Chemistry Theory and Threshold Definition for Reactions and Precipitation in Impure CO2 Transport

Abstract To identify and control the impurity content of CO2 within a non-corrosive range is crucial for Carbon Capture and Storage (CCS)-hub projects that aim to capture CO2 for a wide range of industries. Each CO2 source in combination with its capture process carries their own specific spectrum of impurities (H2O, SOx, H2S, NOx, O2, etc.). Upon mixing or a change in the conditions, these impurities react and may separate out as solids or a polar phase containing water and reaction products such as sulfuric- (H2SO4) and nitric acid (HNO3). Test data have been investigated using chemical equilibrium calculations (CEC) and the definition of an equivalent sulfuric acid concentration Cacid was found to correlate with precipitation. From the CEC the reaction tendency of the composition can be characterised by oxidizing strength (or tendency), and hydration strength (as can be plotted in a stability diagram). Besides the CEC calculated Cacid, an excess of oxygen has also shown to affect the threshold for acid formation and precipitation. Gaps between solubility data from uptake of acid versus formation and precipitation have been identified and attributed to chemical kinetics (incomplete conversion) and phase behaviour kinetics. This paper summarizes the mechanism leading to acid formation and precipitation, and provides an overview of key test results in combination with CEC.