Emulsification characteristics of three-phase emulsion of biodiesel-in nitromethane-in-diesel prepared by microwave irradiation

Microwaves, a form of electromagnetic radiation with high frequencies and short wavelengths, are often used for de-emulsification because various emulsion phases are susceptible to separation owing to the intense twisting of polar molecules and abrupt temperature increases caused by microwave vibration. This study was the first to prepare three-phase emulsions of biodiesel-in-nitromethane-in-diesel (B/N/D) with a microwave reactor by capitalizing on effective mass and heat transfer through microwave irradiation. The emulsification characteristics of these three-phase emulsions were compared with those prepared by magnetic stirring, with the same input energy used during the preparation of both sets of emulsions. Nonionic surfactants Span 80 and Tween 80 were used to assist in the emulsions' formation through a reduction in between-phase interfacial tension. The experimental results show that B/N/D three-phase emulsions prepared via microwave irradiation exhibit superior emulsification characteristics to those prepared via magnetic stirring. These superior characteristics include higher levels of emulsion turbidity and emulsification stability and a smaller mean nitromethane droplet size in the dispersed phase. An increase in the mass fraction of the dispersed phase of nitromethane led to an increase in both the number of dispersed droplets and turbidity of the three-phase emulsions in both cases. However, the droplet sizes of the B/N/D emulsions prepared by microwave irradiation were found to be more stable than those prepared by magnetic stirring. Finally, the mean droplet size and temperature of the three-phase B/N/D emulsions were also larger and lower, respectively, than those of two-phase biodiesel-in-nitromethane emulsions of the same composition, regardless of the preparation method. (C) 2015 Elsevier Ltd. All rights reserved.