Coupled enzymatic hydrolysis and ethanol fermentation: ionic liquid pretreatment for enhanced yields.
BACKGROUND
Pretreatment 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.


RESULTS
Excellent 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.


CONCLUSIONS
Utilization 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.
Department of Chemistry, Technical Chemistry and Sustainable Chemical Technology, Chemical-Biological Centre, Umeå University, 901 87 Umeå, Sweden ; Department of Chemical and Biological Engineering, Chalmers University of Technology, Kemivägen 10, 412 96 Göteborg, Sweden.
Venkata Prabhakar
VP
Soudham
Department of Chemistry, Technical Chemistry and Sustainable Chemical Technology, Chemical-Biological Centre, Umeå University, 901 87 Umeå, Sweden.
Dilip Govind
DG
Raut
Department of Chemistry, Technical Chemistry and Sustainable Chemical Technology, Chemical-Biological Centre, Umeå University, 901 87 Umeå, Sweden.
Ikenna
I
Anugwom
Department of Chemical and Biological Engineering, Chalmers University of Technology, Kemivägen 10, 412 96 Göteborg, Sweden.
Tomas
T
Brandberg
Department of Chemical and Biological Engineering, Chalmers University of Technology, Kemivägen 10, 412 96 Göteborg, Sweden.
Christer
C
Larsson
Department of Chemistry, Technical Chemistry and Sustainable Chemical Technology, Chemical-Biological Centre, Umeå University, 901 87 Umeå, Sweden ; Laboratory of Industrial Chemistry and Reaction Engineering, Johan Gadolin Process Chemistry Centre, Åbo Akademi University, 20500 Åbo-Turku, Finland.
Jyri-Pekka
JP
Mikkola
(Switchable) Ionic liquids; Bio-fuels; Ethanol; Fermentation; Hydrolysis; Lignocellulose; Pretreatment