In Situ Observation of CO₂ Sequestration Reactions Using a Novel Microreaction System

A novel, externally controlled microreaction system has been developed to provide the first in situ observations of the reaction processes that control CO₂ sequestration via mineral carbonation. The system offers pressure (to 20 MPa), temperature (to 250 °C), and activity control suitable for investigating a variety of fluid-fluid and fluid-solid interactions of environmental interest. Mineral sequestration efforts to date have effectively accelerated carbonation, a natural mineral weathering process, to an industrial timescale. However, the associated reaction mechanisms are poorly understood, limiting further process development. Synchrotron X-ray diffraction and Raman spectroscopy have been used to provide the first in situ insight into the associated supercritical mineral carbonation process. Magnesite was found to form directly under the reaction conditions observed (e.g., 150 °C and 15 MPa CO₂), facilitating geologically stable sequestration. Thermodynamic analysis of fluid-phase species concentrations in the Na⁺ buffered H₂O-CO₂ reaction system found the primary aqueous reactant species to be CO₂(aq) and HCO ₃^-, with CO₂(aq) more prevalent under the reaction conditions observed. The microreactor provides a powerful new tool for in situ investigation of a broad range of environmentally, fundamentally, and commercially important processes, including the reactions associated with geological carbon dioxide sequestration.