Molecular Dynamic Simulation and Experiments on N-C7 Asphaltene Pyrolysis under High-Pressure Conditions Using Ceria-Based Nanocatalysts

This work aims to widen our knowledge about the pyrolysis,andcatalytic pyrolysis of asphaltenes at low and high pressure throughexperimental and simulation approaches. Experimentally, asphalteneswere subjected to high-pressure thermogravimetric analysis obtaininga pressure-dependent behavior. As pressure increases, asphaltene reactivityis reduced by the retardation in the thermal cracking temperatureand increment of the coke amount deposition. The coke deposited followsthe order 0.084 MPa (8.0%) < 3.0 MPa (10.0%) < 6.0 MPa (11.0%).When ceria-based nanoparticles were used for the catalytic thermalcracking of asphaltenes, it was obtained that during the low-temperaturerange (<250 & DEG;C), the amount of mass lost was 60, 45, and 38%at 0.084, 3.0, and 6.0 MPa, respectively. The rest of the asphaltenesare cracked in the high-temperature region (HTR), which means thatcoke is not produced in the catalytic reaction regardless of the systempressure. Molecular dynamic calculations were done based on the ReaxFFpotential to provide an atomistic description of asphaltene pyrolysisat 0.084 and 6.0 MPa. The theoretical results were compared with thoseobtained experimentally, achieving successful reproducibility. Duringthe LTR region, the asphaltene aggregate integrity remains withoutsignificant changes, whereas most structural changes in the HTR wereobtained. The number of the species increases with the rising temperature,obtaining at 0.084 MPa, 32, 1515, and 4065 species at 300, 450, and550 & DEG;C, respectively, whereas at 6.0 MPa, 28, 589, and 867 speciesat 300, 450, and 550 & DEG;C were obtained. The variety of the moleculeswas found to be higher at 450 & DEG;C due to the breaking of a largenumber of complex hydrocarbons. This result corroborates that asphaltenesmainly react during HTR, and with increasing pressure, the rate ofreaction is negatively affected. The species are mainly found in theform of reactive radicals such as CHO2 (carboxyl radical),OH (hydroxyl radical), and CHO (aldehyde radical), and molecules ofCO(2), H2O, CH2O, and CO are observedas major O-containing gas products that account for most of the gasphase.