Effects of C3-C5 alcohols on solubility of alcohols/diesel blends

Alcohols with three to five carbon numbers are renewable fuels for blending with diesel fuel, but the separation and purification of the alcohols from solution by fermentation is of great economic significance. If it is possible for alcohol and diesel blending system to contain part of water, the energy can be saved during the alcohol production process. Moreover, alcohols are more hygroscopic than diesel fuel, the blends of alcohols and diesel fuel will absorb water from ambient humidity if the tank is not adequately sealed during the storage and carriage and the excessive water concentration in the blends will cause phase separation. To avoid phase separation, it is important to test the blends of alcohols and diesel for their capacity to hold water. However, little study has been undertaken to systematically investigate the maximum allowable water concentration of alcohols and diesel blends. Therefore, in the current study, different three to five carbon numbers alcohols (n-propanol, iso-propanol, n-butanol, iso-butanol, sec-butanol, tert-butanol, n-pentanol, iso-pentanol, tert-pentanol) were prepared to blend with diesel to investigate the ability to hold water in the system at different ambient temperatures. The alcohol concentration of the blend varied from 10% to 90% in 10% increments in volume. Then water was gradually titrated into the blends by a high-precision pipette until it was no more a homogeneous liquid and the free water occurred, meaning t the start of phase separation. Results showed that all tested alcohols in this study could blend with diesel at any ratio without water addition. When ambient temperature was 0 and 30 degrees C, the allowable water concentration for butanol is the maximum in the system which is the first time to find out four carbon alcohols is the inflection point to be amphiphile in ternary fuel system. Among butanol isomers, tert-butanol could hold more water resulting of its special spherical structure compared to other isomers. Furthermore, to evaluate the influence of temperature on phase solubility, four different temperatures (0, 30, 50, 70 degrees C) were chosen. For alcohols (n-propanol, iso-propanol and tert-butanol) which were miscible with water, the allowable water concentration was gradually increased as increasing temperature. But for the other alcohols tested in this study, the water concentration admitted in the system gradually decreased with temperature increased.