Process NMR for Transesterification Monitoring and Certification of Biodiesel

1H NMR has been used extensively to analyze biodiesel the vegetable oil feeds, reaction intermediates, and final products of the biodiesel transesterification process.

See Oliviera et al, Talanta 69 (2006) 1278-1284 and Gnothe, J. Am. Oil Chem. Soc 78, 1025-1028 (2001)

The final biodiesel product is a B5 (5% Biodiesel) or B20 (20% Biodiesel) blend of biodiesel in refinery produced diesel fuel. Researchers have performed method developments to analyze the biodiesel content in diesel fuels by NIR using 1H NMR as the primary method to quantify the biodiesel content. (See Jin et al, Fuel 86(7-8), 1201-1207 (2007) and Knothe J. Am. Oil Chem. Soc. 77 489-493 (2001). Process NMR at 60 MHz can be used to quantify the biodiesel directly. Below is an example slide of a biodiesel 1H NMR spectrum compared to two different diesel fuel spectra.

The chemistry that is directly observed in the NMR spectrum as well as the distinct chemical regions that are present in the diesel and biodiesel make this analysis relatively straightforward. Chemometrics can be used or quantitation can be obtained directly from a simple spectral calibration.

Biodiesel Production Monitoring

NMR can be used to follow the reaction of biodiesel directly, the following slides show the steps in the transesterification process.

Glycerol content in the biodiesel or unconverted vegetable oil content can be determined easily directly from the spectrum.

Expansion of Incomplete Reaction Series

Work is currently underway to develop NMR calibration models that can predict the various quality parameters specified in ASTM D6751 for biodiesel.

These calibrations, based on either 1H or 13C NMR, when validated would allow rapid testing of biodiesel production batches and would make complete analysis of small production batches economically feasible (there is no point making 300 gallons of biodiesel if you have to perform $1300 of testing on the batch).