Rc. Sun et al., Separation and characterization of lignins from the black liquor of oil palm trunk fiber pulping, SEP SCI TEC, 34(15), 1999, pp. 3045-3058
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, an
d salts. A lignin fraction with a purity of 99.5% was obtained at an optimu
m precipitation pH 1.5 after isolation of the nonlignin materials in ethano
l. 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 signif
icantly to lower 250. The isolated lignin fractions contained syringyl, gua
iacyl, 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 a
cids were associated to lignin by ether linkage. C-13-NMR indicated the pre
sence of beta-O-4 ether bonds, and beta-5 and 5-5' carbon-carbon linkages b
etween the lignin molecules.