The Effect of Shear Rate on Aggregation and Fragmentation of Asphaltene Aggregates

This paper investigates the shear rate influence on asphaltene aggregation in heptane-toluene mixture through experiments and theoretical modeling at constant temperature and pressure. The experiments were performed within a Couette apparatus at different shear rates (129.14 - 1142.39 s(-1)). The size distributions of asphaltene aggregates in time were measured. In all tests, the average diameter of asphaltene aggregates initially increases up to a maximum and then decreases to a steady-state value. The existence of steady state size is believed to occur when the rates of aggregation and fragmentation become equal. A fractal population balance model was used and the aggregation kernel was assumed to be a linear combination of orthokinetic and perikinetic kernels. The Particle Swarm Optimization (PSO) algorithm was employed for estimating the model parameters including orthokinetic and perikinetic collision efficiencies, and , respectively, fractal dimension, , and breakage coefficient, . The results showed that the fractal dimension, the collision efficiency of orthokinetic mechanism and breakup rate coefficient increase with increasing of shear rate. However, the value of perikinetic collision efficiency decreases with the increase in shear rate. Totally, the effect of fluid shear on fragmentation was found to be higher than that on aggregation of asphaltene particles. [GRAPHICS] .