REACTIONS OF OZONE WITH DIBENZO-P-DIOXIN AND DIBENZOFURAN IN PULP

Dibenzo-p-dioxin (DBD) and dibenzofuran (DBF) appear to be important p recursors to chlorinated dioxins formed during chlorine bleaching of p ulp. Reducing the concentration of the precursors prior to chlorinatio n may reduce the formation of dioxins. The high reactivity of electrop hilic chlorine with the precursors in pulp suggests that ozone, anothe r electrophilic reagent, may effectively reduce precursor levels in pu lp. The goal of this work was to find optimal conditions for ozone des truction of DBD and DBF in pulp. Very mild conditions were unsuccessfu l at removing DBD and DBF, however conditions of 2% ozone charge, high consistency and slow ozone delivery rates reduced DBD and DBF by 83% and 68%, respectively. In general, conditions which enhance delignific ation also enhanced precursor degradation. Exposure of pulp to ozone p rior to chlorination may remove enough DBD and DBF to significantly re duce chlorinated dioxin formation with chlorine bleaching.