Kinetics mechanism of asphaltenes liquid-phase pyrolysis

The world energy demand is continuously increasing while the energy supply is still strongly related to fossil fuel, and likely to say so in the near future. However, the availability of high-quality crude oil feedstocks is constantly depleting. Heavy Fuel Oils (HFOs) are expected to play a vital role in the future of the energy supply as fuels for power generation and marine shipping. This work presents the first step in the formulation of a kinetics model aimed to reconstruct the HFOs pyrolytic behavior as the weighted sum of their SARA (Saturates, Aromatics, Resins, Asphaltenes) fractions contribution. In this work, details of the model to describe the asphaltenes pyrolysis is reported. The development of the model followed two main steps. The first one concerned the formulation of a suitable characterization framework being HFOs and asphaltenes complex mixtures made by thousands of different compounds. The characterization framework is based on the design of five pseudo components which are used to generate surrogate mixtures to mimic actual asphaltenes samples. The surrogate mixture is generated as the linear combination of pseudo components to reproduce the sample’s elemental composition. The pseudo components structure was designed taking advantage of experimental information from literature and in-house experiments performed at King Abdullah University of Science and Technology (KAUST). The second step was the development of the pyrolysis kinetics scheme. The formulation of the kinetic model proceeded through chemistry-related considerations intending to reproduce the all-significant pyrolysis products. A reaction pathway is assigned to each pseudo component with the task to approximate the overall kinetics. Model parameters such as activation energy, pre-exponential factors, and stoichiometric coefficients of each reaction were tuned following a data fitting approach to match experimental evidence. The model obtained is predictive and versatile being able to reproduce the pyrolytic behavior of different asphaltenes samples just knowing their elemental composition. The mechanism of asphaltenes represents a first step in the formulation of a comprehensive kinetics scheme for HFOs, which can be adopted for design, tuning, and optimization of combustion modeling processes.