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In this work, the stability of water-in-crude oil emulsions generated in laboratory was investigated using a phenomenological mathematical model based on the population balance equation, considering different phenomena such as the binary coalescence of water droplets, the interfacial coalescence with the resolved water phase, the diffusion of the dispersed phase, and droplet settling. The resulting population balance equation (PBE) was a nonlinear hyperbolic integro-partial differential equation, which for our particular case required numerical techniques for resolution. The PBE was converted into a system of partial differential equations using Kumar’s fixed-pivot technique. The spatial coordinate was discretized using the finite volume method and a first order upwind scheme, while the discretization of the time coordinate was based on a semi-implicit approach. On the basis of this algorithm, the mathematical model was solved against experimental results of water-in-crude oil emulsion destabilization runs, providing suited predictions of droplet size distribution profiles, and of both emulsified water and free-water volumes. [ABSTRACT FROM AUTHOR]

This work aims to evaluate the activity and stability of solid acid catalysts (niobium oxide and sulfated zirconia) in the methyl esterification of oleic acid assisted by microwave heating, an alternative route to the base-catalyzed transesterification reaction using conventional heating. Both catalysts have yielded similar conversions (68% for Nb2O5and 68.7% for sulfated zirconia at 200 °C, t= 20 min, methanol-to-fatty acid molar ratio = 10, 5% w/w catalyst), much higher than the one obtained without catalyst (39.3%), besides a small deactivation after the fourth use (3% for Nb2O5, 11% for sulfated zirconia, compared to the first use). The results have not indicated a pronounced increase on reaction conversions by using microwave heating when compared to conventional data found in the literature. However, microwave irradiation remains attractive for heating esterification systems, since it allows for achieving high temperatures at reduced times. [ABSTRACT FROM AUTHOR]