Rethinking chemical clusters: Greenfield and brownfield transition to net-zero by 2050.

We develop a cluster-level optimization framework to design brownfield transition pathways toward net-zero chemical clusters by 2050, applied to existing ammonia-olefin clusters in the Netherlands. The model represents sequential investment decisions for 2030, 2040, and 2050, includes scope 1-3 emissions, and enables a systematic comparison of greenfield and brownfield configurations. Thirteen olefin and eight ammonia production routes are considered. The results show that, despite reduced flexibility due to legacy assets, net-zero brownfield configurations remain feasible. Plastic gasification combined with methanol-to-olefins emerges as a low-regret option for olefins, while electric steam methane reforming and electrolyzers are robust choices for ammonia. The results support early investment rather than strategic delay. Excluding scope 3 emissions leads to lock-in of fossil-based options that appear cost-effective short-term but raise long-term system costs. Sensitivity analyses highlight uncertainties related to infrastructure and technology availability, bio-feedstock prices, and plastic waste emission accounting.