In iodine-sulfur (I-S) thermo-chemical process for hydrogen production, Bunsen reaction is studied to identify the role of different operating conditions on purity of Bunsen reaction product phases. The focus of this work is to find out the level of contamination in each of the Bunsen reaction product phases. Hydroiodic acid and iodine are contaminants in sulfuric acid phase and sulfuric acid is contaminant in hydroiodic acid phase. Enhancing the level of purity in two product phases will reduce the burden on purification steps in downstream of I-S process. Bunsen reaction has been studied in continuous co-current reactor made of tantalum in the range of 50-75 degrees C, 2-6 bar (g) with HIx (mixture of hydroiodic acid, water and iodine) flow rate of 0.8 I/h- 3.3 I/h, sulfur dioxide 0.06 g/s 0.24 g/s & oxygen 0.008 g/s 0.016 g/s. At 4 bar (g), 70 degrees C with HIx and SO2 flow rates of 1.8 I/h and 0.24 g/s respectively, purity of sulfuric acid phase is maximum i.e. 99.85 mol percent. At 4 bar (g), 60 degrees C with HIx and SO2 flow rates of 1.5 1/h and 0.12 g/s respectively, purity in HIx phase is maximum i.e. 99.66 mol percent. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.