Methodological Selection of Demixing Liquid–Liquid Solvents Used in the Absorption–Regeneration Carbon Capture Process

Since the 19th century, the carbon dioxide concentration in the atmosphere has never been so high due to anthropogenic emissions. This increase in the greenhouse gas concentrations in the atmosphere has been identified as the main cause of global warming. The absorption–regeneration postcombustion carbon capture technology has the highest Technology Readiness Level (TRL) to limit the CO2 emissions. Nevertheless, the type of process is a high consumer of thermal energy to regenerate the liquid solvent used to absorb carbon dioxide. A solution to reduce this high energy demand is the use of liquid–liquid biphasic (or demixing) solvents that have the capacity to split into two phases under certain conditions of temperature and CO2 loading. The present work aims to classify the aqueous liquid–liquid biphasic solvents after a literature review of the existing solvents to determine the most promising ones for further investigations. This methodology is composed of two successive steps. The first step is based on six technoeconomic indicators: the regeneration energy, the CO2 absorption capacity, the CO2 absorption rate, the volume ratio between the two phases, the volatility of organic compounds, and the solvent cost. The contribution of each key indicator is weighted using the analytical hierarchy process method. The result of this first step is the ranking of the 30 solvents identified in the literature. The second step is a Health, Safety, and Environment (HSE) analysis. It excludes 17 solvents containing at least one molecule that presents a serious hazard for human life or the environment. After the application of this methodological evaluation, the final results show that the three most promising aqueous biphasic solvents are, respectively, composed of triethylenetetramine (30 wt %) and propan-1-ol (50 wt %), N,N-dimethylcyclohexylamine (35 wt %) and triethylenetetramine (15 wt %), and diethylethanolamine (64 wt %) and methylaminopropylamine (19 wt %).