Organic compounds in the char deposits characterising the combustion of unauthorised fuels in residential boilers

Abstract

The paper aims to find a way of simply identifying the addition of unauthorised waste (plastics) in residential boilers burning wood as the main fuel. The burning of plastics leaves a trace in char deposits, which are otherwise made up mostly of lignin breakdown products. Identification of combusted plastics in char deposits is made possible by determining unique organic compounds formed during the pyrolysis phase of combustion by pyrolysis gas chromatography. At temperatures above 800 °C, the amount of charring product from the incineration of PET is 19.5 wt%, while for PP, it is 5 wt%, and LDPE with HDPE 2.1 wt%. Combustion of polypropylene with wood has been verified by the presence of the compounds 2,4-dimethyl-1-heptene, 2-methyl-1-pentene, and 2,4,6-trimethyl-1-nonene. The thermal degradation of PE has been demonstrated by the presence of triplets of alkanes, alkenes, and alkadienes. Combustion of PET in domestic waste can be demonstrated by the presence of benzoic acid and its esters, benzoate compounds, and terephthalic acid. In summarising, sampling char in boilers and analysing samples for markers of plastics incineration could be used as a method for identification of unauthorised waste combustion by authorities.