ZSM-5 molecular sieve with high-silicon outer surface as well as preparation method and application of ZSM-5 molecular sieve

Abstract

The invention belongs to the technical field of molecular sieve preparation, and provides a ZSM-5 molecular sieve with a high-silicon outer surface and a preparation method and application thereof. The overall SiO2 / Al2O3 content of the ZSM-5 molecular sieve is less than or equal to 40, and the SiO2 / Al2O3 content of the outer surface of the ZSM-5 molecular sieve crystal grain is greater than 40. The ZSM-5 molecular sieve with the high-silicon outer surface has the characteristics that the outer surface is poor in aluminum and the core is rich in aluminum, and the technical problem that the selectivity and the stability of the ZSM-5 molecular sieve are not ideal enough due to the fact that acid sites are widely located on the outer surface of the molecular sieve can be effectively solved. According to the preparation method provided by the invention, the ZSM-5 molecular sieve with the high-silicon outer surface is synthesized in one step by adopting the high-silicon molecular sieve through a crystal transformation method, the obtained molecular sieve does not need to be post-treated, the preparation process is simple, and the cost can be effectively saved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of molecular sieve preparation, and more particularly to a ZSM-5 molecular sieve with a high-silicon outer surface and a preparation method and application thereof. BACKGROUND

[0002] ZSM-5 molecular sieves are usually synthesized under the guidance of amine organic templates, at which time the product ZSM-5 molecular sieve often has a silicon-rich core and an aluminum-rich outer surface, and acid sites are widely located on the outer surface of the molecular sieve. Too many acid sites on the outer surface of the ZSM-5 molecular sieve can cause a large amount of carbon to deposit on the outer surface in a catalytic reaction, covering the surface or plugging the pore, so that the acid sites in the micropores cannot effectively catalyze the reactants, resulting in rapid deactivation of the molecular sieve catalyst. By passivating the acid sites on the outer surface through an outer surface modification method, the outer surface acidity can be reduced, which can prevent secondary reactions on the surface of the molecular sieve, thereby playing a role in improving the catalytic selectivity and stability. At present, Losch et al. (Applied Catalysis A: General, 2016, 509: 30-37) used tetraethyl orthosilicate to achieve surface passivation of ZSM-5 molecular sieves by a chemical liquid deposition technique, thereby improving the selectivity of the catalyst for lower olefins. The Rimer group (ACS Nano 2015, 9, 4006-4016) prepared a ZSM-5 molecular sieve with passivated surface acidity by adding a silicate-1 shell on the outer surface of the molecular sieve, thereby inhibiting carbon deposition on the outer surface and improving the selectivity of the product in the reaction. Inagaki et al. (ACS Catal. 2013, 3, 74-78) selectively removed the acid sites on the outer surface by an acid treatment method, which slowed down the carbon deposition and prolonged the service life of the molecular sieve catalyst, but not only Al on the surface of the molecular sieve was removed in the acid treatment process, but also Al in the framework of the molecular sieve was removed. The above studies all reduced the surface acid sites through post-treatment methods, thereby slowing down the carbon deposition deactivation of the molecular sieve catalyst, but additional treatment steps are needed after the preparation of the molecular sieve to complete the modification of the molecular sieve, making the molecular sieve preparation process more complex and increasing the cost. Therefore, it is very meaningful to achieve a high-silicon-to-aluminum ratio outer surface during the synthesis of the ZSM-5 molecular sieve. SUMMARY

[0003] The present application aims to provide a ZSM-5 molecular sieve with a high-silicon outer surface and a preparation method and application thereof, to solve the technical problem in the prior art that acid sites of the ZSM-5 molecular sieve are widely located on the outer surface of the molecular sieve, resulting in less than ideal selectivity and stability.

[0004] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is:

[0005] In a first aspect, the present application provides a ZSM-5 molecular sieve with a high-silicon outer surface, wherein the SiO2 / Al2O3 of the whole ZSM-5 molecular sieve is ≤40, and the SiO2 / Al2O3 of the outer surface of the ZSM-5 molecular sieve crystal grain is >40.

[0006] According to some embodiments of the present application, the SiO2 / Al2O3 of the whole ZSM-5 molecular sieve is 25-40.

[0007] And / or according to some embodiments of the present application, the SiO2 / Al2O3 of the outer surface of the ZSM-5 molecular sieve crystal grain is 43-50.

[0008] In a second aspect, the present application provides a preparation method of a ZSM-5 molecular sieve with a high-silicon outer surface, comprising: obtaining a mixed solution comprising a high-silicon molecular sieve, a supplemental aluminum source, an alkali source, an organic template agent and a solvent, performing crystallization treatment on the mixed solution, and performing calcination treatment on the crystallization product to obtain the ZSM-5 molecular sieve.

[0009] The SiO2 / Al2O3 of the high-silicon molecular sieve is 30-100.

[0010] In the present application, the SiO2 / Al2O3 of the high-silicon molecular sieve refers to the SiO2 / Al2O3 of the whole high-silicon molecular sieve, which can be 30, 32, 35, 36, 38, 40, 42, 45, 46, 49, 50, 51, 55, 57, 59, 60, 62, 65, 68, 70, 73, 75, 77, 80, 82, 85, 90, 95, 100, etc.

[0011] If the SiO2 / Al2O3 of the high-silicon molecular sieve is <30, it can result in that a pure-phase ZSM-5 molecular sieve cannot be obtained; and if the SiO2 / Al2O3 of the high-silicon molecular sieve is >100, it can result in that the supplemental aluminum source cannot completely enter the product molecular sieve, and the silicon-aluminum ratio of the obtained product is much higher than the silicon-aluminum ratio of the raw material.

[0012] In the present application, the high-silicon molecular sieve needs to be selected from a molecular sieve with the same structural units as ZSM-5, such as component building units (mel, mor) and ring building units (4R, 5R), and the framework density of the high-silicon molecular sieve is lower than that of the ZSM-5 molecular sieve.

[0013] According to some embodiments of the present application, the high-silicon molecular sieve comprises at least one of a BEA molecular sieve, a FAU molecular sieve, a FER molecular sieve, a MRE molecular sieve and a MWW molecular sieve.

[0014] According to some embodiments of the present invention, the high-silica molecular sieve includes at least one of β molecular sieve, Y molecular sieve, ZSM-35, ZSM-48, MCM-49, MCM-56, MCM-36, and MCM-22.

[0015] According to some embodiments of the present invention, the supplementary aluminum source includes at least one of aluminum sol, boehmite, aluminum hydroxide, aluminum isopropoxide, aluminum sec-butoxide, sodium aluminate, aluminum sulfate, aluminum nitrate, aluminum chloride, and aluminum oxide.

[0016] According to some embodiments of the present invention, the alkali source includes at least one of sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, sodium fluoride, and ammonia water.

[0017] According to some embodiments of the present invention, the organic template agent includes at least one of tetrapropylammonium hydroxide, tetrapropylammonium bromide, tetraethylammonium hydroxide, tetraethylammonium bromide, tetramethylammonium hydroxide, tetramethylammonium bromide, tetrabutylammonium hydroxide, triethylamine, and n-butylammonium.

[0018] According to some embodiments of the present invention, the solvent includes at least one selected from water, methanol, ethanol, propanol, butanol, pentanol, ethylene glycol, diethylene glycol, glycerol, and diglycerol.

[0019] According to some embodiments of the present invention, the silicon source is SiO2, the aluminum source is Al2O3, and the alkali source is OH. - The organic template agent is represented by R, the solvent by I, and the molar ratio of each component in the mixed solution is: SiO2 / Al2O3 = 10~60, OH - / SiO2=0.05~0.5, R / SiO2=0.01~0.8, I / SiO2=3~300.

[0020] In this invention, the silicon source includes a silicon source provided by a high-silicon molecular sieve; the aluminum source includes an aluminum source provided by a high-silicon molecular sieve and a supplementary aluminum source.

[0021] According to some embodiments of the present invention, SiO2 / Al2O3 = 26 to 40.

[0022] According to some embodiments of the present invention, OH - / SiO2=0.1~0.4.

[0023] According to some embodiments of the present invention, R / SiO2 = 0.05 to 0.2.

[0024] According to some embodiments of the present invention, I / SiO2 = 20 to 50.

[0025] According to some embodiments of the present application, the temperature of the crystallization treatment is 100-200℃, preferably 140-180℃; the time of the crystallization treatment is 2-200h, preferably 48-120h.

[0026] According to some embodiments of the present application, the temperature of the calcination is 400-700℃, preferably 500-600℃; the time of the calcination is 0.5-8h, preferably 4-6h.

[0027] According to some embodiments of the present application, the calcination is performed in air.

[0028] According to some embodiments of the present application, the crystallization product is cooled, filtered, washed, dried, and then calcined.

[0029] According to some embodiments of the present application, the temperature of the drying is 50-150℃, preferably 80-120℃; the time of the drying is 0.5-48h, preferably 4-24h.

[0030] In a third aspect, the present application provides a ZSM-5 molecular sieve with high-silicon outer surface, which is prepared by the method of the second aspect.

[0031] In a fourth aspect, the present application provides the use of the ZSM-5 molecular sieve with high-silicon outer surface of the first or third aspect in the field of catalysts.

[0032] The present application has at least the following beneficial effects:

[0033] The ZSM-5 molecular sieve with high-silicon outer surface provided by the present application has the characteristics of aluminum-poor outer surface and aluminum-rich core, which can effectively avoid the technical problem of less-than-ideal selectivity and stability of ZSM-5 molecular sieve due to the wide distribution of acid sites on the outer surface of the molecular sieve.

[0034] The preparation method provided by the present application uses high-silicon molecular sieve to synthesize ZSM-5 molecular sieve with high-silicon outer surface by one-step crystallization method, without the need for post-treatment of the obtained molecular sieve, and the preparation process is simple, which can effectively save costs. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 XRD diffraction pattern of the ZSM-5 molecular sieve prepared in Example 1. DETAILED DESCRIPTION

[0036] In order to make the technical problems, technical solutions and beneficial effects of the present application clearer, the present application will be further described in detail in conjunction with specific examples. It should be understood that the specific examples described herein are only used to illustrate the present application, and do not limit the protection scope of the present application in any way.

[0037] Unless otherwise defined, the technical terms used in the following examples have the same meanings as commonly understood by those skilled in the art to which the present application belongs. The reagents used in the following examples are all conventional biochemical reagents unless otherwise specified; the raw materials, instruments and equipment used in the following examples can be obtained by market purchase or by existing methods; the reagent amount is the amount used in conventional experimental operation unless otherwise specified; the experimental method is a conventional method unless otherwise specified.

[0038] In the various embodiments and comparative examples of the present application, each performance data is tested according to the following test method:

[0039] (1) XRD phase analysis: determined by a D8 Focus diffractometer of Bruker Company, graphite monochromator, Cu target Kα ray light source, wavelength λ of 0.154 nm, 40 kV tube voltage, 40 mA tube current, and recording the diffraction signal in the 2θ range of 3-90° (2° / min scanning speed).

[0040] (2) Molecular sieve bulk element content: obtained by inductively coupled plasma emission spectrometer (ICP) test.

[0041] (3) Molecular sieve surface (<10 nm) element content: obtained by X-ray photoelectron spectroscopy (XPS) test.

[0042] Example 1

[0043] Sodium aluminate, tetrapropylammonium hydroxide and sodium hydroxide were dissolved in water, then MCM-49 molecular sieve (SiO2 / Al2O3=70) was added into the solution, stirred uniformly to obtain a mixed solution, the molar ratio of each component in the mixed solution was SiO2:0.03Al2O3:0.2R:0.2NaOH:42H2O; the mixed solution was loaded into a polytetrafluoroethylene-lined pressure steel kettle, crystallized at 180°C for 96h. After crystallization, it was naturally cooled to room temperature, the crystallization product was filtered, washed, dried at 120°C for 12h, and finally calcined at 550°C in air for 5h to obtain a molecular sieve.

[0044] The XRD pattern of the molecular sieve prepared in this example is shown in Figure 1 It can be seen that it is a ZSM-5 molecular sieve.

[0045] The test results of the SiO2 / Al2O3 of the molecular sieve prepared in this example as a whole and the SiO2 / Al2O3 of the outer surface are shown in Table 1.

[0046] Example 2

[0047] Sodium aluminate, tetraethylammonium hydroxide, sodium hydroxide were dissolved in water, then MCM-49 molecular sieve (SiO2 / Al2O3=55) was added into the solution, stirred uniformly to obtain a mixed solution, the molar ratio of components in the mixed solution was SiO2:0.04Al2O3:0.2R:0.2NaOH:42H2O; the mixed solution was loaded into a pressure steel kettle with a polytetrafluoroethylene liner, crystallized at 180℃ for 96h. After crystallization, it was naturally cooled to room temperature, the crystallization product was filtered, washed, dried at 120℃ for 12h, and finally calcined at 550℃ in air for 5h to obtain a molecular sieve.

[0048] The molecular sieve prepared in this example was ZSM-5 molecular sieve, and the test results of SiO2 / Al2O3 of the whole molecular sieve and the external surface were shown in Table 1.

[0049] Example 3

[0050] Sodium aluminate, tetraethylammonium hydroxide, sodium hydroxide were dissolved in water, then MCM-49 molecular sieve (SiO2 / Al2O3=55) was added into the solution, stirred uniformly to obtain a mixed solution, the molar ratio of components in the mixed solution was SiO2:0.04Al2O3:0.1R:0.25NaOH:30H2O; the mixed solution was loaded into a pressure steel kettle with a polytetrafluoroethylene liner, crystallized at 160℃ for 72h. After crystallization, it was naturally cooled to room temperature, the crystallization product was filtered, washed, dried at 100℃ for 12h, and finally calcined at 550℃ in air for 5h to obtain a molecular sieve.

[0051] The molecular sieve prepared in this example was ZSM-5 molecular sieve, and the test results of SiO2 / Al2O3 of the whole molecular sieve and the external surface were shown in Table 1.

[0052] Example 4

[0053] The molecular sieve preparation method referred to Example 1, except that MCM-49 molecular sieve (SiO2 / Al2O3=70) was replaced by β molecular sieve (SiO2 / Al2O3=80).

[0054] The molecular sieve prepared in this example was ZSM-5 molecular sieve, and the test results of SiO2 / Al2O3 of the whole molecular sieve and the external surface were shown in Table 1.

[0055] Example 5

[0056] The molecular sieve preparation method referred to Example 1, except that MCM-49 molecular sieve (SiO2 / Al2O3=70) was replaced by Y molecular sieve (SiO2 / Al2O3=46).

[0057] The molecular sieve prepared in this example is ZSM-5 molecular sieve. The test results of the SiO2 / Al2O3 of the whole molecular sieve and the SiO2 / Al2O3 of the outer surface are shown in Table 1.

[0058] Example 6

[0059] The molecular sieve was prepared according to the method of Example 1, except that the MCM-49 molecular sieve (SiO2 / Al2O3 = 70) was replaced by ZSM-35 molecular sieve (SiO2 / Al2O3 = 60).

[0060] The molecular sieve prepared in this example is ZSM-5 molecular sieve. The test results of the SiO2 / Al2O3 of the whole molecular sieve and the SiO2 / Al2O3 of the outer surface are shown in Table 1.

[0061] Comparative Example 1

[0062] Sodium aluminate, tetrapropylammonium hydroxide, and sodium hydroxide were dissolved in water, and then silica sol was added. The mixture was stirred to form a gel. The molar ratio of the components in the system was SiO2:0.03Al2O3:0.2R:0.2NaOH:42H2O. The gel was loaded into a polytetrafluoroethylene-lined pressure steel kettle, and crystallization was performed at 180°C for 96 h. After crystallization, the system was naturally cooled to room temperature. The crystallization product was filtered, washed, dried at 120°C for 12 h, and finally calcined at 550°C in air for 5 h to obtain the molecular sieve.

[0063] The molecular sieve prepared in this example is ZSM-5 molecular sieve. The test results of the SiO2 / Al2O3 of the whole molecular sieve and the SiO2 / Al2O3 of the outer surface are shown in Table 1.

[0064] Comparative Example 2

[0065] The molecular sieve was prepared according to the method of Example 1, except that the MCM-49 molecular sieve (SiO2 / Al2O3 = 70) was replaced by MCM-49 molecular sieve (SiO2 / Al2O3 = 25).

[0066] The molecular sieve prepared in this example is a mixture of ZSM-5 molecular sieve and analcime.

[0067] Table 1

[0068]

[0069]

[0070] It should be noted that the foregoing examples have been provided merely for the purposes of illustration and are not intended to limit the application in any way. Descriptions and examples of materials and processes of the application are intended to be illustrative not limiting. Any modifications of the application and other applications of the application will occur to those skilled in the art to which the application pertains and many options for modification of the application will suggest themselves. The application lies in the broadest aspects of the technological concepts involved. Descriptions and examples of specific chemical materials and processes are intended to be illustrative of the application and it is intended that requests for patent protection be limited to one of the specific embodiments described above, described in the following claims, and any equivalents thereof.

Claims

1. A ZSM-5 molecular sieve having a high-silica external surface, characterized in that, The SiO2 / Al2O3 of the ZSM-5 molecular sieve as a whole is ≤40, and the SiO2 / Al2O3 of the outer surface of the ZSM-5 molecular sieve crystal grain is >40.

2. The ZSM-5 molecular sieve of claim 1, wherein, The SiO2 / Al2O3 of the ZSM-5 molecular sieve as a whole is 25-40. And / or, the SiO2 / Al2O3 of the outer surface of the ZSM-5 molecular sieve crystal grain is 43-55.

3. A process for the preparation of ZSM-5 molecular sieve having a high-silica external surface, characterized in that, Comprise: A mixed solution comprising a high-silicon molecular sieve, a supplementary aluminum source, an alkali source, an organic template agent and a solvent is obtained, the mixed solution is subjected to a crystallization treatment, and then the crystallization product is subjected to a calcination treatment to prepare the ZSM-5 molecular sieve; The SiO2 / Al2O3 of the high-silicon molecular sieve is 30-100.

4. The production method according to claim 3, characterized by, The high-silicon molecular sieve comprises at least one of BEA molecular sieve, FAU molecular sieve, FER molecular sieve, MRE molecular sieve and MWW molecular sieve; preferably, the high-silicon molecular sieve comprises at least one of β molecular sieve, Y molecular sieve, ZSM-35, ZSM-48, MCM-49, MCM-56, MCM-36 and MCM-22; And / or, the supplementary aluminum source comprises at least one of aluminum sol, pseudo-boehmite, aluminum hydroxide, aluminum isopropoxide, aluminum sec-butoxide, sodium aluminate, aluminum sulfate, aluminum nitrate, aluminum chloride and aluminum oxide; And / or, the alkali source comprises at least one of sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, sodium fluoride and ammonia water; And / or, the organic template agent comprises at least one of tetrapropylammonium hydroxide, tetrapropylammonium bromide, tetraethylammonium hydroxide, tetraethylammonium bromide, tetramethylammonium hydroxide, tetramethylammonium bromide, tetrabutylammonium hydroxide, triethylamine and n-butylammonium; And / or, the solvent comprises at least one of water, methanol, ethanol, propanol, butanol, pentanol, ethylene glycol, diethylene glycol, glycerol and diglycerol.

5. The production method according to claim 3 or 4, characterized by, The silicon source is calculated as SiO2, the aluminum source is calculated as Al2O3, the alkali source is calculated as OH - The organic template is calculated as R, and the solvent is calculated as I. The molar ratio of the components in the mixed solution is as follows: SiO2 / Al2O3=10-60, OH - / SiO2=0.05-0.5, R / SiO2=0.01-0.8, and I / SiO2=3-300. Preferably, SiO2 / Al2O3 = 26-40; and / or, OH - / SiO2= 0.1-0.4; And / or, R / SiO2 = 0.05-0.2; And / or, I / SiO2 = 20-50.

6. The method of any one of claims 3-5, wherein, The temperature of the crystallization treatment is 100-200°C, preferably 140-180°C; and the time of the crystallization treatment is 2-200h, preferably 48-120h.

7. The method of any one of claims 3-6, wherein, The temperature of the calcination is 400-700°C, preferably 500-600°C; and the time of the calcination is 0.5-8h, preferably 4-6h; And / or, the calcination is performed in air.

8. The method of any one of claims 3-7, wherein, The crystallization product is subjected to cooling, filtration, washing, drying and then calcination; Preferably, the temperature of the drying is 50-150°C, preferably 80-120°C.

9. A ZSM-5 molecular sieve with a high-silicon outer surface, which is prepared by the preparation method in any one of claims 3-8.

10. Application of the ZSM-5 molecular sieve with a high-silicon outer surface in claim 1 or 2 or 9 in the field of catalysts.

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