Argonne Coal Structure Rearrangement Caused by Sorption of CO₂

Abstract

The exposure of powdered unconfined coals to CO 2 results in changes in the coals' physical structures. The presence of water changes the behavior of the coals on exposure to CO 2 . The sorption of CO 2 on seven Argonne premium coals was measured by using attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy as a function of time at constant CO 2 pressure (∼0.62 MPa) and temperature (55 °C). The depth sampled is at least 1 µm, and this ensures that both the bulk and surface of the sample were interrogated. Concentrations of CO 2 in the top 1-7 µm of the coal were measured by using the peak area of the CO 2 ATR-FTIR band near 2333 cm -1 . Diffusion rates were measured by using the time dependence of the area of the 2333 cm -1 band. Surface adsorption is effectively instantaneous. The coals were either extensiVely or briefly dried. The coals were exposed to CO 2 , evacuated, and then exposed to CO 2 a second time. For the extensively dried coals, removal of the CO 2 under vacuum was much faster than CO 2 sorption, indicating a coal structure change caused by CO 2 sorption. The diffusion rate of the CO 2 into the coal was much faster for the second exposure, confirming that the coal underwent a physical structure rearrangement. Structure rearrangement was observed for all seven extensively dried coals and for the Pittsburgh No. 8 briefly dried coal. The presence of residual moisture in the briefly dried coal samples appeared to inhibit or block CO 2 uptake as equilibrium was reached within minutes. The second exposure of the briefly dried coals universally resulted in greater CO 2 uptake that was again instantaneous on our experimental time scale.

Swelling and sorption experiments on methane, nitrogen and carbon dioxide on dry Selar Cornish coal

“…Our equilibration time is much longer than the one reported in Table 4, apart for Majewska et al (2009) who was working with coal blocks and Goodman et al (2006) who plotted pressure decrease versus the squared root of time.…”

“…The equilibration time depends on gas, temperature of the system and the grain sizes of coal used in the experiments. A few authors studied the kinetics of the gas sorption on coal (Clarkson and Bustin, 1999b;Siemons et al, 2003;Busch et al, 2004;Solano-Acosta et al, 2004;Goodman et al, 2006;Gruszkiewicz et al, 2009). CH 4 and CO 2 adsorption occurs much faster in fine grained fractions.…”

Physical properties of selected block Argonne Premium bituminous coal related to CO2, CH4, and N2 adsorption

“…Currently there are gaps in our fundamental understanding of coal interactions with adsorbates such as the kinetics of gas transport through the coal matrix and the swelling/ shrinkage response of coal as adsorbates are introduced and removed. Native coal, defined here as coal possessing its inherent moisture as received with minimal handling and treatment, is considered to be in a strained glassy state with the potential for structural rearrangements upon exposure to CO 2 (Larsen, 2004;Goodman et al, 2005Goodman et al, , 2006. Initial exposure of briefly dried coal to CO 2 leads to physical structural rearrangement (Goodman et al, 2006).…”

“…Native coal, defined here as coal possessing its inherent moisture as received with minimal handling and treatment, is considered to be in a strained glassy state with the potential for structural rearrangements upon exposure to CO 2 (Larsen, 2004;Goodman et al, 2005Goodman et al, , 2006. Initial exposure of briefly dried coal to CO 2 leads to physical structural rearrangement (Goodman et al, 2006). Significant differences in acoustic emission signal between the first and subsequent adsorption cycles provides further evidence of structural rearrangements during the first CO 2 adsorption cycle for dried coal (Majewska and Zietek, 2007).…”

Three-dimensional carbon dioxide-induced strain distribution within a confined bituminous coal

“…The imbibition or dissolution of carbon dioxide, a powerful coal plasticizer, results in the physical structure relaxation and rearrangement (Larsen, 2004;Goodman et al, 2006). Larson and co-workers suggested that rearrangement will induce substantial increase in the self-diffusivity of CO 2 in the coal matrix, although it also appears that as the structure undergoes volumetric relaxation, the excess free volume associated with the glassy state is reduced, resulting in lower diffusion (Duda et al, 1994).…”