Delignified Kraft Pulp Research Articles

Production and Characterization of Trametes versicolor Mutants Unable To Bleach Hardwood Kraft Pulp

Protoplasts of the monokaryotic strain 52J of Trametes versicolor were treated with UV light and screened for the inability to produce a colored precipitate on guaiacol-containing agar plates. Mutants unable to oxidize guaiacol had absent or very low secretion of laccase and manganese peroxidase (MnP) proteins. All isolates unable to secrete MnP were also unable to bleach or delignify kraft pulp. One mutant strain, M49, which grew normally but did not oxidize guaiacol, was tested further with a number of other substrates whose degradation has been associated with delignification by white rot fungi. Compared with the parent, 52J, mutant M49, secreting no MnP and low laccase, could not brighten or delignify kraft pulp, produced less ethylene from 2-keto methiolbutyric acid, released much less (sup14)CO(inf2) from [(sup14)C]DHP (a synthetic lignin-like polymerizate), and produced much less methanol from pulp. This mutant also displayed decreased abilities to oxidize the dyes poly B-411, poly R-478, and phenol red compared with the wild-type strain and was also unable to decolorize kraft bleachery effluent or mineralize its organochlorine. Addition of purified MnP in conjunction with H(inf2)O(inf2), MnSO(inf4), and an Mn(III) chelator to M49 cultures partially restored methanol production, pulp delignification, and biobleaching in some cases.

Bleaching of radiata pine Kraft pulp with the EnZone process

Oxygen delignified Kraft pulps from radiata pine were treated with xylanase in the presence of a quelating agent prior to their chemical bleaching with the sequences WZE OPP, E PWZP and E OPWZP. Enzymes tested included Cartazyme from Sandoz, Ecopulp from Alko-ICI, Irgazyme 40 from Ciba-Genencor and Pulpzyme HB from Novo Nordisk. A positive effect of these xylanases was observed with the sequence Xo-E PWZP, which yielded pulps with a final brightness of 85–86% ISO. Application of the sequence Xo-E OPWZP led to pulps with brightness within the target value of 90% ISO, although enzyme effect in this case was less evident. In turn, enzymes were ineffective in the sequence XQ-WZE OPP. These results emphasize the need to design a proper chemical sequence to optimize biobleaching. In most experiments, beatability of enzyme-treated pulps was slightly affected, requiring up to 15% more revolutions in the PFI mill than the controls to reach the same tensile index.

The Effects of Chlorination Conditions on the AOX and Chlorinated Phenol Content of Kraft Bleach Plant Wastewaters

A central composite experimental design was used to develop models of the yields of Adsorbable Organic Halide (AOX) and chlorophenolic compounds in wastewaters produced by bleaching oxygen delignified kraft pulps. The following five variables were used to control the bleaching conditions: total available chlorine, chlorine dioxide substitution, incoming kappa number, chlorination time and temperature. The total available chlorine and the chlorine dioxide substitution were the most important parameters in all the models developed. The yields (g.tonne−1) of AOX and total chlorophenolic compounds increased linearly with increasing total chlorine application. Elevating the level of chlorine dioxide substitution caused the yield of AOX to decrease linearly while the yield of total chlorophenols diminished in a non-linear manner. Increasing the level of chlorine dioxide substitution at a given total chlorine application is an effective means of reducing the emissions of both AOX and chlorinated phenols.

Delignification of wood pulp by hot alkali treatment following NO2/O2 pretreatment

An effective delignification of kraft pulp without serious depolymerization of the cellulose was achieved by alkali treatment above 100°C, following pretreatment with NO2/O2 at approximately 50°C. Compared at the same degree of delignification the depolymerization of the carbohydrates and the yield were less than after oxygen bleaching of the pretreated pulp.

Studies on Pulp Bleaching (I)

This investigation concerns the comparative chlorination of sulfite and kraft pulps as means of elucidating less-bleachability of kraft pulp. Some of the more important features include : 1. Less chlorine consumption, higher permanganate number, and less delignification of kraft pulp than.those of sulfite pulp would be reasonably interpreted in terms of its smaller reaction surface and more drastic denaturation of its residual lignin.2. By comparing the chlorine consumption of both pulps via substitution reaction we are able to make rough estimation on pulp bleachability.3. It is proposed that substitution reaction, one of the two important reactions during pulp chlorination, is definitly responsible for bleaching effect of sulfite pulp. On the other hand, in case of kraft pulp the extent of bleaching contribution due to oxidation reaction increases more dominantly.