Some Preliminary Results on Oxygen Addition to D-Stage Bleaching (D/O)

ABSTRACT
Radical-radical coupling reactions are quite common in chlorine dioxide or D-stage bleaching. In
the present research, we investigated the possibility of obtaining a higher brightness in D1 and D2 stages
by adding oxygen along with ClO2. If an organic free radical couples with O2 instead of ClO2 then an
extra mole of ClO2 would be available to abstract an electron from another aromatic ring to generate a
reactive radical cation and chlorite anion. Under typical pulp bleaching temperatures, oxygen, a diradical,
abstracts an electron from non-phenolic rings at a very low rate, if at all.
Preliminary results appeared convincing that when D stages were performed in a Quantum
mixer, the use of O2 to inject ClO2 (D/O) was superior to the use of N2 (D/N or simply D1). A moderate
brightness increase was consistently observed when D1 (D/N) was replaced by D/O and the brightness
increase was retained after final bleaching to 90+ brightness. When an eucalyptus kraft pulp was
investigated, the OD0EOP(D/O) sequence gave 89+ brightness and a much lower rate of thermal
reversion as compared to OD0EOP(D/N). Pulp viscosity was unaffected. Mg(OH)2 is preferable to NaOH
for pH control, and pending further research, the end pH should be below 4.9. Chloroform generated in
the effluent increased from 15 μg/L at end pH 4.0 to 18 μg/L at end pH 4.9 and to 130 μg/L at end pH
6.2.
Keywords: Kraft pulp, Bleaching, Chlorine dioxide, Oxygen, Brightness, Chloroform generation 

TAPPI conference proceedings and presentations, technical papers, and publication articles provide technical and management data and solutions on topics covering the Pulp, Paper, Tissue, Corrugated Packaging, Flexible Packaging, Nanotechnology and Converting Industries.

Simply select the quantity, add to your cart and your conference paper, presentation or article will be available for immediate download.