Anionic bio-flocculants from sugarcane for purification of sucrose: An application of circular bioeconomy

In sugar production, polyacrylamide-based anionic flocculants are added for juice treatment, the main objective being to remove impurities that affect the quality of the sugar. However, if they remain in the final product, those polymers can present carcinogenic and neurotoxic actions besides contaminating the soils where the waste is discharged. To overcome this problem, the present study proposes, for the first time, natural flocculants based on cellulose obtained from sugarcane bagasse (residue from sugarcane processing) as substitutes for the flocculants based on polyacrylamide, normally used in sugar cane juice purification. Additionally, cellulose-based flocculants obtained from Acacia wood, developed in a previous study, have also been tested for sugar juice treatment. Acacia wood and sugarcane bagasse were first treated with a choline chloride/levulinic acid solution in a molar ratio of 1:2, at 160 °C, for 4 h. Subsequently, the cellulose-rich samples were modified by a two-stage process (oxidation with sodium periodate followed by reaction with sodium metabisulfite), and polyelectrolytes with different characteristics were produced. The final products obtained were characterized, and their performance in the treatment of sugarcane juice, at different concentrations (10, 50, 100, 250, and 500 mg kg^-1), was evaluated and compared to the synthetic commercial flocculant (Flonex, based on polyacrylamide) usually used by the sugarcane industry in Brazil. The substitution of petrol-based flocculants by natural-based ones, obtained from sugarcane residues, is presented for the first time in this study, with very relevant performance of the new flocculants. Overall, it was possible to produce anionic flocculants, modifying the cellulose obtained from different raw materials, which showed good results in the purification of sucrose, when compared with the commercial polyacrylamide normally used. It is also important to stress that, for the first time, a residue from sugarcane industry could be used with success in the purification of the sugar juice itself, which constitutes a major novelty.