Production of Biojet Fuel from Octadecane and Derivatives of Castor Oil Using a Bifunctional Catalyst Ni–Pd@Al-MCF in a Pressurized CO2–Hexane–Water Solvent

The production of biojet fuel from a model compound octadecane (C18) and the derivatives obtained from the hydrodeoxygenation (HDO) of real-time feedstock castor oil was demonstrated. A one-pot-synthesized Al-modified mesocellular foam (MCF)-encapsulated Ni–Pd catalyst (Ni–Pd@Al-MCF) was used. Under the optimized reaction conditions of 227 °C, 57 bar H2, and 20 bar CO2 pressure for 2.5 h of reaction, 99.4% conversion of the model compound C18 with 98.2% selectivity toward liquid jet-fuel products (LJFPs) with a desired isoalkane/n-alkane ratio of 1.1 was achieved. Ni–Pd@Al-MCF was seen to catalyze the production of biojet fuel from C18 through a bifunctional feature, wherein hydrocracking/hydroisomerization took place at the Brønsted acid sites in Al-MCF, while hydrogenation/dehydrogenation took place at the Ni–Pd metal sites. Simultaneously, the Ni–Pd alloy nanoparticles containing electron-deficient Pdδ+ species accelerated the reaction by intensifying the dissociative adsorption of H2. At an Si/Al ratio of 5, the acidity in Ni–Pd@Al-MCF was found to be optimum. A pressurized CO2–hexane–water functional and greener solvent system was used. Pressurized CO2 not only increased the intraparticle diffusion rate to speed up the reaction but also released carbonic acid by interacting with water, which acted as a promoter in the acid-catalyzed hydrocracking/hydroisomerization of C18. Ni–Pd@Al-MCF was also observed to be stable for at least eight cycles. Finally, the derivatives containing 96.0% C18 obtained from the HDO of castor oil were treated using the developed Ni–Pd@Al-MCF catalyst. 100% conversion with 98.8% selectivity toward LJFPs and an isoalkane/n-alkane ratio of 1.1 was obtained, thereby validating the process for the use of real-time feedstocks.