Optimization of deep eutectic solvent pretreatment for bioethanol production from Napier grass

Abstract

The growing demands of fossil fuel consumption led to the depletion of fossil fuels, and other environmental impacts. As a step toward sustainable development, fossil fuels should be replaced by lignocellulosic biofuels to reduce greenhouse gas emissions. Among the lignocellulosic biomass, Napier grass is an important energy crop due to its high growth rate, less water and nutrient requirement for their growth, and high carbohydrate content. This study focused on the improvement of ethanol production from Napier grass by pretreatment with acidic deep eutectic solvent (DES), choline chloride: lactic acid (ChCl/LA) at a mole ratio of 1:4. The parameters for DES pretreatment included biomass loading (1:5 to 1:20, w/w), temperature (80 to 130 ℃), and time (0.5 to 5 h), which were optimized based on maximized sugar release from enzymatic hydrolysis. Under optimized pretreatment conditions (biomass loading of 1:6.5 (w/w), temperature of 80 ℃ for 5 h), 71 % cellulose recovery and 68 % lignin removal were obtained, which led to a glucose yield of 87.09 % from Ctec2 saccharification. The inhibitor analysis revealed that ChCl/LA pretreatment produced only a negligible amount of inhibitor, acetic acid (0.001 % v/v). Furthermore, fermentation studies were also conducted to evaluate the bioethanol production from the biomass, of which 86.6 % of the theoretical ethanol yield was achieved. Overall, this study demonstrated the significance of ChCl/LA pretreatment for ethanol production from Napier grass and the potential of this lignocellulosic ethanol to achieve reach the goals of the green economy. © 2022 Elsevier Ltd