CO hydrogenation combined with water-gas-shift reaction for synthetic natural gas production: a thermodynamic and experimental study.

The hydrogenation of CO to synthetic natural gas (SNG) needs a high molar ratio of H₂/CO (usually large than 3.0 in industry), which consumes a large abundant of hydrogen. The reverse dry reforming reaction (RDR, 2H₂ + 2CO ↔ CH₄ + CO₂), combining CO methanation with water-gas-shift reaction, can significantly decrease the H₂/CO molar ratio to 1 for SNG production. A detailed thermodynamic analysis of RDR reaction was carried out based on the Gibbs free energy minimization method. The effect of temperature, pressure, H₂/CO ratio and the addition of H₂O, CH₄, CO₂, O₂ and C₂H₄ into the feed gas on CO conversion, CH₄ and CO₂ selectivity, as well as CH₄ and carbon yield, are discussed. Experimental results obtained on homemade impregnated Ni/Al₂O₃ catalyst are compared with the calculations. The results demonstrate that low temperature (200-500 °C), high pressure (1-5 MPa) and high H₂/CO ratio (at least 1) promote CO conversion and CH₄ selectivity and decrease carbon yield. Steam and CO₂ in the feed gas decrease the CH₄ selectivity and carbon yield, and enhance the CO₂ content. Extra CH₄ elevates the CH₄ content in the products, but leads to more carbon formation at high temperatures. O₂ significantly decreases the CH₄ selectivity and C₂H₄ results in the generation of carbon. [ABSTRACT FROM AUTHOR]