(67f) Effects of Coal Interaction with Supercritical CO2: Chemical Structure

The study of the interactions between CO2 and coal has been gaining attention due to the potential application of CO2 sequestration in coal mines. Coal bed sequestration is an attractive approach because not only coal adsorbs CO2, but also CO2 replaces methane originally adsorbed on coal's surface. In a recent work, we reported the physical changes of coal structures after treatment [1]. The objective of this study is to enhance knowledge of solvent effects on coal chemical structure.

Lignite and bituminous coal are exposed to supercritical CO2 in a batch reactor at 80 and 130 ?aC, 2000 to 8100 psig, and with 48 h residence time. The treated coals are characterized by temperature-programmed pyrolysis (TPP) up to 1650 ?aC followed by online analysis by gas chromatography / mass spectrometer. Raw and treated samples are also characterized by Fourier-transform infrared spectrometer. Drying before treatment showed some effects on the physical structure of coal [1], and it is therefore included in the study for its chemical effects.

Results show that drying has no effect on CO emission during TPP for both bituminous coal and lignite. Interaction with supercritical CO2 drastically changes CO emission for treated bituminous coal above 1200 ?aC, but almost no notable effect on treated lignite. Treatment pressure has a significant effect on CO emission for bituminous coal. When coals are treated at higher pressures, higher CO emissions are observed during TPP.

1. Gathitu, B.B., W.Y. Chen, and M.C. MaClure "Effects of Coal Interaction with Supercritical CO2: Physical Structure," Industrial and Engineering Chemistry Research, in press, DOI: 10.1021/ie9000162, 2009.