Cyclodextrin Purification with Hollow Fibers

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Abstract
Cyclodextrins are cyclic 1–4 linked oligomers of α-D-glucopyranose prepared from starch hydrolysis through enzymatic reactions. Mixtures of the three main cyclodextrins (CD), α-, β-, and γ-CDs, are always produced. A possible facile purification process is proposed. Permeation through hollow fibers made of a perfluorinated ionomer membrane, Nafion type, is shown to be an effective way to separate α-CD from β- and γ-CD. α-CD with 95% purity was obtained after permeation through a Nafion hollow fiber of an equimolar 0.02 M solution of the three CDs. The fiber had a 56 cm2/cm3 surface area per volume ratio. Kinetic studies and continuous extraction experiments with a 2-m coiled fiber showed that it is possible to obtain a 11.5 g/L α-CD solution with 92.4% purity or a 0.6 g/L α-CD solution with 97.2% purity, depending on the flow rate. The transport of CDs through the membrane could be due to moving water pools inside the ionomer. The small α-CD fits easily in such pools when the larger β- and γ-CDs are excluded by steric hindrance. Temperature raises increased the permeation rates while decreasing the selectivity. The process could be scaled-up associating hollow fibers in bundle.

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