Absorption of SO₂ in flue gas by activated carbon-loaded deep eutectic solvents: Experiment and calculation

Deep eutectic solvents (DESs) possess a remarkable capacity to absorb SO₂, and their recyclability makes them highly promising for various applications. To enhance both efficiency and cost-effectiveness, this research combined porous activated carbon (AC) with a synthesized DES, ethylene glycol (EG) -imidazole (Im) - methyltriphenylphosphonium bromide (MTPB) (molar ratio 1:2:1). The effects of DES loading amount, space velocity, and flue gas flow rate on the SO₂ absorption performance were investigated systematically. Results showed that the DES/ACs are SO₂ high-performance adsorbents, particularly at high flue gas flow rates, achieving an optimal performance at a DES loading of 25%. Under conditions of 30 °C and a flow rate of 500 ml/min, the absorbent achieved an absorption rate of 0.066 g/g for low-concentration SO₂ (1000 ppm). Four kinetic models: the Bangham, Ho pseudo-second-order, Lagergren first-order, and McKay second-order are applied to investigate the SO₂ absorption dynamics. Both the Bangham and Ho models proved adept at predicting the SO₂ absorption behavior on the surface of DES/AC, which suggests the underlying mechanism to be a combination of surface reactions and micropore diffusion. Thermodynamic analysis indicates that the primary driving force for SO₂ absorption is the molar reaction enthalpy change. Hence, the DESs/AC absorbent shows great potential as a viable option for capturing SO₂ in contaminated gas.