Lead alkyles, gasoline

In addition to the methyl-ethyl lead alkyls, gasolines frequently contain ethylene dichloride and dibromide as scavengers. These latter compounds also give a high response in the Electron capture detector and frequently elute at the same time as one of the lead alkyls. Dawson overcame this difficulty by using a chemically active stationary phase, silver nitrate in Carbowax 400, as a precolumn... 

The reduction ia tetraethyl lead for gasoline production is expected to iacrease the demand for petroleum alkylate both ia the U.S. and abroad. Alkylate producers have a choice of either a hydrofluoric acid or sulfuric acid process. Both processes are widely used. However, concerns over the safety or potential regulation of hydrofluoric acid seem likely to convince more refiners to use the sulfuric acid process for future alkylate capacity. 

The primary source of lead in the environment has historically been anthropogenic emissions to the atmosphere. In 1984, combustion of leaded gasoline was responsible for approximately 90% of all anthropogenic lead emissions. EPA phased out the use of lead alkyls in gasoline, however, and by 1990, auto emissions accounted for only 33% of the annual lead emissions (EPA 1996h). Use of lead additives in motor fuels was totally banned after December 31, 1995 (EPA 1996f). The ban went into effect on February 2, 1996. Atmospheric deposition is the largest source of lead found in soils. Lead is transferred... 

The ASTM-EFA standard method of analyzing lead In gasoline requires extraction of alkyl lead Iodide complexes Into methyllsobutylketone and a subsequent flame atomic absorption analysis of the extract A more direct method has been proposed ( ) which uses Zeeman atomic absorption analysis after sample dilution. Both methods were used to analyze a set of five field collected samples. The results showed a bias (average difference between method results) of 0.0012 g/gal with the standard flame results higher. The correlation coefficient between the results was 0.9998 0.0009, and a pairwise t-test showed no difference between the methods (6). 

Reduction of the amount of non-selective amorphous debris present as in ALPHA and BETA catalysts increases alkylate, gasoline and distillate yields and reduces the amount of secondary reactions leading to coke and wet gas. 

Another limitation on the use of catalytic oxidation is the susceptibility of the catalysts to various deactivators or poisons, although according to the vendor the phase out of the use of volatile lead alkyls as antiknock agents in U.S. gasoline, catalyst poisoning is today rarely encountered. 

Alkyl lead compounds are extremely effective gasoline antiknock agents. By decomposing to form lead oxide compounds during the gasoline combustion process, lead alkyls interrupt the rapid chain scission reactions which lead to combustion knock. Also, lead alkyls help to prevent exhaust valve seat wear and may minimize octane requirement increase. However, unless utilized in conjunction with lead scavengers such as 1,2-dichloromethane, lead deposits can accumulate within the gasoline combustion chamber. 

Parker, W. W., Hudson, R. L. A simplified chromatographic method for separation and identification of mixed lead alkyls in gasoline. Anal. Chem. 35, 1334 (1963). 

Soulages, N. L. Simultaneous determination of lead alkyls and halide scavengers in gasoline by gas chromatography with flame ionisation detection. Anal. Chem. 38, 28(1966). 

The method is suitable for the determination of Pb in gasoline in the range 1—lOOOpgml-1 (0.001—1 gl 1). The gasoline sample is diluted with MIBK and shaken with a solution of iodine in toluene. Iodo lead alkyl species are formed and these are stabilised with a liquid anion exchanger. Thus, the problem of the variable Pb response is overcome. This solution is compared with standards prepared in a similar fashion from Pb chloride in MIBK. 

R. MacKinven, Search for Ash-Free Compounds to Replace Lead Alkyls in Gasoline, Dtsch. Ges. fuer Mineraloelwiss und Kohlechem, 24th Symp. Compend. 74/75, Hamburg, Sep. 30-Oct. 3, 2 (1974) p. 687. 

Thus certain substances added to gasoline, notably the lead alkyls, have a profound effect on antiknock properties and inhibit the precombustion oxidation chain that is known to promote knocking. For a considerable period. 

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