Leaded motor fuels

A motor fuel has an octane number X if it behaves under tightly defined experimental conditions the same as a mixture of X volume % of isooctane and (100 - X)% of n-heptane. The isooctane-heptane binary mixtures are called primary reference fuels. Octane numbers higher than 100 can also be defined the reference material is isooctane with small quantities of tetraethyl lead added the way in which this additive acts will be discussed later. 

The base products, TEL and TML, are liquids having boiling points of 205° and 110° respectively. The contents of additives used are usually expressed in grams of lead per liter of fuel in the past they have reached 0.85 g Pb/1. These concentrations are still found in some of the countries of Africa. Elsewhere, when part or all of the motor fuel pool contains lead, the concentrations are much smaller. Thus in Western Europe they no longer exceed 0.15 g Pb/1. 

The gradual reduction and ultimate elimination of lead has seen considerable effort by the refiner to maintain the octane numbers at satisfactory levels. In Europe, the conventional unleaded motor fuel, Eurosuper, should have a minimum RON of 95 and a minimum MON of 85. These values were set in 1983 as the result of a technical-economic study called RUFIT (Rational Utilization of Fuels in Private Transport). A compromise was then possible between refining energy expenses and vehicle fuel consumption (Anon., 1983). 

The potential advantages of LPG concern essentially the environmental aspects. LPG s are simple mixtures of 3- and 4-carbon-atom hydrocarbons with few contaminants (very low sulfur content). LPG s contain no noxious additives such as lead and their exhaust emissions have little or no toxicity because aromatics are absent. This type of fuel also benefits often enough from a lower taxation. In spite of that, the use of LPG motor fuel remains static in France, if not on a slightly downward trend. There are several reasons for this situation little interest from automobile manufacturers, reluctance on the part of automobile customers, competition in the refining industry for other uses of and fractions, (alkylation, etherification, direct addition into the gasoline pool). However, in 1993 this subject seems to have received more interest (Hublin et al., 1993). 

In addition to their antiknock properties, organic lead compounds possess bactericidal properties and motor fuels with lead are known to inhibit bacterial growth during storage in contact with water. With the disappearance of lead-based compounds, it is necessary to incorporate biocides from the cyclic imine family, (piperidine, pyrrolidine, hexamethyleneimine), alkylpropylene diamines or imidazolines (Figure 9.2). 

Whitcomb, R.M. (1975), Non-lead antiknock agents for motor fuels . Chemical Technology Review No. 49, Noyes Data Corporation, Park Ridge, NJ. 

Lead is an element used in many industrial processes and also has been used in fuels and coatings. Tetraethyl lead was added to gasoline to improve performance as a motor fuel, and elemental lead was extensively used in paints and coatings to improve coverage and durability until the 1970s, when phase-out efforts began to reduce lead emissions to the environment. 

The use of propane as a motor vehicle fuel has been highly developed in some countries, particularly in the USA, Holland and Italy. It is, of course, an entirely lead-free fuel. Very high efficiencies can be obtained using a gaseous fuel in spark-ignition engines since intimate mixing of the fuel and air is much more easily achieved than with a liquid fuel. This results in a much cleaner exhaust, with considerable reductions in CO and hydrocarbons. 

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... 

A further fact must be taken into account, which for obvious reasons did not appear in Haslam s article. As a consequence of our contracts with the Americans, we received from them above and beyond the agreement many very valuable contributions for the synthesis and improvement of motor fuels and lubrication oils, which just now during the war are most useful to us. It need not be especially mentioned that without lead-tetraethyl the present method of warfare would be unthinkable. The fact that since the beginning of the war we could produce lead-tetraethyl is entirely due to the circumstances that, shortly before, the Americans had presented us with the production plans, complete with experimental knowledge. Thus the difficult work of development (one need only recall the poisonous property of lead-tetraethyl, which caused many deaths in the U.S.A.) was spared us, since we could take up the manufacture of this product together with ail the experience that the Americans had gathered over long years. 

The dual role of -hcxanc as a component of refined petroleum fuels and as a highly refined, specialized product for other end uses lead to complications in making estimates of actual production levels. For instance, no formal production statistics could be identified associated with the -hexane contained in heating or motor fuels. Since the late 1980s, no quantitative production figures have been available for those companies documented as producing appreciable amounts of -hexanc for commercial use (SRI 1988, 1990, 1992, 1994, 1995, 1996). The following six facilities are currently documented as producers... 

Another near future objective is to ensure development of technology that enables production of motor-fuel substitutes fhom non petroleum sources. The production of methanol-higher alcohols mixtures fhom natural gas,via syngas, remains a priority objective to obtain octane boosters capable of replacing lead alkyls and to allow the use of additional low-priced methanol. 

Wiese Formula An empirical formula developed by General Motors Research for expressing motor fuel antiknock values above 100. This value is obtained by measuring the number of milliliters of tetraethyl lead added per gallon to achieve the same knocking tendency as the fuel being tested. The determined value is then expressed as a performance number. 

Benzene, a component of motor fuel that is also widely used as an industrial solvent and as a starting material in organic synthesis, is a hematopoietic toxin. Chronic exposure to benzene vapors leads to pancytopenia, that is, decreased production of all types of blood cells (erythrocytes, leukocytes, and platelets). The long-term effect of benzene exposure is acute leukemia. 

Catalytic polymerization is a leading process of the refining industry in the production of high-quality motor fuels and certain petrochemicals. The Solid Phosphoric Acid catalytic process was developed by Vladimir Ipatieff and has since been extensively modified and improved. By this method the catalyst is loaded in a chamber or placed in tubes and the heated charge is passed through it. The olefinic feed stock generally is diluted with low-olefin recycle. 

A few other comments Ethanol is listed by OSHA as a suspect but unproved carcinogen, but OSHA does not have jurisdiction over beverage alcohol, nor, since it is a natural product, does the Delaney Amendment apply. This could lead to paradoxical situations. Ethanol will continue to grow explosively in volume in the next few years as a motor fuel indeed, this has happened in Brazil. The field is extremely volatile, and new developments occur every week, particularly with respect to fermentation and gasohol. Things should be clearer in about five years, and we should remind ourselves to take a similar look at ethanol then. 

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