Thermodynamic analysis of hydrogen production from heavy fuel oil (HFO) model compound via oxidative cracking process

Presently there are more than 700 operational petroleum refineries in the world. All of these refineries have a common problem – the existence and hazard of heavy fuel oil (HFO). HFO is an undesired low-quality residue generated from a petroleum refinery. It is a complex mixture usually consisting of saturates, aromatics, resins, and asphaltenes. HFO is normally disposed of in the landfill and this leads to environmental concerns. Some HFOs undergo costly treatment to be further reused in the transportation and energy sector, but yet it is still not encouraged by authorities due to hazardous emissions (COx and sulphur) that would jeopardize the environment. A potential approach to overcome this scenario is to upgrade HFO to fuel or value-added chemicals via oxidative cracking reaction. In this investigation, a thermodynamic analysis was performed involving n-eicosane and toluene which were selected as model compounds to represent HFO for the oxidative cracking process to produce hydrogen. Thermodynamic properties of the oxidative cracking of n-eicosane and toluene have been studied based on the total Gibbs energy minimization, using HSC Chemistry Software. The impacts of various n-eicosane, toluene, and oxygen ratios at temperatures between 573 and 1273 K at atmospheric pressure were analyzed. 37 reactions have been identified to be involved in the oxidative cracking process. Hydrogen was predicted to be successfully formed alongside other major products, namely CO, CH4, CO2, H2O, and coke. Minor products such as C2H4, C2H6, C3H6, C2H2, C4H10, and CH3∗ have also been identified and their formation trends have been studied. The correlation of major product components at 573K and 1273K for n-eicosane, toluene, and oxygen reactions was also analyzed, where hydrogen is highly favoured at higher temperatures. A ratio of 0.6:0.2:0.2 (n-eicosane:toluene:oxygen) emerged as the best generating the highest amount of hydrogen. Results show that a high ratio of n-eicosane and a low ratio of oxygen elevated hydrogen gas generation. A network of reaction mechanisms has been postulated to show the reactions in the oxidative cracking process.