Vacuum Carbothermic Reduction of Al₂O₃, BeO, MgO-CaO, TiO₂, ZrO₂, HfO₂ + ZrO₂, SiO₂, SiO₂ + Fe₂O₃, and GeO₂ to the Metals. A Thermodynamic Study

Abstract

Thermochemical equilibrium calculations are carried out to elucidate improved conditions for the production of Al, Si, FeSi, Ti, Mg, Hf, Zr, Be, and Ge by the high-temperature carbothermic reduction of their oxides, and for the production of Mg by the silicothermic reduction of MgO–CaO. The onset temperature for the formation of free Al, Be, Si, Ti, Mg, Hf, and Zr in the gas phase is considerably lowered by decreasing the total pressure, enabling their vacuum distillation. An important prediction of vacuum operation is the suppression of undesired by-products, such as Al-carbide, Al₄C₃, and the Al-oxycarbides Al₂OC and Al₄O₄C. These species considerably interfere in the carbothermic Al production at an ambient pressure, as shown in preliminary experiments using induction furnace irradiation. CO coproduced in these reactions may be water-gas shifted to syngas and further processed to hydrogen and liquid fuels.

Keywords:

• aluminum
• coke
• iron
• mathematical modeling
• reduction
• titanium

Notes

^a Taking the HHV of graphite, 393.5 kJ/mol, as representative of coke.

^b Theoretical process heat for changing equilibrium composition from 300 K to 1800 K at 1 bar.

^c Theoretical work for isothermal expansion at 1800 K of product gases from 1 bar to 10⁻⁴ bar.

^d Fuel assumes coke or coal for process heat.

^e Assume 90% chemical yield of methanol from syngas.

Note: By partial WGS (water-gas shift) of CO to H₂, a syngas of molar ratio H₂/CO = 2 may be obtained and converted to methanol.