Determining the blend level of mixtures of biodiesel with conventional diesel fuel by fiber-optic near-infrared spectroscopy and 1H nuclear magnetic resonance spectroscopy
- Cite this article as:
- Knothe, G. J Amer Oil Chem Soc (2001) 78: 1025. doi:10.1007/s11746-001-0382-0
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Biodiesel, defined as the alkyl esters (usually methyl esters) of vegetable oils, is miscible with conventional diesel fuel at all blend levels. Until the present time, no rapid and reliable analytical method has existed for determining the blend level of biodiesel in conventional diesel fuel. In the present work, near-infrared (NIR) and nuclear magnetic resonance (NMR) spectroscopies were used to determine the blend level of biodiesel in conventional diesel fuel. Several regions in the NIR region (around 6005 cm−1 and 4800–4600 cm−1) are suitable for this purpose. The method is rapid and easy to use, and does not require any hardware changes when using the same instrument for monitoring the biodiesel-producing transesterification reaction and determining biodiesel fuel quality. In 1H NMR spectroscopy, the integration values of the peaks of the methyl ester moiety and the aliphatic hydrocarbon protons in biodiesel and conventional diesel fuel were used for determining blend levels. The results of NIR and NMR blend level determinations are in good agreement.