Process integration aspects for the production of fine chemicals illustrated with the biotransformation of gamma-butyrobetaine into L-carnitine

L-carnitine is a fine chemical with pharmaceutical, nutritional and animal food applications. Thus, the product purification forms an essential part of the production process. Consequently, process optimization of biotransformation and downstream processing should be done in an integral way. There are several options for the process design of the biotransformation, e.g. chemostat with cell recycling, one-stage or multistage, fed-batch. Blackman kinetics for the product formation of the biotransformation of gamma-butyrobetaine into L-camitine provided adequate modelling of the bioprocess in order to define the optimal process design with respect to productivity, downstream processing and cost. With respect to these criteria, the fed-batch biotransformation of gamma-butyrobetaine into L-carnitine appeared to be superior over several modes of operation of the continuous process with cell recycling. A lower productivity of the fed-batch process was compensated by a disproportionally cheaper downstream processing or a lower investment cost. Furthermore, process integration considerations determined the choice of raw materials for the biotransformation, such as carbon and nitrogen sources, resulting in optimized or even a reduced number of unit operations of the downstream processing.