Uncovering the potentialities of protic ionic liquids based on alkanolammonium and carboxylate ions and their aqueous solutions as non-derivatizing solvents of Kraft lignin
authors Dias, RM; Lopes, AMD; Silvestre, AJD; Coutinho, JAP; da Costa, MC
nationality International
journal INDUSTRIAL CROPS AND PRODUCTS
author keywords Protic ionic liquids; Kraft lignin solubility; Hydrotropic effect; Ionic liquid recycling; Non-derivatizing solvents
keywords NUCLEAR-MAGNETIC-RESONANCE; PHYSICOCHEMICAL PROPERTIES; STRUCTURAL-CHARACTERIZATION; ENHANCED SOLUBILITY; TECHNICAL LIGNINS; DISSOLUTION; PRETREATMENT; EXTRACTION; ETHANOL; WATER
abstract The present study scrutinized in depth the ability of alkanolammonium-based Protic Ionic Liquids (PILs) with carboxylate anions to dissolve Kraft lignin at 323.15 K. A focus was put on understanding the role of both PIL. ions and water on the dissolution process. The results demonstrated that the anion plays a more important role in lignin dissolution than the cation. Furthermore, lignin dissolution was favored by increasing the alkyl chain of the carboxylate anion, while a smaller cation with lower number of hydroxyalkyl groups performed better. Among the studied solvents, the 2-hydroxyethylarnmonium hexanoate (HEAH) displayed the highest lignin solubility (37 wt%). In general, the addition of water had a negative influence on lignin solubility with the tested PILs. A sharp decrease in lignin solubility curves of 2-hydroxyethylammonium formate (HEAP) and acetate (HEAA) was observed, while a more softly effect was observed for 2-hydroxyethylammonium propionate (HEAP) and HEAH with the addition of water. However, a distinct behavior was observed for 2-hydroxyethylammonium octanoate (HEAD) that acted as hydrotrope enhancing lignin solubility in aqueous solutions to a maximum value at 40 wt% water content. Furthermore, by increasing the temperature, the lignin solubility was favored due to endothermic behavior of lignin dissolution process. The dissolution of Kraft lignin was also performed at 393.15 K to unravel any lignin modification unleashed by PILs. GPC, FTIR-ATR and 2D NMR were employed for lignin characterization and the changes observed between native lignin and recovered lignin samples were negligible demonstrating the non-derivatizing character of the PILs. Moreover, the recycle of 2-hydroxyethylammonium propionate (HEAP) was successfully demonstrated for at least 3 cycles. In this way, PILs are herein revealed as promising solvents to apply in lignin valorization towards more efficient and eco-friendly processes.
publisher ELSEVIER
issn 0926-6690
year published 2020
volume 143
digital object identifier (doi) 10.1016/j.indcrop.2019.111866
web of science category Agricultural Engineering; Agronomy
subject category Agriculture
unique article identifier WOS:000503323200038

Sponsors

1suponsers_list_ciceco.jpg