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Production of acetate-grade pulps by organic acid pulping and TCF Bleaching.

Application: Mills can produce high-purity pulps and cellulose derivatives such as cellulose acetate from Eucalyptus globulus or aspen wood via pulping in organic acid media (Milox or Acetosolv technologies) and TCF bleaching.

This work deals with the production of high-purity pulps from Eucalyptus globulus or aspen wood via pulping in organic acid media (Milox or Acetosolv technologies) and totally chlorine free (TCF) bleaching. The selected delignification technologies cause extended delignification with limited cellulose alteration at comparatively low operating temperatures and pressures. The production of marketable by products (sugars, furfural, acetic acid, and sulphur-free lignin fragments) and the susceptibility of pulps to TCF bleaching are also favorable characteristics of both pulping technologies.

The experimental work focused on the comparative susceptibility of pulps toward TCF bleaching using an optimized sequence [E(O)Z[C.sub.CP]P, to measure their potential as substrates for cellulose acetate production.

Following an alkaline extraction reinforced with oxygen [E(O)] stage, we subjected the pulp samples to an ozone (Z) stage and pH 2 using medium consistency operation. Cold caustic extraction (CCE stage) reduced the hemicellulose content of pulps. After this stage, Milox-processed Eucalyptus pulp presented the lowest kappa number (0.5); the best brightnesses were obtained for Milox-delignified pulps (85.9% and 85.8% for pulps from Eucalyptus and aspen, respectively). The treatments caused limited viscosity loss (23-31 mL/g).

The procedure for TCF-delignification of Milox-and Acetosolv-pulps from Eucalyptus and aspen considered in this work produced high-purity pulps suitable for the manufacture of cellulose derivatives. Among the possibilities examined, Milox-delignified pulps from aspen and Eucalyptus showed the best properties.

Dapia and Parajo are with the Department of Chemical Engineering, University of Vigo (Campus Ourense), Polytechnical Building, Ourense, Spain. Sixta, Borgards, and Harms are with Lenzing A.G. in Lenzing, Austria. Contact Parajo by e-mail at or by fax at +34988387001.
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Title Annotation:Pulping: summary of peer-reviewed material
Author:Parajo, Juan Carlos
Publication:Solutions - for People, Processes and Paper
Date:May 1, 2002
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