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

摘要

The hydrogenation of CO to synthetic natural gas (SNG) needs a high molar ratio of H~(2)/CO (usually large than 3.0 in industry), which consumes a large abundant of hydrogen. The reverse dry reforming reaction (RDR, 2H~(2)?+?2CO???CH~(4)?+?CO~(2)), combining CO methanation with water-gas-shift reaction, can significantly decrease the H~(2)/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, H~(2)/CO ratio and the addition of H~(2)O, CH~(4), CO~(2), O~(2)and C~(2)H~(4)into the feed gas on CO conversion, CH~(4)and CO~(2)selectivity, as well as CH~(4)and carbon yield, are discussed. Experimental results obtained on homemade impregnated Ni/Al~(2)O~(3)catalyst are compared with the calculations. The results demonstrate that low temperature (200–500?°C), high pressure (1–5?MPa) and high H~(2)/CO ratio (at least 1) promote CO conversion and CH~(4)selectivity and decrease carbon yield. Steam and CO~(2)in the feed gas decrease the CH~(4)selectivity and carbon yield, and enhance the CO~(2)content. Extra CH~(4)elevates the CH~(4)content in the products, but leads to more carbon formation at high temperatures. O~(2)significantly decreases the CH~(4)selectivity and C~(2)H~(4)results in the generation of carbon.