(395e) Selective Ring Opening of Decalin over Ion-Exchanged Ir Zeolites

Thermal DeOxygenation (TDO) is a thermal process that converts organic acids from cellulose hydrolyzation into a low-oxygen bio-oil containing substituted naphthalene compounds. The high aromatic content is desirable in gasoline fractions, but middle-distillate cuts, such as jet fuel and diesel, 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 increase the combustion characteristics, but the cetane number was still below specifications.

This research focuses on the ring opening of decalin, a bicyclic molecule with a chemical structure similar to many of the compounds found in hydrogenated TDO oil. Because there is no commercial process for these reactions, there has been little catalyst development in ring opening (hydrodecyclization), especially in the production of paraffins/isoparaffins from cycloparaffins. In our down-flow trickle bed reactor, we use various catalysts to ring open decalin under a variety of operating conditions. In this research, we analyze the effect of catalyst acidity, ion exchanges, and decalin stereochemistry on the reaction products.

Our research has shown that the concentration of Brønsted acid (BA) sites is crucial to determining the reaction pathway (see image). Catalysts with high quantities of BA sites isomerize decalin into unwanted skeletal isomerization products (SkIPs), whereas low concentrations of BA sites push the reaction towards ring opening products (ROPs). The catalyst BA was tuned by ion-exchanging various alkali metals into the zeolite at various concentrations and temperatures to optimize desired products. Our Ir/Cs-exchanged β-zeolites have been shown to produce products with ROP selectivities in excess of 80%, while limiting SkIP formation to less than 5%.

Our research also showed that the decalin stereochemistry played a crucial role in determining the reaction mechanism. Trans-decalin was more likely to produce branched SkIPs, whereas cis-decalin preferentially produced ROPs.