Xin-Sheng Zhang

Studies on chemical activators for electrode I: Electrochemical activation of deactivating cathode for oxalic acid reduction

Electrosynthesis of glyoxylic acid by electroreduction of oxalic acid has long been well known. However, attempts to commercialize the process have encountered problems due to rapid deactivation of the cathode. The cathode activity can be continuously restored by adding small amounts of chemical activators to the catholyte. In this paper the structural effect of chemical activator on electrode reaction is studied. The results show that (1) It is the cation of the chemical activator, but not the anion that affects the current efficiency and the reaction selectivity. (2) The more symmetrical the cation, or the shorter the longest alkyl chain, the higher the current efficiency and the reaction selectivity become. (3) Mechanism of the activation is discussed. Adsorption of the cations of the activator on the cathode surface protects the electrode. (4) Quantitative characterization of the activator molecule is given using some topological indices, with which the activation ability can be predicted, and screening of the proper activator is made possible.

Optimal control of batch electrochemical reactor using K–L expansion

Abstract A control vector parameterization approach using the Karhunen–Loeve (K–L) expansion for optimal control is presented. Optimal control profiles at different initial conditions are represented by a truncated K–L expansion and the optimal control is thus transformed into a parametric optimization with the K–L coefficient(s) as the optimization variable(s). Closed-loop optimal control therefore becomes feasible because the number of optimization variables is minimized. The presented approach is demonstrated on a batch electrochemical reactor in which reduction of oxalic acid glyoxalic acid is carried out under conditions with known or unknown disturbance, or electrode deactivation. The closed-loop control with the K–L expansion outperforms the open-loop optimal control with very little computational effort.

Synthesis of cyclic carbonates from epoxides and CO2 in acetonitrile via the synergistic action of BMIMBr and electrogenerated magnesium

Using 1-butyl-3-methyl- imidazolium bromide (BMIMBr) as the supporting electrolyte and magnesium as the sacrificial anode, a new and highly efficient electrochemically catalytic route was developed for the synthesis of cyclic carbonates from epoxides and CO 2 . Based on the cooperative action of BMIMBr and an electrogenerated magnesium salt obtained under a N 2 atmosphere, CO 2 reacted with a wide range of epoxides to readily generate cyclic carbonates in moderate to excellent yields under mild conditions.

Studies on paired packed-bed electrode reactor: Modeling and experiments

Experiments are carried out in a paired packed-bed electrode reactor with the cathodic reduction of potassium ferricyanide coupled with the anodic oxidation of potassium ferrocyanide as the working system. Eight probes are used to determine the potential distribution. A two-dimensional model is developed and solved by the finite element method. Good agreement is observed between the experimental data and the model predictions for reactors of different sizes and operating conditions. The effect of the operating variables (cell voltage, electrolyte velocity, reactant inlet concentration and electrolyte conductivity) and the sizes of the electrodes on the potential and concentration distributions are investigated by simulation.

Experimental and Theoretical Studies on Preparation of Hydroquinone from Benzene in a Paired Packed-Bed Electrode Reactor

A generalised reaction-diffusion model for describing preparation hydroquinone from benzene in a paired packed-bed electrode reactor is developed. Finite element method is applied for solving the model equations. Experiments were carried out in a rectangular electrode reactor packed lead shots as cathode and porous lead plats as anode. Optimal current efficiency of benzene oxidation and benzoquinone reduction (62.5 % and 95.9 %) was obtained at operating conditions: electrolytes rate, 0.19 m/s; total current, 15 A; packed-bed thickness of anode, 10 mm; cathode , 30 mm, and benzene and benzoquinone concentrations, 24 % and 4 % respectively.