Adsorption Equilibria and Systematic Thermodynamics Analysis of Carbon Dioxide Sequestration on South African Coals Using Nonlinear Three-Parameter Models: Sips, Tóth, and Dubinin–Astakhov

Major Melusi Mabuza () and Mandlenkosi George Robert Mahlobo
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Major Melusi Mabuza: Department of Chemical Engineering Technology, Faculty of Engineering and the Built Environment, University of Johannesburg, P.O. Box 17011, Doornfontein, Johannesburg 2088, South Africa
Mandlenkosi George Robert Mahlobo: Department of Chemical and Materials Engineering, University of South Africa, P.O. Box 392, Roodepoort 1709, South Africa

Energies, 2025, vol. 18, issue 10, 1-20

Abstract: Carbon dioxide (CO 2 ) injection into geologic formations has gained global traction, including in South Africa, to mitigate anthropogenic emissions through carbon capture, utilisation, and storage technology. These technological and technical developments require a comprehensive and reliable study of CO 2 sorption equilibria under in situ unmineable coal reservoir conditions. This paper presents novel findings on the study of the equilibrium adsorption of CO 2 on two South African coals measured at four temperatures between 30 and 60 °C and pressures up to 9.0 MPa using the volumetric technique. Additionally, the sorption mechanism and thermodynamic nature of the process were studied by fitting the experimental data into Langmuir–Freundlich (Sips), Tóth, and Dubinin–Astakhov (DA) isotherm models, and the Clausius–Clapeyron equation. The findings indicate that the sorption process is highly exothermic, as presented by a negative temperature effect, with the maximum working capacity estimated to range between 3.46 and 4.16 mmol/g, which is also rank- and maceral composition-dependent, with high-rank vitrinite-rich coal yielding more sorption capacity than low-rank inertinite-rich coal. The experimental data fit well in Sips and Tóth models, confirming their applicability in describing the CO 2 sorption behaviour of the coals under the considered conditions. The isosteric heat of adsorption varied from 7.518 to 37.408 kJ/mol for adsorbate loading ranging from 0.4 to 3.6 mmol/g. Overall, the coals studied demonstrate well-developed sorption properties that characteristically make them viable candidates for CO 2 sequestration applications for environmental sustainability.

Keywords: anthropogenic emissions; CO 2 sequestration; isotherm models; sorption equilibria; thermodynamics; unmineable coal (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2025
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