JPH0449253A - Production of 2,6-dimethylnaphthalene - Google Patents

Abstract

PURPOSE:To obtain the subject substance by separating the 2,6-isomer from a stock oil mainly containing a dimethylnaphthalene (DMN) isomer mixture, subjecting the residual stock oil to isomerizing reaction, increasing the 2,6-isomer concentration, removing components other than the DMN from the reaction product and circulating most thereof to the first step. CONSTITUTION:2,6-Dimethylnaphthalene (2,6-DMN) is separated from a stock oil mainly containing a DMN isomer mixture according to a continuous separation method, etc., using column chromatography to isomerize the resultant stock oil at the reduced 2,6-DMN concentration in the presence of a solid acid catalyst (e.g. H-ZSM-5 type zeolite) at 20-500 deg.C. Thereby, the 2,6-DMN concentration is increased to a composition near the thermodynamic equilibrium concentration. Low- and high-boiling substances are removed from the isomerizing reaction product and the 1,2-DMN is removed as much as possible. The obtained product is then circulated to the first step. The high-purity 2,6-DMN of >=99% purity can be efficiently produced by the aforementioned method.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for producing 2,6-dimethylnaphthalene. Specifically, the present invention relates to a method for producing 2,6-dimethylnaphthalene from a raw material oil containing a dimethylnaphthalene isomer mixture as a main component.

(Prior Art) 2.6-Dialkylnaphthalene, such as 2,6-dimethylnaphthalene, is used as a raw material for producing polyethylene naphthalate, which has high heat resistance and gas barrier properties, and is a raw material containing a dialkylnaphthalene isomer mixture as a main component. It is produced by separating it from oil.

Conventionally, as a method for obtaining 2,6-dialkylnaphthalene from a feedstock oil containing a mixture of dialkylnaphthalene isomers as a main component, many methods using zeolite-based adsorbents are known.

For example, U.S. Patent No. 3,133,126, U.S. Patent No. 3,134,
782, 3.772,399, 3,840,610
, No. 3,895,080, No. 4,014°949, Japanese Patent Publication No. 49-27578, Japanese Patent Publication No. 51-24505, Japanese Patent Publication No. 52-945, and Dutch Patent No. 7307794.

(Problems to be Solved by the Invention) However, these prior arts do not disclose a specific method for obtaining high-purity 2,6-dialkylnaphthalene with a high yield, such as a purity of 99% or more. Furthermore, impurities in the feedstock containing a mixture of dialkylnaphthalene isomers and the behavior of by-products generated when the dialkylnaphthalene mixture raffinate is isomerized after 2,6-dialkylnaphthalene has been separated from the feedstock have not been completely elucidated. However, there were many problems to be solved in order to produce high-purity 2,6-dialkylnaphthalene in good yield.

The present applicant first proposed a method for separating 2,6-dialkylnaphthalene by combining column chromatography separation and crystallization separation using a specific adsorbent and desorbing agent, and published JP-A-1-168628. ).

This method allows continuous column chromatography separation using a simulated moving bed system and is extremely advantageous in industrial practice, but the behavior of impurities other than dialkylnaphthalene in the feedstock oil is unclear.

In addition, from an economical point of view, it is possible to obtain a dialkylnaphthalene mixture raffinate in which 2,6-dialkylnaphthalene is separated from a feed oil containing a mixture of dialkylnaphthalene isomers and its concentration is reduced. It is preferable to increase the concentration of the dialkylnaphthalene to a composition close to its thermodynamic equilibrium concentration and return it to the separation process.However, during isomerization, at least a portion of the dialkylnaphthalene itself or other hydrocarbons mixed as impurities undergoes dealkylation, Complex side reactions such as disproportionation, hydrogenation, trimerization, decomposition, ring-closing reactions, and ring-closing reactions usually occur together, resulting in light-boiling and high-boiling components as by-products, but the effects of these impurities Knowledge regarding its behavior is unknown, and there are still many problems that need to be resolved in the adoption of industrial processes.

The purpose of the present invention is to solve the above-mentioned problems caused by the conventional method,
The object of the present invention is to establish an industrially advantageous method for producing 2,6-dimethylnaphthalene from a feed oil containing dialkylnaphthalene, especially a mixture of dimethylnaphthalene isomers, as a main component.

(Means for Solving the Problems) As a result of studies to achieve the above object, the present inventors found that dimethyl isomers have large differences in reactivity in their respective isomerization reactions.

That is, for example, as specifically shown in Example 1 of the postscript, the reactivity of the isomerization reaction is high in 2,6-unit, 2.7-unit, 2,3-unit, etc., and the one with medium reactivity is 1. .5-body, 1
．． It was found that 1,2 isomers have extremely low reactivity in isomerization reactions compared to the other isomers mentioned above.

For this purpose, isomerization reaction and separation treatment are combined,
When producing 2゜6-dimethylnaphthalene from a mixture of dimethylnaphthalene isomers, 1,2-dimethylnaphthalene gradually accumulates in the system, even though the content of 1,2-dimethylnaphthalene in the mixture is relatively small. to reduce the target concentration of 2,6-dimethylnaphthalene,
It was determined that driving was impaired.

As a result of further studies based on the above findings, the present invention has been developed by separating 2,6-dimethylnaphthalene from a feedstock oil containing a dimethylnaphthalene isomer mixture as a main component, and isomerizing the separated feedstock component. When adopting a process in which the concentration of 2,6-dimethylnaphthalene is increased and this is recycled to the above-mentioned 2,6-dimethylnaphthalene separation step, low-boiling point components and high-boiling point components other than dimethylnaphthalene that are by-produced by the isomerization reaction. together with 1 in the isomer mixture
．． After pre-removal of 2-dimethylnaphthalene, 2,6
The present invention has been achieved by discovering that extremely high purity 2,6-dialkylnaphthalene can be efficiently produced by recycling it to the separation step of -dimethylnaphthalene.

That is, the gist of the present invention is as follows: (a) a first step of separating 2,6-dimethylnaphthalene from a feed oil containing a mixture of dimethylnaphthalene isomers as a main component; (b) a step of separating 2,6-dimethylnaphthalene in the first step; An isomerization reaction in which feedstock oil containing a mixture of dimethylnaphthalene isomers with a reduced concentration of 6-dimethylnaphthalene is subjected to an isomerization reaction to increase the concentration of 2,6-dimethyllunaphthalene to a composition close to the thermodynamic equilibrium concentration. A second step of obtaining a product, (c) removing components other than dimethylnaphthalene from the isomerization reaction product of the second step, and further removing at least a portion of 1,2-dimethylnaphthalene, and then proceeding to the first step. The present invention relates to a method for producing 2,6-dimethylnaphthalene from a feedstock oil containing a dimethylnaphthalene isomer mixture as a main component, characterized by comprising a circulating third step.

The present invention will be explained in detail below.

The dimethylnaphthalene isomer mixture in the present invention is
2,6-dimethylnaphthalene, 2,7-dimethylnaphthalene, 2,3-dimethylnaphthalene, 1,3-dimethylnaphthalene, 1,8-dimethylnaphthalene, 1, 7-dimethylnaphthalene, 1,6-dimethylnaphthalene, 1 ．．
It means a mixture of isomers such as 5-dimethylnaphthalene, 1,4-dimethylnaphthalene and 1,2-dimethylnaphthalene.

The feedstock oil containing a dimethylnaphthalene isomer mixture as a main component, which is the target of the treatment of the present invention, is generally
(1) Distillates or extracts from gas oil, coal tar or petroleum heavy oil, (2) Decomposition products or modified products of the above fractions or kerosene, (3) Alkylation of naphthalene or methylnaphthalene, or It is a mixture of aromatic hydrocarbons with a boiling point of about 260 to 320°C, such as transalkylation products and (4) dehydrogenation products of alkyl-substituted benzenes, and mainly consists of the above dimethylnaphthalene isomer mixture, with other monomers. Although it contains alkylnaphthalene and further contains trace amounts of impurities such as nitrogen-containing, oxygen-containing, and sulfur-containing compounds, it is desirable to remove these impurities as much as possible in advance before using it in the present invention.

The method of the present invention consists of steps (a), (b), and (c) shown below.

(a) First step: In the first step, 2,6-dimethylnaphthalene is separated from the feedstock oil containing a dimethylnaphthalene isomer mixture as a main component. Various known methods are employed to separate 2,6-dimethylnaphthalene from feedstock oil. For example, a batch method using an adsorbent, a continuous separation method using column chromatography, a crystallization method, and a pressure crystallization method. Alternatively, a host-guest adduct formation method may be used. Among these, a continuous separation method using column chromatography is particularly preferred; for example, a continuous separation method using a simulated moving bed system described in JP-A-1-168628 or a method combining this with a crystallization method is recommended. Ru.

Specifically, X-type zeolites and Y-type zeolites containing alkali metals, zinc, etc. at cation sites are used as adsorbents, and Y-type zeolites containing lithium at cation sites are particularly preferred.
zeolite and using para-xylene and/or ortho-xylene as desorbing agent, the feedstock containing a mixture of dimethylnaphthalene isomers as the main component is continuously chromatographed, preferably in a simulated moving bed mode. This is a method of separating The separation conditions are 60~
Preferably, a temperature of 200° C. and a pressure of between atmospheric pressure and 20 atmospheres are selected. If the product stream of 2,6-dimethylnaphthalene thus separated is further subjected to crystallization separation, 2,6-dimethylnaphthalene of even higher purity can be obtained.

(b) Second step: In this step, the raw oil containing the dimethylnaphthalene isomer mixture with a reduced concentration of 2,6-dimethylnaphthalene after 2,6-dimethylnaphthalene separation in the first step is subjected to an isomerization reaction. An isomerization reaction product in which the concentration of 2,6-dimethylnaphthalene is increased to a composition close to the thermodynamic equilibrium concentration is obtained.

The isomerization reaction is carried out in the gas or liquid phase in the presence of a solid acid catalyst. The reaction is carried out at a temperature of 20 to 500°C and a pressure of about atmospheric pressure to 50 atm, preferably in a hydrogen atmosphere, by introducing the raw material oil containing the dimethylnaphthalene isomer mixture in the gas phase to carry out the isomerization reaction. is desirable.

Particularly suitable isomerization reaction catalysts include, for example, pentasil type zeolite ion-exchanged to hydrogen type, especially H-ZSM.
-5 type zeolite, Y type zeolite ion-exchanged with hydrogen or various metal cations, mordenite type zeolite, and other aluminosilicate-based catalysts.

These zeolite catalysts may support metal components having hydrogenation ability such as nickel, rhenium, palladium, platinum, etc., or may be ion-exchanged with these metals, if necessary.
In industrial practice, these catalysts are combined with silica, alumina, boehmite, alumina sol, bentonite, clay minerals (
It is generally used by molding with natural clay minerals such as kaolinite, seviolite, halloysite, and montmorillonite, and synthetic clays such as lard crosslinked clay.

By carrying out the isomerization reaction under the conditions described above using such a catalyst, it is possible to obtain a reaction product in which the concentration of 2,6-dimethylnaphthalene is increased to a composition close to the thermodynamic equilibrium concentration. . In addition to the above, isomerization can also be carried out in a liquid phase using a Lewis acid catalyst such as aluminum chloride.

(c) Third step: In this step, components with a lower boiling point than dimethylnaphthalene (low boilers) and components with a higher boiling point than dimethylnaphthalene (high boilers) are extracted from the isomerization reaction product. ) is removed as much as possible, and 1°2-dimethylnaphthalene in the dimethylnaphthalene isomer mixture is further removed as much as possible, and then recycled to the first step of separating the 2,6-dimethylnaphthalene, This point is a major feature of the present invention.

Separation of the above-mentioned low-boiling substances and high-boiling substances from the isomerization reaction product,
In addition, various separation operations known per se can be applied to the 1,2-dimethylnaphthalene fraction.

Specifically, for example, the isomerization reaction product obtained in the second step is supplied to a distillation column and low-boiling substances are distilled out of the system from the top of the column,
The bottom liquid is distilled in the same distillation column or introduced into a second distillation column and distilled, and the dimethylnaphthalene isomer mixture is distilled out from the top of the column and recycled to the first step.
．． A method is adopted in which 2-dimethylnaphthalene is distilled off from the middle part of the column or from the bottom of the column, and high-boiling substances are extracted from the bottom of the column. Precision distillation is suitably carried out in a continuous or batch manner using this bottle stand, a packed distillation column, a multi-stage distillation column, etc. operated under a reduced pressure of about 1 to 200 m-Hg. Preferably, the pressure inside the column is set so that the pot temperature is in the range of about 150 to 280°C, and high boiling substances are extracted from the bottom of the column.

It is operated continuously in such a way that 2-dimethylnaphthalene is withdrawn from the middle of the column as a side stream in the gas phase.

The method of the present invention is carried out by repeating the steps (a), (b), and (c) described above, thereby preventing accumulation of 1,2-dimethylnaphthalene in the system. 2,6-dialkylnaphthalene of extremely high purity can be obtained efficiently.

(Examples) The present invention will be described in more detail with reference to Examples below, but the present invention is not limited to these Examples unless the gist thereof is exceeded.

Reference Example 1 [Isomerization reactivity of dimethylnaphthalene isomers 1] Seven types of dimethylnaphthalene isomers shown in Table 1 were examined for their individual isomerization reactivity.

As an isomerization catalyst, ZSM-5 type zeolite (SiO2/Al2O3 = 32.5) produced by the method described in Example 1 of Japanese Patent Publication No. 46-10084 was calcined,
Next, ion exchange is performed to N)14 type, and further calcined to form H+
The H-ZSM-5 type zeolite obtained by converting it into a mold was used.

The above catalyst (particle size 10-20 mesh > 3-1 g (5.2 ml) was placed in a hard glass reactor with an inner diameter of 2011 Il.
A layer of glass beads was filled on top of the catalyst layer, and the dimethylnaphthalene isomer (DMN) shown in Table 1 was supplied alone to this, vaporized and entrained in hydrogen gas, at a temperature of 350°C.
H2/DMN (% ratio) = 28, L) IsV = 0
The isomerization reaction was carried out over 18 days.

The reactivity (conversion rate) of each DMN was as shown in Table 1.

Table 1 From the results in the above table, 1.2-dimethylnaphthalene has significantly lower isomerization reactivity than other isomers, and 2.6
- It is understood that dimethylnaphthalene tends to accumulate within the separation process.

Example 1 [Separation by Column Chromatography] The adsorption separation method using a simulated moving bed was disclosed in Japanese Patent Publication No. 42-15681 and has since become a well-known technique to those skilled in the art. This method was also used in this example. This method uses an oil component containing a mixture of dimethylnaphthalene isomers as a raw material, and uses a desorbing agent to separate a 2,6-dimethylnaphthalene solution, which is a non-adsorbed component, and a solution of another dimethylnaphthalene isomer mixture, which is an adsorbed component. , a method of continuous separation by chromatography, in which the inside is filled with an adsorbent,
The packed bed, whose front end and rear end are connected by a fluid passage, includes an adsorption zone from a raw material supply section to a non-adsorbate extraction section;
The four zones, the purification zone from the extraction section to the adsorbent supply section, the desorption zone from the supply section to the adsorbate extraction section, and the concentration zone from the extraction section to the raw material supply section, are constructed in the above order from upstream. This is a separation method that involves circulating the fluid while forming the fluid, and intermittently moving the positions of the supply section and the extraction section in the downstream direction.

Y-type zeolite ion-exchanged with lithium (particle size distribution 2
Using eight stainless steel columns with an inner diameter of 28 mm and a packing height of 416 mm, packed with
2,6-Dimethylnaphthalene was separated from a feedstock containing a mixture of dimethylnaphthalene isomers at 0°C. Baraxylene was used as a desorption agent.

The raw material was fed at a rate of 1/h from the raw material supply port.

The composition of the raw material is 2,6-dimethylnaphthalene: 13.4
%, 1.2-dimethylnaphthalene is 3.51%,
In addition, dimethylnaphthalene isomers (2,7-dimethylnaphthalene 13.5%, 2,3-dimethylnaphthalene 4.5%, 1.7-dimethylnaphthalene 14.7%, other 1.6-dimethyl It contained isomers such as naphthalene) and small amounts of methylnaphthalenes, ethylnaphthalenes, and biphenyls.

Operation was carried out by feeding bala-xylene at a rate of 366 ml/h from the desorbing agent supply port, controlling the non-adsorbed material flow (product flow) to 84 ml/hr, and the raffinate flow to 393 ml/hr.

19 hours after the start of operation, the concentration distribution in the system reached a steady state, so we analyzed the product flow and found that 78% of baraxylene was present.
．． 8%, 2.6-dimethylnaphthalene 14.8%, 2
, 7-dimethylnaphthalene was 0.2%, 2,3-dimethylnaphthalene was 0.1%, and 1,2-dimethylnaphthalene was not detected. Barraxylene concentration in the raffinate stream: 82.6%, 2,6-dimethylnaphthalene concentration: 0.26%, 1,2-dimethylnaphthalene concentration: 0.
71%, and other components were also detected. From this, it is clear that the entire amount of 1,2-dimethylnaphthalene comes out into the raffinate stream. Therefore, if the raffinate stream is recycled to the isomerization reaction and the isomer component is utilized for the production of 2,6-dimethylnaphthalene, 1,2-dimethylnaphthalene will accumulate in the system.

The purity of 2,6-dimethylnaphthalene was 70.0% when converted to the base excluding baraxylene. Since baraxylene can be easily removed by distillation, the purity of 2,6-dimethylnaphthalene increases from 13.4% to 70.0%, and its recovery rate is calculated to be 73%.

Example 2 [Isomerization] The raffinate component after separating 2,6-dimethylnaphthalene in Example 1 was subjected to batch distillation using a distillation column with a total number of theoretical plates of 50 at a reflux ratio of 3 and a column top pressure of 120 gmHg. The desorbing agent (baraxylene) was distilled off. The bottom liquid contained a dimethylnaphthalene isomer mixture as a main component, but the concentration of 2,6-dimethylnaphthalene had decreased to 1.0%.

An isomerization reaction was carried out using the above pot residue.

As the isomerization catalyst, I-ZSM used in Reference Example 1 was used.
-5 type zeolite was used.

A stainless steel reactor with an inner diameter of 25 + U+ was filled with 20 ml of the above catalyst (particle size 1O ~ 20 mesh), ceramic balls were packed on top of the catalyst layer, and a dimethylnaphthalene isomer mixture (DMN) was charged into this. Supply, vaporize and entrain in hydrogen gas, temperature 380°C, pressure 10 kg/C
-2, H2/DMN% ratio = 25, LH5V = 0.6
When the zero reaction product was analyzed through the isomerization reaction, the concentration of 2,6-dimethylnaphthalene was 1365.
%, and the total recovery rate of dimethylnaphthalene was 97%.

In addition to dimethylnaphthalene, the reaction product contains
Trace amounts of benzene, toluene, xylene (0-1-1, p
- isomer mixtures), compounds with a lower clearing point than dimethylnaphthalene such as naphthalene, methylnaphthalene, and ethylnaphthalene, as well as trimethylnaphthalenes, tetramethylnaphthalenes, pentamethylnaphthalenes, binaphthyl compounds having various numbers of methyl groups, etc. It was found that it contained a compound with a higher boiling point than dimethylnaphthalene.

Example 3 [Isomerization] The raffinate component after 2,6-dimethylnaphthane was separated by column chromatography similar to the first step in Example 1 was subjected to batch distillation to distill off the desorbing agent (paraxylene). A mixture containing dimethylnaphthalene isomers (2,6-dimethylnaphthalene 1.0%, 1.2
The isomerization reaction was carried out using the same catalyst as in Example 2 with 4.8% of dimethylnaphthalene and other dimethylnaphthalene isomers as well as small amounts of methylnaphthalenes, ethylnaphthalenes, and biphenyls.

Into a hard glass reactor with an inner diameter of 201II+, 3.1 g (5.2 pieces 1) of the above catalyst (particle size 10-20 mesh) was added.
A layer of glass beads was filled on top of the catalyst layer, and the above dimethylnaphthalene isomer mixture (DIN)
is supplied and vaporized and entrained in hydrogen gas, at a temperature of 350°C.
H2/DMN (% ratio) = 28, L) lSV = 0
．． 18 to carry out the isomerization reaction.

When the reaction product liquid was analyzed, the concentration of 2,6-dimethylnaphthalene increased to 12.8%, but the concentration of 1,2-dimethylnaphthalene also increased to 5.2%. In addition, 1, 7-1l, 5-12, 3- and 1.3 with high isomerization reactivity
- It is understood that the concentrations of isomers such as dimethylnaphthalene are decreasing and approaching thermodynamic equilibrium compositions,
Only 1.2-dimethylnaphthalene has an equilibrium composition (approximately 6%
), but it was clearly observed that it accumulated within the system.

Example 4 [Isomerization] Dimethylnaphthalene isomerization obtained by distilling off the desorbing agent (baraxylene) from the raffinate component after 2,6-dimethylnaphthalene was separated by column chromatography in the same manner as in Example 1. (3.1% of 2,6-dimethylnaphthalene, 1% of 1,2-dimethylnaphthalene)
The isomerization reaction was carried out using the same catalyst as in Example 3 and under the same conditions.

When the reaction product solution was analyzed, the concentration of 2,6-dimethylnaphthalene increased to 10.5%, but the concentration of 1,2-dimethylnaphthalene was 13.2%, which did not reach the equilibrium composition (approximately 6%) and increased further. did. In addition, l, 7, which has high isomerization reactivity
The concentrations of isomers such as -11,5-12,3- and 1,3-dimethylnaphthalene are decreasing little by little, so each is approaching its thermodynamic equilibrium composition. It was found that only 1,2-dimethylnaphthalene showed a behavior independent of thermodynamic equilibrium and clearly accumulated in the system.

Example 5 [Separation of low-boiling substances, high-boiling substances, and 1.2-isomer] The isomerization reaction product liquid obtained in Example 2 was distilled using a packed batch distillation column with a total number of theoretical plates of 50. .

The pressure at the top of the column was 20**Hg, the reflux ratio was 20, and samples were collected in several fractions depending on the temperature at the top of the column, and analyzed by gas chromatography to determine the composition of each fraction.
It was as shown in Table 2.

Table 2 The formation of the fraction with a tower top temperature of 146-150°C shown in Table 2 is as follows:
1,2-dimethylnaphthalene 50%, 2,3-dimethylnaphthalene 28%, 1,4-dimethylnaphthalene 268%
%, 1.5-dimethylnaphthalene 3.8%, 2.6-dimethylnaphthalene 0.2%, total amount of other compounds 15
% or less. In this way, 1,2-dimethylnaphthalene was concentrated to a concentration of 50%, and the concentration of 2,6-dimethylnaphthalene was about 0.2%, making it possible to separate the two by distillation.

Example 6 [Circulation of isomerized products after separation of low boilers, high boilers and 1,2-isomers] Fraction 2 and fraction 3 in Table 2 obtained in Example 5 were
It was supplied to the column used in Example 1, and 2,6-dimethylnaphthalene was continuously separated by chromatography under the same conditions as in Example 1. The chromatographic pattern was the same as in Example 1, and the purity of 2,6-dimethylnaphthalene was 76% with the exclusion of paraxylene from the product stream.

(Effects of the Invention) According to the present invention, by performing the steps (a), (b), and (c) in the morning, raw oil containing a dimethylnaphthalene isomer mixture as a main component can be obtained with a purity of 99% or more. It is possible to efficiently produce high-purity 2,6-dimethylnaphthalene such as 2,6-dimethylnaphthalene, which greatly contributes to the industrial production of this substance.

Claims (1)

[Claims] (1) (a) A first step of separating 2,6-dimethylnaphthalene from a feedstock oil containing a mixture of dimethylnaphthalene isomers as a main component; (b) Concentration of 2,6-dimethylnaphthalene after separation in the first step. A second step of obtaining an isomerization reaction product in which the 2,6-dimethylnaphthalene concentration has been increased to a composition close to the thermodynamic equilibrium concentration by subjecting the feedstock oil containing a dimethylnaphthalene isomer mixture with a reduced concentration to an isomerization reaction. Step (c) After removing components other than dimethylnaphthalene from the isomerization reaction product in the second step and further removing at least a part of 1,2-dimethylnaphthalene, from the third step circulating to the first step A method for producing 2,6-dimethylnaphthalene from a feedstock oil containing a dimethylnaphthalene isomer mixture as a main component.