Prof. Dr. Konstantinos Triantafyllidis, you and your team are leading the work package focusing on “Thermochemical and catalytic upgrading of hemicellulose, lignin and microbial lipids to biofuels” in the FLEXI-GREEN FUELS project. So, let me ask you: “When did you start your interest for thermochemical/catalytic conversion processes towards biofuels?”

At early 2000’s many researchers working on petroleum catalytic refining processes turned their interest to the “new” renewable and abundant feedstock for producing fuels and chemicals, that of (waste) biomass, either lignocellulosic or lipid biomass. Our initial work, in 2005, focused on the catalytic fast pyrolysis of biomass aiming to the “in-situ” upgrading of the low-quality, highly complex, oxygenated bio-oil, towards de-oxygenated bio-oil, enriched in alkylated phenols, BTX mono-aromatics and naphthalenes. Later, our group investigated and developed “integrated biorefinery” technologies, including hydrothermal pretreatment processes for the selective fractionation of biomass to cellulose, hemicellulose and lignin, as well as down-stream chemo-catalytic processes, including hydrolysis, dehydration, condensation, hydrogenation, hydrodeoxygenation, etc. towards the production of bio-based, high quality, fuels, chemicals and polymers.

What is the most surprising result in these two years of the project?

In the frame of FLEXI-GREEN FUELS project, our group at Aristotle University of Thessaloniki, together with the groups from Karlsruhe Institute of Technology (KIT) and Hulteberg Chemistry & Engineering AB (HUL), have joined forces to investigate and promote the use of alternative (microbial) lipid biomass as well as lignin, an underestimated biorefinery side-product, towards intermediate and upgraded biofuel streams for aviation and shipping. We have been collaborating with KIT in lignin pyrolysis and with HUL in the development of new catalytic materials, but our efforts at AUTH have mainly focused on the hydrodeoxygenation of lignin fast pyrolysis oil (lignin bio-oil) towards hydrocarbon streams that can be utilized in aviation or bunker fuel applications. More specifically, we have managed to convert the light fraction of lignin bio-oil, i.e. consisting of monomer/dimer lignin derived phenolics, to the respective C6-C9 alkyl-cyclohexanes, achieving almost complete hydrodeoxygenation with non-sulfided, nickel (Ni) based zeolitic catalysts under mild hydrotreatment conditions. These small cyclic hydrocarbons will be then evaluated by expert partners of the project (DLR) for their suitability as aviation fuel components.

And what is the most challenging aspect so far?

In the business of lignin valorization, you need to be prepared for demanding process conditions due to the recalcitrant phenolic/aromatic structure and “sticky” nature of lignin, and even more, of lignin bio-oil in which the “reactive” β-Ο-4 ether bonds of parent lignin, are not present anymore. To this end, the hydrodeoxygenation of the heavy fraction of lignin bio-oil, comprising of condensed phenolic/aromatic oligomers and not being miscible with hydrocarbons and petroleum heavy feeds, is a challenging task. We have been working on “reinforcing” the Ni-based zeolitic catalysts with a second metal and by adjusting zeolite’s acidity, at the same time looking at harsher HDO conditions to increase the yield of non-oxygenated cyclo-alkanes and produce a hydrocarbon stream with appropriate chemical and physical properties for aviation fuels. However, at the same time, we are looking at the prospect of utilizing partially deoxygenated lignin oils as shipping fuels alternatives.   

What additional benefits do you expect from the project?

The FLEXI-GREEN FUELS consortium brings together groups, institutions and companies from different fields of the biomass and waste valorization era, with complementary scientific and technological expertise, thus giving us the opportunity to exchange ideas, improve our research and plan new collaborations.   

Thank you for the insights into your thoughts. One last question. What is your favourite technical “research tool” and what can it do?

My favourite “research tool” would be the design and development of novel catalytic materials with an industrial/commercial perspective, that can meet the challenges of bio-refining.