Bioethers

Ethers are a class of carbon compounds that contain an ether group, which looks as follows.

ether

Either carbon in the basic ether above may be attached to other carbons as well. So, this image represents the most basic ether. All that is needed to make an ether is an oxygen atom with a hydrocarbon chain on either side.

Uses

Ethers are currently used as substitutes for lead to improve engine performance. They also decrease oxygen wear and toxic emissions, particularly ozone. The most commonly used fuel additive ethers are methyl-tertiary-butyl-ether (MBTE) and ethyl-tertiary-butyl-ether (ETBE). You are likely to see these abbreviations on petrol pumps.

Bioether

Bioether is made from either wheat or sugar beet. It can also be produced from the waste glycerol that results from the production of biodiesel. Bioether is likely to replace petro-ether as an additive to current fossil fuels. In the future, it is unlikely to be a fuel in and of itself because it has a low energy density. In fact, its energy density is about half that of standard diesel, which means you would need twice the volume of ether to go the same distance. Mostly likely, it will become an additive to other biofuels to reduce emissions.

 

Dimethyl Ether

Diesel

Energy Density (MJ/kg)

28.8

42.7

Cetane Number

55-60

40-55

Despite its drawbacks, there is some interest in using ether, particularly dimethyl ether, as a replacement for diesel fuel. This is made possible by the fact that ether works well in compression ignition engines. The interest stems from the reduced particulate emissions and reduced pollution of ether. In urban environments, where refueling frequently is possible and pollution levels run high, the tradeoff of reduced emissions for more frequent refueling is an attractive one. The only major problem to ether in these settings is that it must be compressed to be a liquid. At standard temperatures and pressures, ether is a gas. To make it transportable, it must be compressed. Of course, compression has benefits as well. If the gas can be compressed enough, then more can be carried and refueling intervals will be longer. China is currently the leader in research regarding replacing diesel fuel with ether.