A method for preparing spherical macroporous silica gel based on secondary growth

Abstract

The application discloses a method for preparing spherical large-pore volume silica gel based on secondary growth, and belongs to the technical field of inorganic non-metallic materials. First, spherical silica gel precursors are prepared through a coprecipitation method; then, 10-40% sodium silicate solution by mass fraction is added to the spherical silica gel precursors, and heating and stirring are conducted at 30-50 DEG C for 0.5-6 hours; liquid is discharged, dilute sulfuric acid by mass fraction is added to the silica gel, the pH value is controlled to be 3-7, and heating and stirring are conducted at 30-50 DEG C for 0.5-3 hours. Then, the temperature is increased to 80-95 DEG C, and heating and stirring are continuously conducted for 2-3 hours; liquid is discharged again, deionized water is added to stir and wash the silica gel, the washing water is filtered and discharged, and the silica gel is repeatedly washed with water until the conductivity of the washing water is less than 20 mu s / cm; and drying and calcination are conducted to obtain silica gel products. Through the reaction of sodium silicate and dilute sulfuric acid in the pre-prepared spherical silica gel, the silica gel skeleton formed is strengthened, the pore structure is prevented from collapsing in the drying process, and thus the large-pore volume silica gel is obtained.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of inorganic non-metallic materials, and particularly relates to a method for preparing spherical silica gel with large pore volume based on secondary growth. BACKGROUND

[0002] Silica gel is a porous substance mainly used as an adsorbent, a drying agent and a catalyst carrier, etc. and its main component is silicon dioxide. The chemical co-precipitation method is a commonly used method for preparing spherical silica gel, specifically, a certain concentration of dilute sodium silicate and dilute sulfuric acid are mixed to generate polysilicic acid, which is sprayed from the equipment into water to form a spherical silica gel precursor, and then the precursor is subjected to aging, acid bubbling, water washing, drying, and finally the finished product is obtained. Since the wet silica gel loses about 85% of water during drying, causing the framework to collapse, the pore volume of the silica gel without further treatment is generally below 1.0 mL / g, which severely limits its application. Therefore, it is of great practical significance to seek a post-treatment method for the spherical silica gel precursor prepared by the chemical precipitation method to obtain silica gel with large pore volume. For the silica gel prepared by the chemical precipitation method, the main methods for increasing the pore volume are as follows: (1) using an easily volatile organic solvent (usually ethanol) to displace water, since the organic solvent volatilizes quickly and has a smaller molecular interaction with silica gel than water, it is beneficial to reduce the degree of framework collapse during drying, thereby obtaining silica gel with large pore volume. However, in actual production, due to safety requirements, the use of a large amount of volatile organic solvents is limited, and this method is difficult to apply in actual production; (2) treating the silica gel precursor under high temperature and high pressure conditions to dissolve small particles and further grow large particles, so that the framework is not easy to collapse during drying, thereby obtaining silica gel with large pore volume. However, this method requires high temperature and high pressure, which puts higher requirements on the actual production process; (3) soaking the silica gel precursor after water washing with a surfactant, which forms an effective support in the pores during drying, and then removing the surfactant by calcination after drying. However, this method uses a large amount of surfactant, greatly increasing the raw material cost, and due to the presence of a large amount of organic matter, the silica gel needs to be further calcined, which increases energy consumption; (4) using microwave drying, spray drying, freeze drying and other drying methods, but these methods increase energy consumption and production equipment cost. SUMMARY

[0003] The present application aims to overcome the shortcomings of the prior art, and seeks to design a method for preparing spherical large-pore-volume silica gel, which does not use organic solvents and surfactants, does not use high-temperature and high-pressure aging treatment, does not use spray drying, microwave drying and other drying methods that increase energy consumption and equipment investment, but performs aging treatment under normal pressure in an aqueous solution and dries using ordinary methods, thereby minimizing process modification costs.

[0004] To achieve the above-mentioned purpose, the method for preparing spherical large-pore-volume silica gel based on secondary growth according to the present application comprises the following steps:

[0005] (1) Pump a sodium silicate solution with a mass fraction of 15-22% and a sulfuric acid solution with a mass fraction of 15-22% into a spherical silica gel reactor to obtain a spherical silica gel precursor;

[0006] (2) Add a sodium silicate solution with a mass fraction of 10-40% to the silica gel solid particles, heat and stir at 30-50℃ for 0.5-6 hours to allow the sodium silicate to be adsorbed inside the spherical silica gel precursor;

[0007] (3) Drain the liquid, add dilute sulfuric acid with a mass fraction of 1.0-6.0% to the silica gel, control the pH value to be 3-7, then heat and stir at 30-50℃ for 0.5-3 hours, at which time the sodium silicate adsorbed inside the spherical silica gel precursor reacts with the sulfuric acid to grow silica gel particles inside the spherical silica gel precursor, and then reheat to 80-95℃ and continue to heat and stir for 2-3 hours to allow small particles to dissolve and large particles to grow, thereby performing aging;

[0008] (4) Finally, wash with water and dry to obtain the finished silica gel.

[0009] Specifically, the step (4) is specifically: drain the liquid in the solution after aging, add deionized water to stir and wash the silica gel, repeat the addition of water to wash the silica gel until the conductivity of the washing water is <20 μs / cm; then dry at 120-200℃ for 2-5 hours to obtain the finished silica gel.

[0010] Preferably, the mass fraction of the sodium silicate solution in step (2) is 12-25%, and the pH value is 4-6.

[0011] The spherical silica gel reactor is an existing device capable of directly obtaining spherical silica gel. In the spherical silica gel reactor, sodium silicate and sulfuric acid react to generate sodium sulfate and spherical silica, the sodium sulfate is dissolved in water and discharged with the solution, the remaining silica gel solid particles are then added into deionized water, then sodium silicate solution is added into the silica gel solid particles, and the silica gel precursor is allowed to adsorb the sodium silicate inside after being stirred at 30-50°C for 0.5-6 hours, then dilute sulfuric acid with a mass fraction of 1.0-6.0% is added, the pH value is controlled to be 3-7, and the sodium silicate adsorbed inside the silica gel is allowed to react at 30-50°C for 0.5-3 hours. The secondary growth of silica gel particles inside the silica gel ball can enhance the silica gel skeleton, and can prevent the pore collapse to a certain extent during drying, and then the silica gel product is obtained after drying to remove water.

[0012] Compared with the prior art, the present application has the following beneficial effects: (1) no organic solvent is used, no surfactant is added, and the aging process does not require high temperature and high pressure, thereby greatly reducing the cost; (2) the secondary growth of silica gel particles inside the silica ball increases the strength of the skeleton inside the silica ball, and can to a certain extent avoid the pore structure collapse during the drying process, thereby obtaining silica gel with large pore volume, and the pore volume is 1.45-1.70 mL / g; (3) the secondary growth process simultaneously performs acid washing, thereby simplifying the preparation process. DETAILED DESCRIPTION

[0013] The present application is further described below through examples.

[0014] Example 1

[0015] The specific process steps of the present example are as follows:

[0016] (1) The sodium silicate solution with a mass fraction of 15% is introduced into the silica gel preparation reactor through a centrifugal pump at a flow rate of 8 m 3 / h, and the sulfuric acid solution with a mass fraction of 15% is introduced into the silica gel preparation reactor at a flow rate of 3 m 3 / h, the sodium silicate and the sulfuric acid are fully mixed and reacted in the mixing reactor, and then sprayed out through a nozzle into a water tank to obtain spherical silica gel precursors;

[0017] (2) The sodium silicate solution with a mass fraction of 12% is added into the spherical silica gel precursor particles, and heated and stirred at 30°C for 2 hours;

[0018] (3) The liquid is discharged, the dilute sulfuric acid with a mass fraction of 1.0% is added into the silica gel, the pH value is controlled to be 6.5, and then heated and stirred at 30°C for 2 hours. Then the temperature is increased to 90°C, and the heating and stirring is continued for 2 hours;

[0019] (4) again drain the liquid, add deionized water to stir the washed silica gel, repeat the addition of water to wash the silica gel until the conductivity of the washing water is <20 μs / cm;

[0020] (5) dry at 120°C for 2 hours to obtain the finished silica gel.

[0021] Example 2:

[0022] The specific process steps of this example are:

[0023] (1) same as Example 1;

[0024] (2) add a 25% by mass sodium silicate solution to the spherical silica gel precursor particles, heat and stir at 30°C for 2 hours;

[0025] (3) drain the liquid, add a 2.0% by mass dilute sulfuric acid to the silica gel, control the pH value to 6.0, then heat and stir at 30°C for 2 hours. Increase the temperature to 90°C and continue to heat and stir for 2 hours;

[0026] (4) again drain the liquid, add deionized water to stir the washed silica gel, repeat the addition of water to wash the silica gel until the conductivity of the washing water is <20 μs / cm;

[0027] (5) dry at 150°C for 2 hours to obtain the finished silica gel.

[0028] Example 3:

[0029] The specific process steps of this example are:

[0030] (1) same as Example 1;

[0031] (2) add a 25% by mass sodium silicate solution to the spherical silica gel precursor particles, heat and stir at 30°C for 2 hours;

[0032] (3) drain the liquid, add a 2.0% by mass dilute sulfuric acid to the silica gel, control the pH value to 4.0, then heat and stir at 30°C for 2 hours. Increase the temperature to 90°C and continue to heat and stir for 2 hours;

[0033] (4) again drain the liquid, add deionized water to stir the washed silica gel, repeat the addition of water to wash the silica gel until the conductivity of the washing water is <20 μs / cm;

[0034] (5) dry at 150°C for 2 hours to obtain the finished silica gel.

[0035] Example 4:

[0036] The specific process steps of this example are as follows:

[0037] (1) The same as Example 1;

[0038] (2) Add a sodium silicate solution with a mass fraction of 25% to the spherical silica gel precursor particles, and heat and stir at 50°C for 2 hours;

[0039] (3) Remove the liquid, add dilute sulfuric acid with a mass fraction of 1% to the silica gel, control the pH value to be 5, then heat and stir at 50°C for 1 hour. Then increase the temperature to 90°C, and continue to heat and stir for 2 hours;

[0040] (4) Remove the liquid again, add deionized water to wash the silica gel, filter and remove the washing water, then repeat the process of adding water to wash the silica gel, until the conductivity of the washing water is less than 20 μs / cm;

[0041] (5) Dry at 150°C for 2 hours to obtain the finished silica gel product.

[0042] Example 5:

[0043] The specific process steps of this example are as follows:

[0044] (1) The same as Example 1;

[0045] (2) Add a sodium silicate solution with a mass fraction of 25% to the spherical silica gel precursor particles, and heat and stir at 30°C for 0.5 hours;

[0046] (3) Remove the liquid, add dilute sulfuric acid with a mass fraction of 1.0% to the silica gel, control the pH value to be 7.0, then heat and stir at 30°C for 0.5 hours. Then increase the temperature to 90°C, and continue to heat and stir for 2 hours;

[0047] (4) Remove the liquid again, add deionized water to wash the silica gel, filter and remove the washing water, then repeat the process of adding water to wash the silica gel, until the conductivity of the washing water is less than 20 μs / cm;

[0048] (5) Dry at 120°C for 2 hours to obtain the finished silica gel product.

[0049] Comparative Example 1:

[0050] (1) The same as Example 1;

[0051] (2) Add deionized water to the spherical silica gel precursor, heat and stir at 90°C for 3 hours to age;

[0052] (3) Remove the liquid, add sulfuric acid with a mass fraction of 5.0% to the silica gel, soak and stir the silica gel for 1 hour to perform acid washing;

[0053] (4) The liquid was drained, deionized water was added and the silica gel was washed with stirring. The water was filtered and drained, and the washing was repeated until the conductivity of the water was < 20 μs / cm;

[0054] (5) Drying at 150°C for 2 hours to obtain the finished silica gel.

[0055] The pore structure of the silica gel prepared in Examples 1-5 and Comparative Example 1 was determined using a Micromeritics ASAP 2460 automatic specific surface and porosity analyzer. The specific surface area of the silica gel prepared in Examples 1-5 and Comparative Example 1 was determined using the BET method. The results are shown in the following table.

[0056] Pore volume (ml / g) Specific surface area (m 2 / g) Example 1 1.49 356 Example 2 1.55 353 Example 3 1.70 329 Example 4 1.61 338 Example 5 1.50 357 Comparative Example 1 Comparative Example 2 1.08 363

Claims

1. A method for preparing spherical macroporous silica gel based on secondary growth, characterized in that, Includes the following steps: (1) Sodium silicate solution and sulfuric acid solution were pumped into a spherical silica gel reactor to obtain spherical silica gel precursor; (2) Add a sodium silicate solution with a mass fraction of 10-40% to the silica gel solid particles, 30-50 ml o Heat and stir at temperature C for 0.5-6 hours; (3) Drain the liquid, add 1.0-6.0% dilute sulfuric acid to the silica gel, control the pH value to 3-7, and then heat for 30-50 minutes. o Heating and stirring at C for 0.5-3 hours allows the sodium silicate adsorbed inside the spherical silicate precursor to react with sulfuric acid, resulting in secondary growth of silicate particles inside the precursor. The temperature is then raised again to 80-95°C. o C. Continue heating and stirring for 2-3 hours; (4) Finally, the silicone product is obtained by washing and drying.

2. The method for preparing spherical macroporous silica gel based on secondary growth according to claim 1, characterized in that, A sodium silicate solution with a mass fraction of 15-22% and a sulfuric acid solution with a mass fraction of 15-22% were pumped into a spherical silica gel reactor to obtain a spherical silica gel precursor.

3. The method for preparing spherical macroporous silica gel based on secondary growth according to claim 1, characterized in that, Step (4) specifically involves: draining the liquid from the aged solution, adding deionized water and stirring to wash the silica gel, filtering and draining the wash water, and then repeatedly adding water to wash the silica gel until the conductivity of the wash water is <20 μs / cm; then at 120-200 o Dry at C for 2-5 hours to obtain the finished silicone product.

4. The method for preparing spherical macroporous silica gel based on secondary growth according to claim 1, characterized in that, In step (2), the sodium silicate solution has a mass fraction of 12-25% and a pH value of 4-6.