Advanced chromatographic methods for lignin characterization

  • Verbesserte chromatographische Methoden zur Lignincharakterisierung

Jestel, Tim Alexander; Spieß, Antje Christine (Thesis advisor); Jupke, Andreas (Thesis advisor); Schwaneberg, Ulrich (Thesis advisor)

Düren : Shaker Verlag (2020)
Book, Dissertation / PhD Thesis

In: Berichte aus der Verfahrenstechnik
Page(s)/Article-Nr.: XV, 158 Seiten : Illustrationen, Diagramme

Dissertation, RWTH Aachen University, 2020

Abstract

Recent biorefineries employ renewable resources such as lignocellulosic biomass for sustainable production of fuels and chemicals. Efficient lignocellulose valorization processes usually include thermochemical or electrochemical lignin degradation. However, complex product mixtures and low yields of target products are challenges in lignin degradation. Furthermore, a qualitative and quantitative assessment of lignin degradation processes is often not possible, due to the lack of suitable analytical methods. This work aims at improving and developing new chromatographic methods for the analysis of lignin in biorefineries and lignin valorizationprocesses. For the analysis of lignin in raw lignocellulosic biomass, an existing method based on high performance anion exchange chromatography coupled to pulsed amperometric detection was extended by the ability to detect lignin derived aldehydes and alcohols that act as fermentation inhibitors. Gel permeation chromatography (GPC) is the standard technique to monitor the lignin molecular weight during lignin removal and degradation. Here, secondary separation effects such as column interactions and lignin association were reduced by the addition of additives to GPC eluents. Liquid chromatography electrospray ionization quadrupole time-of-flight mass spectrometry (LC-ESI-Q-ToF-MS) was used to elucidate the underlying mechanism of lignocellulose treatment with laccases in combination with the mediator 1-hydroxybenzotriazole (HBT). Lignin surface modification by HBT grafting led to reduced unspecific cellulase adsorption and thus, increased glucose yields. Furthermore, Kraft lignin was electrochemically depolymerized to produce valuable degradation products such as carboxylic acids that were detected and quantified by LC-ESI-Q-ToF-MS. To enable a more facilitated analysis of complex lignin degradation processes, GPC and LC-ESI-Q-ToF-MS were coupled. With the help of the new method, the lignin molecular weight as well as lignin degradation products could be determined in a single step without labor intensive sample preparation and dilution steps. Overall, the importance of efficient and accurate analytical methods for lignin analysis during the whole biorefinery process chain was highlighted in this work. By refining existing analytical techniques and coupling of methods, first important steps were successfully taken for a facilitated and comprehensive lignin analysis. Especially, the coupling of different analytical methods has great potential to combine their respective advantages, thereby providing a better understanding of lignin chemistry.

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