Measuring biomass fast pyrolysis kinetics: State of the art

Fast pyrolysis of lignocellulosic biomass is considered to be a promising thermochemical route for the production of drop-in fuels and valuable chemicals. During the past decades, a comprehensive understanding of feedstock structure, fast pyrolysis kinetics, product distribution, and transport effects that govern the process has allowed to design better pyrolysis reactors and/or catalysts. A variety of lignocellulosic biomass feedstocks, like corn stover, pinewood, poplar, and model compounds like glucose, xylan, monolignols have been utilized to study the thermal decomposition at or close to fast pyrolysis conditions. Significant progress has been made in understanding the kinetics by developing unique setups such as droptube, PHASR, and micropyrolyzer reactors in combination with the use of advanced analytical techniques such as comprehensive gas and liquid chromatography (GC, LC) with time-of-flight mass spectrometer (TOF-MS). This has led to initial intrinsic kinetic models for biomass and its main components, namely cellulose, hemicellulose, and lignin, validated using experimental setups where the effects of heat and mass transfer on the performance of the process, expressed using Biot and pyrolysis numbers, are adequately negligible. Yet, not all aspects of fast pyrolysis kinetics of biomass components are equally well understood. The use of time-resolved or multiplexed experimental techniques can further improve our understanding of reaction intermediates and their corresponding kinetic mechanisms. The novel experimental data combined with first principles based multiscale models can reshape biomass pyrolysis models and transform biomass fast pyrolysis to a more selective and energy efficient process.