Long-term Isothermal Stability of Deep Eutectic Solvents

Deep eutectic solvents play an important role in the clean production of chemicals and the fractionation of renewable sources. When dissolving lignin or cellulose at elevated temperatures, the thermal stability of deep eutectic solvents is of great importance. However, studies concerning the long-term isothermal stability of deep eutectic solvents are scarce. In this study, the thermal stability of deep eutectic solvents, namely, choline chloride with oxalic acid dihydrate, glycerol, glycolic, malic acid, and citric acid monohydrate were investigated using thermogravimetric analysis (TGA). The isothermal decomposition experiments were conducted at a constant temperature (60, 80, 100, and 120 °C) for 10 h. These long-term isothermal thermogravimetric studies of the deep eutectic solvents showed a non-linear weight loss as a function of time at each temperature. According to these studies it is recommended to perform fractionation or dissolution of biomass below 80 °C.