Bio-oil fractionation using supercritical fluids

Bio-oils produced by biomass torrefaction and pyrolysis are complex mixtures of organic compounds and water. Their separation into fractions that include compounds of similar properties may be advantageous to maximize carbon efficiency and minimize hydrogen consumption in subsequent processing to produce liquid fuels. Supercritical fluid (SCF) fractionation may offer the same advantages as traditional liquid solvent extraction but with reduced energy demands and reduced predisposition to carry over residual solids into the extracted phase. This contribution describes the fractionation of bio-oil simulant mixtures using SCF carbon dioxide, near-critical propane, and SCF ethane. Bio-oil simulant mixtures representing three fractions obtained by biomass torrefaction and pyrolysis were contacted with the different fluids. The effects of temperature, pressure, and solvent:sample ratio were studied for the extraction using SCF carbon dioxide. The experiments using propane and ethane were performed at 45 °C, twice their critical pressure, and a 10:1 solvent:sample ratio. In general, ethane extracted the least and carbon dioxide extracted the highest quantities. Propane was more selective to separate some of the organics from the different mixtures.