Sheila W. Hedges

Measurement and Modeling of CO2 Solubility in Natural and Synthetic Formation Brines for CO2 Sequestration

CO2 solubility data in the natural formation brine, synthetic formation brine, and synthetic NaCl+CaCl2 brine were collected at the pressures from 100 to 200 bar, temperatures from 323 to 423 K. Experimental results demonstrate that the CO2 solubility in the synthetic formation brines can be reliably represented by that in the synthetic NaCl+CaCl2 brines. We extended our previously developed model (PSUCO2) to calculate CO2 solubility in aqueous mixed-salt solution by using the additivity rule of the Setschenow coefficients of the individual ions (Na(+), Ca(2+), Mg(2+), K(+), Cl(-), and SO4(2-)). Comparisons with previously published models against the experimental data reveal a clear improvement of the proposed PSUCO2 model. Additionally, the path of the maximum gradient of the CO2 solubility contours divides the P-T diagram into two distinct regions: in Region I, the CO2 solubility in the aqueous phase decreases monotonically in response to increased temperature; in region II, the behavior of the CO2 solubility is the opposite of that in Region I as the temperature increases.

Exploratory study of some potential environmental impacts of CO2 sequestration in unmineable coal seams

An initial investigation into the potential environmental impacts of CO2 sequestration in unmineable coal seams has been conducted, focusing on changes in the produced water during enhanced coalbed methane (ECBM) production, using a CO2 injection process (CO2-ECBM). A high volatile bituminous coal, Pittsburgh No. 8, was reacted with synthetic produced water and gaseous carbon dioxide at 40C and 50 bar to evaluate the potential for mobilisation of toxic metals during CO2-ECBM/sequestration. Microscopic and X-ray diffraction analysis of the post-reaction coal samples clearly show evidence of chemical reaction and chemical analysis of the synthetic produced water shows substantial changes in composition. These results suggest that changes to the produced water chemistry and the potential for mobilising toxic trace elements from coal beds are important factors to be considered when evaluating deep, unmineable coal seams for CO2 sequestration.

Selective catalytic reduction of nitric oxide over copper oxide and cerium oxide catalysts

The selective catalytic reduction of nitric oxide with hydrocarbons in an oxygen-containing simulated flue gas has been investigated for a series of copper oxide and cerium oxide alumina supported catalysts at 600–775 K. The activity of these catalysts for the reduction of NO by methane or propane has been investigated in simulated flue gas. The effects of sulphates on the catalyst, and of water vapour and/or gaseous sulphur dioxide have been examined for both the SCR of NOx by propane and direct decomposition of NO. Both copper sulphate on alumina and cerium sulphate on alumina are substantially less active for propane SCR than the respective oxides. Both catalyst types are reversibly inhibited by the presence of water vapour. The effect of sulphur dioxide in the gas stream appears to be only mildly inhibiting, but since the optimum temperature range for propane reduction of NO is the same as the optimum temperature range for SO2 absorption, the CuO/Al2O3 sorbent/catalyst will quickly become sulphated, even at low flue gas SO2 concentrations. Methane was also examined as a reductant, and neither copper oxide/alumina nor cerium oxide/alumina is active for selective catalytic reduction of NOx with methane up to 775 K.