Molecular Model of Xishan Bituminous Coal Surface and Its Wetting Properties

ZQ Zhang and QN Kang and S Wei and T Yun and GC Yan and KF Yan, ENERGY & FUELS, 31, 9094-9100 (2017).

DOI: 10.1021/acs.energyfuels.7b01350

Microscopic understanding of the coal surface structure offers opportunities to enhance coal preparation and utilization. This study contributes to the construction of a surface model of Xishan bituminous coal based on a recently proposed coal bulk model. An XPS survey spectrum reveals that the surface of this coal sample was partially oxidized by atmospheric oxygen. Therefore, different oxygen-containing groups were randomly incorporated into a 3 nm surface layer of the original surface model to represent the realistic oxidized coal surface based on the XPS and NMR results. We also probed the wetting properties of this model both in water and in methanol. The possible reasons for the discrepancy between the computed and experimental values were also discussed. Although both water and methanol can penetrate and fill micropores in the coal surface layer, methanol is found to swell coal to a greater extent than water. The association of coal molecules in this model is caused mainly by van der Waals energy. However, the wetting of the coal surface layer predominantly decreases the electrostatic interactions of coal-coal. In agreement with the wetting experiments, methanol is more effective to reduce the interaction of coal-coal than water.

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