Manometric Sorption Measurements of CO₂ on Moisture-Equilibrated Bituminous Coal

Gas sorption isotherms have been measured on dry and wet Tupton coal at 318.15 K up to a pressure of 160 bar with the manometric method. The aim of this paper is to determine the relevance of the presence of water for CO 2 sorption on coal. The manometric method requires an accurate equation of state (EoS). Experimental measurements conducted with a density meter show that the density of the CO 2 –H 2 O mixture in the gas phase can be calculated using the Span and Wagner EoS for pure CO 2 gas. The density of the CO 2 –H 2 O mixture in the aqueous phase can be described by a Peng–Robinson–Stryjek–Vera (PRSV) EoS optimized for the CO 2 –water system. For the interpretation of the coal experiments, we also measured the adsorption of CO 2 in a wet unconsolidated sand sample. We show that adsorption experiments follow the computations with the PRSV EoS. These experiments also allows us to determine the partial molar volume of CO 2 in water, which agrees well with the literature data. Given the small amount of water in the coal, adsorption of CO 2 in water only gives a small contribution. For the coal experiments, we used a Monte Carlo simulation to establish the error on the excess sorption measurements. Errors ranged from a minimum of 0.6% to a maximum of 4.2%. A comparison of the dry and wet coal samples shows that the presence of 4.6% water in the coal reduces the maximum sorption capacity by 16%.