Abstract
In recent decades, the pulp industry has been changing and improving its manufacturing processes in order to enhance production capacity, product quality and environmental performance. The aim of this study was to evaluate the bleachability effect on the efficient washing and alkaline leaching in eucalyptus and pine Kraft pulps using three different bleaching sequences: AD(EP)D, A/D(EP)DP and D HT(EP)DP. This study was carried out in two stages. In the first part, the optimum conditions for pulp bleaching in order to achieve a brightness of 90% ISO were established. The second step was a comparative study between the pulps that received alkaline leaching and efficient washing with reference pulp (without treatment). The brightness, viscosity, kappa number and HexA in pulp were analyzed. The three sequences studied reached the desired brightness, but the sequence AD(EP)D produced a lower reagent consumption for the same brightness. In the three sequences studied, the efficient washing of the pulp after oxygen delignification has contributed significantly to the removal of dissolved organic and inorganic materials in the pulp and the alkaline leaching decreased significantly the pulp kappa number due to a higher pulp delignification and bleachability.
Highlights
In recent decades, the pulp industry has been changing and improving its manufacturing processes in order to enhance production capacity, product quality and environmental performance
The best possible washing result is obtained when clean water is applied for all washing steps, typically, the pulp washing is done in a countercurrent system, where clean water is applied at the end of the wash cycle and the final filtrate is reused in the previous steps, moving in countercurrent to the input side of the cellulose in the system
The second step was a comparative study between the pulps that received alkaline leaching and efficient washing with reference pulp
Summary
The pulp industry has been changing and improving its manufacturing processes in order to enhance production capacity, product quality and environmental performance. The presence of dissolved organic and inorganic material in the pulp after washing hampers the efficient operation of the bleaching process, mainly due to a higher consumption of chemicals and the consequent increase of color and chemical (COD) and biological (BOD) oxygen demand from industrial plant effluent. The alkaline leaching pulp has as a purpose to remove lignin trapped on the cellulose fibers, resulting in a lower kappa number and lower reagent consumption in the stage. The pulp washing in bleaching removes dissolved organic and inorganic materials that provide suitable conditions for the subsequent bleaching stage minimizing disturbances and reducing the consumption of reagents (FRASSÃO, 2008). The best possible washing result is obtained when clean water is applied for all washing steps, typically, the pulp washing is done in a countercurrent system, where clean water is applied at the end of the wash cycle and the final filtrate is reused in the previous steps, moving in countercurrent to the input side of the cellulose in the system
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