Molecular Modeling of SOX in Supercritical CO2 Environments

Abstract The integrity of Carbon Capture and Storage (CCS) technologies is challenged by the presence of impurities in supercritical carbon dioxide (sc-CO2), compounded by limited field and laboratory data defining safe impurity limits for CO2 transport. Specifically, sulfur oxide (SOX) impurities in sc-CO2 can undergo oxidation and hydration reactions that lead to acid formation and corrosion in CO2 transport pipelines. Quantum chemical calculations were carried out using Density Function Theory (DFT) with the B3LYP method, implemented through atomistic modeling to determine the thermodynamic properties of potential reactions under sc-CO2 conditions. The study identifies SOX impurity reaction pathways in both water-solvated and sc-CO2 phases. Gibbs free energies of formation for key reactions are computed to assess their feasibility. Findings indicate that acids formed in sc-CO2 (micro-hydrated states) promote water precipitation, with SOx significantly promoting acidic phase formation under certain conditions. Several concentrations of sulfuric acid were further tested through electrochemical measurements to assess the corrosion behavior of A106 carbon steel. Based on these insights, we present an integrated framework for predicting corrosion in sc-CO2 environments. The molecular modeling results and experimental approach provide a robust framework for predicting and mitigating corrosion risks, thereby enhancing the safety and efficacy of CCS operations.