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

Abstract

This work aims to widen our knowledge about the pyrolysis, and catalytic pyrolysis of asphaltenes at low and high pressure through experimental and simulation approaches. Experimentally, asphaltenes were subjected to high-pressure thermogravimetric analysis obtaining a pressure-dependent behavior. As pressure increases, asphaltene reactivity is reduced by the retardation in the thermal cracking temperature and increment of the coke amount deposition. The coke deposited follows the 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 thermal cracking of asphaltenes, it was obtained that during the low-temperature range (<250 °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 asphaltenes are cracked in the high-temperature region (HTR), which means that coke is not produced in the catalytic reaction regardless of the system pressure. Molecular dynamic calculations were done based on the ReaxFF potential to provide an atomistic description of asphaltene pyrolysis at 0.084 and 6.0 MPa. The theoretical results were compared with those obtained experimentally, achieving successful reproducibility. During the LTR region, the asphaltene aggregate integrity remains without significant changes, whereas most structural changes in the HTR were obtained. The number of the species increases with the rising temperature, obtaining at 0.084 MPa, 32, 1515, and 4065 species at 300, 450, and 550 °C, respectively, whereas at 6.0 MPa, 28, 589, and 867 species at 300, 450, and 550 °C were obtained. The variety of the molecules was found to be higher at 450 °C due to the breaking of a large number of complex hydrocarbons. This result corroborates that asphaltenes mainly react during HTR, and with increasing pressure, the rate of reaction is negatively affected. The species are mainly found in the form of reactive radicals such as CHO2 (carboxyl radical), OH (hydroxyl radical), and CHO (aldehyde radical), and molecules of CO2, H2O, CH2O, and CO are observed as major O-containing gas products that account for most of the gas phase.

Recent Advances in Carbon Dioxide Sequestration in Deep Unmineable Coal Seams Using CO2-ECBM Technology: Experimental Studies, Simulation, and Field Applications

“…However, most of the researchers developed nanomaterials for the carbon capture and separation process toward carbon sequestration. − It is recommended to develop nanomaterials specifically to enhance CO 2 sequestration in CBM for shallow and deep reservoirs.…”