JP4434779B2 - Method for producing high purity 1,3-dimethylnaphthalene - Google Patents

Description

  The present invention relates to a method for producing 1,3-dimethylnaphthalene useful as a raw material for 1,3-naphthalenedicarboxylic acid used as a modifier for high-performance polymers such as high-performance polyester, liquid crystal polyester, and polyimide.

  1,3-dimethylnaphthalene (hereinafter, dimethylnaphthalene is referred to as DMN) is a raw material for 1,3-naphthalenedicarboxylic acid, which is a high-performance polymer modifier, and requires high purity. DMN has 10 isomers depending on the position of 2 methyl groups. Of these, it is necessary to produce 1,3-DMN substantially free of isomers other than the 1,3-isomer in large quantities and at low cost.

On the other hand, in the case of DMN isomerization, it is known that the isomerization between β-β and the isomerization across the ring are less likely to occur than the isomerization between α-β. That is, DMN isomerization is divided into the following four genera, and isomerization between genera is less likely to occur than in each genus.
Group A 1,5-, 1,6-, 2,6-
Group B 1,8-, 1,7-, 2,7-
C genus 1,4-, 1,3-, 2,3-
Genus D 1,2-

  As a method for producing 1,3-DMN, there are a method of separating naphthalene or methylnaphthalene after methylation, a method of separating from a tar fraction or a petroleum fraction, and the like. However, this method requires separation from many isomer mixtures and cannot be an efficient 1,3-DMN production method.

On the other hand, a method for obtaining 5-phenylhexene-2 in high yield from ethylbenzene and butadiene is disclosed (for example, see Patent Document 1 or 2). In addition, a method for producing 1,4-DMN by cyclization of 5-phenylhexene-2 using a solid acid catalyst to synthesize 1,4-dimethyltetralin and further dehydrogenation is shown (for example, , See Patent Document 3). 1,4-DMN belongs to the same genus as 1,3-DMN, and when 1,4-DMN obtained here is used as a raw material, 1,3 -It has the advantage that DMN can be produced. As a method of isomerizing 1,4-DMN to obtain 1,3-DMN, a method of isomerizing in a liquid phase using hydrogen fluoride (hereinafter referred to as HF) and boron trifluoride (hereinafter referred to as BF3) as catalysts. Is disclosed (for example, see Patent Document 4). However, when only the HF-BF3 catalyst is used, 1,4-DMN can be isomerized to 1,3-DMN with a high isomer ratio, but a relatively large amount of HF-BF3 catalyst can be used. It is necessary to perform the reaction under high temperature conditions, and side reactions such as DMN decomposition and polymerization are likely to occur. In order to suppress side reactions such as DMN decomposition and polymerization, a large amount of solvent is required. In this case, there is a problem that the volumetric efficiency of the apparatus is deteriorated. Further, side reactions can be suppressed by isomerization at a low temperature, but there is a problem that a large amount of 1,4-DMN remains without completing the reaction in a short time.
JP-A-49-134634 US Pat. No. 3,244,758 US Pat. No. 3,775,497 US Pat. No. 3,910,036

  The object of the present invention is to provide a method for producing 1,3-DMN with improved production efficiency by improving the disadvantages of isomerization to 1,3-DMN using the HF-BF3 catalyst as mentioned above. is there.

As a result of diligent studies to solve the above problems, the present inventors use a very small amount of alicyclic saturated hydrocarbon having a five-membered or six-membered ring structure together with HF-BF3 catalyst with respect to DMN. Thus, the inventors have found that a high isomerization rate can be achieved even at a low temperature without causing side reactions such as DMN decomposition and polymerization.
That is, the present invention is a method for producing 1,3-dimethylnaphthalene by carrying out isomerization reaction of dimethylnaphthalene using hydrogen fluoride and boron trifluoride as catalysts, and having a 5-membered ring structure or a 6-membered ring structure. The present invention relates to a method for producing high-purity 1,3-dimethylnaphthalene, characterized by isomerization in a liquid phase in the presence of an alicyclic saturated hydrocarbon having 5 to 10 carbon atoms.

  According to the present invention, in a isomerization reaction of DMN group C (1,4-, 1,3-, 2,3-), a high isomerization ratio to 1,3-DMN can be efficiently and efficiently obtained in a short time. It can be achieved, and its industrial significance is very large.

  DMN used as a raw material in the present invention includes 1,4-DMN and / or 2,3-DMN, and is a total of isomers of group C, that is, 1,4-DMN, 1,3-DMN. In addition, the total of 2,3-DMN is preferably 99% or more. There are no particular restrictions on the method for producing these raw material DMNs, and 1,4-DMN obtained by cyclizing and dehydrogenating 5-phenylhexene-2 as described in Patent Document 3 can also be used. .

  The HF used in the present invention is preferably substantially anhydrous. The amount of HF relative to DMN is in the range of HF / DMN = 5-40 (molar ratio), preferably HF / DMN = 15-30 (molar ratio). If the amount of HF is less than this, the isomerization reaction cannot proceed efficiently. Moreover, when there is too much HF, the process of a reactor and HF collection | recovery will become large and it is not preferable at the point of production efficiency. The amount of BF3 with respect to DMN is in the range of BF3 / DMN = 1.0-5 (molar ratio), preferably BF3 / DMN = 1.1-3 (molar ratio). If the amount of BF3 is smaller than this, the isomer ratio of 1,3-DMN is not sufficiently high, and a larger amount is unnecessary.

  The alicyclic saturated hydrocarbon having a five-membered or six-membered ring structure used in the present invention is an alicyclic saturated carbon having a five-membered or six-membered ring structure connected by a single carbon bond in the molecule. Hydrogen is preferably 5 to 10 carbon atoms, more preferably 5 to 8 carbon atoms. If the number of carbon atoms is 11 or more, the solubility in DMN decreases, which is not preferable. Specific examples include cycloaliphatic saturated hydrocarbons such as cyclopentane, methylcyclopentane, ethylcyclopentane, dimethylcyclopentane, cyclohexane, methylcyclohexane, ethylcyclohexane, and dimethylcyclohexane. These hydrocarbons may be used alone or as a mixture. Can also be used.

  The amount of the alicyclic saturated hydrocarbon having a five-membered or six-membered ring structure used in the present invention is 0.005 to 0.2, preferably 0.01 to 0 in terms of weight ratio to DMN (hydrocarbon / DMN). .1 range. If the amount of alicyclic saturated hydrocarbon is less than this, the progress of the reaction is not sufficient. Although commercially available aliphatic saturated hydrocarbons may contain a small amount of alicyclic saturated hydrocarbons, similar effects can be obtained by adding them in such a proportion that the amount falls within the above range. it can. For example, commercially available n-hexane contains methylcyclopentane having a five-membered ring structure, and when this is added to DMN so that methylcyclopentane is in the above weight ratio, it is equivalent to the above. An effect can be obtained.

  The isomerization reaction in the present invention is preferably carried out at a temperature in the range of −40 to 0 ° C., more preferably in the range of −30 to 0 ° C. At higher temperatures, side reactions such as DMN decomposition and polymerization occur violently, and at lower temperatures, the isomerization rate decreases, which is not preferable.

  As described above, when DMN isomerization reaction according to the method of the present invention is carried out, it has a high isomerization rate in a short time while suppressing the decomposition reaction of DMN, and is economically the target product 1, 3-DMN can be obtained. The isomerization reaction type in the method of the present invention is not particularly limited as long as the oil layer such as DMN and the HF layer can be sufficiently stirred and mixed in the liquid phase, and any of batch type, semi-continuous type, continuous type, etc. A method can also be adopted.

  The reaction product solution obtained by the isomerization reaction is an HF solution of DMN / HF-BF3 complex. By heating, the bond between DMN and HF-BF3 is decomposed, and HF and BF3 are vaporized and separated, recovered and reused. be able to. It is necessary to proceed with the decomposition of the complex as quickly as possible to avoid heat alteration and isomerization of the product. In order to rapidly proceed the thermal decomposition of the complex, it is preferable to decompose it under reflux of a solvent inert to HF-BF3 (for example, a saturated hydrocarbon such as heptane or an aromatic hydrocarbon such as benzene).

Hereinafter, the method of the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.
1,4-DMN was obtained by alkenylating ethylbenzene and 1,3-butadiene by cyclization and dehydrogenation by a known method (purity of 99.0 by gas chromatography analysis (using nonpolar column)). %)It was used.

<Example 1>
An autoclave with a magnetic stirrer with an internal volume of 500 ml (manufactured by SUS316L) capable of controlling the temperature was charged with 150 g (7.5 mol) of anhydrous HF and 22 g (0.32 mol) of BF3, and the liquid temperature was cooled to −10 ° C. 39 g (0.25 mol) of 1,4-DMN added with 0.8 g of cyclopentane was supplied while stirring the contents of the autoclave. Then, after maintaining at the same temperature for 60 minutes, the contents were collected in ice, diluted with hexane, and neutralized to analyze the oil layer obtained by gas chromatography to obtain the reaction results. The reaction results are shown in Table 1.

<Example 2>
The isomerization reaction and the reaction solution were treated in the same manner as in Example 1 except that 0.8 g of cyclohexane was added to 1,4-DMN instead of methylcyclopentane. The reaction results are shown in Table 1.

<Example 3>
The isomerization reaction and the reaction solution were treated in the same manner as in Example 1 except that 0.8 g of methylcyclohexane was added to 1,4-DMN instead of methylcyclopentane. The reaction results are shown in Table 1.

<Example 4>
The isomerization reaction and treatment of the reaction solution were performed in the same manner as in Example 1 except that 78 g of n-hexane containing 1% by weight of methylcyclopentane was used instead of methylcyclopentane. The reaction results are shown in Table 1.

<Comparative Example 1>
The isomerization reaction and treatment of the reaction solution were performed in the same manner as in Example 1 except that methylcyclopentane was not added. The reaction results are shown in Table 1. Compared to Example 1, the isomer ratio of 1,3-DMN was low, which was an unsatisfactory result.

<Comparative example 2>
An isomerization reaction was performed in the same manner as in Example 1 except that 0.8 g of n-heptane which is not an alicyclic saturated hydrocarbon was used instead of methylcyclopentane. The reaction results are shown in Table 1. Compared to Example 1, the isomer ratio of 1,3-DMN was low, which was an unsatisfactory result.

  Table 1 shows the types of additives used in Examples 1 to 4 and Comparative Examples 1 and 2, the weight ratio to DMN, and reaction results. The reaction results shown in Table 1 include the production amount (% by weight) of products having a lower boiling point than DMN produced from the raw material DMN, the production amount (% by weight) of products having a higher boiling point than DMN, and the amount recovered. The DMN amount (% by weight) and the isomer composition ratio (% by weight) in the recovered DMN are shown.

  In the case where nothing is added to DMN (Comparative Example 1) and the case where n-heptane which is not an alicyclic saturated hydrocarbon is added (Comparative Example 2), the isomer ratio of 1,3-DMN is 93%. Before and after the reaction was not fully completed, when the alicyclic saturated hydrocarbon in the present invention was added, the isomer ratio of 1,3-DMN was around 99%, indicating a high isomerization rate. I was able to achieve it. Furthermore, even when n-hexane containing 1% by weight of methylcyclopentane was used (Example 4), an isomer ratio equivalent to that obtained when only methylcyclopentane was added (Example 1) was obtained.

  The high-purity 1,3-DMN obtained by the present invention is useful as a raw material for 1,3-naphthalenedicarboxylic acid used as a modifier for high-performance polymers such as high-performance polyester, liquid crystal polyester, and polyimide.

Claims (4)

A method for producing 1,3-dimethylnaphthalene by performing isomerization reaction of dimethylnaphthalene using hydrogen fluoride and boron trifluoride as a catalyst, and having 5 to 6 or 6 membered ring structure A method for producing high-purity 1,3-dimethylnaphthalene, wherein isomerization is performed in a liquid phase in the presence of 10 alicyclic saturated hydrocarbons. The production of high purity 1,3-dimethylnaphthalene according to claim 1, wherein the amount of the alicyclic saturated hydrocarbon is in the range of 0.005 to 0.2 as a weight ratio to dimethylnaphthalene (hydrocarbon / dimethylnaphthalene). Method. The method for producing high-purity 1,3-dimethylnaphthalene according to claim 1 or 2, wherein the isomerization temperature is in the range of -40 to 0 ° C. The method for producing high-purity 1,3-dimethylnaphthalene according to any one of claims 1 to 3, wherein the dimethylnaphthalene used as a raw material contains 1,4-dimethylnaphthalene and / or 2,3-dimethylnaphthalene.