User:Milton Beychok/Sandbox: Difference between revisions
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: 2 Pb + O<sub>2</sub> → 2 PbO | : 2 Pb + O<sub>2</sub> → 2 PbO | ||
The Pb and PbO would soon accumulate and destroy an engine. For this reason, the TEL used in gasoline was actually part of a blended liquid formulation known as '''''TEL fluid''''' or '''''ethyl fluid''''' that contained [[1,2-Dibromoethane|1,2-dibromoethane]] and [[1,2-Dichloroethane|1,2-dichloroethane]] liquids known as ''lead scavengers''. Those scavengers formed [[lead bromide]] (PbBr) and [[lead chloride]] (PbCl) which are volatile and were emitted from the engine exhaust to the [[atmosphere]]. The complete composition of TEL fluid was: | The Pb and PbO would soon accumulate and destroy an engine. For this reason, the TEL used in gasoline was actually part of a blended liquid formulation known as '''''TEL fluid''''' or '''''ethyl fluid''''' that contained [[1,2-Dibromoethane|1,2-dibromoethane]] and [[1,2-Dichloroethane|1,2-dichloroethane]] liquids known as ''lead scavengers''. Those scavengers formed [[lead bromide]] (PbBr) and [[lead chloride]] (PbCl) which are volatile and were emitted from the engine exhaust to the [[atmosphere]]. The complete composition of TEL fluid was:<ref>[http://www.epa.gov/OUST/cat/Section_2-Historical_Usage.pdf Historical Uses]] A publication of the [[U.S. Environmental Agency]]</ref> | ||
*Tetraethyl lead 61.45% | *Tetraethyl lead 61.45% |
Revision as of 01:30, 15 May 2009
Tetraethyl lead (TEL) is a viscous liquid with the chemical formula (CH3CH2)4Pb. Once widely used (circa 1925 to 1990) to increase the octane rating of gasoline (petrol), TEL usage in gasoline has been largely phased out by most nations[1] primarily because of the toxicity of the lead emissions from spark-ignited internal combustion engines burning gasoline containing TEL. Another reason for discontinuing TEL usage was that it degraded the efficiency of the catalytic converters installed in automotive vehicles to reduce their emissions of air pollutants.
Manufacture and properties
TEL is produced by the alkylation of a sodium-lead alloy using chloroethane as expressed by this chemical equation:
- 4 CH3CH2Cl + 4 NaPb → (CH3CH2)4Pb + 4 NaCl + 3 Pb
which can also be written as:
- 4 mols of chloroethane + 4 mols of sodium-lead alloy → 1 mol of tetraethyl lead + 4 mols of sodium chloride + 3 mols of lead
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The product tetraethyl lead is a viscous colorless liquid that is highly lipophilic and soluble in fats, oils and lipids as well as gasoline and other non-polar hydrocarbons. Other properties of tetraethyl lead are listed in the adjacent table.
At the temperatures found in spark-ignited internal combustion engines, TEL decomposes completely into lead and lead oxide (PbO) and combustible, short-lived ethyl radicals. Lead itself is the reactive agent that enhances the octane rating of gasolines and tetraethyl lead serves as a gasoline-soluble lead carrier.
TEL fluid formulation
When TEL burns, it produces not only carbon dioxide (CO2) and water (H2O), but also lead (Pb):
- (CH3CH2)4Pb + 13 O2 → 8 CO2 + 10 H2O + Pb
The lead can the oxidize further to give lead oxide (PbO):
- 2 Pb + O2 → 2 PbO
The Pb and PbO would soon accumulate and destroy an engine. For this reason, the TEL used in gasoline was actually part of a blended liquid formulation known as TEL fluid or ethyl fluid that contained 1,2-dibromoethane and 1,2-dichloroethane liquids known as lead scavengers. Those scavengers formed lead bromide (PbBr) and lead chloride (PbCl) which are volatile and were emitted from the engine exhaust to the atmosphere. The complete composition of TEL fluid was:[3]
- Tetraethyl lead 61.45%
- 1,2-Dibromoethane 17.85%
- 1,2-Dichloroethane 18.80%
- Inerts & color dye 1.90%
History of tetraethyl lead as a gasoline octane enhancer
References
- ↑ Phasing Lead Out of Gasoline A report issued by the United Nations Environmental Programme (UNEP). See page 8 of 23 pdf pages.
- ↑ 2.0 2.1 2.2 2.3 2.4 2.5 NIST Chemistry WebBook
- ↑ Historical Uses] A publication of the U.S. Environmental Agency