Scale and causes of catalyst activity loss in enzymatic catalyzed reactive distillation

Continuous enzymatic catalyzed reactive distillation (eRD) is a new process that can reduce product inhibition and the need for additional purification steps. However, the enzymatic catalyst is exposed to markedly different conditions than in conventional processes. The enzyme stability, a crucial cost factor, has not been investigated for the application in an eRD and the underlying mechanisms for catalyst deactivation are still unknown. This article presents for the first time a comprehensive study on the scale and causes of enzyme activity reduction in eRD processes. Pilot plant experiments with the transesterification of butyl acetate with hexanol catalyzed by Novozyme 435 confirm the existence of a process window with high reaction rates and low activity loss. The remaining activity after 320 h of operation is investigated in each reactive packing, leading to a new found cause of activity reduction that has so far not been considered for enzymatic catalyzed reactive distillation. The results allow for a better design and operation of eRD processes and the development of enzyme immobilisates that cater to the specific needs of integrated operation.