MWW structure molecular sieve and preparation method thereof, and xylene isomerization catalyst and preparation method thereof

Abstract

A method for preparing an MWW structure molecular sieve and a method for preparing a xylene isomerization catalyst using the molecular sieve, as well as the MWW structure molecular sieve and the xylene isomerization catalyst prepared thereby. The method for preparing the molecular sieve comprises mixing and crystallizing a silicon source, an aluminum source, a first structure directing agent SDA1, a second structure directing agent SDA2 and water. The method for preparing the catalyst comprises (1) preparing an MWW structure molecular sieve; (2) performing ion exchange with an aqueous solution of the first structure directing agent SDA1; (3) performing hydrothermal treatment with an aqueous solution of the second structure directing agent SDA2; and (4) loading a noble metal and activating the catalyst. The prepared MWW structure molecular sieve is a nano-thin sheet molecular sieve with a silicon-aluminum ratio of 20 to 100 and a sheet thickness of 5 to 30 nanometers. The prepared xylene isomerization catalyst comprises 5 to 70% by mass of an MWW structure molecular sieve, 0.01 to 0.5% by mass of a noble metal, and the remainder is an alumina binder. The catalyst can be used for the xylene isomerization reaction containing ethylbenzene, and has significantly improved ethylbenzene conversion capacity and xylene selectivity.

Description

Technical Field

[0001] The present invention relates to a molecular sieve and a catalyst and a preparation method thereof. Specifically, the present invention relates to a method for preparing a nano-sheet-like MWW structure molecular sieve with a specific silicon-aluminum ratio and the MWW structure molecular sieve prepared thereby, as well as a method for preparing a xylene isomerization catalyst using the molecular sieve and the xylene isomerization catalyst prepared thereby. Background Art

[0002] Paraxylene (PX) is an important chemical raw material, mainly used in the production of terephthalic acid, terephthalic acid diesters, phthalic anhydride, and also used in coatings, dyes, pesticides, and pharmaceuticals. With the development of these industries, the demand for PX has grown rapidly. At present, the main process technology for increasing the production of PX is xylene isomerization, which is an important means to convert low-value meta-xylene and o-xylene into PX.

[0003] Through the isomerization reaction of xylene, the paraxylene in the product reaches or approaches the thermodynamic equilibrium value. The product can be separated into PX products through the separation device, and then a small amount of light non-aromatic hydrocarbons, benzene, toluene and C9 + The heavy aromatics are separated out, and the remaining C8 aromatic materials can be recycled as raw materials for isomerization.

[0004] Under existing technical conditions, it is very difficult and uneconomical to separate ethylbenzene from xylenes, whether by efficient distillation or adsorption separation. Therefore, ethylbenzene must be converted at the same time during the xylene isomerization process. There are two different target directions for ethylbenzene conversion: ethylbenzene conversion to xylenes and ethylbenzene dealkylation to benzene. The economic feasibility of the two directions depends on the composition of the raw materials, the energy consumption of the device and the market conditions.

[0005] When the mass fraction of ethylbenzene in the raw material is low, the ethylbenzene deethylation route is often used. The reaction can be completed at a higher space velocity and a lower hydrogen-to-hydrocarbon ratio and pressure conditions, saving energy consumption. When the mass fraction of ethylbenzene in the raw material is high, the deethylation route will produce a large amount of benzene as a by-product. When the price of benzene is low, the economic efficiency will significantly deteriorate. Therefore, high ethylbenzene raw materials often use the route of ethylbenzene conversion to xylene. The reaction path of ethylbenzene conversion to xylene is more complicated, the single-pass processing capacity of the catalyst is lower, and the required hydrogen-to-hydrocarbon ratio, temperature and pressure conditions are more stringent. There are also obvious differences in the types of molecular sieves and acidic characteristics in the catalysts of the two routes.

[0006] CN200910260072.9 is an ethylbenzene conversion isomerization catalyst, and its active component is EUO type molecular sieve. The conversion catalyst can convert ethylbenzene into the target product xylene, maximizing the utilization of raw material resources. With market changes, when the price of C8 aromatics raw materials is high and benzene products are in excess, the economic efficiency of the conversion process will be better than the deethylation process. So far, the main bottleneck limiting the economic efficiency of the use of ethylbenzene conversion catalyst is the low single-pass conversion rate of ethylbenzene, which increases the energy consumption and material consumption of materials in the circulation process.

[0007] The original molecular sieve powder is usually Na type, which needs to be converted into ammonium type by ion exchange with ammonium salt, and then roasted to decompose the ammonium cation into H type, i.e. proton acid (or Acid). In the preparation technology of xylene isomerization catalyst, as shown in patent application CN200510080209.4, it is usually necessary to use an ion exchange method to convert the Na type molecular sieve into the H type molecular sieve. Patent application CN200880120492.0 discloses a method for preparing a xylene isomerization catalyst after ion exchange, preferably ZSM-5 molecular sieve, and ion exchange is performed on the molded support in a solution. The exchange solution usually contains at least one cation source that forms hydrogen, such as NH4 + The hydrogen-forming cations primarily replace the alkali metal cations to provide the hydrogen form of the molecular sieve component after calcination. Suitable compounds for use as solutes in aqueous solution include ammonium nitrate, ammonium sulfate and / or ammonium chloride.

[0008] However, considering the cost and efficiency, there is still a need in the art to further improve the ethylbenzene conversion capacity and xylene selectivity of xylene isomerization reaction catalysts. Summary of the invention

[0009] After a large number of experiments, the inventors have found that by changing and optimizing the synthesis method of the molecular sieve as the active component of the catalyst, a high-activity molecular sieve with a special structure can be produced; and based on the molecular sieve, by optimizing the ion exchange technology to regulate the acid center distribution, a catalyst with higher ethylbenzene conversion ability and xylene selectivity can be prepared.

[0010] Therefore, on the one hand, the present invention provides a method for preparing MWW structured molecular sieve, comprising mixing and crystallizing a silicon source, an aluminum source, a first structure directing agent SDA1, a second structure directing agent SDA2 and water, wherein the molar ratio of the silicon source (calculated as SiO2), the aluminum source (calculated as Al2O3) and water is SiO2:Al2O3:H2O=1:0.01~0.05:20~50; the molar ratio of the first structure directing agent SDA1 is SDA1:SiO2=0.02~0.22; the molar ratio of the second structure directing agent SDA2 is SDA2:SiO2=0.02~0.12.

[0011] In one embodiment of the method for preparing MWW structured molecular sieve according to the present invention, the silicon source is water glass; the aluminum source is one or more selected from aluminum sulfate, aluminum chloride, and aluminum nitrate; the second structure directing agent SDA2 is cycloheximide; the first structure directing agent SDA1 is (R 1 )3N + C n H 2n N + (R 2 )3·2X - , where R 1 and R 2 are all alkyl groups with 1 to 4 carbon atoms, preferably methyl or ethyl. n H 2n is a straight chain alkyl group containing 2 to 10 carbon atoms, X - is a halogen anion, preferably a chloride ion or a bromide ion. More specifically, SDA1 can be selected from dibromohexamethylhexanediamine, dichlorohexaethylbutanediamine, dibromohexamethylpentanediamine, dichlorohexamethyloctanediamine, dichlorohexapropyldecanediamine, and the like.

[0012] In another embodiment of the method for preparing MWW structured molecular sieve according to the present invention, the modulus of the water glass (molar ratio of SiO2:Na2O) is 2-4.

[0013] In another embodiment of the method for preparing MWW structured molecular sieve according to the present invention, the mixing includes first dissolving a first structure directing agent in water to form a solution; adding an aluminum source under stirring conditions, and stirring and mixing for 2 to 12 hours; adding a silicon source to form a liquid sol, and stirring and mixing for 6 to 18 hours; and adding a second structure directing agent, and stirring and mixing evenly.

[0014] In another embodiment of the method for preparing MWW structured molecular sieve according to the present invention, the crystallization temperature is 140-190° C., preferably 165-175° C.; the crystallization time is 20-120 hours, preferably 25-75 hours.

[0015] On the other hand, the present invention provides an MWW structured molecular sieve prepared by the method for preparing an MWW structured molecular sieve according to any of the aforementioned embodiments, wherein the molecular sieve is a nano-flaky molecular sieve having a silicon-aluminum ratio of 20 to 100, preferably 25 to 50; and the thickness of the nano-flaky molecular sieve is 5 to 30 nanometers, preferably 10 to 20 nanometers.

[0016] In another aspect, the present invention provides a method for preparing a xylene isomerization catalyst, the method comprising the following steps:

[0017] (1) A silicon source, an aluminum source, a first structure directing agent SDA1, a second structure directing agent SDA2 and water are mixed and crystallized to obtain an MWW structure molecular sieve, wherein the silicon source is water glass; the aluminum source is one or more selected from aluminum sulfate, aluminum chloride, and aluminum nitrate; the second structure directing agent SDA2 is cycloheximide; the first structure directing agent SDA1 is (R 1 )3N + C n H 2n N + (R 2 )3·2X - , where R 1 and R 2 are all alkyl groups with 1 to 4 carbon atoms, preferably methyl or ethyl. n H 2n is a straight chain alkyl group containing 2 to 10 carbon atoms, X - is a halogen anion, preferably a chloride ion or a bromide ion;

[0018] (2) using the aqueous solution of the first structure directing agent SDA1 to perform ion exchange on the MWW structure molecular sieve obtained in step (1), washing with deionized water and drying after the exchange, and then mixing with an alumina binder, forming and calcining to obtain a catalyst carrier;

[0019] (3) using the aqueous solution of the second structure directing agent SDA2 as a steam source to hydrothermally treat the catalyst support prepared in step (2) to obtain a catalyst support with optimized acid function distribution; and

[0020] (4) The catalyst with optimized acid function distribution obtained in step (3) is impregnated with a solution containing precious metals, and after activation and reduction, the xylene isomerization catalyst is obtained.

[0021] In one embodiment of the method for preparing a xylene isomerization catalyst according to the present invention, the molar ratio of the silicon source (calculated as SiO2), the aluminum source (calculated as Al2O3) and water in step (1) is SiO2:Al2O3:H2O=1:0.01~0.05:20~50; the molar ratio of the first structure directing agent SDA1 is SDA1:SiO2=0.02~0.22; the molar ratio of the second structure directing agent SDA2 is SDA2:SiO2=0.02~0.12.

[0022] In another embodiment of the method for preparing a xylene isomerization catalyst according to the present invention, the mixing in step (1) includes first dissolving a first structure directing agent in water to form a solution; adding an aluminum source under stirring conditions, and stirring and mixing for 2 to 12 hours; adding a silicon source to form a liquid sol, and stirring and mixing for 6 to 18 hours; and adding a second structure directing agent, and stirring and mixing evenly.

[0023] In another embodiment of the method for preparing a xylene isomerization catalyst according to the present invention, the crystallization temperature in step (1) is 140-190° C., preferably 165-175° C.; the crystallization time is 20-120 hours, preferably 25-75 hours.

[0024] In another embodiment of the method for preparing a xylene isomerization catalyst according to the present invention, the concentration of the aqueous solution of the first structure directing agent SDA1 in step (2) is 0.01-0.08 mol / L, preferably 0.04-0.06 mol / L; the liquid-to-solid ratio of the ion exchange is 5-30 mL / g molecular sieve, the temperature of the ion exchange is 50-90°C, and the number of ion exchanges is 2-4 times; the molar content of Na2O in the MWW structured molecular sieve of the obtained catalyst carrier in the total component oxides is 0.01-2.0%, preferably 0.1-0.4%.

[0025] In another embodiment of the method for preparing a xylene isomerization catalyst according to the present invention, the drying in step (2) is carried out at 120° C. for 8 to 24 hours, the calcination is carried out at 540° C. for 2 to 24 hours, and the drying and calcination are carried out in a static atmosphere or at a volume space velocity of 50 to 500 h / s. -1 in a dynamic atmosphere.

[0026] In another embodiment of the method for preparing a xylene isomerization catalyst according to the present invention, the concentration of the aqueous solution of the second structure directing agent SDA2 in step (3) is 0.01-0.08 mol / L, preferably 0.04-0.06 mol / L, the amount of the solution is 5-30 mL / g catalyst carrier, the steam treatment temperature is 200-450°C, preferably 350-400°C, and the treatment time is 3-6 hours.

[0027] In another embodiment of the method for preparing a xylene isomerization catalyst according to the present invention, the noble metal in step (4) is platinum, palladium, rhodium or ruthenium, preferably platinum.

[0028] In another embodiment of the method for preparing a xylene isomerization catalyst according to the present invention, the MWW structured molecular sieve prepared in step (1) is a nano-flake molecular sieve having a silicon-aluminum ratio of 20 to 100, preferably 25 to 50; the thickness of the flakes is 5 to 30 nanometers, preferably 10 to 20 nanometers.

[0029] In another embodiment of the method for preparing a xylene isomerization catalyst according to the present invention, the content of the MWW structured molecular sieve as the acid catalytic active component in the xylene isomerization catalyst accounts for 5 to 70% by mass, preferably 10 to 50% by mass, of the total mass of the catalyst; the content of the precious metal accounts for 0.01 to 0.5% by mass, preferably 0.05 to 0.35% by mass, of the total mass of the catalyst; and the remaining components are alumina binder.

[0030] In yet another aspect, the present invention provides a xylene isomerization catalyst prepared by the method for preparing a xylene isomerization catalyst according to any of the aforementioned embodiments.

[0031] In one embodiment of the xylene isomerization catalyst according to the present invention, the xylene isomerization catalyst comprises a nano-flake MWW structured molecular sieve having a silicon-aluminum ratio of 20 to 100, preferably 25 to 50, and 0.01 to 0.5 mass %, preferably 0.05 to 0.35 mass % of a precious metal.

[0032] In the method for preparing the MWW structured molecular sieve of the present invention, two structure directing agents (SDA1 and SDA2) are used to obtain the MWW structured molecular sieve flakes with a silicon-aluminum ratio of 20 to 100 and a thickness of 5 to 30 nanometers. The MWW structured molecular sieve is ion exchanged with the first structure directing agent, kneaded and molded with a binder, and after molding, is hydrothermally treated with the second structure directing agent to optimize the acid function distribution of the catalyst carrier, followed by loading the precious metal component and activating and reducing to obtain the catalyst of the present invention. When used for the isomerization reaction of xylene containing ethylbenzene, the ethylbenzene conversion capacity and xylene selectivity of the catalyst of the present invention are significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is the XRD spectrum of the Z-1 molecular sieve prepared according to Example 1;

[0034] Figure 2 is the XRD spectrum of the Z-2 molecular sieve prepared according to Example 2;

[0035] Figure 3 is a SEM electron microscope photograph of the Z-1 molecular sieve prepared according to Example 1; and

[0036] Figure 4 This is a SEM electron microscope photograph of the Z-2 molecular sieve prepared according to Example 2. DETAILED DESCRIPTION

[0037] The present application will be further described in detail below in conjunction with the accompanying drawings and embodiments. Through these descriptions, the features and advantages of the present application will become clearer and more explicit.

[0038] In addition, the technical features involved in different embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0039] In one embodiment, the method for preparing a molecular sieve having an MWW structure according to the present invention, i.e., a one-step method for producing a molecular sieve having an MWW structure, comprises mixing and crystallizing a silicon source, an aluminum source, a first structure directing agent (SDA1), a second structure directing agent (SDA2) and water, wherein the silicon source (calculated as SiO2), the aluminum source (calculated as Al2O3) and water are added in a molar ratio of SiO2:Al2O3:H2O=1:0.01~0.05:20~50, the amount of the first structure directing agent SDA1 is in accordance with the molar ratio of SDA1:SiO2=0.02~0.22; the amount of the second structure directing agent SDA2 is in accordance with the molar ratio of SDA2:SiO2=0.02~0.12.

[0040] In one embodiment, the silicon source may be water glass, preferably water glass having a modulus of 2 to 4 (ie, a molar ratio of SiO2:Na2O of 2 to 4).

[0041] In one embodiment, the aluminum source may be aluminum sulfate, aluminum chloride, aluminum nitrate, preferably aluminum sulfate.

[0042] In one embodiment, the first structure directing agent may be of formula (R1)3N + C n H 2n N + (R2)3·2X - The straight-linked diamine dihalide shown, for example, (CH3)3N + C6H 12 N + (CH3)3·2Cl - 、(CH3)3N + C6H 12 N + (CH3)3·2Br - ……, where R 1 and R 2 are all alkyl groups with 1 to 4 carbon atoms, preferably methyl or ethyl, n is 2 to 10, C n H 2n is a straight chain alkyl group containing 2 to 10 carbon atoms, X - is a halogen anion, preferably a chloride ion or a bromide ion.

[0043] In one embodiment, the second structure directing agent may be cycloheximide, preferably cycloheximide.

[0044] More specifically, the first structure directing agent is first dissolved in water to form a solution; then, under stirring conditions, an aluminum source is slowly added and stirred for 2 to 12 hours; then, a silicon source is slowly added to form a liquid sol, and stirred for 6 to 18 hours to make the sol phase uniform; then, a second structure directing agent is added to the sol, stirred and mixed uniformly, and the raw materials are mixed. Next, the mixture is crystallized at a temperature of 140 to 190° C. for 20 to 120 hours, preferably at a temperature of 165 to 175° C. for 25 to 75 hours.

[0045] The molecular sieve with MWW structure prepared in this way is a nano-sheet-shaped molecular sieve with a thickness of 5 to 30 nanometers, preferably 10 to 20 nanometers; and a silicon-aluminum ratio of 20 to 100, preferably 25 to 50.

[0046] The xylene isomerization catalyst of the present invention comprises a molecular sieve having an MWW structure as an active component, which provides an acidic site for the xylene isomerization reaction and an acidic site for converting ethylbenzene into xylene. Generally, as the active component of the xylene isomerization catalyst of the present invention, the content of the molecular sieve having an MWW structure can be 10 to 50% by mass of the entire catalyst.

[0047] In one embodiment, the method for preparing a xylene isomerization catalyst according to the present invention comprises the following steps:

[0048] (1) mixing a silicon source, an aluminum source, a first structure directing agent SDA1, a second structure directing agent SDA2 and water and crystallizing them to obtain an MWW structure molecular sieve;

[0049] (2) using the aqueous solution of the first structure directing agent SDA1 to perform ion exchange on the MWW structure molecular sieve obtained in step (1), washing with deionized water and drying after the exchange, and then mixing with an alumina binder, forming and calcining to obtain a catalyst carrier;

[0050] (3) using the aqueous solution of the second structure directing agent SDA2 as a steam source to hydrothermally treat the catalyst support prepared in step (2) to obtain a catalyst support with optimized acid function distribution; and

[0051] (4) The catalyst with optimized acid function distribution obtained in step (3) is impregnated with a solution containing precious metals, and after activation and reduction, the xylene isomerization catalyst is obtained.

[0052] Specifically, in step (2) of the catalyst preparation method, the MWW structure nanosheet molecular sieve raw powder is subjected to ion exchange using an aqueous solution of the first structure directing agent SDA1, the concentration of the solution is 0.01-0.08 mol / L, preferably 0.04-0.06 mol / L, the exchange liquid-solid ratio is 5-30 mL / g molecular sieve, the exchange temperature is 50-90°C, and the number of exchanges is 2-4 times; the exchanged molecular sieve is washed several times with excess deionized water until no halogen anions are detected in the eluate, and the pH range is 6-8. The Na2O molar content of the washed MWW structure molecular sieve is 0.01-2.0%, preferably 0.1-0.4%. The fully washed MWW structure molecular sieve raw powder is dried at 120°C for 8-24 hours, and the drying can be carried out in a static atmosphere without air flow, or in a dynamic atmosphere with a volume space velocity of 50-500. The dried molecular sieve can be formed according to conventional methods. The formed carrier is dried at 120°C for 8 to 24 hours and air-baked at 540°C for 2 to 24 hours. Baking can be carried out in a static atmosphere without air flow or in a dynamic atmosphere with a volume space velocity of 50 to 500.

[0053] Specifically, in step (3) of the catalyst preparation method, the shaped catalyst carrier containing the MWW structured molecular sieve and alumina is subjected to an optimization treatment for acid function distribution, i.e., a hydrothermal treatment is carried out using an aqueous solution of a second structure directing agent SDA2 as a steam source, wherein the concentration of the SDA2 aqueous solution is 0.01 to 0.08 mol / L, preferably 0.04 to 0.06 mol / L, the amount of the solution is 5 to 30 mL / g of carrier, the steam treatment temperature is 200 to 450°C, preferably 350 to 400°C, and the treatment time is 3 to 6 hours.

[0054] Usually NH4 from ammonium salts is used + Cations exchange ions on sodium-type molecular sieve materials, but the volume of ammonium cations is small, and all sodium ions are non-selectively exchanged for ammonium ions during the exchange process. In this case, cycloheximide is selected as the ion exchanger. Due to the large molecular size of cycloheximide, it cannot enter the deeper pores in the molecular sieve. Therefore, through the shape-selective effect, the amine ions only exchange the sodium ions on the outer surface and pore mouth of the molecular sieve, converting them into amine ions, and then converting them into H ions in the subsequent roasting to form acidic centers.

[0055] It is generally believed that the aluminum ions on the molecular sieve will be displaced and chemically modified during the hydrothermal treatment. If organic amines with shape-selective effects can be added during the hydrothermal process, some of the migrated aluminum ions can be ion-exchanged and shape-selective again.

[0056] The shaped catalyst carrier after the acid function distribution optimization treatment can be impregnated with precious metals and activated and reduced according to conventional methods to obtain the catalyst of the present invention.

[0057] In one embodiment, the noble metal in step (4) of the method for preparing a xylene isomerization catalyst according to the present invention is platinum, palladium, rhodium or ruthenium, preferably platinum.

[0058] In one embodiment, the catalyst according to the present invention comprises a nano-flaky MWW structured molecular sieve as an acidic active component and alumina as a binder, wherein the content of the MWW structured molecular sieve is 10 to 50% by mass, and the remaining component is the alumina binder; in addition, the catalyst of the present invention is also loaded with 0.05 to 0.35% by mass of precious metals.

[0059] The catalyst prepared according to the method of the present invention can be applied to the isomerization reaction of xylene containing ethylbenzene. The isomerization reaction of xylene containing ethylbenzene is a process of contacting with the catalyst in the presence of hydrogen. When the mass fraction of ethylbenzene in the raw material is in the range of 8 to 20%, the weight hourly space velocity of the catalyst is controlled to be 3 to 8 h -1 , pressure is 0.4-1.6MPa, temperature is 300-350°C, and hydrogen-to-hydrocarbon molar ratio is 2.0-4.5. Compared with the existing catalyst, the catalyst of the present invention has improved ethylbenzene conversion capacity and xylene selectivity.

[0060] The catalyst performance is evaluated according to the following calculation method:

[0061] Isomerization equilibrium achievement rate:

[0062] Xylene yield:

[0063] Ethylbenzene conversion rate:

[0064] The present invention is further described below by way of examples, but the present invention is not limited thereto.

[0065] Example

[0066] The following examples synthesize Na-type raw powder of MWW structured nano-flaky molecular sieve.

[0067] Example 1

[0068] Add 450 mL of silicon source (water glass, concentration 24w%, modulus 3.1), 20.2 g of aluminum source (aluminum sulfate), (CH3)3N + C6H 12 N + (CH3)3·2Cl -As the first structure directing agent, the addition amount was 4.1 g; cycloheximide was used as the second structure directing agent, the addition amount was 9.0 g, and the molar ratio of the materials was Na2O:SiO2:Al2O3:SDA1:SDA2:H2O=0.32:1:0.04:0.02:0.12:25. The synthesis temperature was 175°C and the synthesis time was 35 hours.

[0069] Thus, a Na-type MWW structured nano-flaky molecular sieve was obtained, denoted as Z-1, with a silicon-aluminum ratio of 25. The XRD diffraction spectrum of the obtained molecular sieve Z-1 is shown in Figure 1 As shown in the figure, it has a characteristic peak of MWW structure in the range of 5 to 50 degrees. The SEM electron microscope photo of the obtained molecular sieve Z-1 is shown in Figure 3 , as shown in the figure, it has a nano-flake structure.

[0070] Example 2

[0071] In a 2L reactor, add 450mL of silicon source (water glass, concentration 24w%, modulus 3.1), 10.1g of aluminum source (aluminum sulfate), (CH3)3N + C6H 12 N + (CH3)3·2Br - As the first structure directing agent, the addition amount was 60.4 g; cycloheximide was used as the second structure directing agent, the addition amount was 1.5 g, and the molar ratio of the materials was Na2O:SiO2:Al2O3:SDA1:SDA2:H2O=0.32:1:0.02:0.22:0.02:35. The synthesis temperature was 165°C and the synthesis time was 25 hours.

[0072] Thus, a Na-type MWW structured nano-flaky molecular sieve was obtained, denoted as Z-2, with a silicon-aluminum ratio of 50. The XRD diffraction spectrum of the obtained molecular sieve Z-2 is shown in Figure 2 As shown in the figure, it has a characteristic peak of MWW structure in the range of 5 to 50 degrees. The SEM electron microscope photo of the obtained molecular sieve Z-2 is shown in Figure 4 , as shown in the figure, it has a nano-flake structure.

[0073] The following comparative example prepares a conventional xylene isomerization catalyst.

[0074] Comparative Example 1

[0075] Take 3g of commercial Eu-1 molecular sieve powder with a silicon-aluminum ratio of 30 (provided by Changling Catalyst Factory), use 50 ml of 0.05mol / L ammonium chloride aqueous solution at 90°C for 2 hours × 2 times, wash until no chloride ions are detected in the mother liquor, and the pH range is 6-8. The molecular sieve after thorough washing is dried at 120°C in a static atmosphere without air flow for 8 hours. The dried molecular sieve is fully mixed with 17g of aluminum oxide, and 20 ml of 3% nitric acid aqueous solution is added to mix to form a viscous mixture, and extruded into strips. The strips are dried at 120°C for 6 hours, then pelletized and roasted at 540°C for 4 hours. Use water vapor for hydrothermal treatment, the treatment temperature is 350°C, and the treatment time is 6 hours. The treated carrier is impregnated with 20 ml of chloroplatinic acid aqueous solution containing 0.05g of platinum, and a catalyst containing 0.25% by mass of platinum is prepared after drying at 120°C. It was then activated under air to prepare an oxidized catalyst, and reduced under hydrogen for 4 hours to prepare comparative catalyst D-1.

[0076] Comparative Example 2

[0077] Comparative catalyst D-2 was prepared according to the method of comparative example 1, except that 9g of commercial MOR molecular sieve powder (provided by Fushun Catalyst Factory) with a silicon-aluminum ratio of 12 was used, and ion exchange was carried out at 80°C for 2 hours × 3 times with 50 ml of 0.05mol / L dibromohexamethylhexane diamine aqueous solution, and washed until no chloride ions were detected in the mother liquor, and the pH range was 6-8. The molecular sieve after being fully washed was dried at 120°C for 24 hours in a dynamic atmosphere with a volume space velocity of 500. The molecular sieve after drying was fully mixed with 11g of aluminum oxide, and 20 ml of 5% nitric acid aqueous solution was added to mix to form a viscous mixture, and extruded into strips. The strips were dried at 120°C for 12 hours, then pelletized and roasted at 540°C for 12 hours. The aqueous solution of the second structure-directing agent cyclohexyl imine was used as a steam source for hydrothermal treatment, the concentration of the solution was 0.06mol / L, the amount of the solution was 600mL, the steam treatment temperature was 400°C, and the treatment time was 3 hours. The treated carrier was impregnated with 20 ml of chloroplatinic acid aqueous solution containing 0.35 g of platinum, and dried at 120° C. to prepare a catalyst containing 0.35 mass% of platinum. It was then activated in air to prepare an oxidized catalyst, and reduced in hydrogen for 4 hours to prepare comparative catalyst D-2.

[0078] Comparative Example 3

[0079] Comparative catalyst D-3 was prepared according to the method of comparative example 1, except that 3g of Na-type MWW structure molecular sieve Z-1 powder with a silicon-aluminum ratio of 25 synthesized in Example 1 was used, and ion exchange was carried out at 90°C for 2 hours × 4 times with 50 ml of 0.05mol / L ammonium chloride aqueous solution, and washed until no chloride ions were detected in the mother liquor, and the pH range was 6-8. The molecular sieve after sufficient washing was dried at 120°C for 16 hours in a static atmosphere without air flow. The dried molecular sieve was fully mixed with 17g of aluminum oxide, and 15 ml of 4% nitric acid aqueous solution was added to mix to form a viscous mixture, and extruded into strips. The strips were dried at 120°C for 16 hours, then pelletized and calcined at 540°C for 10 hours. The treated carrier was impregnated with 20 ml of chloroplatinic acid aqueous solution containing 0.05g of platinum, and dried at 120°C to prepare a catalyst containing 0.05% by mass of platinum. It was then activated in air to prepare an oxidized catalyst, and reduced under hydrogen for 4 hours to prepare comparative catalyst D-3.

[0080] Comparative Example 4

[0081] Take 9g of Na-type MWW structure molecular sieve Z-2 powder with a silicon-aluminum ratio of 50 synthesized in Example 2, and use 50 ml of 0.04mol / L ammonium nitrate aqueous solution at 50°C for 2 hours × 3 times, wash until no chloride ions are detected in the mother liquor, and the pH range is 6-8. The molecular sieve after being fully washed is dried at 120°C for 18 hours in a dynamic atmosphere with a volume space velocity of 50. The dried molecular sieve is fully mixed with 11g of aluminum oxide, and 20 ml of 4% nitric acid aqueous solution is added to mix to form a viscous mixture, and extruded into strips. The strips are dried at 120°C for 24 hours, then pelletized and roasted at 540°C for 12 hours. Use aqueous solution as a steam source for hydrothermal treatment, the steam treatment temperature is 350°C, and the treatment time is 6 hours. The treated carrier is impregnated with 20 ml of chloroplatinic acid aqueous solution containing 0.35 grams of platinum, and a catalyst containing 0.35% by mass of platinum is prepared after drying at 120°C. The catalyst was activated in air to prepare an oxidized catalyst, and reduced in hydrogen for 4 hours to prepare a comparative catalyst D-4.

[0082] The following examples are used to prepare the xylene isomerization catalyst of the present invention.

[0083] Example 3

[0084] Catalyst C-1 according to the present invention is prepared according to the method of Comparative Example 3, except that the molecular sieve is ion exchanged using an aqueous solution of the first structure-directing agent dibromohexamethylhexanediamine, the concentration of the solution is 0.06 mol / L, the exchange liquid-solid ratio is 30 mL / g molecular sieve, the exchange temperature is 90°C, and the number of exchanges is 4 times; the exchanged molecular sieve is washed several times with excess deionized water until no halogen anions are detected in the eluate, and the pH range is 6 to 8. The Na2O molar content of the MWW structure molecular sieve after washing is 0.4%. The formed carrier is hydrothermally treated using an aqueous solution of the second structure-directing agent cyclohexylimide as a steam source, the concentration of the solution is 0.04 mol / L, the amount of the solution is 5 mL / g carrier, the steam treatment temperature is 350°C, and the treatment time is 6 hours. 0.25% by mass of platinum is impregnated according to the method of Comparative Example 1, and calcined for activation and reduction.

[0085] Example 4

[0086] Catalyst C-2 according to the present invention is prepared according to the method of Example 3, except that the molecular sieve uses 9g of Na-type MWW structure molecular sieve Z-2 with a silicon-aluminum ratio of 50 synthesized in Example 2, and uses an aqueous solution of the first structure-directing agent dichlorohexaethylbutane diamine for ion exchange, the concentration of the solution is 0.04mol / L, the exchange liquid-solid ratio is 5mL / g molecular sieve, the exchange temperature is 50°C, and the number of exchanges is 2 times; the exchanged molecular sieve is washed several times with excess deionized water until no halogen anions are detected in the eluate, and the pH range is 6-8. The Na2O molar content of the MWW structure molecular sieve after washing is 0.2%. The exchanged molecular sieve is mixed with 11g of alumina and extruded into strips. The formed carrier is hydrothermally treated using an aqueous solution of the second structure-directing agent cyclohexyl imine as a steam source, the concentration of the solution is 0.06mol / L, the amount of the solution is 30mL / g carrier, the steam treatment temperature is 400°C, and the treatment time is 3 hours. The treated carrier was impregnated with 20 ml of chloroplatinic acid aqueous solution containing 0.15 g of platinum, and dried at 120° C. to prepare a catalyst containing 0.15 mass% of platinum. It was then activated in air to prepare an oxidized catalyst, and reduced in hydrogen for 4 hours to prepare the catalyst C-2 according to the present invention.

[0087] Example 5

[0088] Catalyst C-3 according to the present invention is prepared according to the method of Example 4, except that 3g of Na-type MWW structure molecular sieve Z-2 with a silicon-aluminum ratio of 50 synthesized in Example 2 is taken, and an aqueous solution of dichlorohexaethylbutanediamine, a first structure directing agent, is used for ion exchange, the concentration of the solution is 0.06mol / L, the exchange liquid-solid ratio is 20mL / g molecular sieve, the exchange temperature is 80°C, and the number of exchanges is 3 times; the exchanged molecular sieve is washed several times with excess deionized water until no halogen anions are detected in the eluate, and the pH range is 6-8. The Na2O molar content of the MWW structure molecular sieve after washing is 0.3%. The exchanged molecular sieve is mixed with 17g of alumina and extruded into strips. The formed carrier is hydrothermally treated using an aqueous solution of cyclohexylimide, a second structure directing agent, as a steam source, the concentration of the solution is 0.05mol / L, the amount of the solution is 5mL / g carrier, the steam treatment temperature is 370°C, and the treatment time is 4 hours. The treated carrier was impregnated with 20 ml of chloroplatinic acid aqueous solution containing 0.30 g of platinum, and dried at 120° C. to prepare a catalyst containing 0.30 mass% of platinum. It was then activated in air to prepare an oxidized catalyst, and reduced in hydrogen for 4 hours to prepare the catalyst C-3 according to the present invention.

[0089] Example 6

[0090] Catalyst C-4 according to the present invention is prepared according to the method of Example 4, except that 6g of Na-type MWW structure molecular sieve Z-2 with a silicon-aluminum ratio of 50 synthesized in Example 2 is taken, and an aqueous solution of the first structure-directing agent dibromohexamethylpentane diamine is used for ion exchange, the concentration of the solution is 0.04mol / L, the exchange liquid-solid ratio is 25mL / g molecular sieve, the exchange temperature is 70°C, and the number of exchanges is 4 times; the exchanged molecular sieve is washed several times with excess deionized water until no halogen anions are detected in the eluate, and the pH range is 6-8. The Na2O molar content of the MWW structure molecular sieve after washing is 0.25%. The exchanged molecular sieve is mixed with 14g of alumina and extruded into strips. The formed carrier is hydrothermally treated using an aqueous solution of the second structure-directing agent cyclohexylimide as a steam source, the concentration of the solution is 0.04mol / L, the amount of the solution is 15mL / g carrier, the steam treatment temperature is 350°C, and the treatment time is 6 hours. The treated carrier was impregnated with 20 ml of chloroplatinic acid aqueous solution containing 0.25 g of platinum, and dried at 120° C. to prepare a catalyst containing 0.25 mass% of platinum. It was then activated in air to prepare an oxidized catalyst, and reduced in hydrogen for 4 hours to prepare the catalyst C-4 according to the present invention.

[0091] Example 7

[0092] Catalyst C-5 according to the present invention is prepared according to the method of Example 4, except that 8g of Na-type MWW structure molecular sieve Z-2 with a silicon-aluminum ratio of 50 synthesized in Example 2 is taken, and an aqueous solution of dichlorohexamethyloctanediamine, a first structure directing agent, is used for ion exchange, the concentration of the solution is 0.055mol / L, the exchange liquid-solid ratio is 15mL / g molecular sieve, the exchange temperature is 90°C, and the number of exchanges is 4 times; the exchanged molecular sieve is washed several times with excess deionized water until no halogen anions are detected in the eluate, and the pH range is 6-8. The Na2O molar content of the MWW structure molecular sieve after washing is 0.4%. The exchanged molecular sieve is mixed with 12g of alumina and extruded into strips. The formed carrier is hydrothermally treated using an aqueous solution of cyclohexylimide, a second structure directing agent, as a steam source, the concentration of the solution is 0.04mol / L, the amount of the solution is 15mL / g carrier, the steam treatment temperature is 350°C, and the treatment time is 6 hours. The treated carrier was impregnated with 20 ml of chloroplatinic acid aqueous solution containing 0.20 g of platinum, and dried at 120° C. to prepare a catalyst containing 0.20 mass% of platinum. It was then activated in air to prepare an oxidized catalyst, and reduced in hydrogen for 4 hours to prepare the catalyst C-5 according to the present invention.

[0093] Example 8

[0094] The catalyst C-6 according to the present invention is prepared according to the method of Example 4, except that 10g of the Na-type MWW structure molecular sieve Z-2 with a silicon-aluminum ratio of 50 synthesized in Example 2 is taken, and an aqueous solution of the first structure-directing agent dibromohexamethylpentane diamine is used for ion exchange, the concentration of the solution is 0.06mol / L, the exchange liquid-solid ratio is 25mL / g molecular sieve, the exchange temperature is 70°C, and the number of exchanges is 4 times; the exchanged molecular sieve is washed several times with excess deionized water until no halogen anions are detected in the eluate, and the pH range is 6-8. The Na2O molar content of the MWW structure molecular sieve after washing is 0.25%. The exchanged molecular sieve is mixed with 10g of alumina and extruded into strips. The formed carrier is hydrothermally treated using an aqueous solution of the second structure-directing agent cyclohexylimide as a steam source, the concentration of the solution is 0.04mol / L, the amount of the solution is 15mL / g carrier, the steam treatment temperature is 350°C, and the treatment time is 6 hours. The treated carrier was impregnated with 20 ml of chloroplatinic acid aqueous solution containing 0.15 g of platinum, and dried at 120° C. to prepare a catalyst containing 0.15 mass% of platinum. It was then activated in air to prepare an oxidized catalyst, and reduced in hydrogen for 4 hours to prepare the catalyst C-6 according to the present invention.

[0095] The following examples illustrate the application of the xylene isomerization catalyst of the present invention.

[0096] Example 9

[0097] 2g of the xylene isomerization catalyst prepared in the above examples and comparative examples was loaded on a continuous flow fixed bed micro hydrogenation device, and the catalyst performance was evaluated using industrial xylene isomerization raw materials. The raw material composition used in the reaction, the evaluation process parameters, the characteristics of the catalysts in each example, and the reaction results are shown in the table below.

[0098] Table 1. Industrial xylene isomerization feedstock composition

[0099] Raw material composition <![CDATA[C8 cycloalkane]]> benzene Toluene Ethylbenzene p-Xylene Meta-Xylene o-Xylene wt% 5.62 0.02 1.03 17.16 0.49 53.36 22.32

[0100] Table 2. Catalysts prepared in Examples and Comparative Examples and their reaction performance

[0101]

[0102]

[0103] By comparing the results of the above embodiments and comparative examples, it can be seen that the catalyst prepared by the catalyst preparation method of the present invention, using nano-flaky molecular sieves with MWW structure, and using structure-directing agent SDA1 as ion exchange agent, and structure-directing agent SDA2 as steam treatment agent, has higher ethylbenzene conversion activity and xylene selectivity than conventional catalysts prepared using EUO or MOR molecular sieves, or catalysts prepared only by conventional ammonium salt ion exchange and hydrothermal treatment.

[0104] The present invention has been described above in conjunction with the preferred embodiments, but these embodiments are only exemplary and serve as an illustration. On this basis, the present invention can be subjected to a variety of substitutions and improvements, all of which fall within the scope of protection of the present invention.

Claims

1. A method for preparing a xylene isomerization catalyst, the method comprising the following steps: (1) A silicon source, an aluminum source, a first structure directing agent SDA1, a second structure directing agent SDA2 and water are mixed and crystallized to obtain an MWW structure molecular sieve, wherein the silicon source is water glass; the aluminum source is one or more selected from aluminum sulfate, aluminum chloride, and aluminum nitrate; the second structure directing agent SDA2 is cycloheximide; the first structure directing agent SDA1 is (R 1 )3N + C n H 2n N + (R 2 )3·2X - , where R 1 and R 2 All are alkyl groups with 1 to 4 carbon atoms, C n H 2n is a straight chain alkyl group containing 2 to 10 carbon atoms, X - is a halogen anion; (2) using the aqueous solution of the first structure directing agent SDA1 to perform ion exchange on the MWW structure molecular sieve obtained in step (1), washing with deionized water and drying after the exchange, and then mixing with an alumina binder, forming and calcining to obtain a catalyst carrier; (3) using the aqueous solution of the second structure directing agent SDA2 as a steam source to hydrothermally treat the catalyst support prepared in step (2) to obtain a catalyst support with optimized acid function distribution; and (4) impregnating the catalyst with optimized acid function distribution obtained in step (3) with a solution containing precious metals, and obtaining the xylene isomerization catalyst after activation and reduction; The molar ratio of the silicon source (calculated as SiO2), the aluminum source (calculated as Al2O3) and water in step (1) is SiO2:Al2O3:H2O = 1:0.01~0.05: 20~50; the molar ratio of the first structure directing agent SDA1 is SDA1:SiO2=0.02~0.22; the molar ratio of the second structure directing agent SDA2 is SDA2:SiO2=0.02~0.12; The mixing in step (1) includes first dissolving a first structure directing agent in water to form a solution; adding an aluminum source under stirring conditions and stirring and mixing for 2 to 12 hours; adding a silicon source to form a liquid sol and stirring and mixing for 6 to 18 hours; and adding a second structure directing agent and stirring and mixing evenly.

2. The method for preparing a xylene isomerization catalyst according to claim 1, wherein R 1 and R 2 It is methyl or ethyl.

3. The method for preparing a xylene isomerization catalyst according to claim 1, wherein X - It is a chloride ion or a bromide ion.

4. The method for preparing a xylene isomerization catalyst according to claim 1, wherein the crystallization temperature in step (1) is 140-190° C. and the crystallization time is 20-120 hours.

5. The method for preparing a xylene isomerization catalyst according to claim 4, wherein the crystallization temperature in step (1) is 165-175°C.

6. The method for preparing a xylene isomerization catalyst according to claim 4, wherein: The crystallization time is 25 to 75 hours.

7. The method for preparing a xylene isomerization catalyst according to claim 1, wherein the concentration of the aqueous solution of the first structure directing agent SDA1 in step (2) is 0.01-0.08 mol / L; the liquid-to-solid ratio of the ion exchange is 5-30 mL / g molecular sieve, and the temperature of the ion exchange is 50-90°C; and the molar content of Na2O in the total component oxides of the MWW structure molecular sieve of the obtained catalyst carrier is 0.01-2.0%.

8. The method for preparing a xylene isomerization catalyst according to claim 7, wherein the concentration of the first structure directing agent SDA1 aqueous solution in step (2) is 0.04-0.06 mol / L.

9. The method for preparing a xylene isomerization catalyst according to claim 7, wherein the molar content of Na2O in the MWW structured molecular sieve of the obtained catalyst carrier in the total component oxides is 0.1-0.4%.

10. The method for preparing a xylene isomerization catalyst according to claim 1, wherein the drying in step (2) is carried out at 120° C. for 8 to 24 hours, the calcination is carried out at 540° C. for 2 to 24 hours, and the drying and calcination are carried out in a static atmosphere or at a volume space velocity of 50 to 500 h / s. -1 in a dynamic atmosphere.

11. The method for preparing a xylene isomerization catalyst according to claim 1, wherein in step (3), the concentration of the aqueous solution of the second structure directing agent SDA2 is 0.01-0.08 mol / L, the amount of the solution is 5-30 mL / g catalyst carrier, the steam treatment temperature is 200-450°C, and the treatment time is 3-6 hours.

12. The method for preparing a xylene isomerization catalyst according to claim 11, wherein the concentration of the aqueous solution of the second structure directing agent SDA2 in step (3) is 0.04-0.06 mol / L.

13. The method for preparing a xylene isomerization catalyst according to claim 11, wherein the steam treatment temperature is 350-400°C.

14. The method for preparing a xylene isomerization catalyst according to claim 1, wherein the noble metal in step (4) is platinum, palladium, rhodium or ruthenium.

15. The method for preparing a xylene isomerization catalyst according to claim 1, wherein the noble metal in step (4) is platinum.

16. The method for preparing a xylene isomerization catalyst according to any one of claims 1 to 14, wherein the MWW structured molecular sieve obtained in step (1) is a nano-flake molecular sieve having a silicon-aluminum ratio of 20 to 100; and the thickness of the flake is 5 to 30 nanometers.

17. The method for preparing a xylene isomerization catalyst according to claim 16, wherein the silicon-aluminum ratio of the MWW structured molecular sieve prepared in step (1) is 25-50.

18. The method for preparing a xylene isomerization catalyst according to claim 16, wherein the thickness of the thin sheet is 10 to 20 nanometers.

19. The method for preparing a xylene isomerization catalyst according to claim 16, wherein the content of the MWW structured molecular sieve as the acid catalytic active component in the xylene isomerization catalyst is 5-70% by mass of the total mass of the catalyst; the content of the noble metal is 0.01-0.5% by mass of the total mass of the catalyst; and the remaining components are alumina binder.

20. The method for preparing a xylene isomerization catalyst according to claim 19, wherein the content of the MWW structured molecular sieve as an acid catalytic active component in the xylene isomerization catalyst is 10-50% by mass.

21. The method for preparing a xylene isomerization catalyst according to claim 19, wherein the content of the noble metal is 0.05-0.35 mass % of the total mass of the catalyst.

22. A xylene isomerization catalyst prepared according to the method for preparing a xylene isomerization catalyst according to any one of claims 1 to 21.

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