Experimental study on the effects of H 2O on PCDD/Fs formation by de novo synthesis in carbon/CuCl 2 model system

Abstract

The effects of H 2O 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, CuCl 2, and quartz, exposed to a flow of 10% O 2/N 2 at 300 °C. The influence of H 2O 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 H 2O converts CuCl 2 to CuCl 2·CuO, and finally to CuO in a flow of 10% O 2/N 2 at 300 °C and that it decreases of organic chlorine (C–Cl) formation. When CuCl 2 is supported on carbon, the addition of H 2O promotes the catalytic oxidation of this carbon. When CuCl 2 is supported on quartz, however, H 2O 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 H 2O does not react with Cu 2Cl 2, which is the catalyst of carbon oxidation. On the basis of the experimental results, the following mechanism is proposed: conversion of CuCl 2 into CuO which is less reactive in de novo synthesis and promotion of catalytic oxidation of carbon by Cu 2Cl 2.