Silica gel desiccant and other desiccant types adsorbs moisture from gas through a chemical reaction. Different desiccant adsorb more than others based on process conditions. For example activated alumina is an excellent moisture adsorber when the relative humidity is 100%. It can adsorb up to 40% its weight at 100% relative humidity. However its efficiency declines as the relative humidity falls. The most common desiccant types used to dry compressed air are...
•  Activated alumina - excellent all purpose desiccant for drying air and most other gases with high relative humidities
•  Silica gel - desiccant silica gel is a very effective desiccant for drying compressed air/gas streams, especially natural gas. Silica gel features excellent adsorption at mid inlet relative humidity
•  Molecular sieve - most effective for applications with low inlet flows and low relative humidities, (Less than 30-35%RH). Can achieve the lowest dewpoints possible to -120°F