Novel Thermomorphic Biphasic Amine Solvents for CO2 Absorption and Low-Temperature Extractive Regeneration

The key challenge in amine-based CO2 capture from flue gases is to reduce the energy consumption required for solvent regeneration. Lipophilic amines exhibit a thermomorphic phase transition upon heating, giving rise to autoextractive behavior, which intensifies desorption at temperatures well below the boiling point of aqueous solutions. The low regeneration temperature of less than 80 °C together with the high cyclic CO2 loading capacity of ∼0.9 mol molabsorbent–1 of such thermomorphic biphasic solvent (TBS) systems permit the use of low-value and even waste heat at temperatures below 100 °C for desorption. In order to reduce the exergy demands still further, techniques for enhancing CO2 release using extractive regeneration with inert solvent addition were investigated at temperatures of 40–50 °C to permit the use of waste heat at temperatures of ∼70 °C or less. The regeneration of 3 M absorbed lipophilic amine solutions with 0.93 mol mol–1 CO2 loading by using various additional solvents and the evaluation of the extractive performance in multiple-stage crosscurrent and countercurrent configurations indicated the promise of adding certain hydrophobic solvents to enhance the low-temperature regeneration of TBS absorbents.