Purification of Kraft cellulose under mild conditions using choline acetate based deep eutectic solvents

Three novel deep eutectic solvents (DESs) were prepared with choline acetate (ChOAc) as the hydrogen bond acceptor (HBA) and three hydrogen bond donors (HBD): glycolic acid (GlyA), levulinic acid (LevA) and imidazole (Im). They showed different, albeit remarkable capabilities of dissolving lignin (from 35% to 100%) and hemicellulose (from 40% to 50%). The solubility was first tested on commercially available hemicellulose in neat DES and in DES aqueous solution. The high values of solubility observed (22-45 wt%) demonstrated the potential of DESs as hemicellulose solvents. A proof of concept test was carried out on Kraft cellulose: our systems provided selective solubilisation of lignin and hemicellulose leading to cellulose purification, as demonstrated by the lignocellulosic content before and after the DES treatment.