Liquid Lignin from the SLRP^TM Process: The Effect of Processing Conditions and Black-Liquor Properties

Abstract

CO₂ acidification of Kraft black liquors was performed at temperatures of 100–150°C and pressures of 5–8 bar in an investigation of the SLRP^TM process. At these conditions, a highly hydrated, lignin-rich liquid (vs. the usual solid) separated out to form a new phase. The solids content/ionic strength of the starting black liquor was found to be a key variable for controlling the bulk and molecular properties of the „liquid-lignin” (LL) phase. For example, black liquors of lower ionic strengths (20% solids) produced LLs with lower ash contents and higher molecular weights, albeit in lower yields. In contrast, higher ionic strengths/solids content (40%) produced LLs in higher yields with higher aromatic and aliphatic hydroxyl contents. Temperature effects were significant only at the highest levels. The degree of hydration of the LL phase was found to be a useful measure of the water available for hydration of ionized/polarizable groups in lignin.

KEYWORDS:

• Black liquor
• CO₂ acidification
• hydration
• lignin
• liquid lignin
• phase behavior

ACKNOWLEDGMENTS

The authors wish to thank Bethany Carter for her help with the GC-MS measurements, Michael Lake and John Blackburn (Liquid Lignin Co.) for providing the black liquors, Alfredo Picado for help with the NMR analysis, and Dan Edie (Clemson) and David Hodge (Michigan State) for their helpful discussions.