Oriented conversion of low-value heavy oil to acetylene and hydrogen using pulsed spark discharge

• Immediate conversion of waste transformer oils in liquid phase to H 2 and C 2 H 2 . • Proportions of H 2 and C 2 H 2 can be selected by repetitive frequency and reaction time. • The electron density in liquid-phase plasma is contrary to gas and gas–liquid phase plasma. • The dominant reaction pathway of gas production is C 2 H 4 →C 2 H 2 +H 2 . • The radical recombination is key to selective product formation. Discharge plasma presents a promising approach for converting heavy oil into light hydrocarbons under room temperature and atmospheric pressure. Among various techniques, repetitive pulsed discharge plasma is preferred for its potential to improve energy efficiency, however the decomposition characteristics and gaseous production pathways of long-chain hydrocarbons remain insufficiently understood. In this study, the decomposed products and process of mineral transformer oil under repetitively pulsed spark discharge in the liquid phase are analyzed by gas chromatography (GC) and optical emission spectroscopy (OES). Experiment results reveal that the proportion of H 2 gas production decreases, while that of C 2 H 2 increases with the prolonged reaction time. Besides, the production of C 2 H 2 is significantly higher at a pulse frequency of 1000 Hz compared to 10 Hz. OES analysis further shows that the electron density decreases as the repetitive pulse frequency increases, a trend that contrasts with prior observations of heavy oil cracking in gas and liquid–gas reaction systems. Despite the reduced energy per pulse at higher frequencies, the total number of breakdown events over the same reaction duration is larger, contributing to enhanced reaction outcomes. These experimental findings are confirmed by plasma kinetics and molecular dynamics simulation, which identified a continuous dehydrogenation process involving H radical reactions with C 2 H 4 as the primary pathway for C 2 H 2 and H 2 production. The study demonstrates the feasibility of C 2 -oriented conversion through the decomposition of heavy oil decomposition under spark discharge, with adjustments to repetitive pulse parameters offering a promising avenue for optimization.