Hi everyone. I am having a problem that hopefully someone here can help me with. For the purposes of flash calculations, I’m trying to find the enthalpy of vaporization of a compound using the Antoine equation and Clapeyron equation. I am using heptane at 15.5597 psia as an example. For the Antoine equation in the form log10(Psat) = A-B/(Tsat+C), where Psat is in units of mmHg and Tsat is in units of °C, I have Antoine coefficients for heptane of A = 6.89385, B = 1264.37, and C = 216.636. At Psat = 15.5597 psia = 804.592 mmHg, this gives me a saturation temperature of Tsat = 100.386 °C. The Clapeyron equation for a vapor-liquid phase change is dPsat/dTsat=Δhvap/(TsatΔνvap). Rearranging yields Δhvap = (dPsat/dTsat)(Tsat•Δνvap). Using the Rackett equation and the Peng-Robinson equation of state, I have found within reasonable accuracy that Δνvap = 4.385 ft3/lb. Taking the derivative of the Antoine equation with respect to temperature yields dPsat/dTsat = BPsatln(10)/(C+Tsat)2. Thus, Δhvap = BPsatTsatΔνvapln(10)/(C+Tsat)2. Plugging everything in results in a value of Δhvap = 198.348 ft3•psi/lb, which is equivalent to 36.703 BTU/lb. The actual value of Δhvap for heptane at 15.5597 psia should be somewhere around 135 BTU/lb. I’ve looked over my method and calculations multiple times but I can’t find an error. Perhaps the Antoine equation cannot be differentiated because it uses empirical parameters? Thanks. Any help would be much appreciated.