A review on the pyrolysis of woody biomass to bio-oil: Focus on kinetic models

The thermal decomposition of woody biomass in the absence of oxygen, or pyrolysis, is a series of complex reactions involving hundreds of compounds. The species of residue, form of residue (bark, sawdust, and other residues), age, storage conditions, among other factors, will impact the composition of the residue which in turn impacts the pyrolytic reactions. The reaction rates must be understood to optimize the pyrolysis reactor. However, the determination of intrinsic kinetics in this system is complex (both due to feedstock composition and the nature of reactions at pyrolysis temperatures) and as such the approach has been to use an overall reaction rate or series of simplified reactions. In this study, a review of large scale pyrolysis process units, reactor mathematical models, mechanisms for conversion of woody biomass and overview of heat of pyrolysis is presented. In addition, the presented kinetic models have been compared to experimental data obtained from pyrolysis of different liginocellulosic biomass (i.e. sawdust, bark, and wood chips) in a lab-scale tube furnace reactor, to determine the “best” kinetic model for the fast pyrolysis of sawmill residues. The results show that the chemical percolation devolatilization model (Lewis et al. Energy Fuels 2013; 27:942–953. doi:10.1021/ef3018783) predicts the pyrolysis products most accurately. Furthermore, the competitive model (Chan et al. Fuel 1985; 64:1505–1513. doi:10.1016/0016-2361(85)90364-3) shows very good agreement for bio-oil experimental data. Although the pyrolysis of biomass has been widely investigated in recent decades, the models have some limitations which could limit their application to a broad spectrum of feedstock and pyrolysis operating conditions.