New low-carbon method for making H2 from waste streams: H2 Generation from H2S and H2O

R.J. Gillis, W.H. Green
Massachusetts Institute of Technology,
United States

Keywords: hydrogen, hydrogen sulfide, emission reduction


During the current commercial hydrocarbon desulfurization process, H2 is consumed to convert sulfur entrained within the hydrocarbon into toxic H2S. The H2S is then converted into S8 by the Claus process and eventually is oxidized into SO2 on the way to making high-volume products such as sulfuric acid and fertilizers. The H2 spent in this desulfurization is created almost entirely from fossil fuels with significant associated CO2 emissions. Alternative H2 production and sulfur processing methods have the potential to significantly lower the environmental impact of a variety of chemical industries. We have discovered a series of reactions that allows the creation of H2 from H2S and H2O, and are developing processes to harness this discovery to generate value and reduce CO2 emissions. With H2S as the primary reactant and H2 as the primary product, this technology is particularly applicable in refinery settings where H2 is consumed and H2S is generated during hydrodesulfurization. The proposed process centers on the alternating creation of HI and then its decomposition to release H2. The impetus for the development of this technology was the fortuitous discovery of the reaction of H2S, H2O, and I2 to form HI and SO2. This reaction coupled with the catalytic decomposition of HI, a well-studied reaction, accomplishes an overall reaction which converts each H2S molecule into 3 H2 molecules. Overall Reaction H2S + 2H2O → 3H2 + SO2 Step-by-Step Mechanism H2S + 2 H2O + 3 I2 → 6 HI + SO2 6 HI → 3 H2 + 3 I2 This work is divided into three sections. First, the circumstances surrounding the discovery of the H2 generating chemistry are shared along with the experimental observations that confirmed the new reaction. Next, the implications of this discovery are explored in analyses both technical and economic. Process modeling investigates the potential of this H2S processing and H2 producing alternative to the Claus process, while levelized cost analyses estimate the break-even carbon taxes where the proposed process would match hydrogen production costs through the current commercial approach , steam methane reforming. Finally, the anticipated path toward commercialization of the new technology is explored.