Natural deep eutectic solvents (NADES) have been shown to have exceptional abilities for phenolic compound extraction from plant material. However, solvent and solute recovery from NADES to achieve a circular process remains challenging. Herein, we propose an alternative low-energy process for NADES recovery using membrane filtration, specifically “open porous” nanofiltration (NF). In this study, a dead-end stirred cell was used to screen eight NF membranes for flux and selectivity. Solvent flux was tested for unused 1, 2-propanediol, a choline chloride and 1, 2-propanediol NADES (ChChlPro₁3), and a betaine and 1, 2-propanediol NADES (BetaPro₁4), revealing decreasing flux in the order 1, 2-propanediol > ChChlPro₁3 > BetaPro₁4 for all membranes. The UA60 membrane offered a good balance between polyphenol retention and solvent flux. At pilot scale, at 35. 8 bar, from 25 to 45 °C, NF permeate flux increased from 3. 5 to 11. 6 L m−2 h−1 and 1. 6 to 5. 5 L m−2 h−1 for the spent 1, 2-propanediol and ChChlPro₁3, respectively, while total phenolic compounds (TPC) retention increased from 58. 6% to 78. 3% and 52. 4% to 72. 2% for spent 1, 2-propanediol and ChChlPro₁3, respectively. NF was identified as a novel, viable low-energy (<200 kJ kg−1) recovery strategy for NADES and other similar viscous solvents, such as 1, 2-propanediol.
Dumpler et al. (Tue,) studied this question.