Influence of the Bleaching Medium on Extraction Delignification Efficiency (II): Oxidized Lignin Solubility, 1996 Pulping Conference Proceedings

Brian N. Brogdon, Thomas J. McDonough, Donald R. Dimmel - Institute of Paper Science and Technology

A softwood kraft pulp was partially oxidized with C1O2 and subsequently subjected to alkaline extraction in water, etha-nol- water or aqueous BaC12. High concentrations of ethanol severely inhibited delignification. Previous experimental work has shown that fiber de-swelling and subsequent pore size reduction was not the lim-iting factor in extraction delignification. The goal of this paper was to determine if oxidized lignin solubility was the limiting factor in delignification when the caustic extraction medium contains high levels of ethanol or BaC12 . Oxidized lignin was isolated from the effluent of an aqueous caustic extraction stage. The solubility of this lignin was measured in the various ethanol-water and BaCl2 solu-tions by UV absorption. The solubility of the lignin de-creased as the amount of ethanol or BaC12 was increased. Measurements of the amount of dissolved material in extrac-tion stages performed with ethanol-water or BaC12 solutions corresponded well with the measured solubilities of the iso-lated lignin. Experimental results indicated that oxidized lignin solubility plays a major role in caustic extraction de-lignification efficiency. The results have significant implica-tions for “organosolv” bleaching sequences and metals man-agement in low effluent mills.