GAS-PHASE FORMATION OF HYDROGEN-CHLORIDE BY THERMAL CHLORINE STEAM REACTION

Electrolysis of HCl solution to form H-2 and Cl2 is of interest in applications such as utility load leveling, solar energy storage and commercial hydrogen production. In the latter case, the chlorine generated must be reconverted to HCl for continued use in the process. The gas phase reaction of steam with chlorine to form hydrogen chloride plus oxygen was investigated for this purpose. Flowing systems with 2, 4 and 8 cm3 min-1 of chlorine and 25 cm3 min-1 of steam were studied from 563 to 873 K. The reactant/product mixture was quenched in 50 cm3 of water at 298 K. The yield of HCl was determined by acid/base titration. After removal of HCl and residual chlorine using alkaline KI solution, oxygen was measured by use of a gas burette. The HCl and O2 analyses were in agreement. Using a Cl2/H2O mole ratio of 4/25, conversion of chlorine was 24.4% at 563 K, 39.7% at 648 K, 53.1% at 773 K and 80.0% at 873 K. Strong photolysis at 563 and 648 K had no observed effect on the product yields. The experimentally determined DELTA-H value from plots of log(K(p)) vs 1/T is in good agreement with the DELTA-H value determined from standard thermochemical tables, for the reaction between chlorine and steam.