Modification of the lignin structure during alkaline delignification of eucalyptus wood by kraft, soda-AQ, and soda-O2 cooking

11 páginas.-- 5 figuras.-- 4 tablas.-- 50 referencias.-- Supporting Information The general conditions for the kraft, soda-AQ, and soda-O2 alkaline cooking of eucalyptus feedstock, are shown in Table S1. The identification and relative molar abundance of the compounds identified in the Py-GC/MS of MWL from eucalyptus wood, and residual and black liquor lignins from kraft, soda-AQ,and soda-O2 pulping at different kappa numbers, are listed in Table S2. This material is available free of charge via the Internet at http://pubs.acs.org/doi/suppl/10.1021/ie401364dThe modification of the lignin structure of an eucalyptus feedstock during alkaline delignification by kraft, soda-AQ, and soda-O2 cooking processes has been investigated by different analytical techniques (size exclusion chromatography (SEC), pyrolysis gas chromatography-mass spectroscopy (Py-GC/MS), 1H-13C two-dimensional nuclear magnetic resonance (2D-NMR), and 31P NMR). The characteristics of the lignins were compared at different pulp kappa levels, and with the native lignin isolated from the wood. The structural differences between the kraft, soda-AQ, and soda-O2 residual lignins were more significant at earlier pulping stages. At the final stages, all the lignin characteristics were similar, with the exception of their phenolic content. Strong differences between lignins from pulps and cooking liquors were observed, including enrichment in guaiacyl units in pulp residual lignin and enrichment in syringyl units in black liquor lignin. A comparison of the alkaline cookings indicate that soda-O2 process produced higher lignin degradation and provided promising results as pretreatment for the deconstruction of eucalyptus feedstocks for subsequent use in lignocellulose biorefineries. © 2013 American Chemical Society.This study has been funded by the EU-Project LIGNODECO (No. KBBE-244362), the Spanish project (No. AGL2011-25379), and the CSIC project (No. 201040E075). Dr. Rencoret thanks the CSIC for a JAE-DOC contract in the program “Junta para la Ampliación de Estudios”, cofinanced by Fondo Social Europeo (FSE). Finally, we thank Suzano Papel e Celulose (Brazil) for providing the pulp and black liquor samples from the alkaline cooking experiments and the corresponding additional data.Peer Reviewe

Uncovering the potentialities of protic ionic liquids based on alkanolammonium and carboxylate ions and their aqueous solutions as non-derivatizing solvents of Kraft lignin

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-hydroxyethylammonium 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 (HEAF) 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 (HEAO) 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 char- acter of the PILs. Moreover, the recycle of 2-hydroxyethylammonium propionate (HEAP) was successfully de- monstrated 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.Suzano Papel & Celulosepublishe