Effects of Operating Conditions on Improving Alkali and Electrical Efficiency in Chlor-Alkali Diaphragm Cell

Abstract

The concentrated brine from seawater desalination plants is generally discharged directly to the sea. To reuse brine, diaphragm type chlor-alkali experiments were carried out to make alkaline solution and gases. For this purpose, a rectangular acrylic reactor, 66.5 g/L of sodium chloride solution, a PTFE hydrophilic filter as asbestos free diaphragm, and IrO2 coated titanium net or plate electrode were used. The experimental results show that sodium hydroxide concentration and chloride removal increased with higher current density, and had inverse linear correlations to the increasing flow rate. The theoretical maximum sodium hydroxide concentration in effluent was estimated as 4.06%. Chloride removal and electric conductivity have a linear correlation with the sodium hydroxide concentration in effluent. Hydroxyl ion production was affected by the surface area of electrode per unit volume and by diaphragm pore size. Back-migration of hydroxyl ions from the cathode to anode is the major reason for side-reactions that cause low faradaic efficiency, including oxygen production in the anode compartment. Over 99% pure hydrogen was produced in the cathode compartment, and the current efficiency of hydrogen production was calculated as 92 - 99%.