Designing catalytic processes for producing fuels and valuable chemicals from triglycerides

Abstract

There is an increasing interest in the development of processes that can convert biomass into fuels and valuable chemicals because of global need for finding sustainable energy sources and mitigating anthropogenic CO$_2$ emission. Among the various biomass feedstocks, triglycerides (e.g., vegetable oil, microalgae oil, and animal fat) have been widely used for the production of bio-fuels. Significant advantages in using triglycerides are not only their low oxygen and sulfur contents but also highly paraffinic backbone in their fatty acid units already quite similar to those of petroleum-derived hydrocarbons. In this thesis, catalytic processes for producing biojet jet fuel and lube base oil from triglycerides were investigated. Generally, single-step hydroconversion of triglyceride into biojet fuel is difficult to operate because metal catalyst is poisoned by CO. In order to overcome this limitation, it is required to design a CO-tolerant metal-acid bifunctional catalyst. It was achieved by introducing Pt and Re supported USY catalyst. Indeed, Pt-Re alloy catalyst itself was not efficient for jet fuel production due to its too strong hydrogenolysis (a side reaction during hydrocracking) activity, but it showed remarkable performance in jet fuel production in the reaction media containing CO and H$_2$O due to suppressed hydrogenolysis activity. Effects of chain length and unsaturation degree of fatty acids on ketonization were also investigated using a TiO$_2$ catalyst. It was observed the desired fatty ketone yield was much lower and catalyst deactivation was much faster in ketonization of long chain unsaturated fatty acid due to a side reaction, ‘McLafferty rearrangement’. From these results, it was possible to design a sustainable process by pre-hydrogenating the double bond of the fatty acid before the ketonization when producing a lube base oil from a natural triglyceride.