Title
Effects of hot dispersion with reductive bleaching on the brightness of deinked pulp in both laboratory and mill machines
Authors
YUAN-SHING PERNG EUGENE I-CHEN WANGWU-HUNG CHUNG and CHIH-PING CHANG

Received March 23, 2013
Published Volume 48 Issue 5-6 May-June
Keywords deinked pulp, bleaching, hot-dispersion, sodium hydrosulfite, formamidine sulfinic acid

Abstract
Effects of disperser bleaching using different concentrations of sodium hydrosulfite (SHS) or formamidine sulfonic acid (FAS) at different temperatures at both laboratory and mill scales on the brightness of deinked pulp were examined in this study. In lab bleaching tests, deinked pulp adjusted to a 2.73% consistency was hot-dispersed at 100 ºC with the addition of SHS or FAS at 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.8%, 1.0%, and 1.2% dosages, and at 40, 60 and 85 ºC for 1 h. The mill trials were run at a pulp consistency of 32%, SHS or FAS dosage of 0.8%, and temperatures of 90, 100, 110, and 115 ºC. SHS and FAS dosages of 0.1%, 0.3%, 0.5%, 0.8%, and 1.2% were also run at a hot dispersion temperature of 100 ºC using a mill disperser. The lab results indicated that there were positive correlations between the bleaching effects and both the reductive bleaching agent dosage and operating temperature. At 40 ºC, SHS performed better than FAS. However, at temperatures above 60 ºC, the converse was true. At a FAS dosage of 0.3%, the pulp reached a saturation brightness at the same level as that achieved by 1.2% of SHS. The mill trials with a hot dispersion unit produced similar results. At 100 ºC, the FAS group had better bleaching effects than the SHS group. At a bleaching dosage of 0.8%, the brightness gap between FAS and SHS groups increased with increasing temperature, and reached 2.8% ISO at 115 ºC. An economic efficiency analysis indicated that when reductive bleaching agents were applied to a hot dispersion unit, the FAS group had unit costs 10% lower than those of the SHS group. Therefore, FAS deserves priority in practical applications.