Long-Term CO2 Sorption on Upper Freeport Coal Powder and Lumps

Powder and lumps of the Argonne Premium Upper Freeport coal were compared in a 9-month-long CO 2 sorption−desorption study. On the basis of the slope analysis, CO 2 induced the lumps swelling by 7%. The powder swelled by 8% and then rapidly shrank by 3% on desorption. This was verified by a “single point” injection of helium and the pressure-and-density technique, which was sufficiently sensitive. Low-pressure Langmuir-fit parameters suggest that the microporous textures of the powder and lumps are similar. The samples demonstrated greatly increased sticking coefficients and a slightly larger number of the “sorption ready” sites, after the CO 2 -induced swelling and structural rearrangement resulted in variable degrees of the matrix shrinkage. No permanent changes in the void volume and dry mass were detected after complete desorption. The observed hysteresis in sorption−desorption behavior of both samples upon the approach to the CO 2 density fluctuation ridge is interpreted as a contribution of condensation and coalescence of CO 2 clusters in mesopores. The differences between the two samples in the magnitude of the enhanced capillary condensation, with or without dissolution, demonstrate the importance of changes in mesoporous texture caused by grinding of coal lumps into powder.