Abstract
Thermochemical methane reforming to syngas is performed on a massive scale in the chemical industry, providing feedstock for many chemical processes such as hydrogen, ammonia and methanol production. The high temperature process heat required for the endothermic reforming reaction could be supplied by conentrated solar energy, in a hybrid solar-fossil process. This can be achieved by re-designing conventional reforming technologies to utilize solar energy as the heat source. Another possible approach is to use a two-step metal oxide redox cycle. Here we compare the two solar thermochemical reforming routes, namely redox reforming and catalytic reforming using thermodynamic analysis and discuss the prospects for both technologies with a focus on methane conversion extents, syngas composition, and energy conversion efficiencies. Further processing of the syngas to liquid fuels is also discussed, in order to highlight how these processes can fit together with gas-to-liquids technologies. The analysis highlights that the redox cycle approach could produce a higher quality syngas, but at the expense of additional thermodynamic constraints, which are sensitive to carbon formation, and also lead to a greater energy demand relative to catalytic reforming.
Highlights
Direct methane reforming is described by the endothermic reactions, CH4 + H2O→CO + 3H2Δh◦1173 K = 218 [kJ mol− 1] (1)CH4 + CO2→2CO + 2H2Δh◦1173 K = 259 [kJ mol− 1] (2)known as wet and dry reforming respectively
The analysis highlights that the redox cycle approach could produce a higher quality syngas, but at the expense of additional thermodynamic constraints, which are sensitive to carbon formation, and lead to a greater energy demand relative to catalytic reforming
In this work we present a thermodynamic analysis of direct solar catalytic reforming and redox reforming with the metal oxides CeO2, Fe3O4, FeO, and ZnO, focusing on the methane conversion extent, as well as on the syngas composition and its suitability for further gas to liquid processes
Summary
Direct methane reforming is described by the endothermic reactions, CH4 + H2O→CO + 3H2. On the other hand, combined dry and wet (mixed) reforming with a controlled content of CO2 in the feedstock can be used to adjust the syngas composition, which has been used for methanol production (Bartholomew and Farrauto, 2011; Rostrup-Nielsen et al, 2002) This has been implemented on an indus trial scale at a gas-to-liquids (GTL) plant, where the CO2 required was available from a near-by ammonia synthesis plant (Holm-Larsen, 2001). In this work we present a thermodynamic analysis of direct solar catalytic reforming and redox reforming with the metal oxides CeO2, Fe3O4, FeO, and ZnO, focusing on the methane conversion extent, as well as on the syngas composition and its suitability for further gas to liquid processes. More suitable for a fixed bed isothermal system, which is practically feasible and commonly applied in the chemical industry
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