Separation and characterization of lignins from the black liquor of oil palm trunk fiber pulping

Six lignin preparations, isolated by a novel two-step precipitation method instead of the traditional one-step precipitation method from the oil palm trunk fiber pulping (OPTFP) black liquor, were found to be relatively free of nonlignin materials such as polysaccharide degradation products, ash, and salts. A lignin fraction with a purity of 99.5% was obtained at an optimum precipitation pH 1.5 after isolation of the nonlignin materials in ethanol. About 94% of the total lignin was recovered by this novel method at this condition, and the value of COD in the treated black liquor reduced significantly to lower 250. The isolated lignin fractions contained syringyl, guaiacyl, and p-hydroxyphenyl units in an approximate molar ratio of 16-20:4-5:1 on the basis of chemical and spectroscopic analysis. Small amounts of p-hydroxybenzoic acids were found to be esterified to lignin, while ferulic acids were associated to lignin by ether linkage. C-13-NMR indicated the presence of beta-O-4 ether bonds, and beta-5 and 5-5' carbon-carbon linkages between the lignin molecules.