Hydrodeoxygenation of lignin-derived model compound for sustainable aviation fuel production using bifunctional catalysts

The development for sustainable and renewable fuels is driven by the current reliance on fossil fuels and a need to reduce contaminant gas emissions and adhere to climate-related regulations. The main challenge for the aviation industry in particular is the transition towards cleaner energy sources. A promising solution is manufacturing hydrocarbons from renewable sources, minimizing the environmental impact and high costs required for alternative green technologies. Lignin is considered as a promising source of materials and biofuels, as it can be
transformed through various thermochemical processes to valuable products. To obtain liquid hydrocarbons, lignin needs to undergo pyrolysis, resulting in bio-oil, which requires additional upgrading due to its low heating value, high viscosity, and acidity. Hydrodeoxygenation can be used to remove the oxygen groups, obtaining hydrocarbons compatible with the existing infrastructure.

In this study, hydrodeoxygenation of isoeugenol, a lignin-derived model compound, was investigated using various bifunctional catalysts in both batch and continuous reactors. A series of bimetallic platinum-rhenium catalysts supported on mesoporous and activated carbon were studied, with the purpose of revealing the role of both metals for hydrogenation and deoxygenation. The results indicated that a higher
rhenium loading resulted in improved activity, providing the oxygen vacancies required for deoxygenation. Further research performed in a continuous reactor allowed high conversion (100%) and deoxygenation level (90%) at 200 ºC.

For the first time studies simulating industrial catalysts and eventual scaling-up were performed for a lignin-derived model compound in batch and continuous reactors using powders and extrudates, respectively, comprising platinum as the active metal, zeolite beta and a binder. The effects of the binder addition, platinum location, and zeolite acidity were evaluated for the powder catalyst, while the effect of platinum location and reaction temperature was evaluated for the extrudates. The addition of binder resulted in a decrease of surface area, total pore volume, and acidity, additionally, the catalysts containing the more acidic zeolite (H-Beta-25) exhibited better catalytic performance (ca. 80% conversion and over 50% yield of the deoxygenated product) compared to the H-Beta-300. The proximity of platinum to acid sites enhanced considerably catalytic activity, resulting in ca. 20% higher conversion when platinum was deposited on the zeolite rather than only on the binder. The extrudates displayed good stability, with a 10% decrease in catalytic activity after 30 hours of time on stream. Additionally, an effectiveness factor of 0.17 and an apparent activation energy of 14.7 kJ/mol revealed the presence of mass transfer limitations. A high conversion (100%) and a significant yield of deoxygenated products (80%), were obtained at 200 ºC.