(449p) Efficient Absorption of SO2 in Simulated Flue Gas by Environmentally Benign Functional Deep Eutectic Solvents

The emission of sulfur dioxide (SO₂), which is mainly from the burning of fossil fuels, has drawn much attention all over the world. The emitted SO₂ is harmful to human body and causes serious environmental pollution, so it is essential to remove SO₂ from the flue gas. Up to now, flue gas desulfurization (FGD) is the most efficient way for the capture of SO₂. Liquid absorbents such as aqueous amines have also been applied for the capture of SO₂. However, this method may cause secondary pollution due to the high volatility of amines. As a result, recyclable liquid solvents with low volatility and high capacity are expected as excellent absorbents for the capture of SO₂. Recently, a new generation of solvents deep eutectic solvents (DESs) are considered as an environmental benign solvent, which is a combination of a salt as hydrogen bond acceptor (HBA) and a hydrogen bond donor (HBD) through hydrogen bond. DESs have many advantages such as low vapor pressure, easy preparation, low price, biodegradability, and so on. Based on the properties of DESs, we designed new functional DESs and used them to capture SO₂ in simulated flue gas.

In this work, we designed and synthesized two kinds of biodegradable functional DESs on betaine (Bet) and L-carnitine (L-car) as HBA, and ethylene glycol (EG) or water as HBD with different ratios of HBA to HBD. They were investigated to absorb SO₂ with different partial pressures at various temperatures. The results are showed as follows. (1) At 40 ^oC with a SO₂ partial pressure of 0.02 atm, SO₂ absorption capacities of the DESs with HBA/HBD mole ratio of 1:3 were 0.332 mol SO₂ / mol HBA for Bet + EG DES and 0.820 mol SO₂ / mol HBA for L-car + EG DES. And SO₂ absorption capacities of the DESs with HBA/HBD mass ratio of 1:1 were 0.155 mol SO₂ / mol HBA for Bet + H₂O DES and 0.606 mol SO₂ / mol HBA for L-car + H₂O DES. (2) The higher the absorption temperature, the lower SO₂ absorption capacities. (3) The lower the SO₂ partial pressure, the lower SO₂ absorption capacities. At 40 ^oC and 3700 ppm SO₂ in simulated flue gas, SO₂ absorption capacities of the DESs with HBA/HBD mole ratio of 1:3 were 0.155 mol SO₂ / mol HBA for Bet + EG DES and 0.606 mol SO₂ / mol HBA for L-car + EG DES. (4) The regeneration experiments demonstrated that the absorption capacities of DESs did not change after five absorption and desorption cycles. (5) The absorption mechanism of SO₂ by DESs was studied by FT-IR, ¹H NMR and ¹³C NMR spectra. It was found that there are strong acidâ??base interactions between SO₂ and â??COO^â?? on HBA for Bet + EG DESs and L-car + EG DESs, and â??COO^â?? on HBA is recovered to â??COOH by stronger acid H₂SO₃ for Bet + H₂O DESs and L-car + H₂O DESs. DESs based on quaternary ammonium inner salts as HBA with EG or water are promising absorbents in the application of FGD for SO₂ capture.

The project is financially supported by the National Natural Science Foundation of China (No. 21176020 and 21306007) and the Research Fund for the Doctoral Program of Higher Education of China (No. 20130010120005).