![Drägersorb Soda Lime](https://upload.wikimedia.org/wikipedia/commons/6/60/Dr%C3%A4gersorb_Soda_Lime.jpg)
Soda lime is a mixture of
NaOH
Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula NaOH. It is a white solid ionic compound consisting of sodium cations and hydroxide anions .
Sodium hydroxide is a highly caustic base and alkali ...
and
CaO Cao or CAO may refer to:
Mythology
*Cao (bull), a legendary bull in Meitei mythology
Companies or organizations
* Air China Cargo, ICAO airline designator CAO
*CA Oradea, Romanian football club
*CA Osasuna, Spanish football club
*Canadian Assoc ...
chemical
A chemical substance is a form of matter having constant chemical composition and characteristic properties. Some references add that chemical substance cannot be separated into its constituent elements by physical separation methods, i.e., wi ...
s, used in
granular
Granularity (also called graininess), the condition of existing in granules or grains, refers to the extent to which a material or system is composed of distinguishable pieces. It can either refer to the extent to which a larger entity is subd ...
form in closed breathing environments, such as
general anaesthesia
General anaesthesia (UK) or general anesthesia (US) is a medically induced loss of consciousness that renders the patient unarousable even with painful stimuli. This effect is achieved by administering either intravenous or inhalational general ...
,
submarine
A submarine (or sub) is a watercraft capable of independent operation underwater. It differs from a submersible, which has more limited underwater capability. The term is also sometimes used historically or colloquially to refer to remotely op ...
s,
rebreather
A rebreather is a breathing apparatus that absorbs the carbon dioxide of a user's breathing, exhaled breath to permit the rebreathing (recycling) of the substantially unused oxygen content, and unused inert content when present, of each breath. ...
s and
recompression chamber
A diving chamber is a vessel for human occupation, which may have an entrance that can be sealed to hold an internal pressure significantly higher than ambient pressure, a pressurised gas system to control the internal pressure, and a supply of ...
s, to remove
carbon dioxide
Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...
from
breathing gas
A breathing gas is a mixture of gaseous chemical elements and compounds used for respiration. Air is the most common and only natural breathing gas, but other mixtures of gases, or pure oxygen, are also used in breathing equipment and enclosed h ...
es to prevent
CO2 retention and
carbon dioxide poisoning
Hypercapnia (from the Greek ''hyper'' = "above" or "too much" and ''kapnos'' = "smoke"), also known as hypercarbia and CO2 retention, is a condition of abnormally elevated carbon dioxide (CO2) levels in the blood. Carbon dioxide is a gaseous pro ...
.
It is made by treating
slaked lime
Calcium hydroxide (traditionally called slaked lime) is an inorganic compound with the chemical formula Ca( OH)2. It is a colorless crystal or white powder and is produced when quicklime (calcium oxide) is mixed or slaked with water. It has ma ...
with concentrated
sodium hydroxide
Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula NaOH. It is a white solid ionic compound consisting of sodium cations and hydroxide anions .
Sodium hydroxide is a highly caustic base and alkali ...
solution.
Chemical components
The main components of soda lime are
*
Calcium oxide
Calcium oxide (CaO), commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, Caustic (substance), caustic, alkaline, crystalline solid at room temperature. The broadly used term "''lime (material), lime''" co ...
, CaO (about 75%)
*
Water
Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a ...
, H
2O (about 20%)
*
Sodium hydroxide
Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula NaOH. It is a white solid ionic compound consisting of sodium cations and hydroxide anions .
Sodium hydroxide is a highly caustic base and alkali ...
, NaOH (about 3%)
*
Potassium hydroxide
Potassium hydroxide is an inorganic compound with the formula K OH, and is commonly called caustic potash.
Along with sodium hydroxide (NaOH), KOH is a prototypical strong base. It has many industrial and niche applications, most of which exp ...
, KOH (about 0.1%).
Anaesthetic use
During the administration of general anaesthesia, the gases expired by a patient, which contain
carbon dioxide
Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...
, are passed through an
anaesthetic machine breathing circuit filled with soda lime granules.
[ Medical-grade soda lime includes an indicating ]dye
A dye is a colored substance that chemically bonds to the substrate to which it is being applied. This distinguishes dyes from pigments which do not chemically bind to the material they color. Dye is generally applied in an aqueous solution an ...
that changes color when the soda lime reaches its carbon dioxide absorbing capacity.
To ensure that a soda lime canister (CO2 absorber) is functioning properly, it should not be used if the indicating dye is activated. Standard anaesthesia machines typically contain up to 2 kg of soda lime granules.
Lithium hydroxide
Lithium hydroxide is an inorganic compound with the formula LiOH. It can exist as anhydrous or hydrated, and both forms are white hygroscopic solids. They are soluble in water and slightly soluble in ethanol. Both are available commercially. While ...
(LiOH) is the alkali hydroxide with the lowest molecular weight (Na: 23 g/mol; Li: 7 g/mol) and is therefore used as CO2 absorbent in space flight
Spaceflight (or space flight) is an application of astronautics to fly spacecraft into or through outer space, either human spaceflight, with or uncrewed spaceflight, without humans on board. Most spaceflight is uncrewed and conducted mainly w ...
s since the Apollo program to spare weight at launch. During Apollo 13 flight, the crew sheltered in the lunar module
The Apollo Lunar Module (LM ), originally designated the Lunar Excursion Module (LEM), was the lunar lander spacecraft that was flown between lunar orbit and the Moon's surface during the United States' Apollo program. It was the first crewed ...
started suffering from high CO2 levels and had to adapt spare absorbent cartridges from the Apollo capsule to the LEM system.
Recent generation of CO2 absorbents have been developed to reduce the risk of formation of toxic by-products as a result of the interaction between the absorbent and inhaled anesthetics (halothane
Halothane, sold under the brand name Fluothane among others, is a general anaesthetic. It can be used to induce or maintain anaesthesia. One of its benefits is that it does not increase the production of saliva, which can be particularly useful i ...
). Some absorbents made from lithium hydroxide (LiOH) are also available for this purpose.
Rebreather use
Exhaled gas must be passed through a carbon dioxide scrubber
A carbon dioxide scrubber is a piece of equipment that absorbs carbon dioxide (CO2). It is used to treat exhaust gases from industrial plants or from exhaled air in life support systems such as rebreathers or in spacecraft, submersible craft or a ...
where the carbon dioxide is absorbed before the gas is made available to be breathed again. In rebreather
A rebreather is a breathing apparatus that absorbs the carbon dioxide of a user's breathing, exhaled breath to permit the rebreathing (recycling) of the substantially unused oxygen content, and unused inert content when present, of each breath. ...
s the scrubber is a part of the breathing loop. Color indicating dye was removed from US Navy
The United States Navy (USN) is the maritime service branch of the United States Armed Forces and one of the eight uniformed services of the United States. It is the largest and most powerful navy in the world, with the estimated tonnage of ...
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 maintain the flow of gas through the scrubbing canister.[
]
Chemical reaction
The overall reaction is:
:CO2 + Ca(OH)2 → CaCO3 + H2O + heat (in the presence of water)
Each mole
Mole (or Molé) may refer to:
Animals
* Mole (animal) or "true mole", mammals in the family Talpidae, found in Eurasia and North America
* Golden moles, southern African mammals in the family Chrysochloridae, similar to but unrelated to Talpida ...
of CO2 (44 g) reacting with one mole of calcium hydroxide
Calcium hydroxide (traditionally called slaked lime) is an inorganic compound with the chemical formula Ca( OH)2. It is a colorless crystal or white powder and is produced when quicklime (calcium oxide) is mixed or slaked with water. It has m ...
(74g) and produces one mole of water (18 g).
The reaction can be considered as a strong-base-catalysed, water-facilitated reaction.[Joseph Pelc (1923). Process of treating lime-containing materials. Application filed August 30, 1921. Serial No. 496,963. Patented Mar. 6, 1923. United States, 1,447,568 Patent Office.]
/ref>
The reaction mechanism of carbon dioxide with soda lime can be decomposed in three elementary steps:
:1) CO2(g) <=>> 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 + NaOH + H2O (NaOH recycled to step 2 – hence a catalyst
Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
)
This sequence of reactions explains the catalytic role played by sodium hydroxide
Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula NaOH. It is a white solid ionic compound consisting of sodium cations and hydroxide anions .
Sodium hydroxide is a highly caustic base and alkali ...
in the system and why soda lime is faster in chemical reactivity than calcium hydroxide alone. The moist NaOH impregnates the surface and the porosity
Porosity or void fraction is a measure of the void (i.e. "empty") spaces in a material, and is a fraction of the volume of voids over the total volume, between 0 and 1, or as a percentage between 0% and 100%. Strictly speaking, some tests measure ...
of calcium hydroxide grains with a high specific surface area. It reacts much more quickly and so contributes to a faster elimination of the CO2 from the rebreathing circuit. The formation of water by the reaction and the moisture from the respiration also act as a solvent for the reaction. Reactions in aqueous phase are generally faster than between a dry gas and a dry solid. Soda lime is commonly used in closed-circuit diving rebreathers and in anesthesia
Anesthesia is a state of controlled, temporary loss of sensation or awareness that is induced for medical or veterinary purposes. It may include some or all of analgesia (relief from or prevention of pain), paralysis (muscle relaxation), ...
systems.
The same catalytic effect by the alkali hydroxide
The alkali hydroxides are a class of chemical compounds which are composed of an alkali metal cation and the hydroxide anion (OH−). The alkali hydroxides are:
*Lithium hydroxide (LiOH)
*Sodium hydroxide (NaOH)
*Potassium hydroxide (KOH)
*Rubidiu ...
s (function of the Na2Oeq content of cement
A cement is a binder, a chemical substance used for construction that sets, hardens, and adheres to other materials to bind them together. Cement is seldom used on its own, but rather to bind sand and gravel ( aggregate) together. Cement mix ...
) also contributes to the carbonation of portlandite
Portlandite is a hydroxide-bearing mineral typically included in the oxide mineral class. It is the naturally occurring form of calcium hydroxide (Ca(OH)2) and the calcium analogue of brucite (Mg(OH)2).
Occurrence
Portlandite occurs in a variety ...
by atmospheric CO2 in concrete
Concrete is a composite material composed of fine and coarse aggregate bonded together with a fluid cement (cement paste) that hardens (cures) over time. Concrete is the second-most-used substance in the world after water, and is the most wi ...
although the rate of propagation of the reaction front is there essentially limited by the CO2 diffusion
Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemical p ...
within the concrete matrix less porous
Porosity or void fraction is a measure of the void (i.e. "empty") spaces in a material, and is a fraction of the volume of voids over the total volume, between 0 and 1, or as a percentage between 0% and 100%. Strictly speaking, some tests measure ...
.
Analogy with the alkali-silica reaction
A similar reaction to above, also catalysed by sodium hydroxide, is the alkali-silica reaction, a slow degradation process causing the swelling and the cracking of concrete
Concrete is a composite material composed of fine and coarse aggregate bonded together with a fluid cement (cement paste) that hardens (cures) over time. Concrete is the second-most-used substance in the world after water, and is the most wi ...
containing aggregates rich in reactive amorphous silica
Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...
. In a very similar way, NaOH greatly facilitates the dissolution of the amorphous silica. The produced sodium silicate then reacts with the calcium hydroxide (portlandite
Portlandite is a hydroxide-bearing mineral typically included in the oxide mineral class. It is the naturally occurring form of calcium hydroxide (Ca(OH)2) and the calcium analogue of brucite (Mg(OH)2).
Occurrence
Portlandite occurs in a variety ...
) present in the hardened cement
A cement is a binder, a chemical substance used for construction that sets, hardens, and adheres to other materials to bind them together. Cement is seldom used on its own, but rather to bind sand and gravel ( aggregate) together. Cement mix ...
paste to form calcium silicate hydrate
Calcium silicate hydrate (or C-S-H) is the main product of the hydration of Portland cement and is primarily responsible for the strength in cement based materials (e.g. concrete).
Preparation
When water is added to cement, each of the compounds u ...
(abbreviated as C-S-H in the cement chemist notation
Cement chemist notation (CCN) was developed to simplify the formulas cement chemists use on a daily basis. It is a shorthand way of writing the chemical formula of oxides of calcium, silicon, and various metals.
Abbreviations of oxides
The main o ...
). This silicification
In geology, silicification is a petrification process in which silica-rich fluids seep into the voids of Earth materials, e.g., rocks, wood, bones, shells, and replace the original materials with silica (SiO2). Silica is a naturally existing and ...
reaction of Ca(OH)2 on its turn continuously releases again sodium hydroxide in solution, maintaining a high pH, and the cycle continues up to the total disappearance of portlandite or reactive silica in the exposed concrete. Without the catalysis
Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
of this reaction by sodium or potassium soluble hydroxides the alkali-silica reaction would not proceed or would be limited to a very slow pozzolanic reaction
The pozzolanic activity is a measure for the degree of reaction over time or the reaction rate between a pozzolan and Ca2+ or calcium hydroxide (Ca(OH)2) in the presence of water. The rate of the pozzolanic reaction is dependent on the intrinsic ...
. The alkali silica reaction can be written like the soda lime reaction, by simply substituting CO2 by SiO2 in the reactions mentioned here above as follows:
:
See also
* Carbon dioxide scrubber
A carbon dioxide scrubber is a piece of equipment that absorbs carbon dioxide (CO2). It is used to treat exhaust gases from industrial plants or from exhaled air in life support systems such as rebreathers or in spacecraft, submersible craft or a ...
* Alkali-silica reaction (ASR)
* Soda–lime glass
Soda–lime glass, also called soda–lime–silica glass, is the most prevalent type of glass, used for windowpanes and glass containers (bottles and jars) for beverages, food, and some commodity items. Some glass bakeware is made of soda-lime ...
, a type of glass made from silica, soda, lime, and aluminum oxide
References
External links
* {{usurped,
Publications on sodalime in diving operations
}
Sofnolime_MSDS
.html" ;"title="MSDS">Sofnolime MSDS
">MSDS">Sofnolime MSDS
Example of a commercial soda lime product that is used in diving and medicine
An Introduction to Sofnolime (Technical Article)
Hydroxides
Calcium compounds
Sodium compounds
Anesthetic equipment
Rebreathers, *
Catalysis