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

Abstract

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 revealed that the proportion of H₂ gas production decreases, while that of C₂H₂ increases with the prolonged reaction time. Besides, the production of C₂H₂ 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 C₂H₄ as the primary pathway for C₂H₂ and H₂ production. The study demonstrates the feasibility of C₂-oriented conversion through the decomposition of heavy oil decomposition under spark discharge, with adjustments to repetitive pulse parameters offering a promising avenue for optimization.