Molecular representation of coal-derived asphaltene based on high resolution mass spectrometry

Abstract

The asphaltene separated by solubility in small molecular alkanes and toluene is the most structurally diverse and complex components in heavy oil, such as vacuum residue and coal tar. The coal-derived asphaltene is always regard as a succession of maltene fraction from small molecules to large molecules, and also a continuum of island- and archipelago-type structures, which is difficult to be identified accurately through current characterization methods. This limits the further study of molecular dynamics and reaction dynamics simulation of asphaltenes. In this work, a representation model of molecular composition and structure for coal-derived asphaltene is developed mainly based on Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) coupled with collision induced dissociation (CID) and traditional methods of nuclear magnetic resonance spectroscopy (13C NMR), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS). Island- and archipelago-type structures are considered qualitatively in the representation of asphaltene. The asphaltene molecules are systematic assembled using stochastic algorithms and optimized by simulated annealing algorithm according to the group contribution method. The bulk properties for simulating asphaltenes are in good agreement with the experimental results giving acceptable predictions for the composition and structure of the asphaltenes. Moreover, the representative average structure asphaltene molecules are obtained using the developed molecular similarity function, which could be applied in the further study of molecular aggregation simulation and reaction kinetics simulation.