Structured Reactors for Enzyme Immobilization: A Monolithic Stirrer Reactor for Application in Organic Media

The use of a Monolithic Stirrer Reactor (MSR) for carrying out enzyme-catalysed reactions in organic media, is presented. The MSR is a convenient tool to compare monolithic catalysts in the absence of external mass transfer limitations. Ceramic honeycomb monoliths have been functionalized with different carbonaceous and polymeric carriers to provide adsorption sites for a lipase from Candida antarctica (CALB). The enzyme-loaded monoliths were employed as stirrer blades in a monolithic stirrer reactor for the acylation of butanol with vinyl acetate in toluene. Two types of ceramic honeycombs were examined and compared; a classical cordierite honeycomb and a new high-porosity mullite advanced ceramic material (ACM), having an open pore structure on the micrometer scale. The ACM and cordierite monoliths were compared in terms of immobilization capacity, activity and stability. The results show that using the MSR, internal and external mass transfer limitations are absent, and that all of the immobilized enzyme is used effectively. The open structure of the ACM monoliths allows for a higher enzyme loading and leads to a higher activity per monolith volume compared to classical cordierite monoliths. No effect of the monolith microstructure on intrinsic enzyme activity was observed; for all carriers, 35% of the free enzyme activity is retained after immobilization. The use of monoliths as stirrer blades allows easy reuse of both the enzyme and the supports-carrier combination.