Catalytic Process for Levoglucosan Conversion into Distillate Range Molecules

Pyrolysis oils are low quality fuels which cannot be used in conventional gasoline or diesel engines largely due to their high oxygen contents. Upgrading strategies for deoxygenation of pyrolysis oils are imperative for use in transportation fuels. In this presentation, we describe a multi-step catalytic process for conversion of levoglucosan (LGA), a major anhydrosugar present in pyrolysis oil, to monofunctional compounds, which can subsequently be coupled to obtain distillate range molecules.

Figure 1. Pathway to convert levoglucosan to distillate range fuels

Sugar syrups produced via the pyrolysis of red oak pyrolysis oil are rich in LGA. Firstly, LGA in this sugar syrup is hydrolyzed to glucose. Following hydrolysis, glucose is converted to sorbitol with high yield by hydrogenation over Ru/C. Monofunctional intermediates are produced in the aqueous-phase hydrodeoxygenation (APHDO) of sorbitol with carbon yields up to 55%. These monofunctional species consist mainly of alcohols (71%) and heterocyclic species (24%). The majority of these species (52%) are C₅ or C₆ compounds, and only small amounts of ketones and acids are formed. The monofunctional intermediates are then converted into distillate range molecules by dehydration-oligomerization. The sorbitol APHDO effluent is fed to a flow-through reactor packed with a solid acid catalyst, SiO₂/Al₂O₃, to convert the monofunctional stream to olefins. Nearly 75% yield to mono-alkenes and dienes is obtained, based on the total carbon in the monofunctionals. Dienes originate from ring opening of heterocyclic compounds. C₂-C₆ olefins thus obtained can be oligomerized over acid catalysts to produce distillate range hydrocarbons.