Screening and evaluation of novel biphasic solvents for energy-efficient post-combustion CO₂ capture

Approximately 50 amine-based aqueous solvent blends of absorption accelerators (monoamines or polyamines) and regeneration promoters [N,N-dimethylcyclohexylamine (DMCA) or 2-(diethylamino) ethanol (DEEA)] were investigated in a screening study to help develop a novel phase transitional carbon dioxide (CO₂) absorption process. Carbon dioxide absorption rates and phase transition behavior at 30°C and phase equilibrium behavior of CO₂ desorption at 80°C were evaluated by using laboratory batch reactors. Relationships between the characteristic structures of solvent components and the observed absorption and desorption performance were qualitatively evaluated. Blending with either DMCA or DEEA, which have different hydrophobicities, only marginally affected the structure-performance relationship of the derived solvent blends. Phase transitions occurred only in solvent blends containing polyamine accelerators. Most polyamine+DEEA solvents showed higher CO₂ loading capacities at 30°C but lower equilibrium pressures of CO₂ at 80°C than did polyamine+DMCA solvents. TETA+DEEA was identified as the most favorable solvent blend in the screening study. Results also suggested that the biphasic solvents with amine accelerators containing 3-4N and 4-6C atoms generally exhibited favorable absorption and desorption performance without major operational concerns.