Catalytic upgrading of sugar fractions from pyrolysis oils in supercritical mono-alcohols over Cu doped porous metal oxide

• Catalytic upgrading of the sugar fraction of pyrolysis oils was investigated.
• Cu doped porous metal oxides were used as the catalyst.
• Supercritical methanol and ethanol were applied as solvents.
• Products with high amounts of mono- and di-alcohols were obtained.
• Products may be used as biofuel (additive) or for hydrocarbon production.

In this work, we report on the catalytic valorization of sugar fractions, obtained by aqueous phase extraction of fast pyrolysis oils, in supercritical methanol (scMeOH) and ethanol (scEtOH) over a copper doped porous metal oxide (Cu-PMO). The product mixtures obtained are, in principle, suitable for direct co-feeding in methanol to hydrocarbon (MTH) processes, as fuel additives, or can be further fractionated or transformed to useful bulk chemicals. The main components of the obtained product mixtures in scMeOH are aliphatic mono-alcohols (51%), diols (22%), esters (15%), ethers (9%) and furanics (3%). Similar product suite is obtained by converting concentrated, 15 wt% sugar fractions with added 50 bar H2 in scEtOH. The extensive depolymerization of the sugar polymers and oligomers contained in the sugar fraction is verified by gel permeation chromatography (GPC) and product stability upon catalytic treatment is confirmed by thermogravimetric analysis (TGA). In addition, model compound studies, using levoglucosan and d-cellobiose allow for more specific insight into the chemical pathways taking place during these transformations. The catalyst is characterized by various techniques, including XRD, NH3-TPD, BET, and TEM. The stability of the catalyst using 5 wt% sugar fraction in scMeOH is also evaluated.

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