Methyl tertiary - butyl ether (MTBE).
Health Effect of Using Lead in Gasoline
Most of the world's developed countries have been concerned about the adverse health effect of using lead as a gasoline octane booster. Recently, a substantial amount of new evidence has become available that indicate that lead level previously thought to be safe apparently may not be. Also in countries where lead has been reduced data are now becoming available that show a direct and corresponding reduction in human blood lead level confirming gasoline lead additives as the major source of lead in humans. At the same time, the availability of oxygenates, plus increased octane production at European refineries, make the removal of lead from gasoline more possible than any time in the past.
New Medical Evidence
Lead has long been known to inhibit major enzymatic processes to have adverse effect on the central nervous system, and to lower the intelligence and affect the behaviour of children. In a US EPA report "costs and benefits of reducing lead in gasoline" March 1989, seven independent studies are presented which consistently found lower (Intelligence Quantity) IQ in children with high blood lead level. The high lead group in the studies have less than 30 micrograms of lead per decilitre of blood, (ug/dl) previously 25 to 30 ug/dl of lead was thought by many experts to be a safe level. Equally disturbing are the studies published in the last five years that demonstrated that blood lead level as low as 10 ug/dl and possibly lower, can lead to reduce infant birth weight, effects on mental development of the fetus during pregnancy, and high blood pressure and hypertension in adults.
Based on the medical evidence now available, the US over one year ago, phased down lead in leaded gasoline to a maximum of 0.026 g/l. Canada also decided reducing lead to 0.026 on Dec. 1989 again because of health concern. On reviewing the most recent medical evidence on lead, a Canada Government report concludes, "From all these findings, it is reasonable to assume that blood lead level should not be allowed to exceed 10 ug/dl and that, in fact, even this limit allows little or no margin of safety".
Correlation Between Lead in Gasoline
and Lead in Blood
As shown in Figure No. 1, the correlation between lead use in gasoline and blood lead level was clearly established by American researchers. A fall of 55 per cent in the amount of lead used in gasoline was accompanied by a 31 per cent reduction in the blood lead level of the average US citizen. These results are confirmed in the UK where the lead reduction in gasoline from 0.4 to 0.15 g/l made in 1986 was followed by 50 per cent reduction in atmosphere lead level and by a significant reduction in blood levels. According to Professors of (Brussels University, Feb. 1984), 90 per cent of the lead in an industrial city atmosphere comes from automobiles. Two isotopic lead experiments were conducted in 1977, one in Italy, the other in Belgium, found that 24 per cent to 25 per cent of the lead in blood came from lead in gasoline.
Current Situation in Europe Today
Ten years ago, the EEC issued a directive calling for the lead contents in gasoline to be reduced for public health reason down to a level of 0.15 g/l. In 1982, the EEC established maximum level of lead allowed in the atmosphere which are in effect today; annual average lead concentration must not exceed 2 ug/m3 of air. Option for replacing lead in gasoline
In order to meet the need for high octane unleaded gasoline, the environmental protection agency (EPA) has approved the use of several high octane blending which is oxygenated component for replacing lead in gasoline such as methanol, TBA, Toluene, Ethanol, but (EPA) granted approval for the use of MTBE as blending due to: (1) Its volatility lies within the normal gasoline range, (2) It is completely miscible with gasoline, it does not create phase separation problems with water, (3) It is blending octane is one of the highest of any oxygenate, (4) MTBE boils near the front end of the gasoline, an important factor, in view of lead phase down and lead's well known property as a front end octane improver.
At present, MTBE is approved for use in U.S. unleaded gasoline at a level upto 15 per cent volume and unleaded gasoline in Europe at a level upto 10 per cent volume of MTBE. SABIC MTBE is produced at lbn Zahr which is one of the world largest and more technically advanced MTBE manufacturing complex with a design capacity to produce 500,000 MT of MTBE annually. The complex uses licensed technology from Air Products and Chemical Inc. and UOP Process International Inc., both US companies and Snamprogetti, a company of Italy's ENI group. MTBE is produced by the reaction of methanol with isobutylene, usually in the presence of an ion-exchange catalyst. The isobutylene is normally part of an unseparated C4 stream which is reacted with methanol.
Fields of Application Boost for
Unlead and low lead gasoline pools are the best markets for MTBE. MTBE utilization offers ecological advantages as it reduces the polluting elements in exhaust gases [Co and Hydrocarbons and especially PNA (polynuclear aromatics)] allows the lead content in gasoline to be reduced without affecting the gasoline. Lead phase down continued at an accelerated rate, reducing the demand for lead regular gasoline to 17 per cent of total demand in 1988 and 11 per cent in 1989. The demand for unleaded premium increased to 24 per cent of total demand in 1989. By 1992 it is expected that all lead gasoline will be removed from the automotive market. The consumption of octane is improving in US and Europe. With its high blending value for (Research Octane Number) RON and (Motor Octane Number) MON, MTBE when used as an additive, can improve gasoline substantially, regardless of type and concentration of the lead alkyls that may be present. MTBE doesn't reduce engine power or increase fuel consumption.
Blending of MTBE in
EPA Regulation allow the use of MTBE in unleaded gasoline upto a concentration corresponding to 2.0 percent wt oxygen (roughly 11% vol). Currently, MTBE is used exclusively as high-octane gasoline blending agent, its blending octane value is rated about 104-110 (RON+MON/2). In general, MTBE is most effective as an octane booster in gasoline blend replacing lead alkyls which react between varying amount of tetraethyle lead (TEL) and tetramethyl lead (TML). The composition of the resulting reaction product mixture, which includes five possible lead alkyls. The heating value of pure MTBE is 10 to 15 per cent less than that of typical gasoline.
PHOTO : FIGURE (1) Fig. 1 Correlation between the use of lead in petrol and blood lead levels
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|Title Annotation:||a gasoline blending agent; Oil and Gas|
|Date:||Jun 1, 1991|
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