(143g) Development of Petrol-Alcohol-Water Microemulsion Fuel as a Substitute for Petrol and Ethanol-Blended Petrol

In response to adverse environmental impacts from mass consumption of fossil petroleum fuels as well as international crude oil reserves being finite, most countries are attempting to find answers to meeting future demand for fuel for transport. Internationally, there is a growing acceptance that renewable ethanol fuel produced from biomass, with its associated environmental benefits, will be the transport fuel of choice for the future. Ethanol/ petroleum fuel blends directly address vehicle emissions and transport fuel security of supply issues. In addition to reducing currently regulated vehicle emissions, the renewable ethanol content of these fuels can result in a net reduction in the emission of unburnt hydrocarbons and particulate matter. Use of ethanol/ petroleum fuel blends initially in the existing vehicle fleet is essential to develop the technology and infrastructure necessary to support wide-scale production and use of ethanol fuel.

Petrol-alcohol-water based microemulsion fuel represents a new and potentially cost-effective option. Microemulsions are optically isotropic, transparent oil and water dispersions which are thermodynamically stable. Microemulsions have received considerable attention in recent years because of their interesting thermodynamic and physico-chemical behavior, and diverse applications. A lot of work has been done in areas like microemulsion gels and preparation of vitamin E emulsions. But preparation, characterization, and testing of microemulsion fuels, comprising of petrol and water, and especially of ethanol-blended petrol and water, remain virtually unexplored.

The petrol-alcohol-water based microemulsion fuel was prepared by stirring a blend of petrol, surfactant, co-surfactant, and water in definite proportions and it was produced under certain carefully defined conditions. To prepare a stable microemulsion fuel, a specific type of surfactant is required to be added in optimum quantity along with a co-surfactant, which in our case was ethanol (both anhydrous, and hydrous ethanol, i.e. ethanol obtained from sugar mills).

Experiments have been conducted to determine the minimum percentage of anhydrous ethanol that was needed to be added to the mixture of petrol and water, starting with fixed initial compositions of petrol (ranging from about 79%-99.5%)-and-water (ranging from about 0.5%-21%) mixtures. A fixed quantity of surfactant was added to this immiscible petrol-water mixture followed by a continuous addition of the co-surfactant (anhydrous ethanol) until a crystal clear mixture was obtained, i.e. a microemulsion (transparent and clear to the naked eye). Other sets of experiments were carried out by starting with fixed quantities of ethanol, surfactant, and petrol, followed by a continuous addition of the water to this mixture until it just about became turbid. A ternary phase diagram was plotted using these data. The diagram had ethanol and surfactant on one axis, water on another, and petrol on the third axis. A number of experiments were carried out to confirm the stability of all the compositions between the defined boundaries (which correspond to the stable microemulsion composition zone) by selecting some random compositions in between. Thus, the boundary compositions of petrol, ethanol, surfactant, water and the interior regions of composition were verified for the formation and stability of microemulsions.

Similar experiments were also carried out using ethanol obtained from sugar mills (hydrous ethanol) instead of anhydrous ethanol. In this case, fixed quantity of petrol, and surfactant was mixed in a 250 ml (air tight) sample bottle (Borosil). The resulting mixture was obviously turbid (unstable, two-phase region). Ethanol obtained from sugar mills (with different purities) was then added drop by drop with constant stirring, using a magnetic stirrer. The addition was continued till a clear transparent mixture was obtained indicating microemulsion formation. The procedure was repeated for different compositions of petrol, and surfactant.

Each microemulsion sample was kept separately in an airtight Borosil glass bottle and it was checked on everyday basis for any instability that could creep-in due to weather changes. Some of the samples were even kept in different environmental conditions to check for their stability. Use was made of an incubator to realize temperatures ranging from 0 ^oC to 40 ^oC. The microemulsions, which were stable on a particular day, did not necessarily imply that they would be stable afterwards. Some of them did become unstable (turbid) after some time, usually within days. The observed instability of microemulsions might have been due to the loss of co-surfactant (ethanol) by evaporation. Although the samples were kept in tightly closed sample bottles, the possibility of evaporation of the co-surfactant was still there. Another cause of instability of the microemulsion samples, occurring after some time, might be the change in the ambient temperature. In case a microemulsion sample turned unstable, it was stabilized using anhydrous ethanol and the composition of that particular microemulsion updated accordingly.

The results suggested that the formation of stable microemulsion started only at around 55 %v/v of ethanol. At high vol% of petrol (or low vol% of ethanol), a stable microemulsion was not obtained. The surfactant was quite effective in obtaining a stable microemulsion at a low volume percentage of about 0.29 – 0.33%. Using these experiments, we were successful in mapping the stable microemulsion zone on the ternary phase diagram for different compositions of petrol, anhydrous/hydrous ethanol, surfactant, and water.