(6gt) Evaluation of the Influence of Ce4+/Ce3+ Redox-Couple on the Cyclyc Regeneration of NiO-Pdo/CeO2 Nanoparticles for Asphaltene Steam Decomposition

The main objective of this study is to evaluate the self-regenerative property of functionalized CeO_{2±𝛅} nanoparticles with a mass fraction of 0.89 % of NiO and 1.1 % of PdO in adsorption processes and subsequent decomposition of n-C₇ asphaltenes in steam gasification processes though a redox cycle.

During each regeneration cycle, the adsorption capacity and the catalytic activity of the nanoparticles were evaluated. To estimate the adsorption capacity of the nanoparticles, adsorption kinetics were studied at a fixed concentration of n-C7 asphaltenes of 10 mg·L-1 as well as adsorption isotherms at three different temperatures at 25°C, 55°C, and 75°C. To evaluate the catalytic activity, the loss of mass of the nanoparticles was evaluated at isothermal conversions with a thermogravimetric analyzer at 230°C, 240°C, and 250°C, and at non-isothermal conditions involving heating of 100°C to 600°C at a 20 °C·min-1 heating rate.

The nanoparticles showed a high affinity for adsorption of n-C7 asphaltenes, and this was maintained during all evaluated regeneration cycles, as observed in the Henry's constant that increased slightly, with changes of 21%, 26% and 31% for 25 °C, 55 °C and 75 °C. Polanyi's adsorption potential decreases by 2.6% for the same amount adsorbed from the zero cycle to the eight. In addition, the catalytic activity of the nanoparticles did not change significantly, showing that they decompose 100% of asphaltenes in all cycles at 210 °C. However, the small decrease in the adsorption capacity and catalytic activity of the nanoparticles is mainly due to the presence and change in concentration and ratio of certain elements such as oxygen and iron at the surface of the nanoparticle, as shown by XPS analyses. Thermodynamic parameters such as, change in enthalpy, entropy and Gibbs free energy, and effective activation energy were calculated in order to compare adsorptive and catalytic performance during each cycle. There is an increase of 9.3% and 2.6% in the case of entropy and enthalpy respectively, and a decrease of 0.5% at 25°C for the Gibbs free energy from cycle 0 to 8 evaluated.

Teaching Interests:

Among thermal enhanced oil recovery, in particular, cyclic steam stimulation (CSS) is a technique commonly used for heavy and extra-heavy oil production. However, this method presents a great limitation in that are economically viable the first 6-7 production cycles, due to the extra-heavy oil residue retained in the reservoir, whose decomposition temperature exceed the operation temperature of de CSS and the lightest oil components vaporization. Taking into account the self-regenerative properties of the CeO2 nanoparticles to change their oxidation state from Ce4+ to Ce3+ in a redox-cycle, and the catalytic advantages that the supporting material acquires with a high metal oxides dispersion over its surface, which allows it to decompose at low temperatures (210 °C) the asphaltenes in the presence of steam, it is proposed to evaluate their performance in catalytic regeneration cycles through continuous adsorption and subsequent decomposition of n-C7 asphaltenes in gasification processes. In this way, if the porous media is decorated with these nanoparticles that are continuously adsorbing and decomposing the heaviest oil fraction, the coke inside the reservoir will be diminished, increasing the recovery factor and the useful life of the technique.