Identification and Quantification of Lignin Monomers and Oligomers from Reductive Catalytic Fractionation of Pine Wood with GC x GC - FID/MS

Hang Thi, Korneel Van Aelst, Sander Van den Bosch, Rui Katahira, Gregg Beckham, Bert Sels, Kevin Van Geem

Research output: Contribution to journalArticlepeer-review

42 Scopus Citations

Abstract

Thorough lignin characterization is vital to understand the physicochemical properties of lignin and to evaluate lignocellulose biorefinery processes. In this study, an in-depth characterization of lignin oil, obtained from reductive catalytic fractionation (RCF) of pine wood, was performed with quantitative GC × GC – FID analysis and qualitative GC × GC – MS. By utilizing high-temperature resistant column sets in the GC × GC system and by applying a derivatization step, unambiguous detection of lignin monomers, dimers, and trimers is enabled. In addition to confirm the identity of eleven monomers, corresponding to 34 wt% of the RCF lignin oil, thirty-six dimers (16 wt%) and twenty-one trimers (7 wt%) were comprehensively identified by analysis of their mass spectra and quantified by a FID, encompassing the identity of an additional 23 wt% of the RCF lignin oil. The proposed structures reveal the interlinkages present in the dimeric and trimeric oligomers, containing β-5, β-1, β–β, 5–5, and a minor fraction of β-O-4 and 4-O-5 bonds. Furthermore, aliphatic end-units in the dimeric and trimeric molecules were identified, consisting of various substituents at the C4 position, that have been previously observed in the RCF-derived lignin monomers. To reduce complexity for analysis, the RCF oil was separated into six fractions, prior to analysis. The structural motifs (inter-unit linkages and end-units) that are found in the different fractions vary significantly, such that the lignin fractions extracted in more polar solvents contained higher molecular weight fragments and more hydroxyl containing structural motifs. The identified structures of individual dimer and trimer molecules by GC × GC align well with and further complement the recent findings from 1H–13C HSQC NMR spectroscopy, demonstrating complementarity between both 2D techniques to obtain a holistic view on both the molecular structures and the distribution of bonds and end-units in RCF oil. The combination of these two techniques provides a powerful tool for future RCF and other lignin depolymerization research.

Original languageAmerican English
Pages (from-to)191-206
Number of pages16
JournalGreen Chemistry
Volume24
Issue number1
DOIs
StatePublished - 7 Jan 2022

Bibliographical note

Publisher Copyright:
This journal is © The Royal Society of Chemistry

NREL Publication Number

  • NREL/JA-2A00-82001

Keywords

  • dimers
  • mass spectrometry
  • molecules
  • monomers
  • nuclear magnetic resonance spectroscopy
  • physicochemical properties

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