Pyrolysis Vapors Upgrading Using Metal Oxides

Pyrolysis Vapors Upgrading using Metal Oxides

Ayman M. Karim¹, Donghai Mei¹, Vanessa Lebarbier¹, Changjun Liu^1,2 and Yong Wang^1,2

¹Pacific Northwest National Laboratory

²Washington State University

The vapors generated during fast pyrolysis of biomass contain a significant fraction of light oxygenates (acetic acid, hydroxyacetaldehyde, hydroxyacetone,..) which are produced through undesired fragmentation reactions during pyrolysis. Hydrodeoxygenation of the light oxygenates would result in light alkanes which are not useful for transportation fuels. Therefore. the light compounds need to be converted to larger molecules before the   hydrodeoxygenation/hydrotreating of the pyrolysis vapors (or bio-oil).

In this contribution, deoxygenation strategies for the upgrading of light oxygenates using metal oxides will be presented. The work combines experimental and density functional theory (DFT) calculations to identify metal oxide(s) for the

1- Upgrading of light oxygenates (building up) to fuel range compounds (C5+)

2- Deoxygenation of biomass depolymerization products (C5+ molecules)

We will show that ketonization and condensation on CeO₂ based mixed oxides is an effective way of re-building the light oxygenates into fuel range molecules. CeO₂ based mixed oxides show a 90+% selectivity to acetone during the ketonization of acetic acid. The ketonization reaction pathway on CeO₂ was investigated using density functional theory calculations and the role of the second metal on selectivity and tolerance to H₂O and CO₂ will be presented.

The deoxygenation of the pyrolysis vapors using partially reduced metal oxides will also be presented. We show that oxygen vacancies on MoO₃ (010) can selectively cleave the C-O bond over C-C bonds. Finally we will discuss the strategies and challenges to combine both approaches in a single upgrading step.