Capturing CO₂ into the precipitate of a phase-changing solvent after absorption

The major drawback of aqueous alkanolamine-based CO₂ capture processes is the high energy penalty for regeneration. To overcome this weakness, we studied the absorption of CO₂ with amines dissolved in nonaqueous solvents. It was observed that triethylenetetramine (TETA) dissolved in ethanol produces a solid precipitate after absorption, which can then be easily separated and regenerated. As a comparison, a TETA/water solution does not form any precipitate after absorbing CO₂. The TETA/ethanol solution offers several advantages for CO₂ capture in absorption rate, absorption capacity, and absorbent regenerability. Both the rate and capacity of CO₂ absorption with the TETA/ethanol solution were significantly higher than with a TETA/water solution, because ethanol not only promotes the solubility of CO₂ in the liquid phase but also facilitates the chemical reaction between TETA and CO₂. This approach was able to capture 81.8% of the absorbed CO₂ in the solid phase as TETA-carbamate. In addition, results show that the decomposition of TETA-carbamate can be completed at 90 °C. Moreover, the cycling absorption/regeneration runs of the TETA/ethanol solution display a relatively stable absorption performance.