Effect of mechanical disruption on the effectiveness of three reactors used for dilute acid pretreatment of corn stover Part 1: chemical and physical substrate analysis.
BACKGROUND
There is considerable interest in the conversion of lignocellulosic biomass to liquid fuels to provide substitutes for fossil fuels. Pretreatments, conducted to reduce biomass recalcitrance, usually remove at least some of the hemicellulose and/or lignin in cell walls. The hypothesis that led to this research was that reactor type could have a profound effect on the properties of pretreated materials and impact subsequent cellulose hydrolysis.


RESULTS
Corn stover was dilute-acid pretreated using commercially relevant reactor types (ZipperClave(®) (ZC), Steam Gun (SG) and Horizontal Screw (HS)) under the same nominal conditions. Samples produced in the SG and HS achieved much higher cellulose digestibilities (88% and 95%, respectively), compared to the ZC sample (68%). Characterization, by chemical, physical, spectroscopic and electron microscopy methods, was used to gain an understanding of the effects causing the digestibility differences. Chemical differences were small; however, particle size differences appeared significant. Sum-frequency generation vibrational spectra indicated larger inter-fibrillar spacing or randomization of cellulose microfibrils in the HS sample. Simons' staining indicated increased cellulose accessibility for the SG and HS samples. Electron microscopy showed that the SG and HS samples were more porous and fibrillated because of mechanical grinding and explosive depressurization occurring with these two reactors. These structural changes most likely permitted increased cellulose accessibility to enzymes, enhancing saccharification.


CONCLUSIONS
Dilute-acid pretreatment of corn stover using three different reactors under the same nominal conditions gave samples with very different digestibilities, although chemical differences in the pretreated substrates were small. The results of the physical and chemical analyses of the samples indicate that the explosive depressurization and mechanical grinding with these reactors increased enzyme accessibility. Pretreatment reactors using physical force to disrupt cell walls increase the effectiveness of the pretreatment process.
National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, CO 80401, USA.
Wei
W
Wang
National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, CO 80401, USA.
Xiaowen
X
Chen
National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, CO 80401, USA.
Bryon S
BS
Donohoe
National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, CO 80401, USA.
Peter N
PN
Ciesielski
National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, CO 80401, USA.
Rui
R
Katahira
National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, CO 80401, USA.
Erik M
EM
Kuhn
Department of Chemical Engineering and Materials Research Institute, Pennsylvania State University, University Park, PA 16802, USA.
Kabindra
K
Kafle
Department of Chemical Engineering and Materials Research Institute, Pennsylvania State University, University Park, PA 16802, USA.
Christopher M
CM
Lee
Department of Forest Biomaterials, North Carolina State University, Raleigh NC 27695, USA.
Sunkyu
S
Park
Department of Chemical Engineering and Materials Research Institute, Pennsylvania State University, University Park, PA 16802, USA.
Seong H
SH
Kim
National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, CO 80401, USA.
Melvin P
MP
Tucker
National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, CO 80401, USA.
Michael E
ME
Himmel
National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, CO 80401, USA.
David K
DK
Johnson
Reactor; biomass; cellulose properties; digestibility; dilute acid pretreatment; substrate accessibility