Meaning
Chemical recycling of plastic waste involves a refining step to remove impurities from pyrolysis oil before it can be fed into a steam cracker to produce new polymers. This purification step results in a hydrotreating loss that represents the reduction in liquid feedstock volume during processing. The process replaces heteroatoms with hydrogen, creating light gases and water.
It does not include the mechanical losses that occur during the initial sorting or shredding of the solid plastic waste.
Feedstock Quality
Post-consumer plastic waste contains varying amounts of chlorine, nitrogen, and oxygen from adhesives, labels, and food residues. These contaminants must be extracted because they poison the catalysts used in polymer synthesis. A high concentration of these elements increases the hydrotreating loss as more by-products are generated.
Process Reaction
Introducing hydrogen at high pressure and temperature breaks the molecular bonds of the contaminants. This chemical action converts chlorine into hydrogen chloride gas and converts oxygen into water vapor, both of which are separated from the liquid hydrocarbon stream. The hydrotreating loss corresponds directly to the weight of these removed elements plus any light paraffinic gases that escape during the reaction.
Consequently, the yield of recycled naphtha is always lower than the volume of raw pyrolysis oil entered into the system.
Economic Consequence
Refining efficiency directly affects the cost of producing circular resins. A higher percentage of waste-derived oil lost during treatment raises the raw material cost of the resulting ethylene or propylene. Moulding companies that contract for certified circular resins must pay a premium to cover these chemical yield losses.
