Chemo-catalytic and electrochemical deoxygenation of bio-derivable 3-hydroxydecanoic acid : production of drop-in fuels and fine chemicals

• Chemokatalytische und elektrochemische Desoxygenierung biologisch ableitbarer 3-Hydroxydecansäure : Herstellung von Drop-In-Kraftstoffen und Feinchemikalien

Mensah, Joel Boakye; Palkovits, Regina (Thesis advisor); Blank, Lars M. (Thesis advisor)

Aachen (2020, 2021)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2020

Abstract

Biomass is projected to play a key role for achieving the global climate goals and limiting climate change. However, to achieve a thorough use of biomass, efficient and versatile biorefinery concepts are necessary. Thus, this work investigated two strategies for the upgrading of bio-derivable 3-hydroxydecanoic acid (3-HDA) as model compound for new hydroxy-fatty acids-based value chains. For the chemo-catalytic hydrodeoxygenation in aqueous phase supported Ru-catalysts were established as most suitable for the selective synthesis of secondary alcohols and alkanes. For one, 79% 2-nonanol and 6% 3-decanol were readily synthesised over Ru/C after only 1 h. A careful analysis of the reaction mechanism and -network identified decarbonylation as principal initial reaction path leading to the selective formation of 2-nonanol, whereas C-O hydrogenolysis was only observed less pronouncedly. Alkane production was found to require the addition of a Brönsted acid as co-catalyst. The selective production of nonane (72%) and decane (12%) was achieved over bifunctional Ru/HZSM-5. Characterisation by means of NH3-TPD and pyridine-IR and correlation with the experimental results revealed that alkane formation proceeded through alcohol-dehydration over acid sites, while the subsequent hydrogenation of the alkenes was catalysed by Ru. The second deoxygenation strategy comprised the electrochemical conversion via Non-Kolbe electrolysis. The screening of different electrolytes and solvent compositions revealed pure methanol combined with Brönsted basic electrolytes as best suited for obtaining high Non-Kolbe yields (95%, after only 30 min). Furthermore, an integration into microbial fermentation could be demonstrated with the electrochemical conversion of 3-HDA in diluted fermentation broth. While the reaction proceeded significantly slower, no significant differences in the C9-oxygenate products were observed. Moreover, experiments in flow enabled a significantly improved productivity in single-pass operation or higher Faradaic efficiencies in a recirculation mode compared to the convention batch process. Finally, the assessment of the fuel properties of the synthesised C9-based oxygenate mix revealed that its overwhelming compliance with the EN 590 diesel standard besides expected low soot combustion properties and reduced NOx-emissions, suggesting a use as drop-in blend in diesel engines.