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Open Access Research

Impact of high biomass loading on ionic liquid pretreatment

Alejandro G Cruz1, Chessa Scullin12, Chen Mu1, Gang Cheng123, Vitalie Stavila2, Patanjali Varanasi1, Dongyan Xu1, Jeff Mentel4, Yi-De Chuang5, Blake A Simmons12 and Seema Singh12*

Author Affiliations

1 Deconstruction Division, Joint BioEnergy Institute, Lawrence Berkeley National Laboratory, Berkeley CA, USA

2 Biological and Materials Science Center, Sandia National Laboratories, Livermore CA, USA

3 Beijing University of Chemical Technology, Beijing, China

4 Malvern Instruments LTD, Worcestershire, WR14 1XZ, UK

5 Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA, USA

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Biotechnology for Biofuels 2013, 6:52  doi:10.1186/1754-6834-6-52

Published: 11 April 2013

Abstract

Background

Ionic liquid (IL) pretreatment has shown great potential as a novel pretreatment technology with high sugar yields. To improve process economics of pretreatment, higher biomass loading is desirable. The goal of this work is to establish, the impact of high biomass loading of switchgrass on IL pretreatment in terms of viscosity, cellulose crystallinity, chemical composition, saccharification kinetics, and sugar yield.

Results

The pretreated switchgrass/IL slurries show frequency dependent shear thinning behavior. The switchgrass/IL slurries show a crossover from viscous behavior at 3 wt% to elastic behavior at 10 wt%. The relative glucan content of the recovered solid samples is observed to decrease with increasing levels of lignin and hemicelluloses with increased biomass loading. The IL pretreatment led to a transformation of cellulose crystalline structure from I to II for 3, 10, 20 and 30 wt% samples, while a mostly amorphous structure was found for 40 and 50 wt% samples.

Conclusions

IL pretreatment effectively reduced the biomass recalcitrance at loadings as high as 50 wt%. Increased shear viscosity and a transition from ‘fluid’ like to ‘solid’ like behavior was observed with increased biomass loading. At high biomass loadings shear stress produced shear thinning behavior and a reduction in viscosity by two orders of magnitude, thereby reducing the complex viscosity to values similar to lower loadings. The rheological properties and sugar yields indicate that 10 to 50 wt% may be a reasonable and desirable target for IL pretreatment under certain operating conditions.

Keywords:
Ionic liquid pretreatment; Biofuels; High biomass loading; Rheology; Cellulose crystallinity