JPH0449252A - Production of 2,6-dimethylnaphthalene - Google Patents

Abstract

PURPOSE:To obtain the subject substance by transmethylating naphthalene in the presence of dimethylnaphthalenes, producing the monomethyl derivative, simultaneously isomerizing the dimethyl derivative, methylating the monomethyl derivative separated from the reaction mixture and then separating the subject substance. CONSTITUTION:Naphthalene is transmethylated in the presence of dimethylnaphthalenes (DMN) to produce monomethylnaphthalenes (MMN) and simultaneously isomerize the DMN (at 300-480 deg.C under ordinary pressure to 10atm). Thereby, DMN enriched with the 2,6-DMN and MMN are produced. The resultant product is then separated into naphthalenes, MMN and DMN to methylate the MMN with a transmethylating agent (e.g. xylene) and produce the DMN. Separation into the unreacted MMN, DMN and unreacted transmethylating agent is then carried out. The 2,6-DMN is subsequently separated and recovered from the DMN obtained in the aforementioned two steps. Thereby, the loss of methyl groups is reduced to provide the useful by-products by using the xylenes. As a result, the objective substance is efficiently produced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an industrially efficient method for producing 2,6-dimethylnaphthalene by methylating naphthalene.

[Prior Art] There are 10 isomers of dimethylnaphthalenes (hereinafter sometimes abbreviated as DMN) obtained by methylating naphthalene and methylnaphthalene. Among these isomers, 2.6-[)MN is particularly useful industrially.

2.6- D M N is oxidized to naphthalene-2,6
-Dicarboxylic acid is provided, and from the polyester obtained using the carboxylic acid as a raw material, synthetic m*, films, etc. of excellent quality can be obtained. Therefore, research on the production method of 2.6-[)MN was conducted from an early stage, and coal dry-distilled oil and F
A method for producing 2.6-DMN from DMN contained in CC cycle oil by crystallization separation or complex extraction separation (Japanese Patent Application Laid-open No. 7551/1983).

(Japanese Patent Publication No. 47-29893), and alkenylation using ortho-xylene and butadiene as raw materials as a synthesis method.
2.6-DM by cyclization one theory hydrogen one reaction one crystallization separation
A method to obtain N was also proposed (G, G.

E berhardt, J., Oro, Ch.
ea, 30.82 (1965).

Equity 1111j Publication No. 50-12430, Special Publication No. 1982
-34570 publication.

Special Publication No. 47-47379, USP 3,2
44,758).

Furthermore, recently, a method of obtaining dimethylnaphthalene by methylating naphthalene or monomethylnaphthalene with methanol (JP-A-60i72937, JP-A-63-834) has been proposed.
Publication No. 4, JP-A-63-14738, JP-A-63
-14739 publication), or a method of obtaining methylnaphthalene or dimethylnaphthalene by transmethylation with polymethylbenzene (Japanese Patent Publication No. 53-5293, JP-A-61-267530, JP-A-63-14737) Public bulletins) etc. have been proposed.

These proposals are single-step, methylnaphthalene,
It is intended to obtain dimethylnaphthalene, and D obtained by methylating naphthalene or monomethylnaphthalene.
No proposal has been found regarding a suitable production process for producing 2.6-D MN from MN by crystallization separation. There is only one thing that the present inventors
45532) proposed a method for efficiently producing 2,6-DMN from a dimethylnaphthalene mixture. The proposal was an innovative method at the time, but by partially hydrogenating the raw DMN mixture, dimethyltetralin, which has two methyl groups in the same ring, and alkylbenzene, which are not partially hydrogenated, can be converted into two methyl groups. Dimethyltetralin, in which each of
．． This is a method for separating and producing 6-DMN, which requires steps of partial hydrogenation and dehydrogenation, and cannot be called an efficient production method.

LObject of the invention] The present invention is based on the above-mentioned i! Solve the problem and 2.6- D M N
The present invention provides a method for efficiently manufacturing. More specifically, a production process consisting mainly of a methylation step for methylating naphthalene or monomethylnaphthalene and a transmethylation/isomerization step efficiently converts 2.6-
It is an object of the present invention to provide a method for manufacturing DMN.

[Configuration of the Invention] The present invention provides methylation of naphthalene in the presence of a catalyst.
．． In producing 6-dimethylnaphthalene, (I) transmethylating naphthalene in the presence of dimethylnaphthalenes to produce monomethylnaphthalenes, and at the same time isomerizing dimethylnaphthalenes; 2.
Step (I) for producing dimethylnaphthalenes and monomethylnaphthalenes rich in 6-dimethylnaphthalene, (I[
) Step (1) in which the transmethylation/isomerization reaction mixture of the first step is separated into naphthalene, monomethylnaphthalenes and dimethylnaphthalenes, (III) the monomethylnaphthalenes separated in step (III) are treated as a transmethylating agent (rV) the transmethylation reaction mixture obtained in the step (1) is converted into unreacted monomethylnaphthalenes;

Step (2) of separating dimethylnaphthalenes, unreacted transmethylating agents and derivatives thereof, and (V) from the dimethylnaphthalenes obtained in step (1) and/or the dimethylnaphthalenes separated in step (2). A method for producing 2,6-dimethylnaphthalene, which is characterized by comprising a V step of separating 2,6-dimethylnaphthalene.

It is preferable to circulate the unreacted transmethylating agent and/or its derivatives separated in the above-mentioned step (1) to the step (2).

In the present invention, dimethylnaphthalene refers to a mixture mainly consisting of isomers of dimethylnaphthalene. Monomethylnaphthalenes refer to mixtures consisting mainly of isomers of monomethylnaphthalene. These may contain impurities depending on the degree of separation and purification, and the degree of inclusion varies.

A major feature of the present invention is that dimethylnaphthalenes are isomerized in the presence of naphthalene, and at the same time as the isomerization, naphthalenes are transmethylated to produce monomethylnaphthalenes.

The present invention will be explained in detail below.

<First step> This step is a step in which naphthalene is transmethylated in the presence of dimethylnaphthalenes and at the same time, dimethylnaphthalenes are isomerized.

More specifically, dimethylnaphthalenes are isomerized in the presence of naphthalene, and at the same time as the isomerization, naphthalene is transmethylated with dimethylnaphthalenes to produce monomethylnaphthalenes, which is rich in 2,6-dimethylnaphthalenes. This is a process for simultaneously producing dimethylnaphthalenes and monomethylnaphthalenes.

To this step, raw material naphthalene and dimethylnaphthalenes with a low content of 2,6-dimethylnaphthalene separated in the V step described below are fed.

Further, unreacted naphthalene separated in the second step described below can be fed.

A solid acid catalyst can be used in this step.

The preferred catalyst used in this step is an aluminosilicate used in the isomerization of dimethylnaphthalenes.

Aluminosilicate catalysts include amorphous aluminosilicate and crystalline aluminosilicate zeolite, both of which can be used.

Amorphous aluminosilicate is 5iOz/Af1203
Those having a molar ratio of 3 to 20, preferably 4 to 15 are used. St in crystalline aluminosilicate
A crystalline aluminosilicate zeolite having a molar ratio of 02/Af20a of 5 to 100 is preferable.

Specific examples of these zeolites include the following.

That is, ZSM-4°-5, -8, - as foujasite Y type 2 mordenite, helierite, pentasil type.
11, -12, -20, -38, -48, etc., and TPZ-10, -12, etc. as exemplified in the examples of the present invention. Pentasil type zeolite is S! Especially in the range of 20310 to 100 above 203 Oz/A, JP-A-6
The crystalline aluminosilicate zeolite described in Publication No. 0-38331 (published on February 27, 1985) is preferably used. Such a catalyst is a crystalline aluminosilicate zeolite having a molar ratio of 5iOz/A-203 in the range of 110 to 100 and a specific X-ray lattice spacing.

A specific example of the method for producing II of this catalyst is described in the same publication. In addition, the above aluminosilicate catalysts are usually H-type catalysts, but these are substituted with various metal ions,
Alternatively, metal oxides impregnated and supported are preferably used from the viewpoint of improving sustainability of catalytic activity. For example, Li
, Na, Mg, Ca, Sr.

Br, B, An, Ti, Zr, Or, Mo, Mn.

Substituted or impregnated supported aluminosilicates with metals selected from the group consisting of Re, Co, Ni, Pd, Zn and Hcd can be used.

In this step, transmethylation of naphthalene and isomerization of DMN are carried out simultaneously, and the reaction conditions are as follows.

The reaction temperature is in the range of 250 to 500°C, preferably 300°C.
-480°C. The pressure ranges from normal pressure to 20 atl, preferably from normal pressure to 10 atl. The reaction can be carried out in either liquid phase or gas phase. It is also possible to coexist hydrogen in the reaction. In this case, hydrogen/
The molar ratio of naphthalene is in the range of 0 to 10, preferably 0 to 10.
The range is 5. naphthalene, dimethylnaphthalenes,
The contact of trimethylnaphthalenes is due to the weight hourly space velocity (W
H8V> in the range of 0.1 to 20, preferably 0.5 to 3
This can be done within the range of What does WH8V mean here?
It represents the total contact amount (9) of the amounts of components involved in the reaction of naphthalene, dimethylnaphthalene, etc. per unit time (h') per SF).

In this step, dimethylnaphthalenes in which the composition of 2,6-dimethylnaphthalene is less than or equal to the thermodynamic equilibrium composition among all dithylnaphthalenes can be fed. Also 2,
Dimethylnaphthalenes having a molar ratio of 6-dimethylnaphthalene/2,7-dimethylnaphthalene of 0.72 or less can be fed.

<Step (II)> This step is a step in which the reaction mixture produced in Step I is separated into naphthalene, monomethylnaphthalenes, and dimethylnaphthalenes.

For separation, conventional means such as distillation and recrystallization can be used. Unreacted naphthalene separated in this step can be used as feed to stage 1I. The dimethylnaphthalenes rich in 2,6-dimethylnaphthalene are separated into 2,6-dimethylnaphthalene in Step V, which will be described later.

Monomethylnaphthalenes are methylated in the next step (2).

Step ■This step is a step of methylating the monomethylnaphthalenes separated in Step ■ with a transmethylating agent,
Dimethylnaphthalenes are mainly produced from monomethylnaphthalenes.

Transmethylating agents used in the transmethylation reaction in the method of the present invention include paraxylene, metaxylene, ortoxin, 1,2,3-trimethylbenzene, 1,2,4-trimethylbenzene, 1,3. 5-
Trimethylbenzene such as trimethylbenzene, 1,2
, 3.4-tetramethylbenzene, 1.2,3.5-tetramethylbenzene, 1,2,4.5-tetramethylbenzene and/or a mixture of xylene and the above polymethylbenzene is preferred. used. When xylene is used as a methylating agent, xylene becomes trimethylbenzene, tetramethylbenzene, benzene, toluene, etc. in the reaction of this step, so it is preferable to use xylene as the methylating agent. Polymethylethylbenzene having an ethyl group such as ethylbenzene, ethyltoluene, and ethylxylene may be mixed into the transmethylating agent, but it promotes transethylation of the ethyl group to monomethylnaphthalene, reducing the yield of methylnaphthalene. The lower the content, the better. Contamination of ethyl group is 10 mol% or less, preferably 5
It is mol% or less, more preferably 1 mol% or less.

It is advantageous to use such a transmethylating agent in a ratio of 0.01 to 2 moles, preferably 0.1 to 1 mole, relative to monomethylnaphthalenes. In order to suppress side reactions, it is preferable to use an excess amount.

The catalyst used in this step is a catalyst containing the amorphous aluminosilicate and crystalline aluminosilicate zeolite used in the first step described above.

The crystalline aluminosilicate zeolite preferably has a molar ratio of S i 02 /A zO3 of 5 to 100.
zeolite catalyst.

Furthermore, Japanese Patent Application Laid-open No. 172937/1988 (September 1985)
The catalyst described in Japanese Patent Application Laid-open No. 112527/1983 (published on May 6, 1988) is preferably used.

In this step, the aluminosilicate-containing catalyst is used,
Monomethylnaphthalenes and xylenes.

Dimethylnaphthalenes are produced from monomethylnaphthalenes by contacting with a transmethylating agent such as trimethylbenzenes and tetramethylbenzenes.

One of the characteristics of the methylation process of monomethylnaphthalenes by the transmethylation reaction in this step is that the methyl group of xylenes, trimethylbenzenes, and tetramethylbenzenes, which are transmethylating agents, is transferred to the monomethylnaphthalene ring, and dimethylnaphthalene is At the same time, it is possible to produce industrially useful benzene and toluene. Methylation of monomethylnaphthalenes with a mixture of xylenes, trimethylbenzenes, and tetramethylbenzenes can be carried out in the gas phase or in the liquid phase. Which method to employ is appropriately selected depending on the activity of the aluminosilicate catalyst employed in this step.

In the method of the present invention, the aluminosilicate-containing catalyst, monomethylnaphthalenes, and methylating agent are contacted in a gas phase or liquid phase at a weight hourly space velocity (WH8V) of 0.0.
It can be carried out in the range of 1 to 100. Here WH8V
is the unit time per aluminosilicate unit (9) (
It is defined as representing the total contact amount (9) of monomethylnaphthalenes and methylating agents in h"). The preferable WH8V value is in the range of 0.1 to 10, especially 0.5 to 10.
The range is 5. If the WH8V value is less than 0.01, a product with a high content ratio of dimethylnaphthalenes as intended in the present invention cannot be obtained. On the other hand, when the WH8V value exceeds 100, the opening time during contact is too short and the conversion rate decreases, which is industrially disadvantageous.

It has already been mentioned that the transmethylation reaction in this step can be carried out in either the liquid phase or the gas phase, but when carried out in the gas phase, it is preferable to carry out the reaction under a hydrogen stream. It may be possible to suppress activity deterioration. The amount of hydrogen supplied is expressed as hydrogen/(methylating agent and monomethylnaphthalenes) ratio (mol) of 0.1 to 2.
0, preferably in the range of 0.5 to 10.

The reaction is also advantageously carried out at a temperature in the range of 250 to 600°C, preferably in the range of 300 to 500°C. Further, the pressure may be reduced pressure, normal pressure, or increased pressure, but is usually normal pressure to increased pressure, for example, 1 to 30 phantom/aI, preferably 1 to 1
It is carried out at a pressure of 0υ/d.

The monomethylnaphthalenes to be methylated in this step are the monomethylnaphthalenes separated in step (1), but this does not need to be pure. Components other than the raw material mixture may include aliphatic hydrocarbons and alicyclic hydrocarbons.

The reaction of the present invention can be carried out in either a fixed bed system or a fluidized bed system. Further, in the case of using a fixed bed system, the fixed bed may be one stage, or may be a multistage system of two or more stages.

<Step (■)> In this step, the dimethylnaphthalenes and unreacted monomethylnaphthalenes produced in the step (■) are removed.

This is a step of separating unreacted transmethylating agents and their derivatives. Examples of the transmethylating agent and its eleven substances include polymethylbenzenes such as xylenes, other high boiling point fractions, benzene, toluene, and the like.

Separation can be carried out by methods known per se,
For example, the reaction mixture obtained in step (1) is sufficiently cooled using a condenser, and the concentrated product and gas are separated using a gas-liquid separator.

Next, the concentrated oil is supplied to a distillation column, and the benzene and toluene fractions and unreacted methylating agents such as xylenes, trimethylbenzenes, tetramethylbenzenes, and monomethylnaphthalenes with a boiling point of approximately 135 to 245°C are extracted. and the boiling point of the product dimethylnaphthalene is approximately 2
It can be separated into a 55-270°C fraction and a fraction with a boiling point of approximately 280°C or higher containing trimethylnaphthalene and tetramethylnaphthalene.

It is preferable that the benzene and toluene obtained by the separation be taken out as industrial raw material products, and the unreacted monomethylnaphthalenes and the fractions of the methylating agents xylenes, trimethylbenzenes, and tetramethylbenzenes be recycled to step (2). It is.

Step (1)> This step is a step of separating 2,6-dimethylnaphthalenes from dimethylnaphthalenes.

The dimethylnaphthalenes separated in the above-described steps (1) and (2) are fed to this step.

The separation of 2.6-dimethylnaphthalene can be carried out by methods known per se, for example by distillation.

This can be carried out by crystallization separation or complex extraction separation.

Regarding crystallization separation and complex extraction separation, see Japanese Patent Application Laid-open No. 48-75.
It can be carried out according to the method described in Japanese Patent Publication No. 54 or Japanese Patent Publication No. 47-29893.

In the present invention, the separation of step (1) and step (2) can also be performed by the same step.

<Process chart> FIG. 1 shows an example of a specific process diagram of the present invention.

Further, FIG. 2 shows an example in which the step (1) and the step (2) are performed in the same step.

[Effects of the Invention] According to the present invention, monomethylnaphthalenes are produced by isomerizing dimethylnaphthalenes in the presence of naphthalene and transmethylating naphthalene simultaneously with the isomerization, and isomerization of only dimethylnaphthalenes. It became possible to reduce the loss of methyl groups caused by oxidation. Furthermore, when methanol or methyl halide is used for monomethylnaphthalenes, side reaction products, water, and hydrogen halides are generated, which causes deterioration of the catalyst and corrosion of the material of the reactor. By using xylenes as a transmethylating agent without using any of these methylating agents, it is possible to produce benzene and toluene which are clean and industrially useful as reaction by-products.2.
It has been achieved to provide an efficient method for producing 6-dimethylnaphthalene.

[Example] Hereinafter, the present invention will be explained in detail by giving examples. It goes without saying that the present invention is not limited to these embodiments.

11Δ''1 Catalyst A 550 g of aluminum sulfate was gradually added to a solution of 425 g of sodium hydroxide dissolved in 8.5 g of pure water with stirring.
A homogeneous solution was obtained. After further adding 1Ks of II salt, 5Ks of silica sol (Si 0230wt%) was added with vigorous stirring to obtain a reaction mixture.

This mixture and 381 g of tetrapropylamine.

327 g of propyl bromide and 5009 g of methyl ethyl ketone
were placed in a 2011 volume stainless steel autoclave and sealed.

While stirring by rotating the stirring blade at 150 revolutions per minute,
The reaction was carried out at 100°C for 1 day and at 160°C for 4 days.

After filtering the reaction product and thoroughly washing the cake with 200 g of pure water, it was dried at 100°C for a day and night, and then calcined at 500°C for 2 days in an air atmosphere to obtain base zeolite 1.3! I got g. This product has a silica-alumina molar ratio of 26
．． 2 ZSM-5 zeolite.

500 g of this zeolite was brought into contact with 10% ammonium chloride aqueous solution 3 times while heating to 70°C.
Ion exchange with 4+ ions, filtering and washing.

After drying, it was calcined at 500°C for 8 hours to convert it into H-type zeolite. 1 part by weight of this H-type zeolite and 1 part by weight of alumina gel were thoroughly mixed, molded into a size of 10 to 20 meshes, and calcined at 450°C for 8 hours to obtain catalyst A.

11 ratio silica sol (Si0230%>13809, aluminum sulfate 153g, sodium hydroxide 176g, water 3
Touch the reaction mixture prepared from the above step! [The base zeolite 1059 used in A was added and charged into a 5-capacity stainless steel autoclave, and the temperature was raised to 180°C with stirring and held for 8F18.

After cooling, the contents were filtered and thoroughly washed with pure water 51.
The mixture was dried at 00° C. overnight to obtain 405 g of cake.

The silica-alumina ratio of this product was 19.6, and the X-ray diffraction pattern was substantially that of the crystalline aluminosilicate zeolite shown in Table 1. This crystalline aluminosilicate zeolite was brought into contact with a 10% ammonium chloride aqueous solution 31 three times while heating to 70°C to perform ion exchange with NH4+ ions, and then filtered.

After washing and drying, it was calcined at 500°C for 8 hours to convert it into H-type zeolite.

1 part by weight of this H-type zeolite and 1 part by weight of alumino gel were thoroughly mixed and formed into a size of 10 to 20 meshes.
Catalyst B was obtained by calcining at 50° C. for 8 hours.

1"Ω 500g of the base zeolite used in the above catalyst A,
The slurry was added to 2 cups of water in which sodium hydroxide of No. 009 was dissolved and stirred to obtain a uniform slurry, which was then charged into a 3I capacity stainless steel autoclay J. While stirring, the temperature was raised to 180°C and held for 8 hours.

After cooling, the contents were filtered, thoroughly washed with 1041 deionized water, and dried overnight at 100° C. to obtain 340 g of cake.

The silica-alumina ratio of this product was 16.8, and the X-ray diffraction pattern showed that it was substantially the crystalline aluminosilicate zeolite shown in Table 1.

This was brought into contact with a 10% ammonium chloride aqueous solution three times while heating to 70°C to exchange ions with NH4+ ions, filtered, washed and dried, and then calcined at 500°C for 8 times of 8W to convert it into H-type zeolite. did.

1 part by weight of this H-type zeolite and 1 part by weight of alumina gel were thoroughly mixed and formed into a size of 10 to 20 meshes.
Catalyst C was obtained by calcining at 50°C for 8 hours.

Table 1 Intensity (1/Io) is d (in) -3,86 (2θ=
The relative intensity of each peak [I/Io (%)] is 100 to 60 when the intensity (Io) of 23.05
is VS (very strong), 60-40 is S (strong), 40
~20 is represented by M (medium), and 20 to 10 is represented by W (weak).

Example 1 (Transmethylation/isomerization) A stainless steel flow-through reaction tube filled with catalyst C5009 contained 40 parts by weight of naphthalene, 15% of 2,6-dimethylnaphthalene, and 21% of 2,7-dimethylnaphthalene. A mixed raw material containing 60 parts by weight of a dimethylnaphthalene mixture was fed at a rate of 500 g/hr. The reaction pressure was 50/cjG under hydrogen pressure, and the reaction temperature was 375°C.
Met. This reaction was continued for about 5 hours until the reaction mixture 25
I got 809.

(Separation) This reaction mixture was distilled using a precision distillation device with 100 theoretical plates to produce 902 g of low-boiling distillate containing mainly naphthalene (from the initial stream to
225℃), monomethylnaphthalene distillation tank 4315F (
225-250℃), dimethylnaphthalene distillation tank 1236
SF (250-275°C) and distillation residue oil 119 were separated. Approximately 98% of the low boiling distillate was naphthalene.

The dimethylnaphthalene distillate contained 20% each of 2.61 dimethylnaphthalene and 2,7-dimethylnaphthalene. Let this be the tank (ω).

(Methylation) Meanwhile, 431 volumes of the above monomethylnaphthalene distillate were placed in another stainless steel flow-through reaction tube filled with 8400 g of catalyst.
1719 g of monomethylnaphthalene containing g and 1.2.4
- A mixture of trimethylbenzene 14535F was delivered in 8 hours. The reaction pressure was 5 kg/ciG under hydrogen pressure, and the reaction temperature was 450°C.

(Separation) The reaction mixture was distilled using the same precision distillation equipment as above, using a low boiling point distillation tank 2747SF (initial stream ~ 250°C) containing mainly xylene, trimethylbenzene, and monomethylnaphthalene.
Dimethylnaphthalene distillation tank 4109 (250-275℃
) and distillation residue oil (15 g). 2 for low boiling point distillers
It contained 0% xylene and 47% monomethylnaphthalene.

The dimethylnaphthalene distillate contained 21% 2,6-dimethylnaphthalene and 20% 2,7-dimethylnaphthalene. Let this be the tank (b).

(Separation) Dimethylnaphthalene mixture 16469 obtained by heating the distillers (field and distiller φ) to 70°C and dissolving them was gradually cooled to 20°C. 2,6-Dimethylnaphthalene 19 was added thereto as a seed crystal, and the resulting cake was filtered by keeping it at 11,120° C. at 20:00, and the cake was further washed with 500 m of methanol. The obtained solid was dried in vacuum at room temperature for 4 hours to obtain 100 g of 2,6-dimethylnaphthalene with a purity of 97%.

In this series of experiments, the monomethylnaphthalene generated in the transmethylation step and the monomethylnaphthalene consumed in the methylation step were balanced, and 2,
The remaining dimethylnaphthalene discharged from the 6-dimethylnaphthalene separation process is recycled to the transmethylation process, so the naphthalene actually consumed is 117 g after deducting the naphthalene generated in the methylation process. , the yield of 2,6-dimethylnaphthalene is 70% based on naphthalene.

Example 2 (Transmethylation/isomerization) In a stainless steel flow-through reaction tube filled with Catalyst A 5009, dimethyl containing 67 parts by weight of naphthalene, 15% of 2.6-dimethylnaphthalene, and 21% of 2.7-dimethylnaphthalene A mixture containing 33 parts by weight of naphthalene mixture was fed at a rate of soog/hr.

The reaction pressure was 5 Ks/iG under hydrogen pressure, and the reaction temperature was 40
It was 0°C. This reaction was continued for 7.5 hours to obtain reaction mixture 36109.

(Methylation) On the other hand, touch a 3-hole stainless steel reaction tube with 15B200 cylinders,
574g of monomethylnaphthalene and 42g of ortho-xylene
8g was charged and held at 350°C for 6 hours.

(Separation) 46109, which is a combination of the two reaction mixtures obtained in the transmethylation/isomerization step and the methylation step, was distilled in a precision distillation device with 100 theoretical plates, and 3322 g of low-boiling components mainly consisting of naphthalene ( Initial flow ~250℃), dimethylnaphthalene distillation tank (containing 20% each of 2,6 and 2,7-dimethylnaphthalene) 12569 (250~275℃)
) and distillation residual oil 339.

(Separation) The dimethylnaphthalene distillate was heated to 10°C, mixed, and gradually cooled to 20°C. To this, 1 g of 2,6-dimethylnaphthalene was added as a seed crystal, and the resulting cake was filtered by keeping it at 30° C. for 20 hours, and the cake was further washed with 400 d of methanol. The obtained solid was dried at room temperature in vacuum for 4 hours to obtain 77 g of 2,6-dimethylnaphthalene with a purity of 97%.

In this example, 90 g of naphthalene was substantially consumed, and the yield of 2,6-dimethylnaphthalene was 69% based on naphthalene.

[Brief explanation of the drawing]

FIG. 1 shows a specific example of the present invention. FIG. 2 shows an example in which the step (1) and the step (2) are performed in the same step. Abbreviations in the figure are as follows. TMB: Trimethylbenzenes DMN: Dimethylnaph tariffs TEMB: Tetramethylbenzenes TMN Nitrimethylnaphthalenes MMN: Monomethylnaphthalenes TEMN: Tetramethylnaphthalenes Patent applicant Teijin Ltd.

Claims (1)

[Claims] 1. Naphthalene is methylated in the presence of a catalyst to produce 2,6-
In producing dimethylnaphthalene, (I) transmethylating naphthalene in the presence of dimethylnaphthalenes to produce monomethylnaphthalenes, and at the same time isomerizing dimethylnaphthalenes to produce dimethyl enriched in 2,6-dimethylnaphthalenes. Step I to produce naphthalenes and monomethylnaphthalenes; (II) Step II to separate the transmethylation/isomerization reaction mixture of Step I above into naphthalenes, monomethylnaphthalenes and dimethylnaphthalenes; (III) Step II. Step III, in which the monomethylnaphthalenes separated in Step II are methylated with a transmethylating agent to produce dimethylnaphthalenes; (IV) the transmethylation reaction mixture obtained in Step III is converted into unreacted monomethylnaphthalenes; (V) the dimethylnaphthalenes obtained in step IV and/or the dimethylnaphthalenes separated in step II; A method for producing 2,6-dimethylnaphthalene, comprising: a V step of separating 2,6-dimethylnaphthalene from . 2. The production method according to claim 1, characterized in that the unreacted transmethylating agent and/or its derivatives separated in step IV are recycled to step III.