Optimal potential–time programming in electrochemical batch reactors

Abstract

In an electrochemical stirred batch reactor where a series of two reactions A harr B harr D takes place, two practical dynamic optimization problems were analysed. More specifically, the optimal profiles of electrode potential which achieve the following performances are determined: (i) maximize the final concentration of product B in a specified batch period tf and fixed final conversion rate of product A; (ii) minimize the terminal time tf required to reach a specified selectivity of B. The reaction considered here is the reduction of oxalic acid (A) to glyoxilic acid (B) followed by the reduction of glyoxilic acid to glycollic acid (D). The optimization is carried out by means of Pontryagin's maximum principle and the computational technique used is the control vector iteration method. The influence of the liquid/solid mass transfer coefficients is mainly investigated. It is shown that, for low conversion rates, the optimized and static operating modes achieve the same performances. For high conversion rates however, the performances obtained in realistic operating conditions by applying optimized electrode potential profiles, are substantially improved with respect to best static electrode potential values.