The development of sustainable aviation fuels from lignin fragments
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Journal Title
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Volume Title
Kemian tekniikan korkeakoulu |
Master's thesis
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Authors
Date
2023-08-22
Department
Major/Subject
Biological and Chemical Engineering for a Sustainable Bioeconomy (Bioceb)
Mcode
Degree programme
Master's Programme in Biological and Chemical Engineering for a Sustainable Bioeconomy
Language
en
Pages
44+9
Series
Abstract
Sustainable Aviation Fuel (SAF) is considered a high-potential solution for the decarbonization of our energy systems, and is under development in many countries of the world (International Air Transport Association, 2022). However, the seven current certified SAF production technologies are unable to fulfill the requirements of aromatic compounds, necessitating a maximum blend proportion of 50 vol% with fossil-based aviation fuels (Cheng and Brewer, 2017, ICAO). Lignin, a major component of lignocellulosic biomass constituting 20-30% of wood resources, is the largest renewable source of aromatics (Tuck et al, 2012). Although typically regarded as a waste stream, lignin valorization is forecasted to improve the economics, sustainability, and circularity of a biorefinery concept, and due to its abundance and aromaticity, constitutes significant potential for industrial use in the replacement of oil-based products (Abu-Omar et al, 2021, Stone et al, 2022). Lignin fragments (LHD) following a proprietary process are composed of monomeric and dimeric fractions and possess a carbon range similar to those found in SAF mixtures. In this work, a hydrodeoxygenation (HDO) reaction was designed and optimized to produce SAF-range hydrocarbon from LHD. Various reaction conditions were manipulated in order to understand the internal reaction kinetics and tune reaction conditions for the desired products, according to whether aromatic components are desired or full saturation products. It was found that the ratio of hydrogen to oxygen ratio has the most significant influence in the product selectivity, followed by the reaction temperature. An increase in the ratio of hydrogen to oxygen content decreased the proportion of aromatic compounds in favour of saturated species, although a minimum molar ratio was required for complete HDO; therefore this minimum ratio is optimal for aromatics production, whereas a higher ratio is optimal for the production of cycloparaffins while minimizing excess hydrogen use and further undesirable reactions such as cracking. An increase in the reaction temperature favours the production of aromatics and favours the HDO reaction while inhibiting the ring hydrogenation reaction. However, the oil yield also decreases with temperature, due to an increased rate of C-C cleavage (i.e., cracking). It was also observed that an increase in reaction duration at a constant temperature led to a decrease in the aromatic fraction, with a very slight decrease in oil yield. This suggests that the ring hydrogenation reaction continues to hydrogenate aromatic species following HDO, and that C-C cleavage is unfavoured. In contrast, at higher temperatures, where the ring hydrogenation reaction is less favoured, increased reaction time does not lead to a decrease in aromaticity, but to decreases in oil yield. This process was found to successfully deoxygenate lignin fragments to produce SAF-range hydrocarbons with a tunable aromatics content, that could be used as a SAF or blended with other SAF pathways in order to provide a 100% fossil-free aviation fuel.Description
Supervisor
Österberg, MonikaThesis advisor
Questell-Santiago, YdnaLukk, Tiit
Keywords
sustainable aviation fuel, biofuel, lignin, biomass valorisation