Base-rich diamino protic ionic liquid mixtures for enhanced CO₂ capture

Mixtures based on the diamino protic ionic liquids (DPILs), N,N-dimethylethylenediammonium formate ([DMEDAH][formate]), 3-(dimethylamino)-1-propylammonium formate ([DMAPAH][formate]) and 3-(dimethylamino)-1-propylammonium octanoate ([DMAPAH][octanoate]) were synthesised at different molar ratios of amine to acid and tested for CO₂ capture. The mixtures of the DPILs with an additional base such as the industrial standard monoethanolamine (MEA) showed enhanced CO₂ capture compared to the stoichiometric DPILs. The thermal stability of the mixtures was investigated and the results indicate that the volatility of the diamine over the mixtures was considerably reduced compared to the pure base. The effect of addition of water was also studied; CO₂ absorption initially increased up to a certain water concentration, then steadily decreased as the -NH2 concentration decreased. In order to further investigate the CO₂ capture by DPILs, the effect of anion was also examined.