(779e) Depolymerization of Lignin Extracted From Kraft Black Liquor

Bethany D. Carter and David A. Bruce*

Department of Chemical and Biomolecular Engineering, Center for Advanced Engineering Fibers and Films, Clemson University, Clemson, SC, 29634-0909, USA.

* Corresponding author. E-mail: dbruce@clemson.edu

Lignin was extracted from Kraft black liquor via the continuous Sequential Liquid Lignin Recovery and Purification (SLRP) process whereby the pH of the incoming black liquor (pH ~ 13.5) was lowered to a pH ~ 9.5 by acidification with CO₂ resulting in lignin precipitation.  The precipitated, liquid lignin phase is then acidified with sulfuric acid until a final pH ~ 2.5 is achieved, whereby the lignin is fully acidified.  The acidified lignin is then leached counter currently with water to lower the lignin’s ash content.  

Lignin extracted from Kraft black liquor via the SLRP process was then depolymerized into smaller more monomeric units that may serve as potential precursors for higher valued chemical.  The depolymerization occurs through cleave of the many ether linkage that connect guaiacyl (G), p-hydroxyphenyl (H), and syringyl (S) units.  The depolymerization of lignin was done in small batch reactors in the presence of varying heterogeneous catalysts, which include Co/Mo on alumina as well as some noble metal supported catalysts such as Pt/Al₂O₃.  The Co/Mo/Al₂O₃ catalyst are typical for use in hydrodesulfurization processes which has good sulfur tolerance, as the Kraft lignin may have residual sulfur from the Kraft pulping process.

Characterization of depolymerized lignin fractions was done using gas chromatography-Mass spectrometry to analyze lighter molecular weight fractions.  Higher molecular weight fractions, which are not easily volatilized, were analyzed using NMR spectroscopy.