An integrated techno-economic-environmental-policy assessment of supercritical biodiesel production: pathway to competitiveness

Despite its promise, biodiesel production via the supercritical methanol (SCM) process has stalled due to limited understanding of interactions among key operating parameters and process-modeling gaps, resulting in contradictory techno-economic (TEA) and life-cycle carbon footprint assessments. In the present study, we integrate experimental optimization with techno-economic, carbon footprint, and policy analyses to identify the path to economic competitiveness for SCM biodiesel production from waste cooking oil (WCO). Response surface modeling based on experimental data was used to quantify interactions among operating parameters and develop a predictive yield model. Under optimal conditions (282.8 °C, 125 bar, methanol-to-oil ratio of 39.17, and reaction time of 43.3 min), biodiesel yield exceeded 92%, and a detailed process flowsheet was developed in Aspen Plus® to quantify material and energy requirements. TEA results indicate that under optimized conditions, SCM biodiesel remains economically challenged, with levelized production costs of 0.9–1.4 $ per kg-biodiesel, depending on plant scale. These costs are driven primarily by high WCO consumption (0.99 kg kg⁻¹-biodiesel) and high-pressure steam demand (3 kg kg⁻¹-biodiesel), required for stoichiometric conversion and energy-intensive distillation, respectively. In contrast, life cycle carbon footprint analysis demonstrates a strong environmental advantage: under renewable electricity and heat supply, SCM biodiesel achieves a carbon intensity of ∼0.28–0.30 kgCO_2eq per kg-biodiesel, substantially lower than fossil diesel (∼4 kgCO_2eq per kg-diesel). Finally, yet most importantly, by quantitatively linking process performance, economics, emissions, and policy, this study identifies carbon pricing (∼100 $ per t-CO₂) and scale-up as critical levers to reconcile the environmental benefits of SCM biodiesel with commercially viable deployment.