Inhibition of de novo synthesis of PCDD/Fs by SO2 in a model system

The effect of sulfur dioxide (SO2) on de novo synthesis of polychlorinated dibenzo-p-dioxins, dibenzofurans (PCDD/F) and biphenyls (PCB) was investigated in model systems containing carbon, activated by cupric chloride (CuCl2). Five types of carbons (activated carbon, three types of carbon blacks, and graphite) were used to test the universal character of our results. The influence of SO2 on speciation and behavior of copper compounds, catalytic oxidation of carbons, and formation of organic chlorine (extractable organic chlorine and non-extractable organic chlorine) was also studied to investigate the inhibition mechanism of SO2 on de novo synthesis. It was found that SO2 can sulfate CuCl2, but does not react with CuO and CuCl2·CuO in a 10% O2/N2 atmosphere at 300 °C. The suppression by SO2 of organic chlorine (C–Cl) formation also confirmed these findings. It was also found that catalytic oxidation of carbons was strongly suppressed by SO2. A dramatic decrease in PCDD/Fs formation was observed for all five carbons, while adding SO2; at the same time the average chlorination level also decreased. However, the inhibiting effect on PCB was less apparent compared with that on PCDD/F. On the basis of the experimental results, the conversion of both cupric and cuprous chloride into the non-reactive sulfate was proposed as inhibition mechanism.