Method for preparing high-purity 2-methyl-6-acylnaphthalene and 2-methyl-7-acylnaphthalene through continuous catalytic reaction and rectification purification and application of high-purity 2-methyl-6-acylnaphthalene and 2-methyl-7-acylnaphthalene

Abstract

The invention discloses a method for preparing high-purity 2-methyl-6-acylnaphthalene and 2-methyl-7-acylnaphthalene through continuous catalytic reaction and rectification purification and application of the high-purity 2-methyl-6-acylnaphthalene and the 2-methyl-7-acylnaphthalene. According to the method, high-purity 2, 6-and 2, 7-acyl naphthalene products can be obtained through fixed bed catalytic synthesis, rectification and crystallization purification, firstly, the molecular sieve catalyst is modified, the catalytic conversion rate and selectivity can be further improved, the formed catalyst is suitable for fixed bed acylation synthesis reaction, the catalyst activity in a catalytic system is high, and the catalytic efficiency is high. The used catalyst can be reused after regeneration treatment. The fixed bed catalytic reaction system, the product and the catalyst can realize solid-liquid separation without hydrolysis quenching, a large amount of acidic wastewater is not generated, the fixed bed catalytic reaction system is environment-friendly, in addition, unreacted 2-methylnaphthalene in a rectification system is recycled, a target object can be purified through rectification and crystallization, a high-purity product is obtained, and the fixed bed catalytic reaction system has a good application prospect.

Description

Technical Field

[0001] The invention relates to the technical field of fine chemical preparation, and in particular to a method for preparing high-purity 2-methyl-6-acylnaphthalene and 2-methyl-7-acylnaphthalene by continuous catalytic reaction and rectification and purification, and application thereof. Background Art

[0002] 2-Methyl-6-acylnaphthalene is an important organic chemical raw material. Polyethylene naphthalate (PEN) obtained by polymerization of its oxidation product with ethylene glycol is a polyester compound with superior chemical and physical properties than polyethylene terephthalate (PET). PEN has broad application prospects in the fields of fibers, films, packaging containers and electronic components.

[0003] 2-Methyl-6-acylnaphthalene is prepared from 2-methylnaphthalene by Friedel-Crafts acylation. Affected by the Friedel-Crafts reaction conditions, the acyl group will be substituted at different positions of 2-methylnaphthalene to generate 2-methyl-6-acylnaphthalene, 2-methyl-7-acylnaphthalene and five other isomers. In addition to 2-methyl-6-acylnaphthalene, its high-purity byproduct 2-methyl-7-acylnaphthalene also has a certain market value. Using Lewis acid catalyst, affected by steric hindrance and group effects, the target product is mainly 2-methyl-6-acylnaphthalene. The research mainly focuses on how to produce 2-methyl-6-acylnaphthalene with high selectivity and separate and purify it to obtain high-purity and high-yield 2-methyl-6-acylnaphthalene. Using a solid-supported molecular sieve catalyst, the products are mainly 2-methyl-6-acylnaphthalene and 2-methyl-7-acylnaphthalene, which are affected by the pore selectivity. The research focuses on how to improve the yield and selectivity of the reaction and how to purify high-purity and high-yield 2-methyl-6-acylnaphthalene and 2-methyl-7-acylnaphthalene. The reaction products at the front end determine the subsequent separation and purification methods. At present, there are few studies on the preparation of high-purity 2-methyl-6-acylnaphthalene and 2-methyl-7-acylnaphthalene based on fixed-bed catalytic reactions. Summary of the invention

[0004] The present invention aims to solve one of the technical problems in the related art at least to a certain extent.

[0005] To this end, an embodiment of the present invention provides a method and application for preparing high-purity 2-methyl-6-acylnaphthalene and 2-methyl-7-acylnaphthalene by continuous catalytic reaction and distillation purification.

[0006] In a first aspect, the present invention provides a method for preparing high-purity 2-methyl-6-acylnaphthalene and 2-methyl-7-acylnaphthalene by continuous catalytic reaction and distillation purification, comprising the following steps:

[0007] (a) under the conditions of a catalyst, the raw materials 2-methylnaphthalene and butyric anhydride are continuously catalytically reacted in a fixed bed reactor to obtain an acylated product;

[0008] (b) fractionating the acylated product under reduced pressure in a distillation tower to obtain a distillation target product;

[0009] (c) melt crystallizing the rectification target product to obtain a crude product of 2-methyl-6-acylnaphthalene and a crude product of 2-methyl-7-acylnaphthalene;

[0010] (d) the crude product of the 2-methyl-6-acylnaphthalene and the crude product of the 2-methyl-7-acylnaphthalene are respectively subjected to solvent recrystallization to obtain high-purity 2-methyl-6-acylnaphthalene and high-purity 2-methyl-7-acylnaphthalene.

[0011] In the step (a), a suitable catalyst is used to carry out a fixed bed reaction, so that continuous and efficient production can be achieved, and mainly an acylation product rich in 2-methyl-6-acylnaphthalene and 2-methyl-7-acylnaphthalene is obtained.

[0012] Furthermore, the catalyst is obtained by in-situ encapsulating phosphotungstic acid on a hydrogen-type beta molecular sieve.

[0013] The hydrogen-type β molecular sieve has a large specific surface area and selective pore selectivity. The phosphotungstic acid catalyst has low hydrothermal stability and a small specific surface area. Loading the phosphotungstic acid catalyst on the hydrogen-type β molecular sieve can not only expand the contact surface between the phosphotungstic acid catalyst and the reaction system, but also improve the reaction activity. At the same time, the phosphotungstic acid loaded in the molecular sieve pores further modifies the pore configuration, which is beneficial to the selective selectivity of the molecular sieve. In addition, the active component is loaded in the molecular sieve pores using in-situ synthesized phosphotungstic acid, which avoids the problem of rapid loss of phosphotungstic acid on the loaded catalyst prepared by the conventional impregnation method and increases the life of the catalyst.

[0014] The in-situ encapsulation is a process of synthesizing phosphotungstic acid directly on the molecular sieve, and the loading amount of phosphotungstic acid is below 30% to avoid blocking of the molecular sieve pores when the loading amount is too high.

[0015] Furthermore, the preparation process of the catalyst includes:

[0016] S1: adding hydrogen-type β molecular sieve, disodium hydrogen phosphate and sodium tungstate in a molar ratio of 1:12 into deionized water and stirring to mix evenly to obtain a slurry;

[0017] S2: adding an acidic solution to adjust the pH value of the slurry to below 3, and reflux with stirring;

[0018] S3: After centrifugal washing, drying and calcining are performed to obtain a supported phosphotungstic acid catalyst powder, which is then molded to obtain a molded supported phosphotungstic acid catalyst.

[0019] In step S1, disodium hydrogen phosphate and sodium tungstate react in a molar ratio of 1:12 to produce phosphotungstic acid, avoiding the generation of other by-products. The purpose of stirring is to mix the materials evenly, and stirring at room temperature for more than 4 hours is sufficient. In addition, it is understandable that the stirring rate can be selected according to the specific situation. In the preparation process of the catalyst, disodium hydrogen phosphate and sodium tungstate are used to react in situ on a molecular sieve to prepare phosphotungstic acid, so that the phosphotungstic acid is encapsulated in situ on the molecular sieve, avoiding the problem of rapid loss of phosphotungstic acid and improving the life of the catalyst.

[0020] In step S2, the reflux stirring temperature is 80-90°C for more than 4 hours. The reflux stirring process is the process of in-situ encapsulation of phosphotungstic acid on the molecular sieve, and the reflux stirring temperature is 80-90°C, which increases the reaction rate while ensuring that the slurry does not boil.

[0021] In step S3, the drying temperature is 100-120°C, and the drying time is more than 12 hours; the calcination temperature is below 300°C, and the calcination time is more than 3 hours. The purpose of drying is to remove part of the water first to avoid the influence of direct calcination on the structure of the molecular sieve. During calcination, the temperature is kept below 300°C, so that the phosphotungstic acid loaded on the molecular sieve maintains a Keggin-type structure, which has high acidity and catalytic activity, avoiding the influence of excessively high calcination temperature on the structure of the phosphotungstic acid, thereby further avoiding the decrease in the activity of the catalyst.

[0022] In addition, in step S3, the molding process of the supported phosphotungstic acid catalyst can adopt the currently available molding method.

[0023] Furthermore, the molar ratio of the 2-methylnaphthalene to the butyric anhydride is 2:1.

[0024] The fixed bed reaction process strictly controls the molar ratio of 2-methylnaphthalene to the butyric anhydride to be 2:1. When the molar ratio of 2-methylnaphthalene to butyric anhydride is 2:1, the conversion rate of butyric anhydride is high, the monoacylation selectivity is 100%, and the selectivity of 2,6-position is also high in various isomers. If the butyric anhydride is excessive, the excess butyric anhydride is adsorbed on the active center of the catalyst to form excess acyl carbon cations, so that the local excess carbon cations continue to attack the aromatic carbon atoms of the complex intermediate, and a series of reactions are likely to form diacylated products, which reduces the reaction activity; if the 2-methylnaphthalene is excessive, the dilution effect of β-methylnaphthalene on the system is obvious, the activity of the reaction system decreases, and the excess β-methylnaphthalene will undergo an isomerization reaction to generate a small amount of 1-methylnaphthalene. The reaction temperature is controlled at about 200°C, and the reaction time is controlled at about 10h to ensure that the raw materials are fully reacted under a slight positive pressure.

[0025] Furthermore, the temperature of the melting crystallization of the distillation target product is 40-60°C.

[0026] Furthermore, the temperature of the melting crystallization of the distillation target product is 45-55°C.

[0027] Since the melting point of 2-methyl-6-butyrylnaphthalene is 41.6-42.5°C and the melting point of 2-methyl-7-butyrylnaphthalene is 70.7-71.5°C, the temperature of the melt crystallization of the crude target product of the distillation is controlled to be 40-60°C, and further to be 45-55°C.

[0028] Furthermore, the distillation pressure in the distillation tower is 2.6-3.9 kPa, the reflux ratio is 10:1, and segmented temperature-controlled distillation is adopted during the distillation process.

[0029] Furthermore, the solvent for the solvent recrystallization is an aqueous solution of one or more of C5-C10 alkanes, C5-C10 cycloalkanes, or one or more of C1-C6 alcohols.

[0030] In some embodiments, the solvent is 85% methanol in water.

[0031] Furthermore, the purity of the high-purity 2-methyl-6-acylnaphthalene and the high-purity 2-methyl-7-acylnaphthalene is above 99%.

[0032] In a second aspect, the present invention proposes the use of the method proposed in the first aspect in the preparation of high-purity 2-methyl-6-acylnaphthalene and 2-methyl-7-acylnaphthalene by fixed bed catalytic reaction.

[0033] Compared with the prior art, the beneficial effects of the present invention are:

[0034] The present invention loads a phosphotungstic acid catalyst with low hydrothermal stability and small specific surface area on a beta molecular sieve catalyst carrier with a large surface and selective pore channel selectivity, which can increase the catalyst reaction activity and further modify the pore channel configuration to facilitate the selectivity of the molecular sieve. The molecular sieve catalyst system avoids the generation of acidic wastewater in a traditional Lewis acid catalytic system, can efficiently achieve solid-liquid separation, and the rear end is coupled with vacuum fractionation, melt crystallization and solvent recrystallization purification sections to obtain high-purity 2-methyl-6-acylnaphthalene and 2-methyl-7-acylnaphthalene.

[0035] The present invention provides a relatively green and environmentally friendly catalytic reaction system and separation and purification process. The catalytic system can be used in a fixed bed reactor, can simplify the reaction steps, improve atom economy, reduce pollution, and efficiently obtain high-purity 2-methyl-6-acylnaphthalene and 2-methyl-7-acylnaphthalene.

[0036] The present invention can obtain high-purity 2,6- and 2,7-acyl naphthalene products through fixed-bed catalytic synthesis, distillation and crystallization purification. First, the molecular sieve catalyst is modified to further improve the catalytic conversion rate and selectivity. The formed catalyst is suitable for fixed-bed acylation synthesis reaction. The catalyst activity is high in the catalytic system, and the used catalyst can be reused after regeneration. In the fixed-bed catalytic reaction system, the product and the catalyst can achieve solid-liquid separation without hydrolysis quenching, and a large amount of acidic wastewater is not generated, which is environmentally friendly. In addition, the unreacted 2-methylnaphthalene in the distillation system is returned for recycling, and the target product can be purified by distillation and crystallization to obtain a high-purity product, which has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

[0038] Figure 1 The present invention is a process flow chart of a method for preparing high-purity 2-methyl-6-acylnaphthalene and 2-methyl-7-acylnaphthalene by continuous catalytic reaction and rectification purification;

[0039] Figure 2 Schematic diagram of the continuous catalytic reaction and vacuum fractionation process of Example 2;

[0040] Figure 3 This is a schematic diagram of the process of melt crystallization and solvent recrystallization in Example 2;

[0041] Figure 4 This is a chromatogram comparison of the target product of distillation in Example 2, the product obtained after melt crystallization and solvent recrystallization. DETAILED DESCRIPTION

[0042] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0043] The process flow of the preparation method of the supported phosphotungstic acid catalyst of the present invention is as follows: Figure 1 As shown, Figure 1 The process flow shown is not described in detail here.

[0044] The following is a detailed description in conjunction with the examples and comparative examples. All chemical raw materials used are commercially available industrial products, methylnaphthalene is purchased from Maclean, purity> 97%; butyric anhydride is purchased from Sinopharm, purity 98%; Hβ molecular sieve is purchased from Tianjin Nankai Catalyst Factory, silicon-aluminum ratio (molar ratio) 25:1, Na content less than 0.5%. Sodium tungstate, disodium hydrogen phosphate, nitric acid, etc. are all purchased from Sinopharm.

[0045] The test materials and reagents used in the following examples, unless otherwise specified, can be obtained from commercial sources.

[0046] Example 1

[0047] Preparation of catalyst:

[0048] Weigh 10.000g of hydrogen β molecular sieve, 0.265g of disodium hydrogen phosphate dihydrate and 5.881g of sodium tungstate dihydrate (the molar ratio of P (disodium hydrogen phosphate) to W (sodium tungstate) is 1:12) and add them into 200mL of deionized water, stir at room temperature for 4h, then add 3mol / L hydrochloric acid to pH=2.0, reflux the slurry at 90℃ with stirring for 4h, then filter and centrifuge to wash, wash the phosphotungstic acid on the surface of the molecular sieve, after the sample is at 110℃ for 15h, calcine at 280℃ for 3h, cool and grind to obtain the modified molecular sieve powder, shape the modified molecular sieve, and prepare a clover-shaped catalyst suitable for fixed bed for use.

[0049] It is understandable that the molding process of the modified molecular sieve powder can adopt existing methods. In some embodiments, the molding process is:

[0050] The modified molecular sieve powder, peptizing agent, binder and deionized water are mixed and put into a kneading machine to knead into a blank; the obtained blank is sealed with a plastic film and aged at room temperature for 10 hours, and then the blank is put into an extruder for extrusion molding, and the mold is a clover-shaped mold; the molded blank is shaped and dried at room temperature for 24 hours, and then placed in an oven at 100°C for 2 hours, and finally baked at 300°C for 6 hours to obtain a molded supported phosphotungstic acid catalyst. Among them, the peptizing agent can be at least one of nitric acid, acetic acid, and citric acid. In this embodiment, nitric acid is used, and the binder is SB powder.

[0051] In the process of preparing the catalyst, the molded blank is first dried at room temperature for 24 hours to shape and remove some moisture, and then placed in an oven at 100°C for 2 hours to remove some moisture. Both of these processes of removing moisture are done at low temperatures to avoid the effect of temperature on the molecular sieve structure. The calcination process temperature is below 300°C, so that the phosphotungstic acid loaded on the molecular sieve maintains a Keggin-type structure, which has high acidity and high catalytic activity.

[0052] Example 2

[0053] The acylation synthesis reaction was carried out in a 10 mL fixed bed reactor. 10 mL of the catalyst prepared in Example 1 was loaded at both ends of the constant temperature section with inert alumina ceramic balls. The catalyst bed was heated to 200° C. under nitrogen protection. Then, a mixed solution of 2-methylnaphthalene and butyric anhydride was input into the fixed bed reactor. The molar ratio of 2-methylnaphthalene to butyric anhydride in the mixed raw material was 2:1. The reaction temperature was controlled at 200° C. and the liquid hourly space velocity was 1.0 h -1 The acylation reaction is carried out, and the product is cooled to room temperature by air heat exchange to obtain the acylated product. Figure 2 As shown, the raw material tank A contains 2-methylnaphthalene, the raw material tank A is maintained at about 50°C, and the raw material tank B contains butyric anhydride. Before the reaction starts, 2-methylnaphthalene and butyric anhydride are transported to the raw material mixing tank at a molar ratio of 2:1 and stirred and mixed evenly. After the reaction starts, the mixed raw materials are transported to the fixed bed reactor for continuous catalytic reaction under catalyst conditions. The acylated product prepared in the fixed bed reactor is stored in a storage tank. A small amount of acylated product is taken for gas chromatography analysis. Due to the excess of 2-methylnaphthalene, based on butyric anhydride, the conversion rate of butyric anhydride is 95%, the selectivity of 2-methyl-6-butyrylnaphthalene is 67%, the selectivity of 2-methyl-7-butyric anhydride is 31%, and the generation of other isomers is less than 2%. The conversion rate and selectivity are calculated using the peak area percentage method and a calculation formula. The conversion rate of butyric anhydride is the ratio of the amount of butyric anhydride reacted to the amount of butyric anhydride added. The selectivity of 2-methyl-6-butyrylnaphthalene is the ratio of the amount of 2-methyl-6-acylnaphthalene in the product to the amount of all methylbutyrylnaphthalene isomers in the product. The selectivity of 2-methyl-7-butyrylnaphthalene is the ratio of the amount of 2-methyl-7-acylnaphthalene in the product to the amount of all methylbutyrylnaphthalene isomers in the product.

[0054] The acylated product in the storage tank is added to the distillation tower, and about 100g of distillation raw materials are added to the initial distillation still. The distillation pressure is 2.6-3.9kPa, and the reflux ratio is 10:1. The temperature of the storage tank, the feed pipe, the lower part of the tower, the lower part of the tower, the lower part of the tower, the lower part of the tower, the upper part of the tower, and the reflux pipe are controlled at 100℃, 160℃, 100℃, and 90℃. The reaction by-products of the distillation tower are taken out, such as n-butyric acid and a small amount of unreacted butyric anhydride, and the unreacted raw material 2-methylnaphthalene is taken out from the upper part of the middle of the distillation tower. This stream of material is returned for reuse, and the acylated crude product is taken out from the upper part of the distillation tower for back-end melt crystallization separation and purification. The bottom of the distillation tower adopts forced circulation to avoid high-temperature polycondensation of the bottom material. After the vacuum distillation, the target distillation product is obtained and stored in a crude product tank, wherein the content of 2-methyl-6-butyrylnaphthalene is about 67%, the content of 2-methyl-7-butyrylnaphthalene is about 31%, and the content of other isomers is about 2%.

[0055] like Figure 3As shown, the distillation target product is subjected to melt crystallization and solvent recrystallization to obtain high-purity 2-methyl-6-acylnaphthalene and high-purity 2-methyl-7-acylnaphthalene, and the specific process is as follows.

[0056] 100 g of the crude products of 2-methyl-6-butyrylnaphthalene and 2-methyl-7-butyrylnaphthalene were spread on a jacketed insulation filtration funnel, and vacuum filtration was started. The jacket was first heated to 40° C., and then slowly heated to 55° C. at a rate of 0.04° C. / min. Filtration was continued at 55° C. for one hour to separate 30 g of 2-methyl-7-butyrylnaphthalene with a purity of 90% (2-methyl-7-butyrylnaphthalene with higher purity) and 70 g of 2-methyl-6-butyrylnaphthalene with a purity of 92.85% (2-methyl-6-butyrylnaphthalene with higher purity).

[0057] The thick product of 50g 2-methyl-6-butyrylnaphthalene is added in the 500mL jacketed bottle, 200g 85% methanol aqueous solution is added in the jacketed bottle, open and stir, mixed solutions is warming up to 55 ℃, thick product is dissolved fully, and stirred one hour at 50 ℃, then be cooled to 20 ℃ at the rate of 0.5 ℃ / min, at 20 ℃, add 1g 2-methyl-6-butyrylnaphthalene crystal seed, then stir half an hour at 20 ℃, a large amount of white solids are separated out, then be cooled to 5 ℃ at the rate of 0.5 ℃ / min, and stir three hours at 5 ℃, suction filtration, solid cold methanol aqueous solution rinsing, drying obtains 42.0g purity and is 99.0% 2-methyl-6-butyrylnaphthalene (high-purity 2-methyl-6-butyrylnaphthalene) then;

[0058] 30 g of the crude product of 2-methyl-7-butyrylnaphthalene was added to a 500 mL jacketed bottle, 150 g of an 85% methanol aqueous solution was added to the jacketed bottle, stirring was started, the mixed solution was heated to 55° C. to completely dissolve the crude product, and stirred at 50° C. for one hour, then cooled to 30° C. at a rate of 0.5° C. / min, 1 g of 2-methyl-7-butyrylnaphthalene seed crystals was added at 30° C., and then stirred at 30° C. for half an hour, a large amount of white solid was precipitated, and then cooled to 20° C. at a rate of 0.5° C. / min, and stirred at 20° C. for three hours, filtered, the solid was rinsed with a cold methanol aqueous solution, and then dried to obtain 25.0 g of 2-methyl-7-butyrylnaphthalene (high-purity 2-methyl-7-butyrylnaphthalene) with a purity of 99.0%.

[0059] The chromatogram comparison of the target product of distillation, the product obtained after melt crystallization and solvent recrystallization is shown in the figure below. Figure 4 As shown. Figure 4 It can be seen that after melt crystallization and solvent recrystallization, 2-methyl-6-acylnaphthalene and 2-methyl-7-acylnaphthalene are separated, and the purity of the obtained product is relatively high.

[0060] Comparative Example 1

[0061] The difference from Example 2 is that only the distillation target product obtained by Example 2 is separated and purified by recrystallization. Specifically, 50g of the distillation target product (crude product) of Example 2 is added to a 500mL jacketed bottle, 250g of 85% methanol aqueous solution is added to the jacketed bottle, stirring is turned on, the mixed solution is warmed up to 55°C, the crude product is dissolved completely, and stirred at 50°C for one hour, then cooled to 30°C at a rate of 1°C / min, slowly stirred at 30°C for half an hour, a large amount of white solid is precipitated, then cooled to 20°C at a rate of 0.5°C / min, and kept at 20°C for three hours, filtered, the solid is rinsed with cold methanol aqueous solution, and then dried to obtain 13g of 2-methyl-7-butyrylnaphthalene (high-purity 2-methyl-7-butyrylnaphthalene) with a purity of 98%, and high-purity 2-methyl-6-butyrylnaphthalene is not obtained.

[0062] Comparative Example 2

[0063] The difference from Example 2 is that only the distillation method is used to separate and purify the acylated product obtained in Example 2. Specifically, the acylated product in the storage tank is added to the distillation tower, and about 100g of distillation raw materials are added to the initial distillation still, the distillation pressure is: 2.6-3.9kPa, and the reflux ratio is: 10:1. The segmented temperature control distillation is adopted, and the storage tank is controlled at 100°C, the feed pipe is 100°C, the lower part of the tower is 180°C, the middle part of the tower is 160°C, the upper part of the tower is 100°C, and the reflux pipe is 90°C. The bottom of the distillation tower adopts forced circulation to avoid high-temperature polycondensation of the bottom material. After the vacuum distillation is completed, the distillation target product is obtained and stored in the crude product tank, wherein the content of 2-methyl-6-butyrylnaphthalene is 68%, the content of 2-methyl-7-butyrylnaphthalene is 30%, and the content of other isomers is 2%. Only distillation can obtain a mixture of 2-methyl-6-butyrylnaphthalene and 2-methyl-7-butyrylnaphthalene, but cannot obtain high-purity 2-methyl-6-butyrylnaphthalene and 2-methyl-7-butyrylnaphthalene products.

[0064] Comparative Example 3

[0065] The difference from Example 1 is that the hydrogen-type β molecular sieve powder is not modified with phosphotungstic acid, and is directly molded according to the molding steps of the modified molecular sieve. The molded hydrogen-type β molecular sieve catalyst is evaluated for catalyst activity using the evaluation conditions of Example 2. The experimental results show that the conversion rate of butyric anhydride is 80%, the selectivity of 2-methyl-6-butyryl naphthalene is 58.8%, the selectivity of 2-methyl-7-butyryl naphthalene is 26.5%, and the other isomers are generated at 14.7%. Due to the high entrainment of isomers in the system, high-purity 2-methyl-7-butyryl naphthalene and 2-methyl-6-butyryl are not obtained through subsequent distillation and crystallization.

[0066] Compared with Example 2, the selectivity of the acylated products 2-methyl-7-butyrylnaphthalene and 2-methyl-6-butyrylnaphthalene in Comparative Example 3 is relatively low, and the content of other isomers is relatively high. It can be seen that the performance of the catalyst used in the present invention is better.

[0067] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms may be for different embodiments or examples. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, unless they are contradictory.

[0068] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0069] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A method for preparing high-purity 2-methyl-6-acylnaphthalene and 2-methyl-7-acylnaphthalene by continuous catalytic reaction and rectification purification, characterized in that: The following steps are involved: (a) under the conditions of a catalyst, the raw materials 2-methylnaphthalene and butyric anhydride are continuously catalytically reacted in a fixed bed reactor to obtain an acylated product; (b) fractionating the acylated product under reduced pressure in a distillation tower to obtain a distillation target product; (c) melt crystallizing the rectification target product to obtain a crude product of 2-methyl-6-acylnaphthalene and a crude product of 2-methyl-7-acylnaphthalene; (d) the crude product of the 2-methyl-6-acylnaphthalene and the crude product of the 2-methyl-7-acylnaphthalene are respectively subjected to solvent recrystallization to obtain high-purity 2-methyl-6-acylnaphthalene and high-purity 2-methyl-7-acylnaphthalene.

2. The method according to claim 1, characterized in that The catalyst is obtained by in-situ encapsulating phosphotungstic acid on a hydrogen-type beta molecular sieve.

3. The method according to claim 2, characterized in that The preparation process of the catalyst comprises: Add hydrogen-type β molecular sieve, disodium hydrogen phosphate and sodium tungstate in a molar ratio of 1:12 into deionized water and stir to mix evenly to obtain a slurry; Adding an acidic solution to adjust the pH value of the slurry to below 3, and reflux with stirring; After centrifugal washing, drying and calcination are performed to obtain supported phosphotungstic acid catalyst powder, which is then molded to obtain a molded supported phosphotungstic acid catalyst.

4. The method according to claim 3, characterized in that The calcination temperature is below 300° C. and the calcination time is above 3 hours.

5. The method according to claim 1, characterized in that The molar ratio of the 2-methylnaphthalene to the butyric anhydride is 2:

1.

6. The method according to claim 1, characterized in that The temperature of the melting crystallization of the distillation target product is 40-60°C.

7. The method according to claim 6, characterized in that The temperature of the melting crystallization of the distillation target product is 45-55°C.

8. The method according to claim 1, characterized in that The solvent for the solvent recrystallization is an aqueous solution of one or more of C5-C10 alkanes, C5-C10 cycloalkanes, or one or more of C1-C6 alcohols.

9. The method according to claim 1, characterized in that The purity of the high-purity 2-methyl-6-acylnaphthalene and the high-purity 2-methyl-7-acylnaphthalene is both above 99%.

10. Use of the method according to any one of claims 1 to 9 in the preparation of high-purity 2-methyl-6-acylnaphthalene and high-purity 2-methyl-7-acylnaphthalene by fixed-bed catalytic reaction.

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