Acetyl Groups in Typha capensis: Fate of Acetates during Organosolv and Ionosolv Pulping.

Idi Audu,Martina Bremer,Heiko Winter,Nicolas Brosse,Anton Hoffmann,Marie-Pierre Laborie,Steffen Fischer

doi:10.3390/polym10060619

Idi Audu, Martina Bremer + Show 5 more

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https://doi.org/10.3390/polym10060619

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Abstract

During biomass fractionation, any native acetylation of lignin and heteropolysaccharide may affect the process and the resulting lignin structure. In this study, Typha capensis (TC) and its lignin isolated by milling (MWL), ionosolv (ILL) and organosolv (EOL) methods were investigated for acetyl group content using FT-Raman, 1H NMR, 2D-NMR, back-titration, and Zemplén transesterification analytical methods. The study revealed that TC is a highly acetylated grass; extractive free TC (TCextr) and TC MWL exhibited similar values of acetyl content: 6 wt % and 8 wt % by Zemplén transesterification, respectively, and 11 wt % by back-titration. In contrast, lignin extracted from organosolv and [EMIm][OAc] pulping lost 80% of the original acetyl groups. With a high acetyl content in the natural state, TC could be an interesting raw material in biorefinery in which acetic acid could become an important by-product.

Highlights

Grass lignins have the distinct feature of containing significant amounts of p-coumaric and ferulic acids [1,2,3], and acylation mainly bound to the γ-carbon of S units [2,3,4]
In recent investigations of Typha capensis (TC), we reported that native TC comprised of ca. 18% extractives, 39% cellulose, 19% hemicellulose and 23%
To the best of our knowledge, the Zemplén transesterification method is demonstrated for the first time to accurately monitor the fate of lignocellulose acetyl groups during pulping

Summary

Introduction

Grass lignins have the distinct feature of containing significant amounts of p-coumaric and ferulic acids [1,2,3], and acylation mainly bound to the γ-carbon of S units [2,3,4]. Acetylation is likely to play a significant role due to the ease of acetate cleavage [5]. In the case of wood pulping with dialkyl imidazolium salts such as 1-ethyl-3-methylimidazolium acetate ([EMIm][OAc]), acetyl transfer was revealed as an important side-reaction [8,9,10]. In [EMIm][OAc], imidazole, a degradation product of imidazolium, plays the role of acetyl transfer onto cellulose [8], a side-reaction catalyzed by Polymers 2018, 10, 619; doi:10.3390/polym10060619 www.mdpi.com/journal/polymers

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