Modeling and Experimental Studies on Phase and Chemical Equilibria in High-Pressure Methanol Synthesis

A solution method was developed to calculate the simultaneous phase and chemical equilibria in high-pressure methanol synthesis (P = 20 MPa, 463 <T <553 K). Algorithms were developed that explicitly consider the existence of a condensed phase and include dew point calculations. A modification of the Soave-Redlich-Kwong equation of state was used to correct for nonideal effects. Binary interaction coefficients were derived from literature data on high-pressure binary vapor liquid equilibria. Predicted equilibrium conversions, with and without formation of a liquid phase, were successfully verified with new experimental results on high-pressure methanol synthesis obtained in a packed bed methanol synthesis reactor. Experimental data coincide very well with model predictions for the equilibrium conversion and gas composition. Remarkably, in some situations the model calculations appeared to predict condensation followed by a disappearing liquid phase (retrograde-like behavior) with increasing extent of the methanol synthesis reactions. Finally, at equilibrium only a gas phase remained present.