(510f) Synthesis of Imidazole and Amine Based Deep Eutectic Solvents for Low Concentration so2 Capture

While the use of fossil fuels for energy production has improved the quality of human life, the environmental problems caused by pollutant emissions are a major drawback to their usage. In particular, the sulfur content in fossil fuels is oxidized in the combustion process and released in the form of sulfur oxides (SO₂ and SO₃), environmental pollutants that adversely affect air quality and the human body. Therefore, industrial facilities where sulfur oxides are mainly discharged should make efforts to reduce them.

Flue gas desulfurization (FGD) is generally used to remove SO₂, which uses lime (Ca(OH)₂) or limestone (CaCO₃) to produce calcium sulfite, which further reacts with oxygen to produce gypsum (CaSO₄·2H₂O). However, the disadvantage is that the reserve of high purity natural limestone required as raw material is limited. As a solution to this issue, wet absorption methods that absorb acidic gases using liquid absorbents are usually considered as an alternative technology. Amine type absorbents are generally considered good absorbents for acidic gases, but they are not suitable as SO₂ absorbents due to high energy required for their regeneration and that they are highly volatile. New absorbents are constantly studied with the aim of overcoming the current difficulties, and recently a new absorbent called Ionic liquids (ILs) emerged. They present stable physicochemical properties such as low vapor pressure and low corrosivity, but due to the complexity of the production process and the high cost of the materials their practical application on the industry does not seem very likely. As a new alternative, Deep eutectic solvent (DES) for acidic gas absorption have been explored since the year 2003. DES are made from the synthesis of a Hydrogen bond acceptor (HBA) and a Hydrogen bond donor (HBD) and is characterized by the drastic decrease of the melting point of the mixture compared to their individual components and are often liquid at room temperature. Depending on their characteristics, DES may be considered as an absorbent for the wet absorption method to absorb acidic gases. DES, like ILs, has low vapor pressure and stable chemical properties, but have the advantage of an easy manufacturing process and low costs. Therefore, DES was selected as the absorbent for wet absorption in this study due to its advantages over the available alternatives.

An important focus of the study is the low concentration SO₂ absorption capacity of DES. Since most industrial processes emit low-concentration SO₂ research on low-concentration absorption must be conducted to achieve practical results. In general, DES physically absorbs SO₂, process suited for high concentration gases, and therefore cannot effectively absorb low concentrations of SO₂. It is important to synthesize DES by selecting HBDs and HBDs that can chemically absorb SO₂. Thus, Imidazole, which has been reported to be able to chemically absorb SO₂ according to its structural properties and types of functional group, was used as HBA. Another focus of research is the use of amine-based materials such as MEA, DEA, and MDEA as HBD.

Gas-analyzer was used to analyze the absorption capacity of DES, and the experiments and analyses were conducted by synthesizing HBA and HBD at a ratio of 1:2, 1:3, 1:4 to find the optimal ratio of the target absorbent. The gas was injected into the absorbent with the composition of SO₂ 5,000 ppm and 99% N₂. The absorption mechanisms were analyzed with Fourier-transform infrared spectroscopy (FT-IR) and Nuclear Magnetic Resonance (NMR). In addition, the density and viscosity of absorbents, which are factors that affect absorption efficiency, were analyzed by mole ratio using a densitometer and viscometer, and Thermogravimetric Analysis (TGA) was performed to analyze thermal stability.