Plasma Cracking of Liquid Hydrocarbons at Room Temperature for Efficient Production of Hydrogen

Abstract

Hydrogen has been formed from liquid hydrocarbon, n-hexadecane, at room temperature and pressure with a pulsed DC plasma discharge. The oil is ‘cracked’ into smaller molecules by the plasma. Gases were the primary products by mass. At the longest treatment time, the mole fraction of hydrogen obtained was 75% of the gas generated, and the specific energy input required to generate a kilogram of hydrogen gas was ∼ 29 kilowatt hours (kWh/kg). This energy input per kilogram of H2 is lower than the thermodynamic threshold for hydrogen production from water; 33.3 kWh/kg from steam and 39.4 kWh/kg from liquid water. The lower energy cost is possible here because the thermodynamic threshold energy for obtaining hydrogen from liquid hydrocarbons can be about ten times lower than the energy required to obtain hydrogen from water; e.g., 3.52 kWh/kg from n-hexadecane. The lowest thresholds for hydrogen formation from hydrocarbons are associated with the formation of solid carbon by-product. Some solid product has been observed here with a ratio of 3 hydrogen atoms for every 2 carbon atoms and a nanostructured morphology. The non-thermal plasma cracking process does not have a traditional catalyst, but argon is bubbled into the plasma reactor to facilitate the discharge.