Absorption Systems for Water Vapor

In the first freeze drying plant [2.9] phosphorous pentoxide has been used to absorb the water vapor, but to day this technique is outdated. The development of refrigeration technology with compressors or NH3 absorption and the availability of LN2 has replaced water absorption by silica gel or similar products. Some trials aiming to revive this technology are detailed in Section 1.2.6. 

---