Chlorinated Diphenoquinones: A New Class of Dioxin Isomeric Compounds Discovered in Fly Ashes, Slags, and Pyrolysis Oil Samples by Using HPLC/ELCD and HRGC/MS

Chlorinated 4,4′-diphenoquinones, previously unknown byproducts of thermal processes in the presence of chlorine, have been discovered in a variety of samples such as oil products from a waste pyrolysis plant, a fly ash from a municipal waste incinerator, and a sample of Kieselrot slag. The pyrolysis plant products also contained tetramethylated and unsubstituted 4,4′-diphenoquinone. All compounds may be generated by oxidative coupling of phenols at elevated temperatures - a reaction that is considered to compete with the formation of the structurally isomeric dioxins. Once built-up, 4,4′-diphenoquinones form a redox pair with die corresponding 4,4′-dihydroxybiphenyls, with variable equilibrium positions depending on the prevailing conditions. For analysis, a cleanup method which involves liquid/liquid partition and solid-phase extraction was developed. The method is suitable for the determination of all substances of this class. Quantitative analysis was carried out by HPLC using an electrochemical detector for the fly ash and slag samples. Pyrolysis oil samples were quantitatively analyzed by GC/MS after derivatization with trifluoroacetic acid anhydride. Substance identification in all samples was performed by GC/MS. The samples were found to be contaminated with chlorinated diphenoquinones in the lower and middle ppb range. Pyrolysis oil products yielded up to 1 ppm methylated diphenoquinones. The amount of diphenoquinones in the samples is compared with their yield of chlorinated dioxins and furans as well as polychlorinated biphenyls (PCBs). Kieselrot especially was contaminated, wim 25 ppm of polychlorinated dibenzo-p-dioxins/-furans (PCDD/F) and 94 ppm of hexachlorobenzene, while the pyrolysis oil samples contained up to 360 ppb of PCDD/F and up to 25 ppm of PCB.