A Comparison Between Alkali Peroxide and Activated Peroxide Processes in Bleaching Hardwoods Chemi-mechanical Pulp

Unbleached chemi-mechanical pulp of 85% pulp yield and produced from hornbeam، beech and populus woods respectively by 3:1: 1 ratio، was used for peroxide bleaching. Two bleaching systems، alkali peroxide (conventional bleaching) and activated peroxide by TAED activator، were used for pulp bleaching. Bleaching treatments included different percentages of hydrogen peroxide and caustic soda consumption. In this research، the hydrogen peroxide consumption rate، pulp yield، process selectivity، bleached pulp brightness and bleaching effluent pollution load (COD) were investigated. Results showed that، brightness values were increased by bleach chemicals charge rising، in both bleaching systems، but the increasing trend was downward. Also، pulp yield was decreased by increase of chemical charges، but residual peroxide was raised. The activated peroxide process compare to conventional process had lower efficiency and brightness improvement values of pulp were less than those of alkali peroxide process. But pulp yield and effluent pollution load was less by activated peroxide bleaching.