Oxidative Effects of Gaseous Oxygen and Ozone on Australian Subbituminous and Bituminous Coals and the Implications for Coal Seam Permeability Enhancement

The use of gaseous ozone as a means for enhancing coal seam permeability has been investigated, including the effect on subbituminous and bituminous coal from the Surat and Bowen Basins, Australia, respectively. To elucidate the oxidative mechanism, the chemical properties of the Surat coal before and after oxidation was examined using Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR) and X-ray Photoelectron Spectroscopy (XPS). Additionally, gas adsorption techniques and optical microscopy were used to assess physical changes arising from the ozone treatment. Although both the oxygen and ozone treatments (two days duration) increased the oxygen content in the molecular structure of the coal, the ozone introduced significantly more, specifically with the generation of aliphatic ester CO groups and aromatic carbonyl/carboxyl CO groups. In terms of the physical structure of the coal, the micropore volume was slightly reduced by the oxygen treatment but almost eliminated by the ozone treatment. Furthermore, oxygen treatment showed little impact on the coal mass loss while ozone oxidation caused a 0.7% loss in coal weight. Additional tests on a Bowen Basin coal showed an increase in the aperture (4.37%) of a cleat after ozone treatment. These results demonstrate the potential of ozone for coal seam permeability enhancement by merging micropores and increasing cleat apertures whilst maintaining the structural integrity of the coal.