot be dissolved,
Decomposition may not occur. Also, if it is too high, the m-NBA which is a problem that the conventional decomposition method has.
Is dissolved in the lower hydrocarbon phase side, and an operation for removing or recovering this is required. At the above temperature, the two-phase liquid consisting of the lower aliphatic alcohol aqueous solution and the lower hydrocarbon and the complex of m-NBA and 2,6-DMN are sufficiently stirred and mixed, and the complex is immediately formed. After decomposition, m-NBA is transferred to the lower aliphatic alcohol aqueous solution phase, and 2,6-DMN is transferred to the lower hydrocarbon phase.

The stirring time at this time is preferably about 10 minutes to 1 hour, because if the stirring time is too short, the decomposition of the complex will be insufficient, and if it is too long, no further decomposition will occur.

Thereafter, the mixture is allowed to stand at the above temperature to separate into a lower hydrocarbon phase and a lower aliphatic alcohol aqueous solution phase to which m-NBA has been transferred, and the lower aliphatic alcohol aqueous solution phase is subjected to the step (5), It returns to the complex formation process of (1). Since this phase contains a large amount of m-NBA, in the complex formation step of (1) above, the m-NBA
Are again used to form the complex. When returning the aqueous alcohol phase to the complex forming step, it is preferable to recover a part or all of the lower aliphatic alcohol. In the case where m-NBA is partially collected and concentrated, it is preferable to heat it during returning so as to completely dissolve m-NBA in the remaining alcohol aqueous solution phase. In the case of recovering all, it is also preferable to cool the aqueous alcohol solution phase to precipitate m-NBA, and return only the precipitated m-NBA to the complex formation step (1).

On the other hand, regarding the lower hydrocarbon phase, (6)
In the separation step (7), a slurry in which crystals mainly composed of 2,6-DMN are precipitated from the step of
DMN is recovered as crystals mainly composed of DMN. Separation can be performed by a conventional method such as centrifugation.

Further, the liquid phase separated from the complex in the step (2) is sent to the isomerization step in the step (8) to carry out an isomerization reaction to improve the concentration of 2,6-DMN. it can. In this isomerization step, for example, the above liquid phase (lower hydrocarbon phase) is added to a pentasil-type crystalline aluminosilicate zeolite of Group IIIB (eg, gallium or aluminum) IIB group (eg, zinc) of the periodic table of elements. It is carried out by contacting with a catalyst containing at least one of them to isomerize DMN in the oil phase into 2,6-DMN. The liquid phase that has undergone the isomerization step is used as a raw material for the complex formation step in (1).

An example of the method of the present invention is shown in FIG.
According to the schematic explanatory view showing the flow of, the explanation will be as follows.

That is, in FIG. 1, reference numeral 2 denotes a complex forming apparatus used in the complex forming step (1) of the present invention, which is equipped with a stirring means, a heating means, a cooling means, a pressure adjusting means or the like (not shown). There is. In the complex forming apparatus 2, the raw material hydrocarbon mixture, aromatic hydrocarbon, and m-NBA introduced from the line 1, the complex introduced from the solid-liquid separation apparatus 4 via the line 6, and the complex decomposition apparatus 8 and M-NBA (and the lower aliphatic alcohol aqueous solution) introduced through the line 9 via the solvent recovery device 14 for the lower aliphatic alcohol aqueous solution phase is heated to a predetermined temperature, stirred and mixed, and mainly 2, A complex of 6-DMN and m-NBA is formed. After that, the liquid containing the above complex is forcibly cooled while being stirred to room temperature, becomes a slurry state in which the complex is deposited, and is sent to the solid-liquid separation device 4 through the line 3, and the liquid of (2) of the present invention is used. The step of separating the complex from the liquid is performed.

The separated complex is sent to the complex forming apparatus 2 via the line 6 (step (3) of the present invention) or the complex decomposing apparatus 8 via the line 5. The latter complex is subjected to the complex decomposition step (4) of the present invention in the complex decomposition device 8. This complex decomposing device 8 is equipped with a stirring means, a heating means, a cooling means, and an oil / water separating means, which are not shown in the figure.
The two-phase liquid consisting of the lower aliphatic alcohol aqueous solution and the lower hydrocarbon introduced from the above is contacted, these are heated to a predetermined temperature and mixed by stirring to decompose the complex. next,
The system in which the complex decomposition had been completed was allowed to stand in this apparatus 8 to transfer m-NBA and a lower hydrocarbon phase to which 2,6-DMN (containing a small amount of other DMN isomers) was transferred. The transferred aqueous alcohol solution phase is separated. And
The lower aliphatic alcohol aqueous solution to which m-NBA has been transferred is sent to the lower aliphatic alcohol aqueous solution recovery device 14 via a line 15, and the step (5) of the present invention is performed. This device 14 is provided with heating means, cooling means, pressure adjusting means, etc. (not shown), and it is also possible to collect all or part of the lower aliphatic alcohol aqueous solution and send it again to the complex decomposing device 8 via line 16. . On the other hand, m-NBA is returned to the complex forming apparatus 2 via the line 9 (step (5) of the present invention) and reused in the complex forming step (1) described above. An appropriate heating means may be provided on the way of the line 9 so that the aqueous phase is introduced into the complex forming apparatus 2 while being heated.

On the other hand, the lower hydrocarbon phase to which the DMNs have been transferred is sent to the lower hydrocarbon recovery device 17 via the line 18 and the step of the present invention (6) is carried out. This device 17 is equipped with a stirring means, a heating means, a cooling means, a pressure adjusting means, etc., which are not shown, and collects part of the lower hydrocarbons,
2,6-DMN (containing a small amount of other DMN isomers) crystals were precipitated, and a part of the lower hydrocarbons was found in line 1
It can also be sent again to the complex decomposition device 8 via 9. Further, the slurry in which the 2,6-DMN crystals are deposited is transferred via line 10 to the solid-liquid separator 11 in which the step (7) of the present invention is performed. For example, when a centrifuge is used as the solid-liquid separator 11, it is possible to wash lower hydrocarbons having DMNs transferred with a lower aliphatic alcohol aqueous solution prior to introduction into the centrifuge. , 6-DMN is preferred for high purity recovery. After this washing, if filtered in a centrifuge,
DMN containing 2,6-DMN in about 99% or more can be obtained.

[0030]

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

Example 1 2,6-DMN was produced according to the schematic explanatory view of FIG. That is, first, 20 fractions of 220 to 260 ° C. having the composition shown in Table 1 obtained by precision distillation of SWA1500BTM were used.
3.0 kg was used as the raw material hydrocarbon oil, and m-NBA8 was added to this.
4.4 kg and toluene 168.9 kg were added, and at 97 ° C, 3
After stirring for 0 minutes, the mixture was cooled to room temperature to form a slurry, and solid-liquid separation was performed in a centrifuge to obtain 94.5 kg of solid (complex).

[0032]

[Table 1]

And all or part of the obtained complex,
131. By mixing the raw material hydrocarbon oil of the above composition, m-NBA, and toluene, and repeating the same operation, 131.
3 kg of solid (complex: 2,6-DMN purity 90.0%) was obtained. At this time, the composition of the charge was 81.
5 kg, toluene 217.4 kg, complex 104.4 kg, m-
The amount of NBA was 33.0 kg (including recycled m-NBA separated and collected in the decomposition step described later). At this time, the weight of the complex returned to the complex formation step and the weight of the complex returned to the subsequent decomposition step were 80% and 20%, respectively, with respect to the produced complex [step (1),
(2), (3), (5)].

Next, a part of the complex obtained in the above step 25.0
kg, 100 kg of n-heptane, and 75.0 kg of 80% aqueous methanol solution were stirred in an autoclave at 40 ° C for 30 minutes, then stirred to 30 ° C, allowed to cool, and allowed to stand for 30 minutes to form an aqueous methanol solution phase. The mixture was taken out and mixed again with 75.0 kg of the above methanol aqueous solution, and the same temperature rising, cooling and standing were repeated once more, and then the methanol aqueous solution phase and
The heptane phase was separated [step (4)].

Subsequently, 71.0 kg of n was obtained from the n-heptane phase.
-Heptane was distilled off and returned to the complex decomposition step. 2,6
Crystals mainly composed of DMN were precipitated to make a slurry [step (6)]. The slurry obtained in the above step was subjected to solid-liquid separation in a centrifuge to obtain 4.7 kg of crystals mainly composed of 2,6-DMN (2,6-DMN purity 99.5%) [step (7 )]. On the other hand, a total of 18.4 kg of m-NBA was recovered from the aqueous methanol solution phase and returned to the complex formation step. The recovered aqueous methanol solution was returned to the complex decomposition step. Regarding the liquid (filtrate) obtained in the solid-liquid separation step [step (2)] after complex formation, a catalyst in which a gallium compound is contained in a pentasil-type crystalline aluminosilicate zeolite packed in a stainless steel reaction tube Was used to carry out an isomerization reaction under the conditions of 400 ° C., LHSV = 1.0 h ⁻¹ and a pressure of 10 atm. As a result,
Isomerized oil, liquid yield 80.0%, DMN concentration 7.95%
(Step (8)) obtained in (excluding toluene content). This isomerized oil was mixed with the above SWA1500BTM and used as a raw material for the complex formation step.

[0036]

INDUSTRIAL APPLICABILITY According to the present invention, 2,6-DMN in a hydrocarbon mixture such as oils and coal tar obtained in each process of the petroleum refining industry can be recovered with high purity and high yield. . Moreover, by circulating each of the components obtained in each process in the system, it is possible to effectively utilize each of the components that are the raw materials in each process, and separate, dry, or purify each component. It is efficient because it does not require a process. Therefore, the recovery of 2,6-DMN is a simple process.
Moreover, it can be performed economically.

[Brief description of drawings]

FIG. 1 is a schematic explanatory diagram showing a flow of each component in the present invention. 1, 3, 5, 6, 7, 9, 10, 12, 15, 16, 1
8, 19: Line 2: Complex formation device 4: Solid-liquid separation device (complex separation) 8: Complex decomposition device 11: Solid-liquid separation device (2,6-DMN isolation) 13: Isomerization device 14: Lower aliphatic Aqueous alcohol recovery system 17: Lower hydrocarbon recovery system

Claims (2)

[Claims] 1. The following steps (1) to (7) (1) contacting a hydrocarbon mixture containing 2,6-dimethylnaphthalene with m-nitrobenzoic acid in the presence of an aromatic hydrocarbon, In the complex formation step of forming a complex mainly composed of -nitrobenzoic acid and 2,6-dimethylnaphthalene and precipitating the complex into a slurry state, the complex separated in the subsequent step (2) and A step of mixing m-nitrobenzoic acid separated from the complex in steps (4) and (5) into the system of the complex forming step to repeatedly form a complex, and deposit the complex to form a slurry state,
(2) A step of separating the slurry obtained in the step (1) into a complex and a liquid, and (3) returning all or part of the complex separated in the step (2) to the step (1). The step of transferring the residue to the step (4), and the complex transferred in the steps (4) and (3) are decomposed by contacting with a two-phase liquid composed of a lower hydrocarbon and a lower aliphatic alcohol aqueous solution. Then, a step of separating the two phases, (5) recovering all or part of the lower aliphatic alcohol aqueous solution from the lower aliphatic alcohol aqueous solution containing m-nitrobenzoic acid obtained in the step (4), m -Step of returning nitrobenzoic acid to the step (1), (6) Part of the lower hydrocarbon is recovered from the lower hydrocarbon phase obtained in the step (4), and 2,6-dimethylnaphthalene is obtained. A step of precipitating crystals mainly composed of to form a slurry state, (7 From the slurry obtained in the step (6), a crystal composed mainly of 2,6-dimethylnaphthalene, comprising the step, which is separated into a phase of lower hydrocarbons 2,
A method for recovering 6-dimethylnaphthalene. 2. The liquid phase obtained in the following steps (8), (8) and (2) is 2,6-
The method for recovering 2,6-dimethylnaphthalene according to claim 1, which further comprises a step of performing isomerization to dimethylnaphthalene.