Corrosion Behavior of Carbon Steel in CO_2 Saturated Amine and Room Temperature Ionic Liquid Solutions

摘要

The aggressive corrosive behaviour of conventional amines is one of main barriers against large-scale commercial amine based CO_2 capture processes. This work shows a recent investigation on the corrosion behaviour of carbon steel CS1018 in three CO_2 absorbents classes. The first class focused on the classical amine solutions; monoethnaolamine (MEA), diethanolamine (DEA) and methyl diethanolamine (MDEA). The second-class included the use of piperazine (PZ) promoter mixed with the same amines used in the first class making them advanced amine CO_2 absorbents. The third class includes the novel mixtures of classical amines and room temperature ionic liquids (RTIL). Imidazolium-based ILs with different anions namely; 1-butyl-3-methyl imidazolium tetrafluoroborate ([C_4MIM][BF_4]), 1-butyl-3methyl imidazolium trifluoromethanesulfonate ([C_4MIM][Otf]), tributyl(methyl)phosphonium acetate ([P4441][Ac]) and choline acetate ([Ch][Ac]) were used in the experiments. Electrochemical polarization techniques were used to determine the absorbent corrosiveness via corrosion rate and polarization behaviour experiments. The process parameters of interest were CO_2 loading and test temperature. In single amine systems, the corrosivity order of CO_2 saturated amines was governed mainly by their characteristic CO2 absorption capacity. Corrosivity order ranking of classical amines at 40 °C was obtained as MDEA > MEA > DEA and the ranking changed to MEA > DEA > MDEA at 80 °C. Piperazine activated amines resulted in lower corrosion rates and higher CO_2 absorption capacity compared to single classical amines. At CO_2 saturation and 80 °C corrosivity ranking was MEA > MEA/MDEA > MEA/PZ > MEA/MDEA/PZ > MDEA > MDEA/PZ. The results of MEA/RTIL mixtures showed that the partial replacement of aqueous phase in MEA solution by hydrophilic RTIL reduced corrosion rates by 40 to 70% compared to aqueous MEA solution. MEA/[P4441][Ac] and MEA/[Ch][Ac] showed promising corrosion inhibition performance compared to imidazolium-based RTILs with corrosivity ranking of MEA/[P4441][Ac] > MEA/[Ch][Ac] > MEA/[C_4MIM][BF_4] at 25 °C and CO_2 saturation condition.