Obtaining parameters for equation of state modeling of Bitumen Thermodynamic properties Michael Greenfield , Nicole Mendoza, Mohammad Masoori University of Rhode Island, USA Bitumen used in road pavement incorporates millions of chemical compounds due to its origin as the heavy components from crude oil processing. Phase behaviors such as wax precipitation and microphase separation in the presence of polymer additives contribute to its mechanical performance. To describe these phenomena, it would be useful to have a thermodynamic approach that could be incorporated into a computationally inexpensive equation of state approach. Toward that end, critical properties, saturation pressure, and acentric factors of the components in two prior molecular-scale model bitumens were estimated using correlation methods of Nannoolal et al. that employ group contributions. These parameters enable using cubic equations of state in simulations that require thermodynamic properties of amorphous bitumen phases, such as phase field models of microstructure induced by wax crystallization. The estimated properties indicate that the components of two model bitumens span different distinct ranges in predicted critical pressure and temperature. These parameters were then used in the Peng-Robinson cubic equation of state to predict densities, thermal expansion coefficients, residual energies, and phase envelopes of model bitumens. The results for thermal expansion show a good consistency with molecular simulation predictions and experimental results. Density predictions were poor but improved with use of the COSTALD correlation. Residual energies were compared with cohesive energies that were computed via molecular simulation of bulk systems and of individual molecules. Phase envelopes indicate that one model contains components that are too volatile, and thus it is a poor representation of bitumen. Finally, wax precipitation was predicted by comparing chemical potential of squalane, one component of the less volatile model bitumen, within pure solid and amorphous bitumen phases. Wax precipitation has been linked to low- temperature cracking in pavement. The chemical potential driving force for crystallization differed for several bitumen models. This demonstrates a mechanism for the chemistry of bitumen to affect phase microstructure, which ultimately influences bitumen mechanical properties. References 1. Derek D. Li and Michael L. Greenfield, "Chemical Compositions of Improved Model Asphalt Systems for Molecular Simulations,'' Fuel , 2014, 115 , 347-356. 2. Liqun~Zhang and Michael~L. Greenfield, "Analyzing Properties of Model Asphalts using Molecular Simulation,'' Energy Fuels , 2007, 21 , 1712-1716.
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