A two-step thermochemical conversion of CH₄ to CO, H₂ and C₂-hydrocarbons below 1173 K

Abstract
A high-temperature thermochernical process using a redox system of metal oxide is proposed for converting CH₄ to CO, H₂, and C₂-hydrocarbons (C₂-HCs). Reactions were performed in a two-step redox cycle. In the first high-temperature and endothermic step, methane is reacted with metal oxide to produce C₂-HCs and the reduced metal oxide : 2CH₄ + metal oxide→C₂H_n + (4-ⁿ/₂)H₂O + reduced metal oxide. In the second step, H₂O or CO₂ is reacted with the reduced metal oxide to generate H₂ or CO at lower temperatures : H₂O + reduced metal oxide→H₂ + metal oxide. CO₂ + reduced metal oxide→CO + metal oxide. The net rations are 2CH₄→C₂H_n + (4-ⁿ/₂)H₂, and 2CH₄ + (4-ⁿ/₂)CO₂→C₂H_n + (4-ⁿ/₂)(CO + H₂O). A thermodynamic analysis showed that redox systems of Fe₃O₄/FeO, SnO₂/SnO and WO₃/WO₂ are promising for the two-step process. The redox system of Fe₃O₄ was experimentally examined. Methane was selectively converted to C₂-HCs, H₂, and CO by the two-step process using the SiO₂-supported Fe₃O₄ (Fe₃O₄/SiO₂) in the temperature range from 1123 to 1173 K. It was found that the high-temperature methane decomposition to bulk carbon was efficiently suppressed over Fe₃O₄/SiO₂. This process offers the efficient endothermic net reaction for converting natural gas to C₂H₄, H₂, and CO with upgraded calorific values, utilizing concentrated solar radiation as the energy source of high-temperature process heat below 1173 K.