Kraft process

About: Kraft process is a research topic. Over the lifetime, 4003 publications have been published within this topic receiving 62684 citations. The topic is also known as: sulfate pulping process & sulfate process.

Xylanases in bleaching: From an idea to the industry

Abstract: The utilization of hemicellulases in bleaching of kraft (sulphate) pulp is considered as one of the most important new large-scale industrial applications of enzymes. This is partly due to the great potential of an environmentally safe method. This method has in a short period also proven to be economically realistic. The main enzymes needed in the enzyme-aided bleaching have been shown to belong to the group of endo-/gb-xylanases. Xylanases act mainly on the relocated, reprecipitated xylan on the surface of the pulp fibres. Enzymatic hydrolysis of this specific type of xylan renders the structure of the fibres more permeable. The hydrolysis of xylan or mannan in the inner fibre layers may also enhance the bleachability. In practical process conditions, properties of the enzymes such as substrate specificity and the pH and temperature optima are of utmost importance. The benefits obtained by enzymes are dependent on the chemical bleaching sequence used as well as on the residual lignin content of pulp. The main goals in the enzyme-aided bleaching of kraft pulps have been the reduction of consumption of chlorine chemicals in the bleaching process and consequently lowering the AOX of the effluents. Enzymes have been applied as a pretreatment both in conventional (C/D)EDED and in ECF (elementary chlorine-free) bleaching sequences. In the production of TCF (totally chlorine-free) pulps, enzymes have also been successfully used for increasing the brightness of pulp.

The effect of morphological changes from pulp fiber towards nano-scale fibrillated cellulose on the mechanical properties of high-strength plant fiber based composites

Abstract: Fibrillated kraft pulp impregnated with phenolic resin was compressed under an extremely high pressure of 100 MPa to produce high strength cellulose nanocomposites To evaluate how the degree of fibrillation of pulp fiber affects the mechanical properties of the final composites, kraft pulp subjected to various levels of refining and high pressure homogenization treatments was used as raw material with different phenolic resin contents It was found that fibrillation solely of the surface of the fibers is not effective in improving composite strength, though there is a distinct point in the fibrillation stage at which an abrupt increase in the mechanical properties of composites occurs In the range between 16 and 30 passes through refiner treatments, pulp fibers underwent a degree of fibrillation that resulted in a stepwise increment of mechanical properties, most strikingly in bending strength This increase was attributed to the complete fibrillation of the bulk of the fibers For additional high pressure homogenization-treated pulps, composite strength increased linearly against water retention values, which characterize the cellulose’s exposed surface area, and reached maximum value at 14 passes through the homogenizer

Lignin oxidation by laccase isozymes from Trametes versicolor and role of the mediator 2,2'-azinobis(3-ethylbenzthiazoline-6-sulfonate) in kraft lignin depolymerization.

Abstract: Two laccase isozymes (I and II) produced by the white-rot fungus Trametes versicolor were purified, and their reactivities towards various substrates and lignins were studied. The N-terminal amino acid sequences of these enzymes were determined and compared to other known laccase sequences. Laccase II showed a very high sequence similarity to a laccase which was previously reported to depolymerize lignin. The reactivities of the two isozymes on most of the substrates tested were similar, but there were some differences in the oxidation rate of polymeric substrates. We found that the two laccases produced similar qualitative effects on kraft lignin and residual lignin in kraft pulp, with no evidence of a marked preference for depolymerization by either enzyme. However, the presence of the mediator 2,2'-azinobis(3-ethylbenzthiazoline-6-sulfonate) prevented and reversed the polymerization of kraft lignin by either laccase. The delignification of hardwood and softwood kraft pulps with the two isozymes and the mediator was compared; either laccase was able to reduce the kappa number of pulp, but only in the presence of 2,2'-azinobis(3-ethylbenzthiazoline-6-sulfonate).

Biotechnological treatment of sulfate-rich wastewaters.

Abstract: Sulfate-rich wastewaters are generated by many industrial processes that use sulfuric acid or sulfate-rich feed stocks (e.g., fermentation or sea food processing industry). Also, the use of reduced sulfur compounds in industry, that is, sulfide (tanneries, kraft pulping), sulfite (sulfite pulping), or thiosulfate (pulp bleaching, fixing of photographs), contaminates wastewaters with sulfate. A major problem for the biological treatment of sulfate-rich wastewaters is the production of H2S. Gaseous and dissolved sulfides cause physical (corrosion, odor, increased effluent COD) or biological (toxicity) constraints that may lead to process failure. H2S is generated by sulfate-reducing bacteria, in both anaerobic and aerobic (anoxic microenvironments) wastewater treatment systems. No practical methods exist to prevent sulfate reduction. Selective inhibition of SRB by molybdate, transition elements, or antibiotics is unsuccessful at full scale. Selection of a treatment strategy for a sulfate-rich wastewater dep...