Continuous pilot plant-scale immobilization of yeast in κ-carrageenan gel beads

A novel continuous two‐phase dispersion process was developed to produce κ‐carrageenan gel microspheres, using static mixers. It was shown that yeast‐loaded carrageenan beads, with controlled diameter and tight size distribution, can be produced on a continuous basis, in a scalable mixer, at production rates appropriate to both pilot plant–scale and, potentially, industrial‐scale operations. Immobilized yeast are intended to be used in continuous brewing operations. The effects of the static mixer diameter (D), the number of mixing elements (Ne), the fluid linear velocity (V), and the volumetric fraction (ϵ) of κ‐carrageenan, on the mean diameter and size distribution of the resulting gel microspheres, were studied. Image analysis showed that mean diameter was strongly influenced by the average linear fluid velocity through the mixer, and by the mixer diameter. The number of mixer elements and the mixer diameter governed bead size dispersion. A productivity of 10 L h−1 of beads was attained using a 1.27‐cm‐diameter static mixer. Because the productivity is proportional to the mixer diameter squared, this process, although suited for the production of small‐size beads (down to 50 μm), would be technically and economically feasible for a large industrial immobilization process. However, because the coefficient of variability increased with mixer diameter, and thus with scale‐up, operational improvements are suggested, such as the use of smaller‐diameter mixers operating in parallel, to reduce the size dispersion. © 2004 American Institute of Chemical Engineers AIChE J, 50: 1599–1605, 2004