The Effect of Methanol in an Acid Producing CO2 Specification

Abstract Specifications for CO2 transport are currently being developed to prevent acid or solid dropouts. While some chemical reactions will be permitted, any reaction product must remain dissolved within the CO2 stream and stay below their solubility limits to meet specification requirements. Sulphuric acid, due to its low solubility, is likely to exceed these limits and pose a corrosion risk. Other reactions could result in formation of elemental sulphur and various salts which may challenge the integrity of the transportation system. The impurities composition which will lead to acid formation is well known through extensive testing with H2O, O2, SO2, H2S, and NO2. Presence of other impurities could influence these reactions, but the practical effect is currently not known. A transparent autoclave equipped with individual injection lines for each impurity was used to simulate the transport environment. Carbon steel samples from welded pipes, produced by a Southern European manufacturer, sourced from both base and welded sections, were suspended in the bulk CO2 to ensure exposure only to dissolved species. Any excess acid formed during the reactions settled at the bottom of the autoclave, preventing direct contact with the test specimens. The reacted impurities were measured to identify possible reactions and observe if there was a difference in the present of methanol. This study investigated the corrosion behaviour of carbon steel exposed to CO2 with an impurity composition that produced strong acids. The effect of methanol addition was studied in one experiment.