Currently, millions of metric tons of H2 are consumed each year desulfurizing fuels. This H2 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 worldwide CO2 emissions in an economically favorable way. With the goal of eventually developing a replacement for the Claus process that also produces H2, we have explored the possibility of decomposing H2S through a thermochemical cycle involving I2. The thermochemical cycle under investigation leverages differences in temperature and reaction conditions to accomplish the unfavorable H2S decomposition to H2 and elemental sulfur over two reaction steps, creating and then decomposing HI. During the experimental investigation of this cycle, unexpected stoichiometry for the reaction between H2S and I2 was observed. Although anticipated to proceed according to H2S + I2 → 2HI + S, the reaction created far more HI than expected. An alternative reaction system was proposed and explored using quantum chemical methods, examining in particular the effects of solvation on the stability of each species. The proposed mechanism suggests that H2S mediates the decomposition of water as the sulfur atom is sequentially oxidized to SO2 with the protons forming HI. The mechanism is consistent with observed HI formation rates. This work is comprised of experimental observations, quantum chemical calculations, and process modeling which together support the potential of this H2S processing and H2 producing alternative to the Claus process.

H2 generation from H2S via an iodine thermochemical cycle

256th National Meeting (2018)

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