A carbon-circular refinery must do more than place CO₂ capture, biomass conversion, and catalytic upgrading in the same flowsheet: it must connect them at integration nodes where carbon losses, feed composition, catalyst durability, hydrogen demand, and separation duty can be evaluated together. This critical review therefore focuses on four nodes: recovery of biogenic CO₂ from biomass processing; coupling of captured CO₂ with biomass-derived methane or syngas; co-processing of CO₂-derived intermediates with biomass-derived oxygenates; and allocation of residual carbon between fuels, chemicals, biochar, and geological storage. For each node, we compare feed conditioning, catalyst function, realistic impurities, deactivation and regeneration, product separation, demonstrated operating evidence, and system-level carbon consequences. Thermochemical routes are distinguished from electrochemical and photoelectrochemical routes rather than treated as interchangeable alternatives. The analysis shows that integration is most credible when a concentrated biogenic CO₂ stream or a compatible biomass-derived co-reactant is available, the catalyst is tested with water and heteroatom-containing feeds, and renewable hydrogen and separation requirements are reported explicitly. High conversion or Faradaic efficiency alone does not establish climate benefit. Reactor-level carbon conversion, plant-wide carbon retention, life-cycle greenhouse-gas reduction, and carbon permanence must be reported separately. A unified set of benchmarking metrics, screening-level carbon and energy balances, and an indicative technology-readiness assessment are used to compare the routes; for example, electrolytic-hydrogen-based CO₂ products deliver a climate benefit only when the electricity used has a low carbon intensity, whereas biomass-derived carbon requires about one-third of the hydrogen per mole of retained carbon. The resulting framework identifies the evidence needed to move integrated CO₂–biomass pathways from conceptual coupling toward durable, scalable operation.

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