CN116395713B - A preparation method of Li-SSZ-13 zeolite molecular sieve - Google Patents

Abstract

The invention discloses a method for preparing a Li-SSZ-13 zeolite molecular sieve, comprising the following steps: first, after mixing a lithium source with deionized water and stirring evenly, a silicon source is added and continued to stir evenly; then, an aluminum source and a structure directing agent OSDA are mixed and stirred evenly and added to the previous mixed solution, and a mixed sol is obtained after sufficient stirring. The sol is transferred to a reactor with a polytetrafluoroethylene liner for reaction; the obtained solid phase product is washed with deionized water to neutrality and dried and roasted; the final product is a Li-SSZ-13 zeolite molecular sieve. The preparation method is simple to operate, and the prepared Li-SSZ-13 zeolite molecular sieve is a microporous structure, which has good application prospects in the fields of gas adsorption and catalysis.

Description

A preparation method of Li-SSZ-13 zeolite molecular sieve

Technical Field

The invention relates to a method for preparing a Li-SSZ-13 zeolite molecular sieve, and belongs to the field of zeolite molecular sieve preparation and gas adsorption.

Background Art

In recent years, with the rapid development of economy, rapid progress of science and technology, and rapid population growth, people's demand for energy has also increased, and the consumption of fossil fuels has risen sharply. The burning of fossil fuels is accompanied by the emission of a large amount of greenhouse gases, resulting in global warming, which in turn causes the continuous deterioration of the global environment and climate. Therefore, controlling the content of CO ₂ in the atmosphere is an urgent problem that needs to be solved.

Zeolite molecular sieve is a porous material, which is often used as an adsorbent in the field of adsorption separation because of its pore size close to the size of gas molecules, excellent thermal stability, good mechanical and chemical stability. SSZ-13 zeolite molecular sieve belongs to CHA type zeolite molecular sieve, with a pore structure of 0.38nm×0.38nm, close to the molecular dynamics diameter of _CO2 , so it has more advantages in selective adsorption of _CO2 .

Hudson et al. (Journal of the American Chemical Society, 2012, 134 (4), 1970-1973) studied the adsorption performance of Cu-/H-SSZ-13 zeolite molecular sieve for CO ₂ /N ₂ and found that the adsorption performance of Cu-/H-SSZ-13 zeolite molecular sieve for CO ₂ was significantly greater than that for N ₂ , which was attributed to the difference in the binding sites of the two gases. Patent CN113387369A discloses a method for preparing Cu-SSZ-13 molecular sieve, using trivalent aluminum source, monovalent sodium source and tetravalent silicon source as main raw materials, copper amine complex and choline cation as templates to prepare Cu-SSZ-13 molecular sieve; wherein the copper amine complex contains divalent copper ions and tetraethylene pentamine. The method of the present invention has low cost and maintains the high catalytic activity of Cu-SSZ-13 molecular sieve under high temperature conditions, belonging to the field of catalysis. Patent CN110028081A discloses a method for synthesizing nano-scale multi-level pore SSZ-13 molecular sieve. NaOH, template agent TMAdaOH and deionized water are mixed, and then Al source and Si source are added to obtain SSZ-13 molecular sieve synthesis liquid, which is then ultrasonically oscillated in an ultrasonic oscillator. During this process, seed crystals are added, and the product obtained after high-temperature reaction is a multi-level porous SSZ-13 molecular sieve. This method prepares nano-scale multi-porous SSZ-13 molecular sieves, but the CO ₂ adsorption capacity is not high.

Summary of the invention

The purpose of the present invention is to provide a preparation method of Li-SSZ-13 zeolite molecular sieve. The Li-SSZ-13 zeolite molecular sieve is synthesized by a direct hydrothermal method. Compared with the traditional ion exchange method for preparing Li-SSZ-13 molecular sieve, the method does not require ammonium exchange and lithium exchange. Compared with the unmodified SSZ-13 molecular sieve, the specific surface area is significantly improved, the adsorption performance is also significantly improved, and the preparation process is simple, convenient and easy to implement.

In order to achieve the above object, the present invention adopts the following technical solution:

A method for preparing Li-SSZ-13 zeolite molecular sieve comprises the following steps:

(1) Stir the lithium source and deionized water to mix evenly, add the silicon source and continue stirring evenly;

(2) adding the aluminum source to the structure directing agent OSDA, heating and stirring to mix evenly;

(3) adding the mixed solution obtained in step (2) to the mixed solution obtained in step (1), and stirring for a certain period of time to obtain a mixed sol; the molar composition of the sol is: _SiO2 / _Al2O3 = _10-200 , _SiO2 /LiOH = 1-50, _SiO2 /OSDA = 0.8-10 _{, H2O} / _SiO2 = 10-500;

(4) transferring the mixed sol obtained in step (3) to a reactor lined with polytetrafluoroethylene and placing it in an oven for reaction; washing the solid phase product obtained by the reaction with deionized water until it is neutral, drying and calcining, to obtain Li-SSZ-13 zeolite molecular sieve.

Preferably, in step (1), the lithium source is lithium hydroxide, lithium chloride, lithium carbonate or lithium sulfate.

Preferably, in step (1), the silicon source is tetraethyl orthosilicate, tetramethyl orthosilicate, fumed silica, sodium silicate, silica sol or water glass.

Preferably, in step (2), the aluminum source is sodium aluminate, aluminum hydroxide, aluminum ore, aluminum n-butoxide, aluminum isopropoxide, aluminum powder or aluminum foil.

Preferably, in step (2), the structure directing agent OSDA is N,N,N-trimethyl-1-adamantyl ammonium hydroxide, N,N,N-trimethyladamantyl ammonium bromide, N,N,N-trimethyladamantyl ammonium iodide, N,N,N-trimethylbenzyl ammonium bromide, N,N,N-trimethylbenzyl ammonium iodide, tetraethylammonium hydroxide or N,N,N-trimethylbenzyl ammonium hydroxide.

Preferably, in step (2), the heating temperature is 50-200°C.

Preferably, in step (3), the stirring time is 0.2 to 7 days.

Preferably, in step (4), the reaction temperature is 120-200° C., and the reaction time is 5-240 h.

Preferably, in step (4), the calcination environment is nitrogen, air, oxygen, ozone or an oxygen/ozone mixture, the calcination temperature is 180-600° C., the calcination time is 4-48 hours, and the heating and cooling rates are 0.2-2° C./min.

Beneficial effects of the present invention:

The present invention synthesizes Li-SSZ-13 zeolite molecular sieve by direct hydrothermal method, and the preparation method is simple to operate. Compared with the preparation of Li-SSZ-13 zeolite molecular sieve by traditional ion exchange, the two-step cumbersome process of ammonium exchange-lithium exchange is not required. The prepared Li-SSZ-13 zeolite molecular sieve is a microporous structure, and compared with the traditional unmodified SSZ-13 molecular sieve, the specific surface area is significantly improved, and the adsorption capacity of _CO2 can reach ^97.54cm3 /g, which has good application prospects in the fields of adsorption and catalysis. The direct hydrothermal method disclosed in the present invention has the beneficial effect of simple steps compared with the ordinary ion exchange method, and the prepared Li-SSZ-13 zeolite molecular sieve has the beneficial effect of significantly higher _CO2 adsorption capacity than the unmodified SSZ-13 molecular sieve.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a scanning electron microscope image of the Li-SSZ-13 zeolite molecular sieve prepared in Examples 1 to 4.

FIG. 2 is an X-ray diffraction diagram of the Li-SSZ-13 zeolite molecular sieve prepared in Examples 1 to 4.

FIG3 is a scanning electron microscope image of the conventional SSZ-13 zeolite molecular sieve prepared in Comparative Example 1.

FIG. 4 is an X-ray diffraction pattern of the conventional SSZ-13 zeolite molecular sieve prepared in Comparative Example 1.

FIG. 5 is a low temperature N ₂ adsorption isotherm of the Li-SSZ-13 zeolite molecular sieve prepared in Examples 1 to 4.

FIG. 6 is a low temperature N ₂ adsorption isotherm of the conventional SSZ-13 zeolite molecular sieve prepared in Comparative Example 1.

FIG. 7 shows the CO ₂ adsorption isotherms of the Li-SSZ-13 zeolite molecular sieves prepared in Examples 1 to 4 and the conventional SSZ-13 zeolite molecular sieve prepared in Comparative Example 1 at 0°C.

DETAILED DESCRIPTION

The present invention is further explained below in conjunction with the examples. The following examples are only used to illustrate the present invention, but are not intended to limit the scope of the present invention.

Example 1

A method for preparing Li-SSZ-13 zeolite molecular sieve comprises the following steps:

(1) Stir and mix lithium hydroxide, a lithium source, and deionized water to mix evenly, add fumed silica, a silicon source, and continue stirring for 2 hours;

(2) adding aluminum hydroxide, an aluminum source, to the structure directing agent OSDA [N,N,N-trimethyl-1-adamantyl ammonium hydroxide (TMAdaOH)], heating and stirring at 80°C for 1 h;

(3) adding the mixed solution obtained in step (2) to the mixed solution obtained in step (1), and stirring for 5 days to obtain a mixed sol; the molar composition of the sol is: _SiO2 / _Al2O3 = ₆₀ , _SiO2 /LiOH=10, _SiO2 /OSDA=3, _H2O / _SiO2 =50;

(4) The mixed sol obtained in step (3) is transferred to a reactor with a polytetrafluoroethylene liner, and placed in a 150°C oven for reaction for 48 hours; the solid phase product obtained by the reaction is washed with deionized water until neutral, placed in a 60°C oven for drying overnight, and then placed in a muffle furnace and calcined at 550°C for 6 hours in an air environment, with a heating and cooling rate of 1°C/min to obtain Li-SSZ-13 zeolite molecular sieve.

Example 2

The same operating steps as in Example 1 were followed, except that the molar composition of the mixed sol obtained in step (3) was: _SiO2 / _Al2O3 = ₆₀ , _SiO2 /LiOH=50, _SiO2 /OSDA=3, _H2O / _SiO2 =50; the solid phase product obtained by the reaction was washed with deionized water until neutral, dried in an oven at 60°C overnight, and then placed in a muffle furnace and calcined at 550°C for 6h in an air environment with a heating and cooling rate of 1°C/min to obtain Li-SSZ-13 zeolite molecular sieve.

Example 3

The same operating steps as in Example 1 were followed, except that the molar composition of the mixed sol obtained in step (3) was: _SiO2 / _Al2O3 = ₆₀ , _SiO2 /LiOH=20, _SiO2 /OSDA=3, _H2O / _SiO2 =50; the solid phase product obtained by the reaction was washed with deionized water until neutral, dried in an oven at 60°C overnight, and then placed in a muffle furnace and calcined at 550°C for 6h in an air environment with a heating and cooling rate of 1°C/min to obtain Li-SSZ-13 zeolite molecular sieve.

Example 4

The same operating steps as in Example 1 were followed, except that the molar composition of the mixed sol obtained in step (3) was: _SiO2 / _Al2O3 = ₆₀ , _SiO2 /LiOH=1, _SiO2 /OSDA=3, _H2O / _SiO2 =50; the solid phase product obtained by the reaction was washed with deionized water until neutral, dried in an oven at 60°C overnight, and then placed in a muffle furnace and calcined at 550°C for 6h in an air environment with a heating and cooling rate of 1°C/min to obtain Li-SSZ-13 zeolite molecular sieve.

Figure 1 is a scanning electron microscope image of the Li-SSZ-13 zeolite molecular sieve prepared in Examples 1 to 4. It can be observed that (a) the Li-SSZ-13 zeolite molecular sieve prepared in Example 1 has a uniform morphology, is cubic, and has a size of about 3 to 4 μm. (b) The Li-SSZ-13 zeolite molecular sieve prepared in Example 2 has a uniform morphology, is cubic, and has a size of about 2 to 3 μm. (c) The Li-SSZ-13 zeolite molecular sieve prepared in Example 3 has a uniform morphology, is spherical, and has a size of about 2 to 3 μm. (d) The Li-SSZ-13 zeolite molecular sieve prepared in Example 4 has a uniform morphology, is ellipsoidal, and has a size of about 2 to 3 μm.

Figure 2 is an X-ray diffraction diagram of the Li-SSZ-13 zeolite molecular sieve prepared in Examples 1 to 4. It can be observed that the Li-SSZ-13 zeolite molecular sieve prepared under various SiO ₂ /LiOH conditions has a typical CHA characteristic diffraction peak, no obvious impurity peak, and high peak intensity; the peak intensity of Example 4 is relatively reduced, which may be due to the increase in the concentration of LiOH and the increase in the pH value of the mixed sol, which has a greater ablation effect on the growth of the molecular sieve than a promotion effect, thereby inhibiting the synthesis of the molecular sieve.

Example 5

The same operating steps as in Example 1 were followed, except that the molar composition of the mixed sol obtained in step (3) was: SiO ₂ /Al ₂ O ₃ =200, SiO ₂ /LiOH=10, SiO ₂ /OSDA=3, H ₂ O/SiO ₂ =50; the solid phase product obtained by the reaction was washed with deionized water until neutral, placed in a 60°C oven for drying overnight, and then placed in a muffle furnace and calcined at 550°C for 6h in an air environment with a heating and cooling rate of 1°C/min. The obtained Li-SSZ-13 zeolite molecular sieve had a CO ₂ adsorption capacity of 85.32 cm ³ /g at 0°C and P/P ₀ =1.

Example 6

The same operating steps as in Example 1 were followed, except that the molar composition of the mixed sol obtained in step (3) was: SiO ₂ /Al ₂ O ₃ =10, SiO ₂ /LiOH=10, SiO ₂ /OSDA=3, H ₂ O/SiO ₂ =50; the solid phase product obtained by the reaction was washed with deionized water until neutral, placed in a 60°C oven for drying overnight, and then placed in a muffle furnace and calcined at 550°C for 6h in an air environment with a heating and cooling rate of 1°C/min. The obtained Li-SSZ-13 zeolite molecular sieve had a CO ₂ adsorption capacity of 88.55 cm ³ /g at 0°C and P/P ₀ =1.

Example 7

The same operating steps as in Example 1 were followed, except that the molar composition of the mixed sol obtained in step (3) was: SiO ₂ /Al ₂ O ₃ =60, SiO ₂ /LiOH=10, SiO ₂ /OSDA=10, H ₂ O/SiO ₂ =10; the solid phase product obtained by the reaction was washed with deionized water until neutral, placed in a 60°C oven for drying overnight, and then placed in a muffle furnace and calcined at 550°C for 6h in an air environment with a heating and cooling rate of 1°C/min. The obtained Li-SSZ-13 zeolite molecular sieve had a CO ₂ adsorption capacity of 90.32 cm ³ /g at 0°C and P/P ₀ =1.

Example 8

The same operating steps as in Example 1 were followed, except that the molar composition of the mixed sol obtained in step (3) was: SiO ₂ /Al ₂ O ₃ =60, SiO ₂ /LiOH=10, SiO ₂ /OSDA=0.8, H ₂ O/SiO ₂ =500; the solid phase product obtained by the reaction was washed with deionized water until neutral, placed in a 60°C oven for drying overnight, and then placed in a muffle furnace and calcined at 550°C for 6h in an air environment with a heating and cooling rate of 1°C/min. The obtained Li-SSZ-13 zeolite molecular sieve had a CO ₂ adsorption capacity of 88.47 cm ³ /g at 0°C and P/P ₀ =1.

Example 9

The same operating steps as in Example 1 were followed, except that the lithium source added in step (1) was lithium hydroxide and lithium chloride, the silicon source was silica sol, the aluminum source added in step (2) was sodium aluminate, and the structure directing agent OSDA was N,N,N-trimethyladamantyl ammonium bromide. The solid phase product obtained by the reaction was washed with deionized water until neutral, dried in an oven at 60°C overnight, and then placed in a muffle furnace and calcined at 550°C for 6h in an air environment with a heating and cooling rate of 1°C/min. The obtained Li-SSZ-13 zeolite molecular sieve had a CO ₂ adsorption capacity of 90.32 cm ³ /g at 0°C and P/P ₀ =1.

Example 10

The same operating steps as in Example 1 were followed, except that the stirring time in step (3) was 0.2 days, the reaction temperature in step (4) was 200° C., and the reaction time was 5 hours. The solid phase product obtained by the reaction was washed with deionized water until neutral, placed in a 60° C. oven for drying overnight, and then placed in a muffle furnace and calcined at 180° C. for 48 hours in an oxygen/ozone mixed environment with a heating and cooling rate of 2° C./min. The obtained Li-SSZ-13 zeolite molecular sieve had a CO ₂ adsorption capacity of 83.76 cm ³ /g at 0° C. and P/P ₀ =1.

Embodiment 11

The same operating steps as in Example 1 were followed, except that the stirring time in step (3) was 7 days, the reaction temperature in step (4) was 120°C, and the reaction time was 240 hours; the solid phase product obtained by the reaction was washed with deionized water until neutral, placed in a 60°C oven for drying overnight, and then placed in a muffle furnace and calcined at 600°C for 4 hours in an oxygen environment, with a heating and cooling rate of 0.2°C/min. The obtained Li-SSZ-13 zeolite molecular sieve had a CO ₂ adsorption capacity of 80.49 cm ³ /g at 0°C and P/P ₀ =1.

Comparative Example 1

(1) Stir and mix sodium hydroxide (sodium source) and deionized water evenly, add fumed silica (silicon source) and continue stirring for 2 hours;

(2) adding aluminum hydroxide, an aluminum source, to the structure directing agent OSDA [N,N,N-trimethyl-1-adamantyl ammonium hydroxide (TMAdaOH)], heating and stirring at 80°C for 1 h;

(3) adding the mixed solution obtained in step (2) to the mixed solution obtained in step (1), and stirring for 24 hours to obtain a mixed sol; the molar composition of the sol is: SiO ₂ /Al ₂ O ₃ = 200, SiO ₂ /NaOH = 5, SiO ₂ /OSDA = 5, H ₂ O/SiO ₂ = 100;

(4) The mixed sol obtained in step (3) is transferred to a reactor with a polytetrafluoroethylene liner, and placed in a 160°C oven for reaction for 4 days; the solid phase product obtained by the reaction is washed with deionized water until neutral, placed in a 60°C oven for drying overnight, and then placed in a muffle furnace and calcined at 550°C for 6h in an air environment, with a heating and cooling rate of 1°C/min to obtain SSZ-13 zeolite molecular sieve.

Figures 5 and 6 are the low-temperature _N2 adsorption isotherms of Li-SSZ-13 and SSZ-13 zeolite molecular sieves prepared in Examples 1 to 4 and Comparative Example 1. It can be seen from the figures that Examples 1 to 4 and Comparative Example 1 present Type I adsorption isotherms. The test results also show that the main pore structure is composed of micropores; the specific surface area of Examples 1 to 4 is also significantly improved relative to Comparative Example 1.

Figure 7 shows the CO ₂ adsorption isotherms of the Li-SSZ-13 zeolite molecular sieves prepared in Examples 1 to 4 and the conventional SSZ-13 zeolite molecular sieve prepared in Comparative Example 1 at 0°C. The test results show that the CO ₂ adsorption performance of the Li-SSZ-13 zeolite molecular sieve is greatly improved compared with the conventional SSZ-13 zeolite molecular sieve, and the maximum adsorption capacity can reach 97.54 cm ³ /g.

Table 1 Low temperature _N2 physical adsorption data of examples and comparative examples

^* Calculated by HK model.

Claims (9)

1. A preparation method of a Li-SSZ-13 zeolite molecular sieve is characterized by comprising the following specific steps:

(1) Stirring and mixing a lithium source and deionized water uniformly, adding a silicon source, and continuously stirring uniformly;

(2) Adding an aluminum source into a structure directing agent OSDA, heating, stirring and uniformly mixing;

(3) Adding the mixed solution obtained in the step (2) into the mixed solution obtained in the step (1), and fully stirring for a certain time to obtain mixed sol; the sol has the molar composition of ：SiO₂/Al₂O₃=10~200,SiO₂/LiOH=1~50,SiO₂/OSDA=0.8~10,H₂O/SiO₂=10~500;

(4) Transferring the mixed sol obtained in the step (3) to a reaction kettle with a polytetrafluoroethylene lining, and putting the reaction kettle into an oven for reaction; washing the solid phase product obtained by the reaction to be neutral by deionized water, drying and roasting to obtain the Li-SSZ-13 zeolite molecular sieve.

2. The method for preparing a Li-SSZ-13 zeolite molecular sieve according to claim 1, wherein in step (1), the lithium source is lithium hydroxide, lithium chloride, lithium carbonate or lithium sulfate.

3. The method for preparing a Li-SSZ-13 zeolite molecular sieve according to claim 1, wherein in step (1), the silicon source is tetraethyl orthosilicate, tetramethyl orthosilicate, fumed silica, sodium silicate, silica sol, or water glass.

4. The method for preparing a Li-SSZ-13 zeolite molecular sieve according to claim 1, wherein in the step (2), the aluminum source is sodium metaaluminate, aluminum hydroxide, aluminum boehmite, aluminum n-butoxide, aluminum isopropoxide, aluminum powder or aluminum foil.

5. The method for preparing a Li-SSZ-13 zeolite molecular sieve according to claim 1, wherein in step (2), the structure directing agent OSDA is N, N-trimethyl adamantylammonium hydroxide, N, N-trimethyl adamantyl ammonium bromide, N, N, N-trimethyl adamantyl ammonium iodide, N, N, N-trimethyl benzyl ammonium bromide, N, N, N-trimethylbenzyl ammonium iodide, tetraethylammonium hydroxide, or N, N-trimethylbenzyl ammonium hydroxide.

6. The method for preparing a Li-SSZ-13 zeolite molecular sieve according to claim 1, wherein in the step (2), the heating temperature is 50-200 ℃.

7. The method for producing a Li-SSZ-13 zeolite molecular sieve according to claim 1, wherein in the step (3), the stirring time is 0.2 to 7 days.

8. The method for preparing a Li-SSZ-13 zeolite molecular sieve according to claim 1, wherein in the step (4), the reaction temperature is 120-200 ℃ and the reaction time is 5-240 h.

9. The method for preparing the Li-SSZ-13 zeolite molecular sieve according to claim 1, wherein in the step (4), the roasting environment is nitrogen, air, oxygen, ozone or oxygen/ozone mixture, the roasting temperature is 180-600 ℃, the roasting time is 4-48 h, and the heating and cooling rates are 0.2-2 ℃ per minute.