Designing emerging biorefineries from bench to planet scale

The petrochemical industry and the plastics it produces are major drivers of climate change, pollution, and biodiversity loss. Unlike the energy sector, defossilising chemicals is challenging because carbon is intrinsic to their structures. Lignocellulosic biomass offers renewable carbon, but current rigid bioplastics, whose cyclic structures are difficult to produce directly by fermentation, often replicate fossil-based structures, limiting resource efficiency and sustainability. While alternatives that may be more straightforward to produce from biomass in chemo-catalytic processes have been proposed, their economic and environmental implications on the chemical industry remain unclear. This thesis develops modelling strategies to support the integration of such emerging biorefineries into defossilisation roadmaps of the chemical sector. I first systematically compared the fossil-free production of drop-in polyethylene terephthalate (PET) and emerging rigid bioplastics with similar properties but higher carbon and oxygen retention. Techno-economic and life-cycle modelling revealed a trade-off between resource feasibility and profitability for producing PET via methanol from gasification. Only monomers structurally closer to biomass, polyethylene furanoate (PEF) and polybutylene xylosediglyoxylate (PBX), were both resource-compatible and cost-competitive under low carbon-tax conditions (30 EUR/t CO2). Simple chemistry-based metrics successfully anticipated economic and environmental trends, providing a tool for early-stage design of bioplastics. To enhance yields of rigid biobased molecules, I established a feedback loop between laboratory experiments and process modelling for valorising lignin aromatics in an Aldehyde-Assisted Fractionation biorefinery. Lignin precipitation emerged from the techno-economic and life-cycle assessment as a key piloting hotspot. Following in-silico modelling and experimental validation, a 2-fold reduction in water, coupled with electrified evaporation and aldehyde production, resulted in lignin monomers cost-competitive with fossil phenols even at carbon taxes 55% below projected EU ETS levels, though with increased dependence on renewable electricity. Finally, by integrating emerging electrified biorefineries into the EnergyScope energy system model, I generated prospective European production systems under alternative defossilisation scenarios for the chemical sector, enabling exploration of configurations capable of meeting the future electricity needs and potentially compatible with absolute environmental sustainability. Compliance with Europe's carbon budget requires full fossil phase-out and deployment of biobased and CO2-electrolysis routes. Because biomass is limited, renewable aromatic production in emerging biorefineries could cut emissions by 22% compared to biomass gasification, but meeting climate targets drives a tripling of electricity demand, large expansions in capacity, and challenges to remaining