The use of ethanol as an alternative fuel and the success of current use

Why must petroleum be replaced?

There is a limited supply of petroleum in the world. Local reserves of oil are likely to run out within the next 20-30 years(Conquering Chemistry, Smith, 2005).Transportation as well as a few more minor contribution are quickly consuming what petroleum still exists. A primary example of this is the the usage in the united states where transportation is responsible for three quarters of petroleum consumption. A major disadvantage of the global reliance on petroleum are trade deficits, supply disruption and price changes.
Why ethanol?
Ethanol is used extensively as a solvent in the manufacture of varnishes and perfumes; as a preservative for biological specimens; in the preparation of essences and flavorings; in many medicines and drugs; as a disinfectant and in tinctures; and as a fuel and gasoline additive The following data are from the Renewable Fuels Association's 2013 Ethanol Industry Outlook (PDF) and show why ethanol is a suitable alternative to petroleum:

Advantages

• Ethanol can operate as a fuel

Ethanol helps in reducing the reliance on imported crude oil- a major contributor to greenhouse gas emissions. Ethanol is used as a solvent and as a starting point for making many other chemicals such as acetic acid and ethyl acetate. It is a renewable resource which is important for the production of transportation fuels. It is commonly known for low level blends such as E10 which is composed of 10% ethanol and 90% gasoline, and the high level blends such as E85 which is a gasoline-ethanol blend containing 51% to 83% ethanol.

Ethanol can be blended with gasoline at levels ranging from 5% to 25% which means it reduces the use of petroleum and hence tail pipe emissions.  Pure ethanol is considered to be anything between 85% and 100% ethanol. This would further reduce the reliance of petroleum, however achieving 100% purity is very difficult and even the more achievable amount of 85% purity can only be used on specially designed engines.

The technology to produce Ethanol is already known and was showed in the first section. With the use of this fuel the reliance on oil is less which can be seen by the following graph.

• Renewable properties

Ethanol is made from carbon dioxide water and sunlight via glucose. The fact that the sugar or starch used to make ethanol is from plants means that it is a renewable and sustainable energy source. When the Ethanol is burnt it returns to carbon dioxide, and water so it has the potential to convert back into ethanol.Below is a diagram of "the ethanol cycle"(Page 34, Figure 1.10, conquering chemistry HSC Course, 4th Edition, Roland Smith):

When ethanol from plants is burnt, the carbon dioxide released is equivalent to the amount absorbed by the plant during photosynthesis which makes the sugar. As a result the use of plant-derived ethanol  does not contribute to the "Greenhouse Effect".

• Production of ethanol will create more job opportunities. The impact Ethanol will have economically with the United States as an example is depicted in the graph below. 

• Ethanol is an easily transportable liquid which readily burns:

Disadvantages

• Up to 75% of agricultural  would need to be sacrificed if ethanol were to replace petroleum in order to grow the crops required. 
• The disposal of the large amount of waste produced by fermentation liquors required for ethanol production would present major environmental problems.
• Massive amounts of Energy are required for the distillation process for the creation of ethanol
• Currently, fossil fuels are used for the heating and transport, and so the process is not as renewable not "Greenhouse-friendly" as first thought.
• Entirely new engines are needed to run on pure ethanol. This is not feasible for manufacturers and car  owners.
• Some car manufacturers opposed concentrations of more than 10% ethanol as it is believed that they could damage car engines.
• A gallon of ethanol contains less energy than a gallon of gasoline which results in lower fuel economy. The more ethanol in the blend the less energy needed.
• It is a high octane fuel, it offers increased vehicle power and performance.
• The release of carbon dioxide contributes to global warming. When the reaction is incomplete either carbon or the toxic carbon monoxide is formed as depicted in the equations below:

Final assessment of the use of ethanol

Ethanol is more expensive than petrol. However, in Australia this is subsided by the government and excise concessions to encourage the production of ethanol from crops have been set up. Car manufacturers have objected to more than 10% concentrations of ethanol. Ethanol is a renewable resource and environmentally friendly, however, the areas of agricultural area which would be over taken and the issues with waste disposal make larger scale use of the product appear unfeasible. 95% of gasoline sold already has some level of ethanol in it. This makes it more environmentally friendly and although it releases less energy,  it offers increased vehicle power and performance as it is a high octane fuel.