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Phase behaviors and fuel properties of palm oil-based microemulsion biofuels using sugar-based surfactants

Due to environmental concerns and current fossil-fuel situations, palm oil has been considered as a potential vegetable oil for renewable biofuel applications in South East Asia. To solve durability problems in diesel engine caused by high viscosity of palm oil, microemulsification has led to more attention as a novel viscosity-reducing technique. Microemulsion biofuels are transparent, thermodynamically stable, and singlephase microemulsions, where the polar phase is solubilized in surfactant aggregates existing in the non-polar phase. Surfactants (surface active agents) play a key role in enhancement of the interaction between polar and non-polar phases. Since sugar-based surfactants have been derived from bio-based resources, they have been introduced to formulate microemulsion biofuels in this study. Three sugar-based surfactants, sorbitan monolaurate (SM20), sorbitan monooleate (SM80), and sorbitan trioleate (ST85) and three alcohols (butanol, hexanol, and octanol) were used as surfactants and co-surfactants, respectively. The objectives of this study are to formulate microemulsion biofuels using sugar-based surfactants, to study the effects of surfactants and co-surfactants on phase behaviors and kinematic viscosities, and to investigate the effect of surfactant/co-surfactant ratio on other fuel properties (i.e. energy content, cold flow properties, density, and ash content). The results show that the microemulsion system using SM80 and octanol at the molar ratio of 1 to 8 was considered as an optimized microemulsion biofuel formulation demonstrating comparable fuel properties to biodiesel. These results provide useful guidance for future design of environmentally friendly microemulsion biofuels.