title: Multi-scale processes of beech wood disintegration and pretreatment with 1-ethyl-3-methylimidazolium acetate/water mixtures.
abstract: BACKGROUND
  The valorization of biomass for chemicals and fuels requires efficient pretreatment. One effective strategy involves the pretreatment with ionic liquids which enables enzymatic saccharification of wood within a few hours under mild conditions. This pretreatment strategy is, however, limited by water and the ionic liquids are rather expensive. The scarce understanding of the involved effects, however, challenges the design of alternative pretreatment concepts. This work investigates the multi length-scale effects of pretreatment of wood in 1-ethyl-3-methylimidazolium acetate (EMIMAc) in mixtures with water using spectroscopy, X-ray and neutron scattering.
  
  
  RESULTS
  The structure of beech wood is disintegrated in EMIMAc/water mixtures with a water content up to 8.6 wt%. Above 10.7 wt%, the pretreated wood is not disintegrated, but still much better digested enzymatically compared to native wood. In both regimes, component analysis of the solid after pretreatment shows an extraction of few percent of lignin and hemicellulose. In concentrated EMIMAc, xylan is extracted more efficiently and lignin is defunctionalized. Corresponding to the disintegration at macroscopic scale, SANS and XRD show isotropy and a loss of crystallinity in the pretreated wood, but without distinct reflections of type II cellulose. Hence, the microfibril assembly is decrystallized into rather amorphous cellulose within the cell wall.
  
  
  CONCLUSIONS
  The molecular and structural changes elucidate the processes of wood pretreatment in EMIMAc/water mixtures. In the aqueous regime with >10.7 wt% water in EMIMAc, xyloglucan and lignin moieties are extracted, which leads to coalescence of fibrillary cellulose structures. Dilute EMIMAc/water mixtures thus resemble established aqueous pretreatment concepts. In concentrated EMIMAc, the swelling due to decrystallinization of cellulose, dissolution of cross-linking xylan, and defunctionalization of lignin releases the mechanical stress to result in macroscopic disintegration of cells. The remaining cell wall constituents of lignin and hemicellulose, however, limit a recrystallization of the solvated cellulose. These pretreatment mechanisms are beyond common pretreatment concepts and pave the way for a formulation of mechanistic requirements of pretreatment with simpler pretreatment liquors.
authors.affiliation: Aachener Verfahrenstechnik-Process Systems Engineering, RWTH Aachen University, Turmstr. 46, 52064 Aachen, Germany ; JARA-ENERGY, Jülich, Germany.
authors.forename: Jörn
authors.initials: J
authors.lastname: Viell
authors.affiliation: Department of Electrical and Computer Engineering, College of Engineering, Northeastern University, 360 Huntington Avenue, Boston, MA 02115 USA.
authors.forename: Hideyo
authors.initials: H
authors.lastname: Inouye
authors.affiliation: Jülich Centre for Neutron Science, Forschungszentrum Jülich GmbH, Outstation at MLZ, Lichtenbergstraße 1, 85747 Garching, Germany.
authors.forename: Noemi K
authors.initials: NK
authors.lastname: Szekely
authors.affiliation: Jülich Centre for Neutron Science, Forschungszentrum Jülich GmbH, Outstation at MLZ, Lichtenbergstraße 1, 85747 Garching, Germany.
authors.forename: Henrich
authors.initials: H
authors.lastname: Frielinghaus
authors.affiliation: Aachener Verfahrenstechnik-Process Systems Engineering, RWTH Aachen University, Turmstr. 46, 52064 Aachen, Germany.
authors.forename: Caroline
authors.initials: C
authors.lastname: Marks
authors.affiliation: Aachener Verfahrenstechnik-Enzyme Process Technology, RWTH Aachen University, Worringer Weg 1, 52074 Aachen, Germany.
authors.forename: Yumei
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Aachener Verfahrenstechnik-Enzyme Process Technology, RWTH Aachen University, Worringer Weg 1, 52074 Aachen, Germany.
authors.forename: Nico
authors.initials: N
authors.lastname: Anders
authors.affiliation: Aachener Verfahrenstechnik-Enzyme Process Technology, RWTH Aachen University, Worringer Weg 1, 52074 Aachen, Germany ; DWI-Leibniz Institute für Interactive Materials, Forckenbeckstr. 40, 52072 Aachen, Germany ; Institute of Biochemical Engineering, Technische Universität Braunschweig, Gaußstr. 17, 38102 Braunschweig, Germany.
authors.forename: Antje C
authors.initials: AC
authors.lastname: Spiess
authors.affiliation: Bioengineering Department and Chemistry and Chemical Biology Department, Northeastern University, 360 Huntington Ave., Boston, MA 02115 USA.
authors.forename: Lee
authors.initials: L
authors.lastname: Makowski
keywords: Crystallinity; Disintegration; EMIMAc; Ionic liquid; Lignocellulose; Microfibrils; Pretreatment; SANS; XRD