Synergistic co-processing of an acidic hardwood derived pyrolysis bio-oil with alkaline Red Mud bauxite mining waste as a sacrificial upgrading catalyst

In this proof-of-concept study we demonstrate that co-processing of an acidic bio-oil (pH < 3) produced by the fast pyrolysis of sawmill residue hardwood chips with alkaline (pH > 12) Red Mud bauxite mining waste originating from the Bayer process can lead to a synergistic upgrading and value addition to both feed materials. The co-processing reaction is carried out in a pressure reactor at 365 °C and yields a stabilized, much less acidic and more energy-dense bio-oil with an oxygen content of 3.5% and heating value of 34 kJ/g compared to 43.1% and 12 kJ/g, respectively, for the crude oil. In the same reaction the Red Mud acts as a sacrificial catalyst and is converted into a partially reduced magnetic neutral gray material with a carbon content of ∼33% (w/w). This neutralized material may have possible use as an iron ore, iron ore pelletization binder or soil additive. The co-processing of the two waste streams – one derived from forestry by-products, the other from bauxite mining and processing operations – may thus offer attractive economic and ecologic synergies. Two principle possible scenarios for an actual realization for such a process on a larger scale are discussed.

Waste not, want not: The use of Red Mud from the Bayer process as a catalyst for the upgrading of highly acidic bio-oil stabilizes the oil through deoxygenation reactions and results in the transformation of the hazardous alkaline bauxite residue into a neutral low-grade iron ore. The co-processing of two waste streams – one from the aluminum and one from the forest industry – thus adds value to both with potential positive economic and ecologic synergies.Figure optionsDownload as PowerPoint slideHighlights
► Alkaline Red Mud bauxite mining waste was reacted with acidic pyrolysis bio-oil.
► The bio-oil was upgraded to a less acidic, chemically stable and more energy dense oil.
► The Red Mud was neutralized and partially reduced to a gray magnetic low-grade iron ore.