(533d) A Study on Imidazole-Alkanolamine-Based Deep Eutectic Solvents (DES) Functionalized for Low-Concentration Sulfur Dioxide Absorption

SO₂ emitted in the process of using fossil fuels adversely affects the human body and air quality, so emissions are strictly controlled by related facilities. The biggest contribution to this is SO₂ removal technology called flue gas desulfurization (FGD).

In the FGD process, SO₂ is removed by spraying limestone slurry, which is widely used due to its technical stability and simplicity. However, the FGD process can potentially cause environmental problems by producing waste and wastewater. Also, in countries with narrow territories such as Republic of Korea, there is a problem with the supply of raw materials because of limited reserves of high-grade limestone. Therefore, we studied wet absorption methods that are more universal and can be used as absorption as candidates for alternative technologies.

Among many absorbents, the use of Deep eutectic solvent (DES) with good tunability and stability as the SO₂ absorbent is considered in this study. DES is prepared by mixing hydrogen bond donors (HBD) and hydrogen bond acceptors (HBA). DES has low vapor pressure and high thermal stability due to hydrogen bonding, making it suitable as an absorbent. In addition, since various materials capable of hydrogen bonding can be selected as precursors, it can be functionalized to be advantageous for SO₂ absorption.

As an acid gas absorbent, one of important factor is the absorption performance at low concentration. According to Henry's law, high concentrations of gas are well absorbed, and low concentrations of gas are poorly absorbed. Since there are facilities where only low concentrations of SO₂ are emitted, it is necessary to use an absorbent that can chemically react with SO₂.

In this study, DES, which has stable physical properties and can efficiently absorb and reabsorb low concentrations of SO₂, was studied. As the HBA of DES, imidazole expected to have excellent reactivity to SO₂ was used. Another focus of this study is the use of SO₂-philic HBDs. In other DES absorbent studies, since research on HBAs is a major issue, substances that do not react with acidic gases such as glycerol and ethylene glycol are used as HBD. However, in this study, the absorption capacity per mass of DES was maximized by using alkanolamine, which is expected to absorb SO₂ as HBD.

The thermal stability changed with the formation of the proposed DES was measured. In addition, a gas absorption experiments were performed to measure the absorption capacity of low-concentration SO₂, and absorption and desorption experiments were repeated to analyze the reusability of the absorbent. As a result, the thermal stability of all precursors used increased as DES was formed. At a concentration of 500 ppm SO₂, the absorption capacity of proposed DES is more than double that reported in related studies. In the reabsorption experiments, the negligible performance decrease was observed due to the loss of the absorbent. At last, the SO₂ absorption mechanism was analyzed through ¹H NMR analysis.