The departments have said that the update to the 40B SAF GREET (Greenhouse gases, regulated emissions, and energy use in transportation) model is to correct a calculation error in how catalyst inputs were calculated for the alcohol-to-jet (AtJ) production pathway.

The calculation error in the previous model resulted in “inaccurate estimates of the emissions associated with the catalyst input,” according to the Internal Revenue Service document released with the update. The updated model should be used for SAF that is sold or used after October 18.

The 40B tax credit, which extends the blender’s tax credit to SAF, expires at the end of 2024.

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