The effect of used cooking oil composition on the specific CO2e emissions embodied in HEFA-SPK production

In this study, the correlation between the composition, hydrogen/carbon (H/C) ratio, and hydrogen/oxygen (H/O) ratio of a used cooking oil (UCO) and the specific emissions embodied in the derived hydroprocessed esters and fatty acids synthetic paraffinic kerosene (HEFA-SPK) is investigated. It is shown that HEFA-SPK produced from UCOs with low concentrations of C18:1, high concentrations of C18:2, and low H/C ratios utilize less energy and more hydrogen during Fuel Production. Hence, HEFA-SPK produced from such UCOs will embody higher gCO₂e for fossil hydrogen utilization scenarios, and lower gCO₂e for green hydrogen utilization scenarios compared with other UCOs. Conversely, it is shown that HEFA-SPK produced from UCOs with high concentrations of C18:1, low concentrations of C18:2 and high H/C ratios utilize more energy and less hydrogen during Fuel Production. Hence, HEFA-SPK derived from such UCOs will embody lower gCO₂e for fossil hydrogen utilization scenarios, and higher gCO₂e for green hydrogen utilization scenarios compared with other UCOs. Monte Carlo simulation gives the emissions embodied in Fuel Production a 95% confidence interval for all UCO-derived HEFA-SPK, showing a similar uncertainty for all compositions. A maximum of +1.1 gCO₂e/MJ_SAF and −1.0 gCO₂e/MJ_SAF is obtained for the upper and lower bounds respectively for the emissions embodied during HEFA-SPK production from UCO. The application of the correlations founded in this study allows for the prediction of the specific emissions embodied in the feedstock-to-fuel conversion of any UCO, providing the C18:1 concentration, C18:2 concentration, H/C ratio and H/O ratio of the UCO is known.