JPH0426635A - Separation of 2,6-dialkylnaphthalene - Google Patents

Abstract

PURPOSE:To separate a 2,6-dialkylnaphthalene from a dialkylnaphthalene isomer mixture, to isomerize a raw material oil having reduced concentration of 2,6- dialkylnaphthalene, to raise concentration of 2,6-dialkylnaphthalene, to partially remove the reaction product and to circulate the resulting substance prepared by eliminating part of components except dialkylnaphthalene from the isomerized reaction product. CONSTITUTION:2,6-Dialkylnaphthalene is separated from a raw material oil comprising a dialkylnaphthalene isomer mixture as a main component by chromatography separation and/or crystallization separation, the raw material oil component is isomerized in the presence of a solid acid catalyst (e.g. H-ZSM-5 type zeolite) in a hydrogen gas flow to increase concentration of 2,6-dialkylnaphthalene to a composition close to concentration of thermodynamic equilibrium and a substance prepared by removing part of components except dialkylnaphthalene from the isomerized reaction product is circulated to the initial process. By the above-mentioned process, high-purity 2,6- dialkylnaphthalene having >=99% purity can be efficiently separated.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for separating 2,6-dialkylnaphthalene. Specifically, 2,6-
The present invention relates to a method for separating dialkylnaphthalenes.

(Prior art) 2.6-Dialkylnaphthalene is used as a raw material for producing polyethylene naphthalene-1, which has high heat resistance and gas barrier properties, and is separated from a feedstock oil containing a mixture of alkylnaphthalene isomers as the main component. There is.

As a separation method, many methods using zeolite adsorbents are conventionally known. For example, U.S. Pat.
3,126, 3,114,782, 3,772,3
99, 3,840,610. Same 3, 895, 08
0, 4,014,949, Special Publication No. 49-27578,
Examples include 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 art techniques do not disclose a specific method for obtaining highly purified 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 applicant previously proposed a method for separating 2,6-dialkylnaphthalene by combining column chromatography separation and crystallization separation using a specific adsorbent and desorbing agent (Japanese Patent Application Laid-Open No. 168628/1999). .

According to this method, it is possible to carry out column chromatography separation continuously using a simulated moving bed method, which is extremely advantageous in industrial practice, but the behavior of impurities other than dialkylnaphthalene in the feedstock oil is unclear. , there are still many problems to be solved.

The object of the present invention is to solve the problems caused by conventional methods and to establish an industrially advantageous method for separating 2,6-dialkylnaphthalene.

(Means for Solving the Problems) As a result of repeated studies to achieve the above object, the present invention separates 2,6-dialkylnaphthalene from feedstock oil,
When employing a process in which the raw oil component after separation is isomerized to increase the concentration of 2,6-dialkylnaphthalene, and this is recycled to the 2,6-dialkylnaphthalene separation step described above, the dialkyl by-product from the isomerization reaction is To separate high-purity 2,6-dialkylnaphthalene without substantially reducing the purity of the desorbing agent or product by removing in advance at least a portion of low-boiling components and high-boiling components other than naphthalene. The present invention was achieved by discovering that this can be done.

That is, the gist of the present invention is as follows: (a) a first step of separating 2,6-dialkylnaphthalene from a feed oil containing a dialkylnaphthalene isomer mixture as a main component; (b) a second step after separation in the first step; An isomerization reaction product in which a feedstock containing a dialkylnaphthalene isomer mixture with a reduced 6-dialkylnaphthalene concentration is subjected to an isomerization reaction to increase the 2,6-dialkylnaphthalene concentration to a composition close to the thermodynamic equilibrium concentration. (c) a step of removing at least a part of components other than dialkylnaphthalene from the isomerization reaction product of the second step, and then recycling the product to the first step. The present invention relates to a method for separating 2,6-dialkylnaphthalene from a feedstock oil containing a mixture of isomers as a main component.

The present invention will be explained in detail below.

Dialkylnaphthalenes in the present invention include naphthalene derivatives having a linear or branched alkyl group having about 1 to 3 carbon atoms as a substituent, such as dimethylnaphthalene, diethylnaphthalene, diisopropylnaphthalene, methylethylnaphthalene, and methylisopropylnaphthalene. are mentioned, with dimethylnaphthalene and diethylnaphthalene being preferred.

Furthermore, the dialkylnaphthalene isomer mixture is a mixture of geometric isomers of the above dialkylnaphthalene, and taking dimethylnaphthalene as an example, 2゜6-dimethylnaphthalene, 2,7-dimethylnaphthalene, 1,3-dimethyl Naphthalene, 2,3-dimethylnaphthalene, 1,8-
Dimethylnaphthalene, 1,6-dimethylnaphthalene, 1
, 7-dimethylnaphthalene, 1.4-dimethylnaphthalene, 1.5-dimethylnaphthalene, 1.2-dimethylnaphthalene, etc.

Feedstock oils containing a dialkylnaphthalene isomer mixture as a main component are generally (1) distillates or extracts from gas oil, coal tar, or petroleum heavy oil; (2)
) Modifications of the above fractions or extracts, (3) Boiling point 26 of naphthalene or alkylated products of methylnaphthalene, etc.
It is a mixture of aromatic hydrocarbons with a temperature of about 0 to 320°C, mainly consisting of the above dialkylnaphthalene isomer mixture, and also contains monoalkylnaphthalene, and further contains trace amounts of impurities such as nitrogen-containing, oxygen-containing, and sulfur-containing compounds. but,
It is desirable to remove these impurities as much as possible before use 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-dialkylnaphthalene is separated from the feedstock oil containing a dialkylnaphthalene isomer mixture as a main component. Various known methods can be used to separate 2,6-dialkylnaphthalene from raw oil. Examples include a batch method using an adsorbent, a continuous separation method using column chromatography, a crystallization method, a pressure crystallization method, and a host-guest type adduct formation method.

Among these, a continuous separation method using column chromatography is preferred, and in particular, for example, JP-A-1-16862
A method that combines a continuous separation method using a simulated moving bed method and a crystallization method described in No. 8 is recommended.

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.
type zeolite and using para-xylene and/or ortho-xylene as desorbing agent, the feedstock containing the dialkylnaphthalene isomer mixture is separated continuously by chromatography, advantageously in simulated moving bed mode. , a solution of an isomer mixture containing 60% by weight or more of 2,6-dialkylnaphthalene and a desorbing agent is obtained, and the solution is crystallized at a concentration of the desorbing agent in the obtained solution of 40 to 90% by weight. A method for separating 2,6-dialkylnaphthalene is mentioned. In addition, separation by chromatography is preferably carried out at 60 to 200°C and about atmospheric pressure to 20 atm.

(b) Second step: In this step, the raw oil containing the dialkylnaphthalene isomer mixture with a reduced concentration of 2,6-dialkylnaphthalene after the 2,6-dialkylnaphthalene separation in the first step is subjected to an isomerization reaction. An isomerization reaction product in which the 2,6-dialkylnaphthalene concentration 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 takes place at a temperature of 20-500°C and at atmospheric pressure ~5
It is desirable to carry out the isomerization reaction by introducing the feedstock oil containing the dialkylnaphthalene isomer mixture in a gas phase under a pressure of about 0 atmospheres, preferably in a hydrogen atmosphere.

Suitable isomerization reaction catalysts include, for example, pentasil type zeolite ion-exchanged to hydrogen type, especially H-ZSM-5.
Examples include Y-type zeolite, Y-type zeolite which may be ion-exchanged with hydrogen or various metal cations, and mordenite-type zeolite. These zeolite-based catalysts are composed of nitrogen, rhenium, palladium,
A metal component having a hydrogenation ability such as platinum may be supported, or ion exchange may be performed with these metals. In industrial practice, these catalysts are molded together with silica, alumina, boehmite, alumina sol, and clay minerals (natural clay minerals such as kaolinite, seviolite, halloysite, montmorillonite, and synthetic clays such as lard crosslinked clay). It is common to use

By carrying out the isomerization reaction under the conditions described above using such a catalyst, a reaction product in which the concentration of 2,6-dialkylnaphthalene is increased to a composition close to the thermodynamic equilibrium concentration can be obtained. . 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 the dialkylnaphthalene (low-boiling substances) and components with a higher boiling point than the dialkylnaphthalene (high-boiling substances), which are by-produced by the isomerization reaction, are isomerized. This is a major feature of the present invention, in that it is removed as much as possible from the reaction product and the remaining dialkylnaphthalene isomer mixture is recycled to the first step.

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 dialkylnaphthalene isomer mixture is distilled from the top of the column and recycled to the first step. Examples include a method in which it is extracted from the system from the bottom, and a method in which it is carried out batchwise or continuously is adopted. In this case, the temperature of the distillation pot (reboiler) should be about 120 to 250°C.
The tower top pressure is set at 1 to 500 lnn111 g, and the process is carried out under reduced pressure.

The method of the present invention is carried out by repeatedly carrying out the steps (a), (b), and (c) described above, whereby extremely high Pure 2,6-dialkylnaphthalene 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.

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 a packed bed filled with an adsorbent and whose front end and rear end are connected by a fluid passage, from a raw material supply section to a non-adsorbent extraction section. The four zones are an adsorption zone, a purification zone from the extraction section to the adsorbent supply section, a desorption zone from the supply section to the adsorbate extraction section, and a concentration zone from the extraction section to the raw material supply section. This separation method consists of circulating the fluid while forming the fluid in the above-mentioned order from distillation, and intermittently moving the positions of the above-mentioned supply section and 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. Paraxylene was used as a desorption agent.

Raw materials were fed through the raw material supply port at a rate of 111 ml/hr.

The composition of the raw material is 2,6-dimethylnaphthalene: 13.4
%, 2.7-dimethylnaphthalene 13.5%, 2,3
-4.5% dimethylnaphthalene, 1. ? - Dimethylnaphthalene was 14.7%, and other isomers such as 1,6-dimethylnaphthalene, ethylnaphthalene, and methylnaphthalene were contained.

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

The concentration distribution in the system reached a steady state 19 hours after the start of operation, and analysis of the product flow revealed that paraxylene was 7.
8.8%, 2,6-dimethylnaphthalene 4.8% per month,
2,7-dimethylnaphthalene was 0.2% and 2,3-dimethylnaphthalene was 0.1%. The purity of 2,6-dimethylnaphthalene was 70.0% when converted to the base excluding paraxylene. Since paraxylene 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 [Separation by column chromatography] Instead of the lithium Y-type zeolite used in Example 1, the upper 81% by volume of each column was filled with lithium Y-type zeolite, and the lower 19% by volume was filled with sodium X-type zeolite. Eight packed columns were used, and the raw materials were 12.7% 2,6-dimethylnaphthalene, 6.9% 2,7-dimethylnaphthalene, and 3.7% 2,3-dimethylnaphthalene.
%, 1,7-dimethylnaphthalene with a composition of 15.6%, and the raw material was fed at a rate of 108 ml/hr from the raw material supply port.
At a flow rate of 270 ml,
Separation was carried out under the same conditions as in Example, except that the non-adsorbed material stream (product stream) was extracted at a flow rate of 65 ml/hr, and the adsorbed material stream was extracted at a flow rate of 313 ml/hr.

The concentration distribution in the system reached a steady state 20 hours after the start of operation, and analysis of the product flow revealed that 7
8.6%, 2,6-dimethylnaphthalene 17°3%,
2,7-dimethylnaphthalene was 0.5% and 2,3-dimethylnaphthalene was 0.1%. The purity of 2,6-dimethylnaphthalene was 80.8%, and the recovery rate was 71%.

Example 3 [Crystallization] The product streams obtained in Examples 1 and 2 above were collected and subjected to crystallization treatment. The raw material composition used for the crystallization treatment was 76.8% paraxylene, 1% 2,6-dimethylnaphthalene,
6.0%, 2,7-dimethylnaphthalene 0.6% and 2
, 3-dimethylnaphthalene is 0.2%, and the purity of 2,6-dimethylnaphthalene calculated on the basis excluding paraxylene is 69.0%.

A cooling crystallization tank with a glass jacket and a stirrer was prepared. The tank diameter is 80 mm and the capacity is 300 ml. 132.8 g of raw material was charged into a crystallization tank, and the temperature was set at 50 rpm.
While stirring at a speed of
It took 94 minutes to cool down to °C. 20 of the precipitated crystals
It was collected by filtration using a 0 mesh filter cloth. The crystals were centrifuged to remove the mother liquor, washed with methanol, and then dried under reduced pressure to obtain 4.86 g of crystals. Quantitative analysis of the composition of this crystal by capillary gas chromatography using bicyclohexyl as an internal standard revealed that 2,6-
Dimethylnaphthalene 99.81%, 2,7-dimethylnaphthalene 0.13%, 2,3-dimethylnaphthalene 0.
04%, 1,7-dimethylnaphthalene and methylnaphthalene were each 0.01%.

Therefore, the recovery rate of 2,6-dimethylnaphthalene is 22.8
%.

6 Example 4 [Isomerization] The raffinate component after 2,6-dimethylnaphthalene was separated in Example 1 was purified using a distillation column with a total number of theoretical plates of 50 at a reflux ratio of 3 and a top pressure of 120 + nm). Batch distillation was performed using Ig to remove the removing agent (baraxylene). The bottom liquid contains a dimethylnaphthalene isomer mixture as a main component, but the concentration of 2,6-dimethylnaphthalene is 1.0.
%.

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

As an isomerization catalyst, ZSM-5 type zeolite (SiO2/Al203 = 32.5) produced according to the method described in Example 1 of Japanese Patent Publication No. 46-10064 was calcined, and then ion-exchanged to NHJ÷ type. The l-ZSM-5 type zeolite obtained by converting the zeolite into the H+ type by further firing was used.

A stainless steel reactor with an inner diameter of 25 m+ was filled with the above catalyst (particle size 10~20 mesh) 201, ceramic balls were filled on top of the catalyst layer, and a dimethylnaphthalene isomer mixture ((IMA) was charged into the reactor). Supply, vaporize and entrain in hydrogen gas, temperature 380℃, pressure 10kg/c
m2, H2/DMA molar ratio=25, LIISV=0
．． 6 to carry out the isomerization reaction. Analysis of the reaction product revealed that the concentration of 2,6-dimethylnaphthalene was 13
．． 5%, and the total dimethylnaphthalene recovery rate is 97%.
In addition to dimethylnaphthalene, the reaction product contained
Trace amounts of benzene, toluene, xylene (0, m-1p-
isomer mixtures), compounds with lower boiling points than dimethylnaphthalene such as naphthalene, methylnaphthalene, and ethylnaphthalene, as well as trimethylnaphthalenes, tetramethylnaphthalenes, pentamethylnaphthalenes, and binaphthyl derivatives having various numbers of methyl groups. It was found that it contained a compound with a higher boiling point than dimethylnaphthalene.

Example 5 [Separation of low boilers and high boilers] Using the same distillation column as in Example 4, Example 4
The isomerization reaction product was distilled. Tower top pressure 20 mm)
Ig, with a reflux ratio of 20, samples were taken divided into several fractions depending on the tower top temperature, and analyzed by gas chromatography to find out the composition of each fraction, as shown in Table 1, low boiling point components and It was found that it is possible to separate high-boiling components.

Table 1 Example 6 [Recirculation of isomerized substances after separation of low boiling substances and high boiling substances] Fraction 2 and fraction 3 in Table 1 obtained in Example 5 were fed to the column used in Example 1. 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 excluding paraxylene from the product stream was 76.
It was 0%.

Comparative Example 1 Chromatography was carried out in the same manner as in Example 1, except that the same amount of a mixture (by weight) of paraxylene and naphthalene was used instead of paraxylene supplied as a desorbing agent. 2,6 dimethylnaphthalene was separated, and Example 4 was prepared from the separated raffinate component.
The removing agent was distilled off in the same manner as above, and then the isomerization reaction was carried out.

The isomerization reaction product was fed as it was to the column used in Example 1 without separating low-boiling substances and high-boiling substances, and 2,6- Separation of dimethylnaphthalene was carried out. The chromatography pattern is the same as in Example 1,
The concentration of 2,6-dimethylnaphthalene in the product stream is 5.3%.
As a result, the separation performance decreased significantly.

Comparative Example 2 Chromatography was carried out in the same manner as in Example 1, except that the same amount of a mixture (by weight) of paraxylene and toluene was used instead of paraxylene supplied as a desorbing agent. Example 4 2,6-dimethylnaphthalene was separated from the raffinate component after separation.
The removing agent was distilled off in the same manner as above, and then the isomerization reaction was carried out.

The isomerization reaction product was fed as it was to the column used in Example 1 without separating low-boiling substances and high-boiling substances, and 2,6- Separation of dimethylnaphthalene was carried out. The chromatographic pattern was the same as in Example 1, the 2,6-dimethylnaphthalene concentration in the product stream was 9.8%, and the separation performance was significantly reduced.

Comparative Example 3 Among the fractions of the isomerization reaction product of Example 4 obtained in Example 5, fractions 4 and 5 in Table 1 were mixed, and further 2,6-dimethylnaphthalene was added to this. Add 2,6
- The concentration of dimethylnaphthalene was adjusted to 13.4%.

This mixture was supplied to a column in the same manner as in Example 1, and 2,6-dimethylnaphthalene was continuously separated by chromatography.

The 2,6-dimethylnaphthalene concentration in the product stream was initially 12
．． 8%, but the separation pattern gradually changed, showing a tendency for poor separation. Trimethylnaphthalene is incorporated into the entire 2,6-dimethylnaphthalene product stream;
The concentration of 2,6-dimethylnaphthalene in the product components excluding the desorbing agent decreased slightly.

(Effects of the Invention) According to the present invention, by combining the steps (a), (b), and (c), a raw material oil containing a dialkylnaphthalene isomer mixture as a main component can be obtained with a purity of 99%.
The above-mentioned highly pure 2,6-dialkylnaphthalene can be efficiently separated, which greatly contributes to the industrial production of this substance.

Claims (4)

[Claims] (1) (a) A first step of separating 2,6-dialkylnaphthalene from a feedstock oil containing a dialkylnaphthalene isomer mixture as a main component; (b) 2,6-dialkylnaphthalene concentration after separation in the first step. A second step of obtaining an isomerization reaction product in which the 2,6-dialkylnaphthalene concentration has been increased to a composition close to the thermodynamic equilibrium concentration by subjecting the feedstock oil containing a dialkylnaphthalene isomer mixture with a reduced concentration to an isomerization reaction. (c) a step in which at least a part of the components other than dialkylnaphthalene is removed from the isomerization reaction product of the second step and then recycled to the first step, wherein the dialkylnaphthalene isomer mixture is the main component. A method for separating 2,6-dialkylnaphthalene from a raw material oil containing 2,6-dialkylnaphthalene. (2) The method according to claim 1, wherein the dialkylnaphthalene isomer mixture is a dimethylnaphthalene isomer mixture. (3) Claim 1, wherein the separation of 2,6-dialkylnaphthalene from the feedstock oil containing a dialkylnaphthalene isomer mixture as a main component in the first step is chromatographic separation and/or crystallization separation. the method of. (4) The method according to claim 1, wherein the isomerization reaction in the second step is carried out in a gas phase in a hydrogen stream in the presence of a solid acid catalyst.