SOLARJET demonstrates full process for thermochemical production of renewable jet fuel from H2O & CO2

28 April 2015

The European consortium SOLARJET (Solar chemical reactor demonstration and Optimization for Long-term Availability of Renewable JET fuel) (earlier post) has experimentally demonstrated the entire process chain for the first production of renewable jet fuel via a thermochemical H₂O/CO₂-splitting cycle using simulated concentrated solar radiation.

The solar-to-fuel energy conversion efficiency was 1.72%, without sensible heat recovery. A total of 291 stable redox cycles were performed, yielding 700 standard liters of syngas of composition 33.7% H₂, 19.2% CO, 30.5% CO₂, 0.06% O₂, 0.09% CH₄, and 16.5% Ar, which was compressed to 150 bar and further processed via Fischer–Tropsch synthesis to a mixture of naphtha, gasoil, and kerosene. Their paper is published in the ACS journal Energy & Fuels.

(a) Schematic of the experimental setup, featuring the main system components of the production chain to solar kerosene from H2O and CO2 via the ceria-based thermochemical redox cycle. (b) Schematic of the solar reactor configuration. The cavity-receiver contains a reticulated porous ceramic (RPC) structure, made from ceria, with dual-scale porosity in the millimeter- and micrometer-scale. Credit: ACS, Marxer et al.Click to enlarge.

Earlier work had identified that the thermochemical splitting of CO₂ and H₂O via two-step metal oxide redox reactions, driven by concentrated solar energy, was a thermodynamically favorable path for producing syngas because it inherently operates at high temperatures and utilizes the entire solar spectrum. The syngas can be further processed via Fischer−Tropsch (FT) synthesis to conventional liquid hydrocarbon fuels.

Among a variety of redox-active metal oxides, non-stoichiometric cerium oxide (ceria) offers fast kinetics and crystallographic stability.

The team had earlier produced in separate experimental solar runs H₂O, CO from CO₂, and syngas by simultaneously splitting a mixture of H₂O and CO₂.

To maximize efficient heat transfer of concentrated solar radiation and rapid chemical kinetics for the the two-step thermochemical cycle, the team engineered a new reticulated porous ceramic (RPC) structure made of pure ceria with dual-scale porosity in the millimeter and micrometer ranges.

The large-scale pores enabled volumetric absorption of incoming radiation whereas the smaller pores in the struts increased the specific surface area, enhancing the surface- limited fuel production rates. This dual-scale RPC delivered up to 10 times higher oxidation rates than those obtained for a single-scale RPC (with nonporous struts).

In the study reported in Energy & Fuels, the SOLARJET team examined the performance of a 4 kW solar cavity-type reactor containing the dual-scale RPC. They optimized the duration of the reduction and oxidation steps to maximize the solar-to-fuel energy conversion efficiency. They also studied fuel yield and composition during CO₂-splitting and simultaneous H₂O/CO₂-splitting.

… to the best of our knowledge, this was the first experimental coupling of solar syngas production from H₂O and CO₂ with the storage, compression, and FT-processing to liquid hydrocarbons. FT-processed kerosene, derived from H₂O and CO₂, can be certified for commercial aviation by minor addendum to the existing D7566 specification for synthesized hydrocarbons.

—Marxer et al.

Resources

• Daniel Marxer, Philipp Furler, Jonathan Scheffe, Hans Geerlings, Christoph Falter, Valentin Batteiger, Andreas Sizmann, and Aldo Steinfeld (2015) “Demonstration of the Entire Production Chain to Renewable Kerosene via Solar Thermochemical Splitting of H₂O and CO₂” Energy & Fuels doi: 10.1021/acs.energyfuels.5b00351