Biodiesel Analysis by NMR
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 Gnoethe, 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.
- Samples were run as received. Sample bottles were shaken and pipetted into a 5 mm id NMR tubes.
- NMR sample tubes were placed into a 60 MHz process NMR system and spectra collected.
- Spectra resolve lignin/cellulosic functionality of the black liquor from the water.
- Spectra show functionality changes as a function of concentration in the samples.
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 un-esterified vegetable oil can be determined easily 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).
For more information on this topic please contact:
Manager, Process and Analytical NMR Services
Process NMR Associates LLC,
87A Sand Pit Rd
Danbury, CT 06810, USA
Tel: (203) 744-5905