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> My first question is, where can I obtain CO2-absorbants for my rebreather > in Germany?. Which stuff is the best one (KOH, Ba(OH)2, NaOH, Ca(OH)2 > ....). From what is the absorbent "SOFNOLIME" from O.C. Lugo CO. Inc., > composed of? Please don`t tell me something about the stoechiometric > ratios of CO2 that could be bound by the absorbants. Please inform me > about the performance and how user-friendy the stuff is. Is there any > experience about temperature dependencies of CO2 absorbance? > I would be very pleasured if you can give me some hints. Hello Andreas, I am afraid I cannot help you with information about obtaining CO2 absorbants in Germany. However, I have been using Sofnolime for a little less than a year now, and I can tell you my opinions of it. I have been using the small particle size (Sofnolime 812 D Grade), and have been very pleased with it. To begin with, it is not as "dusty" as anhydrous Lithium Hydroxide (LiOH), which makes it easier to work with when packing a CO2 absorbant canister. Also, it is not nearly as noxious as LiOH, and I never get a slight throat irritation on long dives as I did with LiOH. With an average work-load on the dive, I get about 2 hours of effective dive time per pound (~4.4 hours per kilogram) of material. My diving companion, who is much larger than I am (but in excellent physical shape), gets about 1.5 hours per pound under similar work loads. These values are based on diving in water that is about 72 degrees F (~22 degrees C). I do not know off the top of my head how well Sofnolime maintains its ability to absorb CO2 at colder temperatures. I have this information, as well as many other detailed specifications, but my files are very disorganized right now so it will take me some time to find it. I do know that LiOH has much better operating characteristics in cold water. I have done some experiments with Sofnolime simulating what would happen during a canister flood (water on the absorbent). To my surprise, I detected no unusual taste or smell and the absorbent did not generate excessive heat (i.e., no "caustic cocktail"). With the small grain size, however, breathing resistance can increase dramatically when the absorbent gets wet. I have also done some experiments on what the symptoms are when the absorbent approaches the end of its life. I was pleased to discover that I can detect subtle symptoms of hypercapnia (excess CO2) about 2 hours before these symptoms begin to get severe. Bear in mind, however, that these experiments did not involve straight non-stop dives; they were based on cumulative use. My understanding is that CO2 absorbent materials do not "recharge" after a period of non-use. However, the bound CO2 seems to become more homogeonoulsy distributed within the absorbent particles, thereby increasing the effective binding potential near the surface of the particles. I do not know this as fact, I am only speculating. However, based on my experiences and from what others have told me, it does seem to be true that a given quanitity of CO2 absorbent material will last longer if used intermittently, than it will during one continuous use. I am not sure if this effect is enhanced with absorbents of larger particle-size, but I suspect it would be. The only problem I have with Sofnolime is its price. I just ordered some more material from O.C. Lugo this morning, and they are charging me ~US$32 for a 4.5 kilogram container. I know that Sodasorb and other types of soda lime absorbents cost much less than this, and I may soon try one of these for comparison. I hope this information is useful. Please let me know if you have any other questions. Aloha, Rich P.S. There is a short but informative article by Ian McKernan about soda lime CO2 absorbents on page 50 of the AquaCorps "HARD" issue.
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