CO2 sorption on coal was estimated by two experiments, one is heat of sorption measurement and the other is 1H-NMR measurement. In the heat of sorption measurement, differential heat of sorption (qd) was compared with the calculated one. Measured qd was same value with calculated one at low pressure. It decreased gradually with pressure and became lower than the calculated one. Since it couldn't be explained by the theory based on physisorption, it is estimated that the coal-CO2 system could not be explained by only simple physisorption.
In 1H-NMR measurement, spin-spin relaxation time (T2) and composition fractions of L1, L2 and G were measured. Composition fractions and T2 of L1 increased with CO2 gas pressure. Furthermore, the correlation was observed between volume increments and dissolution amount at over 10 atm. It indicates that part of CO2 sorption capacity was used to coal relaxation.
