(386a) Separation of Anhydrosugars and Phenolic Species in a Fast Pyrolysis Aqueous Product Stream Using Resin Adsorbents and Simulated Moving Bed Technology
Anhydrosugars are a valuable product present in fast pyrolysis bio-oil with levoglucosan being the most abundant sugar. Appropriate acid pretreatment methods of lignocellulosic biomass before pyrolysis can yield 15 and 23 wt% levoglucosan on a biomass basis for switchgrass and red oak, respectively. A novel fractionating collection system developed at Iowa State University condenses and collects pyrolysis products according to their respective vapor pressures. The anhydrosugars condense in the first fraction alongside phenolic monomers, dimers and oligomers. Water extraction of the first fraction removes approximately 80 wt% of the anhydrosugars and a myriad of phenolic monomers up to their solubility limits in water, for example, 0.8 and 2.7 wt% for 4-vinylphenol and o-cresol, respectively, at 25 °C. The total average phenolics present in the water extraction is approximately 9 wt% and must be reduced to levels near 0.01 wt% to be below toxicity limits for fermentation. This work examines the use of hydrophobic polymeric resin adsorbents for the selective removal of phenolic species from the aqueous phase. Adsorption isotherms and kinetic adsorption parameters were determined for the anhydrosugars and phenolic species adsorption on commercially available hydrophobic polymeric resin adsorbents, SP207 and XAD-4. Isotherm data demonstrates an order of magnitude higher affinity of the resins for phenolic species over anhydrosugars. Although the anhydrosugars adsorb to a similar capacity on the resins as the phenolic species when adsorbing in the absence of phenolics, their presence competitively reduces anhydrosugar adsorption an order of magnitude. Chromatographic column experiments were performed and showed good agreement with breakthrough curves calculated using the adsorption parameters. A simulated moving bed chromatographic process was designed and modeled for the continuous production of a very high purity anhydrosugar stream and separate phenolics stream for a 50 ton per day pyrolysis bio-refinery.