Carbon Sequestration in Coal Seams: Defining the Nature of the Interactions Between CO2 and Coal
The CO2 storage capacity in coal seams is typically estimated from isotherm measurements obtained from manometric techniques. In the calculation of the isotherm, two major parameters must be estimated. First, the compressibility factor must be calculated from an equation of state to account for the non-ideality of CO2 at elevated pressures. Second, the volume change associated with the volume occupied by the sorbed CO2 must be estimated. These two parameters can dramatically affect the shape of the CO2-coal isotherm. Of the few papers that published CO2–coal isotherms at high pressures, a variety of curve shapes have been reported. This lack of agreement reduces the confidence in the accuracy of CO2 storage capacities estimated from volumetric isotherm measurements. In this study, the direct interaction between CO2 and two Argonne premium coals [Pocahontas #3 (low volatile bituminous) and Beulah Zap (lignite)] was probed using Attenuated Total Reflectance – Fourier Transform Infrared (ATR-FTIR) spectroscopy at 328 K and pressures up to 8.0 MPa. Sorbed CO2 on Argonne coals was detected at 2335 cm-1 for Buelah Zap coal and 2332 cm-1 for Pocahontas #3 coal. The energy of adsorption (18.8 - 20.5 kJ/mol), estimated using the Langmuir equation, was consistent with physisorption. The spectral data indicated that only one type of site was available for sorption. No evidence could be found for specific interactions between CO2 and oxygen functional groups in the coals. The CO2-coal sorption isotherm was derived without estimating the CO2 compressibility and adsorbed layer density, both of which are needed in manometric techniques. The ATR-FTIR isotherms (units of net absorbance) and manometric isotherms (units mmol/g) compare well below the critical temperature providing some confidence in the values selected for the gas phase density and adsorbed layer density that were used to calculate absolute adsorption from the manometric data. In summary, we find that sorption of CO2 is energetically similar for the two coal types, is due only to London forces and quadrupole interactions, and occurs preferentially on a hydrocarbon site.
- Research Organization:
- National Energy Technology Laboratory (NETL), Pittsburgh, PA, Morgantown, WV, and Albany, OR (United States)
- Sponsoring Organization:
- USDOE - Office of Fossil Energy (FE)
- DOE Contract Number:
- None cited
- OSTI ID:
- 923843
- Report Number(s):
- DOE/NETL-IR-2005-072; TRN: US200805%%76
- Resource Relation:
- Conference: 2005 International Coalbed Methane Symposium, Tuscaloosa, AL, May 16-20, 2005
- Country of Publication:
- United States
- Language:
- English
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