An experimental and computational study of CO2 absorption in aqueous solutions of tetraethylenepentamine

Abstract

Capturing CO2 directly from the atmosphere and subsequently using it to produce hydrocarbon fuels could help decrease mankind's reliance on fossil fuels and mitigate the risks of climate change. Zero Emission Fuels (ZEF) is developing a small-scale methanol plant, which utilizes atmospheric CO­2 and H2O vapor as feedstocks for renewable methanol synthesis. In this study, the vapor liquid equilibrium (VLE) of CO2 and aqueous solutions of tetraethylenepentamine (TEPA) was measured and correlated using thermodynamic models. The equilibrium pressure of aqueous solutions of 30, 70 and 80 wt% TEPA was measured from 313.15 to 393.15 K using a mechanically stirred and temperature controlled autoclave. The binary VLE data was correlated using Wilson's activity coefficient model. Using the same experimental set-up, the equilibrium solubility of CO2 in aqueous solutions of 30 and 70 wt% TEPA was measured at 313.15, 353.15 and 393.15 K. A simple chemical model, incorporating the extended Debye-Hückel law for activity coefficients of ionic species, was regressed to the ternary VLE data. Additionally, a theory was proposed that the polyamine can be modelled as a multiple of smaller amines, using the ratio of the amine groups as a scaling factor. Both models were applied in a simple process simulation of the absorption and stripping column of the direct air capture unit of ZEF to provide an estimation of the energy demand of the process under different conditions. The lowest regeneration energy demand was 533 kJ/mol CO2 absorbed, which is approximately 3 times higher than that of monoethanolamine, the current benchmark solvent for amine-based CO2 capture. However, through the addition of a rich-lean heat exchanger and process optimization to minimize the required reflux stream, this value could potentially be decreased.