Characterization of asphaltenes aggregation and fragmentation in a shear field

Aggregation and breakup of asphaltenes flocs in a Couette flow device are studied for various values of shear rate (G), volume fraction of particles (φ), and solvent composition (ratio of toluene to n‐heptane in the solution Xs). The number average asphaltene aggregate size initially increases before achieving a maximum size and then decreases until reaching a steady‐state value that reflects a balance between aggregation and fragmentation. Increasing the applied shear rate leads to higher aggregation and fragmentation rates, reducing the steady‐state average aggregate size and the characteristic relaxation time required to achieve a steady state. For a fixed value of G, when either φ is increased or Xs is decreased, the steady‐state floc size increases. The kinetics of the aggregation‐fragmentation process and the attainment of steady state by asphaltenes aggregates were modeled using a population balance approach. The model describes the time evolution of the average floc size using fitted parameters (the breakup coefficient for shear fragmentation, b and the porosity of the aggregates ϵ). Binary breakage was included in calculations and collision efficiency was assumed to be equal to one.