A critical review on biomass pyrolysis: Reaction mechanisms, process modeling and potential challenges

Pyrolysis is a versatile technology for exploiting diversified feedstocks to produce a wide range of products, including biochar, bio-oil, and syngas with high potential in diverse applications. The cardinal motivation of pyrolysis research is to productively use diverse biomass to reduce adverse impacts on ecology and enhance process economics. However, complex reactions of pyrolysis pose operational challenges. Thus, the present review targets the reaction mechanisms and kinetics of pyrolysis to enhance the understanding for better process control, improved performance, and product distribution. Pyrolysis mechanisms of the major structural components of biomass, such as cellulose, lignin, and hemicellulose, as well as proteins, lipids, and carbohydrates, are discussed in detail. Various modeling techniques and tools, viz., mathematical, kinetic, computational fluid dynamic modeling, and machine learning algorithms, have been employed to better understand the pyrolysis mechanisms and product distribution. In addition, the most critical challenges, namely aerosol formation, tar formation and their removal mechanisms, that severely impact the pyrolysis process and products are identified and reported. Thus, the present work critically discusses state-of-art biomass pyrolysis, focusing on the reaction mechanism, modeling, and associated challenges to overcome, given that the pyrolysis products and the process are enhanced.