Giant bamboo plantations are currently being established in the Southern Africa region and can be considered as potential lignocellulosic feedstock for the production of second generation bioethanol. In this study, giant bamboo internodal material was subjected to sulphur dioxide (SO(2)) impregnated steam pretreatment prior to enzymatic hydrolysis. The effect of temperature, residence time, and acidity on the overall sugar recovery and byproduct formation was studied using response surface response technology according to a central composite experimental design (CCD) at a fixed SO(2) concentration of 2.5% (w/w liquid) after impregnation. The results showed that pretreatment conditions with combined severity factor (CSF) values and enzyme dosages greater than 1.72 and 30 FPU/g water insoluble solid, respectively, were required to obtain an efficient glucan digestibility and a good overall glucose recovery. Up to 81.2% of the sugar in the raw material was recovered for a CSF of 2.25. However, considering overall sugar yield and byproducts concentration, the pretreated material obtained with a CSF of 1.62 can be considered as the most appropriate for SSF experiments using a xylose-utilizing yeast. At these conditions, it could be possible to obtain up to 247 L of ethanol per dry ton of giant bamboo considering hexose and pentose sugars fermentation. This amount could be increased up to 292 L of ethanol per dry ton of giant bamboo with the maximum sugar yield obtained (CSF = 2.25) if the microorganism possesses robust fermentative characteristics as well as a high resistance to pretreatment by-products.

Various ionic liquids have been identified as effective pretreatment solvents that can enhance the cellulose digestibility of lignocellulose by removing lignin, one of the main factors contributing to the recalcitrant nature of lignocellulose. 1-Butyl-3-methylimidazolium methylsulfate ([BMiM]MeSO(4)) is a potential delignification reagent, hence its application as a pretreatment solvent for sugarcane bagasse (SB) was investigated. The study also evaluated the benefit of an acid catalyst (i.e., H(2) SO(4)) and the effect of pretreatment conditions, which varied within a time and temperature range of 0-240 min and 50-150°C, respectively. The use of an acid catalyst contributed to a more digestible solid and a higher degree of delignification. However, the [BMiM]MeSO(4)-H(2) SO(4) combination failed to produce a fully digestible solid, as a maximum cellulose digestibility of 77% (w/w) was obtained at the optimum pretreatment condition of 125°C for 120 min. Furthermore, up to half of the lignin content could be extracted during pretreatment, while simultaneously extensive, sometimes complete, removal of xylan, the presence of which, also hampers cellulose digestibility. Hence, [BMiM]MeSO(4) has been identified an effective pretreatment solvent for SB as the application thereof both significantly improved digestibility, and simultaneously removed two of the main factors contributing to the recalcitrant nature of lignocellulose. As xylan and lignin have potential value as precursor chemicals, the existing process may in future be extended toward substrate fractionation, a biorefinery concept where value is added to all feedstock constituents.

No abstract

Biorefineries processing lignocellulose will produce chemicals and fuels from chemical constituents, cellulose, hemicelluloses, and lignin to replace fossil-derived products. Fractionation of sugarcane bagasse into three pure streams of chemical constituents was addressed through dissolution of constituents with the ionic liquids, 1-ethyl-3-methylimidazolium acetate ([EMiM]CH(3)COO) or 1-butyl-3-methylimidazolium methyl sulfate ([BMiM]MeSO(4)). Constituents were isolated from the reaction mixture with the anti-solvents acetone (Ā), acetone-water (AW), and sodium hydroxide (NaOH). Delignification was enhanced by NaOH, although resulting in impure product streams. Xylose pre-extraction (75 % w/w) by dilute acid pretreatment, prior to ionic liquid treatment, improved lignin purity after anti-solvent separation. Fractionation efficiency of the combined process was maximized (84 %) by ionic liquid treatment at 125 °C for 120 min, resulting in 80.2 % (w/w) lignin removal and 76.5 % (w/w) lignin recovery. Ionic liquids achieved similar degrees of delignification, although fully digestible cellulose-rich solids were produced only by [EMiM]CH(3)COO treatment.

No abstract