In situ monitoring of sulfuric acid decomposition by Fourier Transform Infrared (FT-IR) spectroscopy in the sulfur iodine thermochemical reaction for the production of hydrogen

A potential way to produce large amounts of hydrogen for energy needs is the thermal breakdown of sulfuric acid (H₂SO₄) to oxygen, water, and sulfur dioxide (SO₂). The sulfur dioxide can then be reacted with iodide to produce hydrogen iodide and ultimately hydrogen. In order to maximize the efficiency of the process it would be ideal to make in situ measurements of SO₃, SO₂, H₂SO₄, and water in the process stream in order to maximize the efficiency of the system. Fourier transform infrared (FT-IR) spectroscopy is well suited to detection of these gas phase species as they all contain strong infrared modes in the 900 to 3000 wavenumber region, 11 to 3.3 μm. However, the reactive nature of the gases and the high temperatures at which the reactions are run, 650 to 800 °C, makes standard implementation of FT-IR in process monitoring challenging. This is because the infrared detection most be done in a stand off mode and typical window and cell materials used for infrared monitoring will break down under these extreme conditions. This paper presents modifications to typically FT-IR window materials to allow them to be more robust in the environment of interest and gasket materials that can withstand both high temperatures and the oxidative conditions. Infrared spectra of SO₂, SO₃, and H₂SO₄ at elevated temperatures obtained with our system and the quantitative results are presented.