The Bunsen reaction section of IS cycle has two parts, reaction and phase separation. Some previous work focused on phase separation using a simulated reaction mixture with four components (H2SO4, HI, H2O and I-2). Based on phase separation data an operating window was suggested. This previous work had the limitation that reaction was not included. The present work includes both reaction and separation. We demonstrated that the Bunsen reaction ratio is higher than 2, and the azeotropic ratio(mol of HI/mol of HI + H2O) is higher than 0.4 at 293 K and 2 mol of I-2 in the feed. Bunsen reaction was promoted at a lower temperature and higher I-2 content, while phase separation became worse since the generated H2SO4 and HI remained in the HIx phase without separation. We validated the previously suggested optimal window and examined phase separation at the lower temperature region. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.