Opportunities for Oxidation Reactions under Supercritical Conditions

Opportunities for Oxidation Reactions under Supercritical Conditions 

Industrial liquid-phase oxidations of hydrocarbons are usually multiphase processes with a gas phase containing oxygen, and a liquid comprising feed, solvent and a catalyst at temperatures up to 300°C. Such reactions may run in usual batch reactors, bubble colunms, slurry-phase reactors or trickle-bed reactors. Limitations 

A typical heterogeneous catalyst in gas-phase oxidation operates at a higher temperature than homogeneous catalysts and this inevitably decreases selectivities for oxygenated products. An intrinsic problem in heterogeneous catalysis is the deposition of reactants, intermediates and/or products on the catalyst surface, which may lead to catalyst deactivation or selectivity problems. If the desired oxygenated products are intermediates, the residence time on the catalyst surface and adsorption effects determine product yields. 

Supercritical fluids exist beyond their critical loci (temperature, pressure and density) in pure compounds or in a multicomponent mixture. Due to their outstanding liquid- and gas-like properties, they may potentially solve some problems of catalysed liquid- or gas-phase reactions. 

When the system contains more than one chemical compound, the phase behaviour becomes more complex several critical points may exist and critical lines describe the transition from the subcritical to the supercritical region. Some authors point out that the supercritical state is not only dehned by critical temperature and pressure, but also by a minimum density. A widely accepted classihcation describes and distinguishes the phase behaviour according to the nature of the investigated mixtures.  

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