JP2008001717A - Method for producing high purity 2,6-dimethylnaphthalene - Google Patents

Abstract

Provided is a method for industrially advantageously producing high-purity 2,6-dimethylnaphthalene from a dimethylnaphthalene mixture.
SOLUTION: (1) An isomerization step of isomerizing a dimethylnaphthalene mixture in the presence of a catalyst; (2) 2,6-dimethylnaphthalene is separated from the isomerization reaction product by crystallization in the presence of a solvent. Crystallization process, (3) Distillation of the mother liquor of the crystallization process, removing the components having a higher boiling point and lower components than dimethylnaphthalene to obtain a dimethylnaphthalene fraction, and obtained in the distillation process. The dimethylnaphthalene fraction is recycled to the isomerization step.
[Selection figure] None

Description

The present invention relates to a process for producing 2,6-dimethylnaphthalene which is useful as a raw material for 2,6-naphthalenedicarboxylic acid from a mixture of dimethylnaphthalenes.

2,6-naphthalenedicarboxylic acid is a raw material for high-performance polyester used in the production of polyethylene naphthalate fibers and films having excellent tensile strength and heat resistance. 2,6-dimethylnaphthalene (hereinafter, dimethylnaphthalene is referred to as DMN) is a raw material for the 2,6-naphthalenedicarboxylic acid and is required to have a high purity. In other words, 2,6-naphthalenedicarboxylic acid as a raw material for high-performance polyester used in the production of polyethylene naphthalate fibers and films needs to be of high purity, and its raw material, 2,6-DMN is also of high purity. Need to be. Since there are two methyl groups in DMN, there are 10 isomers depending on the position, and 2,6-DMN as a raw material of 2,6-naphthalenedicarboxylic acid is substantially different from other isomers. It must be of high purity not containing.

As a method for producing 2,6-DMN, there are a method of separating from a tar fraction and a petroleum fraction, a method of isomerizing and separating naphthalene or methylnaphthalene after methylation, and the like. These fractions and products contain most of the 10 isomers and it is necessary to separate 2,6-DMN from many isomer mixtures. On the other hand, JP-A-49-134634 discloses a method for obtaining o-tolylpentene-2 from orthoxylene and butadiene in a high yield. JP-A-50-89353 discloses a method for producing 1,5-dimethyltetralin by cyclizing o-tolylpentene-2, and JP-A-48-76852 discloses 1,5-dimethyltetralin. A process for producing 1,5-DMN with high yield and high selectivity by dehydrogenation of is shown. Further, JP-A-50-129534 discloses a method for isomerizing 1,5-DMN to obtain an isomer mixture mainly composed of 1,5-, 1,6-, 2,6-DMN. . Therefore, by combining these methods, an isomer mixture mainly composed of 1,5-, 1,6-, 2,6-DMN can be obtained from ortho-xylene and butadiene, and 2,6- There is also a method for separating DMN.

As described above, in the conventional 2,6-DMN production method, it is necessary to separate and recover 2,6-DMN from the DMN isomer mixture. The boiling point and melting point of the 10 isomers of DMN are as follows. The boiling points of the isomers are very close, and 2,6-DMN is purified by distillation, which is usually used for separation and purification of organic compounds. It is extremely difficult.
Boiling point (° C) Melting point (° C)
1,5-DMN 269 82
1.6-DMN 266 -16
2,6-DMN 262 112
1,7-DMN 263 -14
1,8-DMN 270 65
2,7-DMN 262 98
1,3-DMN 265 -4.2
1,4-DMN 265 6
2,3-DMN 269 104
1,2-DMN 271 -3.5

As is apparent from this table, 2,6-DMN has the highest melting point among DMN isomers. On the other hand, 2,6-DMN is known to form a eutectic with 1,5-DMN, 2,7-DMN, and 2,3-DMN. Therefore, in order to precipitate 2,6-DMN as crystals by crystallization from an isomer mixture, the amount ratio of 2,6-DMN in the mixture to these isomers needs to be larger than the eutectic composition ratio. That is, an isomer mixture in which the molar ratio of 1,5-DMN to 2,6-DMN in the mixture is 1.9 or less, the molar ratio of 2,7-DMN is 1.4 or less, and the molar ratio of 2,3-DMN is 1.1 or less. It is known that 2,6-DMN first precipitates as crystals when the is cooled.

As a method for separating 2,6-DMN from the DMN isomer mixture as described above, a method by crystallization, a method by adsorption, or a complex with 2,6-DMN is formed using a certain organic compound. A method for decomposing the complex after the separation has been proposed. Among these methods, the crystallization method is the simplest and suitable as an industrial separation method. In particular, when an isomer mixture mainly consisting of 1,5-, 1,6-, 2,6-DMN is produced from ortho-xylene and butadiene and separated from this, there are few isomer species in the purified raw material. A method using crystallization is effective. When isolating and isolating naphthalenes after methylation, it is necessary to separate 2,6-DMN from many isomer mixtures when separating from tar fraction and petroleum fraction. In this case, adsorption method and crystallization A combination of methods is used.

Separation and recovery of 2,6-DMN from various DMN isomer mixtures, including DMN isomerization mixtures mainly composed of 1,5-, 1,6-, 2,6- derived from ortho-xylene and butadiene In this case, isomerization is necessary to increase the yield of 2,6-DMN. That is, by isomerizing the DMN isomer mixture obtained as a mother liquor after separating 2,6-DMN, the 2,6-DMN concentration is increased, and 2,6-DMN is separated and recovered from this DMN isomerization mixture. A method of increasing the yield of 2,6-DMN by repeating the operation is effective.

When DMN isomerization is performed, it is known that isomerization between β-β and isomerization beyond a ring are less likely to occur than isomerization between α-β. That is, DMN is divided into the following four genera with respect to isomerization, and isomerization between genera is less likely to occur compared to isomerization within each genus.
2,6-genus (1,5-DMN, 1,6-DMN, 2,6-DMN)
2,7-genus (1,8-DMN, 1,7-DMN, 2,7-DMN)
2,3-genus (1,4-DMN, 1,3-DMN, 2,3-DMN)
1,2-genus (1,2-DMN)

In Japanese Examined Patent Publication No. 57-24331, using a specific isomerization catalyst, isomerization to a different genus occurs, and a mixture of DMN containing some DMN other than 2,6-genus is used as a raw material. In this method, the isomerization product solution is crystallized to separate 2,6-DMN, and then the mother liquor is recycled as an isomerization raw material. However, when the present inventors crystallized using an isomer mixture obtained by isomerizing DMN containing some DMN other than 2,6-genus, high purity 2,6-DMN crystals are obtained. I couldn't.

The object of the present invention is to recover a 2,6-DMN by crystallization from a DMN isomer mixture obtained by isomerizing a DMN mixture as a raw material, and to obtain a high recovery rate from the raw material DMN. An object of the present invention is to provide an industrially advantageous method for producing 2,6-DMN from which 2,6-DMN having a purity can be obtained.

As a result of intensive studies on a method for producing high-purity 2,6-DMN from a DMN mixture by crystallization, the present inventors have obtained a mother liquor for a crystallization process of a DMN isomer mixture obtained by isomerizing the DMN mixture. Is distilled, and the components having a higher boiling point and lower components than dimethylnaphthalene are removed and recycled in the isomerization process, so that high-purity 2,6-DMN crystals can be easily obtained industrially. By adjusting 2,7-DMN, monomethylnaphthalene (hereinafter referred to as MMN) and trimethylnaphthalene (hereinafter referred to as TMN) in the crystallization raw material to a certain concentration or less, high purity 2,6 of 98% or more -The present inventors have found that DMN can be separated and recovered with a high yield.

That is, in the present invention, when 2,6-dimethylnaphthalene is produced from a dimethylnaphthalene mixture, (1) an isomerization step of isomerizing the dimethylnaphthalene mixture in the presence of a catalyst, and (2) an isomerization reaction product, Crystallization step of separating 2,6-dimethylnaphthalene by crystallization in the presence of a solvent, (3) Distilling the mother liquor of the crystallization step to remove components having a higher boiling point and lower components than dimethylnaphthalene, A process for producing high-purity 2,6-dimethylnaphthalene, comprising three steps of a distillation step for obtaining a naphthalene fraction, wherein a part or all of the dimethylnaphthalene fraction obtained in the distillation step is circulated to the isomerization step , And 1,5-dimethylnaphthalene, dimethylnaphthalene containing 1,6-dimethylnaphthalene and 2,6-dimethylnaphthalene as main components High purity characterized in that when 2,6-dimethylnaphthalene is separated from the compound by crystallization, the amount of 2,7-dimethylnaphthalene relative to dimethylnaphthalenes contained in the crystallization raw material is 10% by weight or less. This is a method for producing 2,6-dimethylnaphthalene.

The present inventors have also found that high-performance 2,6-naphthalenedicarboxylic acid or its ester can be produced very advantageously by liquid phase oxidation of 2,6-dimethylnaphthalene obtained by the present invention. . Accordingly, the present invention provides a process for producing 2,6-naphthalenedicarboxylic acid, characterized by subjecting 2,6-dimethylnaphthalene obtained as described above to liquid phase oxidation, and esterifying the 2,6-naphthalenedicarboxylic acid. Also included is a method for producing dimethyl 2,6-naphthalenedicarboxylate, which is characterized by the above.

According to the method of the present invention, highly pure 2,6-DMN can be easily obtained from a DMN mixture. In the method of the present invention, 2,6-DMN having a high purity can be obtained industrially advantageously with a high recovery rate with a simple configuration. Also, by liquid-phase oxidation of the obtained 2,6-DMN, dimethyl 2,6-naphthalenedicarboxylate and high-purity 2,6-naphthalenedicarboxylic acid, which are useful as raw materials for high-performance polyesters, are produced very advantageously. The Therefore, the industrial significance of the present invention is very great.

The 2,6-DMN production method of the present invention comprises three steps, an isomerization step, a crystallization step, and a distillation step, and their relationship is shown in FIG. In the isomerization step, the raw DMN mixture is isomerized in the presence of a catalyst. The isomerization reaction product is sent to a crystallization process, and high purity 2,6-DMN crystals are separated and recovered. The mother liquor after separation of 2,6-DMN crystals is sent to the distillation process, where components with higher boiling points (high boiling point) and components with lower boiling points (low boiling point) than DMN are removed and the DMN fraction enters the isomerization step. Circulated.

As the DMN mixture used as a raw material in the present invention, a DMN mixture mainly composed of 1,5-DMN synthesized using ortho-xylene and butadiene as raw materials is preferably used. At this time, the DMN mixture introduced into the isomerization step includes a DMN mixture containing 1,5-DMN as a main component and 2,6-DMN after crystallization from the isomerization product of the DMN mixture. Since the DMN fraction obtained by distilling the mother liquor is mixed, a dimethylnaphthalene mixture containing 1,5-DMN, 1,6-DMN and 2,6-DMN as main components is obtained. In the method of the present invention, the performance of the isomerization reaction greatly affects the entire process. That is, as the isomerization rate to 2,6-DMN is larger, the one-pass recovery rate in the crystallization process is improved and the DMN circulation amount is reduced, which is economically advantageous. Further, when disproportionation and isomerization to different isomers occur simultaneously, crystal purity is lowered, and these side reactions must be suppressed as much as possible. In particular, when 2,7-DMN is produced, it is difficult to remove by distillation. Therefore, if it is circulated, it accumulates, and not only the crystal purity deteriorates, but also a part of DMN fraction must be extracted. , 2,6-DMN yield will be reduced.

The isomerization catalyst used in the present invention may be any as long as it exhibits acidity, and for example, solid acid, mineral acid, hydrogen fluoride, etc. are used. Examples of the solid acid include silica alumina, alumina, X-type zeolite, Y-type zeolite, mordenite, and β-zeolite, with zeolite being preferred. This zeolite is preferably one in which part or all of the cation is replaced with hydrogen or metal, has a high isomerization rate to 2,6-DMN, and is capable of disproportionation or isomerization to heterogenous isomers. In order to suppress this, hydrogen-substituted mordenite, particularly mordenite composed essentially of hydrogen having a silica / alumina ratio of 100 or more is suitable. This zeolite catalyst can be used as a powder, but depending on the reaction mode, a molded one is used. As molding aids for molding, alumina, silica, clay, acid clay, etc. are generally used, but alumina or silica is preferred.

There are no particular restrictions on the reaction format for carrying out the isomerization reaction, and any of batch and flow methods can be employed, but the flow method is preferred industrially. In the flow type, any reaction method such as a fixed bed, a fluidized bed, and a moving bed may be used, but generally a fixed bed flow type is selected. The reaction may be in the liquid phase or the gas phase, and the pressure at that time is not particularly limited.

DMN as an isomerization raw material may be used as it is, or may be diluted with a solvent or gas. Whether or not a diluent such as a solvent is used is determined in consideration of the entire economy including the crystallization process and the distillation process. Solvents that serve as diluents include aliphatic saturated hydrocarbons, alicyclic saturated hydrocarbons, aromatic hydrocarbons, such as pentane, hexane, heptane, octane, nonane, decane, undecane, dodecane, cyclopentane, cyclohexane, and benzene. , Toluene, xylene and the like are used. Further, when a gas is used as a diluent, those inert to the isomerization reaction such as nitrogen, carbon dioxide, hydrogen, and argon are used. The isomerization reaction can also be carried out using the same type of solvent as that used in the crystallization step.

The isomerization reaction temperature varies depending on the catalyst type and reaction system, but is usually 100 to 500 ° C, preferably 150 to 300 ° C. Space velocity by weight (WHSV) is 0.1 to 10 ^-1, preferably 0.2 to 5 hr ^-1. If the reaction temperature is too high or WHSV is too low, side reactions such as isomerization to dissimilarity or disproportionation are likely to occur. If the reaction temperature is too low, the isomerization rate to 2,6-DMN Becomes smaller.

In the present invention, after the isomerization step, 2,6-DMN crystals are separated and recovered by crystallization. Usually, a separation operation is not required between the isomerization step and the crystallization step, but when a solvent is used in the isomerization step, a solvent separation operation may be required depending on the type of the solvent. The method of crystallization is not particularly limited, and the crystallization is performed by cooling or solvent distillation. The crystallization method may be continuous or batch. When the isomerization reaction product obtained by isomerizing DMN under solvent-free conditions is crystallized as it is, the filterability of the obtained crystal is poor and the crystal purity is hardly improved even by washing. On the other hand, when crystallization is performed in the presence of a solvent by the method of the present invention, the properties of the crystals are improved and crystals with good filterability are obtained.

Examples of the solvent that coexists during crystallization include aliphatic saturated hydrocarbons, alicyclic saturated hydrocarbons, aromatic hydrocarbons, alcohols, etc., but aliphatic saturated hydrocarbons or alicyclic saturated hydrocarbons are Preferably used. Examples of the aliphatic saturated hydrocarbon and alicyclic saturated hydrocarbon used include pentane, hexane, heptane, octane, nonane, decane, undecane, dodecane, cyclopentane, methylcyclopentane, cyclohexane, methylcyclohexane, decalin and the like. is there. By using these solvents, the filterability of the crystals obtained is improved, and high-purity crystals can be obtained efficiently. The solvent used in the isomerization step can be used as it is as the solvent in the crystallization step.

From the mother liquor after crystal separation, components having a boiling point higher and lower than DMN are removed in the distillation step, and only the DMN fraction is circulated in the isomerization step. As mentioned above, DMN has 10 isomers, each having a different boiling point, but higher boiling point components (higher boiling points) than those having the highest boiling point in these DMN isomers and those having the lowest boiling point. The low boiling point component (low boiling point) is separated and removed, and part or all of the obtained DMN fraction is recycled for use in the isomerization step. Since the mother liquor after crystal separation also contains a solvent for crystallization, this solvent is usually contained at a low boiling point, and is further recycled after being separated by distillation.

In order to obtain 2,6-DMN having high purity in the above process, the raw material of the crystallization step is 10% by weight or less, particularly 2,7-DMN concentration with respect to dimethylnaphthalene. It is preferable that the concentration is 5% by weight or less, the MMN concentration is 3% by weight or less, and the TMN concentration is 10% by weight or less. Therefore, considering the amount of MMN and TMN in DMN newly supplied to the isomerization process and the amount of by-products generated when MMN and TMN are by-produced in the isomerization process, It is necessary to control the amount of MMN and TMN in the minute. When the heterogeneous isomers such as 2,7-DMN are included in the DMN newly supplied to the isomerization process, and the heterogenous isomers such as 2,7-DMN are produced in the isomerization process Since it is difficult to separate these heterogenous isomers by distillation, in order to control the 2,7-DMN concentration in the crystallization raw material, before or after the distillation step, preferably during the distillation, It is necessary to extract a part of DMN simultaneously with the high boiling point component and the low boiling point component.

The amount of DMN extracted in order to control the 2,7-DMN concentration in the crystallization raw material is the amount of different isomers in DMN newly supplied, and the amount of different isomers produced in the isomerization process. In addition, it is determined in consideration of the economics of the entire process such as the purity of crystals obtained in the crystallization step and the amount of circulating DMN. In addition, since 2,7-DMN has a property of being entrained in a crystal in a small amount, if the amount of heterogenous isomers in DMN newly supplied and the amount produced in the isomerization reaction are below a certain amount, It is possible to prevent accumulation in the system by removing 2,7-DMN entrained in the crystal from the system as it is.

A DMN mixture mainly composed of 1,5-DMN synthesized from ortho-xylene and butadiene belongs to the aforementioned 2,6-genus, and by isomerization thereof, 1,5-, 1,6- An isomerization reaction product consisting of 2,6-DMN is obtained. The mother liquor after crystallizing and separating 2,6-DMN from this isomerization reaction product mainly contains 1,5-DMN and 1,6-DMN, and can be recycled as an isomerization raw material. . However, in the isomerization reaction, side reactions such as generation of MMN and TMN by disproportionation and formation of 2,7-genus isomer by isomerization outside the genus are likely to occur. MMN and TMN can be removed by distillation, but isomers outside the genus are difficult to remove by distillation. If the mother liquor after crystallization of 2,6-DMN is recycled to the isomerization process, It will be accumulated.

When 2,6-DMN is separated from a DMN isomer mixture by crystallization, 2,6-DMN and 2,7-DMN, 1,5-DMN, and 2,3-DMN may form eutectic crystals. Well known. The binary eutectic composition of 2,6-DMN and these three isomers is as follows.
2,6-DMN / 2,7-DMN = 1.42,6-DMN / 1,5-DMN = 1.92,6-DMN / 2,3-DMN = 1.1 Therefore, on the eutectic principle Then, when the DMN isomerization reaction product containing 2,6-DMN exceeding the above composition ratio is cooled, 2,6-DMN precipitates as crystals. At this time, other components are attached to the crystal as a mother liquor, which should be removed by rinsing with a solvent such as normal heptane.

However, as a result of studies on a method for separating and recovering 2,6-DMN by crystallization from DMN isomerization reaction products, the present inventors have found that partial isomers of 2,7-DMN, 2-MMN and TMN. Behaved differently from other impurities. The present inventors have studied in detail the relationship between the concentration of impurities in the crystallization raw material and the concentration of impurities remaining in the resulting crystal. As a result, 2,7-DMN, MMN or TMN is not present in the crystallization raw material. If it is present to a certain extent, 2,7-DMN, MMN and TMN more than expected in the eutectic theory remain in the crystal, and it is difficult to obtain a high purity crystal. It was.

That is, as a result of the study by the present inventors, isomers other than the above isomers in 1,5-DMN, 1,6-DMN, 1-MMN, and TMN in the DMN isomerization reaction product used as a crystallization raw material. And the like can be easily removed by rinsing the crystal after the 2,6-DMN crystal is precipitated, and increasing the amount of the rinsing liquid decreases its concentration steadily, but 2,7-DMN , 2-MMN and TMN isomers hardly change even when the crystals are rinsed, and are not attached to the crystals as one component in the mother liquor. As a result, it was inevitably taken into the crystal during precipitation.

The amount of the partial isomers of 2,7-DMN, 2-MMN and TMN inevitably contained in the crystal when 2,6-DMN is precipitated as crystals is determined by the amount of dimethylnaphthalenes in the crystallization raw material. In the case where 10 parts by weight of 2,7-DMN is contained with respect to 100 parts by weight of dimethylnaphthalene, 2,7-DMN contained accompanying 2,6-DMN crystals Is 0.7-1.4%. When 5 parts by weight of 2,7-DMN is contained with respect to 100 parts by weight of dimethylnaphthalenes, the amount of 2,7-DMN contained accompanying the 2,6-DMN crystal is 0.4-0. 8%, and when 5 parts by weight of MMN is contained with respect to 100 parts by weight of dimethylnaphthalene, the amount of 2-MMN accompanying the 2,6-DMN crystal is 0.7 to 1.3%. In the case where 5 parts by weight of TMN is contained with respect to 100 parts by weight of dimethylnaphthalenes, the amount of the partial isomer of TMN contained accompanying the 2,6-DMN crystal is 0.2 to 0.6%. Become. Therefore, in order to obtain 2,6-DMN having a high purity of 98% or more, when MMN and TMN are hardly contained in the crystallization raw material (for example, when the total amount of MMN and TMN is 1% or less), It is necessary that 2,7-DMN contained in the crystallization raw material is 10% by weight or less. When a considerable amount of MMN or TMN is contained in the crystallization raw material, the concentration of 2,7-DMN, MMN or TMN remaining in the 2,6-DMN crystal is about 0.5% by weight or less. In order to suppress this, it is necessary that the 2,7-DMN concentration with respect to dimethylnaphthalenes in the crystallization raw material is 5% by weight or less, the MMN concentration is 3% by weight or less, and the TMN concentration is 10% by weight or less.

That is, from the conventional eutectic composition ratio, it is said that only 2,6-DMN is precipitated as crystals by crystallizing a raw material having a composition in which the molar ratio of 2,7-DMN to 2,6-DMN is 1.4 or less. However, according to the present invention, it is clear that even if a minute amount of 2,7-DMN remains in the crystal and rinsing is performed, the amount of 2,7-DMN in the crystal does not decrease. -It is necessary to set the DMN concentration within the above range. MMN has two isomers, 1-MMN and 2-MMN, depending on the position of the methyl group. Among them, 2-MMN remains in the crystal, and 1-MMN adheres to the crystal as one component in the mother liquor and can be easily removed by rinsing. TMN has 16 isomers depending on the position of the methyl group. It is not clear at this time which isomers remain in the crystals. Probably part of an isomer with a methyl group at the β-position. TMN remaining in the crystal is a part of these 16 isomers, and the others are attached to the crystal as one component in the mother liquor like 1-MMN and can be easily removed by rinsing.

When DMN is isomerized, MMN and TMN contained in DMN are also isomerized at the same time, and MMN and TMN in the isomerization reaction product are isomer mixtures. The amount of MMN in the isomerization reaction product varies depending on the amount of MMN in the isomerization raw material and the degree of disproportionation reaction that occurs simultaneously during the isomerization. The amount ratio of 2-MMN to 1-MMN in MMN varies depending on the type of catalyst used in the isomerization and reaction conditions, but is generally in the range of 1 to 3. The type and amount of TMN isomers in the isomerization reaction product vary depending on the type and amount of isomers in the isomerization raw material, and also vary depending on the degree of disproportionation reaction that occurs at the time of isomerization. However, the amount ratio between the TMN isomer remaining in the crystal and the isomer that can be easily removed as a component in the mother liquor varies slightly depending on the catalyst species used in the isomerization and the reaction conditions. It is considered to be within a certain range.

The liquid phase oxidation method of 2,6-DMN is not particularly limited, and various conventionally known methods can be used. Generally, the presence of a Co-Mn-Br catalyst in a solvent such as acetic acid is used. Below, a method of liquid phase oxidation with molecular oxygen can be mentioned. Specifically, acetic acid or hydrous acetic acid containing a small amount of water is used as a solvent, and a cobalt compound, a manganese compound, and a bromine compound are added thereto as a catalyst, and the pressure is 5 to 40 kg / cm ² G and the temperature is about 180 to 250 ° C. Under the conditions, 2,6-DMN is oxidized with an oxygen-containing gas to produce 2,6-naphthalenedicarboxylic acid with a high yield of 80% or more. At this time, the cobalt compound, manganese compound and bromine compound of the catalyst are 0.002 to 0.1 mol as a cobalt atom, 0.01 to 0.2 mol as a manganese atom and as a bromine atom with respect to 1 mol of 2,6-DMN. It is used in a proportion of 0.01 to 0.2 mol.

2,6-Naphthalenedicarboxylic acid is taken out from the reaction completion liquid by a known means. The oxidation reaction format may be either a batch type or a continuous type. The obtained 2,6-naphthalenedicarboxylic acid is further esterified by known means to obtain highly pure dimethyl 2,6-naphthalenedicarboxylic acid. According to the method for producing 2,6-DMN of the present invention, high-purity 2,6-DMN is efficiently produced from a DMN mixture mainly composed of 1,5-DMN obtained using, for example, o-xylene and butadiene as raw materials. It is good, can be produced with high yield, and industrially advantageous. The 2,6-DMN thus obtained is subjected to liquid phase oxidation, so that dimethyl 2,6-naphthalenedicarboxylate and high-purity 2,6-naphthalenedicarboxylic acid useful as a raw material for high-performance polyester are extremely advantageous. To be manufactured.

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. In addition, the density | concentration of each component in each following Example and a comparative example was calculated | required by the gas chromatography.

Abbreviations used in Examples, Comparative Examples, and Tables are as follows.
DMN Dimethylnaphthalene
MMN monomethylnaphthalene
TMN Trimethylnaphthalene
LE Lower boiling point components than dimethylnaphthalene (except MMN)
HE Higher boiling point components than dimethylnaphthalene (except TMN)
WHSV Weight-based space velocity (raw material-g / catalyst-g · hr)

Example 1
200 g of an isomerization product obtained by isomerizing DMN composed mainly of orthoxylene and butadiene using DMN mainly composed of 1,5-DMN as a catalyst with H-type mordenite (manufactured by Tosoh), and 100 g of normal heptane, The sample was placed in a 400 cc glass container equipped with a stirrer, heated to 80 ° C. with stirring and dissolved, and then gradually cooled to 20 ° C. to precipitate crystals. Next, the contents were suction filtered through a G2 glass filter (standard maximum pore size 100 to 150 μm), and the obtained crystals were rinsed three times with 20 g of normal heptane at 0 ° C. Table 1 shows the composition of the isomerization product liquid (raw material) used for crystallization, the crystal after filtration and rinsing. As the rinsing is repeated, 1,5-DMN, 1,6-DMN, L. E and H. All of E was steadily removed, and 57.4 g of high-purity crystals were obtained.

Comparative Example 1
2,7-DMN, MMN, and TMN were added to DMN mainly composed of 1,5-DMN used in Example 1, and isomerization, crystallization, filtration, and rinsing were performed in the same manner as in Example 1. Table 2 shows the composition of the isomerization product liquid (raw material) used for crystallization, the crystal after filtration and rinsing. 1,6-DMN, 1,5-DMN, Other-DMN, L. E and H. It can be seen that E is steadily removed by rinsing, whereas 2,7-DMN, MMN, and TMN are difficult to remove by rinsing.

Example 2
(Cycle 1) Isomerization was performed using DMN containing 2% of 2,7-DMN shown in Table 3 as a raw material, and the isomerization reaction product shown in Table 4 as reaction product liquid (1) was obtained. The isomerization reaction is performed using a catalyst (alumina content 20 wt%) of H-type mordenite (silica / alumina ratio = 203, manufactured by Tosoh), and reaction temperature 220 ° C., WHSV = 1.0, normal pressure liquid phase circulation. The method was implemented. Normal heptane of the same weight as the reaction product solution was added, heated and dissolved at 80 ° C., and then cooled to 20 ° C. to precipitate crystals. The slurry containing crystals was filtered through a G2 glass filter, rinsed with normal heptane cooled to 20 ° C., which was 1/2 weight of the reaction product used for crystallization, and the composition shown in Table 3 as crystals (1) Was obtained with a recovery of 64.2%. Here, the recovery rate is a ratio of 2,6-DMN in the crystal to 2,6-DMN in the crystallization raw material. Next, the mother liquor and rinse solution after crystallization were distilled to obtain a DMN fraction (1). The DMN obtained as a fraction is 95% of the DMN in the mother liquor and rinse solution. The 2,7-DMN concentration in the DMN fraction was 2.94%. The amount ratio of DMN taken out as crystals and DMN that could not be recovered during distillation and DMN fraction (1) was 31:69.

(Cycle 2)
The raw material DMN and the DMN fraction (1) obtained above were mixed at a quantitative ratio of 31:69, the isomerization reaction was carried out under the same conditions as in cycle 1, and the reaction product liquid (2) having the composition shown in Table 3 was obtained. Obtained. The reaction product liquid (2) was crystallized, filtered and rinsed under the same conditions as in cycle 1, and crystals having the composition shown in Table 3 crystals (2) were obtained at a recovery rate of 64.1%. Further, the mother liquor and rinse solution after crystallization were distilled in the same manner as in cycle 1 to obtain DMN fraction (2). The DMN obtained as a fraction is 95% of the DMN in the mother liquor and rinse solution. The 2,7-DMN concentration in the DMN fraction (2) was 3.18%. The ratio of DMN taken out as crystals and DMN that could not be recovered during distillation and DMN fraction (2) was 31:69.

(Cycle 3)
The raw material DMN and the DMN fraction (2) obtained above were mixed in an amount ratio of 31:69, and an isomerization reaction was carried out under the same conditions as in cycle 1 to obtain a reaction product liquid (3). The reaction product liquid (3) was crystallized, filtered and rinsed under the same conditions as in cycle 1 to obtain crystal (3) at a recovery rate of 64.1%. Further, the mother liquor and rinse solution after crystallization were distilled in the same manner as in cycle 1 to obtain a DMN fraction (3). The DMN obtained as a fraction is 95% of the DMN in the mother liquor and rinse solution. The 2,7-DMN concentration in the DMN fraction (2) was 3.42%. The amount ratio of DMN taken out as crystals and DMN that could not be recovered during distillation and DMN fraction (3) was 31:69.

(Cycles 4-5)
Thereafter, the DMN fraction collected in the raw material DMN was added in the same manner, and isomerization, crystallization, and distillation were repeated. Table 3 shows the composition of the reaction product solution and crystals obtained by repeating this cycle. Since the production of 2.7-DMN in the isomerization reaction is small, even if this operation is repeated, the accumulation of 2,7-DMN in the mother liquor is small and high-purity crystals are obtained.

Example 3
(Cycle 1) USY type zeolite (silica / alumina ratio = 6.1, manufactured by Tosoh) was replaced with a catalyst (alumina content 20% by weight) obtained by molding H-type mordenite (silica / alumina ratio = 203, manufactured by Tosoh) with alumina. The reaction product liquid (1) shown in Table 4 was obtained by isomerization in the same manner as in Example 2 except that the catalyst molded with alumina (alumina content 20% by weight) was used. Crystallization, filtration and rinsing were carried out in the same manner as in Example 2 to obtain crystals (1) having the composition shown in Table 4. The recovery rate of 2,6-DMN was 60.4%. Further, the mother liquor and the rinse liquid after crystallization were distilled in the same manner as in Example 2 to obtain a DMN fraction (1). The DMN obtained as a fraction is 95% of the DMN in the mother liquor and rinse solution. The 2,7-DMN concentration in the DMN fraction (1) was 4.22%. The amount ratio of DMN taken out as crystals and DMN that could not be recovered during distillation and DMN fraction (1) was 26:74.

(Cycle 2)
The raw material DMN and the DMN fraction (1) obtained above were mixed in an amount ratio of 26:74, an isomerization reaction was carried out under the same conditions as in cycle 1, and a reaction product liquid (2) having the composition shown in Table 4 was obtained. Obtained. The reaction product liquid (2) was crystallized, filtered and rinsed under the same conditions as in the first cycle to obtain crystals (2) at a recovery rate of 59.9%. Further, the mother liquor and rinse liquid after crystallization were distilled in the same manner as in cycle 1 to obtain a DMN fraction (2). The DMN obtained as a fraction is 95% of the DMN in the mother liquor and rinse solution. The amount ratio of the DMN taken out as crystals and the sum of DMN that could not be recovered during distillation and the DMN fraction (2) was 26:74.

(Cycle 3)
Thereafter, in the same manner as in Example 2, the raw material DMN and the collected DMN fraction were mixed, and isomerization, crystallization, and distillation were repeated. Table 4 shows the compositions of the obtained reaction product liquid (3) and crystals (3). Since the production of 2.7-DMN in the isomerization reaction is larger than that in Example 2, repeating this operation tends to increase the amount of 2,7-DMN accumulated in the system and decrease the purity of the crystal. There are many circulating DMN fractions.

Example 4
The isomerization reaction was carried out under the same conditions as in Example 2 using the same raw materials as in cycle 1 of Example 2. Using the resulting isomerization product solution, crystallization, filtration, and rinsing were performed under the same conditions as in Example 2 except that toluene was used in place of normal heptane as a solvent. Crystals having a recovery rate of 57.2% and a purity of 98.7% were obtained. Table 5 shows the composition of the crystals obtained. Compared with the case where normal heptane is used as a solvent, the recovery rate is slightly lower and the crystal purity obtained is slightly lower.

Comparative Example 2
The isomerization reaction was carried out under the same conditions as in Example 2 using the same raw materials as in cycle 1 of Example 2.
Crystallization and filtration were performed under the same conditions as in Example 2 except that normal heptane was not used as a solvent, using 100 g of the resulting isomerization reaction product solution, and then rinsed with 200 g of normal heptane cooled to 20 ° C. Then, a crystal having a recovery rate of 64.8% and a purity of 97.6% was obtained. Table 5 shows the composition of the obtained crystal. The filterability of the precipitated crystals was poor, and the crystal purity was lower than when using a solvent.

Example 5
Isomerization, crystallization, and distillation were repeated in the same manner as in Example 2 using 1,5-DMN having the composition shown in Table 6 obtained from ortho-xylene and butadiene as raw materials. Table 6 shows the changes in the composition of the reaction product solution and the crystals accompanying the repetition of this cycle. Since 2,7-DMN in the raw material is small and 2.7-DMN is not generated in the isomerization reaction, accumulation of 2,7-DMN in the mother liquor is small even when this operation is repeated, and high-purity crystals are obtained. You can see that

Reference Example 2,7-DMN was added to the isomerization product liquid having the composition shown in Table 7 to prepare a crystallization raw material containing 2,7-DMN at 3%, 6%, 9%, 15% and 20%. 100 g of normal heptane was added to 100 g of each crystallization raw material, taken into a 400 cc glass container equipped with a stirrer, dissolved by heating to 80 ° C. with stirring, and then gradually cooled to 20 ° C. to precipitate crystals. Subsequently, the contents were suction filtered through a G2 filter (standard maximum diameter: 100 to 150 μm), and the obtained crystals were rinsed with 30 g of normal heptane at 0 ° C. three times. Table 7 shows the composition of the crystallization raw material and the obtained crystal. When the concentration of 2,7-DMN in the crystallization raw material is high, 2,7-DMN remains and even after rinsing, high-purity crystals cannot be obtained. The recovery rates of 2,6-DMN for crystallization raw materials containing 3%, 6%, 10%, 16% and 20% of 2,7-DMN are 64.9%, 63.7%, 62.7%, 61.4% and 58.6%, respectively. The recovery rate of 2,6-DMN decreases as the 2,7-DMN concentration in the crystallization raw material increases, and it is 2 if a high concentration of 2,7-DMN is present in the crystallization raw material. Therefore, the recovery rate of 6-DMN will also deteriorate.

Example 6
To 288.9 g of acetic acid, 3.2 g of water, 0.63 g of cobalt acetate (tetrahydrate), 5.37 g of manganese acetate (tetrahydrate) and 1.92 g of hydrogen bromide (47% aqueous solution) were mixed and dissolved to prepare a catalyst solution. Next, 120 g of the catalyst solution was charged into a 0.5 L titanium autoclave (reactor) equipped with a stirrer, a reflux condenser, and a feed pump. The remaining catalyst solution (180 g) was mixed with 30 g of 2,6-dimethylnaphthalene (DMN) obtained from Example 1, charged into a raw material supply tank, and heated to dissolve DMN to prepare a raw material solution. The pressure in the reaction system was adjusted to 18 kg / cm ² G with nitrogen and heated to a temperature of 200 ° C. with stirring. After the temperature and pressure were stabilized, the raw material liquid and compressed air were supplied to the reactor to initiate the oxidation reaction. The raw material liquid was continuously supplied over 1 hour while adjusting the supply air flow rate so that the oxygen concentration in the exhaust gas was 2% by volume. The oxygen partial pressure in the reactor at this time is 0.12 kg / cm ² (absolute pressure). After the supply of the raw material liquid was completed, the air supply was continued for 9 minutes. After completion of the reaction, the autoclave was cooled to room temperature, the reaction product was taken out, suction filtered through a glass filter to separate crystals, and rinsed with 80 g of acetic acid containing 20% by weight of water. The separated cake was weighed and then dried in a drier to obtain 40.65 g of crude NDCA crystals. The NDCA purity in the dried crystals was 96.5% by weight, and the NDCA yield based on the supplied DMN was 94.5 mol%.

It is a flowchart which shows the structure of the high purity 2, 6- dimethylnaphthalene manufacturing method by this invention.

Claims (6)

When 2,6-dimethylnaphthalene is produced from a dimethylnaphthalene mixture, (1) a mordenite catalyst having a molar ratio of silica to alumina of 100 or more, which is substantially a hydrogen type, or alumina and / or silica is used as a molding aid. An isomerization step in which isomerization is performed in the presence of a catalyst formed from mordenite, and (2) when 2,6-dimethylnaphthalene is separated from the isomerization reaction product by crystallization in the presence of a solvent. Crystallization process in which the amount of 2,7-dimethylnaphthalene relative to the dimethylnaphthalene contained is 10% by weight or less, (3) The mother liquor of the crystallization process is distilled to remove components having higher and lower boiling points than dimethylnaphthalene. The dimethylnaphthalene obtained in the distillation step consists of three steps of the distillation step to obtain the dimethylnaphthalene fraction Process for producing a high-purity 2,6-dimethylnaphthalene, characterized by circulating minute part or all the isomerization step. The method for producing high-purity 2,6-dimethylnaphthalene according to claim 1, wherein at least one solvent selected from aliphatic saturated hydrocarbons and alicyclic saturated hydrocarbons is used in the crystallization step. The method for producing high-purity 2,6-dimethylnaphthalene according to claim 1, wherein the dimethylnaphthalene mixture is obtained by using ortho-xylene and butadiene as starting materials. 2. The amount of 2,7-dimethylnaphthalene is 5% by weight or less, the amount of monomethylnaphthalene is 3% by weight or less, and the amount of trimethylnaphthalene is 10% by weight or less based on dimethylnaphthalenes contained in the crystallization raw material. Process for producing high-purity 2,6-dimethylnaphthalene as described A method for producing 2,6-naphthalenedicarboxylic acid, comprising subjecting 2,6-dimethylnaphthalene obtained by the production method according to claim 1 to liquid phase oxidation. A method for producing dimethyl 2,6-naphthalenedicarboxylate, characterized by esterifying 2,6-naphthalenedicarboxylic acid obtained by the production method according to claim 5.

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