Corrosion of Low Alloyed Steel in Mono Ethanol Amine Solution

Abstract

In this work the corrosion rate of UNS⁽¹⁾ K12000 (DIN ⁽²⁾ 17100 ST 52) low-alloy structural steel in monoethanolamine (MEA) solution was studied. The corrosion testing was mainly performed on a rotating disc electrode, and electrochemical impedance was used to estimate the corrosion rate. The parameters studied were rotation rate, influence of oxygen and degradation of the MEA. The results shows a significant increase in the corrosion rate when oxygen was introduced to the system, especially when the rotation rate was high. The corrosion also increased when the MEA solution was degraded.

Introduction

During the last decades CO₂ emissions have gained a lot of attention due to their role in global warming. Aqueous alkanolamines can be used for CO₂ capture from the flue gas of a power plant. The alkanolamine selectively absorbs the CO₂ in an absorber column at low temperature and is then sent to a stripper. In the stripper, the CO₂-rich alkanolamine solution is heated to release almost pure CO₂. The lean alkanolamine solution is then recycled back to the absorber. The idea is further to transport the pure CO₂ into sequestration underground. Among the best suited alkanolamines to be used in a large scale process is MEA.

Corrosion in process equipment in alkanolamine CO₂ separation plants can be a serious problem. ¹ The anode reaction in the system is dissolution of iron metal. Oxygen is present in flue gas, and the cathode reaction can be both oxygen reduction and hydrogen evolution. ²

Corrosion in amines can increase by degradation of amines and formation of heat-stable salts; in particular, oxalic acid accelerates the corrosion. ^3-5 The thermal energy requirement for CO₂ separation decreases significantly with increasing MEA concentration, but higher MEA concentration is also expected to have a pronounced corrosive effect. ⁶ Stress corrosion cracking or hydrogen embrittlement can be a dangerous problem in MEA plants. In 1984 an amine absorber pressure vessel containing MEA ruptured because of hydrogen induced cracking, and 17 lives were lost.^{1, 7, 8}