Over the last few years more and more alternatives for petrol have been sought. As oil reserves run out, petrol prices rise and the climate continues to change, people are increasingly looking towards ethanol fuel as a potential solution to all of these problems.

Ethanol is more commonly known as the alcohol found in alcoholic drinks. It is a colourless and flammable liquid (at room temperature and pressure); it is its flammable nature that makes it useful as a fuel.

Production

The vast majority of ethanol that is used for drinking and in fuels is produced by the fermentation of sugars. This is where certain species of yeast metabolize the sugars anaerobically, that is to say in the absence of oxygen. If oxygen is allowed to be present then the end product will be vinegar. This produces ethanol and carbon dioxide – but the concentration of ethanol in water is very low and this then has to be dealt with at a later stage.



The two main sources for ethanol fuel are either sugar beet which can by fermented directly, or from cereal grains. In the later case the starch must first be broken down into sugars, this is accomplished (for fuels) by treating it with dilute sulphuric acid.

In the US most of the ethanol produce comes from corn, with 10 liters being produced from every thirty five litres of corn. In Brazil, the largest user of ethanol as a fuel, the liquid is obtained by the fermentation of sugar beat.

Currently research is ongoing on the use of alternative crops to corn. The main reason for this is due to the intense farming methods needed to produce it and the large amounts of fertilizers that need to be used.

The final process is to remove the water present in the mixture produced by fermentation. This can be done by fractional distillation and final by ‘drying’ it by chemical means (usually lime or salt). To obtain pure ethanol more complicated processes are invoked.

A fuel

The largest use of ethanol is actually in the motor industry, either as a replacement fuel or as a fuel additive. As a flammable liquid it works in the same way as petrol inside a car.

Most modern cars can happily run on blends containing 10% ethanol by volume without any need for modification. Some modern cars can run on blends containing up to 85% ethanol, giving the driver the option of what to fill up with.

Usage around the world is likely to increase as new legislation comes into affect requiring more biofuels to be used. The US Energy Policy Act of 2005 calls for 7.5 billions gallons to be used in America by 2012.

Controversy

A lot of people question the use of ethanol as a replacement for petrol. One of the biggest concerns comes over the amount of land needed to be farmed to produce the fuel. It is far too space intensive to serve as a total replacement for petrol; if all corn, wheat, rice and soya was used it would only cover around 4% of all of America’s energy needs. This leads directly onto the worry that an increased need for farmland will further put the already depleted rainforests at risk.

On top of this as more corn goes towards making ethanol fuel and more farmland is devoted to it then it will have a direct impact on food prices globally.

There is also ongoing debate as to whether ethanol’s energy balance as a fuel is positive or negative. That is to say does farming it take more energy than it gives off? If so then we are better off just using the original energy we used to grow it for other means.

As an end product ethanol makes a good fuel, although volume for volume it won’t get you as far as petrol (due to lower energy density). It burns far more cleanly than petrol and as a result is far better for the environment. But as a long term solution it seems doubtful and it remains important for society to continue to look for alternatives to the petrol engine.