3rd Post Combustion Capture Conference (PCCC3)
Speciation of iron in MEA solutions: Solubility and Corrosion
Georgios Fytianos, Muhammad Awais, Hanna Knuutila* and Hallvard F. Svendsen
Department of Chemical Engineering, Norwegian University of Science and Technology, N-7491 Trondheim, Norway
Abstract
Corrosion is one of the main challenges in amine based post-combustion CO2 capture. Investigating the parameters that affect
corrosion aggravation or inhibition is of great importance for the further research and development of post-combustion CO2
capture. Some iron compounds have a catalytic role in the degradation of solvents while others can increase the corrosion rate.
The target of this work is to study the speciation of iron in MEA based plants. Towards this direction, experiments focused on the
identification of the various corrosion products, their solubility and their role in the degradation rate. One of the main examined
products was iron carbonate (FeCO3).
Keywords: iron carbonate ; MEA ; corrosion
1. Introduction
Corrosion is one of the main challenges in post-combustion CCS affecting solvent performance efficiency, plant
operation and safety. Since corrosion cannot be avoided, it has to be studied in detail in order to obtain the optimized
materials, inhibitors and process parameters. Various corrosion products can have a catalytic role in the degradation
of MEA. Degradation and corrosion are closely tied in post-combustion CO2 capture (PCCC) plants. Investigating
the parameters that can enhance corrosion is of great importance for the PCCC research and development. The aim
of this work is to study the various iron products which are present in a plant in terms of degradation and corrosion
effect. Some of these products might have a catalytic effect while other might work as corrosion inhibitors.
Furthermore, the solubility of iron products (e.g. iron carbonate, FeCO 3) was measured. Tsuda et al. 1 studied the
effect of iron carbonate on the corrosivity of amine solutions in CO 2 removal units. They reported that corrosion was
inhibited by the formation of FeCO3 scale and further investigated the relationship between solubility and corrosion.
* Corresponding author. Tel.: +47 73594119; fax: +47 735 94080.
E-mail address: [email protected]
2. Materials and Methods
In order to identify the various corrosion products that were formed during the process, X-ray powder diffraction
(XRD) was used. The 316 Stainless steel specimens that were used in thermal degradation experiments were
examined with XRD. The thermal degradation experimental procedure was similar to the one that is described in
Fytianos et al.2 .After the thermal degradation experiments, in almost all of the stainless steel specimens, iron
carbonate was one of the identified compounds. Therefore, in this study, special focus was placed on iron carbonate.
The solubility apparatus used in this work is presented schematically in Figure 1. Inside the glass cell, the MEA
solution is stirred with a Teflon covered stirrer throughout the experiment. For the iron carbonate solubility test,
known amounts of FeSO4 were introduced into the solution. Before each solubility experiment, CO2 gas was
injected into the solution until a desired CO2 partial pressure was reached while the temperature was set to the
required value. For a specific temperature, sampling was undertaken every 24 hours. The total experimental was 72
hours. After sampling, the solution was filtered with a 0.22 μm pore size filter. During each experiment, pH and
temperature were monitored. Total iron was measured with ICP-MS while Fe(II) ion was quantified as a complex
with UV-VIS. For the iron carbonate solubility test, FeSO4 was added to the 30wt% MEA solution. The ferrous iron
concentration could be approximately calculated from the added amount of FeSO4. FeSO4 was added until a visible
precipitate was observed. Ion Chromatography (IC) was used for identification and quantification of glycolate,
propionate, formate, oxalate and acetate formed as degradation products. Higher concentrations in HSS anions (i.e.
formate) would indicate higher degradation. The anions were analysed with a conductivity detector on an ICS-5000
RFIC ThermoScientific System equipped with AS15 analytical column and an ASRS300 suppressor.
Figure 1: Schematic figure of solubility apparatus
3. Results and Discussion
The total iron concentration in an supersaturated ferrous solution in 30wt% MEA with Fe(II) was measured.
Samples after 24, 48 and 72 hours were analyzed with ICP-MS (Figure 2). Tsuda et al.1 used an assumption for the
direct correlation of Fe(II) concentration and the FeCO3 solubility. As it can be observed from Figure 2, the total
iron concentration decreased with increasing temperature at a specific time. Results for ferrous and total iron
concentration will be presented. From literature data3, it is known that FeCO3 solubility in water decreases with
increasing temperature. More solubility results will be presented as well as a discussion on the correlation between
solubility and production rate for the various corrosion products.
Figure 2: ICP-MS results for total iron concentration for the MEA-FeSO4 solution
References
1.
Tsuda, Takahiro, Takeda, Masashi and Hosoya, Keizo. (2010). Effect of iron carbonate on the corrosivity
of amine solutions in CO2 removal units. JGC Corporation, Yokohama 220-6001, Japan. NACE
International Corrosion 2010.
2.
Fytianos, Georgios; Grimstvedt, Andreas Magnar; Knuutila, Hanna; Svendsen, Hallvard Fjøsne. (2014)
Effect of MEA's degradation products on corrosion at CO 2 capture plants. Energy Procedia. vol. 63.
3.
Wei Sun, Srdjan Nešic, Richard C. Woollam. (2009). The effect of temperature and ionic strength on iron
carbonate (FeCO3) solubility limit. Institute for Corrosion and Multiphase Technology, Department of
Chemical Engineering, Ohio University, Athens, OH 45701, USA. BP America Inc., Houston, TX 77079,
USA. Corrosion Science 51 (2009) 1273–1276