Method for producing 1,4-dimethylnaphthalene

Abstract

The present invention provides an industrial method for producing 1,4-dimethylnaphthalene with a low 1,3-dimethylnaphthalene content. In the method for producing 1,4-dimethylnaphthalene, 5-phenyl-2-hexene is cyclized in the presence of an acid catalyst to produce crude 1,4-dimethyl-1,2,3,4-tetrahydronaphthalene, and the crude 1,4-dimethylnaphthalene obtained by dehydrogenation is distilled and purified, wherein the concentration of 1,3-dimethyl-1,2,3,4-tetrahydronaphthalene in 1,4-dimethyl-1,2,3,4-tetrahydronaphthalene is 1.0% or less relative to 1,4-dimethyl-1,2,3,4-tetrahydronaphthalene.

Description

Technical Field

[0001] The present invention relates to a method for producing 1,4-dimethylnaphthalene (hereinafter also referred to as "1,4-DMN") having a low isomer content, particularly a low 1,3-dimethylnaphthalene (hereinafter also referred to as "1,3-DMN"). Background Art

[0002] 1,4-DMN is industrially very important as an intermediate raw material of 1,4-naphthalenedicarboxylic acid, which is a raw material for resins and dyes.

[0003] In the above-mentioned field, it is desired that the isomer content in 1,4-DMN is 1.0% or less, preferably 0.5% or less, and more preferably 0.4% or less.

[0004] The production of dimethyl-1,2,3,4-tetralins based on cyclization reactions has mainly focused on the synthesis of 1,5-dimethyl-1,2,3,4-tetralin (hereinafter referred to as "1,5-DMT") by cyclization of 5-o-tolyl-2-pentene (hereinafter referred to as "OTP"). 1,5-DMT is important as an intermediate for the production of 2,6-naphthalene dicarboxylic acid (hereinafter referred to as "2,6-NDCA") through a dehydrogenation step, an isomerization step, and an oxidation step.

[0005]

[0006] There are many examples of using crystalline silica-alumina catalysts, that is, zeolite catalysts, as OTP cyclization catalysts in liquid phase and gas phase reactions (for example, see Patent Documents 1 to 4).

[0007] Since zeolite catalysts have strong acidity, there is a known method of treating with an alkali metal to adjust the acidity and performing cyclization at 120°C to 250°C (see, for example, Patent Document 5). However, the method described in Patent Document 5 has the disadvantage that it is difficult to adjust the acidity.

[0008] The cyclization reaction is a violent exothermic reaction, and the dehydrogenation reaction is an endothermic reaction. A technology combining the cyclization reaction and the dehydrogenation reaction has been disclosed. The dehydrogenation reaction of 1,5-DMT to 1,5-dimethylnaphthalene (hereinafter also referred to as "1,5-DMN") has a higher temperature than the cyclization reaction of OTP. Therefore, in order to carry out the cyclization and dehydrogenation reactions in one step, a method is disclosed in which the catalyst is treated with an alkali metal or the like, and the cyclization and dehydrogenation are carried out in one process at 200°C to 500°C (for example, refer to Patent Document 6). In the case of the method described in Patent Document 6, there is a problem that the reaction temperature is high and it is difficult to avoid side reactions such as polymerization and isomerization.

[0009] On the other hand, in order to suppress the dimerization of OTP, it is known that a diluent or a solvent is used in a cyclization reaction (for example, refer to Patent Documents 1, 7, and 8).

[0010] In the production of 1,5-DMN based on the dehydrogenation reaction of 1,5-DMT, there are many examples of using palladium, platinum, rhenium, etc. alone or in the form of a supported catalyst in the liquid phase dehydrogenation reaction. On the other hand, the above catalysts and chromia-alumina catalysts are used in the gas phase dehydrogenation reaction (for example, see Patent Documents 9 to 12).

[0011] Thus, many techniques for producing 1,5-DMT or 1,5-DMN from OTP have been studied.

[0012] Meanwhile, studies have been conducted on the production of 1,4-dimethyl-1,2,3,4-tetrahydronaphthalene (hereinafter also referred to as "1,4-DMT") and 1,4-DMN by cyclization of 5-phenyl-2-hexene (hereinafter also referred to as PH).

[0013] For example, a method of cyclizing PH using phosphoric acids and / or a solid phosphoric acid catalyst is known (for example, refer to Patent Documents 7 and 13).

[0014] In addition, a method is also known in which 1,4-DMN is produced in one step from PH via 1,4-DMT by continuously performing gas phase cyclization and gas phase dehydrogenation in the presence of hydrogen (for example, see Patent Document 14). The method of Patent Document 14 describes a solid phosphoric acid catalyst as a gas phase cyclization catalyst.

[0015] However, similar to the case of OTP, the cyclization reaction of PH also uses zeolite as a catalyst in the vast majority of methods (for example, see Patent Documents 4, 15, 16, and 17). When 1,4-DMT produced by the methods described in the literature is dehydrogenated, there is a problem that the concentration of 1,3-DMN in 1,4-DMN exceeds 1.0%.

[0016] The dehydrogenation of 1,4-DMT can be carried out using a dehydrogenation catalyst known in the literature. Of course, the method for 1,5-DMT can also be applied.

[0017] On the other hand, a method of using a supported platinum catalyst as a gas-phase dehydrogenation catalyst (for example, see Patent Document 14) and a method of dehydrogenating 1,4-DMT by controlling specific impurities (for example, see Patent Document 18) are disclosed.

[0018] As a method for purifying 1,4-DMN, there is known a method for separating 1,3-DMN from a mixture of 1,4-DMN and 2,3-dimethylnaphthalene (hereinafter also referred to as "2,3-DMN") by adsorption (for example, see Patent Document 19). However, the method of Patent Document 19 has the disadvantages of only obtaining a mixture of 1,4-DMN and 2,3-DMN and a low removal rate of 1,3-DMN.

[0019] A method of separating 1,4-DMN by removing isomers from a dimethylnaphthalene mixture using an adsorbent has been proposed (see, for example, Patent Document 20). However, the industrial efficiency is poor because an adsorbent having a volume three times or more of that of dimethylnaphthalene is used.

[0020] Prior art literature

[0021] Patent Literature

[0022] Patent Document 1: Korean Patent Application Publication No. 2007-0099241

[0023] Patent Document 2: U.S. Patent Application Publication No. 2007 / 0232842

[0024] Patent Document 3: Japanese Patent Application Laid-Open No. 7-61941

[0025] Patent Document 4: Japanese Patent No. 3-500052

[0026] Patent Document 5: U.S. Patent No. 5,034,561

[0027] Patent Document 6: Japanese Patent Application Laid-Open No. 5-213782

[0028] Patent Document 7: Japanese Patent Application Laid-Open No. 49-9348

[0029] Patent Document 8: Japanese Patent Application Laid-Open No. 2000-239194

[0030] Patent Document 9: Japanese Patent Application Laid-Open No. 6-72910

[0031] Patent Document 10: Japanese Patent Application Laid-Open No. 60-27694

[0032] Patent Document 11: Japanese Patent Application Laid-Open No. 48-67261

[0033] Patent Document 12: U.S. Patent No. 3781375

[0034] Patent Document 13: Japanese Patent Application Laid-Open No. 48-75557

[0035] Patent Document 14: U.S. Patent No. 3775497

[0036] Patent Document 15: U.S. Patent No. 5,284,987

[0037] Patent Document 16: U.S. Patent No. 4,950,825

[0038] Patent Document 17: U.S. Patent No. 5,401,892

[0039] Patent Document 18: Japanese Patent Application Laid-Open No. 7-69942

[0040] Patent Document 19: Japanese Patent Application Laid-Open No. 2006-199689

[0041] Patent Document 20: Japanese Patent Application Laid-Open No. 62-240632 Summary of the invention

[0042] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an industrial production method for isomers, particularly 1,4-DMN having a low content of 1,3-DMN.

[0043] The present inventors have conducted research and found that 1,4-DMN produced by cyclodehydrogenation of PH contains a large amount of 1,3-DMN, which is an isomer. However, since the boiling point difference between 1,4-DMN and 1,3-DMN is small, it is extremely difficult to separate 1,3-DMN from 1,4-DMN by distillation (see Table 1 below).

[0044] [Table 1]

[0045]

[0046] It is known that 1,4-DMN is easily isomerized to 1,3-DMN and 2,3-DMN under the action of an acid catalyst (see, for example, U.S. Patent No. 5118892). Therefore, the isomerization of 1,4-DMN is considered to be the cause of the formation of 1,3-DMN. However, in the experiment, the present inventors failed to reduce 1,3-DMN in 1,4-DMN even when dehydrogenating 1,4-DMT using a catalyst that does not have isomerization activity.

[0047] The inventors of the present invention conducted further research and found that in addition to a trace amount of 1,3-DMN, a considerable amount of 1,3-DMT is present in 1,4-DMT produced by the cyclization reaction of PH. The amount of 1,3-DMN in 1,4-DMT is very small (less than 0.01% relative to 1,4-DMT) and cannot be said to be the causal substance of 1,3-DMN in 1,4-DMN. It was found that 1,3-DMT is converted into 1,3-DMN by dehydrogenation, so 1,3-DMN in 1,4-DMN originates from 1,3-DMT in 1,4-DMT.

[0048]

[0049] That is, the present inventors have found that 1,3-DMT in 1,4-DMT is produced in the cyclization step of PH and is the causal substance of 1,3-DMN in 1,4-DMN, thereby completing the present invention.

[0050] One embodiment of the present invention is a method for producing 1,4-DMN, comprising cyclizing PH in the presence of an acid catalyst to produce crude 1,4-DMT, and dehydrogenating the crude 1,4-DMN to obtain crude 1,4-DMN and refining the crude 1,4-DMN by distillation, wherein the concentration of 1,3-DMT in 1,4-DMT is 1.0% or less relative to 1,4-DMT.

[0051] According to the present invention, it is possible to provide an industrial method for producing isomers, particularly 1,4-DMN having a low content of 1,3-DMN. DETAILED DESCRIPTION

[0052] In this embodiment, PH can be prepared by any method, and is usually obtained by reacting ethylbenzene (1) with 1,3-butadiene (2) in the presence of a basic catalyst (e.g., an alkali metal such as metallic sodium or metallic potassium). This PH is not a pure product, and may contain isomers 5-phenyl-1-hexene (5-Phenyl-1-hexene) and ethylbenzene (etc.) as a solvent, or water.

[0053]

[0054] After removing the alkaline catalyst from the reaction solution, the pH concentration is increased directly or by distillation, and then cyclization is carried out under the action of an acid catalyst to synthesize 1,4-DMT. The cyclization reaction can be carried out intermittently, continuously or semi-continuously under gas phase or liquid phase conditions in the presence of an acid catalyst. The reaction can be carried out under reduced pressure, normal pressure or pressurized conditions.

[0055] The cyclization catalyst can use an isomerization catalyst known in the literature. For example, sulfonic acids such as hydrogen chloride, sulfuric acid, phosphoric acid, hydrogen fluoride, p-toluenesulfonic acid, and other solid acids such as silicon dioxide-alumina can be mentioned. In the case of liquid phase reaction, since it is easy to separate from the cyclization reaction liquid, the catalyst is preferably a solid acid catalyst.

[0056] As the solid acid catalyst, a known isomerization catalyst such as acid clay, solid phosphate, zeolite (crystalline silica-alumina), amorphous silica-alumina, silica-magnesia, silica-calcia, etc. can be used as a cyclization catalyst.

[0057] The present inventors have conducted studies and found that the higher the acidity of the cyclization catalyst and the higher the reaction temperature under the same catalyst, the easier it is for the cyclization reaction to proceed, and 1,3-DMT and other byproducts are likely to be produced in addition to the target substance 1,4-DMT.

[0058] Zeolite catalysts, which are mostly used in cyclization reactions, are good cyclization catalysts, but have the disadvantage of being easy to generate the above-mentioned byproducts due to their high acidity. Zeolite can also be treated with alkali or the like to adjust the acidity, but it is difficult to adjust the acidity. In other words, in order to suppress byproducts such as 1,3-DMT, it is preferred to react gently. By adjusting the catalyst amount, reaction temperature, reaction time, etc. by the acidity of the catalyst, byproducts such as 1,3-DMT can be suppressed.

[0059] The present inventors have conducted studies and found that an amorphous silica-alumina catalyst is preferable from the viewpoint of suppressing the production amount of 1,3-DMT to a low level while maintaining a high reaction rate.

[0060] The amorphous silica-alumina catalyst includes, for example, a catalyst having a composition by mass ratio of SiO2 / Al2O3=8 to 2. Examples thereof include N631L, N631HN, N632L, N632HN, N633L, and N633HN manufactured by JGC Catalysts & Chemicals Co., Ltd.

[0061] As described above, although there are differences in concentration of 1,4-DMT, which is a cyclization product of PH, due to the cyclization conditions, all contain a trace amount of 1,3-DMN and a considerable amount of 1,3-DMT as impurities.

[0062] Among these impurities, 1,3-DMN is a trace amount and is not the main cause of 1,3-DMN in 1,4-DMN. In addition, 1,3-DMN and 1,4-DMT have different boiling points and can be separated by distillation as needed. However, since there is no difference in boiling point between 1,3-DMT and 1,4-DMT, it is extremely difficult to separate by distillation (see Table 1 above). As mentioned above, since there is no difference in boiling point between 1,4-DMN and 1,3-DMN, it is difficult to separate by distillation after the dehydrogenation reaction. That is, in order to reduce 1,3-DMN in 1,4-DMN, it is preferred to reduce 1,3-DMT in 1,4-DMT.

[0063] When amorphous silica-alumina catalyst is used in the liquid phase cyclization reaction, the addition amount (mass) is preferably 0.02% to 10% relative to pH, more preferably 0.1% to 5%, the reaction temperature is preferably 50°C to 220°C, more preferably 100°C to 200°C, and the reaction time is preferably 1 hour to 72 hours, more preferably 2 hours to 48 hours. The amount of catalyst can be a lot, but the cost will become high. When the reaction temperature exceeds 200°C, by-products are easily generated.

[0064] In the liquid phase reaction, for example, when p-toluenesulfonic acid is used as a homogeneous catalyst, the amount (mass) added is 0.05% to 10% relative to pH, preferably 0.3% to 5%, the reaction temperature is 100° C. to 200° C., preferably 120° C. to 180° C., and the reaction time is 0.5 hour to 24 hours, preferably 1 hour to 12 hours. When the reaction temperature is below 200° C., by-products are less likely to be generated.

[0065] In the case of gas phase cyclization reaction, a solid acid catalyst with low acidity, such as an amorphous silica-alumina catalyst, can be used to react at 220°C to 260°C, preferably 220°C to 250°C, in the presence or absence of a diluent. In order to reduce the concentration of 1,3-DMT relative to 1,4-DMT, the lower the acidity of the catalyst and the lower the reaction temperature, the better, but there is a disadvantage that the reaction is not easy to proceed. In addition, the shorter the residence time in the catalyst layer, the lower the cyclization rate of pH, and the lower the 1,3-DMT concentration becomes.

[0066] The 1,4-DMT obtained in this way can suppress the concentration of 1,3-DMT to less than 1.0% relative to 1,4-DMT, preferably less than 0.4%. Therefore, even if it is directly dehydrogenated, the concentration of 1,3-DMN in 1,4-DMN can be less than 1.0% relative to 1,4-DMN. The crude 1,4-DMT is preferably purified by distillation. The 1,4-DMT fraction obtained by distillation has less catalyst poisons such as polymers produced in the cyclization process of PH, so it is also easy to reduce the amount of dehydrogenation catalyst used. Of course, it is also easy to remove the trace amount of 1,3-DMN in 1,4-DMT in the distillation process.

[0067] The distillation conditions of 1,4-DMT vary depending on the impurity content, but generally speaking, it can be carried out intermittently, continuously or semi-continuously at reduced pressure, normal pressure or increased pressure using a distillation tower having 5 to 120 stages, preferably 10 to 80 stages, at a reflux ratio of 0.1 to 30, preferably 0.5 to 10. The higher the number of distillation stages or the higher the reflux ratio, the higher the separation efficiency, but there is a disadvantage that the equipment cost and energy consumption increase.

[0068] As the dehydrogenation catalyst of 1,4-DMT, a dehydrogenation catalyst known in the literature, such as a nickel-based catalyst represented by a Raney nickel catalyst and a stabilized nickel catalyst, a cobalt-based catalyst, a noble metal catalyst, etc., can be used. However, from the aspect of activity, a noble metal-supported catalyst, particularly a palladium catalyst supported on activated carbon or a platinum catalyst, is preferred.

[0069] As mentioned above, since 1,4-DMN is easily isomerized, it is preferable to select a dehydrogenation catalyst that does not isomerize the 1,4-DMN generated during the dehydrogenation process.

[0070] In the present invention, the dehydrogenation reaction can be carried out in a liquid phase, under reduced pressure, normal pressure or increased pressure in any of the following ways: intermittent, continuous or semi-continuous. In addition, in order to carry out the dehydrogenation reaction, the reaction can be carried out while blowing an inert gas such as nitrogen or argon, or a reducing substance such as a nitro compound can be added to carry out the dehydrogenation reaction.

[0071] The dehydrogenation can be carried out under the boiling of 1,4-DMT or 1,4-DMN or under the boiling of the solvent by adding a solvent.

[0072] For example, when dehydrogenation is carried out under normal pressure using a catalyst in which 10% palladium is supported on activated carbon, the amount of catalyst added (by mass) is preferably 0.05% to 10% relative to 1,4-DMT, more preferably 0.1% to 5%, the reaction temperature is 80°C to 270°C, more preferably 120°C to 270°C, and the reaction time is 0.5 hours to 72 hours, more preferably 1 hour to 48 hours. The reaction temperature and reaction time vary greatly depending on the activity of the catalyst, the presence or absence of inactive substances, the addition of reducing substances, and the low boiling point solvent.

[0073] After dehydrogenation, the reaction liquid from which the catalyst is separated contains unreacted 1,4-DMT, 5,8-dimethyl-1,2,3,4-tetrahydronaphthalene (hereinafter also referred to as "5,8-DMT"), etc., in addition to 1,4-DMN. Distillation purification is performed to separate them. Distillation is generally performed intermittently, continuously or semi-continuously at a reflux ratio of 1 to 60, preferably 1 to 30, under reduced pressure, normal pressure or increased pressure using a distillation tower having 10 to 120 theoretical stages, preferably 20 to 80 stages. The more distillation stages there are, or the larger the reflux ratio, the better the separation efficiency, but there are disadvantages of increased equipment construction costs and energy consumption.

[0074] By refining by distillation, high-purity 1,4-DMN with a low impurity content can be obtained.

[0075] [Example]

[0076] Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples. It should be noted that all composition % are in mass %.

[0077] [Example 1]

[0078] (Butadiene addition)

[0079] 5.75 kg of ethylbenzene and 25 g of sodium metal as a catalyst were added to a 10-liter reaction vessel, and 735 g of 1,3-butadiene was added at 110°C for 10 hours under stirring. After the addition was completed, water was added to remove the sodium metal. This operation was repeated 4 times to obtain 26 kg of a reaction solution with a pH of 20.4% and 55.8% of ethylbenzene.

[0080] 19.5 kg of the reaction liquid was distilled at a theoretical stage number of 20 and a reflux ratio of 1 to 10 to obtain 10.6 kg of a distillate (PH solution) having a pH of 35% and ethylbenzene of 60%.

[0081] (Cyclization)

[0082] 2.8 kg of the above distillate (35% pH solution) and 12 g of amorphous silica-alumina catalyst (SiO2: 83%, Al2O3: 13%) were placed in a 5-liter flask equipped with a stirrer and a reflux cooler. While stirring, a portion of the distillate (solvent) was removed while continuing to reflux, and the temperature of the reaction liquid was raised to 170° C. over 4 hours and maintained at this temperature for 6 hours.

[0083] The catalyst was filtered out from the reaction liquid to obtain 2.06 kg of crude 1,4-DMT having the following composition and an unreacted pH of 0.5% or less.

[0084] Ethylbenzene: 47%

[0085] 1,4-DMT: 45%

[0086] 1,3-DMT: 0.16%

[0087] (Dehydrogenation)

[0088] 1.0 kg of crude 1,4-DMT and 5.8 g of 10% Pd / C were added to a 2-liter flask equipped with a stirrer and a reflux cooler. While distilling ethylbenzene from the reflux cooler, the temperature was raised to 250°C over 4 hours and maintained at this temperature for 8 hours. The catalyst was filtered out from the reaction solution to obtain 442 g of crude 1,4-DMN having the following composition.

[0089] 1,4-DMN: 93.3%

[0090] 1,4-DMT: 0.9%

[0091] 5,8-DMT: 2.3%

[0092] 1,3-DMN: 0.34%

[0093] (DMN Distillation)

[0094] 440 g of the crude 1,4-DMN was distilled at 100 mmHg and a reflux ratio of 1 to 10 using a distillation column having 40 theoretical stages to obtain 382 g of purified 1,4-DMN having the following composition.

[0095] 1,4-DMN: 98.3%

[0096] 1,4-DMT: 0.4%

[0097] 5,8-DMT: 0.6%

[0098] 1,3-DMN: 0.35%

[0099] [Example 2]

[0100] (DMT distillation)

[0101] 1.0 kg of the crude 1,4-DMT obtained in Example 1 was distilled at 120 mmHg and a reflux ratio of 5 to 20 using a distillation column having 30 theoretical stages to obtain 426 g of purified 1,4-DMT having the following composition.

[0102] 1,4-DMT: 98.2%

[0103] 1,3-DMT: 0.35%

[0104] (Dehydrogenation)

[0105] 400 g of purified 1,4-DMT and 2.4 g of 10% Pd / C were added to a 500 ml flask equipped with a stirrer and a reflux cooler, and the temperature was raised to 250°C over 4 hours while refluxed, and maintained at this temperature for 8 hours. The catalyst was filtered out from the reaction solution to obtain 382 g of crude 1,4-DMN with the following composition.

[0106] 1,4-DMN: 97.4%

[0107] 1,4-DMT: 0.9%

[0108] 5,8-DMT: 1.9%

[0109] 1,3-DMN: 0.35%

[0110] (DMN Distillation)

[0111] 370 g of crude 1,4-DMN was distilled in the same manner as in Example 1 to obtain 342 g of purified 1,4-DMN having the following composition.

[0112] 1,4-DMN: 98.1%

[0113] 1,4-DMT: 0.4%

[0114] 5,8-DMT: 0.6%

[0115] 1,3-DMN: 0.35%

[0116] [Example 3]

[0117] (Cyclization)

[0118] Into a 2-liter flask equipped with a stirrer and a reflux cooler, 1.4 kg of the 35% pH solution (distillate) of Example 1 and 6 g of the same amorphous silica-alumina catalyst as in Example 1 were placed. While stirring, a portion of the distillate (solvent) was removed while continuing to reflux, and the temperature of the reaction solution was raised to 200° C. over 4 hours and maintained at that temperature for 6 hours.

[0119] The catalyst was filtered out from the reaction solution to obtain 714 g of crude 1,4-DMT having an unreacted pH of 0.5% or less.

[0120] Ethylbenzene: 17%

[0121] 1,4-DMT: 63%

[0122] 1,3-DMT: 0.46%

[0123] (DMT distillation)

[0124] 700 g of crude 1,4-DMT was distilled at 120 mmHg and a reflux ratio of 5 to 20 using a distillation column having 30 theoretical stages to obtain 410 g of purified 1,4-DMT having the following composition.

[0125] 1,4-DMT: 97.8%

[0126] 1,3-DMT: 0.71%

[0127] (Dehydrogenation)

[0128] 400 g of purified 1,4-DMT and 3.0 g of 10% Pd / C were added to a 500 ml flask equipped with a stirrer and a reflux cooler. The temperature was raised to 250°C over 3 hours while distilling off low boiling point components from the reflux cooler, and the temperature was maintained for 8 hours. The catalyst was filtered out from the reaction solution to obtain 380 g of crude 1,4-DMN having the following composition.

[0129] 1,4-DMN: 96.3%

[0130] 1,4-DMT: 0.5%

[0131] 5,8-DMT: 1.3%

[0132] 1,3-DMN: 0.70%

[0133] (DMN Distillation)

[0134] 370 g of the crude 1,4-DMN was distilled at 100 mmHg and a reflux ratio of 1 to 10 using a distillation column having 40 theoretical stages to obtain 322 g of purified 1,4-DMN having the following composition.

[0135] 1,4-DMN: 97.7%

[0136] 1,4-DMT: 0.2%

[0137] 5,8-DMT: 0.4%

[0138] 1,3-DMN: 0.71%

[0139] [Example 4]

[0140] (Cyclization)

[0141] Into a 2-liter flask equipped with a stirrer and a reflux cooler, 1 kg of the 35% pH solution (distillate) of Example 1, 300 g of ethylbenzene and 10 g of p-toluenesulfonic acid were placed. While stirring, a portion of the distillate (solvent) was removed while continuing to reflux, and the temperature of the reaction solution was raised to 154° C. over 4 hours, and maintained at this temperature for 3 hours.

[0142] The catalyst was filtered out from the reaction solution to obtain 950 g of crude 1,4-DMT having an unreacted pH of 0.5% or less.

[0143] Ethylbenzene: 57%

[0144] 1,4-DMT: 32%

[0145] 1,3-DMT: 0.16%

[0146] (DMT distillation)

[0147] 700 g of crude 1,4-DMT was distilled using a distillation column having 30 theoretical stages at 120 mmHg and a reflux ratio of 5 to 20 to obtain 225 g of purified 1,4-DMT having the following composition.

[0148] 1,4-DMT: 97.1%

[0149] 1,3-DMT: 0.49%

[0150] (Dehydrogenation)

[0151] 200 g of purified 1,4-DMT and 1.5 g of 10% Pd / C were added to a 500 ml flask equipped with a stirrer and a reflux cooler. The temperature was raised to 250°C over 3 hours while distilling off low boiling point components from the reflux cooler, and the temperature was maintained for 8 hours. The catalyst was filtered out from the reaction solution to obtain 190 g of crude 1,4-DMN having the following composition.

[0152] 1,4-DMN: 96.5%

[0153] 1,4-DMT: 0.4%

[0154] 5,8-DMT: 1.2%

[0155] 1,3-DMN: 0.49%

[0156] (DMN Distillation)

[0157] 180 g of the crude 1,4-DMN was distilled at 100 mmHg and a reflux ratio of 1 to 10 using a distillation column having 10 theoretical stages to obtain 171 g of purified 1,4-DMN having the following composition.

[0158] 1,4-DMN: 97.6%

[0159] 1,4-DMT: 0.2%

[0160] 5,8-DMT: 0.9%

[0161] 1,3-DMN: 0.49%

[0162] [Comparative Example 1]

[0163] (Cyclization)

[0164] Into a 2-liter flask equipped with a stirrer and a reflux cooler, 1.4 kg of the 35% pH solution (distillate) of Example 1 and 6 g of the same amorphous silica-alumina catalyst as in Example 1 were added. Under stirring, a portion of the distillate (solvent) was removed while continuing to reflux, and the temperature of the reaction liquid was raised to 210° C. over 2 hours, and then slowly raised to 220° C. over 2 hours. This temperature was maintained for 6 hours.

[0165] The catalyst was filtered out from the reaction liquid to obtain 539 g of crude 1,4-DMT having the following composition and an unreacted pH of 0.5% or less.

[0166] Ethylbenzene: <1%

[0167] 1,4-DMT: 79%

[0168] 1,3-DMT: 1.27%

[0169] (DMT distillation)

[0170] 520 g of crude 1,4-DMT was distilled at 120 mmHg and a reflux ratio of 5 to 20 using a distillation column having 30 theoretical stages to obtain 381 g of purified 1,4-DMT having the following composition.

[0171] 1,4-DMT: 96.6%

[0172] 1,3-DMT: 1.55%

[0173] (Dehydrogenation)

[0174] 350 g of purified 1,4-DMT and 3.0 g of 10% Pd / C were added to a 500 ml flask equipped with a stirrer and a reflux cooler. The temperature was raised to 250°C over 3 hours while distilling off low boiling point components from the reflux cooler, and the temperature was maintained for 8 hours. The catalyst was filtered out from the reaction solution to obtain 324 g of crude 1,4-DMN having the following composition.

[0175] 1,4-DMN: 92.1%

[0176] 1,4-DMT: 0.7%

[0177] 5,8-DMT: 2.3%

[0178] 1,3-DMN: 1.48%

[0179] (DMN Distillation)

[0180] 300 g of the crude 1,4-DMN was distilled at 100 mmHg and a reflux ratio of 1 to 10 using a distillation column having 40 theoretical stages to obtain 251 g of purified 1,4-DMN having the following composition.

[0181] 1,4-DMN: 96.5%

[0182] 1,4-DMT: 0.3%

[0183] 5,8-DMT: 0.6%

[0184] 1,3-DMN: 1.55%

[0185] [Comparative Example 2]

[0186] (Cyclization)

[0187] Into a 2-liter flask equipped with a stirrer and a reflux cooler, 1.4 kg of the 35% pH solution (distillate) of Example 1 and 6 g of a Y-type zeolite catalyst (JVK Catalysts, H-Y type) were added. While stirring, a portion of the distillate (solvent) was removed while continuing to reflux, and the temperature of the reaction liquid was raised to 170°C over 4 hours, and maintained at this temperature for 6 hours.

[0188] The catalyst was filtered out from the reaction solution to obtain 1.03 kg of crude 1,4-DMT having an unreacted pH of 0.5% or less.

[0189] Ethylbenzene: 45%

[0190] 1,4-DMT: 43%

[0191] 1,3-DMT: 0.61%

[0192] [Comparative Example 3]

[0193] (Cyclization)

[0194] Into a 2-liter flask equipped with a stirrer and a reflux cooler, 1 kg of the 35% pH solution (distillate) of Example 1, 300 g of ethylbenzene and 10 g of p-toluenesulfonic acid were placed. While stirring, a portion of the distillate (solvent) was removed while continuing to reflux, and the temperature of the reaction solution was raised to 210° C. over 4 hours, and maintained at this temperature for 3 hours.

[0195] The catalyst was filtered out from the reaction solution to obtain 355 g of crude 1,4-DMT having an unreacted pH of 0.5% or less.

[0196] Ethylbenzene: 5%

[0197] 1,4-DMT: 77%

[0198] 1,3-DMT: 1.37%

[0199] It can be seen from the examples that the ratio of 1,4-DMN to 1,3-DMN is determined by the ratio of 1,4-DMT to 1,3-DMT in the 1,4-DMN raw material. 1,3-DMT is generated in the cyclization step of PH, and the more severe the cyclization conditions, the easier it is to generate 1,3-DMT.

[0200] Therefore, in order to reduce the concentration of 1,3-DMN in purified 1,4-DMN, it is important to reduce the ratio of 1,3-DMT to 1,4-DMT by pH cyclization under mild conditions (acidity of the catalyst, amount of the catalyst, temperature, time, etc.).

Claims

1. A method for producing 1,4-dimethylnaphthalene, comprising cyclizing 5-phenyl-2-hexene in the presence of an acid catalyst to produce crude 1,4-dimethyl-1,2,3,4-tetrahydronaphthalene, and distilling and refining the crude 1,4-dimethylnaphthalene obtained by dehydrogenating the crude 1,4-dimethylnaphthalene, wherein the concentration of 1,3-dimethyl-1,2,3,4-tetrahydronaphthalene in 1,4-dimethyl-1,2,3,4-tetrahydronaphthalene is 1.0% or less relative to 1,4-dimethyl-1,2,3,4-tetrahydronaphthalene, and the ratio of 1,3-dimethylnaphthalene to 1,4-dimethylnaphthalene in 1,4-dimethylnaphthalene is 1.0% or less; The cyclization is a liquid phase cyclization reaction; In the liquid phase cyclization reaction, an amorphous silica-alumina catalyst is used as an acid catalyst, the mass addition amount is 0.02% to 10% relative to 5-phenyl-2-hexene, the reaction temperature is 100°C to 200°C, and the amorphous silica-alumina catalyst is SiO 2 / Al 2 O 3 =2~8.

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