The use of ionic liquid for the pretreatment of energy cane bagasse

Abstract

Lignocellulosic biomass appears to be a prospective renewable resource that can be used for the generation of biofuels and bioproducts. The major concern in lignocellulose conversion is overcoming biomass recalcitrance through pretreatment while still maintaining a green, energy efficient and cost-effective process. Energy cane is a promising energy crop with high fiber content, cold tolerance, and less fertilizer and water input requirements as compared to conventional sugarcane. Ionic liquids (ILs) are promising solvents for the pretreatment of lignocellulose as they are thermally stable, environmentally friendly, recyclable, and have low volatility. This study assessed the use of ionic liquid 1-ethyl-3-methylimidazolium acetate ([EMIM][OAc]) as a solvent during the pretreatment of energy cane bagasse (ECB) and its effect on the chemical composition, surface morphology, cellulose crystallinity, and enzymatic hydrolysis of the pretreated biomass. IL-treated ECB resulted in significant lignin removal (32.1%) with slight glucan and xylan losses (8.8% and 14.0%, respectively), and exhibited much higher cellulose and hemicellulose enzymatic digestibilities (87.0%, 64.3%) than untreated (5.5%, 2.8%) or water-treated (4.0%, 2.1%) ECB, respectively. The enhanced digestibilities of IL-treated biomass can be attributed to delignification and reduction of cellulose crystallinity as confirmed by FTIR and XRD analysis. When pretreating ECB with recycled IL, enzymatic digestibility decreased as the number of pretreatment recycles increased. Decreasing the pretreatment temperature from 120 °C to 100 °C and extending the residence time from 30 min to 2 h brought significant improvement to the pretreatment efficiency of recycled [EMIM][OAc] on ECB. However, response surface methodology model indicated that a higher glucose yield of IL-treated biomass could be obtained at higher pretreatment temperatures with shorter residence times. The optimal processing conditions were pretreatment of ECB at 131.9 °C for 28.1 min at 8.4% solids loading resulting in a final glucose yield of 35.96 g glucose per 100 g of native biomass. The results presented in this thesis demonstrated that [EMIM][OAc] can be used as a potential solvent for the pretreatment of lignocellulosic biomass such as ECB. Furthermore, the sugar yields obtained post pretreatment have great potential as building blocks in the production of renewable fuels and chemicals.