Anhydrous Ethanol
Anhydrous Ethanol
Anhydrous ethanol can be used as an additive in petrol, or as a fuel in its own right. Despite this, as an automotive fuel it is usually composed of 85% ethanol with 15% petrol (E85P) and this is the fuel that will be examined in this chapter. The reason for this is that the addition of 15% petrol improves the ignitability of alcohol, especially at low temperature. Other additives have also been trialled as ignition improvers. Ethanol is probably the most widely used alternative automotive fuel in the world, mainly due to Brazils decision to produce fuel alcohol from sugar cane.
The upstream emissions associated with anhydrous ethanol are essentially the same as those associated with hydrated ethanol, with a requirement for extra energy input arising from the extra process step to transform the hydrated ethanol to anhydrous ethanol. 30% more energy is needed to convert hydrated ethanol to anhydrous ethanol.
There is considerable international experience on the use of ethanol in Brazil where sugar-derived ethanol is used as an automotive fuel. The ethanol used in Brazil is called Alcohol and consists of 93% ethanol by volume. The techniques for the production and use of methanol and ethanol as a vehicle fuel are known. Obstacles that hinder the use of alcohols as a vehicular fuel are the relatively high costs of alcohol and the investments necessary to introduce an extra fuel.
Ethanol produces a marked decline in the emissions of air toxics, except for the aldehydes. When weighting factors are applied, the weighted air toxics emissions from ethanol are below those of petrol.
Ethanol is not persistent in the environment. Virtually any environment supporting bacterial populations is believed to be capable of biodegrading ethanol. Atmospheric degradation is also expected to be rapid. Provided that the source of ethanol is not fossil fuels then it satisfies ESD principles. The particulate emissions are lowered as are the emissions of ozone pre-cursors. The concentrations of emitted air toxics are lower from ethanol than from petrol.
Ethanol from sugar or wheat is liable to be a niche fuel and thus there are no sustainability issues associated with it. Large-scale usage of ethanol will require ligno-cellulosic production to be economical. Then it would be possible to establish biomass plantations over the next 50 years that meet the great part of a country’s oil requirements, and specifically to supply most transportation fuels. In addition to the reduction in greenhouse gas emissions, the large-scale planting of tree and shrub crops as ethanol feedstock would help to control dryland salinity and associated problems.
Advantages
As a renewable fuel it produces less fossil CO2 than conventional fuels
Tailpipe emissions of NOx and PM appear to be lower on average.
Air toxic levels (except for aldehydes) are lower than those of conventional fuels.
Disadvantages
Cold starting in cool climates is difficult unless ethanol is blended with petrol as a starting aid, or unless some other starting aid is used.
Anhydrous Ethanol