Identifying Compounds of Concern in Plastic Waste Pyrolysis Oils using Two-Dimensional Supercritical Fluid Chromatography (SFC) - Gas Chromatography (GC)

Plastic waste accumulation is an increasingly difficult problem to solve as more plastic is produced each year without growing the efforts to properly dispose of the waste. Despite various efforts to recycle plastics, much of it still ends up in landfills or waterways before being degraded into microplastics contaminating our environment. Pyrolysis oil is one of the many promising solutions to help alleviate this problem, with the added benefit of getting workable fuel as byproduct. Pyrolysis oil (py-oil) is produced by heating plastics at a very high temperature(800oC) without the presence of oxygen. At different temperatures, different kinds of oil are obtained which are comparable with the traditional fossil fuels. However, the oils that are produced consist of complex carbon mixtures comprised of paraffins, isoparaffins, olefins, naphthenes, and aromatics. Heteroatom content in these hydrocarbons, including oxygen, nitrogen, and sulphur, is also desired to be known to facilitate downstream processing.

Two instruments were used to characterize py-oil, supercritical fluid chromatography (SFC) and gas chromatography-mass spectrometry (GC-MS). Earlier work involving SFC showed fingerprint regions which could discriminate which type of plastic (polyethylene or polypropylene) was used to produce the py-oil. To better understand the differences between the two types of oils, fractions were obtained of the two fingerprint regions. These fractions were analyzed using Gas Chromatography-Mass Spectrometry (GC-MS) as a way to reduce complexity. Additionally, potentially harmful compounds such as alkylphenols, Bisphenol A, and NMP (which are listed by Environmental Protection Agency (EPA) as environmentally hazardous) were specifically targeted to identify the presence of these harmful compounds.