Coal lithotypes before and after saturation with CO2; insights from micro- and mesoporosity, fluidity, and functional group distribution

Abstract

Abstract Four lithotypes, vitrain, bright clarain, clarain, and fusain, were hand-picked from the core of the Pennsylvanian Springfield Coal Member (Petersburg Formation) in Illinois. These lithotypes were analyzed petrographically and for meso- and micropore characteristics, functional group distribution using FTIR techniques, and fluidity. High-pressure CO 2 adsorption isotherm analyses of these lithotypes were performed and, subsequently, all samples were reanalyzed in order to investigate the effects of CO 2 . After the high-pressure adsorption isotherm analysis was conducted and the samples were reanalyzed, there was a decrease in BET surface area for vitrain from 31.5 m 2 /g in the original sample to 28.5 m 2 /g, as determined by low-pressure nitrogen adsorption. Bright clarain and clarain recorded a minimal decrease in BET surface area, whereas for fusain there was an increase from 6.6 m 2 /g to 7.9 m 2 /g. Using low-pressure CO 2 adsorption techniques, a small decrease in the quantity of the adsorbed CO 2 is recorded for vitrain and bright clarain, no difference is observed for clarain, and there is an increase in the quantity of the adsorbed CO 2 for fusain. Comparison of the FTIR spectra before and after CO 2 injection for all lithotypes showed no differences with respect to functional group distribution, testifying against chemical nature of CO 2 adsorption. Gieseler plastometry shows that: 1) softening temperature is higher for the post-CO 2 sample (389.5 °C vs. 386 °C); 2) solidification temperature is lower for the post-CO 2 sample (443.5 °C vs. 451 °C); and 3) the maximum fluidity is significantly lower for the post-CO 2 sample (4 ddpm vs. 14 ddpm).