Biphasic behaviors and regeneration energy of a 2-(diethylamino)-ethanol and 2-((2-aminoethyl)amino) ethanol blend for CO₂ capture

High regeneration energy is one of the bottlenecks of traditional monoethanolamine (MEA) technology for CO₂ capture. A novel process using a biphasic solvent is a potential solution towards a significant reduction in the regeneration energy. A 2-(diethylamino)-ethanol (DEEA) and 2-((2-aminoethyl)amino) ethanol (AEEA) blend is a promising biphasic solvent with high stability and low cost. The biphasic behavior of CO₂ absorption in the DEEA/AEEA blend was investigated to optimize CO₂ capacity and minimize the regeneration energy. 60% DEEA/20% AEEA is the optimal biphasic solvent with 60% higher CO₂ capacity and 44% lower regeneration energy than that of the conventional MEA solvent. ¹³C NMR analysis was performed to reveal the phase separation mechanism. CO₂ reaction products of amine carbamates and bicarbonate (HCO₃^-/CO₃^2-) accumulate in the CO₂-rich phase while unreacted DEEA and AEEA migrate to the CO₂-lean phase. Only sending the CO₂-rich phase into the stripper enables to increase CO₂ partial pressure and reduce the heat duty. On the other hand, a significant increase in the viscosity of the CO₂-rich phase increases the energy penalty by decreasing the heat transfer coefficient of the heat exchanger. Due to the phase separation, the regeneration energy of the DEEA/AEEA biphasic solvent is less affected by the increased viscosity compared to other water-lean solvents. A normalized factor was proposed to incorporate both effects of increased viscosity and phase separation on the regeneration energy of the biphasic solvent.