APPLICATION OF ANTHRAQUINONE IN EXTENDING THE DELIGNIFICATION OF KRAFT AND POLYSULFIDE PULPS .1. PULPING AND BLEACHING OF MIXED HARDWOODS

Delignification of conventional kraft and polysulfide (PS) hardwood pulps was extended to kappa no. 15 by adding anthraquinone (AQ). AQ had the same delignification effect on both kraft and PS pulping. AQ-supplemented pulps consumed 6-8% less chemical (0.9-1.1% less effective alkali) than conventional pulps. Black-liquor solids for the AQ-supplemented processes were 3-4% lower than kraft or PS, implying a 4% lower heat load to the recovery boiler. Bleached PS-AQ pulps required 18% less refining time than kraft pulp to reach a freeness of 500 mL CSF. No significant differences in pulp strength were observed among the four bleached pulps. However, the PS and PS-AQ pulps showed lower double fold and opacity.