Modeling Carbonaceous Mesophase Thermodynamics Using Measured Elemental Compositions

Carbonaceous mesophase is a liquid crystalline material that can form as petroleum is pyrolyzed into coke. The material is thought to be made up of discotic mesogens in the form of planar, polyaromatic molecules. Researchers have previously developed thermodynamic models to predict mesophase formation in different feeds based on molecular weight, independent of the chemical structures found in any given sample of material. Using Fourier transform ion cyclotron resonance mass spectroscopy (FT-ICR MS), we were able to observe how the elemental compositions of hydrocarbon molecules evolved with thermal treatment. Using this information, we devised a new approach for modeling petroleum-based liquid crystal phase behavior using both molecular weight and elemental compositions to describe the material’s composition. This approach permits molecules of large molecular weight to not automatically be considered mesogens and for nonideal solution behavior and mesophase content to be parametrized independently. Through comparing different methods, we also demonstrated the important role nonideal solution effects have on the calculated phase behavior as well as the impact of pseudocomponent number on the size of the mesophase coexistence region. Further theoretical and experimental work is needed to develop more general, predictive models.