It is also divided into coarse hole silica and fine hole silica gel
Silica gel can absorb moisture, but also absorb acetylene and carbon dioxide. As the temperature decreases, the first adsorption is moisture (normal temperature can be about 25 ℃), followed by acetylene and carbon dioxide (the lower the temperature, the stronger the adsorption capacity).
To adsorb water as an example Particle size / mm4 ~ 8 Dynamic adsorption capacity at room temperature /% 6 ~ 8 Air moisture content after drying / g • m-3 0.03 Dew point of air after drying / ℃ -52
Silica gel adsorption capacity of water larger, lower regeneration temperature, the price is cheap, so the air separation plant silicone is mainly used for adsorption of water, at low temperatures are also used to adsorb carbon dioxide and acetylene. Its disadvantage is more powder.
There are two kinds of coarse and fine pores in silica gel, and the two have different pore sizes. Coarse pore silica pore size is 5 ~ 10nm (1nm = 10-9m, called nano), the specific surface area per gram of silica has 100 ~ 300m2 / g much. Its water absorption ability, and not easily broken after water absorption, mechanical strength, commonly used in the dryer to absorb moisture. Pore silica pore size is 2.5 ~ 4nm, the specific surface area of 400 ~ 600m2 / g. Commonly used to adsorb carbon dioxide and acetylene, adsorbed moisture easily broken. Carbon dioxide adsorber adsorption process is carried out at -110 ~ -120 ℃ low temperature, the adsorption of carbon dioxide is better, but also can be adsorbed acetylene. As the temperature below -130 ℃ will have carbon dioxide solid precipitation, solid carbon dioxide not only can not be adsorbed by silica gel, and will block the adsorber. Adsorption of acetylene is carried out in liquid-vapor and liquid oxygen adsorbers, and its adsorption temperature is around -170 to -180°C.