Evaluating CO2 Sorption Capacity of a Number of South African (SA) Coal Types: Comparative Study of the Different Coal Properties at Incremental Pressures up to Supercritical Pressures

The study was aimed at evaluating the CO2 adsorption capacity of various South African coal types to determine the effects of pressure, coal rank and coal composition with regard to their maceral and mineral content. Pure CO2 adsorption isotherms were measured at 35 °C and up to a maximum pressure of ∼85 bar using the volumetric method. Higher ranking coals had shown greater sorption rates compared to lower ranked coals with greater mineral matter content. Increased maceral content, to some degree, shows greater affinity for CO2 uptake, however, there is no clear correlation between the competing nature of vitrinite and inertinite components from these results, further investigation into the inert and reactive components of the maceral components needs closer evaluation as can be seen from the SM coal type result, although the general trend leans toward higher adsorption capacity with regard to higher vitrinite content as a whole for most of the coals tested in this study. Langmuir model was found to generally accurately estimate the sorption capacity of the coals, exhibiting a classic Type 1 adsorption occurring.