CN112624166A - Preparation method of silicon-aluminum-based aerogel and application of prepared silicon-aluminum-based aerogel in aspect of adsorbing heavy metal gas - Google Patents

Preparation method of silicon-aluminum-based aerogel and application of prepared silicon-aluminum-based aerogel in aspect of adsorbing heavy metal gas Download PDF

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CN112624166A
CN112624166A CN202011492751.1A CN202011492751A CN112624166A CN 112624166 A CN112624166 A CN 112624166A CN 202011492751 A CN202011492751 A CN 202011492751A CN 112624166 A CN112624166 A CN 112624166A
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王志飞
张学忠
俞建飞
黄亚继
金保昇
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Abstract

The invention discloses a preparation method of silicon-aluminum based aerogel, which comprises the following steps: (1) adding aluminum isopropoxide into a mixed solution of ethanol and water to obtain a mixed material, heating and refluxing the mixed material under a stirring condition, stopping stirring, continuing heating, cooling to room temperature after heating, and adjusting the pH value of the solution to make the solution acidic to obtain alumina wet sol; (2) adding tetraethoxysilane into a mixed solution of ethanol and water, stirring, and adjusting the pH value of the solution to make the solution acidic to obtain a silica sol precursor solution; (3) and (3) mixing the alumina wet sol obtained in the step (1) with the silica sol precursor solution obtained in the step (2), adjusting the pH value of the mixed solution to be neutral after stirring, standing the mixed solution for at least 12 hours to form silicon-aluminum wet gel, performing solvent exchange by using n-hexane, and drying the silicon-aluminum wet gel in a vacuum drying oven to obtain the silicon-aluminum-based aerogel.

Description

Preparation method of silicon-aluminum-based aerogel and application of prepared silicon-aluminum-based aerogel in aspect of adsorbing heavy metal gas
Technical Field
The invention relates to a preparation method of a silicon-aluminum based aerogel and also relates to application of the silicon-aluminum based aerogel prepared by the preparation method in the aspect of adsorbing heavy metal gas.
Background
Solid wastes generated in human production and life severely pollute water and soil in the nature. Pyrolysis technology is generally employed to render solid waste harmless. However, in the process of pyrolyzing solid waste, especially in the process of pyrolyzing solid waste containing chlorine element, volatile and semi-volatile heavy metals can be easily volatilized to the external environment in the form of chloride, thereby causing secondary pollution to the environment. Therefore, a material capable of efficiently adsorbing heavy metal gas is required to be found. At present, the materials for adsorbing the heavy metal gases are mainly natural raw materials rich in Si and Al, such as kaolin, attapulgite, limestone and the like. However, these materials often occur on the surface of the adsorbent when adsorbing and solidifying heavy metal gas, and cannot permeate into the interior of the adsorbent, resulting in low utilization rate of the adsorbent.
In recent years, silica aerogel has been receiving more and more attention due to its unique pore structure. The silica aerogel has larger specific surface area and porosity, can adsorb and contain more particles, and is favorable for being applied to the adsorption of heavy metal gas in the pyrolysis process. However, the silicon dioxide aerogel has poor thermal stability, and the pore channel is easy to collapse at high temperature, so that the structure is densified, and the silicon dioxide aerogel cannot be applied to heavy metal gas adsorption in the actual high-temperature pyrolysis process.
Disclosure of Invention
The purpose of the invention is as follows: aiming at the problem that the silicon dioxide aerogel in the prior art cannot adsorb heavy metal gas in the high-temperature pyrolysis process, the invention provides the preparation method of the silicon-aluminum-based aerogel.
The technical scheme is as follows: the preparation method of the silicon-aluminum based aerogel comprises the following steps:
(1) adding aluminum isopropoxide into a mixed solution of ethanol and water to obtain a mixed material, heating and refluxing the mixed material under a stirring condition, continuing to heat after stirring is stopped, cooling to room temperature after heating, and adjusting the pH value of the solution to be acidic to obtain alumina wet sol;
(2) adding tetraethoxysilane into a mixed solution of ethanol and water, stirring for no more than 0.5h, and adjusting the pH value of the solution to be acidic to obtain a silica sol precursor solution;
(3) and (3) mixing the alumina wet sol obtained in the step (1) with the silica sol precursor solution obtained in the step (2), adjusting the pH value of the mixed solution to be neutral after stirring, standing the mixed solution for at least 12 hours to form silicon-aluminum mixed wet gel, performing solvent exchange by using n-hexane, and drying the silicon-aluminum mixed wet gel in a vacuum drying oven to obtain the silicon-aluminum-based aerogel.
Wherein in the step (1), the mixing volume ratio of the ethanol and the water is 15-30: 5-10.
Wherein in the step (2), the mixing molar ratio of the ethanol to the water is 5-7: 1-3.
Wherein, in the step (3), the drying temperature is 50-60 ℃, and the drying time is 6-10 h.
Wherein, in the step (3), the molar ratio of silicon-aluminum elements in the obtained silicon-aluminum based aerogel is 1: 1.
The silicon-aluminum-based aerogel prepared by the preparation method of the silicon-aluminum-based aerogel is applied to the aspect of adsorbing heavy metal gas.
The silicon-aluminum-based aerogel is used for adsorbing heavy metal gas in the pyrolysis process, and the temperature of the pyrolysis process is 600-900 ℃.
The silicon-aluminum based aerogel prepared by the invention has large specific surface area and poresThe porosity enables heavy metal gas to enter the pore channels of the aerogel material, so that the utilization rate of the material is improved, and meanwhile, the effect of solidifying heavy metal can be well played, so that the heavy metal adsorption efficiency is improved; the silicon-aluminum based aerogel contains rich Si element and can form silicate with heavy metal oxide; meanwhile, aiming at heavy metal chloride, alumina in the silicon-aluminum-based aerogel can react with chloride in heavy metal gas to generate heavy metal oxide, and then the heavy metal oxide continuously reacts with silica in the aerogel to generate silicate, specifically, a part of heavy metal chloride can be fixed inside the pore channel of the silicon-aluminum-based aerogel in a physical adsorption mode, and the other part of heavy metal chloride forms stable silicate with the silicon-aluminum-based aerogel, so that the adsorption efficiency and the utilization rate of the aerogel material are improved, (such as PbCl for example)2The reaction mechanism is as follows: PbCl2+SiO2+H2O=PbSiO3+2HCl;3PbCl2+Al2O3=2AlCl3+3PbO,PbO+SiO2=PbSiO3)。
Has the advantages that: the preparation method has simple process, can also obtain the alumina sol without using an inducer and a catalyst, and then obtains the silica sol precursor solution by controlling the hydrolysis time of the tetraethoxysilane and the pH value of the reaction solution; the silicon-aluminum based aerogel prepared by the invention has high thermal stability, large specific surface area and porosity, and can keep a stable pore structure at 500-900 ℃, so that the silicon-aluminum based aerogel can be used for adsorbing heavy metal gas in the pyrolysis process.
Drawings
FIG. 1 shows the silica-alumina based aerogels prepared in examples 1 to 6 as a heavy metal gas PbCl2Comparative adsorption performance of (c).
Detailed Description
The technical solution of the present invention is further described with reference to the following specific embodiments.
Example 1
The preparation method of the silicon-aluminum based aerogel comprises the following steps:
(1) 2.5g of Aluminum Isopropoxide (AIP) was added to a mixed solution of ethanol and water in a mixed volume ratio of 15 mL: 5mL of the alumina wet sol is mixed, heated and refluxed for 3 hours at the temperature of 80 ℃ under the stirring condition, the stirring is stopped, the heating is continued for 1 hour, the mixture is cooled to the room temperature, hydrochloric acid is added to adjust the pH value to be 3, and the mixture is stirred for 10min to obtain the alumina wet sol;
(2) adding 2.55g of TEOS into a mixed solution of ethanol and water, wherein the mixing molar ratio of the ethanol to the water is 7: 3, mixing and stirring for 0.5h (silica sol cannot be formed in a short treatment time), and then adjusting the pH value to 2 by using hydrochloric acid to obtain a silica sol precursor solution;
(3) mixing the alumina wet sol obtained in the step (1) with the silica sol precursor solution obtained in the step (2), stirring for 2 hours, adding ammonia water to adjust the pH value to be neutral, standing for 12 hours to form a silicon-aluminum mixed wet gel, exchanging an ethanol solvent with n-hexane without heating and aging, performing solvent exchange with n-hexane (changing the structure of the material by changing the polarity of the solution), and drying in a vacuum drying oven at 50 ℃ for 6 hours to obtain the silicon-aluminum based aerogel (the molar ratio of silicon to aluminum in the silicon-aluminum based aerogel is 1: 1); and grinding the dried silicon-aluminum-based aerogel into fine particles by using a mortar, and screening materials with the size of 40-60 meshes by using a medicine screen to perform an adsorption experiment.
The specific surface area of the silica-alumina-based aerogel prepared in example 1 was 686.22m2·g-1Porosity of 0.57cm3·g-1
0.6g of silica-alumina aerogel is weighed, and 0.06g of PbCl is weighed2Adding into a secondary reaction furnace for PbCl2And (4) performing gas adsorption experiments. Adsorbing at 800 deg.C for 40min with PbCl2The adsorption removal rate of the silica-alumina-based aerogel is 72.58%, which shows that the silica-alumina-based aerogel prepared in example 1 has good heavy metal gas adsorption performance.
Example 2
The preparation method of the silicon-aluminum based aerogel comprises the following steps:
(1) 2.5g of Aluminum Isopropoxide (AIP) was added to a mixed solution of ethanol and water in a mixed volume ratio of 15 mL: 5mL of the alumina wet sol is mixed, heated and refluxed for 3 hours at the temperature of 80 ℃ under the stirring condition, the stirring is stopped, the heating is continued for 1 hour, the mixture is cooled to the room temperature, hydrochloric acid is added to adjust the pH value to be 3, and the mixture is stirred for 10min to obtain the alumina wet sol;
(2) adding 2.55g of TEOS into a mixed solution of ethanol and water, wherein the mixing molar ratio of the ethanol to the water is 7: 3, mixing and stirring for 0.5h (no silica sol is formed in a short treatment time), and then adjusting the pH value to 2 by using hydrochloric acid to obtain a silica sol precursor solution;
(3) mixing the alumina wet sol obtained in the step (1) with the silica sol precursor solution obtained in the step (2), stirring for 2 hours, adding ammonia water to adjust the pH value to be neutral, standing for 12 hours to form a silicon-aluminum mixed wet gel, exchanging an ethanol solvent with n-hexane without heating and aging, performing solvent exchange with n-hexane (changing the structure of the material by changing the polarity of the solution), and drying in a vacuum drying oven at 60 ℃ for 10 hours to obtain the silicon-aluminum based aerogel (the molar ratio of silicon to aluminum in the silicon-aluminum based aerogel is 1: 1); and grinding the dried silicon-aluminum-based aerogel into fine particles by using a mortar, and screening materials with the size of 40-60 meshes by using a medicine screen to perform an adsorption experiment.
0.6g of silica-alumina aerogel is weighed, and 0.06g of PbCl is weighed2Adding into a secondary reaction furnace for PbCl2And (4) performing gas adsorption experiments. Adsorbing at 800 deg.C for 40min with PbCl2The adsorption removal rate of (a) was 71.11%, indicating that the drying temperature and time had little effect on the adsorption efficiency.
Example 3
The preparation method of the silicon-aluminum based aerogel comprises the following steps:
(1) 2.5g of Aluminum Isopropoxide (AIP) was added to a mixed solution of ethanol and water in a mixed volume ratio of 30 mL: 10mL of the alumina wet sol is mixed, heated and refluxed for 3 hours at 80 ℃ under the stirring condition, the stirring is stopped, the heating is continued for 1 hour, the mixture is cooled to the room temperature, hydrochloric acid is added to adjust the pH value to 3, and the mixture is stirred for 10 minutes to obtain the alumina wet sol;
(2) adding 2.55g of TEOS into a mixed solution of ethanol and water, wherein the mixing molar ratio of the ethanol to the water is 7: 3, mixing and stirring for 0.5h (no silica sol is formed in a short treatment time), and then adjusting the pH value to 2 by using hydrochloric acid to obtain a silica sol precursor solution;
(3) mixing the alumina wet sol obtained in the step (1) with the silica sol precursor solution obtained in the step (2), stirring for 2 hours, adding ammonia water to adjust the pH value to be neutral, standing for 12 hours to form a silicon-aluminum mixed wet gel, exchanging an ethanol solvent with n-hexane without heating and aging, performing solvent exchange with n-hexane (changing the structure of the material by changing the polarity of the solution), and drying in a vacuum drying oven at 50 ℃ for 6 hours to obtain the silicon-aluminum based aerogel (the molar ratio of silicon to aluminum in the silicon-aluminum based aerogel is 1: 1); and grinding the dried silicon-aluminum-based aerogel into fine particles by using a mortar, and screening materials with the size of 40-60 meshes by using a medicine screen to perform an adsorption experiment.
0.6g of silica-alumina aerogel is weighed, and 0.06g of PbCl is weighed2Adding into a secondary reaction furnace for PbCl2And (4) performing gas adsorption experiments. Adsorbing at 800 deg.C for 40min with PbCl2The adsorption removal rate of the silica-alumina-based aerogel is 66.54%, which shows that the increase of the ethanol and water content in the step (1) is not beneficial to the adsorption of the silica-alumina-based aerogel on the heavy metal gas, because the aerogel prepared from the ethanol and water with the content has irregular structure, the pore channel is easy to collapse at high temperature, and the structure is densified, so the adsorption performance of the heavy metal gas is reduced.
Example 4
The preparation method of the silicon-aluminum based aerogel comprises the following steps:
(1) 2.5g of Aluminum Isopropoxide (AIP) was added to a mixed solution of ethanol and water in a mixed volume ratio of 15 mL: 5mL of the alumina wet sol is mixed, heated and refluxed for 3 hours at the temperature of 80 ℃ under the stirring condition, the stirring is stopped, the heating is continued for 1 hour, the mixture is cooled to the room temperature, hydrochloric acid is added to adjust the pH value to be 3, and the mixture is stirred for 10min to obtain the alumina wet sol;
(2) adding 2.55g of TEOS into a mixed solution of ethanol and water, wherein the mixing molar ratio of the ethanol to the water is 5: 1, mixing and stirring for 0.5h (no silica sol is formed in a short treatment time), and then adjusting the pH value to 2 by using hydrochloric acid to obtain a silica sol precursor solution;
(3) mixing the alumina wet sol obtained in the step (1) with the silica sol precursor solution obtained in the step (2), stirring for 2 hours, adding ammonia water to adjust the pH value to be neutral, standing for 12 hours to form a silicon-aluminum mixed wet gel, exchanging an ethanol solvent with n-hexane without heating and aging, performing solvent exchange with n-hexane (changing the structure of the material by changing the polarity of the solution), and drying in a vacuum drying oven at 50 ℃ for 6 hours to obtain the silicon-aluminum based aerogel (the molar ratio of silicon to aluminum in the silicon-aluminum based aerogel is 1: 1); and grinding the dried silicon-aluminum-based aerogel into fine particles by using a mortar, and screening materials with the size of 40-60 meshes by using a medicine screen to perform an adsorption experiment.
0.6g of silica-alumina aerogel is weighed, and 0.06g of PbCl is weighed2Adding into a secondary reaction furnace for PbCl2And (4) performing gas adsorption experiments. Adsorbing at 800 deg.C for 40min with PbCl2The adsorption removal rate of (3) is 52.31%, which shows that after the alcohol-water ratio in the step (2) is increased, the prepared silicon-aluminum based aerogel is subjected to PbCl2The adsorption efficiency is reduced because the pore structure and the shape of the prepared silica-alumina-based aerogel are not beneficial to the adsorption of heavy metal gas.
Example 5
The preparation method of the silicon-aluminum based aerogel comprises the following steps:
(1) 5g of Aluminum Isopropoxide (AIP) was added to a mixed solution of ethanol and water at a mixed volume ratio of 15 mL: 5mL of the alumina wet sol is mixed, heated and refluxed for 3 hours at the temperature of 80 ℃ under the stirring condition, the stirring is stopped, the heating is continued for 1 hour, the mixture is cooled to the room temperature, hydrochloric acid is added to adjust the pH value to be 3, and the mixture is stirred for 10min to obtain the alumina wet sol;
(2) adding 2.55g of TEOS into a mixed solution of ethanol and water, wherein the mixing molar ratio of the ethanol to the water is 7: 3, mixing and stirring for 0.5h (no silica sol is formed in a short treatment time), and then adjusting the pH value to 2 by using hydrochloric acid to obtain a silica sol precursor solution;
(3) mixing the alumina wet sol obtained in the step (1) with the silica sol precursor solution obtained in the step (2), stirring for 2 hours, adding ammonia water to adjust the pH value to be neutral, standing for 12 hours to form a silicon-aluminum mixed wet gel, exchanging an ethanol solvent with n-hexane without heating and aging, performing solvent exchange with n-hexane (changing the structure of the material by changing the polarity of the solution), and drying in a vacuum drying oven at 50 ℃ for 6 hours to obtain the silicon-aluminum based aerogel (the molar ratio of silicon to aluminum in the silicon-aluminum based aerogel is 1: 1); and grinding the dried silicon-aluminum-based aerogel into fine particles by using a mortar, and screening materials with the size of 40-60 meshes by using a medicine screen to perform an adsorption experiment.
0.6g of silica-alumina aerogel is weighed, and 0.06g of PbCl is weighed2Adding into a secondary reaction furnace for PbCl2And (4) performing gas adsorption experiments. Adsorbing at 800 deg.C for 40min with PbCl2The adsorption removal rate of (2) is 44.37%, which shows that the silicon-aluminum ratio in the silicon-aluminum based aerogel is reduced, so that the adsorption efficiency is greatly reduced. This is because heavy metals are solidified as silicates by the silica-alumina-based aerogel at high temperatures, and lowering the silica-alumina ratio reduces the formation of silicates and lowers the adsorption efficiency.
Example 6
The preparation method of the silicon-aluminum based aerogel comprises the following steps:
(1) 2.5g of Aluminum Isopropoxide (AIP) was added to a mixed solution of ethanol and water in a mixed volume ratio of 15 mL: 5mL of the alumina wet sol is mixed, heated and refluxed for 3 hours at the temperature of 80 ℃ under the stirring condition, the stirring is stopped, the heating is continued for 1 hour, the mixture is cooled to the room temperature, hydrochloric acid is added to adjust the pH value to be 3, and the mixture is stirred for 10min to obtain the alumina wet sol;
(2) adding 2.55g of TEOS into a mixed solution of ethanol and water, wherein the mixing molar ratio of the ethanol to the water is 7: 3, mixing and stirring for 0.5h (no silica sol is formed in a short treatment time), and then adjusting the pH value to 2 by using hydrochloric acid to obtain a silica sol precursor solution;
(3) mixing the alumina wet sol obtained in the step (1) with the silica sol precursor solution obtained in the step (2), stirring for 2 hours, adding ammonia water to adjust the pH value to be neutral, standing for 12 hours to form a silicon-aluminum mixed wet gel, exchanging an ethanol solvent with n-hexane without heating and aging, performing solvent exchange with n-hexane (changing the structure of the material by changing the polarity of the solution), and drying in a vacuum drying oven at 50 ℃ for 6 hours to obtain the silicon-aluminum based aerogel (the molar ratio of silicon to aluminum in the silicon-aluminum based aerogel is 1: 1); and grinding the dried silicon-aluminum-based aerogel into fine particles by using a mortar, and screening materials with the size of 40-60 meshes by using a medicine screen to perform an adsorption experiment.
0.6g of silica-alumina aerogel is weighed, and 0.06g of PbCl is weighed2Adding into a secondary reaction furnace for PbCl2And (4) performing gas adsorption experiments. Adsorbing at 600 deg.C for 40min with PbCl2The adsorption removal rate of (2) is 54.25%, which shows that the adsorption temperature has great influence on the adsorption efficiency of the adsorbent, and because the temperature is reduced, the effective collision between heavy metal and the silicon-aluminum based aerogel is reduced, so that PbCl2 captured by adsorption sites is reduced, and meanwhile, the generation of silicate is not facilitated, and the adsorption efficiency is reduced.
The calculation process of the adsorption efficiency of the silicon-aluminum-based aerogel prepared in the embodiment 1-6 is as follows:
1. the mass ratio of the added heavy metal to the adsorbent is as follows:
Figure BDA0002839103810000061
m1for adding the mass of heavy metal, m2Is the mass of the adsorbent aerogel.
2. Determination of heavy metal content in adsorbed adsorption material
Digesting the adsorption material, and measuring the concentration w of heavy metal in the adsorbed material by utilizing ICP-MS (inductively coupled plasma-mass spectrometry)
3. Calculation of adsorption efficiency μ
Figure BDA0002839103810000062
V is the constant volume, C is the metal concentration measured by ICP-MS, M1Is PbCl2Molar mass of (a), m1' is the mass of the adsorbed aerogel, M, weighed by digestion2Is the molar mass of Pb, m2' is the mass of aerogel weighed after adsorption, m3Is the mass of heavy metal adsorbed by the aerogel.
TABLE 1 shows the adsorption of PbCl onto silica aerogel at 800 ℃ and the silica-alumina-based aerogel obtained in example 12Comparison of specific surface area and porosity before and after
Figure BDA0002839103810000071
As can be seen from table 1, the silica-alumina-based aerogel prepared in example 1 of the present invention has higher thermal stability and larger specific surface area and porosity than the silica aerogel. After high-temperature adsorption at 800 ℃, the specific surface areas of the silica aerogel and the silicon-aluminum-based aerogel prepared in example 1 are respectively reduced by 150.71m2·g-1And 71.27m2·g-1The results show that the silicon-aluminum based aerogel prepared in example 1 has a pore channel which is not easy to collapse at high temperature, has a stable structure and high thermal stability, and can be applied to adsorption of heavy metal gas in an actual pyrolysis process.

Claims (7)

1. The preparation method of the silicon-aluminum based aerogel is characterized by comprising the following steps:
(1) adding aluminum isopropoxide into a mixed solution of ethanol and water to obtain a mixed material, heating and refluxing the mixed material under a stirring condition, continuing to heat after stirring is stopped, cooling to room temperature after heating, and adjusting the pH value of the solution to be acidic to obtain alumina wet sol;
(2) adding tetraethoxysilane into a mixed solution of ethanol and water, stirring for no more than 0.5h, and adjusting the pH value of the solution to be acidic to obtain a silica sol precursor solution;
(3) and (3) mixing the alumina wet sol obtained in the step (1) with the silica sol precursor solution obtained in the step (2), adjusting the pH value of the mixed solution to be neutral after stirring, standing the mixed solution for at least 12 hours to form silicon-aluminum mixed wet gel, performing solvent exchange by using n-hexane, and drying the silicon-aluminum mixed wet gel in a vacuum drying oven to obtain the silicon-aluminum-based aerogel.
2. The method for preparing a silicoalumino-aerogel according to claim 1, characterized in that: in the step (1), the mixing volume ratio of the ethanol to the water is 15-30: 5-10.
3. The method for preparing a silicoalumino-aerogel according to claim 1, characterized in that: in the step (2), the mixing molar ratio of the ethanol to the water is 5-7: 1-3.
4. The method for preparing a silicoalumino-aerogel according to claim 1, characterized in that: in the step (3), the drying temperature is 50-60 ℃, and the drying time is 6-10 h.
5. The method for preparing a silicoalumino-aerogel according to claim 1, characterized in that: in the step (3), the molar ratio of silicon-aluminum elements in the obtained silicon-aluminum based aerogel is 1: 1.
6. The use of the silica-alumina based aerogel obtained by the method for preparing a silica-alumina based aerogel according to claim 1 for the adsorption of heavy metal gases.
7. The application of the silicon-aluminum based aerogel prepared by the preparation method of the silicon-aluminum based aerogel according to claim 6 in the aspect of adsorbing heavy metal gas is characterized in that: the silicon-aluminum-based aerogel is used for adsorbing heavy metal gas in the pyrolysis process, and the temperature in the pyrolysis process is 600-900 ℃.
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