Liquid-liquid phase-change absorption of SO2 using N, N-dimethylcyclohexylamine as absorbent and liquid paraffin as solvent.

In the present work, liquid-liquid phase-change absorption of SO2 was investigated using N, N-dimethylcyclohexylamine (DMCHA) as an absorbent, and high boiling liquid paraffin (LP) as a solvent to reduce volatilization of the absorbent. The homogenous solution was split into two immiscible phases upon SO2 loading. The phase-change mechanism was attributed to the polarity variation of DMCHA before and after absorption by forming the charge-transfer complex DMCHA·SO2. The viscosity of the lower phase reached a maximum value of 24.5 mPa s at the absorption capacity of 1 mol SO2/mol DMCHA, and the viscosity of the corresponding upper phase was 46.4 mPa s. Both are lower than the reported viscosity of most ionic liquids. This solution exhibited extremely high mass selectivity of SO2/CO2 with a value of 626. The mass absorption capacity was founded to be 1.19 g SO2/g DMCHA at 1 atm, which is comparable with the highest reported mass absorption capacity. At low partial pressure, the absorption capacity still reached 0.78 g/g at 0.1 atm, 0.43 g/g at 0.02 atm and 0.27 g/g at 0.001 atm. Furthermore, DMCHA could be completely regenerated in 10 min via microwave heating. All the results indicated this phase-change solution is a promising candidate for SO2 capture.