New Equation of State for Ethylene Covering the Fluid Region for Temperatures From the Melting Line to 450 K at Pressures up to 300 MPa

Abstract

This work reviews the available data on thermodynamic properties of ethylene and presents a new equation of state in the form of a fundamental equation explicit in the Helmholtz energy. The functional form of the residual part of the Helmholtz energy was developed by using state-of-the-art linear optimization strategies. The new equation of state contains 35 coefficients which were fitted to selected data of the following properties: (a) thermal properties of the single phase (pρT) and (b) of the liquid–vapor saturation curve (ps,ρ′,ρ″) including the Maxwell criterion, (c) speed of sound w of the single-phase region and the saturated vapor and liquid, (d) isochoric heat capacity cv, (e) specific isobaric heat capacity cp of the single-phase region and of the saturated liquid, and (f) second and third thermal virial coefficients B and C. For the density, the estimated uncertainty of the new equation of state is less than ±0.02% for pressures up to 12 MPa and temperatures up to 340 K with the exception of the critical region. Outside the range mentioned above, the estimated uncertainty is less than ±0.03% for pressures up to 30 MPa and temperatures between 235 and 350 K. The new formulation shows reasonable extrapolation behavior up to very high pressures and temperatures. Independent equations for the vapor pressure, for the pressure on the sublimation and melting curve, and for the saturated-liquid and saturated-vapor densities are also included. Tables for the thermodynamic properties of ethylene from 104 to 450 K for pressures up to 300 MPa are given in the appendix.