Solid-Gas Catalysis at Controlled Water Activity
The development of nonaqueous biocatalysis in recent years has expanded the field of applications of enzymes and cells in new bioprocesses. Systems involving biocatalysts suspended in organic solvents, supercritical fluids, or gas phases have overcome numerous problems associated with the use of aqueous media such as low solubility of hydrophobic substrates, unfavorable thermodynamic equilibrium for many reactions, and thermal instability of the bio-catalyst itself. Enzymes or cells, when used in low-water systems, were found to be efficient catalysts with the level of their activity being highly dependent on the degree of hydration. However, low mass transfer efficiency between liquid and solid phases in these nonconventional multiphase systems often remains a serious limitation. This chapter aims to discuss the utility of enzymes in bioreactors containing a mixture of substrates and water vapor as these reactors are relatively unexplored in comparison to those where enzymes are placed directly in aqueous or nonaqueous solvents.
KeywordsWater Activity Saturation Pressure Thermodynamic Activity Fusarium Solani Desulfovibrio Desulfuricans
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