Anti-knocks

Most of the ethylene dichloride produced is utilized for the manufacture of vinyl chloride, which may be obtained from it by pyrolysis or the action of caustic soda. Large quantities are also used in anti-knock additives for gasoline. As a solvent It has been displaced by trichloroethylene and tetrachloroelhyJene. U.S. production 1978 4-75 megatonnes. 

The various additives used to obtain the required properties include anti-knock compounds, anti-oxidants, metal deactivalors, anti-icing additives, etc. 

PbEu (anti-knock agents), radiation and sound shields, in paints, high quality glass. World production 1980 4 0 megatonnes. Lead compounds are toxic and hazardous to health. 

Bromine is used in the manufacture of many important organic compounds including 1,2-dibromoethane (ethylene dibromide), added to petrol to prevent lead deposition which occurs by decomposition of the anti-knock —lead tetraethyl bromomethane (methyl bromide), a fumigating agent, and several compounds used to reduce flammability of polyester plastics and epoxide resins. Silver(I) bromide is used extensively in the photographic industry... 

ETHYL FLUID see MOTOR FUEL ANTI-KNOCK COMPOUND ... 

Proc ing Anti-knock Gasoline y Synihctic Resins... 

A few cases occur in which hot-corrosion and wet corrosion are interdependent, the wet corrosion arising from the condensation of liquids generated during a period at elevated temperatures. The formation of condensates of hydrobromic acid in engines burning anti-knock fuels containing ethylene dibromide is important in this context. Such cases are properly considered as aqueous corrosion. 

The deposits formed in internal combustion engines by high-octane petrols may be classed as ashes they consist of mixtures of lead oxides, bromides and sulphates derived from the anti-knock additives and, of course, exert their main corrosive effect on the parts operating at the highest temperature the exhaust valves and the sparking-plug electrodes. 

Currently available CRMs A number of organolead (tetra- and triaUcyllead) compounds are commercially available to be used as calibrants. There are also a number of interesting CRMs an urban dust certified for trimethyUead and more appear to be in development The interest in organolead compotmds is, however, on the decline due to the gradual disappearance of the tetraethyl anti-knock agent from petrol. 

Methyl tertiary butyl ether (MTBE) is used as an anti-knock additive in petrol (gasoline). 

The symposium s only conclusion was to call for more research, and Ethyl officials were pleased that there were no adverse effects flowing from that particular meeting the press releases underscored the economic hardships that would be caused by the disappearance of lead anti knocks. ... 

Lead is also used in organ pipes, of course. Other uses include the lead-acid battery, radiation shielding, ceramic glazes, and in lead glass. It is a toxic element, and its organic derivatives are also toxic. Tetraethyllead was used for many years as an anti-knock agent in petrol. 

The use of PbEt4 as an anti-knock agent in petrol depends in part on the ability of the ethyl radicals, generated on its thermal decomposition, to combine with radicals produced in the over-rapid combustion of petroleum hydrocarbons chain reactions which are building up to explosion (knocking) are thus terminated short of this. The complete details of how PbEt4 operates are not known, but there is some evidence that minute Pb02 particles derived from it can also act as chain-stoppers . 

Mono( 17-cyclopentadienyl) carbonyl complexes of Ti, Zr, and Hf have been noted only in the patent literature. A U.S patent issued to Ethyl Corporation in 1962 described the use of such complexes as anti-knock agents and lubricant additives. Two examples of complexes purported to have been made are shown below (115). 

So-called green petrol is a preferred alternative to leaded petrol it contains about 3 per cent of the aromatic hydrocarbon benzene (C6H6, IV) as an additive, the benzene acting as a lead-free alternative to PbEt4 as an anti-knocking compound. 

The page http //www.radford.edu/ wkovarik/lead cites some fascinating sidelights on the history of petrol and its additives, and its links are carefully chosen. For example, the excellent page http //www.chemcases.com/tel summarizes the history of tetraethyl lead and the attendant controversies over its addition to petrol. Though quite small, the site http //www.exxon.com/exxon productdataAube encyclopedia/knock.html contains useful information on the anti-knock properties of petrol and its additives. 

Tetraethyl lead (anti-knock agent in gasoline)... 

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