Reaction rate implication in supercritical solvents

Reactions in supercritical media utilize high pressures. Therefore, the effect of pressure on reaction equilibrium as well as reaction rate plays an important role in supercritical phase 

The kinetics of the reaction can be explained in terms of the transition-state theory. According to the theory, the reaction occurs via a transition state species M and the generic elementary reaction can be written as  

K X mole fraction based equilibrium constant fw reaction involving reactants and transition 

AV activation volume (difference between partial molar volumes of activated complex and 

The rate constant in die above equation is expressed in terms of pressure independent units (mole fraction). If the rate constant is expressed in terms of pressiue dependent units (such as concentration), the relevant equation is  

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Heterogeneous catalytic reactions in supercritical solvents Obviously, a solid catalyzed reaction takes place only on the active sites of the porous catalyst with the implication of some mass and heat transport steps prior to and after the reaction. The first step is the diffusion of the reactants through the film surrounding the catalyst particle to the external surface of the catalyst, followed by diffusion of the reactants into the catalyst pore to the active site in the pores. These steps are limited by the dif-fusivity and viscosity of the reactants. In the case of a supercritical fluid phase reaction, the diffusivity is higher than the liquid diffusivity, viscosity is less than the liquid viscosity and therefore, the rate of transfer to the active site will be higher. After the adsorption, reaction and desorption steps, the products have to diffuse out of the pore, and again... 

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