An Interesting Note on Low Energy Industrial Regeneration of Desiccants with Supercritical CO2

[NNadir]

I'll briefly refer to the following paper I came across this morning: Regeneration of Spent Desiccants with Supercritical CO2 Astrid Melissa Rojas Márquez, Iris Beatriz Vega Erramuspe, Brian K. Via, Bhima Sastri, and Sujit Banerjee Industrial & Engineering Chemistry Research 2024 63 (49), 21154-21157.

The paper is open sourced.

It apparently can, in limited circumstances, reduce the energy cost for the removal of water in industrial processes.

Desiccants used in industry are typically dehydrated through temperature swing adsorption. High temperatures of 200–250 °C are required for molecular sieve; (1,2) less aggressive conditions suffice for dessicants such as silica gel (3), where solar dryers can even be used. The energy burden for regeneration is high because the water is removed evaporatively. Supercritical CO2 (sCO2) has recently been used to dewater a wide range of materials ranging from ion exchange resins (4) to sludge. (5) The water is both dissolved and emulsified in the sCO2 (6), which can then be partially expanded to release the water. The energy savings are considerable because the water is removed nonevaporatively at 90 °C. sCO2 has also been used to decontaminate spent sorbents such as activated carbon from compounds such as chlorophenol (7) and xylene. (8) While these spent sorbents are frequently water-laden, especially when they are used to remove dissolved contaminants from water, the focus has been on removing the organic contaminants from the sorbent rather than on dewatering it. This paper describes the removal of water by sCO2 from molecular sieve, activated carbon, graphite and silica gel, and interprets the different conditions that appy to each desiccant. Because use of sCO2 requires a pressure vessel, the approach is especially suitable for high-value low-volume applications, such as the regeneration of desiccants used to capture tritiated water vapor in the nuclear industry. (2,9)

The nuclear plant application is interesting, since the release of tritium generates a lot of public stupidity despite its low risk. This public stupidity has played a role in driving the increasing use of dangerous fossil fuels, causing millions of air pollution deaths each year, destroying ecosystems, and leaving the planet in flames. This form of public stupidity, like many other forms of public stupidity, say like electing a senile moron to the office of President of the United States, kills people.

Tritium levels, which are never zero because tritium forms in the atmosphere from solar radiation albeit at a low level. Levels of tritium in the planetary atmosphere have been falling since 1963, when they peaked as a result of open atmosphere nuclear testing.

Not much isolated tritium exists on Earth, and is chiefly available in Canada, where it is a byproduct of the wonderful CANDU reactors, which utilize deuterium as a moderator. Although the capture cross section of deuterium is very low, accounting for its use as a moderator, it is not zero, and tritium is generated in these reactors by neutron capture.

There is probably not enough isolated tritium on Earth to run a fusion reactor for as long as a year, a subject that is seldom discussed in the magical thinking about fusion energy. However tritium can be generated, as needed, by placing lithium targets in a fission reactor. Tritium in hydrogen bombs is generated using lithium deuteride in situ.

Have a nice Sunday.