| Chlorine is one of the most widely used materials for the chemical process industries. Often chlorine is used to perform some useful chemistry in a process, but is not part of the desired product molecule, and a large amount of waste hydrogen chloride is generated. Often, as with fluorocarbon manufacture, waste HCl is an anhydrous gas. Because considerable energy was first used to manufacture dry chlorine from brine, disposal of dry HCl as an aqueous solution is particularly wasteful.; Our research concerns the development and understanding of recently developed technology to recover chlorine from waste anhydrous HCl. Our approach to understanding and optimizing the process is through mathematical modeling of the phenomena governing cell operation, and through construction and evaluation of lab-scale processes. In an electrochemical membrane reactor with a design similar to a proton-exchange-membrane fuel cell (PEMFC), dry HCl is oxidized at the anode, where chlorine evolves. Hydrogen is evolved at the cathode. The electrolyte and separator is a solid polymer proton-exchange membrane. This permits the direct use of anhydrous HCl, without first dissolving it in water, and allows the production of drier chlorine than aqueous electrolysis.; Because the membrane requires water to maintain conductivity and the anodic side of the membrane is normally dry, the cathodic side of the membrane is exposed to liquid water. Water management in the process is crucial. It directly influences design issues such as the power required, the limiting current, the dryness of the chlorine product, and conversion. We have determined cell performance and the composition of the chlorine product as a function of temperature, pressure, conversion, and cell potential. A model for the two-dimensional gas-phase mass transport through a porous electrode from a ribbed flow field to a planar electrode was also developed. |
