Title: Reductive Catalytic Fractionation of Corn Stover Lignin

Abstract

Reductive catalytic fractionation (RCF) has emerged as an effective biomass pretreatment strategy to depolymerize lignin into tractable fragments in high yields. We investigate the RCF of corn stover, a highly abundant herbaceous feedstock, using carbon-supported Ru and Ni catalysts at 200 and 250 °C in methanol and, in the presence or absence of an acid cocatalyst (H₃PO₄ or an acidified carbon support). Three key performance variables were studied: (1) the effectiveness of lignin extraction as measured by the yield of lignin oil, (2) the yield of monomers in the lignin oil, and (3) the carbohydrate retention in the residual solids after RCF. The monomers included methyl coumarate/ferulate, propyl guaiacol/syringol, and ethyl guaiacol/syringol. The Ru and Ni catalysts performed similarly in terms of product distribution and monomer yields. The monomer yields increased monotonically as a function of time for both temperatures. At 6 h, monomer yields of 27.2 and 28.3% were obtained at 250 and 200 °C, respectively, with Ni/C. The addition of an acid cocatalysts to the Ni/C system increased monomer yields to 32% for acidified carbon and 38% for phosphoric acid at 200 °C. The monomer product distribution was dominated by methyl coumarate regardless of the use of themore » acid cocatalysts. The use of phosphoric acid at 200 °C or the high temperature condition without acid resulted in complete lignin extraction and partial sugar solubilization (up to 50%) thereby generating lignin oil yields that exceeded the theoretical limit. In contrast, using either Ni/C or Ni on acidified carbon at 200 °C resulted in moderate lignin oil yields of ca. 55%, with sugar retention values >90%. Notably, these sugars were amenable to enzymatic digestion, reaching conversions >90% at 96 h. Characterization studies on the lignin oils using two-dimensional heteronuclear single quantum coherence nuclear magnetic resonance and gel permeation chromatrography revealed that soluble oligomers are formed via solvolysis, followed by further fragmentation on the catalyst surface via hydrogenolysis. Overall, the results show that clear trade-offs exist between the levels of lignin extraction, monomer yields, and carbohydrate retention in the residual solids for different RCF conditions of corn stover.« less

Authors:

Anderson, Eric M. ^[1]; Katahira, Rui ^[2]; Reed, Michelle ^[2]; Resch, Michael G. ^[2]; Karp, Eric M. ^[2]; Beckham, Gregg T. ^[2]; Román-Leshkov, Yuriy ^[3]

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+ Show Author Affiliations

1. Department of Chemical Engineering, Massachusetts Institute of Technology, 25 Ames ST Cambridge, Massachusetts 02139, United States, National Bioenergy Center, National Renewable Energy Laboratory, 15013 Denver West PKY Golden, Colorado 80401, United States
2. National Bioenergy Center, National Renewable Energy Laboratory, 15013 Denver West PKY Golden, Colorado 80401, United States
3. Department of Chemical Engineering, Massachusetts Institute of Technology, 25 Ames ST Cambridge, Massachusetts 02139, United States

Publication Date:

2016-09-03

Research Org.:

National Renewable Energy Lab. (NREL), Golden, CO (United States)

Sponsoring Org.:

USDOE Office of Energy Efficiency and Renewable Energy (EERE), Sustainable Transportation Office. Bioenergy Technologies Office; National Science Foundation (NSF); USDOE Office of Science (SC), Workforce Development for Teachers and Scientists (WDTS)

OSTI Identifier:

1375538

Alternate Identifier(s):

OSTI ID: 1339082

Report Number(s):

NREL/JA-5100-67673
Journal ID: ISSN 2168-0485

Grant/Contract Number:  

AC36-08GO28308; 1454299; SC0014664

Resource Type:

Published Article

Journal Name:

ACS Sustainable Chemistry & Engineering

Additional Journal Information:

Journal Name: ACS Sustainable Chemistry & Engineering Journal Volume: 4 Journal Issue: 12; Journal ID: ISSN 2168-0485

Publisher:

American Chemical Society (ACS)

Country of Publication:

United States

Language:

English

Subject:

09 BIOMASS FUELS; biomass; lignin; lignocellulose; pretreatment; carbohydrates; organic polymers; monomers; biopolymers extraction