Imidazole green solvent pre-treatment as a strategy for second-generation bioethanol production from sugarcane bagasse

Abstract

Sugarcane bagasse (SCB) is a potential source for second-generation bioethanol production. However, its recalcitrant structure (carbohydrates and phenolics) hinders the efficient release of sugars. Imidazole is a cheap green solvent that has demonstrated high efficiency in lignocellulosic biomass delignification. The main objective of this work was to study the SCB pre-treatment with imidazole for further enzymatic hydrolysis and bioethanol production. Significant modifications of imidazole-treated biomass were observed in the morphology and composition, such as cellulose enrichment, a great decrease of amorphous compounds (lignin and hemicellulose), and structural disorganization of lignocellulosic fibres. On the other hand, this pre-treatment also shows a substantial improvement of enzymatic conversion performance using Cellic CTec2®/Cellic HTec2® (15 FPU per gram of solid biomass) in all evaluated conditions compared to untreated material. After pre-treatment at 160 °C for 1 h, enzymatic conversion efficiency reached 100% for glucose and xylose, significantly decreasing the hydrolysis time to only 8 h. The hydrolysates obtained were used for bioconversion to bioethanol by S. cerevisiae LPB 2705, giving a high production yield (83.7%), which represents a production of 218 L of ethanol per ton of SCB. This means an increase of up to 4 times the ethanol production compared to untreated material. The results obtained showed the great potential of imidazole in SCB pre-treatment, because it increased the release of fermentable sugars, which leads to an efficient and economic use of agro-industrial waste to generate value-added products and reduce the environmental impact under a biorefinery concept.