A new approach to the upgrading of the traditional propylene carbonate washing process with significantly higher CO2 absorption capacity and selectivity

Although a series of advanced technologies and materials, like ionic liquids and metal organic frameworks, is being developed for carbon capture, traditional techniques, like propylene carbonate (PC) washing, are still widely applied in industry because of their low material costs and ease of operation. Considering the low CO 2 solubility and selectivity in PC, we have tried to improve the PC washing process by adding 2-methylimidazole (mIm) to PC in the presence of ethylene glycol (EG) as cosolvent. A series of EG-mIm-PC complex solvents was prepared and their viscosities measured at different temperatures. The absorption isotherms of CO 2 in these complex absorbents, as well as in pure PC, were measured at 293.15, 303.15, and 313.15 K at 0.1–0.8 MPa. The heats of CO 2 absorption in these solvent mixtures were calculated using the Clausius-Clapeyron equation. For evaluating the effect of mIm on the selectivity of CO 2 over other gas species, the absorption isotherms of CH 4 , N 2 , and H 2 in pure PC and in 24%-mIm complex solvent with highest CO 2 solubility were also measured. The results showed that the viscosities of these complex absorbents, as well as the solubility and heats of absorption of CO 2 in all of them, moderately or slowly increased with an increase in mIm mass fraction, when the mIm content was lower than 20 wt%, and rapidly increased when it surpassed 20 wt%. The CO 2 solubility could be more than doubled when the mIm content reached 24 wt% while viscosity and absorption heat still remains at low levels, that is, lower than 14 mPa·s and 26 kJ/mol, respectively. More importantly, the solubilities of CH 4 , N 2 , and H 2 drastically decreased in the presence of mIm; using the 24 wt%-mIm complex absorbent instead of pure PC, the selectivity of CO 2 over those other gas species increased by: 0.7–2.8 times for CH 4 , 3.9–6.3 times for N 2 , and 3.5–7.7 times for H 2 , with more significant improvements at lower pressure ranges. This work presents a very promising approach to PC washing technology upgrading.