ABSTRACT
Charisma ................................................................................224 6.2.7 Phase Behavior and Solubility ..............................................225 6.2.8 Transport Properties ..............................................................225 6.3 Theoretical Aspects ...........................................................................225 6.3.1 Solubility of Solutes in ScCO2 ..............................................226 6.3.2 Reaction Equilibrium and Kinetics .......................................226 6.4 Reactions Involving ScCO2 as Reactant ............................................228 6.5 Organic Synthesis in ScCO2 ..............................................................228 6.5.1 Hydrogenation .......................................................................229 6.5.2 Hydroformylation ..................................................................234 6.5.3 Oxidation ...............................................................................237 6.5.4 C-C Bond Formation, Alkylation, Acetylation,
Esterification .........................................................................239 6.6 Process Intensification and Scale-Up Aspects ...................................241 6.7 Conclusions .......................................................................................242 Keywords ....................................................................................................243 References ...................................................................................................243
Supercritical fluids (SCFs) are characterized by gas like viscosity and solvating properties of a wide range of organic solvents. Two principal roles are played by them while participating in chemical transformations viz., to dissolve and transport reactant species to coreactants and catalyst particles and impart activation energy to the reactants via solute-solvent collisions. It has been established that the chemical reaction rates within supercritical media are enhanced resulting in reduced energy demand on the chemical process. More frequent higher energy solute-solvent collisions are stated to be responsible for enhanced reaction rates. In addition, heat transfer, micromixing phenomena and catalyst activity are promoted. Supercritical fluids as reaction media also eliminate other energy demanding auxiliary operations that are normally associated with organic solvents. Catalysis in SCF media is endowed with other advantages viz., extended catalyst life due to less coke formation, continuous rinsing of catalyst internal porous structure, switchable or tunable selectivity and safer process. All these advantages are highly relevant to industrial process development. Environmentally benign CO2 and H2O offer significant potential to replace current reliance on a range of hazardous, relatively expensive and environmentally damaging organic solvents that are used on an extensive global basis. An attempt is made in this chapter to highlight the potential applications of supercritical CO2 as sustainble alternatives to the existing technologies of important industrial catalytic processes, like hydrogenation, hydroformylation, oxidation and C-C bond formation, their theoretical aspects and reported process intensification efforts.
