Efficient Absorption of Low Partial Pressure SO₂ by 1-Ethyl-3-methylimidazolium Chloride Plus N-Formylmorpholine Deep Eutectic Solvents

Abstract

The removal of SO2 from flue gas for the improvement of atmospheric quality and human health has attracted sustainable attention. In this work, 1-ethyl-3-methylimidazolium chloride (EmimCl) was paired with N-formylmorpholine (NFM) to form deep eutectic solvents (DESs) as the media for SO2 absorption. The absorption performance of SO2 in EmimCl-NFM DESs with various molar ratios was experimentally measured. Results showed that all the DESs exhibited efficient and reversible absorption behavior for low concentration SO2, with SO2 absorption capacity as high as 0.220 g SO2/g of DES of EmimCl-NFM (1:1) at 293.15 K and SO2 partial pressure of 1.0 kPa, surpassing that of most absorbents/adsorbents previously reported. The DES could retain satisfactory absorption performance and thermal stability after five consecutive cycles. The viscosity, density, thermogravimetric analysis, Fourier transform infrared spectroscopy, and NMR spectroscopy were utilized to characterize systematically the changes between fresh and SO2-loaded DESs. The present DESs showed potential application in the purification of gas containing SO2 due to their easy preparation, high absorption capacity, and good reversibility.