(383a) Ab Initio Estimation of Thermophysical Properties of Biomass-Relevant Compounds

Biomass pyrolysis is the process by which biomass is thermally decomposed into smaller molecules. Pyrolysis of biomass results in the formation of biochar; bio-oil; gases like methane, hydrogen, carbon monoxide; and polycyclic compounds. A good properties model is required to develop a reliable process model; therefore, it is vital to have both a good model and appropriate estimates of model parameters which can be used to predict material properties. Accurate evaluation of enthalpies of formation is necessary to accurately model biomass pyrolysis. Reaction energetics are often modeled based on tabulated data contained in commercial simulator databanks such as aspenONE, however, data are unavailable in these banks for many relevant polycyclic compounds. To work toward establishing a general framework for establishing energetics of biomass pyrolysis reactions, we study a set of 14 dehydration reactions involving the formation of polycyclic compounds in biomass pyrolysis using Density Functional Theory (DFT). We have pursued a model based on the deformation of the molecules from equilibrium geometries based on the nature of the chemical bonds comprising the molecules. Quantities relevant to accurately modeling thermophysical properties of real systems, such as thermal effects and zero-point energies, were computed for these reactions and found to have small effects on both the relative and overall energetics. We have found that the differences in thermophysical stability of these compounds can be attributed to simple geometric descriptors, which we use as a basis for establishing a model Hamiltonian for the system. We show that the condensation reaction and formation of an oxygen bridge and the commensurate introduction of strain with formation of additional cyclic structures is the major contributor to the energy difference in these reactions. We employ these models to predict thermophysical properties of biomass-relevant reactions.