Adsorption of Supercritical CO2on Coal (Basic Experimental Study on Evaluation of Sequestable CO2 in Geologic Formation)

Research Project , Research Report 2002

Sohei SHIMADA Graduate School of Frontier Sciences, The University of Tokyo
Yoshito OOSHIMA Environmental Science Center, The University of Tokyo

Abstract

CO2Sequestration in Coal Seam is one of the options of Geologic CO2Sequestration. In this method CO2is injected into coal seam and at the same time CH4 having been adsorbed in the coal seam is recovered by a displacing mechanism. One of the expected sequestration formations is an uneconomical coal seam for mining due to large depth more than 1000m. At that depth CO2seems to be in a supercritical condition. Adsorption behavior of CO2to coal in such a condition is not yet well established. This implies that the sequestration amount of CO2on coal is not adequately calculated. From the reason described above, studies clarifying the SCF CO2adsorption on coals and finding the correlation between adsorption amount, coal properties and pore size distribution were carried out. An adsorption experimental apparatus was made under the principle of volumetric method. Two kinds of domestic coals and two types of activated carbon having different pore size distribution were used for the measurement for obtaining the adsorption isotherms. The results showed that there was not so much difference in the amount of adsorption between activated carbon and coal, though the activated carbon had much bigger surface area than that of coal. The results showed that (1) The adsorption amount of activated carbons was larger than that of coal up to critical point, (2) Increase ratio of adsorption amount was larger than that of CO2density increase in coals after critical point, (3)Any difference was not observed before and after adsorption experiment in pore size distribution and surface area. From these reasons it could be concluded that ultra-micro pores in coal are closely related to the adsorption of SCF CO2.

Keywords:

CO2, Supercritical CO2, Coal seam, Adsorption, Geologic sequestration