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Influence of Temperature on Aggregation and Stability of Asphaltenes. I. Perikinetic Aggregation

Torkaman, Mohammad, Bahrami, Masoud, Dehghani, Mohammadreza
Energy & Fuels 2017 v.31 no.10 pp. 11169-11180
models, particle size, petroleum, temperature, zeta potential
Asphaltene deposition is one of the most challenging aspects of the petroleum industry that takes place through production, processing, and transportation. In the present study, first, the effect of temperature on the aggregation kinetics of asphaltene in a heptane–toluene mixture is investigated during a set of experiments done at different fixed temperatures. In spite of most previous works in which the collision efficiency is assumed to be constant and equal to one, the obtained experimental data in this study provides deep insights into the mechanism of aggregation of asphaltene particles within an organic medium. A population balance model considering the fractal structure for asphaltene aggregates and variable value for collision efficiency is developed to predict the enlargement of asphaltene floccules with the passage of time. The results show that the assumption of a constant value for collision efficiency is not realistic. The calculated value of collision efficiency decreases with the increase of average particle size during each experiment. Also, the value of collision efficiency decreases with the increase of temperature. In the second part of this work, the zeta potential of asphaltene aggregates in the mixture is measured during the evolution of floccules in separate tests. These results are applied to investigate the asphaltene stability and also to validate the size measurement data obtained in the first part. The measured zeta potentials of evolving particles indicate that the asphaltene aggregates are more stable at high temperatures than at low temperatures. Due to this fact, aggregates reach a significantly smaller mean size at high temperatures in comparison to that at low temperatures.