Experimental study on the effects of H2O on PCDD/Fs formation by de novo synthesis in carbon/CuCl2 model system

The effects of H2O vapor on de novo synthesis of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and biphenyls (PCB) were investigated at two levels (none and 10 vol.%) in various model systems containing five different carbons, CuCl2, and quartz, exposed to a flow of 10% O2/N2 at 300 °C. The influence of H2O was studied on (1) speciation and behavior of copper compounds, (2) catalytic oxidation of carbons of distinct reactivity, and (3) formation of organic chlorine compounds, with the aim to investigate any effects on de novo synthesis. It is found that H2O converts CuCl2 to CuCl2·CuO, and finally to CuO in a flow of 10% O2/N2 at 300 °C and that it decreases of organic chlorine (C–Cl) formation. When CuCl2 is supported on carbon, the addition of H2O promotes the catalytic oxidation of this carbon. When CuCl2 is supported on quartz, however, H2O inhibits carbon oxidation. A decrease in chlorination level of PCDD/Fs and PCBs with water addition is observed for all (six) model ashes; yet this addition affects the yields of PCDD/Fs and PCBs differently. Under the experimental conditions tested H2O does not react with Cu2Cl2, which is the catalyst of carbon oxidation. On the basis of the experimental results, the following mechanism is proposed: conversion of CuCl2 into CuO which is less reactive in de novo synthesis and promotion of catalytic oxidation of carbon by Cu2Cl2.