Influence of extraction treatment on olive tree (Olea europaea) pruning lignin structure

Abstract

Olive tree pruning lignin was studied to be considered as a raw material candidate for biorefinery. Different extraction treatments (organosolv treatment: 60% wt ethanol, 180°C, 90 min; alkali treatment: 90 to 100°C, 7.5% wt NaOH, 90 min; and autohydrolysis process: 180°C, 30 min) were applied to extract lignin. The isolated lignins were deeply characterized to study the effect of the applied extraction conditions on lignin properties. Isolated lignins compositions were measured by determining acid insoluble lignin, acid soluble lignin, sugar content, and ash content. Functional groups (carboxyl groups, carbonyl groups, and OH‐phenolic groups) were analyzed to evaluate the reactivity of the different lignins. Nitrobenze oxidation, structure analyses (attenuated‐total reflection infrared spectroscopy and heteronuclear single quantum coherence) and high performance size exclusion chromatography analyses were carried out to meet olive tree pruning lignin structure. Organosolv treatment yielded the purest lignin while autohydolyisis process yielded medium purity lignin with low molecular weight. Finally, lignin obtained from alkali treatment was very impure and had high inorganic content and sugar contamination. © 2012 American Institute of Chemical Engineers Environ Prog, 32: 1187–1194, 2013