Method for preparing silicon-aluminum molecular sieve based on fluorine-containing ionic liquid

Abstract

The invention discloses a method for preparing a silicon-aluminum molecular sieve based on a multifunctional fluorine-containing ionic liquid, the method uses the fluorine-containing ionic liquid as a solvent, a template agent and a mineralizer at the same time to prepare the silicon-aluminum molecular sieve, and the method specifically comprises the following steps: firstly, fully grinding and mixing solid raw materials including a silicon source, an aluminum source and the fluorine-containing ionic liquid according to a certain proportion; then transferring into a hydrothermal kettle, and crystallizing for 6-120 hours under the condition of 100-180 DEG C; and fully washing and drying the reaction product to obtain the silicon-aluminum type molecular sieve with high crystallinity and controllable silicon-aluminum ratio. According to the method provided by the invention, the use of HF can be avoided, the fluorine-containing ionic liquid is simultaneously used as a solvent, a template agent and a mineralizer, the pre-crystallization process is omitted, the synthesis time is shortened, the pressure of the preparation process is greatly reduced, in addition, the ionic liquid can be recycled, and the cost is reduced. And the waste liquid discharge is reduced.

Description

Technical Field

[0001] The invention relates to a method for preparing a silicon-aluminum molecular sieve, in particular to a method for preparing a silicon-aluminum molecular sieve based on a multifunctional fluorine-containing ionic liquid. Background Art

[0002] Molecular sieves, especially silica-alumina molecular sieves, have good adsorption, shape-selective and catalytic properties due to their unique pore structure and adjustable acid properties, and are widely used in adsorption separation, industrial catalysis and other fields. At present, the preparation of silica-alumina molecular sieves is mainly based on hydrothermal synthesis. The characteristic of this route is that a large amount of water is used as a solvent, and the required synthesis steps are cumbersome, including mixing, pre-crystallization, secondary hydrothermal crystallization, etc.; and the hydrothermal crystallization process has high pressure (1MPa-1 GPa), which poses a safety hazard; in addition, the synthesis process produces a large amount of wastewater, which pollutes the environment. By reducing the amount of water solvent used and the number of drugs in the raw materials, not only can the synthesis steps of molecular sieves be simplified, but also energy can be saved and waste emissions can be reduced.

[0003] Ionic liquids are a class of unconventional media composed of anions and cations. Compared with traditional organic solvents, ionic liquids have the characteristics of low volatility, designable structure, recyclability, and high stability. The synthesis of molecular sieves using ionic liquids as solvents and templates, that is, ion thermal synthesis of molecular sieves, not only avoids the self-generated high pressure of water solvents, but also reduces waste liquid discharge and reduces environmental pollution. Cooper et al. first synthesized the aluminum phosphate molecular sieve AlPO4-11 (Nature, 2004, 430, 1012-1015) at normal pressure using 1-ethyl-3-methylimidazolium bromide as solvent and template. Subsequently, Morris et al. used 1-ethyl-3-methylimidazolium bromide ionic liquid as solvent and template to synthesize a new layered open framework aluminum phosphate molecular sieve SIZ-6 (Chem. Commun., 2006, 380-382). However, existing literature (Acc.Chem.Res., 2007, 40, 1005-1013; Chem.Sci., 2010, 1, 483-487) and patents (CN102627287) indicate that the synthesis of silica-alumina molecular sieves by ionic liquid method still requires the addition of fluorine-containing substances such as HF as a mineralizer to dissolve the silicon source. The present invention uses fluorine-containing ionic liquid as a solvent, template agent, and mineralizer to synthesize silica-alumina molecular sieves, which not only avoids the use of highly toxic and highly corrosive HF in the traditional fluorine-based route, but also eliminates the pre-crystallization process, shortens the synthesis time, and greatly reduces the pressure of the synthesis process. In addition, the ionic liquid can be recycled, reducing waste liquid discharge. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing a silicon-aluminum molecular sieve based on a multifunctional ionic liquid. The method uses a fluorine-containing ionic liquid as a solvent, a template and a mineralizer at the same time, thereby avoiding the use of highly toxic and highly corrosive HF in a traditional fluorine-based route. The silicon-aluminum molecular sieve is prepared by grinding and crystallizing the fluorine-containing ionic liquid and other solid-phase raw materials. Not only is the synthesis process simple, but the low volatility of the ionic liquid can also greatly reduce the pressure of the crystallization process, and the obtained molecular sieve has high crystallinity. At the same time, the ionic liquid can be partially recovered, thereby reducing environmental pollution and realizing green synthesis of the molecular sieve.

[0005] The method for preparing a silicon-aluminum molecular sieve based on a multifunctional fluorine-containing ionic liquid provided by the present invention can be achieved by the following steps:

[0006] (1) mixing a fluorine-containing ionic liquid, a silicon source, and an aluminum source in a certain proportion and grinding them thoroughly;

[0007] (2) transferring the ground raw material to a hydrothermal reactor and crystallizing at 100 to 180° C. for 6 to 120 hours;

[0008] (3) The solid product obtained by crystallization was washed and dried at 80° C. for 12 hours to obtain the final product.

[0009] In the method for preparing silica-alumina molecular sieve based on multifunctional fluorine-containing ionic liquid, the fluorine-containing ionic liquid is one of tetraethylammonium hexafluorophosphate, tetrapropylammonium hexafluorophosphate, tetrabutylammonium hexafluorophosphate, 1-ethyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium hexafluorophosphate, tetraethylammonium tetrafluoroborate, tetrapropylammonium tetrafluoroborate or tetrabutylammonium tetrafluoroborate.

[0010] In the method for preparing silica-alumina molecular sieve based on multifunctional fluorine-containing ionic liquid, the silicon source is one or two of sodium silicate nonahydrate, column chromatography silica gel, fumed silica or nano silica; the aluminum source is one or two of aluminum hydroxide, nano alumina, pseudo-boehmite or sodium aluminate.

[0011] In the method for preparing silicon-aluminum molecular sieve based on multifunctional fluorine-containing ionic liquid, the molar ratio of each component is SiO2:Al2O3:ionic liquid=1:0~0.04:0.194~0.754.

[0012] In the method for preparing silica-alumina molecular sieve based on multifunctional fluorine-containing ionic liquid, the pressure of the silica-alumina molecular sieve preparation process is 0.1MPa to 0.4MPa.

[0013] According to the method of the present invention, by changing the structure, crystallization temperature, crystallization time, silicon source and aluminum source of the fluorine-containing ionic liquid, a silicon-aluminum type molecular sieve with good crystallinity and controllable silicon-aluminum ratio can be prepared, including MFI, TON, BEA, AEI, ANA, and FAU.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] (1) Fluorinated ionic liquids can be used as solvents, templates, and mineralizers at the same time, which reduces the types of raw materials required, eliminates the pre-crystallization process, shortens the preparation time, and significantly reduces the pressure of the crystallization process;

[0016] (2) Based on the designability of ionic liquids, molecular sieves with different topological structures can be prepared by adjusting the structure of ionic liquids, forming a universal method for preparing silicon-alumina molecular sieves based on fluorine-containing ionic liquids;

[0017] (3) After the reaction is completed, the fluorine-containing ionic liquid can be partially recovered, realizing the green preparation of molecular sieves. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The X-ray diffraction pattern of the MFI molecular sieve prepared by the present invention;

[0019] Figure 2 This is a scanning electron microscope photo of the MFI molecular sieve prepared by the present invention;

[0020] Figure 3 The X-ray diffraction pattern of the TON type molecular sieve prepared by the present invention;

[0021] Figure 4 This is a scanning electron microscope photograph of the TON type molecular sieve prepared in the present invention.

[0022] Figure 5 The X-ray diffraction pattern of the ANA type molecular sieve prepared by the present invention;

[0023] Figure 6 This is a scanning electron microscope photograph of the ANA type molecular sieve prepared by the present invention. DETAILED DESCRIPTION

[0024] The present invention will be further described below by means of specific examples.

[0025] Example 1: Preparation of pure silicon MFI molecular sieve sample

[0026] 0.30 g of amorphous silica and 1.25 g of tetrapropylammonium hexafluorophosphate (TPAPF6) were mixed, ground for 5 minutes, transferred to a hydrothermal autoclave, crystallized at 180° C. for 24 hours, and washed and dried to obtain the final product.

[0027] Figure 1 a is the X-ray diffraction pattern of the product obtained in Example 1, which has characteristic diffraction peaks of MFI molecular sieves and has a high degree of crystallinity; Figure 2 a is a scanning electron microscope photograph of the product obtained in Example 1, and the sample exhibits a coffin-shaped morphology with a size of about 20 to 25 microns.

[0028] Example 2: Preparation of Si-Al MFI Molecular Sieve Sample

[0029] 0.30 g of amorphous silica, 1.25 g of tetrapropylammonium hexafluorophosphate (TPAPF6) and 0.078 g of aluminum hydroxide were mixed, ground for 5 minutes, transferred to a hydrothermal autoclave, crystallized at 180° C. for 24 hours, and washed and dried to obtain the final product.

[0030] Figure 1 b is the X-ray diffraction pattern of the product obtained in Example 2, which has characteristic diffraction peaks of MFI molecular sieves and has a high degree of crystallinity; Figure 2 b is a scanning electron microscope photograph of the product obtained in Example 2, and the sample exhibits a coffin-shaped morphology with a size of about 18 to 25 microns.

[0031] Example 3: Preparation of pure silicon MFI molecular sieve sample

[0032] 0.30 g of amorphous silica and 1.03 g of tetrapropylammonium tetrafluoroborate (TPABF4) were mixed, ground for 5 minutes, transferred to a hydrothermal autoclave, crystallized at 180° C. for 24 hours, and washed and dried to obtain the final product.

[0033] Figure 1 c is the X-ray diffraction pattern of the product obtained in Example 3, which has characteristic diffraction peaks of MFI molecular sieves and has a high degree of crystallinity; Figure 2 c is a scanning electron microscope photograph of the product obtained in Example 3, and the sample exhibits a coffin-shaped morphology with a size of about 12 to 16 microns.

[0034] Example 4: Preparation of TON type molecular sieve sample

[0035] 0.3 g of amorphous silica and 0.25 g of 1-ethyl-3-methylimidazolium hexafluorophosphate ([EMIm]PF6) were mixed, ground for 5 minutes, transferred to a hydrothermal autoclave, crystallized at 180° C. for 120 hours, and washed and dried to obtain the final product.

[0036] Figure 3 This is the X-ray diffraction pattern of the product obtained in Example 4, which has characteristic diffraction peaks of TON type molecular sieves and has a high degree of crystallinity; Figure 4 This is a scanning electron microscope photograph of the product obtained in Example 4. The sample has a rod-like morphology with a length of about 50 to 200 microns.

[0037] Example 5: Preparation of ANA type molecular sieve sample

[0038] 0.3 g of amorphous silica, 1.4 g of sodium silicate nonahydrate, 0.02 g of aluminum hydroxide and 0.512 g of 1-ethyl-3-methylimidazolium hexafluorophosphate ([EMIm]PF6) were mixed, ground for 5 minutes, transferred to a hydrothermal autoclave, crystallized at 160° C. for 72 hours, and washed and dried to obtain the final product.

[0039] Figure 5 This is the X-ray diffraction pattern of the product obtained in Example 5, which has characteristic diffraction peaks of ANA type molecular sieves and has a high degree of crystallinity; Figure 6 This is a scanning electron microscope photograph of the product obtained in Example 5. The sample has a spherical morphology with a diameter of about 10 to 20 microns.

[0040] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed in the present invention are within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a silicon-alumina molecular sieve based on a multifunctional fluorine-containing ionic liquid, characterized in that: The preparation method comprises the following steps: (1) mixing solid raw materials of silicon source, aluminum source and fluorine-containing ionic liquid in a certain proportion and grinding them thoroughly; (2) transferring the ground raw material to a hydrothermal reactor and crystallizing at 100 to 180° C. for 6 to 120 hours; (3) The crystallized product is thoroughly washed and dried at 80° C. for more than 12 hours to obtain the final product.

2. The method for preparing a silicon-alumina molecular sieve based on a multifunctional fluorine-containing ionic liquid according to claim 1, characterized in that: The silicon source is one or two of sodium silicate nonahydrate, column chromatography silica gel, fumed silica or nano silicon dioxide; the aluminum source is one or two of aluminum hydroxide, nano aluminum oxide, pseudo-boehmite or sodium aluminate.

3. The method for preparing a silicon-alumina molecular sieve based on a multifunctional fluorine-containing ionic liquid according to claim 1, characterized in that: The ionic liquid is one of tetraethylammonium hexafluorophosphate, tetrapropylammonium hexafluorophosphate, tetrabutylammonium hexafluorophosphate, 1-ethyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium hexafluorophosphate, tetraethylammonium tetrafluoroborate, tetrapropylammonium tetrafluoroborate or tetrabutylammonium tetrafluoroborate, and the ionic liquid plays multiple roles of solvent, template agent and mineralizer.

4. The method for preparing a silicon-aluminum molecular sieve based on a multifunctional fluorine-containing ionic liquid according to claim 1, characterized in that: The molar ratio of each reaction raw material is SiO2:Al2O3:ionic liquid=1:0~0.04:0.194~0.

754.

5. The method for preparing a silicon-aluminum molecular sieve based on a multifunctional fluorine-containing ionic liquid according to claim 1, characterized in that: The pressure range of the silicon aluminum molecular sieve preparation process is 0.1-0.4 MPa.

6. The method for preparing a silicon-aluminum molecular sieve based on a multifunctional fluorine-containing ionic liquid according to claim 1, characterized in that: The topological structure of the silicon-aluminum molecular sieve is one of MFI, TON, BEA, AEI, ANA, and FAU.

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