Diffusion Limitation Causes Decreased Enantioselectivity of Esterification of 2-Butanol by Immobilized Candida Antarctica Lipase B

Diffusion limitation in immobilized enzyme particles may decrease the performance of kinetic resolution processes. In this paper a standard reaction plus diffusion model approach, based on homogeneous enzyme distribution, is used to verify experimentally the influence of the particle diameter on the observed enantioselectivity. This is done for a commercial preparation of immobilized Candida antarctica lipase B in the kinetic resolution of racemic 2-butanol by esterification with vinyl butyrate in heptane. For immobilized enzyme particles with particle diameters ranging from 355-710 μm the apparent enantiomeric ratio is constant at Eapp = 2.5, while for ground particles with a particle diameter of 1 um the intrinsic enantiomeric ratio is E-4.4. This clear example of the influence of diffusion limitation on the observed enantioselectivity can not be described quantitatively in a straightforward way, because the enzyme seems to be present as a layer in the carrier particles.