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.

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The effect of temperature on asphaltene aggregation has not been investigated at different shear rates. Following our previous work, the effects of temperature and shear rate on the evolution of asphaltene aggregate size distribution in a heptane–toluene mixture are experimentally studied within a Couette flow device. At fixed temperature and shear rate, the average diameter of flocs initially increased with time until it reached a maximum value and then declined to a constant steady state size as a result of the balance between the aggregation and fragmentation. Increasing the temperature resulted in a smaller steady state average diameter. Results of experiments indicated that the agitation rate affects the evolution kinetics of asphaltene aggregates less than temperature. The effect of shear rate on the fragmentation rate was found to be higher than that on aggregation which resulted in a maximum in the average steady state diameter versus shear rate. A fractal geometric population balance model was developed to simulate the experimental results and to extract the kinetics of the aggregation and fragmentation processes. In the proposed model, three fitting parameters, including the collision efficiency, the fractal dimension, and the breakup rate coefficient, were used to match the model on experimental data. The calculated collision efficiency was strongly dependent on temperature. The results showed that the collision efficiency decreases with an increase in temperature in both perikinetic and orthokinetic aggregations. On the basis of the obtained breakup rate coefficients, the floc strength decreases with temperature.

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