Kinetics and thermodynamics of 2-propanol dehydration in supercritical water

Abstract

Kinetics and thermodynamics of 2-propanol dehydration in supercritical water (SCW) and the effect of density on this reaction have been investigated in a batch reactor. The studies were performed at water densities between 0.24 and 0.58 g/cm 3 and temperatures between 654 and 686 K. The main reaction products of 2-propanol dehydration were propene and water. Rate of the reaction was found to depend essentially on the water density. Two models are used to predict the effect of SCW density on the rate constant of 2-propanol dehydration reaction: a thermodynamic model (the model of activated complex) and a model of acid-catalyzed reaction. Redlich–Kwong–Soave equation of state was used for calculation of the partial molar volumes of the reaction participants in SCW including a transition state and activation volume of the reaction. Application of the activated complex model demonstrated that the calculated values of the activation volume depend strongly on pressure at fixed temperature, which contradicts the experimental data where the activation volume is independent of pressure. At the same time, the mechanism of 2-propanol dehydration reaction in SCW was shown to correlate well with the acid-catalyzed mechanism in solutions. Rate of the reaction is directly proportional to the concentration of 2-propanol and H 3O + ions. An increase in the H 3O + concentration in SCW with density correlates unequivocally with an increase in the reaction rate.