Novel SO₂ Phase-Change Absorbent: Mixture of N,N‑Dimethylaniline and Liquid Paraffin

In order to avoid the high energy consumption in SO₂ capture with aqueous amine absorbents, a liquid–liquid SO₂ phase-change absorbent (SPCA) was developed in the present work using N,N-dimethylaniline (DMA) as absorbent, and high-boiling liquid paraffin was used as solvent to adjust the boiling point of the solution. The homogeneous solution would form two immiscible liquid phases after SO₂ bubbling, only the SO₂-rich phase needed to be desorbed, which could effectively reduce the energy consumption. Different from the liquid–solid phase-change absorbents developed in our previous work, the liquid–liquid phase-change absorbent avoid their shortcomings such as difficulties in separation of absorption products. The absorption product of SPCA was proved to be a charge-transfer complex DMA·SO₂ by NMR and FTIR characterization, and the phase-change mechanism was attributed to the polarity variation between DMA and DMA·SO₂. The viscosities of SPCAs was lower than 11.65 mPa·s, and the viscosity of SO₂-rich phase was 3.9 mPa·s at 30 °C. The mass absorption capacity was found to be 0.89 g SO₂/g DMA at 1 atm and 20 °C by ignoring liquid paraffin. The SPCA exhibited extremely high mass selectivity of SO₂/CO₂ with the value of 351. In addition, it was found that water had no effect on the structure of the absorption product and the SO₂ capacity of SPCA. SPCA could be completely regenerated in 50 min at 80 °C. All the results showed that the SPCAs composed of DMA/liquid paraffin have a good application prospect.