Catalyst for preparing 2, 6-dimethylnaphthalene through alkylation of 2-methylnaphthalene as well as preparation method and application of catalyst

Abstract

The invention provides a catalyst for preparing 2, 6-dimethylnaphthalene through alkylation of 2-methylnaphthalene as well as a preparation method and application of the catalyst. The preparation method of the catalyst comprises the following steps: adding an MCM-22 molecular sieve into a 0.001-5mol / L solution containing transition metal and rare earth metal elements for ion exchange, and then filtering, washing, drying and roasting to obtain the catalyst, the invention also provides the catalyst prepared by the method and a method for preparing 2, 6-dimethylnaphthalene by alkylation of 2-methylnaphthalene and methanol based on the catalyst. On the premise of ensuring high activity and high stability, the MCM-22 molecular sieve provided by the invention also has good selectivity on dimethylnaphthalene and 2, 6-dimethylnaphthalene.

Description

Technical Field

[0001] The present invention relates to a catalyst for preparing 2,6-dimethylnaphthalene by alkylation of 2-methylnaphthalene, a preparation method thereof and an application thereof, belonging to the field of chemical engineering technology. Background Art

[0002] As a new type of high-performance polyester material, polyethylene naphthalate (PEN) has excellent mechanical properties, heat resistance, gas barrier properties, chemical stability, modulus and dimensional stability, etc., and all its properties are superior to those of traditional polyethylene terephthalate (PET). It is widely used in fields such as electronic components, films, packaging, fibers, nanoplastics, aviation and atomic energy materials. Therefore, it will have a huge market space and excellent application prospects in the future, which in turn makes the demand for 2,6-naphthalenedicarboxylic acid, an important raw material for synthesizing PEN, increase sharply.

[0003] Currently, the method of oxidizing 2,6-alkylnaphthalene is mainly used to prepare 2,6-naphthalenedicarboxylic acid. Compared with other 2,6-dialkylnaphthalenes (such as 2,6-diethylnaphthalene, 2,6-dibutylnaphthalene and 2,6-dipropylnaphthalene, etc.), 2,6-dimethylnaphthalene (2,6-DMN) is more easily oxidized and there is no carbon atom loss during the oxidation process. It is the most suitable raw material for synthesizing 2,6-naphthalenedicarboxylic acid. Therefore, 2,6-DMN is an important monomer for synthesizing PEN polyester materials.

[0004] Amoco Corporation developed a process for synthesizing 2,6-DMN from o-xylene and butadiene through four steps of side-chain alkylation, cyclization, dehydrogenation and isomerization. However, due to the very complex synthesis process, the production of 2,6-DMN is small and the cost is high, which restricts the application development of PEN. 2,6-DMN can be directly separated and extracted from raw materials containing DMN such as coal tar and petroleum cracking heavy aromatics. However, due to the limited abundance of 2,6-DMN in the raw materials (0.5-5%), simply separating it, the purification route still cannot meet the needs of downstream PEN polyester; at the same time, during the process of separating and extracting 2,6-DMN, other naphthalene components such as naphthalene, methylnaphthalene, dimethylnaphthalene, etc. are also effectively enriched. And the route of synthesizing 2,6-DMN by one-step alkylation reaction of 2-methylnaphthalene (2-MN) with methanol (CH 3 OH) using molecular sieve catalyst has the advantages of simple process, wide raw material source and low price, which is beneficial to reducing the production cost of PEN. Therefore, the alkylation reaction of 2-MN with CH 3 OH catalyzed by molecular sieve to synthesize 2,6-DMN is a synthetic route with development prospects.

[0005] Among petrochemical raw materials, catalytic cracking cycle oil (LCO) and ethylene tar are both rich in naphthalene-based bicyclic aromatic hydrocarbons, and their production volumes are respectively above tens of millions of tons and more than one million tons. At present, the utilization routes of LCO mainly include blending gasoline and diesel, and producing chemical products such as BTX through hydroconversion. The utilization routes of ethylene tar mainly include producing petroleum resins, polycondensing to produce carbon fibers or directly using them as fuels, etc. While separating and purifying 2,6-DMN from LCO or ethylene tar, catalytic conversion of other enriched naphthalene components to 2,6-DMN to form a complete process route can effectively ensure the yield of 2,6-DMN, further increase the added value of the raw materials, meet the current demand for improving the added value of products in the refining and chemical transformation, and solve the key technologies in the refining and chemical transformation.

[0006] CN 1151107C discloses the alkylation reaction of 2-MN with CH 3 OH catalyzed by HZSM-5 molecular sieve. It is found that within 100 h of the reaction, the highest selectivity of 2,6-DMN reaches 38.11%, and the highest conversion rate of 2-MN is only 9.49%, and it continuously decreases as the reaction time goes on. The HZSM-5 molecular sieve used in this technology has poor activity and stability.

[0007] SHENG Luyang et al. (SHENG Luyang, ZHAN Junling, ZHANG Xupeng, et al. Preparation of core-shell ZSM-5@Beta molecular sieve and catalytic alkylation to 2,6-dimethylnaphthalene[J]. Journal of Fuel Chemistry and Technology, 2022, 50(9): 1202-1210.) used Hβ molecular sieve to catalyze the alkylation synthesis of 2-MN and CH 3 OH to 2,6-DMN. It is found that after 6 h of the reaction, the conversion rate of 2-MN decreases from about 91% at the beginning of the reaction to 31%, and the selectivity of 2,6-DMN increases from 3% to 11%. The Hβ molecular sieve used in this technology has poor stability.

[0008] WANG Xuyan et al. (Research on the synthesis of 2,6-dimethylnaphthalene by shape-selective catalysis [D]. Dalian: Dalian University of Technology, 2006.) used HZSM-12 molecular sieve to catalyze the alkylation reaction of 2-MN and CH 3 OH for 8.25 h. It is found that the conversion rate of 2-MN decreases from 27% at the beginning of the reaction to 15%. The HZSM-12 molecular sieve used in this technology has poor activity and stability.

[0009] YE Runping, et al. (YE Runping, LIU Qinghua, WEN Zhihui, et al. Shape-selective catalysts of Mg 2+ ion exchange modified SAPO-11 molecular sieves for alkylation of 2-methylnaphthalene[J]. Microporous and Mesoporous Materials, 2022, 346:112291.) used SAPO-11 to catalyze the alkylation reaction of 2-MN with CH 3 OH. It was found that the initial conversion rate of 2-MN was 41.3%, and the selectivity of 2,6-DMN was 29.7%. However, as the reaction time was extended to 6 h, the conversion rate of 2-MN decreased to 13.9%. The SAPO-11 molecular sieve used in this technology had poor activity and stability.

[0010] CN 101972667A discloses a molecular sieve of 7.0 wt% / Ce 2 O 3 / 7.0 wt% MgO / 6.0 wt% NiO modified HMOR. After using it in the alkylation reaction of 2-MN with CH 3 OH for 25 h, it was found that the conversion rate of 2-MN decreased from 35.05% to 31.79%, and the selectivity of 2,6-DMN increased from 60% to 63%. The HMOR molecular sieve used in this technology had poor activity and stability.

[0011] The content disclosed in US 5001295 was compared and studied on the catalytic performance of HZSM-5 and HMCM-22 molecular sieves in the alkylation reaction of 2-MN with CH 3 OH. It was found that compared with the HZSM-5 molecular sieve, the activity and stability of the HMCM-22 molecular sieve in the alkylation reaction of 2-MN with CH 3 OH were greatly improved, and it was expected to achieve efficient and stable conversion of 2-methylnaphthalene in the industrial production process. However, within 240 h, the conversion rate of 2-MN showed a continuous downward trend, and the stability of the HMCM-12 molecular sieve used in this technology was still not high enough. Summary of the Invention

[0012] To solve the above technical problems, the purpose of the present invention is to provide a catalyst for the alkylation of 2-methylnaphthalene to prepare 2,6-dimethylnaphthalene, its preparation method and application, and this catalyst can provide high activity, high selectivity and high stability.

[0013] To achieve the above object, the present invention provides a method for preparing a catalyst for the alkylation of 2-methylnaphthalene to prepare 2,6-dimethylnaphthalene, which comprises the following steps:

[0014] Adding MCM-22 molecular sieve into a solution containing transition metals and rare earth metal elements with a concentration of 0.001-5 mol / L for ion exchange, and then obtaining the catalyst for the alkylation of 2-methylnaphthalene to prepare 2,6-dimethylnaphthalene through filtration, washing, drying, and calcination;

[0015] Wherein, the solid-liquid ratio of the MCM-22 molecular sieve to the solution containing transition metals and rare earth metal elements is 1:5-1:20, g:mL.

[0016] According to a specific embodiment of the present invention, preferably, the concentration of the solution containing transition metals and rare earth metal elements is 0.8-3.5 mol / L.

[0017] According to a specific embodiment of the present invention, preferably, the temperature of the ion exchange is 20-100 °C, and the time is 0.5-24 h.

[0018] According to a specific embodiment of the present invention, preferably, the temperature of the calcination is 200-700 °C, and the time is 0.5-10 h.

[0019] According to a specific embodiment of the present invention, preferably, the transition metals and rare earth metal elements are selected from one or more combinations of iron, cobalt, nickel, ruthenium, rhodium, palladium, rhenium, osmium, iridium, platinum, copper, zinc, molybdenum, magnesium, lanthanum, cerium, neodymium, and samarium; preferably, the transition metal elements and rare earth metal elements are selected from one or more combinations of iron, cobalt, zinc, magnesium, and lanthanum.

[0020] The present invention also provides a catalyst for the alkylation of 2-methylnaphthalene to prepare 2,6-dimethylnaphthalene, which is prepared by the above method for preparing a catalyst.

[0021] According to a specific embodiment of the present invention, preferably, by mass percentage, the catalyst comprises the following components: 70-99.99% of MCM-22 molecular sieve, 0.01-30% of transition metals and rare earth metal elements.

[0022] According to a specific embodiment of the present invention, preferably, by mass percentage, the catalyst comprises the following components: 98-99.8% of MCM-22 molecular sieve, 0.6-1.5% of transition metals and rare earth metal elements.

[0023] According to a specific embodiment of the present invention, preferably, by mass percentage, the sodium element content of the catalyst is 0.00001%-0.15%, and more preferably, the sodium element content is 0.03%.

[0024] According to a specific embodiment of the present invention, preferably, the SiO of the catalyst 2 / Al 2 O 3 has a ratio of 1 - 600:1, a specific surface area of 140 - 700 m 2 / g, and a pore volume of 0.02 - 1.5 cm 3 / g.

[0025] According to a specific embodiment of the present invention, preferably, the SiO of the catalyst 2 / Al 2 O 3 has a ratio of 1 - 600:1, a specific surface area of 360 - 430 m 2 / g, and a pore volume of 0.8 - 1.2 cm 3 / g.

[0026] The present invention also provides a method for the alkylation of 2 - methylnaphthalene with methanol to prepare 2,6 - dimethylnaphthalene. Among them, this method uses the above - mentioned alkylation catalyst, and this method includes the following steps:

[0027] Load the catalyst into a fixed - bed reactor, and in a nitrogen atmosphere, perform in - situ activation pretreatment at 200 - 300 °C for 6 - 8 h;

[0028] Mix 2 - methylnaphthalene, methanol and a solvent to obtain a feed liquid; wherein, the molar ratio of methanol to 2 - methylnaphthalene is 0.5 - 4, and the mass ratio of 2 - methylnaphthalene to (2 - methylnaphthalene + solvent) is 0.1 - 1; preferably, the molar ratio of methanol to 2 - methylnaphthalene is 0.8 - 2.2, and the mass ratio of 2 - methylnaphthalene to (2 - methylnaphthalene + solvent) is 0.5 - 1;

[0029] The solvent includes one or a combination of two or more of benzene, toluene, xylene, trimethylbenzene, tetramethylbenzene. Preferably, the solvent is mesitylene and / or durene;

[0030] Introduce the feed liquid into the reactor to contact with the catalyst bed for reaction to generate a product containing 2,6 - dimethylnaphthalene. Among them, the reaction temperature is 300 - 490 °C; based on the mass space velocity of 2 - methylnaphthalene, the feed mass space velocity of the feed liquid is 0.2 - 6.0 h -1 ; the reaction pressure is 0 - 10 MPa; preferably, the reaction temperature is 300 - 400 °C; based on the mass space velocity of 2 - methylnaphthalene, the feed mass space velocity of the feed liquid is 0.2 - 3.0 h -1 ; the reaction pressure is 0 - 4 MPa.

[0031] The synthesis of 2,6-DMN by the alkylation reaction of 2-methylnaphthalene and methanol over zeolite catalysts is a promising synthetic route. However, currently used zeolite catalysts such as HZSM-5, HZSM-12, SAPO-11, Hβ, HMOR, and HMCM-22 for the alkylation reaction are difficult to simultaneously possess high activity and high stability, and cannot ensure efficient and stable industrial production of 2,6-dimethylnaphthalene. The catalyst provided by the present invention is a methylnaphthalene alkylation catalyst with both high activity and high stability, thus solving the problem that zeolite catalysts are difficult to simultaneously possess high activity and high stability in the alkylation reaction.

[0032] Compared with the background art, the present invention has the following advantages:

[0033] (1) The raw materials used in the present invention are composed of 2-methylnaphthalene, methanol, and a solvent. The alkylation reaction is a multiphase continuous reaction, and the reaction products containing 2,6-dimethylnaphthalene are easily separated from the catalyst. The operation is simple and convenient for industrial production.

[0034] (2) The MCM-22 zeolite modified with transition metals and rare earth metal elements in the present invention maintains the crystal phase structure of the MCM-22 zeolite. However, due to the introduction of transition metals and rare earth metal elements, the zeolite has an appropriate acidity and specific surface area, and the transition metals and rare earth metal elements are in a highly uniform distribution state, promoting the occurrence of the main alkylation reaction and inhibiting the formation of coke, thereby greatly improving the alkylation activity and stability of the zeolite for 2-methylnaphthalene. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 XRD diagrams of Comparative Example 1 and Examples 1-5.

[0036] Figure 2 For Comparative Example 1 and Examples 1-2 of NH 3 -TPD diagrams.

[0037] Figure 3 For Comparative Example 1 and Examples 3-5 of NH 3 -TPD diagrams.

[0038] Figure 4 Alkylation reaction result diagrams of Comparative Example 2 and Examples 6-7.

[0039] Figure 5 Alkylation reaction result diagrams of Comparative Example 2 and Examples 8-10. DETAILED DESCRIPTION OF THE INVENTION

[0040] In order to have a clearer understanding of the technical features, objectives, and beneficial effects of the present invention, the technical solutions of the present invention are described in detail below, but it should not be construed as a limitation on the scope of implementation of the present invention.

[0041] Comparative Example 1

[0042] The physical properties and structural characterization of the MCM-22 molecular sieve purchased from Huawei Ruike were carried out by nitrogen adsorption-desorption instrument, X-ray diffraction (XRD) and ammonia adsorption temperature-programmed desorption (NH 3 -TPD). It was found that the specific surface area of the MCM-22 molecular sieve was 428.5 m 2 / g, the pore volume was 1.22 cm 3 / g. The XRD and NH 3 -TPD results of the MCM-22 molecular sieve are shown in Figure 1 and Figure 2 .

[0043] Example 1

[0044] The MCM-22 molecular sieve (purchased from Huawei Ruike) was added to a 0.8 mol / L lanthanum nitrate solution (99.5% lanthanum(III) hexahydrate, purchased from Sinopharm Chemical Reagent Co., Ltd.) at a solid-liquid ratio (g:ml) of 1:10, ion-exchanged at 60 °C for 1 h, then washed, filtered, dried at 80 °C, and calcined at 550 °C for 4 h. The obtained lanthanum element-modified MCM-22 catalyst (La 1 @MCM-22) has the MCM-22 molecular sieve as the main body.

[0045] By mass percentage, the catalyst contains 99.37% of MCM-22 molecular sieve, 0.03% of sodium element, and 0.6% of lanthanum element; the specific surface area of the catalyst is 420.5 m 2 / g, and the pore volume is 1.18 cm 3 / g.

[0046] The XRD and NH 3 -TPD results of the modified catalyst are shown in Figure 1 and Figure 2 . It can be seen from the XRD results that the crystal phase structure of MCM-22 does not change after La modification, but it can be seen from the NH 3 -TPD results that due to the introduction of La replacing the hydrogen protons in the molecular sieve, the strong acid centers of the molecular sieve are reduced.

[0047] Example 2

[0048] The La 1 @MCM-22 obtained in Example 1 was added to a 3.5 mol / L lanthanum nitrate solution at a solid-liquid ratio (g:ml) of 1:10, ion-exchanged at 90 °C for 12 h, then washed, filtered, dried at 80 °C, and calcined at 550 °C for 4 h. The obtained lanthanum element-modified MCM-22 catalyst (La 2(@MCM-22), the main body is MCM-22 molecular sieve.

[0049] By mass percentage, the catalyst contains 98.47% of MCM-22 molecular sieve, 0.03% of sodium element, and 1.5% of lanthanum element; the specific surface area of the catalyst is 415.7 m 2 / g, and the pore volume is 1.09 cm 3 / g.

[0050] The XRD and NH 3 -TPD results of the modified catalyst are shown in Figure 1 and Figure 2 . It can be seen from the XRD results that the crystal phase structure of MCM-22 does not change after being modified by La. However, it can be seen from the NH 3 -TPD results that due to the introduction of La replacing the hydrogen protons in the molecular sieve, the acid strength of the strong acid and weak acid centers of the molecular sieve decreases, but the acid amount increases.

[0051] Example 3

[0052] The MCM-22 molecular sieve (purchased from Huawei Reike) was added to a 3.5 mol / L iron nitrate solution (iron(III) nitrate nonahydrate (≥98.5%), purchased from Sinopharm Chemical Reagent Co., Ltd.) at a solid-liquid ratio (g:ml) of 1:10 and ion-exchanged at 90 °C for 12 h, then washed, filtered, dried at 80 °C, and calcined at 550 °C for 4 h. The obtained iron element-modified MCM-22 catalyst (Fe@MCM-22), the main body is MCM-22 molecular sieve.

[0053] By mass percentage, the catalyst contains 99.17% of MCM-22 molecular sieve, 0.03% of sodium element, and 0.8% of iron element; the specific surface area of the catalyst is 399.6 m 2 / g, and the pore volume is 0.92 cm 3 / g.

[0054] The XRD and NH 3 -TPD results of the catalyst before and after modification are shown in Figure 1 and Figure 3 . It can be seen from the XRD results that the crystal phase structure of MCM-22 does not change after being modified by Fe. However, it can be seen from the NH 3 -TPD results that due to the introduction of Fe, the strong acid centers of the molecular sieve increase, while the weak acid centers remain basically unchanged.

[0055] Example 4

[0056] Replace the iron nitrate in Example 3 with zinc nitrate, and repeat the steps described in Example 3. The obtained zinc element modified MCM-22 catalyst (Zn@MCM-22) has an MCM-22 molecular sieve as the main body.

[0057] By mass percentage, the catalyst contains 99.16% of MCM-22 molecular sieve, 0.03% of sodium element, and 0.81% of zinc element; the specific surface area of the catalyst is 364.7 m 2 / g, and the pore volume is 0.89 cm 3 / g.

[0058] The XRD and NH 3 -TPD results of the catalyst before and after modification are shown in Figure 1 and Figure 3 . It can be seen from the XRD results that after Zn modification, the crystal phase structure of the MCM-22 molecular sieve has not changed, but from the NH 3 -TPD results, it can be seen that due to the introduction of Zn replacing the hydrogen protons in the molecular sieve, the strong acid and weak acid centers of the molecular sieve are reduced.

[0059] Example 5

[0060] Replace the iron nitrate in Example 3 with magnesium nitrate, and repeat the steps described in Example 3. The obtained magnesium element modified MCM-22 catalyst (Mg@MCM-22) has an MCM-22 molecular sieve as the main body.

[0061] By mass percentage, the catalyst contains 99.14% of MCM-22 molecular sieve, 0.03% of sodium element, and 0.83% of magnesium element; the specific surface area of the catalyst is 360.3 m 2 / g, and the pore volume is 0.92 cm 3 / g.

[0062] The XRD and NH 3 -TPD results of the catalyst before and after modification are shown in Figure 1 and Figure 3 . It can be seen from the XRD results that after Mg modification, the crystal phase structure of the MCM-22 molecular sieve has not changed, but from the NH 3 -TPD results, it can be seen that due to the introduction of Mg replacing the hydrogen protons in the molecular sieve, the strong acid and weak acid centers of the molecular sieve are reduced.

[0063] Comparative Example 2

[0064] Investigate the catalytic performance of unmodified MCM-22 molecular sieve in the alkylation reaction of 2-methylnaphthalene on a fixed-bed reactor. Use a stainless-steel reactor with an inner diameter of 10 mm, and the reaction pressure is 3.2 MPa.

[0065] First, 5.0 g of molecular sieve catalyst was loaded into the reactor. Then, it was pretreated by in-situ activation at 200 - 300 °C for 7 h in a nitrogen atmosphere; Secondly, a raw material liquid was prepared according to the ratio of methanol / 2-methylnaphthalene = 1.02 (mol / mol) and 2-methylnaphthalene / (2-methylnaphthalene + 1,3,5-trimethylbenzene) = 0.8 (wt / wt), and it was mixed evenly.

[0066] Finally, the raw material liquid was introduced into the reactor by a metering pump to contact with the catalyst bed. The reaction conditions were: temperature 350 °C, pressure 3.2 MPa, and space velocity (calculated based on 2-methylnaphthalene) 0.3 h -1 . After the product was condensed, a sample was taken and analyzed on a gas chromatograph. The reaction results are shown in Figure 4 .

[0067] Example 6

[0068] The catalytic performance of La 1 @MCM-22 molecular sieve in the alkylation reaction of 2-methylnaphthalene was investigated on a fixed-bed reactor. A stainless-steel reactor with an inner diameter of 10 mm was used, and the reaction pressure was 3.2 MPa.

[0069] First, 5.0 g of molecular sieve catalyst was loaded into the reactor. Then, it was pretreated by in-situ activation at 200 - 300 °C for 7 h in a nitrogen atmosphere; Secondly, a raw material liquid was prepared according to the ratio of methanol / 2-methylnaphthalene = 1.02 (mol / mol) and 2-methylnaphthalene / (2-methylnaphthalene + 1,3,5-trimethylbenzene) = 0.8 (wt / wt), and it was mixed evenly.

[0070] Finally, the raw material liquid was introduced into the reactor by a metering pump to contact with the catalyst bed. The reaction conditions were: temperature 350 °C, pressure 3.2 MPa, and space velocity (calculated based on 2-methylnaphthalene) 0.3 h -1 . After the product was condensed, a sample was taken and analyzed on a gas chromatograph. The reaction results are shown in Figure 4 .

[0071] Example 7

[0072] The catalytic performance of La 2 @MCM-22 molecular sieve in the alkylation reaction of 2-methylnaphthalene was investigated on a fixed-bed reactor. A stainless-steel reactor with an inner diameter of 10 mm was used, and the reaction pressure was 3.2 MPa.

[0073] First, 5.0 g of molecular sieve catalyst was loaded into the reactor. Then, it was pretreated by in-situ activation at 200 - 300 °C for 7 h in a nitrogen atmosphere; Secondly, a raw material liquid was prepared according to the ratio of methanol / 2-methylnaphthalene = 1.02 (mol / mol) and 2-methylnaphthalene / (2-methylnaphthalene + 1,3,5-trimethylbenzene) = 0.8 (wt / wt), and it was mixed evenly.

[0074] Finally, the raw material liquid was introduced into the reactor by a metering pump to contact with the catalyst bed. The reaction conditions were as follows: temperature was 350 °C, pressure was 3.2 MPa, and space velocity (calculated based on 2-methylnaphthalene) was 0.3 h -1 . After condensation, the product was sampled and analyzed on a gas chromatograph. The reaction results are shown in Figure 4 .

[0075] Example 8

[0076] The alkylation reaction performance of Fe@MCM-22 molecular sieve in catalyzing 2-methylnaphthalene was investigated on a fixed-bed reactor. A stainless-steel reactor with an inner diameter of 10 mm was used, and the reaction pressure was 3.2 MPa

[0077] First, 5.0 g of the molecular sieve catalyst was loaded into the reactor. Then, it was pretreated by in-situ activation at 200 - 300 °C for 7 h in a nitrogen atmosphere. Secondly, the raw material liquid was prepared according to the ratio of methanol / 2-methylnaphthalene = 1.02 (mol / mol) and 2-methylnaphthalene / (2-methylnaphthalene + 1,3,5-trimethylbenzene) = 0.8 (wt / wt), and it was mixed evenly

[0078] Finally, the raw material liquid was introduced into the reactor by a metering pump to contact with the catalyst bed. The reaction conditions were as follows: temperature was 350 °C, pressure was 3.2 MPa, and space velocity (calculated based on 2-methylnaphthalene) was 0.3 h -1 . After condensation, the product was sampled and analyzed on a gas chromatograph. The reaction results are shown in Figure 5 .

[0079] Example 9

[0080] The alkylation reaction performance of Zn@MCM-22 molecular sieve in catalyzing 2-methylnaphthalene was investigated on a fixed-bed reactor. A stainless-steel reactor with an inner diameter of 10 mm was used, and the reaction pressure was 3.2 MPa

[0081] First, 5.0 g of the molecular sieve catalyst was loaded into the reactor. Then, it was pretreated by in-situ activation at 200 - 300 °C for 7 h in a nitrogen atmosphere. Secondly, the raw material liquid was prepared according to the ratio of methanol / 2-methylnaphthalene = 1.02 (mol / mol) and 2-methylnaphthalene / (2-methylnaphthalene + 1,3,5-trimethylbenzene) = 0.8 (wt / wt), and it was mixed evenly

[0082] Finally, the raw material liquid was introduced into the reactor by a metering pump to contact with the catalyst bed. The reaction conditions were as follows: temperature was 350 °C, pressure was 3.2 MPa, and space velocity (calculated based on 2-methylnaphthalene) was 0.3 h -1 . After condensation, the product was sampled and analyzed on a gas chromatograph. The reaction results are shown in Figure 5 .

[0083] Example 10

[0084] The catalytic performance of Mg@MCM-22 zeolite in the alkylation reaction of 2-methylnaphthalene was investigated on a fixed-bed reactor. A stainless-steel reactor with an inner diameter of 10 mm was used, and the reaction pressure was 3.2 MPa.

[0085] First, 5.0 g of zeolite catalyst was loaded into the reactor. Then, it was pretreated by in-situ activation at 200 - 300 °C for 7 h in a nitrogen atmosphere. Secondly, a raw material solution was prepared according to the ratio of methanol / 2-methylnaphthalene = 1.02 (mol / mol) and 2-methylnaphthalene / (2-methylnaphthalene + 1,3,5-trimethylbenzene) = 0.8 (wt / wt), and it was mixed evenly.

[0086] Finally, the raw material solution was introduced into the reactor by a metering pump to contact the catalyst bed. The reaction conditions were: temperature 350 °C, pressure 3.2 MPa, and space velocity (calculated based on 2-methylnaphthalene) 0.3 h -1 . After condensation, the product was sampled and analyzed on a gas chromatograph. The reaction results are shown in Figure 5 .

[0087] From Figure 4 and Figure 5 it can be seen that after 30 h of the alkylation reaction catalyzed by unmodified MCM-22 zeolite, the conversion rate decreased from 49% to 45%. However, within 100 h of the alkylation reaction catalyzed by Fe-, Zn-, Mg-, and La-modified MCM-22 zeolites, the conversion rate of 2-methylnaphthalene did not decrease, and the conversion rate was above 45%, indicating that the modified zeolites have the characteristics of high activity and high stability. Among them, the conversion rate of 2-methylnaphthalene over La-modified MCM-22 zeolite remained at 50% for at least 250 h, which is significantly higher than the results reported in the professional literature in the current field, and has significant industrial application value.

Claims

1. A preparation method of a catalyst for the alkylation of 2-methylnaphthalene to prepare 2,6-dimethylnaphthalene, which comprises the following steps: Adding MCM-22 molecular sieve into a solution containing transition metal and rare earth metal elements with a concentration of 0.001 - 5 mol / L for ion exchange, and then obtaining the catalyst for the alkylation of 2-methylnaphthalene to prepare 2,6-dimethylnaphthalene through filtration, washing, drying, and calcination; Wherein, the solid-liquid ratio of the MCM-22 molecular sieve to the solution containing transition metal and rare earth metal elements is 1:5 - 1:20, g:mL.

2. The preparation method according to claim 1, wherein, the temperature of the ion exchange is 20 - 100 °C, and the time is 0.5 - 24 h.

3. The preparation method according to claim 1, wherein, the temperature of the calcination is 200 - 700 °C, and the time is 0.5 - 10 h.

4. The preparation method according to claim 1, wherein, the transition metal and rare earth metal elements are selected from one or a combination of two or more of iron, cobalt, nickel, ruthenium, rhodium, palladium, rhenium, osmium, iridium, platinum, copper, zinc, molybdenum, magnesium, lanthanum, cerium, neodymium, and samarium.

5. A catalyst for the alkylation of 2-methylnaphthalene to prepare 2,6-dimethylnaphthalene, which is prepared by using the preparation method described in any one of claims 1 - 4.

6. The catalyst according to claim 5, wherein, by mass percentage, this catalyst contains the following components: 70 - 99.99% of MCM-22 molecular sieve, 0.01 - 30% of transition metal and rare earth metal elements.

7. The catalyst according to claim 5, wherein, by mass percentage, the sodium element content of this catalyst is 0.00001% - 0.15%.

8. The catalyst according to claim 5, wherein, The SiO of this catalyst 2 / Al 2 O 3 ratio is 1 - 600:1, the specific surface area is 140 - 700 m 2 / g, and the pore volume is 0.02 - 1.5 cm 3 / g.

9. A method for the alkylation of 2-methylnaphthalene to prepare 2,6-dimethylnaphthalene, which is carried out by using the catalyst described in any one of claims 5 - 8.

10. The method according to claim 9, which comprises the following steps: Loading the catalyst into a fixed-bed reactor, and carrying out in-situ activation pretreatment at 200 - 300 °C for 6 - 8 h in a nitrogen atmosphere; Mixing 2-methylnaphthalene, methanol, and a solvent to obtain a raw material liquid; wherein, the molar ratio of methanol to 2-methylnaphthalene is 0.5 - 4, and the mass ratio of 2-methylnaphthalene to (2-methylnaphthalene + solvent) is 0.1 - 1; The solvent includes one or a combination of two or more of benzene, toluene, xylene, trimethylbenzene, and tetramethylbenzene; Introduce the raw material liquid into the reactor to contact and react with the catalyst bed to generate a product containing 2,6-dimethylnaphthalene; wherein, the reaction temperature is 300 - 490 °C; based on the mass hourly space velocity of 2-methylnaphthalene, the mass hourly space velocity of the raw material liquid feed is 0.2 - 6.0 h -1 ; the reaction pressure is 0 - 10 MPa.

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