Impact of the lignin structure of three lignocellulosic feedstocks on their organosolv delignification. Effect of carbonium ion scavengers

Abstract

Effect of autohydrolysis and aromatic scavengers on delignification patterns were evaluated using miscanthus (MxG), empty palm fruit bunch (EFB) and typha grass residue as feedstocks. Autohydrolysis was carried out without naphthol and in the presence of naphthol followed by delignification by ethanol organosolv process. Despite their close chemical composition, the three feedstocks demonstrated quite different patterns of delignification under the same condition of pretreatment. Nuclear magnetic resonance (NMR) spectroscopic characterization of ethanol organosolv lignins (EOLs) extracted from the three feedstocks revealed information concerning syringyl, guaiacyl and hydroxyphenyl content (S/G/H ratios) which underpinned the differences among the feedstock behavior. The (S + H)/G ratios for MxG, EFB and typha were determined as ̴1.27, ̴2.33 and 2.70 respectively. The major cause of difference in behavior of feedstock during the pretreatment process was attributed to the variation in lignin composition. A good relationship was observed between S/G ratio and the scavenging effect of 2-naphthol. The effect of four additional aromatic scavengers viz. p-cresol, o-cresol, hydroquinone and dihydroxyanthraquinone (DHAQ) tested in miscanthus demonstrated a significant enhancement on delignification; the effect of p-cresol and DHAQ was tantamount to that of naphthol. Cellulolytic enzyme lignin (CEL) extracted from typha grass was also subjected to 13C NMR characterization in order to obtain a more complete picture of typha lignin. Comparison of NMR spectra of CEL and EOL from TC was performed for determining the processing effect in lignin structure.