Higher Kappa Number Research Articles

Preliminary Results on Hydrogen Peroxide Addition to Chlorine Dioxide Bleaching Stages

There are convincing results in the literature indicating that the fiber yield for fully bleached hardwood kraft pulps can be increased by approximately 2% (measured on chip weight as basis) by pulping at milder conditions and bleaching under more aggressive conditions. The kappa number of the unbleached pulp in this scheme would be higher by about 3–5 units. The viability of this process is predicated upon increased throughput in an existing bleach plant without a major retrofit. The feasibility of the principle of this process was investigated by adding hydrogen peroxide to the first two chlorine dioxide stages (D0 and D1) along with sodium molybdate as a catalyst. The incremental peroxide required for bleaching the higher kappa number pulps could in principle be added to either of the two stages without any change in their operating conditions. Our preliminary data suggest that peroxide action in the D1 stage results in a lower rate of cellulose depolymerization and hence is preferable. The recovery of the molybdate catalyst is critical to the feasibility of this process. One possible process of molybdate recovery utilizing selective ion flotation with a cationic surfactant (dodecylamine) was investigated. A recovery of 58% was achieved after two preliminary trials using the column flotation technique. Other literature results suggest that a higher recovery, of the order of >90% is achievable using ion flotation indicating that a highly efficient recovery process for both the molybdate catalyst and the flotation agent can be developed. Thus, this technique of obtaining enhanced yields could provide an economically feasible alternative for production enhancement in pulp mills.

A comparative study of the impact of the cooking process on oxygen delignification

The impact of oxygen delignification on chemical pulps of a given kappa number manufactured in different ways (using kraft, prehydrolysis kraft and magnesium sulphite cooking) has been investigated. The prehistory of the pulps proves to be a very important factor in determining the response to oxygen delignification, i.e. the degree of delignification. It is shown that this is not due to different amounts of hexenuronic acid (HexA) in the different pulps, although this is an important factor behind the high residual kappa number after oxygen delignification of birch kraft pulp. Oxygen delignification of sulphite pulps proves to be efficient even at kappa numbers significantly lower than 10. These pulps show the greatest yield loss over the oxygen delignification. It is likely that Lignin Carbohydrate Complexes (LCC) complexes play a very important role in limiting the speed of reaction of oxygen delignification. Due to the very different prehistories of the pulps investigated, it is probable that the LCC:s are native and not formed during cooking.

酸化鉄法直接か性化技術 Ｉ ソーダキノン蒸解 Ｉ Ｎ材のソーダキノン蒸解

Laboratory studies for direct caustcizing process by ferric oxide in soda quinone pulping conditions were carried out in comparison with kraft pulping. DDA (1, 4-dihydro-9, 10-dihydroxy anthracene sodium salt) was used as quinone with addition of 0.1% as AQ by weight on o. d. wood. In the case of soda quinone pulping of Douglas fir, low temp.-long time pulping at the same H-factor and short time-high alkali pulping at the same τ-factor gave the same Kappa number of pulp, but low temp.-high alkali pulping at the same τ-factor gave a slihgtly high Kappa number pulp. By different pulping conditions, pulp yield and pulp properties were slightly different each other. There are not negligible differences in pulp yield and pulp properties at the same Kappa number by three different Douglas fir chip lot from different pulp mills in Japan. Almost same results with previous reports were obtained by the reappearance tests of soda quinone pulping of Douglas fir and eucalyptus at low Kappa number, and tear strength of soda quinone pulp of Douglas fir was ca. 10% lower than KP by statistical analysis.

Production of bleached softwood pulp by low pollution processes

Some aspects of sulphur-free soda pulping with anthraquinone (AQ) additions and chlorine-free bleaching with oxygen-based treatments were investigated with the aim of producing bleached softwood pulp with kraft-like strength properties. The extent of soda-AQ pulping was studied by pulping to 32, 42 and 68 Kappa number. After oxygen delignification to 10, 15 and 20 Kappa number respectively, the extent of bleaching with ozone, alkali extraction, and hydrogen peroxide treatments (ZEP sequence) was studied. For comparison, oxygen delignified pulps were conventionally bleached with a sequential chlorine/chlorine dioxide, alkali extraction, and chlorine dioxide (D/CED) sequence. A reference kraft pulp at 45 Kappa number was similarly oxygen delignified and bleached. Kraft-like strength properties (as measured by tear/burst relationships) were attainable if soda-AQ pulping was terminated at high Kappa number and was followed by oxygen delignification and D/CED bleaching. This pulp had a 3% (on wood) higher total yield and consumed less active alkali (2.0% as Na2O) than the bleached reference kraft pulp. Soda-AQ pulping followed by oxygen delignification and ZEP bleaching produced pulp with strength properties that were at least 25% less than those of the reference kraft pulp after oxygen delignification and conventional bleaching with chlorine-based treatments. Although the combination soda-AQ pulping to low Kappa number and extended oxygen delignification adversely affected pulp strength properties, it was ZEP bleaching and ozone treatments in particular, which caused the majority of the strength loss.