In this study, a techno-economic and carbon footprint (GHG, CO2-equivalent) analysis was conducted on two alternative biofuels, green diesel and bio-jet fuel, produced from renewable lipids. The focus of the work is the comparison of various lipid feedstocks, including waste cooking oil, and four types of vegetable oils: cardoon, soybean, palm, and sunflower. Process optimization and design were performed to minimize production costs by using the process simulation software Aspen Plus®. Green diesel and bio-jet fuel were obtained via hydrodeoxygenation and hydroisomerization/hydrocracking, respectively. Sensitivity analyses confirmed consistent results across the tested vegetable oils. Hydrodeoxygenation achieved triglyceride molar conversions exceeding 97%, with overall mass yields into the diesel fraction surpassing 79%. Conversely, hydroisomerization/hydrocracking of green diesel resulted in over 90% conversion of n-paraffins and more than 50% overall mass yield. The economic analysis showed that the primary cost factor influencing the payback selling price of the biofuels is the price of the lipid feedstocks. Biofuels are economically viable only when lipid prices are below 1000 €/ton and hydrogen prices are below 3000 €/ton. An important aspect is also represented by the combined-cycle energy recovery system, which strongly affects the overall capital cost and increases internal power generation efficiency. The carbon footprint calculated over a cradle-to-grave boundary showed shows net GHG reductions versus the fossil reference fuels for all scenarios. Net avoided emissions range from 1.74 to 3.63 kgCO2-eq/kg green diesel and from 0.80 to 3.70 kgCO2-eq/kg bio-jet fuel across the investigated feedstocks, approximately 40–84% and 20–95% of the respective savings relative to the fossil reference fuels under the stated background and logistics assumptions. Results are expressed per kg of produced fuel as a functional unit, using literature-derived upstream emission factors for oil supply and background inputs (hydrogen, Italian grid electricity and transport). For the bio-jet configuration, co-product burdens were partitioned by mass; the Discussion section highlights the sensitivity of the GD vs. BJF comparison to co-product handling and allocation choices. In this context, the choice of feedstock is essential in establishing the resulting GHG intensity of the two biofuels. From both economic and climate change perspectives, waste cooking oil emerges as the most promising option, particularly given its classification as waste-derived feedstock in the system boundary, unlike the virgin oil sources.
Giuliano et al. (Tue,) studied this question.