Bioethanol
Bioethanol (ethyl ethanol C2H5OH) is produced by the fermentation of sugary plants; it is a biodegradable substance so if it happened to spill it would not cause negative effects on the environment; it is the main replacement for petroleum as fuel. It is a good alternative fuel because it is carbon neutral: the CO2 released by burning it equal to the CO2 taken up by the plant. It is also considered a renewable source of energy as photosynthesis is the first step of the production. Compared to ordinary gasoline, it burns more completely and so releases less toxic compounds like CO. It is possible to blend bioethanol with petroleum, giving a mix that releases less greenhouse gases than ordinary petroleum. Many types of plants are able to produce bioethanol, they only need to contain sugar or starch. However, bioethanol is very hygroscopic meaning that it can attract and hold on to water molecules fairly well giving it corrosive properties. To produce bioethanol a lot of energy is required and a lot of greenhouse gases are produced in the process. The octane number (a measure of how much pressure a fuel can take before igniting) of bioethanol is more or less 105 which is substantially higher than that of regular fuel meaning the engines of current cars will not be very efficient. The energy content of bioethanol is much lower than regular petroleum which results in less energy produced per unit. Lastly, for the crops to be grown properly a lot of water is required