Nitration of biodiesel of waste oil: Nitrated biodiesel as a cetane number enhancer

Biodiesel has been produced by transesterification of waste frying oil with methanol catalysed by sodium methoxide. The unsaturated fatty acid methyl esters of the biodiesel produced have been nitrated by two alternative nitration methods, showing an incorporation of nitrogen between 3.43 and 5.10 wt.%, in the chemical form of nitro, nitrate and acetoxy functional groups. A detailed gas chromatography–mass spectrometry analysis has been carried out on the nitrated biodiesel samples in order to identify the nitration products of this complex mixture. The nitrated biodiesel has been added to a base diesel fuel in a 1000 mg L−1 concentration resulting in an increase of the cetane number of the fuel by more than five points, from 54.7 to 60.5.