Experimental Study of Organic Ligand Transport in Supercritical CO2 Fluids and Impacts to Silicate Reactivity

AbstractThe interactions between water-saturated supercritical carbon dioxide, organics, and minerals are relatively unknown despite being important to carbon sequestration and enhanced hydrocarbon recovery activities. The goals of this study include verification of organic transport through scCO2 and exploration of whether organic ligands can impact carbonate formation. An in situ near-infrared spectroscopic technique was used to probe supercritical CO2 (scCO2)-organic mixtures at 35°C and 100bar. Observation of C-H bands in the spectra collected from scCO2 equilibrated with a Ca-acetate solution (1.7 m) provided direct evidence of organic partitioning into the scCO2 phase. A series of high pressure X-ray diffraction experiments at 50°C and 90bar were performed to investigate how citrate (0.01-0.5 m) affected the coupled dissolution of forsterite and precipitation of magnesium carbonates in scCO2. In control experiments where no citrate was present, nesquehonite (MgCO3·3H2O) was initially produced as a metastable intermediate that was then converted to magnesite (MgCO3). However, experiments with citrate promoted magnesite, rather than nesquehonite, precipitation, and at the highest concentrations reduced the extent of the carbonation reaction. This paper discusses these unique findings on organic and scCO2 interactions that are not currently being considered in the fate and transport of CO2 in the subsurface