Electrolyte Equation of State The Electrolyte Equation of State is described as follows :

1. Solubility of CO2 in Aqueous Blends of Piperazine and N-Methyldiethanolamine P.W.J. Derks, J.A. Hogendoorn, G.F. Versteeg Dept. of Science & Technology, University of Twente, Enschede, The Netherlands Summary / Conclusion Experimental data are reported on the equilibrium solubility of carbon dioxide into aqueous mixtures of N-methyldiethanol- amine (MDEA) and piperazine (PZ). The Electrolyte Equation of State was used to correlate the experimental data and it was found to describe the CO2-H2O-PZ-MDEA system reasonably well over a wide range of conditions. Electrolyte Equation of State The Electrolyte Equation of State is described as follows : The structure of the final model, and the determination of various interaction parameters is as follows: §Taken from PZ-H2O-CO2 subsystem [Derks et al., AIChE J 2005] # Taken from MDEA-H2O-CO2 subsystem Experimental Results Experimental setup has been validated on CO2 solubility into aqueous 2.0 M MDEA solutions at 40 °C. Carbon dioxide solubilities have been measured in aqueous solutions of 2.8 M MDEA and 0.7 M PZ at 30 and 50 °C. Modelling Results The model was used to correlate the available experimental data. Results are shown in the figure and table below. Speciation of a 3 M MDEA, 1 M PZ solution, loaded with 0.52 mol mol-1 CO2: a Bishnoi & Rochelle, IECR 2003 • Discussion • The CO2 solubility data in aqueous MDEA were in very good agreement with literature. The new solubility data in aqueous PZ-MDEA show a linear trend when plotted on a log-log scale (pressure vs. loading), which is typical for VLE data in amine solutions at low carbon dioxide loadings. Both phenomena indicate that the current experimental results can be regarded as reliable • The Electrolyte EoS model is able to correlate the available experimental solubility data well. However, the very limited speciation data indicate that the prediction of the liquid phase speciation of the EoS model needs improvement The financial support of Shell Global Solutions International NV is gratefully acknowledged. This research is part of the CATO programme, the Dutch national research programme on CO2 Capture and Storage. CATO is financially supported by the Dutch Ministry of Economic Affairs (EZ) and the consortium partners. (www.co2-cato.nl)