Stirred and non-stirred lignin solvolysis with formic acid in aqueous and ethanolic solvent systems at different levels of loading in a 5-L reactor

Document Type: Research Paper

Authors

1 Department of Chemistry, University of Bergen, Norway, Allégaten 41, N-5007 Bergen, Norway.

2 Mjøsvegen 6J, 2380 Brumunddal, Norway.

Abstract

Lignin polymer is biologically and chemically stable and requires highly vigorous conditions for de-polymerization, and subsequent stabilization of the monomeric conversion products to prevent re-polymerization and char production. The Lignin-to-Liquid (LtL) process is a solvolytic conversion of lignin with formic acid. Formic acid has been shown to both catalyze the de-polymerization and supply hydrogen that stabilizes the de-polymerization products. In this paper, lignin from Eucalyptus wood was used as the feedstock, and the LtL-process was performed in both aqueous and ethanolic solvent systems. The experimental variables were different levels of loading in the reactor, stirred and non-stirred conditions, and different reaction temperatures. The bio-oil consisted mostly of phenolic compounds, and the bio-oil yields differed with type of the solvent used, level of loading in the reactor, stirring condition, and operating temperature. More than 55 wt.% of the lignin was recovered as bio-oil at 320 °C at stirred conditions when the reactor was loaded at high level. Overall, the ethanolic solvent together with maximum level of loading in the reactor under stirred condition resulted in the highest bio-oil yield. Elemental balance data for bio-oil and char yields and the molecular composition of the bio-oils were also investigated using, respectively, elemental analysis and GC-MS. Finally, principal component analysis was used as well to systematically explore the relationship between the bio-oil and char yields and the reaction conditions.

Graphical Abstract

Stirred and non-stirred lignin solvolysis with formic acid in aqueous and ethanolic solvent systems at different levels of loading in a 5-L reactor

Highlights

  • Oil yields increased and char yields decreased with a high loading in the reactor at stirred condition.
  • In comparison with water-based system, ethanol-based system tended to give higher oil yields.
  • Oil yields decreased, more or less, with increasing reaction temperature regardless of solvent type.
  • The bio-oils from ethanol-based experiments had the highest H/C and O/C ratios.
  • The bio-oil composition produced in each solvent system was quite stable and independent of other reaction conditions.

 

Keywords


 

On the cover


One of the main concerns for producing biofuels from lignin polymer is its recalcitrant nature against biological/chemical depolymerization. The lignin-to-liquid (LtL) process could be a viable route to overcome this challenge. During this process, lignin polymer is depolymerized in a high-temperature solvolytic aqueous environment in the presence of a hydrogen-donor catalyst such as formic acid. In this issue of Biofuel Research Journal, a group of Norwegian researchers shed light on the effects of different variables (i.e., feeding reactor loading, stirred and non-stirred conditions, and reaction temperature) on the performance of water/ethanolic solvolytic LtL-process with formic acid. They emphasize that the stirred condition with large feeding loadings and at high temperatures would be more promising for lignin-oriented biofuel production at large scale. Cover art by BiofuelResJ.

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