Absorption of CO2 with methanol and ionic liquid mixture at low temperatures

• Solubility data of CO2 in methanol and IL mixture at low temperatures were measured.
• UNIFAC model for ILs was extended to the methanol-CO2 and methanol-IL-CO2 systems.
• Conceptual process design was done using the new mixed absorbents for CO2 capture.

This work proposed the use of methanol (CH3OH) and ionic liquid (IL) mixture, which integrates the advantages of methanol (high solubility and low viscosity) and IL (non-volatility), for CO2 capture at low temperatures (down to 228.2 K). The solubility of CO2 in pure methanol, IL ([OMIM]+[Tf2N]−) and their mixture (80 wt% CH3OH + 20 wt% IL, 50 wt% CH3OH + 50 wt% IL, and 20 wt% CH3OH + 80 wt% IL) was measured at 273.2, 258.2, 243.2 and 228.2 K and pressures up to 3.0 MPa. The UNIFAC model for ILs was extended to the methanol–CO2 and methanol–IL–CO2 systems. The comparison between the predicted and experimental results indicated that the UNIFAC model can well predict the CO2 solubility in pure methanol and in the (methanol + IL) binary mixture at low temperatures. Based on the thermodynamic experimental and modeling studies, the conceptual process design was developed for CO2 removal from syngas using the mixed agent at a low temperature. It was found that the volatile loss of methanol in the absorption column and solvent flash tanks decreases significantly in the case of the mixture of methanol and IL used as an absorbent.