Trojan Horse Strategy for Sustainable PET Plastics: A Comparative Evaluation of Techno-Economic and Lifecycle Impacts

Abstract

Reactive comonomers known as Trojan Horse units can be built into the polyethylene terephthalate (PET) chain so that the polymer depolymerizes under milder conditions at the end of life without losing performance in use. We combined this strategy with bio-based terephthalic acid made from limonene and compared the resulting process with conventional alkaline hydrolysis of PET through a techno-economic analysis and a life cycle assessment. The base case incorporates 5% Trojan Horse units, 16.25% bio-based terephthalic acid, and 48.75% recycled terephthalic acid on a monomer basis. Its minimum selling price is $5.28/kg, compared with $1.32/kg for a plant that makes recycled terephthalic acid alone. Limonene and the nitrated comonomer account for three quarters of that price. The global warming potential is 1.80 kg of CO2-eq per kg of resin. That is 19% below that of virgin PET on the same cradle-to-gate basis but above the 0.91 kg CO2-eq per kg of mechanically recycled PET. Measured kinetics for the nitroterephthalate copolymer shorten the hydrolysis time at 100 °C from 12.5 to 7.6 h, which lowers the fixed capital investment by 20% relative to unmodified PET under the same conditions. Over repeated recycling loops, the normalized global warming potential falls as collection rates rise, and it falls about twice as fast if the Trojan Horse units allow caustic-free hydrolysis.