Low kappa factor bleaching of oxygen delignified hardwood kraft pulp - Xylanase and peroxide applications

The effect of xylanase enzyme pretreatment and hydrogen peroxide reinforced extraction on the bleachability of an oxygen delignified hardwood kraft pulp was investigated. Pulp was fully bleached to 90% ISO brightness at kappa factors ranging from 0.25 to 0.00 in a D (EOP) DD sequence. Chlorine dioxide requirements decreased from 21 kg/t at 0.25 kappa factor to 13 kg/t at 0.05 kappa factor with enzyme pretreatment and the addition of hydrogen peroxide to the extraction stage. Bleach plant effluent AOX and color declined proportionally with decreasing kappa factor. Pulp strength and optical properties were maintained while minimizing the environmental and regulatory impact of producing a fully bleached market pulp. Depending on operating strategies, cost savings of $1 to $4/t were realized. Mills that are limited by chlorine dioxide production capacity can realize capital avoidance savings up to $1 750 000 by practising low kappa factor bleaching technology.