Evaluation of in situ electroenzymatic regeneration of coenzyme NADH in packed bed membrane reactors -: Biosynthesis of lactate

Characterization of our electroenzymatic membrane reactors with respect to transport and reaction processes has been accomplished. Both batch and flow configurations were evaluated using the biosynthesis of lactate from pyruvate as a model system. A key feature is the in situ regeneration of the coenzyme nicotinamide adenine dinucleotide (NADH). Cyclic voltammetry was used to investigate the mechanisms present in the free solution and on porous enzyme immobilized, graphite electrodes. These results were essential for the design and evaluation of the flow-by electrode and subsequent reactor performance studies. The electrodes utilize an immobilized enzyme system [lipoamide dehydrogenase (LipDH) and methyl viologen as a mediator]within porous graphite cathodes, encapsulated by a cation exchange membrane (Nafion 124, DuPont). The free flowing fluid contains the pyruvate/lactate (and coproducts), the enzyme lactate dehydrogenase (LDH) and the coenzyme NADH/NAD(+) system. Lactate yields up to 70% were obtained when the reactor system was operated in a semibatch (i.e., recirculation)mode for 24 h, as compared to only 50% when operated in a simple batch mode for 200 h. The multipass operating scheme permits optimization studies to be conducted on system parameters. Operating regimes where either mass transfer or kinetics control the process synthesis were identified by flow perturbation studies. (C) 2004 The Electrochemical Society.