Abstract:
The effects of supercritical CO
2(ScCO
2)on coal chemical structure play a critical role in CO
2 storage capacity in coal. In this study, CO
2 sequestration processes were replicated using a ScCO
2 geochemical reactor. Four coal samples with different ranks were exposed to ScCO
2 and water under 62.5℃ and 15 MPa. Fourier transform infrared spectroscopy and X-ray diffraction analysis were used to identify the chemical structure of the coal samples before and after ScCO
2-H
2O treatment. Then evolution mechanism of coal chemical structure was studied. The results show that after ScCO
2 treatment, the length of aliphatic hydrocarbon generally increased, and only the abundance of the aromatic hydrocarbon in the fat coal increased. The increase of the abundance of the oxygen-containing groups in coal samples was mainly contributed by the increase of hydrogen bonding groups, except for the anthracite whose abundance of the oxygen-containing groups was affected by the dissolution of low-molecular compounds. Swelling caused by ScCO
2 caused breakage of cross links between the aromatic layers in fat and lean coal, making the structure of crystallite loose. While the formation of C
Ar-C
Ar cross links in the aromatic layer increased the aromaticity and aromatic ring condensation of the fat and lean coal. The falling off of none polycyclic aromatic hydrocarbons in meagre coal and anthracite made the structure of crystallite more compact, and the increase of the length of the aliphatic hydrocarbon reduced the aromaticity and aromatic ring condensation of meagre coal and anthracite.