The 92% GWP reduction (per MJ) of the ethanologen pathway (EP) relative to 2005 gasoline (Fig. 2) is similar to values reported in other SRWC cradle to grave studies.
The reported reductions range from 78% to 120% relative to gasoline and are dependent on the ethanol yield, excess electricity produced the type of electricity that is displaced, direct land use change, and the extent of below ground carbon sequestration.
Relative to 2005 gasoline, the AP GWP is 46% lower (Fig. 2).
This is a significant reduction in GHGs, but does not reduce the GWP as much as the EP.
If hydrogen production is excluded, the increased yield of ethanol in the AP lowers the GWP per MJ to a value comparable to the GWP for the EP.
However, hydrogen is necessary to convert acetic acid to ethanol and its production increases the GWP relative to biorefineries that use an ethanologen for the fermentation step.
Electricity exported from the AP is also lower than in the EP, resulting in a lower GWP credit for the AP.
Targeting a reduction in natural gas use, hydrogen use, or producing hydrogen in a more environmentally efficient process could help lower the GWP of the AP.