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CN-121990593-A - High-dispersity nano beta molecular sieve and preparation method thereof

CN121990593ACN 121990593 ACN121990593 ACN 121990593ACN-121990593-A

Abstract

The invention provides a nano beta molecular sieve with high dispersity and a preparation method thereof, wherein the method comprises the steps of mixing a silicon source, an aluminum source, an alkali source, an organic template agent and water to prepare crystallized gel; crystallizing, quenching to obtain nano molecular sieve slurry, adding flocculant into the nano molecular sieve slurry to flocculate, collecting flocculate, roasting, ammonium-exchanging and roasting to obtain nano beta molecular sieve. Wherein the flocculant comprises a combination of an inorganic ammonium salt and a polydiallyldialkylammonium salt, the molar ratio of the inorganic ammonium salt to the polydiallyldialkylammonium salt is 150-4000, and the molar ratio of the flocculant to a silicon source calculated by SiO 2 is 0.01-0.2. According to the invention, the high-efficiency organic cationic flocculant polydiallyl dialkyl ammonium salt is adopted to replace a part of inorganic ammonium salt, so that the rapid separation of nanocrystalline Beta is realized, and the prepared molecular sieve has the characteristics of rich external specific surface, high micropore exposure degree, large inter-crystal pores and the like.

Inventors

  • LI SHUAI
  • WANG BODI
  • CUI YAN
  • WANG XIAOHUA
  • XIE YIN
  • SHI DEJUN
  • CHI KEBIN

Assignees

  • 中国石油天然气股份有限公司

Dates

Publication Date
20260508
Application Date
20241108

Claims (13)

  1. 1. A method for preparing a nano beta molecular sieve with high dispersity, which comprises the following steps: (1) Preparing crystallization gel, namely mixing a silicon source, an aluminum source, an alkali source, an organic template agent and water to prepare crystallization gel; (2) Crystallizing, namely crystallizing the crystallized gel, and quenching after the crystallization to obtain nano molecular sieve slurry; (3) Flocculation, namely adding a flocculating agent into the nano molecular sieve slurry to flocculate, collecting flocculate and roasting to obtain a Na-type beta molecular sieve, wherein the flocculating agent comprises a combination of inorganic ammonium salt and polydiallyl dialkyl ammonium salt, the molar ratio of the inorganic ammonium salt to the polydiallyl dialkyl ammonium salt is 150-4000:1, and the molar ratio of the flocculating agent to a silicon source calculated by SiO 2 is 0.01-0.2:1; (4) And (3) ammonium exchange and roasting, namely performing ammonium exchange and roasting on the Na-type beta molecular sieve to obtain the nano beta molecular sieve.
  2. 2. The method for preparing a high-dispersity nano-beta molecular sieve according to claim 1, wherein the inorganic ammonium salt comprises one or a combination of more than two of ammonium sulfate, ammonium bisulfate, ammonium chloride and ammonium nitrate.
  3. 3. The method for preparing a high-dispersity nano-beta molecular sieve according to claim 1, wherein the polydiallyl dialkyl ammonium salt comprises one or a combination of more than two of polydiallyl dimethyl ammonium chloride, polydiallyl dimethyl ammonium bromide, polydiallyl dimethyl ammonium nitrate, polydiallyl dimethyl ammonium sulfate, polydiallyl diethyl ammonium chloride, polydiallyl diethyl ammonium bromide, polydiallyl diethyl ammonium nitrate and polydiallyl diethyl ammonium sulfate.
  4. 4. The method for preparing a high-dispersity nano-beta molecular sieve according to claim 1, wherein the polydiallyl dialkylammonium salt has a weight average molecular weight of 10000-800000.
  5. 5. The method for preparing a highly dispersed nano beta molecular sieve according to claim 1, wherein the alkali source is calculated by alkali metal oxide M 2 O, the aluminum source is calculated by Al 2 O 3 , the organic template agent is calculated by organic ammonium cation R + , the silicon source is calculated by SiO 2 , and the molar ratio of each component in the crystallized gel is ：SiO 2 /Al 2 O 3 ＝25-70,R + /SiO 2 ＝0.02-0.25,M 2 O/SiO 2 ＝0.03-0.20,H 2 O/SiO 2 ＝12-50.
  6. 6. The method for preparing a high-dispersity nano-beta molecular sieve according to claim 1, wherein the organic template agent comprises at least one of tetraethylammonium hydroxide, tetraethylammonium bromide and tetraethylammonium chloride.
  7. 7. The method for preparing a high-dispersity nano-beta molecular sieve according to claim 1, wherein the silicon source comprises at least one of tetraethyl orthosilicate, silica sol and coarse pore silica gel.
  8. 8. The method for preparing a high-dispersity nano-beta molecular sieve according to claim 1, wherein the aluminum source comprises at least one of sodium metaaluminate, aluminum nitrate and aluminum sulfate.
  9. 9. The method for preparing a high-dispersity nano-beta molecular sieve according to claim 1, wherein the alkali source comprises at least one of sodium hydroxide, potassium hydroxide and lithium hydroxide.
  10. 10. The method for preparing a high dispersity nano beta molecular sieve according to claim 1, wherein the crystallization condition comprises crystallization at 140-180 ℃ for 20-96 hours.
  11. 11. A high dispersity nano beta molecular sieve obtained by the method for preparing the high dispersity nano beta molecular sieve according to any one of claims 1 to 10.
  12. 12. The high dispersity nano-beta molecular sieve according to claim 11, wherein the nano-beta molecular sieve satisfies one or a combination of two or more of the following conditions: The grain size is 10-50nm; the total surface area is 650-900m 2 /g; the external specific surface area is 150-300m 2 /g; the average pore diameter is 25-50nm; the average pore diameter of adsorption is 60-100nm.
  13. 13. The high dispersity nano- β molecular sieve according to claim 11, wherein the nano- β molecular sieve has BEA topology, the molecular sieve skeleton central atoms are silicon and aluminum, and the proportion of micropore volume to total pore volume is 20-40%.

Description

High-dispersity nano beta molecular sieve and preparation method thereof Technical Field The invention belongs to the technical field of molecular sieve preparation, and particularly relates to a high-dispersity nano beta molecular sieve and a preparation method thereof. Background The Beta molecular sieve has a three-dimensional twelve-membered ring cross pore canal structure, the [100] and [010] directions are straight pore canals, and the pore canal size is[001] The direction is zigzag pore canal, the pore canal size isThe two linear pore channels are vertically intersected and communicated by the zigzag pore channel, and the three-dimensional cross pore channel structure macroporous molecular sieve. The Beta molecular sieve has a unique pore structure and stronger acidity, is widely applied to the traditional petrochemical industry, and also has great application potential in the fields of biomass conversion, environment and the like. At present, the Beta molecular sieve is synthesized mainly by taking tetraethyl ammonium hydroxide (TEAOH) as a template agent, carrying out hydrothermal crystallization for several days at 100-160 ℃, and the prepared crystals are generally large in size (more than 1 mu m) and are not beneficial to mass transfer and diffusion of reactants and products in the catalytic reaction process. It has been fully demonstrated in many years of application to Beta molecular sieves that nano Beta molecular sieves can further enhance their potential catalytic and adsorptive properties due to their larger specific surface area, more exposed active catalytic sites and shorter diffusion paths. In order to obtain the nano-scale Beta molecular sieve, a novel template agent and an additive can be generally introduced into a synthesis system, or the grain size and the morphology of the nano-scale Beta molecular sieve can be regulated by adopting two-step crystallization, microwave-assisted synthesis and other methods. Corma et al successfully prepared Beta molecular sieves having a crystal size of 10-20nm using a novel bifunctional quaternary ammonium salt cationic organic molecule containing a short alkyl chain and a cyclic alkyl chain as a templating agent. Bein et al synthesized Beta molecular sieves with particle sizes of about 200nm using templates containing 4,4' -trimethylbis (N-methyl, N-benzylpiperidine) cations, and novel templates, although capable of obtaining Beta nanomolecular sieves, were relatively complex and costly to synthesize. In Ji Gong, the L-lysine assisted two-step crystallization method is reported, and the nano beta molecular sieve with a wide silicon-aluminum ratio range (6-300) and a particle size of 10-106nm is prepared in a concentrated gel system, wherein the two-step crystallization method faces the problems of complex synthesis process, long synthesis period and lower production efficiency. In addition, the nano Beta molecular sieve prepared by the current method generally has the problems of low solid yield, difficult separation after synthesis and the like, and limits the large-scale industrial production and application of the nano Beta molecular sieve. Aiming at the problems of low yield and undersize separation difficulty of nanocrystalline Beta solid, inorganic ammonium salt can be added to neutralize the charges on the surfaces of molecular sieve particles in the filtering process, so that the potential of the molecular sieve particles is reduced, electrostatic repulsive force among the particles is reduced, and the particles are promoted to aggregate to form flocculates. Disclosure of Invention The inventor finds in experiments that in the process of using inorganic ammonium salt to promote particles to aggregate to form flocculate, the molecular sieve is seriously aggregated to micron-sized particles, so that a mesoporous structure is lost, and incompletely crystallized silicon dioxide is easy to flocculate and block pore channels at the same time, so that a microporous structure is lost. On the premise of keeping the high specific surface area and secondary mesopores of the nano Beta molecular sieve, the realization of high solid yield and rapid separation of the nano Beta is a problem to be solved in the industrial application of the nano Beta molecular sieve. In order to solve the technical problems, the invention aims to provide a nano beta molecular sieve with high dispersity and a preparation method thereof. In order to achieve the above purpose, the present invention provides a method for preparing a nano beta molecular sieve with high dispersity, which comprises: (1) Preparing crystallization gel, namely mixing a silicon source, an aluminum source, an alkali source, an organic template agent and water to prepare crystallization gel; (2) Crystallizing, namely crystallizing the crystallized gel, and quenching after the crystallization to obtain nano molecular sieve slurry; (3) Flocculation, namely adding a flocculating agent into the nano molecu