The ethanol fuel produced from corn is, in my opinion, not a viable option for an alternative fuel. As constant thinker mentioned, there is not enough supply for the demand. Currently, producing the ethanol to provide 1.3% of the total energy used by the transportation sector requires 3.3 million hectares and 14% of the country’s corn production. Furthermore, because corn is an important source of feed for livestock, critics of ethanol fuel claim that fuel ethanol production is raising the price of meat, milk, and eggs in the US.
However, the most damning argument against fuel ethanol is that it takes a great input of energy to produce ethanol. As chemists, we should alll know that producing the 99.5% pure ethanol needed for fuel ethanol (so that the water doesn't cause the ethanol to separate from the gasoline in a gasohol mixture) from the 8% ethanol solution produced by yeast requires multiple distillation steps, which requires large amounts of heat. The distillation and other steps are so energy intensive that experts estimate the input energy is somewhere between 80-130% of the energy contained in the ethanol produced. So, using pessimistic estimates, you actually lose energy by producing ethanol. Because the energy used in the production of ethanol comes from power plants which burn fossil fuels (mostly methane), ethanol produced from corn does not reduce net greenhouse gas emissions by much (in fact, similar reductions in greenhouse gas emissions could be achieved by switching to gas-electric hybrid technology). Balanced against these moderate reductions of greenhouse gas emissions, however, is air and water pollution produced by the biorefineries and distilleries producing ethanol.
Ethanol produced from cellulose solves some of these problems because cellulosic ethanol uses agricultural wastes as feedstock. Indeed, BP estimates that cellulosic ethanol could meet 30% of fuel demand without affecting food production. However, cellulosic ethanol does not solve the fundamental problems of the energy requirements, nor does it solve the problems of the pollution from biorefineries. With cellulosic ethanol, although the yield of sugars is theoretically higher since plants contain much more cellulose than starch, problems arise with breaking down the ethanol into simple sugars (glucose) for the yeast ferment (since yeast cannot ferment cellulose). The costly breakdown steps partly counter any increases in energy efficiency gained from the higher yield of ethanol.
There are some solutions to these problems, such as genetically engineering yeast to withstand higher concentrations of ethanol or engineering enzymes to allow the more efficient hydrolysis of cellulose, but, like hydrogen fuel cell technologies, these technologies require more decades before they can reach the marketplace.