Understanding the role of iron chlorides in the de novo synthesis of polychlorinated dibenzo-p-dioxins/dibenzofurans.

The formation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) was investigated for mixtures of carbon black and iron chloride supported on a ceramic glass powder matrix in a low (2%) oxygen environment. Three iron chloride types (iron(II) chloride tetrahydrate, iron(III) chloride hexahydrate, and iron(II) oxychloride) were studied to gain some insights into their role in de novo formation. The importance of iron(II) and iron(III) chlorides both as chlorinating agents and promoters of low-temperature carbon gasification was observed. Iron(III) oxychloride was shown to be a very effective promoter at 325 degrees C and above; its conversion to iron(III) chloride was suggested as a key step. The predominant product was octachlorodibenzofuran. The oxide support matrix was found to be an important parameter.