(319h) Exploring the Potential of Ni3S2 Based Sulfur Looping Process for Efficient Production of H2 from H2s: A Thermodynamic and Kinetic Study

Hydrogen Sulfide (H₂S) is a poisonous gas that is released during processing of fossil fuels. Despite the rise in utilization of renewable-based energy sources, non-renewable hydrocarbon fuels dominate the world’s energy production scenario and are slated to do so until 2050. Thus, a high amount of H₂S generation will be continued for next couple of decades, making its treatment critical. Claus process is state-of-the-art H₂S abatement technology; however, it suffers from various issues such as unfavorable reaction thermodynamics, high capital cost and requirement of an air separation unit (ASU). Moreover, the Claus process is ineffective in extracting value from H₂S, as it converts the ‘Hydrogen’ content of H₂S into low-value steam (H₂O) instead of valuable hydrogen (H­­₂) gas. To counter this, a sulfur looping process scheme utilizing Ni₃S₂ as a sulfur carrier was established for effectively decomposing H₂S into H₂ and S. It involves two sub-steps – sulfidation and regeneration. In the sulfidation step, Ni₃S₂ reacts with H₂S forming NiS and H₂, and in the subsequent regeneration step, sulfur is recovered as NiS is thermally decomposed back into Ni₃S₂ in presence of CO₂. The sulfur looping scheme has been demonstrated at a laboratory scale fixed bed reactor, wherein ~80% H₂S conversion was achieved at a gas hourly space velocity of 5000 hr ^-1 [1].

In this work, process analysis of sulfur looping was performed, and the results were compared against Claus process to establish the commercial feasibility of the process. Parametric studies were carried out on the sulfur looping process in ASPEN to obtain the reaction and feed conditions for both the sulfidation and regeneration steps. The thermodynamic results obtained were validated using relevant thermogravimetric experiments and X-ray diffraction analysis. After the conditions were determined through the combination of process simulations and experiments, system evaluation parameters such as overall H₂S conversion, H₂ and sulfur yield were calculated for the sulfur looping process and compared against the baseline Claus process. The thermodynamic performance was further quantified by carrying out energy and exergy analysis. Results indicate that for >99% H₂S conversion, ~2.4% higher sulfur yield is obtained for the sulfur looping process with 100% selectivity towards H₂ generation (no steam formation). Moreover, a significant increase of ~19% and ~8% in overall energy and exergy efficiencies, respectively was observed for sulfur looping process due to H₂ production and requirement of fewer processing units. This work further corroborates the superior potential of the novel sulfur looping scheme to replace the existing Claus process as it overcomes its drawbacks and creates a valuable product from a toxic industrial waste. The findings from this study can be used to develop an economical and environmentally sustainable process.

[1] Jangam, Kalyani V., Anuj S. Joshi, Yu-Yen Chen, Shailaja Mahalingam, Ashin A. Sunny, and Liang-Shih Fan. "Synergistic decomposition of H₂S into H₂ by Ni₃S₂ over ZrO₂ support via a sulfur looping scheme with CO₂ enabled carrier regeneration." Chemical Engineering Journal 426 (2021): 131815.