Effect of alcohols on water solubilization in surfactant-free diesel microemulsions

Abstract

Microemulsions are preferred over other methods of mixing two immiscible liquids as they are thermodynamically stable, but require a high percentage of surfactant. Surfactant-free microemulsions, on the other hand, use an amphisolvent instead of surfactants, making them an economical alternative. The current experimental investigation focuses on formulation of surfactant-free water-in-diesel microemulsions with the help of straight-chain aliphatic alcohols as diesel replacement for IC engines. Dynamic light scattering measurements revealed these microemulsions had average water droplets of less than 10 nm. The microemulsions were formulated using single-alcohol, two-alcohols, and three-alcohols. It becomes crucial to study the water solubilization of microemulsions as the addition of water in diesel improves combustion efficiency. The water solubilization in surfactant-free microemulsions was found to be dependent on the hydrophilic–lipophilic balance (HLB) of the alcohols, as it determined the solubilizing property of alcohol. The microemulsions could only be formulated in the HLB range of 6.27 to 7.76 and were found to have maximum water solubilization in the HLB range of 6.67 to 7.63. Butanol had the highest water solubilization in a single alcohol system, butanol–ethanol in the ratio of 3:1 for the two-alcohol system, and propanol–butanol–octanol in the ratio of 3:1:1 for three-alcohol systems. Alcohols with higher HLB were more hydrophilic, causing migration of alcohol from the interface to bulk water. In comparison, alcohol with a lower HLB caused the migration of alcohol from the interface to bulk diesel, which resulted in reduced water solubilizations. Hence, the microemulsions could not be formulated beyond specific HLB range. The formulated microemulsions could be a prospective substitute for diesel fuel as alcohols can be derived from renewable routes.