Corrosion Behavior of Carbon Steel in Piperazine Solutions for Post-Combustion CO2 Capture
Authors: Zheng Liangfu 
Published: February 2020

L. Zheng, J. Landon, W. Zou, J. E. Remias, K. Liu
Center for Applied Energy Research, University of Kentucky, 2540 Research Park Drive, Lexington, KY 40511-8410, United States
Anthropogenic carbon dioxide generation from the combustion of fossil fuels such as coal and natural gas may be a factor to global climate change. One of several mitigation options is to adopt post-combustion CO2 capture and storage, which is a process consisting of the separation of CO2 from industrial and energy-related sources by typically using aqueous solutions of alkanolamines, and then transporting pressurized CO2 to a storage location for long-term isolation from the atmosphere [1-3]. However, one of the issues for the application of this process is corrosion. The documented results have shown that the CO2 captured aqueous solutions of alkanolamines without inhibitor are highly corrosive not only to carbon steels with little alloying of chromium but also to stainless steels with chromium content up to approximately 20 wt.%, which is even worse in the presence of oxygen for post-combustion application [4-6]. This can directly affect the whole system availability as well as the economics due to unplanned downtime, and reduced equipment lifetime. To decrease corrosion in current commercial CO2 capture systems but without affecting its CO2capture efficiency and significantly increasing cost, one of the methods is to apply an alternative solvent with low corrosivity [3-10].
Recent studies have shown that piperazine (PZ), a cyclic secondary amine with two nitrogen groups, has some attractive advantages [7], which make PZ a viable alternative solvent. Moreover, PZ has been routinely reported to be an effective promoter of the absorption rate in CO2 capture solutions [6, 8-10]. Investigation of the corrosion of materials in PZ is not only necessary to understand the mechanism of the corrosion of materials in the existing blends with PZ, such as promoted Methyl diethanolamine, but also to develop new PZ activated blends as well as to apply PZ as a single solvent for CO2 capture in the future. In this work, both electrochemical testing and long-term immersion testing (totaling 1050 h) were applied to investigate the corrosion of carbon steel in CO2-loaded concentrated PZ solutions.
A106 Grade B carbon steel samples, cut from pipes, were used for corrosion investigation. All of the samples were ground with SiC sand paper, and then ultrasonically cleaned with deionized (DI) water and acetone. The effects of CO2 loading on the corrosion rate of A106 in 30 wt.% PZ in the typical operational range (0.23 ~ 0.43 mol CO2/mol alkalinity) and temperatures from 20 to 80 oC were examined by electrochemical measurements such as potentiodynamic polarization and EIS. In addition, long-term immersion corrosion testing was conducted in a traditional corrosion cell for a continuous duration of 1050 h. A set of samples was removed every 150 h to study the impact of duration on the corrosion. The corrosion rate after each run was calculated on the weight loss method. Fig. 1 shows the corrosion rate of A106 as a function of immersion duration. As can be seen, the corrosion rate decreased sharply from approximately 0.14 mmpy after 150 h to approximately 0.02 mmpy after 600 h. Thereafter, a steady-state corrosion process was observed with increases in duration up to 1050 h. To understand the corrosion mechanism, X-ray Diffraction and Scanning Electron Microscopy/Energy Dispersive Spectroscopy were used to characterize the corroded samples. The details will be discussed in the following meeting.
Fig. 1 Corrosion rate of A106 in 0.43 C/N CO2-loaded 30 wt.% PZ at ~100 oC as a function of immersion duration

Acknowledgement

The authors acknowledge the Carbon Management Research Group (CMRG) members, including Duke Energy, Electric Power Research Institute (EPRI), Kentucky Department of Energy Development and Independence (KY-DEDI), Kentucky Power (AEP), and LG&E and KU Energy, for their financial support. Also, the authors acknowledge suggestions and discussions from Ayokunle Omosebi and Xin Gao, and solution analysis from Zhiao Li and Neal C Koebcke.

References

[1] B. Metz, O. Davidson, H. d. Coninck, M. Loos, L. Meyer, IPCC Special Report on Carbon Dioxide Capture and Storage, Cambridge University Press, 2005.
[2] G. T. Rochelle, Science, 325 (2009) 1652-1654.
[3] A. Kohl, R. Nielsen, Gas Purification, 5th ed., Gulf Publishing Company, Houston, 1997.
[4] M. S. DuPart, T. R. Bacon, D. J. Edwards, May (1993), 89-94.
[5] Y. Sun, J. E. Remias, X. Peng, Z. Dong, J. K. Neathery, K. Liu, Corros. Sci., 53 (2011) 3666-3671.
[6] M. Nainar, and A. Veawab, Ind. Eng. Chem. Res., 2009 (48) 9299-9306.
[7] S. A. Freeman, Thermal degradation and oxidation of aqueous piperazine for carbon dioxide capture, Ph.D. Dissertation, The University of Texas at Austin, 2011.
[8] S. Bishnoi, Carbon Dioxide Absorption and Solution Equilibrium in Piperazine Activated Methyldiethanolamine, Ph.D. Dissertation, The University of Texas at Austin, 2000.
[9] H. Dang, CO2 Absorption Rate and Solubility in Monoethanolamine/Piperazine/Water, M. S. Thesis, The University of Texas at Austin, 2001.
J. T. Cullinane, Thermodynamics and Kinetics of Aqueous Piperazine with Potassium Carbonate for Carbon Dioxide Absorption, Ph.D. Dissertation, The University of Texas at Austin, 2005