JPH07206722A - Isomerization of dimethylanaphthalene - Google Patents

Abstract

PURPOSE:To obtain 2,6-dimethylnaphthalene by using a dimethylnaphthalene having a monomethylnaphthalene content suppressed below a prescribed level as a raw material and isomerizing the material in the presence of a hydrogen- type mordenite catalyst in liquid phase. CONSTITUTION:The raw material to be used in this isomerization reaction is a dimethylnaphthalene having a monomethylnaphthalene concentration of <=5wt.%, preferably <=1wt.%. The isomerization reaction of the raw material is carried out in liquid phase at <=270 deg.C using a catalyst consisting of an essentially hydrogen-type mordenite having a molar silica/alumina ratio of >=100. The deposition of coke on the catalyst can be suppressed to enable the continuation of the reaction over a long period without lowering the catalytic activity. Side reactions such as the isomerization to other isomers such as 2,7- dimethylnaphthalene and the disproportionation reaction can be suppressed in the isomerization reaction of dimethylnaphthalene to achieve high isomerization ratio to 2,6-dimethylnaphthalene.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing 2,6-dimethylnaphthalene which is useful as a raw material for 2,6-naphthalenedicarboxylic acid. 2,6-naphthalenedicarboxylic acid is industrially important as a raw material of high-performance polyester used for producing polyethylene naphthalate fibers and films having excellent tensile strength and heat resistance.

[0002]

2. Description of the Prior Art 2,6-Dimethylnaphthalene is 2,6-
It is a raw material for naphthalenedicarboxylic acid, and is required to be highly pure in terms of quality. Dimethylnaphthalene has 10 isomers depending on the positions of 2 methyl groups. Of these, it is necessary to produce 2,6-dimethylnaphthalene substantially free of isomers other than the 2,6-isomer in a large amount and at low cost. When isomerizing dimethylnaphthalene, it is known that isomerization between β-β and isomerization across a ring are less likely to occur than isomerization between α-β. That is, dimethylnaphthalene is divided into the following four genera regarding isomerization, and isomerization between genera is less likely to occur than isomerization within each genus. Genus A 1,5-, 1,6-, 2,6-. Genus B 1,8-, 1,7-, 2,7-. C genus 1,4-, 1,3-, 2,3-. Genus 1,2-.

Known methods for producing 2,6-dimethylnaphthalene include a method in which naphthalene or methylnaphthalene is subjected to isomerization and separation after methylation, a method in which it is separated from a tar fraction, or a petroleum fraction. However, these fractions and products contain most of the isomers of the 4 genus, and it is difficult to isomerize them to efficiently produce 2,6-dimethylnaphthalene, which is a difficult intergeneric isomer. Need to be converted. Further, in order to obtain high-purity 2,6-dimethylnaphthalene, a complicated separation operation from various isomer mixtures is inevitable, which is not feasible as an industrial method for producing 2,6-dimethylnaphthalene. It is low.

JP-A-49-134634 discloses a method for obtaining o-tolylpentene-2 from orthoxylene and butadiene in a high yield. JP-A-50-89353 discloses o-tolylpentene.
A method for producing 1,5-dimethyltetralin by cyclizing -2, and in JP-A-48-76852, 1,5-dimethyltetralin is dehydrogenated to give 1,5-dimethylnaphthalene with high yield and high selectivity. Have been proposed.
1,5-Dimethylnaphthalene belongs to the same genus as 2,6-dimethylnaphthalene, and when 1,5-dimethylnaphthalene obtained here is used as a raw material, 2,6-dimethylnaphthalene is isomerized only within the genus. Can be manufactured. 1,
Many methods have been proposed as a method for producing 2,6-dimethylnaphthalene by isomerizing 5-dimethylnaphthalene. For example, in Japanese Examined Patent Publication No. 47-50622, a method of isomerizing in the gas phase using silica-alumina as a catalyst, US Pat. Patent 4
In 9626260, a method using β zeolite or Y-type zeolite as a catalyst is proposed.

However, in JP-B-47-50622, the isomer ratio of the 2,6-isomer contained in the product liquid is high,
In addition to the large amount of 2,7-form and 1,7-form of a different genus from the 2,6-form, the production amount of monomethylnaphthalene and trimethylnaphthalene due to disproportionation is large. US Patent 4
962260 has few side reactions such as disproportionation,
Many isomers of different genus such as 7-form are produced, and the isomerization rate to 2,6-form is insufficient.

The present inventors have used, as a catalyst, mordenite consisting essentially of hydrogen in which the molar ratio of silica to alumina is 100 or more, and the isomerization reaction of the starting material dimethylnaphthalene at a reaction temperature of 270 ° C. or lower in the liquid phase. It was found that a high isomerization rate to 2,6-dimethylnaphthalene can be obtained by carrying out the above-mentioned reaction and undesired side reactions such as disproportionation and extra-general isomerization can be remarkably suppressed.
A patent application has been filed at 75645.

[0007]

However, the method developed by the present inventors is sufficiently satisfactory in obtaining high reaction results, but is not necessarily satisfactory in that the catalyst performance is stably maintained for a long period of time. There wasn't. The inventors of the present invention have conducted extensive studies to develop a method capable of maintaining high reaction results stably for a long period of time, and the cause of the catalyst performance decreasing as the reaction continues is that coke deposition on the catalyst It turned out to be. Therefore, as a result of extensive studies on the cause of coke formation, it was found that a specific impurity in the raw material was the main cause, and based on this finding, the present invention could be reached and completed.

[0008]

In view of the above facts, the present invention has a problem not only in catalyst performance but also in quality of raw materials when isomerizing dimethylnaphthalene to produce 2,6-dimethylnaphthalene. Since it became clear,
We continued to study the influence of impurities in the raw materials. As a result, it was found that monomethylnaphthalene in the raw material was the main cause of coke formation on the catalyst and gradually decreased the catalyst activity. In the method of the present invention, a raw material in which the amount of monomethylnaphthalene is 5 wt% or less is used for the reaction, and a molar ratio of silica to alumina is 100 or more, and mordenite consisting essentially of hydrogen is used as a catalyst. It is characterized in that the isomerization reaction is carried out at a reaction temperature of 270 ° C. or lower. As a result, it was found that coke formation on the catalyst was suppressed, and the reaction could proceed for a long period of time without lowering the catalytic activity, and the present invention could be completed.

When the raw material contains monomethylnaphthalene, the rate of decrease in the activity of the catalyst is larger than that in the case where it is not contained, which adversely affects the life of the catalyst.
That is, when monomethylnaphthalene is contained, as a side reaction, an adduct of monomethylnaphthalene and dimethylnaphthalene is produced, and a dimerization reaction of monomethylnaphthalene occurs, and these high boiling substances cause coking of the catalyst surface. The catalytic activity is reduced.

Monomethylnaphthalene may be produced as a by-product by a disproportionation reaction when isomerizing dimethylnaphthalene, but when the isomerization reaction is carried out under a predetermined condition using the catalyst of the present invention, monomethylnaphthalene is produced. The amount of by-products such as naphthalene and trimethylnaphthalene is extremely small. Usually, the isomerization product liquid is sent to the crystallization process, 2,6-DMN is collected as crystals, and the mother liquor is recycled to the isomerization process. At this time, the monomethylnaphthalene in the isomerization product liquid is the mother liquor. It will be recycled as it is contained in the isomerized raw material and will be gradually concentrated in the isomerization raw material.

The concentration of monomethylnaphthalene in the raw material dimethylnaphthalene in the method of the present invention is 5 wt% or less,
It is preferably 1 wt% or less. When 5 wt% or more of monomethylnaphthalene is contained in the raw material, the catalyst activity is remarkably reduced, the cycle until catalyst regeneration is shortened, and it is disadvantageous from the economical aspect. Monomethylnaphthalene can be separated and removed from dimethylnaphthalene by distillation, but its difference in boiling points is small, so in order to completely remove it, it is necessary to greatly increase the number of stages and the reflux ratio of the distillation column, which is an enormous amount. It is not an economic process because it consumes energy. Therefore, the concentration of monomethylnaphthalene in the raw material dimethylnaphthalene is determined in consideration of the energy cost of distillation and the catalyst life within the allowable range in the method of the present invention.

In Japanese Patent Publication No. 58-5888, SiO ₂ / Al
_When the isomerization reaction of dimethylnaphthalene is carried out in the liquid phase with hydrogen type mordenite having a ₂ O ₃ ratio of 10 or more and 30 or less as a catalyst, isomers other than 2,6-genus are produced, so that the content of trimethylnaphthalene It is proposed to use a raw material having a content of 10 mol% or less. When the isomerization reaction is carried out by the method of the present invention, the influence of the incorporation of trimethylnaphthalene is hardly seen. Also, monomethylnaphthalene 1
Even if 0 wt% is added, there is an effect in terms of life,
Almost no effect on side reactions such as disproportionation or isomerization outside the group was observed. This is because the mordenite used in the method of the present invention is
This is because the silica-alumina ratio is high and a sufficient isomerization reaction rate can be obtained even at a low temperature, so that there are originally few side reactions such as intermolecular reactions.

In the present invention, mordenite substantially in the hydrogen form is used as the catalyst. The H-type mordenite used in the method of the present invention has higher activity as the SiO ₂ / Al ₂ O ₃ ratio is higher, and the SiO ₂ / Al ₂ O ₃ ratio is 100 or more, more preferably 200 or more. Mordenite includes, for example, Na type and Ca type, but the method of the present invention is characterized by using substantially hydrogen type mordenite, which contains an alkali metal or an alkaline earth metal. Has low activity, and the content of alkali metal or alkaline earth metal in mordenite is 0.5 wt% or less, more preferably 0.1 wt% or less, as the amount of metal in mordenite.

There is no particular limitation on the reaction system for carrying out the isomerization according to the present invention, and either a batch system or a flow system can be used. The flow system also includes reaction systems such as a fixed bed, a moving bed, and a fluidized bed. Any of them can be adopted, but the fixed bed flow system is general. When it is carried out in a fixed bed flow system, mordenite is molded and used. As a molding aid for mordenite, clay such as bentonite, alumina, silica or the like is used, and alumina is excellent as a molding aid for the catalyst of the present invention. Clay such as bentonite contains various metals,
This is a cause of impairing the isomerization activity of the catalyst. Alumina does not reduce the isomerization activity and gives good results in terms of catalyst life.

If the amount of alumina used as a molding aid is small, the catalyst life becomes long, but there is a problem in strength.
If it is increased, there is no problem in strength, but there is a bad influence in terms of catalyst life. Considering this point, the amount of alumina used as a molding aid is 5 with respect to 100 parts by weight of mordenite.
-50 parts by weight, preferably 10-30 parts by weight. Furthermore, the catalyst used in accordance with the method of the present invention and having a reduced activity can be used in an inert gas containing oxygen at 400 ° C. or higher and 600 ° C.
It can be regenerated by heating at the following temperature. By this regeneration operation, it is possible to activate even the initial catalyst activity, and if this regeneration is incorporated, the catalyst can be used for the reaction for an extremely long time.

The isomerization reaction in the method of the present invention is carried out at a reaction temperature of 270 ° C or lower, preferably 150 ° C to 27 ° C.
It is carried out in the range of 0 ° C. At a temperature higher than this, side reactions such as isomerization to different genus and disproportionation easily occur, and at a temperature lower than this, a sufficient isomerization rate cannot be obtained, which is not economical. When the isomerization according to the method of the present invention is carried out by selecting an appropriate temperature of 270 ° C. or lower, 2,6-
The concentration of dimethylnaphthalene reaches a thermodynamic equilibrium concentration, and at the same time, side reactions such as formation and disproportionation of heterogeneous isomers such as 2,7-dimethylnaphthalene hardly occur.

WH when the present invention is carried out by the distribution method
SV is 0.05 to 5 hr ^-1 , preferably 0.1 to 2 h
r ⁻¹ , and more preferably 0.2 to ¹ hr ⁻¹ . WH
When SV is reduced, the isomerization reaction proceeds at low temperature,
It is not economical because it requires a large reactor. WHS
When V is increased, it is necessary to raise the reaction temperature in order to obtain a high isomerization rate, and isomerization to a different genus and disproportionation are likely to occur. When using the batch method, the amount of catalyst used is
The amount is 0.1 to 10 parts by weight, preferably 0.3 to 5 parts by weight, based on 100 parts by weight of the raw material. The reaction time varies depending on the ratio of the catalyst to the raw material and the reaction temperature, but is generally 10 minutes to 2 hours. As described above, when the isomerization reaction of dimethylnaphthalene is carried out by the method of the present invention,
Side reactions and isomerization into different genus are substantially suppressed, a high isomerization rate is achieved, and the target product is stable over a long period of time.
6-Dimethylnaphthalene can be obtained.

[0018]

According to the method of the present invention, in the isomerization reaction of dimethylnaphthalene, isomerization of 2,7-dimethylnaphthalene or the like to a different genus and side reactions such as disproportionation are suppressed,
A high isomerization rate to 2,6-dimethylnaphthalene can be achieved, and the catalytic activity can be maintained for a long period of time, which is of great industrial significance.

[0019]

EXAMPLES The method of the present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples. Examples 1 and 2 and Comparative Example 1 H-type mordenite 10 having a SiO ₂ / Al ₂ O ₃ ratio of 203
0g (manufactured by Toso) and 20g alumina sol (manufactured by Catalyst Kasei:
Alumina content 70wt%) is put into a stainless steel container,
An appropriate amount of pure water was added and kneaded well. After drying at 110 ° C. for 8 hours, it was calcined in air at 500 ° C. for 3 hours and crushed to collect particles having a particle size of 1.0 to 2.0 mm to obtain a catalyst. 5 g of this catalyst was filled in a stainless steel reaction tube having an inner diameter of 13 mm,
After sufficiently substituting with nitrogen, the temperature was raised to 230 ° C. in a nitrogen atmosphere and kept at the same temperature. After stopping the nitrogen, the raw material was fed from the lower part of the reaction tube under the condition of 15 g / hr (the amount of dimethylnaphthalene) to carry out the isomerization reaction. The composition of the reaction product liquid taken out from the upper part of the reaction tube was analyzed by gas chromatography to calculate the reaction results. As a raw material, the concentration of monomethylnaphthalene in dimethylnaphthalene was 0.
Three types of 15 wt% (Example 1), 3.27 wt% (Example 2), and 10.09 wt% (Comparative Example 1) were used. The reaction results are shown in Table 1. When a raw material containing monomethylnaphthalene in an amount of 5 wt% or more is used, a high-boiling substance is remarkably produced, and further, the concentration of 2,6-dimethylnaphthalene is greatly decreased with time, and the catalyst life is affected.

Example 3 and 4 Using the same catalyst as in Example 1, an isomerization reaction was carried out under the same conditions as in Example 1. As a raw material, the concentration of trimethylnaphthalene is 2.83 wt% and the concentration of monomethylnaphthalene is 0.8.
15 wt% (Example 3) and trimethylnaphthalene concentration of 9.92 wt% and monomethylnaphthalene concentration of 0.13 wt% (Example 4) were used. The reaction results are shown in Table 2. If the concentration of monomethylnaphthalene is less than the permissible amount, even if trimethylnaphthalene is contained, no influence on the catalyst life or side reaction is observed.

Example 5 and Comparative Example 2 An H-type mordenite having a SiO ₂ / Al ₂ O ₃ ratio of 16 was mixed with 3
Treatment with normal hydrochloric acid gave H-type mordenite with a SiO ₂ / Al ₂ O ₃ ratio of 154. Using this catalyst, a molded catalyst was prepared in the same manner as in Example 1, and the isomerization reaction was carried out under the same conditions. As a raw material, monomethylnaphthalene concentration is 0.1
5 wt% (Example 5) and 10.12 wt% (Comparative Example 2) were used. The reaction results are shown in Table 3. S
It can be seen that regardless of the iO ₂ / Al ₂ O ₃ ratio, when the monomethylnaphthalene concentration is high, the concentration of 2,6-dimethylnaphthalene decreases greatly with time, and the catalyst life is affected.

The abbreviations used in each table are shown below. MM
N (monomethylnaphthalene). DMN (dimethylnaphthalene). TMN (trimethylnaphthalene). WHSV
(Raw material-g / catalyst-g · hr). Time (time elapsed from the start of the reaction).

[0023]

[Table 1] ───────────────────────────────────── Example 1 Example 2 Comparative Example 1 <Raw materials> MMN 0.15 3.27 10.09 DMN 99.76 96.63 89.80 1,5-^* 13.64 13.64 13.64 1,6-^* 78.76 78.76 78.76 2,6-^* 7.40 7.40 7.40 Others^* 0.20 0.20 0.20 TMN 0.07 0.07 0.06 Low boiling point substances 0.02 0.03 0.05High boiling point 0.00 0.00 0.00 <Reaction conditions> Temperature (℃) 230 230 230 230 230 230 WHSV 3.0 3.0 3.0 3.0 3.0 3.0Time (hr) 61 181 58 178 60 181 <Production liquid> MMN 0.18 0.16 2.98 3.02 9.12 9.27 DMN 99.60 99.69 96.54 96.59 89.64 89.72 1,5-^* 7.85 9.51 7.90 9.49 10.61 12.30 1,6-^* 44.08 43.33 44.02 43.30 42.93 46.62 2,6-^* 47.85 46.96 47.86 47.01 46.24 40.87 Others^* 0.22 0.20 0.22 0.20 0.22 0.21 TMN 0.09 0.06 0.11 0.09 0.09 0.07 Low boiling point substances 0.05 0.03 0.06 0.03 0.08 0.05High boiler 0.08 0.06 0.31 0.27 1.07 0.89 ^* Isomeric ratio in DMN (%).

[0024]

[Table 2] ───────────────────────────────────── Example 3 Example 4 <Raw materials> MMN 0.15 0.15 DMN 97.00 89.91 1,5-^* 13.64 13.64 1,6-^* 78.76 78.76 2,6-^* 7.40 7.40 Others^* 0.20 0.20 TMN 2.83 9.92 Low boiling point substances 0.02 0.02High boiling point 0.00 0.00 <Reaction conditions> Temperature (℃) 230 230 230 230 WHSV 3.0 3.0 3.0 3.0Time (hr) 60 175 55 181 <Production solution> MMN 0.18 0.16 0.17 0.16 DMN 96.85 96.92 89.70 89.83 1,5-^* 7.59 9.45 7.55 9.51 1,6-^* 44.31 43.31 44.41 43.47 2,6-^* 47.88 47.03 47.82 46.82 Others^* 0.22 0.21 0.22 0.20 TMN 2.86 2.83 9.99 9.92 Low boiling point substance 0.05 0.03 0.05 0.02 High boiling point substance 0.08 0.06 0.09 0.07 ──────────────────────────── ─────────

[0025]

[Table 3] ───────────────────────────────────── Example 3 Example 4 <Raw materials> MMN 0.15 10.01 DMN 99.76 89.91 1,5-^* 13.64 13.64 1,6-^* 78.76 78.76 2,6-^* 7.40 7.40 Others^* 0.20 0.20 TMN 0.07 0.0 Low boiler 0.02 0.02High boiling point 0.00 0.00 <Reaction conditions> Temperature (℃) 230 230 230 230 WHSV 3.0 3.0 3.0 3.0Time (hr) 59 180 60 180 <Production liquid> MMN 0.19 0.17 9.12 9.30 DMN 99.59 99.68 89.68 89.71 1,5-^* 13.27 13.12 11.60 16.23 1,6-^* 41.34 41.73 44.47 45.72 2,6-^* 45.17 44.95 43.71 37.85 Others^* 0.22 0.20 0.22 0.21 TMN 0.09 0.06 0.10 0.07 Low boiling point substance 0.05 0.03 0.05 0.05 High boiling point substance 0.08 0.06 1.05 0.84 ──────────────────────────── ─────────

Claims (4)

[Claims] 1. When carrying out an isomerization reaction of dimethylnaphthalene, a raw material having a monomethylnaphthalene concentration of 5 wt% or less is used, and mordenite consisting essentially of hydrogen is used as a catalyst to perform isomerization in a liquid phase. A method for isomerizing dimethylnaphthalene, which comprises: 2. The molar ratio of silica to alumina is 100.
The method according to claim 1, wherein the mordenite is used as a catalyst. 3. The method according to claim 1, wherein a catalyst having 50% by weight or less of mordenite as an auxiliary agent of alumina is used. 4. The method according to claim 1, wherein the reaction temperature for isomerization is 270 ° C. or lower.