New evidence for the role of the borohydride pretreatment on the hydrogen peroxide bleaching of kraft pulp

Abstract

A study was conducted to clarify the role of the borohydride pretreatment on the hydrogen peroxide bleaching process, based on eucalyptus chemical pulps from a laboratory kraft pulping process. The results showed that the borohydride pretreatment is effective at suppressing the effect of the Fe(III) on the oxygen formation from the peroxide decomposition. This paper for the first time quantitatively proves that the carbonyl group content in the pulp can be significantly reduced (∼51.3%). Correspondingly, this paper is also the first to find that the dissolved lignin in the effluents became more stable, since there was no significant change in its UV spectrum. There is also strong evidence that the borohydride pretreated bleaching process produced a lower amount of methanol and oxalate (∼24.3% and ∼11.8% of decrease respectively), and had more residual hydrogen peroxide in the effluents (38.4% at 180 min), compared to the non-borohydride bleaching system. The study also showed that the effect of the borohydride pretreatment on the carbohydrate preservation is not significant.