Soda lime
Encyclopedia
Soda lime is a mixture of chemicals, used in granular form in closed breathing environments, such as general anaesthesia
, submarine
s, rebreather
s and recompression chambers, to remove carbon dioxide
from breathing gas
es to prevent CO2 retention and carbon dioxide poisoning.
It is made by treating slaked lime with concentrated sodium hydroxide solution.
breathing circuit filled with soda lime granules. Medical grade soda lime has indicating dye
that changes color when the soda lime loses its carbon dioxide absorbing capacity.
s the scrubber is a part of the breathing loop. Color indicating dye was removed from US Navy fleet use in 1996 when it was suspected of releasing chemicals into the circuit. In larger environments, such as recompression chambers or submarines, a fan is used to pass gas through the canister.
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.
steps:
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)
General anaesthesia
General anaesthesia is a state of unconsciousness and loss of protective reflexes resulting from the administration of one or more general anaesthetic agents...
, submarine
Submarine
A submarine is a watercraft capable of independent operation below the surface of the water. It differs from a submersible, which has more limited underwater capability...
s, rebreather
Rebreather
A rebreather is a type of breathing set that provides a breathing gas containing oxygen and recycled exhaled gas. This recycling reduces the volume of breathing gas used, making a rebreather lighter and more compact than an open-circuit breathing set for the same duration in environments where...
s and recompression chambers, to remove carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
from breathing gas
Breathing gas
Breathing gas is a mixture of gaseous chemical elements and compounds used for respiration.Air is the most common and only natural breathing gas...
es to prevent CO2 retention and carbon dioxide poisoning.
It is made by treating slaked lime with concentrated sodium hydroxide solution.
Chemical components
The main components of soda lime are- Calcium hydroxideCalcium hydroxideCalcium hydroxide, traditionally called slaked lime, is an inorganic compound with the chemical formula Ca2. It is a colourless crystal or white powder and is obtained when calcium oxide is mixed, or "slaked" with water. It has many names including hydrated lime, builders lime, slack lime, cal, or...
, Ca(OH)2 (about 75%) - WaterWaterWater is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
, H2O (about 20%) - Sodium hydroxide, NaOH (about 3%)
- Potassium hydroxidePotassium hydroxidePotassium hydroxide is an inorganic compound with the formula KOH, commonly called caustic potash.Along with sodium hydroxide , this colorless solid is a prototypical strong base. It has many industrial and niche applications. Most applications exploit its reactivity toward acids and its corrosive...
, KOH (about 1%).
Anesthesia use
While administering general anesthesia, the patient's expired gases, which contain carbon dioxide, are passed through an Anaesthetic machineAnaesthetic machine
The anaesthetic machine is used by anaesthesiologists and nurse anaesthetists to support the administration of anaesthesia...
breathing circuit filled with soda lime granules. Medical grade soda lime has indicating dye
Dye
A dye is a colored substance that has an affinity to the substrate to which it is being applied. The dye is generally applied in an aqueous solution, and requires a mordant to improve the fastness of the dye on the fiber....
that changes color when the soda lime loses its carbon dioxide absorbing capacity.
Undersea use
Exhaled 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 rebreatherRebreather
A rebreather is a type of breathing set that provides a breathing gas containing oxygen and recycled exhaled gas. This recycling reduces the volume of breathing gas used, making a rebreather lighter and more compact than an open-circuit breathing set for the same duration in environments where...
s the scrubber is a part of the breathing loop. Color indicating dye was removed from US Navy fleet use in 1996 when it was suspected of releasing chemicals into the circuit. In larger environments, such as recompression chambers or submarines, a fan is used to pass gas through the canister.
Chemical reaction
The 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.
steps:
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
Mole (unit)
The mole is a unit of measurement used in chemistry to express amounts of a chemical substance, defined as an amount of a substance that contains as many elementary entities as there are atoms in 12 grams of pure carbon-12 , the isotope of carbon with atomic weight 12. This corresponds to a value...
of CO2 (44g) reacted produces one mole of water (18g)
External links
- Sofnolime MSDS Example of a commercial soda lime product that is used in diving and medicine
- Publications on sodalime in diving operations
- Soda Lime A technical introduction to the C02 absorption properties of Sofnolime/Soda Lime.