BackgroundSugarcane bagasse is an abundant and geographically widespread agro-industrial residue with high carbohydrate content, making it a strong candidate feedstock for the bio-based economy. This study examines the use of the low-cost protic ionic liquid triethylammonium hydrogen sulfate ([TEA][HSO4]) to fractionate a range of South African sugarcane bagasse preparations into a cellulose-rich pulp and lignin. The study seeks to optimize pretreatment conditions and examine the necessity of applying a depithing step on bagasse prior to pretreatment.ResultsPretreatment of five bagasse preparations, namely whole, industrially depithed, laboratory depithed (short and long fiber) and pith bagasse with [TEA][HSO4]:[H2O] (4:1 w/w) solutions produced highly digestible cellulose-rich pulps, as assessed by residual lignin analysis and enzymatic hydrolysis. Pretreatment under the optimized condition of 120 °C for 4 h produced a pretreated cellulose pulp with up to 90% of the lignin removed and enabled the release of up to 69% glucose contained in the bagasse via enzymatic hydrolysis. Glucose yields from whole and depithed bagasse preparations were very similar. Significant differences in lignin recovery were obtained for laboratory depithed bagasse compared with whole and industrially depithed bagasse. The silica-rich ash components of bagasse were seen to partition mainly with the pulp, from where they could be easily recovered in the post-hydrolysis solids.ConclusionsThe five bagasse preparations were compared but did not show substantial differences in composition or cellulose digestibility after pretreatment. Evidence was presented that a depithing step appears to be unnecessary prior to ionoSolv fractionation, potentially affording significant cost and energy savings. Instead, lignin re-deposition onto the pulp surface (and, in turn, particle size and shape) appeared to be major factors affecting the conditioning of bagasse with the applied IL. We show that pith bagasse, a common by-product of paper making, can be successfully conditioned for high glucose release while allowing recovery of lignin and silica-rich ash. The glucose yields obtained for bagasse using [TEA][HSO4]-water mixtures were ~ 75% as high as for conventional aprotic ionic liquids such as [Emim][OAc]; this result is highly promising for commercialization of ionoSolv processing given [TEA][HSO4] is 40 times less expensive, thermally stable and recyclable.Electronic supplementary materialThe online version of this article (10.1186/s13068-018-1247-0) contains supplementary material, which is available to authorized users.

aIn South Africa, approximately 3 × 10 6 tons of sugarcane bagasse is produced annually by 14 factories located on the north coast of KwaZuluNatal. It is one of the most readily available lignocellulosic materials for ethanol production through enzymatic saccharification and hydrolysis. Pre-treatment enables disruption of the naturally resistant structure of lignocellulosic biomass to make the cellulose accessible to hydrolysis for conversion to biofuels. In this study, pre-treatment of depithed bagasse and mill-run bagasse was done using acid (3% H2SO4 v/v) followed by alkali (4% NaOH w/v), and the pre-treated solid was subjected to enzymatic hydrolysis. The effects of different conditions for enzymatic saccharification such as enzyme dose, reaction time, and amount of surfactant were studied in detail. The pre-treated substrate (10% w/v) when hydrolysed using 30 FPU/gds/40 FPU/g dry substrate (gds) with 0.4% (v/v) Tween® 80 for 20 h resulted in 608 mg/gds (depithed bagasse) and 604 mg/gds (mill-run bagasse) total reducing sugars.

Globally there is a drive for the use of renewable materials for the production of biofuels or high-end value chemicals. The current production of chemicals from crude oil refining is unsustainable and leads to global warming effects. Biomass is the most attractive renewable energy source for biofuel or fine chemical production. Sugarcane bagasse is a by-product of the sugar milling industry and is abundantly available. In this study lignin was sequentially extracted using ionic liquids. The ionic liquids (ILs) 1-ethyl-3-methylimidazolium acetate ([Emim][OAc]) and triethylammonium hydrogen sulfate ([HNEt3][HSO4]) were used to fractionate the sugarcane bagasse. The pre-treatment of sugarcane bagasse was carried out at different temperatures ranging from 90 - 150 0C and reaction times ranging from 1 - 24 h in a convection oven at a 10 % biomass loading. Both ILs were able to dissolve the raw bagasse samples at 120 0C with [Emim][OAc] giving a lignin maxima of 28.8 % and a low pulp yield of 57 % after 12 h; [HNEt3][HSO4] gave a lignin recovery of 17.2 % and low pulp yield of 58.5 % after 6 h. Regenerated lignin was obtained by adding ethanol/ water to the mixture followed by vacuum filtration. The regenerated pulp materials were characterized by Scanning Electron Microscope (SEM) to study the morphology; Fourier Transform Infrared Spectroscopy (FTIR) to study the characteristic bands and thermal analysis to study the thermal stability.