Molecular-Scale Modeling of Whole Biomass Pyrolysis – Morphological Changes

As pyrolysis takes place, liquid, gas and char are formed. Volatilization is assumed to occur only from a free surface, thereby generating a gradient in liquid content, forcing solid-phase char to move in the opposite direction to maintain volume balance. Plant matter is clearly a complex chemically and morphologically heterogeneous materials and observed chemical and microstructure changes upon pyrolysis are likewise complex. The processes that control these effects of transport, kinetics and microstructure changes on biomass during pyrolysis are likewise complex and not yet well understood. The purpose of this study is to use molecular modeling to simulate microstructure changes during pyrolysis using modeled whole biomass structures. Biovia-Material Studio was used to create a model for whole biomass using the FORCITE module and the molecular mechanics force field pcff at 300 °K. To simulate microstructural changes, whole biomass models were optimized first and then molecular fragments were removed from the matrix. The molecular dynamics was performed on this system at 600 °K using the Molecular Operating Environment (MOE) and NAMD, and the molecular mechanics force field, AMBER. The modeled parameters, density, energy and volume at each time step were measured and compared to the initial whole biomass structures before and after from which molecular-scale morphological changes were inferred.