Ionic liquid and organosolv pretreatments of horse manure: impact on lignin telomerization by organometallic catalysis and methanization

To deal with the high lignin content of horse manure in the methanization process, eco-fractionation and chemical modification strategies of lignin have been proposed, opening up prospects for new lignin-based thermoplastic materials. Firstly, a strategy inspired by the biochemical pathway and based on ionic liquid pretreatment, with appropriate recyclability and biodegradability characteristics, was implemented. A sugar-enriched fraction was recovered after enzymatic hydrolysis and a lignin-enriched fraction was isolated (80% w/w). The second strategy was an organosolv process, using the easily biodegradable 2-methyltetrahydrofurane-3-one, allowing selective extraction of a lignin-enriched fraction (> 80% w/w almost sugar-free) and a partially delignified sugar solid fraction. H/G/S ratios and aryl-ether linkages showed little difference for the two isolated lignins, which may be responsible for the more successful palladium-catalyzed telomerization of 1,3-butadiene on the phenolic and carboxylic hydroxyls of organosolv lignin. Whatever the strategy used, carbohydrate fractions showed competitive biochemical methane potential for methanization.