ISOLATION AND CHARACTERIZATION OF LIGNIN FROM PREHYDROLYSIS LIQUOR OF KRAFT-BASED DISSOLVING PULP PRODUCTION

Lignin separation from the prehydrolysis liquor (PHL) resulting from dissolving pulp production will create new revenue for the dissolving pulp sector, fitting well into the integrated forest biorefinery concept. Lignin will likely become a valuable source of renewable energy (e.g. biofuel) and biomaterials (e.g. plastics, adhesives). In this study, lignin was isolated from PHL by acidification with a dilute H2SO4 solution, followed by purification through dissolution in a dioxane solution (9:1) and re-precipitation with diethyl ether. The characteristics of PHL lignin were compared with those of the dioxane lignin isolated from hardwood (maple, poplar and birch wood chips, in a ratio of 7:2:1), which is the raw material used for dissolved pulp production. Thus, the obtained lignin samples were characterized by UV, FTIR, H-1-NMR spectroscopy, molecular weight determination, elemental and methoxyl analyses. The absorptivity of hardwood lignin at 276 nm was of 10.01 g(-1)cm(-1), while that of PHL lignin was of 17.21 g(-1)cm(-1). The presence of condensed structures in PHL lignin (intense bands at 870 and 890 cm(-1) in the FTIR spectrum) was observed. The lignin isolated from PHL has low molecular weight, and a low methoxyl group per C-9 unit, in comparison with other lignin samples. H-1-NMR data indicate a significant increase of the phenolic hydroxyl content in PHL lignin, caused by the cleavage of the aryl-ether bonds during prehydrolysis. Based on these results, it can be concluded that the lignin isolated from PHL may have a potential for polymer industry.