Evaluation of a reactor model and cathode materials for batch electrolysisof L-cystine hydrochloride

A batch reactor model was used to predict the reactant concentration decay during constant current density (2000 A m(-2)) electrolysis of L-cystine hy drochloride to L-cysteine hydrochloride at a variety of cathode materials i n 2 M HCl at 298 K. A divided parallel plate reactor of 1 dm(2) projected c athode area was operated in the batch recycle mode with a catholyte volume of 2 dm(3). The effect of the average linear flow velocity of the catholyte (0.033-0.123 m s(-1)) was studied and it was found that the system could b e modelled as a batch reactor. At high reactant levels (i.e. at short times ) the rate of reduction was under charge transfer control and at low reacta nt levels (i.e. at longer times) pure mass transport control ensued. The ab ility of the model to describe the experimental data was dependent on the h ydrogen overpotential at the cathode material. A good fit was obtained at h igh hydrogen overpotential cathodes (such as mercury-plated copper and lead ) but the fit was poorer at materials having a lower hydrogen overpotential (which include titanium, carbon, tin, stainless steel, copper, nickel and molybdenum). (C) 1999 Elsevier Science S.A. All rights reserved.