(657b) Separation of Anhydrosugars and Phenolic Species in a Fast Pyrolysis Aqueous Product Stream Using Resin Adsorbents and Simulated Moving Bed Technology

Fast pyrolysis is a promising technology for the thermo-chemical conversion of lignocellulosic biomass into liquid fuels and chemicals. Bio-oil is the liquid product of fast pyrolysis and is a complex mixture of water, anhydrosugars, organic oxygenates including carboxylic acids, alcohols, aldehydes, esters, ethers, furans, ketones, and phenolic monomers, dimers, and oligomers with a variety of functional groups. The chemical complexity of bio-oil necessitates several separation and upgrading strategies be employed before it can be used as a fuel or specific groups of chemicals can be isolated for other applications.

Fractional condensation of the vapors and aerosol products exiting the pyrolyzer makes use of successive condenser stages at progressively lower temperatures and is a practical first step at separating the bio-oil components. A distinction is made between heavy components that condense in the early stages above 120 °C and the remaining light components that condense in the latter, colder stages. The heavy fraction, or “heavy ends”, contains a few percent water and consists of low to high molecular weight phenolic species and anhydrosugars. A water extraction is performed on the heavy ends yielding an organic phase containing the larger water insoluble phenolic species and an aqueous phase containing phenolic monomers to their extent of solubility in water and nearly all of the sugars present. The aqueous phase contains approximately 8 wt% phenolics and 10 to 25 wt% anhydrosugars, depending on the biomass substrate utilized and pyrolysis reactor conditions. One intended application is to hydrolyze the anhydrosugars to glucose and perform fermentation using traditional microorganisms; however, fermentation experiments indicate that the presence of phenolic monomers at concentrations above 0.1 wt% completely inhibit the microorganisms.

This work explores the use of liquid phase adsorbents for the separation of phenolic species and other small organics from sugars in the aqueous phase. Adsorption equilibrium and kinetic parameters were determined for a variety of commercial polymeric resin adsorbents. This information was used to model continuous adsorption processes and assist in the design of a simulated moving bed (SMB) for this application. Single column experiments demonstrate that effective separation of sugars and phenolics is feasible and the target of producing an aqueous sugar product stream with less than 0.1 wt% phenolics is achievable. Construction of a lab-scale SMB is underway, and we intend to report on system parameters such as the purity and recovery of sugar and phenolics in the separated product streams, solvent consumption, and the overall efficiency of the separation.