Abstract:
Six filtrate samples (liquid state) were obtained from selected stages in a totally-chlorine-
free (TCF) bleach pulp mill. The solids were recovered by evaporation on rotary
evaporators and by lyophilization with a freeze drier.
Chemical contents (inorganic and organic chemicals) of the six filtrates were
analyzed quantitatively according to TAPPI Test Methods, 1988. Results showed that
the #1BS filtrate had the largest amount of inorganic and organic chemicals, which
would influence the pulp mill systems the most.
Thin-layer chromatography (TLC) was utilized to qualitatively analyze
carbohydrates by using pre-coated cellulose plates. No free monosaccharides were
detected in the six filtrates as received. The solids were then acid hydrolyzed and the
monosaccharides, D-Glucose, D-Galactose, D-Mannose, D-Xylose, and L-Arabinose
were detected in the hydrolyzates of the solids recovered from the filtrates of the early
stages of bleaching. This showed that these samples contained both cellulose and
hemicelluloses. Wood extractives were also qualitatively determined by TLC using pre-coated
silica plates. The freeze-dried solids were extracted with methanol, with distilled water
and with ethyl acetate. Results revealed that dihydroquercetin, quercetin and catechin
existed in the filtrates from the early stages of bleaching. These catechol-type chemicals
will influence the problem of metallic accumulation severely.
The results of both carbohydrates and wood extractives were supported by Rf
values, Rs (relative resolution) and Rx (relative retention).
Pulsed Fourier Transform carbon-13 nuclear magnetic resonance (NMR)
spectroscopy was applied to study the functional groups, particularly hydroxyl groups, of
the filtrate lignin samples with a proton decoupling method. A commercial kraft
softwood lignin, Aldrich lignin, was used as a reference for the TCF mill filtrate lignins.
A newly emerged method of lignin acetylation with acetyl chloride enriched with
carbon-13 as reagent was introduced The conventional method of using acetic anhydride
to acetylate lignin was used as a reference method. NMR spectra showed that the
conventional method gave more functional group information, but the method of acetyl
chloride acetylation determined the hydroxyl groups with greater resolution and higher
speed. The TCF filtrate lignins were different from the commercial Aldrich lignin. Some
differences were also found among the TCF filtrate lignins. These may be important for
the future research of lignin modeling with metal complexity.
