[Physical and chemical properties] Alias silica silica, silicic acid gel, hydrous silica
A glassy transparent or semi-transparent matt granular or massive body with a microporous structure and high thermal stability
It is soluble in hydrofluoric acid and strong alkali, does not work with other acids, and is insoluble in water, gas, sulfur dioxide , alcohol, ether, benzene, gasoline and other solvents
According to different preparation methods, silica gel has different microporous structure and specific surface area.
The silica gel is divided into fine-pored spherical silica gel, fine-pored block silica gel, coarse-pored spherical silica gel, and coarse-pored block silica gel
[Preparation method] The production methods of silica gel include: sulfuric acid method, which is obtained by reacting sodium silicate and sulfuric acid (other acids can also be used); metathesis method, which is obtained by the action of sodium silicate and water-soluble salts; precipitation method, with the help of It is obtained by the precipitation of silica gel from various organic compounds from alkali metal silicate solutions; electrolysis is obtained by the electrolysis of sodium silicate
Sulfuric acid method is currently commonly used method
(1) Preparation of coarse and fine-pored block silica gel
The coarse and fine pore block silica gel is a glassy transparent or semi-transparent matte granular body or block with a microporous structure and high thermal stability
It is mainly used as a carrier or adsorbent for desiccant, moisture-proofing agent, rust-proofing agent and petrochemical catalyst.
It can also be used for deacidification and regeneration of transformer oil
The raw materials used are sodium silicate with a modulus of 3.
1, sulfuric acid and ammonia
The dilute sodium silicate solution (density 1.
25g/cm 3 , Na 2 O content 6%～6.
2%) and dilute sulfuric acid with a concentration of (30±1.
5)% to be clear When the temperature is ℃, they are sprayed from the reaction nozzle, and when they meet, the silica sol is compounded at a high speed.
The reaction is as follows:
Na 2 SiO 4 +H 2 SO 4 +H 2 O→Na 2 SO 4 +H 4 SiO 4
Silica sol is extremely unstable in acidic medium and immediately condenses into silica gel:
The silicone gel is aged for more than 36 hours in the aging tank, and then the gel is cut into pieces not larger than 3cm and washed with water to remove sodium sulfate (for fine-pored block silica gel, when the water is washed to a certain degree, it needs to be heated and diluted Acid repeated washing)
After washing, if making coarse-pored silica gel, put the silica gel in 0.
18% dilute ammonia water, soak it at 20～30℃ for 16h, until the alkali content in the gel reaches 0.
03%, take it out and dry it
If making fine-pored silica gel, put the silica gel in a 0.
02% dilute sulfuric acid solution and soak it at 25～30℃ for 12 hours until the acid content in the gel reaches 0.
015%, then take it out and dry it
The drying of silica gel is carried out in a tunnel drying room
After the first drying, a vibrating screen is used to screen out relatively neat particles, and then the second drying is performed to obtain the finished product
(2) Preparation of coarse and fine pore spherical silica gel
Spherical silica gel with coarse and fine pores is white transparent or opaque spherical particles
Because its surface is smooth and spherical, it has high mechanical strength, is not easy to break, and has low resistance
Mainly used as desiccant, moisture-proof agent, anti-rust agent and petrochemical catalyst carrier or adsorbent, especially suitable for the acid regeneration of transformer oil
The production method adopts the sulfuric acid method.
The dilute water glass solution and dilute sulfuric acid are mixed in a nozzle.
Under pH=6～7, air granulation is carried out at 20～30℃.
After steam aging, sulfuric acid exchange, oil bleaching, water washing, The product is obtained through the steps of drying and screening
Put the clarified sodium silicate solution with a density of 1.
204g/cm 3 and a Na 2 O content of 5.
25% and a diluted sulfuric acid solution with a concentration of 20% to the reaction nozzle with a certain pressure respectively to make Its high-speed synthesis of silica sol:
Na 2 SiO 4 +H 2 SO 4 +H 2 O→Na 2 SO 4 +H 4 SiO 4
The silica sol is dispersed from the umbrella-shaped distribution plate into the oil bath of the forming column, and shrinks into a spherical shape by its own surface tension
Since silica sol is extremely unstable in acidic medium (pH=6.
6～7) and under heating, it quickly condenses into silica gel within 5～7s:
The spherical gel is carried out by the circulating water at the bottom of the forming column, enters the sieve and is separated
For making coarse-pored spherical silica gel, steam the gel for more than 8 hours, soak it in a 0.
1% to 0.
2% dilute sulfuric acid solution for 12 hours in a washing tank, and then use a 0.
06% synthetic detergent solution to wash off the oil on the surface, and finally Wash with water to remove SO42-, use 0.
1% synthetic detergent solution for surface activation treatment, dry and screen to obtain the finished product
For fine-pored silica gel, the gel is directly subjected to acid exchange for 16 hours in a washing tank.
The exchange liquid contains 2% to 2.
3% sulfuric acid and the temperature is 25 to 30°C
Then use a 0.
06% synthetic detergent solution with a pH of 4 to wash off the oil stains, and then wash with hot water at 40～60℃ until the acid content in the glue is (4～6)×10 -5, then remove and dry.
The finished product is obtained by sieving