A novel structured bioreactor: Development of a monolithic stirrer reactor with immobilized lipase

Cordierite monoliths were functionalized with polyethylenimine (PEI) and with different types of carbon, consisting of carbonized sucrose, carbonized ployfurfurryl alcohol, or carbon nanofibers, in order to create adsorption sites for a lipase from Candida antarctica. The prepared supports were compared in terms of immobilization capacity, activity, and stability. The supports with a carbon nanofiber coating displayed the highest enzyme adsorption capacity. The biocatalysts were assayed in the acylation of 1-butanol with vinyl acetate in toluene, yielding butanyl acetate and acetaldehyde. For catalyst performance testing a novel reactor type was employed, the monolithic stirrer reactor, in which monolithic structures are applied as stirrer blades. No profound effect of stirrer rate on the reaction rate was observed, implicating the absence of external mass transfer limitations. For comparison, free enzyme and a commercial (particulate) immobilized lipase were also included in the study. Compared to the free enzyme, the immobilized lipase shows a significantly lower activity. Increased stability, easy catalyst separation and the possibility to reuse the enzyme in immobilized form can overcome this difference. The commercial immobilized lipase initially has a significantly higher activity than the monolithic biocatalysts, but deactivates relatively fast. For the monolithic biocatalysts, no deactivation was observed; the prepared catalysts were stable for several weeks.