CN113663610B - Macroporous low-density block-shaped composite gel and production process thereof - Google Patents
Macroporous low-density block-shaped composite gel and production process thereof Download PDFInfo
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- CN113663610B CN113663610B CN202111065135.2A CN202111065135A CN113663610B CN 113663610 B CN113663610 B CN 113663610B CN 202111065135 A CN202111065135 A CN 202111065135A CN 113663610 B CN113663610 B CN 113663610B
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- B01J13/00—Colloid chemistry, e.g. the production of colloidal materials or their solutions, not otherwise provided for; Making microcapsules or microballoons
- B01J13/0052—Preparation of gels
- B01J13/0056—Preparation of gels containing inorganic material and water
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- B01J20/02—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material
- B01J20/10—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material comprising silica or silicate
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- B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
- B01J20/28—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties
- B01J20/28014—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties characterised by their form
- B01J20/28047—Gels
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- B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
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- B01J20/28054—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties characterised by their surface properties or porosity
- B01J20/28057—Surface area, e.g. B.E.T specific surface area
- B01J20/28064—Surface area, e.g. B.E.T specific surface area being in the range 500-1000 m2/g
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- B01J20/28054—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties characterised by their surface properties or porosity
- B01J20/28069—Pore volume, e.g. total pore volume, mesopore volume, micropore volume
- B01J20/28076—Pore volume, e.g. total pore volume, mesopore volume, micropore volume being more than 1.0 ml/g
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- B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
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- B01J20/28054—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties characterised by their surface properties or porosity
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- B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
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- B01J20/3085—Chemical treatments not covered by groups B01J20/3007 - B01J20/3078
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- C01B33/00—Silicon; Compounds thereof
- C01B33/113—Silicon oxides; Hydrates thereof
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Abstract
The invention belongs to the technical field of silica gel, and particularly relates to a macroporous low-density block-shaped composite gel and a production process thereof. Common silica gel products in the prior art include macroporous silica gel and fine pore silica gel, and the realization of the high specific surface area and large pore volume performance is generally difficult to meet. In the water washing process, the pore-expanding agent is added and the water washing is combined, so that the product is further expanded. And in the drying process, the low-temperature drying is carried out, the drying time is prolonged, and the reaming is further carried out. The specific surface area and the pore diameter of the silica gel product prepared by the invention are obviously higher than those of the prior art. The preparation process has mild reaction condition and safe and simple operation.
Description
Technical Field
The invention belongs to the technical field of silica gel, and particularly relates to a macroporous low-density block-shaped composite gel and a production process thereof.
Background
Silica gel is a typical porous adsorption material with high activity, is nontoxic and odorless, has stable chemical property, hardly reacts with any substances except strong alkali and hydrofluoric acid, and has a microporous structure. Because of the three-dimensional space reticular porous structure of the silica gel, the silica gel has larger specific surface area, more silanol groups are adhered to the surface of the silica gel, and the silica gel has stronger adsorption performance and can be used as a drying agent, an adsorbent, a catalyst and a catalyst carrier. The adsorption performance of the silica gel has a dense and inseparable relation with the rich pore channel structure and the high specific surface area.
The silica gel forms different skeleton structures according to different production flows and preparation methods, and is commonly macroporous silica gel and fine pore silica gel in the existing silica gel products at present, wherein the pore volume of the macroporous silica gel is larger, the specific surface area is smaller, and the fine pore silica gel has better specific surface area, but the pore volume is smaller. The inventor considers that developing a silica gel product with both large pore volume and high specific surface area has good production significance. Zhao Xipeng the research provides a preparation method of silica gel with large pore volume and high specific surface area, which takes sodium silicate and inorganic acid as raw materials to prepare the silica gel with large pore volume and high specific surface area by a chemical precipitation method, and the silica gel has shallower adsorption capacity and is suitable for producing advertising and office papers such as roll inkjet papers, color inkjet papers, photographic papers and the like. Qu Jichang et al report the effect of the drying regime on the performance of the support silica gel, and according to the results of their studies, different drying regimes have a significant effect on the surface area, pore volume and average pore size of the silica gel.
The existing production method of the silica gel with large pore volume needs steaming, salt soaking and calcination, and preparation by organic solvent replacement, etc., generally has the problems of high energy consumption and high production cost, and some organic solvents are difficult to fully recycle in the production process, thus polluting the environment. For example: chinese patent CN103159220a in 2013, 6 and 19 discloses a preparation method of macroporous silica gel, which uses silicate, inorganic acid, alkaline medium, fatty alcohol or fatty alcohol amine as raw materials, and comprises the following steps: 1) Contacting the alkaline medium with inorganic acid at 20-50deg.C for 10-30min; 2) Adding fatty alcohol or fatty alcohol amine, and reacting at 30-70deg.C for 10-60min; 3) Gradually adding silicate solution with concentration of 1.0-3.0mol/L at the speed of 2.0-5.0 mL/min; 4) Adding fatty alcohol or fatty alcohol amine again, and reacting at 30-70deg.C for 10-30min; 5) Then adding silicate solution gradually at the speed of 2.0-5.0mL/min, and then adjusting the pH value of the solution to 6-8 by using inorganic acid; 6) Heating to 60-90 deg.c for 1-7 hr, acidifying, washing and drying to obtain silica gel. According to the preparation method of the macroporous silica gel, fatty alcohol or fatty alcohol amine is used twice, and belongs to an organic solvent, and on one hand, the fatty alcohol or fatty alcohol amine can be removed only by high-temperature drying or activating treatment in the later production process, so that the energy consumption is high, and the production cost is high; on the other hand, the organic solvents are difficult to fully recycle in the production process, and environmental pollution is caused. Chinese patent CN103387239a proposes a method for washing silica gel with seawater, which improves the water washing rate by weak alkalinity of seawater, but weak alkalinity of seawater easily damages the internal microstructure of silica gel, which causes unreasonable pore size of silica gel, affects subsequent water absorption effect of silica gel, and has high seawater transportation equipment and investment cost, which cannot be applied in large scale.
Current methods of aerogel production generally include supercritical drying and atmospheric drying methods. Supercritical drying is to heat and pressurize the solution in the gel channel to supercritical state, in which state the interface between liquid and gas will disappear and capillary force will not exist. The gel is decompressed and dried under the supercritical state, so that the original structure of the gel can be well maintained, but the pressure and the temperature of the supercritical point of common liquid are relatively high, for example, the supercritical point of methanol is 239.4 ℃ and approximately 81 atmospheres, and the high pressure and the high temperature lead the aerogel preparation equipment to be expensive, difficult to operate, high in cost and meanwhile have the danger of explosion leakage.
The normal pressure drying method does not need high temperature and high pressure, and has safe operation and low cost. The normal pressure drying firstly uses a solvent with low surface tension (such as n-hexane) to replace the original solvent with high surface tension (such as water) in the gel pore canal through solvent exchange, and simultaneously inert modification is carried out on the groups on the surface of the gel pore canal, so that the hydroxyl groups with higher activity on the surface of the gel pore canal are modified into chemically inert silyl groups, and thus, the hydroxyl groups are prevented from being condensed due to the volume shrinkage of the gel in the drying process. The aerogel material prepared by the method can reach the aerogel material prepared by supercritical drying in terms of structure and performance. Because the traditional normal pressure drying requires a plurality of steps of gel pore canal solvent exchange and surface hydrophobization treatment, the preparation period is generally long, the operation is complicated, and the waste water and waste liquid formed by repeated solvent replacement can cause serious environmental pollution, so that the preparation cost of the aerogel is also increased.
The freeze-drying method fully utilizes the characteristic of the solvent, and when the solvent is frozen into a solid state, the volume of the solvent expands, so that gel particles which are originally close to each other are properly separated, and the phenomenon of drying shrinkage is overcome. However, freeze drying also has many disadvantages such as long drying cycles, some degree of network structural damage caused by freeze expansion of the pore solvent, and the like.
At present, the specific surface area and the pore diameter of the silica gel product prepared in the prior art are remarkably poor, and the preparation process has a plurality of problems. The specific surface area and pore size are both significantly higher than those of prior art silica gel products and processes capable of preparing such products.
Disclosure of Invention
Aiming at a plurality of problems existing in the prior art of gel and production process thereof, the invention provides a macroporous low-density block-shaped composite gel and production process thereof. The specific surface area and the pore diameter of the prepared product are obviously higher than those of the prior art; the preparation process has mild reaction condition and safe and simple operation, and the prepared target product has relatively large pore size and relatively high specific surface area.
The invention is realized by the following technical scheme:
a macroporous low-density block composite gel, the pore size of the composite gel is 18-25 nm, the pore volume is 2.5-3.5 mL/g, and the specific surface area is 530-560 m 2 /g。
The production process of the gel comprises the following steps:
step 1): taking a sulfuric acid aqueous solution with the mass concentration of 20-35% for standby;
step 2): taking water glass with the mass concentration of 15-25% for standby;
step 3): adding the sulfuric acid aqueous solution obtained in the step 1) into the water glass obtained in the step 2), controlling the pH value of a reaction system to be 7.5-8.0, and reacting at 35-50 ℃ to obtain silicic acid gel;
step 4): aging the silicic acid gel obtained in the step 3) at 60-90 ℃ for 35-38 hours;
step 5): after aging, cutting gel into gel blocks with the size of 5-15 mm;
step 6): transferring the wet silica gel block obtained in the step 5) into a water washing tank with a built-in heating coil, adding washing liquid, and washing at a controlled temperature;
step 7): and (3) after the water washing is finished, replacing the washing liquid in the step (6), taking out the wet glue block, and drying in vacuum to obtain a target product.
Preferably, the washing liquid in the step 6) is an aqueous solution of 2-6% of reaming auxiliary agent by mass percent.
Preferably, the reaming aid is (NH 4 ) 2 HPO 4 、(NH 4 ) 3 PO 4 Any one or more of ammonium bicarbonate.
Preferably, the washing temperature in the step 6) is 70-75 ℃.
Preferably, the washing operation step in the step 6) is that the washing liquid is added into a water washing tank, heated to the washing temperature, and kept stand for 3 to 4 hours, and then the washing liquid is discharged from the bottom of the tank; repeating the above operation until no sulfate radical is detected in the washing liquid; and (3) finishing washing;
preferably, the replacement liquid in the step 7) is an ethanol water solution with the volume fraction of 50-80%.
Preferably, the drying temperature in the step 7) is 25-35 ℃ and the drying time is 20-28 h.
The production process of the gel comprises the following steps of:
step 1): taking a sulfuric acid aqueous solution with the mass concentration of 30% for later use;
step 2): taking water glass with the mass concentration of 20% for later use;
step 3): adding the sulfuric acid aqueous solution obtained in the step 1) into the water glass obtained in the step 2), controlling the pH value of a reaction system to be 7.5-8.0, and reacting at 35-50 ℃ to obtain silicic acid gel;
step 4): aging the silicic acid gel obtained in the step 3) at 60-90 ℃ for 36h;
step 5): after aging, cutting gel into gel blocks with the size of 5-10 mm;
step 6): transferring the wet silica gel block obtained in the step 5) into a water washing tank with a built-in heating coil, adding an aqueous solution of ammonium bicarbonate with the mass fraction of 3%, heating to 70-75 ℃, standing for 3-4 h, and discharging washing liquid from the bottom of the tank; repeating for 3 times, detecting that no sulfate radical exists, and finishing washing;
step 7): and (3) after the water washing is finished, replacing the washing liquid in the step (6) with an ethanol water solution with the volume fraction of 75%, taking out wet gel blocks, and carrying out vacuum drying at the drying temperature of 30 ℃ for 24 hours to obtain a target product.
The invention has the beneficial effects that:
1) The product prepared by the invention has larger aperture and specific surface area.
2) The reaming agent and the temperature rise are adopted in the washing process, so that the sulphate can be effectively washed, the reaming effect is further achieved, and the application of reagents such as ammonia water is effectively avoided.
3) A drying stage, namely replacing the raw materials by ethanol water solution and carrying out low-temperature vacuum drying; avoid the defect that prior art freeze drying and supercritical drying brought, in this process ethanol aqueous solution and low temperature long-time drying have effectually played the reaming effect.
4) The method has mild reaction conditions, safe and simple operation process and is suitable for industrialization.
Detailed Description
The invention is further illustrated by the following examples, with the understanding that: the examples of the present invention are intended to be illustrative of the invention and not to be limiting of the invention, so that simple modifications to the invention which are based on the method of the invention are within the scope of the invention as claimed.
In the following examples, various processes and methods, which are not described in detail, are conventional methods well known in the art.
Example 1
A production process of a macroporous low-density block composite gel comprises the following steps:
step 1): taking a sulfuric acid aqueous solution with the mass concentration of 30% for later use;
step 2): taking water glass with the mass concentration of 20% for later use;
step 3): adding the sulfuric acid aqueous solution obtained in the step 1) into the water glass obtained in the step 2), controlling the pH value of a reaction system to be 7.8, and reacting at 40 ℃ to obtain silicic acid gel;
step 4): aging the silicic acid gel obtained in the step 3) at 80 ℃ for 36 hours;
step 5): after aging, cutting gel into gel blocks with the size of 5-10 mm;
step 6): transferring the wet silica gel block obtained in the step 5) into a water washing tank with a built-in heating coil, adding an aqueous solution of ammonium bicarbonate with the mass fraction of 3%, heating to 70-75 ℃, standing for 3.5h, and discharging a washing liquid from the bottom of the tank; repeating for 3 times, detecting that no sulfate radical exists, and finishing washing;
step 7): and (3) after the water washing is finished, replacing the washing liquid in the step (6) with an ethanol water solution with the volume fraction of 75%, taking out wet gel blocks, and carrying out vacuum drying at the drying temperature of 30 ℃ for 24 hours to obtain a target product.
Example 2
A production process of a macroporous low-density block composite gel comprises the following steps:
step 1): taking sulfuric acid with the mass concentration of 20% for standby;
step 2): taking water glass with the mass concentration of 15% for later use;
step 3): adding the sulfuric acid obtained in the step 1) into the water glass obtained in the step 2), controlling the pH value of a reaction system to be 7.5, and reacting at 35 ℃ to obtain silicic acid gel;
step 4): aging the silicic acid gel obtained in the step 3) at 60 ℃ for 35 hours;
step 5); after aging, cutting gel into gel blocks with the size of 5-10 mm;
step 6): transferring the wet silica gel block obtained in the step 5) into a water washing tank with a built-in heating coil, adding an aqueous solution of ammonium bicarbonate with the mass fraction of 2%, heating to 70-75 ℃, standing for 3 hours, and discharging a washing liquid from the bottom of the tank; repeating for 4 times, detecting that no sulfate radical exists, and finishing washing;
step 7): and (3) after the water washing is finished, replacing the washing liquid in the step (6) with an ethanol water solution with the volume fraction of 50%, taking out wet gel blocks, and carrying out vacuum drying at the drying temperature of 25 ℃ for 28 hours to obtain a target product.
Example 3
A production process of a macroporous low-density block composite gel comprises the following steps:
step 1): taking a sulfuric acid aqueous solution with the mass concentration of 35% for standby;
step 2): taking water glass with the mass concentration of 25% for later use;
step 3): adding the sulfuric acid aqueous solution obtained in the step 1) into the water glass obtained in the step 2), controlling the pH value of a reaction system to be 8.0, and reacting at 50 ℃ to obtain silicic acid gel;
step 4): aging the silicic acid gel obtained in the step 3) at 90 ℃ for 38 hours;
step 5): after aging, cutting gel into gel blocks with the size of 5-10 mm;
step 6): transferring the wet silica gel block obtained in the step 5) into a water washing tank with a built-in heating coil, adding an aqueous solution of ammonium bicarbonate with the mass fraction of 6%, heating to 70-75 ℃, standing for 4 hours, and discharging a washing liquid from the bottom of the tank; repeating for 5 times, detecting that no sulfate radical exists, and finishing washing;
step 7): and (3) after the water washing is finished, replacing the washing liquid in the step (6) with an ethanol water solution with the volume fraction of 80%, taking out wet gel blocks, and carrying out vacuum drying at the drying temperature of 35 ℃ for 20 hours to obtain a target product.
Example 4
A production process of a macroporous low-density block composite gel comprises the following steps:
step 1): taking a sulfuric acid aqueous solution with the mass concentration of 30% for later use;
step 2): taking water glass with the mass concentration of 20% for later use;
step 3): adding the sulfuric acid aqueous solution obtained in the step 1) into the water glass obtained in the step 2), controlling the pH value of a reaction system to be 7.8, and reacting at 40 ℃ to obtain silicic acid gel;
step 4): aging the silicic acid gel obtained in the step 3) at 80 ℃ for 36 hours;
step 5): after aging, cutting gel into gel blocks with the size of 5-10 mm;
step 6): transferring the wet silica gel block obtained in the step 5) into a water washing tank with a built-in heating coil, and adding 3% of (NH) 4 ) 2 HPO 4 Heating to 70-75 ℃, standing for 3.5h, and discharging the washing liquid from the bottom of the tank; repeating for 3 times, detecting that no sulfate radical exists, and finishing washing;
step 7): and (3) after the water washing is finished, replacing the washing liquid in the step (6) with an ethanol water solution with the volume fraction of 75%, taking out wet gel blocks, and carrying out vacuum drying at the drying temperature of 30 ℃ for 24 hours to obtain a target product.
Example 5
A production process of a macroporous low-density block composite gel comprises the following steps:
step 1): taking a sulfuric acid aqueous solution with the mass concentration of 30% for later use;
step 2): taking water glass with the mass concentration of 20% for later use;
step 3): adding the sulfuric acid aqueous solution obtained in the step 1) into the water glass obtained in the step 2), controlling the pH value of a reaction system to be 7.8, and reacting at 40 ℃ to obtain silicic acid gel;
step 4): aging the silicic acid gel obtained in the step 3) at 80 ℃ for 36 hours;
step 5): after aging, cutting gel into gel blocks with the size of 5-10 mm;
step 6): transferring the wet silica gel block obtained in the step 5) into a water washing tank with a built-in heating coil, and adding 3% of (NH) 4 ) 3 PO 4 Heating to 70-75 ℃, standing for 3.5h, and discharging the washing liquid from the bottom of the tank; repeating for 3 times, detecting that no sulfate radical exists, and finishing washing;
step 7): and (3) after the water washing is finished, replacing the washing liquid in the step (6) with an ethanol water solution with the volume fraction of 75%, taking out wet gel blocks, and carrying out vacuum drying at the drying temperature of 30 ℃ for 24 hours to obtain a target product.
Comparative example 1
A production process of a macroporous low-density block composite gel comprises the following steps:
step 1): taking a sulfuric acid aqueous solution with the mass concentration of 30% for later use;
step 2): taking water glass with the mass concentration of 20% for later use;
step 3): adding the sulfuric acid aqueous solution obtained in the step 1) into the water glass obtained in the step 2), controlling the pH value of a reaction system to be 7.8, and reacting at 40 ℃ to obtain silicic acid gel;
step 4): aging the silicic acid gel obtained in the step 3) at 80 ℃ for 36 hours;
step 5): after aging, cutting gel into gel blocks with the size of 5-10 mm;
step 6): transferring the wet silica gel block obtained in the step 5) into a water washing tank with a built-in heating coil, adding purified water, heating to 70-75 ℃, standing for 3.5h, and discharging washing liquid from the bottom of the tank; repeating for 3 times, detecting that no sulfate radical exists, and finishing washing;
step 7): and (3) after the water washing is finished, replacing the washing liquid in the step (6) with an ethanol water solution with the volume fraction of 75%, taking out wet gel blocks, and carrying out vacuum drying at the drying temperature of 30 ℃ for 24 hours to obtain a target product.
Comparative example 2
A production process of a macroporous low-density block composite gel comprises the following steps:
step 1): taking a sulfuric acid aqueous solution with the mass concentration of 30% for later use;
step 2): taking water glass with the mass concentration of 20% for later use;
step 3): adding the sulfuric acid aqueous solution obtained in the step 1) into the water glass obtained in the step 2), controlling the pH value of a reaction system to be 7.8, and reacting at 40 ℃ to obtain silicic acid gel;
step 4): aging the silicic acid gel obtained in the step 3) at 80 ℃ for 36 hours;
step 5): after aging, cutting gel into gel blocks with the size of 5-10 mm;
step 6): transferring the wet silica gel block obtained in the step 5) into a water washing tank with a built-in heating coil, adding an aqueous solution of ammonium bicarbonate with the mass fraction of 3%, heating to 70-75 ℃, standing for 3.5h, and discharging a washing liquid from the bottom of the tank; repeating for 3 times, detecting that no sulfate radical exists, and finishing washing;
step 7): and (3) after the water washing is finished, replacing the washing liquid in the step (6) with a pure water solution, taking out wet glue blocks, and carrying out vacuum drying at the drying temperature of 30 ℃ for 30 hours to obtain a target product.
Performance test of the product of the above example:
TABLE 1 Performance test results
| Examples | Average pore diameter (nm) | Pore volume (mL/g) | Specific surface area (m) 2 /g） |
| Example 1 | 25.0 | 3.5 | 560 |
| Example 2 | 18.6 | 2.5 | 537 |
| Example 3 | 24.2 | 3.3 | 546 |
| Example 4 | 20.3 | 2.7 | 532 |
| Example 5 | 22.5 | 3.0 | 534 |
| Comparative example 1 | 10.8 | 1.0 | 370 |
| Comparative example 2 | 16.3 | 1.2 | 295 |
Claims (2)
1. The production process of the macroporous low-density block composite gel is characterized by comprising the following steps of:
step 1): taking a sulfuric acid aqueous solution with the mass concentration of 20-35% for standby;
step 2): taking water glass with the mass concentration of 15-25% for standby;
step 3): adding the sulfuric acid aqueous solution obtained in the step 1) into the water glass obtained in the step 2), controlling the pH value of a reaction system to be 7.5-8.0, and reacting at 35-50 ℃ to obtain silicic acid gel;
step 4): aging the silicic acid gel obtained in the step 3) at 60-90 ℃ for 35-38 hours;
step 5): after aging, cutting gel into gel blocks with the size of 5-15 mm;
step 6): transferring the wet silica gel block obtained in the step 5) into a water washing tank with a built-in heating coil, adding washing liquid, and washing at a controlled temperature;
step 7): after the water washing is finished, the washing liquid in the step 6) is replaced, and then the wet glue block is taken out and dried in vacuum to obtain a target product;
the pore size of the composite gel is 18-25 nm, the pore volume is 2.5-3.5 mL/g, and the specific surface area is 530-560 m < 2 >/g;
the washing liquid in the step 6) is water of reaming auxiliary agent with mass fraction of 2% -6%A solution; the reaming assistant is (NH) 4 ) 2 HPO 4 、(NH 4 ) 3 PO 4 Any one or more of ammonium bicarbonate; the washing temperature is 70-75 ℃;
the washing operation steps in the step 6) are as follows: adding the washing liquid into a water washing tank, heating to the washing temperature, standing for 3-4 h, and discharging the washing liquid from the bottom of the tank; repeating the above operation until no sulfate radical is detected in the washing liquid, and finishing washing;
the replacement liquid in the step 7) is ethanol water solution with the volume fraction of 50-80%;
the drying temperature in the step 7) is 25-35 ℃ and the drying time is 20-28 h.
2. The production process according to claim 1, characterized by comprising the steps of:
step 1): taking a sulfuric acid aqueous solution with the mass concentration of 30% for later use;
step 2): taking water glass with the mass concentration of 20% for later use;
step 3): adding the sulfuric acid aqueous solution obtained in the step 1) into the water glass obtained in the step 2), controlling the pH value of a reaction system to be 7.5-8.0, and reacting at 35-50 ℃ to obtain silicic acid gel;
step 4): aging the silicic acid gel obtained in the step 3) at 60-90 ℃ for 36h;
step 5): after aging, cutting gel into gel blocks with the size of 5-10 mm;
step 6): transferring the wet silica gel block obtained in the step 5) into a water washing tank with a built-in heating coil, adding an aqueous solution of ammonium bicarbonate with the mass fraction of 3%, heating to 70-75 ℃, standing for 3-4 h, and discharging washing liquid from the bottom of the tank; repeating for 3 times, and detecting that no sulfate radical exists;
step 7): and (3) after the water washing is finished, replacing the washing liquid in the step (6) with an ethanol water solution with the volume fraction of 75%, taking out wet gel blocks, and carrying out vacuum drying at the drying temperature of 30 ℃ for 24 hours to obtain a target product.
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