Comparative evaluation of sugarcane leaf biomass pretreatment: Conventional alkali/acid vs. deep eutectic solvent approach for enhanced bioethanol production
Neelu Raina, Malinee Sriariyanun, Suttichai Assabumrungrat, Chawalit Ngamcharussrivichai, Santi Chuetor
Abstract
This work draws insights into comparative efficiency between three binary deep-eutectic solvents (DES) and the sequential alkali/acid pretreatment techniques. The ability of DES to convert sugarcane leaf (SCL) biomass into fermentable sugars was reviewed at different temperatures (25, 80 and 121 °C) and residence time periods (24, 3 and 1 h), respectively. DESs are suitable solvents for solubilizing lignocellulose highlighting their cost-effectiveness and reduced environmental footprint compared to conventional methods. On the other hand, sequential alkali/acid (SAA) pretreatment was carried out at 121 °C and 90 °C for 60 min. After DES pretreatment, the maximum cellulose concentration attained was 0.435 g/g biomass using choline chloride: acetic acid (CA121) mixture at 121 °C for 60 min. The process also indicated 23.29 kWh/kg energy consumption and 15 L/kg biomass as wastewater generated. In comparison to native biomass, evaluation of the pretreated biomass showed that cellulose concentration of 0.902 g/g biomass (2.5-fold increase) resulted from the sequential alkali/acid pretreatment using 1.5M NaOH followed by 1.5M H 2 SO 4 (121 °C for 60 min). Also, the energy consumption and the waste water generation were 53.8 kWh/kg and 53.3 L/kg biomass respectively. Biochemical analysis using FTIR and XRD showed that the sequential alkali/acid pretreatment method was more effective in removing hemicellulose and lignin compared to DES. The optimized enzymatic hydrolysis of pretreated biomass hydrolysate achieved 0.831 g/g biomass glucose concentration attaining an ethanol yield of 487 kg per ton of SCL biomass (equivalent to 106 L/ton) with a cumulative productivity of 14 kg per ton per hour.