(255g) Decoloration of Molasses By Ultrafiltration and Nanofiltration: Understanding the Mechanisms of High Sucrose Retention

Membrane technology provides a green approach to recover sucrose from cane molasses. However, the trade-off between color removal and sucrose permeation by membrane filtration debases the efficiency and limits the application. In this study, ten commercially-available and one self-made ultrafiltration (UF) and nanofiltration (NF) membranes were used for decoloration of molasses. By investigating the effect of membrane properties, solute component and operating parameters on the molasses filtration behaviors, the mechanisms of high sucrose retention were clarified. For polyether sulfone (PES) membrane, the high retention of pigments and sucrose was mainly caused by the pore narrowing effect due to irreversible fouling. Polyamide (PA) NF membranes showed high antifouling ability, and a suitable pore size (~500 Da) was important to achieve high color removal and sucrose permeation. Although regenerated cellulose (RC) membranes exhibited excellent antifouling performance to molasses, the membrane swelling induced by high temperature (60 °C) limited their application. Reducing sugar in molasses produced negligible effect on the sucrose retention, while inorganic salts resulted in pore swelling and smaller hydration diameter of sucrose due to salting-out effect, thus improving the sucrose permeation. However, such positive effect was weakened or eliminated by the pigments and colloids in molasses. High temperature could accelerate the sucrose permeation, but it also attenuated concentration polarization layer, thus intensifying the sucrose retention increase induced by high permeate flux. If a loose NF membrane was selected for decoloration of molasses, minimizing fouling formation, removing large pigments and colloids by pretreatments to reappear salting-out effect, operating at high temperature and low permeate flux could increase sucrose permeation.