From Screening to Scale-Up: The DoE-Based Optimization of Electrochemical Reduction of l‑Cystine at Metal Cathodes

Design of experiment (DoE) is a powerful statistical tool in establishing improved chemical processes. An optimization and scale-up of the electrochemical reduction of l-cystine to l-cysteine is presented. Subsequent to an electrode screening of 17 metals and alloys in divided batch-type cells, the lead electrode was selected for a systematic optimization in flow cells with a geometric cathodic surface area ranging from 10 to 100 cm². Using two consecutive factorial designs, parameters like substrate concentration, current density, electrode gap, amount of applied charge, and number of cell passages were screened for significant effects onto the l-cystine conversion. A multiresponse optimization combining the product conversion and Faradaic efficiency was performed to account for economic considerations.