Methane dry reforming via a ceria-based redox cycle in a concentrating solar tower

Drop-in fuels produced using solar energy can provide a viable pathway towards sustainable transportation, especially for the long-haul aviation sector which is strongly dependent on jet fuel. This study reports on the experimental testing of a solar reactor using concentrated solar energy for the production of syngas, a mixture of mainly H<INF>2</INF> and CO, which serves as the precursor for the synthesis of kerosene and other liquid hydrocarbon fuels. The thermochemical conversion route is based on the dry reforming of CH<INF>4</INF>via a 2-step redox cyclic process utilizing the intermediation of non-sacrificial ceria (CeO<INF>2</INF>), comprising: (1) the endothermal reduction of CeO<INF>2-delta<INF>ox</INF></INF> with CH<INF>4</INF> to form CeO<INF>2-delta<INF>red</INF></INF> and syngas (delta denoting the non-stoichiometry); and (2) the exothermal oxidation of CeO<INF>2-delta<INF>red</INF></INF> with CO<INF>2</INF> to form CO and the oxidized state of CeO<INF>2-delta<INF>ox</INF></INF>. The solar reactor consists of a cavity-receiver lined with a reticulated porous ceramic (RPC) structure and an axial tubular section at the cavity's rear filled with a packed-bed of agglomerates, both RPC and agglomerates made of pure ceria. Testing is performed at a high-flux solar tower at conditions and scale relevant to industrial implementation. For a solar radiative power input of 10 kW (corresponding to a mean solar flux of 560 suns) at temperatures in the range 800-1000 degrees C, with reacting gas flow rates of 105 normal L min-1 and concentrations of CH<INF>4</INF> (reduction step) and CO<INF>2</INF> (oxidation step) of up to 20% in Ar, the solar-driven redox reforming process yields a peak CH<INF>4</INF> molar conversion of 70% and a peak H<INF>2</INF> selectivity of 68%. Co-feeding of CH<INF>4</INF> and CO<INF>2</INF> during the reduction step resulted in the highest solar-to-fuel energy efficiency of 27%, defined as the ratio of the higher heating value of the syngas produced over the sum of the solar radiative power input through the solar reactor's aperture and the higher heating value of CH<INF>4</INF> fed to the solar reactor. Regardless of the operational mode, the syngas product composition was similar at equal delta attained during the reduction. The addition of the tubular packed bed increased the syngas yield by 32%.