AC Plasmas Directly\nExcited in Liquid-Phase Hydrocarbons\nfor H<sub>2</sub> and Unsaturated C<sub>2</sub> Hydrocarbon Production

AC plasmas directly excited within liquid hydrocarbons\nwere investigated\nfor the production of hydrogen and unsaturated C<sub>2</sub> hydrocarbon\nin a recirculating liquid “jet” flow configuration.\nArc discharges were excited at two different frequencies (60 Hz and\n17.3 kHz) in C<sub>6</sub>–C<sub>8</sub> hydrocarbons (hexane,\ncyclohexane, benzene, toluene, and xylene) to produce H<sub>2</sub>, C<sub>2</sub>H<sub>4</sub>, C<sub>2</sub>H<sub>2</sub>, and CH<sub>4</sub>, along with liquid and solid carbon byproducts. AC frequency\nwas seen to modify the plasma properties and gas bubble formation\ndynamics, significantly influencing the efficiency and reaction pathway.\nHigher discharge frequency increased energy efficiency more than 2-fold\nby minimizing thermal losses and favored the production of hydrogenated\ncompounds due to shorter reactant–plasma contact times. Further\noptimization of hexane conversion was achieved by introducing fluid\nflow around the plasma electrodes, which led to competitively low\nspecific energy requirements (SERs) of 3.2 kWh/kg C<sub>2</sub>H<sub>4</sub>, 4.9 kWh/kg C<sub>2</sub>H<sub>2</sub>, and 24.3 kWh/kg H<sub>2</sub>. The effect of hydrocarbon feed chemistry was analyzed, showing\nthat hexane and cyclohexane are preferable for C<sub>2</sub> hydrocarbon\nsyntheses, whereas aromatic hydrocarbons produce more H<sub>2</sub>. Gas bubble dynamics and liquid/solid products were analyzed using\nhigh-speed imaging, optical emission spectroscopy (OES), gas chromatography–mass\nspectrometry (GC-MS), scanning electron microscopy/transmission electron\nmicroscopy (SEM/TEM), and Raman spectroscopy. This work contributes\nto the understanding of plasma conversion mechanisms within liquids\nand demonstrates the potential for the energy-efficient transformation\nof hydrocarbons with plasma in unique reaction environments.