Asphaltene Adsorption onto Alumina Nanoparticles: Kinetics and Thermodynamic Studies

Asphaltene adsorption onto nanoparticles is an attractive subject for the heavy oil industry for two important reasons. First, nanoparticles would remove asphaltenes from the heavy oil rapidly and thus making the remaining fraction of oil transportable for conventional processing. Second, nanoparticles could be employed as catalysts for upgrading asphaltenes into light usable distillates. The first part has been investigated in this study, while the second part will be communicated shortly. In this study, the adsorption of asphaltenes from heavy oil model solutions onto colloidal nanoparticles of gamma-Al2O3 is investigated. Batch adsorption experiments were carried out at different initial asphaltene concentrations and temperatures. The effects of the following variables on the amount of asphaltene adsorbed have been investigated, namely, contact time, initial concentration of asphaltenes, temperature, heptane/toluene ratio (H/T), coexisting molecules, and water content. Asphaltene adsorption kinetics and isotherms were obtained. The adsorption was fast, and equilibrium was approached within 2 h. The pseudo-first-order and pseudo-second-order kinetic models were applied to the experimental data, with a better fitting to the pseudo-second-order model. The resultant isotherms are in good agreement with the Langmuir isotherm model. The thermodynamics of asphaltene adsorption onto the gamma-Al2O3 nanoparticles indicated that the adsorption was spontaneous and exothermic in nature.