On the theoretical basis for the low bleaching chemical requirement of hot chlorine dioxide bleaching of hardwood kraft pulp

摘要

There are two different ways of utilising the benefits of hot acid treatment - a reduced chlorine dioxide requirement to reach a target brightness and a reduced brightness reversion - either in the form of A~* treatment followed by chlorine dioxide bleaching or in the form of hot chlorine dioxide bleaching, D~*. The asterisk "*" is here used to denote a treatment at a high temperature and with a long retention time. In the literature it has been reported that the beneficial effects differ depending on how the hot acid treatment technology is implemented. In order to clearify the situation, the theoretical basis of the hot acid treatment and the hot chlorine dioxide bleaching are explored. It is concluded that the presence of 2-furoic acid and other degradation products of HexA hydrolysis are detrimental for the bleaching response of chlorine dioxide bleaching. This implies that the most beneficial way of making use of hot acid treatment is to utilise hot chlorine dioxide bleaching, e.g. in a sequence such as D~*(OP)D.