CN-121974368-A - Two-step crystallization method for synthesizing mesoporous molecular sieve with high aluminum content under alkaline metal/alkaline earth metal auxiliary neutral condition

Abstract

The invention discloses a two-step crystallization method for synthesizing a mesoporous molecular sieve with high aluminum content under the auxiliary neutral condition of alkali metal/alkaline earth metal, which comprises the following steps of dissolving a template agent and inorganic salt in deionized water, and fully stirring to obtain a uniform template agent solution; and uniformly mixing a silicon source with deionized water, alkali metal salt or alkaline earth metal salt or transition metal salt/dilute sulfuric acid solution respectively to prepare silicate solution and metal salt solution. The invention provides a two-step crystallization strategy to improve the aluminum introduction efficiency of a mesoporous molecular sieve under neutral conditions. Firstly, pre-implanting ions of alkaline earth metal or alkali metal or transition metal into mesoporous silicate frameworks in the primary crystallization process, and then, in the secondary crystallization stage, metal ions in the frameworks can interact with aluminum species to serve as preferential anchor points to effectively promote aluminum to enter the frameworks, so that the neutral synthesis of the mesoporous molecular sieve with high aluminum content is cooperatively realized.

Inventors

• LIU HONGTAO
• WANG JIE
• ZHENG ZHIHAO
• WAN PINGYU

Assignees

• 安庆北化大科技园有限公司
• 北京化工大学

Dates

Publication Date

20260505

Application Date

20260407

Claims (8)

1. 1. The two-step crystallization method for synthesizing the mesoporous molecular sieve with high aluminum content under the auxiliary neutral condition of alkali metal/alkaline earth metal is characterized by comprising the following steps of: s1, dissolving a template agent and inorganic salt containing alkali metal/alkaline earth metal in deionized water, and fully stirring in a water bath to obtain a uniform template agent solution; S2, mixing and stirring a silicon source, a sulfuric acid solution and deionized water in a water bath to obtain a silicate solution; S3, mixing aluminum salt with deionized water, and stirring for dissolution to obtain an aluminum salt solution; And S4, dropwise adding the solution in the step S2 into the template agent solution under the water bath condition, crystallizing to form a mixture of silicate precursors and mother liquor, dropwise adding the solution in the step S3 into the mixture of silicate precursors and mother liquor, keeping the pH value within a certain range, assembling under the water bath condition, then loading the solid product and the mother liquor into a reaction kettle for crystallization, and finally carrying out suction filtration, washing to be neutral, drying and roasting to obtain the mesoporous aluminosilicate product.
2. 2. The two-step crystallization method for synthesizing a mesoporous molecular sieve having a high aluminum content under an alkali metal/alkaline earth metal-assisted neutral condition according to claim 1, wherein the template agent in step S1 comprises a triblock copolymer F68：PEO 80 PPO 30 PEO 80 、F127:PEO 106 PPO 70 PEO 106 、P123:PEO 20 PPO 70 PEO 20 、F88:PEO 100 PPO 39 PEO 100 、 P103:PEO 17 PPO 85 PEO 17 、P65:PEO 20 PPO 30 PEO 20 、L121:PEO 5 PPO 70 PEO 5 .
3. 3. The two-step crystallization method for synthesizing the mesoporous molecular sieve with high aluminum content under the auxiliary neutral condition of alkali metal/alkaline earth metal according to claim 1, wherein the inorganic salt containing the alkali metal/alkaline earth metal in the step S1 comprises one or more of magnesium chloride, magnesium sulfate, magnesium nitrate, calcium chloride, calcium sulfate, calcium nitrate, lithium chloride, lithium sulfate, lithium nitrate, ferric chloride, ferric sulfate and ferric nitrate.
4. 4. The two-step crystallization method for synthesizing the mesoporous molecular sieve with high aluminum content under the auxiliary neutral condition of alkali metal/alkaline earth metal according to claim 1, wherein the silicon source in the step S2 comprises one or more of tetraethoxysilane, silica sol, silica powder, silicic acid, white carbon black and water glass.
5. 5. The two-step crystallization method for synthesizing a mesoporous molecular sieve having a high aluminum content under an alkali/alkaline earth metal-assisted neutral condition according to claim 1, wherein the aluminum source in step S3 comprises one or more of aluminum sulfate, pseudo-boehmite, aluminum chloride, aluminum citrate, aluminum hydroxide, sodium metaaluminate, aluminum isopropoxide, aluminum chloride, or aluminum nitrate.
6. 6. The two-step crystallization method for synthesizing a mesoporous molecular sieve with high aluminum content under the auxiliary neutral condition of alkali metal/alkaline earth metal according to claim 1, wherein the concentration of sulfuric acid in the step S2 is 0.5M-10M.
7. 7. The two-step crystallization method for synthesizing a mesoporous molecular sieve with high aluminum content under the neutral condition assisted by alkali metal/alkaline earth metal according to claim 1, wherein in the step S4, the molar ratio of the species is n (Al 2 O 3 ): n(Na 2 O): n(SiO 2 ): n(H 2 O) n (template agent) n (inorganic salt) =1:10-30:10-40:100-500:0.1-5:0.00001-0.10, and the crystallization time under the condition of 80-150 ℃ is 12-72 h.
8. 8. The two-step crystallization method for synthesizing a mesoporous molecular sieve with high aluminum content under the auxiliary neutral condition of alkali metal/alkaline earth metal according to claim 1, wherein the dropping rate of the two solutions in the step S4 is between 1 and 120 mL/min, and the dropping rates of the two solutions are not necessarily the same.

Description

Two-step crystallization method for synthesizing mesoporous molecular sieve with high aluminum content under alkaline metal/alkaline earth metal auxiliary neutral condition Technical Field The invention relates to the technical field of mesoporous molecular sieve synthesis, in particular to a two-step crystallization synthesis method for synthesizing a mesoporous molecular sieve with high aluminum content under the auxiliary neutral condition of alkali metal/alkaline earth metal. Background Because of the large specific surface area, regular and adjustable pore channel structure and other excellent characteristics, the aluminum loaded mesoporous molecular sieve has wide prospect in the field of macromolecular transformation, but the lower Al introduction efficiency leads to the poor hydrothermal stability of the pore wall of the amorphous structure with lower acidity and hydrothermal stability of the molecular sieve, and greatly limits the application of the molecular sieve in harsh chemical processes, such as catalytic cracking (FCC) processes. The one-step method is used as a simpler path for synthesizing the Al-SBA-15, however, the method still has the limitations of insufficient acid sites, poor texture properties (such as low specific surface area and pore volume) and the like. In order to solve the problems, researchers at home and abroad develop various synthesis methods to improve the introduction efficiency of aluminum in a molecular sieve framework; Improving the efficiency of aluminum incorporation into the molecular sieve framework, pH adjustment was used to synthesize high aluminum content Al-SBA-15, dumitriu et Al (Microporous and Mesoporous Materials, 2012, 163:51-64) reported studies of incorporating aluminum into mesoporous Al-SBA-15 using the "pH adjustment" method, which resulted in studies of Al-SBA-15 with significantly increased Al incorporation through a process of crystallization under acidic conditions followed by crystallization under neutral conditions. The results show that as the aluminum incorporation increases, both the short-range and long-range mesoporous order and texture properties of the material are improved. Nuclear Magnetic Resonance (NMR) characterization confirmed that the aluminum species in the calcined Al-SBA-15 exists mainly in a tetra-coordinated form. Acidity testing further shows that the incorporation of aluminum significantly increases the total number of acid sites on the surface of the material. Then the amount of the acid sites is not matched with the introduction amount of aluminum, which indicates that part of the aluminum sites are covered and the acid characteristics cannot be fully displayed. Al species are present in ionic form in a solution under acidic conditions, so that it is difficult to introduce the Al species into the framework of a molecular sieve, and although some documents report that Al species are introduced into the framework by a multistage acidic crystallization method, the amount of introduction is still low, so that the improvement of acidity is limited. For this reason, researchers have developed one-step synthetic strategies to address the above challenges by introducing specific adjuvants or precisely adjusting the pH of the synthetic medium. And the like (Microporous and Mesoporous Materials, 2011, 142 (1): 341-346) provides an Al-SBA-15 synthesis method based on fluoride ion (NaF) regulation and control, so that the controllable introduction of aluminum content and the remarkable improvement of the hydrothermal stability of the material are successfully realized. In this strategy, F - acts as a mineralizer effectively promoting the hydrolysis-condensation process of the silicon-aluminum species, thereby enhancing the degree of framework cross-linking. By adjusting the feeding ratio of the aluminum source, the content of the skeleton aluminum can be accurately controlled within a certain range, and further the directional regulation and control of the acid property of the material can be realized. However, the method has obvious limitations that the reaction system always maintains a stronger acid environment (pH=1.65), the applicability of the reaction system under mild conditions is limited, and in addition, the introduction of F - not only increases the difficulty and cost of wastewater treatment, but also brings certain environmental and operation risks. Xing et Al (Microporous and Mesoporous Materials, 2017, 239:316-327) synthesized a series of Al-SBA-15 samples under acidic conditions by direct hydrothermal method, and systematically studied the regulation and control effects of the addition of the pore-expanding agent Trimethylbenzene (TMB) on the material structure and the acidic site. The result shows that the introduction of TMB can effectively enlarge the aperture of the material, and simultaneously improve the introduction amount of aluminum, so that Al-SBA-15 with large pore channels and high aluminum content can