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Title: Kinetic Modelling and Experimental Studies for the Effects of Fe 2+ Ions on Xylan Hydrolysis with Dilute-Acid Pretreatment and Subsequent Enzymatic Hydrolysis

High-temperature (150-170 degrees C) pretreatment of lignocellulosic biomass with mineral acids is well established for xylan breakdown. Fe 2+ is known to be a cocatalyst of this process although kinetics of its action remains unknown. The present work addresses the effect of ferrous ion concentration on sugar yield and degradation product formation from corn stover for the entire two-step treatment, including the subsequent enzymatic cellulose hydrolysis. The feedstock was impregnated with 0.5% acid and 0.75 mM iron cocatalyst, which was found to be optimal in preliminary experiments. The detailed kinetic data of acid pretreatment, with and without iron, was satisfactorily modelled with a four-step linear sequence of first-order irreversible reactions accounting for the formation of xylooligomers, xylose and furfural as intermediates to provide the values of Arrhenius activation energy. Based on this kinetic modelling, Fe 2+ turned out to accelerate all four reactions, with a significant alteration of the last two steps, that is, xylose degradation. Consistent with this model, the greatest xylan conversion occurred at the highest severity tested under 170 ⁰C/30 min with 0.75 mM Fe 2+, with a total of 8% xylan remaining in the pretreated solids, whereas the operational conditions leading to the highest xylose monomermore » yield, 63%, were milder, 150 degrees C with 0.75 mM Fe 2+ for 20 min. Furthermore, the subsequent enzymatic hydrolysis with the prior addition of 0.75 mM of iron(II) increased the glucose production to 56.3% from 46.3% in the control (iron-free acid). The detailed analysis indicated that conducting the process at lower temperatures yet long residence times benefits the yield of sugars. The above kinetic modelling results of Fe 2+ accelerating all four reactions are in line with our previous mechanistic research showing that the pretreatment likely targets multiple chemistries in plant cell wall polymer networks, including those represented by the C-O-C and C-H bonds in cellulose, resulting in enhanced sugar solubilization and digestibility.« less
Authors:
ORCiD logo [1] ; ORCiD logo [2] ;  [2] ;  [2] ;  [2] ;  [3] ;  [4] ;  [1] ;  [2]
  1. National Renewable Energy Lab. (NREL), Golden, CO (United States). Biosciences Center
  2. National Renewable Energy Lab. (NREL), Golden, CO (United States). National Bioenergy Center
  3. Univ. of North Dakota, Grand Forks, ND (United States). Chemical Engineering Department
  4. Univ. of North Dakota, Grand Forks, ND (United States). Chemistry Department
Publication Date:
Report Number(s):
NREL/JA-5100-70815
Journal ID: ISSN 2073-4344; CATACJ; TRN: US1801718
Grant/Contract Number:
AC36-08GO28308; SC0000997
Type:
Accepted Manuscript
Journal Name:
Catalysts
Additional Journal Information:
Journal Volume: 8; Journal Issue: 2; Journal ID: ISSN 2073-4344
Publisher:
MDPI
Research Org:
National Renewable Energy Lab. (NREL), Golden, CO (United States); Energy Frontier Research Centers (EFRC) (United States). Center for Direct Catalytic Conversion of Biomass to Biofuels (C3Bio)
Sponsoring Org:
USDOE Office of Energy Efficiency and Renewable Energy (EERE), Bioenergy Technologies Office (EE-3B); USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
09 BIOMASS FUELS; pretreatment; enzymatic hydrolysis; bio-ethanol; Lewis acid; iron co-catalyst; kinetics
OSTI Identifier:
1423190