Abstract
The main objective of this work is the catalyst optimization of Fe2O3-, Co3O4-, NiO- and/or PdO- (transition element oxides—TEO) functionalized CeO2 nanoparticles to maximize the conversion of asphaltenes under isothermal conditions at low temperatures (<250 °C) during steam injection processes. Adsorption isotherms and the subsequent steam decomposition process of asphaltenes for evaluating the catalysis were performed through batch adsorption experiments and thermogravimetric analyses coupled to Fourier-transform infrared spectroscopy (FTIR), respectively. The adsorption isotherms and the catalytic behavior were described by the solid-liquid equilibrium (SLE) model and isothermal model, respectively. Initially, three pairs of metal oxide combinations at a mass fraction of 1% of loading of CeNi1Pd1, CeCo1Pd1, and CeFe1Pd1 nanoparticles were evaluated based on the adsorption and catalytic activity, showing better results for the CeNi1Pd1 due to the Lewis acidity changes. Posteriorly, a simplex-centroid mixture design of experiments (SCMD) of three components was employed to optimize the metal oxides concentration (Ni and Pd) onto the CeO2 surface by varying the oxides concentration for mass fractions from 0.0% to 2.0% to maximize the asphaltene conversion at low temperatures. Results showed that by incorporating mono-elemental and bi-elemental oxides onto CeO2 nanoparticles, both adsorption and isothermal conversion of asphaltenes decrease in the order CeNi1Pd1 > CePd2 > CeNi0.66Pd0.66 > CeNi2 > CePd1 > CeNi1 > CeO2. It is worth mentioning that bi-elemental nanoparticles reduced the gasification temperature of asphaltenes in a larger degree than mono-elemental nanoparticles at a fixed amount of adsorbed asphaltenes of 0.02 mg·m−2, confirming the synergistic effects between Pd and Fe, Co, and Ni. Further, optimized nanoparticles (CeNi0.89Pd1.1) have the best performance by obtaining 100% asphaltenes conversion in less than 90 min at 220 °C while reducing 80% the activation energy.
Highlights
The demand for conventional crude oils increases every day worldwide, and it is expected that in the future these reserves will decrease substantially [1]
The main objective of this study was to find the best combination of transition elements oxides (Pd, Ni, Co, and Fe) and their optimum concentration in the surface of a CeO2 nanoparticulated support that allow for the improvement of the conversion of n-C7 asphaltene during steam injection processes at low temperatures (
The dynamic light scattering (DLS) results showed that the mean hydrodynamic diameter of the CeO2 nanoparticles was 22 nm, confirming its nanometric nature in agreement with the value reported by the provider
Summary
The demand for conventional crude oils increases every day worldwide, and it is expected that in the future these reserves will decrease substantially [1]. The use of fossil fuels such as heavy crude oil (HO) and extra heavy crude oil (EHO) has become an important source for the alternative energy supply [3] This type of crude oil has a high content of heavy hydrocarbons, such as asphaltenes, that drastically increase the viscosity of crude oil and reduce the American Petroleum Institute (API) gravity [4]. Thermal methods are used with the aim of viscosity reduction for improving the mobility ratio, productivity, and recovery of this type of crude oil [5,6,7] Some of these methods such as steam injection processes do not generate changes in the quality of crude oil. The temperatures employed in steam injection processes do not exceed 240 ◦C [12], while the decomposition temperature of asphaltenes in the presence of steam occurs around 450–550 ◦C [13,14,15]
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