HIGH-TEMPERATURE CONVERSION OF CH4 TO C-2-HYDROCARBONS AND H-2 USING A REDOX SYSTEM OF METAL-OXIDE

A high-temperature thermochemical process using a redox system of meta l oxide is proposed for converting CH4 to C-2-hydrocarbons (C-2-HCs) a nd H-2. Reactions were performed in a two-step redox cycle. In the fir st high-temperature and endothermic step, methane is reacted with meta l oxide to produce C-2-HCs and the reduced metal oxide. The reduced me tal oxideis reoxidized with water to generate H-2 at a low temperature in the second step. A thermodynamic analysis showed that redox system s of Fe3O4/FeO, SnO2/SnO, and WO3/WO2 are promising for the two: step process. The redox system of Fe3O4 was experimentally examined. Highly selective conversion could be repeated with SiO2-supported Fe3O4 (Fe3 O4/SiO2) to produce C-2-HCs (mainly C2H4) and H-2 alternately in the d ifferent steps at temperatures from 1123 to 1173 K; evolution of COx a nd deposition of bulk carbon were scarcely observed. Experimental stud ies using unsupported Fe3O4 showed that the formation of C-2-HCs in th e first high-temperature step occurred favorably for the reduction fro m Fe3O4 to FeO in comparison to that from FeO to alpha-FeO. The two-st ep process using Fe3O4/SiO2 is superior to the production efficiencies of C-2-HCs and H-2 obtained by the direct single-step conversion of C H4; which offers the efficient conversion of natural gas utilizing hig h-temperature heat such as concentrated solar radiation.