Hydrogenolysis of Lignocellulosic Biomass with Carbon Monoxide or Formate in Pressurized Hot Water

Schuchardt, Ulf; Gallo, Jean Marcel R.

doi:10.1039/9781782620099-00242

Cited by 1 publication

(3 citation statements)

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“…This liquor showed a marked increase in formic acid concentration, from 5.4 to 18.9 mM, in the initial hour of Poplar wood cooking, after which, the formic acid levels gradually decreased to 13.2 mM at 6 h. This result suggests that formic acid is also utilized as a reducing agent in the Organosolv process. Previous works on hydrogenolysis of lignocellulosic substrates in the presence of formate/formic acid elucidated this route of formic acid consumption (Scheme a–c) . This process involves the formylation of hydroxyl groups occurring in sugars and lignin, followed by the elimination of CO 2 , leading to species hydrodeoxygenation.…”

Section: Resultsmentioning

confidence: 98%

“…Hydrodeoxygenation of alcohol moieties occurring in sugars and lignin via formylation and CO2 elimination. (32) Regarding the formation of acetic acid, Figure 1b shows that, after 1h cooking of Poplar at 200ºC, the levels of acetic acid in the CUB liquor became higher than those in the Organosolv liquor. Surprisingly, acetic acid levels decreased throughout the course of the Organosolv process, while maintaining at a much higher concentration in the CUB liquor.…”

Section: Methodsmentioning

confidence: 97%

“…Previous works on hydrogenolysis of lignocellulosic substrates in the presence of formate/ formic acid elucidated this route of formic acid consumption (Scheme 2a−c). 32 This process involves the formylation of hydroxyl groups occurring in sugars and lignin, followed by the elimination of CO 2 , leading to species hydrodeoxygenation.…”

Section: ■ Introductionmentioning

confidence: 99%

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

Graça

Woodward

Kennema

et al. 2018

ACS Sustainable Chem. Eng.

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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. An apparent 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. the higher pH of CUB liquors compared to those from the Organosolv process (∆pH = 1-2), suggesting that Raney Ni should be able to decompose acidic content in the liquor by reductive processes, (7),(13) mostly in the form of acetic acid and formic acid. (6),(7),(14)-(19) Acetic acid is produced via the hydrolysis of the acetyl groups (deacetylation) of hemicellulose. The concentration of acetic acid is especially significant in the hydrolysates of hardwoods as Oacetyl groups substitute a considerable number of the OH-groups of the xylose units. (18),(20),(21) Indeed, acetyl groups account for 3-5% of hardwood's composition, while this number is 1-2% in softwoods. (21) On the other hand, formyl groups rarely occur in woods. Typically, formyl contents do not exceed 0.04% of the wood composition. (21) It...

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Section: Resultsmentioning

confidence: 98%

Section: Methodsmentioning

confidence: 97%