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 CO2 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 CO2-H2O mixture in the gas phase can be calculated using the Span and Wagner EoS for pure CO2 gas. The density of the CO2 H2O mixture in the aqueous phase can be described by a Peng-Robinson-Stryjek-Vera (PRSV) EoS optimized for the CO2-water system. For the interpretation of the coal experiments, we also measured the adsorption of CO2 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 CO2 in water, which agrees well with the literature data. Given the small amount of water in the coal, adsorption of CO2 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%.