Alkylate Petrol. Environmental Aspects of Volatile Hydrocarbon Emissions
Abstract: All hydrocarbons emitted from production and use of petrol are hazardous to human health and the environment, but to a different extent for individual compounds. This thesis compares and characterizes C2-C8 hydrocarbons related to alkylate petrol and conventional petrol. Production of alkylate depends on cat-cracking, and studies linked to fluid catalytic cracking (FCC) are included.Quantitative proportions and retention data of more than sixty C5-C7 alkenes in conventional petrol and FCC petrol naphtha were assessed by gas chromatography and gas chromatography-mass spectrometry. The naphtha contained about 40% alkenes. Speciated hydrocarbon emissions from the FCC unit consisted of about 15-20% alkenes, 5% or less arenes and 80% alkanes. Specific hydrocarbons in refuelling vapour and in two-stroke engine exhaust were determined for alkylate and conventional petrol using adsorbent sampling and gas chromatography on an alumina column. About 90% of the amount of hydrocarbons in exhaust from the two-stroke engine was unburnt petrol. Major advantages of the alkylate petrol were found to be low proportions of benzene, alkylbenzenes and alkenes in the fuel. The compositions of fuel alkanes and combustion-formed alkenes differed markedly for the two fuels. Today almost all alkylate produced worldwide is mixed into petrol for automobiles. A separate study concludes that it would be better to use alkylate as fuel for small engines. The main reason is that hydrocarbon emissions for two-stroke engines are more than one order of magnitude larger per litre petrol consumed. Both in Europe and in the US, the present production of alkylate is large enough to replace conventional petrol in most small engines, without seriously affecting the pool of petrol for automobiles.
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