Enzymatic Oxidation of Steroids in Organic Solvent using a STR‐Plug Flow Reactor and Continuous Product Separation

One of the first and most extensively studied biocatalytic reactions in organic solvents is the oxidation of cholesterol to cholestenone by whole cells of Nocardia rhodochrous containing cholesterol oxidase (E.C. 1.1.3.6). Merely by suspending these cells in organic solvents like tetrachloromethane, Buckland et al.' showed that 70 mg cholestenone could be produced per gram wet weight of cells per hour in a batch reactor at 16% (w/vol) cholesterol. For industrial applications continuous reactions are generally more economic than batch reactions. Continuous product separation avoids cumbersome recovery of reaction components as biocatalysts or cofactors. This study shows the production of cholestenone in a continuous reactor containing either purified cholesterol oxidase entrapped in reversed micelles or whole cells of N. rhodochrous suspended in organic solvent. Using kinetic equations, a reactor was designed allowing high conversions. To separate the product and to recycle the biocatalyst a hollow fiber membrane unit was tested.