Showing papers by "Pratima Bajpai published in 2006"

Enzymes improve ecf bleaching of pulp

Abstract: The delignification efficiency of different laccase enzymes was examined on the eucalyptus Kraft pulp. Laccase enzyme from Trametes versicolor showing the highest delignification was selected and used in the elemental chlorine free bleaching sequence. An appreciable reduction in chlorine dioxide consumption was also obtained. Further reduction in chlorine dioxide consumption was obtained when the same laccase treated pulp was subjected to an acid treatment after the extraction stage followed by DEpD sequence. Elemental chlorine free bleaching was also performed using the xylanase-laccase treated pulp. Xylanase treatment was incorporated to the laccase mediator system in the elemental chlorine free bleaching both sequentially and simultaneously. The bleaching sequence DEpD was followed and in both the cases, reduction in chlorine dioxide consumption was more in comparison to control. Chlorine dioxide consumption reduced further when xylanase-laccase treated pulp was given an additional acid treatment. The final pulp properties of the treated pulps were comparable to the control pulp.

Use of enzymes for reduction in refining energy - : laboratory studies

Abstract: We performed laboratory and process-scale studies with mixtures of cellulase and hemicellulase enzymes for reducing the refining/beating energy requirement of different types of pulp. Those included hardwood kraft pulp, long fiber fraction of bamboo pulp, old corrugated containers (OCC), and mixed pulp containing new double-lined kraft cuttings (NDLKC) and long fiber fraction of bamboo pulp. In the laboratory, the refining energies were reduced by 18%-45% for different pulps with these enzymes.The strength properties of pulps were not affected by enzyme treatment. In the process scale trials, use of one of the enzyme products in the production of high strength extensible sack kraft paper (ESKP) reduced the required refining energy by 25 kWh/metric ton of pulp. It also yielded savings in steam consumption per ton of paper of about 20% from various sections of the machine operation. The mill was able to bypass one double disc refiner (DDR) when the furnish was changed to 60% unbleached bamboo kraft pulp (long fraction) and 40% NDLKC for producing normal ESKP. This reduced the energy requirement by about 54 kWh/metric ton of pulp, with an 8% savings in steam consumption per ton of paper. The mill was able to produce high strength paper having high porosity without sacri ficing other strength properties. Trials with the same enzyme in a mill producing mainly coated white paper showed a reduction in refining energy of about 70 kWh/metric ton of softwood pulp and 30 kWh/metric ton of hardwood pulp. Steam consumption on the paper machine was reduced by approximately 0.5 ton steam/metric ton of paper. By using enzymes, the mill eliminated a refining bottleneck in its softwood line and increased production by 12%. The strength properties of the pulps were not affected. In a mill producing heavy base papers, enzyme use enabled the mill to bypass one 180 kW triple disc refiner (TDR). Pulp strength and other properties were within the specified limits and comparable to those of the control. All these mills have started using enzyme on regular basis.