Efficient and selective absorption of SO2 by low-viscosity matrine-based deep eutectic solvents

Designing excellent liquid absorbents with low viscosity for efficient and selective absorption of sulfur dioxide (SO2) from flue gas is important but still challenging. Herein, matrine-based binary deep eutectic solvents (DESs) were prepared by mixing matrine (Mat) with three different amides including N-methylformamide (MFA), N-ethylformamide (EFA), and N-methylacetamide (MAA). It is found that the viscosities of these three DESs were lower than 20 cP at room temperature, which is significantly lower than other previous DESs or ILs that have been reported. Moreover, the results of SO2 capture showed that the absorption rate of SO2 by the Mat-MFA (1:2) DES was very fast (<3 min) to achieve a relatively large absorption capacity (0.84 g/g at 293.2 K and 1 bar). Mat-MFA (1:2) DES also displayed very high selectivity (576) for the SO2/CO2 (10/90, v/v) mixture, which is higher than most of the liquid absorbents and solid adsorbents currently reported. Furthermore, breakthrough experiments verified the good separation performance of Mat-MFA (1:2) DES in capturing 2% SO2 in the mixture of SO2/N2 or SO2/CO2, respectively. The results illustrated that the features of low viscosity, fast absorption rate, and high selectivity of SO2 capture make the matrine-based DESs have great potential for flue gas desulfurization.