A Review on Ionic Liquids as Novel Absorbents for SO2 Removal

Abstract

SO2 emissions are a significant source of atmospheric pollution. The natural sources such as biological decay and sea spray emit about 130 million tons of sulfur per year, and the anthropogenic sources such as coal combustion, petroleum, and smelting operations release an additional 132 million tons of sulfur dioxide annually into the atmosphere. The largest signal contribution to the anthropogenic emission of about 70% is made by coal combustion. The natural sources of sulfur dioxide are probably present in gases emitted all through the volcanic activity. Additionally, SO2 emissions contribute to the formation of smog, which is a significant human health concern. SO2 also induces an involuntary coughing reflex. The taste threshold limit is 0.3 ppm while SO2 produces an unpleasant smell at 0.5 ppm. However, the identification of a material that can selectively and reversibly capture SO2 has proven to be difficult. This paper critically discusses the recent advances of ionic liquids for SO2 capture, including the absorption capacity, desorption performance of various other absorbents like wet lime and wet limestone. In addition, some strategies recently developed to enhance the absorption processes have been briefly introduced, such as ionic liquid mixtures, solidified ionic liquids. Moreover, the drawbacks of the industrial application of this technology have been proposed.