The Interactions of Coal with CO2 and Its Effects on Coal Structure

The interactions of coal with CO 2 at pressures of up to 30 bar concerning mechanisms of diffusion, the strength of interactions, and the irreversibility of uptake for the permanent disposal of CO 2 into coal fields have been studied. Differential scanning calorimetry was used to investigate coal/CO 2 interactions for North Dakota, Wyodak, Illinois No. 6, and Pittsburgh No. 8 coals. It was found that the first interactions of CO 2 with coals led to strongly bound carbon dioxide on coal. Energy values attributed to the irreversible storage capacity for CO 2 on coals were determined. The lowest irreversible sorption energy was found for North Dakota coal (0.44 J/g), and the highest value was for the Illinois No. 6 coal (8.93 J/g). The effect of high-pressure CO 2 on the macromolecular structure of coal was also studied by means of differential scanning calorimetry. It was found that the temperature of the second-order phase transition of Wyodak coal decreases with an increase in CO 2 pressure significantly, indicating that high-pressure CO 2 diffuses through the coal matrix, causes significant plasticization effects, and changes the macromolecular structure of the Wyodak coal. Desorption characteristics of CO 2 from the Pittsburgh No. 8 coal were studied by temperature-programmed desorption mass spectrometry. It was found that CO 2 desorption from the coal is an activated process and follows a first-order kinetic model. The activation energy for CO 2 desorption from the Pittsburgh No. 8 coal increased with the preadsorbed CO 2 pressure, indicating that CO 2 binds more strongly and demands more energy to desorb from the Pittsburgh No. 8 coal at higher pressures.