(20g) Enhanced Hydrogenation of Oleic Acid By RF Heating Via Magnetically Susceptible Nanoparticles

An alternative, emerging approach to heat catalyst is by induction heating via magnetic Fe₃O₄ nanoparticles. Using radio waves (RF), heat is generated locally within the magnetically susceptible particle. By locating the heat generation at the surface, heat transfer efficiency is increased, and it may have a positive effect on yield and selectivity by minimizing the temperature gradient across the catalyst.

Hollow microspheres consisting of ~23 nm Fe₃O₄ nanoparticles were synthesized and decorated with palladium (1.0 wt.%) or platinum (3.0 wt.%). The RF-driven hydrogenation was performed in a semibatch glass slurry reactor with catalyst, oleic acid, dodecane solvent, and hydrogen bubbled through at 1 atm and compared to conventional heating. Magnetic fields were used corresponding to liquid bulk temperatures near 70, 110, and 150 °C. At 70° C, the palladium showed an additional 12% conversion in RF compared to thermal, with both exhibiting greater than 90% selectivity to stearic acid. The difference in conversion closed between the two methods at 110 °C, with stearic acid selectivity still greater than 90%. At 150 °C, RF heating increased conversion by 5.5%.

The platinum catalyst displayed markedly different behavior. Cracked acid (C16-C17) products were obtained along with stearic and nonadecanoic acid. The oleic acid conversion was significantly lower than the previous. The selectivity to the C16-C17 acid products was much higher with RF heating (and decreased stearic acid) at both 70 and 110 °C. Stearic acid became the primary product at 150 °C, with high selectivity to the C16 and C17 acids, although little difference in selectivities between thermal and RF heating. The variance in selectivity between RF and thermal at 70 and 110 ° C is believed to be due to localized hot spots. Future work involves applying the RF heating techniques to drive higher temperature and endothermic reactions such as dehydrogenations.