Reaction mechanisms and multi-scale modelling of lignocellulosic biomass pyrolysis

In this work about pyrolysis of lignocellulosic biomass, the individual reaction mechanisms of cellulose, hemicellulose and lignin are initially described. The recent advances in the understanding of the fundamental reaction pathways are described, including quantum-mechanical calculations, and the description of pyrolysis as a two-step process, i.e., primary pyrolysis and secondary charring, the effect of the presence of an intermediate liquid compound, and the influence of inorganic species are discussed.The need to describe biomass pyrolysis as the sum of the contributions of its individual components is then emphasised. The process of determining biomass mass loss kinetics is analysed, and the product composition and heat of reaction that are experimentally obtained during pyrolysis are presented, along with detailed schemes that can be used to predict them.Finally, it is demonstrated that a multi-scale consideration of pyrolysis on multiple levels – specifically, on molecular, particle and reaction levels – is required to accurately describe biomass pyrolysis. Intra-particle phenomena and particle models are discussed and the reactor level is analysed with a focus placed on fixed bed and fluidised bed pyrolysis. In summary, a list of 10 research focal points that will be important in the future is presented.