Online optical monitoring of asphaltene aggregation

An optical method is employed to investigate asphaltene aggregation kinetics in real time using a photometric dispersion analyzer (PDA). The size of the aggregates is obtained by coupling photographic technique and image analysis with the online output of the PDA. The aggregation and breakup of the flocs are studied in a stirred tank for various volume fractions of particle (phi), stirring speed, and solvent composition (i.e., ratio of toluene-to-heptane in the solution, T:H). Initially, the average aggregate size increases and eventually reaches a steady-state value that reflects a balance between aggregation and fragmentation. Increasing the stirring speed reduces the steady-state size. At a certain stirring speed, when either phi is increased or T:H is decreased, the steady-state floc size increases. The presence of maltenes in the bitumen greatly retards the aggregation kinetics of asphaltenes. A cyclic- and tapered-shear schedule decreases the average floc size. The steady-state size attained at a certain stirring speed depends on the shear history of the flocs.