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Ozone bleaching with organic solvents as additive: pulp quality
2001 (English)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

The effect that alcohol addition to the reaction medium in ozone bleaching has on the selectivity of the ozone stage and thus the strength properties of the fully bleached pulp has been investigated. The pulp samples used in the experiments were collected at SCA Östrand pulp mill. The current bleaching sequence in this mill was performed in laboratory scale and compared with an alternative bleaching sequence where the ozone stage is performed directly after the oxygen treatment of the pulp. The alcohols tested were ethylene glycol and tert-butanol. A pre-trial was made with these alcohols showing that ethylene glycol was the most effective one. Therefore, the further trials were performed with ethylene glycol. The statistical software MODDE was used to plan the experiments and evaluate the results. It was found that the presence of ethylene glycol in the reaction medium during the ozone stage had a significant improving effect on the viscosity of the fully bleached pulp, when the ozone charge was high. Increasing the amount of ethylene glycol from 0 to 20% weight improved the selectivity, but further addition did not give much more effect. When ethylene glycol is present during the ozone bleaching, the ozone stage is more selective than the hydrogen peroxide stage. An increase in ozone charge therefore improved the selectivity of the whole sequence mainly by decreasing the need of hydrogen peroxide in the OP-stage. A rough estimate showed that the total cost of bleaching chemicals decreased with ozone charge but increased with amountof ethylene glycol in reaction medium. The cost and the recovery efficiency of ethylene glycol determine whether the ethylene glycol addition is economically favourable or not. The strength property measurements showed that the tensile strength and the tear strength increased compared to a reference. It was noticeable that the pulp was refined slower with a PFI mill. The fibres in the pulp bleached with ethylene glycol present during the ozone stage seem to be stronger and more stiff compared to the fibres in the reference pulp.

Place, publisher, year, edition, pages
Keyword [en]
Technology, chemistry, ozone, bleaching, ozone bleaching, pulp, organic, solvents, alcohols, ethylene glycol, tert-butanol
Keyword [sv]
URN: urn:nbn:se:ltu:diva-50247ISRN: LTU-EX--01/227--SELocal ID: 7833c465-4f3a-4f08-8ebe-9a6d3fd5a243OAI: diva2:1023604
Subject / course
Student thesis, at least 30 credits
Educational program
Chemical Engineering, master's level
Validerat; 20101217 (root)Available from: 2016-10-04 Created: 2016-10-04Bibliographically approved

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