Regeneration of Spent Desiccants with Supercritical CO₂

Supercritical CO₂ (sCO₂) dehydrates desiccants such as silica gel, activated carbon, graphite, and molecular sieve by dissolving and emulsifying the water. Despite differences in the surface area of these desiccants, the amount of water removed under comparable conditions is the same. The main advantage of sCO₂ dewatering over conventional hot-air regeneration lies in situations where the exhaust contains environmentally sensitive components, e.g., in nuclear detritiation operations where the small footprint and closed cycle benefits of the sCO₂ process are especially significant. Calculations show that depressurizing the spent sCO₂ to half its initial pressure drops out most of the water, after which the CO₂ can be repressurized and reused. sCO₂ dewatering requires about half the energy needed for thermal drying because the water is removed nonevaporatively.