Green methods for obtaining deep eutectic solvents (DES)

A group of materials with great application potential are deep eutectic solvents (DES). This paper presents an alternative approach to methods of obtaining them, using microwave radiation and ultrasound as energy sources. One of the main challenges associated with DES is to find economical methods to obtain them on an increased scale. By using already finished DES that are in the liquid phase as a medium to initiate energy transfer to raw materials and initiate DES formation, it is possible to obtain DES using ultrasound and microwaves. The time required to obtain selected DES, e.g., choline chloride with urea, has been reduced to 4–5 min, with a 12-fold increase in process yields with further potential for scale-up (30 g/h for the conventional process, to as much as 800 g/h using the microwave process). The heating efficiency of microwave and ultrasonic methods is 74.5% and 53.3%, respectively, while the conventional heating process shows a heating efficiency of 5.0%. The presented results confirm the possibility of increasing the scale of obtaining DES, which will help to use these valuable solvents on a large scale in the future. At the same time, it was confirmed that by designing the process appropriately and relying only on DES raw materials and products, it is feasible to use alternative sources of energy in obtaining processes.