Unleaded petrol

To meet Emission Standards, new 1991 models are designed to run on unleaded petrol, and therefore, new engines working at a higher compression ratio will be from 8 to 10% more efficient than older ones. 

The main concern regarding tetraalkyl lead has been about human health hazards, a concern that has resulted in the progressive replacement of leaded petrol by unleaded petrol in most countries (Environmental Health Criteria 85). There has been particular concern about possible brain damage to children in polluted urban areas. Little work has been done on the effects of organolead compounds on wildlife or ecosystems, so the following account will be brief. 

Chemical behaviour is generally satisfactory with water, detergents, acids, bases, alcohols and amines but is limited to unsatisfactory versus aliphatic and aromatic hydrocarbons, chlorinated solvents, oils, fuels, and unleaded petrol. 

Organic heavy metal compounds are produced by the chemical industry (e.g. tetraethyl lead was produced and added to petrol as an anti knocking agent for more than 30 years in the UK, until unleaded petrol became available in the mid-1980s). They can also be synthesised in some living organisms (e.g. bacteria). 

Kidney tumors caused by several different compounds, including 1,4-dichlorobenzene, isophorone, and unleaded petrol, have been found to be both sex dependent and species dependent. Thus, only male rats suffer from oc2-p-globulin nephropathy and renal tubular adenocarcinoma as a result of the accumulation of a compound-protein complex in the epithelial cells of renal proximal tubules (see chap. 6). The synthesis of the protein involved, a2-[i-globulin, is under androgenic control in the male rat. 

The catalytic converter acts as a device to speed up reactions which involve the pollutant gases, converting them to less harmful products, such as nitrogen and carbon dioxide. It should be noted that catalytic converters can only be used with unleaded petrol as the lead poisons the catalyst, preventing it from catalysing the reactions. For a further discussion of catalytic converters see Chapter 7, p. 110. 

Drucker s examples are health, dining and food, care for environment, class structure and feminism. There are many chemical examples here particularly under care for the environment e.g. CFCs replacements, unleaded petrol, City diesel, solar electricity and fuel cells. 

Acute exposure to unleaded gasoline and a variety of light hydrocarbons present in gasoline produces a nephropathy in male rats characterized by (1) an excessive accumulation of protein (hyaline droplets) in epithelial cells of proximal tubule, (2) accumulation of casts at the corticomedullary junction, and (3) evidence of mild tubular regeneration. This nephropathy only occurs in male rats female rats and mice do not show any renal pathology. A number of chemicals present in unleaded petrol when tested alone have been shown to produce nephropathy and, in particular 2,2,4-trimethylpentane and decalin have been used as model compounds. Certain other industrial chemicals (1,4-dichlorobenzene and isophorone), natural products (o-limonene), and pharmaceuticals (levamisole) also produce this male-rat-specific nephropathy. Chronic exposure of male rats to unleaded petrol, 1,4-dichlorobenzene, isophorone, or o-limonene ultimately leads to the induction of a low incidence of renal adenomas and carcinomas. 

Vyskocil A, Tusl M, Obrsal J, et al. 1988. A subchronic inhalation study with unleaded petrol in rats. J Appl Toxicol 8 239-242. 

Benzene (see Fig. 2.4) is another pollutant component of automotive fuels. It occurs naturally in crude oil and is a useful component because it can prevent pre-ignition in unleaded petrol (the production process is usually adjusted so that the benzene concentration is about 5%). There is evidence that in some locations, where there has been a switch to fuels with high concentrations of aromatic hydrocarbons, there has been a sharp increase in photochemical smog. This is due to the high reactivity of these hydrocarbons in the urban atmosphere. This problem should draw our attention to the way in which the solution of one obvious environmental problem (lead from petrol) may introduce a second rather more subtle problem (i.e. increased photochemical smog from reactive aromatic compounds). 

Larssen S, ROYSETOand VadsetM (1997) Origin and patterns of distribution of trace elements in street dust unleaded petrol and urban lead. Atmos Environ 31 2733-2740. 

ZSM-5 based catalysts are widely used commercially, either in their unpromoted acidic form, or as metal promoted catalysts. The aromatisation of light paraffins is an example of a refining process where ZSM-5 catalysts are often encountered. With the global shift towards higher octane unleaded petrol, aromatisation is one of the processes that can be used to produce high octane blending stock. In a Fischer-Tropsch environment, where the unrefined Fischer-Tropsch product contains very little aromatics, this is an especially attractive option. However, Fischer-Tropsch derived material does not only contain paraffins, but also contains olefins and oxygenates. 

Many trace metals are present in leaded and unleaded petrol, diesel oil, anti-wear substances added to lubricants, brake pads and tyres, and are emitted by vehicle exhaust pipes (Caselles et al. 2002). Soluble metals have been implieated in particulate matter-associated respiratory or eardiopulmonary disease in healthy and compromised individuals (Frampton et al. 1999 Chapman et al. 1997). Since man has about 70% body mass as water and given the solubility of WS trace metals in water, WS metals possess an appreciative damage to our health. 

Table 1 gives the typical chemical compositions of some of the main fuels by individual molecules, by families of molecules or by analysis of the elements. These include natural gases (NG), liquefied petroleum gases (LPG), unleaded petrols, turbojet fuels, diesel fuels and diesel fuel oils, heavy fuels, low-energy gases. 

Petrol is the main fuel for the spark-ignition engine. Two large categories of petrol can be distinguished leaded and unleaded petrols, and in addition substitutes for common petrol. 

In these unleaded petrols, the anti-knocking leaded additives have been replaced by oxygenated compounds, mainly ethers, MTBE and ETBE (Table Ic). 

Alcohols can be used instead of ethers to replace the leaded additives. Thus the gasohol is an unleaded petrol containing 10 % ethanol. The American consumption of gasohol... 

With the notable exception of sulphuric acid, the most important chemical of all (and to a much smaller degree phosphoric acid and urea), which suffered a significant decrease, all the other chemicals achieved an increase in 1993 compared with 1988. The most spectacular increase goes to methyl r-butyl ether (MTBE) which was way down the list in 1988 but is now 9th and climbing. Demand for this is increasing enormously because it is used instead of tetraethyl lead to increase the octane rating of unleaded petrol. 

Figure 1 The use of a selective stationary phase column for the high-speed analysis of ethanol in unleaded petrol.

The Automobile Association in the UK [50] has reported a study on the effect of unleaded petrol on the use of plastics in cars, particularly car engines. It was found that the alcohols, solvents and high aromatic fractions used as replacements for lead additives in petrol will have a detrimental effect upon plastic components, which will come into contact with the fuel, such as fuel lines and PU floats. 

Kelley et al. [125] measured the carbon isotope values of BTEX (benzene, toluene, ethylbenzene, and xylenes) at a petrol-contaminated site in southern California. The BTEX data were determined using a purge and trap connected to a GC-MS and also using GC-IRMS. The results indicated that there were two sources of contamination at the site, and also that the leaded and unleaded petrols at one of the sites had different carbon isotope values. 

Elimination of hazard Total elimination is not always possible, but sometimes possible, for example, if unleaded petrol is used, attendants are not in the hazard of lead contamination. 

Data reproduced with permission from ref. 52. 90% Unleaded petrol + 10% ethanol. 

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