A Microfluidic Reactor to Study the Oxidation Stability of Fuels: Application to a Sustainable Aviation Fuel Surrogate

One potential solution to diminish the aviation carbon footprint is to blend Sustainable Aviation Fuel (SAF) into jet fuels. However, the thermal stability and oxidation stability of standard jet fuels may be affected by the addition of SAF, and a better understanding of liquid fuel oxidation kinetics is needed. The development of a kinetically well-defined reactor to study this phenomenon remains a challenge, and it is in this context that a new Si-glass microfluidic reactor with a fluid supply made of inert poly(ether ether ketone) (PEEK) has been developed. The experimental rig PEEK-ACHU (Autoxidation μChip Heated Unit) was used to investigate the oxidation stability of a SAF surrogate, and the results were compared to Induction Period (IP) measurements obtained in a standard PetroOxy device. A mixture of n-decane and iso-octane was used as the surrogate SAF. The thermal oxidation stability of the mixtures was studied in the microreactor, working at conditions up to 453 K and 40 bar, with a gas–liquid segmented flow that allows the liquid oxidation to occur in homogeneous, self-agitated, liquid slugs, without oxygen diffusion/depletion kinetic limitations. PEEK-ACHU enables residence times as long as 3.8 h to be reached on a 4 in. diameter Si/glass wafer, with visual access to the reactor, and a well-defined kinetic study of the liquid fuel autoxidation. The total hydroperoxide (ROOH) concentration was quantified at the exit of the microreactor using a specifically designed HPLC device with a post-column reactor for iodometric titration. For comparison, the same analysis was conducted on the SAF oxidized in the PetroOxy apparatus with the same residence time. The results show that the microfluidic apparatus can perform reliable autoxidation measurements with well-controlled operating parameters. The visual access of the reactor is relevant for further investigations, such as spectroscopic monitoring of the deposit formation.