Characterization and determination of the S/G ratio via Py-GC/MS of agricultural and industrial residues

To explore the potential values of lignin from agricultural residues (apple tree pruning, olive tree pruning and almond shell) and industrial residues (kraft black liquor) were used as raw materials for lignin extraction by different fractionation processes (kraft, organosolv, acetosolv and acetosolv and formosolv processes). The isolated lignins were characterized by Py-GC/MS, FTIR and GPC. The fractionation process influenced greatly the average molecular weight (Mw) that was measured by GPC. The harsh conditions during the acetosolv and acetosolv-formosolv processes promoted the repolymerization phenomena giving high Mw lignins. The EKL presented lower Mw due to higher retention times. All lignins exhibit higher relative abundances of S-type of phenols except for the almond shell lignin where G-type of phenols were the most abundant ones. The S/G ratios for hardwood type of lignin were analogous which ranged from 2.30 to 2.71, whereas almond shells lignin revealed an S/G ratio of 0.94. Kraft liquid fraction showed the highest lignin content (6.39%) and consequently the highest S/G ratio (2.71).