Enhancing Low-Temperature Phase Stability of a 50/50 Methanol/Hydrocarbon Blend

Separation of roughly equal volume mixtures of methanol and gasoline into two phases at low temperature may cause problems for vehicles that are designed to operate on these mixtures. Cosolvent alcohols (C₂-C₁₂) and surfactants were evaluated as additives for enhancing phase stability at -25°C of a blend containing SO volume percent methanol, 40 percent isooctane, and 10 percent toluene (simulating a 50/50 methanol/gasoline mixture).

For alcohol cosolvents, the amount required decreased with increasing carbon number (number of carbon atoms per molecule) from about 50 percent with C₂ to about 6 percent for C₈ through C₁₂ A simple cost analysis indicated that decanol (C₁₀) provided the minimum treatment cost for preventing separation at -25°C: $0.13/galloπ. Of the various commercial nonionic surfactants and various anionic fatty acid surfactants evaluated, only palmitic acid (C₁₆) showed good effectiveness.