JPH0578264A - Method for separating and recovering 2,6-dimethylnaphthalene - Google Patents

Abstract

PURPOSE:To readily separate and recover 2,6-dimethylnaphthalene in a hydrocarbon oil formed by reaction for forming a charge transfer complex by reacting the 2,6-dimethylnaphthalene in the presence of an oxygen-containing organic solvent and crystallizing the resultant reaction product. CONSTITUTION:2,6-Dimethylnaphthalene in a hydrocarbon oil and m-nitrobenzoic acid are heated at 40-150 deg.C and reacted in an oxygen-containing organic solvent (e.g. methanol). The resultant reaction product is then cooled to afford a complex, which is brought into contact with a solvent and decomposed to increase the purity of the 2,6-dimethylnaphthalene in the complex without lowering the recovery ratio of the 2,6-dimethylnaphthalene. Thereby, the 2,6- dimethylnaphthalene is separated and recovered. The dimethylnaphthalene is converted into naphthalenedicarboxylic acid by oxidation, which is useful as a raw material for dyes, pigment and functional polymers such as engineering plastics or liquid crystal polymers.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for separating and recovering 2,6-dimethylnaphthalene in hydrocarbon oil by a charge transfer complex forming reaction.

[0002]

2. Description of the Related Art Dimethylnaphthalene is a light cracked gas oil (Light C) obtained by catalytically cracking petroleum vacuum gas oil.
Cycle Oil (hereinafter abbreviated as LCO)), which is contained in naphtha-modified residual oil and coal tar, becomes naphthalenedicarboxylic acid by oxidation, and is used as a raw material for functional polymers such as dyes, pigments, engineering plastics, and liquid crystal polymers. It is an important substance that can be used.

In particular, polyethylene naphthalate (PEN), which is a polyester of naphthalene-2,6-dicarboxylic acid obtained by oxidizing 2,6-dimethylnaphthalene and ethylene glycol, is used as fibers, films, bottles and the like. Of which the acid moiety of polyethylene terephthalate (PET) is widely known is replaced with this naphthalene-2,6-dicarboxylic acid, and its use is promising. Since polyethylene naphthalate has a higher elastic modulus and excellent heat resistance than PET, it is possible to make a base film such as a video tape thin, thereby enabling long-time recording. Can be expected. In addition, polyamides, polythioesters and the like are also known. Furthermore, 2,6-dimethylnaphthalene 2,6
Compounds functionalized at the − position have also attracted attention as raw materials for liquid crystal polymers. The liquid crystal polymer has a property of being highly oriented like a crystal in a molten state, and can be a functional polymer material having high strength and high elastic modulus. As a specific example, 2
There is a copolymer of -hydroxy-6-naphthoic acid and p-hydroxy-benzoic acid. 2,6-Dimethylnaphthalene as a raw material of these functional polymer materials is required to have a high purity of about 95% by weight or more.

As a method for separating 2,6-dimethylnaphthalene from the LCO fraction, the naphtha reforming residual oil, or the coal tar, distillation and cooling separation have been proposed.

It is known that the LCO fraction contains about 70-80% aromatics, of which about 20-40% are bicyclic aromatics. However, dimethylnaphthalene is contained in only about 5-10% and 2,6-dimethylnaphthalene is contained in only about 1-2%. Dimethylnaphthalene has a boiling point range of 10 kinds of isomers of about 260 to 270 ° C.
Due to their close proximity within, it is difficult to separate the individual isomers by distillation. Furthermore, even if an attempt is made to separate by cooling by utilizing the difference in freezing point, a eutectic mixture is produced, so that one component cannot be separated from this eutectic mixture by a recrystallization method or a partial melting method. As an example of the eutectic mixture, for example, in the case of a binary system, 2,6-dimethylnaphthalene is 2,7
-With dimethylnaphthalene in a molar ratio of about 2: 3, 2,
It is known to form a binary eutectic mixture with 3-dimethylnaphthalene in a molar ratio of about 1: 1.1.

In any case, even if a dimethylnaphthalene mixture is concentrated and separated by distillation from a raw material such as oil or coal tar obtained in each process of the petroleum refining industry such as LCO fraction, 2,6- Concentrating dimethylnaphthalene is difficult.

As a method other than the above, there is a method of forming and separating a charge transfer complex, and 2,6-dimethylnaphthalene is separated by forming a charge transfer complex from a hydrocarbon oil containing 2,6-dimethylnaphthalene. A method using m-nitrobenzoic acid (Japanese Patent Publication No. 47-29)
893) is known.

A charge transfer complex is a molecular compound formed by partial transfer of electrons from a substance of an electron donor to a substance of an electron acceptor to form a bond.

Although m-nitrobenzoic acid selectively forms a complex with 2,6-dimethylnaphthalene, it also forms a complex in which some components other than 2,6-dimethylnaphthalene are incorporated during the reaction or crystallization.

In order to increase the purity of 2,6-dimethylnaphthalene in the complex, there is a method of reducing the amount of m-nitrobenzoic acid used, but in this case, the yield of the complex product is reduced and the starting material is reduced. It is not an effective means because the recovery rate of 2,6-dimethylnaphthalene from the product decreases. As a means for improving the purity of 2,6-dimethylnaphthalene in the complex without lowering the recovery rate of 2,6-dimethylnaphthalene, in the presence of monocyclic aromatic hydrocarbons such as benzene, toluene, xylene, etc. 6-Dimethylnaphthalene and m-
Although a method for forming a complex of nitrobenzoic acid has been proposed (Japanese Patent Publication No. 47-29893), the amount of 2,
The purity of 6-dimethylnaphthalene is about 50-60 wt%, which is still insufficient. There is also a method of increasing the purity of 2,6-dimethylnaphthalene in the complex by performing a complex formation reaction, separating the complex and unreacted oil, and recrystallizing the complex in a solvent. However, there is a problem in that the process becomes complicated due to multiple steps.

[0011]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and in forming a charge transfer complex of 2,6-dimethylnaphthalene and m-nitrobenzoic acid in a hydrocarbon oil. Another object is to provide a method for separating and recovering 2,6-dimethylnaphthalene by increasing the purity of 2,6-dimethylnaphthalene in the complex without lowering the recovery rate of 2,6-dimethylnaphthalene. Is.

[0012]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the present inventor has found that high purity by reacting and crystallization in the presence of an oxygen-containing organic compound solvent in a raw material. The present invention has been completed by finding a method for separating and recovering 2,6-dimethylnaphthalene.

That is, the present invention relates to 2, in hydrocarbon oils.
A method for separating and recovering 6-dimethylnaphthalene by a charge transfer complex forming reaction with m-nitrobenzoic acid, wherein the reaction and crystallization are performed in the presence of an oxygen-containing organic compound solvent. The method of separating and collecting

In the method of the present invention, the raw material can be any hydrocarbon oil containing 2,6-dimethylnaphthalene, and it contains nitrogen-containing compounds such as quinoline and indole and sulfur-containing compounds such as thiophene and thionaphthene. However, there is no particular problem. In addition, 2,6 in the raw hydrocarbon oil
-A raw material having a low dimethylnaphthalene concentration of, for example, about 3% by weight can be used, and these raw materials can be used at a boiling point range of dimethylnaphthalene of about 260 to 270 ° C.
More preferably, the fraction is predistilled. There is no particular limitation on the mixing ratio of the raw material hydrocarbon oil and m-nitrobenzoic acid, but it is known that m-nitrobenzoic acid forms a 2/1 mol / mol complex with 2,6-dimethylnaphthalene. Therefore, in order to effectively recover 2,6-dimethylnaphthalene, it is preferable to use m-benzoic acid in an amount about 2 times, especially about 3 times the mol of 2,6-dimethylnaphthalene in the raw material. A complex is immediately formed by contacting the raw material with m-nitrobenzoic acid, but in order to make the reaction more efficient, it is preferably contacted for about 10 minutes to 1 hour. The reaction temperature may be room temperature, but is about 40 to 150 ° C., preferably about 5 to increase the solubility of the complex-forming substance.
A method in which the reaction is carried out by heating to 0 to 100 ° C. and the complex is precipitated by cooling is preferably used.

The oxygen-containing organic compound solvent used in the present invention includes alcohols such as methanol, ethanol and isopropanol, ethers such as diethyl ether and diisopropyl ether, ketones such as acetone and methyl ethyl ketone, ethyl acetate and diethyl malonate. And the like, and any of them can be used in the reaction system to improve the solubility of m-nitrobenzoic acid in the reaction system and accelerate the reaction. The timing and addition method of these solvents are not particularly limited before cooling the system to precipitate the crystals of the complex. For example, m-nitrobenzoic acid is added to a system in which methanol or the like is added to the feed oil. Or adding slurry of m-nitrobenzoic acid and methanol to the raw oil,
A method may be considered in which the feedstock oil and m-nitrobenzoic acid are heated to the reaction temperature in advance and methanol or the like is added. The reason for this is that the presence of the above solvent in the reaction system causes m-
This is because it is considered that the purity of 2,6-dimethylnaphthalene at the time of crystallization of the complex can be increased by improving the solubility of nitrobenzoic acid in the reaction system and promoting the reaction.

The amount to be added is not particularly limited as long as it does not reduce the recovery rate of the complex at the crystallization temperature of the complex, but the larger the amount of the oxygen-containing organic compound solvent such as methanol, the longer the crystallization. Therefore, it is preferable to use a small amount of 2,6-dimethylnaphthalene within a range that does not reduce the purity.

The specific amount of the oxygen-containing organic compound solvent such as methanol added depends on the concentration of 2,6-dimethylnaphthalene in the raw material oil used and the amount of m-nitrobenzoic acid used. On the other hand, about 1/50 to 1/2 (volume / weight), preferably about 1/20 to 1/5 (volume / weight)
Just add it.

The present invention relates to a method for producing a suitable complex of m-nitrobenzoic acid and 2,6-dimethylnaphthalene for obtaining highly pure 2,6-dimethylnaphthalene. The method for decomposing the obtained complex is (1) A method in which 2,6-dimethylnaphthalene is difficult to dissolve, but m-nitrobenzoic acid is in contact with a solvent in which it is easily soluble, (2) m-nitrobenzoic acid is difficult to dissolve, but 2,6-dimethylnaphthalene Is a method of bringing the complex into contact with a solvent which is easily dissolved, (3) a method of bringing the complex into contact with two solvents which are immiscible with each other (1) and (2) simultaneously or alternately, and (4) the complex at room temperature or higher, and Preferably, a method of heating to a temperature below the decomposition temperature of m-nitrobenzoic acid can be adopted.

Decomposition method (1) is a method of decomposing this complex by bringing m-nitrobenzoic acid into contact with a solvent in which 2,6-dimethylnaphthalene is difficult to dissolve and m-nitrobenzoic acid is easily dissolved. As such a solvent, an alkaline aqueous solution or the like is preferable. Examples thereof include water-soluble alkali metal and alkaline earth metal hydroxides, oxides, carbonates, aqueous ammonia and other aqueous solutions of water-soluble amines, and sodium hydroxide, potassium hydroxide, aqueous ammonia and the like are preferable. Used for. Taking the case of using an aqueous solution of sodium hydroxide as an example, an aqueous solution containing m-nitrobenzoic acid and an equivalent amount or more of sodium hydroxide and having an amount capable of dissolving sodium m-nitrobenzoate is sufficient. By separating the solid liquid after the decomposition, 2,6-dimethylnaphthalene can be recovered with high purity.

Decomposition method (2) is a method of decomposing this complex by contacting a solvent in which m-nitrobenzoic acid is difficult to dissolve and 2,6-dimethylnaphthalene is easily dissolved. Suitable solvents for this method include, for example, propane, butane, petroleum ether, pentane, hexane,
Heptane, octane, decane, ligroin, cyclopentane, cyclohexane, etc., having 3 to 10 carbon atoms, especially 5 to 8 carbon atoms.
The aliphatic hydrocarbons of, especially saturated hydrocarbons thereof are preferred. Although the complex can be decomposed even at room temperature, it is preferably decomposed at about 90 ° C. or higher in the presence of a solvent in an amount 10 times or more the weight of the complex, and solid m-nitrobenzoic acid and 2,6-dimethyl dissolved in the solvent. After separating the naphthalene, the solvent is cooled or distilled off, whereby highly pure 2,6-dimethylnaphthalene can be separated and recovered.

The decomposition method (3) is a method of bringing the complex into contact with the two solvents (1) and (2) which are immiscible with each other simultaneously or alternately. In this case, 2,6 after complex decomposition
-Since dimethylnaphthalene is dissolved in the solvent layer of (2), after separating the solvent layer of (2), a part of the solvent is distilled off and cooled, or if all is distilled off, the raw material hydrocarbon The dimethylnaphthalene mixture is separated.

The decomposition method according to (4) is a method of decomposing the complex by heating. In this case, the heat may be applied directly, but it is preferable to heat in an atmosphere of nitrogen, carbon dioxide, hydrogen, or a lower hydrocarbon gas. This is because, when thermally decomposed in an oxidizing atmosphere, the 2,6-dimethylnaphthalene isomer mixture obtained by decomposition and desorption tends to be colored or decomposed. Further, steam may be used instead of the above-mentioned inert gas for decomposition. Also, (1),
The method of (4) may be used in combination in the presence of the solvent used in (2) and (3).

The heating temperature may be any number of times as long as it is below the temperature at which 2,6-dimethylnaphthalene does not decompose, but it is preferably below the decomposition temperature in order to recover and reuse m-nitrobenzoic acid.

[0024]

EXAMPLES The present invention will now be specifically described with reference to examples, but the present invention is not limited to these examples.

Example 1 5 ml of methanol was added to 100 g of a 260-270 ° C. bottom oil distilled from an aromatic extractor having the composition shown in Table 1.
36.6 g of m-nitrobenzoic acid was added, and the mixture was heated at 90 ° C. for 1 hour with stirring, reacted, and then allowed to cool to room temperature. After separating the precipitated solid by filtration, it was washed quickly with petroleum ether,
Unreacted hydrocarbon oil was separated and removed to obtain a solid composed of 43.6 g of the complex and unreacted crystals of m-nitrobenzoic acid. To determine the purity and yield of 2,6-dimethylnaphthalene in the complex, the total amount of this solid was added to a mixed liquid of a 5% sodium hydroxide aqueous solution layer and an n-hexane layer and shaken to decompose the complex. The n-hexane layer was separated and collected, and then n-hexane was distilled off to give a white hydrocarbon mixture 14.
4 g was obtained. The results of composition analysis of this separated product using a gas chromatograph are shown in Table 1.

Comparative Example 1 A complex was obtained by the same procedure as in Example 1 except that 36.6 g of m-nitrobenzoic acid was added to 100 g of a stock oil having the same composition as in Example 1 and methanol was not added. Table 1 shows the solid yield of the complex and m-nitrobenzoic acid (hereinafter simply referred to as "complex yield"), the composition of the hydrocarbon mixture obtained by decomposition, and the recovery rate of 2,6-dimethylnaphthalene. ..

In the table, mNBA is m-nitrobenzoic acid, D
MN is dimethylnaphthalene, MN is methylnaphthalene,
BP is an abbreviation for biphenyl and EN is an abbreviation for ethylnaphthalene (the same applies to the tables below).

[0028]

[Table 1]

Examples 2 and 3 100 g of feed oil having the same composition as in Example 1 was added to 10 g of methanol.
ml, 20 ml, and 36.6 g of m-nitrobenzoic acid were added,
A complex was obtained by treating in the same manner as in Example 1. Table 2 shows the complex yield, the composition of the hydrocarbon mixture obtained by decomposition, and the recovery rate of 2,6-dimethylnaphthalene.

[0030]

[Table 2]

Examples 4, 5 and 6 To 100 g of the stock oil having the same composition as in Example 1, ethanol, ethyl acetate, 5 ml of methyl ethyl ketone and 36.6 g of m-nitrobenzoic acid were added and treated in the same manner as in Example 1. To obtain the complex. Table 3 shows the complex yield, the composition of the hydrocarbon mixture obtained by decomposition, and the recovery rate of 2,6-dimethylnaphthalene.

Comparative Example 2 To 100 g of raw material oil having the same composition as in Example 1, 5 ml of toluene was added.
And 36.6 g of m-nitrobenzoic acid were added and treated in the same manner as in Example 1 to obtain a complex. Table 3 shows the complex yield, the composition of the hydrocarbon mixture obtained by decomposition, and the recovery rate of 2,6-dimethylnaphthalene.

[0033]

[Table 3]

As is clear from Tables 1 to 3, in the present invention, high purity (59.5 wt% of the comparative example) was obtained without lowering the recovery rate of 2,6-dimethylnaphthalene from the feed oil.
The purity of 2,6-dimethylnaphthalene can be decomposed and recovered with a purity of about 64-79 wt% with respect to%.

[0035]

INDUSTRIAL APPLICABILITY The present invention relates to 2,6-dimethylnaphthalene and m-nitrobenzoic acid contained in oils obtained in various processes of the petroleum refining industry such as LCO fractions and hydrocarbon oils such as coal tar. In the case of forming the charge transfer complex of (2), 2,6-dimethylnaphthalene can be efficiently separated and recovered by a simple means, and its utility is great.

[Procedure amendment]

[Submission date] September 18, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Claim 1

[Correction method] Change

[Correction content]

Claims (1)

[Claims] 1. A method for separating and recovering 2,6-dimethylnaphthalene in hydrocarbon oil by a charge transfer complex forming reaction with m-nitrobenzoic acid, wherein the reaction and crystallization are carried out in the presence of an oxygen-containing organic compound solvent. 2,6-
Method for separating and recovering dimethylnaphthalene.