Thermodynamic and Pilot-Scale Assessment of Al2O3 Reduction in Nitrogen--Hydrogen RF Plasma

Abstract

The Hall–Héroult electrolytic process has dominated global aluminum production for nearly 140 years, but it faces hard limits in efficiency and generates significant carbon, fluorine, and hazardous solid waste emissions. This work presents a thermodynamic and pilot-scale assessment of aluminum production via direct reduction of alumina (Al₂O₃) in nitrogen–hydrogen radio frequency (RF) plasma. In contrast to the conventional Hall–Héroult process, the proposed approach eliminates carbon electrodes, cryolite, and fluorinated byproducts. A thermodynamic analysis based on hydrogen reduction of Al₂O₃ indicates a theoretical minimum energy requirement of approximately 6.5 MWh per ton of aluminum (MWh/t Al), including both reaction enthalpy and sensible heat contributions. Preliminary estimates derived from an APT-100 RF plasma system (~100 kVA) suggest a specific energy consumption (SEC) of approximately 12.1 MWh/t Al under pilot-scale conditions. Projected performance at higher power levels (~1 MW), assuming improved plasma efficiency and heat recovery, indicates the potential to approach ~6.8 MWh/t Al. These projected values are based on simplified energy balance assumptions and require experimental validation. The analysis defines key process parameters, assumptions, and scaling limitations. In addition to aluminum production, the process enables the formation of aluminum nitride (AlN) as a valuable byproduct. The results suggest that RF plasma reduction represents a promising pathway for low-emission aluminum production, subject to further experimental confirmation.