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来自维基百科的基础知识视频讲座，Soda lime From Wikipedia,LimeSoda lime is a mixture of chemicals, used in granular form in closed breathing environments, such as general anaesthesia, submarines, rebreathers and recompression chambers, to remove carbon dioxide from breathing gases to prevent CO2 retention and carbon dioxide poisoning.[1][2]
It is made by treating slaked lime with concentrated sodium hydroxide solution.
Chemical componentsThe main components of soda lime are
Calcium hydroxide, Ca(OH)2 (about 75%)
Water, H2O (about 20%)
Sodium hydroxide, NaOH (about 3%)
Potassium hydroxide, KOH (about 1%).
[edit] Anesthetic useWhile administering general anesthesia, the patient's expired gases, which contain carbon dioxide, are passed through an Anaesthetic machine breathing circuit filled with soda lime granules.[1] Medical grade soda lime has indicating dye that changes color when the soda lime loses its carbon dioxide absorbing capacity.
Undersea useExhaled gas must be passed through a "carbon dioxide scrubber" where the carbon dioxide is absorbed before the gas is made available to be breathed again. In rebreathers the scrubber is a part of the breathing loop.[2][3] Color indicating dye was removed from US Navy fleet use in 1996 when it was suspected of releasing chemicals into the circuit.[4] In larger environments, such as recompression chambers or submarines, a fan is used to pass gas through the canister.[2]
Chemical reactionThe overall reaction is:
CO2 + Ca(OH)2 → CaCO3 + H2O + heat (in the presence of water)
The reaction can be considered as a strong base catalysed, water facilitated reaction.
Mechanism:
1) CO2 + H2O → CO2 (aq) (CO2 dissolves in water - slow and rate determining)
2) CO2 (aq) + NaOH → NaHCO3 (bicarbonate formation at high pH)
3) NaHCO3 + Ca(OH)2 → CaCO3 + H2O + NaOH (NaOH recycled to step 2) - hence a catalyst)
Each mole of CO2 (44g) reacted produces one mole of water (18g)
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