Production method and production system of 2, 6-dimethylnaphthalene

Abstract

The invention relates to the technical field of production of 2, 6-dimethylnaphthalene, and discloses a production method and a production system of 2, 6-dimethylnaphthalene, and the production method comprises the following steps: (1) under a liquid phase condition, in the presence of an alkyl transfer catalyst, contacting reaction raw materials with a transfer alkylating agent to obtain a product mixture; the content of the 2, 6-dimethylnaphthalene is not less than 15wt% on the basis of the total content of the bicyclic aromatic hydrocarbon in the product mixture; (2) rectifying the product mixture to obtain a light component and a heavy component containing the dimethylnaphthalene isomer, and returning the light component to the step (1) to provide at least part of reaction raw materials; (3) mixing the heavy component obtained by rectification with a complexing agent, carrying out complexing crystallization, and then carrying out alkali washing to obtain a 2, 6-dimethylnaphthalene crude product; and (4) mixing the 2, 6-dimethylnaphthalene crude product with a solvent, and recrystallizing. The method has the advantages of high purity and high yield of the 2, 6-dimethylnaphthalene.

Description

Technical Field

[0001] This invention relates to the field of 2,6-dimethylnaphthalene production technology, and specifically to a method and system for producing 2,6-dimethylnaphthalene. Background Technology

[0002] 2,6-Dimethylnaphthalene is an important organic compound intermediate widely used in pesticides, pharmaceuticals, and dyes. With the development of downstream industries and the increasing demand for high-performance products, the purity requirements for 2,6-dimethylnaphthalene are also becoming increasingly stringent. In the pharmaceutical industry, 2,6-dimethylnaphthalene is a crucial raw material for many drug intermediates and active ingredients, such as a precursor to the anticancer drug methotrexate. Pharmaceutical products have extremely strict purity requirements for raw materials; the presence of impurities can affect efficacy or cause adverse reactions. In the pesticide industry, 2,6-dimethylnaphthalene is also an important intermediate for many insecticides and herbicides. As pesticide products develop towards higher efficiency and lower toxicity, the purity requirements for raw materials are also increasing. In the dye and plastic additive fields, high-purity 2,6-dimethylnaphthalene helps improve the color brightness and performance stability of products. Furthermore, the novel polyester material polyethylene naphthalate (PEN) also requires high-purity 2,6-dimethylnaphthalene as a monomer.

[0003] Currently, the only industrialized production route for 2,6-dimethylnaphthalene is the side-chain alkylation reaction of o-xylene with butadiene by BP Amoco, followed by cyclization and dehydrogenation aromatization to obtain 1,5-dimethylnaphthalene. The 1,5-dimethylnaphthalene isomerizes to obtain the dimethylnaphthalene isomer, which is then separated and purified to obtain 2,6-dimethylnaphthalene with a purity of over 95 wt%. This technology is complex and costly, hindering the application and development of PEN.

[0004] 2,6-Dimethylnaphthalene can be synthesized in one step via alkylation reaction using naphthalene and methylnaphthalene as raw materials. The reaction process is simple and the raw material sources are abundant, making it a potential route for low-cost production of 2,6-dimethylnaphthalene.

[0005] CN1762932A and CN100357237C disclose a method for producing 2,6-dimethylnaphthalene by alkyl transfer reaction of 2-methylnaphthalene with trimethylbenzene, tetramethylbenzene, and pentamethylbenzene under supercritical reaction conditions using modified molecular sieve as a catalyst. The reaction results show that the conversion rate of 2-methylnaphthalene is 52%, but the selectivity of 2,6-dimethylnaphthalene is low, and the reaction temperature and pressure are high, resulting in high energy consumption. The yield of high-purity 2,6-dimethylnaphthalene product is low, which is not conducive to industrial production.

[0006] CN101092320A discloses a method for separating and purifying 2,6-dimethylnaphthalene, including isomerization and crystallization steps. First, a distillation column is used to purify the mixture rich in 1,5-dimethylnaphthalene isomers generated by the dehydrogenation reaction of 1,5-dimethyltetrahydronaphthalene, separating high-boiling-point substances from unreacted 1,5-dimethyltetrahydronaphthalene and low-boiling-point substances. Then, the dimethylnaphthalene mixture is subjected to an isomerization reaction in the presence of an isomerization catalyst. Subsequently, the isomerization product is subjected to melt crystallization and solution crystallization sequentially.

[0007] The existing methods for producing 2,6-dimethylnaphthalene all have problems with energy consumption, yield, and stability, and further development of process routes for producing high-purity 2,6-dimethylnaphthalene is needed. Summary of the Invention

[0008] The purpose of this invention is to overcome the problems of low yield and low purity of 2,6-dimethylnaphthalene in the prior art, and to provide a production method and system for 2,6-dimethylnaphthalene, which has the characteristics of high purity and high yield of 2,6-dimethylnaphthalene product.

[0009] To achieve the above objectives, the present invention provides a method for producing 2,6-dimethylnaphthalene, the method comprising:

[0010] (1) Under liquid phase conditions, in the presence of an alkyl transfer catalyst, the reactants are contacted with a transfer alkylating agent to obtain a product mixture; wherein the reactants include at least one of naphthalene, 1-methylnaphthalene and 2-methylnaphthalene; the transfer alkylating agent is at least one of methyl-substituted monocyclic aromatic hydrocarbons; based on the total content of bicyclic aromatic hydrocarbons in the product mixture, the content of 2,6-dimethylnaphthalene is not less than 15 wt%;

[0011] (2) The product mixture is distilled to obtain a light component and a heavy component containing a dimethylnaphthalene isomer. The light component is returned to step (1) to provide at least a portion of the reaction feedstock.

[0012] (3) The heavy components obtained by distillation are mixed with a complexing agent for complexation crystallization, and then washed with alkali to obtain crude 2,6-dimethylnaphthalene;

[0013] (4) Mix the crude 2,6-dimethylnaphthalene with a solvent and recrystallize it.

[0014] Preferably, the alkyl transfer catalyst comprises a support and an active metal component supported on the support; wherein the support comprises a twelve-membered ring molecular sieve and a binder; and the active metal component is selected from at least one transition metal.

[0015] Preferably, the amount of Brønsted acid in the alkyl transfer catalyst is 100-400 μmol / g, more preferably 150-350 μmol / g.

[0016] Preferably, the ratio of the amount of Brønsted acid to the amount of Lewis acid is 1-3:1, more preferably 1.2-3:1.

[0017] Another aspect of the present invention provides a production system for 2,6-dimethylnaphthalene, comprising: a raw material supply unit, an alkyl transfer reaction unit, a distillation unit, a first crystallization unit, and a second crystallization unit, sequentially connected along the material flow direction; wherein,

[0018] The raw material supply unit is used to supply reaction raw materials and transfer alkylating agents to the alkyl transfer reaction unit; wherein, the reaction raw materials include at least one of naphthalene, 1-methylnaphthalene, and 2-methylnaphthalene; and the transfer alkylating agent is at least one of methyl-substituted monocyclic aromatic hydrocarbons.

[0019] The alkyl transfer reaction unit includes a fixed-bed reactor, which is filled with an alkyl transfer catalyst for contacting the reactants with a transfer alkylating agent to carry out an alkyl transfer reaction.

[0020] The distillation unit includes a distillation column for distilling the product mixture from the alkyl transfer reaction unit. The top material outlet of the distillation column is connected to the raw material supply unit, and the bottom material outlet is connected to the first crystallization unit.

[0021] The first crystallization unit includes a first crystallizer and a first washing filter connected in sequence, used to mix heavy components from the distillation unit with a complexing agent for complexation crystallization and alkali washing to obtain crude 2,6-dimethylnaphthalene;

[0022] The second crystallization unit includes a second crystallizer for recrystallizing crude 2,6-dimethylnaphthalene by mixing it with a solvent.

[0023] The method for producing 2,6-dimethylnaphthalene provided by this invention couples the alkyl transfer reaction and product purification steps. By sequentially subjecting the product obtained from the liquid-phase alkyl transfer reaction to distillation, complexation crystallization, and recrystallization, the overall process offers advantages such as high naphthalene / methylnaphthalene conversion, high dimethylnaphthalene selectivity, and high purity and yield of 2,6-dimethylnaphthalene, meeting the needs of 2,6-dimethylnaphthalene as a drug precursor and polymer monomer. Furthermore, the reaction and separation processes are simple, energy-efficient, environmentally friendly, and highly efficient, making it suitable for industrial-scale application. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of a production system for 2,6-dimethylnaphthalene in some embodiments of the present invention.

[0025] Explanation of reference numerals in the attached figures

[0026] 1 Fixed-bed reactor 2 Distillation column 3 First crystallizer

[0027] 4 First washing filter 5 Second crystallizer 6 Second washing filter

[0028] S1 reactant, S2 light component, S3 complexing agent

[0029] S4 solvent, S5 2,6-dimethylnaphthalene product Detailed Implementation

[0030] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0031] The first aspect of this invention provides a method for producing 2,6-dimethylnaphthalene, the method comprising:

[0032] (1) Under liquid phase conditions, in the presence of an alkyl transfer catalyst, the reactants are contacted with a transfer alkylating agent to obtain a product mixture; wherein the reactants include at least one of naphthalene, 1-methylnaphthalene and 2-methylnaphthalene; the transfer alkylating agent is at least one of methyl-substituted monocyclic aromatic hydrocarbons; based on the total content of bicyclic aromatic hydrocarbons in the product mixture, the content of 2,6-dimethylnaphthalene is not less than 15 wt%;

[0033] (2) The product mixture is distilled to obtain a light component and a heavy component containing a dimethylnaphthalene isomer. The light component is returned to step (1) to provide at least a portion of the reaction feedstock.

[0034] (3) The heavy components obtained by distillation are mixed with a complexing agent for complexation crystallization, and then washed with alkali to obtain crude 2,6-dimethylnaphthalene;

[0035] (4) Mix the crude 2,6-dimethylnaphthalene with a solvent and recrystallize it.

[0036] The method for producing 2,6-dimethylnaphthalene provided by this invention couples the alkyl transfer reaction and the product purification step. By sequentially subjecting the product obtained from the liquid-phase alkyl transfer reaction to distillation, complexation crystallization, and recrystallization, the overall process has the advantages of high naphthalene / methylnaphthalene conversion, high dimethylnaphthalene selectivity, and high purity and yield of 2,6-dimethylnaphthalene. Moreover, the reaction and separation processes are simple, energy consumption is low, environmentally friendly, and production efficiency is high, making it suitable for industrial promotion.

[0037] The present invention has a wide range of options for the alkyl transfer catalyst and the conditions of the liquid-phase alkyl transfer reaction in step (1), so as to meet the requirement that the content of 2,6-dimethylnaphthalene is not less than 15 wt%, preferably not less than 20 wt%, and more preferably 20-40 wt%, based on the total content of bicyclic aromatic hydrocarbons in the product mixture.

[0038] According to some preferred embodiments of the present invention, the alkyl transfer catalyst comprises a support and an active metal component supported on the support; wherein the support comprises a twelve-membered ring molecular sieve and a binder; and the active metal component is selected from at least one transition metal.

[0039] Preferably, the amount of Brønsted acid in the alkyl transfer catalyst is 100-400 μmol / g, more preferably 150-350 μmol / g.

[0040] Preferably, the ratio of the amount of Brønsted acid to the amount of Lewis acid is 1-3:1, more preferably 1.2-3:1.

[0041] The inventors of this invention discovered that by using a carrier containing a twelve-membered ring molecular sieve to support a transition metal, the unique pore structure of the twelve-membered ring molecular sieve, combined with a suitable content of Brønsted acid and Lewis acid, can be used in the alkyl transfer reaction to prepare 2,6-dimethylnaphthalene. This results in a reaction between naphthalene, methylnaphthalene, and monocyclic aromatic hydrocarbons containing methyl groups, achieving not only a high naphthalene / methylnaphthalene conversion rate but also high selectivity and yield for 2,6-dimethylnaphthalene. This also ensures that the bicyclic aromatic hydrocarbons in the product mixture contain a suitable content of 2,6-dimethylnaphthalene.

[0042] In this invention, the contents of Brønsted acid and Lewis acid in the alkyl transfer catalyst are determined by pyridine probe infrared spectroscopy.

[0043] According to the present invention, preferably, the alkyl transfer catalyst has a specific surface area of ​​250-700 m². 2 / g, preferably 300-650m 2 / g.

[0044] According to the present invention, preferably, the pore volume of the alkyl transfer catalyst is 0.28-0.7 mL / g, more preferably 0.3-0.68 mL / g.

[0045] In this invention, the specific surface area and pore volume of the alkyl transfer catalyst are obtained by BET full analysis method.

[0046] The present invention allows for a wide selection of the twelve-membered ring molecular sieve, for example, it can be at least one of Y-type molecular sieve, Beta-type molecular sieve, MCM-22 molecular sieve, MCM-56 molecular sieve, SAPO-5 molecular sieve, SAPO-37 molecular sieve, and SAPO-40 molecular sieve. More preferably, the twelve-membered ring molecular sieve is selected from at least one of Y-type molecular sieve, Beta-type molecular sieve, and SAPO-5 molecular sieve. Using the above-mentioned preferred molecular sieve types facilitates the diffusion of reactants into the pores and their contact with the acid centers, thereby further improving the catalytic activity of the alkyl transfer catalyst and increasing the yield of the target product.

[0047] According to the present invention, preferably, the molar ratio of silica to alumina in the twelve-membered ring molecular sieve is 0.1-30, more preferably 0.8-25. In the present invention, the molar ratio of silica to alumina in the twelve-membered ring molecular sieve is obtained by X-ray fluorescence spectrometry (XRF).

[0048] This invention does not particularly limit the type of binder in the support; any binder conventionally used in catalyst supports in the art can be applied to this invention, such as at least one of alumina, kaolin, attapulgite, bentonite, diatomaceous earth, and silica. Preferably, the binder is alumina to further improve the catalytic activity and strength of the catalyst.

[0049] According to some preferred embodiments of the present invention, based on the total amount of the carrier, the content of the twelve-membered ring molecular sieve is 60-80 wt%, preferably 65-75 wt%; and the content of the binder is 20-40 wt%, preferably 25-35 wt%.

[0050] According to the present invention, the active metal component in the alkyl transfer catalyst is selected from at least one transition metal, such as at least one selected from Cu, Zn, Ag, Ni, Co, Fe, Mn, Cr, Mo, Ru, Rh, Pd, and Pt, preferably at least one selected from Cu, Fe, and Zn, and more preferably Cu and / or Fe. Using the above-mentioned preferred active metal composition helps to further modulate the acidity of the molecular sieve, thereby improving the catalytic activity and selectivity of the catalyst.

[0051] According to the present invention, preferably, based on the total amount of the alkyl transfer catalyst, the content of the support is 90-99.9 wt%, more preferably 92-99 wt%, and the content of the active metal component, calculated by element, is 0.1-10 wt%, more preferably 1-8 wt%. In the above-mentioned preferred cases, it is advantageous to obtain the desired acidity and pore distribution.

[0052] In this invention, the content of each component in the alkyl transfer catalyst is obtained by X-ray fluorescence spectroscopy (XRF).

[0053] The present invention does not impose any particular limitation on the preparation method of the alkyl transfer catalyst. Those skilled in the art can use any known method to satisfy the above composition and structure.

[0054] According to some preferred embodiments of the present invention, the method for preparing the alkyl transfer catalyst includes:

[0055] S1. Mix the twelve-membered ring molecular sieve with the binder precursor, then mold and dry it to obtain the carrier precursor;

[0056] S2. The carrier precursor is brought into contact with acid solution for heat treatment, followed by a first drying and a first calcination.

[0057] S3. In the presence of ultrasound, the product of the first calcination is impregnated with a solution containing an active metal component precursor, and then subjected to a second drying and a second calcination.

[0058] In this invention, the twelve-membered ring molecular sieve has the same definition as described above, and will not be repeated here. Preferably, the twelve-membered ring molecular sieve is a hydrogen-form twelve-membered ring molecular sieve.

[0059] Preferably, the specific surface area of ​​the twelve-membered ring molecular sieve is 280-740 m². 2 / g, preferably 340-730m 2 / g.

[0060] Preferably, the pore volume of the hydrogen-type twelve-membered ring molecular sieve is 0.26-0.66 mL / g, and more preferably 0.28-0.64 mL / g.

[0061] In this invention, the binder precursor refers to any substance that can be obtained by calcination, which is well known to those skilled in the art. For example, the precursor of alumina can be boehmite.

[0062] According to some preferred embodiments of the present invention, the dry basis mass ratio of the twelve-membered ring molecular sieve to the binder precursor is 60-80:20-40, preferably 65-75:25-35.

[0063] The present invention does not particularly limit the molding method, and those skilled in the art can choose according to actual needs, such as extrusion molding.

[0064] A solvent may also be introduced during the molding process. According to some preferred embodiments of the present invention, step S1 includes: mixing a twelve-membered ring molecular sieve, a binder precursor, and a solvent, followed by molding and drying to obtain a carrier precursor. The present invention does not have particular requirements regarding the specific type of the solvent; preferably, the solvent is an aqueous solution of an acid, preferably selected from at least one aqueous solution of nitric acid, acetic acid, citric acid, oxalic acid, and formic acid. Preferably, the concentration of the acid in the solvent is 1-5 wt%.

[0065] Preferably, the mass ratio of the adhesive solvent to the total mass of the twelve-membered ring molecular sieve and the binder precursor is 0.2-0.6:1.

[0066] According to some preferred embodiments of the present invention, the drying conditions in step S1 include: a temperature of 30-200°C, preferably 60-180°C; and a time of 0.1-72 h, preferably 4-48 h.

[0067] In this invention, preferably, the molding process does not include a baking process.

[0068] In this invention, the appropriate content of Brønsted acid and Lewis acid in the catalyst is adjusted by the heat treatment described in step S2 and the loading of the active metal component in step S3, and the catalyst is further adjusted to have an appropriate number and size of pores.

[0069] According to some preferred embodiments of the present invention, in step S2, the acid solution is provided by an aqueous solution of acid, the concentration of which is 0.5-3 mol / L, preferably 0.5-2.5 mol / L.

[0070] The present invention has a wide range of choices for the types of acids, and can use conventional organic acids and / or inorganic acids in the art. Preferably, the acid is selected from at least one of citric acid, ethylenediaminetetraacetic acid, malic acid, tartaric acid, sulfuric acid, phosphoric acid and nitric acid, and is preferably citric acid and / or phosphoric acid.

[0071] Preferably, the amount of acid solution used is 5-15 mL, more preferably 8-12 mL, relative to 1 g of the carrier precursor.

[0072] According to some preferred embodiments of the present invention, the heat treatment temperature is 40-100℃, preferably 60-90℃, and the time is 5-24h, preferably 6-18h. Using the above preferred embodiments is beneficial for further optimizing the acid distribution of the catalyst and improving the catalytic activity and selectivity of the catalyst.

[0073] According to some preferred embodiments of the present invention, the temperature of the first drying is 30-200°C, preferably 60-180°C, and the time is 0.1-72h, preferably 4-48h.

[0074] According to some preferred embodiments of the present invention, the temperature of the first calcination is 380-580°C, preferably 400-520°C, and the time is 0.5-20h, preferably 3-12h.

[0075] In this invention, the impregnation in step S3 is carried out in the presence of ultrasound. The product of the first calcination can be impregnated in a solution containing an active metal component precursor, and then the ultrasound treatment can be turned on.

[0076] This invention allows for a wide range of selection for the active metal component precursor, and can employ soluble compounds of active metal components conventional in the art, such as nitrates and / or chlorides of transition metals. This invention also does not impose particular requirements on the concentration and amount of the solution containing the active metal component precursor, as long as the required amount of transition metal is met. Preferably, the concentration of the solution containing the active metal component precursor is 0.1-1 mol / L.

[0077] According to some preferred embodiments of the present invention, the ultrasonic conditions include: an ultrasonic power density of 0.1-20 W / cm². 2 Preferably 5-15W / cm 2 The preferred embodiments described above facilitate the uniform dispersion of the active metal components.

[0078] According to the present invention, preferably, the impregnation temperature is 40-100°C, more preferably 60-90°C; and the time is 5-24h, more preferably 6-18h.

[0079] The present invention does not particularly limit the conditions for the second drying, as long as excess impregnation liquid can be removed. Preferably, the temperature for the second drying is 30-200°C, and the time is 0.1-72 hours.

[0080] Preferably, the second calcination temperature is 400-600℃ and the time is 0.5-20h.

[0081] According to the present invention, preferably, the second drying and the second calcination are carried out under an inert atmosphere, which may be provided by nitrogen.

[0082] According to the present invention, preferably, in step (1), the transfer alkylating agent is selected from any one or a mixture of several of toluene, xylene, trimethylbenzene, and tetramethylbenzene. The xylene can be at least one of o-xylene, p-xylene, and m-xylene; the trimethylbenzene can be at least one of pseudotrimethylbenzene, ternarytrimethylbenzene, and mesitylene; the tetramethylbenzene is at least one of pseudotetramethylbenzene, ternarytezene, and mesitylene. The present invention does not have particular requirements regarding the source of the transfer alkylating agent, and it can also be provided by mixed C8 aromatics, mixed C9 aromatics, mixed C10 aromatics, etc. The mixed C8 aromatics, mixed C9 aromatics, and mixed C10 aromatics have conventional definitions in the art. Mixed C8 aromatics include xylene and ethylbenzene; mixed C9 aromatics include trimethylbenzene, methyl ethylbenzene, and propylbenzene; and mixed C10 aromatics include tetramethylbenzene, diethylbenzene, and methylpropylbenzene, etc. Preferably, the methyl-substituted aromatics (i.e., xylene, trimethylbenzene, or tetramethylbenzene) in the mixed C8 aromatics, mixed C9 aromatics, and mixed C10 aromatics each account for approximately 40-60 mol%.

[0083] According to some preferred embodiments of the present invention, the molar ratio of the reactant to the transfer alkylating agent is 1:(1-10), preferably 1:(2-7).

[0084] According to the present invention, the contact described in step (1) can be carried out under mild liquid phase conditions and the reaction temperature is not higher than 400°C, which has a high raw material conversion rate and product selectivity, and a high yield of 2,6-dimethylnaphthalene.

[0085] Preferably, the liquid phase conditions include: a reaction temperature of 150-400℃, more preferably 250-350℃; a reaction pressure of 0.5-5 MPa, more preferably 2-4 MPa; and a weight hourly space velocity (WHSV) of 0.1-5 h⁻¹ for the reactants. -1 Preferably 0.5-3h -1 In this invention, unless otherwise specified, all pressures refer to gauge pressure. By employing the preferred embodiments described above, while ensuring high raw material conversion rates and product selectivity, reaction energy consumption can be further reduced, and the economic efficiency of the reaction process can be improved.

[0086] According to some preferred embodiments of the present invention, the distillation in step (2) is carried out in a distillation column, the heavy component collected at the bottom of the column contains a mixture of dimethylnaphthalene isomers, and the light component collected at the top of the column includes unreacted reactants, transfer alkylating agents and other possible low-boiling products.

[0087] In this invention, the light component is returned to step (1) to provide at least a portion of the reaction feedstock. It is understood that when the obtained light component is returned to the feedstock, the feedstock amount is correspondingly reduced so that the content of the reaction feedstock and the transfer alkylating agent in the reactor feed remains unchanged. Using the above-described preferred embodiment is beneficial for improving the utilization rate of the reaction feedstock and reducing material costs.

[0088] In this invention, the distillation in step (2) is used to separate a mixture of dimethylnaphthalenes, including 2,6-dimethylnaphthalene and any one or more isomers thereof, from the product mixture obtained from the alkyl transfer reaction.

[0089] The present invention does not particularly limit the specific conditions of the distillation, as long as the dimethylnaphthalene isomer can be separated from other components. Preferably, the distillation conditions are such that the total amount of dimethylnaphthalene isomers in the obtained heavy components is not less than 95 wt%, preferably not less than 97 wt%. The total amount of dimethylnaphthalene isomers refers to the total content of 2,6-dimethylnaphthalene and any one or more of its isomers.

[0090] Preferably, in step (2), the distillation conditions include: a bottom temperature of 150-300℃, preferably 170-290℃, and a top pressure of 0.005-0.15MPa, preferably 0.01-0.12MPa. The theoretical number of plates in the distillation column is preferably 50-150. By adopting the above-mentioned preferred operating conditions, the separation efficiency and resolution of the dimethylnaphthalene mixture can be further improved, and the utilization rate of raw materials and the yield of 2,6-dimethylnaphthalene can be increased.

[0091] In this invention, complexation crystallization is used to separate 2,6-dimethylnaphthalene from a dimethylnaphthalene mixture obtained by distillation, comprising 2,6-dimethylnaphthalene and any one or more isomers thereof. The complexation crystallization can be carried out according to the method disclosed in CN1990439A.

[0092] According to some preferred embodiments of the present invention, in step (3), the complexing agent comprises m-nitrobenzoic acid and methanol. Preferably, the mass ratio of m-nitrobenzoic acid to methanol is 0.3-8:1, more preferably 0.5-5:1.

[0093] According to some preferred embodiments of the present invention, the mass ratio of the complexing agent to the heavy component is 0.4-4:1, preferably 1.2-2.4:1. In the above preferred cases, the yield of 2,6-dimethylnaphthalene can be further improved through the synergistic effect of distillation and complexation crystallization.

[0094] According to the present invention, preferably, the temperature of the complexation crystallization is 80-120°C, more preferably 90-100°C; and the time of complexation crystallization is 10-50 min, more preferably 20-30 min.

[0095] Preferably, the alkaline washing in step (3) includes contacting the complexed crystallized solid product with an alkaline solution.

[0096] Preferably, the alkaline solution is an aqueous solution of an alkali, and the alkali is preferably sodium hydroxide.

[0097] Preferably, the concentration of the alkaline solution is 5-20% by weight.

[0098] Preferably, the molar ratio of alkali in the alkaline solution to m-nitrobenzoic acid in the complexing agent is 0.8-1.2:1, more preferably 0.9-1.1:1.

[0099] According to the present invention, preferably, the recrystallization temperature is 10-30°C, more preferably 15-25°C.

[0100] In this invention, the recrystallization method may include: dissolving crude 2,6-dimethylnaphthalene in a solvent under heating conditions, and then cooling to 10-30°C, preferably 15-25°C.

[0101] According to some preferred embodiments of the present invention, the solvent is a low-carbon alcohol, such as a C1-C3 fatty alcohol compound, preferably methanol and / or ethanol.

[0102] Preferably, the mass ratio of the solvent to crude 2,6-dimethylnaphthalene is 1-3:1.

[0103] Another aspect of the present invention provides a production system for 2,6-dimethylnaphthalene, comprising: a raw material supply unit, an alkyl transfer reaction unit, a distillation unit, a first crystallization unit, and a second crystallization unit, sequentially connected along the material flow direction; wherein,

[0104] The raw material supply unit is used to supply reaction raw material S1 and transfer alkylating agent to the alkyl transfer reaction unit; wherein, the reaction raw material includes at least one of naphthalene, 1-methylnaphthalene and 2-methylnaphthalene; and the transfer alkylating agent is at least one of methyl-substituted monocyclic aromatic hydrocarbons;

[0105] The alkyl transfer reaction unit includes a fixed-bed reactor, which is filled with an alkyl transfer catalyst for contacting the reactant S1 with the transfer alkylating agent to carry out the alkyl transfer reaction.

[0106] The distillation unit includes a distillation column for distilling the product mixture from the alkyl transfer reaction unit. The top material outlet of the distillation column is connected to the feed supply unit, and the obtained light component S2 is returned to the feed supply unit. The bottom material outlet is connected to the first crystallization unit.

[0107] The first crystallization unit includes a first crystallizer and a first washing filter connected in sequence, used to mix heavy components from the distillation unit with complexing agent S3 for complexation crystallization, and then perform alkaline washing to obtain crude 2,6-dimethylnaphthalene;

[0108] The second crystallization unit includes a second crystallizer for recrystallizing crude 2,6-dimethylnaphthalene with solvent S4 to obtain 2,6-dimethylnaphthalene product S5.

[0109] The present invention will be described in detail below through embodiments.

[0110] The following preparation examples illustrate the preparation of the alkyl transfer catalyst in this invention.

[0111] Preparation Example 1

[0112] (1) Take H-Beta molecular sieve with a silica / alumina molar ratio of 25 (specific surface area of ​​693 m²) 2 The mixture of 0.56 mL / g (with a pore volume of 0.56 mL / g) and pseudoboehmite (produced by Condea, Germany, brand name Pural SB powder) at a dry basis mass ratio of 65:35 was prepared. Dilute nitric acid with a mass ratio of 1:2 was added to the mixture and kneaded. The mixture was then extruded and dried at 110°C for 4 hours to obtain the carrier precursor.

[0113] (2) The carrier precursor was placed in a citric acid solution with a concentration of 1 mol / L. The amount of acid solution was 10 mL relative to 1 g of the carrier precursor. The solution was treated at 80 °C for 8 h, then dried at 110 °C for 4 h, and calcined at 520 °C for 5 h.

[0114] (3) The sample treated in step (2) was immersed in a 0.2 mol / L Cu(NO3)2 solution, and the immersion solution was subjected to ultrasonic treatment with an ultrasonic power density of 10 W / cm². 2 The processing time is 6 hours and the temperature is 60℃.

[0115] (4) The sample treated in step (3) was dried at 110°C for 4 hours under a nitrogen atmosphere and calcined at 560°C for 5 hours to obtain catalyst A1. X-ray fluorescence spectroscopy (XRF) analysis showed that the Cu content in the catalyst was 2.13% by mass.

[0116] The amount of Brønsted acid in the catalyst was determined to be 212 μmol / g, the ratio of Brønsted acid to Lewis acid was 2.6, and the specific surface area was 610 m². 2 / g, pore volume is 0.6mL / g.

[0117] Preparation Example 2

[0118] (1) Take HY molecular sieve with a silica / alumina molar ratio of 7 (specific surface area of ​​604 m²) 2 The mixture of 0.32 mL / g (with a pore volume of 0.32 mL / g) and pseudoboehmite (produced by Condea, Germany, brand name Pural SB powder) at a dry basis mass ratio of 65:35 was prepared. Dilute nitric acid with a concentration of 1% by mass was added to the mixture at a mass ratio of 1:2, and the mixture was kneaded, extruded into strips, and then dried at 110°C for 4 hours to obtain the carrier precursor.

[0119] (2) The carrier precursor was placed in a citric acid solution with a concentration of 1 mol / L. The amount of acid solution was 10 mL relative to 1 g of the carrier precursor. The solution was treated at 80 °C for 8 h, then dried at 110 °C for 4 h, and calcined at 520 °C for 5 h.

[0120] (3) The sample treated in step (2) was impregnated in a 0.2 mol / L Fe(NO3)3 solution, and the impregnation solution was subjected to ultrasonic treatment with an ultrasonic power density of 5 W / cm². 2 The processing time is 6 hours and the temperature is 60℃.

[0121] (4) The sample treated in step (3) was dried at 110°C for 4 hours under a nitrogen atmosphere and then calcined at 560°C for 5 hours to obtain catalyst A2. X-ray fluorescence spectroscopy (XRF) analysis showed that the Fe content in the catalyst was 1.93% by mass.

[0122] The amount of Brønsted acid in the catalyst was determined to be 320 μmol / g, the ratio of Brønsted acid to Lewis acid was 1.5, and the specific surface area was 521 m². 2 / g, pore volume is 0.28mL / g.

[0123] Preparation Example 3

[0124] The method is the same as in Example 1, except that the acid treatment in step (2) is not performed. The carrier precursor is dried at 110°C for 4 hours, calcined at 520°C for 5 hours, and then impregnated in a 0.2 mol / L Cu(NO3)2 solution. The impregnation solution is then subjected to ultrasonic treatment with an ultrasonic power density of 5 W / cm². 2 The processing time is 6 hours and the temperature is 60℃.

[0125] The treated sample was then dried at 110°C for 4 hours under a nitrogen atmosphere and calcined at 560°C for 5 hours to obtain catalyst A3. X-ray fluorescence spectroscopy (XRF) analysis showed that the Cu content in the catalyst was 2.32% by mass. The Brønsted acid content in the catalyst was determined to be 80 μmol / g, the ratio of Brønsted acid to Lewis acid was 0.5, and the specific surface area was 505 nm. 2 / g, pore volume is 0.5mL / g.

[0126] The following examples illustrate the production method of 2,6-dimethylnaphthalene in this invention.

[0127] In the following examples, the reaction results were calculated according to the following formula:

[0128] Alkyl transfer reaction unit:

[0129] The conversion rate of naphthalene / methylnaphthalene (%) = (amount of naphthalene / methylnaphthalene in the raw material - amount of naphthalene / methylnaphthalene in the product) ÷ (amount of naphthalene / methylnaphthalene in the raw material) × 100%;

[0130] 2,6-Dimethylnaphthalene single-pass yield (%) = (amount of 2,6-dimethylnaphthalene in the product) ÷ (amount of bicyclic aromatic hydrocarbons in the product - amount of naphthalene / methylnaphthalene in the product) × conversion rate;

[0131] Distillation unit:

[0132] 2,6-Dimethylnaphthalene single-pass yield (%) = (amount of 2,6-dimethylnaphthalene in crude 2,6-dimethylnaphthalene) ÷ (amount of 2,6-dimethylnaphthalene in distillation column feed) × 100%;

[0133] Crystallization unit:

[0134] 2,6-Dimethylnaphthalene single-pass yield (%) = (amount of 2,6-dimethylnaphthalene product) ÷ (amount of 2,6-dimethylnaphthalene in crude 2,6-dimethylnaphthalene) × 100%;

[0135] Overall process flow:

[0136] Total single-pass yield of 2,6-dimethylnaphthalene (%) = Single-pass yield of 2,6-dimethylnaphthalene from alkyl transfer reaction unit × Yield of 2,6-dimethylnaphthalene from distillation unit × Yield of 2,6-dimethylnaphthalene from crystallization unit.

[0137] Example 1

[0138] Adopting such Figure 1 The production system for 2,6-dimethylnaphthalene is shown.

[0139] (1) Liquid-phase alkyl transfer catalyst A1 was packed into a fixed-bed reactor. 2 kg / h of feed containing 2-methylnaphthalene and pseudotrimethylbenzene (molar ratio 1:3) was introduced into the liquid-phase alkyl transfer fixed-bed reactor. The reactor was operated at 350 °C, 2.5 MPa, and a mass hourly space velocity (HHSV) of 1.0 h⁻¹. -1 Under certain conditions, a liquid-phase alkyl transfer reaction was carried out to obtain a product mixture. The composition of the product mixture is shown in Table 1. Based on the total content of bicyclic aromatic hydrocarbons in the product mixture, the content of 2,6-dimethylnaphthalene is 26.4 wt%.

[0140] (2) The product mixture obtained in step (1) is fed into a distillation column and distilled under the conditions of a top pressure of 0.005 MPa, a bottom temperature of 173 °C, and 150 theoretical plates. The component except dimethylnaphthalene collected from the top of the column is returned to step (1) and mixed with the raw material to carry out alkyl transfer reaction. The content of all dimethylnaphthalene isomers in the heavy component collected from the bottom of the column is 97%.

[0141] (3) The collected heavy components were fed into the first crystallizer. The complexing agent was a mixed solution of m-nitrobenzoic acid and methanol (mass ratio 1:1). The mass ratio of the complexing agent to the heavy components was 2:1. The mixture was kept at 90°C for 25 min, filtered, and then washed with 10 wt% sodium hydroxide solution (molar ratio of sodium hydroxide to m-nitrobenzoic acid was 1:1) to obtain crude 2,6-dimethylnaphthalene (purity 80.4%). The complexing agent was then recovered.

[0142] (4) The crude 2,6-dimethylnaphthalene product was introduced into the second crystallizer and mixed with methanol at a mass ratio of 1:3. The mixture was kept at a constant temperature of 25°C for 60 min. After crystallization, it was filtered and dried to obtain the 2,6-dimethylnaphthalene product.

[0143] The total single-pass yield of 2,6-dimethylnaphthalene was calculated to be 20.2%, with a purity of 98.9%.

[0144] Table 1

[0145]

[0146]

[0147] *The heavy components include: ethylnaphthalene, trimethylnaphthalene, etc.

[0148] Example 2

[0149] (1) Liquid-phase alkyl transfer catalyst A2 was packed into a fixed-bed reactor. 2.2 kg / h of feed containing 2-methylnaphthalene and pseudotrimethylbenzene (molar ratio 1:3) was introduced into the liquid-phase alkyl transfer fixed-bed reactor. The reactor was operated at 360 °C, 2.0 MPa, and a mass hourly space velocity of 1.0 h⁻¹. -1Under certain conditions, a liquid-phase alkyl transfer reaction was carried out to obtain a product mixture, in which the content of 2,6-dimethylnaphthalene in the bicyclic aromatic hydrocarbons was 24.1 wt%.

[0150] (2) The product mixture obtained in step (1) is fed into a distillation column and distilled under the conditions of a top pressure of 0.12 MPa, a bottom temperature of 285 °C, and 50 theoretical plates. The component except dimethylnaphthalene collected from the top of the column is returned to step (1) and mixed with the raw material to carry out alkyl transfer reaction. The content of dimethylnaphthalene isomer in the heavy component collected from the bottom of the column is 98%.

[0151] (3) The collected heavy components were sent to the first crystallizer. The complexing agent was a mixed solution of m-nitrobenzoic acid and methanol (mass ratio 1:1). The complexing agent and heavy components were mixed at a mass ratio of 2:1. The mixture was kept at 90°C for 25 min, filtered, and then washed with 12wt% sodium hydroxide solution (the molar ratio of sodium hydroxide to m-nitrobenzoic acid was 1:1) to obtain crude 2,6-dimethylnaphthalene and the complexing agent was recovered.

[0152] (4) The crude 2,6-dimethylnaphthalene product was introduced into the second crystallizer and mixed with methanol at a mass ratio of 1:3. The mixture was kept at a constant temperature of 30°C for 40 min. After crystallization, it was filtered and dried to obtain the 2,6-dimethylnaphthalene product.

[0153] The total single-pass yield of 2,6-dimethylnaphthalene was calculated to be 19.5%, with a purity of 98.6%.

[0154] Example 3

[0155] (1) Liquid-phase alkyl transfer catalyst A1 was packed into a fixed-bed reactor. 2 kg / h of feed containing 2-methylnaphthalene and pseudotrimethylbenzene (molar ratio 1:3) was introduced into the liquid-phase alkyl transfer fixed-bed reactor. The reactor was operated at 350 °C, 2.5 MPa, and a mass hourly space velocity (WHSV) of 1.2 h⁻¹. -1 Under certain conditions, a liquid-phase alkyl transfer reaction was carried out to obtain a product mixture. The content of 2,6-dimethylnaphthalene in the bicyclic aromatic hydrocarbons of the product mixture was 25.8 wt%.

[0156] (2) The product mixture obtained in step (1) is fed into a distillation column and distilled under the conditions of a top pressure of 0.006 MPa, a bottom temperature of 180 °C, and 150 theoretical plates. The component except dimethylnaphthalene collected from the top of the column is returned to step (1) and mixed with the raw material to carry out alkyl transfer reaction. The content of dimethylnaphthalene isomer in the heavy component collected from the bottom of the column is 98%.

[0157] (3) The collected heavy components were sent to the first crystallizer. The complexing agent was a mixed solution of m-nitrobenzoic acid and methanol (mass ratio 1:1). The complexing agent and heavy components were mixed at a mass ratio of 2:1. The mixture was kept at 90°C for 25 min, filtered, and then washed with 15 wt% sodium hydroxide solution (the molar ratio of sodium hydroxide to m-nitrobenzoic acid was 1:1) to obtain crude 2,6-dimethylnaphthalene and the complexing agent was recovered.

[0158] (4) The above crude 2,6-dimethylnaphthalene was introduced into the second crystallizer and mixed with the solvent methanol at a mass ratio of 1:3. The mixture was kept at a constant temperature of 28°C for 50 min. After cooling and crystallization, it was filtered and dried to obtain the 2,6-dimethylnaphthalene product.

[0159] The total single-pass yield of 2,6-dimethylnaphthalene was calculated to be 18.8%, with a purity of 98.7%.

[0160] Example 4

[0161] The method of Example 1 was followed, except that in step (1), alkyl transfer catalyst A3 was used instead of A1. The resulting product mixture contained 17.4 wt% 2,6-dimethylnaphthalene in its bicyclic aromatic hydrocarbons.

[0162] Following steps (2)-(4) of the method in Example 1, the total single-pass yield of 2,6-dimethylnaphthalene was calculated to be 10.2%, and the purity was 98.8%.

[0163] Example 5

[0164] The method of Example 1 is different except that in step (3), the mass ratio of the complexing agent to the mass of the heavy component is 1:1, the temperature is kept constant at 90°C for 25 min, filtered, and then washed with 10 wt% sodium hydroxide solution (the molar ratio of sodium hydroxide to m-nitrobenzoic acid is 1:1) to obtain crude 2,6-dimethylnaphthalene.

[0165] Then, step (4) solvent crystallization is carried out according to the method of Example 1.

[0166] The total single-pass yield of 2,6-dimethylnaphthalene was calculated to be 17.1%, with a purity of 98.7%.

[0167] Example 6

[0168] The method is the same as in Example 1, except that in step (4), crude 2,6-dimethylnaphthalene is introduced into the second crystallizer and mixed with methanol solvent at a mass ratio of 1:5. The mixture is kept at a constant temperature of 25°C for 60 min. After crystallization, it is filtered and dried to obtain the 2,6-dimethylnaphthalene product.

[0169] The total single-pass yield of 2,6-dimethylnaphthalene was calculated to be 18.3%, with a purity of 98.6%.

[0170] Comparative Example 1

[0171] The liquid-phase alkyl transfer reaction was carried out according to the method of Example 1 to obtain a mixture of products.

[0172] In step (2), the obtained product mixture is introduced into a second crystallizer and mixed with methanol solvent at a mass ratio of 1:3. The mixture is kept at a constant temperature of 25°C for 60 min. After cooling and crystallization, it is filtered and dried to obtain crude 2,6-dimethylnaphthalene.

[0173] The crude 2,6-dimethylnaphthalene was then fed into the first crystallizer and mixed with a complexing agent, a mixture of m-nitrobenzoic acid and methanol (mass ratio 1:1), at a mass ratio of 2:1. The mixture was kept at 90°C for 25 minutes, filtered, and then washed with a 10 wt% sodium hydroxide solution (the molar ratio of sodium hydroxide to m-nitrobenzoic acid was 1:1). The purity of the 2,6-dimethylnaphthalene in the solid product was 85.4%, which did not meet the purity requirements of the product.

[0174] The comparison between the above examples and comparative examples shows that the production method provided by the present invention can obtain high-purity 2,6-dimethylnaphthalene with a purity of over 98%, which meets the requirements for 2,6-dimethylnaphthalene as a drug precursor and polymer monomer, while also having a high yield. Compared with the examples, the method of the comparative examples cannot obtain the required high-purity 2,6-dimethylnaphthalene.

[0175] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for producing 2,6-dimethylnaphthalene, characterized in that, The method includes: (1) Under liquid phase conditions, in the presence of an alkyl transfer catalyst, the reactants are contacted with a transfer alkylating agent to obtain a product mixture; wherein the reactants include at least one of naphthalene, 1-methylnaphthalene and 2-methylnaphthalene; the transfer alkylating agent is at least one of methyl-substituted monocyclic aromatic hydrocarbons; based on the total content of bicyclic aromatic hydrocarbons in the product mixture, the content of 2,6-dimethylnaphthalene is not less than 15 wt%; (2) The product mixture is distilled to obtain a light component and a heavy component containing a dimethylnaphthalene isomer. The light component is returned to step (1) to provide at least a portion of the reaction feedstock. (3) The heavy components obtained by distillation are mixed with a complexing agent for complexation crystallization, and then washed with alkali to obtain crude 2,6-dimethylnaphthalene; (4) Mix the crude 2,6-dimethylnaphthalene with a solvent and recrystallize it.

2. The production method according to claim 1, wherein, Based on the total content of bicyclic aromatic hydrocarbons in the product mixture, the content of 2,6-dimethylnaphthalene is not less than 20 wt%, preferably 20-40 wt%. Preferably, the alkyl transfer catalyst comprises a support and an active metal component supported on the support; wherein the support comprises a twelve-membered ring molecular sieve and a binder; and the active metal component is selected from at least one transition metal. Preferably, the amount of Brønsted acid in the alkyl transfer catalyst is 100-400 μmol / g, more preferably 150-350 μmol / g; Preferably, the ratio of the amount of Brønsted acid to the amount of Lewis acid is 1-3:1, more preferably 1.2-3:1; Preferably, the alkyl transfer catalyst has a specific surface area of ​​250-700 m². 2 / g, preferably 300-650m 2 / g; Preferably, the pore volume of the alkyl transfer catalyst is 0.28-0.7 mL / g, and more preferably 0.3-0.68 mL / g.

3. The production method according to claim 2, wherein, The twelve-membered ring molecular sieve is selected from at least one of Y molecular sieve, Beta molecular sieve, MCM-22 molecular sieve, MCM-56 molecular sieve, SAPO-5 molecular sieve, SAPO-37 molecular sieve, and SAPO-40 molecular sieve, preferably at least one of Y molecular sieve, Beta molecular sieve, and SAPO-5 molecular sieve. Preferably, the molar ratio of silica to alumina in the twelve-membered ring molecular sieve is 0.1-30; Preferably, the binder is selected from at least one of alumina, kaolin, attapulgite, bentonite, diatomaceous earth and silica, and is preferably alumina; Preferably, based on the total amount of the carrier, the content of the twelve-membered ring molecular sieve is 60-80 wt%, more preferably 65-75 wt%; and the content of the binder is 20-40 wt%, more preferably 25-35 wt%.

4. The production method according to claim 2 or 3, wherein, The active metal component is selected from at least one of Cu, Fe and Zn, more preferably Cu and / or Fe; Preferably, based on the total amount of the alkyl transfer catalyst, the content of the support is 90-99.9 wt%, more preferably 92-99 wt%, and the content of the active metal component, calculated by element, is 0.1-10 wt%, more preferably 1-8 wt%.

5. The production method according to any one of claims 1-4, wherein, In step (1), the transfer alkylating agent is selected from at least one of toluene, xylene, trimethylbenzene, and tetramethylbenzene; Preferably, the molar ratio of the reactant to the transfer alkylating agent is 1:(1-10), more preferably, and even more preferably 1:(2-7); Preferably, the liquid phase conditions include: a reaction temperature of 150-400℃, more preferably 250-350℃; a reaction pressure of 0.5-5 MPa, more preferably 2.0-4.0 MPa; and a weight hourly space velocity (WHSV) of 0.1-5 h⁻¹ for the reactants. -1 Preferably 0.5-3h -1 .

6. The production method according to any one of claims 1-5, wherein, In step (2), the total amount of dimethylnaphthalene isomer in the recombinant components is not less than 95 wt%, preferably not less than 97 wt%; Preferably, in step (2), the distillation conditions include: a bottom temperature of 150-300℃, a theoretical number of plates of 50-150, and a top pressure of 0.005-0.15MPa.

7. The production method according to any one of claims 1-6, wherein, In step (3), the complexing agent includes m-nitrobenzoic acid and methanol; Preferably, the mass ratio of m-nitrobenzoic acid to methanol is 0.3-8:1, more preferably 0.5-5:1; Preferably, the mass ratio of the complexing agent to the heavy component is 0.4-4:1, and more preferably 1.2-2.4:

1.

8. The production method according to any one of claims 1-7, wherein, The temperature for complexation crystallization is 80-120℃, preferably 90-100℃; the time for complexation crystallization is 10-50 min, preferably 20-30 min. Preferably, the alkaline washing in step (3) includes: contacting the complexed crystallized solid product with an alkaline solution; Preferably, the alkaline solution is an aqueous solution of an alkali, and the alkali is preferably sodium hydroxide; Preferably, the concentration of the alkaline solution is 5-20% by weight; Preferably, the molar ratio of the alkali in the alkaline solution to the m-nitrobenzoic acid in the complexing agent is 0.8-1.2:

1.

9. The production method according to any one of claims 1-8, wherein, In step (4), the solvent is an alcohol compound, preferably methanol and / or ethanol; Preferably, the mass ratio of the solvent to crude 2,6-dimethylnaphthalene is 1-3:1; Preferably, the recrystallization temperature is 10-30℃, and more preferably 15-25℃.

10. A system for producing 2,6-dimethylnaphthalene, comprising: The raw material supply unit, alkyl transfer reaction unit, distillation unit, first crystallization unit, and second crystallization unit are sequentially connected along the logistics direction; among them, The raw material supply unit is used to supply reaction raw materials and transfer alkylating agents to the alkyl transfer reaction unit; wherein, the reaction raw materials include at least one of naphthalene, 1-methylnaphthalene, and 2-methylnaphthalene; and the transfer alkylating agent is at least one of methyl-substituted monocyclic aromatic hydrocarbons. The alkyl transfer reaction unit includes a fixed-bed reactor, which is filled with an alkyl transfer catalyst for contacting the reactants with a transfer alkylating agent to carry out an alkyl transfer reaction. The distillation unit includes a distillation column for distilling the product mixture from the alkyl transfer reaction unit. The top material outlet of the distillation column is connected to the raw material supply unit, and the bottom material outlet is connected to the first crystallization unit. The first crystallization unit includes a first crystallizer and a first washing filter connected in sequence, used to mix the heavy components from the distillation unit with a complexing agent for complexation crystallization and alkali washing to obtain crude 2,6-dimethylnaphthalene; The second crystallization unit includes a second crystallizer for recrystallizing crude 2,6-dimethylnaphthalene by mixing it with a solvent.

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