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Influence of pulping conditions on eucalyptus kraft pulp yield, quality, and bleachability.

Application: These findings may allow mills to adjust their pulping process conditions for improved pulp yields or to improve pulp bleachability, according to their needs and desire.

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This study evaluates the effect of cooking residual alkali and temperature on kraft pulp yield, bleachability, and quality. We cooked Eucalyptus grandis chips at 170[degrees]C and 160[degrees]C to kappa number 16-17 using high/low residual alkali (14-18 and 3-4 g/L). We determined process yield and pulp quality by measuring strength properties, carbohydrate composition, hexenuronic acid content, alkali-leachable lignin content, and residual lignin nature. We oxygen delignified the pulps, bleached them to full brightness with the sequences D(EOP)DD and D(EOP)(ZE)D, and determined their bleachability and brightness stability.

The highest screened yield (54.2%) and viscosity (64.6 mPa.s) were achieved using low temperature and low residual alkali during pulping. Pulps cooked at low residual alkali showed about 1.7%-2.1% higher yield, 20%-30% higher viscosity, and higher strength properties (except for tear index) than those cooked at high residual alkali. Lower temperature and/or residual alkali during pulping favored pulp refining. Pulps produced at high residual alkali showed slightly lower oxygen delignification efficiency (2%-3%) but significantly higher (10%-15%) bleachability, regardless of cooking temperature.

We found that cooking hardwoods at high temperature and white liquor alkalinity reduces pulp yield, viscosity, and beatability. However; it has the potential of increasing digester throughput and pulp bleachability. The gains in pulp bleachability are not sufficient to economically justify the significant yield losses associated with such practice. High alkali and temperature conditions are justified only when digester throughput is the mill bottleneck.

Colodette and Gomide are professors at the Federal University of Vicosa, Brazil; Russell Girard is application engineer at Praxair Inc., St. Laurent, QC, Canada, Jaaskelainen and Argyropoulos are with McGill University/Paprican, Montreal, QC, Canada. Contact Colodette by email at colodett@mail.ufv.br.
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Title Annotation:Pulping: summary of peer-reviewed material
Author:Argyropoulos, Dimitris S.
Publication:Solutions - for People, Processes and Paper
Date:Mar 1, 2002
Words:322
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Next Article:Fireside behavior of black liquors containing boron.


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