Gibbs Reactor equilibrium calculations

[Stephan]

I try to follow the equilibrium calculations within COFE and Gibbs reactor for steam reformation.

CH4+H2O->CO+3H2
p=1.9 bar = 1.9*10^5 Pa
T=923K
x(H2O)=0.75
x(CH4)=0.25

I took simulated equilibrium mole fractions (x) from COFE simulation results, multiplied them with the fugacity coefficients (f) from COFE simulation results and calculated equilibirum constant Kx from those values.
Kx=(x(H2)*f(H2))^3*x(CO)*f(CO)/(x(H2O)*f(H2O)*x(CH4)*f(CH4))

Now I tried to optain the same Kx value via Gibbs energy.

For each component I took enthalpyF and entropyF from COFE simualtion results.
(enthalpyF seems to be enthalpy of formation at standard conditions + enthalpy delta at reaction conditions, same for entropy)
From those values I calculated reaction enthalpy and reaction entropy.
From those I obtained Gibbs energy Gr = Hr-T*Sr
From Gr I got K+=e^(-Gr/)(R*T)
From K+ I obtained Kx by: Kx=K+*(101325Pa/p Simulation)^2

However, Kx values calculated both ways do not match.
Kx calculated from component concentrations is 1,15
Kx calculated from Gibbs energy is 0,32.

Did I miss anything here?

[jasper]

I am unable to rework your numbers. You took pure compounds heat of formation and abs entropy? These are at reference conditions - in this case you miss the Cp contributions.

[Stephan]

I am unable to rework your numbers. You took pure compounds heat of formation and abs entropy? These are at reference conditions - in this case you miss the Cp contributions.

I reworked the post.

[jasper]

Taking the pure compound entropy and enthalpy contributions (at proper T,P, for composition of 1?) you still miss out on the excess terms.

[jasper]

Perhaps use the partial molar enthalpies (at proper T,P,X) and entropies instread? These are equal to the mole number derivatives, or enthalpyF.Dmoles and entropyF.Dmoles (available from the calculator).

[Stephan]

Does the Gibbs reactor use enthalpyF.Dmoles and entropyF.Dmoles?
Do those include the excess terms?

[jasper]

No - it uses mixture enthalpyF and entropyF and mimimizes Gibbs energy based on that (at constant T&P; at constant P&H it maximizes EntropyF, both multiplied by total flow to give J/s or J/K/s units) using a directional search (which yes, requires enthalpyF.Dmoles and entropyF.Dmoles). Yes - those include excess terms.