A prediction method of vapor pressures for pure substances

Abstract

From the viewpoint of engineering, a new prediction method of vapor pressures was proposed by directly determining the coefficients of the vapor pressure equation from a boiling point, or a single point vapor pressure data (Ohe, 2019). The proposed method was applied for various kinds of organic substances with satisfactory accuracy. It has the potential to be applied for inorganic substances, since it has no limitation for predicting vapor pressures. In this paper, the method is applied to thirty-seven inorganic substances: rare-earth elements, general inorganic substances, isotopes, and the whole average error is 5.04% with satisfactory accuracy. When predicting, the temperature range of the predicted vapor pressure and the reference vapor pressure must be in agreement with each other. The reason is that even for the same substance, the coefficients of the vapor pressure equation differ when the temperature range is different, resulting in greater error. The Clausius-Clapeyron and the Antoine equations were selected as the vapor pressure ones. Various vapor pressure equations have been proposed, but since the method uses a slope in the straight line of the logarithmic value of the vapor pressure against the reciprocal of the absolute temperature, other equations cannot be used. Furthermore, the Wagner equation requires a critical constant and cannot be used to estimate substances that have only boiling point data. However, if the temperature range is not wide, the Antoine equation can be calculated with the same accuracy as the Wagner equation.