Minireview: direct catalytic conversion of sour natural gas (CH4 + H2S + CO2) components to high value chemicals and fuels

Abstract

The abundance of natural gas reserves can facilitate the transition from fossil derived to fully renewable chemical and fuel generation. Natural gas, however, can contain more than 10% sour gas molecules (chiefly CO₂ and H₂S), especially in the Middle East and Russia. Currently, the most common sour natural gas separation technologies rely on the use of various amine-based absorption–desorption cycles in absorption towers, membrane separation and cryogenic processes. However, these processes are quite expensive and, unfortunately, result in the necessity for further processing of the sour gas stream. We feel that the implementation of catalytic activation of the sour gas stream, so as to form useful products, has been underexplored and thus has yet to be fully developed. In this paper, we present a series of catalytic reactions for the sour gas components so as to obtain useful chemicals or fuels, such as carbon disulfide (CS₂), hydrogen (H₂), ethylene (C₂H₄), ammonium sulfate ((NH₄)₂SO₄) and ammonium thiosulfate ((NH₄)₂S₂O₃). Particular catalytic reactions which can form those products are (a) CH₄ reforming with H₂S on supported metal oxide catalysts, (b) CO₂ + H₂S + H₂ catalytic reaction on K₂O/WO₃/Al₂O₃ to yield a CH₃SH intermediate, (c) olefin production via CH₃SH coupling on zeolites and supported metal oxides and (d) H₂S + NH₃ catalytic reaction to yield ammonium sulfate ((NH₄)₂SO₄) and ammonium thiosulfate ((NH₄)₂S₂O₃) on partial oxidation catalysts. Thermodynamic considerations, together with catalyst design techniques, are discussed for each reaction.