Corrosion and corrosion control in carbon dioxide absorption process using aqueous amine solutions

Corrosion constitutes the major operating difficulty in CO₂ absorption plants using aqueous amine solutions and has a significant impact on the plant's economy. It is difficult to control corrosion problems in a cost-effective manner as knowledge of corrosion in this system is limited and inconclusive. Thus, the purpose of this thesis was to perform studies in order to obtain a better understanding of corrosion in an aqueous amine-CO ₂ environment.; This thesis provides comprehensive information on the corrosion behavior of carbon steel-1020 in an aqueous amine-CO₂ system. The direct impact of the important process parameters was investigated by conducting corrosion experiments using an electrochemical polarization technique under a wide range of test conditions. These were amine type (single and mixed amines), amine concentration (1.0 to 5.0 kmol/m3), solution temperature (30 to 80°C). CO₂ loading (0.00 to 0.40 mol/mol) and oxygen content (0 to 10% feed gas). The experimental results showed that corrosion behavior was significantly affected by the process parameters. Increases in amine concentration, solution temperature, CO₂ loading and oxygen content accelerated the rate of corrosion. Different single amines and mixed amines yielded different degrees of system corrosiveness.; To quantify the relationship between corrosion rate and the process parameters, empirical corrosion correlations for monoethanolamine (MEA), diethanolamine (DEA) and 2-amino-2-methyl-1-propanol (AMP) systems were developed by regressing the obtained corrosion data. The corrosion rate was found to obey the Arrhenius equation in conjunction with change in temperature and have a power relationship with CO₂ loading and amine concentration.; A mechanistic corrosion model, built as a Fortran-90 program, was established to identify the oxidizing agents responsible for corrosion reactions in an aqueous amine-CO₂ system. The model incorporated the rigorous electrolyte-NRTL (Austgen et al.) equilibrium model and mixed potential theory in order to simulate the concentrations of chemical species and the polarization behavior taking place at a metal-solution interface. The simulation results, based on the MEA system, indicated that HCO₃− and H₂O are the primary oxidizing agents and H+ plays an insignificant role in the reduction reaction.; In addition, this thesis investigated the possibility of using low-toxic corrosion inhibitors instead of heavy-metal inhibitors, for CO₂ absorption systems. The performance of eight low-toxic organic inhibitors (amines, carboxylic acid and sulfoxide) were evaluated by conducting electrochemical corrosion experiments with carbon steel-1020 specimens immersed in 3.0 kmol/m 3 MEA solutions under CO₂ saturation. The experimental results showed that carboxylic acid had the best inhibition performance (as high as 92%), followed by sulfoxide and long-chain aliphatic amine. Their performance depended upon inhibitor concentration and temperature.