New approach for selective separation of dilute products from simulated clostridial fermentation broths using cyclodextrins

The ability of cyclodextrins (CD) to form crystalline insoluble complexes with organics was explored in this study in view of a selective separation of dilute products obtainable from three clostridial fermentation systems. To this purpose, a product or a product mixture at a concentration of 0.150 m M each were treated with α‐CD or β‐CD (0.150 m M ) in aqueous solutions as well as in a nutrient broth as a simulated fermentation medium. In the acetone‐butanol‐ethanol system, and in the butanol‐ iso ‐propanol system, α‐CD was found to precipitate selectively 48% and 46% butanol after 1 h agitation at 30°C. However, β‐CD was found to be superior for the butyric acid‐acetic acid system because it selectively precipitated 100% butyric acid under the same conditions. Cooling the three product system with α‐CD to 4°C for 24 h increased significantly the crop of precipitates but decreased the selectivity for either butanol or butyric acid. Cyclodextrins were thus shown to offer potentially a new exciting possibility for downstream processing of low‐concentration fermentation products.