Separation of sugars and phenolics from the heavy fraction of bio-oil using polymeric resin adsorbents

This work describes the equilibrium and kinetic adsorption of levoglucosan and a mixture of phenolic species from an aqueous solution on two polymeric resin adsorbents, SP207 and XAD4. The separation of sugars from phenolic species is of interest as these species comprise a product stream from a unique fractionating bio-oil recovery system. Levoglucosan is the major sugar present in this product stream, with mannose, xylose, galactose, and cellobiosan present in minor extents. The phenolic species are a complex mixture of mono- and di-substituted phenols; however, we treat them as a single group of similar chemical species that must be removed before the aqueous sugar solution can be used as fermentation substrate. Adsorption isotherms and mass transfer coefficients were determined at 22 °C. Levoglucosan isotherms were fit with linear and Langmuir models. Phenolic species isotherms were fit with both Langmuir and Freundlich models although they more clearly exhibited Langmuir adsorption behavior. Adsorption equilibria show that both polymeric resins have an order of magnitude greater mass adsorption capacity for phenolic species compared to levoglucosan when the mixture is used as the applied solution. However, the kinetics of adsorption are approximately an order of magnitude slower for phenolic species versus levoglucosan. The equilibrium-dispersive model for column chromatography was applied using the determined adsorption equilibria and kinetic parameters and compared to column elution experiments. The model provided a good fit to the column data; however, the fit was improved by replacing the single component isotherms with competitive Langmuir isotherm expressions and modestly lowering the phenolics mass transfer coefficient.