Simultaneous Recovery of Hydrogen and Chlorine from Industrial Waste Dilute Hydrochloric Acid

N Paidimarri,U Virendra,S Vedantam

doi:10.1155/2016/8194674

Abstract

Recovery of chlorine from byproduct HCl has inevitable commercial importance in industries lately because of insufficient purity or too low concentration to recycle it. Instead it is being neutralized in industries before disposing to meet stringent environmental conditions. Although recovery through catalytic oxidation processes is studied since the 19th century, their high operating conditions combined with sluggish reaction kinetics and low single pass conversions make electrolysis a better alternative. The present motive of this work is to develop a novel electrolysis process which in contrast to traditional processes effectively recovers both hydrogen and chlorine from dilute HCl. For this, an electrolytic cell with an Anionic Exchange Membrane has been designed which only allows the passage of chlorine anions from catholyte to anolyte separating the gasses in a single step. The catholyte can be as low as 3.59 wt% because of fixed anolyte concentration of 1.99 wt% which minimizes oxygen formation. Preliminary results show that the simultaneous recovery of hydrogen and chlorine is possible with high conversion up to 98%. The maximum current density value for 4.96 cm2membrane surface area (70% active surface area) is 2.54 kAm−2, which is comparable with reported commercial processes. This study is expected to be useful for process intensification of the same in a continuous process environment.

Highlights

Generated hydrochloric acid/hydrogen chloride is often byproduct of chlorine consuming process such as chlorination of organic compounds
Conversion put forward is the percentage of feed electrolysed and it is determined by estimating the final concentration of catholyte after the electrolysis; estimated based on titrimetry, it is to note that the conversion is the percentage of feed HCl that got electrolysed
Simultaneous recovery of chlorine and hydrogen from industrially waste hydrochloric acid has been carried out using electrolysis in an electrolytic cell as a batch process

Summary

Introduction

Generated hydrochloric acid/hydrogen chloride is often byproduct of chlorine consuming process such as chlorination of organic compounds. The byproduct HCl produced has many uses depending upon concentration; all the uses are summarized in Scheme 1. This byproduct HCl needs to be treated for trace amounts of impurities before it is put to use which increases operational costs. It is not always possible to locate use for dilute HCl produced and shipping it to over large distances is not an economically lucrative option. The option of evaporating may look as a feasible alternative for producing concentrated HCl from dilute, but with evaporation the HCl concentration cannot be increased more than a certain value because of HCl boiling point being very less in comparison to water. Through distillation high purity HCl can be recovered from water, but the major problem would be high energy demand and need to use exorbitant metals when using concentrated HCl at high temperatures

Methods

Results

Conclusion