557 / 2018-09-30 17:54:55

Sustainable one-step hydroprocessing of fatty acids into bio-aviation fuel ingredients

生物质液体燃料 > 生物质液体燃料

Aviation fuel, nowadays in much demand worldwide, is a type of customized fuel that consists of various types of hydrocarbons, e.g., alkanes, isoalkanes, cycloalkanes and aromatics, with a specific carbon chain length ranging from 8 to16. The current aviation fuel production originates from fossil fuel refining, which has not only caused the fast depletion of earth-stored fuels but also brought about severe CO2-induced environmental issues. Using waste lips or fatty acids as the building feedstock provides a promising approach against the mentioned two defects, as they show a similar carbon chain molecular structure to that of fossil fuel, and more importantly, they are entirely clean and renewable. However, some differences, compared with petroleum, still exist because of the presence of approximately 10% of oxygen contents in the feedstock, which proposes new requirements for the current catalytic reaction system. In this regard, we employed fatty acids as the example feedstock and aimed to investigate the specific reaction pathways and catalytic mechanisms of this hydroconversion process, with the purpose of exploring the practical synthesis of aviation fuel ingredients. Other than the C8-C16 alkanes and isoalkanes that are of current interest, aromatic hydrocarbon (AHC) is also an essential component in aviation fuel. We found that employing the bifunctional Ni/HZSM-5 as the catalyst with tuned B/L acid sites allowed the synthesis of ample aromatic hydrocarbons, and the corresponding synthesizing pathway primarily consisted of hydrodeoxygenation, hydrocracking, cyclization and aromatization reaction (Scheme 1). Besides, massive H2, also acting as a feedstock, is commonly used in this process, which makes the route uneconomical. We further explored the possible alternative of greenhouse gas CO2 instead of H2 as the reaction medium to deoxygenate fatty acids and found that the synthesis of C8-C15 aviation fuel-range alkanes was enhanced (Scheme 2). The reason for this lied in the rearrangement of internal hydrogen in fatty acids promoted by CO2. This new route of using CO2 as the reaction medium will contribute to the future CO2 utilization chemistry and provide an economical and promising approach for the production of sustainable alkane products originated from fatty acids or waste lips.