Issue 12, 2024

Choline and lactic acid covalently incorporate into the lignin structure during deep eutectic solvent pulping

Abstract

Deep eutectic solvent (DES) pulping is a promising alternative to conventional pulping techniques, mainly owing to the favourable solvent properties and reduced environmental impact. DES lignin, however, still awaits complete structural characterisation, especially in terms of the potential incorporation of DES constituents. Here, we describe the structural modification of lignin during lactic acid : choline chloride DES pulping of Miscanthus biomass in unprecedented detail. We show that DES pulping induces β-O-4 aryl ether cleavage and extensive substitution by DES incorporation. The covalent incorporation of both lactic acid and choline was confirmed through saponification of the precipitated lignin and lignin model compound studies. Detailed multidimensional NMR analysis allowed us to validate aliphatic and benzylic lactic acid esterification as well as benzylic choline and lactic acid etherification of β-O-4 aryl ethers. We demonstrate that these reactions occur in all process phases by comprehensive analysis of the precipitated, residual and solubilised lignin fractions, together comprising 93% w/w of the initial lignin in Miscanthus. Covalent lactic acid and choline incorporation occurs independently of biomass type (grass, hardwood and softwood) and can be modulated by water content, reaction duration and temperature. Going forward, these new insights will offer ample opportunities for producing lignins with unique structural features and ultimately will open up new avenues for specific functional ingredient applications. Our work thus clearly advances the DES biorefinery concept and contributes to the valorisation of lignin in general.

Graphical abstract: Choline and lactic acid covalently incorporate into the lignin structure during deep eutectic solvent pulping

Supplementary files

Article information

Article type
Paper
Submitted
22 Feb 2024
Accepted
10 May 2024
First published
15 May 2024
This article is Open Access
Creative Commons BY-NC license

Green Chem., 2024,26, 7101-7112

Choline and lactic acid covalently incorporate into the lignin structure during deep eutectic solvent pulping

G. van Erven, V. J. P. Boerkamp, J. W. van Groenestijn and R. J. A. Gosselink, Green Chem., 2024, 26, 7101 DOI: 10.1039/D4GC00909F

This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence. You can use material from this article in other publications, without requesting further permission from the RSC, provided that the correct acknowledgement is given and it is not used for commercial purposes.

To request permission to reproduce material from this article in a commercial publication, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party commercial publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements