Techno-economic assessment of green primary and secondary plastics production pathways

Peer-reviewed paper 9-021-26

Polypropylene production relies predominantly on fossil resources for process energy and carbon feedstock. This study compares fossil primary production, renewable-carbon primary routes based on biomass, renewable hydrocarbons, or CO₂ and hydrogen, and recycling pathways under German industrial cost conditions within the European carbon-pricing framework.

Literature-based process data are harmonised to a functional unit of 1 tonne of polypropylene pellets at the plant gate. A parametric model combines annualised capital and operating expenditure, energy and material requirements, and pathway-specific emissions. Electricity, natural-gas, hydrogen, and CO₂ prices vary over time, while material-feedstock prices remain constant in the baseline. Hypothetical costs for end-of-life emissions caused by the use of fossil feedstocks are reported separately.

Mechanical recycling has the lowest levelised production costs and comparatively low direct process emissions. Chemical recycling routes are more expensive because of conversion losses, additional processing, and, where conventional steam cracking is used, high direct emissions. Hydrogen-intensive power-to-X routes remain the most expensive options. Biomethanol-to-propylene and the renewable-hydrocarbon routes offer economically promising alternatives to CO₂/H₂-based primary production, although their competitiveness remains sensitive to feedstock prices and process-energy requirements.

Pathway competitiveness therefore depends on process structure, energy prices, feedstock assumptions, and the regulatory treatment of fossil carbon embedded in products. Electrification can reduce process emissions but does not eliminate end-of-life emissions from fossil feedstocks. The results underscore the distinction between energy decarbonisation and feedstock defossilisation and show that pathway rankings remain conditional on key feedstock and technology assumptions. Industrial planning should consider these options alongside feedstock availability and product-quality constraints.

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