(754g) Thermodynamic Modelling of FeCO3 Solubility Using the Extended Uniquac Model

CO₂ corrosion is receiving more attention these days, as we need to reduce the emission of greenhouse gases. CO₂ is present in many processes including biogas, carbon capture and storage, the cement-, and in the oil and gas industries, and their presence result in corrosion of the equipment and pipelines, which over time will lead to significant production losses and costly shutdowns.

One way to reduce corrosion is to engineer/manipulate/tailor the precipitation of the protective layer formed by FeCO₃. Detailed knowledge of the FeCO₃ solubility is important in the prediction on CO₂ corrosion as studies suggest that the protective layer is not forming below 60 °C[1]–[5].

This study focus on the thermodynamic modelling of FeCO₃ solubility in water, salt solutions, and under the influence of CO₂ partial pressure. The purpose is to create a thermodynamic model, which describes these systems. It is important that the model is able to accurately predict phase equilibria and physical/chemical properties of this system. The Extended UNIQUAC model is applied as it has previously been shown to be able to model these kind of systems [6]. Parameters in the thermodynamic model are determined based on the obtained experimental data.

The interaction parameters, u⁰ and u^T, the surface, and volume parameters, r and q used in the Extended UNIQUAC model are fitted using experimental SLE data. The parameters in the model are optimized by minimizing the sum of squared residuals of each data point.

Through comparing the obtained experimental SLE data with the model, the validity/ability of the Extended UNIQUAC is corroborated.

This work is relevant for future understanding, and process simulation of systems dealing with CO₂ corrosion.

References

[1] S. Kakooei, M. C. Ismail, B. Raja, H. Mohebbi, S. S. Emamian, and M. Moayedfar, “Formation of nano-scale FeCO3 protective corrosion product in carbon dioxide-saturated 3% sodium chloride solution,” Key Eng. Mater., vol. 740 KEM, no. June, pp. 3–8, 2017.

[2] J. Hernandez, A. Munoz, and J. Genesca, “Formation of iron-carbonate scale-layer and corrosion mechanism of API X70 pipeline steel in carbon dioxide-saturated 3% sodium chloride,” AFINIDAD LXIX, vol. 560, pp. 251–258, 2012.

[3] W. Farida, T. Hemmingsen, T. Berntsen, and P. Rabindran, “Effect of Precorrosion and Temperature on the Formation Rate of Iron Carbonate Film,” Pipeline Technol. Conf., 2012.

[4] A. Kahyarian, M. Achour, and S. Nesic, CO2 corrosion of mild steel. Elsevier Ltd, 2017.

[5] G. Schmitt and Michaela Hörstmeier, “Fundamental aspects of CO2 metal loss corrosion - Part II: Influence of different parameters on CO2 corrosion mechanisms,” Corrosion, vol. 06112, pp. 1–26, 2006.

[6] K. Thomsen, “Aqueous electrolytes : model parameters and process simulation,” Ph.D thesis, DTU, 1997. https://doi.org/10.11581/dtu:00000074