Submitted to: Energy and Fuels
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/11/2011
Publication Date: 10/12/2011
Citation: Strahan, G.D., Mullen, C.A., Boateng, A.A. 2011. Characterizing biomass fast pyrolysis oils by 13C-NMR and chemometric analysis. Energy and Fuels. 25:5452-5461.
Interpretive Summary: To meet the renewable fuels standards set by the US government, 21 billion gallons of advanced bio-fuels will need to be produced by 2022. One promising process is to use fast pyrolysis to convert biomass to produce bio-oil which can be refined to “green” gasoline and diesel fuels that are indistinguishable from those produced from petroleum. It can also be used as produced as a boiler fuel or used as a feedstock for production of chemicals. For any of these uses knowledge on the chemical compounds that make up pyrolysis oil is needed. The composition of the pyrolysis oil can differ depending on the identity of the biomass from which it is produced. We used a technique called nuclear magnetic resonance spectroscopy(NMR) which can provide structural information on the types of all compounds in the oil. Using NMR approach, we were able to classify pyrolysis oils similar as based on energy content. This information will be important to potential end users of biomass pyrolysis oils including boiler operators, refiners and chemical producers.
Technical Abstract: Several biomass fast pyrolysis oils were characterized by 13C and DEPT NMR analysis to determine chemical functional group compositions as related to their energy content. Pyrolysis oils were produced from a variety of feedstocks including energy crops, woods, animal wastes and oil seed presscakes, and were also compared with fossil fuels (gasoline and diesel). The 13C and DEPT NMR spectra of the bio-fuels and two fossil fuel samples were measured, and each spectrum was divided into distinct regions according to the chemical shift ranges appropriate for various functional groups. The spectral intensities of each region were then quantified and the carbon proton substitution numbers were determined. This approach provided helpful information on the chemical compositions of the oils, but was found to oversimplify the information contained in the 13C NMR spectra, resulting in a substantial loss of important details. Hence, a chemometric method of analysis based on principle component analysis (PCA) was used to extract more of the useful information from the 13C NMR spectra. The intensities of the 13C NMR spectra from 15 pyrolysis oil and two fossil fuel samples were binned in 2 ppm increments and subjected to unsupervised PCA. Comparison of the PCA scores plots with their respective loadings plots enabled a determination of the chemical shifts, and hence the chemical functional groups that were most important in discriminating amongst the clusters. The clustering of the biomass samples based on PCA results were shown to track with their biological origin and their energy contents. Therefore 13C NMR PCA analysis was shown to be a powerful and facile technique for classifying biomass fast pyrolysis oils.