Integrating DES Pretreatment and Enzymatic Saccharification for Napier Grass Valorization

Napier grass, a promising energy crop, offers significant potential for bioethanol production due to its high lignocellulosic content, rapid growth, and wide availability. This study investigates the use of deep eutectic solvents (DES) for pretreatment, focusing on choline chloride: sorbitol (ChCl: S), ethylene glycol: citric acid (EG: CA), and choline chloride: citric acid (ChCl: CA). The study employs the optimization of pretreatment parameters with ChCl: S, including reaction time (0.5 to 5 h), solid-to-liquid (S/L) (1:5 to 1:20 w/w) ratio, and temperature (90 to 130°C), to enhance delignification, polysaccharide recovery, and bioethanol yield. Comprehensive biomass characterisation before and after pretreatment was performed. At optimum pretreatment conditions of 90°C, 2.75 h and 1:5 S/L ratio, the results demonstrated significant delignification and hemicellulose removal with increased cellulose enrichment, particularly with ChCl: S. Subsequent enzymatic hydrolysis and fermentation yielded higher sugar recovery and ethanol production compared to untreated biomass. The highest glucose concentration obtained was 5.19 mg/ml for biomass pretreated with EG: CA. In addition, the maximum bioethanol conversion yield attained was 38.43% for pretreatment with ChCl: S. This study highlights the novel application of these DES formulations to Napier grass and provides critical insights into their mechanisms and efficacy. The findings contribute to developing sustainable and cost-effective biorefinery processes, paving the way for improved bioethanol production from non-food biomass resources while addressing environmental and economic challenges.