Fractionation of lignosulphonates released during the early stages of delignification

Abstract

High-yield spent bisulphite liquor (HY-SBL) from sulphonated black spruce wood (Piceamariana) was fractionated by gel permeation chromatography (GPC) and by high-performance liquid chromatography (HPLC). The GPC fractionation gave a wide bimodal distribution, whereas with HPLC, a more detailed resolution was seen with the bulk of the fraction giving several clearly defined peaks. The paucidisperse material was further concentrated by a bulk fractionation of the crude SBL which included complexing the lignosulphonates with dicyclohexylamine. The isolated paucidisperse material was found to be dialyzable and to constitute 90% of the lignosulphonate in the sample of SBL. If the bisulphite pulp obtained was recooked in fresh acid sulphite liquor to a lower yield, most of the lignosulphonate dissolved was widely polydisperse with no indication of the discrete components resolvable by HPLC. However, 25% of the lignin made soluble was in the form of the paucidisperse fractions. In all, we were able to obtain about 50% of the lignin in spruce wood as a relatively low molecular weight lignosulphonate resolvable into discrete fractions by HPLC.