Assessment of Q(OP)D(PO) bleachability of softwood kraft pulp

Abstract

Bleachability is evaluated as how easily a pulp sample is bleached and it depends on the structure of residual lignin and carbohydrates. Also, the bleachability varies depending on the bleaching sequence. ECF light sequences have been improved significantly in the recent years. However, we still don’t fully understand how ECF light bleach plants are optimally run. This work studies the bleachability of softwood kraft pulp in an ECF light bleaching sequence, (OO)Q(OP)D(PO). Three pulp samples with brown stock kappa number 27, 32 and 35 were bleached and studied for residual lignin, hexenuronic acid and carbohydrate content. It was found that in the bleaching stages that are highly delignifying, it is beneficial with a higher kappa number for the delignifying bleachability. However, in the bleaching stages where the objective is brightness increase, the brightness gain bleachability is improved by a lower kappa number. We also intended to determine which of the three samples had the best suited kappa number for this particular bleaching sequence. According to our results, the bleaching was most effective with kappa number around 32. Although an even higher kappa number resulted in higher yield after cooking, it seemed that this bleaching sequence cannot preserve the yield gain.

Synergism of enzymes in chemical pulp bleaching from an industrial point of view: A critical review

“…It is possible to distinguish the bleaching efficiency of an enzyme treatment since delignification effect and brightness gain can be used to evaluate the effectiveness of one treatment. [61] The kappa number value includes the residual lignin and other oxidizable structures, such as HexA, which are present in the unbleached pulp. [62] The desired brightness increase, which is one of the main objectives of bleaching, is also related to the removal of the residual lignin to a large degree.…”

Solar-Driven Photobleaching of Lignocellulosic Biomass

“…Among the methods applied in the bleaching process are the use of chlorinated compounds or hydrogen peroxide. H2O2 is the main bleaching agent in the pulp industry [7,8]. The per hydroxyl anion (HOO -) removes the conjugated carbonyl groups from the lignin structure.…”

The effect of treating pine regular kraft pulp with peracetic acid before O2-delignification on the consumption of ClO2 in D0ED1 bleaching

“…Although these mills fulfill the current environmental legislation requirements in terms of effluent discharge, the regulations may change in the future, and the pulp industry is therefore seeking new pulp bleaching methods to minimize the environmental impact. Consequently, one of the main research trends in kraft pulp bleaching over many years has been to reduce the amount of chlorine compounds discharged from bleaching processes to the sewage treatment plants of kraft pulp mills (Karim 2011;Tripathi et al 2020;Starrsjö et al 2021;Oliveira et al 2022). This can be achieved by bleaching pulps with lower levels of lignin and hexenuronic acid residues than conventional, as well as optimizing the parameters of this process.…”