CN116002707A - Molecular sieve with MWW structure and preparation method thereof, xylene isomerization catalyst and preparation method thereof - Google Patents

Abstract

A method for preparing an MWW molecular sieve and a method for preparing a xylene isomerization catalyst by using the molecular sieve, and the MWW molecular sieve and the xylene isomerization catalyst prepared by the method. The preparation method of the molecular sieve comprises the steps of mixing and crystallizing a silicon source, an aluminum source, a first structure directing agent SDA1, a second structure directing agent SDA2 and water. The preparation method of the catalyst comprises (1) preparing MWW structure molecular sieve; (2) Ion-exchanging with a first structure directing agent SDA1 aqueous solution; (3) Carrying out hydrothermal treatment by using a second structure directing agent SDA2 aqueous solution; (4) supporting noble metal and activating. The MWW molecular sieve is nanometer lamellar molecular sieve, the silicon-aluminum ratio is 20-100, and the thickness of the lamella is 5-30 nanometers. The prepared dimethylbenzene isomerization catalyst comprises 5-70 mass% of MWW structure molecular sieve, 0.01-0.5 mass% of noble metal and the balance of alumina binder. The catalyst can be used for the dimethylbenzene isomerization reaction containing ethylbenzene, and has obviously improved ethylbenzene conversion capability and dimethylbenzene selectivity.

Description

Molecular sieve with MWW structure and preparation method thereof, xylene isomerization catalyst and preparation method thereof

technical field

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-flaky MWW structure molecular sieve with a specific silicon-to-aluminum ratio and the MWW structure molecular sieve prepared therefrom, and the preparation of the molecular sieve by using the molecular sieve A process for a xylene isomerization catalyst and a xylene isomerization catalyst prepared thereby.

Background technique

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

Through the xylene isomerization reaction, p-xylene in the product reaches or approaches the thermodynamic equilibrium value, and the product can be separated from the PX product through the separation device, and then a small amount of light non-aromatic hydrocarbons, benzene, toluene and C ₉ ⁺ heavy aromatics are separated out, the remaining C ₈ aromatics materials can be recycled as raw materials for isomerization.

Under the current technical conditions, it is very difficult and uneconomical to separate ethylbenzene from xylene, regardless of high-efficiency rectification or adsorption separation. Therefore, ethylbenzene must be converted simultaneously during the xylene isomerization process. There are two different target directions for ethylbenzene conversion: conversion of ethylbenzene to xylenes and dealkylation of ethylbenzene to benzene. The economics of both directions depend on the composition of the feedstock, the energy consumption of the plant and the market conditions.

When the mass fraction of ethylbenzene in the raw material is low, the ethylbenzene deethylation route is often used, which can complete the reaction at a higher space velocity and lower hydrogen-to-hydrocarbon ratio and pressure conditions, saving energy; when the ethylbenzene in the raw material When the mass fraction is high, a large amount of benzene will be by-produced by the deethylation route. When the price of benzene is low, the economy will be significantly worse. Therefore, the route of converting ethylbenzene into xylene is often used for high-ethylbenzene raw materials. The reaction path of conversion of ethylbenzene to xylene is more complex, the single-pass processing capacity of the catalyst is lower, and the required conditions such as hydrogen-to-hydrocarbon ratio, temperature and pressure are more stringent. The types of molecular sieves and acidic characteristics in the catalysts of the two routes are also significantly different.

CN200910260072.9 is an ethylbenzene conversion type isomerization catalyst, the active component of which is EUO molecular sieve. The conversion catalyst can convert ethylbenzene into the target product xylene, which maximizes the utilization of raw material resources. As the market changes, when the raw material price of C8 aromatics is high and the benzene product is surplus, the economic efficiency of the conversion process will be better than that of the deethylation process. So far, the main bottleneck limiting the economical use of ethylbenzene conversion catalysts is the low single-pass conversion of ethylbenzene, which increases the energy and material consumption of materials in the recycling process.

酸)。在二甲苯异构化催化剂的制备技术上，如专利申请CN200510080209.4所示，通常需要采用离子交换方法使Na型分子筛转化为H型分子筛。专利申请CN200880120492.0公开一种经过离子交换的二甲苯异构化催化剂的制备方法，优选ZSM-5分子筛，将成型载体在溶液中进行离子交换。交换所用溶液通常包含至少一种形成氢的阳离子源，如NH₄ ⁺。形成氢的阳离子主要代替碱金属阳离子，以在煅烧后提供分子筛成分的氢形式。在水溶液中用作溶质的合适的化合物包括硝酸铵、硫酸铵和/或氯化铵。The raw molecular sieve powder is usually Na type, which needs to be ion-exchanged with ammonium salt, converted into ammonium type, and roasted to decompose the ammonium cation into H type, that is, protonic acid (or called

acid). In terms of the preparation technology of xylene isomerization catalysts, as shown in patent application CN200510080209.4, it is usually necessary to convert Na-type molecular sieves into H-type molecular sieves by ion exchange. Patent application CN200880120492.0 discloses a preparation method of an ion-exchanged xylene isomerization catalyst, preferably ZSM-5 molecular sieve, and performs ion exchange on a formed carrier in a solution. The solution used for the exchange generally contains at least one source of hydrogen-forming cations, such as NH ₄ ⁺ . 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.

However, considering cost and efficiency, there is still a need in the art to further improve the ethylbenzene conversion capability and xylene selectivity of xylene isomerization catalysts.

Contents of the invention

After a large number of tests, the present inventors can obtain a highly active molecular sieve with a special structure by changing and optimizing the synthesis method of the molecular sieve as the active component of the catalyst; , a catalyst with higher ethylbenzene conversion ability and xylene selectivity could be prepared.

Therefore, in one aspect, the present invention provides a method for preparing a molecular sieve with a MWW structure, 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 silicon source (calculated as _SiO2 ), the molar ratio of aluminum source ( _calculated as _Al2O3 ) and water is _SiO2 : _Al2O3 : _H2O =1: _0.01 ～0.05:20～50; the first The molar ratio of the structure-directing agent SDA1 is SDA1:SiO ₂ =0.02-0.22; the molar ratio of the second structure-directing agent SDA2 is SDA2:SiO ₂ =0.02-0.12.

In one embodiment of the method for preparing a molecular sieve with a MWW structure according to the present invention, the silicon source is water glass; the aluminum source is one or more selected from aluminum sulfate, aluminum chloride, aluminum nitrate; The second structure-directing agent SDA2 is cycloheximide; the first structure-directing agent SDA1 is (R ¹ ) ₃ N ⁺ C _n H _2n N ⁺ (R ² ) ₃ ·2X ^- , where R ¹ and R ² is an alkyl group with 1 to 4 carbon atoms, preferably methyl or ethyl, C _n H _2n is a straight chain alkyl group containing 2 to 10 carbon atoms, X ^- is a halogen anion, preferably chloride ion or bromide ion. More specifically, SDA1 may be selected from dibromohexamethylhexanediamine, dichlorohexaethylbutanediamine, dibromohexamethylpentanediamine, dichlorohexamethyloctanediamine, dichlorohexamethyloctanediamine, Hexapropyldecanediamine, etc.

In another embodiment of the method for preparing a molecular sieve with a MWW structure according to the present invention, the modulus (molar ratio of SiO ₂ :Na ₂ O) of the water glass is 2-4.

In another embodiment of the method for preparing a molecular sieve with a MWW structure according to the present invention, the mixing includes first dissolving the 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; add the silicon source to form a liquid sol, and stir and mix for 6-18 hours; and add the second structure directing agent, and stir and mix evenly.

In another embodiment of the method for preparing molecular sieves with a MWW structure 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 to 75 hours.

In another aspect, the present invention provides a molecular sieve with a MWW structure prepared by the method for preparing a molecular sieve with a MWW structure according to any one of the foregoing embodiments, the molecular sieve is a nano-sheet molecular sieve, and its silicon-aluminum ratio is 20-100, preferably 25-50; And the thickness of the nano flake molecular sieve is 5-30 nanometers, preferably 10-20 nanometers.

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

(1) mix and crystallize silicon source, aluminum source, first structure directing agent SDA1, second structure directing agent SDA2 and water, make MWW structure molecular sieve, wherein said silicon source is water glass; Described 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 ) ₃ N ⁺ C _n H _2n N ⁺ (R ² ) ₃ ·2X ^- , where R ¹ and R ² are both alkyl groups with 1 to 4 carbons, preferably methyl or ethyl, and C _n H _2n is a group containing 2 to 10 carbons A straight-chain alkyl group of atoms, X ^- is a halide anion, preferably a chloride ion or a bromide ion;

(2) Use the aqueous solution of the first structure-directing agent SDA1 to ion-exchange the MWW structure molecular sieve prepared in step (1), wash and dry with deionized water after the exchange, then mix with alumina binder and form and roasting to obtain a catalyst carrier;

(3) using the aqueous solution of the second structure directing agent SDA2 as a steam source to perform hydrothermal treatment on the catalyst carrier prepared in step (2) to obtain a catalyst carrier with optimized acid function distribution; and

(4) impregnating the catalyst with optimized acid function distribution prepared in step (3) with a solution containing noble metal, and after activation and reduction, the xylene isomerization catalyst is obtained.

In one embodiment of the method for preparing a xylene isomerization catalyst according to the present invention, the silicon source (as SiO ₂ ), the aluminum source (as Al ₂ O ₃ ) and water feed intake described in step (1) The molar ratio is SiO ₂ :Al ₂ O ₃ :H ₂ O=1:0.01～0.05:20～50; the molar ratio of the first structure directing agent SDA1 is SDA1:SiO ₂ =0.02～0.22; The molar ratio of the two structure-directing agents SDA2 is SDA2:SiO ₂ =0.02-0.12.

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

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 temperature The time is 20 to 120 hours, preferably 25 to 75 hours.

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-solid ratio of the ion exchange is 5 to 30mL/g molecular sieve, the temperature of the ion exchange is 50 to 90°C, and the number of ion exchanges is 2 to 4 times; the _Na2 The molar content of O in the full-component oxide is 0.01-2.0%, preferably 0.1-0.4%.

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, and the roasting is carried out at 540° C. for 2 to 24 hours , and the drying and roasting are carried out in a static atmosphere or in a dynamic atmosphere with a volumetric space velocity of 50-500h ^-1 .

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 solution dosage is 5-30mL/g catalyst carrier, the steam treatment temperature is 200-450°C, preferably 350-400°C, and the treatment time is 3-6 hours.

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.

In another embodiment of the method for preparing a xylene isomerization catalyst according to the present invention, the molecular sieve with a MWW structure prepared in step (1) is a nano-sheet molecular sieve, and its silicon-aluminum ratio is 20-100, preferably 25 ~50; the thickness of the flakes is 5~30 nanometers, preferably 10~20 nanometers.

In another embodiment of the method for preparing a xylene isomerization catalyst according to the present invention, the content of molecular sieves with a MWW structure as an acid catalytic active component in the xylene isomerization catalyst accounts for 5 to 70% of the total mass of the catalyst. % by mass, preferably 10-50% by mass; the content of the noble metal accounts for 0.01-0.5% by mass of the total mass of the catalyst, preferably 0.05-0.35% by mass; the remaining components are alumina binders.

In yet another aspect, the present invention provides a xylene isomerization catalyst prepared according to the method for preparing a xylene isomerization catalyst according to any of the foregoing embodiments.

In one embodiment of the xylene isomerization catalyst according to the present invention, the xylene isomerization catalyst comprises a nano-flaky MWW structure molecular sieve with a silicon-to-alumina ratio of 20-100, preferably 25-50, and 0.01- 0.5% by mass, preferably 0.05 to 0.35% by mass of noble metal.

In the method for preparing molecular sieves with MWW structure of the present invention, two structure-directing agents (SDA1 and SDA2) are used to obtain molecular sieve flakes with MWW structure having a silicon-aluminum ratio of 20-100 and a thickness of 5-30 nanometers. The molecular sieve with the MWW structure is ion-exchanged by the first structure-directing agent, kneaded with the binder, and then hydrothermally treated by the second structure-directing agent to optimize the acid function distribution of the catalyst carrier, followed by loading The noble metal component is activated and reduced to obtain the catalyst of the present invention. When used in the xylene isomerization reaction containing ethylbenzene, the ethylbenzene conversion ability and xylene selectivity of the catalyst of the present invention are significantly improved.

Description of drawings

Fig. 1 is the XRD spectrogram of the Z-1 molecular sieve prepared according to embodiment 1;

Fig. 2 is the XRD spectrogram of the Z-2 molecular sieve prepared according to embodiment 2;

Fig. 3 is the SEM electron micrograph of the Z-1 molecular sieve prepared according to embodiment 1; And

FIG. 4 is an SEM electron micrograph of the Z-2 molecular sieve prepared according to Example 2.

Detailed ways

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 specific.

In addition, the technical features involved in the different embodiments of the present application described below may be combined as long as they do not constitute a conflict with each other.

In one embodiment, the method for preparing a molecular sieve with a MWW structure according to the present invention, that is, a one-step method for a molecular sieve with a MWW structure, includes a silicon source, an aluminum source, a first structure-directing agent (SDA1), a second structure-directing agent (SDA2) is mixed with water and crystallized, wherein silicon source (calculated as SiO ₂ ), aluminum source (calculated as Al ₂ O ₃ ) and water, according to SiO ₂ :Al ₂ O ₃ :H ₂ O=1:0.01～ The molar ratio of 0.05:20～50 is fed, the amount of the first structure directing agent SDA1 is in accordance with the molar ratio SDA1:SiO ₂ =0.02～0.22; the amount of the second structure directing agent SDA2 is in accordance with the molar ratio SDA2:SiO ₂ =0.02～ 0.12.

In one embodiment, the silicon source may be water glass, preferably water glass with a modulus of 2-4 (ie the molar ratio of SiO ₂ :Na ₂ O is 2-4).

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

In one embodiment, the first structure directing agent may be a straight diamine dihalide represented by the formula (R ₁ ) ₃ N ⁺ C _n H _2n N ⁺ (R ₂ ) ₃ · ^2X- , for example, (CH ₃ ) ₃ N ⁺ C ₆ H ₁₂ N ⁺ (CH ₃ ) ₃ ·2Cl ^- , (CH ₃ ) ₃ N ⁺ C ₆ H ₁₂ N ⁺ (CH ₃ ) ₃ ·2Br ^- ..., where R ¹ and R ² are 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 Chloride or Bromide.

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

More specifically, the first structure-directing agent is first dissolved in water to form a solution; then, under stirring conditions, the aluminum source is slowly added and stirred and mixed for 2 to 12 hours; then the silicon source is slowly added to form a liquid sol, and stirred and mixed for 6 to 12 hours. Make the phase state of the sol uniform for 18 hours; then add the second structure directing agent into the sol, stir and mix evenly, and then complete the mixing of raw materials. Next, the mixture is crystallized at a temperature of 140-190° C. for 20-120 hours, preferably at a temperature of 165-175° C. for 25-75 hours.

The molecular sieve with MWW structure thus prepared is a molecular sieve in the shape of nano flakes, with a thickness of 5-30 nanometers, preferably 10-20 nanometers; a silicon-aluminum ratio of 20-100, preferably 25-50.

The xylene isomerization catalyst of the present invention contains a molecular sieve with a MWW structure as an active component, which provides acid sites for xylene isomerization and simultaneously provides acid sites for conversion of ethylbenzene into xylene. Usually, as an active component of the xylene isomerization catalyst of the present invention, the content of the molecular sieve with MWW structure may be 10-50% by mass of the entire catalyst.

In one embodiment, according to the method for preparing xylene isomerization catalyst of the present invention, the method comprises the steps of:

(1) Mix and crystallize silicon source, aluminum source, first structure directing agent SDA1, second structure directing agent SDA2 and water to obtain MWW structure molecular sieve;

(2) Use the aqueous solution of the first structure-directing agent SDA1 to ion-exchange the MWW structure molecular sieve prepared in step (1), wash and dry with deionized water after the exchange, then mix with alumina binder and form and roasting to obtain a catalyst carrier;

(3) using the aqueous solution of the second structure directing agent SDA2 as a steam source to perform hydrothermal treatment on the catalyst carrier prepared in step (2) to obtain a catalyst carrier with optimized acid function distribution; and

(4) impregnating the catalyst with optimized acid function distribution prepared in step (3) with a solution containing noble metal, and after activation and reduction, the xylene isomerization catalyst is obtained.

Specifically, in the step (2) of the catalyst preparation method, ion exchange is performed on the raw powder of MWW structure nanosheet molecular sieve using the aqueous solution of the first structure-directing agent SDA1, and the concentration of the solution is 0.01-0.08mol/L, Preferably 0.04-0.06mol/L, exchange liquid-solid ratio of 5-30mL/g molecular sieve, exchange temperature 50-90°C, exchange times 2-4 times; exchanged molecular sieves are washed several times with excess deionized water until washed No halogen anions are detected in the effluent, and the pH range is 6-8. The Na ₂ O molar content of the molecular sieve with MWW structure after washing 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. 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. Molecular sieves after drying can be molded by conventional methods. The molded carrier is dried at 120° C. for 8 to 24 hours, and air roasted at 540° C. for 2 to 24 hours. Calcination can be carried out in a static atmosphere without air flow, or in a dynamic atmosphere with a volume space velocity of 50-500.

Specifically, in step (3) of the catalyst preparation method, the shaped catalyst carrier containing MWW structure molecular sieve and alumina is subjected to optimization treatment of acid function distribution, that is, the aqueous solution of the second structure directing agent SDA2 is used as the steam source Hydrothermal treatment, the concentration of the SDA2 aqueous solution is 0.01-0.08mol/L, preferably 0.04-0.06mol/L, the solution dosage is 5-30mL/g carrier, the steam treatment temperature is 200-450°C, preferably 350-400°C, the treatment Time 3 ~ 6h.

Usually, NH ₄ ⁺ cations in ammonium salts are used to ion-exchange 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, cyclohexyl Imine is used as an ion exchanger. Due to the large molecular size of cyclohexyl imine, it cannot enter the deeper pores in the molecular sieve. Therefore, through the shape-selective effect, the amine ions are only exchanged for sodium ions on the outer surface and pores of the molecular sieve. , converting it into amine ions, and in the subsequent calcination into H ions, forming an acidic center.

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

The molded catalyst support after acid function distribution optimization treatment can be impregnated with precious metals according to conventional methods and then activated and reduced to obtain the catalyst of the present invention.

In one embodiment, the noble metal described 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.

In one embodiment, the catalyst according to the present invention comprises nanoflake MWW structure molecular sieve as acidic active component and alumina as binder, wherein the content of MWW structure molecular sieve is 10-50% by mass, and the remaining components are Alumina binder; in addition, the catalyst of the present invention is also loaded with 0.05-0.35% by mass of noble metal.

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

Catalyst performance is evaluated as follows:

Isomerization equilibrium achievement rate:

Xylene Yield:

Conversion rate of ethylbenzene:

The present invention is further illustrated by examples below, but the present invention is not limited thereto.

Example

The following example synthesizes the Na-type raw powder of MWW structure nano flake molecular sieve.

Example 1

Add silicon source (water glass, concentration 24w%, modulus 3.1) 450mL, aluminum source (aluminum sulfate) 20.2g in 2L reactor, (CH ₃ ) ₃ N ⁺ C ₆ H ₁₂ N ⁺ (CH ₃ ) ₃ · 2Cl ^- as the first structure-directing agent, the addition amount is 4.1g; cyclohexyl imine is used as the second structure-directing agent, the addition amount is 9.0g, and the molar ratio of each material fed is Na ₂ O:SiO ₂ :Al ₂ O ₃ :SDA1:SDA2:H ₂ O=0.32:1:0.04:0.02:0.12:25. The synthesis temperature was 175° C., and the synthesis time was 35 hours.

In this way, a Na-type molecular sieve with a MWW structure of nanometer flakes was prepared, denoted as Z-1, and the silicon-aluminum ratio was 25. The XRD diffraction spectrum of the obtained molecular sieve Z-1 is shown in Fig. 1, as shown in the figure, there are characteristic peaks of MWW structure in the range of 5-50 degrees. The SEM electron micrograph of the obtained molecular sieve Z-1 is shown in Fig. 3, which has a nano-sheet structure as shown in the figure.

Example 2

Add silicon source (water glass, concentration 24w%, modulus 3.1) 450mL, aluminum source (aluminum sulfate) 10.1g, (CH ₃ ) ₃ N ⁺ C ₆ H ₁₂ N ⁺ (CH ₃ ) ₃ in 2L reaction kettle 2Br ^- as the first structure directing agent, the addition amount is 60.4g; cyclohexyl imine is used as the second structure directing agent, the addition amount is 1.5g, and the molar ratio of each material is Na ₂ O:SiO ₂ :Al ₂ O ₃ :SDA1:SDA2:H ₂ O=0.32:1:0.02:0.22:0.02:35. The synthesis temperature was 165° C., and the synthesis time was 25 hours.

In this way, a Na-type molecular sieve with a MWW structure of nanometer flakes was prepared, denoted as Z-2, and the silicon-aluminum ratio was 50. The XRD diffraction pattern of the obtained molecular sieve Z-2 is shown in Fig. 2, as shown in the figure, there are characteristic peaks of MWW structure in the range of 5-50 degrees. The SEM electron micrograph of the obtained molecular sieve Z-2 is shown in Fig. 4, which has a nano-sheet structure as shown in the figure.

The following comparative examples prepare conventional xylene isomerization catalysts.

Comparative example 1

Take 3g of commercial Eu-1 molecular sieve powder (provided by Changling Catalyst Factory) with a silicon-aluminum ratio of 30, use 50 milliliters of 0.05mol/L ammonium chloride aqueous solution at 90°C for 2 hours × 2 times, and wash into the mother liquor No chloride ion was detected, and the pH range was 6-8. Dry the fully washed molecular sieve at 120° C. for 8 hours in a static atmosphere without air flow. The dried molecular sieve was thoroughly mixed with 17g of alumina, and 20ml of 3% nitric acid aqueous solution was added to make a viscous mixture, which was then extruded into strips. Dry the strips at 120°C for 6 hours, then cut into pellets, and bake at 540°C for 4 hours. The hydrothermal treatment is carried out with steam, the treatment temperature is 350° C., and the treatment time is 6 hours. The treated carrier was impregnated with 20 ml of an aqueous solution of chloroplatinic acid containing 0.05 g of platinum, and dried at 120° C. to prepare a catalyst containing 0.25% by mass of platinum. Then, it was activated under air to prepare a catalyst in an oxidized state, and was reduced under hydrogen for 4 hours to prepare comparative catalyst D-1.

Comparative example 2

Prepare contrast catalyst D-2 by the method for comparative example 1, difference is to adopt the commodity MOR molecular sieve (Fushun Catalyst Factory provides) powder 9g that silicon-alumina ratio is 12, with the dibromohexamethyl hexane of 50 milliliters 0.05mol/L The diamine aqueous solution is subjected to ion exchange at 80°C for 2 hours x 3 times, washed until no chlorine ions are detected in the mother liquor, and the pH range is 6-8. Dry the fully washed molecular sieve at 120° C. for 24 hours in a dynamic atmosphere with a volume space velocity of 500. The dried molecular sieve was thoroughly mixed with 11 g of alumina, and 20 ml of 5% nitric acid aqueous solution was added to form a viscous mixture, which was then extruded into strips. Dry the strips at 120°C for 12 hours, then cut into pellets, and bake at 540°C for 12 hours. The aqueous solution of the second structure-directing agent cycloheximide was used as the steam source for hydrothermal treatment. The concentration of the solution was 0.06 mol/L, the solution dosage was 600 mL, the steam treatment temperature was 400° C., and the treatment time was 3 hours. The treated carrier was impregnated with 20 ml of an aqueous solution of chloroplatinic acid containing 0.35 g of platinum, and dried at 120° C. to prepare a catalyst containing 0.35% by mass of platinum. Then it was activated under air to prepare a catalyst in an oxidized state, and it was reduced under hydrogen for 4 hours to prepare comparative catalyst D-2.

Comparative example 3

Prepare comparative catalyst D-3 by the method for comparative example 1, the difference is that the Na type MWW structure molecular sieve Z-1 powder 3g that adopts the silicon aluminum ratio synthesized in the embodiment 1 is 25, with 50 milliliters of 0.05mol/L chloride The ammonium aqueous solution is ion-exchanged at 90°C for 2 hours x 4 times, washed until no chloride ions are detected in the mother liquor, and the pH range is 6-8. Dry the fully washed molecular sieve at 120° C. for 16 hours in a static atmosphere without air flow. The dried molecular sieve was thoroughly mixed with 17g of alumina, and 15ml of 4% nitric acid aqueous solution was added to form a viscous mixture, which was then extruded into strips. Dry the strips at 120°C for 16 hours, then cut into pellets, and bake at 540°C for 10 hours. The treated carrier was impregnated with 20 ml of chloroplatinic acid aqueous solution containing 0.05 g of platinum, and dried at 120° C. to prepare a catalyst containing 0.05 mass % of platinum. Then, it was activated under air to prepare a catalyst in an oxidized state, and was reduced under hydrogen for 4 hours to prepare comparative catalyst D-3.

Comparative example 4

Take 9 g of the Na-type MWW structural molecular sieve Z-2 powder with a silicon-aluminum ratio of 50 synthesized in Example 2, use 50 ml of 0.04 mol/L ammonium nitrate aqueous solution at 50° C. for 2 hours × 3 times, and wash until the mother liquor No chloride ions are detected in the medium, and the pH range is 6-8. Dry the fully washed molecular sieve at 120° C. for 18 hours in a dynamic atmosphere with a volume space velocity of 50. The dried molecular sieve was thoroughly mixed with 11 g of alumina, and 20 ml of 4% nitric acid aqueous solution was added to form a viscous mixture, which was then extruded into strips. Dry the strips at 120°C for 24 hours, then cut into pellets, and bake at 540°C for 12 hours. The hydrothermal treatment was performed using an aqueous solution as a steam source, the steam treatment temperature was 350° C., and the treatment time was 6 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% by mass of platinum. Then it was activated under air to prepare a catalyst in an oxidized state, and it was reduced under hydrogen for 4 hours to prepare comparative catalyst D-4.

The following examples prepare xylene isomerization catalysts of the present invention.

Example 3

Catalyst C-1 according to the present invention was prepared according to the method of Comparative Example 3, except that the molecular sieve was ion-exchanged with an aqueous solution of the first structure-directing agent dibromohexamethylhexanediamine, and the concentration of the solution was 0.06mol/L. The exchange liquid-solid ratio is 30mL/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 anion is detected in the eluate, and the pH range is 6～ 8. The Na ₂ O molar content of the molecular sieve with the MWW structure was 0.4% after washing. The molded support was hydrothermally treated using the aqueous solution of the second structure-directing agent cycloheximide as the steam source. The concentration of the solution was 0.04 mol/L, the amount of the solution was 5 mL/g support, the steam treatment temperature was 350°C, and the treatment time was 6 Hour. According to the method of Comparative Example 1, 0.25% by mass of platinum was impregnated, and activated and reduced by roasting.

Example 4

Catalyst C-2 according to the present invention is prepared according to the method of Example 3, except that the molecular sieve uses 9 g of the Na-type MWW structure molecular sieve Z-2 with a silicon-aluminum ratio of 50 synthesized in Example 2, and uses the first structure-directing agent 2 The aqueous solution of chlorohexaethylbutanediamine is ion-exchanged, 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 exchange times are 2 times; the exchanged molecular sieve uses excessive Wash with deionized water several times until no halogen anions are detected in the eluate, and the pH range is 6-8. The Na ₂ O molar content of the molecular sieve with MWW structure was 0.2% after washing. The exchanged molecular sieve was mixed with 11g of alumina and extruded into a rod. The molded carrier was hydrothermally treated using the aqueous solution of the second structure-directing agent cycloheximide as the steam source. The concentration of the solution was 0.06 mol/L, the solution dosage was 30 mL/g carrier, the steam treatment temperature was 400°C, and the treatment time was 3 Hour. The treated carrier was impregnated with 20 ml of aqueous chloroplatinic acid solution containing 0.15 g of platinum, and dried at 120° C. to prepare a catalyst containing 0.15% by mass of platinum. It was then activated under air to prepare a catalyst in an oxidized state, and then reduced under hydrogen for 4 hours to prepare catalyst C-2 according to the present invention.

Example 5

Catalyst C-3 according to the present invention was prepared according to the method of Example 4, except that 3 g of Na-type MWW structure molecular sieve Z-2 with a silicon-aluminum ratio of 50 synthesized in Example 2 was used, and the first structure-directing agent dichloro The aqueous solution of hexaethylbutanediamine was ion-exchanged, the concentration of the solution was 0.06mol/L, the exchange liquid-solid ratio was 20mL/g molecular sieve, the exchange temperature was 80°C, and the exchange times were 3 times; the exchanged molecular sieve used excess Wash with ion water several times until no halogen anions are detected in the eluate, and the pH range is 6-8. After washing, the Na ₂ O molar content of the molecular sieve with MWW structure was 0.3%. The exchanged molecular sieve was mixed with 17g of alumina and extruded into a rod. The molded carrier was hydrothermally treated using the aqueous solution of the second structure-directing agent cycloheximide as the steam source. The concentration of the solution was 0.05mol/L, and the solution dosage was 5mL/g carrier. The steam treatment temperature was 370°C, and the treatment time was 4 Hour. The treated carrier was impregnated with 20 ml of an aqueous solution of chloroplatinic acid containing 0.30 g of platinum, and dried at 120° C. to prepare a catalyst containing 0.30 mass % of platinum. Then, it was activated under air to prepare a catalyst in an oxidized state, and then reduced under hydrogen for 4 hours to prepare catalyst C-3 according to the present invention.

Example 6

Catalyst C-4 according to the present invention was prepared according to the method of Example 4, except that 6 g of Na-type MWW structure molecular sieve Z-2 with a silicon-aluminum ratio of 50 synthesized in Example 2 was used, and the first structure-directing agent dibromo The aqueous solution of hexamethylpentanediamine was ion-exchanged, the concentration of the solution was 0.04mol/L, the exchange liquid-solid ratio was 25mL/g molecular sieve, the exchange temperature was 70°C, and the exchange times were 4 times; the exchanged molecular sieve used excess Wash with ion water several times until no halogen anions are detected in the eluate, and the pH range is 6-8. The Na ₂ O molar content of the molecular sieve with MWW structure after washing is 0.25%. The exchanged molecular sieve was mixed with 14g of alumina and extruded into a rod. The molded carrier was hydrothermally treated using the aqueous solution of the second structure-directing agent cycloheximide as the steam source. The concentration of the solution was 0.04 mol/L, the solution dosage was 15 mL/g carrier, the steam treatment temperature was 350°C, and the treatment time was 6 Hour. The treated carrier was impregnated with 20 ml of an aqueous solution of chloroplatinic acid containing 0.25 g of platinum, and dried at 120° C. to prepare a catalyst containing 0.25% by mass of platinum. Then, it was activated under air to prepare a catalyst in an oxidized state, and then reduced under hydrogen for 4 hours to prepare catalyst C-4 according to the present invention.

Example 7

Catalyst C-5 according to the present invention was prepared according to the method of Example 4, except that 8 g of the Na-type MWW structure molecular sieve Z-2 with a silicon-aluminum ratio of 50 synthesized in Example 2 was used, and the first structure-directing agent dichloro The aqueous solution of hexamethyloctanediamine is ion-exchanged, 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 exchange times are 4 times; the exchanged molecular sieve uses excess Wash with ion water several times until no halogen anions are detected in the eluate, and the pH range is 6-8. The Na ₂ O molar content of the molecular sieve with the MWW structure was 0.4% after washing. The exchanged molecular sieve was mixed with 12g of alumina and extruded into a rod. The molded carrier was hydrothermally treated using the aqueous solution of the second structure-directing agent cycloheximide as the steam source. The concentration of the solution was 0.04 mol/L, the solution dosage was 15 mL/g carrier, the steam treatment temperature was 350°C, and the treatment time was 6 Hour. 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. Then, it was activated under air to prepare a catalyst in an oxidized state, and then reduced under hydrogen for 4 hours to prepare catalyst C-5 according to the present invention.

Example 8

Catalyst C-6 according to the present invention is prepared according to the method of Example 4, except that the Na-type MWW structure molecular sieve Z-2 with a silicon-aluminum ratio of 10 g synthesized in Example 2 is 50, and the first structure-directing agent dibromide is used. The aqueous solution of hexamethylpentanediamine was ion-exchanged, the concentration of the solution was 0.06mol/L, the exchange liquid-solid ratio was 25mL/g molecular sieve, the exchange temperature was 70°C, and the exchange times were 4 times; the exchanged molecular sieve used excess Wash with ion water several times until no halogen anions are detected in the eluate, and the pH range is 6-8. The Na ₂ O molar content of the molecular sieve with MWW structure after washing is 0.25%. The exchanged molecular sieve was mixed with 10g of alumina and extruded into a rod. The molded carrier was hydrothermally treated using the aqueous solution of the second structure-directing agent cycloheximide as the steam source. The concentration of the solution was 0.04 mol/L, the solution dosage was 15 mL/g carrier, the steam treatment temperature was 350°C, and the treatment time was 6 Hour. The treated carrier was impregnated with 20 ml of an aqueous solution of chloroplatinic acid containing 0.15 g of platinum, and dried at 120° C. to prepare a catalyst containing 0.15% by mass of platinum. Then, it was activated under air to prepare a catalyst in an oxidized state, and then reduced under hydrogen for 4 hours to prepare catalyst C-6 according to the present invention.

The following examples illustrate the use of the xylene isomerization catalysts of the present invention.

Example 9

2 g of the xylene isomerization catalysts prepared in the above examples and comparative examples were loaded on the continuous flow fixed bed miniature hydrogenation device, and the performance evaluation of the catalyst was performed with industrial xylene isomerization raw materials. The raw material composition used in the reaction, the evaluation process parameters and the characteristics of the catalysts of each embodiment, the reaction results are shown in the table below.

Table 1. Composition of raw materials for industrial xylene isomerization

Raw material composition <![CDATA[C₈cycloalkane]]> benzene toluene Ethylbenzene p-xylene m-xylene O-xylene wt% 5.62 0.02 1.03 17.16 0.49 53.36 22.32

Catalyst and reaction performance prepared in table 2. embodiment and comparative example

Comparing the results of the above examples and comparative examples, it can be seen that according to the catalyst preparation method of the present invention, the nano-sheet molecular sieve of the MWW structure is used, and the structure-directing agent SDA1 is used as the ion exchanger, and the structure-directing agent SDA2 is used as the steam treatment agent, The prepared catalyst has higher ethylbenzene conversion activity and xylene selectivity than conventional catalysts prepared by using EUO or MOR molecular sieves, or catalysts prepared only by conventional ammonium salt ion exchange and hydrothermal treatment.

The present invention has been described above in conjunction with preferred embodiments, but these embodiments are only exemplary and illustrative. On this basis, various replacements and improvements can be made to the present invention, all of which fall within the protection scope of the present invention.

Claims (17)

1. A method for preparing a MWW structure molecular sieve, comprising mixing and crystallizing silicon source, aluminum source, the first structure-directing agent SDA1, the second structure-directing agent SDA2 and water, wherein the silicon source (by _SiO ) 1. The molar ratio of aluminum source (according to Al ₂ O ₃ ) and water is SiO ₂ : Al ₂ O ₃ : H ₂ O=1:0.01～0.05:20～50; the consumption of the first structure directing agent SDA1 The molar ratio is SDA1:SiO ₂ =0.02-0.22; the molar ratio of the second structure directing agent SDA2 is SDA2:SiO ₂ =0.02-0.12. 2. according to the method for preparing MWW structure molecular sieve of claim 1, wherein said silicon source is water glass; Described aluminum source is one or more selected from aluminum sulfate, aluminum chloride, aluminum nitrate; The second structure-directing agent SDA2 is cycloheximide; the first structure-directing agent SDA1 is (R ¹ ) ₃ N ⁺ C _n H _2n N ⁺ (R ² ) ₃ ·2X ^- , where both R ¹ and R ² is an alkyl group with 1 to 4 carbon atoms, preferably methyl or ethyl, 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. 3. The method for preparing a molecular sieve with a MWW structure according to claim 2, wherein the water glass has a modulus (SiO ₂ :Na ₂ O molar ratio) of 2-4. 4. The method for preparing a molecular sieve with a MWW structure according to any one of claims 1 to 3, wherein said mixing comprises first dissolving the first structure directing agent in water to form a solution; adding an aluminum source under stirring conditions, and stirring and mixing 2-12 hours; adding the silicon source to form a liquid sol, and stirring and mixing for 6-18 hours; and adding the second structure-directing agent, and stirring and mixing evenly. 5. The method for preparing molecular sieves with MWW structure according to claim 4, wherein the crystallization temperature is 140-190° C., preferably 165-175° C.; the crystallization time is 20-120 hours, preferably 25-100° C. 75 hours. 6. A MWW structure molecular sieve prepared according to the method for preparing a MWW structure molecular sieve according to any one of claims 1 to 5, which is a nano flake molecular sieve with a silicon-aluminum ratio of 20 to 100, preferably 25 to 50; The thickness of the flakes is 5-30 nm, preferably 10-20 nm. 7. A method for preparing a xylene isomerization catalyst, the method comprising the steps of: (1) mix and crystallize silicon source, aluminum source, first structure directing agent SDA1, second structure directing agent SDA2 and water, make MWW structure molecular sieve, wherein said silicon source is water glass; Described 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 ) ₃ N ⁺ C _n H _2n N ⁺ (R ² ) ₃ ·2X ^- , where R ¹ and R ² are both alkyl groups with 1 to 4 carbons, preferably methyl or ethyl, and C _n H _2n is a group containing 2 to 10 carbons A straight-chain alkyl group of atoms, X ^- is a halide anion, preferably a chloride ion or a bromide ion; (2) Use the aqueous solution of the first structure-directing agent SDA1 to ion-exchange the MWW structure molecular sieve prepared in step (1), wash and dry with deionized water after the exchange, then mix with alumina binder and form and roasting to obtain a catalyst carrier; (3) using the aqueous solution of the second structure directing agent SDA2 as a steam source to perform hydrothermal treatment on the catalyst carrier prepared in step (2) to obtain a catalyst carrier with optimized acid function distribution; and (4) impregnating the catalyst with optimized acid function distribution prepared in step (3) with a solution containing noble metal, and after activation and reduction, the xylene isomerization catalyst is obtained. 8. according to the method for preparing xylene isomerization catalyst of claim 7, wherein described in step (1) silicon source (by SiO ₂ count), aluminum source (by Al ₂ O ₃ count) and the feed molar ratio of water SiO ₂ :Al ₂ O ₃ :H ₂ O=1:0.01～0.05:20～50; the molar ratio of the first structure directing agent SDA1 is SDA1:SiO ₂ =0.02～0.22; the second structure The molar ratio of the directing agent SDA2 is SDA2:SiO ₂ =0.02˜0.12. 9. according to the method for preparing xylene isomerization catalyst according to claim 7 or 8, wherein said mixing in step (1) comprises earlier dissolving the first structure-directing agent in water, forms a solution; Adds aluminum source under stirring condition , and stir and mix for 2-12 hours; add silicon source to form a liquid sol, and stir and mix for 6-18 hours; and add the second structure-directing agent, and stir and mix evenly. 10. The method for preparing a xylene isomerization catalyst according to claim 9, wherein the crystallization temperature in step (1) is 140 to 190° C., preferably 165 to 175° C.; the crystallization time is 20 ~120 hours, preferably 25-75 hours. 11. The method for preparing a xylene isomerization catalyst according to claim 7, wherein the concentration of the aqueous solution of the first structure-directing agent SDA1 in step (2) is 0.01 to 0.08 mol/L, preferably 0.04 to 0.06 mol/L The liquid-solid ratio of the ion exchange is 5-30mL/g molecular sieve, and the temperature of the ion exchange is 50-90°C; the molar content of _Na2O in the molecular sieve with MWW structure of the obtained catalyst carrier is 0.01 -2.0%, preferably 0.1-0.4%. 12. The method for preparing a xylene isomerization catalyst according to claim 7, wherein the drying in step (2) is carried out at 120° C. for 8 to 24 hours, and the roasting is carried out at 540° C. for 2 to 24 hours, and the Drying and roasting are carried out in a static atmosphere or in a dynamic atmosphere with a volumetric space velocity of 50-500h ^-1 . 13. The method for preparing a xylene isomerization catalyst according to claim 7, wherein the concentration of the second structure directing agent SDA2 aqueous solution in step (3) is 0.01～0.08mol/L, preferably 0.04～0.06mol/L , the solution dosage is 5-30mL/g catalyst carrier, the steam treatment temperature is 200-450°C, preferably 350-400°C, and the treatment time is 3-6 hours. 14. The method for preparing a xylene isomerization catalyst according to claim 7, wherein the noble metal in step (4) is platinum, palladium, rhodium or ruthenium, preferably platinum. 15. According to the method for preparing xylene isomerization catalyst according to any one of claims 1 to 14, wherein the MWW structure molecular sieve prepared in the step (1) is a nano flake molecular sieve, and its silicon-aluminum ratio is 20-100, It is preferably 25-50 nm; the thickness of the flake is 5-30 nm, preferably 10-20 nm. 16. The method for preparing a xylene isomerization catalyst according to claim 15, wherein the content of the MWW structure molecular sieve as an acid catalytic active component in the xylene isomerization catalyst is 5 to 70% by mass of the total mass of the catalyst, It is preferably 10-50% by mass; the content of the noble metal is 0.01-0.5% by mass of the total mass of the catalyst, preferably 0.05-0.35% by mass; the remaining components are alumina binders. 17. A xylene isomerization catalyst prepared according to the method for preparing a xylene isomerization catalyst according to any one of claims 7-14.

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