Study on the reaction mechanism of C8+ aliphatic hydrocarbons obtained directly from biomass by hydropyrolysis vapor upgrading

Aviation fuel production is an important direction for biomass utilization, however, the direct transformation of biomass into aviation fuel is a bottleneck in this field. Among all the biomass-to-liquid thermochemical routes, the pyrolysis process can directly produce bio-oil in a continuous industrial manner. Herein, Ni-Mo/γ-Al2O3 catalyst was used to investigate the hydropyrolysis (HP) vapor upgrading (VU) process of lignocellulosic biomass to obtain bio-oil with high selectivity of aviation fuel components. The VU temperature of 300–350℃ was conducive to generating liquid fuel with C8+ aliphatics as the main component of jet fuel. It was indicated that the yield of the oil phase was 6.4 wt% with an HHV of 46.2 MJ/kg, while the selectivity of aliphatics reached 72.6% with C8+ aliphatics was 59.9%. Moreover, it was found that all three components of biomass could be transformed into long-chain aliphatics by coupling reaction. The hydroxyalkylation is the main way and the aldehyde group is the directing group of the carbon-increasing, which was supported by the results of the quantum chemical calculation. Further, the reaction network for the HP-VU process of lignocellulosic biomass with C8+ aliphatics as the main product was proposed to provide a theoretical understanding of the carbon-increasing in biomass hydropyrolysis.