Macromolecular rearrangement caused by CO2 adsorption in coal

Abstract

Macromolecule rearrangement is an important reason for coal adsorption induced deformation. The process of carbon dioxide (CO2) sequestration in a coal seam induces coal deformation, which yields challenges in terms of the injectability of CO2 and the safety of sequestration. We report the molecular rearrangement characteristics of coal with adsorbed CO2 that is completely different from macroscopic coal deformation. In-situ spectroscopy was used to monitor the Raman and infrared responses during the CO2 injection process in coal. The interlayer characteristics and defects of coal macromolecules were highly responsive to the adsorption process. The adsorption of CO2 could lead to the increase of interlayer shear vibration intensity and cause irreversible damage to the defective part of coal. Quantum chemistry simulations showed that CO2 can adsorb on the edge of the coal aromatic nucleus (AN) and cause layer slip in the AN. In the rearrangement process, the AN of coal macromolecules tend to increase the layer spacing and slip to the direction of more overlapping between layers. Our study reveals a potential molecular mechanism for coal deformation via CO2 adsorption; provides a new insight into coal adsorption deformation, and indicates that coal macromolecular rearrangement can be attributed to the change of interlayer interaction.