Methods for studying the de novo formation of dioxins at a laboratory scale.

Abstract

A new methodology is proposed for comparative study of filter dust samples regarding their organic load and their potency with respect to de novo synthesis (i.e. a catalytic oxidation of carbon and accompanying generation of dioxins, dioxin surrogates and precursors). It involves testing samples of filter dust, resulting from previous field studies, with the purpose of evaluating their original organic charge, as well as studying the details of carbon oxidation and associated formation of dioxin surrogates and precursors. Advantages as well as limitations of various test methods and applications, used in the study of dioxins at a laboratory scale are discussed. Samples are characterised by SEM-ERF, XRF, and by conventional, extraction and purification-based dioxin analysis. A thermo-gravimetric analyzer (TGA) is used as a basic de novo synthesis reactor, as well as desorption test unit. It indicates successive weight losses, associated mainly with the evolution of water, carbon dioxide and - to a lesser and often non-measurable extent - other, organic compounds, such as precursors and surrogates. The latter can be monitored by various means, mainly MSD, FID, ECD, TCD and FTIR. The following classes of compounds can be routinely monitored: int. al. benzene, toluene, alkylaromatics, naphthalene, biphenyl, PAH, phenols, benzofuran, dibenzofuran, as well as some lower chlorinated congeners of these classes. DTA is used for monitoring the heat effect. The latter in some samples sometimes precedes the evolution of carbon dioxide, when this evolving carbon dioxide is re-absorbed by lime, as is the case for acid gas neutralization residues. Thermal desorption is used for liberating organics, either directly from dust or from sorbing resins. In the first case, numerous filter dust samples were examined with the aim of developing diagnostic methods with respect to the quality of combustion and identity and amount of Products of Incomplete Combustion. Also the influence of desorption temperature, time and of sample weight were examined. Matrix effects are apparent, when spiking the samples. In the second case, both breakthrough of light volatiles and carry-over of semi-volatiles were systematically examined. Finally, Pollut-Eval tests provide an easy and simple method for screening samples as a preparation for deeper study.