abstract
Hot-water extraction of industrial aspen woodchips (mainly Populus tremuloides) and
subsequent soda pulping were carried out in an M/K digester. It was found that mass
removal of woodchips was 4.74% at 160 C for 15 min with a water-to-wood ratio of 4:1, and
that mass removal increased with extraction time and temperature. The mass removal
reached 21.38% at 160 C for 210 min. Less than 6% lignin (on total wood mass) from virgin
woodchips was dissolved in the extraction liquor. The concentrations of xylose, acetic acid,
formic acid and furfural in the extraction liquor were measured by 1
H NMR, which were
found to increase with extraction time and temperature. Furfural increased sharply beyond
150 min of extraction at 160 C. The residual woodchips were subjected to soda pulping at
150 C for 3 h with 20% effective alkali and a liquor-to-wood ratio of 4.5:1. Compared with
the control sample, the overall pulp yield for extracted woodchips decreased little while
rejects decreased sharply. Kappa number of the pulps decreased with increasing extraction
time and temperature. Viscosity of the pulp increased with increasing extraction
temperature and duration for the first 90 min. Beyond 90 min of extraction, the resulting
pulp viscosity decreased with increasing duration of extraction. The water-to-wood ratio
had little effect on the entire process. Considering bioconversion of extracted hemicellulose
to fuel/chemicals and the resultant pulping characteristics, hot-water extraction
at 165 C for 90 min with a water-to-water ratio of 5:1 for aspen woodchips seems to be
optimum.
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