Biofuels are quite a hot topic at the moment. There is an ongoing debate about subsidies for corn ethanol in the United States, and a more general discussion about the overall merits and shortfalls of the biofuel approach. One compound that features prominently in the debate is ethanol: the two-carbon molecule familiar to martini drinkers everywhere.
Unfortunately, ethanol has a number of properties that make it unappealing as a fuel:
- While oil and water are famously difficult to mix, water mixes easily with ethanol. This makes it more difficult and expensive to store and transport. Pipelines are especially afflicted by this issue. Ethanol that has been blended with gasoline can seperate when it comes into contact with water.
- Moving through pipelines and sloshing around in storage tanks, ethanol is also prone to collect various sorts of crud and impurities. These must then be filtered out at a later stage.
- Ethanol is corrosive to both metals and rubber compounds. As such, it can increase the level of maintenance required in all of the machinery that comes into contact with it, as well as diminishing the lifetime of that equipment.
- Ethanol has a lower energy density than conventional liquid fossil fuels. That means less distance travelled for any particular volume, as well as a larger ratio of fuel weight to total weight for vehicles with a particular range.
- The volatility of ethanol is also problematic. The fact that it turns to gas easily (and has high vapour pressure) can be problematic in hot environments.
- Finally, ethanol is made in ways that have both direct and indirect negative consequences. The direct production of ethanol from corn raises food prices (affecting the poor, in particular). Corn agriculture also uses fertilizers (causing eutrophication of rivers) and pesticides. Large increases in land use for bioethanol production may also lead to deforestation, as crops that can be grown in areas presently forested (like soya in the Amazon) get displaced from existing agricultural lands.
None of this is to say that ethanol is without advantages – nor that it will have no role in the future energy mix. I am simply laying out some of the problems that need to be overcome, or that will otherwise limit the adoption of bioethanol as fuel.