Understanding the impact of ionic liquid pretreatment on eucalyptus

Abstract

Background: The development of cost-competitive biofuels necessitates the realization of advanced biomass pretreatment technologies. Ionic liquids provide a basis for one of the most promising pretreatment technologies and are known to allow effective processing of cellulose and some biomass species. Results & discussion: Here, we demonstrate that the ionic liquid 1-ethyl-3-methyl imidazolium acetate, [C2mim][OAc], induces structural changes at the molecular level in the cell wall of Eucalyptus globulus. Deacetylation of xylan, acetylation of the lignin units, selective removal of guaiacyl units (increasing the syringyl:guaiacyl ratio) and decreased β-ether content were the most prominent changes observed. Scanning electron microscopy images of the plant cell wall sections reveal extensive swelling during [C2mim][OAc] pretreatment. X-ray diffraction measurements indicate a change in cellulose crystal structure from cellulose I to cellulose II after [C2mim][OAc] pretreatment. Enzymatic saccharification of the pretreated material produced increased sugar yields and improved hydrolysis kinetics after [C2mim][OAc] pretreatment. Conclusion: These results provide new insight into the mechanism of ionic liquid pretreatment and reaffirm that this approach may be promising for the production of cellulosic biofuels from woody biomass.

Acknowledgments

The authors thank William Heller for his assistance with the small-angle neutron scattering experiments. We also thank Hoon Kim and Dan Yelle for help with polysaccharide NMR assignments. The authors thank Seema Singh, Lan Sun, Chenlin Li and Joanna Chen for their assistance with the preparation of the cross-sections of Eucalyptus globulus. The authors thank ArborGen and Novozymes for the gifts of the E. globulus biomass and cellulase cocktails, respectively.

Ethical conduct of research

The authors state that they have obtained appropriate institutional review board approval or have followed the principles outlined in the Declaration of Helsinki for all human or animal experimental investigations. In addition, for investigations involving human subjects, informed consent has been obtained from the participants involved.

Financial & competing interests disclosure

Small-angle neutron scattering experiments are performed at Oak Ridge National Laboratory’s High Flux Isotope Reactor, which is supported by the Scientific User Facilities Division, Office of Basic Energy Sciences, US Department of Energy (DOE). This work was part of the DOE Joint BioEnergy Institute (http://www.jbei.org) supported by the US DOE, Office of Science, Office of Biological and Environmental Research, through contract DE-AC02-05CH11231 between Lawrence Berkeley National Laboratory and the US Department of Energy, and was also supported in part by the DOE Great Lakes BioEnergy Research Center (DOE Office of Science BER DE-FC02-07ER64494). The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

No writing assistance was utilized in the production of this manuscript.