CO2 Sequestration: Temperature and Gas Compositional Effects on the Kinetics and Mineralogical Reactions
Prashanth N. Mandalaparty1, Kyeongseok Oh, Milind Deo, and Joseph Moore2. (1) Chemical Engineering, University of Utah, 50 S Central Campus Drive Merill Engineering Building Rm 3290, Salt Lake city, UT 84112, (2) Energy and GeoSceince Institue, University of Utah, 423 Wakara Way suite 300,, Salt Lake City, UT 84108
The alarming rate of the CO2 emissions, which is eventually the main cause for global warming, is increasing the concern for the growing need to look for different means of depositing the atmospheric carbon dioxide. Geological sequestration of CO2 seems to provide an answer to this problem, where CO2 is concentrated and pumped into deep saline aquifers, coal formations or depleted oil reservoirs. Despite the care taken during the purification and isolation of flue gases from coal fired power plants, there are traces of other gases such as SO2 remain in the flue gas stream. The reactive behavior of pure CO2, CO2+ SO2 within this geologically and chemically complex environment is being studied. The experimental apparatus consists of a series of 6 isolated high pressure reactors operated at different conditions and with different feed gas compositions to study and observe the mineralogical changes in both the rock and water chemistries. A 3g rock sample was prepared by mixing equal amounts of finely ground (100μm) quartz, calcite, andesine, dolomite, chlorite and magnesite, which is usually called arkose or dirty sand. Brine was prepared from laboratory grade sodium chloride with a concentration of 2g/30cc. The long term batch experiments with pure CO2 as feed gas were carried out at 100C and 200C as different sets in four separate reactors to evaluate the dependence of kinetics and the mineralogical changes on temperature. The operating pressure was constant at ~2000PSI. The system operating at 200C and 2000PSI was held at these conditions for a period of 37 days before depressurizing. The system held at 100C and 2000PSI was depressurized after a period of 62 days. The mineralogical changes in the rock were analyzed using SEM/EDS and XRD analysis. The brine chemistry was analyzed using ICP-MS for cations and ion chromatography for anions. Each mineral in this complex geological environment shows evidence of participating in the geo-chemical reactions. On analyzing the system which was at 200C and 2000PSI for changes in the rock compositions, interesting results were found. Layers of calcite were seen growing on the surface of the arkose. Analcime deposits are almost omnipresent either occurring as large connected aggregates or as deposits on the surfaces of other minerals. Ankerite deposition was observed as an amorphous mass intergrown with the starting minerals. The growth of these new phases indicates the complex geo-chemical interactions taking place. The temperature dependence of these reactions is being evaluated by analyzing the set of experiments carried out at 100C and 2000PSI. The changes in the brine chemistry for both sets are being analyzed. The rates of these reactions will be computed by computing the changes in the compositions of the initial and the final rock samples provided by the XRD analyses and its dependence on temperature will be evaluated. The experiments with 10%SO2 and 90% CO2 are being carried out in which anhydrite precipitation and dolomite deposition are expected due to increased acidity and sulphate concentration. The data has been analyzed in light of the published equilibrium and kinetic models. These experiments will help in evaluating the gas compositional effects on the kinetics and the mineralogical reactions.