In 2021, the U.S. government released the Sustainable Aviation Fuel Grand Challenge, which pledges a goal of supplying sustainable aviation fuel (SAF) to meet 100% of fuel demand by 2050. SAF currently makes up less than 0.1% of the total jet fuel industry and is nearly twice as expensive as jet fuel sold from a typical refinery (FAA, 2022). There are currently nine SAF production pathways that have been approved by ASTM, one of which is known as Alcohol-to-Jet-Synthetic Paraffinic Kerosene (ATJ-SPK). A 2019 white paper by Gevo outlines the principles of ATJ-SPK, where starchy alcohols are converted to isobutanol, which is then converted to paraffinic kerosene through well-established processes of dehydration, oligomerization, and hydrogenation (Gevo, 2019).

An ATJ-SPK plant was designed with the intention of exploring the environmental and economic viability of a pure ethanol feed. To date, most developed ATJ-SPK plants have an isobutanol feed. The designed plant follows the three established steps: dehydration, oligomerization, and hydrogenation. For ethanol dehydration, Ni-HZSM-5 catalyst was used to convert ethanol to ethylene. The oligomerization and hydrogenation steps were both accomplished using two reactors in series with two unique catalysts. This design decision was made to target reactions in the C9-C16 range, ideal for kerosene jet fuel. For the first and second oligomerization reactors, Ni-H-β and Al2O3/SiO3 catalysts were used, respectively. Feed to the hydrogenation reactors consisted of mostly C8-C17 olefins, where a Ni-C catalyst was used in the first reactor, and a 0.3% Pt/Al2O3 was used in the second reactor. Paraffins were separated by size into SAF, diesel, and gasoline.

Analysis revealed the economic viability of the designed ethanol feed ATJ-SPK process is highly dependent on the Sustainable Aviation Fuel Credit created by the Inflation Reduction Act. The credit gives $1.25 per gallon of SAF sold, given that the SAF has a 50% reduction in lifetime greenhouse gas emissions. The following process reduces GHG emissions by almost exactly 50%, putting the process at risk for not receiving the SAF tax credit if an unexpected source of emissions is discovered. Furthermore, the SAF tax credit expires in 2025, so there is little long-term economic viability of the designed process. With the discontinuation of government incentives, achieving the ambitious 2050 emissions goal for the aviation industry becomes even more challenging. If the United States is committed to these targets, additional tax incentives will likely be essential. The following design can be used as a baseline for future ethanol feed ATJ-SPK processes, and may prove viable if there are additional economic incentives established for SAFs as the 2030, 2040, and 2050 goals of the aviation industry to reduce emissions become a top environmental priority.