阅读说明：本技术 一种动态合成纳米kl分子筛的方法及应用 (Method for dynamically synthesizing nano KL molecular sieve and application ) 是由 王苹 李珂 陈会民 丁湘浓 王熙 于 2021-09-03 设计创作，主要内容包括：本发明公开一种动态合成纳米KL分子筛的方法,涉及沸石制备技术领域。其为将钾源、铝源、硅源和水混合制得溶胶,经陈化和晶化等步骤后制得。本发明可在低硅铝比投料、不加模板剂和结构导向剂的条件下,合成出具有高结晶度和多级孔结构的KL分子筛。将本发明所提供的KL分子筛用于低碳烷烃芳构化反应中,可以明显提高芳烃收率特别是C8芳烃收率。与传统方法相比,该方法制备工艺简单,原料利用率高,成本低,具有广阔的应用前景。(The invention discloses a method for dynamically synthesizing a nano KL molecular sieve, and relates to the technical field of zeolite preparation. The preparation method comprises the steps of mixing a potassium source, an aluminum source, a silicon source and water to prepare sol, aging, crystallizing and the like. The method can synthesize the KL molecular sieve with high crystallinity and a hierarchical pore structure under the conditions of feeding with low silicon-aluminum ratio and without adding a template agent and a structure directing agent. When the KL molecular sieve provided by the invention is used in the aromatization reaction of low-carbon alkane, the yield of aromatic hydrocarbon, particularly C8 aromatic hydrocarbon, can be obviously improved. Compared with the traditional method, the method has the advantages of simple preparation process, high utilization rate of raw materials, low cost and wide application prospect.)

1. A method for dynamically synthesizing a nano KL molecular sieve is characterized by comprising the following steps: comprises the following steps of (a) carrying out,

(1) k mixing potassium source, aluminum source, silicon source and water₂O:Al₂O₃:SiO₂:H₂Mixing O0.1-9: 1:1-20:50-500 molar ratio to prepare sol;

(2) stirring and aging the sol prepared in the step (1);

(3) and (3) placing the aged sol prepared in the step (2) in a closed container, and crystallizing for 6h-10d at the temperature of 110 ℃ and 250 ℃.

2. The method for dynamically synthesizing nano KL molecular sieves according to claim 1, wherein the method comprises the following steps: in the step (1), the molar ratio of the potassium source, the aluminum source, the silicon source and the water is K₂O:Al₂O₃:SiO₂:H₂O＝0.5-5:1:3-16:70-400。

3. The method for dynamically synthesizing nano KL molecular sieves according to claim 1, wherein the method comprises the following steps: the volume of the closed container is 30mL-1m³。

4. The method for dynamically synthesizing nano KL molecular sieves according to claim 1, wherein the method comprises the following steps: the crystallization process is dynamic crystallization.

5. The method for dynamically synthesizing nano KL molecular sieves according to claim 4, wherein the method comprises the following steps: the crystallization temperature in the crystallization process is 185 ℃ and the crystallization time is 6-36 h.

6. The method for dynamically synthesizing nano KL molecular sieves according to claim 1, wherein the method comprises the following steps: the aging temperature is room temperature, and the aging time is 4-24 h.

7. The method for dynamically synthesizing nano KL molecular sieves according to claim 1, wherein the method comprises the following steps: the potassium source is one or more than two of potassium hydroxide, potassium chloride and potassium oxide.

8. The method for dynamically synthesizing nano KL molecular sieves according to claim 1, wherein the method comprises the following steps: the aluminum source is one or more than two of pseudo-boehmite, activated alumina, aluminum hydroxide, aluminum isopropoxide, hydrated alumina, potassium aluminate, aluminum trichloride, aluminum sulfate and aluminum nitrate.

9. The method for dynamically synthesizing nano KL molecular sieves according to claim 1, wherein the method comprises the following steps: the silicon source is one or more than two of silica sol, ethyl orthosilicate, white carbon black and water glass.

10. The use of the nano KL molecular sieve prepared by the method for dynamically synthesizing the nano KL molecular sieve according to any one of claims 1 to 9, as a carrier for preparing a catalyst for aromatization of lower alkanes.

Technical Field

The invention relates to the technical field of molecular sieves, in particular to a method for dynamically synthesizing a nano KL molecular sieve and application thereof.

Background

The LTL zeolite belongs to a hexagonal system, a framework consists of cancrinite cages (CAN cages) and hexagonal column cages (D6R), the CAN cages and the D6R cages are alternately connected around a six-fold axis direction of a C axis, and then the cage rotates according to the six-fold axis to generate a one-dimensional twelve-membered ring circular pore channel structure with a twelve-membered ring, so that the zeolite has good hydrothermal stability. The widest part of the main pore diameterThe narrowest point is aboutBelongs to the group of large-pore zeolites (Monatsheftete fur Chemie/Chemical Monthly,2005,136(1): 77-89). The LTL zeolite has unique adsorption performance and catalytic performance, has good thermal stability, and is a catalytic material with excellent thermal stability; can be used as a catalyst for preparing hydrocarbon conversion processes such as cracking, isomerization, aromatization, alkylation, lube hydrocracking and the like. Wherein, the Pt/KL catalyst prepared by taking LTL zeolite as a carrier is widely applied to aromatization reaction.

The Pt/LTL catalyst is a base-catalyzed aromatization catalyst with excellent aromatization performance, and has the advantages of high liquid yield and high aromatic yield compared with acid-catalyzed aromatization. However, the low selectivity of the catalyst to aromatics and the short single-pass life are the main defects, and the industrial application of the catalyst is limited. To improve catalyst stability, LTL zeolites have been modified in a number of ways.

In the technical scheme disclosed in U.S. patent application publication No. US5773381, Cs-containing L zeolite is prepared by adding Cs ions during the synthesis of LTL zeolite, and the zeolite can be used for aromatic isomerization or aromatization reaction.

According to the technical scheme disclosed by the Chinese invention patent application with the patent application number of CN201310137862.4, the structure and the property of the prepared FeKL heteroatom zeolite are changed by introducing the heteroatom Fe, and the catalyst loaded with Pt has better n-hexane aromatization performance.

The Chinese patent application with the publication number of CN101746774A discloses a method for synthesizing LTL zeolite containing Sn heteroatom, and the catalyst prepared by using the zeolite to load Pt not only has higher benzene selectivity but also has better stability when used in n-hexane aromatization reaction.

However, the above prior art still has the condition of carbon deposition and the like, which has adverse effect on arylation.

In the process of synthesizing KL zeolite, how to increase the yield of KL zeolite has been a concern, and researchers have done a lot of work to solve the problem of low yield.

In the technical scheme disclosed by the invention patent with the publication number of CN85103013B, the silicon-aluminum ratio in the feeding of a synthesis system is improved, and the feeding ratio (molar ratio) is 6.6K₂O:Al₂O₃:28SiO₂:440H₂O, and crystallizing the KL zeolite for 60 to 72 hours at the temperature of 100 ℃ in a pressure kettle. However, the technical scheme has the main problems of higher silicon-aluminum ratio of the fed materials, low silicon utilization rate and high synthesis cost.

The Chinese patent application with the publication number of CN1070383A discloses a technical scheme that L zeolite can be synthesized by adding a guiding agent under the conditions of lower silica-alumina ratio and alkali-silica ratio. Although the directing agent provides crystal nuclei for the synthesis of the L zeolite, thereby accelerating the crystallization speed, the directing agent needs 72 hours for aging, and the time is long, so that the industrial production efficiency is influenced.

U.S. Pat. publication No. US3947482 discloses that L zeolite can be synthesized by adding an organic templating agent to a substrate, but the introduction of the templating agent increases the difficulty of post-treatment, adversely affects the crystal structure of the zeolite during removal of the templating agent, and increases the synthesis cost.

Disclosure of Invention

The first purpose of the present invention is to overcome the deficiencies of the prior art, and to provide a method for dynamically synthesizing a KL molecular sieve, which can improve the yield of L-type zeolite and reduce the synthesis cost; the diffusion path of molecules is shortened, so that the aromatic selectivity of the catalyst is improved, and the one-way service life of the catalyst is prolonged; hetero atoms are introduced to improve the performance of the molecular sieve carrier; the synthesis process is successfully subjected to pilot test, so that the synthesis process is closer to industrialization.

The invention also aims to provide application of the dynamically synthesized nano KL molecular sieve in preparing a catalyst for aromatization of low-carbon alkane.

In order to achieve the purpose of the invention, the invention adopts the technical scheme that:

a dynamically synthesized KL molecular sieve has an LTL structure confirmed by the International Zeolite Association, and is synthesized by mixing a potassium source, an aluminum source, a silicon source and water to prepare sol, and aging and crystallizing the sol to obtain the KL molecular sieve with high crystallinity.

Specifically, the method for dynamically synthesizing the nano KL molecular sieve comprises the following steps:

(1) k mixing potassium source, aluminum source, silicon source and water₂O:Al₂O₃:SiO₂:H₂Mixing O0.1-9: 1:1-20:50-500 molar ratio to obtain sol,

(2) stirring and aging the sol prepared in the step (1),

(3) and (3) placing the aged sol prepared in the step (2) in a closed container, and crystallizing at the temperature of 110-250 ℃ for 6h-10d to obtain the high-crystallinity LTL molecular sieve.

Preferably, the molar ratio of the potassium source to the aluminum source to the silicon source to the water is K₂O:Al₂O₃:SiO₂:H₂O ═ 0.5-5:1:3-16: 70-400. The silicon-aluminum ratio of the fed material is low, the product is well crystallized, and the yield can reach 91 percent.

The volume of the closed container is 30mL-1m³From pilot to pilot.

The crystallization process is static crystallization.

Preferably, the crystallization process is dynamic crystallization. The above-mentionedDynamic crystallization to simulate industrial production conditions and is between 10L and 1m³And successfully crystallizing in a closed kettle to obtain the KL type molecular sieve with high crystallinity.

Preferably, the crystallization temperature in the crystallization process is 120-185 ℃, and the crystallization time is 6-36 h.

The aging temperature is room temperature, and the aging time is 4-24 h.

The potassium source is one or more than two of potassium hydroxide, potassium chloride and potassium oxide.

The aluminum source is one or more than two of pseudo-boehmite, activated alumina, aluminum hydroxide, aluminum isopropoxide, hydrated alumina, potassium aluminate, aluminum trichloride, aluminum sulfate and aluminum nitrate.

The silicon source is one or more than two of silica sol, ethyl orthosilicate, white carbon black and water glass.

The invention discloses application of a dynamically synthesized nano KL molecular sieve as a carrier for preparing a catalyst for aromatization of low-carbon alkane.

One or more than two metals of Pt, Ru, Pd and Sn are loaded on the carrier, and the loading amount of the metals is 0.05-4.0%.

Wherein, the aromatization of the normal alkane can be carried out in a fixed bed reactor, and the number of carbon atoms in the normal alkane is 6, 7 or 8.

The reaction conditions of the aromatization may specifically be: the mass space velocity of the normal alkane is 0.8 to 4h^-1The molar ratio of the hydrogen to the normal alkane is 0.2-6.0:1, the reaction pressure is 0.1-3MPa, and the reaction temperature is 250-550 ℃.

Compared with the prior art, the invention has the following advantages and effects: synthesizing a KL molecular sieve with high crystallinity and a hierarchical pore structure under the conditions of feeding with a low silicon-aluminum ratio and without adding a template agent and a structure directing agent; when the KL molecular sieve provided by the invention is used in the aromatization reaction of low-carbon alkane, the yield of aromatic hydrocarbon, particularly C8 aromatic hydrocarbon, can be obviously improved; compared with the traditional method, the preparation method has the advantages of simple preparation process, high raw material utilization rate, low cost and wide application prospect, and the yield can reach 91%.

Drawings

FIG. 1 is an XRD spectrum of a sample of example 1 of the present invention;

FIG. 2 is a graph showing the physical adsorption of the sample in example 1 of the present invention;

FIG. 3 is an SEM photograph of a sample in example 1 of the present invention.

Detailed Description

The present invention is further illustrated by the following examples, but the scope of the invention is not limited to the above-described examples.

The following table is a list of synthesis conditions for examples 1-5 of the present invention:

example 1

A method for dynamically synthesizing a nano KL molecular sieve comprises the following steps: 12.25g KOH was weighed in a 500mL beaker, 10g pure water was added, and after stirring well, 7.06g Al (OH) was added₃The solution was heated to 95 ℃ and stirred to clarify the solution. After the solution was cooled, 117.12g of pure water was added and 49.48g of silica sol was weighed in a 500mL beaker, and then the clear Al (OH) solution was added by a separatory funnel₃The solution was added dropwise to the silica sol and stirring was continued for 8 h. Stopping stirring, and filling the gel into a 200mL crystallization kettle. And (4) putting the crystallization kettle into an oven, and dynamically crystallizing for 18 hours at 170 ℃. After crystallization is finished, the crystallization kettle is taken out, and then the sample is centrifugally washed by pure water until the pH value is 7 or 8. The sample was transferred to a crucible and placed in a 120 ℃ oven for drying for 12 h.

Grinding the molecular sieve into powder, and analyzing by XRD spectrogram, wherein the molecular sieve is KL molecular sieve and contains mesopores as shown in figures 1 and 2. As shown in FIG. 3, the molecular sieve obtained was cylindrical and had a size of 200 nm.

The KL molecular sieve is used as a carrier to load metal Pt (0.5 wt%) to prepare a catalyst, and normal octane is used as a raw material to evaluate the aromatization performance of the catalyst in a fixed bed reactor. The mass space velocity (WHSV) is 1h^-1The hydrogen-hydrocarbon ratio was 6 (molar ratio), the reaction pressure was 1MPa, and the reaction temperature was 500 ℃. Wherein the liquid phase product is condensed and then analyzed off-line, and the gas phase product is on-lineAnd (6) analyzing.

The catalyst prepared by the carrier shows excellent catalytic performance in the aromatization reaction of n-octane, and under the condition of 95 percent of conversion rate, the yield of aromatic hydrocarbon reaches 62 percent, the yield of C8 aromatic hydrocarbon reaches 30 percent, the yield of methylbenzene reaches 19 percent, the yield of benzene reaches 17 percent, and the yield of liquid reaches 88 percent. From the data, the catalyst prepared by the KL molecular sieve has higher aromatic hydrocarbon yield and liquid yield in the aromatization reaction of n-octane,

example 2

The method for dynamically synthesizing the nano KL molecular sieve comprises the following steps of: 1.53g KOH was weighed in a 100mL beaker, 2g pure water was added, and after stirring well, 3.53g Al (OH) was added₃The solution was heated to 95 ℃ and stirred to clarify the solution. After the solution was cooled, 9g of pure water was added. 30g of silica sol was weighed into another 100mL beaker, and the clear Al (OH) was added via a separatory funnel₃The solution was added dropwise to the silica sol and stirring was continued for 24 h. Stopping stirring, and filling the gel into a 30mL crystallization kettle. And (4) putting the crystallization kettle into an oven, and dynamically crystallizing for 6 hours at 185 ℃. After crystallization is finished, the crystallization kettle is taken out, and then the sample is centrifugally washed by pure water until the pH value is 7 or 8. The sample was transferred to a crucible and placed in a 120 ℃ oven for drying for 12 h. The molecular sieve has LTL topological structure through XRD spectrogram analysis.

Example 3

The method for dynamically synthesizing the nano KL molecular sieve comprises the following steps of: 130.13g of KOH were weighed in a 2000mL beaker, 100g of pure water was added, and after stirring well, 30g of Al (OH) was added₃The solution was heated to 95 ℃ and stirred to clarify the solution. After the solution was cooled, 1030g of pure water was added. 473.79g of silica sol was weighed into a 2000mL beaker, and the clear Al (OH) was added via a separatory funnel₃The solution was added dropwise to the silica sol and stirring was continued for 4 h. Stopping stirring, and filling the gel into a 2L crystallization kettle. And (4) putting the crystallization kettle into an oven, and dynamically crystallizing for 24 hours at 120 ℃. After crystallization is finished, the crystallization kettle is taken out, and then the sample is centrifugally washed by pure water until the pH value is 7 or 8. The sample was transferred to a crucible and placed in a 120 ℃ oven for drying for 12 h. The molecular sieve has LTL topological structure through XRD spectrogram analysis.

Example 4

The method for dynamically synthesizing the nano KL molecular sieve comprises the following steps of: 781g KOH was weighed in a 10L bucket, 800g pure water was added, and after stirring well, 300g Al (OH) was added₃The solution was heated to 95 ℃ and stirred to clarify the solution. After the solution was cooled, 7454.3g of pure water was added. 473.79g of silica sol was weighed into another 10L bucket, and then clarified Al (OH)₃The solution was added dropwise to the silica sol and stirring was continued for 10 h. Stopping stirring, and filling the gel into a 10L crystallization kettle. And (4) placing the crystallization kettle into an oven, and dynamically crystallizing for 36 hours at 175 ℃. After crystallization is finished, the crystallization kettle is taken out, and then the sample is centrifugally washed by pure water until the pH value is 7 or 8. The sample was transferred to a crucible and placed in a 120 ℃ oven for drying for 12 h. The molecular sieve has LTL topological structure through XRD spectrogram analysis.

Example 5

The method for dynamically synthesizing the nano KL molecular sieve comprises the following steps of: 672.35kg KOH was weighed, 152kg pure water was added, and 310kg Al (OH) was added after stirring well₃The solution was heated to 95 ℃ and stirred to clarify the solution. After the solution was cooled, 6000.33kg of pure water was added. 2447.91kg of silica sol were weighed out and the clear Al (OH)₃The solution was added dropwise to the silica sol and stirring was continued for 17 h. Stopping stirring, and filling the gel at 1m³In a crystallization kettle. And (4) placing the crystallization kettle into an oven, and dynamically crystallizing for 22 hours at 175 ℃. After crystallization is finished, the crystallization kettle is taken out, and then the sample is centrifugally washed by pure water until the pH value is 7 or 8. The sample was transferred to a crucible and placed in a 120 ℃ oven for drying for 12 h. The molecular sieve has LTL topological structure through XRD spectrogram analysis.

The nano KL molecular sieves obtained in the above examples 2-5 were used as carriers to load metal Pt (0.1 wt%, 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 3.5 wt%) to prepare catalysts, and the aromatization performance of n-octane was evaluated in a fixed bed reactor using n-octane as a raw material. Experiments prove that the catalyst prepared by the carrier shows excellent catalytic performance in the aromatization reaction of n-octane, and under the condition of 95 percent of conversion rate, the yield of aromatic hydrocarbon reaches about 60 percent, the yield of C8 aromatic hydrocarbon is about 30 percent, the yield of methylbenzene is about 20 percent, the yield of benzene is about 20 percent, and the yield of liquid is about 90 percent. The catalyst prepared by the KL molecular sieve has higher aromatic hydrocarbon yield and liquid yield in the normal octane aromatization reaction.

The above embodiments are only some of the embodiments of the present invention, and the embodiments are not intended to limit the scope of the present invention, and all equivalent changes made by using the contents of the present invention are covered by the scope of the present invention claimed in the claims.