Ethanol-in-palm oil/diesel microemulsion-based biofuel: Phase behavior, viscosity, and droplet size

• Surfactants and cosurfactants were studied for formulating optimized biofuel.
• Surfactant had greater effect on viscosity than cosurfactant.
• Viscosity of biofuel tends to be greater with smaller size of droplets.
• Methyl oleate surfactant can reduce viscosity and produce uniform droplet size.
• Biofuel was formulated without byproducts and less energy consumption.

Increased environmental awareness and depletion of resources are driving industry to develop viable fuels from renewable resources. Vegetable oils are one alternative being considered for the production of renewable fuels. Surfactant reverse micelle microemulsions can be used as an alternative method for reducing high viscosities of vegetable oil without chemical wastes generated from the transesterification reaction. The objective of this research is to study the effects of surfactant saturation, unsaturation, and ethylene oxide groups on the phase behavior, kinematic viscosity, and microemulsion-droplet size with the goal of formulating optimized surfactant based biofuel. Four nonionic surfactants, stearyl alcohol (saturated), oleyl alcohol (unsaturated), methyl oleate (unsaturated with ester group), and Brij-010 (EO groups), were investigated in this research. It was found that the presence of methyl oleate unsaturated surfactant can greatly reduce the bulk viscosity and produce uniformly size of microemulsion droplets while use the least amount of surfactant for solubilizing ethanol-in-oil in the system. Thus, these results show that reverse micelle microemulsion can produce biofuels with desirable viscosity and fuel properties as compared to diesel.