Metallurgical and Materials Transactions B

, Volume 42, Issue 1, pp 254–260 | Cite as

Solar Aluminum Production by Vacuum Carbothermal Reduction of Alumina—Thermodynamic and Experimental Analyses

  • M. Kruesi
  • M. E. Galvez
  • M. Halmann
  • A. SteinfeldEmail author


Thermochemical equilibrium calculations indicate the possibility of significantly lowering the onset temperature of aluminum vapor formation via carbothermal reduction of Al2O3 by decreasing the total pressure, enabling its vacuum distillation while bypassing the formation of undesired by-products Al2O, Al4C3, and Al-oxycarbides. Furthermore, the use of concentrated solar energy as the source of high-temperature process heat offers considerable energy savings and reduced concomitant CO2 emissions. When the reducing agent is derived from a biomass source, the solar-driven carbothermal reduction is CO2 neutral. Exploratory experimental runs using a solar reactor were carried out at temperatures in the range 1300 K to 2000 K (1027 °C to 1727 °C) and with total pressures in the range 3.5 to 12 millibar, with reactants Al2O3 and biocharcoal directly exposed to simulated high-flux solar irradiation, yielding up to 19 pct Al by the condensation of product gases, accompanied by the formation of Al4C3 and Al4O4C within the crucible. Based on the measured CO generation, integrated over the duration of the experimental run, the reaction extent reached 55 pct at 2000 K (1727 °C).


Carbothermal Reduction Exergy Efficiency Reaction Extent Solar Reactor Sample Surface Temperature 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.







Stefan–Boltzmann constant (5.6705 × 10−8 W/m2K4)


heat capacity (J/kg K)


thickness (mm)


thermal conductivity (W/m K)


mass (kg)

\( \dot{q}_{\text{solar}} \)

solar radiative flux (W/m2)


time (s)


temperature (K)




water–gas shift


enthalpy change (kJ/mol)


Gibbs free energy change (kJ/mol)



The authors thank V. Gianini, P. Haueter, L. Schlumpf, and A. Frei for technical support with the reactor design and during the solar experimental campaign.


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Authors and Affiliations

  • M. Kruesi
    • 1
  • M. E. Galvez
    • 2
  • M. Halmann
    • 3
  • A. Steinfeld
    • 1
    • 4
    Email author
  1. 1.Department of Mechanical and Process EngineeringETH ZurichZurichSwitzerland
  2. 2.Instituto de CarboquimicaMiguel Luesma CastanZaragozaSpain
  3. 3.Department of Environmental Sciences and Energy ResearchWeizmann Institute of ScienceRehovotIsrael
  4. 4.Solar Technology LaboratoryPaul Scherrer InstituteVilligenSwitzerland

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