Methylnaphthalene alkylation catalyst as well as preparation method and application thereof

Abstract

The invention provides a methylnaphthalene alkylation catalyst as well as a preparation method and application thereof. The preparation method of the methylnaphthalene alkylation catalyst comprises the following steps: carrying out hydrothermal aging on an HMCM-22 molecular sieve; the HMCM-22 molecular sieve subjected to hydrothermal aging is placed in acid liquor for acid treatment, and the methylnaphthalene alkylation catalyst is obtained. 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 HMCM-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 methylnaphthalene alkylation catalyst, a preparation method thereof and an application thereof, and belongs to the technical field of chemical engineering. Background Art

[0002] As a new 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 the fields of electronic components, films, packaging, fibers, nanoplastics, aviation and atomic energy materials, etc. 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] At present, 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 to synthesize 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 and purifying it still cannot meet the requirements 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 sources 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, with production volumes of over ten million tons and over one million tons respectively. Currently, the utilization routes of LCO mainly include blending with gasoline and diesel, as well as obtaining 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 it as fuel, 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 refining transformation to increase high-value-added products, and solve the key technologies of refining transformation.

[0006] Lijun Jin et al. (Lijun Jin, Yunming Fang, Haoquan Hu; Selective synthesis of 2,6-dimethylnaphthalene by methylation of 2-methylnaphthalene with methanol on Zr / (Al)ZSM-5; Catalysis Communications, 2006, 7(5): 255-259) used (NH 4 ) 2 ZrF 6 modified HZSM-5 zeolite to catalyze the alkylation reaction of 2-MN and found that the replacement of some Al atoms in the framework by Zr atoms led to a decrease in acid strength, which was beneficial to the formation of 2,6-DMN, increasing the selectivity of 2,6-DMN to 56.0% and the ratio of 2,6- / 2,7-DMN to 3.0. Although Zr-modified HZSM-5 showed obvious shape selectivity, the conversion rate of 2-MN was only 10% within 2 h and decreased rapidly over time. Moreover, the HZSM-5 zeolite used in this technology had poor activity and stability.

[0007] Jin LJ et al. (Jin LJ, Hu HQ, Wang XY, Liu C; Methylation of 2-methylnaphthalene with methanol to 2,6-dimethylnaphthalene over ZSM-5 modified by Zr and Si; Industrial & Engineering Chemistry Research, 2006, 45(10): 3531-3536) further used (NH 4 ) 2 SiF6 Modification. It was found that due to the introduction of Si, the stability of the catalyst was improved. After 10 h of reaction, the conversion of 2-MN decreased from 32% at the initial stage of the reaction to 20%, and the selectivity of 2,6-DMN was at best 52%. The HZSM-5 molecular sieve used in this technology has poor activity and stability.

[0008] The catalytic performance of HZSM-5 and HMCM-22 molecular sieves in the alkylation reaction of 2-MN with CH 3 OH was studied by comparing with the content disclosed in US 5001295A. It was found that compared with the HZSM-5 molecular sieve, since the pore size of the HMCM-22 molecular sieve (0.41×0.51 nm

[001] ) is smaller than the molecular diameter of 2-MN (0.58 nm), the alkylation reaction of 2-MN occurs in the cavities on the outer surface of the molecular sieve, making the HMCM-22 molecular sieve exhibit better reaction activity and stability, and is expected to achieve efficient and stable conversion of 2-MN in the industrial production process. However, since the alkylation reaction is not restricted by the pore channels, the HMCM-22 molecular sieve exhibits a lower selectivity for 2,6-DMN and a ratio of 2,6- / 2,7-DMN. In addition, inevitably, methanol is converted into coke under the catalytic action of acid centers, resulting in a decrease in reaction stability. Specifically, within 240 h of the reaction, the conversion of 2-MN has been showing a downward trend. Although the HMCM-22 molecular sieve shows good reaction activity in the alkylation of 2-MN with CH 3 OH, the selectivity of DMN and the selectivity of 2,6-DMN are not high, resulting in a low yield of 2,6-DMN. At the same time, the formation of coke leads to a decrease in reaction stability. Summary of the Invention

[0009] To solve the above technical problems, the object of the present invention is to provide a methylnaphthalene alkylation catalyst and a preparation method thereof, which can provide high activity, high selectivity and high stability.

[0010] To achieve the above object, the present invention provides a preparation method of a methylnaphthalene alkylation catalyst, which includes the following steps:

[0011] Hydrothermally age the HMCM-22 molecular sieve; place the hydrothermally aged HMCM-22 molecular sieve in an acid solution for acid treatment to obtain the methylnaphthalene alkylation catalyst;

[0012] Wherein: the HMCM-22 molecular sieve has a flaky porous structure, and the SiO 2 / Al 2 O 3 ratio is 1-72:1, the specific surface area is 150-800 m 2 / g, and the pore volume is 0.01-1.6 cm3 / g, the sodium element content is 0.00001% - 0.15%;

[0013] The hydrothermal aging is carried out with water vapor, and the temperature of the hydrothermal aging is 300 - 700 °C and the time is 1 - 10 hours;

[0014] The liquid - solid mass ratio of the acid solution to the HMCM - 22 molecular sieve after hydrothermal aging is 10 - 50:1, the concentration of the acid solution is 1 - 8 mol / L, the temperature of the acid treatment is 30 - 100 °C, and the time is 1 - 12 hours; the acid solution is hydrochloric acid and / or citric acid.

[0015] In the above - mentioned preparation method of the methylnaphthalene alkylation catalyst, preferably, before the hydrothermal aging, the HMCM - 22 molecular sieve is activated, and the activation is to heat it to 200 - 400 °C at a rate of 5 - 30 °C / min and activate for 1 - 4 hours.

[0016] In the above - mentioned preparation method of the methylnaphthalene alkylation catalyst, preferably, in the hydrothermal aging process, the HMCM - 22 molecular sieve is placed in the reaction tube of the hydrothermal aging device, and 10% - 100% of water vapor is introduced into the reaction tube at a pressure of 0.1 - 1 MPa and a rate of 1 - 10 ml / h for hydrothermal aging.

[0017] In the above - mentioned preparation method of the methylnaphthalene alkylation catalyst, preferably, the HMCM - 22 molecular sieve has a flaky porous structure, the SiO 2 / Al 2 O 3 ratio is 49 - 72:1, the specific surface area is 300 - 600 m 2 / g, the pore volume is 0.7 - 1.6 cm 3 / g, and the sodium element content is 0.00001% - 0.1%.

[0018] In the above - mentioned preparation method of the methylnaphthalene alkylation catalyst, preferably, the HMCM - 22 molecular sieve has a flaky porous structure, the SiO 2 / Al 2 O 3 ratio is 49 - 72:1, the specific surface area is 390 - 400 m 2 / g, the pore volume is 1.1 - 1.3 cm 3 / g, and the sodium element content is 0.00001% - 0.1%.

[0019] In the above - mentioned preparation method of the methylnaphthalene alkylation catalyst, preferably, the preparation method further includes the following steps:

[0020] Wash the acid-treated HMCM-22 molecular sieve with deionized water. When the pH of the washing liquid is 6 - 7, dry the HMCM-22 molecular sieve at 80 - 120 °C for 12 h, and then calcine it at 400 - 550 °C for 2 - 6 h.

[0021] According to a specific embodiment of the present invention, preferably, the preparation method of the above-mentioned methylnaphthalene alkylation catalyst comprises the following specific steps:

[0022] a. Place the HMCM-22 molecular sieve in the middle of the stainless steel reaction tube of the hydrothermal aging device, heat it to 200 - 400 °C at a rate of 5 - 30 °C / min, and activate it for 1 - 4 h; then, turn on the high-pressure pump to introduce 10% - 100% (0.1 - 1 MPa) steam into the reaction tube at a rate of 1 - 10 ml / h, and treat it at 300 - 700 °C for 1 - 10 h.

[0023] b. Add the hydrothermally aged HMCM-22 molecular sieve to the acid solution with a liquid-solid mass ratio of 10 - 50:1, and the acid solution can be one of hydrochloric acid and citric acid; heat the mixture of the molecular sieve and the acid solution to 30 - 100 °C and soak it for 1 - 12 h; then, wash the acid-treated molecular sieve with deionized water. When the pH of the washing liquid is 6 - 7, dry the molecular sieve at 80 - 120 °C for 12 h, and then calcine it at 400 - 550 °C for 2 - 6 h to obtain the methylnaphthalene alkylation catalyst.

[0024] According to a specific embodiment of the present invention, preferably, the preparation method of the above-mentioned methylnaphthalene alkylation catalyst comprises the following specific steps:

[0025] a. Place the HMCM-22 molecular sieve in the middle of the stainless steel reaction tube of the hydrothermal aging device, heat it to 200 - 250 °C at a rate of 5 - 10 °C / min, and activate it for 2 h; then, turn on the high-pressure pump to introduce 70% - 80% (0.1 - 0.5 MPa) steam into the reaction tube at a rate of 5 ml / h, and treat it at 300 - 600 °C for 2 - 7 h, preferably, treat it at 350 - 550 °C for 2 - 7 h.

[0026] b. Add the hydrothermally aged HMCM-22 molecular sieve to the hydrochloric acid solution with a liquid-solid mass ratio of 10 - 30:1, heat it to 30 - 100 °C, and soak it for 1 - 12 h; then, wash the acid-treated molecular sieve sample with deionized water. When the pH of the washing liquid is 6 - 7, dry the molecular sieve sample at 80 - 100 °C for 12 h, and then calcine it at 450 - 500 °C for 3 - 4 h to obtain the methylnaphthalene alkylation catalyst.

[0027] The present invention also provides a methylnaphthalene alkylation catalyst, which is prepared by the preparation method of the above-mentioned methylnaphthalene alkylation catalyst.

[0028] The present invention also provides a method for preparing 2,6-dimethylnaphthalene by alkylation of 2-methylnaphthalene with methanol. In this method, the above-mentioned methylnaphthalene alkylation catalyst is used, and the method comprises the following steps:

[0029] Loading the catalyst into a fixed-bed reactor;

[0030] Mixing 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 / 2-methylnaphthalene is 0.8 - 2.2, and the mass ratio of 2-methylnaphthalene / (2-methylnaphthalene + solvent) is 0.5 - 1;

[0031] Introducing the feed liquid into the reactor to contact with the catalyst bed for reaction to generate a product containing 2,6-dimethylnaphthalene;

[0032] Wherein, 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.

[0033] In the above method, preferably, after loading the catalyst into the fixed-bed reactor, the catalyst is in-situ activated and pretreated in a nitrogen atmosphere at 200 - 600 °C for 1 - 8 h.

[0034] In the above method, preferably, the solvent includes one or a combination of two or more of benzene, toluene, xylene, mesitylene, and durene; more preferably, the solvent includes mesitylene and / or durene.

[0035] In the above method, 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.

[0036] According to the specific implementation embodiments of the present invention, preferably, the method for preparing 2,6-dimethylnaphthalene by alkylation of 2-methylnaphthalene with methanol provided by the present invention comprises the following specific steps:

[0037] The alkylation reaction of 2-methylnaphthalene is catalyzed by HMCM-22 zeolite modified by hydrothermal aging / acid treatment, and the specific steps are as follows: First, the zeolite catalyst prepared above is loaded into a fixed-bed reactor, and then in-situ activation pretreatment is carried out at 200-600 °C for 1-8 h in a nitrogen atmosphere; Second, 2-methylnaphthalene, methanol and a solvent are mixed to obtain a raw material liquid; Among them, 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; Among them, the solvent can be one or a combination of two or more of benzene, toluene, xylene, mesitylene, and durene; Finally, the raw material liquid is introduced into the reactor by a metering pump to contact with the catalyst bed layer for reaction to generate a product containing 2,6-dimethylnaphthalene, the reaction temperature is 300-490 °C, and the mass hourly space velocity of the raw material liquid feed is 0.2-6.0 h -1 (based on the mass hourly space velocity of 2-methylnaphthalene), and the reaction pressure is 0-10 MPa.

[0038] According to the specific implementation of the present invention, preferably, the method for preparing 2,6-dimethylnaphthalene by alkylation of 2-methylnaphthalene and methanol provided by the present invention includes the following specific steps:

[0039] First, the zeolite catalyst is loaded into a fixed-bed reactor, and then in-situ activation pretreatment is carried out at 200-300 °C for 6-8 h in a nitrogen atmosphere; Second, 2-methylnaphthalene, methanol and a solvent are mixed to obtain a raw material liquid; Among them, 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; Among them, the solvent is mesitylene and / or durene; Finally, the raw material liquid is introduced into the reactor by a metering pump to contact with the catalyst bed layer for reaction to generate a product containing 2,6-dimethylnaphthalene, the reaction temperature is 300-400 °C, and the mass hourly space velocity of the raw material liquid feed is 0.2-3.0 h -1 , and the reaction pressure is 0-4 MPa.

[0040] The synthesis of 2,6-DMN by the alkylation reaction of 2-methylnaphthalene and methanol catalyzed by zeolite is a synthetic route with development prospects. However, the HMCM-22 zeolite currently used for catalyzing the alkylation reaction has problems of low selectivity of DMN and 2,6-DMN, resulting in low yield of 2,6-DMN. At the same time, the formation of carbon deposition due to side reactions of alkylation leads to a decrease in reaction stability. On the premise of ensuring high activity and high stability, the HMCM-22 zeolite provided by the present invention has good selectivity for DMN and 2,6-DMN and can solve the above technical problems.

[0041] Compared with the background technology, the present invention has the following advantages:

[0042] (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. The reaction product containing 2,6-dimethylnaphthalene is easily separated from the catalyst, with simple operation and convenient for industrial production;

[0043] (2) The HMCM-22 molecular sieve modified by hydrothermal aging / acid treatment used in the present invention maintains the crystal phase structure of the HMCM-22 molecular sieve. However, due to the introduction of secondary mesopores in the molecular sieve, it is beneficial to the diffusion of 2-MN, 2,6-DMN and coke precursors; at the same time, the molecular sieve has appropriate acidity, which promotes the occurrence of the main alkylation reaction and inhibits the formation of coke, thereby greatly improving the alkylation activity, selectivity and stability of the molecular sieve for 2-methylnaphthalene. Among them, the HMCM-22 molecular sieve modified by hydrothermal aging at 550 °C + acid treatment maintains a conversion rate of 2-methylnaphthalene of 58% within 250 h, a DMN selectivity of 70%-75%, a 2,6-DMN selectivity of 16%-17%, and a 2,6- / 2,7-DMN ratio of 1.19, indicating that the modified molecular sieve has the characteristics of high activity, high selectivity and high stability. The above results are significantly higher than the results reported in the professional literature in the current field and have significant industrial application value. Description of the Drawings

[0044] Figure 1 XRD diagrams for Comparative Examples 1-3 and Examples 1-2.

[0045] Figure 2 For Comparative Examples 1-3 and Examples 1-2 of NH 3 -TPD diagrams.

[0046] Figures 3 - 6 Alkylation reaction result diagrams for Comparative Examples 4-6 and Examples 3-4, where Figures 3 - 6 are the 2-MN conversion rate results, DMN selectivity results, 2,6-DMN selectivity results, and 2,6- / 2,7-DMN ratio respectively. Detailed Embodiments

[0047] For 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.

[0048] Comparative Example 1

[0049] The HMCM-22 molecular sieve purchased from Huawerike has a SiO 2 / Al 2 O 3 ratio of 28, a total pore specific surface area of 428.5 m 2 / g, and a mesopore specific surface area of 130.8 m2 / g, the pore volume of the whole pores is 1.221 cm 3 / g, the pore volume of the mesopores is 0.744 cm 3 / g. The XRD and NH 3 -TPD results are shown in Figure 1 and Figure 2 .

[0050] Comparative Example 2

[0051] Place the MCM-22 molecular sieve of Comparative Example 1 in the middle of the stainless steel reaction tube of the hydrothermal aging device, heat it to 200 °C at a rate of 5 °C / min, and activate for 2 h; then, turn on the high-pressure pump to introduce 80% (0.1 MPa) steam into the reaction tube at a rate of 5 ml / h, and treat it at 350 °C for 2 h; the obtained molecular sieve is denoted as MCM-22-350-2.

[0052] The SiO 2 / Al 2 O 3 ratio of the molecular sieve is 28, the specific surface area of the whole pores is 352.6 m 2 / g, the specific surface area of the mesopores is 139.2 m 2 / g, the pore volume of the whole pores is 1.053 cm 3 / g, the pore volume of the mesopores is 0.763 cm 3 / g, the XRD and NH 3 -TPD results are shown in Figure 1 and Figure 2 .

[0053] From the above results, it can be seen that after hydrothermal aging of the MCM-22 molecular sieve, the SiO 2 / Al 2 O 3 ratio and the crystal phase structure are basically unchanged, but due to the dealumination of the molecular sieve, secondary mesopores are introduced, resulting in an increase in the specific surface area and pore volume of the mesopores and a decrease in acidity.

[0054] Comparative Example 3

[0055] Place the HMCM-22 molecular sieve of Comparative Example 1 in the middle of the stainless steel reaction tube of the hydrothermal aging device, heat it to 200 °C at a rate of 5 °C / min, and activate for 2 h; then, turn on the high-pressure pump to introduce 80% (0.1 MPa) steam into the reaction tube at a rate of 5 ml / h, and treat it at 550 °C for 7 h; the obtained molecular sieve is denoted as MCM-22-550-7.

[0056] The SiO 2 / Al 2 O 3 ratio of the molecular sieve is 30, the specific surface area of the whole pores is 381.5 m2 / g, the specific surface area of the mesopores is 141.6 m 2 / g, the pore volume of the total pores is 1.022 cm 3 / g, the pore volume of the mesopores is 0.784 cm 3 / g, XRD and NH 3 -TPD results are shown in Figure 1 and Figure 2 .

[0057] From the above results, it can be seen that after the hydrothermal aging of the MCM-22 molecular sieve, the SiO 2 / Al 2 O 3 ratio and the crystal phase structure are basically unchanged. However, due to the dealumination of the molecular sieve, secondary mesopores are introduced, resulting in an increase in the specific surface area and pore volume of the mesopores and a decrease in acidity.

[0058] Example 1

[0059] The MCM-22 molecular sieve obtained in Comparative Example 2 was added to a 2 mol / L hydrochloric acid solution at a liquid-solid mass ratio of 20:1, heated to 80 °C, and soaked for 2 h; then, the acid-treated molecular sieve sample was washed with deionized water. When the pH of the washing solution was 6-7, the molecular sieve sample was dried at 80 °C for 12 h and then calcined at 500 °C for 4 h; the obtained molecular sieve was denoted as MCM-22-350-2-AT.

[0060] The SiO 2 / Al 2 O 3 ratio of the molecular sieve is 49, the specific surface area of the total pores is 392.2 m 2 / g, the specific surface area of the mesopores is 148.3 m 2 / g, the pore volume of the total pores is 1.105 cm 3 / g, the pore volume of the mesopores is 0.835 cm 3 / g, XRD and NH 3 -TPD results are shown in Figure 1 and Figure 2 .

[0061] From the above results, it can be seen that after the hydrothermal aging of the MCM-22 molecular sieve, the crystal phase structure remains unchanged. However, due to the further removal of the amorphous Al removed by hydrothermal aging filled in the secondary mesopores by acid treatment, the SiO 2 / Al2O 3 ratio of the molecular sieve increases, the specific surface area and pore volume of the mesopores increase, but the acidity decreases.

[0062] Example 2

[0063] The MCM-22 molecular sieve obtained in Comparative Example 3 was added to 2 mol / L hydrochloric acid solution at a liquid-solid mass ratio of 20:1, heated to 80 °C, and soaked for 2 h; then, the acid-treated molecular sieve sample was washed with deionized water. When the pH of the washing solution was 6-7, the molecular sieve sample was dried at 80 °C for 12 h and then calcined at 500 °C for 4 h; the obtained molecular sieve was denoted as MCM-22-550-7-AT.

[0064] The SiO 2 / Al 2 O 3 ratio of the molecular sieve was 72, the specific surface area of the total pores was 399.1 m 2 / g, the specific surface area of the mesopores was 159.9 m 2 / g, the pore volume of the total pores was 1.296 cm 3 / g, the pore volume of the mesopores was 0.894 cm 3 / g, the XRD and NH 3 -TPD results are shown in Figure 1 and Figure 2 .

[0065] From the above results, it can be seen that after the hydrothermal aging of the MCM-22 molecular sieve, the crystal phase structure did not change. However, due to the further removal of the amorphous Al removed by hydrothermal aging in the secondary mesopores by acid treatment, the SiO 2 / Al2O 3 ratio of the molecular sieve increased, the specific surface area and pore volume of the mesopores increased, but the acidity decreased.

[0066] Comparative Example 4

[0067] The catalytic performance of the unmodified MCM-22 molecular sieve in the alkylation reaction of 2-methylnaphthalene was investigated in 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. The specific process was as follows:

[0068] 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 in a nitrogen atmosphere for 7 h;

[0069] 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 .

[0071] The product was sampled after condensation and analyzed on a gas chromatograph. The reaction results are shown in Figures 3 - 6 。

[0072] Comparative Example 5

[0073] The performance of MCM-22-350-2 molecular sieve in catalyzing the alkylation 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. The specific process was as follows:

[0074] 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;

[0075] 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;

[0076] Finally, the raw material liquid 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 (based on 2-methylnaphthalene) 0.3 h -1 。

[0077] The product was sampled after condensation and analyzed on a gas chromatograph. The reaction results are shown in Figures 3 - 6 。

[0078] Comparative Example 6

[0079] The performance of MCM-22-550-7 molecular sieve in catalyzing the alkylation 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. The specific process was as follows:

[0080] 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;

[0081] 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;

[0082] Finally, the raw material liquid 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 (based on 2-methylnaphthalene) 0.3 h -1 。

[0083] The product was sampled after condensation and analyzed on a gas chromatograph. The reaction results are shown in Figures 3 - 6 。

[0084] Example 3

[0085] The performance of MCM-22-350-2-AT zeolite in catalyzing the alkylation 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. The specific process is as follows:

[0086] First, 5.0 g of the zeolite catalyst was loaded into the reactor, and then it was pretreated by in-situ activation at 200 - 300 °C in a nitrogen atmosphere for 7 h;

[0087] Second, 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;

[0088] Finally, the raw material liquid 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 (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 Figures 3 - 6 .

[0089] Example 4

[0090] The performance of MCM-22-550-7-AT zeolite in catalyzing the alkylation 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. The specific process is as follows:

[0091] First, 5.0 g of the zeolite catalyst was loaded into the reactor, and then it was pretreated by in-situ activation at 200 - 300 °C in a nitrogen atmosphere for 7 h;

[0092] Second, 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;

[0093] Finally, the raw material liquid 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 (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 Figures 3 - 6 .

[0094] Figures 3 - 6 They are the conversion rate results of 2-MN, the selectivity results of DMN, the selectivity results of 2,6-DMN, and the ratio of 2,6- / 2,7-DMN, respectively.

[0095] It can be seen from Figures 3 - 6 that for the MCM-22 catalyst without hydrothermal aging / acid treatment modification, the conversion rate decreased from 49% to 45% after 30 h of reaction, the DMN selectivity was 68%-72%, the 2,6-DMN selectivity was 13%-14%, and the ratio of 2,6- / 2,7-DMN was 1.01.

[0096] For the MCM-22 molecular sieve after hydrothermal aging / acid treatment, the conversion rate of 2-MN did not decrease within 100 h of the catalytic alkylation reaction. Among them, for the MCM-22 molecular sieve with hydrothermal aging at 550 °C + acid treatment, the conversion rate of 2-MN remained at 58% within 250 h, the DMN selectivity was 70%-75%, the 2,6-DMN selectivity was 16%-17%, and the ratio of 2,6- / 2,7-DMN was 1.19, indicating that the modified molecular sieve has the characteristics of high activity, high selectivity and high stability.

[0097] The above results are all significantly higher than the results reported in the professional literature in the current field and have significant industrial application value.

Claims

1. A preparation method of a methylnaphthalene alkylation catalyst, which comprises the following steps: Hydrothermally age the HMCM-22 molecular sieve; Place the hydrothermally aged HMCM-22 molecular sieve in an acid solution for acid treatment to obtain the methylnaphthalene alkylation catalyst; Wherein: The HMCM-22 molecular sieve has a flaky porous structure, and the SiO 2 / Al 2 O 3 ratio is 1-72:1, the specific surface area is 150-800 m 2 / g, the pore volume is 0.01-1.6 cm 3 / g, and the sodium element content is 0.00001%-0.15%; The hydrothermal aging is carried out using water vapor, the temperature of the hydrothermal aging is 300 - 700 °C, and the time is 1 - 10 hours; The liquid-solid mass ratio of the acid solution to the hydrothermally aged HMCM-22 molecular sieve is 10 - 50:1, the concentration of the acid solution is 1 - 8 mol / L, the temperature of the acid treatment is 30 - 100 °C, and the time is 1 - 12 hours; the acid solution is hydrochloric acid and / or citric acid.

2. The preparation method according to claim 1, wherein, Before the hydrothermal aging, activate the HMCM-22 molecular sieve, and the activation is to heat it to 200 - 400 °C at a rate of 5 - 30 °C / min for 1 - 4 hours.

3. The preparation method according to claim 1, wherein, In the hydrothermal aging process, place the HMCM-22 molecular sieve in the reaction tube of the hydrothermal aging device, and introduce 10% - 100% of water vapor into the reaction tube at a pressure of 0.1 - 1 MPa and a rate of 1 - 10 ml / h for hydrothermal aging.

4. The preparation method according to claim 1, wherein, The HMCM-22 molecular sieve has a flaky porous structure, and the SiO 2 / Al 2 O 3 ratio is 49 - 72:1, the specific surface area is 300 - 600 m 2 / g, the pore volume is 0.7 - 1.6 cm 3 / g, and the sodium element content is 0.00001% - 0.1%.

5. A methylnaphthalene alkylation catalyst, which is prepared by the preparation method according to any one of claims 1 - 4.

6. A method for preparing 2,6-dimethylnaphthalene by alkylation of 2-methylnaphthalene and methanol, wherein, This method is carried out using the catalyst according to claim 5, and this method comprises the following steps: Load the catalyst into a fixed-bed reactor; Mix 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; Introduce the raw material 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 hourly space velocity of 2-methylnaphthalene, the mass hourly space velocity of the feed liquid is 0.2 - 6.0 h -1 ; the reaction pressure is 0 - 10 MPa.

7. The method according to claim 6, wherein, After loading the catalyst into the fixed-bed reactor, subject the catalyst to in-situ activation pretreatment in a nitrogen atmosphere at 200 - 600 °C for 1 - 8 h.

8. The method according to claim 6, wherein, The solvent includes one or a combination of two or more of benzene, toluene, xylene, trimethylbenzene, and tetramethylbenzene.

9. The method according to claim 8, wherein, The solvent includes mesitylene and / or durene.

10. The method according to claim 6, wherein, The reaction temperature is 300 - 400 °C; based on the mass space velocity of 2-methylnaphthalene, the mass space velocity of the feed liquid is 0.2 - 3.0 h -1 ; the reaction pressure is 0 - 4 MPa.

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