Thermodynamic properties of the butenes: Part II. Short fundamental equations of state

Experimental measurements of density, vapor pressure, and the critical point for 1-butene, isobutene, cis-2-butene, and trans-2-butene were discussed in Part I of this work. The equations of state presented in this work were developed from these measurements and other information from the literature using a short functional form explicit in the Helmholtz energy. The functional form is based on temperature and density polynomial terms used in previous work, with both the coefficients of the equations of state and the exponents on temperature polynomial terms fitted to substance-specific data sets. Uncertainties of properties calculated using the new equations are typically 0.1% in density in the liquid phase, 0.5% in heat capacities for the saturated liquid, and 0.25–0.5% in vapor pressure. Deviations in the critical region are higher for all properties except vapor pressure. The equations are valid from the triple points of the fluids to temperatures of 525 K, with pressures to 50 MPa.