Heterogeneous SCFs reactions

Our research program is thus aimed at gaining a fundamental understanding of the behavior of heterogeneous catalytic reactions at SCF conditions based on phase and reaction equilibria considerations as well as kinetic and mass-transfer rate considerations. Such an understanding is essential to the rational design of SCF reaction schemes. 

Tiltscher, Wolf, and Schelchshorn (1984) describe the influence of an SCF reaction medium on the activity of a heterogeneous catalyst used in a... 

Heterogeneously catalyzed reactions in SCFs must, by definition, involved at least two separate phases, the reaction mixture and the solid catalyst, and frequently may contain more. There has been considerable argument as to whether a singlephase reaction mixture is needed to exploit the advantages of a supercritical fluid, but these arguments really lie out of the scope of this chapter [25]. Suffice it to say... 

This chapter reviews the field of heterogeneous catalytic reactions in SCFs [5-8]. By exploiting the unique solvent properties of SCFs, it may be possible to enhance reaction rates while maintaining or improving selectivity. The following benefits can be expected. 

Heterogeneous enzymatic reactions in liquids are often limited by diffusion rates, but there are usually no diffusion limitations in SCFs. Consequently, many enzymatic reactions are considerably faster in SCFs than in liquids. 

The global reaction rates for heterogeneously catalysed reactions comprise several elementary processes such as diffusion, adsorption/desorption and surface reaction. Thus, the situation becomes more complex, as described above. Due to mass transfer and phase boundaries, the overall reaction rate is completely different from the intrinsic reaction rate on active sites on the catalyst surface. The residence time behaviour in a reactor under SCF conditions has to be considered (for modelling in SCCO2 and SCH2O, see Refs. 32, 33). Supercritical fluids have the potential to affect some of these elementary steps, in particular mass transfer and... 

This invention describes the oxidation of olefins to the corresponding glycols by reaction over a heterogeneous catalyst in an SCF reaction mixture. 

SCFs offer several benefits in heterogeneous catalysis. They can act as a vehicle to improve transport in catalysts by reducing capillary condensation and pore plugging(2Q). SCFs have been used to accelerate gas-solid reactions by... 

In order to study the effect of SCF operating conditions on reaction equilibrium and kinetics, an experimental facility has recently been completed and successfully tested as described in the following section. The heterogeneous catalytic isomerization of 1-hexene over Pt/ y-Al20o catalyst is chosen as the model reaction system i.e., a reaction system that undergoes simultaneous deactivation by coking. 

This phenomenon can be explained from two aspects one from the actual course and specialty of a heterogeneous electro-organic reaction, and the other from special physico-chemical properties of SCFs. The effect of pressure on the solubility of benzaldehyde and benzyl alcohol in SC CO2 is shown Figure 16. Tlie significant effect of pressure on the solubility is one ofthe reasons for tlie variation of FE and selectivity ofbenzaldehyde. When the solubility of benzaldehyde in SC CO2 increased dramatically, more benzaldehyde produced enters SC CO2 phase, and thus the FE and selectivity ofbenzaldehyde were enhanced. When the pressure reached a certain value, the solubility of benzyl alcohol (the reactant) in SC CO2 also increased considerably, which is not favorable to producing benzaldehyde. When the pressure is lower than 9.3 MPa, the first factor is dominant and thus the FE and selectivity ofbenzaldehyde increased with pressure. However, as pressure was larger than about 9.3 MPa, the second factor became dominant. Therefore a maximum value in FE or selectivity occurred. 

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