JPH0539231A - Production of beta-methylnaphthalene - Google Patents

Abstract

PURPOSE:To provide a method for readily and stably producing highly pure beta-methylnaphthalene by simple operations over a long period from a methylnaphthalene oil containing alpha-naphthalene and beta-naphthalene. CONSTITUTION:beta-methylnaphthalene is produced by a process comprising a combination of a hydrogenative desulfurization step using a methylnaphthalene oil as a raw material oil to remove the sulfur compounds of impurities, an isomerization step for isomerizing the by-produced methyltetralin compounds, and an isomerization step for isomerizing alpha-methylnaphthalene into the beta- methylnaphthalene.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for economically producing β-methylnaphthalene from α-methylnaphthalene-containing oil in a high yield.

[0002]

BACKGROUND OF THE INVENTION β-Methylnaphthalene (2-methylnaphthalene) is used as a raw material for vitamin K, which is a drug, and 2,6-naphthalenedicarboxylic acid, which is an intermediate raw material for polyester synthetic resins having heat resistance and high tensile strength. It is an important compound.

However, in order to serve these purposes,
It is important to have a high degree of purity, and in particular, isomers of α-methylnaphthalene (1-methylnaphthalene) and organic sulfur compounds and organic nitrogen compounds that act as catalyst poisons or reaction inhibitors should be excluded as much as possible.

Hitherto, as a method for separating and recovering high-purity β-methylnaphthalene, a method combining distillation and crystallization (JP-A-57-95923) and a method using an adsorbent (JP-A-SHO). 59-88432), a method of adding alkanolamines and distilling (Japanese Patent Laid-Open Publication No. Sho 6-62).
No. 2-153233) is proposed.

Further, a method for forming an inclusion compound (Japanese Patent Publication No. 02-215733, Japanese Patent Publication No. 02-25563).
No. 0) is also proposed.

However, when the former three methods described above are applied to the separation of isomers such as α-methylnaphthalene and β-methylnaphthalene which are very close in physical and chemical properties, the apparatus is inevitably used. It causes an increase in size and precision, which is economically disadvantageous. On the other hand, the latter method is economically disadvantageous because an expensive agent for forming an inclusion complex is used.

Further, these conventional methods are limited to β
-It is a method of separating and recovering methylnaphthalene, and theoretically, the recovery rate of β-methylnaphthalene cannot exceed 100%.

[0008]

DISCLOSURE OF INVENTION Problems to be Solved by the Invention From the α-methylnaphthalene-containing oil by isomerizing unnecessary α-methylnaphthalene contained in the α-methylnaphthalene-containing oil to useful β-methylnaphthalene, When research was conducted to obtain β-methylnaphthalene in good yield, the activity life of the solid acid catalyst used for isomerization was unexpectedly short and β-methylnaphthalene was produced economically and advantageously only after this problem was solved. I knew that it would be possible to do.

Thus, an object of the present invention is to provide a method for economically advantageously producing β-methylnaphthalene from an α-methylnaphthalene-containing oil, and more specifically to an α-methylnaphthalene-containing oil. The α-methylnaphthalene is isomerized to β-methylnaphthalene while maintaining the activity of the catalyst used for isomerizing the α-methylnaphthalene contained therein, and β-methylnaphthalene is produced in good yield and economically.
-To provide a method for obtaining from a methylnaphthalene-containing oil.

[0010]

As a result of further research to achieve the above object, the present inventor has conducted an isomerization reaction on a desulfurized oil obtained by subjecting an oil containing α-methylnaphthalene to a hydrodesulfurization step. Surprisingly, we discovered the fact that the activity of the solid acid catalyst used for the isomerization reaction persists, and further investigated its cause.By subjecting the α-methylnaphthalene-containing oil to a hydrodesulfurization step, A portion of methylnaphthalene in the oil is nuclear hydrogenated to produce a small amount of methyltetralin, and this small amount of methyltetralin extremely effectively prevents deactivation (deterioration) of the solid acid catalyst and maintains the life of the catalyst. If the amount of methyltetralin to be supplied to the isomerization step is appropriately controlled by using the produced methyltetralin, the activity of the solid acid catalyst used in the isomerization step will be more sustained. The present invention has been completed by finding a series of facts.

Usually, the hydrodesulfurization step is a step for removing sulfur compounds, and the fact that the isomerization step can be efficiently carried out by adding such a step before the isomerization step is completely absent. It was unexpected and surprising. Needless to say, unnecessary sulfur compounds are removed by applying a hydrodesulfurization step, the obtained β-methylnaphthalene becomes highly pure, and the purpose of hydrodesulfurization is also achieved.

That is, the present invention comprehensively isomerizes α-methylnaphthalene-containing oils using a solid acid catalyst to obtain β-methylnaphthalene-containing oils.
A method for producing methylnaphthalene, which is a method for producing β-methylnaphthalene characterized by including a hydrodesulfurization step of the α-methylnaphthalene-containing oil as a pretreatment step for isomerization, and α- A method for producing β-methylnaphthalene by isomerizing methylnaphthalene-containing oil with a solid acid catalyst, wherein a part or all of methyltetralin produced as a by-product by hydrodesulfurizing α-methylnaphthalene-containing oil is isomerized. The method for producing β-methylnaphthalene is characterized in that it is supplied to a chemical conversion step.

From the following detailed description of the invention, the more preferred embodiments of the invention and the advantages derived therefrom will be self-evident.

The raw material α-methylnaphthalene-containing oil used in the present invention contains no tar base compound and indole, and has a methylnaphthalene content (total content of α-methylnaphthalene and β-methylnaphthalene). 8
Oils containing 0% by weight or more, particularly 90% by weight or more of methylnaphthalene are preferable.

Such a methylnaphthalene oil is generally easily produced by a known method from a washing oil obtained by fractionating coal tar. For example, a sulfuric acid washing method or an azeotropic distillation method is used to remove the tar base compound, and a solvent extraction method, an alkali melting method and / or an oligomer chlorination method, an azeotropic distillation method, or the like is used to remove the indole. It is possible to separate and remove the by using a distillation method.

Α-methylnaphthalene and β-before hydrodesulfurization
If the total content of methylnaphthalene is less than 80% by weight, the energy load per unit operation becomes large,
It is preferably 80% by weight or more, and particularly preferably 90% by weight or more. On the other hand, if it is 80% by weight or more, methyltetralin necessary and sufficient in the isomerization step can be obtained during hydrodesulfurization.

An example of the method for producing β-methylnaphthalene of the present invention will be described below according to the production flow shown in FIG. The present invention is not limited to this flow,
The purpose is achieved even if the combination is changed appropriately.

First, a raw material oil containing methylnaphthalene 1
Is introduced into the hydrodesulfurization facility 2 to perform a hydrodesulfurization step. One of the roles of the hydrodesulfurization step which is the first step of the method for producing β-methylnaphthalene of the present invention is to remove the sulfur compound contained in the methylnaphthalene-containing oil. The hydrodesulfurization method can be performed according to a known hydrodesulfurization method. The removal rate of sulfur compounds may be determined according to the specifications of the product and is not particularly limited. Further, the amount of methyltetralin produced by the nuclear hydrogenation reaction of methylnaphthalene as a side reaction is not particularly limited. This is because the total concentration of α-methylnaphthalene and β-methylnaphthalene in the methylnaphthalene-containing oil before hydrodesulfurization is 8
If it is 0% by weight or more, a sufficient amount of methyltetraline is produced in the hydrodesulfurization step in the isomerization step, and a distillation step is provided as a step before the isomerization step after hydrodesulfurization to shift to the isomerization step. This is because the concentration of methyltetralin in the supplied methylnaphthalene-containing oil can be controlled.
Further, when a little naphthalene is contained in the α-methylnaphthalene-containing oil, a part of it becomes tetralin in the hydrodesulfurization step, which functions to prevent the activity of the solid acid catalyst from decreasing in the isomerization step. Have.

The catalyst used in the hydrodesulfurization in the present invention is a catalyst carrying at least one selected from molybdenum, cobalt and nickel, more preferably cobalt molybdenum / alumina, nickel molybdenum / alumina or Examples include catalysts of cobalt / nickel / molybdenum / alumina, that is, catalysts in which molybdenum and at least one selected from cobalt and nickel are supported on an alumina carrier, and these are commercially available. The supported amount of molybdenum is 1 to molybdenum element.
It is preferable that the amount of cobalt carried is 25% by weight, the amount of cobalt element is 0.5 to 15% by weight, and the amount of nickel carried is 0.5 to 15% by weight as nickel element. The catalyst used in the hydrodesulfurization step of the present invention is not limited to these, as long as it is a catalyst capable of achieving a hydrodesulfurization and an appropriate (not excessive) nuclear hydrogenation of methylnaphthalene. Elements other than the above may be added to the extent that the object of the present invention is not impaired.

As the reaction conditions in the desulfurization reaction, the temperature is 240 to 400 ° C., preferably 260 to 350 ° C., the pressure is atmospheric pressure to 100 kg / cm ² G, preferably 1.0 to 20 kg.
It is better to do it at / cm ² G.

When the temperature and the pressure are set lower than the above ranges, the desulfurization activity is lowered so that the desired desulfurization rate cannot be obtained, and when the temperature and the pressure are set higher, the hydrogenation of methylnaphthalene becomes remarkable and the yield is increased. Bring about a decline. Generally, as the desulfurization rate increases, the hydrogenation rate of methylnaphthalene tends to increase. Liquid hourly space velocity in hydrodesulfurization process (amount of feedstock oil per liter of catalyst) (LHS
V) is usually 0.2 to 10.0 (l / l · hr).

Hydrogen flow rate [GHSV (hr
⁻¹ ] / liquid hourly space velocity [LHSV (hr ⁻¹ )] is preferably 30 or more. G
When the HSV / LHSV is less than 30, the desulfurization activity is significantly reduced.

Β-methylnaphthalene is separated and produced in the following second step, the distillation (A) step. The distillation (A) step is composed of a distillation column 4 and a rectification column 7, and in the distillation column 4, impurities having a boiling point lower than that of β-methylnaphthalene from the hydrodesulfurized oil 3 (mainly composed of methyltetralin,
(Including tetralin and naphthalene in some cases) is separated as a top fraction 5 to obtain a bottom fraction 6. The bottom fraction 6 is combined with the top fraction 17 of the distillation column 16 in the distillation (B) step and supplied to the rectification column 7, where the product β-methylnaphthalene is separated as a fraction 8. However, the distillate 9 remains. The operating conditions of the distillation column 4 and the rectification column 7 are the product specifications and the content of α-methylnaphthalene in the raw material 10 (combined liquid of the fractions 5 and 9) of the isomerization step of the next step is 35 wt% or more,
More preferably, it may be set so as to satisfy the condition of 50% by weight or more. If the content of α-methylnaphthalene in the fraction 10 as the raw material for the isomerization step is less than 35 wt%, the efficiency of the isomerization step will be poor in terms of the thermodynamic equilibrium of this isomerization reaction. It is not particularly limited in the range of 35 wt% or more, but it may be determined by a technical limit value in designing and operating the distillation columns 4 and 7.

The fraction 10 from the distillation (A) step is supplied to the isomerization equipment 11 as a raw material for the isomerization step, where α-methylnaphthalene is isomerized to β-methylnaphthalene. .. The present invention can be achieved by using a solid acid catalyst such as zeolite or silica / alumina as the isomerization catalyst, preferably zeolite as the solid acid catalyst. A more preferable solid acid catalyst is a Y-type zeolite, and a particularly preferable one is a dealuminated Y-type zeolite, which achieves a longer life than a silica-alumina catalyst. The dealuminated Y-type zeolite is obtained by subjecting the Y-type zeolite to steam treatment and / or acid treatment.

In the isomerization step of the present invention, WH
The SV (weight of the feedstock oil that passes over a unit weight of the catalyst per hour) is preferably 0.1 to 20 h ^-1 , more preferably 0.1 to 10 h ^-1 . If WHSV is too large, a sufficiently large conversion cannot be obtained, while WH
If the SV is too small, the amount of packed catalyst and the reactor volume increase, which is uneconomical. The reaction temperature in the isomerization step is 300 to 600 ° C, preferably 350 to 550 ° C. The pressure may be normal pressure, increased pressure close to normal pressure, or high pressure, and may be gas phase reaction under low pressure or liquid phase reaction under high pressure.

Methyltetralin, which is distilled off as an overhead fraction in the distillation column 4, and in some cases, part or all of the fraction 5 containing tetralin is fed to the isomerization step. In this way, the life of the solid acid catalyst used in the isomerization step is greatly extended.

The methyltetralin content of the distillate 10 or the content of methyltetralin and tetralin is 0.1 to 1
0.0 wt% is preferable, and 0.4 to 5 is more preferable.
It is 0% by weight. If the content of these hydrogenated products is too small, the effect of suppressing the activity decrease is poor, and if it is too large, side reactions other than the isomerization reaction (disproportionation reaction, etc.) become prominent and the yield of β-methylnaphthalene Is reduced.

The methyltetralin content or the content of methyltetralin and tetralin of fraction 10 can be adjusted by the flow rate of fraction 5 combined with fraction 9.

The fraction 12 that has undergone the isomerization step is then sent to the distillation (B) step. The distillation (B) step is composed of distillation columns 13 and 16, and its role is to distill the low boiling point material and the high boiling point material generated in the hydrodesulfurization step and the isomerization step out of the system. That is, a low boiling point substance is distilled out of the system from methylnaphthalene in the distillation column 13, and a high boiling point substance is distilled out of the system in the distillation column 16. The overhead fraction 17 from the distillation column 16 is circulated to the distillation (A) step and combined with the fraction 6.

The operating conditions of the distillation columns 13 and 16 are as follows: the methylnaphthalene-containing fraction 1 circulated in the distillation (A) step.
It may be determined so that 7 has a composition almost equivalent to that of the fraction 6, and it is not particularly necessary to increase the β-methylnaphthalene content in the fraction 17. Here, the presence or absence of the distillation column 13 can be determined according to the product specifications.

In the present invention, as shown in Example 2, a system of isomerizing immediately after hydrodesulfurization can be used, and hydrodesulfurization, isomerization and distillation do not impair the object of the present invention. Proper combinations can be made within the range.

According to the production method of the present invention described in detail above, (1) isomerization by a small amount of methyltetralin, which is a by-product produced in the hydrodesulfurization step of the α-methylnaphthalene-containing oil before the isomerization step, The life of the solid acid catalyst in the acidification step becomes long. (2) Since the solid acid catalyst used for the isomerization catalyst has the ability to dehydrogenate methyltetralin, the methyltetralin produced in the hydrodesulfurization step is dehydrogenated to methylnaphthalene, and α-methylnaphthalene therein is Since it is isomerized to β-methylnaphthalene, the yield of β-methylnaphthalene increases and its purity is high. (3) By appropriately combining the hydrodesulfurization step, the isomerization step, and the distillation step, the conversion rate from α-methylnaphthalene to β-methylnaphthalene can be made extremely high, and β-methylnaphthalene can be increased as a whole. It is possible to obtain in yield.

[0033]

EXAMPLES The present invention will be specifically described below based on examples.

(Example 1) The results carried out according to the production flow of β-methylnaphthalene shown in FIG. 1 will be specifically described. Results of representative distillates are listed in Table 1. Α-Methylnaphthalene-containing oil 1 containing no tar base and indole (methylnaphthalene content = 94.9% by weight, sulfur compound concentration = 3.0% by weight) is a commercially available hydrodesulfurization catalyst (cobalt / molybdenum / alumina). Using a fixed-bed flow tube reactor filled with the mixture, a reaction temperature of 300 ° C., a reaction pressure of 2 kg / cm ² G, LHSV: 1.0 (l / l · hr), GHSV: 1
Hydrodesulfurization treatment was performed under the condition of 00 (l / l · hr)
Was removed to 0.3% by weight. Then, the fraction 5 is distilled off in the distillation column 4 of the distillation (A) step to obtain a fraction 6 having a β-methylnaphthalene content = 64.7 wt%, and the distillation column 7 continues to produce the product β-methyl. Naphthalene 8
(Product purity = 98.0% by weight, sulfur compound concentration = 0.3
Wt%) was recovered. The β-methylnaphthalene recovery rate in Fraction 8 was 80% by weight based on β-methylnaphthalene contained in Fraction 1. The fraction 10 which is a combined liquid of the fractions 5 and 9 distilled in the distillation (A) step contained 2.6% by weight of methyltetralin, and the α-methylnaphthalene content was 67.2. % By weight. The proportion of β-methylnaphthalene in methylnaphthalene in this fraction 10 was 25% by weight.

Next, solid acid catalyst (SiO ₂ / Al ₂ O ₃ (molar ratio)
= 18, the cation site having a lattice constant of 24.30 Å is exchanged with protons for dealuminized Y-type zeolite).
WHSV (weight of raw material passing over a unit weight of catalyst per hour) 1.5h ^-1 isomerizes α-methylnaphthalene, and β-methylnaphthalene accounts for 62% by weight of all methylnaphthalene. Increased to. From the isomerized fraction 12 in the next distillation (B) step, methylnaphthalene-containing fraction 17 (β-methylnaphthalene content =
66.2% by weight) was recovered. When this fraction 17 was circulated to the fraction 6 in the distillation (A) step, the β-methylnaphthalene recovery rate of the fraction 8 increased to 126% by weight based on the β-methylnaphthalene contained in the fraction 1.

The activity of the isomerization catalyst in this isomerization step is 3
It was maintained well during the 30 days of operation. That is, the β-methylnaphthalene content of the fraction 12 at the beginning of the operation was 56.5% by weight, and the β-methylnaphthalene content of the same fraction after 330 days was 50.0% by weight.

As described above, the recovery rate of β-methylnaphthalene can be remarkably improved by the production method of the present invention comprising the hydrodesulfurization step → the distillation (A) step → the isomerization step → the distillation (B) step. The sulfur compound concentration in the product can be reduced.

[0038] * 1: Fraction 1 is a feedstock oil containing α-methylnaphthalene * 2: MN is an abbreviation for methylnaphthalene * 3: MT is an abbreviation for methyltetralin * 4: MN is the total amount of β-MN and α-MN * 5: When the fraction 17 was circulated to the distillation column 7 (The recovery rate was calculated based on the amount of β-methylnaphthalene contained in the α-methylnaphthalene-containing oil of fraction 1.)

(Comparative Example) The same procedure was carried out as in Example except that the fraction 5 (distillate containing methyltetralin) distilled from the distillation (A) step of the example was not supplied to the isomerization step.

The catalytic activity of isomerization tends to gradually deteriorate, and α-methylnaphthalene is converted into β after 80 days of operation.
No longer isomerized to methylnaphthalene.

(Embodiment 2) The results of carrying out according to the manufacturing flow shown in FIG. 2 will be described. Table 2 shows the results of representative distillates
Described in. Α without tar base and indole
-Methylnaphthalene-containing oil 101 (total content of α-methylnaphthalene and β-methylnaphthalene = 80% by weight,
(Sulfur compound concentration = 2.8% by weight) is hydrodesulfurized in the same manner as in Example 1 to obtain 0.4% by weight of the sulfur compound in the fraction 103.
Removed. This fraction 103 contains tetralin and methyltetralin in a total amount of 1.0% by weight (tetralin / methyltetralin = 1/9: molar ratio, nuclear hydrogenation ratio 1.1 mol%), and accounts for methylnaphthalene. The proportion of β-methylnaphthalene was 25% by weight. Then
This fraction 103 was fed to the isomerization step filled with the same solid acid catalyst as used in Example 1 to carry out the isomerization reaction under the same conditions as in Example 1, and as a result, β-methylnaphthalene was converted to all methyl groups. Fraction 119 was obtained, the proportion of which in naphthalene was increased to 64% by weight. This fraction 119 was subjected to a distillation step (a low boiling point oil was separated and removed in a distillation column 124, and a high boiling point oil was separated and removed in a distillation column 125), and a product β-methylnaphthalene fraction 122 was recovered. The β-methylnaphthalene recovery rate in the product was 144% by weight based on the fraction 101, the product purity was 97.0% by weight, and the sulfur compound concentration was 0.4% by weight.

The activity of the isomerization catalyst in this isomerization step is 1
It was maintained well during the 50 days of operation. That is, the β-methylnaphthalene content of the fraction 119 at the beginning of the operation was 48.5% by weight, and the β-methylnaphthalene content of the same fraction after 150 days was 45.0% by weight.

[0043]

[0044]

According to the present invention, α contained in the feedstock oil
-When converting methylnaphthalene into β-methylnaphthalene to produce a product, it is possible to prevent deterioration of the isomerization catalyst by an industrially advantageous method, and to economically and easily produce a high-purity β containing less sulfur content. -Methylnaphthalene can be obtained in high yield.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a production flow of β-methylnaphthalene of the present invention.

FIG. 2 is a diagram showing an example of a production flow of β-methylnaphthalene of the present invention.

[Explanation of symbols]

1, 101 Raw material oil (oil containing α-methylnaphthalene) 2, 102 Hydrodesulfurization equipment 5, 6, 9, 10, 14, 15, 17, 18, 120,
121,123 Distillation fraction Fraction 4,7,13,16,124,125 Distillation tower 8,122 Product (β-methylnaphthalene) 11,111 Isomerization equipment 3,103 Hydrodesulfurized oil 12,119 Isomerization treatment oil

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical indication C07B 61/00 300 (72) Inventor Tatsuya Shinsawa 1 Kawasaki-cho, Chiba-shi, Chiba Kawasaki Steel Stock Corporate Technology Research Division (72) Inventor Toshihide Suzuki 1 Kawasaki-cho, Chiba City, Chiba Prefecture Corporate Technology Research Division

Claims (12)

[Claims] 1. A method for producing β-methylnaphthalene by isomerizing an α-methylnaphthalene-containing oil with a solid acid catalyst, which comprises hydrogenating the α-methylnaphthalene-containing oil as a pretreatment step for isomerization. A method for producing β-methylnaphthalene, which comprises a desulfurization step. 2. A method for producing β-methylnaphthalene by isomerizing α-methylnaphthalene-containing oil with a solid acid catalyst, which comprises methyltetralin produced as a by-product by hydrodesulfurizing α-methylnaphthalene-containing oil. Is supplied to the isomerization step. A method for producing β-methylnaphthalene. 3. The β-methyl according to claim 1, wherein the sum of the α-methylnaphthalene content and the β-methylnaphthalene content in the α-methylnaphthalene-containing oil before hydrodesulfurization is 80% by weight or more. Method for producing naphthalene. 4. The method for producing β-methylnaphthalene according to claim 1, wherein the solid acid catalyst is a zeolite catalyst. 5. The method for producing β-methylnaphthalene according to claim 4, wherein the zeolite catalyst is Y-type zeolite. 6. The content of methyltetralin in the hydrodesulfurized oil of the methylnaphthalene-containing oil supplied to the isomerization step is 0.1 to 10.0% by weight. Method for producing β-methylnaphthalene. 7. The total content of tetralin and methyltetralin in the hydrodesulfurized oil of the methylnaphthalene-containing oil supplied to the isomerization step is 0.1 to 10.0% by weight. The method for producing β-methylnaphthalene according to any one of claims. 8. In the hydrodesulfurization step, molybdenum,
The method for producing β-methylnaphthalene according to any one of claims 1 to 7, wherein a catalyst supporting at least one selected from cobalt and nickel is used. 9. A catalyst supporting molybdenum and at least one selected from cobalt and nickel is used in the hydrodesulfurization step.
The method for producing β-methylnaphthalene according to any one of claims. 10. The sulfur compound contained in the methylnaphthalene-containing oil is removed in the hydrodesulfurization step.
The method for producing β-methylnaphthalene according to any one of 1. 11. An α-methylnaphthalene-containing oil is subjected to a hydrodesulfurization step, and the resulting hydrodesulfurized oil is then subjected to a distillation step (A). In the distillation step (A), a methyltetralin fraction is obtained. , A β-methylnaphthalene fraction and a fraction consisting of α-methylnaphthalene and β-methylnaphthalene are fractionated, and the β-methylnaphthalene fraction is taken out as a product,
At least a part of the methyltetralin fraction is fed to the isomerization step, and a fraction consisting of α-methylnaphthalene and β-methylnaphthalene is fed to the isomerization step, and in the subsequent isomerization step, in the presence of a solid acid catalyst. Is subjected to an isomerization reaction from α-methylnaphthalene to β-methylnaphthalene,
The reaction product from the isomerization step is optionally subjected to a distillation step (B) to remove low-boiling substances and / or high-boiling substances from α-methylnaphthalene and β-methylnaphthalene out of the system, and A method for producing β-methylnaphthalene, which comprises circulating the distillation step (A). 12. An α-methylnaphthalene-containing oil is subjected to a hydrodesulfurization step, the resulting hydrodesulfurized oil is directly subjected to an isomerization reaction step, and the resulting product is subjected to a distillation step. A method for producing β-methylnaphthalene, which comprises obtaining a β-methylnaphthalene fraction as a product.