Measurement techniques for carbon dioxide sorption capacity on various coal samples: critical review

Underground carbon sequestration is proposed as a geologic disposal technique for the long-term storage of CO2 emissions to mitigate climate change and air pollution. Coal bed seams have large CO2 adsorption capacity, long time CO2 trapping and extra enhanced coal-bed methane recovery (CBM). However, CO2 sorption capacity is one of significant steps required to be determined accurately in any feasibility evaluation of carbon sequestration. Hence, in lab scale, there are three methods for CO2 adsorption capacity measurements namely manometric volumetric, gravimetric and new capsule techniques for gas sorption on variety of sorbents. The manometric and volumetric methods require accurate determination of cell and void volumes and suitable equation of state (EoS). The gravimetric method requires a very accurate sensitive balance and less buoyancy effect and it is the best technique for small amounts (milligrams) of sorbents and the adsorption equilibrium can be mentored. Among all gas adsorption measurement techniques, the newly developed method "capsule method" exhibits the highest CO2 adsorption capacity on Polish coal by 4.08 mmol g because capsule method that directly measures CO2 uptake of solid coal matrix cylinders, without the application of the equation of state (EoS) for CO2 or volumetric corrections. The main advantage of capsule method is that it is independent of any Equation of State (EoS), and it has no volumetric effects or impurities distort the shape of the gas adsorption isotherm. The disadvantage of capsule method is time-consuming and it is not easy to implement.