| 1. |
- Brännvall, Elisabet, et al.
(författare)
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Separate bleaching of pulp fractions enriched in earlywood and latewood fibers
- 2007
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Ingår i: Journal of wood chemistry and technology. - : Informa UK Limited. - 0277-3813 .- 1532-2319. ; 27:2, s. 99-112
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Tidskriftsartikel (refereegranskat)abstract
- Unbleached softwood kraft pulp was fractionated in hydrocyclones into a fine fraction, enriched in earlywood fibers, and a coarse fraction, enriched in latewood fibers. The response to individual bleaching chemicals and the bleachability in bleaching sequences of the pulp fractions was studied. The light absorption coefficient, light scattering coeffient, and brightness were higher in the unbleached fine fraction than in the coarse fraction. Hydrogen peroxide managed to reduce the light absorption coefficient of the earlywood enriched fine fraction more efficiently than that of the latewood enriched fraction. In the TCF-sequence the light absorption coefficient of the fine fraction was reduced to the level of the coarse fraction at a given consumption of bleaching chemicals. In the ECF-sequence the difference in light absorption coefficient remained between the fractions. At a given consumption of bleaching chemicals, the fine fraction had higher brightness than the coarse fraction, 2%- and 1%-units on the ISO-scale in the TCF and ECF bleaching sequence, respectively.
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| 2. |
- Dahlman, Olof, et al.
(författare)
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Processing of xylan from hardwood spent cooking liquors
- 2008
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Ingår i: 2008 Nordic Wood Biorefinery Conference - Proceedings. - 9789186018139 ; , s. 114-119
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Konferensbidrag (refereegranskat)abstract
- The paper reports conditions suitable for recovering and processing 4-O-methylglucuronoxylans from birch and eucalyptus spent kraft cooking liquors. The black liquor originating from the initial heating-up phase in birch kraft cooking exhibits a high xylan and low lignin concentration. The maximum concentration of polymeric xylan was found in the cooking liquor just before the cook reached its final cooking temperature. For eucalyptus kraft cooking, however, lignin was more abundant than xylan in the cooking liquor throughout the whole cook. Birch and eucalyptus xylan, exhibiting good purity, were produced by employing a process chain involving, redrawing of xylan-rich spent liquor early in the cook, upgrading of the spent liquor employing ultrafiltration with diafiltration followed by precipitation and drying.
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| 3. |
- Olm, Leelo, et al.
(författare)
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High sulphidity kraft pulping
- 2009
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Ingår i: Nordic Pulp & Paper Research Journal. - 0283-2631 .- 2000-0669. ; 24:4, s. 433-439
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Tidskriftsartikel (refereegranskat)abstract
- The object of this project was to evaluate the effect of high sulphidity on the performance of the kraft cooking process. Softwood (SW) mix (50/50 of spruce, Picea abies, and pine, Pinus sylvestris) and a hardwood (HW: birch, Betula pendula) have been explored as wood raw material. The reference kraft cook was carried out at 35% sulphidity. The laboratory kraft cooking trials showed that the rate of delignification in kraft cooking increases with increasing sulphidity for both these raw materials. An increase in sulphidity from 35% to 80% increases the apparent delignification rate by a factor of almost two. The faster delignification rate could be exploited as an increase in production and/or as a reduction in EA charge (2%-units for both raw materials) and/or as a decrease in cooking temperature (5°C for SW) at the same production. The yield of softwood kraft pulp at a given kappa number was not affected by the increase in sulphidity. For hardwood, the combination of high sulphidity and reduced effective alkali charge gave an increase in pulp yield of one %-unit. The pulp viscosity at a given kappa number was increased. The high sulphidity in SW kraft cooking (at a given EAcharge) led to a slightly better bleachability in an OD(E+P)DD bleaching sequence. The fully bleached SW kraft pulp at 80% sulphidity had a slightly higher tear index and higher fibre strength than the corresponding reference kraft pulp at 35% sulphidity. The other strength properties were virtually unchanged. The fully bleached HW kraft pulp at 80% sulphidity showed better optical properties, light scattering and opacity, which are, in fact, the critical properties for fully bleached hardwood pulps.
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| 4. |
- Tormund, Disa, et al.
(författare)
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Delignification and bleaching response of earlywood and latewood
- 2006
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Ingår i: Journal of wood chemistry and technology. - : Informa UK Limited. - 0277-3813 .- 1532-2319. ; 26:4, s. 325-337
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Tidskriftsartikel (refereegranskat)abstract
- The delignification response in cooking and the impact of bleaching on earlywood and latewood were studied. Spruce earlywood and latewood chips were pulped by the kraft process and subsequently treated with one bleaching chemical at a time. In cooking, latewood required a higher alkali charge to reach the same kappa number. No difference in the light absorption coefficient between the different fiber types was observed. After oxygen delignification the earlywood fibers had a higher light absorption coefficient at the same kappa number. The difference in light absorbing material was maintained when bleaching was performed with chlorine dioxide, ozone, and peracetic acid. Hydrogen peroxide decreased the light absorbing structures in the earlywood to the same level as for latewood. The earlywood pulp had a higher brightness at a given kappa number than the latewood. The higher brightness remained through all bleaching operations and was primarily due to a higher light scattering ability.
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| 5. |
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