One-step high-value conversion of heavy oil into H2, C2H2 and carbon nanomaterials by non-thermal plasma

Non-thermal plasma is promising for cracking the abundant but low-quality heavy oil into value-add chemicals due to its wide feedstock adaptability and high conversion rate. In this work, heavy oil cracking characteristics by microsecond pulsed spark discharge plasma were investigated in terms of pulse voltage, pulse repetition frequency and discharge power. Experiment results indicate pulse voltage and pulse repetition frequency are the main factors to control product yields and distribution. Pulse voltage determines single pulse energy and influences discharge stability and gas temperature. Pulse repetition frequency determines discharge intervals and affects collision reactions and quenching process. The maximum heavy oil conversion rate was 50.4% and the mass yields of H2 and C2H2 were 3.3% and 19.7% with 10.1 W discharge power, and H2 and C2H2 production energy consumption were 25.2 kW·h/m3H2 and 55.4 kW·h/m3C2H2. Compared with thermal plasma, heavy oil conversion rate of this work increased 12% with above 95% reduction in discharge power, and this work has a significant advantage in H2 and C2H2 production energy consumption. Carbon nanomaterials composed of carbon nanoflakes and nanoparticles can be obtained while producing H2 and C2H2. Especially, there were few-layers graphene nanoflakes (GNFs) in the carbon nanomaterials, which realized the full utilization of heavy oil. The possible reaction mechanism of heavy oil cracking was discussed using saturates-nucleating-aromatics-flaking theory. This work provides an effective COx-free method for one-step production of H2, C2H2 and carbon nanomaterials, which has wide application prospects for heavy oil utilization.