Sugarcane bagasse pretreatment using three imidazolium-based ionic liquids; mass balances and enzyme kinetics

Abstract

BackgroundEffective pretreatment is key to achieving high enzymatic saccharification efficiency in processing lignocellulosic biomass to fermentable sugars, biofuels and value-added products. Ionic liquids (ILs), still relatively new class of solvents, are attractive for biomass pretreatment because some demonstrate the rare ability to dissolve all components of lignocellulosic biomass including highly ordered (crystalline) cellulose. In the present study, three ILs, 1-butyl-3-methylimidazolium chloride ([C4mim]Cl), 1-ethyl-3-methylimidazolium chloride ([C2mim]Cl), 1-ethyl-3-methylimidazolium acetate ([C2mim]OAc) are used to dissolve/pretreat and fractionate sugarcane bagasse. In these IL-based pretreatments the biomass is completely or partially dissolved in ILs at temperatures greater than 130°C and then precipitated by the addition of an antisolvent to the IL biomass mixture. For the first time mass balances of IL-based pretreatments are reported. Such mass balances, along with kinetics data, can be used in process modelling and design.ResultsLignin removals of 10% mass of lignin in bagasse with [C4mim]Cl, 50% mass with [C2mim]Cl and 60% mass with [C2mim]OAc, are achieved by limiting the amount of water added as antisolvent to 0.5 water:IL mass ratio thus minimising lignin precipitation. Enzyme saccharification (24 h, 15FPU) yields (% cellulose mass in starting bagasse) from the recovered solids rank as: [C2mim]OAc(83%) > >[C2mim]Cl(53%) = [C4mim]Cl(53%). Composition of [C2mim]OAc-treated solids such as low lignin, low acetyl group content and preservation of arabinosyl groups are characteristic of aqueous alkali pretreatments while those of chloride IL-treated solids resemble aqueous acid pretreatments. All ILs are fully recovered after use (100% mass as determined by ion chromatography).ConclusionsIn all three ILs regulated addition of water as an antisolvent effected a polysaccharide enriched precipitate since some of the lignin remained dissolved in the aqueous IL solution. Of the three IL studied [C2mim]OAc gave the best saccharification yield, material recovery and delignification. The effects of [C2mim]OAc pretreatment resemble those of aqueous alkali pretreatments while those of [C2mim]Cl and [C4mim]Cl resemble aqueous acid pretreatments. The use of imidazolium IL solvents with shorter alkyl chains results in accelerated dissolution, pretreatment and degradation.

Multi-Scale Structural Studies of Sequential Ionic Liquids and Alkali Pretreated Corn Stover and Sugarcane Bagasse

“…The conversion yield for cellulose was 72% on the sample treated with H 2 SO 4 and 1% NaOH which was comparatively much better as compared to the 22% in case of untreated sample [54]. Similarly, Karatzos et al [55] observed the compositional and structural characteristics of sugarcane bagasse after pretreating it with three of the ionic liquids: 1-ethyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium chloride and 1-ethyl-3-methylimidazolium acetate. The concerned study found 1-ethyl-3-methylimidazolium acetate to be the most effective in delignification and also in saccharification yields.…”

The combination of plant-expressed cellobiohydrolase and low dosages of cellulases for the hydrolysis of sugar cane bagasse

“…The compositions of untreated bagasse and bagasse pretreated in the Mackay Renewable Biocommodities Pilot Plant with dilute H 2 SO 4 steam explosion, dilute NaOH steam explosion, and glycerol/HCl steam explosion under conditions described in our previous study [23] are presented in Table 1. The compositions of untreated (depithed) and bagasse pretreated at the laboratory scale with acidified EC/EG [38], BMIMCl [39], and ballmilling are presented in the same table. Percentages of glucan (cellulose), xylan (the majority of hemicellulose), lignin, and ash were calculated on a dry mass basis.…”

“…The EC/EG pretreatment was undertaken at a solidto-liquid ratio of 4:1 (w/w) in the presence of 1.2% (w/w) H 2 SO 4 at 90°C for 30 min using the method described by Zhang et al (2013) [38]. The ionic liquid pretreatment was undertaken with BMIMCl containing 0.7% (w/w) water at a 10:1 (w/w) liquid-to-solid ratio at 150°C for 1 h using the method described by Karatzos et al (2012) [39]. Ball-milling was achieved using a Pulverisette 6 (Fritsch, GmbH) at ambient temperature using 10 min on/off for a total of 16 h. All pretreated bagasse samples were washed extensively with deionised water and freeze dried.…”

Structure and Saccharification of Sugarcane Bagasse Pretreated with Acid Coupled Alkaline

“…switchgrass), agricultural or forestry residues (e.g. sugarcane bagasse), present an abundant renewable energy resource [1]. Along with the decreasing reserves of fossil fuel resources and the increasing of world energy demand, the utilization of biomass as renewable and sustainable feedstock to produce alternative fuels and chemicals have attracted much interest in recent years.…”