Modelling the Fluid Phase Behaviour of Multifunctional Alkanolamines and Carbon Dioxide Using the SAFT-γ Approach

Given growing concerns on climate change, and particularly greenhouse gas emissions, the development of technologies for the capture of carbon dioxide (CO2) to prevent its release into the atmosphere is increasingly pressing. A likely medium-term solution for large-point emission sources, such as coal-or gas-fired power stations, is the use of solvent-based absorption processes. However, such processes, which often rely on the use of aqueous alkanolamine solutions as a solvent, incur a large economic penalty and it is necessary to identify alternatives that can reduce this cost. A key challenge for CO2 capture is thus the design of solvents and solvent blends with thermodynamic properties which would improve the economic performance of capture processes. Given the importance of being able to predict the thermodynamic properties of such solvents, we have developed molecular models for use with the statistical associating fluid theory (SAFT). Specifically, the purpose is to identify mixtures that are good candidates for CO2 absorption using transferable intermolecular potential models and a group contribution framework within SAFT. In the proposed approach chemical equilibrium is treated with a physical approach, so that reaction products are treated implicitly. We investigate the applicability of the SAFT-gamma (group contribution) equation of state to carbon dioxide, water and alkanolamine mixtures, and discuss how SAFT-gamma opens avenues for thermodynamic property prediction, decreasing the dependence on experimental data. The aqueous solvents examined include ethylamine, propylamine, ethanol, propanol, monoethanolamine (MEA) and 3-amino-1-propanol. We present calculations and predictions of the fluid phase behaviour of these components and of a number of their aqueous mixtures.