Research pick: Burying the carbon - "In-depth analysis of coal chemical structural properties response to flue gas saturation: perspective on long-term CO2 sequestration"

Odd as it may seem, coal seams that cannot be mined might provide an underground storage medium for carbon dioxide produced by industries burning coal above ground. Research in the International Journal of Oil, Gas and Coal Technology has undertaken controlled experiments designed to simulate the deep geological environments where carbon dioxide might be trapped as a way to reduce the global carbon footprint and ameliorate some of the impact of our burning fossil fuels. Coal seams represent a potential repository for long-term storage of carbon dioxide sequestered from flue gases, as they can trap a lot of carbon dioxide gas in a small volume.

Major Mabuza of the University of Johannesburg, Johannesburg, Kasturie Premlall of Tshwane University of Technology, Pretoria, and Mandlenkosi G.R. Mahlobo of the University of South Africa, Florida, South Africa, subjected coals to a synthetic flue gas for 90 days at high pressure (9.0 megapascals) and a mildly high raised temperatures of 60 degrees Celsius. These conditions were intended to replicate the pressures and temperatures found deep underground, providing a realistic model for how coal might behave when used for carbon dioxide sequestration.

The team then looked at how the chemical structure of coal was changed by exposure to flue gas under these conditions using various advanced analytical chemistry techniques – carbon-13 solid-state nuclear magnetic resonance spectroscopy, universal attenuated total reflectance-Fourier transform infrared spectroscopy, field emission gun scanning electron microscopy with energy dispersive X-ray spectroscopy, and wide-angle X-ray diffraction.

The results showed that exposure to synthetic flue gas led to major changes to the chemical makeup of the coal. For instance, key functional groups, such as aliphatic hydroxyl groups, aromatic carbon-hydrogen bonds, and carbon-oxygen bonds, were all weakened by the process and the overall physical properties of the coal were also changed.

By clarifying how coal interacts with flue gas under simulated, but realistic, conditions, the team fills important gaps in our knowledge about the long-term stability and effectiveness of carbon dioxide storage below ground and specifically in coal seams.

Mabuza, M., Premlall, K. and Mahlobo, M.G.R. (2024) ‘In-depth analysis of coal chemical structural properties response to flue gas saturation: perspective on long-term CO2 sequestration’, Int. J. Oil, Gas and Coal Technology, Vol. 36, No. 5, pp.1–17.