Measurements of Vapor Pressure of a Series of Edible Oils

Abstract

The vapor pressure of a series of edible oils (soybean oil, rape seed oil, cotton-seed oil, safflower oil, rice wax and sesami oil) were measured in a range of 250 to 330°C using an assembly of U-tube mercury manometer and vacuum pump. The application of the Riedel's type equation to the results was tried to obtain relationship between the vapor pressure and the temperature. The results obtaind could be summarized, as follows: (1) The vapor pressure increased with increasing temperature. For soybean oil, rape seed oil, cotton-seed oil and rice wax they showed sigmoid curves which had a inflection point at about 290°C. As to sesami oil the curve had the constant value in a range from 280 to 300°C. Only in safflower oil the curve showed simple exponential type. (2) Generally, vapor pressure was estimated from the integral of the Clausius-Clapeyron's equation assuming constant evaporation heat. Such equation could not express on these simoid type curves. Thus the Riedel's type equation with 4 parameters was introduced. As the results, the data of each oil could be ftted to the equation by the leasts squares method as follows: ln Pvp=A+B·T^-1+C·ln T+D·T⁶ The results agreed well with the experimental results whoce standard deviations were in the range of 0.3026-0.9043kPa. The latent heat of evaporakion could be estimated from the Eqation.