Synergistic Effects of Ultrasound and Deep Eutectic Solvent Pretreatment on Sugarcane Leaves Bioconversion to Ethanol

Abstract

The increasing accumulation of sugarcane agricultural waste poses a significant environmental challenge, highlighting the urgent need for innovative valorization strategies such as converting sugarcane leaves into bioethanol through efficient pretreatment technologies. Therefore, this study investigates the effect of pretreatment using a combination of ultrasonic and deep eutectic solvents (DESs), ethylene glycol: citric acid (EG/CA) and choline chloride: citric acid (ChCl/CA), on sugarcane leaves’ compositions and properties. DES-assisted pretreatment was conducted using a solid-to-liquid ratio of 1:5 (w/w) at 90 °C and 100 rpm stirring speed for 3.15 h. Ultrasound-assisted pretreatment was optimized for amplitude and duration. The reducing sugar concentration obtained after pretreatment increased by 2.89 times for EG/CA and 3.41 times for ChCl/CA compared to the untreated sample (3.75 g/L). However, combining EG/CA pretreatment with ultrasound at 40% amplitude for 30 min enhanced reducing sugar concentration to 8.49 g/L with the highest crystallinity index (CrI) of 50.09%. Applying ultrasonic pretreatment before DES effectively improved the sugar release, resulting in an ethanol yield of 17.14%. Additionally, Fourier-transform infrared spectroscopy (FT-IR) was employed to examine chemical structural modifications of the biomass, verifying the effectiveness of ultrasound-assisted DES pretreatment. These findings highlight the potential of ultrasound-assisted DES pretreatment as an effective alternative for lignocellulosic biomass processing.