FORMATION MECHANISMS OF POLYCHLORINATED DIBENZO-P-DIOXINS AND DIBENZOFURANS DURING PULP CHLORINATION

Experiments have been conducted to help establish the source of polych lorinated dibenzo-p-dioxins and poly-chlorinated dibenzofurans (PCDD/F ) that are produced during bleaching of pulp with high levels of chlor ine. Conditions have been established for observing the progressive de velopment of ring chlorination of dibenzo-p-dioxin (DBD) and dibenzofu ran (DBF), which were adsorbed onto cotton linters. The distribution a nd isomer patterns of the mono-, di-, tri-, and tetrachlorinated diben zofurans produced as a function of time for the chlorination of DBF-sp iked cotton linters were similar to that obtained from chlorination of an extracted pulp; this result indicates that DBF is probably the pri ncipal PCDF precursor in pulp. Because of the greater reactivity of DB D, few lower chlorinated PCDD were observed; the mechanism of PCDD for mation is less clear.