(48d) Metal Oxide Based Two-Step Solar Driven Methane Reforming and H2O/CO2 Splitting Thermochemical Cycle

Natural gas can be converted into value added products
such as syngas (a mixture of H₂ and CO) and H₂ by number
of ways such as e.g. catalytic steam reforming, dry methane reforming, or
partial oxidation. The resulting syngas might need to be augmented by addition
of H₂. Metal oxide (MO) based two-step solar thermochemical CH₄
reforming process received much attention. Instead of using a traditional
catalyst, the steam (or dry) reforming is executed in two different steps: (1)
the strongly endothermic methanothermal reduction of a MO and (2) its slightly
exothermal re-oxidation by either steam or CO₂, the latter resulting
in dry reforming of methane. Thus, the metal oxide is recycled between a high
valent and a low valent state and is not consumed during the cycle. The
methanothermal reduction of CH₄ produces syngas with a H₂/CO
ratio equal to 2.0, which is highly suitable for the production of synthetic
liquid fuels via Fischer-Tropsch process. Side reactions such as the water-gas
shift reaction is avoided as CH₄ and H₂O vapor, as
reactive gases, are used in two different reactions. The reduced MO or metals
can be either used to produce pure H₂ (re-oxidized by H₂O)
or CO (re-oxidized by CO₂). Additional syngas is obtained if the
re-oxidation is performed with a mixture of H₂O and CO₂.
Therefore, the proposed cycle allows producing syngas with a H₂/CO
ratio in the range of 1-3 (Figure 1). In this study, the solar
reforming-splitting cycle is studied thermodynamically and experimentally. The
equilibrium and solar reactor efficiency analysis for the MO based solar
reforming-splitting cycle was performed using HSC Chemistry software and its
thermodynamic database. In the experimental section, various metal oxides were
synthesized, characterized, and furthermore examined towards solar reforming
and splitting experiments using a high temperature TGA. The gases coming out
from the TGA were analyzed using GC-MS. The results obtained in the
thermodynamic and experimental investigation will be presented in detail.

Figure 1: Typical MO based solar reforming-splitting
cycle.