Pyrolysis oil is not necessarily a cheaper alternative to fossil naphtha. Producing cracker-grade pyrolysis oil involves collecting and preprocessing plastic waste, pyrolysis itself, and extensive purification and upgrading. These additional steps can make the resulting feedstock considerably more expensive than conventional naphtha.
Pyrolysis oil is generally blended with conventional naphtha rather than completely replacing it. ICIS distinguishes between non-upgraded pyrolysis oil, typically used at around 5% or less, and naphtha-substitute grades that can be used at approximately 20%. In such cases, roughly 80–95% of the cracker feed remains conventional feedstock.
Before entering a steam cracker, pyrolysis oil usually requires substantial upgrading. Chlorine, nitrogen and oxygen compounds, metals and other contaminants must be reduced to levels compatible with sensitive petrochemical equipment. Hydrotreatment, filtration and other purification processes consume additional energy and increase production costs. Even upgraded material can present challenges including fouling, corrosion and coke formation. Blending with conventional naphtha helps manage these risks.
Energy and carbon balance: Pyrolysis requires significant heat, while subsequent upgrading and hydrotreatment consume additional energy and hydrogen. The environmental performance therefore depends on the entire process rather than the pyrolysis reactor alone.
Feedstock quality: The composition of plastic waste matters. PVC can introduce chlorine, while PET and polyamides introduce oxygen- and nitrogen-containing compounds. Additives, pigments, fillers, metals and residues further complicate purification.
Yield: One tonne of plastic waste does not produce one tonne of usable pyrolysis oil. Part of the feedstock becomes gases, char and other residues, while additional losses occur during processing and upgrading.
Sorting remains necessary: Pyrolysis should not be understood as a technology capable of accepting unlimited quantities of completely unsorted plastic waste. Feedstock preparation and contamination control remain important.
Hydrogen requirement: Upgrading pyrolysis oil can require hydrogen to remove unwanted compounds. This adds another input, another cost and potentially additional emissions, depending on how the hydrogen is produced.
Mass balance: Once recycled feedstock enters a cracker alongside much larger quantities of fossil feedstock, the resulting molecules cannot practically be traced back to their individual origin. Recycled content is therefore allocated to particular products through a mass-balance accounting system.
Economics: The relevant comparison is not simply pyrolysis oil versus naphtha. It is waste collection + sorting and preprocessing + pyrolysis + purification + upgrading + hydrogen + certification versus the cost of conventional petrochemical feedstock.
Scale and reliability: Petrochemical crackers depend on highly consistent feedstocks. Producing material of comparable and predictable quality from heterogeneous plastic waste remains one of the fundamental technical and economic challenges facing chemical recycling.