Nitrogen-Centric Optimization of Polyamide Chemical Recycling: A Reaction Network Flux Analysis with New Metrics for Nitrogen Atom Economy and Nitrogen Footprint
Year: 2026
Type: preprint
Abstract: Polyamide 6 and 66 (PA6/PA66) are the only commodity plastics with structural nitrogen (12.4 wt%), yet chemical recycling frameworks treat nitrogen fate as an uncontrolled byproduct. We extend Reaction Network Flux Analysis (RNFA) to a full C-H-O-N mass balance and introduce two new metrics—Nitrogen Atom Economy (NAE) and Nitrogen Footprint (NF)—enabling the first systematic nitrogen-centric optimisation of PA6/PA66 depolymerization. Across 795 NLP solves (GAMS/BARON) spanning six products, five depolymerization route families, and five objective weight scenarios, three findings emerge. First, nitrogen-centric optimisation achieves NAE = 87–100% across all products, compared with the conventional unoptimised baseline of ∼60%. Second, carbon-only objective functions generate NF 6–62× higher than nitrogen-inclusive weighting; for caprolactam and 6-ACA, two economically identical routes differ by up to 62× in nitrogen footprint. Any objective weight w2 ≥ 0.3 on the nitrogen term recovers >90% of the achievable NF reduction. Third, for five of six products, the nitrogen-optimal configuration is simultane- ously the economic optimum—no cost penalty is incurred. These results support a seventh guiding principle for nitrogen-containing polymer upcycling: maximise nitrogen circularity, extending the six-principle framework of Jehanno et al. beyond carbon-centric assessment to address the planetary nitrogen boundary, currently transgressed by a factor of ∼2.4.
Source: ChemRxiv
Author: Huiting Yang
Institution: RWTH Aachen University
Language: English
Subfield: Polymers and Plastics
Field: Materials Science
Domain: Physical Sciences
Open Access status: green
Funder: RWTH Aachen University
OpenAlex ID: W7205006099