Formation and Fate of Carboxylic Acids in the Lignin-First Biorefining of Lignocellulose via H-Transfer Catalyzed by Raney Ni

Ines Graca, Robert T. Woodward, Marco Kennema, Roberto Rinaldi*

*Corresponding author for this work

Research output: Contribution to journalArticle

8 Citations (Scopus)

Abstract

Lignin-first biorefining constitutes a new research field in which the overarching objective is the prevention of lignin recalcitrance while providing high-quality pulps. For this purpose, the solvent extraction of lignin is performed in the presence of a hydrogenation catalyst, employing H2 pressure or an H-donor solvent (e.g., 2-propanol), and thus leading to passivation of reactive lignin fragments via reductive processes. As a result, lignin-first biorefining methods generate high-quality pulps in addition to low-molecular-weight lignin streams with high molecular uniformity. Nonetheless, upon cooking lignocellulose in solvent mixtures containing water, other processes on the lignocellulosic matrix take place, releasing soluble intermediates. In fact, hemicellulose undergoes deacetylation, to a variable extent, releasing acetic acid into the liquor. Moreover, formic acid can also be formed as a degradation product of hemicellulose C6-sugars also released into the liquor. However, despite this general notion, the formation and fate of these carboxylic acids during the cooking of lignocellulosic substrates, and the effects these acids may have on hydrogenation catalyst performance remain poorly understood. In this report, we examine both the formation and subsequent fate of formic acid and acetic acid during lignocellulose deconstruction for both a lignin-first biorefining method (via H-transfer reactions in the presence of Raney Ni catalyst) and its equivalent Organosolv process with no added acid or hydrogenation catalyst. A mechanism for the mitigation of formic acid formation in the presence of Raney Ni catalyst is outlined via the hydrogenation of sugars to sugar alcohols. Furthermore, the effects of the carboxylic acids on Raney Ni performance are assessed, using the transfer-hydrogenation of phenol to cyclohexanol/cyclohexanone as a model reaction, elucidating inhibition rates of the acids. Finally, we conclude with the implications of these results for the design of lignin-first biorefining processes. In a broader context, understanding of the formation and fate of carboxylic acids during CUB is crucial to producing high-quality pulps with high degrees of polymerization and high xylan contents.

Original languageEnglish
Pages (from-to)13408-13419
Number of pages12
JournalACS Sustainable Chemistry and Engineering
Volume6
Issue number10
DOIs
Publication statusPublished - 1 Oct 2018

Fingerprint

Lignin
carboxylic acid
Carboxylic Acids
Carboxylic acids
formic acid
lignin
Hydrogenation
catalyst
Formic acid
Catalysts
Pulp
sugar
Cooking
Acetic acid
Sugars
Acetic Acid
acetic acid
Acids
acid
Cyclohexanols

Keywords

  • 2-Propanol
  • Carboxylic acid
  • Catalyst stability
  • Catalytic H-transfer
  • Lignin-first biorefining
  • Raney Ni

ASJC Scopus subject areas

  • Chemistry(all)
  • Environmental Chemistry
  • Chemical Engineering(all)
  • Renewable Energy, Sustainability and the Environment

Cite this

Formation and Fate of Carboxylic Acids in the Lignin-First Biorefining of Lignocellulose via H-Transfer Catalyzed by Raney Ni. / Graca, Ines; Woodward, Robert T.; Kennema, Marco; Rinaldi, Roberto.

In: ACS Sustainable Chemistry and Engineering, Vol. 6, No. 10, 01.10.2018, p. 13408-13419.

Research output: Contribution to journalArticle

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abstract = "Lignin-first biorefining constitutes a new research field in which the overarching objective is the prevention of lignin recalcitrance while providing high-quality pulps. For this purpose, the solvent extraction of lignin is performed in the presence of a hydrogenation catalyst, employing H2 pressure or an H-donor solvent (e.g., 2-propanol), and thus leading to passivation of reactive lignin fragments via reductive processes. As a result, lignin-first biorefining methods generate high-quality pulps in addition to low-molecular-weight lignin streams with high molecular uniformity. Nonetheless, upon cooking lignocellulose in solvent mixtures containing water, other processes on the lignocellulosic matrix take place, releasing soluble intermediates. In fact, hemicellulose undergoes deacetylation, to a variable extent, releasing acetic acid into the liquor. Moreover, formic acid can also be formed as a degradation product of hemicellulose C6-sugars also released into the liquor. However, despite this general notion, the formation and fate of these carboxylic acids during the cooking of lignocellulosic substrates, and the effects these acids may have on hydrogenation catalyst performance remain poorly understood. In this report, we examine both the formation and subsequent fate of formic acid and acetic acid during lignocellulose deconstruction for both a lignin-first biorefining method (via H-transfer reactions in the presence of Raney Ni catalyst) and its equivalent Organosolv process with no added acid or hydrogenation catalyst. A mechanism for the mitigation of formic acid formation in the presence of Raney Ni catalyst is outlined via the hydrogenation of sugars to sugar alcohols. Furthermore, the effects of the carboxylic acids on Raney Ni performance are assessed, using the transfer-hydrogenation of phenol to cyclohexanol/cyclohexanone as a model reaction, elucidating inhibition rates of the acids. Finally, we conclude with the implications of these results for the design of lignin-first biorefining processes. In a broader context, understanding of the formation and fate of carboxylic acids during CUB is crucial to producing high-quality pulps with high degrees of polymerization and high xylan contents.",
keywords = "2-Propanol, Carboxylic acid, Catalyst stability, Catalytic H-transfer, Lignin-first biorefining, Raney Ni",
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note = "This work was conducted with the financial support provided by the ERC Consolidator Grant LIGNINFIRST (Project Number: 725762). The authors are thankful to Brazilian Synchrotron Light Laboratory (LNLS) for measurements in the DXAS beamline (Project Number: 20160732). R.R. and M.K. are grateful to Dr. Fabian Meemken (ETH Z{\"u}rich) for granting us the access to the ATR-IR facilities.",
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AU - Kennema, Marco

AU - Rinaldi, Roberto

N1 - This work was conducted with the financial support provided by the ERC Consolidator Grant LIGNINFIRST (Project Number: 725762). The authors are thankful to Brazilian Synchrotron Light Laboratory (LNLS) for measurements in the DXAS beamline (Project Number: 20160732). R.R. and M.K. are grateful to Dr. Fabian Meemken (ETH Zürich) for granting us the access to the ATR-IR facilities.

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N2 - Lignin-first biorefining constitutes a new research field in which the overarching objective is the prevention of lignin recalcitrance while providing high-quality pulps. For this purpose, the solvent extraction of lignin is performed in the presence of a hydrogenation catalyst, employing H2 pressure or an H-donor solvent (e.g., 2-propanol), and thus leading to passivation of reactive lignin fragments via reductive processes. As a result, lignin-first biorefining methods generate high-quality pulps in addition to low-molecular-weight lignin streams with high molecular uniformity. Nonetheless, upon cooking lignocellulose in solvent mixtures containing water, other processes on the lignocellulosic matrix take place, releasing soluble intermediates. In fact, hemicellulose undergoes deacetylation, to a variable extent, releasing acetic acid into the liquor. Moreover, formic acid can also be formed as a degradation product of hemicellulose C6-sugars also released into the liquor. However, despite this general notion, the formation and fate of these carboxylic acids during the cooking of lignocellulosic substrates, and the effects these acids may have on hydrogenation catalyst performance remain poorly understood. In this report, we examine both the formation and subsequent fate of formic acid and acetic acid during lignocellulose deconstruction for both a lignin-first biorefining method (via H-transfer reactions in the presence of Raney Ni catalyst) and its equivalent Organosolv process with no added acid or hydrogenation catalyst. A mechanism for the mitigation of formic acid formation in the presence of Raney Ni catalyst is outlined via the hydrogenation of sugars to sugar alcohols. Furthermore, the effects of the carboxylic acids on Raney Ni performance are assessed, using the transfer-hydrogenation of phenol to cyclohexanol/cyclohexanone as a model reaction, elucidating inhibition rates of the acids. Finally, we conclude with the implications of these results for the design of lignin-first biorefining processes. In a broader context, understanding of the formation and fate of carboxylic acids during CUB is crucial to producing high-quality pulps with high degrees of polymerization and high xylan contents.

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