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International Journal of Polymer Science
Volume 2015, Article ID 314891, 11 pages
http://dx.doi.org/10.1155/2015/314891
Review Article

Evaluating Lignin-Rich Residues from Biochemical Ethanol Production of Wheat Straw and Olive Tree Pruning by FTIR and 2D-NMR

1NMR Facility of Research (SGIker), Joxe Mari Korta Center, University of the Basque Country (UPV/EHU), Avenida Tolosa 72, 20018 San Sebastián, Spain
2INIA-CIFOR, Forestry Products Department, Cellulose and Paper Laboratories, Ctra de la Coruña Km 7.5, 28040 Madrid, Spain
3CIEMAT, Renewable Energy Division, Biofuels Unit, Avenida Complutense 40, 28040 Madrid, Spain

Received 15 December 2014; Revised 24 February 2015; Accepted 5 March 2015

Academic Editor: Alireza Ashori

Copyright © 2015 José I. Santos et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Lignin-rich residues from the cellulose-based industry are traditionally incinerated for internal energy use. The future biorefineries that convert cellulosic biomass into biofuels will generate more lignin than necessary for internal energy use, and therefore value-added products from lignin could be produced. In this context, a good understanding of lignin is necessary prior to its valorization. The present study focused on the characterization of lignin-rich residues from biochemical ethanol production, including steam explosion, saccharification, and fermentation, of wheat straw and olive tree pruning. In addition to the composition and purity, the lignin structures (S/G ratio, interunit linkages) were investigated by spectroscopy techniques such as FTIR and 2D-NMR. Together with the high lignin content, both residues contained significant amounts of carbohydrates, mainly glucose and protein. Wheat straw lignin showed a very low S/G ratio associated with p-hydroxycinnamates (p-coumarate and ferulate), whereas a strong predominance of S over G units was observed for olive tree pruning lignin. The main interunit linkages present in both lignins were β-O- ethers followed by resinols and phenylcoumarans. These structural characteristics determine the use of these lignins in respect to their valorization.