Progress in Understanding the Four Dominant Intra-Particle Phenomena of Lignocellulose Pyrolysis: Chemical Reactions, Heat Transfer, Mass Transfer, and Phase Change

Four principal intra-particle phenomena occur in a highly concerted manner during the pyrolysis of lignocellulosic materials: heat transfer, mass transfer, chemical reactions, and phase changes. Achieving a holistic understanding of these processes has been challenged by their intricate coupling, high temperatures, and rapid rates at which they occur. Heat and mass transfer have been well studied at the single-particle level but their coupling with chemical reactions and phase change within single particle models remains problematic. Equally challenging is the multiscale coupling of reactor- and single particle-scale models. Too little attention has been given to phase change. Similarly, the presence of oligomeric compounds (constituting up to 20% of the oil) has not been fully accounted for in chemical reaction schemes and physical models developed for pyrolysis. Recent studies have shown that a multiscale approach is key to predictive modelling across a variety of reactor systems. Historical and recent developments are outlined in this pyrolysis review paper regarding these four intra-particle phenomena, as well as modelling efforts to capture their effect on product yields and composition. It is critical for the design of future biomass pyrolysis systems to appropriately account for all four intra-particle phenomena and their inter-connectivities in order to predict, achieve, and maintain optimal operation.