A new experimental method to determine the CO2 sorption capacity of coal

Enhanced Coalbed Methane production (ECBM) involves the injection of CO2 to desorb CH4 from coal seams, and offers significant potential for deploying Carbon Capture and Storage (CCS). An essential starting parameter, determined in the laboratory, is the absolute CO2 storage potential of the coal matrix, being the sum of the adsorption and pore-filling capacity. Unfortunately, conventional methods to determine storage capacity in the laboratory (i.e. the manometric and gravimetric sorption methods) may be subject to errors. Although many improvements are made to these techniques, there is no independent method available to determine the uptake of CO2 in the coal matrix. We report a newly developed technique that directly measures CO2 uptake of solid coal matrix cylinders, without the application of the EoS for CO2 or volumetric corrections of any kind. The technique makes use of a capsule composed of ductile metals (Au and In) to jacket a coal matrix sample, and traps the CO2 taken up by coal matrix samples directly. The samples were saturated with CO2 at a fixed CO2 pressure between 0 and 16 MPa and a temperature of 40 °C. Our results show that (1) nearly all of the CO2 present in our samples is adsorbed to the coal surface, and (2) the uptake of CO2 by our samples is directly dependent on the chemical potential of free CO2. Further testing is however required to understand the adsorption behaviour of our samples, and to assess the broader applicability of the new technique