Kraft cooking with varying alkali concentration: Influence on TCF-bleachability
1998 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, Vol. 13, no 1, 57-63 p.Article in journal (Refereed) Published
The TCF-bleachability of softwood pulps produced by kraft pulping processes with varying alkali concentrations was investigated. The cooks began with a hydrogen sulfide ion pretreatment at low alkalinity, i.e. simulating a black liquor preimpregnation. The alkalinity in the cooks was varied in three different ways: already at the beginning of the cook, both at 40 % sulfidity and at a HS- concentration of 0.3 mol/l (2-stage cooks), and in the final part of a modified kraft cook (4-stage cooks) simulating an ITC (Isothermal cooking) cook. The pulps had the same kappa number after the cook, about 17, and were oxygen delignified before bleaching. The influence of the alkali concentration profile in the cook on the bleachability was studied with a QPQP*-sequence (Q=chelating agent stage, P*=peroxide-stage with the addition of 0.05 % Mg ions). The bleachability (pulp brightness achieved for a given consumption of bleaching agent per kappa number) was found to reach a maximum for pulps with a residual alkali concentration in the vicinity of 0.5 mol/l. The bleachability was however affected to only a minor extent by the alkali concentration during the cook. The hexeneuronic acid content was found to decrease with increasing alkali concentration and this was taken into consideration when calculating the chemical consumption per amount of lignin. The process selectivity (pulp viscosity at a given brightness) decreased with increasing residual alkali. The bleachability was not improved by conducting the cook with a levelled out active cooking chemical profile, when the comparison was made at the same residual alkali concentration, but the selectivity was improved.
Place, publisher, year, edition, pages
1998. Vol. 13, no 1, 57-63 p.
kraft pulp, softwood, chlorine-free bleaching, bleachability, effective alkali, oxygen, hydrogen peroxide, pulp brightness, pulp viscosity, hexenuronic acid, PULPS
Paper, Pulp and Fiber Technology Materials Engineering
IdentifiersURN: urn:nbn:se:kth:diva-13902ISI: 000075150100008OAI: oai:DiVA.org:kth-13902DiVA: diva2:328079
QC 201007012010-07-012010-07-012010-07-01Bibliographically approved