(25e) Molecular Modeling of Pyrolysis Induced Shrinkage of Cellulose

Pyrolysis of lingocellulosic biomass could become a significant source of renewable chemicals and fuels in the near future. In addition to bio-oil production, fast pyrolysis of biomass produces significant quantities of synthesis gases and char. The processes that control these events are complex and not yet well understood. Among many unanswered questions is that regarding the mechanism(s) responsible for pyrolysis induced shrinkage? Ultimately, shrinkage affects transport properties including porosity and thermal conductivity, and is in-part responsible for the morphology and properties of the resulting biochar, a valuable by-product. The purpose of this study is to use molecular modeling to simulate the effect of shrinkage using model cellulose structures and recent knowledge regarding the mechanism of cellulose thermal degradation. Materials Studio was used to create and optimize a model for crystalline and amorphous cellulose. To simulate the effect of shrinkage, cellulose models were optimized first and then molecular fragments were removed from the cellulose matrix as test bed. Using the FORCITE module and the molecular mechanics force field, pcff, molecular dynamics was performed on this cellulosic system at 300 K using an NPT ensemble. The modeled parameters, density, energy and hydrogen bonding at each time step were measured and compared to the initial cellulose structures before and after from which molecular-scale morphological changes were inferred.