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BACKGROUND Enzymatic hydrolysis of cellulose in lignocellulosic materials suffers from slow reaction rates due to limited access to enzyme adsorption sites and to the high crystallinity of the cellulose. In this study, an attempt was made to facilitate enzymatic hydrolysis by pretreatment of cellulosic materials using the ionic liquid (IL) 1‐allyl‐3‐methylimidazolium formate ([Amim][HCO2]) under mild reaction conditions. The effect of the IL was compared with that of thermochemical pretreatment under acidic conditions. RESULTS The lignocellulosic substrates investigated were native and thermochemically pretreated Norway spruce and sugarcane bagasse. Microcrystalline cellulose (Avicel) was included for comparison. The IL treatments were performed in the temperature range 45–120 °C and, after regeneration and washing of the cellulosic substrates, enzymatic saccharification was carried out at 45 °C for 72 h. After 12 h of hydrolysis, the glucose yields from regenerated native spruce and sugarcane bagasse were up to nine times higher than for the corresponding untreated substrates. The results also show positive effects of pretreatment using [Amim][HCO2] on the hydrolysis of xylan and mannan. Conclusion The present work demonstrates that both native wood and agricultural residues are readily soluble in [Amim][HCO2] under gentle conditions, and that pretreatment with ionic liquids such as [Amim][HCO2] warrants further attention as a potential alternative to conventional pretreatment techniques. © 2013 Society of Chemical Industry

BackgroundPretreatment is a vital step upon biochemical conversion of lignocellulose materials into biofuels. An acid catalyzed thermochemical treatment is the most commonly employed method for this purpose. Alternatively, ionic liquids (ILs), a class of neoteric solvents, provide unique opportunities as solvents for the pretreatment of a wide range of lignocellulose materials. In the present study, four ionic liquid solvents (ILs), two switchable ILs (SILs) DBU–MEA–SO2 and DBU–MEA–CO2, as well as two ‘classical’ ILs [Amim][HCO2] and [AMMorp][OAc], were applied in the pretreatment of five different lignocellulosic materials: Spruce (Picea abies) wood, Pine (Pinus sylvestris) stem wood, Birch (Betula pendula) wood, Reed canary grass (RCG, Phalaris arundinacea), and Pine bark. Pure cellulosic substrate, Avicel, was also included in the study. The investigations were carried out in comparison to acid pretreatments. The efficiency of different pretreatments was then evaluated in terms of sugar release and ethanol fermentation.ResultsExcellent glucan-to-glucose conversion levels (between 75 and 97 %, depending on the biomass and pretreatment process applied) were obtained after the enzymatic hydrolysis of IL-treated substrates. This corresponded between 13 and 77 % for the combined acid treatment and enzymatic hydrolysis. With the exception of 77 % for pine bark, the glucan conversions for the non-treated lignocelluloses were much lower. Upon enzymatic hydrolysis of IL-treated lignocelluloses, a maximum of 92 % hemicelluloses were also released. As expected, the ethanol production upon fermentation of hydrolysates reflected their sugar concentrations, respectively.ConclusionsUtilization of various ILs as pretreatment solvents for different lignocelluloses was explored. SIL DBU–MEA–SO2 was found to be superior solvent for the pretreatment of lignocelluloses, especially in case of softwood substrates (i.e., spruce and pine). In case of birch and RCG, the hydrolysis efficiency of the SIL DBU–MEA–CO2 was similar or even better than that of DBU–MEA–SO2. Further, the IL [AMMorp][OAc] was found as comparably efficient as DBU–MEA–CO2. Pine bark was highly amorphous and none of the pretreatments applied resulted in clear benefits to improve the product yields.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-015-0310-3) contains supplementary material, which is available to authorized users.

The chemical composition of marabou (Dichrostachys cinerea) wood and its treatment with acetic acid were investigated. Two different treatment approaches, direct acetosolv and combined acid prehydrolysis/acetosolv, were evaluated. The effects of acetic acid concentration (50%, 70% and 90%) and temperature (normal boiling temperature and 121°C) on yield of solids, solubilization of lignin and hemicelluloses and recovery of cellulose were evaluated for both treatments. High solubilization of marabou components was observed in the direct acetosolv treatment at 121°C, especially at the highest acetic acid concentration, where around 84.8% of lignin and 78% of hemicelluloses were removed. When the material was subjected to acid prehydrolysis prior to acetosolv treatment, lignin solubilization was improved, especially at low acetic acid concentrations. Above 80% of the solubilized lignin was recovered from the liquors in the direct acetosolv treatment, but the recovery was lower in the combined treatment. Cellulose was well preserved in all the treatment schemes.