JPH09124520A - Separation and recovery of 2,7-dimethylnaphthalene - Google Patents

Abstract

PROBLEM TO BE SOLVED: To selectively separate and recover the subject compound in high recovery and purity by applying a specific treatment to a hydrocarbon mixture composed mainly of 2,7-dimethylnaphthalene and dimethylnaphthalenes having melting points lower than that of 2,7-dimethylnaphthalene. SOLUTION: A hydrocarbon mixture composed mainly of 2,7- dimethylnaphthalene (2,7-DMN) and other dimethylnaphthalenes (DMN) having melting points lower than that of 2,7-DMN is added to ethyl alcohol under heating to dissolve at least a part of the mixture. The obtained solution or slurry is cooled to selectively precipitate 2,7-DMN and filtered at a temperature to keep the low-melting DMN in liquid state to separate the 2,7-DMN. In the case of using a hydrocarbon mixture produced by the alkenylation of p-xylene with 1,3-butadiene followed by cyclization, dehydrogenation and isomerization, the main component other than 2,7-DMN is 1,7-DMN and the cooling temperature is preferably -14 deg.C to +30 deg.C.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to 2,7-dimethylnaphthalene (hereinafter, “dimethylnaphthalene” is referred to as “DMN”).
For details of the separation and recovery method of
The present invention relates to a method for separating and recovering 2,7-DMN from a hydrocarbon mixture containing DMN and DMNs having a lower melting point (typically 1,3-DMN and 1,7-DMN) as main components.

[0002]

2. Description of the Related Art 2,7-DMN is a compound useful as a raw material for highly functional polymers and pharmaceuticals.

As a method for producing DMNs, conventional methods have been used.
There is a method of separating from high boiling point fractions generated in the process of petroleum refining and tar content derived from coal, and a method of alkylating naphthalene. However, the DMN fraction obtained by these methods is a mixture of various DMN isomers,
In most cases, 2,7-DMN and 2,6-DMN, which have similar physical properties such as melting point and boiling point, coexist, so that it is difficult to selectively recover 2,7-DMN. there were.

On the other hand, a method for producing DMNs containing little or little 2,6-DMN is also disclosed. For example, a production method in which p-xylene and 1,3-butadiene are used as raw materials for alkenylation, cyclization, dehydrogenation and isomerization (JP-A-47-31935, WO9).
1/164284, JP-A-50-58050, JP-A-4
7-37418), DMNs are 2,7-D
It is a hydrocarbon mixture containing MN and 1,7-DMN as main components. In addition, DMNs obtained by cyclizing the side chain of butenyl-m-xylene and subsequent dehydrogenation are
It is a hydrocarbon mixture containing 2,7-DMN and 1,3-DMN as main components.

As a means for separating and recovering 2,7-DMN from these DMNs containing almost no 2,6-DMN, the mixture of DMNs is directly cooled to 2,7-D.
A method of precipitating MN or a method of fractional crystallization from a solution using methanol as a solvent (Japanese Patent Laid-Open No. 49-132).
No. 040) is disclosed. However, these methods have not been put to practical use because the recovery rate of 2,7-DMN is low and the purity of the recovered material is not good.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide:
To provide a method capable of selectively separating and recovering 2,7-DMN from a hydrocarbon mixture in which 7-DMN and DMNs having a lower melting point are mixed with high recovery and high purity. is there.

[0007]

Means and Actions for Solving the Problems
The method for separating and recovering 7-DMN is a method for separating and recovering 2,7-DMN from a mixture of 2,7-DMN and DMNs having a lower melting point, and the mixture is added to ethyl alcohol under heating. At least a part of it is dissolved, the resulting solution or slurry is cooled to selectively precipitate 2,7-DMN, and dimethylnaphthalene having a low melting point is filtered at a temperature keeping a liquid state to give 2,7-DMN. -Characterized in that the DMN is separated.

DMNs having a lower melting point than 2,7-DMN are 1,7-DMN, 1,3-DMN and 1,4-DM.
N, 1,6-DMN, 1,2-DMN and 1,8-D
This is MN. In addition, DMNs include 2,7-DMN
There are higher melting points, 2,6-DMN and 2,3-DMN. Needless to say, the DMN mixture to be treated in the present invention contains 2,7-DMN in the highest possible proportion. Specifically, those containing at least 10% by mass, preferably 20% by mass or more of 2,7-DMN, and 2,7-DMN occupying the largest part in all hydrocarbons are preferable. A low content of 2,7-DMN is disadvantageous for its selective precipitation. 2,7-D
2,6-DMN and 2,3-DMN, which have a higher melting point than MN
Is preferably as small as possible, and is preferably 30% by mass or less based on the total DMN.

The above-mentioned hydrocarbon mixture is obtained by the above-mentioned process, that is, p-xylene and 1,3-butadiene as starting materials, and alkenylation, cyclization, dehydrogenation and isomerization reactions. can get. The product contains 2,7-DMN and 1,7-DMN as the main components, as will be seen in Examples described later. A DMN mixture can also be obtained by cyclizing butenyl-m-xylene (1,3-dimethyl-4-butenylbenzene) to form a naphthene ring and dehydrogenating. The main product is 2,7-D, as also shown in the examples below.
MN and 1,3-DMN. The invention can be advantageously applied to these mixtures.

When the DMN mixture is added to ethanol with heating and all or part of it is dissolved, a DMN-dissolved solution or a slurry in which a part of the DMN-containing solution remains undissolved is formed. . The solids in the slurry are mostly 2,7-DMN. When this solution or slurry is cooled, the largest component, the most 2,
7-DMN is precipitated from the solution, and the precipitate or the precipitate and the solid content that has been left undissolved before are combined by filtration to obtain a 2,7-DMN with improved purity.

As can be understood from the above-mentioned purification mechanism, the amount of ethyl alcohol to which the DMN mixture is added in the practice of the present invention depends on the composition of DMNs, particularly the desired content of 2,7-DMN. Can be properly selected
It is important for obtaining high effect of separation and recovery. Usually D
Ethyl alcohol is used in an amount 0.5 times (by weight), preferably 3 times to a maximum of 10 times the amount of the MN mixture.
If the amount of ethyl alcohol is too small, the absolute precipitation amount of 2,7-DMN selectively produced by a mechanism in which dissolution-precipitation and melting-solidification are performed in parallel is small, and separation and recovery cannot be achieved. On the other hand, even if it is used in an excessively large amount, the amount of 2,7-DMN that is not precipitated and remains dissolved increases, and the recovery rate decreases, and a large apparatus is required.

The cooling temperature of the solution of the DMN mixture or the slurry containing the solid content in the solution depends on the desired 2,7-DM.
A temperature higher than the melting point of DMNs having a lower melting point than N is desirable from the viewpoint of the purity of the recovered 2,7-DMN. If the cooling temperature is too low, the components other than 2,7-DMN also solidify and the purity of the recovered product does not increase. On the other hand, if it is too high, the desired 2,7-DMN will not be precipitated or will remain in a small amount, making separation and recovery impossible.

The DMN mixture obtained by cyclization, dehydrogenation and isomerization of 5-p-tolyl-2-pentene obtained by the alkenylation reaction of p-xylene and 1,3-butadiene described above is 2, The main components other than 7-DMN are 1,
In the case of 7-DMN, which is a target, the suitable temperature for cooling is higher than -14 ° which is the melting point of 1,7-DMN and is + 50 ° C or lower, preferably + 30 ° C or lower.
The DMN mixture produced by cyclization and dehydrogenation of butenyl-m-xylene has 1,3-DMN as the main component other than 2,7-DMN, and if this is the target, the cooling temperature is It is higher than -4 ° which is the melting point of 1,3-DMN and is + 50 ° C or lower, preferably + 30 ° C or lower.

Therefore, the amount of ethyl alcohol used and the cooling temperature should be determined so that the purity and the recovery rate are appropriately balanced in accordance with the purity level and the cost level required for the target 2,7-DMN. It will be.

[0015]

【Example】

Example 1 5-p-Tolyl-2-pentene obtained by the alkenylation reaction of P-xylene and 1,3-butadiene was cyclized, dehydrogenated, and subsequently isomerized to give 2, A hydrocarbon mixture containing 7-DMN and 1,7-DMN as main components was obtained. The composition of this mixture is shown in Table 1.

Table 1 Component mass% 2,7-DMN 41 1,7-DMN 38 2,6-DMN 8 1,6-DMN 7 Other DMN 1 Methylnaphthalene 1 Other 4 10 g of this hydrocarbon mixture is ethyl 30 g of alcohol was added, and the mixture was heated to 60 ° C. and dissolved. After allowing to stand and naturally cooling to 25 ° C., the precipitate was separated by filtration and collected. The collected precipitate was washed with 10 g of ethyl alcohol. The purity and recovery rate of the target 2,7-DMN are shown in Table 2 below.

Example 2 To 10 g of a hydrocarbon mixture containing 2,7-DMN and 1,7-DMN as main components obtained in the same manner as in Example 1, 60 g of ethyl alcohol was added, and the mixture was heated to 60 ° C. Heated. After naturally cooling to 25 ° C., the precipitate was separated by filtration and collected. The collected precipitate was washed with 10 g of ethyl alcohol. The target 2,7-DMN purity and recovery are shown in Table 2 below.
Shown in

Example 3 The same process as in Example 1 was carried out except that the cooling temperature was 0 ° C. 2,7-DMN recovered
Table 2 also shows the purity and recovery rate of.

[Comparative Example 1] The same treatment as in Example 1 was carried out except that the mixture was heated without adding ethyl alcohol and allowed to cool. The purity and recovery of the resulting 2,7-DMN are also shown in Table 2.

[Comparative Example 2] The same treatment as in Example 1 was carried out except that the same amount of methyl alcohol was used instead of 60 g of ethyl alcohol. The purity and recovery of the resulting 2,7-DMN are also shown in Table 2.

[Comparative Example 3] The same treatment as in Example 1 was carried out except that the same amount of n-heptane was used instead of 60 g of ethyl alcohol. The purity and recovery of the resulting 2,7-DMN are also shown in Table 2.

Table 2 2,7-DMN Purity (mass%) Recovery (mass%) Example 1 96 53 Example 2 99 48 Example 3 95 75 Comparative Example 1 80 55 Comparative Example 2 85 54 Comparative Example 3 93 24 From the data in Table 2, first, when a sufficient amount of ethyl alcohol was used (Example 2, 6-fold amount), compared to when a smaller amount was used (Example 1, 3-fold amount), It was found that the recovered 2,7-DMN had a high purity and instead a low recovery, then cooling was carried out at a lower temperature (25 ° C).
It can be seen that the recovery rate is remarkably increased but the purity is slightly lowered when the reaction is performed up to 0 ° C. (Example 3).
Comparative examples show that 2,7-DMN recovered without ethyl alcohol or with other solvents.
Indicates that the purity and the recovery rate are low.

Example 4 Cyclization and dehydrogenation of butenyl-m-xylene gave 2,7-DMN and 1,2
A hydrocarbon mixture containing 3-DMN as a main component was obtained.
The composition of the mixture is shown in Table 3.

Table 3 Component Mass% 2,7-DMN 37 1,3-DMN 29 2,6-DMN 4 1,6-DMN 5 Other DMN 12 Other 13 To 10 g of this hydrocarbon mixture, 30 g of ethyl alcohol was added. In addition, it heated at 60 degreeC. After allowing to stand and naturally cooling to 25 ° C., the precipitate was collected. 10 g of recovered precipitate
Washed with ethyl alcohol. 2,7-D obtained
The purity and recovery of MN are shown in Table 4 below.

Example 5 The same process as in Example 4 was repeated except that the amount of ethyl alcohol used was increased to 60 g.
The purity and recovery of the obtained 2,7-DMN are shown in Table 4.
Shown in

[Example 6] The same process as in Example 4 was carried out except that the cooling temperature was 0 ° C. 2,7-D obtained
The purity and recovery of MN are shown in Table 4.

[Comparative Example 4] The same treatment as in Example 4 was carried out except that ethyl alcohol was heated and the mixture was allowed to cool. Table 4 shows the purity and the recovery rate of the obtained 2,7-DMN.

[Comparative Example 5] The same treatment as in Example 4 was carried out except that the same amount of methyl alcohol was used instead of 30 g of ethyl alcohol. Table 4 shows the purity and the recovery rate of the obtained 2,7-DMN.

[Comparative Example 6] The same procedure as in Example 4 was repeated except that 30 g of ethyl alcohol was replaced with the same amount of n-heptane. Table 4 shows the purity and the recovery rate of the obtained 2,7-DMN.

Table 4 2,7-DMN Purity (mass%) Recovery (mass%) Example 4 94 51 Example 5 98 44 Example 6 93 73 73 Comparative Example 4 74 51 Comparative Example 5 82 53 53 Comparative Example 6 89 23 The data in Table 4 show that 2,7-DMN can be effectively separated and recovered when the present invention is applied to a DMN mixture obtained from a starting material different from the DMN mixture in Table 2. The results differ depending on the operating conditions, indicating that the tendency is similar to that shown in Table 2.

[0031]

According to the present invention, 2,7-DMN is replaced with other DM
When separated and recovered from the mixture with Ns, it does not contain a large amount of 2,6-DMN and has a lower melting point than 2,7-DMN.
2,7-DMN can be obtained with a high degree of purity and recovery from a mixture containing Ns by a simple operation.

Claims (4)

[Claims] 1. A method for selectively separating and recovering 2,7-dimethylnaphthalene from a mixture with other dimethylnaphthalene, which comprises 2,7-dimethylnaphthalene and dimethylnaphthalene having a lower melting point. Is added to ethyl alcohol under heating to dissolve at least a part of the mixture, and the resulting solution or slurry is cooled to selectively precipitate 2,7-dimethylnaphthalene and has a low melting point. A method for separating and recovering 2,7-dimethylnaphthalene, which comprises filtering and separating at a temperature at which dimethylnaphthalene is kept in a liquid state. 2. A mixture of 2,7-dimethylnaphthalene and other dimethylnaphthalenes, 1) a hydrocarbon mixture containing 2,7-dimethylnaphthalene and 1,7-dimethylnaphthalene as a main component, or 2) 2. The method for separating and recovering according to claim 1, wherein any one of 3,7-dimethylnaphthalene and a hydrocarbon mixture containing 1,3-dimethylnaphthalene as a main component is used. 3. The method according to claim 1, wherein the mixture of 2,7-dimethylnaphthalene and another dimethylnaphthalene is added to 0.5 to 10 times by mass of ethyl alcohol. 4. The method for separating and recovering according to claim 1, wherein the solution or slurry in which the dimethylnaphthalene mixture is dissolved or partially dissolved is cooled to the following temperature: 1) The dimethylnaphthalene mixture is carbonized according to claim 1). -14 ° to + 50 ° C when it is a hydrogen mixture, and -4 ° to + 50 ° C when the 2) dimethylnaphthalene mixture is the hydrocarbon mixture of claim 2).