| Summary: | A study was done to determine the kinetics and stoichiometry of hypochlorite bleaching of pinus radiata kraft pulp obtained from the extraction stage of a chlorine, caustic extraction and hypochlorite (CEH) bleaching sequence. The "differential method" of experimentation was used, where bleaching chemicals are charged at the start of the experiment and allowed to decrease as bleaching proceeds. The bleaching rate is found to be dependent on temperature, chromophore concentration (approximated by the specific light absorption coefficient), hypochlorite ion concentration (OCl-) and hydroxide ion concentration (alkalinity, OH-). Bleaching rate increases with chromophore concentration and hypochlorite ion concentration but decreases with increasing alkalinity. The bleaching rate, [formula here], for the hypochlorite bleaching of CE-prebleached pinus radiata kraft pulp can be expressed by the following kinetic equation.
[formula here]
where
Ck : specific light absorption coefficient at 457 nm, [m² kg-¹].
[OH-] : hydroxide ion concentration, [mol 1-¹].
[OCl-] : hypochlorite ion concentration, [mol 1-¹]
and the Arrhenius' activation energy is approximately 64 kJ mol-¹
The stoichiometry of the bleaching reaction can be described by the following two equations.
[formulas here]
Where
Cko : initial specific light absorption coefficient, [m²kg-¹]
OCo : initial hypochlorite charge, [moles per kg O.D. pulp]
OCl : hypochlorite charge at time=t, [moles per kg O.D. pulp].
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