Identification of organochlorides in distilled fractions of plastic pyrolysis oil using GC × GC coupled with high-resolution time-of-flight mass spectrometry (GC × GC-HR-TOFMS) and GC coupled with a halogen selective detector (GC-XSD)

Abstract

To support the transition toward a more circular economy, various technologies have been explored to convert plastic waste into valuable materials. Among these is pyrolysis, a thermochemical process that produces gas, solid, and liquid products, where the latter is known as plastic pyrolysis oil (PPO). These oils typically contain hydrocarbons and impurities such as oxygenates, nitrogenates, and organochlorides, depending on the composition of the plastic feedstock and process conditions. Since these contaminants must be removed before PPOs can be used in industrial steam crackers, their speciation is essential to define appropriate upgrading strategies. In this context, this study evaluates a gas chromatograph coupled with a halogen selective detector (GC-XSD) system, in combination with a comprehensive gas chromatograph system coupled with high resolution time-of-flight mass spectrometry (GC × GC-HR-TOFMS), for the identification of organochlorides in hydrocarbon matrices. Initially, the selectivity of the XSD, reactor temperature, and response to Cl standards were assessed. The method was then applied to the distilled fractions of a PPO. Using GC × GC-HR-TOFMS, several organochlorides were identified, including 1-chlorobutane, which was found at the highest concentration in the first distilled fraction (50–100 °C), and 3-(chloromethyl)heptane and 1,3-dichlorobezene, which were eluted primarily in the third fraction (150–200 °C). Other compounds, such as 1,2-dichloroethane, chlorobenzene, and 2-chloroethyl benzoate, were also detected at lower concentrations. The GC-XSD was proved to exhibit robust and selective capability for organochloride speciation in PPOs and could be potentially implemented in quality control and routine laboratories. When combined with hyphenated techniques such as GC × GC-HR-TOFMS, GC-XSD also facilitates the identification of unknown organochlorides.