CN114804144A - Low silicon/aluminum ratio nano Beta molecular sieve and synthetic method thereof - Google Patents

Abstract

The invention relates to a low silicon/aluminum ratio nanometer Beta molecular sieve and a synthesis method thereof, wherein the Beta molecular sieve has a three-dimensional 12-membered ring pore channel structure, has excellent performance for larger molecular reaction and plays an important role in the field of petrochemical industry. The invention provides a preparation method of low silicon/aluminum ratio nanometer Beta, which comprises the following steps: mixing and dissolving water and an alkali source, adding an aluminum source, uniformly mixing, adding a double-head quaternary ammonium salt serving as an organic template agent, adding a silicon source, stirring and mixing to form a gel precursor, and transferring to an oven for hydrothermal crystallization for a period of time at a certain temperature. And (3) carrying out suction filtration, washing and drying on the reactant to obtain Beta molecular sieve raw powder. The Beta molecular sieve synthesized by the invention has the size of 10-50nm and improves the acid siteThe number of the dots is simultaneously beneficial to the diffusion of molecules; the synthesis method has the advantages of less template agent consumption and synthesis system H ₂ Low O/Si content, high product yield and the like, and is very suitable for batch production and amplification.

Description

A kind of low silicon/aluminum ratio nano Beta molecular sieve and synthesis method

technical field

The present invention designs the field of molecular sieve synthesis methods, in particular to a synthesis method of a low silicon/aluminum ratio nano-Beta molecular sieve.

Background technique

Beta molecular sieve has a three-dimensional 12-membered ring pore structure, which has important uses in the catalytic reaction of macromolecules, such as in the field of petrochemical production. For this kind of reaction, carbon deposition is generally serious, which leads to blockage of pores and thus deactivation. Therefore, it is of great significance to improve the diffusion properties of catalysts. Among them, hierarchical porous nanostructured molecular sieves have attracted more and more attention, and they have higher acid sites. Use efficiency, and can shorten the diffusion path and reduce side reactions to generate carbon deposits.

In recent years, there have been some strategies to synthesize nano-Beta molecular sieves. Ding et al. (Micropor. Mesopor. Mater., 2006, 94, 1) used tetraethylammonium hydroxide (TEAOH) as a template agent under dynamic crystallization conditions to synthesize Beta molecular sieves (SiO ₂ /Al with a particle size of about 30 nm) ₂ O ₃ =32), this method requires the addition of a large amount of quaternary ammonium stencil (TEAOH/SiO ₂ =0.6); Zhang et al. A variety of nano-Beta molecular sieves with grain size in the range of 10-106nm and SiO ₂ /Al ₂ O ₃ adjustable in the range of 12-600 were synthesized by crystallization method. This method also needs to add a large amount of quaternary ammonium salt template agent (TEAOH /SiO ₂ =0.55) and amino acids (L-lysine/SiO ₂ =0.1-0.3). Chio et al. (Chem. Commun., 2009, 2845) synthesized hierarchically porous nano-Beta zeolite through pseudocrystal transformation of mesoporous gels at the nanoscale, using organic cyclic biquaternary ammonium salts as templates to synthesize 10-15nm Beta molecular sieve (SiO ₂ /Al ₂ O ₃ =30); Liu et al. (J.Mater.Chem., 2012, 22, 18631) used a complex long-chain polyquaternium salt surfactant ([ C ₁₆ H ₃₃ -N ⁺ (CH ₃ ) ₂ -C ₆ H ₁₂ -N ⁺ (CH ₃ ) ₂ -CH ₂ -(pC ₆ H ₄ )-CH ₂ -N ⁺ (CH ₃ ) ₂ -C ₆ H ₁₂ -N ⁺ ( _CH3 ) ₂ - _CH2- ( _pC6H4 ) _{-CH2 -} N ⁺ ( _CH3 ) _{2 - C6H12} - _N ⁺ ( _CH3 ) ₂ - _C16H33 ][ Br ^- ] ² [Cl ^- ] ₄ ) synthesized Beta zeolite with a particle size of about 10-30 nm (SiO ₂ /Al ₂ O ₃ =32); Kore et al. (RSC Adv., 2013, 3, 1317) also used complex Beta molecular sieves (SiO ₂ /Al ₂ O ₃ =32) with a particle size of about 10-20 nm were synthesized using polyquaternium salts as template agents. To sum up, the Beta zeolite obtained by the above method has a high silicon-to-aluminum ratio, generally has a low Al content, and the used organic template has a complex structure.

Therefore, it is necessary to find a more convenient and low-cost method to synthesize nano-Beta with high aluminum content and low silicon/aluminum ratio.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a simpler biquaternary ammonium salt as an organic template agent, and to synthesize a low silicon/aluminum ratio nano-Beta zeolite.

Provided is a method for hydrothermally synthesizing low silicon/aluminum ratio nano-Beta molecular sieves, comprising the following steps:

After mixing the alkali source and deionized water evenly, add the aluminum source and stir to dissolve, continue to add the biquaternary ammonium salt organic template, add the silicon source after dissolving to form a gel precursor, and transfer it to an oven at 130-170 degrees dynamic hydrothermal In 2-10 days, the reaction product is cooled, filtered, washed and dried to obtain the original powder of Beta molecular sieve;

The amount of each reaction raw material added was controlled so that the molar ratio of the following components in the reaction system was SiO ₂ : 0.025-0.083Al ₂ O ₃ : 0.03-0.13M ₂ O : 0.015-0.2SDA: 8-40H ₂ O, The preferred molar ratio range is SiO ₂ : 0.04-0.07Al ₂ O ₃ : 0.06-0.1M ₂ O: 0.025-0.1 SDA: 10-25H ₂ O, M is alkali metal Na, K or Na and K, SDA is biquaternary Ammonium salt templating agent.

In the present invention, the aluminum source is metal aluminum powder, sodium metaaluminate, aluminum nitrate, aluminum sulfate, and a mixture of two or more thereof in a certain proportion.

In the present invention, the bisquaternary ammonium salt template agent includes 1,6-bistriethylenediaminohexane bromide, 1,4-bistriethylenediaminobutane bromide, 1,5-bistriethylenediaminobutane bromide, Triethylenediaminopentane bromide or 1,4-bistriethylenediamine p-xylene chloride, or a mixture of two or more thereof in a certain proportion.

In the present invention, the silicon source is water glass, silica sol, fumed silica, ethyl orthosilicate, or a mixture of two or more thereof in a certain proportion. In the present invention, the diquaternary ammonium salt template agent 1 , 6-bistriethylenediaminohexane bromide is prepared by the following method:

Dissolve triethylenediamine in the ethanol solution, then add a certain amount of 1,6-dibromohexane, stir to dissolve, stir and reflux at 80 degrees for 24 hours, and then rotate to evaporate the solid, filter and wash with ether, vacuum Dry in an oven at 50 degrees for 12 hours to obtain an organic template agent 1,6-bistriethylenediaminohexane bromide salt

In the present invention, the bisquaternary ammonium salt template agent 1,4-bistriethylenediaminobutane bromide is prepared by the following method:

Dissolve triethylenediamine in ethanol solution, then add a certain amount of 1,4-dibromohexane, stir to dissolve, stir and reflux at 80 degrees for 24 hours, then rotate to evaporate the solid, filter and wash with ether, vacuum Dry in an oven at 50 degrees for 12 hours to obtain an organic template agent 1,4-bistriethylenediaminobutane bromide

In the present invention, the bis-quaternary ammonium salt template agent 1,4-bistriethylenediamine p-xylene chloride is prepared by the following method:

Dissolve triethylenediamine in ethanol solution, then add a certain amount of 1,4-dichloro-p-xylene, stir to dissolve, stir and reflux at 80 degrees for 24 hours, and then rotate to evaporate the solid, filter and wash with ether, Dry in a vacuum oven at 50 degrees for 12 hours to obtain an organic template agent 1,4-bistriethylenediamine p-xylene chloride

In the present invention, the silicon source is water glass, silica sol, fumed silica, or a mixture of two or more thereof in a certain proportion.

Compared with the present synthetic method, the present invention has the advantages of:

1. The present invention adopts an organic structure-directing agent with simpler and cheaper structure, easy-to-obtain raw materials and simple synthesis to synthesize ultra-small and low-silicon/aluminum ratio nano-Beta molecular sieve, and the silicon-aluminum ratio can be as low as SiO ₂ /Al ₂ O ₃ =15 -20, and the size is only 10-20nm.

2. The synthesized nano-Beta molecular sieve has abundant hierarchical pores, which can improve the utilization efficiency and diffusion efficiency of the acidic site of the molecular sieve, and has potential application value in petrochemical industry.

Description of drawings

Fig. 1. XRD spectrum of the product of Example 1;

Figure 2. SEM image of the product of Example 1;

Fig. 3. XRD pattern of embodiment 2 product;

Figure 4. SEM image of the product of Example 2;

Fig. 5. XRD pattern of embodiment 3 product;

Figure 6. TEM image of the product of Example 3;

Fig. 7. XRD pattern of embodiment 4 product;

Figure 8. TEM image of the product of Example 4;

Figure 9. XRD pattern of the product of Example 5;

Figure 10. TEM image of the product of Example 5;

Figure 11. XRD pattern of the product of Example 6;

Figure 12. TEM image of the product of Example 6;

Figure 13. XRD pattern of the product of Example 7.

Detailed ways

The 1,6-bis-triethylenediaminohexane bromide used is prepared by the following method: dissolve 26g of triethylenediamine in 130mL of ethanol solution, then add 24.4g of 1,6-dibromohexane, stir to dissolve, The mixture was stirred and refluxed at 80 degrees for 24 hours, then the solid was separated out by rotary evaporation, filtered and washed with diethyl ether, and dried in a vacuum oven at 50 degrees for 12 hours to obtain the organic template 1,6-bistriethylenediaminohexane bromide salt.

The 1,4-bis-triethylenediaminobutane bromide used is prepared by the following method: dissolve 20 g of triethylenediamine in 80 mL of ethanol solution, then add a certain amount of 1,4-dibromohexane, stir to dissolve , stirred and refluxed at 80 degrees for 24 hours, then rotary-evaporated to separate out the solid, filtered and washed with ether, and dried in a vacuum oven at 50 degrees for 12 hours to obtain the organic template 1,4-bistriethylenediaminobutane bromide salt.

The 1,4-bistriethylenediamine-based p-xylene chloride used is prepared by the following method: Dissolve 20 g of triethylenediamine in 80 mL of ethanol solution, then add 10 g of 1,4-dichloro-p-xylene, stir to dissolve , stirred and refluxed at 80 degrees for 24 hours, then rotary-evaporated to separate out the solid, filtered and washed with ether, and dried in a vacuum oven at 50 degrees for 12 hours to obtain the organic template 1,4-bistriethylenediamine p-xylene chloride salt.

Example 1

Mix 2g NaOH and 2.5g Al(NO ₃ ) ₃ ·9H ₂ O, add 60g water for stirring and dissolving, then add 2g 1,6-bistriethylenediaminohexane bromide as a template agent, and after stirring evenly, Add 10 g of silica sol with a mass concentration of 40% silica, stir evenly to form a gel precursor, age at 25 degrees for 10 hours, transfer to an oven at 160 degrees for dynamic hydrothermal crystallization for 6 days, cool and suction, filter and wash, dry Dried to get the product. The product was calcined at 550 degrees for 10 hours and weighed, and the calculated product yield (based on the sum of the mass of SiO ₂ and Al ₂ O ₃ in the raw material) was 87%.

Figure 1 is the XRD spectrum corresponding to the product, and Figure 2 is the SEM image corresponding to the product. It can be seen from the figure that the structure of the product is Beta molecular sieve by X-ray diffraction analysis, and it can be seen from the electron microscope photo that the product is in the form of nanoparticles, and the size is 10-50nm.

Example 2

Dissolve 1g of NaOH in 60g of water, add 0.18g of Al powder and stir to dissolve, then add 2g of 1,5-bistriethylenediaminohexane bromide as a template agent, after stirring evenly, add 10g of silica containing 40% The silica sol was stirred evenly to form a gel precursor, aged at 60 degrees for 3 hours, transferred to an oven at 160 degrees for dynamic hydrothermal crystallization for 3 days, cooled, filtered and washed, and dried to obtain the product. The product was calcined at 550 degrees for 10 hours and weighed, and the calculated product yield (based on the sum of the mass of SiO ₂ and Al ₂ O ₃ in the raw material) was 71%.

Fig. 3 is the XRD spectrum corresponding to the product, and Fig. 4 is the SEM image corresponding to the product. It can be seen from the figure that the structure of the product is a mixed phase of Beta and Anaclime-C molecular sieves by X-ray diffraction analysis. It can be seen from the electron microscope photos that the product has a nanoparticle shape with a size of 50-500nm.

Example 3

Mix 1.6g NaOH and 2.6g Al ₂ (SO ₄ ) ₃ , add 40g water for stirring and dissolving, then add 1g 1,6-bistriethylenediaminohexane bromide and 2g 1,4-bistriethylenedi Aminobutane bromide was used as a template agent. After stirring evenly, 8 g of fumed silica was added to form a gel precursor, which was aged at 30 degrees for 5 hours, and transferred to an oven at 150 degrees for dynamic hydrothermal crystallization for 3 days. After cooling, suction filtration and washing, drying is performed to obtain the product. The product was calcined at 550 degrees for 10 hours and weighed, and the calculated product yield (based on the sum of the mass of SiO ₂ and Al ₂ O ₃ in the raw material) was 94%.

Figure 5 is the XRD spectrum corresponding to the product, and Figure 6 is the transmission electron microscope (TEM) photo corresponding to the product. It can be seen from the figure that the structure of the product is a pure phase of Beta molecular sieve by X-ray diffraction analysis, and it can be seen from the electron microscope photos that the product is a nanoparticle shape with a size of 10-20nm.

Example 4

Mix 2g NaOH and 1.457g NaAlO ₂ , add 30g water to stir and dissolve, then add 1g 1,6-bis-triethylenediaminohexane bromide and 1g 1,4-bis-triethylenediamine-p-xylene chloride Salt is used as a template agent. After stirring evenly, 5g of fumed silica is added to form a gel precursor, aged at 40 degrees for 5 hours, transferred to an oven at 150 degrees for dynamic hydrothermal crystallization for 6 days, and washed with cooling and suction filtration. , drying to get the product. The product was calcined at 550 degrees for 10 hours and weighed, and the calculated product yield (based on the sum of the mass of SiO ₂ and Al ₂ O ₃ in the raw material) was 88%.

FIG. 7 is the XRD spectrum corresponding to the product, and FIG. 8 is the transmission electron microscope (TEM) photo corresponding to the product. It can be seen from the figure that the structure of the product is a pure phase of Beta molecular sieve by X-ray diffraction analysis, and it can be seen from the electron microscope photos that the product is a nanoparticle shape with a size of 10-20nm.

Example 5

Mix 1.3g NaOH with 0.5g NaAlO ₂ and 1.6g Al ₂ (SO ₄ ) ₃ , add 40g water for stirring and dissolving, then add 3g 1,5-bistriethylenediaminopentane bromide as template agent, stir After homogenization, add 21 g of ethyl orthosilicate, stir evenly to form a gel precursor, and volatilize ethanol at a 40-degree opening for 6 hours, transfer it to an oven at 140-degree dynamic hydrothermal crystallization for 8 days, cool, suction, filter, wash, and dry. Dried to get the product. The product was calcined at 550 degrees for 10 hours and weighed, and the calculated product yield (based on the sum of the mass of SiO ₂ and Al ₂ O ₃ in the raw material) was 91%.

Figure 9 is the XRD spectrum corresponding to the product, and Figure 10 is the transmission electron microscope (TEM) photo corresponding to the product. It can be seen from the figure that the structure of the product is a pure phase of Beta molecular sieve by X-ray diffraction analysis, and it can be seen from the electron microscope photos that the product is a nanoparticle shape with a size of 10-20nm.

Example 6

Dissolve 1.2g of KOH and 1g of NaOH in 30g of deionized water, add 1.3g of boehmite powder and stir to dissolve, then add 3g of 1,4-bistriethylenediamine p-xylene chloride as a template agent, and after stirring evenly, Add 8g of fumed silica, stir evenly to form a gel precursor, age at 40 degrees for 3 hours, transfer to an oven for 150 degrees of dynamic hydrothermal crystallization for 5 days, cool, suction, filter, wash, and dry to obtain the product. The product was calcined at 550 degrees for 10 hours and weighed, and the calculated product yield (based on the sum of the mass of SiO ₂ and Al ₂ O ₃ in the raw material) was 95%.

Figure 11 is the XRD spectrum corresponding to the product, and Figure 12 is the transmission electron microscope (TEM) photo corresponding to the product. It can be seen from the figure that the structure of the product is a pure phase of Beta molecular sieve by X-ray diffraction analysis, and it can be seen from the electron microscope photo that the product is a nanoparticle shape with a size of 10-50nm.

Example 7

Mix 1.0g NaOH and 1.457g NaAlO ₂ , add 40g water for stirring and dissolving, then add 3g 1,4-bistriethylenediamine p-xylene chloride as a template agent, after stirring evenly, add 10g containing 40% Silica sol of silicon dioxide and 4g fumed silica, stirred evenly to form a gel precursor, aged at 50 degrees for 3 hours, transferred to an oven at 150 degrees for dynamic hydrothermal crystallization for 3 days, cooled, suction filtered, washed, and dried get product. The product was calcined at 550 degrees for 10 hours and weighed, and the calculated product yield (based on the sum of the mass of SiO ₂ and Al ₂ O ₃ in the raw material) was 90%.

Figure 13 is the XRD spectrum corresponding to the product. It can be seen from the figure that the structure of the product is pure Beta molecular sieve phase by X-ray diffraction analysis.

Comparative example

The preparation of hydrogen type Beta molecular sieve catalyst: after a certain amount of Beta molecular sieve gained in Example 3 was roasted at 550 degrees, it was added to the NH ₄ Cl solution of 2 mol/L, and the molecular sieve mass and NH ₄ Cl solution volume ratio was 1:30, The temperature was 80 degrees, exchanged for 6 hours, and washed with suction, repeated three times. Then calcined at 540 degrees Celsius for 5 hours in an air atmosphere to obtain the corresponding hydrogen-type Beta molecular sieve. The molecular sieves obtained in Example 4 and Example 5 and commercial Na-Beta molecular sieves (silicon-aluminum ratio: SiO ₂ /Al ₂ O ₃ =40) were exchanged and calcined in the same manner to obtain corresponding hydrogen-type molecular sieves.

Catalytic reaction test:

Alkylation reaction test of benzene and benzyl alcohol: add 39 g of benzene, 5.4 g of benzyl alcohol, and 1 g of hydrogen-type Beta molecular sieve into a round-bottomed flask, and react under reflux at 80 degrees for 5 hours with stirring, and take samples for chromatographic analysis. The results are shown in Table 1, the Beta molecular sieves obtained in Examples 3, 4 and 5 have much higher conversion and benzylbenzene selectivity than commercial Beta molecular sieves.

Alkylation reaction test of naphthalene and isopropanol: The reaction adopts a fixed bed method, naphthalene, isopropanol and cyclohexane are mixed in a molar ratio of 1/2/10, and the mixed solution is injected into the catalyst by a high performance liquid chromatography pump In the bed layer, the reaction temperature was 200 degrees, the pressure was 1 atm, and the feed space velocity was WHSV=5h ^-1 ; the condensed liquid was collected and sampled for chromatographic analysis. Table 2 shows the analytical results of samples collected 2-3 hours after the start of the reaction. The results show that the Beta molecular sieves obtained in Examples 3, 4 and 5 have much higher conversions than commercial Beta molecular sieves.

Table 1. Test results of benzene and benzyl alcohol alkylation reaction catalyst Benzyl alcohol conversion/% Benzylbenzene selectivity/% Commercial Beta 10 59 Example 3 53 73 Example 4 47 67 Example 5 59 76

Table 2. Test results of naphthalene and isopropanol alkylation reaction

Claims (9)

1. a method for synthesizing low silicon/aluminum ratio nano Beta molecular sieve, comprising the steps: After mixing and stirring the alkali source, aluminum source (in terms of Al ₂ O ₃ ) and water (in terms of H 2 O ), add double-ended quaternary ammonium salt template agent (in terms of SDA), and continue to add silicon source (in terms of amount of H ₂ O). Calculated by SiO ₂ ) stirring, aging to form a gel precursor, after dynamic hydrothermal crystallization, solid-liquid separation, washing and drying of the solid to obtain powder Beta molecular sieve _; It is a mixture of one or two of NaOH or KOH; The amount of reaction raw materials added, the molar ratio of each component is in the range of SiO ₂ : 0.025-0.083Al ₂ O ₃ : 0.03-0.13M ₂ O: 0.015-0.2SDA: 8-40H ₂ O, the preferred molar ratio range is SiO ₂ : 0.04-0.07Al ₂ O ₃ : 0.06-0.1 M ₂ O: 0.025-0.1 SDA: 10-25 H ₂ O. 2. the method for synthesizing low silicon/aluminum ratio nano Beta molecular sieve according to claim 1, is characterized in that: described aluminum source is one or two in metal aluminum powder, sodium metaaluminate, aluminum nitrate, aluminum sulfate more than one mixture. 3. the method for synthesizing low silicon/aluminum ratio nano Beta molecular sieve according to claim 1, is characterized in that: described double quaternary ammonium salt template agent comprises 1,6-bis-triethylenediaminohexane bromide, 1,4-Bistriethylenediaminobutane bromide, 1,5-bistriethylenediaminepentane bromide or 1,4-bistriethylenediamine-p-xylene chloride, medium one or a mixture of two or more. 4. the method for synthesizing low silicon/aluminum ratio nano Beta molecular sieve according to claim 1, is characterized in that: described silicon source is a kind of in water glass, silica sol, fumed silica, tetraethyl orthosilicate or a mixture of two or more. 5. the method for synthesizing low silicon/aluminum ratio nano Beta molecular sieve according to claim 1, is characterized in that: described hydrothermal temperature is 110-190 degree, and preferred hydrothermal temperature is 140-170 degree, more preferably The crystallization temperature was 150 degrees. 6. the method for synthesizing low silicon/aluminum ratio nano Beta molecular sieve according to claim 1 or 5, is characterized in that: described dynamic hydrothermal time is 1-10 days, and preferred hydrothermal time is 2-7 days, A more preferred hydrothermal time is 3-5 days. 7. The method for synthesizing low silicon/aluminum ratio nano-Beta molecular sieves according to claim 1, wherein the temperature of the described aging step is 20-80 degrees, and the preferred temperature is 30-60 degrees. 8. the synthetic low silicon/aluminum ratio nano Beta molecular sieve method according to claim 1 or 7, is characterized in that, described ageing step needs 0.5-24 hour, and preferred ageing time is 2-15 hour, more The preferred time is 2-5 hours. 9 . A nano-Beta molecular sieve with a low silicon/aluminum ratio obtained by the method of claim 1 , wherein the molecular sieve has a grain size of 10-50 nm. 10 .

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