Date of Award

Spring 5-2022

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Chemical Engineering

Advisor

M. Clayton Wheeler

Second Committee Member

Thomas J. Schwartz

Third Committee Member

William J. DeSisto

Additional Committee Members

Brian G. Frederick

Douglas W. Bousfield

Abstract

Thermal DeOxygenation (TDO) is a process that converts organic acids produced from cellulose hydrolysis and dehydration into a low-oxygen bio-oil containing substituted naphthene compounds. The high aromatic content is desirable for gasoline fractions, but middle distillates such as diesel and jet fuel require upgrading via hydrogenation and ring opening to achieve better combustion characteristics. Previous research has demonstrated that TDO oil could be hydrogenated over high-surface-area nickel catalysts to improve the combustion characteristics, but the cetane number was still below the specifications.

Multiple supported catalysts were synthesized by ion exchange and incipient wetness impregnation, and the catalysts were characterized by N2 physisorption, H2 chemisorption, NH3 temperature programmed desorption, and X-ray diffraction. Catalysts were evaluated for the ring opening of decalin, a bicyclic molecule with similar composition to compounds found in hydrogenated TDO oil. Using our trickle-bed reactor, we selected catalysts that showed promise due to a high product cetane number and high activity (as measured by turnover frequency or reaction rate). The best candidate, Ir/SiO2, yielded products with a cetane number increase of 5-6 points and possessed a high activity (5.7 ks-1, 481 mmol g-1 h-1).

Iridium and platinum catalysts were used to determine the ring opening mechanisms of mono- and tri-branched alkylnaphthenes. We utilized product selectivities to ascertain the endocyclic hydrogenolysis mechanism and we observed these differences as the substituent size changed. Iridium catalysts preferentially cleaved unsubstituted C-C bonds, while Pt/SiO2 cleaved substituted bonds, especially as the substituent bulkiness increased. Tri-branched alkylnaphthenes were also ring opened, and we observed the product distribution diverged from the three commonly accepted mechanisms.

Lastly, we focused on the application of these catalysts to produce diesel and jet fuel from TDO oil. Several catalysts were evaluated, and the Ir/SiO2 catalyst was determined to be optimal for this process. We also evaluated several different methods of converting TDO oil into fuels. The Ir/SiO2 catalyst proved tolerable of unsaturated compounds in the feedstock, and we showed that the ring opened TDO oil products could be used as blending agents or drop-in substitutes for diesel and jet fuels.

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