Decarboxylation of oleic acid using iridium catalysis to form products of increased aromatic content compared to ruthenium systems

Authors: Doll, Kenneth - Ken; Moser, Bryan; KNOTHE, GERHARD - Former ARS Employee

Submitted to: International Journal of Sustainable Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/3/2021
Publication Date: 9/15/2021
Citation: Doll, K.M., Moser, B.R., Knothe, G. 2021. Decarboxylation of oleic acid using iridium catalysis to form products of increased aromatic content compared to ruthenium systems. International Journal of Sustainable Engineering. 14(6):2018-2024. https://doi.org/10.1080/19397038.2021.1978589.
DOI: https://doi.org/10.1080/19397038.2021.1978589

Interpretive Summary: The synthesis of synthetic hydrocarbons suitable for jet fuel, from renewable resources, has been a high research priority for most of this century. The chemical reaction called decarboxylation has been used in order to take the oxygen atoms out of the molecules in a natural product, such as those derived from soybean oil, to produce a fuel that is a true petroleum replacement. Although catalysts that perform this reaction have been developed, the amount of aromatic molecules they cause to form in the fuel is low. An appropriate level of these aromatic molecules are beneficial because they alter fuel density and, more importantly, they are proven to reduce shrinkage in elastomeric seals and reduce seal failure. A new iridium-based decarboxylation technology reported here produces fuel aromatic contents greater than prior technologies, so that this new renewable fuel can be blended with conventional jet fuel in any proportion and still leave sufficient aromatic molecules in the fuel. The new technology has been studied under a variety of conditions and compares well with a previously invented method. This research will benefit the producers of vegetable oils suitable for fuel use, such as soybean oil and high oleic soybean oil, as well as the renewable fuel industry.

Technical Abstract: The decarboxylation of 9-cis-octadecenoic (oleic) acid to aromatic and aliphatic hydrocarbons suitable as blend components for aviation fuel applications utilising ruthenium dodecacarbonyl [Ru3(CO)12] with a variety of other catalysts is presented. Due to the different relative rates of decarboxylation and hydrogenation/dehydrogenation, different product distributions are possible when the catalyst is varied. Chloro-1,5-cyclooctadiene iridium (I) dimer [(C8H12IrCl)2] gave a similar conversion to the ruthenium system but provided an altered product distribution. Aromatic contents of up to 35% were achieved in the iridium system, thereby providing a wider range of blending options for fuel producers. Additionally, both catalytic systems were found to decarboxylate high-oleic soybean oil fatty acids, giving a product of similar energy content to that obtained using high grade oleic acid.