Optimization of Pyrolytic Bio-Oil Upgrading Using Zeolite Catalysts

The catalytic upgrading of biomass-derived pyrolysis vapors presents a promising route for sustainable aviation fuel (SAF) production. While promising, current technologies can only be blended with traditional jet fuel as they lack aromatic hydrocarbons. To counter this, this study aimed to optimize process conditions to maximize aromatic hydrocarbon yields while minimizing oxygenate content and benzene production using zeolite catalysts and pyrolysis oils from cellulose as a fuel additive for SAF. Specifically, the targets were to (1) reduce total oxygenates to <1%, (2) maximize non-benzene aromatic yield, and (3) limit benzene selectivity to <8%, enabling the final blend to meet the <0.8 vol% benzene limit for SAF, where the upgraded bio-oil is used as a fuel additive.

Catalysts with SiO₂:Al₂O₃ ratios of 30:1, 50:1, and 80:1 were evaluated under varying conditions of temperature and catalyst amount. A Box-Behnken response surface design was used to statistically evaluate the influence of these three factors. Experiments were performed using a fixed-bed reactor, and liquid-phase products were collected post-reaction and analyzed by GC-MS.

The response surface model identified optimal conditions at 411 °C, 1.33 g catalyst loading, and a SiO₂:Al₂O₃ ratio of approximately 67:1. Due to time limitations, this optimal acidity was achieved through physical blending of the 50:1 and 80:1 ZSM-5 catalysts in the final test run. Results showed significantly reduced oxygenate content and improved aromatic selectivity, with benzene levels approaching the targeted regulatory threshold. These findings underscore the importance of fine-tuning catalyst acidity and reaction conditions for tailoring SAF-relevant product distributions from model bio-oil mixtures.