Study On Process Of Producing Chlorine By Direct Electrolysis Of Seawater

There are three main problems existed in the technology of direct electrolysis of seawater, including low current efficiency, high energy consumption and short service life of anode. According to these problems, this article discusses the process of producing chlorine from seawater direct electrolysis from three aspects. Firstly, study the influence of the composition and temperatures of seawater on the electrode potentials by measuring polarization curves. Secondly, discuss the influence of the composition and temperatures, the velocities of seawater and the electrode gaps on the current efficiencies and the cell potentials. Lastly, use EIS, SEM and EPMA to study the deactivation mechanism of the anodes used in the seawater electrolysis.When the current density is low, the anodic reaction is controlled by electrochemical reaction, and the polarization curves accord with the Tafel equation. When the current density is high, the anodic reaction is controlled by confusion, and the polarization curves are not accordance with the Tafel equation. The cyclic vohammetry is used to study the reversibility of the anodic reaction, it is discovered that the chlorine evolution reaction is a complete reversible reaction.The anodic electrode potentials decrease with the increasing of the CY concentration of the seawater. The existence of Ca²⁺ and Mg²⁺ has some effects on the anodic potentials. The electrode potentials decreased with the increasing of the temperature. The potential of chlorine evolution decreases with the increasing of the CY concentration and temperature.The increases of the CY, Ca²⁺ and Mg²⁺ concentration can increase the current efficiencies and decrease the cell potentials. With the decrease of the temperature, the current efficiencies increase and the cell potentials decrease. Increasing the electrode gap lead to the increase of the cell potentials and has little influence on the current efficiencies. With the increase of the velocities of seawater, the current efficiencies increase and the cell potentials decrease.The equivalent circuit model of the metal oxide anodes used in seawater electrolysis can be described as LR_s (QdlR_ct) (Q_fR_f). The L is attributed to the complex microstructure of the electrode. The (Q_dlR_ct) describes the electrochemical behavior of the electrode/solution The (Q_fR_f) is accounted for the physical impedance of the Ti-support / active oxide coating. The main reason for the deactivation of the anode is the formation of TiO₂ between Ti base and the active coating. The dissolution of the active components and the mechanical lose are not the main reasons for the deactivation of the anodes, but they accelerate the formation of TiO₂.