Soda lime
Soda lime, a
Chemical components
The primary components of soda lime include: calcium oxide (CaO) constituting approximately 75%, water (H
2O) accounting for around 20%, sodium hydroxide (NaOH) making up about 3%, and potassium hydroxide (KOH) present at approximately 0.1%.
Anaesthesia
During
Recent carbon dioxide absorbents have been developed to minimize the risk of toxic by-product formation resulting from the interaction between the absorbent and
Space flight
In space flights,
Rebreather use
Exhaled gas undergoes a crucial process: it must pass through a carbon dioxide scrubber where carbon dioxide is absorbed before the gas is circulated for breathing again. In
Chemical reaction
The overall chemical reaction is:
- CO2 + Ca(OH)2 → CaCO3 + H2O + heat (in the presence of water)
Each mole of CO2 (44 g) reacts with one mole of calcium hydroxide (74 g) and produces one mole of water (18 g).
The reaction can be considered as a strong-base-catalysed, water-facilitated reaction.[5]
The reaction mechanism of carbon dioxide with soda lime can be decomposed in three elementary steps:
- 1) (CO2 dissolves in water – slow and rate-determining),
- 2) (bicarbonate formation at high pH),
- 3) (NaOH recycled to step 2 – hence a catalyst).
This sequence of reactions explains the catalytic role played by sodium hydroxide in the system and why soda lime is faster in chemical reactivity than calcium hydroxide alone.[6] The moist sodium hydroxide impregnates the surface and the porosity of calcium hydroxide grains with a high specific surface area.[7] It reacts much more quickly and so contributes to a faster elimination of the carbon monoxide 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 the anesthesia breathing circuit in anesthesia systems.[8][9]
The same catalytic effect by the alkali hydroxides (function of the Na2Oeq content of cement) also contributes to the carbonation of portlandite by atmospheric CO2 in concrete although the rate of propagation of the reaction front is there essentially limited by the carbon dioxide diffusion within the concrete matrix less porous.[10]
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
reaction 1: SiO2 + NaOH → NaHSiO3 silica dissolution by NaOH:
high pHreaction 2: NaHSiO3 + Ca(OH)2 → CaSiO3 + H2O + NaOH C-S-H precipitation
and regeneration of NaOHsum (1+2): SiO2 + Ca(OH)2 → CaSiO3 + H2O global reaction: Pozzolanic reactioncatalysed by NaOH
See also
- Carbon dioxide scrubber
- Alkali–silica reaction
- Soda–lime glass, a type of glass made from silica, soda, lime and aluminum oxide
References
- ^ ISBN 978-0-7817-5745-4. Archived from the originalon 13 July 2011. Retrieved 1 July 2010.
- ^ ISBN 978-0-7020-2571-6.
- ^ Richardson, Drew; Menduno, Michael; Shreeves, Karl (eds). (1996). "Proceedings of Rebreather Forum 2.0". Diving Science and Technology Workshop. Diving Science and Technology: 286. Archived from the original on September 15, 2008. Retrieved 2009-03-18.
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: CS1 maint: multiple names: authors list (link) CS1 maint: unfit URL (link) - PMID 8653065. Archived from the original on November 16, 2007. Retrieved 2009-03-18.)
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: CS1 maint: unfit URL (link - ^ 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.
- ISSN 1381-2386.
- ISSN 0377-0486.
- .
- ^ Freeman, Brian S.; Berger, Jeffrey S. (2014). Anesthesiology Core Review: Part One Basic Exam. Chapter 17: Absorption of Carbon Dioxide. McGraw-Hill Education. Retrieved 22 April 2020 – via Access Medicine.
- ISBN 978-0-8031-5667-8.
External links
- Publications on sodalime in diving operations[usurped]
- Sofnolime MSDS Example of a commercial soda lime product that is used in diving and medicine
- An Introduction to Sofnolime (Technical Article)