Inferring the role of NiO nanoparticles from the thermal behavior of virgin and adsorbed hydrocarbons

Simultaneous analysis of differential thermogravimetry (DTG) and differential scanning calorimetry (DCS) data is the key for identifying probable reactions and extracting their kinetic parameters under isothermal and non-isothermal conditions. However, an assumption of kinetically controlled thermal behavior needs to be adequately examined. Mass transfer limitations as well as multiple reactions of multiple species may be encountered while studying the thermal behavior of virgin and adsorbed crude oils. This, in turn, leads to uncertainties on the actual role of the adsorbent. In this paper we address these challenges and reflect on recent publication by Nassar et al. (2013) pertaining to catalyzed oxidation of adsorbed asphaltenes onto NiO nanoparticles. More specifically, we show that accounting for mass loss due to the adsorbent nanoparticles increases the value of the activation energy and, subsequently, influences conclusions on the role of the nanoparticle. In addition, we show that, for a given temperature zone, presenting heat flow profiles per gram of mass lost within that zone provides more reliable comparison between the size of reaction peaks. Finally, we address the heat treatment of oil and its effect on the adsorbed species, and explore the role of surface exposure and the interaction between the nanoparticles and the heavy oil fractions. (C) 2015 Elsevier Ltd. All rights reserved.