Bio-oil Analytical Methodology for Characterization
Thermochemical processing, through fast pyrolysis, converts biomass into char, bio-oil, and gaseous products. While the bio oil product from this conversion is primarily researched for use in combustion applications it is a potential source for both transportation fuels and chemical extraction.
Efforts to characterize and fractionate bio-oil into its various components have been conducted at CSET. Bio-oil production research performed by utilizing CSET’s fast pyrolyzer system, which is equipped with a fractionating bio-oil collection system, has resulted in the separation of various fractions of bio-oil based on bio-oil components’ condensation temperatures. Physical characterization of the bio-oil fractions, as shown in Table 1, shows that the bio-oil fractions have different properties.
- Table 1. Wet chemistry test comparisons of fractions collected from cornstover fast pyrolysis.
The goal of this project is to chemically characterize the individual fractions. These fractions have been analyzed using gas chromatography-mass spectrometry (GC/MS), percent carbon, hydrogen, nitrogen, sulfur, and oxygen via CHNSO analysis, and other wet chemistry techniques for specific chemical measurements.
An important aspect of this research is to determine the parameters which influence the chemical composition of the fractions in order to improve the stability of the bio-oil product. Bio-oil instability is directly related to its high water content, various degradation reactions, and phase separation. Desirable improvements include minimizing the water content of the bio-oil. The high water content is responsible for high percentages of oxygen and lower heating values in comparison to petroleum fuels.
Current GC/MS methodologies utilized by researchers in the thermochemical processing field are being evaluated. Published literature reports hundreds of molecular species are obtainable from fast pyrolysis of biomass and a multitude of these compounds are listed as identifiable with GC/MS.
- Chromatogram of the electro-static precipitator (ESP) fraction of corn stover fast pyrolysis.
Recent GC/MS studies conducted at ISU, using acetone as solvent to determine ethylene glycol, found peaks in the resulting spectra corresponding to adducts formed between the solvent and analyte leading to unwanted peaks in the analysis. These aberrations appear to be related to injector temperature. Literature describing typical GC/MS methodology indicates that the analysis is performed at 250ºC or higher which may result in solvent interactions with the solute.
Current methodology studies are important for the correct characterization of bio-oil chemical composition. This knowledge, in conjunction with unique fractionation techniques developed at ISU, provides the potential for higher value application opportunities for biomass fast pyrolysis products.
Research done by:
Marjorie Rover
Iowa State University CSET, 0411 Marston Hall, Ames, Iowa 50011-2153
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