Fuel Oxygenates

Abstract

Anti-knock fuel additives based on metals (mostly tetra-ethyl lead) for increase the octane number of gasoline have disadvantages (in addition to toxicity of lead). Nowadays organic compounds (oxygenates and aromatic solvents) are used for increase the octane number of gasoline and its better burning. Their advantage is that they are fully burned and ash is not formed. The disadvantage of these organic compounds is that large quantities (to 15 % vol. oxygenates and 35 % vol. aromatic solvents) are needed for increase the octane number of gasoline while very small amounts (~ 100 ppm) are needed for the additives based on metals. Therefore these organic compounds are not additives and are the components of gasoline. Fuel oxygenates are organic substances (oxygenated hydrocarbons) containing at least one oxygen atom in the molecule. As oxygenates contain oxygen atoms in their molecules less oxygen from the air is needed for the burning of gasoline. Oxygenates are alcohols and ethers soluble in gasoline. Their properties, benefits and disadvantages are described. Oxygenates are polar substances and solubility of water is significantly higher in oxygenates than in petroleum products (nonpolar hydrocarbons). The danger of water absorption and dissolution in blends gasoline/oxygenates and further separation of oxygenates from gasoline is analysed.