Characterization of Various Fast-Pyrolysis Bio-Oils by NMR Spectroscopy

NMR spectroscopy, including H-1, C-13, and DEPT spectra, was used to characterize fast-pyrolysis oils from numerous energy crops and other agricultural feedstocks. The bio-oils studied were produced from switchgrass, alfalfa stems, corn stover, guayule (whole plant and latex-extracted bagasse), and chicken litter. The H-1 and C-13 NMR spectra were integrated over spectral regions to quantify classes of carbon and hydrogen atoms in each bio-oil sample. DEPT spectra were used to quantify by protonation, and the number of the carbon atoms in each of those classes was used to give further information on the types of molecules that are found in the bio-oil. The NMR spectra of the bio-oils varied greatly. The percentage of carbons and protons in the upfield regions of the NMR spectra tracked with the energy content of the bio-oil as well as the feedstock type, but there was no such consistent trend for the aromatic content. Degrees of branching in the aliphatic portions of the bio-oils were inferred from percentages of CH1, CH2, and CH3 groups. Aromatic portions were found to be extremely complex, with substituted aromatic carbons outnumbering unsubstituted aromatic carbons > 2:1 in most cases. Fully substituted carbons represented 27-37% of all the carbons in the sample.