Soy biodiesel is high emitter of acrolein

Soy biodiesel emits the highest levels of acrolein, a toxic aldehyde, from a range of four fuels when used in trucks, say US researchers. Biodiesel was introduced to reduce the dependence on fossil fuels and it is generally produced by the transesterification of fatty acids in animal fats or plant oils. While it is cleaner than fossil fuel diesel, there is concern over the emission of nitrogen oxides and other pollutants like unsaturated aldehydes, some of which are toxic.

Robert Okamoto from the California Air Resources Board and Thomas Cahill from Arizona State University have compared the aldehyde emissions from four types of diesel when used to run two types of truck. Soybean biodiesel, animal biodiesel, renewable diesel and California ultralow sulphur diesel were tested in two heavy duty trucks (model years 2000 and 2008) and the aldehydes were analysed by GC/MS.

The emission rate of acrolein from soy biodiesel was the highest of the four fuels, although levels of all aldehydes were reduced in the more modern truck, due to the presence of a diesel particulate filter. The other fuels emitted roughly the same levels of acrolein. Emissions were lower when the trucks were in the cruise drive cycle compared with an urban cycle.