Simultaneous Catalytic Isomerization and Hydrogenation of Alkenes by Al-MCM-41 for the Production of Sustainable Aviation Fuel from a Lipid Pyrolysis Product
Creators: Kaal, Zakaria Mohamed Said
Publisher: name: University of Alberta Library
Year: 2024

<p>Demand for aviation has been projected to increase considerably in the near and long term future.<br>
As a result of mandates, goals and targets for achieving net-zero emissions for the aviation sector<br>
by various governments and organizations, the demand for a renewable and sustainable aviation<br>
fuel is expected to increase exponentially. The use of hydrogen and noble metal loaded catalysts<br>
has been popular in the synthesis and upgrading of renewable hydrocarbons including sustainable<br>
aviation fuel, to increase the proportion of branched isomers to lower the freezing point of the fuel,<br>
and lower the amount of undesirable alkenes, which can lower the oxidative stability of the fuel.<br>
In this thesis, the use of Al-MCM-41 as a catalyst for isomerizing and hydrogenating model<br>
alkenes was studied in the absence of hydrogen and a noble or transition metal. The conversion of<br>
the model hydrocarbons was studied at various temperatures, and under various gas environments.<br>
To understand the effect of the structure of the alkene on the conversion, experiments were<br>
conducted with a 1-alkene and an internal alkene. A sequential analysis was performed to elucidate<br>
the reaction mechanism and intermediaries. The reaction over the catalyst was then studied on a<br>
complex mixture of hydrocarbons, to understand the conversion in the presence of different<br>
hydrocarbon groups, and to observe the effects of the addition of water and free fatty acids on the<br>
reaction.<br>
The upgrading of a lipid pyrolysis product was scaled up from batch microreactors to a continuous<br>
flow through reactor, operating for 12 hours. The product collected was then distilled to yield a jet<br>
equivalent cut, and tested against several specifications set out by the ASTM D1655 standards for<br>
aviation turbine fuel.<br>
The catalyst exhibited no effect on the alkane, but yielded a high conversion of the alkene (58 ±<br>
6% wt.) in the presence of hydrogen. 31 ± 4% wt. of the liquid product was branched hydrocarbons,<br>
and 17 ± 3% wt. of the liquid product was branched alkanes. The results when the hydrogen was<br>
replaced with nitrogen were statistically the same, indicating that the hydrogenation and<br>
isomerization can occur using in situ hydrogen, generated from the formation of aromatics. The<br>
use of a lipid pyrolysis off-gas that contained some light hydrocarbons showed that some light<br>
alkenes can contribute to the reaction. It was observed that the catalyst, when operating in a<br>
complex mix of hydrocarbons, can selectively target the alkenes, transforming them into both<br>
branched and n-alkanes. Free fatty acids were shown to have a strong inhibitory effect on the<br>
catalyst, and water presence in the feed presented a slight decrease in the isomerization reaction<br>
(but not in the hydrogenation of alkenes). Scale up experiments on the lipid pyrolysis products<br>
were successful, exhibiting a product with a similar composition as the batch experiments. The<br>
freezing point of the distilled jet equivalent cut was -56.32 ± 0.04 °C and met all of the<br>
specifications tested, except for the acidity. This was perhaps due to the lipidic nature of the<br>
hydrocarbon source.</p>