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CN-121974369-A - Method for preparing small-grain Y-type molecular sieve by taking fluorine-containing silicon powder as silicon source

CN121974369ACN 121974369 ACN121974369 ACN 121974369ACN-121974369-A

Abstract

The invention discloses a method for preparing a small-grain Y-shaped molecular sieve by taking fluorine-containing silicon powder as a silicon source. The invention belongs to the technical field of recycling and recovering dangerous solid wastes. The method comprises the steps of preparing fluorine-silicon-aluminum activated gel as a self-activated species by mixing industrial byproduct fluorine-containing silicon powder with an alkali source, an aluminum source and deionized water instead of a traditional silicon source, preparing synthetic gel by mixing the self-activated species, the fluorine-containing silicon powder, the aluminum source and the alkali source, placing the synthetic gel in a rotary oven for dynamic sectional hydrothermal crystallization, and performing programmed regulation and control on the pH value of a synthetic system in a crystal growth stage to obtain the small-grain NaY molecular sieve with the average grain size of 350nm. In the preparation process of the molecular sieve, the fluorine-containing silicon powder is used for replacing a conventional silicon source, so that the resource utilization of the fluorine-containing silicon powder can be realized, the synthesis cost is reduced, the added value of a product is improved, meanwhile, the existence of fluorine can promote crystallization, the crystallization time is shortened, and the synthesized small-grain Y molecular sieve can improve mass transfer, the reaction conversion rate and the selectivity of a target product and has wide application prospect.

Inventors

  • TAN JUAN
  • ZHANG SHU
  • DENG XUEMEI
  • JI WENYU
  • LIU JING

Assignees

  • 大连理工大学

Dates

Publication Date
20260505
Application Date
20260306

Claims (9)

  1. 1. The method for preparing the small-grain Y-type molecular sieve by taking the fluorine-containing silicon powder as a silicon source is characterized by comprising the following steps of: step 1, preparing self-activated species, namely mixing an alkali source, an aluminum source, fluorine-containing silicon powder and deionized water, stirring, standing and aging to prepare fluorine-silicon-aluminum activated gel; Step 2, preparing synthetic gel, namely mixing fluorine-containing silicon powder, an aluminum source, an alkali source, deionized water and fluorine-silicon-aluminum activated gel, and stirring to prepare reaction gel; Step 3, a hydrothermal crystallization stage, namely transferring the synthetic gel to a hydrothermal reaction kettle, and placing the hydrothermal reaction kettle in a rotary oven for dynamic sectional crystallization, wherein the crystallization temperature of the first stage is 30-80 ℃, the crystallization time is 1-5 hours, the crystallization temperature of the second stage is 80-110 ℃, and the crystallization time is 4-12 hours; and step 4, washing, filtering, separating and drying the solid product after crystallization to obtain the small-grain NaY molecular sieve.
  2. 2. The method of claim 1, wherein the molar ratio of components in the activated gel is Na 2 O:Al 2 O 3 :SiO 2 :H 2 O=4-12:1:6-20:200-300.
  3. 3. The method according to claim 1, wherein the molar ratio of the components in the reaction gel is Na 2 O:Al 2 O 3 :SiO 2 :H 2 O=5-10:1:11-15:180-300.
  4. 4. The method according to claim 1, wherein the stirring rate in the step 1 is 600-800 rpm, the stirring time is 1-3 h, and the standing and aging time is 12-48 h.
  5. 5. The method of claim 1, wherein the stirring in step 2 is performed at a rate of 500 to 1200 rpm and for a period of 2 to 5 h.
  6. 6. The method according to claim 1, wherein the acid solution in step 3 is one or more selected from the group consisting of citric acid, tartaric acid and acetic acid, and the acid solution has a concentration of 8-12wt%.
  7. 7. The method of claim 1, wherein the alkali source is sodium hydroxide or potassium hydroxide, and the aluminum source is one or more of sodium aluminate, aluminum sulfate, and aluminum sol.
  8. 8. The method of claim 1, wherein the self-activating species is added in the amount of 3% -20% by mole of Al 2 O 3 in the system in step 2.
  9. 9. The method according to claim 1, wherein in step 3, the first crystallization and the second crystallization are performed under stirring, the stirring speed of the first crystallization is 30-80 rpm, and the stirring speed of the second crystallization is 300-800 rpm.

Description

Method for preparing small-grain Y-type molecular sieve by taking fluorine-containing silicon powder as silicon source Technical Field The invention belongs to the technical field of recycling and recovery of dangerous solid wastes, and relates to a method for preparing a small-grain Y-shaped molecular sieve by taking fluorine-containing silicon powder as a silicon source. Background In the process of producing hydrofluoric acid from phosphate rock, a large amount of fluorine-containing silicon powder can be produced, and about 0.5 ton of fluorine-containing silicon powder can be produced per 1 ton of hydrofluoric acid. At present, the fluorine-containing silicon powder is not effectively utilized, the stacking is mainly adopted, the granularity of the fluorine-containing silicon powder is very fine, dust pollution is easily caused by stacking a large amount of fluorine-containing silicon powder, fluorine in the fluorine-containing silicon powder can be decomposed and volatilized along with the time extension, and generated fluorine-containing waste gas enters the environment to threaten human health. The fluorine-containing silicon powder contains a large amount of silicon dioxide and a certain amount of fluorine resources, and if the fluorine-containing silicon powder is not utilized, serious resource waste can be caused. Therefore, the promotion of clean and efficient utilization of the fluorine-containing silicon powder is very important. Chinese patent CN112939003B discloses a method for preparing mesoporous material SBA-15 by taking fluorine-containing silicon slag as a silicon source and synchronously recovering fluorine, and shows the application potential of the solid waste in the fields of catalysis, separation and the like. In terms of microporous zeolite synthesis, CN103121693B discloses a method for preparing 4A zeolite by one-step crystallization using fluorine-containing silica slag, but the synthesis process still needs to rely on seed crystal directing agent prepared in advance with conventional silicon source. CN118529744A adopts a more green dry gel method, and uses fluorine-containing silica slag to prepare Beta molecular sieve, so that the solid-liquid separation step of the traditional hydrothermal method is avoided. CN116947062a realizes the preparation of high-performance titanium-silicon molecular sieve TS-1 from fluorine-containing silicon slag, which is excellent in cyclohexanone ammoxidation, however, the route still cannot avoid the use of costly organic template agent. CN117735569a provides a resource scheme for co-producing aluminosilicate molecular sieve and cryolite, realizing recovery of fluorine element, but the corresponding process flow is more complex. CN120841536a discloses a method for synthesizing Y-type molecular sieve by using fluorine-containing silicon powder and recovering fluorine resource, synthesizing high-purity Y-type molecular sieve with less crystal defect, defluorinating in gel configuration stage, the sodium fluoride precipitate is generated and separated, and the synthesized gel has little residual fluorine, so that the effect of the fluorine is not fully utilized, and the problems that the fluorine-containing silicon powder contains more impurities and the fluorine and silicon are difficult to separate are mainly solved. In summary, although the prior art has realized the resource utilization of the fluorine-containing silica slag, the prior art still generally faces common challenges such as dependence on an external guiding agent or an expensive template agent, complex fluorine resource recovery and molecular sieve synthesis flow procedures. In the fields of petrochemical industry and fine chemical industry, a Y-type zeolite molecular sieve is used as a core solid acid catalyst and an adsorbent, and the global consumption of the zeolite molecular sieve is in the first place for a long time. The Y-type molecular sieve is composed of three-dimensionally crossed twelve-membered ring pore canal, has super-cage aperture of 7.4A, and the unique FAU-type crystal structure provides ideal nanometer space for shape-selective conversion and separation of bulk raw material molecules. The traditional synthesis of the silicon-based composite material has double challenges, namely economy, dependence on a high-cost chemical silicon source, and performance limitation, and obvious internal diffusion limitation of a conventional micron-sized large-grain product, and insufficient reaction efficiency and carbon deposition resistance when heavy and large-molecular raw materials are treated. The preparation of the small-grain Y-shaped molecular sieve is a key to break through the diffusion bottleneck. However, shortening the crystallization time and reducing the grain size are often contradictory. Although research has been attempted to accelerate crystallization by optimizing seed crystals, increasing temperature, etc., there is a possibility that the time is shortened