Preparation method of al-doped siO2 molecular sieve and application thereof

Abstract

The application discloses a preparation method of Al-doped SiO2 molecular sieve and application thereof. The application comprises the following steps: 1, respectively adding an aluminum source and a silicon source into a sodium hydroxide aqueous solution, stirring uniformly to obtain a mixed solution, then adding a template agent into the mixed solution, and stirring for 8-16 hours to obtain a reaction mixture; 2, transferring the mixture prepared in the step 1 into a polytetrafluoroethylene-lined stainless steel reaction kettle, crystallizing at a temperature of 150-200 DEG C for 24-72 hours; 3, washing the reaction mixture crystallized in the step 2 for multiple times, then drying in an oven, and obtaining a light yellow powder after calcination; 4, dissolving the prepared light yellow powder in a 0.5-3 mol / L ammonium salt solution, heating and stirring, cooling and washing, and drying and calcining to obtain the Al-SiO2 molecular sieve. The catalyst prepared by the application has low preparation cost and is easy to recycle, can effectively catalyze the methylation reaction of naphthalene under normal pressure, and has improved conversion rate and selectivity, and has a good industrial application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of converting polycyclic aromatic hydrocarbons into high value-added products through catalytic alkylation, and in particular to a method for preparing 2,6-dimethylnaphthalene by using an Al-doped SiO2 molecular sieve through methylation of naphthalene. Background Art

[0002] 2,6-Dimethylnaphthalene (2,6-DMN) is an important polycyclic aromatic hydrocarbon (PAH). Its oxidation product, 2,6-naphthalenedicarboxylic acid (NDA), can be used to produce the high-performance polyester polyethylene naphthalate (PEN). PEN is highly sought after for its excellent physical and mechanical properties, heat resistance, gas barrier properties, and UV radiation resistance, making it a highly promising polymer material. However, the complex production process and high production costs of the starting material, 2,6-DMN, severely restrict its large-scale application. Currently, most plants that have commercialized the production of 2,6-DMN utilize a four-step synthesis process involving o-xylene and butadiene, followed by alkylation, cyclization, dehydrogenation, and isomerization. This involves difficult raw material availability, high energy consumption, complex purification processes, and serious environmental pollution from byproducts. Consequently, researchers have turned their attention to the one-step alkylation reaction of naphthalene or methylnaphthalene (NA or 2-MN) with methanol.

[0003] Regarding this route, (1) Patent CN101020619 uses ionic liquid as a catalyst to prepare 2,6-DMN. The target product has high selectivity, but this method is a batch homogeneous reaction. The reaction product and the catalyst are difficult to separate, making it difficult to industrialize. (2) Patent CN1762932 studies the use of different modified molecular sieves to prepare 2,6-DMN from β-methylnaphthalene. The reaction conditions are relatively harsh and must be carried out under high pressure, which also requires high equipment requirements. In addition, the raw material used is β-methylnaphthalene, which is expensive.

[0004] In general, research on the preparation of 2,6-DMN using naphthalene as a raw material is relatively limited, and current research still faces challenges such as complex catalyst preparation, high equipment requirements, and low catalytic activity. Therefore, developing catalyst systems suitable for this reaction to further improve reaction yields is of great significance. Summary of the Invention

[0005] To address the problems of low catalytic activity and harsh reaction conditions in the existing 2,6-DMN preparation process, the present invention provides a method for preparing an Al-doped SiO2 molecular sieve catalyst. By regulating the acidity and pore structure, this method achieves the goal of highly active catalytic naphthyl methylation to produce 2,6-DMN. Furthermore, the method offers the advantages of mild reaction conditions and low energy consumption. The catalyst is simple to prepare and can be easily separated and recovered for recycling.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0007] Step 1: Add an aluminum source and a silicon source to a sodium hydroxide aqueous solution respectively, stir evenly to obtain a mixed solution, then add a template to the mixed solution, stir for 8 to 16 hours, and obtain a reaction mixture.

[0008] Step 2: Transfer the mixture prepared in step 1 to a stainless steel reactor lined with polytetrafluoroethylene, with a crystallization temperature of 150 to 200° C. and a crystallization time of 24 to 72 hours.

[0009] Step 3: Wash the reactant after crystallization in step 2 several times, then dry it in an oven, and calcine it to obtain a light yellow powder.

[0010] Step 4: dissolve the prepared light yellow powder in 0.5-3 mol / L ammonium salt solution, heat and stir, cool and wash, dry and roast to obtain Al-SiO2 molecular sieve.

[0011] The aluminum source in step 1 is any one of aluminum isopropoxide, pseudo-boehmite, sodium metaaluminate or aluminum chloride.

[0012] The silicon source in step 1 is any one of silica sol, isopropyl silicate, silicic acid or nano-scale silicon dioxide powder.

[0013] The template agent in step 1 is one of triethanolamine, tetrapropylammonium hydroxide (TPAOH), cetyltrimethylammonium bromide (CTAB) or ethylenediamine.

[0014] The molar ratio of the silica sol, sodium aluminate, sodium hydroxide, template and water in step 1 is 1:(0-0.264):0.1:(0.08-0.24):20.

[0015] More preferably, the molar ratio of silica sol, sodium aluminate, sodium hydroxide, template and water is 1:0.066:0.1:0.16:20.

[0016] The ammonium salt in step 4 is one of ammonium chloride, ammonium nitrate or ammonium sulfate.

[0017] The drying temperature in steps 3 and 4 is 70-120° C., and the drying time is preferably 6-12 hours.

[0018] The calcination temperature in steps 3 and 4 is 300-700° C., and the calcination time is preferably 4-7 hours.

[0019] A method for preparing 2,6-dimethylnaphthalene by using Al-doped SiO2 molecular sieve for methylation of naphthalene is specifically implemented as follows:

[0020] The prepared Al-SiO2 molecular sieve was placed in a fixed bed reactor, and the catalyst was filled with quartz sand above and below. It was activated at 400-500°C for 1 hour, and then lowered to 200-400°C with a nitrogen flow rate of 20-100 mL / min.

[0021] Naphthalene, methanol and mesitylene are mixed evenly in a molar ratio of 1:3-15:1-6 to prepare a raw material liquid, and injected into a fixed bed reactor with a metering pump. -1 The alkylation reaction was carried out under the following conditions to obtain the target product 2,6-DMN.

[0022] Beneficial effects of the present invention:

[0023] The present invention prepares the target product through a continuous heterogeneous reaction process. The reactants are easily separated from the catalyst, and the catalyst can be recycled after secondary calcination. Naphthalene, a readily available and inexpensive raw material, undergoes a secondary methylation reaction at atmospheric pressure. The reaction temperature, 300°C, is lower than that of other patents, reducing the requirements for reaction equipment. Furthermore, the reaction meets the requirements for high activity and selectivity.

[0024] The catalyst of the present invention has low preparation cost and is easy to recover subsequently. It can effectively catalyze the methylation reaction of naphthalene under normal pressure conditions, and both the conversion rate and the selectivity are significantly improved, thus having good industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is the SEM image of the Al-doped SiO2 molecular sieve prepared in Example 1.

[0026] Figure 2 This is the TEM image of the Al-doped SiO2 molecular sieve prepared in Example 1. DETAILED DESCRIPTION

[0027] The present invention will be further described below with reference to the accompanying drawings and specific examples. It should be understood that these examples are intended to illustrate the present invention only and are not intended to limit the scope of the present invention. The operating methods in the following examples where specific conditions are not specified are generally performed under conventional conditions or the conditions recommended by the manufacturer. The raw materials used in the following specific embodiments were purchased from the market. Unless otherwise specified, room temperature is 25°C.

[0028] Example 1

[0029] In this embodiment, a method for preparing 2,6-DMN by using an Al-doped SiO2 molecular sieve for methylation of naphthalene includes the following steps:

[0030] The first step is to prepare Al-SiO2 molecular sieve:

[0031] a. Separately adding silica sol and sodium aluminate to a sodium hydroxide solution, stirring for 2 h, then adding CTAB to the mixed solution, and stirring for another 12 h to obtain a reaction mixture, wherein the molar ratio of the silica sol, sodium aluminate, sodium hydroxide, CTAB, and water is 1:0.066:0.1:0.16:20;

[0032] b. The reaction mixture prepared in step a was crystallized in a closed polytetrafluoroethylene-lined stainless steel reactor at a crystallization temperature of 150° C. for 72 h;

[0033] c. Wash the reactant after crystallization in step b several times, collect the solid sample, and dry it in a 90℃ oven overnight. Grind the dried sample with a mortar and spread it evenly on a porcelain ark, and heat it in a muffle furnace at 550℃ for 3℃·min -1 The catalyst precursor was obtained by calcining at a heating rate of 500 nm for 5 h.

[0034] d. Dissolve the precursor in 1 mol / L ammonium chloride solution, heat and stir, cool and wash, and then dry and calcine (the drying and calcination temperature is the same as step c). The resulting powder is Al-SiO2 (denoted as S1).

[0035] The second step is naphthyl methylation reaction:

[0036] The Al-SiO2 molecular sieve prepared in step 1 was placed in the middle bed of the fixed bed reactor, and the catalyst was filled with quartz sand above and below. It was activated at 400°C for 1 hour, then dropped to 300°C with a nitrogen flow rate of 80 mL / min. Naphthalene, methanol and mesitylene were mixed in a molar ratio of 1:12:2 to prepare a raw material solution, and injected into the fixed bed reactor with a metering pump. The mixture was stirred at room temperature with a mass space velocity of 1 h. -1 The alkylation reaction was carried out under the following conditions to obtain the target product 2,6-DMN. Quantitative analysis by gas chromatography showed that the conversion rate of naphthalene was 68.5% and the selectivity of 2,6-DMN was 42.4%.

[0037] Comparative Example 1

[0038] In this embodiment, a method for preparing 2,6-DMN by using an Al-doped SiO2 molecular sieve for methylation of naphthalene includes the following steps:

[0039] The first step is to prepare Al-SiO2 molecular sieve:

[0040] a. Adding silica sol and sodium metaaluminate to a sodium hydroxide solution respectively, stirring for 2 h, then adding TPAOH to the mixed solution, and stirring for another 12 h to obtain a reaction mixture, wherein the molar ratio of the silica sol, sodium metaaluminate, sodium hydroxide, TPAOH and water is 1:0.066:0.1:0.16:20;

[0041] b. The reaction mixture prepared in step a was crystallized in a closed polytetrafluoroethylene-lined stainless steel reactor at a crystallization temperature of 150° C. for 72 h;

[0042] c. Wash the reactant after crystallization in step b several times, collect the solid sample, and dry it in a 90℃ oven overnight. Grind the dried sample with a mortar and spread it evenly on a porcelain ark, and heat it in a muffle furnace at 550℃ for 3℃·min -1 The catalyst precursor was obtained by calcining at a heating rate of 500 nm for 5 h.

[0043] d. Dissolve the precursor in 1 mol / L ammonium chloride solution, heat and stir, cool and wash, and then dry and calcine (the drying and calcining temperature is the same as step c). The resulting powder is Al-SiO2 (denoted as S2).

[0044] The second step is naphthyl methylation reaction:

[0045] The Al-SiO2 molecular sieve prepared in step 1 was placed in the middle bed of the fixed bed reactor, and the catalyst was filled with quartz sand above and below. It was activated at 400°C for 1 hour, then dropped to 300°C with a nitrogen flow rate of 80 mL / min. Naphthalene, methanol and mesitylene were mixed in a molar ratio of 1:12:2 to prepare a raw material solution, and injected into the fixed bed reactor with a metering pump. The mixture was stirred at room temperature with a mass space velocity of 1 h. -1 The alkylation reaction was carried out under the following conditions to obtain the target product 2,6-DMN. Quantitative analysis by gas chromatography showed that the conversion rate of naphthalene was 23.2% and the selectivity of 2,6-DMN was 24.2%.

[0046] Comparative Example 2

[0047] In this embodiment, a method for preparing 2,6-DMN by using an Al-doped SiO2 molecular sieve for methylation of naphthalene includes the following steps:

[0048] The first step is to prepare Al-SiO2 molecular sieve:

[0049] a. Separately adding silica sol and sodium aluminate to a sodium hydroxide solution, stirring for 2 h, then adding triethanolamine to the mixed solution, and stirring for another 12 h to obtain a reaction mixture, wherein the molar ratio of the silica sol, sodium aluminate, sodium hydroxide, triethanolamine, and water is 1:0.066:0.1:0.16:20;

[0050] b. The reaction mixture prepared in step a was crystallized in a closed polytetrafluoroethylene-lined stainless steel reactor at a crystallization temperature of 150° C. for 72 h;

[0051] c. Wash the reactant after crystallization in step b several times, collect the solid sample, and dry it in a 90℃ oven overnight. Grind the dried sample with a mortar and spread it evenly on a porcelain ark, and heat it in a muffle furnace at 550℃ for 3℃·min -1 The catalyst precursor was obtained by calcining at a heating rate of 500 nm for 5 h.

[0052] d. Dissolve the precursor in 1 mol / L ammonium chloride solution, heat and stir, cool and wash, and then dry and calcine (the drying and calcining temperature is the same as step c). The resulting powder is Al-SiO2 (denoted as S3).

[0053] The second step is naphthyl methylation reaction:

[0054] The Al-SiO2 molecular sieve prepared in step 1 was placed in the middle bed of the fixed bed reactor, and the catalyst was filled with quartz sand above and below. It was activated at 400°C for 1 hour, then dropped to 300°C with a nitrogen flow rate of 80 mL / min. Naphthalene, methanol and mesitylene were mixed in a molar ratio of 1:12:2 to prepare a raw material solution, and injected into the fixed bed reactor with a metering pump. The mixture was stirred at room temperature with a mass space velocity of 1 h. -1 The alkylation reaction was carried out under the following conditions to obtain the target product 2,6-DMN. Quantitative analysis by gas chromatography showed that the conversion rate of naphthalene was 4% and the selectivity of 2,6-DMN was 5%.

[0055] Comparative Example 3

[0056] In this embodiment, a method for preparing 2,6-DMN by using an Al-doped SiO2 molecular sieve for methylation of naphthalene includes the following steps:

[0057] The first step is to prepare Al-SiO2 molecular sieve:

[0058] a. Adding silica sol and sodium aluminate to a sodium hydroxide solution respectively, stirring for 2 h, then adding ethylenediamine to the mixed solution, and stirring for another 12 h to obtain a reaction mixture, wherein the molar ratio of the silica sol, sodium aluminate, sodium hydroxide, ethylenediamine and water is 1:0.066:0.1:0.16:20;

[0059] b. The reaction mixture prepared in step a was crystallized in a closed polytetrafluoroethylene-lined stainless steel reactor at a crystallization temperature of 150° C. for 72 h;

[0060] c. Wash the reactant after crystallization in step b several times, collect the solid sample, and dry it in a 90℃ oven overnight. Grind the dried sample with a mortar and spread it evenly on a porcelain ark, and heat it in a muffle furnace at 550℃ for 3℃·min -1 The catalyst precursor was obtained by calcining at a heating rate of 500 nm for 5 h.

[0061] d. Dissolve the precursor in 1 mol / L ammonium chloride solution, heat and stir, cool and wash, and then dry and calcine (the drying and calcination temperature is the same as step c). The resulting powder is Al-SiO2 (denoted as S4).

[0062] The second step is naphthyl methylation reaction:

[0063] The Al-SiO2 molecular sieve prepared in step 1 was placed in the middle bed of the fixed bed reactor, and the catalyst was filled with quartz sand above and below. It was activated at 400°C for 1 hour, then dropped to 300°C with a nitrogen flow rate of 80 mL / min. Naphthalene, methanol and mesitylene were mixed in a molar ratio of 1:12:2 to prepare a raw material solution, and injected into the fixed bed reactor with a metering pump. The mixture was stirred at room temperature with a mass space velocity of 1 h. -1 The alkylation reaction was carried out under the following conditions to obtain the target product 2,6-DMN. Quantitative analysis by gas chromatography showed that the conversion rate of naphthalene was 10% and the selectivity of 2,6-DMN was 6%.

[0064] Comparative Example 4

[0065] In this embodiment, a method for preparing 2,6-DMN by methylating a SiO2 molecular sieve with naphthalene includes the following steps:

[0066] The first step is to prepare SiO2 molecular sieve:

[0067] a. Adding silica sol to sodium hydroxide solution and stirring for 2 h, then adding CTAB to the mixed solution and stirring for another 12 h to obtain a reaction mixture, wherein the molar ratio of the silica sol, sodium hydroxide, CTAB and water is 1:0.1:0.16:20;

[0068] b. The reaction mixture prepared in step a was crystallized in a closed polytetrafluoroethylene-lined stainless steel reactor at a crystallization temperature of 150° C. for 72 h;

[0069] c. Wash the reactant after crystallization in step b several times, collect the solid sample, and dry it in a 90℃ oven overnight. Grind the dried sample with a mortar and spread it evenly on a porcelain ark, and heat it in a muffle furnace at 550℃ for 3℃·min -1 The catalyst precursor was obtained by calcining at a heating rate of 500 nm for 5 h.

[0070] d. Dissolve the precursor in 1 mol / L ammonium chloride solution, heat and stir, cool and wash, and then dry and calcine (the drying and calcining temperature is the same as step c). The resulting powder is Al-SiO2 (denoted as S5).

[0071] The second step is naphthyl methylation reaction:

[0072] The Al-SiO2 molecular sieve prepared in step 1 was placed in the middle bed of the fixed bed reactor, and the catalyst was filled with quartz sand above and below. It was activated at 400°C for 1 hour, then dropped to 300°C with a nitrogen flow rate of 80 mL / min. Naphthalene, methanol and mesitylene were mixed in a molar ratio of 1:12:2 to prepare a raw material solution, and injected into the fixed bed reactor with a metering pump. The mixture was stirred at room temperature with a mass space velocity of 1 h. -1 The alkylation reaction was carried out under the following conditions to obtain the target product 2,6-DMN. Quantitative analysis by gas chromatography showed that the conversion rate of naphthalene was 10.5% and the selectivity of 2,6-DMN was 38.8%.

[0073] Example 2

[0074] In this embodiment, a method for preparing 2,6-DMN by using an Al-doped SiO2 molecular sieve for methylation of naphthalene includes the following steps:

[0075] The first step is to prepare Al-SiO2 molecular sieve:

[0076] a. Adding silica sol and sodium aluminate to a sodium hydroxide solution respectively, stirring for 2 h, then adding CTAB to the mixed solution, and stirring for another 12 h to obtain a reaction mixture, wherein the molar ratio of the silica sol, sodium aluminate, sodium hydroxide, CTAB and water is 1:0.033:0.1:0.16:20;

[0077] b. The reaction mixture prepared in step a was crystallized in a closed polytetrafluoroethylene-lined stainless steel reactor at a crystallization temperature of 150° C. for 72 h;

[0078] c. Wash the reactant after crystallization in step b several times, collect the solid sample, and dry it in a 90℃ oven overnight. Grind the dried sample with a mortar and spread it evenly on a porcelain ark, and heat it in a muffle furnace at 550℃ for 3℃·min -1 The catalyst precursor was obtained by calcining at a heating rate of 500 nm for 5 h.

[0079] d. Dissolve the precursor in 1 mol / L ammonium chloride solution, heat and stir, cool and wash, and then dry and calcine (the drying and calcining temperature is the same as step c). The resulting powder is Al-SiO2 (denoted as S6).

[0080] The second step is naphthyl methylation reaction:

[0081] The Al-SiO2 molecular sieve prepared in step 1 was placed in the middle bed of the fixed bed reactor, and the catalyst was filled with quartz sand above and below. It was activated at 400°C for 1 hour, then dropped to 300°C with a nitrogen flow rate of 80 mL / min. Naphthalene, methanol and mesitylene were mixed in a molar ratio of 1:12:2 to prepare a raw material solution, and injected into the fixed bed reactor with a metering pump. The mixture was stirred at room temperature with a mass space velocity of 1 h. -1 The alkylation reaction was carried out under the following conditions to obtain the target product 2,6-DMN. Quantitative analysis by gas chromatography showed that the conversion rate of naphthalene was 44.8% and the selectivity of 2,6-DMN was 36.1%.

[0082] Example 3

[0083] In this embodiment, a method for preparing 2,6-DMN by using an Al-doped SiO2 molecular sieve for methylation of naphthalene includes the following steps:

[0084] The first step is to prepare Al-SiO2 molecular sieve:

[0085] a. Separately adding silica sol and sodium aluminate to a sodium hydroxide solution, stirring for 2 h, then adding CTAB to the mixed solution, and stirring for another 12 h to obtain a reaction mixture, wherein the molar ratio of the silica sol, sodium aluminate, sodium hydroxide, CTAB, and water is 1:0.132:0.1:0.16:20;

[0086] b. The reaction mixture prepared in step a was crystallized in a closed polytetrafluoroethylene-lined stainless steel reactor at a crystallization temperature of 150° C. for 72 h;

[0087] c. Wash the reactant after crystallization in step b several times, collect the solid sample, and dry it in a 90℃ oven overnight. Grind the dried sample with a mortar and spread it evenly on a porcelain ark, and heat it in a muffle furnace at 550℃ for 3℃·min -1 The catalyst precursor was obtained by calcining at a heating rate of 500 nm for 5 h.

[0088] d. Dissolve the precursor in 1 mol / L ammonium chloride solution, heat and stir, cool and wash, and then dry and calcine (the drying and calcining temperature is the same as in step c). The resulting powder is Al-SiO2 (denoted as S7).

[0089] The second step is naphthyl methylation reaction:

[0090] The Al-SiO2 molecular sieve prepared in step 1 was placed in the middle bed of the fixed bed reactor, and the catalyst was filled with quartz sand above and below. It was activated at 400°C for 1 hour, then dropped to 300°C with a nitrogen flow rate of 80 mL / min. Naphthalene, methanol and mesitylene were mixed in a molar ratio of 1:12:2 to prepare a raw material solution, and injected into the fixed bed reactor with a metering pump. The mixture was stirred at room temperature with a mass space velocity of 1 h. -1 The alkylation reaction was carried out under the following conditions to obtain the target product 2,6-DMN. Quantitative analysis by gas chromatography showed that the conversion rate of naphthalene was 40.2% and the selectivity of 2,6-DMN was 33.5%.

[0091] Example 4

[0092] In this embodiment, a method for preparing 2,6-DMN by using an Al-doped SiO2 molecular sieve for methylation of naphthalene includes the following steps:

[0093] The first step is to prepare Al-SiO2 molecular sieve:

[0094] a. Separately adding silica sol and sodium aluminate to a sodium hydroxide solution, stirring for 2 h, then adding CTAB to the mixed solution, and stirring for another 12 h to obtain a reaction mixture, wherein the molar ratio of the silica sol, sodium aluminate, sodium hydroxide, CTAB, and water is 1:0.264:0.1:0.16:20;

[0095] b. The reaction mixture prepared in step a was crystallized in a closed polytetrafluoroethylene-lined stainless steel reactor at a crystallization temperature of 150° C. for 72 h;

[0096] c. Wash the reactant after crystallization in step b several times, collect the solid sample, and dry it in a 90℃ oven overnight. Grind the dried sample with a mortar and spread it evenly on a porcelain ark, and heat it in a muffle furnace at 550℃ for 3℃·min -1 The catalyst precursor was obtained by calcining at a heating rate of 500 nm for 5 h.

[0097] d. Dissolve the precursor in 1 mol / L ammonium chloride solution, heat and stir, cool and wash, and then dry and calcine (the drying and calcination temperature is the same as step c). The resulting powder is Al-SiO2 (denoted as S8).

[0098] The second step is naphthyl methylation reaction:

[0099] The Al-SiO2 molecular sieve prepared in step one was placed in the middle bed of a fixed bed reactor, and quartz sand was filled above and below the catalyst. The catalyst was activated at 400°C for 1 h, then reduced to 300°C, and the nitrogen flow rate was 80 mL / min. Naphthalene, methanol, and mesitylene were mixed in a molar ratio of 1:12:2 to prepare a raw material solution, which was injected into the fixed bed reactor using a metering pump. The alkylation reaction was carried out under the conditions of normal pressure and a mass space velocity of 1 h -1 The conversion rate of naphthalene was 26.1%, and the selectivity of 2,6-DMN was 34.4%.

[0100] Example 5

[0101] The S1 molecular sieve prepared was placed in a fixed bed reactor, and quartz sand was filled above and below the catalyst. The catalyst was activated at 400°C for 1 h, then reduced to 350°C, and the nitrogen flow rate was 80 mL / min. Naphthalene, methanol, and mesitylene were mixed in a molar ratio of 1:12:2 to prepare a raw material solution, which was injected into the fixed bed reactor using a metering pump. The alkylation reaction was carried out under the conditions of normal pressure and a mass space velocity of 1 h -1 The conversion rate of naphthalene was 69%, and the selectivity of 2,6-DMN was 36.8%.

[0102] Example 6

[0103] The S1 molecular sieve prepared was placed in a fixed bed reactor, and quartz sand was filled above and below the catalyst. The catalyst was activated at 400°C for 1 h, then reduced to 250°C, and the nitrogen flow rate was 80 mL / min. Naphthalene, methanol, and mesitylene were mixed in a molar ratio of 1:12:2 to prepare a raw material solution, which was injected into the fixed bed reactor using a metering pump. The alkylation reaction was carried out under the conditions of normal pressure and a mass space velocity of 1 h -1 The conversion rate of naphthalene was 26.9%, and the selectivity of 2,6-DMN was 34.5%.

[0104] Example 7

[0105] The S1 molecular sieve prepared was placed in a fixed bed reactor, and quartz sand was filled above and below the catalyst. The catalyst was activated at 400°C for 1 h, then reduced to 300°C, and the nitrogen flow rate was 80 mL / min. Naphthalene, methanol, and mesitylene were mixed in a molar ratio of 1:12:2 to prepare a raw material solution, which was injected into the fixed bed reactor using a metering pump. The alkylation reaction was carried out under the conditions of normal pressure and a mass space velocity of 0.5 h -1The alkylation reaction was carried out under the conditions, so as to obtain the target product 2,6-DMN. Quantitative analysis by gas chromatography showed that the conversion rate of naphthalene was 56.6%, and the selectivity of 2,6-DMN was 34.2%.

[0106] Example 8

[0107] The prepared S1 molecular sieve was placed in a fixed bed reactor, and quartz sand was filled above and below the catalyst. The catalyst was activated at 400°C for 1 h, then reduced to 300°C, and the nitrogen flow rate was 80 mL / min. Naphthalene, methanol and mesitylene were mixed in a molar ratio of 1:12:2 to prepare a raw material solution, which was injected into the fixed bed reactor by a metering pump. The alkylation reaction was carried out under the conditions, so as to obtain the target product 2,6-DMN. Quantitative analysis by gas chromatography showed that the conversion rate of naphthalene was 56.6%, and the selectivity of 2,6-DMN was 34.2%. -1 The alkylation reaction was carried out under the conditions, so as to obtain the target product 2,6-DMN. Quantitative analysis by gas chromatography showed that the conversion rate of naphthalene was 56.6%, and the selectivity of 2,6-DMN was 34.2%.

[0108] Example 9

[0109] The prepared S1 molecular sieve was placed in a fixed bed reactor, and quartz sand was filled above and below the catalyst. The catalyst was activated at 400°C for 1 h, then reduced to 300°C, and the nitrogen flow rate was 80 mL / min. Naphthalene, methanol and mesitylene were mixed in a molar ratio of 1:12:2 to prepare a raw material solution, which was injected into the fixed bed reactor by a metering pump. The alkylation reaction was carried out under the conditions, so as to obtain the target product 2,6-DMN. Quantitative analysis by gas chromatography showed that the conversion rate of naphthalene was 56.6%, and the selectivity of 2,6-DMN was 34.2%. -1 The alkylation reaction was carried out under the conditions, so as to obtain the target product 2,6-DMN. Quantitative analysis by gas chromatography showed that the conversion rate of naphthalene was 56.6%, and the selectivity of 2,6-DMN was 34.2%.

[0110] Example 10

[0111] The prepared S1 molecular sieve was placed in a fixed bed reactor, and quartz sand was filled above and below the catalyst. The catalyst was activated at 400°C for 1 h, then reduced to 300°C, and the nitrogen flow rate was 80 mL / min. Naphthalene, methanol and mesitylene were mixed in a molar ratio of 1:12:2 to prepare a raw material solution, which was injected into the fixed bed reactor by a metering pump. The alkylation reaction was carried out under the conditions, so as to obtain the target product 2,6-DMN. Quantitative analysis by gas chromatography showed that the conversion rate of naphthalene was 56.6%, and the selectivity of 2,6-DMN was 34.2%. -1 The alkylation reaction was carried out under the conditions, so as to obtain the target product 2,6-DMN. Quantitative analysis by gas chromatography showed that the conversion rate of naphthalene was 56.6%, and the selectivity of 2,6-DMN was 34.2%.

[0112] The application discloses a method for preparing 2,6-DMN by naphthalene methylation by using Al-doped SiO2 molecular sieves, wherein cheap and easily obtained naphthalene is used as a raw material, naphthalene, methanol and mesitylene are uniformly mixed at an optimal molar ratio of 1:12:2 and then are uniformly put into a reaction, and the use amount of expensive solvent mesitylene is reduced to the maximum. The influence of different Al content doped SiO2 molecular sieves, different template agent dosages, different temperatures and mass space velocities on the reaction is explored, so that the optimal reaction conditions are determined. When the molar ratio of the dosages of silica sol, sodium metaaluminate, sodium hydroxide, CTAB and water is 1:0.066:0.1:0.16:20, the conversion rate of naphthalene is 68.5%, the selectivity of 2,6-DMN is 42.4% and the optimal catalytic activity is reached under the conditions of normal pressure and a reaction temperature of 300 DEG C and a mass space velocity of 1h -1 .

[0113] Furthermore, it is understood that various modifications and changes can be made to the application by those skilled in the art having the benefit of the teachings of the present description. Such modifications and changes are therefore intended to fall within the scope of the application as defined by the appended claims.

Claims

1. A method for preparing 2,6-DMN by catalytic methylation of naphthyl, characterized in that: The prepared molecular sieve catalyst was placed in the middle bed of a fixed-bed reactor, and quartz sand was filled above and below the catalyst. It was activated with nitrogen at 400°C for 1 hour at a nitrogen flow rate of 80 mL / min, and then the temperature was lowered to 300°C for the naphthalene methylation reaction. The raw material liquid was injected into the fixed-bed reactor using a metering pump, and the target product 2,6-DMN was obtained through gasification, reaction, and condensation. The molecular sieve catalyst is Al-doped SiO2 molecular sieve, and the preparation steps include: Step 1: adding an aluminum source and a silicon source to a sodium hydroxide aqueous solution respectively, stirring uniformly to obtain a mixed solution, then adding a template to the mixed solution, stirring for 8 to 16 hours, and obtaining a reaction mixture; Step 2: Transfer the mixture prepared in step 1 to a stainless steel reactor lined with polytetrafluoroethylene, with a crystallization temperature of 150 to 200° C. and a crystallization time of 24 to 72 hours; Step 3: Wash the reactant after crystallization in step 2 several times, then dry it in an oven, and calcine it to obtain a light yellow powder; Step 4: dissolving the prepared light yellow powder in 0.5-3 mol / L ammonium salt solution, heating and stirring, cooling and washing, drying and roasting to obtain Al-doped SiO2 molecular sieve; The aluminum source in step 1 is sodium metaaluminate; the silicon source is silica sol; the template in step 1 is cetyltrimethylammonium bromide (CTAB); The molar ratio of the silica sol, sodium metaaluminate, sodium hydroxide, template and water in step 1 is 1:(0-0.264):0.1:(0.08-0.24):20; The ammonium salt in step 4 is one of ammonium chloride, ammonium nitrate or ammonium sulfate; The drying temperature in steps 3 and 4 is 70-120° C., and the drying time is 6-12 hours; the roasting temperature is 300-700° C., and the roasting time is 4-7 hours.

2. The method for preparing 2,6-DMN by catalytic methylation of naphthyl according to claim 1, characterized in that: The nitrogen flow rate is 80 mL / min, the raw material liquid is a mixture of naphthalene, methanol and mesitylene in a molar ratio of 1:12:2, the mass of the Al-doped SiO2 molecular sieve is 0.5 g; the pressure is normal pressure; the pump flow rate is 0.3 mL / min, that is, the space velocity is 1 h -1 .

Images