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A process for dewatering spent ion exchange resins (gel and porous) used in nuclear power plants by supercritical CO2 (sCO2) is described. The amount of water removed by sCO2 is much higher than that expected from solubility considerations alone. Water from gel-type resins is both dissolved by and emulsified in sCO2. Emulsification also occurs in the absence of solids when water alone is contacted by sCO2. It is not a factor for microporous resins where an additional mechanism, viscous fingering, is involved. It appears that bulk water is emulsifiable but not if it is held in pores. Dewatering via viscous fingering has been previously invoked for matrices such as wood and sludge. The resins can be dewatered and dried with sequential batches of sCO2 at sub-boiling temperatures. The CO2 can then be potentially reused after expansion and separation from the entrained water. Partial decompression of the water-laden sCO2 would lead to cooling, which would drop the water solubility substantially. A reduction of temperature from 90 oC to 65oC reduces the solubility of water in sCO2 by a factor of five. The condensed water could then be separated with a hydrocyclone. The footprint of sCO2 is much smaller than the conventional drying process. The energy costs are also much lower because evaporation of water is avoided. [ABSTRACT FROM AUTHOR]

A process for dewatering spent ion exchange resins (gel and porous) used in nuclear power plants by supercritical CO2 (sCO2) is described. The amount of water removed by sCO2 is much higher than that expected from solubility considerations alone. Water from gel-type resins is both dissolved by and emulsified in sCO2. Emulsification also occurs in the absence of solids when water alone is contacted by sCO2. It is not a factor for microporous resins where an additional mechanism, viscous fingering, is involved. It appears that bulk water is emulsifiable but not if it is held in pores. Dewatering via viscous fingering has been previously invoked for matrices such as wood and sludge. The resins can be dewatered and dried with sequential batches of sCO2 at sub-boiling temperatures. The CO2 can then be potentially reused after expansion and separation from the entrained water. Partial decompression of the water-laden sCO2 would lead to cooling, which would drop the water solubility substantially. A reduction of temperature from 90 oC to 65oC reduces the solubility of water in sCO2 by a factor of five. The condensed water could then be separated with a hydrocyclone. The footprint of sCO2 is much smaller than the conventional drying process. The energy costs are also much lower because evaporation of water is avoided. [ABSTRACT FROM AUTHOR]

Supercritical CO 2 (sCO 2 ) 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 sCO 2 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 sCO 2 process are especially significant. Calculations show that depressurizing the spent sCO 2 to half its initial pressure drops out most of the water, after which the CO 2 can be repressurized and reused. sCO 2 dewatering requires about half the energy needed for thermal drying because the water is removed nonevaporatively., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)