(25a) Thermocatalytic Conversion of Ethanol – a Pathway to Sustainable Aviation Fuel

Commercial aviation fuel is responsible for ~13% of transportation greenhouse gas (GHG) emission. To meet the target of complete decarbonization by 2050, airlines have committed to carbon-neutral growth which requires non-fossil sourced fuels or sustainable aviation fuels (SAF). While electrification is not viable, decarbonization of SAF requires an effort to develop new economically viable technologies from biobased or waste carbon resources. In this direction, ethanol, largest biobased product manufactured in the world shows tremendous potential due to its availability in large quantities and at reasonable price. Global production of ethanol in the United States reaches about 16 billion gallons/year in various distributed facilities. Given the increasing availability of ethanol, building additional markets via the novel ethanol processing technologies that are robust and economically viable is a foreseeable pathway for creating value to ethanol producer.

In the present study we developed a process that utilizes wet ethanol as the feedstock and convert it to SAF in a series of chemical steps. The first step of this process is ketonization of the ethanol which generated acetone, 2-pentanone and 2-heptanone. Over the different mixed metal oxide catalyst, Pd promoted ZnO-ZrO2 exhibited the highest performance. In-situ formation of Pd-Zn alloy was attributed to the active site which promoted rapid dehydrogenation and hydrogen transfer in conjunction of efficient C-C coupling on acid-base sites that form long chain ketones.¹ In the next step, when mixed ketones were subjected to Pd/Mg₄AlO catalyst a pool of C₈-C₁₈ ketones were formed via aldol and cross aldol condensation which upon hydrogenation produces corresponding alkanes and iso-alkanes which are ideal for jet fuels. When Mg₄AlO was obtained as catalyst cyclic ketones were obtained as the products which typically falls beyond the jet range (>C₁₅). Additionally rapid deactivation of the catalysts was also noted in this case. Introducing small amount of Pd as promoter not only prevents the catalyst deactivation but also generates mixture of oxygenates that are required for jet range (C₉-C₁₆). Effect of different process parameters was investigated which shows an effect on products obtained. The difference in reactivity was attributed to difference in active sites and overall reaction mechanism which will be discussed in detail.

1. Subramaniam, S.; Guo, M. F.; Bathena, T.; Gray, M.; Zhang, X.; Martinez, A.; Kovarik, L.; Goulas, K. A.; Ramasamy, K. K. Angew Chem. Int. Ed. 2020, 59, 2-10.