CN112919482B - Preparation method of porous silica with high specific surface area - Google Patents

Abstract

The invention provides a preparation method of porous silica with high specific surface area, which comprises the steps of adding a proper amount of slaked lime into water glass solution for reaction, selectively leaching obtained precipitate by an acid solution to obtain suspension, carrying out solid-liquid separation on the suspension, and washing and drying the obtained solid product to obtain the porous silica with high specific surface area. The porous silica with high specific surface area prepared by the invention has good dispersibility, uniform granularity and S _BET 704-870m ² And/g, can be applied to the fields of separation adsorption, catalysis, photoelectricity, biology, carriers and the like.

Description

A method for preparing high specific surface area porous silica

Technical field

The invention relates to the field of preparation of inorganic materials, and in particular to a preparation method of high specific surface area porous silica.

Background technique

Porous silica, also known as precipitated hydrated silica and white carbon black, is an amorphous SiO ₂ material, mainly used in rubber, coatings, papermaking, catalysis, carriers, adsorption and other fields.

At present, the preparation methods of silica mainly include precipitation method, sol-gel method and gas phase method. Silica produced by the precipitation method is also called precipitated hydrated silica. It uses inorganic silicon as the silicon source, sulfuric acid, hydrochloric acid, and carbonic acid as acidifiers, and is produced through precipitation, filtration, and drying. The production of silica by precipitation method has a simple process and low equipment requirements. Inorganic silicon is often used as raw material. The specific surface area of the resulting silica is generally 50-200m ² /g. Silica produced by the sol-gel method is also called silica gel. It mainly uses organic silicon as the silicon source and is produced through the steps of gelation, aging, drying and activation. The specific surface area of the obtained silica is generally 100-500m ² /g. Silica produced by the gas phase method is nanoscale silica. It is produced by reacting organohalosilanes such as SiCl ₄ with O ₂ and H ₂ at 1200-1800°C, followed by cooling, separation and deacidification. The particle size is uniform and general. is 10-40nm, and the specific surface area is generally 200-400m ² /g.

Chinese patent CN103754885B discloses a method for preparing porous silica by acid leaching. The asbestos tailings powder is leached with a hydrochloric acid solution. The slurry after the reaction is filtered and washed to separate the solid and liquid components. The solid residue obtained by filtration and Caustic soda reacts under heating conditions to generate a slurry containing sodium silicate. Filter the above slurry containing sodium silicate, remove the solid residue, add sodium salt, add water to adjust to a suitable concentration, add dispersant, and add acid to precipitate. , obtain hydrated silica precipitate, and the precipitated product is aged, filtered, washed, and dried to obtain porous silica with a specific surface area of 300-370m ² /g.

Chinese patent CN103303929B discloses a method for preparing high-transparency and highly-dispersible silica. Sodium gluconate is used as a sustained-release agent and added to a sodium silicate solution for aging and filtration. The resulting filter cake is beaten in a high-speed disperser and added to the slurry. Fatty acid amide is added to react, and the slurry after the reaction is spray-dried to obtain white carbon black with a specific surface area of 251-257m ² /g.

Chinese patent CN106564924B discloses a one-step method for preparing silica and calcium chloride by using calcium silicate. Stir the calcium silicate and water thoroughly, let it stand, and add the suspension or the supernatant after sedimentation and separation. After the surfactant polyethylene glycol, quickly add hydrochloric acid dropwise to make the system pH less than 1 to obtain a sol. Add a certain amount of concentrated ammonia water to the sol to make the pH to 6-7 to obtain a gel. Then quickly add hydrochloric acid dropwise until the pH is less than 1, and filter. The washed filter cake is dried and burned to obtain white carbon black with a specific surface area of 493.17m ² /g.

Chinese patent CN106430223B discloses a method for preparing high specific surface area silica using fluorosilicate. Add additives containing alcoholic hydroxyl groups to the aqueous solution, then add the fluorosilicate to the aqueous solution, stir evenly, and add ammonia dropwise. , continue the reaction; after the reaction is completed, it is aged, filtered, washed and dried to obtain white carbon black with a specific surface area of 220m ² /g.

Chinese patent CN105060307B discloses a high specific surface area silica and its production method. Solid sodium silicate and water are added to a static autoclave, water vapor is introduced into the kettle and dissolved to obtain hydrated dilute liquid sodium silicate, and water and water are added to the reaction kettle. Mix dilute liquid sodium silicate, then drop inorganic acid aqueous solution at a constant rate into the mixed solution, add steam to heat and pressurize, then acidify with sulfuric acid to obtain silica slurry, press filter and wash the filter cake, and put the filter cake in the slurry tank Slurry and spray dry to obtain white carbon black with a specific surface area of 200-450m ² /g.

Chinese patent CN107285350A discloses a method for leaching fly ash with hydrochloric acid to extract alumina and co-produce white carbon black. White carbon black is prepared through the sol-gel method, that is, adding surfactant polyethylene glycol to a calcium silicate aqueous solution, heating and stirring ; After reaching the specified temperature, quickly add fly ash leaching residual liquid to adjust the pH value of the system to less than 1. Add a certain amount of concentrated ammonia dropwise to adjust the pH value to 6-7; then quickly add a certain amount of fly ash. Extract the residual liquid, adjust the pH value to less than 1, filter, and then wash with distilled water until the pH is neutral to obtain a white carbon black product.

However, when preparing the above-mentioned porous silica, it is necessary to add organic dispersants and repeatedly adjust the pH of the solution to avoid gel agglomeration, resulting in a reduction in the specific surface area of the product; and in subsequent steps, it needs to be removed by methods such as high-temperature roasting and solvent extraction. Organic dispersant; harsh reaction conditions and complex production process. In addition, organic wastewater is easily generated during the preparation process, causing environmental pollution. Therefore, the preparation method of porous silica with simple process, no pollution and low cost is the future development direction.

Contents of the invention

In view of the above-mentioned deficiencies in the prior art, the present invention provides a method for preparing porous silica with high specific surface area. Water glass solution and slaked lime are mixed to generate calcium silicate particles with uniform particle size, and acid leaching is used to make the calcium silicate skeleton into Calcium ions and unreacted slaked lime dissolve into the solution, increasing the specific surface area of the particles. At the same time, the product maintains the skeleton structure of calcium silicate, thereby obtaining porous silica with uniform particle size and high specific surface area.

The technical solutions adopted by the present invention are as follows:

A method for preparing high specific surface area porous silica. An appropriate amount of slaked lime is added to a water glass solution to perform a precipitation reaction. The resulting precipitate is selectively leached with an acid solution to obtain a suspension. The suspension is subjected to solid-liquid separation to obtain a solid product. The high specific surface area porous silica is obtained after washing and drying; the conditions for the precipitation reaction are: the modulus of the water glass solution is 0.6-3.3, and the mass fraction of _SiO2 in the water glass solution is 8-10wt% , the reaction temperature is 15-70°C, the reaction time is 30-180min; the conditions for selective leaching of the acid solution are: the concentration of H ⁺ in the acid solution is 1-12mol/L, the leaching temperature is 15-90°C, and the leaching condition is The time is 0.5-168h.

Preferably, the mass ratio of the slaked lime, water glass solution and acid solution is 1:8-10:20-50.

Preferably, the acid solution is hydrochloric acid or nitric acid.

Specifically, the preparation method of high specific surface area porous silica includes the following steps:

S1. Add an appropriate amount of slaked lime to the water glass solution to perform a precipitation reaction to obtain a mixed slurry. The conditions for the precipitation reaction are: the modulus of the water glass solution is 0.6-3.3, and the mass fraction of SiO ₂ in the water glass solution is 8 -10wt%, reaction temperature is 15-70°C, reaction time is 30-180min, stirring speed is 50-800r/min;

S2. Filter, wash and dry the slurry obtained in step S1 to obtain solid powder. The drying conditions are: drying temperature is 30-200°C, and drying time is 0-48h;

S3. Selectively leaching the solid powder obtained in step S2 with an acid solution to obtain a suspension. The conditions for selective leaching of the acid solution are: the concentration of H ⁺ in the acid solution is 1-12 mol/L, and the leaching temperature is 15-15 mol/L. 90℃, leaching time is 0.5-168h, stirring speed is 50-1500r/min;

S4. The suspension obtained in step S3 is subjected to solid-liquid separation. The obtained solid product is washed and dried to obtain the high specific surface area porous silica; the drying conditions are: the drying temperature is 60-200°C, Drying time is 6-48h.

The principle of the present invention is as follows:

The preparation principle of the high specific surface area porous silica of the present invention is that calcium silicate is converted into silica through acidification, slaked lime and water glass solution are used as raw materials to generate calcium silicate precipitates with uniform particle size, and the calcium silicate skeleton is made by acid leaching. Unreacted hydrated lime is dissolved into the solution; at the same time, the proton concentration in the solution is high and the proton competitiveness is strong. The protons will exchange a large amount of calcium ions on the calcium silicate skeleton without changing the original calcium silicate skeleton structure, thus increasing the particle size. Specific surface area.

Due to the high alkalinity of the water glass solution, hydrated lime can only be slowly released into the solution. The precipitation reaction between slaked lime and water glass proceeds slowly, generating calcium silicate particles with rich pores and uniform particle size. The reaction equation is as follows:

Ca(OH) ₂ (s)+Na ₂ SiO ₃ →CaSiO ₃ (s)+2NaOH

During the acid leaching process of calcium silicate, the mixed unreacted calcium hydroxide reacts with the acid, and the product is a soluble salt, and the calcium ions are dissolved into the solution; at the same time, the proton concentration in the solution is high, the proton competitiveness is strong, and a large number of protons will The calcium ions in the calcium silicate skeleton are exchanged without changing the original calcium silicate skeleton structure, thereby increasing the specific surface area of the particles. The reaction equation is as follows:

Ca(OH) ₂ (s)+2H ⁺ →2H ₂ O+Ca ²⁺

CaSiO ₃ (s)+2H ⁺ →H ₂ SiO ₃ (s)+Ca ²⁺

Compared with the prior art, the present invention has the following beneficial effects:

(1) The present invention relates to a method for preparing high specific surface area porous silica. An appropriate amount of slaked lime is added to a water glass solution for reaction, and the resulting precipitate is selectively leached with an acid solution to obtain a suspension, and the suspension is subjected to solid-liquid separation. , the obtained solid product is washed and dried to obtain high specific surface area porous silica. The obtained product has good dispersion, uniform particle size, and S _BET of 704-870m ² /g.

(2) The method of the present invention does not go through the sol-gel process, no gel is produced, the process is short, the operation is simple, and the cost is low. It is expected to realize further resource utilization of water glass and slaked lime.

(3) The method of the present invention does not require organic dispersants, secondary impurity removal, and no environmental pollution.

(4) The porous silica prepared by the present invention has uniform particle size and high specific surface area, and can be used in fields such as separation and adsorption, catalysis, optoelectronics, biology, and carriers.

Description of the drawings

Figure 1 is a process flow chart of the preparation method of high specific surface area porous silica according to the present invention.

Detailed ways

The particle size distribution of the high specific surface area porous silica prepared in the following examples was analyzed by a wet laser particle size analyzer; the specific surface area was analyzed by the BET method.

Example 1:

(1) Add an appropriate amount of slaked lime to the water glass solution to perform a precipitation reaction to obtain a mixed slurry. The conditions for the precipitation reaction are: the modulus of the water glass solution is 1.0, and the mass fraction of SiO ₂ in the water glass solution is 8.6wt %, the reaction temperature is 15°C, the reaction time is 120min, the stirring speed is 150r/min, and the mass ratio of slaked lime and water glass solution is 1:9.5;

(2) Filter, wash and dry the slurry obtained in step (1) to obtain solid powder. The drying temperature is 120°C and the drying time is 18 hours;

(3) The solid powder obtained in step (2) is leached with hydrochloric acid to obtain a suspension. The leaching conditions are: the concentration of hydrochloric acid is 1mol/L, the leaching temperature is 50°C, the leaching time is 12h, the stirring speed is 150r/min, slaked lime The mass ratio to hydrochloric acid is 1:30;

(4) Perform solid-liquid separation on the suspension obtained in step (3). The solid product obtained is washed and dried to obtain high specific surface area porous silica. The drying temperature is 105°C and the drying time is 6 hours.

Analysis and testing results of the sample obtained in this example: the silica content is 99.2%, the specific surface area S _BET is 762.27m ² /g, the pore volume is 0.53cm ³ /g, the average pore diameter is 5.86nm, and the median particle diameter is 6.43μm , D ₁₀ is 4.42μm, D ₉₀ is 9.76μm.

Example 2:

(1) Add an appropriate amount of slaked lime to the water glass solution to perform a precipitation reaction to obtain a mixed slurry. The conditions for the precipitation reaction are: the modulus of the water glass solution is 0.6, and the mass fraction of SiO ₂ in the water glass solution is 10 wt%. , the reaction temperature is 45°C, the reaction time is 30min, the stirring speed is 350r/min, and the mass ratio of slaked lime and water glass solution is 1:8.0;

(2) Filter, wash and dry the slurry obtained in step (1) to obtain solid powder. The drying temperature is 60°C and the drying time is 48 hours;

(3) The solid powder obtained in step (2) is leached with hydrochloric acid to obtain a suspension. The leaching conditions are: the concentration of hydrochloric acid is 12mol/L, the leaching temperature is 90°C, the leaching time is 4h, the stirring speed is 425r/min, slaked lime The mass ratio to hydrochloric acid is 1:20;

(4) Perform solid-liquid separation on the suspension obtained in step (3). The solid product obtained is washed and dried to obtain high specific surface area porous silica. The drying temperature is 60°C and the drying time is 12 hours.

Analysis and testing results of the sample obtained in this example: the silica content is 99.0%, the specific surface area S _BET is 744.47m ² /g, the pore volume is 0.98m ³ /g, the average pore diameter is 8.78nm, and the median particle diameter is 21.89 μm , D ₁₀ is 11.69μm, D ₉₀ is 44.85μm.

Example 3:

(1) Add an appropriate amount of slaked lime to the water glass solution to perform a precipitation reaction to obtain a mixed slurry. The conditions for the precipitation reaction are: the modulus of the water glass solution is 3.3, and the mass fraction of SiO ₂ in the water glass solution is 8.0wt %, the reaction temperature is 70°C, the reaction time is 180min, the stirring speed is 400r/min, and the mass ratio of slaked lime and water glass solution is 1:9.0;

(2) Filter, wash and dry the slurry obtained in step (1) to obtain solid powder. The drying time is 0 h;

(3) The solid powder obtained in step (2) is leached with hydrochloric acid to obtain a suspension. The leaching conditions are: the concentration of hydrochloric acid is 4mol/L, the leaching temperature is 20°C, the leaching time is 80h, the stirring speed is 550r/min, slaked lime The mass ratio to hydrochloric acid is 1:40;

(4) Perform solid-liquid separation on the suspension obtained in step (3). The solid product obtained is washed and dried to obtain high specific surface area porous silica. The drying temperature is 200°C and the drying time is 8 hours.

Analysis and testing results of the sample obtained in this example: the silica content is 99.8%, the specific surface area S _BET is 771.27m ² /g, the pore volume is 0.75cm ³ /g, the average pore diameter is 5.89nm, and the median particle diameter is 7.09μm , D ₁₀ is 4.79μm, D ₉₀ is 10.79μm.

Example 4:

(1) Add an appropriate amount of slaked lime to the water glass solution to perform a precipitation reaction to obtain a mixed slurry. The conditions for the precipitation reaction are: the modulus of the water glass solution is 3.3, and the mass fraction of SiO ₂ in the water glass solution is 10.0wt %, the reaction temperature is 30°C, the reaction time is 60min, the stirring speed is 800r/min, and the mass ratio of slaked lime and water glass solution is 1:8.6;

(2) Filter, wash and dry the slurry obtained in step (1) to obtain solid powder. The drying temperature is 115°C and the drying time is 30 hours;

(3) The solid powder obtained in step (2) is leached with nitric acid to obtain a suspension. The leaching conditions are: the concentration of nitric acid is 12mol/L, the leaching temperature is 60°C, the leaching time is 48h, the stirring speed is 50r/min, slaked lime The mass ratio with nitric acid is 1:50;

(4) Perform solid-liquid separation on the suspension obtained in step (3). The solid product obtained is washed and dried to obtain high specific surface area porous silica. The drying temperature is 145°C and the drying time is 28 hours.

Analysis and testing results of the sample obtained in this example: the silica content is 99.4%, the specific surface area S _BET is 742.94m ² /g, the pore volume is 0.52cm ³ /g, the average pore diameter is 4.21nm, and the median particle diameter is 5.89μm , D ₁₀ is 4.07μm, D ₉₀ is 8.74μm.

Example 5:

(1) Add an appropriate amount of slaked lime to the water glass solution to perform a precipitation reaction to obtain a mixed slurry. The conditions for the precipitation reaction are: the modulus of the water glass solution is 1.6, and the mass fraction of SiO ₂ in the water glass solution is 9.0wt %, the reaction temperature is 65°C, the reaction time is 90min, the stirring speed is 550r/min, and the mass ratio of slaked lime and water glass solution is 1:8.3;

(2) Filter, wash and dry the slurry obtained in step (1) to obtain solid powder. The drying temperature is 70°C and the drying time is 12 hours;

(3) The solid powder obtained in step (2) is leached with hydrochloric acid to obtain a suspension. The leaching conditions are: the concentration of hydrochloric acid is 8mol/L, the leaching temperature is 80°C, the leaching time is 12h, the stirring speed is 800r/min, slaked lime The mass ratio to hydrochloric acid is 1:20;

(4) Perform solid-liquid separation on the suspension obtained in step (3). The solid product obtained is washed and dried to obtain high specific surface area porous silica. The drying temperature is 70°C and the drying time is 24 hours.

Analysis and testing results of the sample obtained in this example: the silica content is 98.7%, the specific surface area S _BET is 773.61m ² /g, the pore volume is 0.71cm ³ /g, the average pore diameter is 5.37nm, and the median particle diameter is 7.75μm , D ₁₀ is 5.32μm, D ₉₀ is 11.49μm.

Example 6:

(1) Add an appropriate amount of slaked lime to the water glass solution to perform a precipitation reaction to obtain a mixed slurry. The conditions for the precipitation reaction are: the modulus of the water glass solution is 0.8, and the mass fraction of SiO ₂ in the water glass solution is 9.3wt %, the reaction temperature is 20°C, the reaction time is 30min, the stirring speed is 200r/min, and the mass ratio of slaked lime and water glass solution is 1:8.5;

(2) Filter, wash and dry the slurry obtained in step (1) to obtain solid powder. The drying time is 0 h;

(3) The solid powder obtained in step (2) is leached with hydrochloric acid to obtain a suspension. The leaching conditions are: the concentration of hydrochloric acid is 1mol/L, the leaching temperature is 25°C, the leaching time is 0.5h, and the stirring speed is 550r/min. The mass ratio of hydrated lime to hydrochloric acid is 1:30;

(4) Perform solid-liquid separation on the suspension obtained in step (3). The solid product obtained is washed and dried to obtain high specific surface area porous silica. The drying temperature is 150°C and the drying time is 6 hours.

Analysis and testing results of the sample obtained in this example: the silica content is 99.0%, the specific surface area S _BET is 870.16m ² /g, the pore volume is 0.80cm ³ /g, the average pore diameter is 6.90nm, and the median particle diameter is 4.37 μm. , D ₁₀ is 2.99μm, D ₉₀ is 6.60μm.

Example 7:

(1) Add an appropriate amount of slaked lime to the water glass solution to perform a precipitation reaction to obtain a mixed slurry. The conditions for the precipitation reaction are: the modulus of the water glass solution is 2.0, and the mass fraction of SiO ₂ in the water glass solution is 9.2wt %, the reaction temperature is 50°C, the reaction time is 150min, the stirring speed is 700r/min, and the mass ratio of slaked lime and water glass solution is 1:10;

(2) Filter, wash and dry the slurry obtained in step (1) to obtain solid powder. The drying temperature is 30°C and the drying time is 3 hours;

(3) The solid powder obtained in step (2) is leached with nitric acid to obtain a suspension. The leaching conditions are: the concentration of nitric acid is 2mol/L, the leaching temperature is 15°C, the leaching time is 168h, the stirring speed is 70r/min, slaked lime The mass ratio with nitric acid is 1:45;

(4) Perform solid-liquid separation on the suspension obtained in step (3). The solid product obtained is washed and dried to obtain high specific surface area porous silica. The drying temperature is 130°C and the drying time is 16 hours.

Analysis and testing results of the sample obtained in this example: the silica content is 99.9%, the specific surface area S _BET is 704.99m ² /g, the pore volume is 0.47cm ³ /g, the average pore diameter is 4.03nm, and the median particle diameter is 7.91μm , D ₁₀ is 5.55μm, D ₉₀ is 11.30μm.

Example 8:

(1) Add an appropriate amount of hydrated lime to the water glass solution to perform a precipitation reaction to obtain a mixed slurry. The conditions for the precipitation reaction are: the modulus of the water glass solution is 1.2, and the mass fraction of SiO ₂ in the water glass solution is 9.8wt %, the reaction temperature is 35°C, the reaction time is 70min, the stirring speed is 300r/min, and the mass ratio of slaked lime and water glass solution is 1:8.1;

(2) Filter, wash and dry the slurry obtained in step (1) to obtain solid powder. The drying temperature is 145°C and the drying time is 24 hours;

(3) The solid powder obtained in step (2) is leached with hydrochloric acid to obtain a suspension. The leaching conditions are: the concentration of hydrochloric acid is 10mol/L, the leaching temperature is 40°C, the leaching time is 4h, the stirring speed is 700r/min, slaked lime The mass ratio to hydrochloric acid is 1:35;

(4) Perform solid-liquid separation on the suspension obtained in step (3). The solid product obtained is washed and dried to obtain high specific surface area porous silica. The drying temperature is 200°C and the drying time is 48 hours.

Analysis and testing results of the sample obtained in this example: the silica content is 99.0%, the specific surface area S _BET is 739.00m ² /g, the pore volume is 0.72cm ³ /g, the average pore diameter is 6.13nm, and the median particle diameter is 3.87μm , D ₁₀ is 2.49μm, D ₉₀ is 5.89μm.

Example 9:

(1) Add an appropriate amount of slaked lime to the water glass solution to perform a precipitation reaction to obtain a mixed slurry. The conditions for the precipitation reaction are: the modulus of the water glass solution is 0.6, and the mass fraction of SiO ₂ in the water glass solution is 8.0wt %, the reaction temperature is 15°C, the reaction time is 120min, the stirring speed is 50r/min, and the mass ratio of slaked lime and water glass solution is 1:9.3;

(2) Filter, wash and dry the slurry obtained in step (1) to obtain solid powder. The drying temperature is 200°C and the drying time is 6 hours;

(3) The solid powder obtained in step (2) is leached with hydrochloric acid to obtain a suspension. The leaching conditions are: the concentration of hydrochloric acid is 1mol/L, the leaching temperature is 15°C, the leaching time is 2h, the stirring speed is 1500r/min, slaked lime The mass ratio to hydrochloric acid is 1:50;

(4) Perform solid-liquid separation on the suspension obtained in step (3). The solid product obtained is washed and dried to obtain high specific surface area porous silica. The drying temperature is 80°C and the drying time is 36 hours.

Analysis and testing results of the sample obtained in this example: the silica content is 99.0%, the specific surface area S _BET is 728.59m ² /g, the pore volume is 0.75cm ³ /g, the average pore diameter is 8.44nm, and the median particle diameter is 10.36μm , D ₁₀ is 6.98μm, D ₉₀ is 14.97μm.

Example 10:

(1) Add an appropriate amount of slaked lime to the water glass solution to perform a precipitation reaction to obtain a mixed slurry. The conditions for the precipitation reaction are: the modulus of the water glass solution is 2.8, and the mass fraction of SiO ₂ in the water glass solution is 9.3wt %, the reaction temperature is 25°C, the reaction time is 45min, the stirring speed is 600r/min, and the mass ratio of slaked lime and water glass solution is 1:8.7;

(2) Filter, wash and dry the slurry obtained in step (1) to obtain solid powder. The drying temperature is 180°C and the drying time is 24 hours;

(3) The solid powder obtained in step (2) is leached with hydrochloric acid to obtain a suspension. The leaching conditions are: the concentration of hydrochloric acid is 6mol/L, the leaching temperature is 25°C, the leaching time is 24h, the stirring speed is 600r/min, slaked lime The mass ratio to hydrochloric acid is 1:25;

(4) Perform solid-liquid separation on the suspension obtained in step (3). The solid product obtained is washed and dried to obtain high specific surface area porous silica. The drying temperature is 60°C and the drying time is 18 hours.

Analysis and testing results of the sample obtained in this example: the silica content is 99.9%, the specific surface area S _BET is 709.47m ² /g, the pore volume is 0.65cm ³ /g, the average pore diameter is 6.89nm, and the median particle diameter is 4.43μm , D ₁₀ is 3.51μm, D ₉₀ is 6.97μm.

Comparative example 1:

The mass ratio of slaked lime and water glass solution in step (1) is 1:95, and other step conditions are the same as in Example 1.

In Comparative Example 1, calcium silicate colloid was generated after the reaction between slaked lime and water glass solution, and calcium silicate solid powder could not be obtained.

Comparative example 2:

The water glass solution described in Example 1 was reacted with 1 mol/L hydrochloric acid, and the mass ratio of the water glass solution and hydrochloric acid was 1:30.

Comparative Example 2 did not produce any precipitation or colloid.

Comparative example 3:

The water glass solution described in Example 1 was reacted with 1 mol/L hydrochloric acid, and the mass ratio of the water glass solution and hydrochloric acid was 1:10.

Comparative Example 3 did not produce any precipitation or colloid.

Comparative example 4:

Using the water glass solution described in Example 1 and 12 mol/L hydrochloric acid to react, the mass ratio of the water glass solution to hydrochloric acid was 10:1.

Comparative Example 4 After hydrochloric acid is added, a large amount of silicic acid colloid is rapidly generated, which cannot be stirred and filtered, and high specific surface area porous silica with uniform particle size cannot be obtained.

Comparative example 5:

The calcium silicate solid powder obtained in step (2) in Example 1 was tested.

The analysis and testing results of the sample obtained in this comparative example: the silica content is 51.30%, the calcium oxide content is 47.90%, the calcium silicate specific surface area S _BET is 34.31m ² /g, the pore volume is 0.23cm ³ /g, and the average pore diameter is 31.88 nm, the median particle size is 5.67 μm, D ₁₀ is 3.99 μm, and D ₉₀ is 8.29 μm.

From Comparative Example 1, it can be seen that when the amount of slaked lime is too small, too little calcium silicate is produced. In this case, colloid is produced instead of precipitation. From Comparative Examples 2, 3, and 4, it can be seen that water glass solution reacts directly with hydrochloric acid to obtain uniform particle size. Silica precipitates. It can be seen from Comparative Example 5 that the generated calcium silicate particle size is uniform but the specific surface area is too small, which is consistent with the principle of the present invention.

Claims (1)

1. A method for preparing high specific surface area porous silica, which is characterized in that it consists of the following steps: (1) Add an appropriate amount of slaked lime to the water glass solution to perform a precipitation reaction to obtain a mixed slurry. The conditions for the precipitation reaction are: the modulus of the water glass solution is 0.8, and the mass fraction of SiO ₂ in the water glass solution is 9.3wt %, the reaction temperature is 20°C, the reaction time is 30min, the stirring speed is 200r/min, and the mass ratio of slaked lime and water glass solution is 1:8.5; (2) Filter, wash and dry the slurry obtained in step (1) to obtain solid powder. The drying time is 0 h; (3) The solid powder obtained in step (2) is leached with hydrochloric acid to obtain a suspension. The leaching conditions are: the concentration of hydrochloric acid is 1mol/L, the leaching temperature is 25°C, the leaching time is 0.5h, and the stirring speed is 550r/min. The mass ratio of hydrated lime to hydrochloric acid is 1:30; (4) Perform solid-liquid separation on the suspension obtained in step (3). The solid product obtained is washed and dried to obtain high specific surface area porous silica. The drying temperature is 150°C and the drying time is 6 hours.