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You are here : Home > Training > EFPG Days > 8- Ozonisation of high kappa pulps (slides 9-17)

Last update : August 16, 2003

			Second Session : The Yield Issue
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					VIII - Ozonation of high kappa pulps New possibilities (slides 9-17) Dinah Nyangiro (EFPG)

	9 - Ozone delignification   Ozone bleaching is more selective than kraft pulping (+ 2% yield gain)   High kappa pulp O3 delignification is more selective than low kappa (+ 1.5% yield gain)				10 - Full bleaching Treatment % ISO brightness *Yield DPv *ClO2 27 KN DEDED 90 44.5 1374 3.5 52 KN ZDEDED 91 46.8 1451 3.5 * % on pulp: DPv - Viscosimetric degree of polymerisation

	11 - Effect of quinone groups Lignin Quinone Total carbonyl 27 KN 0.045 0.26 52 KN 0.016 0.15 TMP 0.010 0.13 Quantitative 19F NMR analysis of residual lignin. Results expressed as number of functional group per aromatic ring with an accuracy of 5%.				12 - Strength properties Tear index as a function of tensile index for three different pulps : 52 OODEDnD, 27 DEDnD and 52 ZDEDnC. Strength properties are comparable to conventional ECF sequence on 27 kappa number pulp.

	13 - Improved selectivity (1) First hypothesis: ozone lignin reaction is 105 faster than ozone cellulose reaction     N.A. Ozone-lignin reaction produces muconic acid derivatives which are soluble in alkali medium Ozone-cellulose reaction proceeds by chain cleavage, formation of carbonyl groups and production of lactones.

	14 - Ozone pulp reaction Structural changes on kraft residual lignin hinder additional fragmentation reactions causing the residual lignin to be less reactive towards the pulping chemicals.      High KN pulp residual lignin could be more reactive towards bleaching chemicals   The high quantity of this relatively reactive lignin could favor the ozone-lignin reaction				15 - Improved selectivity (2) Second hypothesis: cellulose degradation Shorter cooking process leads to lower free phenolic groups content. Hydroxyl radical has been identified as the major cause of cellulose degradation during ozonation. Therefore reduced probability of hydroxyl radical formation.

	16 - Residual lignin analysis All through Kraft process modifications of lignin structure occur progressively, leading to the formation of free phenolic groups and dimethoxylation. Lignin Phenolic OH Carboxyl OCH3 27 KN 0.61 0.19 0.73 52 KN 0.55 0.13 0.79 TMP 0.30 0.005 0.89 Analysis by 13C NMR				17 - Conclusion High kappa number pulp HC ozonation at ambient temperature leads to: 1 -  2.3% bleached pulp yield increase 2 - competitive strength properties 3 - higher brightness 4 - higher lignin content, which is the major cause for increased selectivity

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