An integrated green fractionation of coconut husk: Hydrothermal and deep eutectic solvent pretreatment for enhanced sugar and lignin production

Coconut husk was explored for sugar and lignin production using an integrated approach combining hydro- thermal treatment (HT) and deep eutectic solvent (DES) pretreatments, followed by enzymatic saccharification, to enhance lignocellulose fraction recovery. Optimized HT conditions yielded 4.802 g/L of total reducing sugars, including 0.223 g/L glucose and 0.998 g/L xylose, with minimal degradation products. Subsequent DES pretreatment with choline chloride and lactic acid effectively removed lignin, recovering high-purity lignin with a native-like structure. The combined pretreatment resulted in a cellulose-rich solid, enhancing saccharification yield by 3.24-fold compared to single pretreatments. This improvement stemmed from the extensive disruption and removal of non-cellulose components, confirmed by solid characterizations. The integrated process demonstrated a synergistic effect, achieving 31.3 % total sugar recovery and 48 % lignin recovery, highlighting the potential of coconut husk as a promising biorefinery feedstock.