Deriving Full-Range Vapor Pressure Equation and Acentric Factor from Boiling Point, and Estimation of Critical Pressure

Abstract

Abstract In a vapor pressure equation in the form of the Antoine equation, A and B can be expressed as van der Waals constants. If C is defined as c by dividing it into gas constant and critical temperature, c can be expressed as a function in the form of a third-degree polynomial of reduced temperature. Using this, the vapor pressure of full-range temperature can be calculated. The c function is third-degree polynomial, but since the values are known at absolute zero and critical points, there are two required coefficients. Using the characteristics of the c function, a full-range vapor pressure equation can be derived from only one vapor pressure data such as boiling point, and acentric factor can be obtained, and critical pressure estimated. For 32 substances including 6 elements, this method was applied to estimate the full-range vapor pressure, acentric factor, and critical pressure from only the boiling point data, and the results were compared with actual data. In addition, it was applied to 16 elements to derive a full-range vapor pressure equation. Using the characteristics of local minimum point, the critical pressures of unknown elements like phosphorous, arsenic, and gold could be estimated in addition to the 21 elements whose critical pressures were previously known.