Abstract
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.
Highlights
Pretreatment is a vital step upon biochemical conversion of lignocellulose materials into biofuels
I.e., spruce and pine, are rich in glucomannans, while both birch and reed canary grass are rich in glucoxylanes (Table 1)
It was demonstrated that (S)ionic liquid (IL) treatments could significantly improve the enzymatic hydrolysis of biomass
Summary
Pretreatment is a vital step upon biochemical conversion of lignocellulose materials into biofuels. In a typical biomass conversion process, the raw material is pre-treated to improve the accessibility of polysaccharides for their further conversion into monosaccharides. This is typically performed via processing of biomass in environmentally harmful chemicals, such as sulfuric acid that facilitates the hydrolysis and extraction of sugars leaving most of the lignin in the solid residue. Lignin can be removed by the use of alkaline solutions or organic solvents, leaving solids rich in sugar polysaccharides. A number of pretreatment methods based on the use of different solvents, e.g., acids, alkali, organic solvents and/or other techniques like steam explosion, ammonia fiber explosion, etc. Enzymes can be used to further degrade and hydrolyze the polysaccharides into monosaccharides which can be used to produce various products such as alcoholic fuels (e.g., ethanol, butanol) via fermentation [14,15,16,17]
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