1, acid desiccant: such as concentrated sulfuric acid, phosphorus pentoxide, silica gel,

2, basic desiccant: soda lime (NaOH and CaO mixture), NaOH solid, lime.

3, neutral desiccant: CaCl2 and so on.

[Note] Using desiccant drying gas should be a "no absorption, no reaction"principle to choose. Acidic acid gas can be used desiccant, desiccant Alkaline alkaline gas. Reducing gas is not dried with concentrated sulfuric acid, CaCl2 not be used to dry and NH3.

Cl2, HCl, CO2, NO2, CO, NO, SO2 and other gases commonly used in concentrated sulfuric acid drying; and NH3, H2S, HBr, HI, C2H4, C2H2 can not generally be dried with concentrated sulfuric acid.

NH3 generally is  used in soda lime drying;

H2S, HBr, HI generally dried with phosphorus pentoxide.