Revisiting organosolv strategies for sustainable extraction of valuable lignin
Résumé
An innovative and sustainable strategy for the selective extraction of lignin from lignocellulosic biomass has been designed, namely the CoffeeCat process, in which only green solvents and reagents are required: (i) water, (ii) 2-methyltetrahydrofuran-3-one (coffee furanone) recognized as a food grade ingredient and readily biodegradable and (iii) glutamic acid. Two fractions have been isolated from Miscanthus x giganteus, the delignified fraction (DL-glu) and the enriched-lignin fraction (L-glu). Competitive extraction yields of 27% and 43% of enriched-lignin fractions were respectively obtained at 140 °C (Lglu-140) and 180 °C (L-glu-180), based on the lignin content of the original biomass. The structural properties of these lignins were characterized by spectroscopic (FTIR and NMR), microscopic (SEM) and separative (SEC-MALLS) methods. Compared to other processes described in the literature, our strategy involved the isolation of lignin fractions with high purity (up to 84%). Both fractions have been valorized: (i) the DL-glu fractions have been subjected to ionic liquid pretreatment and subsequent enzymatic hydrolysis leading to a total depolymerization of the constitutive cellulose (99%) and to an efficient conversion of hemicellulose into xylose (70%); (ii) the L-glu fractions have been used to produce lignin nanoparticles (LNPs) in a mixture of 2-methyltetrahydrofuran-3-one/water (1/110 v/v). The size distribution (272 ± 9 nm and 472 ± 6 nm), charge (−29.2 ± 0.8 mV and −20.8 ± 0.4 mV) and regular spherical shape of these LNPs have been determined using Zetasizer-DLS measurements and SEM images of L-glu-140 and L-glu-180, respectively. In addition, the possibility of easy incorporation of the L-glu fraction into polylactic acid without requiring previous lignin modification has been preliminarily explored. The CoffeeCat process was thus demonstrated as a relevant eco-solution for an integrated lignocellulosic biorefinery. Sustainability spotlight This work is based on the CoffeeCat process to design a sustainable strategy for a full-component renery of lignocellulose. The strategy uses green solvents (the food approved 2-methyltetrahydrofuran-3-one and water) and reagents (glutamic acid) to selectively extract at 140 °C a nearly carbohydrate-free lignin with high b-O-4 linkage content. Synergistic ionic liquid pretreatment applied to the remaining delignied biomass led to total conversion of polysaccharides into platform sugars. The physico-chemical properties of the extracted lignin could open the way of designing biocompatible nanoparticles and facilitating the formulation of PLA-lignin biocomposites. Miscanthus is used as an example for potential biomass feedstock. This work is in line with points 12 and 13 of the UN's Sustainable Development Goals (combat climate change and ensure sustainable production patterns).
Domaines
ChimieOrigine | Fichiers éditeurs autorisés sur une archive ouverte |
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