Researchers at the University of California, Berkeley, have developed an innovative yellow powder called COF-999 that efficiently removes carbon dioxide (CO₂) from the air and could therefore help combat the greenhouse effect. The question was raised on Taucher.net as to whether this material would be suitable as a replacement for lime in rebreathers.
What is COF-999?
When viewed under a scanning electron microscope, COF-999 appears as a network of tiny, basketball-like structures with billions of pores. It is a so-called covalent organic framework (COF), consisting of carbon and nitrogen atoms arranged in a hexagonal structure. The microscopic pores contain amines - basic compounds that specifically bind CO₂ molecules when air flows through them. The bound CO₂ can be released again through moderate heating (around 60 °C), extracted and stored underground, for example. The powder remains intact and can be reused. Even after 300 cycles, it showed constant performance in the experiment.
Suitability for rebreathers
However, there are question marks over its use in rebreathers. On the one hand, COF-999 is so light that it could nebulize, enter the breathing circuit and possibly be inhaled by the diver. Secondly, the question arises as to whether the material binds CO₂ efficiently enough to compete with standard lime.
COF-999 has a CO₂ binding capacity of 2.05 mmol per gram under a relative humidity of 50 %. One mole of an ideal gas occupies about 22.4 liters under normal conditions, so 2.05 mmol can bind about 45.9 ml of CO₂. This means that 1 kg of COF-999 can absorb around 45.9 liters of CO₂. For comparison: 1 kg of Sofnolime 797, the standard lime for rebreathers, binds around 150 liters of CO₂ - many times more than COF-999 can do.
Deviations in the test conditions
However, a direct comparison of the materials is difficult, as COF-999 was tested under conditions that differ greatly from those in the rebreather. The powder was developed for the separation of CO₂ from normal ambient air, in which the CO₂ concentration is around 400 ppm. However, the CO₂ concentration in exhaled air is around 40,000 ppm, a hundred times higher. How COF-999 behaves under these conditions is unclear.
Another point is the humidity: the exhaled air has a relative humidity of 100 %, while COF-999 was only tested at 50 % humidity.
Conclusion
The question of whether COF-999 is suitable as a lime substitute for rebreathers cannot be answered definitively at present. The option of reusing the powder through moderate heating would be promising, but there are numerous unanswered questions - particularly with regard to binding capacity under real diving conditions. In addition, the price of the experimental material is unknown and it remains questionable whether it would be affordable for diving.
Commentaires