title: Effect of mechanical disruption on the effectiveness of three reactors used for dilute acid pretreatment of corn stover Part 2: morphological and structural substrate analysis.
abstract: BACKGROUND
  Lignocellulosic biomass is a renewable, naturally mass-produced form of stored solar energy. Thermochemical pretreatment processes have been developed to address the challenge of biomass recalcitrance, however the optimization, cost reduction, and scalability of these processes remain as obstacles to the adoption of biofuel production processes at the industrial scale. In this study, we demonstrate that the type of reactor in which pretreatment is carried out can profoundly alter the micro- and nanostructure of the pretreated materials and dramatically affect the subsequent efficiency, and thus cost, of enzymatic conversion of cellulose.
  
  
  RESULTS
  Multi-scale microscopy and quantitative image analysis was used to investigate the impact of different biomass pretreatment reactor configurations on plant cell wall structure. We identify correlations between enzymatic digestibility and geometric descriptors derived from the image data. Corn stover feedstock was pretreated under the same nominal conditions for dilute acid pretreatment (2.0 wt% H2SO4, 160°C, 5 min) using three representative types of reactors: ZipperClave® (ZC), steam gun (SG), and horizontal screw (HS) reactors. After 96 h of enzymatic digestion, biomass treated in the SG and HS reactors achieved much higher cellulose conversions, 88% and 95%, respectively, compared to the conversion obtained using the ZC reactor (68%). Imaging at the micro- and nanoscales revealed that the superior performance of the SG and HS reactors could be explained by reduced particle size, cellular dislocation, increased surface roughness, delamination, and nanofibrillation generated within the biomass particles during pretreatment.
  
  
  CONCLUSIONS
  Increased cellular dislocation, surface roughness, delamination, and nanofibrillation revealed by direct observation of the micro- and nanoscale change in accessibility explains the superior performance of reactors that augment pretreatment with physical energy.
authors.affiliation: Biosciences Center, National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, CO, 80401, USA.
authors.forename: Peter N
authors.initials: PN
authors.lastname: Ciesielski
authors.affiliation: Biosciences Center, National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, CO, 80401, USA.
authors.forename: Wei
authors.initials: W
authors.lastname: Wang
authors.affiliation: National Bioenergy Center, National Renewable Energy Laboratory, Golden, CO, USA.
authors.forename: Xiaowen
authors.initials: X
authors.lastname: Chen
authors.affiliation: Biosciences Center, National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, CO, 80401, USA.
authors.forename: Todd B
authors.initials: TB
authors.lastname: Vinzant
authors.affiliation: National Bioenergy Center, National Renewable Energy Laboratory, Golden, CO, USA.
authors.forename: Melvin P
authors.initials: MP
authors.lastname: Tucker
authors.affiliation: Biosciences Center, National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, CO, 80401, USA.
authors.forename: Stephen R
authors.initials: SR
authors.lastname: Decker
authors.affiliation: Biosciences Center, National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, CO, 80401, USA.
authors.forename: Michael E
authors.initials: ME
authors.lastname: Himmel
authors.affiliation: Biosciences Center, National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, CO, 80401, USA.
authors.forename: David K
authors.initials: DK
authors.lastname: Johnson
authors.affiliation: Biosciences Center, National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, CO, 80401, USA.
authors.forename: Bryon S
authors.initials: BS
authors.lastname: Donohoe
keywords: Biomass conversion; Delamination; Dilute acid pretreatment; Nanofibrillation; Quantitative image analysis; Severity factor